WO2020067563A1

WO2020067563A1 - Method for producing water-absorbing resin powder and water-absorbing resin powder

Info

Publication number: WO2020067563A1
Application number: PCT/JP2019/038462
Authority: WO
Inventors: 智嗣松本; 藤野　眞一
Original assignee: 株式会社日本触媒
Priority date: 2018-09-28
Filing date: 2019-09-30
Publication date: 2020-04-02
Also published as: JP7355900B2; JPWO2020067563A1; JP2022166050A; CN112703053B; CN112703053A; JP7116796B2; KR20210041070A

Abstract

A method for producing a water-absorbing resin powder which has been surface-crosslinked with a substance that is not a water-soluble polyvalent-metal salt and which contains a water-soluble polyvalent-metal salt, the method comprising spraying an aqueous polyvalent-metal salt solution having a polyvalent-metal salt concentration of 5 wt% or higher, with heating in a fluidized-bed mixer, over water-absorbing resin particles which are undergoing or have undergone surface crosslinking. By the production method, a water-absorbing resin powder having excellent liquid permeability can be easily obtained.

Description

Method for producing water-absorbent resin powder and water-absorbent resin powder

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

2. Description of the Related Art For sanitary materials such as disposable diapers, sanitary napkins, incontinence pads, etc., absorbents having hydrophilic fibers such as pulp and a water-absorbing resin as constituent materials are widely used for the purpose of absorbing body fluids.

In recent years, these sanitary materials have become more sophisticated and thinner, and the amount of water-absorbent resin used per sanitary material and the ratio of water-absorbent resin to the entire absorbent body composed of water-absorbent resin and hydrophilic fibers have increased. Tend to. In other words, by reducing the number of hydrophilic fibers having a low bulk specific gravity and using a large amount of a water-absorbent resin having excellent water absorbency and a large bulk specific gravity, the ratio of the water-absorbent resin in the absorber is increased and the water absorption is reduced. Instead of sanitary materials.

(4) As the ratio of the water-absorbent resin to the entire absorber increases, the performance requirements of the water-absorbent resin also increase. For example, not only the water absorption capacity under no pressure (CRC), but also the water absorption capacity under pressure (AAP) so that water can be absorbed even when weight is applied, or liquid permeability (eg, , GBP and SFC).

要求 In addition, the demand for handleability of water-absorbent resin is increasing for efficient production of absorbers. Above all, since the water-absorbing resin exhibits hygroscopicity, it is required to have a hygroscopic fluidity (also called anti-caking property) so that the handling property as a powder does not change regardless of humidity.

技術 Technologies for adding additives mainly to the surface of the water-absorbent resin particles have been developed to satisfy these requirements.

For example, it is known to use a polyvalent metal salt for improving liquid permeability. Patent Document 1 discloses that a water-absorbing polymer particle is coated with a non-reactive coating agent such as a polyvalent metal salt by a continuous method. A process for spray-coating in a fluidized bed reactor at a temperature in the range of 0 ° C. to 150 ° C. is disclosed. Patent Literatures 2 to 7 disclose methods for improving liquid permeability (SFC) by mixing a polyvalent metal salt with a water-absorbent resin at the time of surface crosslinking or after surface crosslinking.

As a method for improving surface crosslinking, Patent Literatures 8 and 9 disclose a method for surface crosslinking of a water-absorbent resin, in which a surface-crosslinking agent is mixed with a heated water-absorbent resin particle while flowing using a gas flow to perform surface crosslinking. It has been 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 cross-linked by heating in a fluidized bed mixer.

Patent Documents 14 to 16 disclose a method of granulating water-absorbent resin fine particles by spraying a binder in a fluidized bed granulator to improve the water absorption rate. Patent Document 17 discloses a polyvalent metal salt. A water-absorbing resin composition for spraying an aqueous solution is disclosed. Further, Patent Documents 18 and 19 disclose a method of adding a polyvalent metal salt aqueous solution which is improved to obtain a water-absorbing resin having both excellent liquid permeability and excellent moisture absorption fluidity. According to Patent Document 18 (Comparative Example 2), when powdery aluminum sulfate hydrate was added to the water-absorbent resin, the moisture-absorbing 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 moisture absorption fluidity is also widely used. For example, in order to improve liquid permeability (SFC), Patent Document 20 discloses a water-absorbing resin to which silica or the like is added, and Patent Document 21 discloses a water-absorbing resin to which a water-insoluble metal phosphate is added. Patent Document 22 discloses a water-absorbing resin to which a water-insoluble polyvalent metal complex salt is added in order to improve the moisture-absorbing fluidity. However, the addition of such water-insoluble inorganic fine particles may cause a problem in that either the liquid permeability or the fluidity of moisture absorption is insufficient, or may lower the water absorption capacity under pressure.

特許 Also, Patent Document 23 discloses a technique for adding fine alum particles to neutralize ammonia, which is a cause of urinary odor, but has poor liquid permeability and insufficient moisture absorption fluidity.

Japanese Unexamined Patent Publication "Tokuhoku 2009-52287" Japanese Unexamined Patent Publication "JP-A-2005-097519" International Publication No. 2000/053664 pamphlet WO 2000/053644 pamphlet WO 2001/074913 pamphlet Japanese Unexamined Patent Publication "Tokuhyo 2004-508432" WO 2007/121941 pamphlet Japanese Unexamined Patent Publication "JP-A-7-242709" Japanese Unexamined Patent Publication "JP-A-7-224204" WO 2003/044120 pamphlet International Publication No. 2013/110414 pamphlet WO 2013/110415 pamphlet WO 2009/028568 pamphlet Japanese Unexamined Patent Publication "Tokuhei 3-501493" Japanese Unexamined Patent Publication "JP-A-6-313043" Japanese Unexamined Patent Publication "JP-A-6-313042" Japanese Unexamined Patent Publication "JP-A-61-257235" Japanese Unexamined Patent Publication "JP 2005-113117 A" Japanese Unexamined Patent Publication "JP 2005-344103 A" WO 2007/037522 pamphlet WO2002 / 060983 pamphlet WO 2014/054656 pamphlet Japanese Unexamined Patent Publication "JP-A-2000-79159"

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

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

The present inventors have conducted intensive studies in order to achieve the above object, and as a result, in a fluidized bed mixer, spray a polyvalent metal salt aqueous solution onto the water-absorbing resin particles at the time of surface crosslinking or after surface crosslinking under heating. As a result, it has been found that a water-absorbent resin powder excellent in liquid permeability, moisture-absorbing fluidity, and water absorption capacity under pressure can be obtained. Furthermore, they found that a water-absorbing resin powder having unprecedented fine polyvalent metal fine particles on the surface was excellent in liquid permeability, moisture-absorbing fluidity, and water absorption under pressure, and completed the present invention.

That is, the present invention (1) 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, wherein the polyvalent metal salt has a concentration of 5% by weight or more. Having a spraying step of spraying the aqueous solution of the valent metal salt onto the water-absorbent resin particles at the time of surface crosslinking with the organic surface crosslinking agent or after the surface crosslinking in the fluidized bed mixer, and the air temperature at the spray position of the aqueous solution of the polyvalent metal salt. Is 50 ° C. or more.

The invention (2) of the present application is a method for producing a water-absorbent resin powder which is surface-crosslinked with an organic surface crosslinker and contains a water-soluble polyvalent metal salt. On the other hand, there is provided a method for producing a water-absorbent resin powder, which comprises adding 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.

Further, the invention (3) of the present application relates to a water-absorbing resin powder which 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-absorbing resin powder. Provided is a water-absorbent resin powder to which (SEM image analysis) water-soluble polyvalent metal salt particles adhere.

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

According to one embodiment of the present invention, a water-absorbent resin powder having excellent temporal color tone can be easily produced.

3 is an SEM image of a water-absorbent resin powder of Example 1.

Hereinafter, the method for producing a water-absorbent resin powder according to one embodiment of the present invention and the water-absorbent resin powder according to one embodiment of the present invention will be described in detail, but the scope of the present invention is not limited to these descriptions. In addition, other than the examples described below, modifications and implementations can be made as appropriate without departing from the spirit of the present invention.

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

Unless otherwise specified in this specification, “A to B” representing a numerical range means “A or more and B or less”. Further, “ppm” means “ppm by weight” or “ppm by mass” unless otherwise specified. Further, “to acid (salt)” means “to acid and / or salt thereof”, and “(meth) acryl” means “acryl 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, “water-absorbent resin” means a water-swellable, water-insoluble polymer gelling agent, and is generally in a powder form. 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 means 0 to 50% by weight. In addition, as long as the required performance (CRC and Ext) is satisfied, even a water-absorbing resin composition containing an additive or the like is referred to as a "water-absorbing resin" in this specification.

For convenience, in this specification, the water-absorbent resin before surface treatment or surface crosslinking of the aqueous polyvalent metal salt solution is referred to as “water-absorbent resin particles”, and the water-absorbent resin after surface treatment and surface crosslinking is referred to as “water-absorbent resin”. Resin powder ".

[1-2] “EDANA” and “ERT”
"EDANA" is an abbreviation of European Disposables and Nonwovens Associations, and "ERT" is an abbreviation of EDANA Recommended Test Methods, which is a standard for water-absorbing resin, which is a European standard (almost a global standard). It is. In this specification, unless otherwise specified, the measurement is performed based on the original ERT (publicly known document; revised in 2002).

