JP2022088139A - Method for producing water-absorbing resin particle - Google Patents

Abstract

To provide a method for producing water-absorbing resin particles containing granulated particles which can efficiently recover an aggregate obtained by kneading a mixture containing polymer fine powder and an aqueous liquid containing water from a mixer used for kneading the mixture without greatly impairing performance of the obtained water-absorbing resin particles.SOLUTION: There is provided a method for producing water-absorbing resin particles containing granulated particles. The method includes the steps of: mixing polymer fine powder having a temperature of 0°C or higher and lower than 70°C and an aqueous liquid containing water having a temperature of 0°C or higher and lower than 40°C and thereby forming a mixture, and kneading the mixture in a mixer to obtain an aggregate of the polymer fine powder; removing at least a part of water from the aggregate taken out from the mixer and thereby obtaining a dried aggregate; and pulverizing the dried aggregate to form granulated particles.SELECTED DRAWING: None

Description

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

Conventionally, an absorber containing water-absorbent resin particles has been used as an absorbent article for absorbing a liquid containing water as a main component such as urine. Fine powder generated during the manufacturing process of the water-absorbent resin particles may be aggregated to form granulated particles having a particle size suitable for application to an absorbent article. The granulated particles can be obtained, for example, by a production method including a step of heating an aqueous liquid and mixing the heated aqueous liquid and the water-absorbent resin powder at high speed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 11-106514

The granulated particles used for the water-absorbent resin particles are formed by kneading a mixture containing a polymer fine powder and an aqueous liquid containing water, and are formed at a high temperature from the viewpoint of improving the strength and performance of the granulated particles. Polymer fine particles and / or high temperature aqueous liquids are used.

However, since the agglomerates tend to adhere to the inner wall of the mixer used for kneading the mixture, the stirring blade, etc., it takes time and effort to recover the agglomerates from the mixer, which is the reason for the granulated particles. It has been found that production efficiency can be reduced.

Therefore, one aspect of the present invention is a method for producing water-absorbent resin particles containing granulated particles, in which a polymer fine powder and an aqueous liquid containing water can be obtained without significantly impairing the performance of the obtained water-absorbent resin particles. Provided is a method in which agglomerates obtained by kneading the containing mixture can be efficiently recovered from the mixer used for kneading the mixture.

One aspect of the present invention provides a method for producing water-absorbent resin particles containing granulated particles. In this method, a mixture is formed by mixing a polymer fine powder having a temperature of 0 ° C. or higher and lower than 70 ° C. and an aqueous liquid containing water having a temperature of 0 ° C. or higher and lower than 40 ° C., and the mixture is placed in a mixer. A step of obtaining an agglomerate of polymer fine particles by kneading with the above, and a step of obtaining a dried agglomerate by removing at least a part of water from the agglomerate taken out from the mixer. It comprises a step of crushing the dried agglomerates to form granulated particles.

According to one aspect of the present invention, there is a method for producing water-absorbent resin particles containing granulated particles, wherein the aqueous liquid containing polymer fine powder and water is used without significantly impairing the performance of the obtained water-absorbent resin particles. It is possible to provide a method in which agglomerates obtained by kneading a mixture containing the above can be efficiently recovered from the mixer used for kneading the mixture.

It is a schematic diagram which shows the measuring method of the absorption magnification under pressure. It is a schematic diagram which shows the measuring apparatus of the non-pressurized DW of a water-absorbent resin particle.

Hereinafter, some embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

As used herein, "(meth) acrylic" means both acrylic and methacrylic. Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". The same is true for other similar terms. "(Poly)" shall mean both with and without the "poly" prefix. Within the numerical range described stepwise herein, the upper or lower limit of the numerical range at one stage may be optionally combined with the upper or lower limit of the numerical range at another stage. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. "Water-soluble" means that it exhibits a solubility in water of 5% by mass or more at 25 ° C. The materials exemplified in the present specification may be used alone or in combination of two or more. "Saline" means a 0.9% by mass sodium chloride aqueous solution. Sieve means JIS standard sieve. "Drying" means removing at least a portion of the water from the object.

One embodiment of the method for producing water-absorbent resin particles is by mixing a polymer fine powder having a temperature of 0 ° C. or higher and lower than 70 ° C. and an aqueous liquid containing water having a temperature of 0 ° C. or higher and lower than 40 ° C. The mixture was formed and kneaded in the mixer to obtain agglomerates of polymer fine particles, and dried by removing at least a part of water from the agglomerates taken out from the mixer. It includes a step of obtaining an agglomerate and a step of crushing the dried agglomerate to form granulated particles.

[Polymer fine powder]
The polymer fine powder is recovered by pulverizing the dry gel containing the crosslinked polymer and classifying the pulverized dry gel into two or more particle groups having different particle size distributions. Hereinafter, an example of a method for obtaining polymer fine powder will be described in detail. The water-containing gel polymer is formed, for example, by polymerizing a monomer in a reaction solution which is a monomer aqueous solution containing a monomer and water.

The monomer may contain an ethylenically unsaturated monomer, and the ethylenically unsaturated monomer may be a water-soluble ethylenically unsaturated monomer. Examples of ethylenically unsaturated monomers include unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid and carboxylic acid-based monomers such as salts thereof; (meth) acrylamide, Nonionic monomers such as N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N-diethylaminoethyl ( Amino group-containing unsaturated monomers such as meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide, and quaternized products thereof; vinyl sulfonic acid, styrene sulfonic acid, 2- Examples thereof include sulfonic acid-based monomers such as (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, and salts thereof. The ethylenically unsaturated monomer can contain at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and salts thereof. The salt of the unsaturated carboxylic acid ((meth) acrylic acid, etc.) may be, for example, an alkali metal salt (sodium salt, potassium salt, etc.) or an ammonium salt.

In the ethylenically unsaturated monomer having an acid group (for example, (meth) acrylic acid), the acid group may be neutralized in advance with a neutralizing agent (alkaline neutralizing agent). Examples of neutralizers include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide, potassium carbonate; ammonia. The neutralizing agent may be an aqueous solution of these components. The acid group of the ethylenically unsaturated monomer may be neutralized before, during or after the polymerization of the ethylenically unsaturated monomer.

The degree of neutralization of the ethylenically unsaturated monomer is 10 mol% or more, 30 mol% or more, and 50 mol from the viewpoint of easily obtaining good water absorption performance by increasing the osmotic pressure and enhancing the safety. % Or more, or 60 mol% or more, and may be 100 mol% or less, 90 mol% or less, 85 mol% or less, or 80 mol% or less. As used herein, the degree of neutralization means the degree of neutralization of all the acid groups of the ethylenically unsaturated monomer used in the polymerization.

The content of the monomer (for example, (meth) acrylic acid compound) in the reaction solution is 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, based on the total mass of the reaction solution. It may be 30% by mass or more, or 35% by mass or more. The content of the monomer in the reaction solution may be 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, or 40% by mass or less.

The content of the (meth) acrylic acid compound is 50 mol% or more, 70, based on the total amount of monomers contained in the reaction solution or the total amount of ethylenically unsaturated monomers contained in the reaction solution. It may be mol% or more, 90 mol% or more, 95 mol% or more, 97 mol% or more, or 99 mol% or more. Even if the monomer contained in the reaction solution is substantially composed of a (meth) acrylic acid compound, that is, 100 mol% of the monomer contained in the reaction solution is a (meth) acrylic acid compound. good.

