JP6990888B1 - Poly (meth) acrylic acid (salt) -based water-absorbent resin and absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel water-absorbent resin and an absorber capable of providing an absorbent article in which swelling of a water-absorbing portion is suppressed at the time of use in a thin absorbent article. The water-absorbent resin of the present invention is a particulate poly (meth) acrylic acid (salt) -based water-absorbent resin having a swelling gel compression rate of 3% or more represented by the following (formula 1). It is a water-absorbent resin. Swelling gel compressibility [%] = (D1-D2) / D1 × 100 (Equation 1). (Here, D1 includes a piston 12 having a diameter of 59 mm and a cell 11 having an inner diameter of 60 mm provided with a mesh-shaped bottom portion 15, and 1.0 g of the water-absorbent resin 16 is sprayed on the bottom portion 15. 11 was placed in a petri dish 13 containing a 0.9% by mass sodium chloride aqueous solution, and the water-absorbent resin 16 was allowed to absorb the 0.9% by mass sodium chloride aqueous solution for 5 minutes. The thickness [mm] of the swollen gel layer formed by the resin 16, and D2 is the piston so that the cell 11 is placed on a sieve having an opening of 4750 μm and a load of 0.7 psi is applied to the swollen gel layer. It is the thickness [mm] of the swollen gel layer formed by the water-absorbent resin 16 after the operation of placing the weight 14 on the weight 12 and allowing the cell 11 to stand for 10 seconds and then removing the weight 14 is repeated 10 times. .) [Selection diagram] None

Description

The present invention relates to a water-absorbent resin and an absorber. More specifically, the present invention relates to a poly (meth) acrylic acid (salt) -based water-absorbent resin and an absorber.

In recent years, in sanitary materials such as disposable diapers, menstrual napkins, and incontinence pads, a water-absorbent resin as a constituent material thereof has been widely used as a water-absorbing agent from the viewpoint of body fluid absorption. Examples of such a water-absorbent resin include a hydrolyzate of a starch-acrylonitrile graft copolymer, a neutralized product of a starch-acrylic acid graft polymer, and a saponified product of a vinyl acetate-acrylic acid ester copolymer (meth). ) Acrylic acid partially neutralized polymer Cross-linked products are known, but from the viewpoint of water absorption performance, poly (meth) using (meth) acrylic acid and / or a salt thereof as the main component of the monomer. Acrylic acid (salt) -based water-absorbent resin is the most industrially produced.

A water-absorbent resin having excellent gel elasticity is known for suppressing gel blocking. For example, Patent Documents 1 to 5 disclose water-absorbent resins having excellent elastic force after water absorption when used as an absorber. The water-absorbent resins described in Patent Documents 1 to 5 can maintain a sufficiently high elastic force even when the proportion of fibrous substances in the absorbent core in the absorber is low (high-concentration core), and thus have an absorbent performance. Can be made thinner without damaging.

International Publication WO2019 / 189485 Patent 4880144 Patent 03107909 Japanese Unexamined Patent Publication No. 9-3123 International Publication WO2019 / 189445

The water-absorbent resin having excellent elasticity described in the prior art is a water-absorbent resin that swells due to liquid absorption (water absorption), and the core continues to swell when the absorbent article is attached, which makes the user uncomfortable. Met.

One embodiment of the present invention has been made in view of the above problems, and an object thereof is a novel water-absorbent resin capable of providing an absorbent article in which the swelling of a water-absorbing portion is suppressed during use in a thin absorbent article. The purpose is to provide an absorber.

In order to provide an absorbent article in which the swelling of the water-absorbing portion during use in the thin absorbent article is suppressed, the present inventors have a poly (meth) acrylic acid (salt) -based water absorption having a high compression rate of the swelling gel. We have independently found that the sex resin is suitable, and have completed the present invention.

That is, the water-absorbent resin according to the embodiment of the present invention is a poly (meth) acrylic acid (salt) -based water-absorbent resin, and has a swelling gel compressibility of 3% or more represented by the following (formula 1). be:
Swelling gel compressibility [%] = (D1-D2) / D1 × 100 (Equation 1)
(Here, D1 includes a piston having a diameter of 59 mm and a cell having an inner diameter of 60 mm having a mesh-like bottom, and 0.9 mass of the cell on which 1.0 g of the water-absorbent resin is sprayed on the bottom. The thickness of the swollen gel layer formed by the water-absorbent resin when placed in a petri dish containing a% sodium chloride aqueous solution and the water-absorbent resin absorbs the 0.9% by mass sodium chloride aqueous solution for 5 minutes [ mm], and in D2, the cell is placed on a sieve having an opening of 4750 μm, and a weight is placed on the piston so that a load of 0.7 psi is applied to the swollen gel layer, and the cell is placed on the cell. The thickness [mm] of the swollen gel layer formed by the water-absorbent resin after the operation of removing the weight after standing for a second is repeated 10 times).

The water-absorbent resin according to the embodiment of the present invention is agglomerates of spherical particles.

The water-absorbent resin according to the embodiment of the present invention has a mass average particle diameter (D50) of 50 to 700 μm.

The water-absorbent resin according to the embodiment of the present invention has a D2 of less than 15 mm.

The water-absorbent resin according to the embodiment of the present invention has a D1 of less than 15 mm.

The water-absorbent resin according to the embodiment of the present invention has a water absorption ratio (AAP) of 18 g / g or more under pressure.

The water-absorbent resin according to one embodiment of the present invention is obtained by reverse phase suspension polymerization in a hydrophobic organic solvent.

The water-absorbent resin according to one embodiment of the present invention is obtained by extruding spherical particles with an extruder having a porous plate.

The absorber according to one embodiment of the present invention contains the water-absorbent resin according to one embodiment of the present invention and does not contain (1) hydrophilic fibers or (2) contains hydrophilic fibers. The mass of the water-absorbent resin is 50% by mass or more in the total of 100% by mass of the water-absorbent resin and the hydrophilic fiber.

According to one embodiment of the present invention, it is possible to provide a water-absorbent resin and an absorbent body that can provide an absorbent article in which the swelling of the water-absorbing portion is suppressed during use in a thin absorbent article.

It is a perspective view which shows the appearance structure of the measuring apparatus of the swelling gel compressibility as seen from one direction. It is sectional drawing which shows a part of the measuring apparatus of the swelling gel compressibility. It is a top view in the process of making the absorption sheet for evaluation made in Example. It is sectional drawing of the absorption sheet for evaluation produced in an Example.

Hereinafter, the present invention will be described while showing the best mode. It should be understood that the terms used herein are used in the meaning commonly used in the art unless otherwise noted. Accordingly, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, this specification (including definitions) takes precedence. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the claims.

[1] Definition of terms [1-1] Water-absorbent resin The "water-absorbent resin" in the present invention refers to a water-swellable and water-insoluble polymer gelling agent, which satisfies the following physical properties. That is, the physical properties of the CRC defined by ERT441.2-02 as "water swellability" is 5 g / g or more, and the Ext defined by ERT470.2-02 as "water-insoluble" is 50% by weight or less. Refers to a polymer gelling agent that satisfies the above conditions.

The water-absorbent resin can be appropriately designed according to its use, 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 water-absorbent resin is not limited to a form in which the total amount (100% by mass) is a polymer, and the water-absorbent resin composition contains additives and the like within a range satisfying the physical properties (CRC, Ext). It may be in the form of.

Further, the water-absorbent resin in the present invention is not limited to the final product, but is an intermediate in the manufacturing process of the water-absorbent resin (for example, a water-containing gel-like crosslinked polymer after polymerization (water-containing gel polymer) or a dried polymer after drying. , Water-absorbent resin powder before surface cross-linking, etc.), and together with the water-absorbent resin composition, all of these are collectively referred to as "water-absorbent resin".

Examples of the shape of the water-absorbent resin in one embodiment of the present invention include a sheet shape, a fibrous shape, a film shape, a particle shape, and a gel shape. The shape of the water-absorbent resin in one embodiment of the present invention is preferably particulate. The water-absorbent resin in one embodiment of the present invention is more preferably a particulate poly (meth) acrylic acid (salt) -based water-absorbent resin.

[1-2] "EDANA" and "ERT"
"EDANA" is an abbreviation for European Disposables and Nonwovens Associations, and "ERT" is a European standard (almost world standard) method for measuring water-absorbent resin (EDANA Recommended Test Method). .. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the original ERT (revised in 2002 / publicly known literature).

[1-3] Others In the present specification, "XY" indicating a range means "X or more and Y or less".

In the present specification, "ppm" means "mass ppm" unless otherwise specified.

In the present specification, "-acid (salt)" means "-acid and / or a salt thereof". "(Meta) acrylic" means "acrylic and / or methacrylic". "Poly (meth) acrylic acid (salt) -based water-absorbent resin" means a water-absorbent resin containing a repeating unit derived from (meth) acrylic acid (salt) as a main component, and is specifically used for polymerization. Of the total monomer (excluding the cross-linking agent), (meth) acrylic acid (salt) is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, still more preferably 90 to 100 mol%, and particularly preferably. Refers to a water-absorbent resin containing substantially 100 mol%.

In the present specification, the unit of volume "liter" may be expressed as "l" or "L".

In the present specification, "weight" and "mass", "weight%" and "mass%", and "parts by weight" and "parts by mass" are treated as synonyms.

[2] Water-absorbent resin [2-1] Shape of water-absorbent resin In the present invention, the water-absorbent resin is preferably in the form of particles, specifically, in the form of amorphous crushed, spherical, football-like, or aggregate. Etc. are preferable. Among them, the water-absorbent resin has spherical particles (for example, poly (meth) acrylic acid (salt)) because a high gel compression rate can be obtained because the particle shape of the water-absorbent resin is spherical, especially in the form of aggregates. It is preferably aggregate-like particles (spherical particles containing a water-absorbent resin). The spherical particles of the water-absorbent resin can be said to be primary particles, and the aggregate-like particles of the water-absorbent resin can be said to be aggregate-like secondary particles formed by aggregating spherical primary particles. Here, the “spherical” includes not only a true sphere but also a substantially spherical one having an aspect ratio of 1.0 to 1.2.

[2-2] CRC
"CRC" is an abbreviation for Centrifuge Retention Capacity (centrifuge holding capacity), and means the water absorption ratio of a water-absorbent resin under no pressure.

The CRC of the water-absorbent resin of the present invention is preferably 30 g / g or more, more preferably 32 g / g or more, still more preferably 34 g / g or more. The upper limit of the CRC is not particularly limited, and the higher the CRC of the water-absorbent resin, the more preferable, but from the viewpoint of the balance between the other physical properties of the water-absorbent resin and the CRC, it is preferably 50 g / g or less, more preferably 48 g. It is / g or less, and more preferably 46 g / g or less.

When the CRC is 30 g / g or more, the water-absorbent resin has a sufficient absorption amount and can be suitably used as an absorber for absorbent articles such as disposable diapers. Further, when the CRC is 50 g / g or less, a decrease in the rate of absorption of body fluids such as urine and blood in the water-absorbent resin is prevented, and the water-absorbent resin is used for high water absorption rate type disposable diapers and the like. Suitable for. The CRC value can be controlled by changing the type and amount of the internal cross-linking agent, the surface cross-linking agent, and the like. An example of the CRC measurement method will be described in detail in Examples.

[2-3] Ext
"Ext" is an abbreviation for Extremes (water-soluble component), and means the amount of soluble component extracted from the water-absorbent resin. The water-soluble content is measured according to the EDANA method (ERT470.2-02).

The Ext of the water-absorbent resin of the present invention is preferably 30% by mass or less, more preferably 20% by mass or less, and further preferably 10% by mass or less. The lower limit of Ext is 0% by mass, but from the viewpoint of the balance between Ext and other physical properties of the water-absorbent resin, it is preferably 2% by mass or more, and more preferably 4% by mass or more.

When the Ext is 30% by mass or less, a decrease in the rate of absorbing body fluids such as urine and blood in the water-absorbent resin is prevented, and the water-absorbent resin is suitable for use in high-water absorption rate type disposable diapers and the like. .. The value of Ext can be controlled by changing the type and amount of the polymerization initiator, the internal cross-linking agent, the surface cross-linking agent and the like, and can also be controlled by using a chain transfer agent in the polymerization step.

