JP2002121291A - Water-absorbing resin powder and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a water-absorbing resin powder excellent in particle size distribution and physical properties, preventing their adhesion and coagulation in their production process, also excellent in energy efficiency, drying efficiency and productivity. SOLUTION: The method for producing the water-absorbing resin powder comprises heating for drying a water-containing gel state cross linked polymer obtained by polymerizing an aqueous monomer solution containing a cross linking agent and then crushing, and is characterized by having 200-600 μm range mean particle diameter of the water-absorbing resin particles after crushing and <=15 wt.% ratio of particles having 150-850 μm diameter, and compulsorily cooling the dried polymer after the heat-drying before the crushing or at the crushing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water-absorbent resin powder and a method for producing the same. More specifically, a method for producing a water-absorbent resin powder having excellent particle size distribution and physical properties, which prevents adhesion and agglomeration in the production process and provides a production method that is further excellent in energy efficiency, drying efficiency, and productivity. Is what you do. Furthermore, in a method of obtaining a modified water-absorbing resin powder by adding an aqueous liquid to the obtained powder, even if a special mixer or an organic solvent is not particularly used, the uniform mixing of the aqueous liquid is further improved. And a method for further improving the physical properties of the water-absorbent resin powder.

[0002]

2. Description of the Related Art In recent years, for the purpose of absorbing a large amount of water, a water-absorbent resin has been widely used as one of materials constituting sanitary materials such as disposable diapers, sanitary napkins, incontinence pads and the like. In addition to hygienic materials, water-absorbing resins are widely used for the purpose of absorbing and retaining water, such as soil water retention agents and drip sheets for foods and the like. As the above water-absorbing resin, for example, a cross-linked polyacrylic acid partially neutralized product,
Starch-hydrolyzate of acrylonitrile copolymer, starch-
Neutralized acrylic acid graft polymer, saponified vinyl acetate-acrylic acid ester copolymer, hydrolyzed product of acrylonitrile copolymer or acrylamide copolymer or cross-linked product thereof, cross-linked carboxymethyl cellulose, 2-acrylamide A crosslinked copolymer of 2-methylpropanesulfonic acid (AMPS), a crosslinked product of polyethylene oxide, a crosslinked product of polyallylamine, a crosslinked product of polyelemine, and the like are known, and most of them are used in powder form.

As a method for producing these water-absorbent resins, a water-containing gel-like cross-linked polymer obtained by polymerizing an aqueous solution of a monomer containing a cross-linking agent, if necessary, is dried and further pulverized, if necessary, to obtain a powder. Although the method of obtaining is the mainstream, the hydrogel crosslinked polymer of the water-absorbing resin has a high water-absorbing ability,
Due to the tackiness, adhesion, and low heat resistance, drying and pulverization after drying were extremely difficult, the productivity was low, and the physical properties and energy efficiency of the resulting water-absorbent resin were very poor. As a method for drying the water-containing gel-like crosslinked polymer of the water-absorbent resin, for example, drum dryer drying (Japanese Patent Laid-Open No.
4-53165), a method of mixing a dried powdery acrylic acid polymer and a hydrogel and stirring and drying the mixture (Japanese Patent Application Laid-Open No. 57-57).
117551), azeotropic dehydration (JP-A-57-1987)
No. 14), drying at a specific dew point (JP-A-1-26604 / US Pat. No. 4,920,202), and freeze-drying (JP-A-1-26204).
304127, JP-A-1-304128), a method of stirring and drying in a cylindrical dryer (JP-A-2-240112)
US Pat. No. 5,275,773), a method in which a gel is extruded through specific pores and then dried (US Pat. No. 5,275,773).
), Microwave drying (JP-A-5-209010 / U.S. Pat. No. 5,075,344), a method of drying with hot air after using a specific gel shredding machine (JP-A-5-230124),
A method of drying with hot air while measuring the differential pressure (Japanese Patent Laid-Open No. 8-73)
No. 518), a method of adding a surfactant and drying by stirring (Japanese Patent Application Laid-Open No. 8-134134), a method of drying by standing, pulverizing, and then stirring or fluid-drying (Japanese Patent Application Laid-Open No. 11-24).
No. 0914 / European Patent No. 0926162).

[0004] Further, for drying, a drying method of laminating a hydrogel cross-linked polymer on a punching metal or a wire mesh is known. Due to the adhesion and clogging, particularly in hot air drying, there is a problem that the drying efficiency is greatly reduced due to a decrease in air permeability. Therefore, in order to prevent such adhesion and clogging, a drying method using a special conveyor having pins (Japanese Patent Laid-Open No. 7-270070 / German Patent 19511769).
No.) is also known. Further, in addition to physical properties (water absorption capacity, water-soluble content, liquid permeability, etc.), the particle size distribution of the water-absorbent resin is important.
No. 132802 / US Pat. No. 5,061,259;
-196802 / U.S. Pat. No. 5,244,735, JP-A-2-191604 / US Pat. No. 4,973,632, JP-A-6-507564 / US Pat. No. 5,419,956, and EP-0629411) are also known. Water-absorbing resin having a plurality of distributions (EP08452
No. 72, JP-A-11-130978) are also known.

[0005] Therefore, efficient classification is required as a classification method for adjusting the target particle size. As a classification method for a water-absorbent resin after drying, a method using a heated or heated sieve (Japanese Patent Laid-Open No. -202187 / European Patent 0
855232) and a method using a classification network coated with Teflon or the like (JP-A-11-156299) are also known. A method of classifying undried matter before drying or during the pulverizing step (Japanese Patent Application Laid-Open No. 11-292919 / European Patent 0
No. 948997) is also known. However, even in these methods, the water-absorbent resin and its hydrogel cross-linked polymer are very difficult to dry or pulverize after drying due to their high water-absorbing ability and tackiness, and low heat resistance. The properties and particle size distribution of the resulting water-absorbent resin are reduced, and
Energy efficiency and productivity were very poor. In addition, agglomeration of the powder is observed in the production process even after pulverization or classification, which causes a problem that production efficiency and quality are reduced.

Further, there is known a method for improving the particle size distribution and absorption under pressure characteristics of a water-absorbent resin powder by adding water alone or an aqueous liquid containing additives to the obtained polymer powder. The method involves granulation (US Pat. No. 5,369,148).
No. 5) and surface crosslinking (US Pat. Nos. 5,409,771 and 542).
Nos. 2405 and 5597873) and reduction of residual epoxy compounds (US Pat. No. 5,981,070). However, since the water-absorbing resin instantaneously absorbs water and exhibits adhesiveness, conventionally, the uneven mixing of the aqueous liquid has not only led to an insufficient improvement in the physical properties, and in some cases, the water-absorbing resin has an unsatisfactory property. Agglomerates of the water-absorbing resin produced by the uniform mixing adhered to the mixer, making continuous operation itself difficult. In addition, polyhydric alcohol as a cross-linking agent or its solvent is also preferable in terms of physical properties and safety, but because of its high hydrophilicity and viscosity, evenly mixing these polyhydric alcohol aqueous solutions into the water-absorbent resin among these aqueous liquids Was particularly difficult.

Therefore, when a water-based resin powder is modified by adding an aqueous liquid, a special mixer is used (European Patent No. 045).
0923, EP0812873, etc.), the use of inorganic powders (US Pat. No. 4,587,308), and the technique of using an organic solvent in an aqueous liquid (US Pat. No. 4,734,478) are known. The use of a volatile organic solvent has been accompanied by a problem of causing deterioration in physical properties in addition to cost, environmental problems and safety. Furthermore, when adding an aqueous liquid to a water-absorbent resin, the properties of the resin (AUL / Absorbency un
der Load) in a specific range (WO98 / 4)
No. 9221) is also known, but in such a method, the applied water-absorbent resin powder is very limited and its production is difficult.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to efficiently dry a hydrogel cross-linked polymer without thermal deterioration due to the above-mentioned current situation. Or by grinding and adjusting the particle size, it is possible to produce a water-absorbent resin powder having a narrow particle size distribution and high physical properties, while preventing adhesion and agglomeration in the production process,
It is another object of the present invention to provide a manufacturing method that is energy efficient and exhibits high productivity. Furthermore, in the method of adding an aqueous liquid, the mixing property is further improved, and the water absorption is achieved by adding a uniform aqueous liquid (particularly an aqueous solution of a crosslinking agent or an aqueous solution of polyhydric alcohol) without using a special mixer or an organic solvent. Another object of the present invention is to improve the physical properties of the conductive resin powder.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, after heating and drying a hydrogel cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent, A method for producing a water-absorbent resin powder to be crushed,
The average particle diameter of the water-absorbent resin powder after the pulverization is 200 to 6
00 μm, and 150 μm or less to 8 μm.
The production method characterized in that the ratio of particles having a particle size of 50 μm or more is 15% by weight or less and the dried polymer after heating and drying is cooled before or during pulverization. Further, the present inventors have found that heat deterioration and adhesion during drying are extremely small, and that pulverization after drying is extremely efficient, and the present invention has been completed.

Further, by cooling the water-absorbent resin powder and further adjusting the bulk specific gravity, the mixing property of an aqueous liquid (particularly, an aqueous solution of a cross-linking agent or an aqueous solution of a polyhydric alcohol), which has been difficult in the past, is improved. The inventors have found that the physical properties can be improved and completed the present invention. That is, the method for producing a water-absorbent resin powder according to the present invention is a method for producing a water-absorbent resin powder in which a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated, dried, and then pulverized. The average particle diameter of the water-absorbent resin powder after the pulverization is in the range of 200 to 600 μm, and the ratio of particles of 150 μm or less to 850 μm or more is 15% by weight or less. It is characterized by cooling before or during grinding.

Another method for producing a water-absorbent resin powder according to the present invention is to provide a method for producing a water-absorbent resin powder by heating and drying a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent. Wherein the heat obtained by forcibly cooling the dried polymer after heating and drying is reused for forced heating in the process of producing the water-absorbent resin. Also,
Another method for producing a water-absorbent resin powder according to the present invention is to heat and dry a hydrogel crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent, and then pulverize the powder obtained in a mixing machine. A method for producing a water-absorbent resin powder by adding an aqueous liquid, wherein the heating and drying temperature is in the range of 110 to 230 ° C, cooling the dried polymer to 80 to 35 ° C before adding the aqueous liquid, and , The bulk specific gravity of the dry polymer after grinding is 0.6
It is characterized by being at least 5 g / ml.

Further, another method for producing a water-absorbent resin powder according to the present invention is obtained by heating and drying a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent, followed by pulverization. A method for producing a water-absorbent resin powder in which an aqueous liquid is added to a powder in a mixer, wherein the heating and drying temperature is 110 to 230 ° C.
That the dry polymer is 80 to 80% before addition of the aqueous liquid.
Cooling to 35 ° C., and when the inner wall temperature of the mixer is 4
A stirring mixer at 0 ° C. or higher;
It is characterized by reheating to 30 ° C.

Another method for producing a water-absorbent resin powder according to the present invention is to provide a water-absorbent resin powder obtained by heating and drying a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent and then pulverizing it. Wherein the dried polymer after heating and drying is forcibly cooled; the dried polymer is pulverized into a water-absorbent resin powder having a bulk specific gravity of 0.65 g / ml or more; The powder is further subjected to surface crosslinking.

Another method for producing a water-absorbent resin powder according to the present invention is to provide a method for producing a water-absorbent resin powder by heating and drying a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent. Wherein the dried polymer after heating and drying is forcibly cooled; the dried polymer is pulverized into a water-absorbent resin powder having a bulk specific gravity of 0.65 g / ml or more; It is characterized in that an aqueous liquid is further added to the powder, and the aqueous liquid is added by a stirring mixer whose inner wall is heated.