[1-3-1] Centrifuge Retention Capacity (CRC) (ERT441.2-02)
“CRC” is an abbreviation of Centrifuge Retention Capacity (centrifuge retention capacity), which means the water absorption capacity of a water-absorbent resin under no pressure (sometimes referred to as “water absorption capacity”). Specifically, 0.2 g of the water-absorbing resin is put into a nonwoven fabric bag, then immersed in a large excess of 0.9% by mass aqueous sodium chloride solution for 30 minutes to allow free swelling, and then centrifuged (250 G). ) Means water absorption capacity (unit: g / g) after draining for 3 minutes.

[1-3-2] "Ext" (ERT470.2-02)
“Ext” is an abbreviation of Extractables and means a water-soluble component (a water-soluble component amount) of the water-absorbent resin.

Specifically, it refers to the amount of dissolved polymer (unit: wt%) after adding 1.0 g of the water-absorbing resin to 200 mL of 0.9 wt% aqueous sodium chloride solution and stirring at 500 rpm for 16 hours. The measurement of the amount of dissolved polymer is performed 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"
As used herein, the term "liquid permeability" of a water-absorbent resin powder refers to the fluidity of a liquid passing between particles of a water-absorbent resin or a gel swelling the same under a load or no load. As representative measurement methods, there are SFC and GBP.

“SFC (Saline Flow Conductivety)” refers to the liquid permeability of a 0.69% by mass aqueous sodium chloride 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. 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 a water-absorbent resin powder according to one embodiment of the present invention (hereinafter, also simply referred to as “production method”) includes (1) an organic surface cross-linking agent. A water-absorbent resin powder containing a water-soluble polyvalent metal salt, the surface of which is crosslinked in a fluidized bed mixer with a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more. A method for producing a water-absorbent resin powder, comprising a spraying step of spraying water-absorbent resin particles at the time of or after surface cross-linking, wherein the air temperature at the spray position of the aqueous polyvalent metal salt solution is 50 ° C or higher.

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 under a high-temperature atmosphere in a fluidized bed mixer, so that the polyvalent metal salt aqueous solution is in a spray-dried state. It is presumed that they adhere to the surface of the water-absorbent resin in a fine lump.

The method (2) for producing a water-absorbent resin powder according to one 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, 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 crosslinker Provide a way.

により According to the above configuration, it is possible to obtain a water-absorbent resin powder excellent in liquid permeability, moisture-absorbing fluidity, and water absorption capacity under pressure.

Further, with the above configuration, a water-absorbing resin powder having water-soluble polyvalent metal salt particles adhered to the surface can be obtained.

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

(2-1) Step of preparing monomer aqueous solution This step is a step of preparing a monomer aqueous solution. Note that a monomer slurry may be used instead of the monomer aqueous solution as long as the water-absorbing performance of the obtained water-absorbent resin is not reduced, but in this section, the monomer aqueous solution will be described for convenience. .

Acrylic acid (salt), methacrylic acid (salt), (anhydride) 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) acrylamido-2-methylpropanesulfonic acid (salt) and (meth) acryloxyalkanesulfonic 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 include hydrophilic monomers such as (meth) acrylates, and salts thereof. Among these, an acid group-containing unsaturated monomer is preferred, a carboxyl group-containing unsaturated monomer such as acrylic acid (salt) and methacrylic acid (salt) is more preferred, and acrylic acid (salt) is even more preferred. 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 monomers is 10 to 100 mol%, more preferably 50 to 100 mol%, particularly 90 to 100 mol%. In one embodiment of the present invention, such polyacrylic acid is used. (Salt) -based water-absorbing resins are preferably used.

The acid group-containing unsaturated monomer is preferably partially in a salt form, preferably a salt with a monovalent basic compound, more preferably an alkali metal salt or an ammonium salt, and further preferably a sodium salt. is there.

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

The above neutralization ratio is the same even when neutralizing a polymer instead of a monomer. In addition, the above-described neutralization ratio is also applied to the neutralization ratio of the water-absorbent resin powder as the final product.

(Internal crosslinking agent)
In one embodiment of the present invention, it is preferable to use an internal crosslinking agent in this step. As the internal cross-linking agent, the compounds exemplified in US Pat. No. 6,241,928 are 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 absorbing performance of the resulting water-absorbing resin, preferably a compound having two or more polymerizable unsaturated groups, more preferably having thermal decomposability at the following drying temperature, and a polymerizable unsaturated group And more preferably a compound having two or more polymerizable unsaturated groups having a (poly) alkylene glycol structural unit is used as an internal crosslinking agent.

として As the polymerizable unsaturated group, preferably, an allyl group, a (meth) acrylate group, more preferably, a (meth) acrylate group is used. The (poly) alkylene glycol structural unit is preferably polyethylene glycol, and the number n is preferably from 1 to 100, more preferably from 6 to 50.

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

内部 The internal cross-linking agent added in this step undergoes a cross-linking reaction in the polymerization step or, for example, in the drying step after the polymerization step. In one embodiment of the present invention, the internal cross-linking is not limited to the above-described embodiment, and the internal cross-linking may be performed by adding an internal cross-linking agent to the hydrogel cross-linked polymer during or after the polymerization step. Further, a radical cross-linking method using a radical polymerization initiator, a radiation cross-linking method using an active energy ray such as an electron beam or an ultraviolet ray, and the like can also be adopted. Further, these methods can be used in combination.

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

Specifically, a hydrophilic polymer such as starch, starch derivative, cellulose, cellulose derivative, polyvinyl alcohol, polyacrylic acid (salt), crosslinked polyacrylic acid (salt), preferably 50% by weight or less, more preferably Can be added at 20% by weight or less, more preferably at 10% by weight or less, particularly preferably at 5% by weight or less (the lower limit is 0% by weight). Further, a carbonate, an azo compound, a foaming agent such as air bubbles, a surfactant, a chelating agent, a chain transfer agent and the like are preferably used in an amount of 5% by weight or less, more preferably 1% by weight or less, and further preferably 0.5% by weight. The following can be added (the lower limit is 0% by weight).

The above-mentioned substance may be added not only in the form of being added to the aqueous monomer solution but also in the course of 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 (eg, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) is used. can get. These polymers and water-absorbent resin compositions are also included in the scope of the present invention.

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

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

The “concentration of the monomer component” is a value determined by the following formula (1), and the weight of the aqueous monomer solution is calculated based on the graft component, the water-absorbing resin, and the hydrophobicity in the inverse suspension polymerization. Does not include solvent weight.

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

(Polymerization initiator)
The polymerization initiator used in one embodiment of the present invention is not particularly limited because it is appropriately selected depending on the polymerization form and the like. Examples of the polymerization initiator include a thermal decomposition-type polymerization initiator, a photo-decomposition-type polymerization initiator, and a redox-based polymerization initiator using a reducing agent that promotes the decomposition of these polymerization initiators. 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-absorbing resin, peroxides or azo compounds are preferable, peroxides are more preferable, and persulfates are more preferable among the peroxides.

使用 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% based on the monomer.

Note that, instead of the polymerization initiator, radiation, an electron beam, an active energy ray such as ultraviolet light may be irradiated to carry out the polymerization reaction, or these active energy rays and the polymerization initiator may be used in combination. .

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

As specific polymerization forms, continuous belt polymerization is described in U.S. Pat. No. 4,893,999, U.S. Pat. No. 6,241,928 and U.S. Patent Application Publication No. 2005 / 215,734, and continuous kneader polymerization is described in U.S. Pat. And the like. By employing these continuous aqueous polymerization methods, the production efficiency of the water-absorbing resin is improved.

(2-3) Gel Pulverizing Step In this step, the hydrogel obtained in the above polymerization step is gel-pulverized by a screw extruder such as a kneader or a meat chopper, or a gel pulverizer such as a cutter mill, and the like. This is a step of obtaining a hydrogel (hereinafter, referred to as "particulate hydrogel"). When the polymerization step is kneader polymerization, the polymerization step and the gel pulverization step are performed simultaneously. Further, when a particulate hydrogel is directly obtained in the polymerization process such as gas phase polymerization or reverse phase suspension polymerization, the gel pulverizing step may not be performed.

(2-4) Drying Step This step is a step of drying the particulate hydrogel obtained in the polymerization step and / or the gel pulverizing step to a desired resin solid content to obtain a dried polymer. The resin solid content is determined from the loss on 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, and further preferably 90% by weight. It is preferably from 98 to 98% by weight, particularly preferably from 92 to 97% by weight.

The method for drying the particulate hydrogel is not particularly limited, but includes, for example, heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, azeotropic distillation with a hydrophobic organic solvent. Drying by dehydration and high-humidity drying using high-temperature steam are included. Among them, hot air drying is preferable from the viewpoint of drying efficiency, and among the hot air dryings, band drying in which hot air drying is performed on a ventilation belt is more preferable.

乾燥 The drying temperature (temperature of hot air) in the hot air drying is preferably from 120 to 250 ° C, more preferably from 150 to 200 ° C, from the viewpoint of the color tone and drying efficiency of the water-absorbent resin. The drying conditions other than the above-mentioned drying temperature, such as the wind speed of the hot air and the drying time, may be appropriately set according to the water content and the total weight of the particulate hydrogel to be dried and the amount of the target resin solids. Good. For example, when performing band drying, various conditions described in WO 2006/100300, WO 2011/025012, WO 2011/025013, WO 2011/111657 and the like are appropriately applied. Applied.

