WO2015108084A1 - Process for producing absobent article - Google Patents

Abstract

Provided is a process for producing an absorbent article, said process enabling, in producing an absorbent article, water-absorbing resin particles which have absorbed moisture and therefore have lost fluidity to recover the fluidity without deterioration in the water absorption characteristics. A process for producing an absorbent article which contains both water-absorbing resin particles and water-insoluble inorganic particles as essential components, characterized by including a step for mixing the water-absorbing resin particles with the water-insoluble inorganic particles so as to make the content of the water-insoluble inorganic particles fall within a range of 0.01 to less than 10 mass% relative to 100 mass% of the water-absorbing resin particles.

Description

Method for manufacturing absorbent article

The present invention relates to a method for producing absorbent articles such as paper diapers and sanitary napkins, so-called incontinence pads.

Absorbent articles such as paper diapers and sanitary napkins, so-called incontinence pads, usually include an absorbent body, a liquid-permeable top sheet, and a liquid-impermeable back sheet. As a constituent material of the absorber, water-absorbing resin particles intended to absorb body fluid are widely used. As the water-absorbent resin particles, polyacrylic acid (salt) -based water-absorbent resins are often used from the viewpoint of water absorption characteristics.

For the purpose of improving the performance of the polyacrylic acid (salt) water-absorbing resin used in the absorber, for example, in Japanese Translation of PCT International Publication No. 2003-525105 (International Publication No. 01/30290), 30% or more of free acid groups are contained. It is described that the absorption performance of a liquid containing an electrolyte such as urine is improved by an absorbent containing polyacrylic acid and rehydrated layered double hydroxide anionic soil.

The water-absorbing resin particles are processed and absorbed by processing the water-absorbing resin particles and the fiber base material while maintaining the water-absorbing properties such as excellent water absorption when in contact with an aqueous liquid such as body fluid. When producing a body, even if the water-absorbent resin particles absorb moisture at the time of production or transportation, it has a handling property that exhibits excellent fluidity.

The polyacrylic acid (salt) water-absorbing resin is usually stored for a certain period of time after being manufactured as an article (absorber). Further, depending on the storage environment, it may be stored under high humidity conditions. At the time of storage, the polyacrylic acid (salt) water-absorbing resin may absorb moisture in the air and the water-absorbing resin particles may lose fluidity.

One object of the present invention is to provide a method for producing an absorbent article that recovers the fluidity of water-absorbent resin particles that have lost fluidity due to moisture absorption during the production of the absorbent article, without impairing the water-absorbing properties. It is to be.

In addition, the absorbent article is required to have a high absolute absorption amount of body fluid or the like as a basic physical property. Therefore, another object of the present invention is to provide an absorbent article having a high absorption amount.

The present invention is a method for producing an absorbent article comprising at least water-absorbing resin particles and water-insoluble inorganic particles, wherein the water-absorbing resin particles and the water-insoluble inorganic particles are added to 100% by mass of the water-absorbing resin particles. The present invention also relates to a method for producing an absorbent article, comprising a step of mixing such that the ratio of the water-insoluble inorganic particles is 0.01% by mass or more and less than 10% by mass.

Hereinafter, the present invention will be described in detail, but the scope of the present invention is not limited to these descriptions, and other than the following examples, the scope of the present invention can be changed and implemented as appropriate without departing from the spirit of the present invention. Moreover, in this invention, a weight and mass, weight% and mass%, a weight part, and a mass part are the same meaning, and use in a sentence is unified to a mass, a mass%, and a mass part.

[1] Definition of Terms (1-1) Water Absorbing Agent In the present specification, the “water absorbing agent” is an aqueous liquid gelling agent obtained mainly with water-absorbing resin particles. Here, the main component means that the content of the water-absorbing resin particles in the water-absorbing agent is preferably 70% by mass or more of the water-absorbing agent, more preferably 80% by mass or more, and still more preferably 90% by mass or more. (The upper limit is 100% by mass, preferably 99.99% by mass). Water-absorbing agents include water-absorbing resin particles, cationic polymer compounds, water-soluble polyvalent metal cation-containing compounds, surfactants, coloring inhibitors, urine resistance improvers, deodorants, fragrances, antibacterial agents, foaming Agents, pigments, dyes, fertilizers, oxidizing agents, reducing agents and the like may be contained in an amount of 0 to 10% by mass, preferably 0.1 to 1% by mass, respectively.

(1-2) Surface-crosslinked water-absorbing resin In the present specification, “surface-crosslinked water-absorbing resin” is an aqueous liquid gelling agent obtained by subjecting water-absorbing resin particles to a surface-crosslinking step.

(1-3) Polyacrylic acid (salt) water-absorbing resin The “water-absorbing resin” in the present specification means a water-swelling, water-insoluble polymer gelling agent. “Water swellability” means that the CRC (water absorption capacity under no pressure) specified by ERT441.2-02 is 5 g / g or more, and “water-insoluble” means ERT470.2- Extr defined in 02 (water-soluble component) is 0 to 50% by mass.

Further, the total amount (100% by mass) of the water-absorbent resin is not limited to the polymer, and may contain additives and the like within the range of maintaining the above performance, and the water-absorbent resin composition containing a small amount of additives. Is also collectively referred to as a water-absorbing resin in the present invention. The shape of the water-absorbing resin is powdery, particularly preferably a powdery water-absorbing resin having a particle size and water content described later, and is referred to as water-absorbing resin particles.

As used herein, “polyacrylic acid (salt) water-absorbing resin” optionally includes a graft component, and as a repeating unit, acrylic acid and / or a salt thereof (hereinafter referred to as “acrylic acid (salt)”). Is a polymer containing as a main component.

Specifically, among the total monomers (excluding the crosslinking agent) used in the polymerization, a polymer containing acrylic acid (salt) is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, More preferably, it refers to a water-absorbent resin containing 90 to 100 mol%, particularly preferably substantially 100 mol%. In the present invention, polyacrylate type (neutralization type) polymers are also collectively referred to as polyacrylic acid (salt) water-absorbing resins.

(1-4) “EDANA” and “ERT”
“EDANA” is an abbreviation for European Disposables and Nonwovens Associations, and “ERT” is an abbreviation for a method for measuring water-absorbent resin (EDANA Recommended Test Methods), which is a European standard. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the ERT original (known document: revised in 2002).

(A) "CRC" (ERT441.2-02)
“CRC” is an abbreviation for Centrifugation Retention Capacity (centrifuge retention capacity) and means water absorption capacity without pressure (hereinafter also referred to as “water absorption capacity”). Specifically, after 0.200 g of the water-absorbing resin in the non-woven fabric was freely swollen for 30 minutes with respect to a large excess of 0.9 mass% sodium chloride aqueous solution (physiological saline), further using a centrifuge. Water absorption ratio after draining at 250 G (unit: [g / g]).

(B) “AAP” (ERT442.2-02)
“AAP” is an abbreviation for Absorption Against Pressure, which means water absorption capacity under pressure. Specifically, 0.900 g of the water-absorbent resin was swollen under a load of 2.06 kPa (0.3 psi) for 1 hour against a 0.9 mass% sodium chloride aqueous solution (physiological saline). It is a water absorption magnification (unit; [g / g]).

(C) “PSD” (ERT420.2-02)
“PSD” is an abbreviation for Particle Size Distribution and means a particle size distribution measured by sieving. The mass average particle size (D50) and the particle size distribution width are measured by the same method as “Average Particle Diameter and Distribution of Particle Diameter” described in European Patent 0349240.

(1-5) Others In this specification, “X to Y” indicating a range means “X or more and Y or less” including X and Y. Further, “t (ton)” as a unit of mass means “Metric ton” (metric ton), and “ppm” means “mass ppm” unless otherwise noted. Further, “˜acid (salt)” means “˜acid and / or salt thereof”, and “(meth) acryl” means “acryl and / or methacryl”. Further, regarding physical properties and the like, unless otherwise specified, measurement is performed at room temperature (20 to 25 ° C.) and relative humidity 40 to 50% RH.