The reaction solution may contain a polymerization initiator. The polymerization reaction may be initiated by heating or exposing the reaction solution containing the polymerization initiator. The polymerization initiator may be a photopolymerization initiator, a thermal radical polymerization initiator, or a combination thereof. The polymerization initiator may be water-soluble. The thermal radical polymerization initiator may contain at least one selected from the group consisting of azo compounds and peroxides from the viewpoint of easily enhancing water absorption performance.

Examples of azo compounds include 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2'-azobis {2- [N- (4-chlorophenyl) amidino] propane}. Dihydrochloride, 2,2'-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (N-benzylamidino) propane] dihydrochloride , 2,2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [N- (2-Hydroxyethyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2 -(2-Imidazoline-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2-yl) propane] Dihydrochloride, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidine-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1 -(2-Hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] Can be mentioned. The azo compounds are 2,2'-azobis (2-methylpropionamide) dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, and 2 from the viewpoint that good water absorption performance can be easily obtained. , 2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, and 2,2'-azobis [N- (2-carboxyethyl)- 2-Methylpropionamidine] It may contain at least one selected from the group consisting of tetrahydrate.

Examples of peroxides are persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t. Examples thereof include organic peroxides such as -butylperoxyacetate, t-butylperoxyisobutyrate, and t-butylperoxypivalate. Peroxides are potassium persulfate, ammonium persulfate, from the viewpoint of easily obtaining water-absorbent resin particles having good water-absorbing performance and easily reducing the amount of unreacted monomers contained in the water-absorbent resin particles. And at least one selected from the group consisting of sodium persulfate may be contained.

The content of the polymerization initiator is a monomer (from the viewpoint of easily obtaining water-absorbent resin particles having good water-absorbing performance and from the viewpoint of easily reducing the amount of unreacted monomer contained in the water-absorbent resin particles. For example, 0.001 mmol or more, 0.005 mmol or more, 0.01 mmol or more, 0.05 mmol or more, 0.1 mmol or more, 0.15 mmol or more, per 1 mol of (meth) acrylic acid compound). It may be 0.3 mmol or more, or 0.5 mmol or more. The content of the polymerization initiator is 1 mol of a monomer (for example, (meth) acrylic acid compound) from the viewpoint of easily obtaining water-absorbent resin particles having good water absorption performance and from the viewpoint of easily avoiding a rapid polymerization reaction. On the other hand, it may be 5 mmol or less, 4 mmol or less, 2 mmol or less, 1 mmol or less, 0.9 mmol or less, 0.7 mmol or less, or 0.6 mmol or less.

The reaction solution may contain a reducing agent. Examples of reducing agents include sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid.

The reaction solution may contain an oxidizing agent. Examples of oxidizing agents include hydrogen peroxide, sodium perborate, perphosphate and salts thereof, and potassium permanganate.

The reaction solution may contain a cross-linking agent for cross-linking the polymer produced by the polymerization of the monomer. The cross-linking agent contained in the aqueous monomer solution may be referred to as an internal cross-linking agent. The internal cross-linking agent may be a compound having two or more reactive functional groups (for example, a polymerizable unsaturated group). Examples of internal cross-linking agents are di or tri (meth) acrylics of polyols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, (poly) glycerin. Acid esters; Unsaturated polyesters obtained by reacting the above polyol with unsaturated acids (maleic acid, fumaric acid, etc.); (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly). ) Glycidyl group-containing compounds such as glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) glycerin polyglycidyl ether, glycidyl (meth) acrylate; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; Di or tri (meth) acrylic acid esters obtained by reacting polyepoxide with (meth) acrylic acid; polyisocyanate (tolylene diisocyanate, hexamethylene diisocyanate, etc.) and hydroxyethyl (meth) acrylic acid are reacted. Di (meth) acrylic acid carbamyl esters obtained; allylated starch; allylated cellulose; diallyl phthalate; N, N', N "-triallyl isocyanurate; divinylbenzene; pentaerythritol; ethylenediamine; polyethyleneimine. ..

The content of the internal cross-linking agent is 0.001 mmol or more and 0.005 per 1 mol of an ethylenically unsaturated monomer (for example, (meth) acrylic acid compound) from the viewpoint that good water absorption performance can be easily obtained. It may be mmol or more, 0.01 mmol or more, 0.05 mmol or more, 0.1 mmol or more, 0.2 mmol or more, or 0.3 mmol or more. The content of the internal cross-linking agent is 5 mmol or less, 4 mmol or less, 3 mmol or less, 2 mmol or less, 1 mmol or less, 0.5 mmol or less, or 0.4 mmol from the viewpoint that good water absorption performance can be easily obtained. It may be as follows.

The reaction solution may further contain a chain transfer agent, a thickener, an inorganic filler and the like. Examples of chain transfer agents include thiols, thiol acids, secondary alcohols, hypophosphorous acid, phosphorous acid and achlorine. Examples of thickeners include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene glycol, polyacrylic acid, polyacrylic acid neutralizer, and polyacrylamide. Examples of inorganic fillers include metal oxides, ceramics and viscous minerals.

During the polymerization reaction, the reaction solution may be stirred without stirring. The form of polymerization may be, for example, batch, semi-continuous, or continuous. For example, when continuous polymerization is adopted in a static polymerization method in which the monomer aqueous solution is not stirred, the polymerization reaction is carried out while continuously supplying the monomer aqueous solution to a reaction vessel (for example, a belt conveyor-shaped reaction vessel). A hydrogel-like polymer can be continuously obtained.

The temperature of the reaction solution during the polymerization reaction, that is, the polymerization temperature may be, for example, 0 to 130 ° C. or 10 to 110 ° C. The polymerization time may be, for example, 1 to 200 minutes or 5 to 100 minutes.

(Rough crushing process)
The reaction solution gels as the polymerization reaction progresses, and a hydrogel-like polymer is formed. A dry gel is formed by removing a part of water from the formed hydrogel-like polymer. A dry gel may be formed by a method including coarsely crushing the hydrogel-like polymer and removing a part of water in the coarsely crushed water-containing gel-like polymer. By coarsely crushing the water-containing gel-like polymer and then drying it, water can be removed more efficiently from the water-containing gel-like polymer.

The coarsening of the hydrogel polymer may be carried out using, for example, a kneader (pressurized kneader, double-armed kneader, etc.), a meat chopper, a cutter mill, or a roughing machine such as a pharmacomill. The lumpy hydrogel polymer may be pre-cut into, for example, about 5 cm square, and the cut hydrogel polymer may be coarsely crushed. When the polymerization reaction is carried out by stirring polymerization with an apparatus such as a kneader, the polymerization of the monomer and the coarse crushing of the hydrogel polymer may be carried out substantially at the same time. The minimum width of the coarsely crushed hydrogel polymer may be, for example, 0.2 to 15 mm, or 1.0 to 10 mm. The maximum width of the coarsely crushed hydrogel polymer may be 0.2 to 200 mm, or 1.0 to 150 mm.