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

(2-5) Pulverizing Step and Classifying Step In this step, the dried polymer obtained in the drying step is pulverized (pulverizing step), and adjusted to a predetermined particle size (classifying step) to reduce the water-absorbent resin particles. This is the step of obtaining. When the dry polymer obtained in the drying step is out of the following particle size, it is preferable to perform this step at least before the surface crosslinking step.

Examples of equipment used in the pulverizing step of one embodiment of the present invention include a high-speed rotary pulverizer such as a roll mill, a hammer mill, a screw mill, and a pin mill; a vibration mill, a knuckle type pulverizer, a cylindrical mixer, and the like. It is used together if necessary.

分 Also, the classification step of one embodiment of the present invention is not particularly limited, and includes, for example, a sieve classification and an airflow classification.

The particle size of the water-absorbent resin particles obtained in this step is, as a weight average particle size (D50), usually 100 to 2000 μm, preferably 200 to 600 μm, more preferably 200 to 550 μm, further preferably 250 to 500 μm, and particularly preferably. Is 350 to 450 μm. Further, the ratio of the water-absorbent resin particles having a particle diameter 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, and still more preferably 1% by weight. It is as follows. Further, the ratio of the water-absorbent resin particles having a particle diameter 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, and still more preferably 1% by weight. It is as follows. The lower limit of the ratio of the water-absorbing resin particles is preferably as small as possible in each case, and 0% by weight is desired, 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 0.20 to 0.50, more preferably 0.25 to 0.40, and still more preferably 0.27 to 0.35. is there. The particle size of the water-absorbent resin particles is measured using a standard sieve according to the measurement method disclosed in US Pat. No. 7,638,570 and EDANA@ERT420.2-02.

粒子 The particle size and particle size distribution described above are also applied to the water absorbent resin powder as the final product. Therefore, the water-absorbent resin powder is preferably subjected to a surface cross-linking treatment (surface cross-linking step) as described later so as to maintain the particle diameter and the particle size distribution in the above ranges. More preferably, the particle size is adjusted.

(2-6) Surface Cross-linking Step The production method according to one embodiment of the present invention relates to a method for preparing a water-absorbent resin particle having a concentration of 5% by weight or more at the time of surface crosslinking or after surface crosslinking in a fluidized bed mixer. Spraying step. That is, the production method according to one 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 “surface crosslinking step”.

Surface cross-linking means providing 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 crosslinking density can be formed by radical crosslinking on the surface, surface polymerization, a crosslinking reaction with a surface crosslinking agent, or the like. In terms of physical properties, the surface cross-linking in one embodiment of the present invention intends surface cross-linking with an organic surface cross-linking agent that covalently bonds to a functional group of the water-absorbent resin.

手順 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 crosslinking agent, and includes, for example, the following procedures (I) and (II).

(I) Step of mixing organic surface cross-linking agent with water-absorbent resin Surface cross-linking with an organic surface cross-linking agent according to one embodiment of the present invention includes surface cross-linking polymerization with a polymerizable monomer and covalent bonding with a functional group of the water-absorbing resin. Alternatively, surface cross-linking with an organic surface cross-linking agent capable of ionic bonding may be mentioned.

The organic surface cross-linking agent of one embodiment of the present invention is preferably an organic cross-linking agent capable of forming a cross-linked structure through a covalent bond reaction with a functional group, particularly a carboxyl group, of the water-absorbing resin. Particularly preferably, the following organic crosslinking 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, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol Polyhydric alcohol (crosslinked with COOH and dehydration esterification of the water-absorbing resin);
Epoxy compounds 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, glycidol, etc. Cross-linked with COOH and epoxy groups);
Polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine (crosslinked by amidation with COOH of a water-absorbent resin), and inorganic or organic salts thereof (for example, azetidinium) Salt, etc.);
Polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline;
Carbonic acid 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-dioxan-2-one, 4-methyl-1 Alkylene carbonate compounds such as 1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one;
Mono- or polyvalent oxazolidinone compounds such as oxazolidinone;
Haloepoxy such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin, cationic polymer compound (for example, Kaimen manufactured by Deck Hercules; registered trademark); γ-glycidoxypropyltrimethoxysilane, γ- Silane coupling agents such as aminopropyltriethoxysilane; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3- Oxetane compounds such as ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol, 3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, and polyvalent oxetane compounds; One of these organic surface crosslinking agents may be used alone, or two or more thereof may be used in combination. Preferably, one or more organic surface crosslinking agents selected from polyhydric alcohols, polyglycidyls, alkylene carbonates, and oxazolidinone compounds are used.

The amount of the organic surface cross-linking agent used depends on the compound to be used and the combination thereof, but is preferably in the range of 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, per 100 parts by weight of the water-absorbing resin particles. More preferably, it is in the range of parts by weight. In one embodiment of the present invention, the organic surface crosslinker can be used dissolved in water (ie, as an organic surface crosslinker aqueous solution). The amount of the water is preferably 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. In one embodiment of the present invention, a hydrophilic organic solvent may be used in addition to water. Further, in mixing the aqueous solution of the organic surface cross-linking agent with the water-absorbent resin particles, the effect of the present invention is not impaired, for example, 0 to 10 parts by weight, preferably 0 to 5 parts by weight per 100 parts by weight of the water-absorbent resin particles. The water-insoluble fine particle powder, the surfactant, and the like may coexist in a weight part, more preferably 0 to 1 weight part.

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

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

The method for mixing the water-absorbing resin particles and the organic surface cross-linking agent is not particularly limited. For example, a method of immersing the water-absorbing resin particles in a hydrophilic organic solvent and mixing the organic surface cross-linking agent aqueous solution, And a method in which an aqueous solution of an organic surface crosslinking agent is sprayed or dropped and mixed.

(4) It is preferable that the mixing device used for mixing the water-absorbent resin particles and the aqueous solution of the organic surface cross-linking agent has a large mixing force in order to uniformly and surely mix these substances. Examples of the mixing device include a cylindrical mixer, a double-walled conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a double-arm kneader, and a pulverizer. A kneader, a rotary mixer, an air-flow mixer, a turbulizer (trademark), a batch Ploughshare (trademark) mixer, a continuous Ploughshare (trademark) mixer, a Schugi (trademark) mixer, a fluidized bed mixer, and the like are preferable. .

(II) A 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 from 1 minute to 2 hours, more preferably from 5 minutes to 1 hour. The heat treatment can be performed using a usual dryer or heating furnace. When the heat treatment temperature is lower than 40 ° C., the absorption characteristics such as the absorption capacity under pressure may not be sufficiently improved. When the heat treatment temperature exceeds 300 ° C., the water-absorbent resin particles may be deteriorated, and various performances may be reduced.

Apparatuses used for heating the mixture of the water-absorbent resin particles and the aqueous solution of the organic surface cross-linking agent (apparatus for optionally adding a polyvalent metal salt aqueous solution by spraying) include, for example, a drum dryer, a paddle dryer, 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.

The surface cross-linking step in one embodiment of the present invention includes a method in which a treatment liquid containing a radically polymerizable compound is added to water-absorbent resin particles, and then the surface is cross-linked by irradiation with active energy. Further, a surfactant may be added to the treatment liquid, and the surface of the water-absorbent resin particles may be cross-linked by irradiation with active energy.

This step improves the water absorption capacity of the water-absorbent resin particles under pressure. The surface-crosslinked water-absorbent resin particles usually have a water absorption capacity under pressure in a preferred range 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 one 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 the heating in the surface crosslinking step from the viewpoint of stopping the progress of the extraneous surface crosslinking reaction and improving the handleability of the powder (water-absorbent resin powder).

Specifically, in the cooling step, the water-absorbent resin particles that have been heated to a high temperature in the surface cross-linking step are brought into contact with a cooling medium such as cold air or a cooling transfer surface to be forcibly cooled.

The cooling temperature is preferably 30 to 100 ° C, more preferably 40 to 80 ° C. If the cooling temperature is too low, the powder properties of the water-absorbent resin powder may be deteriorated, or the physical properties of the water-absorbent resin powder may be reduced. Note that the “cooling temperature” means the temperature of the cool air when using cool air, and the temperature of the transfer surface when using a cooling transfer surface. Further, when both the cold air and the cooling transmission surface are used, it is preferable that the temperature is intended, and both of them satisfy the above range.

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

装置 The apparatus used in this step includes, for example, a paddle dryer, a fluidized bed dryer, a pneumatic transport device, a band dryer and the like. 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 or the water-soluble polyvalent metal salt particles are added to the surface of the water-absorbent resin particles in the fluidized bed mixer. This is a step of adhering water-soluble polyvalent metal salt particles to the surface and treating the surface of the water-absorbing resin particles.

(2-7-1) Spraying Step The production method (1) according to one embodiment of the present invention 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. Then, a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is mixed with a water-absorbent resin powder particle (preferably a surface-crosslinked water-absorbent resin particle) at the time of surface crosslinking or after surface crosslinking in a fluidized bed mixer. ), Wherein the air temperature at the spray position of the aqueous polyvalent metal salt solution is 50 ° C. or higher. Further, in the production method (1) according to one embodiment of the present invention, preferably, the water-absorbent resin particles after the surface cross-linking are simultaneously performed in the fluidized bed mixer.