[2-4] AAP
"AAP" is an abbreviation for Absorption Against Pressure, and means the water absorption ratio under pressure of the water-absorbent resin. In the present invention, AAP is measured according to the EDANA method (ERT442.2.2) except that the load condition is changed to 4.83 kPa (0.7 psi). Specifically, using a 0.9% by mass (mass /% by mass) sodium chloride aqueous solution, 0.9 g of a water-absorbent resin was swollen under a pressure of 4.83 kPa for 1 hour, and then AAP (absorption ratio under pressure). ) (Unit: g / g) is measured.

The AAP of the water-absorbent resin of the present invention is preferably 18 g / g or more, more preferably 20 g / g or more, still more preferably 23 g / g or more, from the viewpoint of water absorption characteristics when used as a sanitary material. The upper limit of AAP of the water-absorbent resin is not particularly limited, but is preferably 40 g / g or less.

[2-5] Moisture content The "moisture content" is measured according to the EDANA method (ERT430.2-02) except that the sample amount is changed to 1.0 g and the drying temperature is changed to 180 ° C. An example of the method for measuring the water content will be described in detail in Examples.

The water content of the water-absorbent resin of the present invention is not particularly limited, but is preferably 1% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, still more preferably 2% by mass to 13% by mass, still more preferably. It is 5% by mass to 13% by mass, more preferably 8% by mass to 13% by mass, and particularly preferably 10% by mass to 13% by mass. When the water content is 1% by mass to 20% by mass, it is possible to prevent a decrease in the rate of absorption of body fluids such as urine and blood in the water-absorbent resin, and the water-absorbent resin can be used for high water absorption rate type paper omelets and the like. Suitable for use.

[2-6] Mass average particle size (D50)
The “mass average particle size (D50)” is described in “(3) Mass-Average Particle Diameter (D50) and Logistic Standard Deviation” (σζ) of Division described in columns 27 and 28 of US Pat. No. 7,638,570. Measured in compliance.

The mass average particle size (D50) of the water-absorbent resin of the present invention is preferably 50 μm to 700 μm, more preferably 50 μm to 500 μm, and further preferably 100 μm to 400 μm. The proportion of particles having a mass average particle diameter of less than 45 μm in 100% by mass of the water-absorbent resin is preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less, and particularly preferably 10% by mass. % Or less. When the mass average particle diameter is 200 μm or more, there is little dust and the handling is good. Further, when the mass average particle diameter is 700 μm or less, it is possible to prevent a decrease in the rate of absorption of body fluids such as urine and blood in the water-absorbent resin, and the water-absorbent resin can be used as a high-water absorption rate type disposable diaper or the like. Suitable for use.

[2-7] Number average particle diameter When the water-absorbent resin is an aggregate-like particle (secondary particle), the number average particle diameter of the primary particles (for example, spherical particles) constituting the aggregate (the aggregate-like particle). Is measured using an electron microscope. The number average particle size of the primary particles of the water-absorbent resin is preferably 5 μm to 800 μm, more preferably 8 μm to 500 μm, further preferably 10 μm to 300 μm, still more preferably 10 μm to 200 μm, and particularly preferably 30 μm to 30 μm. It is 200 μm. An example of the method for measuring the number average particle size will be described in detail in Examples.

[2-8] Bulk Density The "bulk density" is measured according to the EDANA method (ERT460.2-02).

The bulk density of the water-absorbent resin of the present invention is preferably 0.68 g / cm3 to 1.00 g / cm3, preferably 0.69 g / cm3 to 0.95 g / cm3, and most preferably 0.68 g / cm3 to 0. It is 90 g / cm3. When the bulk density is 0.68 to 1.00 g / cm3, a decrease in the rate of absorption of body fluids such as urine and blood in the water-absorbent resin is prevented, and the water-absorbent resin is a paper omelet of a high water absorption rate type. Suitable for use in etc.

[2-9] Liquid permeability The "liquid permeability" of the water-absorbent resin in the present invention refers to the flowability of the liquid passing between the particles of the swollen gel under load or no load, and is typical. As a measurement method, there is GBP (Gel Bed Permeability / gel bed permeability). "GBP" refers to the liquid permeability of a 0.9 mass% sodium chloride aqueous solution to a water-absorbent resin under load or under free swelling, in accordance with the GBP test method disclosed in WO 2005/016393. Be measured. However, in the present invention, the particle size of the water-absorbent resin is measured without being classified into 300 μm or more and 600 μm or less. It is preferable to exhibit liquid permeability even when the swelling of the absorption core is suppressed, and the GBP of the water-absorbent resin is preferably 5 × 10 ^-9 cm ² , more preferably 10 × 10 ^-9 cm ² , and further preferably 15. × ^10-9 cm ² .

[2-10] Swelling gel compression rate The "swelling gel compression rate" in the present invention is a water-absorbent resin when a load is repeatedly applied to the swelling gel of the water-absorbent resin in a cell having a mesh-like bottom. It is a novel physical property value showing the thickness change (compression rate) of the swollen gel. The "swelling gel compression rate" is measured by a method described later. A water-absorbent resin having a large "swelling gel compressibility" is used, for example, in a thin water-absorbing sheet for light incontinence, because the swelling gel layer of the water-absorbent resin is compressed when a repeated load is applied, so that even when used for a long time. This is preferable because the swelling of the absorption core is suppressed. The "swelling gel compression rate" is 3.0% or more, preferably 3.5% or more, more preferably 4.0% or more, still more preferably 4.5% or more, and particularly preferably 5.0% or more. .. The upper limit of the swelling gel compressibility is preferably 30% or less, 25% or less, and 20% or less in this order from the viewpoint of maintaining the absorption performance of the swelling gel of the water-absorbent resin.

[2-11] Gel thickness before compression D1
In the measurement of the "swelling gel compressibility", the thickness D1 of the gel before compression is a numerical value from the viewpoint of preventing discomfort due to excessive swelling of the absorbent core when the absorbent resin is used for an absorbent article. Lower is preferable. The thickness D1 of the gel before compression is preferably 20 mm or less, more preferably 15 mm or less, still more preferably less than 15 mm. The lower limit of D1 is not particularly limited, but may be more than 0 mm, preferably 5 mm or more, more preferably 10 mm or more, still more preferably 12 mm or more.

[2-12] Gel thickness after compression D2
In the measurement of the "swelling gel compressibility", the thickness D2 of the gel after compression prevents discomfort due to the swelling of the absorbent core when the absorbent resin is used for the absorbent article and a load (body weight) is applied. From the viewpoint, the lower the value, the better. The "thickness D2 of the gel after compression" is preferably 18 mm or less, more preferably 15 mm or less, still more preferably less than 15 mm. The lower limit of D2 is not particularly limited, but may be more than 0 mm, preferably 5 mm or more, more preferably 10 mm or more, still more preferably 12 mm or more.

A device for measuring the swelling gel compressibility will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view showing an external configuration of a swelling gel compressibility measuring device as viewed from one direction. FIG. 2 is a cross-sectional view showing a part of a device for measuring the swelling gel compressibility. As shown in FIG. 1, the swelling gel compressibility measuring device includes a cell 11, a piston 12, a petri dish 13, and a weight 14. As shown in FIG. 2, the inner diameter of the cell 11 is 60 mm, and the diameter of the piston 12 is 59 mm. Further, as shown in FIG. 2, the cell 11 includes a bottom portion 15, and the bottom portion 15 is a stainless steel mesh, which is formed of a mesh having an opening of 36 μm (that is, 400 mesh).

A method for measuring the swelling gel compressibility will be described with reference to FIGS. 1 and 2. First, as shown in FIG. 2, the water-absorbent resin 16 is sprayed on the bottom portion 15 of the cell 11 having an inner diameter of 60 mm and having the mesh-shaped bottom portion 15. Next, as shown in FIG. 2, a piston 12 having a diameter of 59 mm is placed in the cell 11 from above the sprayed water-absorbent resin 16. Next, as shown in FIG. 1, the cell 11 having the piston 12 and the water-absorbent resin 16 is placed in the petri dish 13 and left for 5 minutes. Here, although not shown in FIG. 1, a 0.9% by mass sodium chloride aqueous solution is present in the petri dish 13. Therefore, by such an operation, the water-absorbent resin 16 can be made to absorb the 0.9 mass% sodium chloride aqueous solution for 5 minutes, whereby the water-absorbent resin 16 forms a layer of a swelling gel (swelling gel layer). do. In addition, in FIG. 1, the weight 14 is described on the piston 12 existing inside the cell 11 placed in the petri dish 13, but in the actual measurement of the swelling gel compression rate, it is 0.9% by mass. When the cell 11 having the piston 12 and the water-absorbent resin 16 is placed in the petri dish 13 containing the sodium chloride aqueous solution, the weight 14 is not placed on the piston 12. As will be described later, the weight 14 is placed on the piston 12 in the cell 11 installed on the sieve. In FIG. 1, the state when the weight 14 is placed on the piston 12 in the cell 11 installed on the sieve is conveniently shown by using the piston 12 in the cell 11 placed in the petri dish 13. It's just that.

After forming the swelling gel layer on the water-absorbent resin 16 in the cell 11, the thickness [mm] of the swelling gel layer is measured, and this is designated as D1. Next, the cell 11 having the swelling gel layer and the piston 12 on the water-absorbent resin 16 is taken out from the petri dish 13 and placed on a sieve having an opening of 4750 μm. Subsequently, (1) an operation of placing a weight 14 on the piston 12 in the cell 11 and allowing the cell 11 to stand for 10 seconds so that a load of 0.7 psi is applied to the swollen gel layer of the water-absorbent resin 16. , (2) After that, the operation of removing the weight 14 is repeated 10 times. Then, the thickness [mm] of the swollen gel layer formed by the water-absorbent resin 16 is measured, and this is designated as D2.

Subsequently, the swelling gel compression rate is calculated from D1 and D2 based on the following formula (1):
Swelling gel compressibility [%] = (D1-D2) / D1 × 100 (Equation 1).
[2-13] Additives Contained In the present invention, the water-absorbent resin may contain additives for exhibiting various functions. Specific examples of the additive include organic powders such as surfactants, compounds having a phosphorus atom, oxidizing agents, organic reducing agents, inorganic reducing agents, water-insoluble inorganic fine particles, chelating agents, polyvalent metal salts, and metal soaps. , Deodorant, antibacterial agent, pulp, thermoplastic fiber and the like. The amount of the additive used (addition amount) is appropriately set according to the use of the obtained water-absorbent resin, but is 5% by mass or less, preferably 3 by mass, based on the water-absorbent resin (for example, water-absorbent resin powder). It is mass% or less, more preferably 1 mass% or less. The lower limit is 0.001% by mass or more, preferably 0.01% by mass or more, based on the water-absorbent resin (for example, water-absorbent resin powder). As the water-insoluble inorganic fine particles, the compound disclosed in "[5] Water-insoluble inorganic fine particles" of International Patent Publication No. 2011/040530 is applied to the present invention.

[3] Method for producing water-absorbent resin As the method for producing the water-absorbent resin of the present invention, any of aqueous solution polymerization, reverse phase suspension polymerization, vapor phase droplet polymerization and other polymerization methods may be used, but the present invention It is preferable to adopt the reverse phase suspension polymerization method from the viewpoint that the physical properties of the water-absorbent resin can be easily controlled. As a method for producing the water-absorbent resin of the present invention, the reverse phase suspension polymerization method will be described below as an example. In particular, unlike general reverse phase suspension polymerization including a co-boiling dehydration step in a hydrophobic organic solvent after polymerization and a surface cross-linking step in a dispersion system, a separation step of a reverse phase suspension polymerization gel and gel preparation are performed. A preferred embodiment of the method for producing a water-absorbent resin of the present invention will be described by taking as an example a production method including a grain step, a water-containing gel drying step (preferably hot air drying), and a surface cross-linking step (preferably powder surface treatment).

