JPWO2020067563A1 - Manufacturing method of water-absorbent resin powder and water-absorbent resin powder - Google Patents

Abstract

A method for producing a water-absorbent resin powder that is surface-crosslinked with a substance other than the water-soluble polyvalent metal salt and contains the water-soluble polyvalent metal salt, and the concentration of the polyvalent metal salt under heating is 5% by weight or more. A water-absorbent resin powder having excellent liquid permeability can be easily obtained by a method for producing a water-absorbent resin powder in which an aqueous solution is sprayed onto the water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in a fluidized layer mixer.

Description

The present invention relates to a method for producing a water-absorbent resin powder and a water-absorbent resin powder.

As sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads, absorbent bodies made of hydrophilic fibers such as pulp and water-absorbent resins are widely used for the purpose of absorbing body fluids.

In recent years, these sanitary materials have become highly functional and thin, and the amount of water-absorbent resin used per sanitary material and the ratio of water-absorbent resin to the entire absorber composed of water-absorbent resin and hydrophilic fiber have increased. Tend to do. That is, by reducing the number of hydrophilic fibers having a small bulk specific density and using a large amount of water-absorbent resin having excellent water absorption and a large bulk specific density, the ratio of the water-absorbent resin in the absorber is increased and the amount of water absorption is reduced. We are trying to make the sanitary material thinner.

As the ratio of the water-absorbent resin to the entire absorber increases, the performance requirements for the water-absorbent resin also increase. For example, not only the water absorption ratio (CRC) under no pressure but also the water absorption ratio (AAP) under pressure is required so that water can be absorbed even under weight, and liquid permeability (for example) to prevent gel blocking is required. , GBP and SFC) are required.

In addition, there is an increasing demand for handleability of the water-absorbent resin for efficient production of the absorber. Above all, since the water-absorbent resin exhibits hygroscopicity, moisture-absorbing fluidity (also known as anti-caking property) is required so that the handleability as a powder does not change regardless of humidity.

In order to meet these requirements, techniques for adding additives to the surface of water-absorbent resin particles have been mainly developed.

For example, it is known to use a polyvalent metal salt for improving liquid permeability, and Patent Document 1 states that a non-reactive coating agent such as a polyvalent metal salt is continuously applied to water-absorbent polymer particles. Discloses a method for producing a water-absorbent substance, which comprises a step of spray coating in a fluidized bed reactor in the range of 0 ° C. to 150 ° C. Patent Documents 2 to 7 disclose a method for improving liquid permeability (SFC) by mixing a polyvalent metal salt with a water-absorbent resin at the time of surface cross-linking or after surface cross-linking.

As a method for improving surface cross-linking, Patent Documents 8 and 9 describe a method for surface cross-linking of a water-absorbent resin, in which a surface cross-linking agent is mixed with water-absorbent resin particles heated while flowing and a surface cross-linking agent is mixed with the water-absorbent resin particles. It is disclosed. Patent Document 10 discloses a method for producing a water-absorbent resin in which a surface cross-linking agent is sprayed on a monomer forming a fluidized bed. Patent Documents 11 to 13 disclose a surface cross-linking method in which a surface cross-linking agent and a separately added water-absorbent resin are heated and cross-linked by a fluidized bed mixer.

In order to improve the water absorption rate, Patent Documents 14 to 16 disclose a method for granulating water-absorbent resin fine particles in which a binder is sprayed in a fluidized bed granulator, and Patent Document 17 discloses a polyvalent metal salt. A water-absorbent resin composition for spraying an aqueous solution is disclosed. Further, Patent Documents 18 and 19 disclose a method for adding an aqueous solution of a polyvalent metal salt, which is improved in order to obtain a water-absorbent resin having excellent liquid permeability and moisture absorption and fluidity. According to Patent Document 18 (Comparative Example 2), when aluminum sulfate hydrate was powder-added to the water-absorbent resin, the hygroscopic fluidity was poor.

On the other hand, a method of adding water-insoluble inorganic fine particles such as silicon dioxide to improve liquid permeability or hygroscopic fluidity is also very widely used. For example, in order to improve liquid permeability (SFC), Patent Document 20 discloses a water-absorbent resin to which silica or the like is added, and Patent Document 21 discloses a water-absorbent resin to which a water-insoluble metal phosphate is added. Further, in order to improve the hygroscopic fluidity, Patent Document 22 discloses a water-absorbent resin to which a water-insoluble multivalent metal composite salt is added. However, the addition of such water-insoluble inorganic fine particles may cause insufficient liquid permeability or moisture absorption and fluidity, or may reduce the water absorption ratio under pressure.

Further, although Patent Document 23 discloses a technique of adding fine particles of alum to neutralize ammonia which is a cause of urine odor, it has poor liquid permeability and insufficient moisture absorption and fluidity.

Japanese Patent Publication "Special Table 2009-522387" Japanese Patent Publication "Japanese Patent Laid-Open No. 2005-077519" International Publication No. 2000/053664 Pamphlet International Publication No. 2000/053644 Pamphlet International Publication No. 2001/074913 Pamphlet Japanese Patent Publication "Special Table 2004-508432" International Publication No. 2007/121941 Pamphlet Japanese Patent Publication "Japanese Patent Laid-Open No. 7-242709" Japanese Patent Publication "Japanese Patent Laid-Open No. 7-224204" International Publication No. 2003/044120 Pamphlet International Publication No. 2013/11414 Pamphlet International Publication No. 2013/11415 Pamphlet International Publication No. 2009/028568 Pamphlet Japanese Patent Gazette "Special Table 3-501493 Gazette" Japanese Patent Publication "Japanese Patent Laid-Open No. 6-313043" Japanese Patent Publication "Japanese Patent Laid-Open No. 6-313402" Japanese Patent Publication "Japanese Patent Laid-Open No. 61-257235" Japanese Patent Publication "Japanese Unexamined Patent Publication No. 2005-113117" Japanese Patent Publication "Japanese Unexamined Patent Publication No. 2005-344103" International Publication No. 2007/037522 Pamphlet International Publication No. 2002/060983 Pamphlet International Publication No. 2014/054656 Pamphlet Japanese Patent Publication "Japanese Patent Laid-Open No. 2000-79159"

However, from the viewpoint of easily producing a water-absorbent resin powder having excellent liquid permeability, moisture absorption and fluidity, and water absorption ratio under pressure, there is room for further improvement in the above-mentioned prior art.

The present invention has been made in view of the above problems, and an object of the present invention is a method for easily producing a water-absorbent resin powder having excellent liquid permeability, moisture absorption and fluidity, and a water absorption ratio under pressure, and a water-absorbent resin. To provide powder.

As a result of diligent studies to achieve the above object, the inventors of the present application spray a polyvalent metal salt aqueous solution on the water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in a fluidized bed mixer under heating. As a result, it has been found that a water-absorbent resin powder having excellent liquid permeability, moisture-absorbing fluidity, and water-absorbing ratio under pressure can be obtained. Further, they have found that the water-absorbent resin powder in which fine polyvalent metal fine particles present on the surface are excellent in liquid permeability, moisture absorption and fluidity, and water absorption ratio under pressure, and have completed the present invention.

That is, the present invention (1) is a method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt, and the concentration of the polyvalent metal salt is as high as 5% by weight or more. It has a spraying step of spraying a valent metal salt aqueous solution onto water-absorbent resin particles at the time of surface cross-linking with an organic surface cross-linking agent or after surface cross-linking in a fluidized layer mixer, and the air temperature at the spray position of the polyvalent metal salt aqueous solution. Provided is a method for producing a water-absorbent resin powder having a temperature of 50 ° C. or higher.

Further, the present invention (2) is a method for producing a water-absorbent resin powder which is surface-crosslinked with an organic surface-crosslinking agent and contains a water-soluble polyvalent metal salt. On the other hand, a method for producing a water-absorbent resin powder is provided, in which water-soluble polyvalent metal salt particles having a volume average particle diameter of 0.3 to 15 μm measured by a laser diffraction / scattering method are added.

Further, the present invention (3) is a water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt, and has a number average particle diameter of 0.3 to 15 μm on the surface of the water-absorbent resin powder. Provided is a water-absorbent resin powder to which water-soluble polyvalent metal salt particles of (SEM image analysis) are attached.

According to one aspect of the present invention, a water-absorbent resin powder having excellent liquid permeability, moisture absorption and fluidity, and water absorption ratio under pressure can be easily produced.

Further, according to one aspect of the present invention, it is possible to easily produce a water-absorbent resin powder having an excellent color tone over time.

It is an SEM image of the water-absorbent resin powder of Example 1.

Hereinafter, the method for producing the water-absorbent resin powder according to the embodiment of the present invention and the water-absorbent resin powder according to the embodiment of the present invention will be described in detail, but the scope of the present invention is not limited to these explanations. However, other than the following examples, changes and implementations can be appropriately made without impairing the gist of the present invention.

Specifically, the present invention is not limited to each of the following embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in the different embodiments may be appropriately combined. The obtained embodiments are also included in the technical scope of the present invention.

Unless otherwise specified in the present specification, "A to B" representing a numerical range means "A or more and B or less". Also, unless otherwise noted, "ppm" means "weight ppm" or "mass ppm". Further, "-acid (salt)" means "-acid and / or a salt thereof", and "(meth) acrylic" means "acrylic and / or methacryl", respectively.

[1] Definition of terms [1-1] "Water-absorbent resin""Water-absorbent resin particles""Water-absorbent resin powder"
In the present specification, the "water-absorbent resin" means a water-swellable water-insoluble polymer gelling agent, and is generally in the form of powder. Here, "water swellability" means that the CRC defined by ERT441.2-02 is 5 g / g or more, and "water insoluble" is defined by ERT470.2-02. Ext is 0% by weight to 50% by weight. As long as the required performance (CRC and Ext) is satisfied, even a water-absorbent resin composition containing an additive or the like is referred to as a "water-absorbent resin" in the present specification.

For convenience, in the present specification, the water-absorbent resin before surface treatment or surface cross-linking of the polyvalent metal salt aqueous solution is referred to as "water-absorbent resin particles", and the water-absorbent resin after surface treatment and surface cross-linking is referred to as "water-absorbent resin". It is called "sex resin powder".

[1-2] "EDANA" and "ERT"
"EDANA" is an abbreviation for European Disposables and Nonwovens Associations, and "ERT" is an abbreviation for EDANA Recommended Test Methods, which is a European standard (almost the world standard). Is. In this specification, unless otherwise specified, the measurement is performed in accordance with the original ERT (publicly known document; revised in 2002).

[1-3-1] Centrifuge Holding Capacity (CRC) (ERT441.2-02)
"CRC" is an abbreviation for Centrifuge Retention Capacity, and means the water absorption ratio of a water-absorbent resin under no pressure (sometimes referred to as "water absorption ratio"). Specifically, 0.2 g of a water-absorbent resin is placed in a non-woven fabric bag, and then immersed in a large excess of 0.9 mass% sodium chloride aqueous solution for 30 minutes for free swelling, and then a centrifuge (250 G). ) For 3 minutes, the water absorption ratio (unit: g / g).

[1-3-2] "Ext" (ERT470.2-02)
"Ext" is an abbreviation for Extremes, and means a water-soluble component (amount of water-soluble component) of a water-absorbent resin.

Specifically, it refers to the amount of dissolved polymer (unit:% by weight) after 1.0 g of a water-absorbent resin is added to 200 mL of a 0.9 wt% sodium chloride aqueous solution and stirred at 500 rpm for 16 hours. The amount of dissolved polymer is measured using pH titration.

[1-3-3] "FLOWRATE" (ERT450.2-02)
"FLOWRATE" means the powder fluidity of the water-absorbent resin. Specifically, it refers to the speed (unit: g / s) at which 100 g of the water-absorbent resin flows down from the opening (diameter 10 mm) of the conical hopper. Hereinafter, "FLOWRATE" may be referred to as "FR".

[1-4] "Liquid permeability"
In the present specification, the "liquid permeability" of the water-absorbent resin powder refers to the flowability of the liquid passing between the particles of the water-absorbent resin or the gel in which the water-absorbent resin powder is swollen under a load or no load. , SFC and GBP are typical measurement methods.

"SFC (Saline Flow Conductivety)" refers to the liquid permeability of a 0.69 mass% sodium chloride aqueous solution to a water-absorbent resin under a load of 2.07 kPa, and conforms to the SFC test method disclosed in US Pat. No. 5,669,894. Is measured.

"GBP (Gel Bed Pearmeability)" is measured by the method disclosed in WO2004 / 096304.

[2] Method for producing water-absorbent resin powder The method for producing water-absorbent resin powder according to an embodiment of the present invention (also simply referred to as "production method" in the present specification) is described in (1) as an organic surface cross-linking agent. This is a method for producing a water-absorbent resin powder that is surface-crosslinked and contains a water-soluble polyvalent metal salt. A polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is surface-crosslinked in a fluidized layer mixer. Provided is a method for producing a water-absorbent resin powder, which comprises a spraying step of spraying on the water-absorbent resin particles at the time or after surface cross-linking, and the air temperature at the spray position of the polyvalent metal salt aqueous solution is 50 ° C. or higher.