[2] Method for Producing Absorbent Article The method for producing an absorbent article of the present invention is a method for producing an absorbent article comprising at least water-absorbent resin particles and water-insoluble inorganic particles. And a step of mixing water-insoluble inorganic particles so that a ratio of the water-insoluble inorganic particles is 0.01% by mass or more and less than 10% by mass with respect to 100% by mass of the water-absorbent resin particles. It is a manufacturing method of an absorptive article.

According to the method for producing an absorbent article of the present invention, it is possible to recover the fluidity of the water-absorbent resin particles that have lost the fluidity due to moisture absorption without impairing the water-absorbing characteristics. Moreover, according to the manufacturing method of the absorbent article of this invention, an absorbent article with high absorption amount can be provided. Furthermore, according to the method for manufacturing an absorbent article of the present invention, an absorbent article having an excellent balance between the absorption amount and the return amount can be provided.

First, a method for producing polyacrylic acid (salt) -based water absorbent resin particles, which is a preferred embodiment of the method for producing water absorbent resin particles, will be described.

(2-1) Step of Preparing Acrylic Acid (Salt) Monomer Aqueous Solution In this specification, “acrylic acid (salt) monomer aqueous solution” means a single amount mainly composed of acrylic acid (salt). This is an aqueous solution of the body that contains components that make up the water-absorbing resin particles such as crosslinking agents, grafting components and trace components (chelating agents, surfactants, dispersants, etc.) as necessary. And a polymerization initiator added to the polymerization.

The acrylic acid (salt) may be unneutralized or salt type (completely neutralized type or partially neutralized type), and the monomer aqueous solution may exceed the saturation concentration, and acrylic acid ( Even a supersaturated aqueous solution of salt) or a slurry aqueous solution (aqueous dispersion) is treated as the acrylic acid (salt) monomer aqueous solution of the present invention. In addition, it is preferable to use the acrylic acid (salt) type monomer aqueous solution below saturation concentration from a viewpoint of the physical property of the water-absorbent resin particle obtained.

Also, water is preferred as the monomer solvent, and acrylic acid (salt) monomers are treated as aqueous solutions. Here, the “aqueous solution” means that 100% by mass of the solvent is not limited to water, and a water-soluble organic solvent (for example, alcohol) is preferably used in an amount of 0 to 30% by mass, more preferably 0 to 5% by mass. In the present invention, these are treated as aqueous solutions.

In the present specification, the “acrylic acid (salt) -based monomer aqueous solution being prepared” refers to a monomer aqueous solution containing acrylic acid (salt) as a main component before all components are mixed. It refers to an aqueous solution of acrylic acid (salt), and specifically includes an aqueous solution of acrylic acid and a completely neutralized or partially neutralized acrylate solution.

The final acrylic acid (salt) system can be obtained by further neutralizing the acrylic acid (salt) monomer aqueous solution being prepared, mixing water as a solvent, or mixing the above-mentioned trace components. A monomer aqueous solution is used. In addition, about this final acrylic acid (salt) monomer aqueous solution, the state before the polymerization is started before being charged into the polymerization apparatus or after being charged into the polymerization apparatus, “after the preparation before the polymerization step” Acrylic acid (salt) monomer aqueous solution ”.

(Monomer)
The monomer to be used is not particularly limited as long as it becomes a water-absorbent resin particle by polymerization. For example, (meth) acrylic acid, (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl Sulfonic acid, allyltoluenesulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid Anionic unsaturated monomers (salts) such as 2-hydroxyethyl (meth) acryloyl phosphate; mercapto group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; (meth) acrylamide, N- Contains amide groups such as ethyl (meth) acrylamide and N, N-dimethyl (meth) acrylamide Saturated monomer; amino group-containing unsaturated monomer such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide Etc. These monomers may be used alone or in combination of two or more.

The content (amount used) of acrylic acid (salt) is usually 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, based on the entire monomer (excluding the internal crosslinking agent). More preferably, it is 90 mol% or more, particularly preferably 95 mol% or more (the upper limit is 100 mol%). In addition, in this invention, polyacrylic acid (salt) is not limited to non-neutralization (neutralization rate 0 mol%), but is a concept including partial neutralization or complete neutralization (neutralization rate 100 mol%).

In the present invention, the neutralization rate of the acrylic acid (salt) monomer or the hydrogel crosslinked polymer after polymerization is not particularly limited, but the properties of the water-absorbent resin particles obtained and the reactivity with the surface crosslinking agent In view of the above, it is preferably 40 to 90 mol%, more preferably 50 to 80 mol%, still more preferably more than 70 mol% and 80 mol% or less.

However, when the neutralization rate is low, the water absorption rate (for example, FSR and Vortex) tends to decrease. Conversely, when the neutralization rate is high, the polyacrylic acid (salt) water-absorbing resin particles and the surface cross-linking agent are used. In particular, the reactivity with alkylene carbonate tends to decrease, and the productivity, liquid permeability (for example, SFC) and water absorption capacity under pressure (for example, AAP and PUP) tend to decrease. The sum is preferred. In applications that may come into contact with the human body, such as paper diapers, neutralization after polymerization is not required.

In addition, from the viewpoint of the non-pressurized water absorption capacity (CRC) and the pressurized water absorption capacity (AAP) of the obtained water-absorbent resin particles, the acrylic acid (salt) monomer or the hydrogel crosslinked polymer is partially or entirely. May be in a salt form, monovalent salts such as sodium salt, lithium salt, potassium salt, ammonium salt, amines are preferred, alkali metal salt is more preferred, sodium salt and / or potassium salt is more preferred, cost and physical properties In view of the above, sodium salt is particularly preferable.

(Polymerization inhibitor)
The acrylic acid (salt) monomer may contain a polymerization inhibitor. The polymerization inhibitor is not particularly limited, and examples thereof include N-oxyl compounds, manganese compounds, and substituted phenol compounds disclosed in International Publication No. 2008/096713. Of these, substituted phenol compounds are preferred, and methoxyphenols are more preferred.

Examples of the methoxyphenol include o, m, p-methoxyphenol, and methoxyphenol having one or more substituents such as a methyl group, a t-butyl group, and a hydroxyl group. -Methoxyphenol is particularly preferred.

The content of the polymerization inhibitor in the acrylic acid (salt) monomer is preferably 10 to 200 ppm, and in the following order, preferably 5 to 160 ppm, 10 to 160 ppm, 10 to 100 ppm, and 10 to 80 ppm. ˜70 ppm is most preferred. When the content is 10 to 200 ppm, the resulting water-absorbent resin particles have little deterioration in color tone (coloration such as yellowing and yellowing), and are not intended when the polymerization inhibitor is removed by purification such as distillation. Less risk of causing polymerization.

(Internal crosslinking agent)
The aqueous monomer solution may contain an internal crosslinking agent as required. As the internal cross-linking agent, known ones can be used. For example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethyl Roll propane tri (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, tri Allyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol Polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl (meth) acrylate, and the like. Among these, in consideration of reactivity, one or more kinds can be used, and among them, it is preferable to use a compound having two or more polymerizable unsaturated groups.

In addition, when two or more kinds of internal cross-linking agents are used in combination, the internal cross-linked structure can be changed by changing the reactivity of the functional group, so that an amide compound, a (meth) acrylate compound, an allyl compound, an amine compound It is preferable to select and use an internal cross-linking agent having a different functional group from the above exemplified compounds such as an imine compound, an alcohol compound, a carbonate compound, and a glycidyl compound.

The amount of the internal cross-linking agent to be used can be appropriately determined depending on the desired properties of the water-absorbent resin particles, but is preferably 0.001 to 5 mol%, based on the total acrylic acid (salt) monomer. 005 to 2 mol% is more preferable, and 0.01 to 1 mol% is still more preferable. When two or more types of internal cross-linking agents are used in combination, the amount of each internal cross-linking agent used is preferably 0.001 to 5 mol% with respect to the entire acrylic acid (salt) monomer. 0.005 to 2 mol% is more preferable, and 0.01 to 1 mol% is still more preferable.