The method for removing water from the hydrogel-like polymer, that is, drying, may be, for example, natural drying, heat drying, blast drying, freeze drying, or a combination thereof. Water may be removed from the hydrogel polymer or a crushed product thereof under normal pressure or reduced pressure. The drying device used is, for example, a hot air dryer, a vacuum dryer, a ventilation belt type dryer, a ventilation band type dryer, a rotary ventilation dryer, a stirring dryer, a fluidized layer dryer, a vibration fluidized dryer, or a vacuum dryer. It may be a machine.

The heating temperature (drying temperature) for drying the water-containing gel polymer and the drying time can be adjusted so that a dry gel having a predetermined water content is formed. For example, the maximum drying temperature may be 80 ° C. or higher, 100 ° C. or higher, 120 ° C. or higher, 140 ° C. or higher, 160 ° C. or higher, 170 ° C. or higher, or 180 ° C. or higher, and the maximum is 250 ° C. or lower and 220 ° C. or lower. , 200 ° C or lower, 190 ° C or lower, or 180 ° C or lower. The drying temperature may be the set temperature of the drying apparatus or the exposure atmosphere temperature of the hydrogel-like polymer. The drying time may be, for example, 15 minutes or more, 20 minutes or more, 25 minutes or more, or 30 minutes or more, and may be 120 minutes or less, 90 minutes or less, or 60 minutes or less.

The water content of the water-containing gel-like polymer before drying is a water-containing gel from the viewpoint of easily adjusting the water content of the obtained dried gel and suppressing the deterioration of the solid content in the water-containing gel-like polymer. It may be 50% by mass or more, 55% by mass or more, or 70% by mass or less, 65% by mass or less, or 60% by mass or less with respect to the total mass of the state polymer. The water content of the hydrogel polymer before drying can be adjusted, for example, by adjusting the water content of the aqueous monomer solution used for the polymerization of the crosslinked polymer.

The water content of the dry gel may be, for example, 20% by mass or less, 10% by mass or less, or 5% or less. In the present specification, the water content is the water content based on the wetting standard, that is, the mass ratio of the water content to the total amount of the water-containing gel polymer.

The dry gel is ground to form a powder containing particles that pass through a sieve with an opening of 180 μm. For crushing dry gel, for example, roller mill (roll mill), stamp mill, jet mill, high-speed rotary crusher (hammer mill, pin mill, rotor mill, rotor beater mill, etc.), container-driven mill (rotary mill, vibration mill, etc.) A crusher such as a planetary mill) can be used. The grinder may include a particle outlet with an opening that controls the maximum particle size of the particles. The particle outlet may be, for example, a perforated plate, screen, or grid. The maximum diameter of the opening may be 0.1 to 5 mm, 0.3 to 3.0 mm, or 0.5 to 1.5 mm.

The crushed dry gel is a powder of polymer particles containing a crosslinked polymer, which is, for example, polymer fine particles containing particles that pass through a sieve with an opening of 180 μm and particles that do not pass through a sieve with an opening of 180 μm. It is classified into a group of particles containing. The polymer fine powder is a fraction of particles having a relatively small particle size among the powders before classification, and mainly contains particles that pass through a sieve having an opening of 180 μm. The polymer fine powder may further contain particles that do not pass through a 180 μm sieve. The mass ratio of the particles passing through the sieve having an opening of 180 μm to the total amount of the polymer fine powder may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more. The mass ratio of the particles passing through the sieve having an opening of 180 μm to the total amount of the polymer fine powder may be 100% by mass or less.

Here, for "particles passing through a sieve with a mesh opening of 180 μm", polymer particles obtained after pulverization are placed in a JIS standard sieve with a mesh opening of 180 μm, and a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.) is used. It means particles that have passed through a sieve having an opening of 180 μm after being classified for 10 minutes under the conditions according to JIS Z 8815 (1994).

The pulverized dry gel can be classified by, for example, sieving, screen classification, wind classification, or the like. In the case of sieving, it was pulverized by a combination of two or more sieves including, for example, a bottom sieve having a mesh size of 106 to 180 μm and a top sieve having a mesh size larger than that of the bottom sieve. The dried gel can be classified. In that case, the particles that have passed through the lowermost sieve may be recovered as polymer fine powder. The mesh opening of the lowermost sieve may be 180 μm, but is not limited to this, and may be, for example, 120 to 180 μm. The particle group composed of the particles remaining on each sieve can be recovered as a particle group containing particles that do not pass through the sieve having an opening of 180 μm. This particle group can be a mixture of particles remaining on some or all of the two or more sieves. For example, the particles remaining on the uppermost sieve may be excluded from the particle group. The mesh opening of the uppermost sieve may be, for example, 850 to 1000 μm. A group of particles containing particles that do not pass through a sieve having a mesh size of 180 μm can be used to obtain a product of water-absorbent resin particles without the need for granulation. The crushed dry gel may be classified according to JIS Z 8815 (1994) using a low-tap type shaker (manufactured by Iida Seisakusho Co., Ltd.).

[Granulated particles]
A mixture is formed by mixing a polymer fine powder having a temperature of 0 ° C. or higher and lower than 70 ° C. and an aqueous liquid containing water having a temperature of 0 ° C. or higher and lower than 40 ° C., and the mixture is kneaded in a mixer. By forming an agglomerate of polymer fine particles, removing the agglomerate from the mixer, and removing at least a part of water from the agglomerate to obtain a dried agglomerate. Granulated particles can be obtained by methods including crushing the dried agglomerates to form granulated particles.

The temperature of the polymer fine powder and the temperature of the aqueous liquid are adjusted so that the temperatures of the polymer fine powder and the aqueous liquid at the time of contact between the polymer fine powder and the aqueous liquid are within the above ranges, respectively. For example, when the entire amount of the aqueous liquid is added to the polymer fine powder in the mixer at one time, the temperature of the polymer fine powder and the aqueous liquid immediately before the addition of the aqueous liquid is within the above-mentioned predetermined range. By adjusting, the polymer fine powder having a temperature within a predetermined range and the aqueous liquid can be mixed. When the aqueous liquid is added little by little to the polymer fine powder in the mixer, the temperature of the polymer fine powder immediately before the first contact with the aqueous liquid and the temperature immediately before the contact with the polymer fine powder or the kneaded mixture. By adjusting the temperature of the aqueous liquid to be within the above range, the polymer fine powder having a temperature within a predetermined range and the aqueous liquid can be mixed. The aqueous liquid may be added by spraying, and in that case, the temperature of the aqueous liquid immediately before being sprayed may be adjusted to be within the above-mentioned predetermined range, so that the aqueous liquid having a temperature within the predetermined range can be added. It can be mixed with the polymer fine powder.

The aqueous liquid to be mixed with the polymer fine powder for granulation may contain other components in addition to water. Examples of other components that the aqueous solution may contain include water-soluble salts, water-soluble polymerizable monomers, cross-linking agents, and hydrophilic organic solvents. The cross-linking agent can be selected from, for example, an internal cross-linking agent or a compound similar to the surface cross-linking agent described later. The ratio of water in the aqueous liquid may be 90 to 100% by mass based on the mass of the aqueous liquid.

The amount of the aqueous liquid mixed with the polymer fine powder is 80 parts by mass or more with respect to 100 parts by mass of the dry solid content of the polymer fine powder from the viewpoint of making it easy to uniformly knead the mixture containing the polymer fine powder and the aqueous liquid. , 90 parts by mass or more, 100 parts by mass or more, or 105 parts by mass or more. The amount of the aqueous solution may be 150 parts by mass or less, 130 parts by mass or less, or 110 parts by mass or less with respect to 100 parts by mass of the dry solid content of the polymer fine powder from the viewpoint of efficient drying of the agglomerates. .. "Dry solid content of polymer fine powder" means the mass of the portion of the polymer fine powder excluding water.