Hereinafter, the step of spraying the aqueous polyvalent metal salt solution onto the water-absorbing resin particles at the time of surface crosslinking or after the surface crosslinking is also referred to as “spraying step”.

In one embodiment of the present invention, "spraying the polyvalent metal salt aqueous solution onto the water-absorbent resin particles at the time of surface crosslinking" means that when performing surface crosslinking in a fluidized bed mixer, mixing of an organic surface crosslinking agent or organic surface crosslinking. Spraying a polyvalent metal salt aqueous solution simultaneously or separately during the reaction with the agent. Specifically, a fluidized bed mixer is used as a mixer for the organic surface cross-linking agent 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 the organic surface cross-linking agent. And an aqueous polyvalent metal salt solution can be separately sprayed using a fluidized bed mixer separately from the organic surface crosslinking agent mixer and heating device.

Here, when a 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 penetrates into the water absorbent resin particles. On the other hand, since the polyvalent metal salt is desired to precipitate on the surface of the water-absorbent resin particles, when the aqueous solution of the polyvalent metal salt is sprayed in this step, the organic surface crosslinking agent and the aqueous solution of the polyvalent metal salt are separately sprayed, that is, the organic surface crosslinking is performed. It is preferable to spray the polyvalent metal salt aqueous solution from an addition port different from the addition port of the agent, 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. .

Alternatively, a fluidized bed mixer may be used as a cooler in the cooling step to spray an aqueous solution of a polyvalent metal salt. 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. This is synonymous with the subsequent spraying of the aqueous polyvalent metal salt solution onto the water-absorbing resin particles. In the surface treatment step, since the spraying is preferably performed from the top of the fluidized bed mixer, even if the temperature of the cold air is lower than the preferred temperature range of the surface treatment step of one embodiment of the present invention, the high-temperature water-absorbent resin particles After passing through the layer, if the air temperature at the spray position is within the above range, the present invention can be stably performed.

As a fluidized bed mixer for forming a fluidized bed, a known mixer sold as a fluidized bed dryer / cooler or a fluidized bed granulator can be used. For example, in a laboratory scale, a spray dryer {Pulvis} GB series is used. (Manufactured by Yamato Scientific Co., Ltd.) can be used.

(4) 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., and further preferably 200 ° C. or lower. In this specification, the “wind temperature at the spray position” is the wind temperature near the spray port, and the wind temperature near the spray port can be measured by a thermometer. In addition, as described later, since the spray port is preferably installed in a space portion in the fluidized bed mixer, it can also be referred to as the temperature of the space portion in the fluidized bed mixer. When the air temperature at the spray position is the above temperature, the solvent component (particularly water) is suitably evaporated from the aqueous solution of the polyvalent metal salt to form a fine water-soluble polyvalent metal salt (in the present specification, “water-soluble polyvalent metal salt”). Metal salt particles) can be attached to the surface of the water-absorbent resin powder. That is, before the sprayed aqueous solution of the polyvalent metal salt is absorbed by the water-absorbent resin, the droplets of the aqueous solution of the polyvalent metal salt rapidly dry on the air layer or the surface of the water-absorbent resin in the fluidized-bed mixer. It is presumed that the fine water-soluble polyvalent metal salt adheres to the surface of the water-absorbent resin in a lump, a substantially spherical shape, or a bump.

温度 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. This temperature is, specifically, in the case of a batch type fluidized bed mixer, the temperature of the water absorbent resin particles immediately before spraying, in the case of a continuous type fluidized bed mixer, in the case of a continuous type fluidized bed mixer, the water absorbent resin particles at a position immediately before the spraying point Intended temperature.

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

において In the spraying step, the spraying of the aqueous solution of the polyvalent metal salt may be performed from the upper part of the fluidized bed mixer, or may be performed 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 may be installed at the lower part. However, from the viewpoint of easy formation of water-soluble polyvalent metal salt particles, it is preferable that the aqueous solution of the polyvalent metal salt is sprayed from above the fluidized bed mixer. In general, a fluidized bed mixer is configured to fluidize water-absorbent resin particles introduced into a lower portion by sending hot air from a lower portion.In order to prevent the water-absorbent resin particles from excessively rising, a fluidized bed mixer is generally used. The top of the mixer is widened to reduce the wind speed. When a polyvalent metal salt aqueous solution is sprayed from the upper part of the fluidized bed mixer, in the related art, huge aggregates are easily formed, and there is a possibility that the flow of the water absorbent resin particles may be stopped. Thus, 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 bed 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-absorbing resin particles. It is considered that solid water-soluble polyvalent metal salt particles are easily formed (precipitated) on the surface of the conductive resin particles. On the other hand, when the polyvalent metal salt aqueous solution is sprayed from the lower portion of the fluidized bed mixer, the solvent component of the polyvalent metal salt aqueous solution does not evaporate, and the polyvalent metal salt aqueous solution immediately contacts the water-absorbing resin particles. It is considered that water-soluble polyvalent metal salt particles are hardly formed.

The amount of 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 0.1 part by weight, per 100 parts by weight of the surface-crosslinked water-absorbing resin particles. More preferably, it is 5 parts by weight. When the ratio of the water-soluble polyvalent metal salt is in the above range, a water-absorbent resin powder having excellent liquid permeability can be obtained.

中 In the present specification, the water-soluble polyvalent metal salt is intended to mean a salt of a metal having a valence of 2 or more, preferably 3 or more, especially trivalent or tetravalent. "Water-soluble" is intended to dissolve 5% by weight or more in water at 20 ° C, where the solubility is calculated without water of crystallization (eg, an aqueous solution of aluminum sulfate 18-hydrate is aluminum sulfate). Calculated as concentration). 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 simply referred to as “polyvalent metal salt”.

As the polyvalent metal salt that can be used in one embodiment of the present invention, a salt or hydroxide of a polyvalent metal cation is intended, and in particular, an organic acid salt or an inorganic acid salt of a polyvalent metal, Includes aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum nitrate, potassium aluminum bisulfate, sodium aluminum bisulfate, potassium alum, ammonium alum, sodium alum, 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. Part of the polyvalent metal salt may be a hydroxide, that is, a basic salt. Further, it is preferable to use salts having these waters of crystallization. Further, depending on the solubility, polyvalent metals such as aluminum, magnesium, calcium, zinc, zirconium and organic acids (for example, anisic 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, 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.

Particularly preferred from the viewpoint of physical properties are water-soluble aluminum salts (aluminum compounds). Among them, aluminum chloride, polyaluminum chloride, and aluminum sulfate are preferable from the viewpoint of being easily adjusted to the concentration of the polyvalent metal salt of one embodiment of the present invention. Aluminum nitrate, potassium aluminum bisulfate, sodium aluminum bisulfate, potassium alum, ammonium alum, sodium alum, sodium aluminate are preferred, aluminum sulfate is particularly preferred, aluminum sulfate 18 hydrate, aluminum sulfate 14-18 hydrate, etc. Hydrous crystalline powder can be most preferably used. These may be used alone or in combination of two or more.

The concentration of the polyvalent metal salt in the aqueous solution of the polyvalent metal salt is preferably 5% by weight or more, more preferably 11% by weight or more, further preferably 15% by weight or more, and more preferably 20% by weight. The above is particularly preferred. The upper limit of the concentration is intended to be a saturated concentration, and is preferably 40% by weight or less, more preferably 30% by weight or less. The higher the concentration, the easier it is to form massive polyvalent metal salt particles 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 an increase in viscosity are likely to occur.

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

In the surface treatment step, an organic acid (salt) may be sprayed with the same solution or another solution simultaneously with the aqueous polyvalent metal salt solution. By using an organic acid (salt), it is possible to prevent the polyvalent metal salt (for example, aluminum ion) from penetrating inside the water-absorbing resin particles, and to uniformly diffuse the polyvalent metal salt particles on the surface of the water-absorbing resin particles. As a result, the liquid permeability of the water-absorbent resin particles is greatly improved. Further, by using the organic acid (salt), 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 related art can be solved. It is possible to exhibit an effect that fine dots can be uniformly attached (localized) to the entire vicinity of the surface of the resin particles.

The organic acid (salt) may be directly mixed with the water-absorbing resin particles, but is preferably mixed with the polyvalent metal salt. It is more preferable to mix both the organic acid (salt) and the polyvalent metal salt 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 the organic acid (salt) include anisic 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 salts such as sodium and potassium or ammonium salts thereof. Can be Among them, hydroxycarboxylic acids such as glycolic acid, tartaric acid, lactic acid, 3-hydroxypropionic acid, malic acid, salicylic acid, and gluconic acid, and alkali metal salts and ammonium salts thereof are preferable. These may be used alone or in combination of two or more.