When the amount used (the total amount in the case of two or more combinations) is 0.001 to 5 mol%, the water-absorbent resin particles obtained have a low water-soluble content, and the amount of water absorption under pressure can be reduced. The water-absorbent resin particles obtained can be adequately secured and the crosslinking density of the resulting water-absorbent resin particles becomes appropriate, so that the amount of water absorption is sufficient. The internal cross-linking agent may be added to the acrylic acid (salt) monomer aqueous solution after preparation before the polymerization step, or a part thereof may be added after the start of polymerization.

(2-2) Aqueous solution polymerization step (Polymerization method)
Examples of the polymerization method for obtaining water-absorbent resin particles include spray polymerization, droplet polymerization, bulk polymerization, precipitation polymerization, aqueous solution polymerization, or reverse phase suspension polymerization. Preferably, the monomer is an aqueous solution. Aqueous polymerization is used.

The aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, U.S. Pat. Nos. 4,462,001, 4,873,299, 4,286,682, 4,973,632, and 4,985,518. , No. 5124416, No. 5,250,640, No. 5,264,495, No. 5,145,906, No. 5,380,808, European Patent Nos. 081636, 09555086, No. 0922717, etc. This also applies to the present invention.

The concentration of the aqueous monomer solution during the polymerization is not particularly limited, but is preferably 20% by mass to saturated concentration or less, more preferably 25 to 80% by mass, and further preferably 30 to 70% by mass. When the concentration is 20% by mass or more, a decrease in productivity can be suppressed. It is to be noted that the polymerization in the monomer slurry (aqueous dispersion of acrylate) shows a decrease in physical properties. Therefore, the polymerization is preferably carried out at a saturated concentration or less (see Japanese Patent Application Laid-Open No. 1-318021).

Also, in order to promote polymerization and improve physical properties, a dissolved oxygen degassing step (for example, a substitution step with an inert gas) may be provided as necessary during the polymerization. In addition, for the purpose of increasing the water absorption speed, increasing the surface area, increasing the drying speed, etc., bubbles (particularly inert gas) and various foaming agents (for example, organic or inorganic carbonates, azo compounds, urea compounds) are included during polymerization. At the time of polymerization or drying, for example, foaming may be performed so that the volume becomes 1.001 to 10 times.

The polymerization step in the present invention can be carried out at normal pressure, reduced pressure, or increased pressure, but is preferably carried out at normal pressure (or in the vicinity thereof, usually atmospheric pressure ± 10 mmHg). The temperature at the start of the polymerization is preferably 15 to 130 ° C., more preferably 20 to 120 ° C., although it depends on the type of polymerization initiator used.

(Polymerization initiator)
The polymerization initiator used in the present invention is appropriately determined depending on the polymerization form and is not particularly limited, and examples thereof include a photodegradable polymerization initiator, a thermal decomposition polymerization initiator, and a redox polymerization initiator. Polymerization is initiated by these polymerization initiators.

Examples of the photodegradable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds. Specifically, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylbenzoin, α-phenylbenzoin, anthraquinone, methylanthraquinone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2 -Phenylacetone, benzyldiacetylacetophenone, benzophenone, p-chlorobenzophenone, 2-hydroxy-2-methylpropiophenone, diphenyl disulfide, tetramethylthiuram sulfide, α-chloromethylnaphthalene, anthracene, hexachlorobutadiene, pentachlorobutadiene, Michler's ketone 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzyldimethyl ketal, bis (2,4,6- Limethylbenzoyl) -phenylphosphine oxide, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropanone-1,2-hydroxy-2-methyl-1-phenylpropan-1-one, And 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one. Such a photodegradable polymerization initiator may be a commercially available product, such as Irgacure (registered trademark) 184 (hydroxycyclohexyl-phenyl ketone), Irgacure (registered trademark) 2959 (1- [4- (2 -Hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one) and the like.

Examples of the thermal decomposition polymerization initiator include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide; 2 Azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride and 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride.

Furthermore, examples of the redox polymerization initiator include a system in which a reducing compound such as L-ascorbic acid or sodium bisulfite is used in combination with the persulfate or peroxide.

Also, it is a preferable aspect to use the photodecomposition polymerization initiator and the thermal decomposition polymerization initiator in combination. Furthermore, active energy rays such as ultraviolet rays, electron beams, and γ rays may be used alone or in combination with the above polymerization initiator.

The amount of the polymerization initiator used is preferably 0.0001 to 1 mol%, more preferably 0.0005 to 0.5 mol%, based on the monomer. It is preferable that the amount used be in the above-mentioned range since the color tone deterioration of the water-absorbent resin particles is small and the residual monomer is also small.

(Additives, etc.)
In the above polymerization, a chain transfer agent such as hypophosphorous acid (salt), a chelating agent such as diethylenetriaminepentaacetic acid (salt), a coloring inhibitor described later or A urine resistance improver or the like may be added.

(More suitable polymerization method)
In the present invention, the polymerization method of the acrylic acid (salt) monomer aqueous solution is a reverse phase suspension from the viewpoint of the physical properties (for example, water absorption rate and liquid permeability) of the water absorbent resin particles and the ease of polymerization control. At least one of polymerization, spray polymerization, droplet polymerization or aqueous solution polymerization, particularly aqueous solution polymerization is employed.

As an example of a preferred embodiment of the aqueous solution polymerization, the polymerization initiation temperature is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, further preferably 60 ° C. or higher, particularly preferably 70 ° C. or higher, and most preferably 80 ° C. or higher (the upper limit is High-temperature initiating aqueous solution polymerization to the boiling point) or the monomer concentration is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more (the upper limit is 90% by mass or less, preferably 80% by mass). % Or less, more preferably 70% by mass or less), and high-concentration / high-temperature initiating aqueous solution polymerization combining these.

As the polymerization form, kneader polymerization or belt polymerization is preferable. As the preferable form of the aqueous solution polymerization, continuous belt polymerization (US Pat. Nos. 4,893,999, 6,241,928, US Patent Application Publication No. 2005/215734, International Publication No. 2008/114847), continuous kneader polymerization, batch kneader polymerization (disclosed in US Pat. Nos. 6,987,151, 6,710,141, and International Publication No. 2008/114848).

Furthermore, high temperature initiation continuous aqueous solution polymerization, high concentration continuous aqueous solution polymerization, and high concentration / high temperature initiation continuous aqueous solution polymerization, which combine the above preferred embodiments and preferred polymerization forms, can be mentioned.

Another preferable example is batch kneader polymerization or continuous kneader polymerization in which the polymerization start temperature is 15 ° C. or more and the monomer concentration is 30% by mass or more.

In the above polymerization, the polymerization start time (the time from when the polymerization initiator is added until the polymerization starts) is preferably more than 0 and within 300 seconds, and more preferably from 1 to 240 seconds.

(2-3) Gel Grinding Step In this step, the hydrous gel-like crosslinked polymer (hereinafter referred to as “hydrous gel”) obtained through the above-described polymerization step (particularly aqueous solution polymerization) is gel-crushed to form a particulate hydrous powder. This is an optional step for obtaining a gel (hereinafter referred to as “particulate hydrous gel”).

In the aqueous solution polymerization, the water-containing gel is finely divided by gel pulverization, particularly gel pulverization by kneading, so that both the water absorption speed and the liquid permeability can be achieved, and the impact resistance is also improved. That is, aqueous polymerization in which gel pulverization is performed particularly during polymerization (for example, kneader polymerization) or after polymerization (for example, belt polymerization, and further, kneader polymerization if necessary) is preferable.

The gel pulverizer that can be used in the present invention is not particularly limited. For example, a gel pulverizer having a plurality of rotary stirring blades such as a batch-type or continuous double-arm kneader, a single-screw extruder, and a twin-screw extruder. , Meat chopper and the like. Among these, a screw type extruder having a perforated plate at the tip is preferable, and examples thereof include a screw type extruder disclosed in Japanese Patent Application Laid-Open No. 2000-063527.