The method for producing the water-absorbent resin according to the present invention is not particularly limited, but a water-containing gel polymer is obtained by polymerizing the monomer in a state where droplets containing the monomer are dispersed or suspended in a hydrophobic organic solvent. It is preferable to include a polymerization step for obtaining the above.

As a method for producing a water-absorbent resin (polymerization method), for example, a water-containing gel weight is obtained by polymerizing the monomer in a state where droplets containing the monomer are dispersed or suspended in a liquid phase composed of a hydrophobic organic solvent. A method for obtaining a coalescence, in other words, a method for obtaining a hydrogel polymer by reverse phase suspension polymerization is preferable, and the polymerization method may be a batch method or a continuous method. In the batch-type production method, a monomer aqueous solution is added or dropped into a hydrophobic organic solvent in a reaction apparatus and mixed, so that the droplets of the monomer aqueous solution are dispersed or suspended in the hydrophobic organic solvent. This is a production method for obtaining a hydrogel polymer by polymerizing the monomer after making it turbid. On the other hand, in the continuous production method, the aqueous monomer solution is continuously sent to the hydrophobic organic solvent in the reaction apparatus, and the droplets of the aqueous monomer solution are dispersed or suspended in the hydrophobic organic solvent. After that, the monomer is polymerized, and the hydrous gel polymer formed by the polymerization reaction and the hydrophobic organic solvent are continuously discharged from the reaction apparatus. A preferred embodiment of the present invention is batch reverse phase suspension polymerization. In the method for producing a water-absorbent resin according to the present invention, a separation step may be provided to separate the hydrous gel polymer obtained in the polymerization step from the hydrophobic organic solvent.

The method for producing the water-absorbent resin according to the present invention is, for example, an arbitrary monomer aqueous solution preparation step; an arbitrary dispersion step; a polymerization step; an arbitrary separation step; an arbitrary gel sizing step; a drying step; a hydrophilization treatment step. including. Further, after the drying step, optionally, a cooling step, a crushing step, a classification step, a surface cross-linking step, a water-containing (rewetting) step, another additive addition step, a granulation step, a fine powder removal step, a granulation step and a fine powder It can include a reuse process and the like. Further, a transportation step, a storage step, a packing step, a storage step, and the like may be further included.

Hereinafter, each step will be described.

[3-1] Monomer Aqueous Solution Preparation Step The monomer aqueous solution is an aqueous solution containing a monomer that is a raw material of a water-absorbent resin, and is dispersed or suspended in a hydrophobic organic solvent for reverse-phase suspension polymerization. It is a solution that makes it turbid.

As the solvent of the monomer aqueous solution, water or a mixture of water and a water-soluble organic solvent (for example, alcohol) is preferably used, and water is even more preferable. In the case of a mixture of water and a water-soluble organic solvent, the water-soluble organic solvent (for example, alcohol, etc.) is preferably 30% by mass or less, preferably 5% by mass or less, in the mixture (100% by mass). More preferred.

As the monomer, a water-soluble ethylenically unsaturated monomer is preferably used. Examples of water-soluble ethylenically unsaturated monomers include (meth) acrylic acid, (anhydrous) maleic acid, itaconic acid, acrylate, vinyl sulfonic acid, allyltoluene sulfonic acid, vinyl toluene sulfonic acid, and styrene sulfonic acid. , 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) ) Acid group-containing unsaturated monomers such as acrylate, 2-hydroxyethyl (meth) acryloyl phosphate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate; (meth) acrylamide, N-ethyl (meth). ) Acrylate, N, N-dimethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidin, N-acryloylpyrrolidine, N -Amid group-containing unsaturated monomers such as vinylacetamide; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, Amino group-containing unsaturated monomer such as N, N-diethylaminoethyl (meth) acrylate; mercapto group-containing unsaturated monomer; phenolic hydroxyl group-containing unsaturated monomer; lactam group-free such as N-vinylpyrrolidone Examples include saturated monomers.

When a water-soluble ethylenically unsaturated monomer is used, a polymerization inhibitor is added to the monomer aqueous solution as necessary in consideration of the stability of the water-soluble ethylenically unsaturated monomer. You may.

When a water-absorbent resin is produced using an acid group-containing unsaturated monomer having an acid group such as a carboxyl group among the water-soluble ethylenically unsaturated monomers, the acid group is neutralized. Neutralized salts can be used. In this case, the salt (neutralizing salt) of the acid group-containing unsaturated monomer is preferably a salt with a monovalent cation, and is at least one selected from an alkali metal salt, an ammonium salt and an amine salt. It is more preferably an alkali metal salt, further preferably at least one selected from a sodium salt, a lithium salt and a potassium salt, and particularly preferably a sodium salt.

Among these, from the viewpoint of the water absorption performance of the obtained water-absorbent resin, the water-soluble ethylenically unsaturated monomer is preferably an acid group-containing unsaturated monomer and / or a salt thereof, and more preferably (meth). ) Acrylic acid (salt), (anhydrous) maleic acid (salt), itaconic acid (salt) and / or silica skin acid (salt), more preferably (meth) acrylic acid (salt), particularly preferably. Acrylic acid (salt).

When an acid group-containing unsaturated monomer is used as the monomer, the acid group-containing unsaturated monomer and the neutralized salt of the acid group-containing unsaturated monomer are used from the viewpoint of the water absorption performance of the obtained water-absorbent resin. It is preferable to use in combination with. When an acid group-containing unsaturated monomer and a neutralized salt of the acid group-containing unsaturated monomer are used in combination, the total amount of the acid group-containing unsaturated monomer and its neutralized salt is obtained 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 number of moles (100 mol%) is preferably 40 mol% or more, more preferably 40 mol% to 95 mol%, still more preferably 50 mol. % To 90 mol%, even more preferably 55 mol% to 85 mol%, and particularly preferably 60 mol% to 80 mol%.

In the production method according to the present invention, any one of the above-exemplified monomers may be used alone in the preparation of the aqueous monomer solution, and any two or more kinds of monomers may be appropriately mixed. May be used. Further, as long as the object of the present invention is achieved, a monomer other than the above-exemplified monomer can be further mixed and used with the above-exemplified monomer.

When two or more kinds of monomers are used in combination in the preparation of the aqueous monomer solution, the monomer used for polymerization preferably contains (meth) acrylic acid (salt) as a main component. In this case, the ratio of (meth) acrylic acid (salt) to the entire monomer (100 mol%) used for polymerization is usually 50 mol% or more, preferably 50 mol% or more, from the viewpoint of the water absorption performance of the obtained water-absorbent resin. It is 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more (upper limit is 100 mol%).

In the preparation of the monomer aqueous solution, an internal cross-linking agent can be used, if necessary. Examples of the internal cross-linking agent include conventionally known internal cross-linking agents having two or more polymerizable unsaturated groups or two or more reactive groups in one molecule. Examples of the internal cross-linking agent include N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and the like. Trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, tri. Allyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1 , 4-Butandiol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl (meth) acrylate and the like. Only one kind of these internal cross-linking agents may be used, or two or more kinds thereof may be used.

It may be appropriately determined depending on the physical characteristics of the desired water-absorbent resin, but usually, the amount of the internal cross-linking agent used is 0.0001 to 5 mol% with respect to the entire monomer (100 mol%) used for the polymerization. It is more preferably 0.001 to 3 mol%, and even more preferably 0.005 to 1.5 mol%.

Further, the substances exemplified below (hereinafter referred to as "other substances") can also 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 4 metal salts of acetic acid, diethylenetriamine 5 metal salts of acetic acid; polyacrylic acid (salt) and crosslinked compounds thereof; starch; cellulose; starch-cellulose derivative; hydroxyethyl cellulose; polyvinyl alcohol; and the like. As for other substances, one kind may be used alone, or two or more kinds may be used in combination.

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 with respect to the entire monomer (100% by mass) used for the polymerization, which is more preferable. Is 1% by mass or less, and even more preferably 0.1% by mass or less.

The case where polyacrylic acid (salt) and a crosslinked product thereof, starch, cellulose, starch-cellulose derivative and / or polyvinyl alcohol are used as other substances will be described. The total concentration of these polyacrylic acid (salt) and its crosslinked product, starch, cellulose, starch-cellulose derivative, hydroxyethyl cellulose, and polyvinyl alcohol is based on the total concentration (100% by mass) of the monomer used for the polymerization. It is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

Further, the dissolved oxygen in the aqueous monomer solution may be reduced by raising the temperature or substituting with an inert gas.

"Initiator of polymerization"
A polymerization initiator may be used in the preparation of the monomer aqueous solution. When a polymerization initiator is used to prepare the monomer aqueous solution, gelation and viscosity increase of the monomer aqueous solution may occur. Therefore, the addition of the polymerization initiator to the monomer aqueous solution is carried out in (1). ) Immediately before dispersing and / or suspending the monomer aqueous solution in a hydrophobic organic solvent. (2) Cool the monomer aqueous solution and start the polymerization at a temperature lower than room temperature (for example, 20 ° C or lower, preferably around 0 ° C). It is preferable to mix with the agent, or (3) subject the monomer aqueous solution and the polymerization initiator to the dispersion step while line-mixing them. As the polymerization initiator, a pyrolysis type polymerization initiator is preferably used. The pyrolysis-type polymerization initiator refers to a compound that is decomposed by heat to generate a radical, but a 10-hour half-life temperature is preferable from the viewpoint of storage stability of the pyrolysis-type polymerization initiator and production efficiency of the water-absorbent resin. A water-soluble compound having a temperature of 0 ° C to 120 ° C, more preferably 30 ° C to 100 ° C, still more preferably 50 ° C to 80 ° C is preferably used as the polymerization initiator.

From the viewpoint of handleability and physical properties of the water-absorbent resin, the polymerization initiator is preferably a water-soluble polymerization initiator, and more preferably a water-soluble radical polymerization initiator.

Examples of the water-soluble radical polymerization initiator include persulfates such as hydrogen peroxide, ammonium persulfate, and sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, and t-butyl. Peroxides such as cumylperoxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, hydrogen peroxide; 2,2'-azobis (2-amidinopropane) ) Dihydrochloride, 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, etc. Water-soluble azo-based compounds; and the like. As the polymerization initiator, one of these types may be used alone, or two or more types may be used in combination. Among these, a persulfate or a water-soluble azo compound is preferable, sodium persulfate, potassium persulfate, ammonium persulfate, or 2,2'-azobis (2-amidinopropane) dihydrochloride is more preferable. Is sodium persulfate used.

The amount of the thermally decomposable polymerization initiator used is appropriately set according to the type of the monomer and the polymerization initiator, and is not particularly limited, but from the viewpoint of production efficiency, the entire monomer used for the polymerization (1). With respect to the molar), it is preferably 0.001 g / mol or more, more preferably 0.005 g / mol or more, and further preferably 0.01 g / mol or more. Further, the amount of the thermally decomposable polymerization initiator used is preferably 2 g / mol with respect to the entire monomer (1 mol) used for the polymerization from the viewpoint of improving the water absorption performance of the water-absorbent resin. Hereinafter, it is more preferably 1 g / mol or less.

Further, the thermally decomposable polymerization initiator may be used in combination with other polymerization initiators such as a photodegradable polymerization initiator, if necessary. Specific examples of the photodegradable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives and the like.

Further, the thermal decomposition type polymerization initiator and the reducing agent can be used in combination to prepare a redox-based polymerization initiator. In the redox-based polymerization initiator, the pyrolysis-type polymerization initiator functions as an oxidizing agent. The reducing agent used is not particularly limited, but for example, (heavy) sulfite such as sodium sulfite and sodium hydrogen sulfite; reducing metal salt such as ferrous salt; L-ascorbic acid (salt), amines and the like. Can be mentioned.

"Concentration of monomer in aqueous monomer solution"
In the present invention, the concentration of the monomer in the aqueous monomer solution (100% by mass) is selected according to the selected monomer and the type of the hydrophobic organic solvent, but the lower limit is set in terms of production efficiency. It is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and the upper limit is preferably 100% by mass or less, more preferably 90% by mass. % Or less, more preferably 80% by mass or less, still more preferably 70% by mass or less.