The amount of the organic acid (salt) to be used is at most within twice the number of moles of the polyvalent metal salt, preferably within one time, more preferably within 0.5 times. If the amount of the organic acid (salt) used is too large, troubles in production 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 one embodiment of the present invention can be carried out by a method other than the above-mentioned spraying step. The invention (2) of the present application is a method for producing a water-absorbent resin powder surface-crosslinked with an organic surface crosslinker and containing a water-soluble polyvalent metal salt. And a method for producing a water-absorbent resin powder, which comprises adding water-soluble polyvalent metal salt particles having a volume average particle diameter of 0.3 to 15 μm as measured by a laser diffraction / scattering method. For example, after a polyvalent metal salt aqueous solution is formed into water-soluble polyvalent metal salt particles by a spray drying method or an azeotropic dehydration method, it can be added to the water-absorbing resin particles. In this case, a water-absorbing resin powder having substantially spherical water-soluble polyvalent metal salt particles attached thereto is 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, a measuring solvent is appropriately selected so that the water-soluble polyvalent metal salt particles do not dissolve. Further, in order to prevent aggregation of the water-soluble polyvalent metal salt particles, the volume average particle diameter is measured after applying ultrasonic vibration to the measurement solvent to which the water-soluble polyvalent metal salt particles are added. In addition, the absence of large water-soluble polyvalent metal salt particles that cannot be measured by the laser diffraction / scattering method was confirmed in advance by passing the water-soluble polyvalent metal salt particles through a standard sieve having openings of 38 μm or 45 μm. You may. The amount of the water-soluble polyvalent metal salt particles on the 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 measured water-soluble polyvalent metal salt particles. And 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.

形状 The shape of the water-soluble polyvalent metal salt particles is preferably substantially spherical. However, the water-soluble polyvalent metal salt particles may slightly aggregate within the range of the volume average particle diameter. The closer the shape of the water-soluble polyvalent metal salt particles to be added to a sphere, the better the flowability 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 at a magnification of 2000 times and performing image analysis of the photograph.

(4) When adding the water-soluble polyvalent metal salt particles to the water-absorbing resin particles, they may be dry-blended or may be added together with the 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; at room temperature such as diethylene glycol, triethylene glycol, and polyethylene glycol having a molecular weight of 200 to 600; It can be added together with an organic solvent such as liquid polyethylene glycol. The amount of the organic solvent to be 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-absorbing resin particles. In addition, as long as the water-soluble polyvalent metal salt particles do not dissolve, water may be contained in these organic solvents. Since the dry-blended water-soluble polyvalent metal salt particles are easily peeled off from the water-absorbing resin powder, the above-mentioned solvent is preferably added after the dry-blending.

装置 A known mixer is used for adding the water-soluble polyvalent metal salt particles to the water-absorbent resin particles, and the apparatus is not particularly limited. For example, a vertical type, a horizontal type, and an obliquely-oriented stirring mixer or a fluidized bed mixer can be used. Furthermore, mixing during pneumatic transport is also possible. Specifically, a cylindrical mixer, a double-walled conical mixer, a vertical or horizontal high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a double-arm kneader, a rotary mixer Type mixer, air-flow type mixer, fluidized bed mixer. When the water-soluble polyvalent metal salt particles are added together with the organic solvent, a mixer equipped with a mechanism for loosening aggregates and a heating mechanism for drying is preferable. Specific examples include a paddle dryer, a steam tube dryer, a drum dryer, a fluidized-bed dryer, and a screw-type mixer or kneader equipped with a heating jacket.

(2-8) Other Addition Step 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 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 use amount (addition amount) of the additive is not particularly limited because it is appropriately determined according to its use, but is preferably 3 parts by weight or less based on 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 addition include a powder, a liquid, a solution, and a dispersion liquid. It is preferably added 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 added to the water-absorbent resin particles or the water-absorbent resin powder in one embodiment of the present invention. It is preferred to use. The above-mentioned cationic polymer is a cationic polymer having an amino group, and further is a water-soluble cationic polymer, and is preferably a water-soluble cationic polymer that dissolves in water at 25 ° C. in an amount of 2% by weight or more, more preferably 5% by weight or more. It is a polymer. For example, polyalkyleneimines such as polyethyleneimine, polyetherpolyamine, polyetheramine, polyvinylamine, polyalkylamine, polyallylamine, polydiallylamine, poly (N-alkylallylamine), monoallylamine-diallylamine copolymer, N-alkyl Allylamine-monoallylamine copolymer, monoallylamine-dialkyldiallylammonium salt / copolymer, diallylamine-dialkyldiallylammonium salt / copolymer, polyethylene polyamine, polypropylene polyamine, polyamidine and the like; and salts thereof are preferred. Further, a modified cationic polymer described in WO 2009/041727 is more preferably mentioned.

The water-insoluble inorganic fine particles preferably have an average particle size measured by a Coulter counter method in the range of preferably 0.001 to 200 μm, more preferably 0.005 to 50 μm, and still more preferably 0.01 to 10 μm. It is. The water-insoluble inorganic fine particles are preferably hydrophilic fine particles, for example, a metal oxide such as silica (silicon dioxide) or titanium oxide, zinc and silicon, or a composite hydrate containing zinc and aluminum (for example, WO 2005/010102), silicic acid (salt) such as natural zeolite and synthetic zeolite, kaolin, talc, clay, bentonite, calcium phosphate, barium phosphate, silicic acid or a salt thereof, clay, diatomaceous earth, silica gel, zeolite, Examples include bentonite, hydroxyapatite, hydrotalcite, vermiculite, perlite, isolite, activated clay, quartz sand, quartzite, strontium ore, fluorite, and bauxite. Of these, silicon dioxide and silicic acid (salt) are more preferred, and silicon dioxide is even more preferred. The silicon dioxide is preferably fumed silica or colloidal silica, and is preferably colloidal silica in view of the balance of water absorption properties.

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

界面 Further, it is preferable to apply a surfactant so that the water-soluble polyvalent metal salt particles attached to the surface of the water-absorbent resin powder do not peel off due to friction or the like. If a surfactant is used, it is preferably used in an amount of 0.0001 to 0 parts by weight based on 100 parts by weight of the water-absorbent resin particles or the water-absorbent resin powder in order to prevent a decrease in the physical properties of the water-absorbent resin powder during water absorption. 0.1 part by weight. The amount of the surfactant used can also be referred to as the content of the surfactant in the water-absorbent resin powder. In order to prevent adverse effects on the water absorption properties, as another index, when the components of the water absorbent resin powder are extracted with a 0.9% by weight aqueous sodium chloride solution, the surface tension of the extract is preferably 60 to 75 mN / m, more preferably 65-72 mN / m. In the case of a water-absorbing resin powder to which no surfactant is added, the above-mentioned surface tension usually shows about 71 to 75 mN / m.

中でも Among the above-mentioned additives, the water-absorbent resin of the present invention preferably contains a chelating agent from the viewpoint of preventing coloration with time and preventing urine deterioration. As the chelating agent of the present invention, from the viewpoint of the effect, a polymer compound or a non-polymer compound, among which a non-polymer compound is preferable, specifically, an amino polycarboxylic acid, an organic polyphosphoric acid, and an inorganic polyvalent phosphoric acid Compounds selected from are preferred. From the viewpoint of effects, the molecular weight of the chelating agent is preferably from 100 to 5,000, more preferably from 200 to 1,000. In the absence of a chelating agent, the resulting water-absorbent resin is inferior in coloration and deterioration.

Here, polyvalent has a plurality of such functional groups in one molecule, and has 2 to 30, more preferably 3 to 20, especially 4 to 10 such functional groups. In addition, these chelating agents are preferably water-soluble chelating agents, specifically, water-soluble chelating agents that dissolve in an amount of 1 g or more, more preferably 10 g or more in 100 g (25 ° C.) of water.

Examples of the amino polycarboxylic acid include imino diacetic acid, hydroxyethyl imino diacetic acid, nitrilotriacetic acid, nitrilotripropionic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, trans-1,2-diaminocyclohexane. Tetraacetic acid, N, N-bis (2-hydroxyethyl) glycine, diaminopropanol tetraacetic acid, ethylenediamine dipropionic acid, hydroxyethylenediamine triacetic acid, glycol ether diamine tetraacetic acid, diaminopropane tetraacetic acid, N, N'-bis (2 -Hydroxybenzyl) ethylenediamine-N, N'-diacetic acid, 1,6-hexamethylenediamine-N, N, N ', N'-4acetic acid and salts thereof, among which diethylenetriaminepentaacetic acid (salt) Or or trietile Tetramine 6 acetate (salt) are more preferable, diethylenetriaminepentaacetic acid (salt) is more preferable.

Examples of the organic polyvalent phosphoric acid include ethylenediamine-N, N'-di (methylenephosphinic acid), ethylenediaminetetra (methylenephosphinic acid), cyclohexanediaminetetra (methylenephosphonic acid), ethylenediamine-N, N'-diacetate-N , N'-di (methylenephosphonic acid), ethylenediamine-N, N'-di (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), polymethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) And the above-mentioned amino polyvalent phosphoric acids, such as dinitrometic acid-di (methylenephosphinic acid), nitriloacetic acid- (methylenephosphinic acid), nitriloacetic acid-β-propionic acid-methylenephosphonic acid, and nitrilotris (methylenephosphonic acid). ), 1-hydroxyethylidene diphosphonic acid, and the like. In addition, examples of the inorganic polyvalent phosphoric acid include pyrophosphoric acid, tripolyphosphoric acid, and salts thereof. As the chelating agent of the present invention, ethylenediaminetetra (methylenephosphonic acid) (salt) is preferable.