In the gel grinding step of the present invention, the temperature of the hydrogel before gel grinding (gel temperature) is preferably 60 to 120 ° C., more preferably 65 to 110 ° C., from the viewpoints of particle size control and physical properties. When the gel temperature is within the above range, the hardness (softness) of the hydrogel is optimized, and the particle shape and particle size distribution can be easily controlled during gel pulverization. The gel temperature can be controlled by the temperature during polymerization, heating or cooling after polymerization, and the like.

Further, the mass average particle diameter (D50) (specified by sieve classification) of the particulate hydrogel after gel pulverization is preferably 0.5 to 10 mm, more preferably 1.0 to 10 mm, and 2.0 to 8.0 mm. Is more preferable. Further, the ratio of coarse particles having a particle diameter of more than 10 mm contained in the particulate hydrogel to be subjected to the subsequent drying step is preferably 10% by mass or less, more preferably 5% by mass or less of the entire particulate hydrous gel. 1 mass% or less is still more preferable.

In the present invention, the polymerization step and the gel grinding step are a kneader polymerization method in which the water-containing gel-like crosslinked polymer is gel-ground during polymerization, a method in which the water-containing gel-like crosslinked polymer obtained by continuous belt polymerization is subjected to the gel grinding step, Any method of performing the polymerization step and the gel grinding step in a batch can be carried out.

(2-4) Drying step This step is a step of drying the hydrogel obtained through the above polymerization step and the like to obtain a dry polymer. In addition, when the said superposition | polymerization process is aqueous solution polymerization, gel grinding | pulverization (fine-graining) is performed before drying of a hydrogel and / or after drying. Moreover, the dry polymer (aggregate) obtained by a drying process may be supplied to a grinding | pulverization process as it is.

The drying method in the present invention is not particularly limited, and various methods can be employed. Specific examples include heat drying, hot air drying, vacuum drying, infrared drying, microwave drying, azeotropic dehydration drying with a hydrophobic organic solvent, and high humidity drying using high-temperature steam. Or 2 types can also be used together. The drying temperature is preferably from 100 to 300 ° C, more preferably from 150 to 250 ° C.

Also, the drying time depends on the surface area and water content of the hydrogel, the type of dryer, etc., and for example, 1 minute to 5 hours is preferable, and 5 minutes to 1 hour is more preferable. Further, the resin solid content obtained from loss on drying (1 g of sample (hydrogel or water-absorbent resin particles) is dried at 180 ° C. for 3 hours) is preferably 80% by mass or more, more preferably 85 to 99% by mass, and more preferably 90 to 98 mass% is still more preferable.

(2-5) Pulverization / Classification Step This step is a step for pulverizing and / or classifying the dried polymer obtained in the drying step to obtain water absorbent resin particles having a specific particle size. The (2-3) gel pulverization step is different in that the object to be pulverized has undergone a drying step. Further, the water absorbent resin particles after the pulverization step may be referred to as a pulverized polymer.

(Particle size distribution)
The mass average particle diameter (D50) of the water-absorbing resin particles used in the subsequent surface cross-linking step is preferably in the range of 200 to 600 μm from the viewpoint of water absorption speed, liquid permeability, water absorption capacity under pressure, and the like. The range of 550 μm is more preferable, the range of 250 to 500 μm is still more preferable, and the range of 300 to 450 μm is particularly preferable.

Further, the smaller the number of fine particles having a particle diameter of less than 150 μm defined by standard sieve classification, the better. From the viewpoint of liquid permeability, the content of the fine particles is preferably 0 to 5% by mass, more preferably 0 to 3% by mass, 0 to 1% by mass is more preferable. Further, the smaller the coarse particles having a particle size of 850 μm or more, preferably 710 μm or more, as defined by the standard sieve classification, the better. From the viewpoint of water absorption rate, the content of coarse particles is preferably 0 to 5% by mass, 3% by mass is more preferable, and 0 to 1% by mass is even more preferable.

The particle size distribution range is preferably 150 μm or more and less than 850 μm, more preferably 150 μm or more and less than 710 μm, from the viewpoint of water absorption speed, liquid permeability, water absorption capacity under pressure, etc. It is more preferable that 98% by mass or more is included, and 99% by mass or more is more preferable (the upper limit is 100% by mass).

The particle size can be controlled in the polymerization step, the gel pulverization step, or the pulverization / classification step in the drying step, but is particularly preferably performed in the classification step after drying. The particle size is measured using a JIS standard sieve (Z8801-1 (2000)) according to a method defined in International Publication No. 2004/69915 or EDANA-ERT420.2-02.

Further, the shape of the water-absorbent resin particles of the present invention may be a spherical shape or an aggregate thereof, or may be an indeterminate shape (crushed shape) obtained through a pulverization process on a hydrous gel or a dry polymer. From the viewpoint, an irregular shape (crushed) or a granulated product thereof is preferable.

In order to further solve the problem of the present invention, the above particle size is preferably applied to the water-absorbing agent, preferably after the surface crosslinking step. That is, the water-absorbing agent of the present invention is preferably contained in a range of 150 μm or more and less than 850 μm, more preferably 150 μm or more and less than 710 μm, from the viewpoint of water absorption speed, liquid permeability, water absorption capacity under pressure, etc. It is more preferable that 98% by mass or more is included, and 99% by mass or more is more preferable (the upper limit is 100% by mass).

(2-6) Fine powder recovery step Water-absorbing property including a classification step after the drying step (including the second classification step after the surface cross-linking step, the same shall apply hereinafter), and passing through a standard sieve having a mesh size of 150 μm. After separating the resin fine particles, it is preferable to collect (reuse) the water-absorbent resin fine particles or a water additive thereof in a step before the drying step. The coarse particles removed in the classification step may be re-pulverized as necessary, and the water absorbent resin fine particles removed in the classification step may be discarded or used for other purposes. Or you may use for this fine powder collection | recovery process.

The water absorption rate (for example, FSR) can be further improved by removing the water absorbent resin fine particles.

That is, in the production method of the present invention, the fine powder collecting step includes water-absorbing resin fine particles (particularly those containing 70% by mass or more of particles having a particle size of 150 μm or less. May be referred to as “fine powder.”) And then collected as it is, or hydrated or granulated, and collected before the drying step, preferably in the polymerization step, gel grinding step or drying step. Refers to a process.

By collecting the fine powder, the particle size of the water-absorbing resin particles can be controlled, and the water absorption rate can be further improved by this step.

The fine powder to be recovered may be a fine powder before the surface cross-linking step or a fine powder after the surface cross-linking step, and the amount of fine powder recovered is preferably 1 to 40% by mass of the dry polymer, and more preferably 5 to 30% by mass.

The fine powder recovery method suitable for the present invention is a method in which a water-absorbent resin fine powder or a hydrate or granulated product thereof is mixed with an aqueous monomer solution before polymerization or a water-containing gel during polymerization, if necessary. is there. The method for recovering the monomer aqueous solution before the polymerization is WO 92/001008 and 92/020723, and the method for recovering the hydrogel during polymerization is WO 2007/074167, No. 2009/109563, No. 2009/153196, No. 2010/006937, and a recovery method to a drying step (dryer) are disclosed in US Pat. No. 6,228,930, etc. The recovery method is preferably applied to the present invention.

(2-7) Surface cross-linking agent addition step This step is an optional step for preparing water-absorbing resin particles containing a surface cross-linking agent for use in the surface cross-linking step. In general, surface cross-linking is performed by adding an organic surface cross-linking agent described later, polymerizing monomers on the surface of water-absorbent resin particles, or adding a radical polymerization initiator such as persulfate, and heating / ultraviolet irradiation. Is called. In the present invention, it is preferable to add an organic surface cross-linking agent to the water absorbent resin particles obtained in the classification step, and further to the water absorbent resin particles including the water absorbent resin particles obtained through the fine powder collection step. Moreover, you may perform simultaneously the liquid permeability improving agent addition process mentioned later.