In one embodiment of the present invention, the polyvalent metal salt aqueous solution is spray-dried by spraying the polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more in a fluidized bed mixer in a high temperature atmosphere. Therefore, it is presumed that it adheres to the surface of the water-absorbent resin in the form of fine lumps.

Further, the method (2) for producing a water-absorbent resin powder according to an embodiment of the present invention is a method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt. Production of water-absorbent resin powder by adding polyvalent metal salt particles having a volume average particle diameter of 0.3 to 15 μm measured by a laser diffraction / scattering method to a water-absorbent resin surface-crosslinked with an organic surface cross-linking agent. Provide a method.

With the above configuration, it is possible to obtain a water-absorbent resin powder having excellent liquid permeability, moisture absorption and fluidity, and water absorption ratio under pressure.

Further, with the above configuration, it is possible to obtain a water-absorbent resin powder in which water-soluble polyvalent metal salt particles are attached to the surface.

Hereinafter, typical steps (2-1) to (2-9) as a method for producing the water-absorbent resin according to the embodiment of the present invention will be described, but the water-absorbent resin according to the embodiment of the present invention will be described. The production method includes a surface cross-linking step and a spraying step described later, and other steps are optionally included.

(2-1) Preparation Step of Monomer Aqueous Solution This step is a step of preparing a monomer aqueous solution. A monomer slurry solution may be used instead of the monomer aqueous solution as long as the water absorption performance of the obtained water-absorbent resin is not deteriorated, but in this section, the monomer aqueous solution will be described for convenience. ..

As the monomers that can be used in this step, acrylic acid (salt), methacrylic acid (salt), (anhydrous) maleic acid (salt), fumaric acid (salt), crotonic acid (salt), itaconic acid (salt), vinyl. Acid group-containing unsaturated monomers such as sulfonic acid (salt), 2- (meth) acrylamide-2-methylpropanesulfonic acid (salt), (meth) acryloxialcan sulfonic acid (salt); N-vinyl-2 -Pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol Examples thereof include hydrophilic monomers such as (meth) acrylate and salts thereof. Among these, an acid group-containing unsaturated monomer is preferable, a carboxyl group-containing unsaturated monomer such as acrylic acid (salt) and methacrylic acid (salt) is more preferable, and acrylic acid (salt) is even more preferable. In one embodiment of the present invention, a plurality of types of monomers can be combined. The amount of acrylic acid (salt) used in all the monomers is 10 to 100 mol%, further 50 to 100 mol%, particularly 90 to 100 mol%, and in one embodiment of the present invention, such polyacrylic acid. A (salt) -based water-absorbent resin is preferably used.

The acid group-containing unsaturated monomer is preferably partially salt-type, preferably a salt with a monovalent basic compound, more preferably an alkali metal salt or an ammonium salt, and even more preferably a sodium salt. be.

The neutralization rate in one embodiment of the present invention is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, still more preferably 50 to 80 mol%, particularly preferably 50 to 80 mol%, based on the acid group of the monomer. Is 60-75 mol%. If the neutralization rate is less than 10 mol%, the water absorption ratio may be significantly reduced. On the other hand, when the neutralization rate exceeds 90 mol%, a water-absorbent resin having a high water-absorbing ratio under pressure may not be obtained.

The neutralization rate is the same even when the polymer is neutralized instead of the monomer. The above neutralization rate is also applied to the neutralization rate of the water-absorbent resin powder as the final product.

(Internal cross-linking agent)
In one embodiment of the present invention, it is preferable to use an internal cross-linking agent in this step. As the internal cross-linking agent, the compound exemplified in US Pat. No. 6,241,928 is also applied to one embodiment of the present invention, and one or more compounds are selected from these in consideration of reactivity.

Further, from the viewpoint of the water absorption performance of the obtained water-absorbent resin, a compound having two or more polymerizable unsaturated groups is preferable, and more preferably, a compound having thermal decomposition property at the following drying temperature and a polymerizable unsaturated group. A compound having two or more, more preferably a compound having two or more polymerizable unsaturated groups having a (poly) alkylene glycol structural unit is used as an internal cross-linking agent.

Examples of the polymerizable unsaturated group include an allyl group, a (meth) acrylate group, and more preferably a (meth) acrylate group. Further, polyethylene glycol is preferable as the (poly) alkylene glycol structural unit, and the number of n is preferably 1 to 100, more preferably 6 to 50.

The amount of the internal cross-linking agent used is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, based on the entire monomer. The desired water-absorbent resin can be obtained by setting the amount used within the above range. If the amount used is too small, the gel strength tends to decrease and the water-soluble content tends to increase, and if the amount used is too large, the water absorption ratio of the water-absorbent resin tends to decrease, which is not preferable. ..

The internal cross-linking agent added in this step undergoes a cross-linking reaction in a polymerization step or, for example, a drying step after the polymerization step. In one embodiment of the present invention, the internal cross-linking is not limited to the above-mentioned form, and an internal cross-linking agent may be added to the water-containing gel-like cross-linked polymer during the polymerization step or after the polymerization step to carry out the cross-linking. Further, a method of radical cross-linking using a radical polymerization initiator, a method of radiation cross-linking using an electron beam or an active energy ray such as ultraviolet rays, or the like can also be adopted. Moreover, these methods can also be used together.

(Other substances added to the monomer aqueous solution)
In one embodiment of the present invention, the following substances can be added at the time of preparing the aqueous monomer solution from the viewpoint of improving the physical properties of the obtained water-absorbent resin.

Specifically, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), and crosslinked polyacrylic acid (salt) are preferably 50% by weight or less, more preferably. Can be added in an amount of 20% by weight or less, more preferably 10% by weight or less, particularly preferably 5% by weight or less (the lower limit is 0% by weight). Further, carbonates, azo compounds, foaming agents such as bubbles, surfactants, chelating agents, chain transfer agents and the like are preferably 5% by weight or less, more preferably 1% by weight or less, still more preferably 0.5% by weight. It can also be added below (lower limit is 0% by weight).

The above-mentioned substance may be added not only in the form added to the aqueous monomer solution but also in the form added during the polymerization, or these forms may be used in combination.

When a water-soluble resin or a water-absorbent resin is used as the hydrophilic polymer, a graft polymer or a water-absorbent resin composition (for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) may be used. can get. These polymers and water-absorbent resin compositions are also within the scope of the present invention.

(Concentration of monomer component)
In this step, each of the above substances is added when preparing the monomer aqueous solution. The concentration of the monomer component in the aqueous monomer solution is not particularly limited, but from the viewpoint of the physical properties of the water-absorbent resin, it is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, still more preferably 30. ~ 70% by weight.

Further, when aqueous solution polymerization or reverse phase suspension polymerization is adopted, a solvent other than water can be used in combination as necessary. In this case, the type of solvent is not particularly limited.

The above-mentioned "concentration of the monomer component" is a value obtained by the following formula (1), and the weight of the aqueous monomer solution includes the graft component, the water-absorbent resin, and the hydrophobicity in the reverse phase suspension polymerization. The weight of the solvent is not included.

(Concentration of monomer component (% by weight)) = (weight of monomer component) / (weight of aqueous monomer solution) × 100 ... Equation (1)
(2-2) Polymerization Step In this step, the monomer aqueous solution obtained in the above-mentioned monomer aqueous solution preparation step is polymerized to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as “hydrogen gel”). It is a process.

(Polymerization initiator)
The polymerization initiator used in one embodiment of the present invention is appropriately selected depending on the polymerization form and the like, and is not particularly limited. Examples of the polymerization initiator include a thermal decomposition type polymerization initiator, a photodegradable polymerization initiator, and a redox-based polymerization initiator in which a reducing agent that promotes the decomposition of these polymerization initiators is used in combination. Specifically, one or more of the polymerization initiators disclosed in US Pat. No. 7,265,190 are used. From the viewpoint of the handleability of the polymerization initiator and the physical properties of the water-absorbent resin, a peroxide or an azo compound is preferably used, a peroxide is more preferably used, and a persulfate is more preferably used among the peroxides.

The amount of the polymerization initiator used is preferably 0.001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the monomer component. The amount of the reducing agent used is preferably 0.0001 to 0.02 mol% with respect to the monomer.

Instead of the above-mentioned polymerization initiator, the polymerization reaction may be carried out by irradiating with active energy rays such as radiation, electron beam, and ultraviolet rays, or these active energy rays and the polymerization initiator may be used in combination. ..

(Polymerization form)
The polymerization mode applied to one embodiment of the present invention is not particularly limited, but is preferably spray / droplet polymerization in the gas phase, aqueous solution polymerization or reverse phase from the viewpoint of water absorption characteristics and ease of polymerization control. Suspension polymerization, more preferably aqueous solution polymerization or reverse phase suspension polymerization, still more preferably aqueous solution polymerization. Among the aqueous solution polymerizations, continuous aqueous solution polymerization is particularly preferable, and both continuous belt polymerization and continuous kneader polymerization are applied.

As specific polymerization forms, continuous belt polymerization is described in US Pat. No. 4,893999, US Pat. No. 6,241,928 and US Patent Application Publication No. 2005/215734, and continuous kneader polymerization is described in US Pat. No. 6,987,151 and US Pat. No. 6,710,141. Etc., respectively. By adopting these continuous aqueous solution polymerizations, the production efficiency of the water-absorbent resin is improved.

(2-3) Gel crushing step In this step, the hydrous gel obtained in the above polymerization step is gel crushed by, for example, a screw extruder such as a kneader or a meat chopper, or a gel crusher such as a cutter mill, and is in the form of particles. This is a step of obtaining a hydrogel (hereinafter referred to as "particulate hydrogel"). When the above-mentioned polymerization step is kneader polymerization, the polymerization step and the gel crushing step are carried out at the same time. Further, when a particulate hydrogel such as vapor phase polymerization or reverse phase suspension polymerization is directly obtained in the polymerization process, the gel pulverization step may not be carried out.

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

The method for drying the particulate hydrogel is not particularly limited, but for example, heat drying, hot air drying, vacuum drying, fluidized layer drying, infrared drying, microwave drying, drum dryer drying, co-boiling with a hydrophobic organic solvent. Examples include drying by dehydration and high-humidity drying using high-temperature steam. Among them, hot air drying is preferable from the viewpoint of drying efficiency, and among hot air drying, band drying in which hot air drying is performed on a ventilation belt is more preferable.

The drying temperature (temperature of the hot air) in the hot air drying is preferably 120 to 250 ° C., more preferably 150 to 200 ° C. from the viewpoint of the color tone of the water-absorbent resin and the drying efficiency. Drying conditions other than the above-mentioned drying temperature, such as the wind speed and drying time of hot air, may be appropriately set according to the moisture content and total weight of the particulate hydrogel to be dried and the amount of the target resin solid content. good. For example, when performing band drying, the conditions described in International Publication No. 2006/100300, International Publication No. 2011/025012, International Publication No. 2011/0250513, International Publication No. 2011/111657, etc. are appropriately applied. Applies.

By setting the above-mentioned drying temperature and drying time within the above ranges, the CRC (water absorption ratio), Ext (water-soluble component), and color tone of the obtained water-absorbent resin can be set within the desired ranges (see [3] below). be able to.

(2-5) Grinding Step and Classification Step In this step, the dry polymer obtained in the drying step is crushed (grinding step) and adjusted to a particle size within a predetermined range (classifying step) to obtain water-absorbent resin particles. This is the process of obtaining. When the dried polymer obtained by the drying step deviates from the following particle size, it is preferable to carry out this step at least before the surface cross-linking step.

Examples of the equipment used in the crushing step of the embodiment of the present invention include high-speed rotary crushers such as roll mills, hammer mills, screw mills and pin mills; vibration mills, knuckle type crushers, cylindrical mixers and the like. And used together as needed.

Further, the classification step of one embodiment of the present invention is not particularly limited, and examples thereof include sieve classification and air flow classification.

The particle size of the water-absorbent resin particles obtained in this step is usually 100 to 2000 μm, preferably 200 to 600 μm, more preferably 200 to 550 μm, still more preferably 250 to 500 μm, particularly preferably 250 to 500 μm, as the weight average particle size (D50). Is 350 to 450 μm. The ratio of the water-absorbent resin particles having a particle size of less than 150 μm to the entire water-absorbent resin particles obtained in this step is preferably 10% by weight or less, more preferably 5% by weight or less, still more preferably 1% by weight. It is as follows. The ratio of the water-absorbent resin particles having a particle size of 850 μm or more to the entire water-absorbent resin particles obtained in this step is preferably 5% by weight or less, more preferably 3% by weight or less, still more preferably 1% by weight. It is as follows. In any case, the lower limit of the ratio of these water-absorbent resin particles is preferably as small as 0% by weight, but may be about 0.1% by weight. Further, the logarithmic standard deviation (σζ) of the particle size distribution of the water-absorbent resin particles is preferably 0.25 to 0.50, more preferably 0.25 to 0.40, still more preferably 0.27 to 0.35. be. The particle size of the water-absorbent resin particles is measured using a standard sieve according to the measuring methods disclosed in US Pat. No. 7,638,570 and EDANA ERT4200.2-02.

The above-mentioned particle size and particle size distribution are also applied to the water-absorbent resin powder as a final product. Therefore, it is preferable that the water-absorbent resin powder is subjected to a surface cross-linking treatment (surface cross-linking step) as described later so as to maintain the particle size and particle size distribution in the above range, and a sizing step is provided after the surface cross-linking step. It is more preferable that the particle size is adjusted.