Further, the water-absorbent resin powder according to the present invention is a water-absorbent resin powder having an absorption capacity under pressure (1.96 kPa) of 25 g / g or more obtained through any of the production methods of the present invention. The absorbent article according to the present invention contains the water absorbent resin powder. Further, another water-absorbent resin powder according to the present invention is obtained by heating and drying a hydrogel cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent, and then pulverizing the obtained powder in a mixer. (1) Bulk specific gravity obtained by adding a polyhydric alcohol aqueous solution containing no volatile organic solvent is 0.65 g / ml.
As described above, (2) the average particle diameter is 200 to 600 μm, and (3) 1
The total of particles of 50 μm or less to 850 μm or more is 10
% Or less, (4) a water-absorbent resin powder having an absorbency against pressure (1.96 kPa) of 25 g / g or more, and another absorbent article according to the present invention contains the water-absorbent resin powder.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. The method for producing a water-absorbent resin powder of the present invention is a method for producing a water-absorbent resin powder, which is obtained by heating and drying a hydrogel cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent, followed by grinding. The average particle size of the water-absorbent resin powder after pulverization is in the range of 200 to 600 μm, and the ratio of particles having a size of 150 μm or less to 850 μm or more is 15% by weight or less. This is a production method characterized by occasionally cooling.

First, the method for producing the hydrogel crosslinked polymer of the present invention will be described below. The water-absorbent resin in the present invention is 3 to 100 of its own weight under no load during saturated swelling.
0 times, preferably 5 to 1000 times, more preferably 10 times
A crosslinked polymer capable of absorbing 交換 800-fold, more preferably 100-700-fold ion-exchanged water to form a water-insoluble swollen hydrogel. In the present invention, the term "water-insoluble" generally means that the amount of water-soluble components in the water-absorbent resin is 40% by weight or less, preferably 20% by weight or less, and more preferably 15% by weight or less.
% By weight, particularly preferably 10% by weight or less, most preferably 5% by weight or less. In addition, the measuring method of these physical properties is demonstrated in the column of the below-mentioned Example. If the amount of the water-soluble component is large, not only the physical properties (absorption under pressure, amount of liquid passing under pressure, etc.) are lowered, but also it becomes difficult to uniformly add the aqueous liquid of the water-absorbing resin powder, which is not preferable.

The hydrogel crosslinked polymer used in the method for producing a water absorbent resin powder according to the present invention is a polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. Examples of the water-containing gel-like crosslinked polymer include one or a mixture of water-absorbing cationic, anionic, and nonionic crosslinked polymers.From the viewpoint of maximizing the effects of the present invention,
Preferably, the anionic crosslinked polymer is essentially used as a main component, and more preferably, the main component of the functional group is a carboxyl group. In the present invention, the anionic crosslinked polymer is preferably a water-containing gel-like crosslinked polymer using acrylic acid (salt) as the acid group-containing unsaturated monomer (salt) because of its effect. It is further preferable that the crosslinked polymer is a hydrogel cross-linked polymer obtained by polymerizing 90 mol%, more preferably 0 to 80 mol% of neutralized acrylic acid (salt), and in particular, 0 to 10 mol% is neutralized. It is even more preferred that the polymer is a hydrogel crosslinked polymer obtained by polymerizing acrylic acid (salt). That is, conventionally, in the crosslinked polyacrylic acid, particularly the crosslinked polyacrylic acid which is unneutralized or lowly neutralized, the physical property is greatly reduced in the drying step and the pulverizing step. Therefore, the method of the present invention is suitably applied.

The above-mentioned monomer contains the above-mentioned acrylic acid (salt) as a main component, and if necessary, other monomers other than the above-mentioned acrylic acid (salt), ie, the above-mentioned acrylic acid (salt). Other copolymerizable monomers may be included, and a water-absorbing resin may be obtained from a monomer other than acrylic acid. The monomer other than acrylic acid used is not particularly limited, but specifically, for example, methacrylic acid, maleic acid, crotonic acid, sorbic acid, itaconic acid, cinnamic acid, maleic anhydride , Vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfone Acid, unsaturated monomer containing an acid group such as 2-hydroxyethyl (meth) acryloyl phosphate and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2- Hydroxyethyl (meth) acrylate, 2-hydroxypro Unsaturated non-hydrophilic group-containing unsaturated monomer such as meth (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, And the like. One of these other monomers may be used alone, or two or more of them may be used as a mixture. When these other unsaturated monomers are used, the ratio of the other unsaturated monomers in the monomer containing acrylic acid is 50 mol%.
The content may be set to be equal to or less than 30 mol% or less.

When an acid group-containing monomer or a base-containing monomer is used in the present invention, the acid group-functional group or the base functional group of the monomer or polymer may be neutralized. The neutralizing agent used in the present invention is not particularly limited, and a known inorganic or organic base or acid can be used for the monomer or the polymer. For example, when an acid group-containing monomer is used in the present invention, specific examples of the base of the monomer or polymer neutralizer include, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, and carbonate. Lithium, ammonium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate,
Inorganic bases such as ammonium bicarbonate, ethanolamine, diethanolamine, triethanolamine, polyethyleneimine, polyallylamine, (poly) lysine,
Organic bases such as (poly) arginine. When a base-containing monomer is used in the present invention, similarly, an inorganic acid or an organic acid is appropriately selected as a neutralizing agent.

When a high-molecular neutralizing agent (for example, polyamine) is used, a crosslinked product may be used. Among these neutralizing agents, alkali metal salts, particularly lithium salts and sodium salts, are preferably used. 50 of the acid groups of the resin
~ 90 mol%, furthermore 60-80 mol% are neutralized. The final neutralization ratio of the water absorbent resin obtained in the present invention is preferably in the above range. The neutralization may be carried out as an aqueous solution, dispersion or gel of the above base or acid, or may be carried out by so-called dry blending (powder mixing) in which the base or acid is added as a solid. In addition, the neutralization may be a monomer, may be performed with a hydrogel crosslinked polymer before drying, or may be performed on a dried polymer or a pulverized product or a classified product after drying. Neutralization may be used in combination. Further, the neutralization may completely react the acid group and the base, or only partially react by a method such as dry blending, to obtain a water-absorbent resin composition that is a mixture of the acid group and the base. It may be neutralized by obtaining.

In the case of neutralization according to the present invention, post-neutralization, particularly post-neutralization of a dry polymer, is a preferred method of the present invention. One. That is, in the present invention, the unneutralized or low-neutralized crosslinked polyacrylic acid can be efficiently dried (pulverized) without deteriorating its physical properties. Therefore, the method of post-neutralizing the crosslinked polyacrylic acid powder is preferable because a water absorbent resin having higher physical properties can be obtained. When the above hydrogel cross-linked polymer is obtained, the means may be radical cross-linking or self-cross-linking as long as the polymer becomes water-insoluble, but the cross-linked structure is usually formed using an internal cross-linking agent. To be introduced inside. The internal crosslinking agent may be a compound having a plurality of polymerizable unsaturated groups and / or reactive groups in one molecule, and may have a plurality of substituents in one molecule which copolymerize and / or react with a monomer. Any compound may be used. Also,
When a compound having a plurality of reactive substituents in one molecule is used, a cross-linking agent may be uniformly added to a water-soluble or water-insoluble polymer gel after polymerization to post-crosslink the inside.

Specific examples of the internal crosslinking agent include N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, Trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate,
Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, Triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether,
Ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol,
Examples thereof include ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate, but are not particularly limited.

These internal crosslinking agents may be used alone or in combination of two or more. It is preferable to use an internal cross-linking agent having a plurality of polymerizable unsaturated groups in one molecule at the time of polymerization among the internal cross-linking agents exemplified above, since the physical properties of the obtained water-absorbing resin can be further improved. The amount of the internal cross-linking agent used depends on the type of the cross-linking agent and the desired cross-linking density, but is preferably 0.005 to 3 mol%, more preferably 0.01 to 3 mol%, based on the monomer.
-1.5 mol%, more preferably 0.05-1 mol%
Used in the range. The amount of the internal crosslinking agent used is 0.0
If the amount is less than 05 mol% or more than 3 mol%, there is a possibility that a water-absorbing resin having desired physical properties cannot be obtained.

In the above polymerization, starch, starch derivative, cellulose, cellulose derivative,
Hydrophilic polymers such as polyvinyl alcohol, polyacrylic acid (salt) and crosslinked polyacrylic acid (salt) (the addition amount of the above is 0 to 4 with respect to 100 parts by weight of monomer)
0 parts by weight, more preferably 0 to 10 parts by weight); a chain transfer agent such as hypophosphorous acid (salt), a chelating agent,
A blowing agent such as a carbonate or the like (the addition amount of the above-mentioned compounds is preferably 0 to 5 parts by weight, more preferably 0 to 1 part by weight based on 100 parts by weight of the monomer).
The method for polymerizing the above monomers is not particularly limited, and for example, known methods such as aqueous solution polymerization, reversed phase suspension polymerization, bulk polymerization, and precipitation polymerization can be employed.
Among these, from the viewpoint of easy control of the polymerization reaction and the performance of the obtained water-absorbent resin, in the present invention, a method of polymerizing a monomer component into an aqueous solution, that is, aqueous solution polymerization and reverse phase suspension polymerization are used. preferable.

The reversed-phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, US Pat.
46261, 4683274, 5244735
And US patents. Aqueous solution polymerization is a method of polymerizing a monomer aqueous solution without using a dispersion solvent. For example, US Pat. No. 4,625,001 and US Pat.
Nos. 4286082, 4973632, 49
No. 85518, No. 5124416, No. 5250640
Nos. 5,264,495, 5,145,906, 53
U.S. Patents such as 80808;
No. 6, No. 0955086, No. 0922717, and the like. The present invention is not particularly limited to the polymerization method including these, but the present invention is particularly preferably used for aqueous solution polymerization, which has conventionally been difficult to dry and pulverize.

When the aqueous solution polymerization and the reversed phase suspension polymerization are employed as the above polymerization method, the concentration of the monomer component, that is, the ratio of the monomer in the aqueous solution is not particularly limited, but the physical properties are not limited. From 10 to 70% by weight, more preferably from 15 to 60% by weight, even more preferably from 20 to 70% by weight.
To 50% by weight, particularly preferably 30 to 45% by weight. The reaction conditions such as reaction temperature and reaction time are as follows:
It may be appropriately set according to the monomer used, and is not particularly limited, but is usually in the range of 0 ° C to the boiling point or lower, preferably 10 to 110 ° C, more preferably 15 to 100 ° C (minimum to The polymerization is carried out at the maximum temperature (or the starting temperature to the peak temperature), and the polymerization is preferably carried out in an atmosphere of an inert gas such as nitrogen. Further, the atmosphere during the polymerization may be reduced or increased in pressure, but is usually performed at normal pressure.

To initiate the polymerization, for example, potassium persulfate,
A radical polymerization initiator such as ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, or an ultraviolet polymerization initiator is used as required. All active energy rays such as ultraviolet rays and electron beams can be used, and these may be used in combination. When such an oxidizing radical polymerization initiator is used, for example, sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-
Redox polymerization may be carried out using a reducing agent such as ascorbic acid in combination. The amount of these polymerization initiators used is 0.001.
The range is preferably from 2 to 2 mol%, more preferably from 0.01 to 0.5 mol%. Incidentally, the polymerization initiator is usually
It may be added by dissolving or dispersing in a solvent such as water.

The crosslinked hydrogel polymer obtained by the above polymerization is finely divided as necessary and then dried.
In the present invention, drying is preferably performed in terms of physical properties as well.
(Preferably 1 cm or less, more preferably 5 mm or less). As the fragmentation method for converting the hydrogel crosslinked polymer into particles in the present invention, the fragmentation may be performed simultaneously with the polymerization using a kneader or the like, or the fragmentation may be separately performed after the polymerization. Alternatively, the fragmentation during polymerization and the fragmentation after polymerization may be used in combination. If the hydrogel polymer is not dried in the form of particles, for example, in the form of a film,
Physical properties and particle size may be poor.