(Organic surface cross-linking agent)
As the organic surface crosslinking agent that can be used in the present invention, from the viewpoint of the physical properties of the water-absorbing resin particles obtained, a carboxyl group that is a functional group of the polyacrylic acid (salt) -based water-absorbing resin particles, An organic compound having a reactive group such as a hydroxyl group and / or an amino group that undergoes dehydration amidation reaction is preferable. The organic compound is not limited to an alcohol compound or an amine compound having a hydroxyl group or an amino group directly, and even if it is a cyclic compound such as an alkylene carbonate compound or an oxazolidinone compound, a reactive group and / or a hydroxyl group and an amino group are generated. A compound having a reactive group that directly reacts with the carboxyl group is also included.

Examples of organic surface crosslinking agents include polyhydric alcohol compounds, epoxy compounds, polyvalent amine compounds or condensates thereof with haloepoxy compounds, oxazoline compounds, (mono, di, or poly) oxazolidinone compounds, oxetane compounds, alkylene carbonate compounds, and the like. An epoxy compound, a polyhydric alcohol compound, an alkylene carbonate compound, and an oxazolidinone compound are more preferable. These may be used alone or in combination of two or more.

Specific examples of the organic surface crosslinking agent include (di, tri, tetra, poly) ethylene glycol, (di, poly) propylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, (Poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, di- or triethanol Polyalcohol compounds such as amine, pentaerythritol, sorbitol; epoxy compounds such as (poly) ethylene glycol diglycidyl ether, (di, poly) glycerol polyglycidyl ether, glycidol; 2-oxazolidone, N-hydroxyethyl-2-oxazolidone, 1,2-ethylenebisoxa Oxazoline compounds such as phosphorus; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4- Dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxane-2-one , Alkylene carbonate compounds such as 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, 1,3-dioxopan-2-one; epichlorohydrin Haloepoxy compounds such as epibromhydrin and α-methylepichlorohydrin, and polyvalent amine adducts thereof (for example, Kaymen (registered trademark) manufactured by Hercules); γ-glycidoxy Silane coupling agents such as propyltrimethoxysilane and γ-aminopropyltriethoxysilane; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3 Oxetane compounds such as oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl 3-oxetane ethanol, 3-chloromethyl-3-methyl oxetane, 3-chloromethyl-3-ethyl oxetane, polyvalent oxetane compounds, And cyclic urea compounds such as 2-imidazolidinone.

The polyhydric alcohol is preferably a polyhydric alcohol having 2 to 8 carbon atoms, more preferably a polyhydric alcohol having 3 to 6 carbon atoms, and still more preferably a polyhydric alcohol having 3 to 4 carbon atoms. Furthermore, a diol is preferable, and examples thereof include ethylene glycol, propylene glycol, 1,3-propanediol, and 1,4-butanediol. Of these, polyhydric alcohols selected from propylene glycol (1,2-propanediol), 1,3-propanediol, and 1,4-butanediol are more preferable.

The epoxy compound is preferably a polyglycidyl compound, ethylene glycol diglycidyl ether is preferably used, the oxazoline compound is preferably 2-oxazolidinone, and the alkylene carbonate compound is 1,3-dioxolan-2-one. (Ethylene carbonate) is preferably used.

Furthermore, it is preferable to use a combination of two or more compounds selected from polyhydric alcohol compounds, epoxy compounds, oxazoline compounds, and alkylene carbonate compounds. From the viewpoint of higher physical properties, a combination of a polyhydric alcohol and the organic surface cross-linking agent other than the polyhydric alcohol is preferable, a combination of a polyhydric alcohol and an epoxy compound and / or an alkylene carbonate compound is more preferable, and CRC is improved. From the viewpoint, it is more preferable to use a combination of at least a polyhydric alcohol and an alkylene carbonate compound.

When combining the plurality of organic surface cross-linking agents, particularly in the combination of the polyhydric alcohol and the organic surface cross-linking agent other than the polyhydric alcohol, the ratio (mass ratio) is 1 except for the polyhydric alcohol: polyhydric alcohol. : 100 to 100: 1 is preferable, 1:50 to 50: 1 is more preferable, and 1:30 to 30: 1 is still more preferable.

The temperature of the solvent in which these are mixed is appropriately determined. However, if the temperature is too low, the solubility and viscosity may become too low. When water is used as a surface cross-linking agent, water heated to room temperature or higher (preferably 30 to 100 ° C., more preferably 35 to 70 ° C., and further preferably 40 to 65 ° C.) is used as the solvent.

That is, other compounds to be mixed with non-polymeric organic compounds (especially solid surface crosslinking agents, and further cyclic compounds such as solid polyhydric alcohols and alkylene carbonates), particularly water, are preferably heated. It is more preferable that it is in the temperature range.

The alkylene carbonate compound or the polyhydric alcohol compound, particularly the solid alkylene carbonate compound, is preferably heated in advance before mixing with water. The heating temperature is preferably higher than the temperature of the aqueous surface crosslinking agent solution after the addition of water. Specifically, in the case of a solid alkylene carbonate compound, polyhydric alcohol, particularly solid polyhydric alcohol is also heated and melted. The temperature is preferably 30 to 100 ° C., more preferably 35 to 70 ° C., and still more preferably 40 to 65 ° C.

(Solvent and concentration)
The total amount of the organic surface cross-linking agent added is preferably 0.001 to 15 parts by mass, and 0.01 to 5 parts by mass with respect to 100 parts by mass of the water absorbent resin particles before the addition. More preferably.

Moreover, when using 2 types chosen from compounds other than a polyhydric alcohol compound and a polyhydric alcohol as said organic surface crosslinking agent, a polyhydric alcohol compound with respect to 100 mass parts of said water absorbent resin particles before addition. Is preferably 0.001 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and the total amount of compounds other than polyhydric alcohols is 0.001 to 10 parts by mass. It is preferably 0.01 to 5 parts by mass.

The organic surface cross-linking agent is preferably added as an aqueous solution. The amount of water used in the aqueous solution is preferably 0.5 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the water absorbent resin particles before the addition treatment. Note that the amount of water includes crystallization water, hydration water, and the like, which are surface crosslinking agents.

Furthermore, a hydrophilic organic solvent may be added to the organic surface cross-linking agent aqueous solution, and the amount of the hydrophilic organic solvent is more than 0 parts by mass with respect to 100 parts by mass of the water-absorbing resin particles before the addition treatment. The amount is preferably not more than mass parts, more preferably more than 0 mass parts and not more than 5 mass parts. Examples of the hydrophilic organic solvent include primary alcohols having 1 to 4 carbon atoms, more preferably 2 to 3 carbon atoms, and lower ketones having 4 or less carbon atoms such as acetone. In the case of volatile alcohols having a temperature of less than 150 ° C., more preferably less than 100 ° C., the volatile alcohol is volatilized during the surface cross-linking treatment, so that no residue remains, which is more preferable.

Specifically, lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol and t-butyl alcohol; ketones such as acetone; dioxane, tetrahydrofuran, methoxy (poly ) Ethers such as ethylene glycol; Amides such as ε-caprolactam and N, N-dimethylformamide; Sulphoxides such as dimethyl sulfoxide; Polyhydric alcohols such as polyoxypropylene and oxyethylene-oxypropylene block copolymers Is mentioned.

Furthermore, when mixing the surface cross-linking agent solution with the water-absorbent resin particles, the water-insoluble fine particles and the surfactant are added to 100 parts by weight of the water-absorbent resin particles before the addition treatment within a range that does not hinder the effects of the present invention. On the other hand, it is preferably more than 0 parts by mass and 10 parts by mass or less, more preferably more than 0 parts by mass and 5 parts by mass or less, still more preferably more than 0 parts by mass and 1 part by mass or less. In this case, the surfactant used is disclosed in US Pat. No. 7,473,739. Examples of the water-insoluble fine particles include silicon dioxide (silica), zeolite, talc, and titanium dioxide.

The concentration of the surface crosslinking agent in the surface crosslinking agent solution is appropriately determined. From the viewpoint of physical properties, it is preferably 1 to 80% by mass, more preferably 5 to 60% by mass, still more preferably 10 to 40% by mass, and particularly preferably. Is an aqueous solution of 15 to 30% by mass. The remainder contains the hydrophilic organic solvent and other components.