(2-6) Surface Crosslinking Step In the production method according to the embodiment of the present invention, a polyvalent metal salt aqueous solution having a concentration of 5% by weight or more is subjected to surface crosslinking or after surface crosslinking in a fluidized bed mixer. Has a spraying step of spraying on. That is, the production method according to the embodiment of the present invention includes a step of surface-crosslinking the water-absorbent resin particles with an organic surface-crosslinking agent. Hereinafter, this step is also referred to as a “surface cross-linking step”.

The surface cross-linking is to provide a portion having a higher cross-linking density in the surface layer of the water-absorbent resin particles (near the surface, usually about several tens of μm from the surface of the water-absorbent resin particles). A portion having a high crosslink density can be formed by radical cross-linking on the surface, surface polymerization, a cross-linking reaction with a surface cross-linking agent, or the like. From the viewpoint of physical characteristics, the surface cross-linking according to the embodiment of the present invention is intended to be surface cross-linking with an organic surface cross-linking agent covalently bonded to the functional group of the water-absorbent resin.

The procedure of this step is not particularly limited as long as the water-absorbent resin particles can be surface-crosslinked using an organic surface cross-linking agent, and includes, for example, the following procedures (I) and (II).

(I) Step of mixing an organic surface cross-linking agent with a water-absorbent resin As the surface cross-linking by the organic surface cross-linking agent of the embodiment of the present invention, surface cross-linking polymerization using a polymerizable monomer or covalent bonding with a functional group of the water-absorbent resin Alternatively, surface cross-linking with an organic surface cross-linking agent capable of ionic bonding can be mentioned.

The organic surface cross-linking agent according to the embodiment of the present invention is preferably an organic cross-linking agent capable of forming a cross-linked structure by covalently reacting with a functional group of the water-absorbent resin, particularly a carboxyl group. Particularly preferably, the following organic cross-linking agents are used. For example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, Glycerin, polyglycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol , 1,2-Cyclohexanol, Trimethylol Propane, Diethanolamine, Triethanolamine, Polyoxypropylene, Oxyethylene-Oxypropylene Block Copolymer, Pentaerythritol, Sorbitol and other polyhydric alcohols (COOH and dehydrated ester of water-absorbent resin) Cross-linking with propylene glycol);
Epoxy compounds (water-absorbent resin) such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol. Crosslinked with COOH and epoxy group);
Polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine (crosslinked with COOH of water-absorbent resin by amidation) and their inorganic or organic salts (for example, azetidineium). Salt, etc.);
Multivalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate;
Multivalent oxazoline compounds such as 1,2-ethylene bisoxazoline;
Carbonated derivatives such as urea, thiourea, guanidine, dicyandiamide, 2-oxazolidinone;
1,3-Dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3- Dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxane-2-one, 4-methyl-1 , 3-Dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, 1,3-dioxopan-2-one and other alkylene carbonate compounds;
Mono or multivalent oxazolidinone compounds such as oxazolidinone;
Haloepoxy, cationic polymer compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin (eg, Kaimen manufactured by Deck Hercules; registered trademark); γ-glycidoxypropyltrimethoxysilane, γ- Silane coupling agents such as aminopropyltriethoxysilane; 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3- Ethyl-3-oxetan ethanol, 3-butyl-3-oxetan ethanol, 3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, oxetane compounds such as polyvalent oxetane compounds; and the like. Only one kind of these organic surface cross-linking agents may be used, or two or more kinds thereof may be used in combination. Preferably, one or more organic surface cross-linking agents selected from polyhydric alcohols, polyhydric glycidyl, alkylene carbonates and oxazolidinone compounds are used.

The amount of the organic surface cross-linking agent used depends on the compounds used and their combinations, etc., but is preferably in the range of 0.001 to 10 parts by weight, preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water-absorbent resin particles. It is more preferably within the range of parts by weight. In one embodiment of the present invention, the organic surface cross-linking agent can be used by being dissolved in water (that is, as an aqueous solution of the organic surface cross-linking agent). The amount of water is preferably in the range of 0.5 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the water-absorbent resin particles. Further, in one embodiment of the present invention, it is also possible to use a hydrophilic organic solvent in addition to water. Further, when the organic surface cross-linking agent aqueous solution is mixed with the water-absorbent resin particles, the effect of the present invention is not hindered, for example, 0 to 10 parts by weight, preferably 0 to 5 parts by weight with respect to 100 parts by weight of the water-absorbent resin particles. Water-insoluble fine particle powder, surfactant and the like may coexist in parts by weight, more preferably 0 to 1 part by weight.

In one embodiment of the present invention, it is not excluded that the water-absorbent resin is surface-crosslinked with a polyvalent metal salt in addition to the above-mentioned organic surface-crosslinking agent. When the water-absorbent resin is surface-crosslinked with a polyvalent metal salt, a water-soluble polyvalent metal salt is added in a surface treatment step separately from the polyvalent metal salt as a surface cross-linking agent.

Non-crosslinkable water-soluble inorganic bases (preferably alkali metal salts, ammonium salts, alkali metal hydroxides, and ammonia or water thereof) to more uniformly mix the water-absorbent resin particles and the organic surface cross-linking agent. (Oxide) and non-reducing alkali metal salt pH buffer (preferably hydrogen carbonate, dihydrogen phosphate, hydrogen phosphate, etc.) are further added to the water-absorbent resin particles and the organic surface cross-linking agent. May be good. The amount of these used depends on the type and particle size of the water-absorbent resin particles, but is preferably 0.005 to 10 parts by mass, preferably 0.05 to 5 parts by mass, based on 100 parts by mass of the solid content of the water-absorbent resin particles. Parts by mass are more preferred.

The method of mixing the water-absorbent resin particles and the organic surface cross-linking agent is not particularly limited. For example, a method of immersing the water-absorbent resin particles in a hydrophilic organic solvent and mixing the organic surface cross-linking agent aqueous solution, or directly to the water-absorbent resin particles. , A method of spraying or dropping an aqueous solution of an organic surface cross-linking agent and mixing them can be exemplified.

The mixing device used when mixing the water-absorbent resin particles and the aqueous solution of the organic surface cross-linking agent preferably has a large mixing force in order to mix these substances uniformly and reliably. Examples of the above mixing device include a cylindrical mixer, a double-walled conical mixer, a high-speed stirring type mixer, a V-shaped mixer, a ribbon type mixer, a screw type mixer, a double-armed kneader, and a crushing type. Kneaders, rotary mixers, airflow mixers, turbulizers (trademarks), batch-type Ploughshare ™ mixers, continuous Ploughshare ™ mixers, Schugi ™ mixers, fluidized layer mixers and the like are suitable. ..

(II) Heating step of heating a mixture of the water-absorbent resin particles and the aqueous solution of the organic surface cross-linking agent The water-absorbent resin particles after mixing the organic surface cross-linking agent are heated to promote surface cross-linking. The heating temperature is in the range of 40 to 300 ° C., preferably 120 to 250 ° C., more preferably 150 to 250 ° C. The heat treatment time is preferably 1 minute to 2 hours, more preferably 5 minutes to 1 hour. The heat treatment can be carried out using a normal dryer or a heating furnace. If the heat treatment temperature is less than 40 ° C., the absorption characteristics such as the absorption ratio under pressure may not be sufficiently improved. If the heat treatment temperature exceeds 300 ° C., the water-absorbent resin particles may be deteriorated and various performances may be deteriorated.

Devices used when heating a mixture of water-absorbent resin particles and an aqueous solution of an organic surface cross-linking agent (and a device for optionally spraying and adding a polyvalent metal salt aqueous solution) include, for example, a drum dryer, a paddle dryer, and a fluidized bed dryer. A band dryer and the like can be mentioned. Among these, a paddle dryer is preferable from the viewpoint of stirring power.

Further, as a surface cross-linking step in one embodiment of the present invention, a method of adding a treatment liquid containing a radically polymerizable compound to the water-absorbent resin particles and then irradiating with active energy to carry out surface cross-linking can be mentioned. Further, it is also possible to add a surfactant to the treatment liquid and irradiate it with active energy to surface-crosslink the water-absorbent resin particles.

By this step, the water absorption ratio of the water-absorbent resin particles under pressure is improved. The surface-crosslinked water-absorbent resin particles usually already have a water absorption ratio under pressure in a preferable range, which will be described later. That is, the surface-crosslinked water-absorbent resin particles usually have an AAP (0.7 psi) of 15 g / g or more when the CRC is 25 g / g or more.

(III) Cooling Step The production method according to the embodiment of the present invention may further include (III) a step of cooling the water-absorbent resin particles. Hereinafter, this step is also referred to as a “cooling step”.

The cooling step is preferably performed after heating in the surface cross-linking step from the viewpoint of stopping the progress of the excess surface cross-linking reaction and improving the handleability of the powder (water-absorbent resin powder).

Specifically, the water-absorbent resin particles that have become hot due to heating in the surface cross-linking step are forcibly cooled by contacting them with a refrigerant such as cold air or a cooling transfer surface in the cooling step.

The cooling temperature is preferably 30 to 100 ° C, more preferably 40 to 80 ° C. If the cooling temperature is too low, the powder characteristics of the water-absorbent resin powder may deteriorate, or the physical properties of the water-absorbent resin powder may deteriorate. The "cooling temperature" is intended to be the temperature of the cold air when cold air is used, and the temperature of the transmission surface when the cooling transmission surface is used. Further, when the cold air and the cooling transfer surface are used together, it is preferable that the temperature is intended for each and the above range is satisfied for both of them.

The cooling time is preferably 1 minute to 1 hour, more preferably 5 minutes to 40 minutes.

Examples of the device used in this step include a paddle dryer, a fluidized bed dryer, an air transport device, and a band dryer. However, in this step, the paddle dryer uses a refrigerant, and the fluidized bed dryer and the band dryer use cold air.

(2-7) Surface Treatment Step In this step, the water-soluble polyvalent metal salt aqueous solution is sprayed on the water-absorbent resin particles in the fluidized layer mixer, or the water-soluble polyvalent metal salt particles are added to the surface of the water-absorbent resin particles. This is a step of adhering water-soluble polyvalent metal salt particles to the surface of the water-absorbent resin particles to perform surface treatment.

(2-7-1) Spraying Step The production method (1) according to the embodiment of the present invention is a method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface-crosslinking agent and contains a water-soluble polyvalent metal salt. Then, a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is subjected to surface cross-linking or surface cross-linking in a fluidized layer mixer, and water-absorbent resin powder particles (preferably water-absorbent resin particles after surface cross-linking). ), And the air temperature at the spraying position of the above-mentioned polyvalent metal salt aqueous solution is 50 ° C. or higher. Further, in the production method (1) according to the embodiment of the present invention, the water-absorbent resin particles are preferably cooled at the same time after surface cross-linking in the fluidized bed mixer.

Hereinafter, the step of spraying the polyvalent metal salt aqueous solution on the water-absorbent resin particles at the time of surface cross-linking or after the surface cross-linking is also referred to as a “spraying step”.

In one embodiment of the present invention, "spraying a polyvalent metal salt aqueous solution onto water-absorbent resin particles at the time of surface cross-linking" means that when surface cross-linking is performed in a fluidized layer mixer, an organic surface cross-linking agent is mixed or organic surface cross-linking is performed. The polyvalent metal salt aqueous solution is sprayed simultaneously or separately at the time of reaction with the agent. Specifically, a fluidized bed mixer is used as a mixer for organic surface cross-linking agents to spray a polyvalent metal salt aqueous solution, or a fluidized bed mixer is used as a heating device for water-absorbent resin particles mixed with an organic surface cross-linking agent. Can be used to spray a polyvalent metal salt aqueous solution, or a fluidized bed mixer can be used separately from the organic surface cross-linking agent mixer and heating device to spray the polyvalent metal salt aqueous solution separately.

Here, when the polyvalent metal salt aqueous solution is sprayed using a fluidized bed mixer as a mixer for the organic surface cross-linking agent, it is preferable that the organic surface cross-linking agent slightly permeates into the water-absorbent resin particles. On the other hand, since the polyvalent metal salt is desired to be deposited on the surface of the water-absorbent resin particles, when the polyvalent metal salt aqueous solution is sprayed in this step, the organic surface cross-linking agent and the polyvalent metal salt aqueous solution are separately sprayed, that is, the organic surface cross-linking. It is preferable to spray the polyvalent metal salt aqueous solution from an addition port different from the agent addition port, and it is more preferable to spray the polyvalent metal salt aqueous solution after dropping or spraying the organic surface cross-linking agent on the water-absorbent resin particles. ..

It is also possible to spray the polyvalent metal salt aqueous solution using a fluidized bed mixer as a cooler in the cooling step. Although the cooling step is described in "Surface cross-linking step" for convenience, the surface cross-linking reaction is substantially completed when the cooling step is performed. Therefore, when the polyvalent metal salt aqueous solution is sprayed in this step, the surface cross-linking is performed. It is synonymous with the subsequent spraying of a polyvalent metal salt aqueous solution on the water-absorbent resin particles. In the surface treatment step, spraying is preferably performed from the upper part of the fluidized bed mixer, so that even if the temperature of the cold air is lower than the preferable temperature range of the surface treatment step of one embodiment of the present invention, the high temperature water-absorbent resin particles can be sprayed. After passing through the layer, if the air temperature at the spraying position is within the above range, the present invention can be stably carried out.