The amount of the chelating agent, particularly the above-mentioned preferable chelating agent, is 0.0001 part by weight or more, 0.001 part by weight or more, 0.01 part by weight or more, and 0.02 part by weight or more with respect to 100 parts by weight of the water absorbent resin. Preferably at least 1 part by weight, at most 0.03 parts by weight, at least 0.05 parts by weight, at least 0.06 parts by weight, preferably at most 1 part by weight, at most 0.5 parts by weight, at most 0.2 parts by weight, at most 0.15 parts by weight. It is preferred in the order of parts by weight or less. Thereby, it is excellent in prevention of coloring with time, prevention of deterioration of urine, heat resistance, light resistance, antibacterial property, safety, handling property and the like.

中でも Among the above-mentioned additives, it is preferable to use an oxidizing agent and / or a reducing agent in the water-absorbent resin of the present invention after the polymerization step from the viewpoints of reducing residual monomers and preventing coloring. 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; chlorate; Salt, chlorite, hypochlorite and the like can be mentioned. Of these, persulfates are preferred from the viewpoint of reducing residual monomers. These oxidizing agents may be used alone or in combination of two or more.

イオ Sulfur-based, phosphorus-based, and nitrogen-based reducing agents are particularly preferred as the reducing agent of the present invention. Specifically, for example, sulfites (eg, sodium sulfite, potassium sulfite, ammonium sulfite, etc.), bisulfites (eg, sodium bisulfite, potassium bisulfite, ammonium bisulfite, etc.), pyrosulfite, dithionite Acid, trithionate, tetrathionate, thiosulfate, sulfinatoacetic acid derivatives such as 2-hydroxy-2-sulfinatoacetic acid, dimethyl sulfoxide, thiourea dioxide, nitrite, nitrogen such as amino acids and ethanolamine Organic compounds, phosphites, hypophosphites, and the like. Among these, a sulfur-based inorganic reducing agent, particularly, a sulfite, a hydrogen sulfite, a pyrosulfite, and a dithionite are preferable, and as such salts, a sodium salt, a potassium salt, and an ammonium salt are preferable. Among them, sodium sulfite and sodium hydrogen sulfite are particularly preferable. These reducing agents may be used alone or in combination of two or more.

Further, the amount of the oxidizing agent or the reducing agent 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, preferably 0.06 parts by weight or more, preferably 3 parts by weight or less, 1 part by weight or less, 0.7 parts by weight or less, and preferably 0.5 parts by weight or less. .

(2-9) Other Steps In one embodiment of the present invention, in addition to the above-described steps, a sizing step, a fine powder removing step, a fine powder reusing step, and the like can be provided as necessary. Further, one or more steps such as a transport step, a storage step, a packing step, and a storage step may be further included. Note that the sizing step includes a step of classifying and removing the fine powder after the heat treatment step and a step of classifying and pulverizing when the water-absorbent resin aggregates and exceeds a desired size. In addition, the step of reusing the fine powder includes a step of adding the fine powder as it is or a large hydrogel in the fine powder granulation step and adding it in any step of the process of producing the water absorbent resin.

[3] Characteristics of Water Absorbent Resin Powder The present invention also relates to a water absorbent resin powder which is surface-crosslinked with an organic surface crosslinking agent and contains a water-soluble polyvalent metal salt. 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" refers to a state in which solids of water-soluble polyvalent metal salt particles are three-dimensionally present on the surface of a water-absorbent resin. The valent metal salt is present on the surface of the water-absorbent resin powder. It suffices that at least one polyvalent metal salt particle having a number average particle diameter of 0.3 to 15 μm (SEM image analysis) adheres to one water-absorbent resin on average, preferably 10 or more, and more preferably 100 or more. It is preferred that more than one are attached.

SEM image analysis means analysis on an image acquired using a scanning electron microscope. The number average particle size of the water-soluble polyvalent metal salt particles was randomly selected from 20 water-soluble polyvalent metal particles observed at a magnification of 2,000 under a scanning electron microscope. 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 perfect circles, the smallest one of the distances between two parallel tangents, that is, the minimum Feret diameter is regarded as the particle diameter.

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

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

The water-soluble polyvalent metal salt particles are preferably close to a circle in an SEM image, and more preferably a circle. The powder flowability of the water-soluble polyvalent metal salt particles is improved as the particles become closer to a circle in the SEM image. The circular shape means a graphic having a circularity of 0.8 or more. The degree of circularity means that in each of the water-soluble polyvalent metal salt particles, the total length of the outer periphery in the shape when the water-soluble polyvalent metal salt particles are observed from a certain direction is L, and the area in the shape is S. Is a value obtained by the following equation (2).
Circularity = 4π · S / L ² Equation (2)
In the SEM image analysis, the coating area of the water-soluble polyvalent metal salt particles is preferably from 0.1 to 50%, more preferably from 0.5 to 20%, based on the area of the water-absorbing resin powder. More preferably, it is 1 to 10%. The coverage 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 obtained at 2000 times, Is a value obtained by dividing by the area of.

場合 If the water-soluble polyvalent metal salt particles are difficult to distinguish from other additives on the SEM image, it can be confirmed by using SEM together with various element mapping techniques. 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, and 30 [10 ⁻⁷ · cm ³ · s · g ⁻¹ ]. The above is more preferable. Although the upper limit is not particularly limited as the higher value, it is preferably 500 [10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or less, more preferably 200 [10 ⁻⁷ ·) from the viewpoint of balance with other physical properties. cm ³ · s · g ⁻¹ ] or less.

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

Ａ The AAP (0.7 psi) of the water-absorbent resin powder according to one embodiment of the present invention is preferably 15 g / g or more, more preferably 20 g / g or more, and even more preferably 24 g / g or more. The upper limit is not particularly limited as the upper limit, but 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. The AAP (0.7 psi) is measured according to the EDANA method (ERT442.2-02) by changing the load condition to 4.83 kPa (0.7 psi) as in the examples described later.

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

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

The water content of the water-absorbent resin powder according to one embodiment of the present invention (defined by the loss on drying 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 preferably 1 to 12% by weight, more preferably 3 to 10% by weight. By controlling the water content, the impact resistance and the water absorption rate of the water-absorbent resin powder are improved. The water content is controlled by the amount of water evaporated in the drying process and the surface crosslinking process, the amount of water of the aqueous solution of the polyvalent metal salt to be sprayed, the temperature and time of drying (particularly spray drying) in the fluidized bed, and the addition of water. it can. In one embodiment of the present invention, since the aqueous solution of the polyvalent metal salt is sprayed in the fluidized-bed mixer, the total amount of the added water is not usually reflected in the water content of the water-absorbing resin particles. As a result of drying at least a part of the water in the aqueous solution of the polyvalent metal salt to be sprayed, 80% by weight or less, more preferably 1 to 70% by weight, particularly 5 to 60% by weight of the water in the aqueous solution of the polyvalent metal salt to be sprayed % 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 one embodiment of the present invention is 50% by weight or less, preferably 35% by weight or less, more preferably 25% by weight or less, and still more preferably 15% by weight. It is as follows. The lower limit 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 does not decrease and the water-absorbing resin powder having excellent liquid permeability is obtained. Furthermore, since it has little rewet, it is suitable as an absorbent for sanitary articles such as paper diapers. Note that Ext can be controlled with an internal crosslinking agent or the like.

初期 In the initial color tone of the water-absorbent resin powder according to one embodiment of the present invention, the L value is preferably 85 or more, more preferably 88 or more, and further preferably 90 or more in the Hunter Lab color system. The upper limit is 100, but if the value is at least 80, no problem occurs due to the color tone. 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 from 0 to 10, more preferably from 0 to 7, and even more preferably from 0 to 5. As the L value approaches 100, the whiteness increases, and as the a value and the b value approach 0, the color becomes low and substantially white.

The temporal color tone of the water-absorbent resin powder according to one embodiment of the present invention is, in the Hunter Lab color system, the L value is preferably 70 or more, more preferably 75 or more, still more preferably 80 or more, and particularly preferably 83 or more. is there. The upper limit is 100, but if the value is at least 80, no problem occurs due to the color tone. 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 from 0 to 15, more preferably from 0 to 12, and even more preferably from 0 to 10. As the L value approaches 100, the whiteness increases, and as the a value and the b value approach 0, the color becomes low and substantially white. The water-absorbent resin powder according to one embodiment of the present invention has a smaller change in the color tone over time with respect to the initial color tone, that is, is less likely to be colored, as compared with a conventional water-absorbent resin to which a polyvalent metal salt is added.
The initial color tone and the color tone over time are measured in accordance with the color evaluation before and after the color acceleration test described in WO2009 / 005114.

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

[4] Aspect of the present invention That is, the present invention may be the following aspects.

(Method for producing water-absorbent resin powder)
1. A method for producing a water-absorbent resin powder surface-crosslinked with an organic surface crosslinker and containing a water-soluble polyvalent metal salt, wherein a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is mixed with a fluidized bed. A method for producing a water-absorbent resin powder, comprising: a spraying step of spraying water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in an machine, wherein the air temperature at the spray position of the aqueous solution of the polyvalent metal salt is 50 ° C or higher. .

{2. 2. The method for producing a water-absorbent resin powder according to 1, wherein the aqueous polyvalent metal salt solution is sprayed on the water-absorbent resin particles after surface crosslinking in the fluidized bed mixer. With such a configuration, the physical properties 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 cooling of the water-absorbent resin particles after surface crosslinking is performed simultaneously with the spraying step in the fluidized bed mixer. With such a configuration, the physical properties of the obtained water-absorbing resin are improved, and the water-absorbing resin is sprayed at the same time as cooling, so that the process is simplified.