The temperature of the surface cross-linking agent solution is appropriately determined based on the solubility of the organic surface cross-linking agent used, the viscosity of the aqueous solution, etc., but is preferably −10 to 100 ° C., more preferably 5 to 70 ° C., and further preferably 10 to 65 ° C. A range of 25 to 50 ° C. is particularly preferable. By being within the above range, before mixing or reacting with the water-absorbent resin particles, the cyclic compound is hydrolyzed (for example, decomposition from ethylene carbonate to ethylene glycol, decomposition from oxazolidinone to ethanolamine), water, This is preferable because there are few harmful effects such as volatilization of the hydrophilic organic solvent and the mixing property is lowered, and there is little possibility that the surface crosslinking agent solution is solidified or the surface crosslinking agent is precipitated.

(Use of acid or base in the surface cross-linking agent solution)
The surface crosslinking agent solution may contain an acid or base in addition to the organic surface crosslinking agent, water, hydrophilic organic solvent, surfactant and water-insoluble fine particles in order to promote the reaction and uniform mixing of the surface crosslinking agent. Good.

As the acid or base, an organic acid or a salt thereof, an inorganic acid or a salt thereof, or an inorganic base is used, and is preferably 0 to 10 parts by mass, more preferably 100 parts by mass with respect to 100 parts by mass of the water absorbent resin particles before the addition treatment. Is suitably used in an amount of 0.001 to 5 parts by mass, more preferably 0.01 to 3 parts by mass. The organic acid is preferably a water-soluble organic acid having 1 to 6 carbon atoms, more preferably 2 to 4 carbon atoms, a water-soluble saturated organic acid, particularly a saturated organic acid containing a hydroxyl group.

Other examples include non-crosslinkable water-soluble inorganic bases (preferably alkali metal salts, ammonium salts, alkali metal hydroxides, and ammonia or hydroxides thereof), and non-reducing alkali metal salt pH buffering agents. (Preferably bicarbonate, dihydrogen phosphate, hydrogen phosphate, etc.).

(Method of adding organic surface crosslinking agent solution)
By the addition treatment, the organic surface cross-linking agent is added to the water-absorbent resin particles. The method of the addition treatment is not particularly limited. For example, the water-absorbing resin particles are immersed in a hydrophilic organic solvent to adsorb the added cross-linking agent, or the added cross-linking agent solution is sprayed or dropped directly on the water-absorbing resin particles. From the viewpoint of uniformly adding a predetermined amount, the latter is preferable. Furthermore, in order to add uniformly, it is preferable to perform the addition treatment while stirring the water-absorbent resin particles, and it is preferable to spray the surface cross-linking agent solution.

In the addition treatment, two or more types of crosslinking agents having different compositions may be added simultaneously using different spray nozzles, for example, but a single composition is preferred from the viewpoint of uniformity and the like. Moreover, if it is a single composition, you may use several spray nozzles in consideration of the magnitude | size of an addition processing apparatus, the processing amount, the spray angle of a spray nozzle, etc. FIG.

Examples of the apparatus used for the addition treatment (hereinafter sometimes referred to as a mixing apparatus) include, for example, a cylindrical mixer, a double wall conical mixer, a V-shaped mixer, a ribbon mixer, and a screw-type mixer. Suitable are a machine, a fluidized-type furnace, a rotary disk mixer, an airflow-type mixer, a double-arm kneader, an internal mixer, a pulverizing kneader, a rotary mixer, a screw-type extruder, a turbuler, a pro-share mixer, etc. . Furthermore, in large-scale production such as commercial production, an apparatus capable of continuous mixing is preferable. Moreover, the same apparatus may be used for each addition process, and a different apparatus may be used.

The water absorbent resin particles used in this step are preferably heated and kept warm, and the temperature is preferably in the range of 30 to 100 ° C., more preferably 35 to 80 ° C., still more preferably 40 to 70 ° C. It is. By heating and holding at the above-mentioned suitable temperature, surface treatment is less likely to be insufficient or non-uniform due to precipitation of the surface cross-linking agent, moisture absorption of the water-absorbing resin particles, etc. There is little possibility that precipitation of the surface cross-linking agent or the like occurs due to evaporation of the liquid.

(2-8) Surface cross-linking step In this step, heat treatment is performed to cross-link the surface of the water-absorbent resin particles or the vicinity of the surface in order to improve the water absorption capacity and liquid permeability under pressure. It is an optional process. It can be carried out simultaneously with the surface cross-linking agent addition step or after the surface cross-linking agent addition step, preferably after the surface cross-linking agent addition step. Further, this step may be performed once or a plurality of times under the same conditions or different conditions.

The heating temperature is preferably 250 ° C. or lower, more preferably 70 to 200 ° C., and particularly preferably 90 to 180 ° C. when damage resistance is considered as a physical property of the water-absorbent resin particles obtained. On the other hand, when emphasizing water absorption performance, the heating temperature is more preferably 120 to 280 ° C., further preferably 150 to 250 ° C., and particularly preferably 170 to 230 ° C. The heating time is preferably 1 minute to 2 hours.

(Heating device)
As the heating device used in the present invention, a continuous or batch type (batch type) heating device provided with a gas discharge mechanism and / or a gas supply mechanism for setting a predetermined atmosphere in a known dryer or heating furnace, A continuous heating device is preferable.

As the heating method of the heating device, a conduction heat transfer type, a radiation heat transfer type, a hot air heat transfer type, and a dielectric heating type are suitable. More preferred is a conductive heat transfer and / or hot air heat transfer type heating method, and still more preferred is a conductive heat transfer type method.

The so-called control temperature of the heating device is not limited as long as the water-absorbent resin particles can be heated to an appropriate temperature, and need not be constant from the beginning to the end of the process. However, in order to prevent partial overheating and the like, the temperature is preferably 50 to 300 ° C.

Also, an apparatus equipped with a mechanism for continuously stirring and / or flowing the object to be heated in order to increase the heating efficiency and perform uniform heat treatment is preferable. As a stirring and / or fluidizing method, a grooved stirring method, a screw type, a rotary type, a disk type, a kneading type, a fluidized tank type, etc. are preferable, such as a stirring method using a stirring blade (paddle) or a rotary retort furnace. A stirring method by movement of the heat transfer surface itself is more preferable. The stirring and / or flow mechanism is intended to perform a uniform heat treatment, and therefore, when the amount of treatment is small, for example, when the thickness of an object to be heated is less than 1 cm, it may not be used. It doesn't matter.

The heating device includes a gas discharge mechanism for discharging steam generated from the object to be heated, and controls the dew point and temperature of the atmosphere of the heating unit (inside the heating device) by adjusting the mechanism, for example, the discharge amount. You can also. The heating unit is not a so-called heat source such as a heater or a dielectric coil but a place for raising the temperature of an object to be heated.

When the gas is discharged from the outlet of the heat treatment product as well as the simple exhaust port, the outlet mechanism also corresponds to the discharge mechanism. Further, it is preferable to adjust the amount of gas discharged and the pressure using a blower or the like. Further, the number of exhaust locations is not limited to one, and a plurality of exhaust locations can be provided in consideration of the size of the heating device and the adjustment state of the dew point and temperature.

The heating device includes a gas supply mechanism, and the dew point and temperature of the atmosphere of the heating unit can be controlled by adjusting the mechanism, for example, the supply amount.

The gas pressure in the heating part is preferably slightly reduced from normal pressure. As the range, the differential pressure with respect to atmospheric pressure is preferably 0 to −10 kPa, more preferably 0 to −5 kPa, and further preferably 0 to −2 kPa.

When industrial continuous production is performed, a batch processing system or a continuous processing system heating apparatus having the above-described mechanism can be used.

In the case of batch processing (batch method), the heated object is placed in one or more trays that are substantially evenly distributed, or the heated object is filled in a single tank or multiple tanks. A method of heating while stirring with a stirring blade or the like, a fluidized tank or the like is used. In the case of a continuous processing method, a method of transferring the material to be heated to a belt or a plurality of trays substantially evenly, a method of transferring while stirring with a stirring blade or a screw, etc. A method of transporting by the method is used.