As the fluidized bed mixer for forming the fluidized bed, known fluidized bed dryers / coolers and fluidized bed granulators sold can be used. For example, in the case of lab scale, the spray dryer Pulvis GB series can be used. (Manufactured by Yamato Scientific Co., Ltd.) etc. can be used.

In the spraying step, the air temperature at the spraying position is 50 ° C. or higher, preferably 60 ° C. or higher, more preferably 80 ° C. or higher, and further preferably 100 ° C. or higher. The upper limit of the air temperature is preferably 250 ° C. or lower, more preferably 220 ° C. or lower, and further preferably 200 ° C. or lower. In the present specification, the "air temperature at the spray position" is the air temperature near the spray port, and the air temperature near the spray port can be measured by a thermometer. Since the spray port is preferably installed in the space portion in the fluidized bed mixer as described later, it can also be said to be the temperature of the space portion in the fluidized bed mixer. When the air temperature at the spraying position is the above temperature, the solvent component (particularly water) is suitably evaporated from the polyvalent metal salt aqueous solution, and the fine water-soluble polyvalent metal salt (in the present specification, "water-soluble polyvalent" is used. (Also referred to as "metal salt particles") can be attached to the surface of the water-absorbent resin powder. That is, before the sprayed polyvalent metal salt aqueous solution is absorbed by the water-absorbent resin, the droplets of the polyvalent metal salt aqueous solution are rapidly dried on the surface of the air layer or the water-absorbent resin in the fluidized layer mixer. It is presumed that fine water-soluble polyvalent metal salts adhere to the surface of the water-absorbent resin in a lumpy, substantially spherical, or bumpy shape.

In the spraying step, the temperature of the water-absorbent resin particles introduced is preferably 50 to 250 ° C, more preferably 60 to 220 ° C. Specifically, in the case of a batch type fluidized bed mixer, the temperature of the water-absorbent resin particles immediately before spraying, and in the case of a continuous type fluidized bed mixer, the temperature of the water-absorbent resin particles at a position immediately before the spraying location. Intended for temperature.

In the spraying step, the method for spraying the polyvalent metal salt aqueous solution is not particularly limited, but from the viewpoint that the size of the droplets to be sprayed is preferable, it is preferable to use a two-fluid spray.

In the spraying step, the spray of the polyvalent metal salt aqueous solution may be performed from the upper part of the fluidized bed mixer or from the lower part of the fluidized bed mixer. That is, in the fluidized bed mixer, the spray may be installed at the upper part or at the lower part. However, from the viewpoint of easiness of forming water-soluble polyvalent metal salt particles, it is preferable that the polyvalent metal salt aqueous solution is sprayed from the upper part of the fluidized bed mixer. Generally, in a fluidized bed mixer, hot air is sent from the lower part to fluidize the water-absorbent resin particles introduced into the lower part, and in order to prevent the water-absorbent resin particles from flying up excessively, a normal fluidized bed is usually used. The upper part of the mixer is widened to slow down the wind speed. When a polyvalent metal salt aqueous solution is sprayed from the upper part of the fluidized bed mixer, huge agglomerates are likely to be formed in the prior art, and the flow of the water-absorbent resin particles may be stopped. Then, the flow of the water-absorbent resin particles can be maintained. Furthermore, when the polyvalent metal salt aqueous solution is sprayed from the upper part of the fluidized layer mixer, the solvent component of the polyvalent metal salt aqueous solution evaporates in the process until the polyvalent metal salt aqueous solution reaches the water-absorbent resin particles, so that water absorption occurs. It is considered that solid water-soluble polyvalent metal salt particles are likely to be formed (precipitated) on the surface of the sex resin particles. On the other hand, when the polyvalent metal salt aqueous solution is sprayed from the lower part of the fluidized layer mixer, the polyvalent metal salt aqueous solution immediately comes into contact with the water-absorbent resin particles without evaporating the solvent component of the polyvalent metal salt aqueous solution. It is considered that water-soluble polyvalent metal salt particles are unlikely to be formed.

The water-soluble polyvalent metal salt in the aqueous polyvalent metal salt solution is preferably 0.01 to 1 part by weight, preferably 0.05 to 0 parts by weight, based on 100 parts by weight of the surface-crosslinked water-absorbent resin particles. More preferably, it is 5 parts by weight. When the water-soluble polyvalent metal salt is in the above ratio, a water-absorbent resin powder having excellent liquid permeability can be obtained.

In the present specification, the water-soluble polyvalent metal salt is intended to be a salt of a metal having a valence of divalent or higher, preferably trivalent or higher, particularly trivalent or tetravalent. "Water-soluble" is intended to dissolve in water at 20 ° C. in an amount of 5% by weight or more, where the solubility is calculated excluding water of crystallization (eg, an aqueous solution of 18 hydrate of aluminum sulfate is aluminum sulfate. (Calculated with the concentration as). A water-soluble polyvalent metal salt having a solubility of 11% by weight or more, further 15% by weight or more, particularly 20% by weight or more is preferably applied in one embodiment of the present invention. In the present specification, the "water-soluble polyvalent metal salt" is also simply referred to as "polyvalent metal salt".

The polyvalent metal salt that can be used in one embodiment of the present invention is intended to be a salt or hydroxide of a polyvalent metal cation, and is particularly an organic or inorganic acid salt of a polyvalent metal, which is typical. Aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum nitrate, potassium aluminum bissulfate, sodium aluminum bissulfate, potassium myoban, ammonium myoban, sodium myoban, sodium aluminate, calcium chloride, calcium nitrate, magnesium chloride, magnesium sulfate. , Magnesium nitrate, zinc chloride, zinc sulfate, zinc nitrate, zirconium chloride, zirconium sulfate, zirconium nitrate and the like can be exemplified. The polyvalent metal salt may be partially a hydroxide, that is, a basic salt. Moreover, it is preferable to use a salt having these waters of crystallization. Further, depending on the solubility, polyvalent metals such as aluminum, magnesium, calcium, zinc, zirconium and organic acids (eg, anisic acid, benzoic acid, formic acid, valeric acid, citric acid, glyoxylic acid, glycolic acid, glutaric acid, etc. Succinic acid, tartaric acid, lactic acid, fumaric acid, propionic acid, 3-hydroxypropionic acid, malonic acid, imidinoacetic acid, malic acid, isethionic acid, adipic acid, oxalic acid, salicylic acid, gluconic acid, sorbic acid, p-oxybenzoic acid Etc.) can be exemplified in combination with.

Water-soluble aluminum salts (aluminum compounds) are particularly preferable from the viewpoint of physical properties, and aluminum chloride, polyaluminum chloride, and aluminum sulfate are particularly preferable from the viewpoint of easily adjusting the concentration of the polyvalent metal salt according to the embodiment of the present invention. , Aluminum nitrate, potassium aluminum sulphate, sodium bissulfate, potassium alum, ammonium alum, sodium alum, sodium aluminate is preferable, aluminum sulfate is particularly preferable, aluminum sulfate 18 hydroxide, aluminum sulfate 14-18 hydroxide, etc. Hydrous crystallized powder can be most preferably used. Only one of these may be used, or two or more thereof may be used in combination.

The concentration of the polyvalent metal salt in the aqueous polyvalent metal salt solution is preferably 5% by weight or more, more preferably 11% by weight or more, further preferably 15% by weight or more, and 20% by weight. The above is particularly preferable. The upper limit of the above concentration is intended to be a saturated concentration, preferably 40% by weight or less, and more preferably 30% by weight or less. The higher the concentration, the more likely it is that massive polyvalent metal salt particles will form on the surface of the water-absorbent resin particles. However, if the concentration is excessively high, manufacturing problems such as clogging of the spray nozzle and increase in viscosity are likely to occur.

The liquid temperature of the aqueous solution of the polyvalent metal salt to be added may be room temperature, and may be appropriately cooled or heated, for example, 0 to 100 ° C. in order to adjust the mixing property and solubility.

In the surface treatment step, the organic acid (salt) may be sprayed with the same solution or another solution at the same time as the aqueous solution of the polyvalent metal salt. By using an organic acid (salt), polyvalent metal salts (for example, aluminum ions) are suppressed from penetrating into the water-absorbent resin particles, and the polyvalent metal salt particles are uniformly diffused on the surface of the water-absorbent resin particles. Therefore, the liquid permeability of the water-absorbent resin particles is greatly improved. Further, by using an organic acid (salt), it is possible to solve the problem that the metal component adheres to the surface of the water-absorbent resin particles in a planar and non-uniform manner as in the conventional case, and the metal component can absorb water. The effect of being able to uniformly adhere (localize) to the entire surface of the resin particles in the form of fine dots can be exhibited.

The organic acid (salt) may be mixed with the water-absorbent resin particles as it is, but is preferably mixed with the polyvalent metal salt. Further, it is more preferable to mix the organic acid (salt) and the polyvalent metal salt together as an aqueous solution, and it is particularly preferable to mix the organic acid (salt) and the polyvalent metal salt as a common aqueous solution.

Examples of organic acids (salts) include anis acid, benzoic acid, formic acid, valeric acid, citric acid, glyoxylic acid, glycolic acid, glutaric acid, succinic acid, tartaric acid, lactic acid, fumaric acid, propionic acid, and 3-hydroxypropion. Acids, malonic acid, imidinoacetic acid, malic acid, isethionic acid, adipic acid, oxalic acid, salicylic acid, gluconic acid, sorbic acid, p-oxybenzoic acid, and alkali metal and ammonium salts such as sodium and potassium. Be done. Of these, hydroxycarboxylic acids such as glycolic acid, tartrate acid, lactic acid, 3-hydroxypropionic acid, malic acid, salicylic acid, and gluconic acid, and alkali metal salts and ammonium salts thereof are preferable. Only one of these may be used, or two or more thereof may be used in combination.

The amount of the organic acid (salt) used is preferably at most twice the number of moles of the polyvalent metal salt, more preferably one time or less, still more preferably 0.5 times or less. If the amount of organic acid (salt) used is too large, manufacturing problems such as clogging of the spray nozzle and increase in viscosity are likely to occur.

(2-7-2) Step of Adding Water-Soluble Polyvalent Metal Salt Particles The method for producing a water-absorbent resin powder according to an embodiment of the present invention can also be carried out by a method other than the above-mentioned spraying step. The present invention (2) is a method for producing a water-absorbent resin powder which is surface-crosslinked with an organic surface-crosslinking agent and contains a water-soluble polyvalent metal salt, and is for water-absorbent resin particles surface-crosslinked with an organic surface-crosslinking agent. Provided is a method for producing a water-absorbent resin powder, to which water-soluble polyvalent metal salt particles having a volume average particle diameter of 0.3 to 15 μm measured by a laser diffraction / scattering method are added. For example, the polyvalent metal salt aqueous solution can be made into water-soluble polyvalent metal salt particles by a spray-drying method or an azeotropic dehydration method, and then added to the water-absorbent resin particles. In this case, a water-absorbent resin powder to which substantially spherical water-soluble polyvalent metal salt particles are attached can be obtained. At this time, the amount of the polyvalent metal salt used is preferably in the same range as that described in the spraying step.

Here, the volume average particle diameter of the water-soluble polyvalent metal salt particles measured by the laser diffraction / scattering method is preferably 0.3 to 15 μm, more preferably 0.3 to 10 μm, and further preferably 0.3 to 5 μm. preferable. When measuring by the laser diffraction / scattering method, the measurement solvent is appropriately selected so that the water-soluble polyvalent metal salt particles are not dissolved. Further, in order to prevent aggregation of the water-soluble polyvalent metal salt particles, the volume average particle diameter is measured after ultrasonic vibration is applied to the measurement solvent to which the water-soluble polyvalent metal salt particles are added. It should be confirmed in advance that there are no large water-soluble polyvalent metal salt particles that cannot be measured by the laser diffraction / scattering method by passing the water-soluble polyvalent metal salt particles through a standard sieve having a mesh size of 38 μm or 45 μm. You may. The amount of water-soluble polyvalent metal salt particles on a standard sieve having a mesh size of 45 μm is preferably 10% by weight or less, more preferably 5% by weight or less, based on the total amount of water-soluble polyvalent metal salt particles to be measured. Yes, more preferably 1% by weight or less. Water-soluble polyvalent metal salt particles having the above volume average particle diameter are added to the water-absorbent resin particles with respect to the water-absorbent resin particles surface-crosslinked with the organic surface cross-linking agent.

The shape of the water-soluble polyvalent metal salt particles is preferably substantially spherical. However, the water-soluble polyvalent metal salt particles may be slightly aggregated within the range of the volume average particle size. The closer the shape of the water-soluble polyvalent metal salt particles to be added is to a spherical shape, the better the fluidity of the water-absorbent resin powder. The shape of the water-soluble polyvalent metal salt particles can be confirmed by taking a scanning electron microscope (SEM) photograph of the water-soluble polyvalent metal salt particles magnified 2000 times and performing image analysis of the photograph.