Additives such as an internal cross-linking agent, a surfactant, a density adjusting agent, a thickener, and a chelating agent can be added to the aqueous monomer solution as long as the object of the present invention is not impaired. The type and amount of the additive can be appropriately selected depending on the combination of the monomer and the hydrophobic organic solvent used.

[3-2] Dispersion Step The dispersion step is a step of dispersing or suspending droplets containing a monomer in a hydrophobic organic solvent (for example, droplets of a monomer aqueous solution). In the following, when the term "dispersion" is simply used, the concept includes suspension. More specifically, the monomer aqueous solution is added to a hydrophobic organic solvent, mixed and stirred to disperse the droplets containing the monomer. In the dispersion step, for example, a stirring device provided with stirring blades (propeller blade, paddle blade, anchor blade, turbine blade, Faudler blade, ribbon blade, flat plate blade, etc.) may be used. When a stirring device having such a stirring blade is used, the dispersed droplet diameter (droplet diameter of the dispersed monomer aqueous solution) can be adjusted by the type of the stirring blade, the blade diameter, and the rotation speed. The stirrer can be particularly preferably used when performing batch reverse phase suspension polymerization. Further, the dispersion liquid can be obtained by the method described in International Publication No. 2009/025253, 2013/018571 and the like. In the case of continuous reverse phase suspension polymerization, in the dispersion step, the monomer aqueous solution and the hydrophobic organic solvent are continuously and separately supplied to the disperser, and the monomer is dispersed in the hydrophobic organic solvent. It is preferable to prepare a droplet containing the above.

When performing continuous reverse phase suspension polymerization, the disperser used in the dispersion step includes a spray nozzle, a high-speed rotary shear type stirrer (rotary mixer type, turbo mixer type, disk type, double cylinder type, etc.). Examples thereof include a cylindrical nozzle such as a needle, an orifice plate in which a large number of holes are directly provided in the plate, a spray nozzle, and a centrifugal atomizer such as a rotary wheel, but the present invention is not particularly limited.

"Hydrophobic organic solvent"
Preferred hydrophobic organic solvents include at least one organic solvent selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons and halogenated hydrocarbons. Specific examples include aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclooctane, and decalin; benzene, toluene, xylene, and the like. Aromatic hydrocarbons; examples include halogenated hydrocarbons such as chlorbenzene, brombenzene, carbon tetrachloride, 1,2-dichloroethane and the like. Among these, n-hexane, n-heptane and cyclohexane are preferable from the viewpoint of availability and quality stability. It is also possible to use it as a mixed solvent in which two or more kinds of hydrophobic organic solvents are mixed.

In the present invention, a dispersion aid such as a surfactant or a polymer additive may be added to the hydrophobic organic solvent, if necessary, as long as the object of the present invention is not impaired. The type of the dispersion aid is appropriately selected depending on the combination of the hydrophobic organic solvent and the monomer used, and examples of the dispersion aid that can be used include the following surfactants and polymer additives.

Specific examples of the surfactant include sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, and polyoxyethylene sorbitol fatty acid ester. Polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl Alkyl ether, polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl glucon amide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, phosphoric acid ester of polyoxyethylene alkyl ether, and phosphoric acid ester of polyoxyethylene alkyl allyl ether. And so on. Of these, two or more may be used in combination. Further, a polymerizable surfactant having a polymerizable property can also be used. Specific examples of the polymerizable surfactant include compounds having the following structures.

In the formula, R ¹ and R ² are hydrogen, methyl or ethyl independently of each other, and n means an integer of 3 to 20. Among the above-mentioned surfactants, sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol. Fatal acid esters such as fatty acid esters are preferable, and sucrose fatty acid esters are particularly preferable.

The HLB value of the surfactant used in the present invention is preferably in the range of 1 to 20, more preferably 1 to 10, and even more preferably 3 to 6.

Specific examples of the polymer additive include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, and maleic anhydride-modified ethylene / propylene / diene ternary copolymer (). EPDM), maleic anhydride-modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene , Ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, hydroxyethyl cellulose and the like. Among them, from the viewpoint of dispersion stability of the monomer aqueous solution, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride / ethylene copolymer, maleic anhydride / Preferants are propylene copolymers, maleic anhydride / ethylene / propylene copolymers, polyethylene, polypropylene, ethylene / propylene copolymers, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymers. Of these, two or more may be used in combination. Further, these polymer additives may be used in combination with the above-mentioned surfactant. Above all, it is preferable to use a polymer additive, and it is more preferable to use a maleic anhydride-modified ethylene / propylene copolymer. Further, in another preferred embodiment, the polymer additive is used alone without using a surfactant.

The amount of the dispersion aid used is appropriately set according to the polymerization form, the monomer aqueous solution, the type of the hydrophobic organic solvent, and the like. Specifically, the concentration of the dispersion aid in the hydrophobic organic solvent (100% by mass) is preferably 0.0001 to 2% by mass, more preferably 0.0005 to 1% by mass.

[3-3] Polymerization Step In the polymerization step, the monomers in the droplets containing the monomers obtained in the dispersion step are polymerized to obtain a hydrogel polymer (hereinafter, also simply referred to as hydrogel). It is a process.

"Reactor"
As the reaction apparatus used in the polymerization step, the dispersion apparatus used in the dispersion step may be used as it is, or another apparatus may be used. In the case of batch type reverse phase suspension polymerization, the apparatus used in the dispersion step can be used as it is as a reaction apparatus, which is suitable in terms of workability. When the reaction device is a device different from the dispersion device, the dispersion liquid of the monomer obtained in the dispersion step is supplied to the reaction device.

Further, the shape of the reaction device in which the polymerization reaction is carried out is not particularly limited, and a known reaction device can be used. As described above, a stirrer that can be suitably used in the dispersion step can also be suitably used in the polymerization reaction. In the case of the continuous production method, the shape of the reaction device is preferably such that the monomer (aqueous solution) is a droplet-like dispersed phase in a hydrophobic organic solvent which is a continuous phase formed in the reaction device. It has a shape that allows polymerization reaction while moving. Examples of such a reaction device include a reaction device in which a tubular reaction tube is arranged in a vertical type, a horizontal type, or a spiral type. In this embodiment, since the monomer (aqueous solution) is supplied into the hydrophobic organic solvent moving in the reaction section (reaction tube), the droplets of the monomer aqueous solution do not stay and are hydrophobic organic. Move with the solvent. As a result, contact between monomer reactants having different polymerization rates is suppressed.

Further, the reaction device may be provided with a temperature adjusting means (for example, a heating means) so that the continuous phase inside the reaction device can be heated or cooled from the outside, if necessary.

"Polymerization temperature"
The polymerization temperature, which is the reaction temperature in the polymerization step, may be appropriately set depending on the type and amount of the polymerization initiator used, but is preferably 20 ° C to 100 ° C, more preferably 40 ° C to 90 ° C. If the polymerization temperature is higher than 100 ° C., a rapid polymerization reaction occurs, which is not preferable. The polymerization temperature means the temperature of the hydrophobic organic solvent as a dispersion medium (hereinafter referred to as “Td”).

In the polymerization step, since the monomer (aqueous solution) is dispersed in the hydrophobic organic solvent in the form of droplets, the temperature of the monomer aqueous solution rapidly rises due to heat transfer from the hydrophobic organic solvent. .. When the polymerization initiator contained in the droplets is a thermal decomposition type polymerization initiator, the thermal decomposition type polymerization initiator is decomposed and radicals are generated as the temperature rises. Then, the polymerization reaction is started by the generated radicals, and a hydrogel is formed as the polymerization reaction progresses.

In the case of the continuous production method, the formed hydrogel is moved inside the reactor by the moving continuous phase, and is discharged from the reactor together with the hydrophobic organic solvent forming the continuous phase.

When the aqueous monomer solution contains a thermally decomposable polymerization initiator, the Td is preferably 70 ° C. or higher, more preferably 75 ° C. or higher, still more preferably 80 ° C. or higher from the viewpoint of the polymerization rate. be. The upper limit of Td is not particularly limited, but is appropriately selected from the viewpoint of safety as long as it does not exceed the boiling point of the hydrophobic organic solvent forming a continuous phase.

"Multi-stage reverse phase suspension polymerization"
In the production method of the present invention, multi-stage polymerization may be performed from the viewpoint of obtaining an appropriate aggregate particle size (particle size of aggregate-like particles). Specifically, after the completion of the first-stage polymerization step, multi-stage polymerization can be carried out by further adding the monomer aqueous solution and carrying out a polymerization reaction or the like. In the multistage polymerization, the reaction solution may be appropriately stirred.

"Inorganic fine particles"
In the production method of the present invention, inorganic fine particles may be added to the hydrogel polymer during and / or after the polymerization is completed from the viewpoint of obtaining an appropriate aggregate particle size.

Examples of the inorganic fine particles that can be used in the present invention include silicon dioxide, aluminum oxide, titanium dioxide, calcium phosphate, calcium carbonate, magnesium phosphate, calcium sulfate, diatomaceous soil, bentonite, zeolite, and other metal oxides. In particular, silicon dioxide, aluminum oxide, and titanium dioxide are preferable.

Good results can be obtained when the amount of the inorganic fine particles added is generally 0.001 to 1 part by mass, preferably 0.001 to 0.5 part by mass with respect to the hydrogel polymer (100 parts by mass). When the amount of the inorganic fine particles added is in this range, the effect of adding the inorganic fine particles is efficiently exhibited, and the influence of the inorganic fine particles on the water absorption performance is small, which is preferable.

[3-4] Separation Step The separation step is a step of separating the hydrous gel polymer obtained in the polymerization step from the hydrophobic organic solvent. The type and structure of the apparatus used in the separation step are not particularly limited, but for example, known apparatus used for filtration, sedimentation, centrifugation, squeezing and the like can be used. Further, the mixture of the hydrous gel polymer and the hydrophobic organic solvent is heated under normal pressure or reduced pressure using a stirrer having a stirring blade used in the polymerization step, and distilled to obtain the hydrophobic gel polymer and the hydrophobic organic. It may be separated from the solvent. In batch reverse phase suspension polymerization, distillation under normal pressure or reduced pressure is preferably performed.

[3-5] Gel sizing step In the gel sizing step, the hydrous gel polymer separated from the hydrophobic organic solvent in the separation step is hydrated gel using a gel sizing device having an extruding part and a porous plate. Is sized. As a result, a sized hydrogel polymer (hereinafter, the hydrogel after gel sizing is referred to as a sizing gel) can be obtained. The gel sizing step is an arbitrary step. By having the gel sizing step, it becomes easy to control the compressibility of the swollen gel of the water-absorbent resin.

The hydrogel polymer used in this gel sizing step is a single particle shape of a spherical gel or an aggregate shape of a spherical gel. The lower limit of the average particle size of the hydrogel polymer is not particularly limited, but is preferably 0.01 mm or more, more preferably 0.03 mm or more, still more preferably 0.05 mm or more, still more preferably 0.1 mm or more. The upper limit is not particularly limited, but is preferably 20 mm or less, more preferably 10 mm or less. When the hydrous gel polymer has a single particle shape, the particle size thereof is used, and when the hydrous gel polymer has an aggregate shape, the particle size of each spherical gel constituting the aggregate is used as the particle size of the water-containing gel polymer. It is called the primary particle size. In the present invention, the average primary particle size of the hydrogel polymer is not particularly limited, but is preferably 5 to 2000 μm, more preferably 5 to 1000 μm, and further, from the viewpoint of suppressing the generation of fine powder in the drying step. It is preferably 5 to 800 μm, more preferably 8 to 500 μm, even more preferably 10 to 300 μm, and particularly preferably 10 to 200 μm.

In addition, a device having a cutter may be installed in front of the gel sizing device having the extrusion action part and the perforated plate to crush large aggregates of the hydrogel polymer.

"Water-containing gel temperature"
The lower limit of the temperature of the hydrous gel that enters (puts in) the gel sizing device is not particularly limited, but is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, from the viewpoint of granulation efficiency and suppression of damage to the hydrous gel. Is. The upper limit of the water-containing gel temperature at the time of charging the gel sizing device is not particularly limited, but is generally 100 ° C. or lower.