In addition, when performing an addition process both before and after heat processing, you may perform an addition process using the apparatus same as the said addition process, or a different apparatus. In particular, when a continuous production apparatus is used, it may be preferable in terms of production efficiency to use the same apparatus for the addition treatment before heating and the heat treatment, and use a separate apparatus for the addition treatment after heating.

In addition, the water-absorbent resin particles taken out from the heating device as necessary are preferably less than 100 ° C., more preferably 0 to 95 ° C., for the purpose of suppressing excessive crosslinking reaction and improving the handleability in the subsequent process. Preferably, it may be cooled to 40 to 90 ° C.

Water-absorbent resin particles are obtained by the above steps (2-1) to (2-8).

(2-9) Other additives In the method for producing an absorbent article of the present invention, other additives are added at any stage in order to impart various functions to the water absorbent resin particles (surface crosslinked water absorbent resin). You may have the process of adding an agent and obtaining a water absorbing agent.

Examples of the additives include liquid permeability improvers, organic fine particles, cationic polymer compounds, water-soluble polyvalent metal cation-containing compounds, surfactants, coloring inhibitors, urine resistance improvers, deodorants, fragrances, Antibacterial agents, foaming agents, pigments, dyes, fertilizers, oxidizing agents, reducing agents, and the like may be mentioned, and the functions of the additive may be imparted or enhanced.

Unless otherwise specified, the amount of the additive is preferably less than 10% by mass (lower limit 0% by mass), more preferably less than 5% by mass, and even more preferably 1% by mass with respect to 100% by mass of the water-absorbent resin particles. Is less than. These additives can be added simultaneously with or separately from the surface cross-linking agent addition step.

(Liquid permeability improver)
The liquid permeability improver referred to in the present invention improves the saline flow conductivity (SFC) of the water-absorbent resin particles after the addition of the liquid permeability improver compared to before the addition of the liquid permeability improver. A substance.

Examples of liquid permeability improvers include water-soluble polyvalent metal cation-containing compounds. The polyvalent metal cation is preferably a divalent or higher valent metal cation, more preferably 2 to 4 valent, and still more preferably trivalent.

The water-soluble refers to a compound that dissolves in 100 g of water (25 ° C.), preferably 1 g or more, more preferably 10 g or more. The polyvalent metal compound containing the polyvalent metal cation may be mixed with the water-absorbent resin particles as it is (mainly in solid form), but it is preferable to mix an aqueous solution with the water-absorbent resin particles.

The polyvalent metal cation element that can be used in the present invention is at least one metal selected from a typical metal and a transition metal having a group number of 4 to 11, and includes Mg, Ca, Ti, Zr, V, One selected from Cr, Mn, Fe, Co, Ni, Pd, Cu, Zn, Cd, and Al is preferable, Mg, Ca, Zn, and Al are more preferable, and Al is particularly preferable.

As the polyvalent metal compound containing the polyvalent metal cation, the anion of the counter may be either organic or inorganic and is not particularly limited. For example, water-soluble aluminum salts such as aluminum acetate, aluminum lactate, aluminum acrylate, aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum nitrate, potassium bissulfate aluminum, sodium bissulfate aluminum; calcium chloride, calcium nitrate, magnesium chloride, Examples thereof include water-soluble alkaline earth metal salts such as magnesium sulfate and magnesium nitrate; transition metal salts such as zinc chloride, zinc sulfate, zinc nitrate, copper sulfate, cobalt chloride, zirconium chloride, zirconium sulfate and zirconium nitrate. Of these, aluminum compounds are particularly preferred. Among these, aluminum sulfate is preferred, and water-containing crystal powders such as aluminum sulfate 14-18 hydrate can be most suitably used.

When an organic acid polyvalent metal salt is used, preferred anions are anisic acid, benzoic acid, p-hydroxybenzoic acid, formic acid, valeric acid, citric acid, glycolic acid, glyceric acid, glutaric acid, chloroacetic acid, chloropropionic acid. , Cinnamic acid, succinic acid, acetic acid, tartaric acid, lactic acid, pyruvic acid, fumaric acid, propionic acid, 3-hydroxypropionic acid, malonic acid, maleic acid, butyric acid, isobutyric acid, imidinoacetic acid, malic acid, isothionic acid, methyl Examples include bases corresponding to acids such as maleic acid, adipic acid, itaconic acid, crotonic acid, oxalic acid, salicylic acid, gluconic acid, gallic acid, sorbic acid and stearic acid. Of these, tartrate and lactate are preferred, and lactate such as aluminum lactate and calcium lactate is most preferred.

The mixing method of the polyvalent metal cation is an aqueous solution containing the polyvalent metal cation in the water-absorbent resin particles, particularly an aqueous solution having a polyvalent metal cation concentration of preferably 1 to 60% by mass, more preferably 10 to 50% by mass. Furthermore, it may be heated at about 40 to 150 ° C., more preferably about 60 to 100 ° C., if necessary after mixing. The amount of water used is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass with respect to 100 parts by mass of the water-absorbent resin particles.

More preferably, a polyhydric alcohol or α-hydroxycarboxylic acid is used together during mixing. The polyhydric alcohol is appropriately selected from the above-mentioned various compounds, and the α-hydroxycarboxylic acid is selected from various compounds described in the column of the coloration inhibitor and urine resistance improving agent described later. The polyhydric alcohol or α-hydroxycarboxylic acid is less than water and is preferably 0 to 4 parts by weight, more preferably 0.01 to 3 parts by weight, and still more preferably 100 parts by weight of the water absorbent resin particles. Used at 0.1 to 0.5 parts by weight.

The polyvalent metal compound is used in an amount of 0.001 to 1 mass with respect to 100 parts by mass of the water-absorbent resin particles as a polyvalent metal cation (for example, in the case of an aluminum salt, Al ³⁺ regardless of the type of salt). In the range of 0.005 to 0.5 parts by weight, more preferably in the range of 0.01 to 0.2 parts by weight, particularly in the range of 0.02 to 0.1 parts by weight. preferable.

When the polyvalent metal cation content with respect to 100 parts by mass of the water-absorbent resin particles is 0.001 part by mass or more, the SFC is sufficiently improved, and when the content is 1 part by mass or less, AAP is maintained. The

(Organic fine particles)
Examples of the organic fine particles include organic fine powders such as calcium lactate, aluminum lactate, and metal soap (polyvalent metal salt of long chain fatty acid). The organic fine particles have a volume average particle size (specified by a laser diffraction scattering particle size meter) of preferably 10 μm or less, and more preferably 1 μm or less. The lower limit of the volume average particle diameter of the organic fine particles is not particularly limited, but is preferably 5 nm or more.

These may be mixed with the water-absorbent resin particles as a powder, mixed with an aqueous dispersion (slurry, for example, colloidal silica), or may be mixed with being dispersed in a surface cross-linking agent or an aqueous solution thereof. .

The addition amount of the organic fine particles to be used is preferably 0.01 to 3 parts by mass, more preferably 0.1 to 1.0 part by mass with respect to 100 parts by mass of the water absorbent resin particles to be added. preferable.

(Cationic polymer compound)
The cationic polymer compound is not particularly limited, but is disclosed in US Pat. Nos. 5,382,610, 7098284, WO2009 / 110645, 2009/041731, and 2009/041727. The disclosed cationic polymer compound can be suitably used. Among these, polyethyleneimine, polyvinylamine, polyallylamine, and a dimethylamine / ammonia / epichlorohydrin condensate are preferable.

The molecular weight of the cationic polymer compound is preferably 1,000 to 5,000,000, more preferably 2,000 to 1,000,000, and even more preferably 10,000 to 500,000.

The cationic polymer compound is preferably water-soluble. Here, the term “water-soluble” means that preferably 1 g or more dissolves in 100 g of water at 25 ° C.

The cationic polymer compound may be directly mixed with the water-absorbent resin particles, may be mixed with a solution, particularly an aqueous solution, or may be mixed after being dissolved in a surface crosslinking agent or an aqueous solution thereof.