The particle size of the hydrogel crosslinked polymer prior to drying is preferably from 45 to 4000 μm, more preferably from 5 to 4000 μm in terms of drying efficiency and physical properties.
0 to 2000 μm, more preferably 100 to 1500 μ
m, more preferably in the range of 200 to 1000 μm. Apparatus suitable for such subdivision include, for example, a kneader, a vertical slitter with a cutter blade, a horizontal slitter with a cutter blade, a cutter-type crusher with a rotary blade, and a predetermined hole diameter. A meat chopper can be exemplified. If the weight-average particle size of the hydrogel cross-linked polymer is out of the above range, the resulting water-absorbent resin powder may cause a decrease in water absorption capacity or an increase in water-soluble components.

The hydrogel crosslinked polymer thus obtained is essentially heated and dried. The drying in the present invention means that the above hydrogel crosslinked polymer has a solid content of 80% by weight or more,
The solid state is preferably 85% by weight or more, more preferably 90% by weight or more, and particularly preferably 93% by weight or more. Further, such drying in the present invention does not necessarily need to be a dry polymer having a solid content of 100% by weight (zero moisture), and is preferably 99% by weight or less, more preferably 98% by weight or less, and still more preferably 98% by weight or less. Preferably no more than 97% by weight, most preferably 97-93% by weight
The hydrated gel-like crosslinked polymer is dried up to the range of.

That is, when the solid content after drying is high, the physical properties due to surface cross-linking are also easily improved, and the powder is less likely to coagulate in the subsequent production process and is easier to handle with the powder. Not only is required, but also a decrease in physical properties may be caused by an increase in fine powder at the time of pulverization, subsequent steps or use, or drying for a long time. However, in the present invention in which forced cooling is performed after drying, in order to prevent agglomeration of the powder in the production process and to pulverize the dried polymer, the solid content of the excessively dried polymer or the water-absorbent resin powder is reduced as in the related art. Since it is not necessary to raise, the drying time can be shortened and the physical properties can be improved. The heating drying method used in the present invention is not particularly limited, and may be, for example, one of drying methods such as hot air drying, thin film drying using a drum dryer, a reduced pressure drying method, stirring drying, and fluidized bed drying. Two or more kinds can be used, and continuous or batch drying is not particularly limited.
Among these, from the viewpoint of physical properties and drying efficiency, in the present invention, hot-air drying, particularly continuous hot-air drying, is preferably used.

In the hot air drying, a particulate hydrogel cross-linked polymer is laminated on a wire mesh / or a punching metal having holes or slits, and the gel is vertically or horizontally oriented, preferably vertically. In the direction, hot air may be ventilated into the gaps between the stacked particles. As a wire mesh or a hole diameter used, for example, in the case of a hole or a wire mesh, 0.1 to 5 m
m, and moreover, it may have a ventilation hole of about 0.2 to 2 mm. The lamination of the gel on a wire mesh or a punching metal is performed in such a manner that the water-containing gel-like crosslinked polymer has a constant thickness of 1 to 20 cm, preferably 1.5 to 10 cm, more preferably 2 to 8 cm from the viewpoint of physical properties after drying. What is necessary is just to laminate | stack the union.

The drying temperature for drying the above hydrogel crosslinked polymer is usually 100 from the viewpoint of physical properties and productivity.
° C or higher, more preferably 110 to 230 ° C, preferably 130 ° C.
The temperature may be set to about 200 to 200C, particularly preferably about 150 to 190C. The drying temperature is defined by the material temperature or the temperature of the heat medium (such as hot air), but is preferably specified by the heat medium temperature. Further, the drying temperature may be constant during the drying period, or may be appropriately changed during the drying in the above temperature range. Furthermore, when drying with hot air, the dew point of the hot air is preferably 40 to 100 ° C. from the viewpoint of physical properties and energy efficiency.
More preferably 50 to 90 ° C, still more preferably 60 to 90 ° C.
85 ° C. range.

The dry polymer thus obtained is compulsorily cooled, then milled, or simultaneously. In the present invention, the forced cooling and the pulverization may be performed simultaneously, but preferably, the pulverization is performed after the forced cooling. The forced cooling referred to in the present invention is an external and intentional cooling operation or a cooling step of the dried polymer, and the pulverization is a step of pulverizing the obtained dried polymer or its aggregate (block-like material) with fluidity. It is a mechanical operation to make a powder, and furthermore, crushing does not lead to physical destruction of the dried polymer or reduction of the particle size.
This is a mechanical operation for lightly disaggregating to about mm. It is also noted that the particulate hydrogel crosslinked polymer that has been laminated and dried tends to become a block-shaped dried product that has lost fluidity due to aggregation between particles after drying. Such a block is an aggregate of dried polymer particles, and thus has continuous voids and air permeability to the inside of the block. However, since there is no fluidity due to aggregation, the block (crushing) step is performed. Need.

In the present invention, the forced cooling may be performed by cooling the dried polymer to a predetermined temperature by intentionally providing a cooling step between the drying step and the pulverizing step. A method in which the dried polymer is placed in a container (hopper) or a cylinder having a cooling heat transfer surface and stirred as required, and is forcibly cooled; Examples of the method include forced cooling by passing cold air through the polymer, forced cooling simultaneously with transportation using cooled air, and a low-temperature screw conveyor having a cooling heat transfer surface. Among these methods, from the viewpoint of cooling efficiency and fluidity of the dried polymer, in the present invention, preferably,
A method of passing cool air is used, and in that case, only the surface of the dried polymer may be ventilated, but preferably, the laminated dried polymer or its block-like material is vertically or horizontally, preferably vertically. In addition, it is preferable to ventilate the voids of the laminated particles so that more efficient forced cooling can be performed. When the layers are stacked, the thickness is preferably in the above-described range.

In the present invention, forced cooling is indispensable before or during pulverization, and is a small-scale polymerization / drying / pulverization in a laboratory / Furthermore, each experimental operation is discontinuous with a few intervals. Unlike lab-scale drying and crushing, which are apt to be allowed to cool naturally because they are vacant for 10 minutes to several hours or more, rather than forced-cooling before or during crushing in production-scale drying, the object of the present invention is Was not achieved. That is, the present invention provides a large-scale production equipment (for example, 1 t /
It is more suitable for continuous drying of 10 days / day or more, preferably 10 t / day or more), continuous grinding and subsequent addition of a continuous aqueous liquid.

If the forced cooling after heating and drying, which is a feature of the present invention, is not performed, the efficiency of pulverization or classification is greatly reduced, and a water-absorbent resin powder having an excellent particle size distribution cannot be obtained with high productivity. Furthermore, when hot-air drying is performed on a wire mesh or a punched metal, conventionally, the dried polymer adheres to the wire mesh or the punched metal or causes clogging, which significantly reduces air permeability, drying efficiency, and productivity. In the present invention, there is no such problem, and it is not necessary to attach a special anti-adhesion device (Japanese Patent Laid-Open No. 27070/1995) or to attach a dryer or to periodically remove clogging. In addition, by forcibly cooling before or during pulverization, the resulting water-absorbent resin powder has an excellent particle size distribution and pulverization speed, and furthermore, powder agglomeration in a pulverizer and in a manufacturing process is greatly reduced. . Further, it is not necessary to excessively dry the water-absorbing resin powder in order to prevent agglomeration of the powder in the subsequent manufacturing process, so that the drying time is shortened and the physical properties are improved.

The cold air (gas) used in the method of the present invention is appropriately determined depending on the temperature of the target dry polymer, but is preferably 60 ° C. or less, and more preferably 50 to −50 in view of the cooling efficiency.
C., more preferably from 40 to -10.degree. C., particularly preferably from 35 to 5.degree. C., in which case the gas has a dew point of preferably 60.degree. C. or less, more preferably 50.degree.
It is below ° C. Such a gas may be an inert gas such as nitrogen, or a mixed gas of an inert gas and air, but preferably air, particularly air that has passed through a filter.
Furthermore, the wind speed is 10-0.1 m / sec,
The cooling air is about 0.5 m / sec, and the cooling time is preferably 60 to 0.1 minutes, more preferably 20 to 0.2 minutes, and further preferably 10 to 0.5 minutes.

As the forced cooling temperature in the present invention, in order to achieve the present invention, the temperature of the dried polymer is 95 ° C. or less, preferably 85 to 35 ° C., more preferably 80 to 40 ° C.
More preferably, it is forcibly cooled to the range of 70 to 45 ° C. The forced cooling temperature is obtained by appropriately measuring the material temperature with a contact thermometer or a non-contact thermometer (such as an infrared thermometer), and is controlled as necessary.
When the temperature of the dried polymer exceeds 95 ° C., the drying efficiency is low due to difficulty in peeling from the wire mesh or the punching metal of the dryer, and the efficiency of the pulverization and classification of the dried polymer is greatly reduced. It is difficult to obtain an excellent water-absorbent resin powder having a narrow particle size distribution. Also, if the cooling temperature is too low,
In addition to requiring a large amount of time and equipment for cooling, unexpectedly, agglomerates of the water-absorbent resin powder are generated during pulverization and classification, which is not preferable. In addition, excessive cooling may be disadvantageous in terms of physical properties and energy even in forced heating and surface crosslinking described below.

In order to achieve the present invention, the temperature decrease of the dried polymer due to the forced cooling depends on the heating / drying temperature. Is preferably 40 ° C. or more, more preferably 60 ° C. or more, still more preferably 80 ° C. or more, and particularly preferably 100 ° C. or more. What is necessary is just to forcibly cool to the temperature of a union (for example, more preferably 80 to 40 degreeC). The heat removed from the dried polymer by forced cooling is preferably recycled. For example, as described above, in the present invention, the heat drying is hot air drying (particularly preferably,
150 to 180 ° C.), and forced cooling is air cooling (particularly preferably, the polymer is forcibly cooled to 70 to 45 ° C.).
However, in the case of performing forced cooling by hot air drying and air cooling according to the present invention, the cool air used for forced cooling of the dried polymer is appropriately controlled by the amount of air, the amount of ventilation, the temperature of the polymer, and the like. Warm air or hot air (usually 50 ° C. or higher, preferably 50 to 200 ° C., more preferably 60 to 200 ° C.)
150 ° C., more preferably 70 to 110 ° C.). It may be used for the manufacturing process.

The heat obtained by forced cooling in the present invention is:
It is preferably reused. As a manufacturing process to be reused, there is a warming process and the like, but the above-mentioned drying process is most preferable. That is, the cold air used for forced cooling in the present invention becomes hot air after aeration of the dried polymer. Therefore, in the present invention, preferably, hot air after forced cooling (for example, 60 to 150) is used.
C.) can be supplied to an air supply port of a hot air dryer through a pipe to perform continuous drying as a raw material of hot air used for drying. In this way, in the hot air drying of the present invention, since hot air is produced by using hot air generated by forced cooling instead of using room temperature air, a large amount of energy can be saved by that much, It has the advantage of not discharging wind (waste gas) to the environment. From the viewpoint of such recycling, forced cooling in which cold air is passed through the polymer is used for forced cooling in the present invention, and hot air drying is used for heating and drying in the present invention.

That is, the present invention relates to a method for producing a water-absorbent resin powder, which comprises heating and drying a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent, followed by pulverization,
Also provided is a method for producing a water-absorbent resin powder, characterized in that heat obtained by forcibly cooling a dried polymer after heating and drying is reused for forced heating in a process for producing a water-absorbent resin. Here, reusing for forced heating means that the heat obtained in the forced cooling step is used in the forced heating step, and the forced cooling step and the forced heating step are included in the same production line. Or may be steps included in separate production lines.

When hot air drying and air cooling are performed in the present invention, a fluidized bed or the like may be separately provided as a drying device and a cooling device. For example, when continuous hot air drying is performed, a belt-type dryer is used. It is also a preferable method to use a part of the latter half of the dryer in the cooling step by using the above method. In such a case, even if a cooling device is not separately provided, the latter half of the belt of the hot air dryer is preferably 1/4 to 1/20, preferably 1/8 of the latter half.
A forced cooling step may be performed by separately dividing a portion of about 1/16 and sending cool air as a cooling device, and furthermore, heat taken from the dried polymer may be recycled. In the present invention, since the heat obtained by forced cooling of the dried polymer is reused, a process with excellent energy efficiency can be achieved. In addition, by forcibly cooling the latter half of the dryer, the releasability of the dried polymer from the wire mesh and punched metal of the belt is dramatically improved, and there is no clogging of the belt. preferable.