"Gel sizing device"
In the present specification, "gel sizing" means to produce grains having a substantially uniform shape and size from a wet powder-like raw material by extruding a wet mass of powder into a columnar shape from a small hole of a porous plate. It is an operation. That is, by using the porous plate, the hydrogel having the shape of coarse agglomerates excessively aggregated in the solvent separation step of the previous step is crushed, and the monoparticle-like hydrogel having a small particle size is appropriately aggregated. Will be done. Therefore, by this step, it is possible to obtain a hydrous gel (granulation gel) having a granulated shape having a relatively uniform particle size. The sizing gel may contain a single particle water-containing gel.

The "gel granulator having an extrusion action part and a porous plate" used in the gel sizing step has an extrusion action part and a porous plate (die or screen), and the extrusion action part is usually a porous plate. The device is not particularly limited as long as it has an extrusion member that extrudes and supplies the contents toward the surface and can produce grains of a certain size by extruding the material from the perforated plate (for example, an extruder). Further, a plurality of the above-mentioned devices may be prepared and the plurality of devices may be used side by side in series.

Further, the shape of the hole of the perforated plate (die or screen) is not particularly limited, and a shape suitable for use such as a polygonal shape such as a perfect circle, an ellipse, and a hexagon, and a triangular shape can be arbitrarily selected. Although it is possible, a perfect circle or an ellipse is preferable from the viewpoint of sizing strength. The pore diameter of the pores of the perforated plate is not particularly limited, but is preferably 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.8 mm or less. By being below such an upper limit, it is possible to prevent the size of the obtained sizing gel from increasing more than necessary, and to reduce the amount of fine powder generated during drying using a stirring type dryer in the downstream process. Can be done. The pore diameter is preferably 0.3 to 1.5 mm, more preferably 0.3 to 0.8 mm. When the pore diameter of the perforated plate is 0.3 mm or more, it can be efficiently extruded when performing the extrusion operation.

The hole diameter is defined as follows. First, when the hole is not a perfect circle, the geometric mean value of the minor axis and the major axis of the hole is adopted as the hole diameter. If the pore diameters of the pores of the perforated plate are different, the pore diameters of all the holes are calculated, and the geometric mean value thereof is adopted as the pore diameter of the pores of the perforated plate. Furthermore, if the pore size of the perforated plate changes from the extruding part side of the perforated plate to the opposite side (the pore diameter changes in the thickness direction of the perforated plate), the value that minimizes the pore diameter is adopted. ..

In this step, an additive may be further added to the hydrogel polymer. Additives that can be added in this step include polymerization initiators, oxidizing agents, reducing agents, chelating agents, thickeners, surfactants, cross-linking agents, acids, bases, foaming agents, organic or inorganic fine particles, and polyvalent metals. Examples thereof include salts, and among them, additives that can control the degree of aggregation include starch, cellulose, starch-cellulose derivative, thickener such as polyvinyl alcohol, surfactant, fine powder of water-absorbent resin, cross-linking agent, and many. Valuable metal salts and the like are preferable.

[3-6] Drying Step The drying step is a step of drying the hydrogel. In the present invention, the drying method in the drying step is not particularly limited. As a drying method, co-boiling dehydration in a hydrophobic dispersion solvent used in the conventional reverse phase suspension polymerization may be used, but as a more preferable method for obtaining the water-absorbent resin of the present invention by reverse phase suspension polymerization. Instead of the co-boiling dehydration, either stirring drying or static drying can be preferably adopted, but stirring drying is preferable in order to maintain the particle size of the gel controlled in the gel sizing step. In the drying step, an apparatus equipped with a heating means may be used to heat the hydrogel. Further, when stirring and drying is adopted, a rotary dryer provided with a rotary container may be used as the drying device.

The dried polymer composed of particles obtained in this drying step can be directly used as a water-absorbent resin for various purposes. Further, when the water-absorbent resin is produced by this production method, the dried polymer obtained in the drying step can be subjected to the surface cross-linking step described later. In this case, the dry polymer used in the surface cross-linking step described later is also referred to as "water-absorbent resin powder" for convenience.

"Additive"
Additives may be added to the hydrogel as long as the effects of the present invention are not impaired. The additive may be added to the hydrated gel during heating of the hydrated gel by the heating means and / or during stirring (rotation) of the hydrated gel by the rotating container, or before the drying step (before heating the hydrated gel by the heating means). And / or may be added to the water-containing gel before stirring (rotating) the water-containing gel with a rotating container. Furthermore, an additive may be added to the hydrogel in any step prior to the drying step. With the additive, excessive adhesion between the water-containing gels during drying can be reduced, and a water-absorbent resin having an excellent water absorption rate can be obtained.

Examples of additives added to hydrous gels include drying aids.

Specifically, from the viewpoint of industrial efficiency, when handling a particulate hydrogel having a diameter of 1 mm or less, it is preferable to add a drying aid to the hydrogel. In particular, by adding a drying aid to the water-containing gel before the drying step of the present invention, a water-absorbent resin having an excellent water absorption rate can be obtained. That is, a preferred embodiment of the present invention comprises adding a drying aid to the hydrogel polymer.

"Drying aid"
The drying aid is added for the purpose of maintaining the fluidity of the hydrogel during stirring and drying, and examples of the drying aid include a surfactant and a polymer lubricant. As a drying aid, a polymer lubricant and a surfactant may be used in combination.

The amount of the drying aid added is appropriately set according to the water content of the drying aid and the type of gel fluidizing agent. The total amount of the drying aid added is preferably 0.001% by mass to 0.5% by mass, more preferably 0.01% by mass to 0.3% by mass, based on the solid content (100% by mass) of the hydrogel. %, More preferably 0.02% by mass to 0.2% by mass. Further, in a preferred embodiment of the present invention, the hydrogel polymer contains a drying aid of less than 0.08% by mass with respect to the solid content (100% by mass) of the hydrogel polymer in the drying step. By drying the hydrous gel obtained by reverse phase suspension polymerization as in the present embodiment using a rotary dryer, the hydrogel is difficult to fuse and the particle size can be easily adjusted by crushing or the like. .. Therefore, when the hydrogel is dried using a rotary dryer, the amount of the drying aid used can be reduced.

The addition of the drying aid to the hydrogel polymer is preferably performed in a step prior to the drying step, and specifically, (1) is added to the hydrogel separated from the hydrophobic organic solvent in the separation step (2). ) Addition to the sizing gel before the drying step, (3) Addition to the monomer aqueous solution in the monomer aqueous solution preparation step, (4) Addition to the hydrophobic organic solvent in the dispersion step, and the like. The addition of the drying aid to the water-containing gel polymer is more preferably performed in the step immediately before the drying step, from after the step before the drying step (for example, the gel sizing step) to before the drying step. It is more preferable to do it in the meantime. Further, after the drying aid is added to the hydrogel polymer in the pre-drying step (for example, gel sizing step), and after the pre-drying step (for example, gel sizing step) and before the drying step. It is also a preferable form to add a drying aid to the hydrogel polymer in the meantime. The form of adding the drying aid before the drying step is, for example, a form in which the hydrogel polymer and the drying aid are charged into the dryer; the hydrogel polymer is added to the hydrogel polymer before the hydrogel polymer is charged into the dryer. Examples thereof include a form in which a drying aid is added. Further, the drying aid may overlap with the surfactant and / or the polymer additive used as the dispersion aid in the dispersion step.

Specific examples of the surfactant used as a drying aid include (1) sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, and sorbitol fatty acid ester. , Polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block Copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphoric acid esters of polyoxyethylene alkyl ethers, and polyoxy Nonionic surfactants such as the phosphoric acid ester of ethylene alkylallyl ether, (2) alkyldialkylaminoacetic acid betaines such as capril dimethylaminoacetic acid betaine, lauryldimethylaminoacetic acid betaine, myristyldimethylaminoacetic acid betaine, stearyldimethylaminoacetic acid betaine; Alkylamide propyl betaine such as lauric acid amide propyl betaine, palm oil fatty acid amide propyl betaine, palm kernel oil fatty acid amide propyl betaine, alkyl hydroxy sulfobetaine such as lauryl hydroxy sulfobetaine, 2-alkyl-N-carboxymethyl-N-hydroxy Alkylcarboxymethyl hydroxyethyl imidazolinium betaine such as ethyl imidazolinium betaine Amphoteric surfactant such as imidazolinium betaine, (3) Alkyl aminodiacetate such as monosodium laurylaminodiacetate, potassium laurylaminodiacetate, sodium myristylaminodiacetate Examples thereof include anionic surfactants such as monoalkali metals, (4) cationic surfactants such as long-chain alkyldimethylaminoethyl quaternary salts, and the like. Of these, two or more may be used in combination.

Specific examples of the polymer lubricant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, and maleic anhydride-modified ethylene / propylene / diene ternary copolymer (EPDM). , Maleic anhydride-modified polybutadiene, Maleic anhydride / ethylene copolymer, Maleic anhydride / propylene copolymer, Maleic anhydride / ethylene / propylene copolymer, Maleic anhydride / butadiene copolymer, Polyethylene, Polypropylene, Ethylene -Examples include propylene copolymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymers, ethylene / acrylic acid copolymers, ethyl cellulose, hydroxyethyl cellulose, polyalkylene oxides such as polyethylene glycol and the like. The molecular weight (weight average molecular weight) of these polymer lubricants is preferably appropriately selected in the range of 2 to 2 million, more preferably 4 to 1 million. Of these, two or more may be used in combination.

"Particle size distribution of dry polymer"
As for the particle size distribution of the dried polymer obtained in the drying step, the proportion of particles having a particle diameter of 850 μm or more (the proportion of particles not passing through a sieve having an opening particle diameter of 850 μm) is preferable in 100% by mass of the dried polymer. Is 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less. According to the method of the present embodiment, the formation of coarse particles is significantly suppressed by combining with drying using a stirring type dryer, so that the ratio of particle diameter of 850 μm or more can be set to the above preferable range. Will be. The proportion of particles having a particle size of 1400 μm or more (the proportion of particles not passing through a sieve having an opening particle diameter of 1400 μm) in 100% by mass of the dried polymer is preferably 40% by mass or less, more preferably 35% by mass or less, and further. It is preferably 30% by mass or less.

[3-7] Surface Cross-linking Step The water-absorbent resin (for example, water-absorbent resin powder) obtained through the drying step (and any subsequent step) is preferably surface-crosslinked with a surface cross-linking agent. This surface cross-linking is a process of providing a portion having a high cross-linking density on the surface layer of the water-absorbent resin (for example, water-absorbent resin powder) (a portion several tens of μm from the surface of the water-absorbent resin (for example, water-absorbent resin powder)). By performing the surface cross-linking treatment, various water-absorbing properties of the water-absorbent resin can be improved. Here, by appropriately adjusting the cross-linking density, it is possible to obtain a particularly excellent absorption ratio under pressure.

In the present invention, surface cross-linking in a state of being dispersed in a hydrophobic organic solvent performed by conventional reverse-phase suspension polymerization and surface cross-linking to a dry powder generally performed in aqueous solution polymerization are performed. Known surface cross-linking techniques, including those used, are appropriately applied, but in the present invention, surface cross-linking to a water-absorbent resin that has undergone a gel separation step and a drying step is preferable from the viewpoint of improving the absorption ratio under pressure. The surface cross-linking agent used in this step is also shown as a "post-crosslinking agent" in the known technique in order to distinguish it from the internal cross-linking agent used in the monomer aqueous solution preparation step.

In the present invention, the surface cross-linking step may be performed after the above-mentioned drying step or during the drying step. In a known surface cross-linking step, generally, a surface cross-linking agent is mixed with a hydrogel polymer (for example, a water-containing gel cross-linking polymer) or a dry polymer of a dried product thereof (for example, a cross-linking polymer), and the mixture is heated. In the present invention, these steps may be separately provided after the above-mentioned drying step, or in the drying step, a surface cross-linking agent is added to the hydrogel polymer to carry out the surface cross-linking reaction and drying of the polymer. May be performed at the same time. In addition, when the water-absorbent resin is produced by the batch-type reverse phase suspension polymerization method, the hydrophobic organic solvent and the hydrogel polymer can be separated by performing distillation in the separation step after the polymerization reaction. However, a surface-crosslinked water-absorbent resin (for example, water-absorbent resin particles) can be obtained by adding a surface-crosslinking agent to the hydrogel polymer even during the separation step.