When the water-soluble polyvalent metal salt particles are added to the water-absorbent resin particles, they may be dry-blended or added together with an organic solvent. For example, volatile alcohols such as methanol, ethanol, propanol and isopropyl alcohol; polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol and glycerin; diethylene glycol, triethylene glycol and polyethylene glycol having a molecular weight of 200 to 600 at room temperature. Liquid polyethylene glycol: Can be added with organic solvents such as. The amount of the organic solvent used is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the water-absorbent resin particles. Moisture may be contained in these organic solvents as long as the water-soluble polyvalent metal salt particles are not dissolved. Since the dry-blended water-soluble multivalent metal salt particles are easily peeled off from the water-absorbent resin powder, the above solvent is preferably added after the dry blend.

A known mixer is used as the apparatus used when adding the water-soluble polyvalent metal salt particles to the water-absorbent resin particles, and the apparatus is not particularly limited. Examples thereof include a vertical type, a horizontal type, a stirring mixer in an oblique direction, and a fluidized bed mixer. In addition, mixing during air transport is also possible. Specifically, a cylindrical mixer, a double-walled conical mixer, a vertical or horizontal high-speed stirring type mixer, a V-shaped mixer, a ribbon type mixer, a screw type mixer, a double-armed kneader, and a rotary type mixer. Examples include a type mixer, an air flow type mixer, and a fluidized bed mixer. When water-soluble polyvalent metal salt particles are added together with an organic solvent, a mixer equipped with a mechanism for loosening agglomerates and a heating mechanism for drying is preferable. Specific examples thereof include a paddle dryer, a steam tube dryer, a drum dryer, a fluidized bed dryer, a screw type mixer with a heating jacket, a kneader, and the like.

(2-8) Other Additive Steps In one embodiment of the present invention, other additives can be added to the water-absorbent resin particles or the water-absorbent resin powder. Examples thereof include chelating agents, oxidizing agents, reducing agents, cationic polymers, hydrophilic polymers, α-hydroxycarboxylic acids, surfactants, water-insoluble inorganic fine particles, fragrances, deodorants, antibacterial agents and the like. The amount of the additive used (addition amount) is appropriately determined according to the intended use and is not particularly limited, but is preferably 3 parts by weight or less with respect to 100 parts by weight of the water-absorbent resin particles or the water-absorbent resin powder. , More preferably 1 part by weight or less. Examples of the form of the additive at the time of the above addition include powder, liquid, solution, dispersion, etc. However, when water is contained, the water-soluble polyvalent metal salt particles should not be dissolved or surface treatment should be performed. It is preferable to add it before the step.

Among the above additives, in order to further improve the SFC of the water-absorbent resin powder, at least one of the cationic polymer and / or the water-insoluble inorganic fine particles is made into the water-absorbent resin particles or the water-absorbent resin powder in one embodiment of the present invention. It is preferable to use it. The cationic polymer is a cationic polymer having an amino group, and further is a water-soluble cationic polymer, preferably a water-soluble polymer that dissolves in water at 25 ° C. in an amount of 2% by weight or more, further 5% by weight or more. It is a polymer. For example, polyalkyleneimine such as polyethyleneimine, polyetherpolyamine, polyetheramine, polyvinylamine, polyalkylamine, polyallylamine, polydialylamine, poly (N-alkylallylamine), monoallylamine-diallylamine copolymer, N-alkyl. Allylamine-monoallylamine copolymers, monoallylamine-dialkyldiallylammonium salts / copolymers, diallylamine-dialkyldiallylammonium salts / copolymers, polyethylenepolyamines, polypropylenepolyamines, polyamidines, etc .; and salts thereof are preferred. Further, the modified cationic polymer described in International Publication No. 2009/041727 is more preferable.

The water-insoluble inorganic fine particles have an average particle diameter of preferably 0.001 to 200 μm, more preferably 0.005 to 50 μm, still more preferably 0.01 to 10 μm, as measured by the Coulter counter method. Is. The water-insoluble inorganic fine particles are preferably hydrophilic fine particles, and are, for example, metal oxides such as silica (silicon dioxide) and titanium oxide, and composite hydrous oxides containing zinc and silicon, or zinc and aluminum (for example,). (Example in International Publication No. 2005/010102), silicates such as natural zeolite and synthetic zeolite, kaolin, talc, clay, bentonite, calcium phosphate, barium phosphate, silicate or its salt, clay, diatomaceous earth, silica gel, zeolite, Examples thereof include bentonite, hydroxyapatite, hydrotalcite, vermucurite, pearlite, isolite, activated clay, silica gel, silica gel, strontium ore, fluorite, and bokisite. Of these, silicon dioxide and silicate (salt) are more preferable, and silicon dioxide is even more preferable. As the silicon dioxide, fumed silica or colloidal silica is preferable, and colloidal silica is preferable from the viewpoint of balance of water absorption characteristics.

If a cationic polymer is used, the amount used is preferably 0.001 to 1 part by weight with respect to 100 parts by weight of the water-absorbent resin particles or the water-absorbent resin powder, and if water-insoluble inorganic fine particles are used, the amount used is the same. Is preferably 0.001 to 1 part by weight with respect to 100 parts by weight of the water-absorbent resin particles or the water-absorbent resin powder. The amount of the cationic polymer and / or water-insoluble inorganic fine particles used can also be referred to as the content of the cationic polymer and / or water-insoluble inorganic fine particles in the water-absorbent resin powder.

Further, it is preferable to apply a surfactant so that the water-soluble polyvalent metal salt particles adhering to the surface of the water-absorbent resin powder are not peeled off by friction or the like. If a surfactant is used, the amount used is preferably 0.0001 to 0 with respect to 100 parts by weight of the water-absorbent resin particles or the water-absorbent resin powder in order to prevent deterioration of the physical properties of the water-absorbent resin powder during water absorption. .1 part by weight. The amount of the surfactant used can also be said to be the content of the surfactant in the water-absorbent resin powder. In addition, as another index, the surface tension of the extract is preferably 60 to 75 mN / when the component of the water-absorbent resin powder is extracted with a 0.9 wt% sodium chloride aqueous solution so as not to adversely affect the water-absorbing physical characteristics. The amount used is determined so as to be in the range of m, more preferably 65 to 72 mN / m. In the case of the water-absorbent resin powder to which no surfactant is added, the surface tension is usually about 71 to 75 mN / m.

Among the above additives, the water-absorbent resin of the present invention preferably contains a chelating agent from the viewpoint of preventing coloration over time, preventing urine deterioration, and the like. As the chelating agent of the present invention, a polymer compound or a non-polymer compound, particularly a non-polymer compound is preferable from the viewpoint of effect, and specifically, an amino polyvalent carboxylic acid, an organic polyvalent phosphoric acid, and an inorganic polyvalent phosphoric acid. Compounds selected from are preferred. From the viewpoint of effect, the molecular weight of the chelating agent is preferably 100 to 5000, more preferably 200 to 1000. In the absence of a chelating agent, the water-absorbent resin is inferior in terms of coloring and deterioration.

Here, the multivalent has a plurality of the functional groups in one molecule, and has 2 to 30 and further 3 to 20, particularly 4 to 10 such functional groups. Further, these chelating agents are preferably water-soluble chelating agents, specifically, water-soluble chelating agents that dissolve 1 g or more, more preferably 10 g or more, in 100 g (25 ° C.) of water.

Examples of the amino polyvalent carboxylic acid include imino diacetic acid, hydroxyethyl imino 2 acetic acid, nitrilo 3 acetic acid, nitrilo 3 propionic acid, ethylenediamine 4 acetic acid, diethylenetriamine 5 acetic acid, triethylenetetramine 6 acetic acid, and trans-1,2-diaminocyclohexane. 4 Acetic acid, N, N-bis (2-hydroxyethyl) glycine, diaminopropanol 4 acetic acid, ethylenediamine 2 propionic acid, hydroxyethylenediamine 3 acetic acid, glycol ether diamine 4 acetic acid, diaminopropane 4 acetic acid, N, N'-bis (2) -Hydroxybenzyl) ethylenediamine-N, N'-2 acetic acid, 1,6-hexamethylenediamine-N, N, N', N'-4 acetic acid and salts thereof, among others, diethylenetriamine-5 acetic acid (salt). , Or triethylenetetramine 6 acetic acid (salt) is more preferred, and diethylenetriamine 5 acetic acid (salt) is even more preferred.

Examples of the organic polyvalent phosphoric acid include ethylenediamine-N, N'-di (methylenephosphinic acid), ethylenediaminetetra (methylenephosphinic acid), cyclohexanediaminetetra (methylenephosphonic acid), ethylenediamine-N, N'-diacetic acid-N. , N'-di (methylenephosphonic acid), ethylenediamine-N, N'-di (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), polymethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) And the above aminopolyphosphates such as these salts, nitriloacetate-di (methylenephosphinic acid), nitrilogicacetic acid- (methylenephosphinic acid), nitriloacetate-β-propionic acid-methylenephosphonic acid, nitrilotris (methylenephosphonic acid). ), 1-Hydroxyethylidene diphosphonic acid, and the like. Examples of the inorganic polyphosphoric acid include pyrophosphoric acid, tripoliphosphoric acid and salts thereof. As the chelating agent of the present invention, ethylenediaminetetra (methylenephosphonic acid) (salt) is preferable.

The amount of the chelating agent used, particularly the above-mentioned preferable chelating agent, is 0.0001 parts by weight or more, 0.001 parts by weight or more, 0.01 parts by weight or more, and 0.02 with respect to 100 parts by weight of the water-absorbent resin. The order is preferably 1 part by weight or more, 0.03 parts by weight or more, 0.05 parts by weight or more, and 0.06 parts by weight or more, 1 part by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, and 0.15 parts by weight. It is preferable in the order of parts by weight or less. As a result, it is excellent in prevention of coloration over time, prevention of urine deterioration, heat resistance, light resistance, antibacterial property, safety, handleability and the like.

Among the above additives, the water-absorbent resin of the present invention preferably uses an oxidizing agent and / or a reducing agent after the polymerization step from the viewpoint of reducing residual monomers and preventing coloration. Examples of the oxidizing agent of the present invention include persulfates such as ammonium persulfate, sodium persulfate and potassium persulfate, organic peroxides such as t-butyl peroxide and benzoyl peroxide, hydrogen peroxide, chlorates and bromates. Examples include salts, chlorites, hypochlorates and the like. Of these, persulfate is preferable from the viewpoint of reducing residual monomers. These oxidizing agents may be only one kind or two or more kinds.

Further, as the reducing agent of the present invention, sulfur-based, phosphorus-based, and nitrogen-based reducing agents are particularly suitable. Specifically, for example, sulfite (for example, sodium sulfite, potassium sulfite, ammonium sulfite, etc.), hydrogen sulfite (for example, sodium hydrogen sulfite, potassium hydrogen sulfite, ammonium hydrogen sulfite, etc.), pyrosulfite, nitione. Sulfinatoacetic acid derivatives such as acid salts, trithionates, tetrathionates, thiosulfites, 2-hydroxy-2-sulfinatoacetic acid, dimethylsulfoxides, thiourea dioxide, nitrites, nitrogens such as amino acids and ethanolamines. Examples include contained organic compounds, bisulfites, hypobisulfites, and the like. Among these, sulfur-based inorganic reducing agents, particularly sulfites, hydrogen sulfites, pyrosulfites, and nitionates are preferable, and sodium salts, potassium salts, and ammonium salts are preferably mentioned as their salts. Of these, sodium sulfite and sodium hydrogen sulfite are particularly preferable. These reducing agents may be only one kind or two or more kinds.

The amount of the oxidizing agent or reducing agent used is 0.0001 parts by weight or more, 0.001 parts by weight or more, 0.01 parts by weight or more, 0.02 parts by weight or more with respect to 100 parts by weight of the water-absorbent resin. 0.03 parts by weight or more, 0.05 parts by weight or more, 0.06 parts by weight or more are preferable, and 3 parts by weight or less, 1 part by weight or less, 0.7 parts by weight or less, 0.5 parts by weight or less are preferable in this order. ..

(2-9) Other Steps In one embodiment of the present invention, in addition to the steps described above, a granulation step, a fine powder removing step, a fine powder reuse step, and the like can be provided as necessary. Further, one or more steps such as a transportation step, a storage step, a packing step, and a storage step may be further included. The granulation step includes a step of classifying and removing fine powder after the heat treatment step and a step of classifying and crushing when the water-absorbent resin aggregates and exceeds a desired size. Further, the step of reusing the fine powder includes a step of converting the fine powder as it is or making it into a large water-containing gel in the fine powder granulation step and adding it in any step of the manufacturing step of the water-absorbent resin.

[3] Characteristics of Water-absorbent Resin Powder The present invention is a water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt, and has number average particles on the surface of the water-absorbent resin powder. Provided is a water-absorbent resin powder to which water-soluble polyvalent metal salt particles having a diameter of 0.3 to 15 μm (SEM image analysis) are attached. "Adhesion of water-soluble polyvalent metal salt particles" is a state in which solid water-soluble polyvalent metal salt particles are sterically present on the surface of the water-absorbent resin, and has a thickness such as substantially spherical, bumpy, or lumpy. Valuable metal salts are present on the surface of the water-absorbent resin powder. It is sufficient that one or more polyvalent metal salt particles having a number average particle diameter of 0.3 to 15 μm (SEM image analysis) are attached to each grain of the water-absorbent resin, preferably 10 or more, and further 100. It is preferable that more than one is attached.