The dried polymer thus forcibly cooled to a predetermined temperature is then pulverized or classified, preferably indispensably pulverized and further classified. The drying and pulverization or classification are preferably performed in a continuous process, and the time from the outlet of the dryer to the inlet of the pulverizer is within 10 minutes, preferably within 5 minutes, more preferably within 2 minutes. In the present invention, even in such a continuous process, the drying efficiency and the pulverization efficiency can be significantly improved by inserting a forced cooling step between the drying step and the pulverization step. In the present invention, as a pulverizing method,
It is not particularly limited as long as the dried polymer or its aggregate (block-like material) can be made into a fluid powder, preferably a powder having an average particle diameter of 2 mm or less. For example, a hammer mill, a roll mill, or A method of pulverization using a jet air flow type pulverizer or the like, and one or more of various conventionally known pulverization or pulverization methods can be used. Further, when the aggregation during drying is weak, the aggregation of the polymer may be loosened by vibrating and classifying the dried polymer without using a pulverizer, and a pulverization step may be performed.

In the present invention, after the above-mentioned pulverization, classification is performed as necessary / preferably, and coarse particles and fine powder are removed. The average particle size of the water-absorbent resin powder thus obtained is determined depending on the purpose. For example, when the purpose is a sanitary material, the finally obtained water-absorbent resin powder has an average particle size of 200 to 600 μm, Is 300 to 600 μm,
Further, the particle size is in the range of 300 to 550 μm, and preferably, the total of particles having a size of 150 μm or less to 850 μm or more is 15% by weight or less, more preferably 10% by weight or less, and further preferably 5% by weight or less. In particular, in the present invention, the average particle diameter of the water-absorbent resin powder obtained after pulverization and used in the next step is within the above range, that is, 20%.
It is preferably in the range of 0 to 600 µm, and more preferably, the proportion of particles having a size of 150 µm or less to 850 µm or more is 15% by weight or less.

The bulk specific gravity of the water-absorbent resin powder thus obtained is determined by the true specific gravity (g / g) which is uniquely determined by the monomer composition.
cm ³ ), for example, when the water-absorbing resin is sodium polyacrylate, particularly when the neutralization ratio is 50 to 90 mol%, and more preferably 60 to 80 mol%, the bulk specific gravity is usually 0.63 g / ml. Above, especially 0.65 g / ml (J
ISK-3362). In the method of forced cooling of the present invention, the water-absorbent resin powder after pulverization has few scales and is more rounded and has a uniform shape. .89 g / ml, more preferably 0.67
-0.88 g / ml, more preferably 0.73-0.1 g / ml.
87 g / ml, more preferably 0.74 to 0.86 g
/ Ml, more preferably 0.75 to 0.85 g / ml
It is adjusted to.

When the bulk specific gravity after the pulverization is lower than 0.63 g / ml, it becomes difficult to mix the aqueous liquid described below even if the temperature is controlled, and the physical properties are reduced (absorption capacity under pressure, liquid permeability under pressure). In addition, the impact resistance (process damage) of the water-absorbent resin powder may be reduced, and the transport cost may be increased due to a decrease in weight per unit volume. If the bulk specific gravity is higher than 0.89 g / ml, it may be difficult to secure a liquid passing space between the gels when the liquid is swollen under pressure. After the above-mentioned pulverization, coarse particles (for example, 850 μm on product) and fine powder (for example, 150 μm pass product) may be appropriately recycled in some cases. The particle size distribution may be obtained by re-grinding coarse particles and removing or collecting fine particles. However, the sharpness of the particle size distribution in the present invention greatly reduces the need for such recycling. The method for recycling the fine powder of the water absorbent resin is described in US Pat.
Nos. 5,264,495 and 5,478,879, and European Patents 0812873, 0888517, 08
No. 44270, etc., and these fine powder recycling methods can also be applied to the present invention. Also, the recycle amount of the fine powder is 15% by weight or less of the whole, preferably 1%.
%, More preferably 2 to 8% by weight. In the present invention, a water-absorbent resin powder having a sharp particle size distribution can be obtained with high productivity by pulverization. Therefore, recycling a small amount of fine powder is preferable because a water-absorbent resin powder having a sharp particle size distribution can be obtained.

According to the present invention in which cooling is performed before pulverization, the particle size distribution is sharper than before, the pulverization time for obtaining such particle size distribution is shortened, and coarse water-absorbent resin powder having a target particle size or more is obtained. Coarse particles (e.g., 850 μm)
This also has the effect of reducing the labor for recycling, such as re-crushing of (m-on product) and re-classifying fine powder (for example, 150 μm pass product). It is preferable that the water-absorbent resin powder after pulverization and classification after cooling is further heated or forcibly heated in the next step. 40-100 as the heat retention temperature from outside
℃, even more in the range of 50-90 ℃, by keeping the water-absorbent resin powder at such a temperature, the handleability of the water-absorbent resin powder is also improved, aggregation and attachment of the water-absorbent resin powder in the manufacturing process Is prevented. In the present invention, the dried polymer is dared to be forcibly cooled and pulverized or classified, thereby improving the drying efficiency and the pulverization efficiency. Separately, the cooled water-absorbent resin powder is kept warm or forcedly heated (reheated). Just fine.

When an aqueous liquid, particularly an aqueous solution of a crosslinking agent, is added in the present invention, the water-absorbent resin powder obtained by forcibly cooling before pulverization is further forcibly cooled after pulverization to adjust the temperature. Is preferred. The means for controlling or cooling the temperature is not particularly limited. However, since the water-absorbent resin powder after pulverization has an increased fluidity and specific surface area, the above-mentioned cooling means can be more applied. Method of forced cooling by throwing into a container (hopper) or cylinder stirred by
A method of sufficiently cooling on a continuous belt, a method of forcibly cooling by passing cool air through the polymer, a method of forcibly cooling simultaneously with transportation using cooled air, a low-temperature screw conveyor having a cooling heat transfer surface, etc. are used. However, it is preferable to use at least one method.

That is, the temperature of the water-absorbent resin powder before the addition of the aqueous liquid is preferably 80 to 35 ° C., more preferably 70 to 35 ° C., further preferably 60 to 35 ° C. by the above-mentioned forced cooling and, if necessary, further warming and cooling. After cooling (control) to 35 ° C, particularly preferably in the range of 50 to 35 ° C, the aqueous liquid is added. If the temperature of the water-absorbent resin powder before the addition of the aqueous liquid is high, the mixing of the aqueous liquid becomes uneven, and
Forcibly cooling or leaving to cool to less than 35 ° C. not only takes a long time, but also causes agglomeration of the cooled powder and increases energy loss at the time of reheating, which is not preferable. Because the water-absorbent resin powder obtained above has an excellent particle size distribution,
Crosslinking the surface is suitable for further improving the physical properties. For the surface crosslinking, the following forced heating may be separately performed.

That is, in consideration of the forced heating step of the water-absorbent resin powder after pulverization or classification, the forced cooling step of the present invention, which is seemingly useless in terms of both energy and process, is surprisingly effective in drying efficiency. In addition, the pulverization efficiency was relatively increased, and the mixing property of the aqueous liquid with the obtained water-absorbent resin powder was also improved. The surface cross-linking agent used in the present invention is not particularly limited as long as it is a compound capable of reacting with the functional group of the polymer. As the surface crosslinking agent, specifically, for example, propylene glycol,
Polyhydric alcohols such as glycerin and butanediol,
Polyhydric epoxy compounds such as ethylene glycol diglycidyl ether (poly) polyamine compounds such as ethyleneimine, alkylene carbonate compounds, polyvalent oxazoline compounds, haloepoxy compounds and polyamine adducts thereof (epihalohydrin adducts of polyamide-polyamide;
Trade name Kymene; manufactured by Hercules), mono, di or polyoxazolidinone compounds, polyvalent metals and the like, but are not particularly limited. One of these surface cross-linking agents may be used alone, or two or more of them may be appropriately used in combination. When used in combination in the present invention, among the surface cross-linking agents, a surface cross-linking agent obtained by combining a first surface cross-linking agent and a second surface cross-linking agent having different solubility parameters (SP values) (see US Pat. No. 5,422,405). It is preferable to use a water-absorbent resin powder having particularly excellent absorption capacity under high pressure (for example, 4.90 kPa or more).

The amount of the surface cross-linking agent to be used is appropriately determined depending on its kind, reaction conditions, and the like. Is used in the range of 0.01 to 5 parts by weight, more preferably 0.5 to 4 parts by weight. When mixing the above polymer and the surface cross-linking agent, water, steam, or an aqueous liquid composed of water and a hydrophilic organic solvent may be added as necessary during or after the mixing. The amount of water used in this case depends on the type and particle size of the polymer used, but is 10 parts by weight or less, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the solid content of the water-absorbent resin powder. 10 parts by weight,
More preferably, it is in the range of 1 to 5 parts by weight.

The hydrophilic organic solvent is not particularly limited, but specifically, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, is
o-propyl alcohol, n-butyl alcohol, is
lower alcohols such as o-butyl alcohol and t-butyl alcohol; ketones such as acetone; ethers such as dioxane and tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. . When mixing the polymer and the surface cross-linking agent, for example, after dispersing the polymer in the aqueous liquid, the surface cross-linking agent may be mixed, the surface dissolved in water or aqueous liquid The crosslinking agent may be directly sprayed or dropped onto the polymer and mixed. In the case of mixing using water, fine powder insoluble in water, various organic acids, inorganic acids, surfactants and the like may coexist. Among these mixing methods, spray mixing is preferable, and the aqueous liquid at that time is added in fine droplets of 500 μm or less, and more preferably 300 μm or less.

In the present invention, when an aqueous liquid is added, the inner wall of the mixer preferably has a temperature higher than room temperature, and the inner wall temperature of the mixer is 40 ° C. or higher, preferably 45 to 100 ° C. , More preferably 50 to 95 ° C,
More preferably, the temperature is maintained at 55 to 90 ° C, and the inner wall temperature is higher than that of the water-absorbent resin powder before the addition of the aqueous liquid, preferably 40 ° C or lower, more preferably 20 ° C or lower, particularly 10 ° C or lower. Preferably, there is. Note that, in the present invention, the inner wall is the inner surface of the mixer including the stirring blade, and in the case of continuous mixing, it is preferable to control the temperature at a steady state temperature, and particularly to control the metal part indispensably. .

When the inner wall temperature of the mixer is below room temperature,
Even if the temperature of the powder is controlled, the water-absorbent resin powder to which the aqueous liquid has been added may adhere to the inner wall, or the physical properties of the obtained water-absorbent resin powder may decrease.If the inner wall temperature is too high, There is a possibility that the cross-linking agent or the like in the aqueous solution may be crushed, or the mixing of the aqueous liquid may become uneven. Control of the inner wall temperature of the mixer is not limited as long as the temperature can be controlled, for example,
It may be controlled by external heating such as hot air or heat medium,
In addition, the mixer itself is provided with a structure capable of keeping sufficient heat, and further, a mixture of a powder or an aqueous liquid at a specific temperature is mixed continuously and in a large amount (for example, 500 kg / hr or more) to thereby reduce the inner wall of the mixer. It may be controlled, may be controlled using the heat of hydration of the water-absorbent resin powder by addition of the aqueous liquid or the frictional heat at the time of mixing, or may be used in combination, but is preferably used. .