[3-8] Other Steps In the method for producing a water-absorbent resin according to the present invention, in addition to the above-mentioned steps, a cooling step, a pulverization step, a water-containing (rewetting) step, and addition of other additives are required. It can include a step, a classification step, a sizing step, and a fine powder reuse step. Further, a transportation step, a storage step, a packing step, a storage step, and the like may be further included.

(Cooling process)
In the optional cooling step, the particulate dry polymer obtained in the drying step is cooled by using a known cooling means to obtain a particulate dry polymer cooled to a desired temperature. be able to.

(Crushing process)
It is preferable to go through a pulverization step of pulverizing the particulate dry polymer obtained in the drying step (and any subsequent cooling step). A water-absorbent resin (for example, a water-absorbent resin powder) whose particle size or particle size distribution is controlled by undergoing a pulverization step is obtained.
In the crushing step, for example, a high-speed rotary crusher such as a roll mill, a hammer mill, a screw mill, or a pin mill, a vibration mill, a knuckle type crusher, a cylindrical mixer, or the like is appropriately selected and used as the crushing means.

(Rewetting process)
In the optional rewetting step, the water-absorbent resin (for example, water-absorbent resin particles) obtained in the surface cross-linking step is mixed with a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent and an α-hydroxycarboxylic compound. This is a step of adding at least one additive selected from the group consisting of acid compounds.
The additive is preferably added to the water-absorbent resin (for example, water-absorbent resin particles) as an aqueous solution or a dispersion (slurry). The additive may be added and mixed at the same time as the above-mentioned surface cross-linking agent solution. Specifically, the method described in International Patent Publication No. 2015/053372 “(2-7) Rewetting step” is also applied to the present invention.

(Other additive addition process)
In the present invention, additives other than the above-mentioned additives can be added in order to add various functions to the water-absorbent resin. Specific examples of the additive include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders such as metal soaps, deodorants, antibacterial agents, pulps and thermoplastics. Examples include fibers. As the water-insoluble inorganic fine particles, the compound disclosed in "[5] Water-insoluble inorganic fine particles" of International Patent Publication No. 2011/040530 is applied to the present invention. Among these additives, a polyvalent metal salt, a cationic polymer, and inorganic fine particles that preferably improve the liquid permeability may be added to the water-absorbent resin so as not to impair the water-absorbing physical characteristics, especially when the swelling gel is compressed. preferable.

(Granulation process)
The "granulation step" means a step of loosening loosely aggregated water-absorbent resin (for example, water-absorbent resin powder) through the surface cross-linking step to adjust the particle size. In addition, this granulation step includes a fine powder removal step and a classification step after the surface cross-linking step. The sizing step is preferably carried out from the viewpoint of adjusting the particle size of the water-absorbent resin and obtaining stable water-absorbing physical characteristics.

(Fine powder reuse process)
The “fine powder reuse step” means a step of supplying the fine powder of the water-containing gel or the water-absorbent resin generated by sieving classification or the like in each of the above steps as it is or after granulating the fine powder to any of the steps. The fine powder reuse step is preferably carried out from the viewpoint of reducing the production loss of the water-absorbent resin.

[4] Use of the water-absorbent resin The water-absorbent resin and the absorber according to the embodiment of the present invention can provide an absorbent article in which the swelling of the water-absorbing portion is suppressed during use in a thin absorbent article. More specifically, in the water-absorbent resin and the absorbent body according to the embodiment of the present invention, the gel layer of the absorbent core is compressed by repeatedly applying a load (body weight) during use in a thin absorbent article, so that it takes a long time. It is possible to provide an absorbent article in which the swelling of the core is suppressed even in use. The use of the water-absorbent resin of the present invention is not particularly limited, but preferably includes absorbents of absorbent articles such as paper diapers (for infants and adults), menstrual napkins, and incontinence pads. In particular, it can be suitably used as an absorber for thin high-concentration paper diapers, which has had a problem of swelling of the absorption core due to the swelling gel after absorbing liquid. Examples of other absorbent articles include, for example, soil water retention agents, seedling raising sheets, seed coating materials, dew condensation prevention sheets, drip absorbers, freshness-preserving materials, disposable cairo, cooling bandanas, ice packs, medical waste liquid solidification. Agents, residual soil solidifying materials, water damage prevention waste liquid gelling agents, water-absorbing soil sac, disaster simple toilets, wet cloth materials, cosmetic thickeners, water blocking materials for electrical and electronic communication cables, gasket packing, sustained-release agents for fertilizers , Various sustained-release agents (space disinfectants, fragrances, etc.), pet sheets, cat sand, wound protection dressing materials, dew condensation prevention building materials, oil moisture removers, paints, adhesives, anti-blocking agents, light Examples thereof include diffusing agents, matting agents, additives for decorative boards, additives for artificial marble, additives for resins such as additives for toner, and the like.

Further, as a raw material for the absorber, an absorbent material such as pulp fiber can be used together with the water-absorbent resin. In this case, the content (core concentration) of the water-absorbent resin in 100% by mass of 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. It is ~ 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 for the upper layer portion of the absorbent article, the absorbent article can be kept in a clean white state. Further, since the absorber having the core concentration within the above range is excellent in diffusivity of body fluids such as urine and blood, efficient liquid distribution is expected to improve the absorption amount.

More specifically, the above-mentioned absorber may be an absorber containing the water-absorbent resin according to the embodiment of the present invention and not containing hydrophilic fibers. Alternatively, the above-mentioned absorber contains the water-absorbent resin and the hydrophilic fiber according to the embodiment of the present invention, and the mass of the water-absorbent resin is 100% by mass of the total of the water-absorbent resin and the hydrophilic fiber. It may be an absorber having an amount of 50% by mass or more.

When the absorber contains the water-absorbent resin and the hydrophilic fiber according to the embodiment of the present invention, the mass of the water-absorbent resin is preferably 50 in a total of 100% by mass of the water-absorbent resin and the hydrophilic fiber. Mass% or more and less than 100% by mass, more preferably 60% by mass or more and less than 100% by mass, more preferably 70% by mass or more and less than 100% by mass, more preferably 80% by mass or more and less than 100% by mass, still more preferably 90% by mass. It is less than 100% by mass, particularly preferably 90% by mass to 95% by mass. When the mass of the water-absorbent resin in the absorber is within the above range, (1) when the absorber is used for the upper layer of the absorbent article, the absorbent article can be kept in a clean white state. It has advantages and / or (2) because the absorber is excellent in diffusivity of body fluids such as urine and blood, it has an advantage that the absorption amount can be expected to be improved by efficient liquid distribution.

The hydrophilic fiber is not particularly limited, and examples thereof include pulp fiber, cotton linter crosslinked cellulose fiber, rayon, cotton, wool, acetate, vinylon and the like.

The present invention will be described in more detail with reference to Examples and Comparative Examples shown below, but the present invention is not limited thereto, and can be obtained by appropriately combining the technical means described in each Example. Examples are also included in the scope of the present invention. In addition, although the display of "parts" or "%" may be used in the examples, it represents "parts by mass" or "% by mass" unless otherwise specified. Unless otherwise specified, each operation is performed at room temperature (for example, 25 ° C.). As the electrical equipment (including the measurement of the physical properties of the water-absorbent resin) used in Examples and Comparative Examples, a power supply of 60 Hz at 200 V or 100 V was used unless otherwise specified.

<Evaluation method>
[Number average particle size]
Scanning electron micrographs (SEMs) of water-absorbent resin or water-absorbent resin powder were taken. Fifty primary particles in front of agglomerate particles (secondary particles) are randomly selected from the photographs, the major axis and minor axis are measured for each primary particle, and the product of the measured values is averaged. The value obtained (the geometric mean value of the measured values) was taken as the primary particle size. The primary particle diameters of each of the 50 primary particles were calculated, and the average value of the obtained values was taken as the average primary particle diameter of the water-absorbent resin.

[Moisture content]
The water content was measured according to the EDANA method (ERT430.2-02). In the measurement, the mass of the sample (water-absorbent resin or water-absorbent resin powder) was changed to 1.0 g, the drying temperature was changed to 180 ° C., and the drying time was changed to 3 hours. Specifically, after putting 1.0 g of a sample (water-absorbent resin or water-absorbent resin powder) into an aluminum cup having a bottom surface diameter of 50 mm, the aluminum cup (aluminum cup containing water-absorbent resin or water-absorbent resin powder). The total mass W1 (g) of was accurately weighed. Next, the aluminum cup (a water-absorbent resin or an aluminum cup containing a water-absorbent resin powder) was allowed to stand in an oven set to an atmospheric temperature of 180 ° C. After 3 hours, the aluminum cup (a water-absorbent resin or an aluminum cup containing a water-absorbent resin powder) was taken out from the oven, and the total mass W2 (g) was accurately weighed. When the mass of the sample (water-absorbent resin or water-absorbent resin powder) used for this measurement is M (1.0 g), the water content (mass%) of the sample is determined according to the following (Formula 2). rice field.
Moisture content (% by mass) = {(W1-W2) / M} x 100 (Equation 2).

[Mass average particle diameter (D50)]
The mass average particle size (D50) is described in "(3) Mass-Average Particle Diameter (D50) and Logirhythmic Standard Distribution (σζ) of Division" described in columns 27 and 28 of US Pat. No. 7,638,570. Measured according to the method.

[CRC]
The CRC (centrifuge holding capacity) was measured according to the EDANA method (ERT441.2-02). Specifically, after 0.2 g of the water-absorbent resin is placed in a bag made of a non-woven fabric, the non-woven fabric is immersed in a large excess of 0.9 mass% sodium chloride aqueous solution for 30 minutes to freely swell the water-absorbent resin. After that, the water absorption ratio (unit: g / g) after draining the water-absorbent resin with a centrifuge (250 G) for 3 minutes was determined.

[AAP]
The AAP (absorption factor under pressure) was measured according to the EDANA method (ERT442.2.2). The load condition was changed to 4.83 kPa (0.7 psi).

[Ext]
The Ext (water-soluble content) of the water-absorbent resin of this example and the comparative example was measured according to the EDANA method (ERT470.2-02).

〔The bulk density〕
The bulk density of the water-absorbent resin of the present invention was measured according to the EDANA method (T460.2-02).

[Swelling gel compression rate]
The swelling gel compression rate of the water-absorbent resin of the present invention was measured by the procedure shown below. The measuring device used for measuring the swelling gel compressibility will be described with reference to FIGS. 1 and 2.

1.0 g of the water-absorbent resin 16 was uniformly sprayed on the bottom 15 of the cell 11 having an inner diameter of 60 mm, the bottom 15 of which was made of a stainless steel mesh (opening 36 μm = 400 mesh). Next, a piston 12 having a diameter of 59 mm and a diameter of 108 g was mounted in the cell 11 from above the water-absorbent resin 16. Then, the cell 11 was placed in a 19.8 cm × 19.8 cm chalet 13 containing 180 g of a 0.9 mass% (mass / mass%) sodium chloride aqueous solution at 25 ° C., and the water-absorbent resin 16 was placed. Was allowed to absorb the 0.9 mass% sodium chloride aqueous solution for 5 minutes. By such an operation, the water-absorbent resin 16 swelled to form a swelling gel layer. Then, the thickness (D1 [mm]) of the swollen gel layer formed by the swollen water-absorbent resin 16 was measured. Subsequently, the cell 11 is placed on a JIS standard sieve having an opening of 4750 μm with the piston 12 mounted, and a weight of 1283 g is placed on the piston so that a load of 0.7 psi is applied to the swollen gel. The operation of removing the weight 14 after placing the 14 and allowing the cell to stand for 10 seconds was repeated 10 times. Immediately after the weight 14 was removed, a load was applied for the next 10 seconds. Then, the thickness (D2 [mm]) of the swollen gel layer formed by the swollen water-absorbent resin 16 was measured, and the swollen gel compression rate was calculated from the following (Equation 1).
Swelling gel compressibility [%] = (D1-D2) / D1 × 100 (Equation 1).