SEM image analysis means analysis of images obtained using a scanning electron microscope. For the number average particle size of the water-soluble polyvalent metal salt particles, 20 water-soluble polyvalent metal particles observed at 2000 times under a scanning electron microscope were randomly selected, and the 20 water-soluble polyvalent metal salt particles were selected. The diameter is measured with a ruler, the measured value is corrected by the observation magnification of a microscope, and the average value of the corrected measured values is calculated. When the water-soluble polyvalent metal salt particles are not a perfect circle, the smallest distance between two parallel tangents, that is, the minimum ferret diameter is regarded as the particle diameter.

The number average particle size of the water-soluble polyvalent metal salt particles is 0.3 to 15 μm, preferably 0.3 to 10 μm, and more preferably 0.3 to 5 μm.

Further, assuming a sphere having the particle size of the attached water-soluble polyvalent metal salt particles as the diameter, the volume average particle size is preferably 0.3 to 15 μm, more preferably 0.3 to 10 μm, and 0.3 to 0.3 to. 5 μm is more preferable.

The water-soluble polyvalent metal salt particles are preferably close to a circle in the SEM image, and more preferably a circle. The powder fluidity of the water-soluble polyvalent metal salt particles improves as they approach a circle in the SEM image. The circular shape is intended to be a figure having a circularity of 0.8 or more. The circularity means that the total length of the outer circumference of each water-soluble polyvalent metal salt particle in the shape when the water-soluble polyvalent metal salt particle is observed from a certain direction is L, and the area in the shape is S. , It is a value obtained by the following formula (2).
Circularity = 4π · S / L ² ... Equation (2)
The coating area of the water-soluble polyvalent metal salt particles in the SEM image analysis is preferably 0.1 to 50%, more preferably 0.5 to 20%, based on the area of the water-absorbent resin powder. It is preferably 1 to 10%, more preferably 1 to 10%. The covering area of the water-soluble polyvalent metal salt particles is the total area of all the water-soluble polyvalent metal salt particles that can be confirmed on the water-absorbent resin powder in the SEM image acquired at 2000 times. It is a value obtained by dividing by the area of.

When the water-soluble polyvalent metal salt particles are difficult to distinguish from other additives on the SEM image, it can be confirmed by using various element mapping methods and SEM in combination. Examples of the element mapping method include an energy dispersive X-ray spectrometer (EDS) and an electron probe microanalyzer (EPMA).

The SFC of the water-absorbent resin powder according to one embodiment of the present invention ^{is preferably 10 [10-7} · cm ³ · s · g ^-1 ] or more, preferably 30 [ ^10-7 · cm ³ · s · g ^-1 ]. The above is more preferable. The upper limit is preferably as high as the value, but is not particularly limited, but from the viewpoint of balance with other physical properties, it is preferably 500 [ ^10-7 · cm ³ · s · g ^-1 ] or less, more preferably 200 [ ^10-7 ·. cm ³ · s · g ^-1 ] or less.

The CRC of the water-absorbent resin powder according to one embodiment of the present invention is preferably 25 g / g or more, more preferably 27 g / g or more. The upper limit value is preferably as high as the value, but is not particularly limited, but is preferably 50 g / g or less, more preferably 40 g / g, from the viewpoint of balance with other physical properties.

The AAP (0.7 psi) of the water-absorbent resin powder according to the embodiment of the present invention is preferably 15 g / g or more, more preferably 20 g / g or more, still more preferably 24 g / g or more. The upper limit value is preferably 30 g / g or less, more preferably 28 g / g or less, from the viewpoint of balance with other physical properties, particularly SFC, although the higher value is preferable and not particularly limited. The AAP (0.7 psi) is measured according to the EDANA method (ERT442.2.22) by changing the load condition to 4.83 kPa (0.7 psi) as in the examples described later.

The hygroscopic fluidity of the water-absorbent resin powder according to one embodiment of the present invention is preferably 50% by weight or less, preferably 30% by weight or less, when stored at 25 ° C. and 70% relative humidity for 1 hour. Is more preferable, and 10% by weight or less is further preferable.

The surface tension when the component of the water-absorbent resin powder according to the embodiment of the present invention is extracted with 0.9% by weight saline solution is preferably in the range of 60 to 72 mN / m, more preferably 65 to 72 mN / m. It is in the range of m.

The water content of the water-absorbent resin powder according to the embodiment of the present invention (specified by the weight loss when 1.0 g of the water-absorbent resin powder is dried at 180 ° C. for 3 hours) is 0.1 to 15% by weight. Is more preferable, 1 to 12% by weight is more preferable, and 3 to 10% by weight is further preferable. By controlling the water content, the impact resistance and water absorption rate of the water-absorbent resin powder are improved. Moisture content is controlled by the amount of water evaporated in the drying process and surface cross-linking process, the amount of water in the polyvalent metal salt aqueous solution to be sprayed, the temperature and time of drying in the fluidized bed (particularly spray drying), and the addition of water. can. In one embodiment of the present invention, since the polyvalent metal salt aqueous solution is sprayed in the fluidized bed mixer, the total amount of added water is usually not reflected in the water content of the water-absorbent resin particles. As a result of drying at least a part of the water in the sprayed polyvalent metal salt aqueous solution, 80% by weight or less of the water in the sprayed polyvalent metal salt aqueous solution, further 1 to 70% by weight, particularly 5 to 60% by weight. % Is absorbed by the water-absorbent resin particles, and as a result, the water content of the water-absorbent resin powder is preferably improved.

The Ext (water-soluble content) of the water-absorbent resin powder according to the embodiment of the present invention is 50% by weight or less, preferably 35% by weight or less, more preferably 25% by weight or less, still more preferably 15% by weight. It is as follows. The lower limit value is not particularly limited, but is preferably about 0% by weight, more preferably about 0.1% by weight. When the Ext is 50% by weight or less, the gel strength is not weakened and the water-absorbent resin powder has excellent liquid permeability. Furthermore, since there is little rewetting, it is suitable as an absorber for sanitary goods such as disposable diapers. The Ext can be controlled by an internal cross-linking agent or the like.

The initial color tone of the water-absorbent resin powder according to the embodiment of the present invention is preferably 85 or more, more preferably 88 or more, and further preferably 90 or more in the L value in the Hunter Lab color system. The upper limit is 100, but if at least 80 is shown, the problem due to the color tone does not occur. The a value is preferably -3 to 3, more preferably -2 to 2, and even more preferably -1 to 1. Further, the b value is preferably 0 to 10, more preferably 0 to 7, and even more preferably 0 to 5. The whiteness increases as the L value approaches 100, and the a value and b value become less colored and substantially white as the value approaches 0.

The color tone of the water-absorbent resin powder according to the embodiment of the present invention is preferably 70 or more, more preferably 75 or more, still more preferably 80 or more, and particularly preferably 83 or more in the Hunter Lab color system. be. The upper limit is 100, but if at least 80 is shown, the problem due to the color tone does not occur. The a value is preferably -3 to 3, more preferably -2 to 2, and even more preferably -1 to 1. Further, the b value is preferably 0 to 15, more preferably 0 to 12, and even more preferably 0 to 10. The whiteness increases as the L value approaches 100, and the a value and b value become less colored and substantially white as the value approaches 0. The water-absorbent resin powder according to the embodiment of the present invention tends to have a smaller change in color tone over time with respect to the initial color tone, that is, to be difficult to color, as compared with the conventional water-absorbent resin powder to which a polyvalent metal salt is added.
The initial color tone and the color tone over time are measured according to the color evaluation before the color promotion test and after the color promotion test described in WO2009 / 00114.

The particle size and polymer structure of the water-absorbent resin powder are as described above.

[4] Aspects of the present invention That is, the present invention can be the following aspects.

(Manufacturing method of water-absorbent resin powder)
1. 1. A method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt. A polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is mixed with a fluidized layer. A method for producing a water-absorbent resin powder, which comprises a spraying step of spraying on the water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in the machine, and the air temperature at the spraying position of the polyvalent metal salt aqueous solution is 50 ° C. or higher. ..

2. The method for producing a water-absorbent resin powder according to 1, wherein the aqueous solution of the polyvalent metal salt is sprayed onto the water-absorbent resin particles after surface cross-linking in the fluidized bed mixer. With such a configuration, the physical characteristics of the obtained water-absorbent resin are improved.

3. 3. The method for producing a water-absorbent resin powder according to 1 or 2, wherein the water-absorbent resin particles after surface cross-linking are cooled in the fluidized bed mixer at the same time as the spraying step. With such a configuration, the physical characteristics of the obtained water-absorbent resin are improved and the spray is sprayed at the same time as cooling, so that the process is simplified.

4. The method for producing a water-absorbent resin powder according to any one of 1 to 3, wherein the temperature of the water-absorbent resin particles introduced in the spraying step is 50 to 250 ° C. With such a configuration, the physical characteristics of the water-absorbent resin are improved.

5. The method for producing a water-absorbent resin powder according to any one of 1 to 4, wherein in the spraying step, the polyvalent metal salt aqueous solution is sprayed from the upper part of the fluidized bed mixer. With such a configuration, the physical properties of the obtained water-absorbent resin are improved, and manufacturing troubles are reduced.

6. Any of 1 to 5, wherein at least a part of the water in the sprayed polyvalent metal salt aqueous solution is dried, and 80% by weight or less of the water in the sprayed polyvalent metal salt aqueous solution is absorbed by the water-absorbent resin particles. The method for producing a water-absorbent resin powder according to.

7. A method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface-crosslinking agent and contains a water-soluble polyvalent metal salt. A method for producing a water-absorbent resin powder, to which water-soluble polyvalent metal salt particles having a volume average particle diameter of 0.3 to 15 μm measured in 1 are added.

8. The method for producing a water-absorbent resin powder according to any one of 1 to 7, wherein the water-soluble polyvalent metal salt is 0.01 to 1 part by weight with respect to 100 parts by weight of the water-absorbent resin particles. With such a configuration, the physical characteristics of the obtained water-absorbent resin are improved.

9. The method for producing a water-absorbent resin powder according to any one of 1 to 8, wherein the water-soluble polyvalent metal salt is a water-soluble aluminum salt. With such a configuration, the physical characteristics of the obtained water-absorbent resin are improved.

(Water-absorbent resin powder)
10. A water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt. A water-absorbent resin powder having a number average particle diameter of valent metal salt particles of 0.3 to 15 μm. With such a configuration, the physical characteristics of the water-absorbent resin are improved.

11. The water-absorbent resin powder according to 10, wherein the water-soluble polyvalent metal salt particles obtained by SEM image analysis have a circularity of 0.8 or more defined by the following formula.

(Circularity) = 4π ・ S / L ²
(In the formula, the outer circumference of the attached water-soluble polyvalent metal salt particles is L, and the area of the attached water-soluble polyvalent metal salt particles is S).
12. 10. The water-absorbent resin powder according to 10 or 11, wherein the coverage area of the water-soluble polyvalent metal salt particles by SEM image analysis is 0.1 to 50% with respect to the area of the water-absorbent resin powder. With such a configuration, the physical characteristics of the water-absorbent resin are improved.

13. The water-absorbent resin powder according to any one of 10 to 12, wherein the CRC is 25 g / g or more and the AAP (0.7 psi) is 15 g / g or more. With such a configuration, the physical characteristics of the water-absorbent resin are improved.

14. The water-absorbent resin powder according to any one of 10 to 13, wherein the weight average particle size is 100 to 2000 μm. With such a configuration, the physical characteristics of the water-absorbent resin are improved.

[5] Differences from Conventional Techniques With respect to the inventions described in Patent Documents 1 to 22, one embodiment of the present invention is a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more under heating. Is an invention relating to a method for producing a water-absorbent resin powder, which is sprayed onto the water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in a fluidized layer mixer.

Although not limited to the reaction mechanism, in one embodiment of the present invention, a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is sprayed in a fluidized bed mixer under heating. The aqueous solution of the polyvalent metal salt is in a spray-dried state, and the water-soluble polyvalent metal salt forms a fine mass having an average particle diameter of 0.3 to 15 μm and adheres to the surface of the water-absorbent resin to allow the water-absorbent resin to pass through. It is estimated that the sex will improve. That is, by spraying and adding a polyvalent metal salt aqueous solution in a fluidized bed under heating, droplets of the polyvalent metal salt aqueous solution are dried on the surface of the air layer or a water-absorbent resin that flows in the air layer, and are solid polyvalent. It is presumed that the metal salt is attached.

In the conventional addition of the polyvalent metal salt aqueous solution under stirring, the polyvalent metal salt aqueous solution is added to the layer of the agitated water-absorbent resin particles, so that the polyvalent metal salt is absorbed by the water-absorbent resin, or The water-absorbent resin is coated by being thinly stretched by contact between the water-absorbent resins. On the other hand, in one embodiment of the present invention, a substantially spherical / massive solid polyvalent metal salt as shown in FIG. 1 adheres to the surface of the water-absorbent resin in a point-like discontinuous manner. In the conventional surface treatment of the water-absorbent resin with the aqueous solution of the polyvalent metal salt, the water-absorbent resin is coated with the polyvalent metal salt, whereas one embodiment of the present invention has a new shape as shown in FIG. Gives a water-absorbent resin.