The temperature of the polymer fine powder mixed with the aqueous liquid is 65 ° C. or lower, 60 ° C. or lower, 55 ° C. or lower, 50 ° C. or lower, 45 ° C. or lower, from the viewpoint of facilitating more efficient recovery of aggregates from the mixer. 40 ° C or lower, 35 ° C or lower, 30 ° C or lower, 25 ° C or lower, 20 ° C or lower, 15 ° C or lower, 10 ° C or lower, 5 ° C or lower or 3.5 ° C or lower may be used, 1 ° C or higher, 3.5 ° C or lower. ° C or higher, 5 ° C or higher, 10 ° C or higher, 15 ° C or higher, 20 ° C or higher, 25 ° C or higher, 30 ° C or higher, 35 ° C or higher, 40 ° C or higher, 45 ° C or higher, 50 ° C or higher, 55 ° C or higher or 60 ° C or higher. May be. The temperature of the polymer fine powder can be adjusted, for example, by heating a container or a mixer containing the polymer fine powder before being mixed with the aqueous liquid with a water bath or the like.

The temperature of the aqueous liquid mixed with the polymer fine powder is 35 ° C. or lower, 30 ° C. or lower, 25 ° C. or lower, 20 ° C. from the viewpoint of facilitating more efficient recovery from the mixer used to form the agglomerates. Below, it may be 15 ° C. or lower, 10 ° C. or lower, 5 ° C. or lower, or 3.5 ° C. or lower, 1 ° C. or higher, 3.5 ° C. or higher, 10 ° C. or higher, 15 ° C. or higher, 20 ° C. or higher, or 25 ° C. It may be above ° C. The temperature of the aqueous liquid may be lower than the temperature of the polymer fine powder from the viewpoint of facilitating the more efficient recovery of the agglomerates from the mixer.

The difference between the temperature of the polymer fine powder and the temperature of the aqueous liquid at the time when the polymer fine powder and the aqueous liquid are mixed, in other words, at the time when the polymer fine powder and the aqueous liquid first come into contact with each other, is 60 ° C. or less and 50 ° C. or less. , 40 ° C. or lower, 35 ° C. or lower, 30 ° C. or lower, 25 ° C. or lower, 20 ° C. or lower, 15 ° C. or lower, 10 ° C. or lower, or 5 ° C. or lower.

The time for kneading the mixture containing the polymer fine powder and the aqueous liquid (kneading time) is such that the polymer fine powder and the entire amount of the aqueous liquid are mixed from the viewpoint of making it easy to uniformly mix the polymer fine powder and the aqueous liquid. From 10 to 150 seconds, 20 to 130 seconds, or 30 to 110 seconds.

The mixture containing the polymer fine powder and water can be kneaded in the mixer using, for example, various stirrers having stirring blades. The stirring blade may be, for example, a flat plate blade, a lattice blade, a paddle blade, a propeller blade, an anchor blade, a turbine blade, a Faudler blade, a ribbon blade, a full zone blade, or a Maxblend blade. The flat plate blade has a shaft (stirring shaft) and a flat plate portion (stirring portion) arranged around the shaft. The flat plate portion may have a slit or the like. By using a flat plate blade as the stirring blade, it tends to be easy to knead the mixture uniformly. Examples of the stirring type mixer include a mortar mixer, a continuous kneader, and a ladyge mixer.

The temperature of the mixture during kneading in the mixer is less than 70 ° C, 65 ° C or less, 60 ° C or less, 55 ° C or less, 50 ° C or less, 45 ° C or less, less than 40 ° C, 35 ° C or less, 30 ° C or less. , 25 ° C or lower, 20 ° C or lower, 15 ° C or lower or 10 ° C or lower, 0 ° C or higher, 5 ° C or higher, 10 ° C or higher, 15 ° C or higher, 20 ° C or higher, 25 ° C or higher, 30 ° C or higher, It may be 35 ° C. or higher, 40 ° C. or higher, 45 ° C. or higher, or 50 ° C. or higher. While the mixture is kneaded in the mixer, the mixer may be appropriately kept warm or may be placed in an environment of a predetermined temperature. For example, the mixture may be kneaded in a mixer placed in an environment of 0 ° C. or higher and lower than 40 ° C.

The aggregate of the polymer fine powder formed by kneading may be a lump containing a crosslinked polymer and water. By removing at least a portion of the water from the agglomerates, a dried agglomerate is obtained. When the agglomerates are lumps, from the viewpoint of improving the drying efficiency, the lumps may be cut to a maximum width of about 3 to 10 mm and then dried.

The drying temperature for drying the agglomerates may be 80 ° C. or higher, 100 ° C. or higher, 120 ° C. or higher, 140 ° C. or higher, or 150 ° C. or higher, 250 ° C. or lower, 200 ° C. or lower, 180 ° C. or lower, 160 ° C. It may be ℃ or less, or 150 ℃ or less. The time for drying the agglomerates (drying time) may be set according to conditions such as the drying temperature, and may be, for example, 15 minutes or more, 30 minutes or more, 45 minutes or more, or 60 minutes or more, and 120 minutes or less. , 90 minutes or less, or 60 minutes or less.

By pulverizing the dried agglomerates, a powder of granulated particles is formed. For the pulverization of the agglomerate, the same method as the above-mentioned method for pulverizing a dry gel can be applied. The powder obtained by pulverizing the agglomerates may be classified to obtain granulated particles having a desired particle size distribution, and the particle size may be adjusted. That is, the method according to the present embodiment may include a step of crushing the dried agglomerates and a step of classifying the crushed agglomerates to obtain granulated particles having an adjusted particle size. The pulverized aggregate may be classified so as to obtain a particle group that passes through a sieve having an opening of 850 μm and does not pass through a sieve having an opening of 180 μm, for example. The crushing of the dried agglomerates and the classification of the crushed agglomerates may be performed at the same time.

(Surface cross-linking of granulated particles)
The method according to the present embodiment may further include a step of surface cross-linking the granulated particles. The granulated particles are surface-crosslinked by heating, for example, a cross-linking agent solution containing a cross-linking agent for performing surface cross-linking (hereinafter, may be referred to as “surface cross-linking agent”) and a mixture containing the granulated particles. be able to. Granulated particles before or after classification (after adjusting the particle size) can be surface-crosslinked. The surface-crosslinked granulated particles may be dried and / or classified.

The surface cross-linking agent may be, for example, a compound containing two or more functional groups (reactive functional groups) having reactivity with a functional group derived from an ethylenically unsaturated monomer. Examples of surface cross-linking agents are alkylene carbonate compounds such as ethylene carbonate; ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol. , And polyol compounds such as polyglycerin; (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylolpropane triglycidyl ether (poly) propylene glycol polyglycidyl ether, and Polyglycidyl compounds such as (poly) glycerol polyglycidyl ethers; haloepoxy compounds such as epichlorohydrin, epibromhydrin, and α-methylepicrolhydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylenediisocyanate; 3-methyl. -3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, and 3-butyl-3-oxetane Examples thereof include oxetane compounds such as ethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; and hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide.