[Thickness compression rate of absorbent sheet (absorbent)]
(1) Preparation of Absorbent Sheet (Absorbent) Using FIGS. 3 and 4, a method for producing the absorbent sheet (absorbent) 20 used for measuring the thickness compression rate of the absorbent sheet (absorbent) will be described. FIG. 3 is a plan view of the evaluation absorption sheet 20 produced in the examples during the production process. FIG. 3 shows a spraying region of the water-absorbent resin 16 (that is, a water-absorbent resin spraying region 22) on the adhesive surface of the adhesive tape 21. FIG. 4 is a cross-sectional view of the evaluation absorption sheet 20 produced in the examples. FIG. 4 shows the internal configuration of the evaluation absorption sheet 20 obtained from the gills. 3 and 4 can be said to be drawings showing a method for producing an absorber according to an embodiment of the present invention.

First, as shown in FIG. 3, the adhesive surface of the adhesive tape 21 (vinyl tape No. 21S manufactured by NITTO DENKO) cut into a size of 10 cm × 10 cm is covered with an inner region (that is, adhesive) by 1 cm from the edges of the four sides of the adhesive tape 21. 1.0 g of 1.0 g of water-absorbent resin 16 is sprayed on a region of 8 cm × 8 cm in the center of the tape (water-absorbent resin spraying region 22), and a non-woven fabric 23 (air-laid) of 10 cm × 10 cm from above the water-absorbent resin 16 is further sprayed. A non-woven fabric (with a grain size of 46.6 g / m2) is placed, and the non-woven fabric 23 and the adhesive surfaces on the four sides of the adhesive tape 21 are bonded to each other to form a laminated structure (adhesive tape 21, water-absorbent resin 16, non-woven fabric 23) shown in FIG. , Are laminated in this order), and an evaluation absorption sheet 20 was produced. The evaluation absorbent sheet 20 can be said to be an absorbent body containing the water-absorbent resin 16 and not containing hydrophilic fibers.

(2) Measurement of thickness compression rate of absorbent sheet (absorbent) 20 The absorbent sheet 20 (absorbent) for evaluation is placed on an acrylic plate (10 cm x 23 cm, thickness 0.3 cm) on a flat table. , 25 mL of a 0.9 mass% sodium chloride aqueous solution at 20 ° C. was added to the evaluation absorption sheet 20 over 2 minutes to swell the water-absorbent resin 16 in the evaluation absorption sheet 20. Three minutes after the addition of the 0.9% by mass sodium chloride aqueous solution was completed, the thickness (D1'[mm]) of the absorption sheet 20 for evaluation was measured. Subsequently, another acrylic plate (10 cm × 23 cm, thickness 0.3 cm) was placed on the evaluation absorbent sheet 20. Further, the operation of placing a weight of 1.0 kg on an acrylic plate, allowing it to stand for 10 seconds, and removing the weight was repeated 10 times. Immediately after removing the weight, a load was applied for the next 10 seconds. After that, the acrylic plate on the evaluation absorption sheet 20 is removed, the thickness (D2'[mm]) of the evaluation absorption sheet 20 is measured, and the thickness compression rate of the evaluation absorption sheet 20 (absorbent) is measured from the following (Equation 3). Was calculated.
Thickness compressibility [%] = (D1'-D2') / D1'x100 (Equation 3).

[Example 1]
800 g of n-heptane was placed in a 2000 ml four-neck separable flask equipped with a stirrer, a reflux cooler, a thermometer, a nitrogen gas introduction tube and a dropping funnel, and a maleic anhydride-modified ethylene-propylene copolymer was used as a dispersion aid. (High wax (registered trademark) HW2203A / manufactured by Mitsui Kagaku Co., Ltd.) 0.88 g was added, and the maleic anhydride-modified ethylene-propylene copolymer was dissolved in n-heptane to obtain a heptane solution. Then, nitrogen gas was blown into the obtained heptane solution to expel the dissolved oxygen in the heptane solution.

Separately, in a flask, 127 g of sodium acrylate, 36 g of acrylic acid, 0.097 g of polyethylene glycol diacrylate (n = 9), 0.008 g of diethylenetriamine 5 acetate / 5 sodium, 0.67 g of hydroxyethyl cellulose as a thickener, and ions. A monomer aqueous solution (1) consisting of 215 g of exchanged water was prepared, and nitrogen gas was blown into the monomer aqueous solution (1) to expel the dissolved oxygen dissolved in the monomer aqueous solution (1). Next, 1.2 g of a 15% (mass / mass%) aqueous solution of sodium persulfate was added to the monomer aqueous solution (1) in this flask, and then the entire amount of the obtained solution was added to the separable flask. The monomer aqueous solution (1) was dispersed in the heptane solution by stirring the mixed solution in the separable flask at 210 rpm. Then, the bath temperature was raised to 60 ° C. to start the polymerization reaction, the bath temperature was maintained at 60 ° C. for 2 hours, the polymerization was stopped, filtration was performed by suction filtration, and the residue was air-dried overnight to contain water. A gel polymer (1) was obtained. The average primary particle size of the hydrogel polymer (1) was 180 μm.

Next, the hydrous gel polymer (1) (gel temperature: 90 ° C.) is charged into a gel sizing device having a screw and a porous plate having a pore size of 0.8 mm, and the sizing gel is discharged from the gel sizing device. (1) was obtained.

Subsequently, the sizing gel (1) was dried using a cylindrical container rotary dryer. Specifically, in an atmosphere of a temperature of 200 ° C., the rotary container provided in the cylindrical container rotary dryer is rotated at 75 rpm, and the heated sizing gel (1) is supplied to the cylindrical container rotary dryer. And dried to obtain a dry polymer (1). The water content of the dry polymer (1) was 10% by mass.

Subsequently, the dry polymer (1) is supplied to a roll mill (crusher) and pulverized to adjust the particle size, and further classified using a sieve having an opening particle diameter of 150 μm to obtain the water-absorbent resin powder (1). Obtained. The mass average particle size of the water-absorbent resin powder (1) was 380 μm.

From 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.385 parts by mass of ethylene carbonate, 0.644 parts by mass of propylene glycol and 2.6 parts by mass of ion-exchanged water with respect to 100 parts by mass of the water-absorbent resin powder (1). The surface cross-linking agent solution was sprayed and mixed uniformly using a high-speed continuous mixer.

The obtained mixture was introduced into a heat treatment machine whose atmospheric temperature was adjusted to 195 ° C. ± 2 ° C., heat-treated for 30 minutes, and then the powder temperature was forcibly cooled to 60 ° C. to absorb water crosslinked. A sex resin powder (1) was obtained.

27.5% by mass of aluminum sulfate aqueous solution (8% by mass in terms of aluminum oxide) 1.17 parts by mass and 60% by mass of sodium lactate aqueous solution with respect to 100 parts by mass of the surface-crosslinked water-absorbent resin powder (1). A surface cross-linking agent solution consisting of 0.196 parts by mass and 0.029 parts by mass of propylene glycol was uniformly mixed. Further, 10.0% by mass of water was uniformly mixed with 100 parts by mass of the water-absorbent resin powder (1) after mixing.

Then, it was crushed (grain size) until it passed through a JIS standard sieve having an opening of 710 μm to obtain a water-absorbent resin (1). The obtained water-absorbent resin (1) was in the form of particles, and more specifically, it was agglomerates of spherical particles. The physical characteristics of the obtained water-absorbent resin (1) are shown in Tables 1 to 3.

[Example 2]
Take 800 g of cyclohexane in a 2000 ml four-neck separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introduction tube and a dropping funnel, and use sucrose fatty acid ester (DK ester (registered trademark) F-) as a dispersion aid. 50 / HLB = 6) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. was added, and the sucrose fatty acid ester was dissolved in cyclohexane to obtain a cyclohexane solution. Then, nitrogen gas was blown into the obtained cyclohexane solution to expel the dissolved oxygen in the cyclohexane solution.

Separately, in a flask, a monomer consisting of 141 g of sodium acrylate, 36 g of acrylic acid, and 0.022 g of N, N'-methylenebisacrylamide, 0.71 g of hydroxyethyl cellulose as a thickener, and 327.65 g of ion-exchanged water. An aqueous solution (2) was prepared, and nitrogen gas was blown into the monomeric aqueous solution (2) to expel the dissolved oxygen dissolved in the monomer aqueous solution (2). Next, 0.95 g of a 15% aqueous solution of sodium persulfate was added to the monomer aqueous solution (2) in the flask, and then the entire amount of the obtained solution was added to the separable flask, and the separable flask was added. The aqueous monomer solution (2) was dispersed in the cyclohexane solution by stirring the mixed solution at 370 rpm. Then, the bath temperature was raised to 60 ° C. to start the polymerization reaction, the bath temperature was maintained at 60 ° C. for 2 hours, the polymerization was stopped, filtration was performed by suction filtration, and the residue was air-dried overnight to contain water. A gel polymer (2) was obtained. The average primary particle size of the hydrogel polymer (2) was 195 μm.

Next, the hydrous gel polymer (2) (gel temperature: 90 ° C.) is charged into a gel sizing device having a screw and a porous plate having a pore size of 0.8 mm, and the sizing gel (gel temperature: 90 ° C.) is discharged from the gel sizing device. 2) was obtained.

Next, 3.2 kg of the sizing gel (2) obtained above was put into a heat insulating chamber. As a result of heating in the heat insulating chamber, the temperature of the sizing gel (2) at the time of supplying the dryer was 80 ° C.

Subsequently, the sizing gel (2) was dried using a cylindrical container rotary dryer. Specifically, in an atmosphere of a temperature of 200 ° C., the rotary container provided in the cylindrical container rotary dryer is rotated at 75 rpm, and the heated sizing gel (2) is supplied to the cylindrical container rotary dryer. And dried to obtain a dry polymer (2). The water content of the dry polymer (2) was 8% by mass.

Subsequently, the dry polymer (2) is supplied to a roll mill (crusher) and pulverized to adjust the particle size, and further classified using a sieve having an opening particle diameter of 150 μm to obtain the water-absorbent resin powder (2). Obtained. The mass average particle size of the water-absorbent resin powder (2) was 110 μm.

A surface cross-linking agent solution consisting of 0.1 part by mass of ethylene glycol diglycidyl ether, 1.0 part by mass of isopropyl alcohol and 3.0 parts by mass of ion-exchanged water is sprayed on 100 parts by mass of the water-absorbent resin powder (2). It was sprayed and mixed uniformly using a high speed continuous mixer.

The obtained mixture was introduced into a heat treatment machine whose atmospheric temperature was adjusted to 100 ° C., heat-treated for 40 minutes, and then the powder temperature was forcibly cooled to 60 ° C. to obtain surface-crosslinked water-absorbent resin powder. (2) was obtained.

27.5% by mass of aluminum sulfate aqueous solution (8% by mass in terms of aluminum oxide) 1.17 parts by mass and 60% by mass of sodium lactate aqueous solution with respect to 100 parts by mass of the surface-crosslinked water-absorbent resin powder (2). A surface cross-linking agent solution consisting of 0.196 parts by mass and 0.029 parts by mass of propylene glycol was uniformly mixed.

Then, it was crushed (grain size) until it passed through a JIS standard sieve having an opening of 300 μm to obtain a water-absorbent resin (2). The obtained water-absorbent resin (2) was in the form of particles, and more specifically, it was spherical particles. The physical characteristics of the obtained water-absorbent resin (2) are shown in Tables 1 to 3.

[Example 3]
Take 500 g of n-heptane in a 2000 mL five-necked cylindrical round-bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube, and sucrose fatty acid ester (S-370) as a dispersion aid. / Mitsubishi Chemical Co., Ltd., HLB = 3) was added, dispersed, and the temperature was raised to dissolve the sucrose fatty acid ester in n-heptane to obtain a heptane solution. Then, the obtained heptane solution was cooled to 55 ° C.