The above-mentioned Patent Documents 1 to 22 do not suggest a method for producing a water-absorbent resin powder and a water-absorbent resin powder according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. In the following, for convenience, "parts by weight" may be simply referred to as "parts" and "liter" may be simply referred to as "L". Moreover, "weight%" may be described as "wt%".

The various performances of the water-absorbent resin particles were measured by the following methods. Unless otherwise specified, the following measurements shall be performed under the conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%. When the object to be measured is other than the water-absorbent resin particles, the water-absorbent resin particles are read as the object and applied unless otherwise specified.

<Saline flow inducibility (SFC)>
The SFC of the water-absorbent resin powder according to one embodiment of the present invention was measured according to the measuring method described in US Pat. No. 5,669894.

<Centrifuge retention capacity (CRC)>
The CRC of the water-absorbent resin powder according to one embodiment of the present invention was measured according to the EDANA method (ERT441.2-02).

<Water absorption ratio under pressure (AAP)>
The AAP of the water-absorbent resin powder according to one embodiment of the present invention was measured according to the EDANA method (ERT442.2-02). The load condition was changed to 4.83 kPa (0.7 psi).

<Powder fluidity (FLOWRATE (FR))>
The FR of the water-absorbent resin powder according to one embodiment of the present invention was measured according to the EDANA method (ERT450.2-02).

<Blocking Ratio (BR)>
Approximately 2 g of water-absorbent resin powder was uniformly sprayed on an aluminum cup having a diameter of 52 mm on the bottom surface, and then left in a constant temperature and humidity chamber at a temperature of 25 ° C. and a relative humidity of 70% RH for 1 hour. After 1 hour, the water-absorbent resin powder in the aluminum cup was gently transferred onto a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm) with an opening of 2000 μm, and a low-tap type sieve shaker (manufactured by Iida Seisakusho Co., Ltd.). Classified for 8 seconds using an ES-65 type sieve shaker (rotation speed 230 rpm, impact number 130 rpm), the weight (i (g)) of the water-absorbent resin powder remaining on the sieve, and the water absorption that passed through the sieve. The weight (j (g)) of the resin powder was measured. Then, the moisture absorption blocking rate was calculated according to the following formula (3). The closer the moisture absorption blocking rate is to 0% by weight, the higher the moisture absorption fluidity.
Moisture absorption blocking rate (% by weight) = ((i (g)) / (i (g) + j (g))) × 100 ... Equation (3)
<Surface tension of extract>
The surface tension of the extract of the water-absorbent resin powder is a value measured for the extract extracted from the water-absorbent resin powder with a 0.9 wt% sodium chloride aqueous solution. Specifically, 50 mL of 0.9% by mass sodium chloride aqueous solution (physiological saline) whose temperature was adjusted to 23 ° C. to 25 ° C. was put into a well-washed beaker having a capacity of 100 mL, and the surface of the physiological saline solution was added. The tension is measured using a surface tensiometer (automatic surface tension meter K11, manufactured by Cruz), and it is confirmed that the measured value of the surface tension is within the range of 71 mN / m to 75 mN / m. Subsequently, a sufficiently washed 25 mm long fluororesin rotor and 0.5 g of a water-absorbent resin are added to the physiological saline solution, and the mixture is stirred at 500 rpm for 4 minutes. Then, the stirring was stopped to allow the swollen water-absorbent resin to settle, and the value measured for the supernatant liquid in the same manner as above was taken as the surface tension.

<Moisture content>
In the EDANA method (ERT430.2-02), 1 g of water-absorbent resin particles or powder was changed to a drying weight loss when dried at 180 ° C. for 3 hours (windless oven).

<Volume average particle size of polyvalent metal salt particles in polyvalent metal salt aqueous solution>
Cyclohexane and polyvalent metal salt particles were placed in a test tube, and the polyvalent metal salt particles were dispersed by an ultrasonic cleaner. This dispersion was analyzed by a laser diffraction / scattering method to determine the volume average particle size of the polyvalent metal salt particles.

[Production Example 1: Production of water-absorbent resin particles (polymerization, drying, pulverization, classification)]
5500 g of sodium acrylate aqueous solution having a neutralization rate of 75% and a monomer concentration of 38% by weight, and 4.5 g of polyethylene glycol diacrylate (average molecular weight 523) in a kneader with a jacket having an internal volume of 10 L and having two sigma type blades. After charging and mixing, nitrogen was blown in and degassed. Next, the contents of the kneader were adjusted to 30 ° C. with stirring, and 28.3 g of a 10 wt% sodium persulfate aqueous solution and then 2.0 g of 1 wt% L-ascorbic acid were injected. Later, a hydrogel having a particle size of 1 to 5 mm was obtained. This hydrous gel was spread to 50 cm × 70 cm on a stainless mesh having an opening of 300 μm, and dried at 180 ° C. for 40 minutes in a hot air dryer (product name: 71-6S manufactured by Satake Chemical Machinery Co., Ltd.). The obtained dried polymer was pulverized by a roll mill and classified with a standard sieve having a mesh size of 850 μm and 150 μm to obtain water-absorbent resin particles (1) having a particle size of 150 to 850 μm (weight average particles (D50) were 370 μm). Obtained.

[Production Example 2: Surface cross-linking of water-absorbent resin particles]
While stirring 100 parts by weight of the water-absorbent resin particles (1) obtained in Production Example 1 at high speed, 0.001 part by weight of polyoxyethylene sorbitan monosteert (TWEEN60), 0.3 part by weight of ethylene carbonate, and propylene glycol. An aqueous solution of a surface cross-linking agent consisting of 0.6 parts by weight and 3 parts by weight of deionized water was spray-added and heated with a paddle dryer at 200 ° C. for 40 minutes while stirring. Further, the surface-crosslinked water-absorbent resin particles (1) were passed through a sieve having an opening of 850 μm while loosening the agglomeration. Here, the surface cross-linking agent is an organic cross-linking agent that crosslinks with a carboxyl group which is a functional group of the water-absorbent resin particles (1) by a covalent bond (dehydration reaction of COOH and OH).

The surface-crosslinked water-absorbent resin particles (1) thus obtained had a weight average particle (D50) of 380 μm. Table 1 shows the measurement results of various physical property values of the obtained surface-crosslinked water-absorbent resin particles (1). The surface tension of the extract of the surface-crosslinked water-absorbent resin particles (1) was 70 mN / m. The surface tension of the water-absorbent resin powders obtained in Examples and Comparative Examples following Production Example 1 was about 70 mN / m.

[Example 1: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 27% by weight under heating]
The surface-crosslinked water-absorbent resin particles (1) obtained in Production Example 2 were sprayed with a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 27% by weight in a fluidized bed mixer under heating.

Specifically, 500 g of water-absorbent resin particles (1) are charged into a fluidized bed mixer (product name: Pulvis GB22, manufactured by Yamato Scientific Co., Ltd.) that forms a fluidized bed, and hot air; 100 ° C., air volume: 0.2 m ³ / The water-absorbent resin particles (1) were warmed while flowing under the condition of min (punching; 8 cmφ, wind speed: 0.66 m / s). After the temperature of the water-absorbent resin particles (1) and the exhaust temperature of the fluidized bed reached 80 ° C., 5 g of a 27 wt% aluminum sulfate aqueous solution (1 wt% with respect to 100 wt% of the water-absorbent resin particles) was applied at a rate of 15 g / min. I sprayed it. Further, the water-absorbent resin particles sprayed with the aqueous aluminum sulfate solution were mixed in the fluidized bed mixer for 5 minutes to obtain the water-absorbent resin powder (1). Table 1 shows the measurement results of various physical property values.

The concentration of the saturated aqueous solution of aluminum sulfate (20 ° C.) is about 50% by weight, and it is estimated that in Example 1, the aqueous solution of aluminum sulfate is spray-dried and added to the water-absorbent resin particles at the same time. As a result, as shown in FIG. 1, adhesion of spherical particles of aluminum sulfate hydrate was observed. Based on the acquired SEM image, the number average particle size of the aluminum sulfate hydrate was 3 μm, the coating area was 2% with respect to the area of the water-absorbent resin powder, and the circularity was 0.85. Further, in the above operation, 73% by weight of water and 27% by weight of aluminum sulfate were added to the water-absorbent resin particles, and the water content of the water-absorbent resin was improved by about 0.2%. That is, 27% by weight of the added water was absorbed.

[Comparative Example 1: Addition of an aqueous solution of a polyvalent metal salt having a concentration of a polyvalent metal salt of 4% by weight at room temperature]
Blower: 24 ° C (water-absorbent resin temperature; 24 ° C), air volume: 0.6 m ³ / min (punching; 8 cmφ, wind speed; 2.0 m / s) while flowing water-absorbent resin particles, 4% by weight An attempt was made to produce a water-absorbent resin powder in the same manner as in Example 1 except that 25 g of an aqueous solution of aluminum sulfate (5% by weight based on 100% by weight of water-absorbent resin particles) was used. However, after spraying the aqueous solution of aluminum sulfate, the water-absorbent resin particles immediately stopped flowing and became aggregates.

[Comparative Example 2: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 4% by weight under heating]
An attempt was made to produce a water-absorbent resin powder in the same manner as in Example 1 except that 25 g of a 4-weight% aluminum sulfate aqueous solution (5% by weight with respect to 100% by weight of the water-absorbent resin particles) was used. However, after spraying the aqueous solution of aluminum sulfate, the water-absorbent resin particles immediately stopped flowing and became aggregates.

[Comparative Example 3: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 4% by weight under heating (changing the air volume)]
When an attempt was made to produce a water-absorbent resin powder in the same manner as in Comparative Example 2 except that the air volume was 0.36 m ³ / min (punching; 8 cmφ, wind speed; 1.2 m / s), the flow of the water-absorbent resin particles did not stop. However, the water-absorbent resin particles were scattered in the fluidized bed mixer. Further, the water-absorbent resin particles sprayed with the aqueous aluminum sulfate solution were mixed in the fluidized bed mixer for 5 minutes to obtain a comparative water-absorbent resin powder (3). Table 1 shows the measurement results of various physical property values of the comparative water-absorbent resin powder (3). In addition, in the observation by SEM, no particles or lumps of aluminum sulfate hydrate were observed on the surface of the comparative water-absorbent resin powder (3).

[Comparative Example 4: Addition of an aqueous solution of a polyvalent metal salt having a concentration of a polyvalent metal salt of 4% by weight at room temperature (change of spray direction)]
When the production of the water-absorbent resin powder was attempted in the same manner as in Comparative Example 1 except that the aqueous solution of aluminum sulfate was sprayed upward from the vicinity of the punching metal, the flow of the water-absorbent resin particles did not stop. Further, the water-absorbent resin particles sprayed with the aqueous aluminum sulfate solution were mixed in the fluidized bed mixer for 5 minutes to obtain a comparative water-absorbent resin powder (4). Table 1 shows the measurement results of various physical property values of the comparative water-absorbent resin powder (4). In addition, in the observation by SEM, no particles or lumps of aluminum sulfate hydrate were observed on the surface of the comparative water-absorbent resin powder (4).

[Reference Example 1]
When an aqueous aluminum sulfate solution having a polyvalent metal salt concentration of 27% by weight was sprayed in the fluidized bed mixer without using the water-absorbent resin particles in Example 1, fine powder of aluminum sulfate hydrate was obtained. .. When this fine powder was classified with a sieve having a mesh size of 45 μm to remove large agglomerates, fine particles of aluminum sulfate hydrate having a volume average particle diameter of 4 μm measured by a laser diffraction / scattering method were obtained.

[Example 2]
0.25 parts by weight of the aluminum sulfate hydrate obtained in Reference Example 1 was added to 100 parts by weight of the surface-crosslinked water-absorbent resin particles (1) obtained in Production Example 2, mixed, and the water-absorbent resin powder (1) 2) was obtained. Table 1 shows the measurement results of various physical property values of the water-absorbent resin powder (2). Based on the SEM image of the obtained water-absorbent resin powder (2), the number average particle size of aluminum sulfate hydrate was 2 μm.

[Example 3]
In Example 2 above, the water-absorbent resin powder (3) was obtained in the same manner as in Example 2 except that 0.5 part by weight of the aluminum sulfate hydrate obtained in Reference Example 1 was added and mixed. rice field. Table 1 shows the measurement results of various physical property values of the water-absorbent resin powder (3).

[Comparative Example 5]
100 parts by weight of the surface-crosslinked water-absorbent resin particles (1) obtained in Production Example 2 are placed in a plastic container, and 1 part by weight of a 27% by weight aluminum sulfate aqueous solution is added and mixed with a syringe while stirring with a spatula, and 80 parts by weight are added. It was heated in a windless oven at ° C for 30 minutes. Further, the aggregate was passed through a sieve having an opening of 850 μm while breaking down to obtain a comparative water-absorbent resin powder (5). Table 1 shows the measurement results of various physical property values of the comparative water-absorbent resin powder (5).

[Comparative Example 6]
Place 100 parts by weight of the surface-crosslinked water-absorbent resin particles (1) obtained in Production Example 2 in a plastic container, and stir with a syringe to 1 part by weight of a 27% by weight aluminum sulfate aqueous solution and 0.3% by weight of 60% by weight sodium lactate. A liquid consisting of 0.025 parts by weight of propylene glycol was added by a syringe, mixed, and heated in a windless oven at 80 ° C. for 30 minutes. Further, the aggregate was passed through a sieve having an opening of 850 μm while breaking down to obtain a comparative water-absorbent resin powder (6). Table 1 shows the measurement results of various physical property values of the comparative water-absorbent resin powder (6).