Further, in such a method, the mixer having the specific inner wall temperature is preferably a high-speed stirring mixer having a stirring blade, and its rotation speed is usually 10 rpm.
Above, preferably 100 to 10000 rpm, more preferably 300 to 5000 rpm, most preferably 500 rpm
The mixture is stirred and mixed at 3000 rpm, and the stirring time is usually within 5 minutes, preferably within 3 minutes, more preferably within 1 minute, and more preferably within 0.2 minutes. Further, an air-flow stirring type mixer having a plurality of stirring blades is more preferable as the mixer. In the method of the present invention, the aqueous liquid is preferably an aqueous solution of a cross-linking agent, since the physical property improvement by the improvement of the mixing property is large. A polyhydric alcohol aqueous solution containing a crosslinking agent other than a polyhydric alcohol, particularly an aqueous solution containing only a polyhydric alcohol as a crosslinking agent, and / or
Alternatively, it is preferable that the aqueous liquid does not contain an organic solvent other than the polyhydric alcohol, particularly a volatile organic solvent, since the effect of the present invention is remarkably exhibited. When the inner wall temperature of the mixer is to be increased, the addition of the aqueous liquid of the present invention requires a crosslinking agent which is inactive even at the inner wall temperature, for example, the reaction temperature 110 required for reheating.
It is suitably applied to a crosslinking agent having a temperature of not less than ° C, particularly a polyhydric alcohol. In the present invention, the polyhydric alcohol may be used as a cross-linking agent, may be used at a reaction temperature or lower to be used as a solvent for the cross-linking agent, or may be used in combination. In addition, the crosslinking agent other than the polyhydric alcohol to be used is exemplified in the above-mentioned crosslinking agent and the following literature. Examples of the polyhydric alcohol that most remarkably exhibits the effects of the present invention in terms of physical properties include polyhydric alcohols having 3 to 8 carbon atoms, and further selected from glycerin, propylene glycol, butanediol, pentanediol, and hexanediol. At least one kind of polyhydric alcohol (the substitution position of the diol does not matter) is preferably used.

The volatile organic solvent referred to in the present invention is a solvent having a boiling point of not higher than the temperature of the crosslinking reaction described below, particularly an organic solvent having a boiling point of not higher than 100 ° C., and further not higher than 85 ° C. In the present invention, adding an aqueous liquid without using these organic solvents is preferable because a water-absorbent resin excellent in environmental, cost and safety aspects can be obtained. In the present invention, after mixing the above polymer and the surface cross-linking agent, forcible heating is performed as necessary depending on the type of the cross-linking agent to cross-link the vicinity of the surface of the polymer. The temperature of the forced heating depends on the surface cross-linking agent used, but is preferably 100 ° C. or higher, more preferably 110 to 230 ° C., and still more preferably 160 to 230 ° C.
220 ° C., and the time of forced heating is appropriately determined,
It is preferably in the range of 1 to 120 minutes, more preferably 5 to 60 minutes. Examples of the apparatus used for forced heating include a groove type mixing dryer, a rotary dryer, a disk dryer, a fluidized-bed dryer, a flash dryer, and an infrared dryer. Preferably, these heating devices are provided separately from the mixing device, and they are connected to each other.

These surface cross-linking methods are described in European Patent Nos. 0349240, 0605150 and 04509.
No. 23, No. 0812873, No. 0450924, No. 0668080, etc., various Japanese patents such as Japanese Patent Application Laid-Open Nos. Hei 7-242709 and 7-224304, U.S. Pat.
Nos. 3, 538,983, 5,610,220, 5,
No. 633316, No. 5674633, No. 546297
No. 2 and other various US patents, International Patent Publication WO99 / 42
No. 494, WO99 / 43720, WO99 / 424
It is also described in various international patents such as No. 96, and these surface cross-linking methods can be applied to reheating and addition of an aqueous liquid in the present invention.

As described above, in the present invention, an aqueous liquid is added in a mixer to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinker, and then pulverizing the resultant. A method for producing a water-absorbent resin powder, wherein the heating and drying temperature is in the range of 110 to 230 ° C, the dry polymer is cooled to 80 to 35 ° C before the addition of the aqueous liquid, and the dry weight after pulverization. The present invention also provides a method for producing a water-absorbent resin powder, wherein the bulk specific gravity of the coalesced product is 0.65 g / ml or more. The present invention also provides a water-absorbent resin in which a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent is heated and dried, and then pulverized and then an aqueous liquid is added to a powder obtained in a mixer. A method for producing a powder, wherein the heating and drying temperature is 110 to 110.
230 ° C. range, cooling the dried polymer to 80-35 ° C. before adding the aqueous liquid, and a stirring mixer having an inner wall temperature of 40 ° C. or higher;
Also provided is a method for producing a water-absorbent resin powder, which is characterized by reheating to 10 to 230 ° C.

In these two methods, the effect of the present invention is more remarkable as the difference between the drying temperature and the cooling temperature is larger, and the preferable temperature range is as described above. The absorbency against pressure of the water-absorbent resin powder thus obtained (1.9)
6 kPa) and a water absorption capacity under no load (physiological saline) are preferably 25 g / g or more, more preferably 27 g / g or more, further preferably 30 g / g or more, and particularly preferably 35 g or more.
/ G or more. Further, the water-soluble component, the particle size, the bulk specific gravity, the water absorption ratio, and the like are in the above-mentioned ranges. Further, the absorption capacity under pressure (4.90 kPa) is preferably 23 g / g or more, more preferably 25 g / g or more, and further preferably 27 g / g or more. According to the present invention, the water absorbent resin powder having such high physical properties can be easily and stably produced.

The method for producing a water-absorbent resin powder according to the present invention is a method for producing a water-absorbent resin powder in which a water-containing gel-like cross-linked polymer obtained by polymerizing an aqueous monomer solution containing a cross-linking agent is heated, dried and ground. The method comprises forcibly cooling the dried polymer after heating and drying, and pulverizing the dried polymer to obtain a bulk specific gravity of 0.1.
It is characterized in that a water-absorbent resin powder of 65 g / ml or more is obtained, and the surface of the cooled water-absorbent resin powder is further crosslinked.

The method for producing a water-absorbent resin powder according to the present invention is a method for producing a water-absorbent resin powder in which a water-containing gel-like crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent is heated, dried, and ground. Forcibly cooling the dried polymer after heating and drying, and pulverizing the dried polymer to obtain a bulk specific gravity of 0.1.
65 g / ml or more of the water-absorbent resin powder, adding the aqueous liquid to the cooled water-absorbent resin powder, adding the aqueous liquid with a stirring mixer whose inner wall is heated,
It is characterized by.

Accordingly, the present invention provides a method for preparing a hydrogel cross-linked polymer obtained by polymerizing an aqueous monomer solution containing a cross-linking agent by heating and drying, and then pulverizing the powder to obtain a volatile organic solvent in a mixer. The total of particles having (1) a bulk specific gravity of 0.65 g / ml or more, (2) an average particle diameter of 200 to 600 μm, and (3) 150 μm or less to 850 μm or more obtained by adding an aqueous polyhydric alcohol solution not containing 10% by weight or less,
(4) It also provides a water-absorbent resin powder having an absorption capacity under pressure (1.96 kPa) of 25 g / g or more. The present invention has improved continuous mixing of an aqueous liquid into a water-absorbent resin powder, and has been improved under pressure even with a polyhydric alcohol aqueous solution, which was conventionally difficult to mix without using a volatile organic solvent. A water-absorbent resin powder having a high absorption capacity and a high bulk specific gravity can be provided.

The water-absorbent resin powder of the present invention obtained as described above may be further used, if necessary, with a deodorant, an antibacterial agent, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber. , Plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, chelating agents, antioxidants, water, water-soluble polymers, binders, salts, etc., to impart various functions. Good.
Water-absorbent resin powder obtained by including the production method of the present invention,
Because of its excellent particle size distribution and physical properties, it is possible to obtain a water-absorbent resin powder exhibiting further higher physical properties by surface crosslinking and subsequent neutralization. Further, in the present invention, such a water-absorbent resin powder can be obtained easily with high productivity, without attachment or aggregation in the production process, with low energy cost and low cost.

For this reason, the water-absorbent resin powder of the present invention can be used for a wide range of applications, but is particularly suitable for sanitary materials / absorbent articles such as disposable diapers / sanitary napkins and composites with hydrophilic fiber materials such as pulverized pulp. And can be preferably used as a sanitary material. In addition, since the water-absorbent resin powder of the present invention has high physical properties, it is preferably used in a sanitary material having a high core concentration (weight ratio of the water-absorbent resin powder to the total amount of the fiber and the water-absorbent resin powder) in the sanitary material. For example, the water-absorbent resin powder can be suitably used in a sanitary material having a concentration of 30 to 100% by weight, preferably 40 to 95% by weight or more, and more preferably 50 to 90% by weight.

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The properties of the water-absorbent resin powder were measured by the following methods. In addition, polymerization, drying, pulverization, and the like in Examples were performed by a series of continuous operations simulating actual production. (A) Water absorption capacity under no load 0.200 g of the water-absorbent resin powder was added to a non-woven bag (60 mm
× 60 mm) and heat-sealed, then immersed in a large excess (about 200 g) of 0.9% by weight physiological saline at room temperature. After 60 minutes of immersion, the bag is pulled up and drained at 250 G for 3 minutes using a centrifuge.
(G) was measured. Further, the same operation was performed without using the water-absorbing resin powder, and the weight W0 (g) at that time was measured. Then, from these weights W1 and W0, the water absorption capacity (g / g) under no load was calculated according to the following equation (a).

Water absorption capacity without load (g / g) = (weight W
1 (g) -Weight W0 (g) -0.2) /0.2 (g) (b) Amount of water-soluble component 1.000 g of water-absorbent resin powder was swelled and dispersed in 184.3 g of physiological saline, After stirring in a 200 ml beaker for 16 hours, the swollen gel was separated by filter paper and filtered. Then, the obtained filtrate is subjected to neutralization titration of carboxyl groups using a 0.1 N (0.1 mol / l) aqueous solution of sodium hydroxide and a 0.1 N (0.1 mol / l) aqueous solution of hydrochloric acid, whereby a water-absorbent resin powder ( The amount of the water-soluble polymer (= water-soluble polyacrylic acid (salt)) in the filtrate dissolved from the swelled gel), that is, the water-soluble component amount (% by weight) of the water-absorbent resin powder was calculated.

(C) Solid Content of Water Absorbent Resin 1.000 g of the water absorbent resin powder obtained from the dried polymer was placed in an aluminum cup (inner diameter 53 mm × height 23 mm) and placed in
The resultant was dried again in an airless oven at 80 ° C. for 3 hours, and the solid content (% by weight) of the water-absorbent resin powder (or dried polymer) was calculated from the loss on drying (g). In addition, about the dry polymer, the solid content was measured by the same method as the above after grinding, and it was set as the solid content of the dry polymer. (D) Particle size distribution and average particle size
m, 300 μm, 150 μm), and each particle size of each sieve (850 μm on product / 850-600 μm / 600)
３００300 μm / 300-150 μm / 150 μm pass product). If necessary, a JIS standard sieve was added, and the obtained particle size distribution was plotted on log probability paper to determine the weight average particle size (D50).

(E) Absorbency under pressure According to the method disclosed in the examples of EP0888517, EP0817873 and EP0811636, the water-absorbent resin powder was added to physiological saline in 5%.
The absorbency against pressure at 0 g / cm ² (equivalent to about 4.90 kPa) was measured. That is, the water-absorbent resin powder 0.90
While uniformly applying a load of 50 g / cm ² (approximately 4.90 kPa) to 0 g, the weight W2 (g) of the physiological saline absorbed by the water-absorbent resin powder at room temperature for 60 minutes,
It measured using the balance. And, from the above weight W2,
According to the following formula b, the water absorption capacity (g / g) under pressure 60 minutes after the start of absorption was calculated, and 50 g / cm ² (about 4.90)
kPa) as the absorption capacity under pressure.