4. 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 properties of the water-absorbing resin are improved.

5. 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 above the fluidized bed mixer. With such a configuration, the physical properties of the obtained water-absorbent resin are improved, and troubles in production are reduced.

6. At least a portion of the water in the sprayed aqueous polyvalent metal salt solution is dried, and 80% by weight or less of the sprayed water of the aqueous polyvalent metal salt solution is absorbed by the water-absorbent resin particles. 3. The method for producing a water-absorbent resin powder according to item 1.

7. A method for producing a water-absorbent resin powder surface-crosslinked with an organic surface crosslinker and containing a water-soluble polyvalent metal salt, wherein the water-absorbent resin surface-crosslinked with the organic surface crosslinker is subjected to a laser diffraction / scattering method. A method for producing a water-absorbent resin powder, which comprises adding water-soluble polyvalent metal salt particles having a volume average particle diameter of 0.3 to 15 μm measured in the step.

8. 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 based on 100 parts by weight of the water-absorbent resin particles. With such a configuration, the physical properties of the obtained water-absorbent resin are improved.

9. 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 properties of the obtained water-absorbent resin are improved.

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

{11. 11. The water-absorbent resin powder according to 10, wherein the circularity of the water-soluble polyvalent metal salt particles as determined by SEM image analysis is 0.8 or more.

(Circularity) = 4π · S / L ²
(In the formula, L is the outer circumference of the attached water-soluble polyvalent metal salt particles, and S is the area of the attached water-soluble polyvalent metal salt particles.)
12. 12. 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% based on the area of the water-absorbent resin powder. With such a configuration, the physical properties of the water-absorbing resin are improved.

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

{14. 14. The water-absorbent resin powder according to any one of 10 to 13, which has a weight average particle size of 100 to 2000 μm. With such a configuration, the physical properties of the water-absorbing resin are improved.

[5] Difference from Conventional Technique In contrast to the inventions described in Patent Documents 1 to 22, one embodiment of the present invention provides a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more under heating. The present invention relates to a method for producing a water-absorbent resin powder by spraying water-absorbent resin particles onto or after surface cross-linking in a fluidized bed mixer.

Although not limited to the reaction mechanism, in one embodiment of the present invention, by spraying a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more 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 is formed into fine aggregates having an average particle diameter of 0.3 to 15 μm and adheres to the surface of the water-absorbent resin. It is estimated that the property is improved. That is, by spraying and adding an aqueous solution of a polyvalent metal salt in a fluidized bed under heating, droplets of the aqueous solution of a polyvalent metal salt are dried on the surface of the gas-absorbing resin or the water-absorbing resin flowing in the gas layer, and the solid polyvalent metal salt is dried. It is estimated that the metal salt is attached.

In the conventional addition of a polyvalent metal salt aqueous solution with stirring, the polyvalent metal salt aqueous solution is added to the layer of the stirred 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 an embodiment of the present invention, a substantially spherical / lumped solid polyvalent metal salt as shown in FIG. 1 is discontinuously attached to the surface of the water-absorbent resin in a dotted manner. In the conventional surface treatment of a water-absorbent resin with a polyvalent metal salt aqueous solution, the water-absorbent resin is coated with a polyvalent metal salt, whereas an embodiment of the present invention has a new shape as shown in FIG. Gives water absorbent resin.

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.

本 Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. Hereinafter, “parts by weight” may be simply referred to as “parts” and “liter” may be simply referred to as “L” for convenience. Further, “wt%” may be described as “wt%”.

諸 Various properties of the water absorbent resin particles were measured by the following methods. Unless otherwise specified, the following measurements are performed at room temperature (20 to 25 ° C.) and a humidity of 50 RH%. When the object to be measured is other than the water-absorbing resin particles, the water-absorbing resin particles are replaced with the object and applied unless otherwise specified.

<Saline flow conductivity (SFC)>
The SFC of the water-absorbent resin powder according to one embodiment of the present invention was measured according to the measurement method described in US Pat. No. 5,669,894.

<Centrifuge holding 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 capacity under pressure (AAP)>
AAP of the water-absorbent resin powder according to one embodiment of the present invention was measured in accordance with 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 in accordance with the EDANA method (ERT450.2-02).

<Blocking Ratio (BR)>
About 2 g of the water-absorbing resin powder was uniformly spread on an aluminum cup having a diameter of 52 mm on the bottom surface, and then left for 1 hour in a thermo-hygrostat at a temperature of 25 ° C. and a relative humidity of 70% RH. One hour later, the water-absorbent resin powder contained in the aluminum cup was gently transferred onto a JIS standard sieve (the inner diameter of 80 mm) having a mesh size of 2000 μm, and a low tap sieve shaker (manufactured by Iida Seisakusho Co., Ltd.) ES-65 sieve shaker; 230 rpm, impact 130 rpm), classified for 8 seconds, the weight (i (g)) of the water-absorbent resin powder remaining on the sieve and the water absorption passed through the sieve The weight (j (g)) of the resin powder was measured. Then, the moisture absorption blocking ratio was calculated according to the following equation (3). The closer the moisture absorption blocking rate is to 0% by weight, the higher the moisture absorption fluidity is.
Moisture absorption blocking ratio (% by weight) = ((i (g)) / (i (g) + j (g))) × 100 Formula (3)
<Surface tension of extract>
The surface tension of the extract of the water-absorbent resin powder is a value measured for an extract extracted from the water-absorbent resin powder with a 0.9% by weight aqueous sodium chloride solution. Specifically, 50 mL of a 0.9% by mass aqueous sodium chloride solution (physiological saline) adjusted to 23 ° C. to 25 ° C. is put into a well-washed 100 mL beaker, and the surface of the physiological saline is added. The tension is measured using a surface tensiometer (K11, an automatic surface tensiometer) to confirm that the measured value of the surface tension is in the range of 71 mN / m to 75 mN / m. Subsequently, a well-washed 25-mm-long rotor made of fluororesin and 0.5 g of water-absorbent resin are put into the physiological saline and stirred at 500 rpm for 4 minutes. Thereafter, 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 defined as the surface tension.

<Moisture content>
In the EDANA method (ERT430.2-02), the measurement was made by changing the loss on drying when 1 g of the water-absorbent resin particles or powder was dried at 180 ° C. for 3 hours (airless oven).

<Volume average particle diameter 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 an aqueous sodium acrylate solution having a neutralization ratio of 75% and a monomer concentration of 38% by weight, and 4.5 g of polyethylene glycol diacrylate (average molecular weight: 523) were placed in a jacketed kneader having a capacity of 10 L having two sigma-type blades. After charging and mixing, degassing was performed by blowing nitrogen. Next, the content of the kneader was adjusted to 30 ° C. while stirring, and 28.3 g of a 10% by weight aqueous sodium persulfate solution and then 2.0 g of 1% by weight L-ascorbic acid were injected. Later, a hydrogel having a particle size of 1 to 5 mm was obtained. The hydrogel was spread on a stainless mesh having a mesh size of 300 μm to a size of 50 cm × 70 cm, and dried at 180 ° C. for 40 minutes using a hot-air dryer (product name: 71-6S manufactured by Satake Chemical Machinery Co., Ltd.). The obtained dried polymer is pulverized by a roll mill and classified with a standard sieve having openings of 850 μm and 150 μm to obtain water-absorbent resin particles (1) having a particle diameter of 150 to 850 μm (weight average particle (D50) is 370 μm). Obtained.

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

表面 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 properties 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 performed after 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 the water-absorbing resin particles (1) were charged into a fluidized bed mixer (product name; Pulvis GB22, manufactured by Yamato Scientific Co., Ltd.) for forming a fluidized bed, and hot air: 100 ° C., air volume: 0.2 m ³ / The water-absorbent resin particles (1) were heated while flowing under the conditions of min (punching: 8 cmφ, wind speed: 0.66 m / s). After the temperature of the water-absorbent resin particles (1) and the fluidized bed exhaust temperature reached 80 ° C., 5 g of a 27% by weight aqueous solution of aluminum sulfate (1% by weight based on 100% by weight of the water-absorbent resin particles) was added at a speed of 15 g / min. And sprayed. Furthermore, water-absorbent resin particles (1) were obtained by mixing the water-absorbent resin particles sprayed with the aluminum sulfate aqueous solution in a fluidized bed mixer for 5 minutes. Table 1 shows the measurement results of various physical property values.

Note that the concentration of the saturated aqueous solution of aluminum sulfate (20 ° C.) is about 50% by weight. In Example 1, it is estimated that the aqueous solution of aluminum sulfate is added to the water-absorbent resin particles simultaneously with the spray drying. As a result, adhesion of spherical particles of aluminum sulfate hydrate was observed as shown in FIG. Based on the acquired SEM image, the number average particle diameter of 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 improvement of the water content of the water-absorbent resin was about 0.2%. That is, 27% by weight of the added water was absorbed.

[Comparative Example 1: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 4% by weight at room temperature]
4% by weight while flowing the water-absorbent resin particles under the conditions of blowing: 24 ° C. (water-absorbent resin temperature: 24 ° C.), air volume: 0.6 m ³ / min (punching: 8 cmφ, wind speed: 2.0 m / s) Production of a water-absorbent resin powder was attempted in the same manner as in Example 1 except that 25 g of an aqueous solution of aluminum sulfate (5% by weight with respect to 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 aggregated.