Separately, 73.6 g of acrylic acid was charged in a 500 mL Erlenmeyer flask, and while cooling this from the outside, 102.2 g of a 30% by mass (mass / mass%) sodium hydroxide aqueous solution was dropped onto the Erlenmeyer flask. , 75 mol% of acrylic acid was neutralized. Further, as a thickener, 0.71 g of hydroxyethyl cellulose, 68.6 g of ion-exchanged water, 0.11 g of potassium persulfate, and 0.0092 g of ethylene glycol diglycidyl ether were added to the Erlenmeyer flask, and a single amount for the first-stage polymerization was added. A body solution (3A) was prepared.

The entire amount of this first-stage polymerization monomer aqueous solution (3A) is added to the five-necked cylindrical round-bottom flask under stirring at a stirring speed of 450 rpm to obtain a monomer aqueous solution (3A). Was dispersed in a heptane solution. Then, the inside of the system was sufficiently replaced with nitrogen, the temperature was raised, the bath temperature was maintained at 70 ° C., the polymerization reaction was carried out for 1 hour, and then the polymerization slurry liquid was cooled to room temperature.

95.28 g of acrylic acid is charged in another Erlenmeyer flask having a volume of 500 mL, and 132.2 g of a 30 mass% sodium hydroxide aqueous solution is added dropwise to the Erlenmeyer flask while cooling the mixture to neutralize 75 mol% of acrylic acid. did. Further, 51.2 g of ion-exchanged water, 0.14 g of potassium persulfate, and 0.0357 g of ethylene glycol diglycidyl ether were added to the Erlenmeyer flask to prepare a monomer aqueous solution (3B) for the second stage polymerization. It was cooled using an ice water bath.

After adding the entire amount of this second-stage polymerization monomer aqueous solution (3B) to the polymerization slurry liquid, the inside of the system is sufficiently replaced with nitrogen, and then the bath temperature is raised to 70 ° C. to carry out the polymerization reaction. After the polymerization reaction was carried out for 2 hours, the residue was filtered off by suction filtration, and the residue was air-dried overnight to obtain a hydrogel polymer (3). The primary particle size of the hydrogel polymer (3) was 70 μm.

Next, the hydrous gel polymer (3) (gel temperature: 90 ° C.) is charged into a gel sizing device having a screw and a porous plate having a pore size of 0.8 mm, and the sizing gel (gel temperature: 90 ° C.) is discharged from the gel sizing device. 3) was obtained.

Subsequently, the sizing gel (3) was dried using a cylindrical container rotary dryer. Specifically, in an atmosphere of a temperature of 200 ° C., the rotary container provided in the cylindrical container rotary dryer is rotated at 75 rpm, and the heated sizing gel (3) is supplied to the cylindrical container rotary dryer. And dried to obtain a dry polymer (3). The water content of the dry polymer (3) was 7% by mass.

Subsequently, the dry polymer (3) is supplied to a roll mill (crusher) and pulverized to adjust the particle size, and further classified using a sieve having an opening particle diameter of 150 μm to obtain the water-absorbent resin powder (3). Obtained. The mass average particle size of the water-absorbent resin powder (3) was 400 μm.

Subsequently, a surface cross-linking agent solution consisting of 0.18 parts by mass of ethylene glycol diglycidyl ether, 1.5 parts by mass of propylene glycol and 5.0 parts by mass of ion-exchanged water with respect to 100 parts by mass of the water-absorbent resin powder (3). Was sprayed and mixed uniformly using a high speed continuous mixer.

The obtained mixture was introduced into a heat treatment machine whose atmospheric temperature was adjusted to 100 ° C., heat-treated for 40 minutes, and then the powder temperature was forcibly cooled to 60 ° C. to obtain surface-crosslinked water-absorbent resin powder. (3) was obtained.

With respect to 100 parts by mass of the surface-crosslinked water-absorbent resin powder (3), 1.17 parts by mass (mass / mass%) of an aluminum sulfate aqueous solution (8% by mass in terms of aluminum oxide), 60 parts by mass. A surface cross-linking agent solution consisting of 0.196 parts by mass of a mass% sodium lactate aqueous solution and 0.029 parts by mass of propylene glycol was uniformly mixed.

Then, it was crushed (grain size) until it passed through a JIS standard sieve having an opening of 710 μm to obtain a water-absorbent resin (3). The obtained water-absorbent resin (3) was in the form of particles, and more specifically, it was agglomerates of spherical particles. The physical characteristics of the obtained water-absorbent resin (3) are shown in Tables 1 to 3.

[Comparative Example 1]
A water-absorbent resin was obtained by aqueous solution polymerization. That is, in a 1 L capacity polypropylene container, 296 g of a 48.5 mass% sodium hydroxide aqueous solution, 354 g of acrylic acid, 1.00 g of polyethylene glycol diacrylate (average number of ethylene oxide units 9), and 0.1 mass% diethylenetriamine 5 21.66 g of an aqueous solution of 5 sodium acetate and 319 g of ion-exchanged water were added, and the added raw materials were stirred to prepare a comparative monomer aqueous solution (1) composed of these raw materials.

Stirring of the comparative monomer aqueous solution (1) was continued, and the comparative monomer aqueous solution (1) was heated. When the liquid temperature of the comparative monomer aqueous solution (1) reached 78 ° C., 15.8 g of a 3.8 wt% sodium persulfate aqueous solution was added to the comparative monomer aqueous solution (1), and the obtained mixed solution was added. Was immediately poured into a stainless steel butt-type reactor (bottom surface; 340 × 340 mm, height; 25 mm, inner surface; Teflon® coating) in an open-air system, and the polymerization reaction started shortly thereafter. The stainless steel butt-type reactor was preset to have a surface temperature of 50 ° C. using a hot plate (NEO HOTPLATE HI-1000 / manufactured by Inuchi Seieidou Co., Ltd.).

The polymerization reaction proceeded by expanding and foaming in all directions toward the upper side of the butt-type reactor while generating water vapor, and then contracted to a size slightly larger than the bottom surface of the reactor. The polymer obtained by this operation was designated as a comparative hydrogel polymer (1). The polymerization reaction (expansion / contraction) was completed in about 1 minute, and the comparative hydrogel polymer (1) was kept in the reaction apparatus for 3 minutes thereafter. These series of operations were performed in an open system to the atmosphere.

The obtained comparative hydrogel polymer (1) was pulverized using a meat chopper (No. 32 type / manufactured by Hiraga Seisakusho Co., Ltd.) equipped with a die having a die hole diameter of 9.5 mm. In the gel crushing, the comparative hydrogel polymer (1) 2.4 (kg / min) and water vapor 5.0 (kg / h) were met with the screw shaft rotation speed of the meat chopper set to 130 rpm. I went by putting it in the chopper.

Then, the comparative hydrogel polymer (1) was dried using a hot air dryer to obtain a comparative dry polymer (1). The drying was carried out by spreading the comparative hydrogel polymer (1) crushed by a meat chopper on a stainless steel wire mesh having an opening of 850 μm and allowing hot air at 180 ° C. to aerate for 30 minutes.

Comparative dry polymer (1) was pulverized using a roll mill (WML type roll crusher / manufactured by Inoguchi Giken Co., Ltd.), and then classified using JIS standard sieves with openings of 850 μm and 150 μm for comparison of amorphous crushed form. A water-absorbent resin powder (1) was obtained. The mass average particle size of the comparative water-absorbent resin powder (1) was 340 μm.

Comparative water-absorbent resin powder (1) A surface composed of 0.024 parts by mass of ethylene glycol diglycidyl ether, 0.308 parts by mass of ethylene carbonate, 0.515 parts by mass of propylene glycol and 2.08 parts by mass of ion-exchanged water in 100 parts by mass. The cross-linking agent solution was uniformly mixed. The obtained mixture was introduced into a heat-treated atmosphere adjusted to an atmospheric temperature of 190 ° C ± 2 ° C, heat-treated for 30 minutes, and then the powder temperature was forcibly cooled to 60 ° C to achieve surface-crosslinked comparative water absorption. A sex resin powder (1) was obtained.

A solution consisting of 45% by mass of diethylenetriamine 5 acetate 3 sodium salt 0.022 part by mass and 1 part by mass of ion-exchanged water was uniformly mixed with 100 parts by mass of the surface-crosslinked comparative water-absorbent resin powder (1) for comparative water absorption. Sexual resin particles (1) were obtained.

To 100 parts by mass of the obtained comparative water-absorbent resin particles (1), 0.35 part by mass of silicon dioxide (Leoloseal (registered trademark) QS-20 / Oriental Silicas Corporation) on the fine particles was added and mixed to perform comparative water absorption. The sex resin (1) was obtained. The physical characteristics of the obtained comparative water-absorbent resin particles (1) are shown in Tables 1 to 3.

The following can be seen from Tables 1 to 3. The water-absorbent resins (1) to (3) of Examples 1 to 3 have a swelling gel compression rate of 3% or more, and can provide an absorbent article in which the swelling of the water-absorbing portion is suppressed during use in a thin absorbent article. It can be said that it is a water-absorbent resin. On the other hand, in the comparative water-absorbent resin (1) of Comparative Example 1, the absolute values of the swelling gel thicknesses D1 and D2 are small, but the swelling gel compressibility (%) is negative, which is larger than the thickness D1 before loading. The thickness D2 after loading is rather larger. Further, as shown in Table 3, when the comparative water-absorbent resin (1) of Comparative Example 1 is used for the absorbent sheet, the absorbent sheet after loading is thicker than that of Examples 1 to 3.

The water-absorbent resin and the absorber according to one embodiment of the present invention can provide an absorbent article in which the swelling of the water-absorbing portion is suppressed during use in a thin absorbent article. Therefore, the water-absorbent resin and the absorber according to the embodiment of the present invention can be suitably used for absorbents of absorbent articles such as paper diapers (for infants and adults), menstrual napkins, and incontinence pads. ..

10: Measuring device for swelling gel compression rate 11: Cell 12: Piston 13: Petri dish 14: Weight 15: Bottom 16: Water-absorbent resin 20: Evaluation absorbent sheet 21: Adhesive tape 22: Water-absorbent resin spraying area 23: Non-woven fabric

Claims (9)

Particulate poly (meth) acrylic acid (salt) -based water-absorbent resin having a swelling gel compressibility of 3% or more represented by the following (formula 1):
Swelling gel compressibility [%] = (D1-D2) / D1 × 100 (Equation 1)
(Here, D1 includes a piston having a diameter of 59 mm and a cell having an inner diameter of 60 mm having a mesh-like bottom, and 0.9 mass of the cell on which 1.0 g of the water-absorbent resin is sprayed on the bottom. The thickness of the swollen gel layer formed by the water-absorbent resin when placed in a petri dish containing a% sodium chloride aqueous solution and the water-absorbent resin absorbs the 0.9% by mass sodium chloride aqueous solution for 5 minutes [ mm], and in D2, the cell is placed on a sieve having an opening of 4750 μm, and a weight is placed on the piston so that a load of 0.7 psi is applied to the swollen gel layer, and the cell is placed on the cell. The thickness [mm] of the swollen gel layer formed by the water-absorbent resin after the operation of removing the weight after standing for a second is repeated 10 times). The water-absorbent resin according to claim 1, wherein the water-absorbent resin is agglomerates of spherical particles. The water-absorbent resin according to claim 1 or 2, wherein the mass average particle diameter (D50) is 50 to 700 μm. The water-absorbent resin according to any one of claims 1 to 3, wherein the water-absorbent resin has a D2 of less than 15 mm. The water-absorbent resin according to any one of claims 1 to 4, wherein the water-absorbent resin has a D1 of less than 15 mm. The water-absorbent resin according to any one of claims 1 to 5, wherein the water absorption ratio (AAP) under pressure is 18 g / g or more. The water-absorbent resin according to any one of claims 1 to 6, which is obtained by reverse phase suspension polymerization in a hydrophobic organic solvent. The water-absorbent resin according to any one of claims 1 to 7, which is obtained by extruding spherical particles with an extruder having a porous plate. The mass of the water-absorbent resin containing the water-absorbent resin according to any one of claims 1 to 8 and containing (1) no hydrophilic fibers or (2) containing hydrophilic fibers. Is 50% by mass or more in the total 100% by mass of the water-absorbent resin and the hydrophilic fiber.

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