Formula b; absorption capacity under pressure (g / g) = weight W2 (g) / weight of water-absorbent resin powder (g) In the same measurement, the load was 20 g / cm ² (approximately 1.96 kPa). (Equivalent), it is referred to as the water absorption capacity under pressure (1.96 kPa). (F) Bulk specific gravity Using a bulk specific gravity measuring device (manufactured by Kuramochi Scientific Instruments), JI
It was measured according to S K 3362. (In addition, as a method for measuring the bulk specific gravity, European Patent Application No.
See also 000-35941. ) That is, the temperature is 25
In a room having a temperature of ± 2 ° C and a relative humidity of 30 to 50%, 120 g of the water-absorbent resin powder was put into a funnel with a damper closed, the damper was opened immediately, and the sample was dropped into a receiver (100 ml). After the sample raised from the receiver was ground with a glass rod, the weight (g) of the receiver containing the sample was accurately measured to 0.1 g, and the bulk specific gravity (g / ml) was calculated.

(G) Impact Resistance The impact resistance of the water-absorbent resin powder was measured in accordance with European Patent 08117873 (US Pat. No. 6,071,976) according to the following method.
After vibrating for 0 minutes, the decrease in the absorption capacity under pressure was evaluated. (H) Weight average particle size of hydrogel crosslinked polymer The hydrogel crosslinked polymer (hydrogel) only slightly swells or shrinks, and the particle size distribution was measured using a 20% by weight saline solution. That is, 30 g of the hydrogel was dispersed in 1000 g of a 20% by weight saline solution, and stirred at 300 rpm for 2 hours using a stirrer chip. After 2 hours the dispersion is
Stacked JIS standard sieve (9500 μm mesh, 200 mesh
0 μm, 850 μm, 600 μm, 300 μm, 75 μ
m / JIS Z8801 / Stainless steel sieve / 20c inner diameter
m) and further poured sequentially using 6000 g of 20% by weight saline to classify the hydrogel. Next, after the back side of the sieve is sufficiently drained with paper, the weight of each particle size of the hydrogel is determined, and the swelling magnification is determined from the total weight (g) and the initial weight (30 g), and the swelling of each particle size (μm) is determined. Previous particle size (μ
m) and plotted on log probability paper to determine the weight average particle diameter D50 of the hydrogel.

(Production Example 1) Polymerization and Drying of Unneutralized Crosslinked Polyacrylic Acid 1066.61 g of acrylic acid, 9.12 g of N, N'-methylenebisacrylamide as a copolymerizable crosslinking agent, and 4280.11 g of water The monomer aqueous solution (1) was degassed with nitrogen gas for 60 minutes, and then charged into an openable and closable closed polymerization vessel. Next, the upper part of the container is put under a nitrogen stream,
At a liquid temperature of 23 ° C., 32.27 g of a 10% by weight aqueous solution of 2,2′-azobis (2-amidinopropane) dihydrochloride and 1% by weight of a 10% by weight aqueous solution of hydrogen peroxide were used as polymerization initiators.
When 0.66 g and 26.64 g of a 1% by weight aqueous solution of L-ascorbic acid were respectively added, polymerization started about 5 minutes later, and then, static polymerization was performed for 1 hour. The obtained polymer was taken out of the container and had a pore size of 7.5 mm.
By using a meat chopper (manufactured by Hiraga Manufacturing Co., Ltd.) to obtain a particulate hydrogel crosslinked polymer (1) having an average particle diameter of 1500 μm.

Next, the particulate hydrogel crosslinked polymer (1) is spread over a wire mesh having an opening of 300 μm with a layer thickness of about 50 mm and laminated, and then heated to 135 ° C. (dew point 65 ° C.) in the vertical direction of the gel. Hot air drying was performed by passing hot air at 1 m / sec for 1 hour. In this way, a block-like substance composed of the particulate dry polymer (1) with a solid content of 95% by weight was obtained,
The material temperature was about 135 ° C. (Production Example 2) Polymerization and drying of partially neutralized crosslinked polyacrylic acid 673.79 g of acrylic acid and 3 of sodium acrylate
5904.7 g of a 7% by weight aqueous solution, 15.87 g of polyethylene glycol diacrylate (average number of polyethylene glycol units: 8) as an internal crosslinking agent and 71 of water
An aqueous monomer solution (2) consisting of 4.2 g is
After the degassing, the aqueous solution was supplied to a reactor having an inner volume of 10 L and covered with a jacketed stainless steel double-armed kneader having two sigma-type blades and replacing the reaction system with nitrogen while maintaining the temperature at 20 ° C. Continued.

Next, 19.55 g of a 20% by weight aqueous solution of sodium persulfate and 1.47 g of a 1.0% by weight aqueous solution of L-ascorbic acid were added while rotating the blades, and polymerization started after 1 minute. After minutes, the reaction reached peak temperature. The resulting hydrogel crosslinked polymer was finely divided into a size of about 5 mm. Thereafter, stirring was further continued, and 60 minutes after the start of the polymerization, the average particle diameter was 1600.
The hydrogel crosslinked polymer (2) having a particle size of μm was taken out. Next, the particulate hydrogel crosslinked polymer (2) is spread over a wire mesh having an opening of 300 μm with a layer thickness of about 50 mm and laminated, and then hot air at 170 ° C. (dew point 5
(0 ° C.) at 1 m / sec for 1 hour to perform hot air drying. In this way, a block of the dry polymer (2) having a solid content of 96% by weight was obtained, and the material temperature was about 170 ° C.

Production Example 3 Polymerization and Drying of Crosslinked Partially Neutralized Polyacrylic Acid In Production Example 2, 425.1 g of acrylic acid and 37% by weight of sodium acrylate were used instead of the aqueous monomer solution (2). 4497.2 g of an aqueous solution, 1.40 g of trimethylolpropane triacrylate as an internal crosslinking agent and water 57
Except for using a monomer aqueous solution (3) consisting of 7.7 g,
By performing aqueous solution polymerization in a kneader in the same manner as in Production Example 2, a particulate hydrogel crosslinked polymer (3) having an average particle size of 1700 μm was obtained. Next, the particulate hydrogel crosslinked polymer (3) was dried with hot air at 170 ° C. for 1 hour in the same manner as in Production Example 2. In this way, a block of the dry polymer (3) having a solid content of 95% by weight was obtained, and the material temperature was about 170 ° C.

Production Example 4 Polymerization and Drying of Crosslinked Partially Neutralized Polyacrylic Acid In Production Example 2, 369 g of acrylic acid and 3907 g of a 37% by weight aqueous solution of sodium acrylate were used instead of the aqueous monomer solution (2). Aqueous polymerization in a kneader in the same manner as in Production Example 2, except that an aqueous monomer solution (4) consisting of 4.99 g of polyethylene glycol diacrylate (average number of polyethylene glycol units n = 8) and 1216 g of water was used as an internal crosslinking agent. By performing, the average particle diameter 17
A 00 μm particulate hydrogel crosslinked polymer (4) was obtained.
Next, a particulate hydrogel crosslinked polymer (4) was produced in Production Example 2.
Continuous hot-air drying was performed in the same manner as described above. Thus, the solid content 95
A block of the dry polymer (4) in the form of particles was obtained at a weight percentage of about 170 ° C.

(Production Example 5) Polymerization and Drying of Crosslinked Partially Neutralized Polyacrylic Acid 100 parts of acrylic acid, 656.4 parts of a 37% by weight aqueous solution of sodium acrylate, polyethylene glycol diacrylate (average number of polyethylene glycol units n =
8) 0.77 parts and 216.7 parts of deionized water were sufficiently mixed to prepare an aqueous monomer solution (5). The obtained monomer aqueous solution (5) is continuously fed at a rate of 290 kg / h by a metering pump, and nitrogen gas is continuously blown in the middle of the pipe to reduce the oxygen concentration of the monomer aqueous solution (5) to 0.5 ppm.
I did it below. Further, 2,2′-azobis (amidinopropane) dihydrochloride (trade name V-5) was added to the aqueous monomer solution (5).
0, manufactured by Wako Pure Chemical Industries, Ltd.), four kinds of aqueous initiator solutions of sodium persulfate, L-ascorbic acid and hydrogen peroxide were sequentially line-mixed (0.08 parts / initiator solids (component) /
0.08 parts / 0.008 parts / 0.006 parts)
It was continuously supplied to a steel endless belt polymerization machine (having a flat belt having a 50 mm weir on both sides) moving at a speed of cm / min so as to have a thickness of 25 mm. Polymerization starts immediately, and the polymer thus obtained is discharged from the end of the belt polymerization machine, and is further cut by a continuous cutter at about 5 to 10 c.
After cutting into m pieces, the mixture was pulverized with a meat chopper (pore diameter 9 mm) to obtain a particulate hydrogel crosslinked polymer (5) having an average particle diameter of 1600 μm.

Next, the particulate hydrogel crosslinked polymer (5) is loaded on a punching metal to a thickness of 50 mm,
Continuous hot air drying (180 ° C. hot air (dew point: 60 ° C.) for 20 minutes in the vertical direction) was performed by a belt dryer. In this way, a block of the dry polymer (5) having a solid content of 94% by weight was obtained, and the material temperature was about 180 ° C.
Met. (Example 1) ... forced cooling of the dried polymer (1) to 60 ° C With respect to the block-like material (material temperature about 135 ° C) of the particulate dried polymer (1) obtained in Production Example 1. In place of hot air, a block of the dry polymer (1) in the form of particles is forcibly cooled to 60 ° C. by passing cold air (1 m / sec) at room temperature in the vertical direction in the vertical direction. I took it out. At the same time as taking out, block-like aggregates on the wire mesh are crushed, and 30
Within 2 seconds, the obtained particulate dried product (1) was placed in a three-stage roll granulator (roll gap 1.0 mm /
(0.45 mm / 0.25 mm). At the time of drying, the openings 30 of the block-like material of the dried polymer (1)
The releasability from the 0 μm wire mesh was very good, and the particle size distribution of the water-absorbent resin powder (1) obtained by pulverization is shown in Table 1.

Example 2 Forced cooling to 45 ° C. In the same manner as in Example 1, the block was forcibly cooled to 45 ° C. by adjusting the time for cooling air to flow.
And the obtained particulate dried product (2) was similarly ground. At the time of drying, the releasability of the block of the dried polymer (1) from the metal mesh having an opening of 300 μm was very good, and the particle size distribution of the water-absorbent resin powder (2) obtained by pulverization is shown in Table 1. . (Example 3) ... Forced cooling to 95 ° C. In Example 1, after the block-like material was forcibly cooled to 95 ° C. by adjusting the ventilation time of the cool air, Example 1 was performed.
And the obtained particulate dried product (3) was similarly ground. At the time of drying, the releasability of the dried polymer (1) from the 300 μm wire mesh of the block-like material was slightly better than that of Examples 1 and 2, but was excellent. The water-absorbent resin powder (3) obtained by pulverization was excellent. Table 1 shows the particle size distribution.

(Embodiment 4) ... Forced cooling to 80.degree. C. In the first embodiment, the block was forcibly cooled to 80.degree.
And the obtained particulate dried product (4) was pulverized in the same manner. Upon drying, the releasability of the block of the dried polymer (1) from the 300 μm mesh was better than that of Examples 1 and 2, but was good. Table 1 shows the particle size distribution. (Example 5) ... forced cooling of the dried polymer (2) to 40 ° C With respect to the block-like material (material temperature about 170 ° C) of the particulate dried polymer (2) obtained in Production Example 2. Then, instead of hot air, a block of the dry polymer (2) in the form of particles is forcibly cooled to 40 ° C. by passing cold air (1 m / sec) at room temperature in the up-down direction. I took it out. At the same time as taking out, block-like aggregates on the wire mesh are crushed, and 30
Within 2 seconds, the obtained particulate dried product (5) was placed in a three-stage roll granulator (roll gap was 1.0 mm /
(0.45 mm / 0.25 mm). At the time of drying, the openings 30 of the block-like material of the dried polymer (2)
The releasability from a 0 μm wire mesh was very good, and the particle size distribution of the water-absorbent resin powder (5) obtained by pulverization is shown in Table 1.