The amount of the surface cross-linking agent is 0.001 to 40 mmol per 1 mol of the total amount of the monomer units calculated from the mass of the granulated particles from the viewpoint of appropriately increasing the cross-linking density near the surface of the granulated particles. , Or 0.01 to 20 mmol.

The cross-linking agent liquid may contain water. The amount of water in the cross-linking agent liquid may be 1 to 20 parts by mass with respect to 100 parts by mass of the granulated particles.

The heating temperature for surface cross-linking of the granulated particles may be, for example, 20 to 250 ° C. The heating time may be 1 to 200 minutes or 5 to 100 minutes.

The water-absorbent resin particles obtained by the method according to the present embodiment may further contain a gel stabilizer, a deodorant, a metal chelating agent, inorganic particles and the like, in addition to the granulated particles. Examples of the metal chelating agent include polycarboxylic acid compounds such as ethylenediamine 4acetic acid, diethylenetriamine5 acetic acid, and triethylenetetraamine6 acetic acid, and salts thereof. Examples of the inorganic particles include silica particles.

The shape of the water-absorbent resin particles obtained by the production method according to the present embodiment may be, for example, a crushed shape or a shape formed by aggregating crushed particles. The medium particle size of the water-absorbent resin particles may be 250 μm or more, 280 μm or more, 300 μm or more, 320 μm or more, or 340 μm or more, and may be 850 μm or less, 800 μm or less, 750 μm or less, 700 μm or less, 650 μm or less, 600 μm or less, 550 μm. Hereinafter, it may be 500 μm or less, 450 μm or less, 420 μm or less, 400 μm or less, or 380 μm or less.

The centrifuge holding capacity (CRC) of the water-absorbent resin particles obtained by the method according to the present embodiment may be, for example, 25 g / g or more, 30 g / g or more, or 32 g / g or more, and 60 g / g or less. , 50 g / g or less, 40 g / g or less, or 35 g / g or less.

The water-absorbent resin particles obtained by the method according to the present embodiment have a water absorption ratio (AAP, Absorption Against Pressure) at 2.07 kPa (0.3 psi), for example, 15 g / g or more, 20 g / g or more, or It may be 24 g / g or more, and may be 40 g / g or less, 30 g / g or less, or 25 g / g or less. The absorption ratio of the water-absorbent resin particles under a pressure of 2.07 kPa is measured by the method described in Examples described later.

The 10-minute value of the non-pressurized DW of the water-absorbent resin particles obtained by the method according to the present embodiment is, for example, 20 mL / g or more, 25 mL / g or more, or 28 mL / g or more, 32 mL / g or more. It may be 65 mL or less, 50 mL / g or less, 40 mL / g or less, or 35 mL / g or less. The 10-minute value of the non-pressurized DW can be measured by the method described in Examples described later. The 10-minute value of the non-pressurized DW is the water absorption rate represented by the amount of the water-absorbent resin particles that have absorbed the physiological saline solution within 10 minutes after the contact with the physiological saline solution under no pressurization. .. The non-pressurized DW is represented by an absorption amount [mL / g] per 1 g of water-absorbent resin particles before absorption of physiological saline.

The water-absorbent resin particles obtained by the production method according to the present embodiment have excellent water absorption, and are, for example, sanitary materials such as disposable diapers and sanitary products, agricultural and horticultural materials such as water-retaining agents and soil improvers, water-stopping agents, and dew condensation prevention. It can be used in fields such as industrial materials such as agents.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
[Polymerization process]
515.50 g (7.15 mol) of acrylic acid was placed in a round bottom cylindrical separable flask equipped with a stirrer and having an inner diameter of 11 cm and an internal volume of 2 L. After adding 441.00 g of ion-exchanged water into the separable flask while stirring acrylic acid, 449.90 g of 48% by mass sodium hydroxide was added dropwise under an ice bath to make acrylic having a monomer concentration of 45% by mass. 1406.40 g of a sodium acid partial neutralizing solution (neutralization degree of acrylic acid 75 mol%) was prepared.

To 130.67 g of sodium acrylate partial neutralizing solution, 194.98 g of ion-exchanged water and 1.39 g of polyethylene glycol diacrylate (internal cross-linking agent, Blemmer ADE-400A, manufactured by Nichiyu Co., Ltd.) were added to the reaction solution (single amount). Body aqueous solution) was obtained. The reaction solution was supplied to a stainless steel double-armed kneader (manufactured by Irie Shokai Co., Ltd.) with an internal volume of 3 L and a jacket equipped with a thermometer and a nitrogen blow tube and two sigma-shaped blades with openable and closable lids. Nitrogen gas was replaced for 60 minutes in a nitrogen gas atmosphere while maintaining the temperature of the supplied reaction solution at 25 ° C. After substituting nitrogen gas in the kneader, the reaction solution was stirred at a rotation speed of 30 rpm to 44.32 g (3.72 mmol) of a 2.0 mass% sodium persulfate aqueous solution and 0.5 mass% L-. When 7.58 g of an aqueous solution of ascorbic acid was added, the temperature began to rise after about 1 minute, and the polymerization started. Eight minutes after the temperature rise, the thermometer showed a maximum temperature of 75 ° C., then stirring was continued while maintaining the jacket temperature at 60 ° C., and 60 minutes after the start of polymerization, the produced hydrogel-like polymer was taken out. ..

[Drying process]
The obtained hydrogel-like polymer was put into a meat chopper (12VR-750SDX manufactured by Kiren Royal Co., Ltd.) and coarsely crushed. The diameter of the hole in the plate located at the outlet of the meat chopper was 6.4 mm. The obtained coarsely crushed hydrogel polymer was spread on a wire mesh having an opening of 0.8 cm × 0.8 cm and dried with hot air at 180 ° C. for 30 minutes to obtain a dry gel.

[Crushing process]
The obtained dry gel was pulverized by a centrifugal pulverizer (ZM200 manufactured by Retsch, screen diameter 1 mm, 12000 rpm) to obtain 569.25 g of crushed dry gel in an amorphous crushed form.

[Classification process]
The crushed dry gel was classified by a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.) for 10 minutes according to JIS Z 8815 (1994) using a sieve with an opening of 180 μm, and remained on a sieve with an opening of 180 μm. A fraction was obtained and a fraction passed through a 180 μm sieve was obtained. At this time, the fraction remaining on the sieve with a mesh opening of 180 μm is subjected to the above crushing step again, and the powder obtained after the crushing step is classified using a sieve with a mesh opening of 180 μm and placed on a sieve with a mesh opening of 180 μm. The remaining fraction and the fraction that passed through a sieve having an opening of 180 μm were obtained. The fractions obtained by each classification and passed through a sieve having an opening of 180 μm were added together to obtain 341.55 g of polymer fine powder. When the water content of the polymer fine powder was measured according to the water content measuring method described later, the water content of the polymer fine powder was 4.9%.

[Granulation process]
30 g of the obtained polymer fine powder was placed in a round-bottomed cylindrical separable flask (mixer) having an inner diameter of 11 cm and an internal volume of 2 L equipped with a thermometer and a stirrer, and immersed in a water bath adjusted to 1 ° C. The temperature of the polymer fine powder was adjusted. A lithographic blade having a slit was attached to the stirrer as a stirring blade provided with a shaft and a flat plate portion. The flat plate portion of the stirring blade was welded to the shaft and had a curved tip, and four slits extending along the axial direction of the shaft were formed. The four slits were arranged in the width direction of the flat plate portion, the width of the inner two slits was 1 cm, and the width of the outer two slits was 0.5 cm. The length of the flat plate portion was about 10 cm, and the width of the flat plate portion was about 6 cm.