（まとめ）
製造例２（表面架橋された吸水性樹脂粒子）を用いて、多価金属塩を添加する実施例１の吸水性樹脂粉末（１）（多価金属塩の濃度が２７％の多価金属塩水溶液の加熱下での添加）と比較例１〜４の比較吸水性樹脂粉末（１）〜（４）（多価金属塩の濃度が４重量％の多価金属塩水溶液の加熱下または室温での添加）とを製造した。これらの対比により、多価金属塩の濃度が５重量％以上の多価金属塩を加熱下で噴霧する本発明の一実施形態の製造方法では、凝集もなく安定的に吸水性樹脂粉末が得られるとともに、吸水性樹脂粉末の通液性（ＳＦＣ）および吸湿流動性が高いことが分かる。また流動層混合機を用いないで多価金属塩を添加する従来の高通液性、高吸湿流動性技術に相当する比較例５、６により得られた比較吸水性樹脂粉末と比べても実施例１〜３で得られた吸水性樹脂粉末は通液性、吸湿流動性に優れていることが分かる。さらに、シリカ等を添加した吸水性樹脂と異なり、本発明の一実施形態の製造方法で得られた表面架橋された吸水性樹脂粒子は、加圧下吸水倍率（ＡＡＰ）が製造例２の表面架橋された吸水性樹脂粒子とほぼ同等の加圧下吸水倍率を示す。実施例１の吸水性樹脂粉末は、図１に示すように、数平均粒子径３μｍ程度の球状の多価金属塩（硫酸アルミニウム）の粒子の付着がＳＥＭ画像で観察された。さらに実施例１で得られた吸水性樹脂粉末の含水率から噴霧した水溶液中の水が乾燥したことが示唆される。

(summary)
Water-absorbent resin powder of Example 1 to which a polyvalent metal salt is added using Production Example 2 (surface-crosslinked water-absorbent resin particles) (1) (Polyvalent metal salt having a polyvalent metal salt concentration of 27%) Addition of aqueous solution under heating) and comparison of Comparative Examples 1 to 4 Water-absorbent resin powders (1) to (4) (polyvalent metal salt concentration of 4% by weight under heating or at room temperature Addition) and manufactured. Based on these comparisons, in the production method of one embodiment of the present invention in which a polyvalent metal salt having a polyvalent metal salt concentration of 5% by weight or more is sprayed under heating, a water-absorbent resin powder can be stably obtained without aggregation. It can be seen that the water-absorbent resin powder has high liquid permeability (SFC) and moisture absorption and fluidity. Further, it is also compared with the comparative water-absorbent resin powders obtained in Comparative Examples 5 and 6 corresponding to the conventional high liquid permeability and high moisture absorption fluidity techniques in which a polyvalent metal salt is added without using a fluidized bed mixer. It can be seen that the water-absorbent resin powders obtained in Nos. 1 to 3 are excellent in liquid permeability and hygroscopic fluidity. Further, unlike the water-absorbent resin to which silica or the like is added, the surface-crosslinked water-absorbent resin particles obtained by the production method of one embodiment of the present invention have a surface-crosslinked water absorption ratio (AAP) of Production Example 2 under pressure. It shows a water absorption ratio under pressure that is almost the same as that of the water-absorbent resin particles. As shown in FIG. 1, in the water-absorbent resin powder of Example 1, adhesion of spherical polyvalent metal salt (aluminum sulfate) particles having a number average particle diameter of about 3 μm was observed on the SEM image. Further, the water content of the water-absorbent resin powder obtained in Example 1 suggests that the water in the sprayed aqueous solution has dried.

[Manufacturing Example 3]
Water-absorbent resin particles (3) were obtained in the same manner as in Production Example 1 except that the amount of polyethylene glycol diacrylate used was changed to 11.2 parts by weight in Production Example 1.

[Manufacturing Example 4]
The surface-crosslinked water-absorbent resin particles (4) were obtained in the same manner as in Production Example 2 except that the water-absorbent resin particles (3) were used in Production Example 2. Table 2 shows the measurement results of various physical property values of the surface-crosslinked water-absorbent resin particles (4).

[Example 4]
A water-absorbent resin powder (4) was obtained in the same manner as in Example 3 except that the surface-crosslinked water-absorbent resin particles (4) were used in Example 3. Table 2 shows the measurement results of various physical property values of the water-absorbent resin powder (4).

[Comparative Example 7]
A comparative water-absorbent resin powder (7) was obtained in the same manner as in Comparative Example 5 except that the surface-crosslinked water-absorbent resin particles (4) were used in Comparative Example 5. Table 2 shows the measurement results of various physical property values of the comparative water-absorbent resin powder (7).

[Comparative Example 8]
A comparative water-absorbent resin powder (8) was obtained in the same manner as in Comparative Example 6 except that the surface-crosslinked water-absorbent resin particles (4) were used in Comparative Example 6. Table 2 shows the measurement results of various physical property values of the comparative water-absorbent resin powder (8).

（まとめ）
内部架橋剤の使用量を変更して、表面架橋された吸水性樹脂粒子（１）よりもＣＲＣの低い表面架橋された吸水性樹脂粒子（２）を作製し、実施例４、比較例７、８の吸水性樹脂粉末を製造した。これらについて各種物性値を測定したところ、ＳＦＣの違いがより明確になった。すなわち、実施例４の吸水性樹脂粉末（４）は比較例７の比較吸水性樹脂粉末（７）よりもＳＦＣが高く、吸湿ブロッキング率が低く、０重量％に近いことから、通液性および吸湿流動性の面で明らかに優れている。また、実施例４の吸水性樹脂粉末（４）は比較例８の比較吸水性樹脂粉末（８）に対しても、吸湿ブロッキング率が低く、０重量％に近いことから、吸湿流動性の面で優れている。

(summary)
By changing the amount of the internal cross-linking agent used, surface-crosslinked water-absorbent resin particles (2) having a lower CRC than the surface-crosslinked water-absorbent resin particles (1) were prepared, and Example 4, Comparative Example 7, 8 water-absorbent resin powders were produced. When various physical property values were measured for these, the difference in SFC became clearer. That is, the water-absorbent resin powder (4) of Example 4 has a higher SFC than the comparative water-absorbent resin powder (7) of Comparative Example 7, has a lower moisture absorption blocking rate, and is close to 0% by weight. Clearly excellent in terms of moisture absorption and fluidity. Further, the water-absorbent resin powder (4) of Example 4 has a lower moisture absorption blocking rate than the comparative water-absorbent resin powder (8) of Comparative Example 8 and is close to 0% by weight. Is excellent.

[Reference example 2]
By adding 2 parts by weight of a 13.5% by weight aqueous aluminum sulfate solution to 4 parts by weight of polyethylene glycol (molecular weight 200) with vigorous stirring, a dispersion liquid (1) in which aluminum sulfate hydrate was precipitated and dispersed was obtained.

[Example 5]
6 parts by weight of the dispersion liquid (1) obtained in Reference Example 2 was added dropwise to 100 parts by weight of the surface-crosslinked water-absorbent resin particles (1) obtained in Production Example 2 while stirring. Further, it was dried in an oven at 180 ° C. for 30 minutes and passed through a sieve having an opening of 850 μm to obtain a water-absorbent resin powder (5). Table 3 shows the measurement results of various physical property values of the water-absorbent resin powder (5). When observed on the SEM image, the aluminum sulfate hydrate was a slightly elongated polyhedron, and the number average particle size was 1 μm. There was no dust.

[Reference Example 3]
0.5 parts by weight of the aluminum sulfate hydrate obtained in Reference Example 1 was dispersed in a mixed solution of 4 parts by weight of polyethylene glycol (molecular weight 200) and 1.5 parts by weight of deionized water to obtain the dispersion liquid (2). Obtained.

[Example 6]
In Example 5, a water-absorbent resin powder (6) was obtained in the same manner except that 6 parts by weight of the dispersion liquid (2) obtained in Reference Example 3 was added instead of the dispersion liquid (1). Table 3 shows the measurement results of various physical property values of the water-absorbent resin powder (6). When observed on the SEM image, the shape of the aluminum sulfate hydrate was a mixture of spherical and polyhedrons, the number average particle diameter was 1 μm, and the circularity was 0.81. There was no dust.

[Comparative Example 9]
In Example 5, the comparative water-absorbent resin (9) was prepared in the same manner except that an aqueous solution consisting of 4 parts by weight of polyethylene glycol (molecular weight 200) and 2 parts by weight of deionized water was added instead of the dispersion liquid (1). Obtained. Table 3 shows the measurement results of various physical property values of the comparative water-absorbent resin (9).

実施例５，６、比較例９におけるＦ.Ｒ.の比較から、硫酸アルミニウム粒子が含まれていることにより、吸水性樹脂のＦ.Ｒ.が向上していることがわかる。また、実施例５と実施例６を比較すると、球状の硫酸アルミニウム粒子が含まれていると、吸水性樹脂のＦ．Ｒ．とＳＦＣが向上することが分かる。さらに、表１の記載と表３の記載との対比から、球状硫酸アルミニウムをポリエチレングリコールとともに添加すると、吸水性樹脂のＳＦＣが大きく向上することが分かる。

From the comparison of FR in Examples 5 and 6 and Comparative Example 9, it can be seen that the inclusion of aluminum sulfate particles improves the FR of the water-absorbent resin. Further, when Example 5 and Example 6 are compared, it is found that the water-absorbent resin F.I. R. It can be seen that SFC is improved. Furthermore, from the comparison between the description in Table 1 and the description in Table 3, it can be seen that the addition of spherical aluminum sulfate together with polyethylene glycol greatly improves the SFC of the water-absorbent resin.

[Example 7]
Aluminum lactate was ground in a mortar to obtain aluminum lactate particles having a volume average particle diameter of 4 μm.

0.5 part by weight of the obtained aluminum lactate was added to and mixed with 100 parts by weight of the surface-crosslinked water-absorbent resin (1) to obtain a water-absorbent resin powder (7). Table 4 shows the measurement results of various physical property values of the water-absorbent resin powder (7).

Since the water-absorbent resin powder produced by using the present invention has excellent liquid permeability, it can be suitably used for various sanitary materials such as paper diapers and sanitary napkins, and other various water-absorbent resins.

Claims (14)

A method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt. A polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is mixed with a fluidized layer. A method for producing a water-absorbent resin powder, which comprises a spraying step of spraying on the water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in the machine, and the air temperature at the spraying position of the polyvalent metal salt aqueous solution is 50 ° C. or higher. .. The method for producing a water-absorbent resin powder according to claim 1, wherein the aqueous solution of the polyvalent metal salt is sprayed onto the water-absorbent resin particles after surface cross-linking in the fluidized bed mixer. The method for producing a water-absorbent resin powder according to claim 1 or 2, wherein the water-absorbent resin particles after surface cross-linking are cooled at the same time as the spraying step in the fluidized bed mixer. The method for producing a water-absorbent resin powder according to any one of claims 1 to 3, wherein the temperature of the water-absorbent resin particles introduced in the spraying step is 50 to 250 ° C. The method for producing a water-absorbent resin powder according to any one of claims 1 to 4, wherein in the spraying step, the polyvalent metal salt aqueous solution is sprayed from the upper part of the fluidized bed mixer. 2. The method for producing a water-absorbent resin powder according to any one of the following items. A method for producing a water-absorbent resin powder that is surface-crosslinked with an organic surface-crosslinking agent and contains a water-soluble polyvalent metal salt. A method for producing a water-absorbent resin powder, to which water-soluble polyvalent metal salt particles having a measured volume average particle diameter of 0.3 to 15 μm are added. The production of the water-absorbent resin powder according to any one of claims 1 to 7, wherein the water-soluble polyvalent metal salt is 0.01 to 1 part by weight with respect to 100 parts by weight of the water-absorbent resin particles. Method. The method for producing a water-absorbent resin powder according to any one of claims 1 to 8, wherein the water-soluble polyvalent metal salt is a water-soluble aluminum salt. A water-absorbent resin powder that is surface-crosslinked with an organic surface cross-linking agent and contains a water-soluble polyvalent metal salt. A water-absorbent resin powder having a number average particle diameter of valent metal salt particles of 0.3 to 15 μm. The water-absorbent resin powder according to claim 10, wherein the water-soluble polyvalent metal salt particles obtained by SEM image analysis have a circularity of 0.8 or more as defined by the following formula.
(Circularity) = 4π ・ S / L ²
(In the formula, the outer circumference of the attached water-soluble polyvalent metal salt particles is L, and the area of the attached water-soluble polyvalent metal salt particles is S). The water-absorbent resin powder according to claim 10 or 11, wherein the coverage area of the water-soluble polyvalent metal salt particles by SEM image analysis is 0.1 to 50% with respect to the area of the water-absorbent resin powder. The water-absorbent resin powder according to any one of claims 10 to 12, wherein the CRC is 25 g / g or more and the AAP (0.7 psi) is 15 g / g or more. The water-absorbent resin powder according to any one of claims 10 to 13, wherein the weight average particle size is 100 to 2000 μm.

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