Example 6 Addition of aqueous liquid and reheating Water-absorbent resin powder (5) 1 obtained by including a forced cooling step
1,4-butanediol / propylene glycol / water / isopropanol =
By mixing a solution of a surface cross-linking agent consisting of 0.32 / 0.50 / 2.73 / 0.45 (parts by weight) and further reheating at 210 ° C. for 30 minutes, the surface cross-linked water-absorbing agent is obtained. A resin powder (6) was obtained. The water absorption capacity without load of the water absorbent resin powder (6) was 28 g / g, and the water absorption capacity under pressure (4.
90 kPa) was 25 g / g.

With respect to the water-absorbent resin powder (5) obtained in Example 5, the water absorption capacity without load and the amount of water-soluble components were measured, and were 31 g / g and 5% by weight, respectively. . The bulk specific gravity of the water-absorbent resin powder (5) before the addition of the aqueous liquid was 0.67 g / ml, and the temperature was 35 ° C. (Example 7) Post-neutralization Carboxyl groups were post-neutralized by dry blending (powder mixing) the water-absorbent resin powder (1) obtained in Example 1 and a predetermined amount of sodium carbonate powder. In, 75 mol%
A neutralized water-absorbent resin powder (7) was obtained. The water absorption capacity of the water-absorbent resin powder (7) under no load was 42 g / g, and the amount of the water-soluble component was 3% by weight.

Further, the water-absorbent resin powders (2) to (4) obtained in Examples 2 to 4 were similarly post-neutralized. The water absorption capacity under no load was 42 g / g, and the water-soluble component amount Is 3% by weight
Met. (Comparative Example 1) No forced cooling In Example 1, the dried polymer (1) obtained in Production Example 1 was taken out of the dryer without using cool air ventilation, and at the same time, a block-shaped material was obtained in Example 1. Pulverized in the same manner as in Example 1 to obtain the obtained comparative particulate dry product (1)
20 ° C.) was similarly ground. At the time of drying, the releasability of the block of the dried polymer (1) from the metal mesh having a mesh size of 300 μm is poor. (Uniformity and drying speed) decreased. Table 1 shows the particle size distribution of the comparative water absorbent resin powder (1) obtained by the pulverization.

(Comparative Example 2) No forced cooling In Example 5, the dried polymer (2) obtained in Production Example 2 was taken out of the dryer without using cool air, and at the same time the block-like material was removed. Crushed in the same manner as in Example 1 to obtain a comparative dry particulate material (2) (at the time of pulverization,
20 ° C.) was similarly ground. At the time of drying, the releasability of the block of the dried polymer (2) from the 300-μm mesh was poor, and the particles of the dried polymer (2) were clogged with the mesh, and the drying efficiency during continuous drying was observed. (Uniformity and drying speed). Table 1 shows the particle size distribution of the comparative water-absorbent resin powder (2) obtained by pulverization.

(Comparative Example 3) Addition of aqueous liquid and post-heating / without forced cooling With respect to comparative water-absorbent resin powder (2) obtained in Comparative Example 2 (without forced cooling of dry polymer (2)). An aqueous liquid was added in the same manner as in Example 6 (with forced cooling of the same polymer). 35
In the comparative water-absorbent resin powder (2) not cooled to ~ 80 ° C,
Even when adjusted to the same particle size as the water-absorbent resin powder (5), the powder temperature was high, so that aggregation and adhesion in the mixer were gradually observed, and continuous mixing was difficult. (Example 8) ... forced cooling of the dried polymer (3) The block-like material (material temperature: about 170 ° C) of the particulate dried polymer (3) obtained in Production Example 3 was replaced with hot air. Then, a block of the dry polymer (3) in the form of particles was forcibly cooled to 50 ° C. by passing cold air (1 m / sec) at room temperature in the vertical direction, and then taken out of the air-cooled cooling device. At the same time as taking out, block-like aggregates on the wire mesh are crushed, and 3
Within 0 seconds, the obtained particulate dried product (6) was placed in a three-stage roll granulator (roll gap 1.0 mm from above).
/0.45 mm / 0.10 mm).
At the time of drying, the openings 3 of the block-like material of the dried polymer (3)
The peelability from the 00 μm wire mesh is very good.
Table 1 shows the particle size distribution of the water-absorbent resin powder (8) obtained by the pulverization. The water absorption capacity of the water-absorbent resin powder (8) under no load was 44 g / g, and the amount of the water-soluble component was 17% by weight.

(Example 9) The change of the pulverization conditions In Example 8, the pulverization conditions of the dried polymer (6) were changed. That is, the pulverization of the particulate dried product (6) is pulverized with a pin mill (sample mill KII-1 manufactured by Fuji Paudal Industry Co., Ltd., 85% by weight of 850 to 150 μm), and further a mohogenizer (Nippon Seiki High Speed Homogenizer; MX) −
The surface was polished in 7) to obtain a water-absorbent resin powder (9). Table 1 shows the particle size distribution. (Example 10) Addition of aqueous liquid to 0.74 g / ml of bulk specific gravity
Water-absorbent resin powder (9 ° C.) classified at 50 μm and having a temperature of 40 ° C.
A) Propylene glycol / water / ethanol = 0.3 / 100 parts by weight (bulk specific gravity 0.74 g / ml)
An aqueous liquid composed of 2.5 / 1 (parts by weight) is spray-added in a high-speed mixer, and further stirred in a 210 ° C. oil bath and heat-treated for 30 minutes to obtain a surface-crosslinked water-absorbent resin powder. (10) was obtained. Table 2 shows the water absorption capacity under no load, the absorption capacity under pressure (1.96 kPa), and the absorption capacity under load (4.90 kPa). Further, the value of the absorption capacity under pressure after the impact resistance test is shown in parentheses.

(Example 11): Bulk specific gravity 0.63 g / ml
Addition of aqueous liquid to water The water-absorbent resin powder (8) obtained in
The water-absorbent resin powder (8
A) (bulk specific gravity 0.63 g / ml),
An aqueous liquid was added in the same manner as described above, and heat treatment was further performed for 30 minutes. Table 2 shows the analysis results of the obtained water-absorbent resin powder (11).
Shown in (Example 12) Addition of aqueous liquid to bulk specific gravity of 0.73 g / ml The water-absorbent resin powder (9) obtained in Example 9 was prepared in the range of 500 to 1
Water-absorbent resin powder (9 ° C.) classified at 50 μm and having a temperature of 40 ° C.
B) An aqueous liquid was added to 100 parts by weight (bulk specific gravity 0.73 g / ml) in the same manner as in Examples 10 and 11, and a heat treatment was further performed for 25 minutes. The obtained water-absorbent resin powder (1
Table 2 shows the analysis results of 2).

Example 13 Bulk specific gravity 0.63 g / ml
Addition of aqueous liquid to water The water-absorbent resin powder (8) obtained in
The water-absorbent resin powder (8
B) (bulk specific gravity 0.63 g / ml),
An aqueous liquid was added in the same manner as in Nos. 1 to 12, and a heat treatment was further performed for 25 minutes. Table 2 shows the analysis results of the obtained water-absorbent resin powder (13). (Example 14) ... forced cooling of dry polymer (4) The block-like material (material temperature: about 170 ° C) of particulate dry polymer (4) obtained in Production Example 4 was replaced with hot air. Then, a block of the particulate dry polymer (4) was forcibly cooled to 65 ° C. by passing cold air (1 m / sec) at room temperature in the vertical direction, and then taken out of the air-cooled cooling device. At the same time as taking out, block-like aggregates on the wire mesh are crushed, and 3
Within 0 seconds, the obtained particulate dried product (8) was placed in a three-stage roll granulator (roll gap 1.0 mm from above).
/0.45 mm / 0.09 mm).
At the time of drying, the releasability of the dried polymer (4) from the metal mesh having a mesh size of 300 μm was very good. The water absorption capacity of the obtained water-absorbent resin powder (14) under no load was 43 g / g, the amount of water-soluble component was 10% by weight, and the particle size distribution is shown in Table 1.

(Example 15) Addition of aqueous liquid and post-heating / powder temperature 60 ° C. The water-absorbent resin powder (1) having a temperature of 60 ° C. obtained in Example 14
4) To 500 g of an aqueous solution consisting of ethylene glycol diglycidyl ether / propylene glycol / water = 0.1 / 3/1 (% by weight), the inner wall temperature was raised to 6 by external heating.
High-speed mixing (rotation speed: 320 rpm) in a Loedige mixer (M5R; manufactured by Lodige) controlled at 0 ° C. As a result, even if an organic solvent was not used, the water-absorbing resin powder was hardly attached and continuous mixing was possible. Further, the mixture was stirred and heated in a 205 L oil bath with a 5 L mortar mixer (manufactured by Nishi Nihon Seisakusho) for 50 minutes to obtain a surface-crosslinked water-absorbent resin powder (15). Table 2 shows the results.

(Example 16) Addition of aqueous liquid and post-heating / powder temperature 40 ° C. The water-absorbing resin powder (1) having a temperature of 60 ° C. obtained in Example 14
In contrast to 4), the temperature was continuously cooled by air to 40 ° C. Thereafter, an aqueous liquid was added in the same manner as in Example 15 using the water-absorbent resin powder (14) at a temperature of 40 ° C., and the adhesion to the mixer was further reduced. The obtained mixture was subjected to a heat treatment in the same manner as in Example 12 to obtain a water-absorbent resin powder (16). Table 2 shows the analysis results. (Example 17) Addition of aqueous liquid and post-heating / mixer inner wall at room temperature In Example 14, the external heating of the mixer was stopped and the aqueous liquid was added by the mixer at room temperature. It increased and continuous operability decreased.

Example 18 Forced Cooling of Dry Polymer (5) The block of the particulate dry polymer (5) obtained in Production Example 5 (material temperature about 180 ° C.) Then, instead of hot air, cold air (1 m / s) at room temperature is continuously supplied in the vertical direction to forcibly cool the block of the particulate dry polymer (5) to 60 ° C. Taken out of the cooling apparatus, and further dried polymer (5) was added
Continuous polymerization, continuous drying, and continuous pulverization were carried out by continuously supplying g / h to a roll pulverizer. Upon drying, the releasability of the dried polymer (5) from the punching metal was very good, and the particle size distribution of the water-absorbent resin powder (18) obtained by pulverization is shown in Table 1. The water absorption capacity of the water-absorbent resin powder (18) under no load was 55 g / g, and the water-soluble content was 6% by weight.

The cold air used for forced cooling of the block of the particulate dry polymer (5) was heated to about 90 ° C. by use of the forced cooling. The raw material was supplied to the air supply port of the belt hot air drier of Production Example 5 through a pipe to perform continuous drying of Production Example 5 as a raw material of hot air (180 ° C.) used for drying. Thus, instead of using air at room temperature in the hot air drying of Production Example 5, about 9
Since the hot air of 180 ° C. is produced using the hot air of 0 ° C., there is an advantage that the energy is largely saved and the hot air (exhaust gas) is not discharged into the environment. (Example 19) Addition of aqueous liquid and post-heating / powder temperature 50 ° C. The water-absorbent resin powder (18) obtained through the forced cooling step in Example 18 was mixed at a powder temperature of 50 ° C. with a high-speed continuous mixer (turbulizer). / 1000 rpm) at a rate of 100 kg / h, and further, to the water absorbent resin powder (18), 1,4-butanediol / propylene glycol / water / isopropanol = 0.32 / 0.50 / 2.73 / 0. 51 (% by weight
Spray solution with a surface diameter of about 2
Sprayed at 50 μm. The resulting mixture is then
By performing a continuous reheating treatment at 40 ° C. for 40 minutes, a surface-crosslinked water-absorbent resin powder (19) was obtained. Table 2 shows the results. The inner wall temperature of the high-speed continuous mixer (turbulizer) at the time of continuous mixing was about 70 to 80 ° C. due to the powder temperature and frictional heat.