While checking the temperature of the polymer fine powder by contacting the tip of the thermometer with the polymer fine powder, adjust the temperature of the polymer fine powder to 3.5 ° C, and then immediately remove the water bath from the separable flask and separate the separator. The bull flask was placed in an environment of 25 ° C. ± 2 ° C. In this state, while rotating the stirring blade of the stirrer at 284 rpm, 30 g of ion-exchanged water at 3.5 ° C. was put into the flask containing the polymer fine powder at one time. The aggregate (A) was obtained by kneading the mixture of the polymer fine powder and the ion-exchanged water in a separable flask for 60 seconds. After kneading for 60 seconds, the agglomerate (A) was pierced with a 1 cm tip of a thermometer within 5 seconds to measure the temperature of the agglomerate. As a result, the temperature of the agglomerate (A) was 8 ° C. After measuring the temperature of the agglomerate (A), the peeling rate described later was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (A) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including the cut) of the agglomerate (A) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (A).

The dried agglomerate (A) was pulverized by a centrifugal pulverizer (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), and the obtained powder was classified by a sieve having an opening of 850 μm and a sieve having an opening of 180 μm. .. By classification, granulated particles (A), which were fractions that passed through a sieve with a mesh size of 850 μm and did not pass through a sieve with a mesh size of 180 μm, were obtained.

[Surface cross-linking process]
A mixture was obtained by mixing 10 g of the granulated particles (A) with a surface cross-linking agent solution containing 0.031 g of ethylene carbonate, 0.050 g of propylene glycol, and 0.200 g of deionized water. The obtained mixture was heat-treated at 200 ° C. for 35 minutes and then classified with a sieve having an opening of 850 μm to obtain water-absorbent resin particles (A) as a fraction that passed through a sieve having an opening of 850 μm.

(Example 2)
Aggregates (B) were obtained in the same manner as in Example 1 except that the temperature of the ion-exchanged water charged into the separable flask was changed from 3.5 ° C. to 25 ° C. in the granulation step. After kneading for 60 seconds, the agglomerate (B) was pierced with a 1 cm tip of a thermometer within 5 seconds to measure the temperature of the agglomerate. As a result, the temperature of the agglomerate (B) was 32 ° C. After measuring the temperature of the agglomerate (B), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (B) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including the cut) of the agglomerate (B) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (B). The dried agglomerates (B) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (B) were obtained.

Water-absorbent resin particles (B) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (B) in the surface cross-linking step.

(Example 3)
In the granulation process, the temperature of the water bath was adjusted to 10 ° C, the temperature of the polymer fine powder was adjusted to 15 ° C, and the temperature of the ion-exchanged water to be charged into the separable flask was changed from 3.5 ° C to 15 ° C. Agglomerates (C) were obtained in the same manner as in Example 1 except that the mixture was changed to. After kneading for 60 seconds, the agglomerate (C) was pierced with a 1 cm tip of a thermometer within 5 seconds to measure the temperature of the agglomerate. As a result, the temperature of the agglomerate (C) was 19 ° C. After measuring the temperature of the agglomerate (C), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (C) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including the cut) of the agglomerate (C) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (C). The dried agglomerates (C) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and fractions that did not pass through a sieve having an opening of 180 μm. Granulated particles (C) were obtained.

Water-absorbent resin particles (C) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (C) in the surface cross-linking step.

(Example 4)
In the granulation step, the same as in Example 1 except that the temperature of the water bath was adjusted to 65 ° C. and the temperature of the polymer fine powder was adjusted to 60 ° C. to obtain an aggregate (D). After kneading for 60 seconds, the agglomerate (D) was pierced with a 1 cm tip of a thermometer within 5 seconds and the temperature of the agglomerate was measured. As a result, the temperature of the agglomerate (D) was 46 ° C. After measuring the temperature of the agglomerate (D), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (D) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including cut) of the agglomerates (D) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (D). The dried agglomerates (D) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (D) were obtained.

Water-absorbent resin particles (D) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (D) in the surface cross-linking step.

(Example 5)
In the granulation process, the temperature of the water bath was adjusted to 65 ° C, the temperature of the polymer fine powder was adjusted to 60 ° C, and the temperature of the ion-exchanged water to be charged into the separable flask was changed from 3.5 ° C to 25 ° C. Agglomerates (E) were obtained in the same manner as in Example 1 except that the mixture was changed to. After kneading for 60 seconds, the agglomerate (E) was pierced with a 1 cm tip of a thermometer within 5 seconds to measure the temperature of the agglomerate. As a result, the temperature of the agglomerate (E) was 53 ° C. After measuring the temperature of the agglomerate (E), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (E) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including cut) of the agglomerates (E) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (E). The dried agglomerates (E) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (E) were obtained.

Water-absorbent resin particles (E) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (E) in the surface cross-linking step.

(Comparative Example 1)
In the granulation step, the same procedure as in Example 1 was carried out except that the temperature of the ion-exchanged water charged into the separable flask was changed from 3.5 ° C. to 50 ° C. to obtain an aggregate (F). After kneading for 60 seconds, the agglomerate (F) was pierced with a 1 cm tip of a thermometer within 5 seconds and the temperature of the agglomerate was measured. As a result, the temperature of the agglomerate (F) was 39 ° C. After measuring the temperature of the agglomerate (F), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (F) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including cut) of the agglomerates (F) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (F). The dried agglomerates (F) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and fractions that did not pass through a sieve having an opening of 180 μm. Granulated particles (F) were obtained.

Water-absorbent resin particles (F) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (F) in the surface cross-linking step.

(Comparative Example 2)
In the granulation step, the same procedure as in Example 1 was carried out except that the temperature of the ion-exchanged water charged into the separable flask was changed from 3.5 ° C. to 80 ° C. to obtain an aggregate (G). After kneading for 60 seconds, the agglomerate (G) was pierced with a 1 cm tip of a thermometer within 5 seconds and the temperature of the agglomerate was measured. As a result, the temperature of the agglomerate (G) was 40 ° C. After measuring the temperature of the agglomerate (G), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates (G) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including cut) of the agglomerates (G) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (G). The dried agglomerates (G) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (G) were obtained.

Water-absorbent resin particles (G) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (G) in the surface cross-linking step.

(Comparative Example 3)
In the granulation step, the same as in Example 1 except that the temperature of the water bath was adjusted to 85 ° C. and the temperature of the polymer fine powder was adjusted to 80 ° C. to obtain an aggregate (H). After kneading for 60 seconds, the agglomerate (H) was pierced with a 1 cm tip of a thermometer within 5 seconds to measure the temperature of the agglomerate. As a result, the temperature of the agglomerate (H) was 55 ° C. After measuring the temperature of the agglomerate (H), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates (H) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including cut) of the agglomerates (H) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (H). The dried agglomerates (H) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (H) were obtained.

Water-absorbent resin particles (H) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (H) in the surface cross-linking step.