[Comparative Example 2: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 4% by weight under heating]
Production of a water-absorbent resin powder was attempted in the same manner as in Example 1 except that 25 g of a 4% by weight 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 aggregated.

[Comparative Example 3: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 4% by weight under heating (air volume change)]
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 changed to 0.36 m ³ / min (punching: 8 cmφ, wind speed: 1.2 m / s), but the flow of the water-absorbent resin particles stopped. However, water-absorbent resin particles scattered in the fluidized bed mixer. Furthermore, the water-absorbing resin particles sprayed with the aluminum sulfate aqueous solution were mixed in a fluidized bed mixer for 5 minutes to obtain a comparative water-absorbing resin powder (3). Table 1 shows the measurement results of various physical properties of the comparative water absorbent resin powder (3). Observation by SEM showed no particles or lumps of aluminum sulfate hydrate on the surface of the comparative water absorbent resin powder (3).

[Comparative Example 4: Addition of a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 4% by weight at room temperature (change of spray direction)]
An attempt was made to produce a water-absorbing resin powder 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, but the flow of the water-absorbing resin particles did not stop. Further, the water-absorbing resin particles sprayed with the aluminum sulfate aqueous solution were mixed for 5 minutes in a fluidized bed mixer to obtain a comparative water-absorbing resin powder (4). Table 1 shows the measurement results of various physical properties of the comparative water absorbent resin powder (4). Observation by SEM showed no particles or lumps of aluminum sulfate hydrate on the surface of the comparative water absorbent resin powder (4).

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

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

[Example 3]
A water-absorbent resin powder (3) was obtained in the same manner as in Example 2 except that 0.5 parts by weight of the aluminum sulfate hydrate obtained in Reference Example 1 was added and mixed. Was. Table 1 shows the measurement results of various physical properties 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 were placed in a plastic container, and 1 part by weight of a 27% by weight aqueous aluminum sulfate solution was added and mixed with a syringe while stirring with a spatula. Heated in a windless oven at 30 ° C. for 30 minutes. Further, the powder was passed through a sieve having an opening of 850 μm while disintegrating aggregates to obtain a comparative water absorbent resin powder (5). Table 1 shows the measurement results of various physical properties of the comparative water absorbent resin powder (5).

[Comparative Example 6]
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 aqueous solution of aluminum sulfate and 0.3% by weight of 60% by weight sodium lactate are stirred with a spatula. A liquid composed 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 powder was passed through a sieve having an opening of 850 μm while disintegrating aggregates to obtain a comparative water-absorbent resin powder (6). Table 1 shows the measurement results of various physical properties of the comparative water absorbent resin powder (6).

(Summary)
Water-absorbent resin powder (1) of Example 1 in which a polyvalent metal salt is added using Production Example 2 (surface-crosslinked water-absorbent resin particles) (a polyvalent metal salt having a polyvalent metal salt concentration of 27%) Water-absorbent resin powders (1) to (4) (addition of aqueous solution under heating) and Comparative Examples 1 to 4 (under heating or at room temperature of aqueous solution of polyvalent metal salt having a polyvalent metal salt concentration of 4% by weight) Was added. According to 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 high hygroscopic fluidity. In addition, the comparative example was compared with the comparative water-absorbent resin powder obtained in Comparative Examples 5 and 6, which corresponded to the conventional high liquid permeability and high hygroscopic fluidity technology in which a polyvalent metal salt was added without using a fluidized bed mixer. It can be seen that the water-absorbent resin powders obtained in 1 to 3 are excellent in liquid permeability and hygroscopic fluidity. Furthermore, 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 water absorption under pressure (AAP) of the surface cross-linked of Production Example 2. It shows a water absorption capacity under pressure almost equivalent to that of the obtained water-absorbent resin particles. 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 in the SEM image as shown in FIG. Furthermore, the water content of the water-absorbent resin powder obtained in Example 1 suggests that the water in the sprayed aqueous solution was dried.

[Production Example 3]
Water-absorbing 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.

[Production Example 4]
The procedure of Production Example 2 was repeated, except that the water-absorbent resin particles (3) were used, to obtain surface-crosslinked water-absorbent resin particles (4). Table 2 shows the measurement results of various physical properties 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. Table 2 shows the measurement results of various physical properties 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. Table 2 shows the measurement results of various physical properties 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. Table 2 shows the measurement results of various physical properties of the comparative water absorbent resin powder (8).

(Summary)
The amount of the internal crosslinking agent was changed to produce surface-crosslinked water-absorbent resin particles (2) having a lower CRC than the surface-crosslinked water-absorbent resin particles (1). 8 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, a low moisture absorption blocking ratio, and is close to 0% by weight. Clearly superior in terms of moisture absorption fluidity. Further, the water-absorbent resin powder (4) of Example 4 also has a low moisture-absorbing blocking ratio and is close to 0% by weight with respect to the comparative water-absorbent resin powder (8) of Comparative Example 8, so that the water-absorbent fluidity is low. Is excellent.

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

[Example 5]
To 100 parts by weight of the surface-crosslinked water-absorbent resin particles (1) obtained in Production Example 2, 6 parts by weight of the dispersion (1) obtained in Reference Example 2 was added dropwise while stirring. It was further dried in an oven at 180 ° C. for 30 minutes, and passed through a sieve having openings of 850 μm to obtain a water-absorbent resin powder (5). Table 3 shows the measurement results of various physical properties of the water-absorbent resin powder (5). In addition, when observed by the SEM image, the aluminum sulfate hydrate was a slightly elongated polyhedron, and the number average particle diameter 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 mixture of 4 parts by weight of polyethylene glycol (molecular weight: 200) and 1.5 parts by weight of deionized water to obtain a dispersion (2). Obtained.

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

[Comparative Example 9]
A comparative water absorbent resin (9) was prepared in the same manner as in Example 5, 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 properties of the comparative water absorbent resin (9).

The comparison of FR in Examples 5 and 6 and Comparative Example 9 shows that the presence of the aluminum sulfate particles improves the FR of the water-absorbing resin. In addition, comparing Example 5 and Example 6, when spherical aluminum sulfate particles are contained, the F.C. R. It can be seen that SFC is improved. Further, from the comparison between the description in Table 1 and the description in Table 3, it can be seen that when spherical aluminum sulfate is added together with polyethylene glycol, the SFC of the water absorbent resin is greatly improved.

[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 parts 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 properties of the water-absorbent resin powder (7).

水性 The water-absorbent resin powder produced by using the present invention is excellent in liquid permeability, so that it can be suitably used for various sanitary materials such as disposable diapers and sanitary napkins, and other various water-absorbent resins.

Claims

A method for producing a water-absorbent resin powder surface-crosslinked with an organic surface crosslinker and containing a water-soluble polyvalent metal salt, wherein a polyvalent metal salt aqueous solution having a polyvalent metal salt concentration of 5% by weight or more is mixed with a fluidized bed. A method for producing a water-absorbent resin powder, comprising: a spraying step of spraying water-absorbent resin particles at the time of surface cross-linking or after surface cross-linking in an machine, wherein the air temperature at the spray position of the aqueous solution of the polyvalent metal salt is 50 ° C or higher. .
The method for producing a water-absorbent resin powder according to claim 1, wherein the aqueous polyvalent metal salt solution is sprayed on the water-absorbent resin particles after surface crosslinking in the fluidized bed mixer.
The method for producing a water-absorbent resin powder according to claim 1 or 2, wherein cooling of the water-absorbent resin particles after surface crosslinking is performed simultaneously with the spraying step in the fluidized bed mixer.
方法 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.
(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 above the fluidized bed mixer.
6. The water-absorbent resin particles according to claim 1, 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 of the sprayed polyvalent metal salt aqueous solution is absorbed by the water-absorbing resin particles. A method for producing a water-absorbent resin powder according to any one of the preceding claims.
A method for producing a water-absorbent resin powder surface-crosslinked with an organic surface crosslinker and containing a water-soluble polyvalent metal salt, wherein a water-absorbent resin particle surface-crosslinked with an organic surface crosslinker is subjected to a laser diffraction / scattering method. A method for producing a water-absorbent resin powder, comprising adding water-soluble polyvalent metal salt particles having a measured volume average particle diameter of 0.3 to 15 μm.
The production of a 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 based on 100 parts by weight of the water-absorbent resin particles. Method.
方法 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-absorbing resin powder surface-crosslinked with an organic surface cross-linking agent and containing a water-soluble polyvalent metal salt, wherein water-soluble polyvalent metal salt particles adhere to the surface of the water-absorbing resin powder, and A water-absorbent resin powder having a number average particle diameter of the valent metal salt particles of 0.3 to 15 μm.
The water-absorbent resin powder according to claim 10, wherein the circularity of the water-soluble polyvalent metal salt particles determined by SEM image analysis is 0.8 or more as defined by the following equation.
(Circularity) = 4π · S / L 2
(In the formula, L is the outer circumference of the attached water-soluble polyvalent metal salt particles, and S is the area of the attached water-soluble polyvalent metal salt particles.)
12. 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 CRC is 25 g / g or more and 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 diameter is 100 to 2000 μm.