(Example 20) Addition of aqueous liquid and post-heating / powder temperature 50 ° C. In Example 19, the aqueous solution of the surface crosslinking agent was changed to ethylene glycol diglycidyl ether / propylene glycol / water / isopropanol = 0.03 / 1 / 3 / 0.9
(% By weight / based on powder), and sprayed onto the water-absorbent resin powder (18).
By performing a continuous reheating treatment at 35 ° C for 35 minutes, a surface-crosslinked water-absorbent resin powder (20) was obtained. Table 2 shows the results. (Example 21) Addition of aqueous liquid and post-heating / powder temperature 30 ° C The water-absorbent resin powder (18) obtained in Example 18 was powdered at a temperature of 3
Except for further cooling to 0 ° C., a surface crosslinking agent aqueous solution was mixed in the same manner as in Example 19, and further, a continuous reheating treatment was performed at 195 ° C. for 40 minutes. By cooling to a powder temperature of 30 ° C., a little coagulation was observed during continuous mixing / transportation over a long operation, and the reaction time was slightly extended. Table 2 shows the results.

(Comparative Example 4) Addition of aqueous liquid and post-heating / without forced cooling In Example 14, the dried polymer (4) was taken out of the dryer and immediately pulverized without forced cooling. Water absorbent resin powder (3) was obtained. Then, Example 15
850 μm in place of the water-absorbent resin powder (14)
An aqueous liquid was similarly added to the comparative water-absorbent resin powder (3) whose particle size was adjusted to not more than m. In the comparative water-absorbent resin powder (3) which was not forcibly cooled to 40 to 80 ° C., even if it was adjusted to the same particle size as in Example 15, agglomeration and adhesion in the mixer were gradually observed, and continuous operation was difficult. Was. Table 2 shows the results.

(Comparative Example 5): Pulverization of dry polymer (5)
However, without forced cooling In Example 18, the dried polymer (5) was supplied to the same roll grinder as in Example 18 without forced cooling. Two hours after the start of the continuous pulverization, an abnormal sound of the pulverizer derived from the aggregates and adhesion of the aggregates began to occur. Table 1 shows the particle size distribution of the comparative water absorbent resin powder (5) obtained by pulverization. (Comparative Example 6) Addition of aqueous liquid and post-heating / no forced cooling In Example 19, the comparative water-absorbent resin powder (5) obtained in Comparative Example 5 was used instead of the water-absorbent resin powder (19). Except for this point, the same operation as in Example 19 was carried out to obtain a surface-crosslinked comparative water absorbent resin powder (6). Table 2 shows the results.

Example 22 Preparation of Sanitary Material Using a mixer, 50 parts by weight of the surface-crosslinked water-absorbent resin powder (19) obtained in Example 19 and 50 parts by weight of ground wood pulp were used. Dry mixed. Then, the obtained mixture was air-purified to obtain 12 cm × 38.
cm web. Pressure 2kg / cm ² (about 1
By pressing at 93 kPa), the basis weight is about 526 g / m
^{Thus, 2} absorbers (1) were obtained. Next, by incorporating the absorber (1) between the bag sheet (liquid impermeable sheet) having the leg gather and the liquid permeable top sheet, the weight 4
7 g of a disposable diaper (1) having a core concentration of 50% by weight was prepared.

20 g / cm ² for the disposable diaper (1)
(Approximately 1.93 kPa) with a flat plate-shaped weight,
When physiological saline was injected from the center hole of the plate under pressure, the disposable diaper (1) obtained from the water-absorbent resin powder (19) obtained through the cooling step showed a saturated absorption capacity of about 470 g. . (Comparative Example 7) ... Preparation of sanitary material Same as Example 22 except that the comparative water absorbent resin powder (6) obtained in Comparative Example 6 was used instead of the water absorbent resin powder (19) in Example 22. In this manner, a comparative diaper (1) was obtained. As in Example 22, the comparative disposable diaper (1) was given a load of 20 g / cm ² (about 1.93 kPa) with a flat plate-shaped weight, and physiological saline was injected under pressure from the center hole of the plate. The comparative disposable diaper (1) exhibited a saturated absorption capacity of about 410 g, and was inferior to the disposable diaper (1) obtained from the water-absorbent resin powder (19) having undergone the cooling step.

[0099]

[Table 1]

[0100]

[Table 2]

Examples 1 to 7 and Example 1 shown in Table 1
No. 4, the average particle diameter of the water-absorbent resin powder after pulverization was 200 μm.
m to 600 μm, and the ratio of particles having a size of 150 μm or less to 850 μm or more is 15% by weight or less, which is a preferable range in the present invention. On the other hand, in Comparative Examples 1 and 2, the average particle size of the water-absorbent resin powder after pulverization is out of the range of 200 μm to 600 μm, and the ratio of particles having a size of 150 μm or less to 850 μm or more exceeds 15% by weight. I understand.
Further, from the results shown in Table 1, the present application in which the dried polymer is forcibly cooled after heating and drying, preferably in the range of 85 ° C to 35 ° C, more preferably 80 to 40 ° C, and still more preferably 70 to 45 ° C. In Examples 1 to 5, ON products (850 μm or more) deviating from the predetermined particle size were significantly reduced as compared with Comparative Examples 1 and 2 of the present invention in which forced cooling was not performed, and the present invention is excellent in average particle size and particle size distribution. You can see that it is.

Further, from the results shown in Table 1, in the present invention, the adhesion and clogging of the dried polymer to the wire mesh are reduced,
It can be seen that the drying efficiency (drying speed, uniformity) increases.
In addition, it can be seen that there is no significant difference between the temperatures of 40 ° C. and 60 ° C., and that the temperature up to 60 ° C. is sufficient when considering the size of the cooling equipment. Further, although not described in the table, the water-absorbent resin powder of the present invention also has an advantage that aggregation after pulverization is small. From the results shown in Table 2, it can be seen that in the present invention, the addition of the aqueous liquid was uniform and the physical properties were excellent. Example 1
A comparison of 0 to 13 shows that when the bulk specific gravity after pulverization is 0.65 g / ml or more, the water absorption capacity under pressure (in particular, 4.90 kPa) is further improved. As shown in the parentheses in the table, the absorption capacity under pressure (1.93 kPa and 4.90 kPa) hardly decreases even after the impact, and the impact resistance and liquid permeability are excellent. Comparison of Examples 15 to 17 shows that the temperature of the powder and the temperature of the inner wall of the mixer are important for the addition of the aqueous liquid.

Further, although the above examples are compared in a series of continuous operations, the effect of the present invention is that in the case of continuous production, in particular, 1 t / day or more, preferably 10 t / day, of a water-absorbent resin powder per line. It appears more remarkably when continuous drying for more than one day, continuous grinding and subsequent addition of an aqueous liquid.
It should be noted that specific embodiments or examples made in the section of the detailed description of the invention clarify the technical contents of the present invention, and are limited to only such specific examples in a narrow sense. It should not be construed, but may be practiced with various modifications within the spirit of the invention and the scope of the following claims.

[Brief description of the drawings]

FIG. 1 is a process chart showing a typical example of a process for producing a water-absorbent resin powder of the present invention. The present invention is suitable for a continuous process including polymerization, drying and pulverization, and shows an example thereof.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Nobuyuki Harada 992, Nishioki, Okihama-shi, Abashi-ku, Himeji-shi, Hyogo Nippon Shokubai Co., Ltd. Inside Nippon Shokubai (72) Inventor Shinichi Fujino 992, Nishioki, Okihama-shi, Abashiri-ku, Himeji-shi, Hyogo Japan F-Term (in reference) AJ09Q AK01P CA01 CA04 CA05 CA23 CA31 GC26 GC32 HA53 JA60

Claims (19)

[Claims] 1. A method for producing a water-absorbent resin powder, comprising heating and drying a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent, followed by grinding. Has an average particle size of 200 to 6
00 μm, and 150 μm or less to 8 μm.
A method for producing a water-absorbent resin powder, wherein the proportion of particles having a particle size of 50 μm or more is 15% by weight or less, and the dried polymer after heating and drying is cooled before or during pulverization. 2. The method for producing a water-absorbent resin powder according to claim 1, wherein the surface of the pulverized water-absorbent resin powder is further crosslinked. 3. The temperature of the heating and drying is in the range of 110 to 230 ° C., the temperature of the forced cooling after the heating and drying is 85 to 35 ° C., and the temperature of the surface crosslinking after the pulverization is 110 to 230 ° C. A method for producing the water-absorbent resin powder according to claim 2. 4. The process for producing a water-absorbent resin powder according to claim 1, wherein the solid content of the dried polymer is 93 to 97% by weight. 5. The method for producing a water-absorbent resin powder according to claim 1, wherein the hydrogel crosslinked polymer is laminated in a particle form to a fixed thickness of 1 to 20 cm and dried. 6. The method for producing a water-absorbent resin powder according to claim 1, wherein heat obtained by forced cooling of the dried polymer is reused. 7. A pulverized water-absorbent resin powder having a bulk specific gravity of 0.6
The method for producing a water-absorbent resin powder according to any one of claims 1 to 6, wherein the amount is 5 g / ml or more. 8. The method for producing a water-absorbent resin powder according to claim 1, wherein after pulverization, the obtained water-absorbent resin powder is further forcibly heated or kept warm. 9. The method for producing a water-absorbent resin powder according to any one of claims 1 to 8, further comprising adding an aqueous liquid to the obtained water-absorbent resin powder after pulverizing after forced cooling. 10. A process for producing a water-absorbent resin powder, comprising heating and drying a water-containing gel-like crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent, and then pulverizing the dried polymer. A method for producing a water-absorbent resin powder, wherein heat obtained by forced cooling is reused for forced heating in a process for producing a water-absorbent resin. 11. A water-absorbent resin powder in which an aqueous liquid is added to a powder obtained by heating and drying a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent, followed by pulverization in a mixer. The heating and drying temperature is in the range of 110 to 230 ° C., the dry polymer is cooled to 80 to 35 ° C. before adding the aqueous liquid, and the bulk specific gravity of the dry polymer after pulverization 0.65 g
/ Ml or more, a method for producing a water-absorbent resin powder. 12. The method for producing a water-absorbent resin powder according to claim 11, wherein forced cooling of the dried polymer is performed before pulverization. 13. The method according to claim 11, wherein the aqueous liquid is an aqueous polyhydric alcohol solution. 14. A water-absorbent resin powder in which an aqueous liquid is added in a mixer to a powder obtained by heating and drying a water-containing gel-like crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinker, and then pulverizing the powder. Wherein the heating and drying temperature is in the range of 110 to 230 ° C, the dry polymer is cooled to 80 to 35 ° C before adding the aqueous liquid, and the inner wall temperature of the mixer is 40 ° C or higher. A method of producing a water-absorbent resin powder, characterized by being a stirring mixer of (1) and reheating to 110 to 230 ° C. 15. A method for producing a water-absorbent resin powder, comprising heating and drying a water-containing gel-like crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent, and then pulverizing the dried polymer. Forced cooling, pulverizing the dried polymer into a water-absorbent resin powder having a bulk specific gravity of 0.65 g / ml or more, and further surface-crosslinking the cooled water-absorbent resin powder. Method for producing resin powder. 16. A method for producing a water-absorbent resin powder, comprising heating and drying a water-containing gel-like cross-linked polymer obtained by polymerizing an aqueous monomer solution containing a cross-linking agent, and pulverizing the dried polymer. Forced cooling, pulverizing the dried polymer into a water-absorbent resin powder having a bulk specific gravity of 0.65 g / ml or more, further adding an aqueous liquid to the cooled water-absorbent resin powder, A method for producing a water-absorbent resin powder, which is added by a heated stirring mixer. 17. The absorption capacity under pressure (1.96 kPa) obtained through the production method according to any one of claims 1 to 16 is 25 g.
/ G or more of water-absorbent resin powder. 18. A multivalent polymer containing no volatile organic solvent in a mixer obtained by heating and drying a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinker and then pulverizing the same. (1) a bulk specific gravity of 0.65 g / ml or more, and (2) an average particle diameter of 200 to 6 obtained by adding an alcohol aqueous solution.
(3) a water-absorbent resin powder having an absorption capacity under pressure (1.96 kPa) of 25 g / g or more; (3) a total of particles of 150 μm or less to 850 μm or more being 10% by weight or less; 19. An absorbent article comprising the water-absorbent resin powder according to claim 17.