(Comparative Example 4)
In the granulation process, the temperature of the water bath was adjusted to 85 ° C, the temperature of the polymer fine powder was adjusted to 80 ° C, and the temperature of the ion-exchanged water to be charged into the separable flask was changed from 3.5 ° C to 25 ° C. Aggregate (I) was obtained in the same manner as in Example 1 except that it was changed to. After kneading for 60 seconds, the agglomerate (I) was pierced with a 1 cm tip of a thermometer within 5 seconds and the temperature of the agglomerate was measured. As a result, the temperature of the agglomerate (I) was 59 ° C. After measuring the temperature of the agglomerate (I), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates of the agglomerates (I) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount (including cut) of the agglomerates (I) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (I). The dried agglomerates (I) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (I) were obtained.

Water-absorbent resin particles (I) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (I) in the surface cross-linking step.

(Comparative Example 5)
In the granulation process, the temperature of the water bath was adjusted to 85 ° C, the temperature of the polymer fine powder was adjusted to 80 ° C, and the temperature of the ion-exchanged water to be charged into the separable flask was changed from 3.5 ° C to 80 ° C. Agglomerates (J) were obtained in the same manner as in Example 1 except that the mixture was changed to. After stirring for 60 seconds, the agglomerate (J) was pierced with a 1 cm tip of a thermometer within 5 seconds to measure the temperature of the agglomerate. As a result, the temperature of the agglomerate (J) was 65 ° C. After measuring the temperature of the agglomerate (J), the peeling rate was measured within 1 minute.

After finishing the measurement of the peeling rate, the large agglomerates (J) were cut to a size of 3 to 10 mm so that the maximum width of the agglomerates was about 10 mm or less. The entire amount of the agglomerate (J) (including the cut one) was dried by hot air drying at 150 ° C. for 60 minutes to obtain a dried agglomerate (J). The dried agglomerates (J) were pulverized by a centrifugal crusher (ZM200 manufactured by Retsch, screen diameter 1 mm, 6000 rpm), passed through a sieve having an opening of 850 μm, and did not pass through a sieve having an opening of 180 μm. Granulated particles (J) were obtained.

Water-absorbent resin particles (J) were obtained in the same manner as in Example 1 except that the granulated particles (A) were changed to the granulated particles (J) in the surface cross-linking step.

The water content, peeling rate, and performance of the water-absorbent resin particles of the polymer fine powder were measured by the following procedure. Table 1 shows the measured peeling rate and the evaluation results of the water-absorbent resin particles.

<Measurement method of water content>
The water content of the polymer fine powder was measured by the following method. 2.0 g of polymer fine powder was weighed as a measurement sample in a pre-constant aluminum foil case (No. 8, mass W1 (g)), and the total mass W2 (g) was precisely weighed. After precision weighing, the aluminum foil case and the measurement sample were dried for 2 hours in a hot air dryer (manufactured by ADVANTEC, model: FV-320) whose internal temperature was set to 200 ° C. After allowing the dried aluminum foil case and the measurement sample to cool in a desiccator, the total mass W3 (g) of the aluminum foil case and the measurement sample was precisely weighed. The water content of the measurement sample was calculated from the following formula.
Moisture content (% by mass) = [{(W2-W1)-(W3-W1)} / (W2-W1)] × 100

<Peeling rate>
A round-bottomed cylindrical flask with an internal volume of 2 L containing agglomerates was turned upside down by 180 ° over 3 seconds on a receiver. At this time, the weight of the agglomerates that fell on the receiver was measured and used as the peeling amount [g]. The peeling rate was calculated from the measured peeling amount and the charged amount [g] (total of 30 g of agglomerates and 30 g of ion-exchanged water) from the following formula. The measurement was performed in an environment with a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. When the peeling rate is large (for example, the peeling rate is 70% or more), it can be said that the agglomerates can be efficiently recovered from the mixer.
Peeling rate [%] = peeling amount / charging amount x 100

<Centrifugal holding capacity>
The centrifuge holding capacity (CRC) was measured by the following procedure with reference to the EDANA method (NWSP 241.0.R2 (15), pages 769 to 778). The measurement was performed in an environment where the temperature was 25 ° C. ± 2 ° C. and the humidity was 50% ± 10%.

A non-woven fabric having a size of 60 mm × 170 mm (product name: Heat Pack MWA-18, manufactured by Nippon Paper Papylia Co., Ltd.) was folded in half in the longitudinal direction to adjust the size to 60 mm × 85 mm. A 60 mm × 85 mm non-woven fabric bag was produced by crimping the non-woven fabrics to each other with a heat seal at each end in the lateral direction (a crimping portion having a width of 5 mm was formed at each end in the lateral direction along the longitudinal direction). .. 0.2 g of particles to be measured (water-absorbent resin particles) were precisely weighed and contained inside the non-woven fabric bag. Then, the non-woven fabric bag was closed by crimping the end portion opposite to the folded portion in the longitudinal direction with a heat seal.

The entire non-woven fabric bag was completely moistened by floating the non-woven fabric bag on 1000 g of physiological saline placed in a stainless steel vat (240 mm × 320 mm × height 45 mm) without folding the non-woven fabric bag. One minute after the nonwoven fabric bag was floated on the saline solution, the nonwoven fabric bag was immersed in the saline solution using a spatula to obtain a nonwoven fabric bag containing the gel.

Thirty minutes after the non-woven fabric bag was put into the physiological saline solution (a total of 1 minute of floating time and 29 minutes of immersion time), the non-woven fabric bag was taken out from the physiological saline solution. The non-woven fabric bag taken out was placed in a centrifuge (manufactured by Kokusan Co., Ltd., model number: H-122), and the non-woven fabric bag was dehydrated for 3 minutes after the centrifugal force in the centrifuge reached 250 G. After dehydration, the mass Ma [g] of the non-woven fabric bag containing the mass of the gel was weighed. The same operation was performed on the non-woven fabric bag not containing the particles to be measured, and the mass Mb [g] of the non-woven fabric bag after dehydration was measured. The CRC [g / g] was calculated based on the following formula, with the scale value of 0.2 g of the mass of the particles to be measured used for the measurement as Mc [g].
CRC = [(Ma-Mb) -Mc] / Mc

<Water absorption ratio under pressure>
The absorption magnification (AAP) under a pressure of 2.07 kPa (0.3 psi) was measured using the measuring device 110 shown in FIG. First, a weight 112 (cross section: circular, total weight: 577.38 g) adjusted to a pressure of 2.07 kPa, a plastic cylinder 114 having an inner diameter of 60 mm, and one end (bottom surface) of the cylinder 114 were arranged. A measuring device 110 provided with a wire mesh 116 having a 400 mesh (opening 38 μm) was prepared. The weight 112 is a cylinder having a disc portion 112a (diameter 59 mm), a rod-shaped portion 112b extending from the center of the disc portion 112a in a direction perpendicular to the disc portion 112a, and a through hole inserted into the rod-shaped portion 112b in the center. It has a portion 112c and. The disk portion 112a of the weight 112 has a diameter substantially equal to the inner diameter of the cylinder 114 so that it can move in the longitudinal direction of the cylinder 114 inside the cylinder 114. The diameter of the cylindrical portion 112c is smaller than the diameter of the disc portion 112a. One end of the cylinder 114 is open but shielded by the wire mesh 116, and the other end of the cylinder 114 is open so that the weight 112 can be inserted. Inside the cylinder 114, 0.90 g of measurement target particles (water-absorbent resin particles) 120 were uniformly sprayed on the wire mesh 116. Then, after the weight 112 is inserted inside the cylinder 114 and the weight 112 is placed on the measurement target particle 120, the total mass of the measuring device 110 (the total mass of the measuring device 110 and the measurement target particle 120 before liquid absorption). Wa [g] was measured.

After placing a glass filter 140 (ISO4793 P-250) with a diameter of 90 mm and a thickness of 7 mm in the center of the bottom surface of the recess of the stainless petri dish 130 with a diameter of 150 mm, 0 so that the water surface is at the same height as the upper surface of the glass filter 140. A 90% by mass aqueous sodium chloride solution (25 ° C ± 2 ° C) was added. A sheet of filter paper 150 with a diameter of 90 mm (manufactured by ADVANTEC Toyo Co., Ltd., product name: (No. 3), thickness 0.23 mm, reserved particle diameter 5 μm) was placed on the glass filter 140 so that the entire surface was wet. And the excess liquid was removed. Then, the above-mentioned measuring device 110 was placed on the filter paper 150, and the liquid was absorbed under a load. After 1 hour, the measuring device 110 was lifted and the total mass of the measuring device 110 (total mass of the measuring device 110 and the particles 120 to be measured after absorbing liquid) Wb [g] was measured. From Wa and Wb, the absorption rate (AAP) [g / g] under 2.07 kPa pressurization was calculated based on the following formula.
AAP [g / g] = (Wb [g] -Wa [g]) /0.90 [g]

<Unpressurized DW>
The non-pressurized DW of the water-absorbent resin particles was measured using the measuring device Z shown in FIG. The measurement was performed 5 times for one type of water-absorbent resin particles, and the average value of the measured values at 3 points excluding the minimum value and the maximum value was obtained.

The measuring device Z has a burette portion 71, a conduit 72, a flat plate-shaped measuring table 73, a nylon mesh 74, a frame 75, and a clamp 76. The burette portion 71 was connected to a burette 71a on which a scale was written, a rubber stopper 71b for sealing the opening at the upper portion of the burette 71a, a cock 71c connected to the tip of the lower portion of the burette 71a, and a lower portion of the burette 71a. It has an air introduction pipe 71d and a cock 71e. The burette portion 71 is fixed by a clamp 76. The measuring table 73 has a through hole 73a having a diameter of 2 mm formed in the center thereof, and is supported by a frame 75 having a variable height. The through hole 73a of the measuring table 73 and the cock 71c of the burette portion 71 are connected by a conduit 72. The inner diameter of the conduit 72 is 6 mm.

The measurement was performed in an environment with a temperature of 25 ° C. and a humidity of 60 ± 10%. First, the cock 71c and the cock 71e of the burette portion 71 were closed, and the physiological saline 77 adjusted to 25 ° C. was put into the burette 71a through the opening at the upper part of the burette 71a. After sealing the opening of the burette 71a with the rubber stopper 71b, the cock 71c and the cock 71e were opened. The inside of the conduit 72 was filled with saline 77 to prevent air bubbles from entering. The height of the measuring table 73 was adjusted so that the height of the water surface of the physiological saline 77 that reached the inside of the through hole 73a was the same as the height of the upper surface of the measuring table 73. After the adjustment, the height of the water surface of the physiological saline 77 in the burette 71a was read by the scale of the burette 71a, and the position was set as the zero point (reading value at 0 seconds).

A nylon mesh 74 (100 mm × 100 mm, 250 mesh, thickness: about 50 μm) was laid in the vicinity of the through hole 73a on the measuring table 73, and a cylinder having an inner diameter of 30 mm and a height of 20 mm was placed in the center thereof. 1.00 g of water-absorbent resin particles 78 were uniformly sprayed on this cylinder. Then, the cylinder was carefully removed to obtain a sample in which the water-absorbent resin particles 78 were dispersed in a circle in the central portion of the nylon mesh 74. Next, the nylon mesh 74 on which the water-absorbent resin particles 78 were placed was quickly moved so that the center thereof was at the position of the through hole 73a so that the water-absorbent resin particles 78 did not dissipate, and the measurement was started. The time when air bubbles were first introduced into the burette 71a from the air introduction pipe 71d was defined as the start of water absorption (0 seconds).

The decrease amount of the physiological saline 77 in the burette 71a (that is, the amount of the physiological saline 77 absorbed by the water-absorbent resin particles 78) is sequentially read in units of 0.1 mL, and calculated from the start of water absorption of the water-absorbent resin particles 78. After 3 minutes, the weight loss Wc [g] of the physiological saline 77 was read. From Wc, the ternary value of non-pressurized DW was obtained by the following formula. The non-pressurized DW is the amount of water absorbed per 1.00 g of the water-absorbent resin particles 78.
Unpressurized DW value [mL / g] = Wc / 1.00

From Table 1, the mixture obtained by mixing the polymer fine powder having a temperature of 0 ° C. or higher and lower than 70 ° C. and water (aqueous liquid) having a temperature of 0 ° C. or higher and lower than 40 ° C. is kneaded and aggregated. It can be confirmed that the releasability of the agglomerates from the mixer is improved by obtaining the above. Further, from Table 1, when Examples 1 to 5 and Comparative Examples 1 to 5 are compared, the temperature of the polymer fine particles to be mixed is 0 ° C. or higher and lower than 70 ° C., and the temperature of water is 0 ° C. or higher and lower than 40 ° C. Even so, it can be confirmed that the performance of the obtained water-absorbent resin particles can be substantially maintained.

71a ... burette, 71b ... rubber stopper, 71c, 71e ... cock, 71d ... air introduction pipe, 72 ... conduit, 73 ... measuring table, 73a ... through hole, 74 ... nylon mesh, 75 ... pedestal, 76 ... clamp, 77 ... Physiological saline, 78 ... water-absorbent resin particles, 114 ... cylinder, 110 ... measuring device, 112 ... weight, 112a ... disk part, 112b ... rod-shaped part, 112c ... columnar part, 116 ... wire mesh, 120 ... particles to be measured, 130 ... Stainless steel burette, 140 ... Glass filter, 150 ... Filter paper, Z ... Measuring device.

Claims (4)

A method for producing water-absorbent resin particles containing granulated particles.
A mixture is formed by mixing a polymer fine powder having a temperature of 0 ° C. or higher and lower than 70 ° C. and an aqueous liquid containing water having a temperature of 0 ° C. or higher and lower than 40 ° C., and the mixture is kneaded in a mixer. By doing so, the step of obtaining the agglomerates of the polymer fine powder and
A step of obtaining the dried agglomerates by removing at least a part of water from the agglomerates taken out from the mixer.
The step of crushing the dried agglomerates to form granulated particles, and
Including, how. The method of claim 1, wherein the temperature of the mixture is less than 70 ° C. while the mixture is being kneaded. The method according to claim 1 or 2, wherein the difference between the temperature of the polymer fine powder and the temperature of the aqueous liquid containing water at the time of mixing the polymer fine powder and the aqueous liquid is 60 ° C. or less. Claims 1 to 3 in which the amount of the aqueous liquid mixed with the polymer fine powder is 80 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass by mass of the portion of the polymer fine powder excluding water. The method described in any one of the above.

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