(Water-soluble polyvalent metal cation-containing compound)
The water-soluble polyvalent metal cation-containing compound refers to a compound other than a multi-component metal compound containing a metal cation, which is preferably divalent or higher, more preferably trivalent or higher. Examples of the trivalent or higher metal cation include aluminum, zirconium, and titanium, and among these, aluminum is preferable. Examples of the polyvalent metal cation-containing compound include aluminum sulfate, aluminum chloride, zirconium chloride oxide, zirconium carbonate ammonium, zirconium carbonate potassium, zirconium carbonate potassium, zirconium sulfate, zirconium acetate, zirconium nitrate, and other inorganic salts of polyvalent metals, acetic acid And polyvalent metal compounds such as organic salts of polyvalent metals such as aluminum, aluminum lactate, zirconium hydroxychloride, titanium triethanolamate, and titanium lactate. Among these, a compound containing aluminum as a polyvalent metal cation is preferable.

The water-soluble polyvalent metal cation-containing compound may be mixed directly with the water-absorbent resin particles as a powder, or may be mixed with a solution, particularly an aqueous solution, or dissolved and mixed in a surface crosslinking agent or an aqueous solution thereof. May be.

The amount of the water-soluble polyvalent metal cation-containing compound added is preferably 0.001 to 5 parts by mass in terms of the amount of polyvalent metal cation with respect to 100 parts by mass of the water-absorbing resin particles to be added. The amount is more preferably 0.01 to 2 parts by mass, and still more preferably 0.01 to 1 part by mass.

Further, it may be added a plurality of times. In this case, for example, when added twice, the (mass) ratio is preferably in the range of 1/99 to 99/1, more preferably in the range of 10/90 to 90/10. It is prescribed. Exceeding these ranges is not preferable because it is very close to the same situation as the one-time addition and the effect of the multiple-time addition becomes poor.

When adding a water-soluble polyvalent metal cation-containing compound as an aqueous solution, in addition to water, a hydrophilic organic solvent (alcohol or polyglycol) or a surfactant is used in combination to improve dispersibility, solubility and mixing properties. Also good. The amount of water to be used is appropriately determined depending on the type and addition method of the additive. For example, it is preferably 0 part by mass (dry mixing) to 50 parts by mass, more preferably 100 parts by mass of the water absorbent resin particles. Is 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass.

(Surfactant)
Furthermore, the polyacrylic acid (salt) -based water-absorbent resin particles may contain a surfactant, and the production method of the present invention preferably includes a step of mixing the surfactant in any step.

The surface of the water-absorbing resin particles of the present invention is coated with a surfactant to obtain water-absorbing resin particles having a high water absorption rate and high liquid permeability. The surfactant is not particularly limited, but the surfactant disclosed in International Publication No. 97/017397 and US Pat. No. 6,107,358, that is, nonionic surfactant, anionic surfactant, cationic interface. Examples include activators and amphoteric surfactants. These surfactants may be polymerizable or reactive with acrylic acid (salt) monomers or water-absorbing resin particles.

The type and amount of the surfactant to be used are appropriately determined. From the viewpoint of surface tension, it is preferably 0 to 0.5 parts by mass, more preferably 0.00001, relative to 100 parts by mass of the water-absorbent resin particles. It is used in the range of ~ 0.1 parts by mass, more preferably 0.001 to 0.05 parts by mass. Among these surfactants, anionic surfactants, nonionic surfactants, or silicone surfactants are preferably used from the viewpoint of effects, and nonionic surfactants or silicone surfactants are used. More preferably.

(Anticolorant and urine resistance improver)
In the present invention, chelating agents (especially organophosphorus chelating agents and aminocarboxylic acid chelating agents) and α-hydroxycarboxylic acids (especially malic acid (salts) are used for the purpose of preventing coloring and deterioration, reducing residual monomers, and the like. )), A coloring inhibitor or a urine resistance improver selected from inorganic or organic reducing agents (especially sulfur-based inorganic reducing agents). In addition, water-absorbing resin particles having a large surface area generally tend to be easily colored or deteriorated. Among them, a chelating agent is preferably included from the viewpoint of preventing coloration over time and improving urine resistance. Further, from the viewpoint of preventing coloring, a chelating agent, α-hydroxycarboxylic acid (salt), inorganic or organic reduction is preferable. And a compound selected from the group consisting of an agent (particularly a sulfur-based inorganic reducing agent) and a phosphorus compound. Accordingly, a preferred embodiment of the present invention includes a chelating agent addition step of adding a chelating agent.

Examples of the chelating agent include chelating agents disclosed in US Pat. Nos. 6,599,989, 6,469,080, and European Patent No. 2,163,302, particularly non-polymer chelating agents, organophosphorus chelating agents, and aminocarboxylic acid chelating agents. Agents, inorganic polyvalent phosphoric acid, and amino polyvalent phosphoric acid.

Organic phosphorus chelating agents include nitriloacetic acid-di (methylenephosphinic acid), nitriloacetic acid- (methylenephosphinic acid), nitriloacetic acid-β-propionic acid-methylenephosphonic acid, nitrilotris (methylenephosphonic acid), 1-hydroxy And ethylidene diphosphonic acid. Examples of aminocarboxylic acid chelating agents include iminodiacetic acid, hydroxyethyliminodiacetic acid, nitrilotriacetic acid, nitrilo-3-propionic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, trans-1,2-diaminocyclohexane. 4-acetic acid, N, N-bis (2-hydroxyethyl) glycine, diaminopropanol tetraacetic acid, ethylenediamine 2-propionic acid, hydroxyethylenediamine triacetic acid, glycol ether diamine tetraacetic acid, diaminopropane tetraacetic acid, N, N′-bis (2 -Hydroxybenzyl) ethylenediamine-N, N'-2acetic acid, 1,6-hexamethylenediamine-N, N, N ', N'-4 acetic acid and salts thereof.

Examples of the inorganic polyvalent phosphoric acid include metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, hexametaphosphoric acid, and salts thereof.

Examples of aminopolyvalent phosphoric acid include ethylenediamine-N, N′-di (methylenephosphinic acid), ethylenediaminetetra (methylenephosphinic acid), cyclohexanediaminetetra (methylenephosphonic acid), ethylenediamine-N, N′-diacetic acid-N , N'-di (methylenephosphonic acid), ethylenediamine-N, N'-di (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), polymethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) And salts thereof.

Preferred examples of the salt include monovalent salts, particularly alkali metal salts such as sodium salts and potassium salts, ammonium salts, and amine salts, and sodium salts and potassium salts are particularly preferable.

Among the chelating agents, aminocarboxylic acid chelating agents, amino polyvalent phosphoric acids, and salts thereof are preferably used from the viewpoint of preventing coloring. Of these, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, trans-1,2-diaminocyclohexanetetraacetic acid, ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and salts thereof are more preferably used. Among these, ethylenediaminetetra (methylenephosphonic acid) or a salt thereof is most preferable.

Examples of the α-hydroxycarboxylic acid include malic acid (salt), succinic acid (salt), and lactic acid (salt) disclosed in US Patent Application Publication No. 2009/0312183.

Examples of the inorganic or organic reducing agent include sulfur-based reducing agents disclosed in US Patent Application Publication No. 2010/0062252 and the like, particularly sulfites and bisulfites.

The inorganic reducing agent in the present invention is distinguished from the reducing agent as the polymerization initiator used in the polymerization step. That is, the inorganic reducing agent refers to a compound having a reducing property, as long as it has a reducing inorganic element, and specifically includes a compound having a reducing sulfur atom or a reducing phosphorus atom. And preferably a compound containing a reducing sulfur atom or a water-soluble compound containing a reducing phosphorus atom. Therefore, even if it is an inorganic compound or an organic compound, if it has a reducing sulfur atom or a reducing phosphorus atom, it is regarded as the inorganic reducing agent of the present invention.

The inorganic reducing agent may be an acid type, but is preferably a salt type, and the salt is more preferably a monovalent or polyvalent metal salt, and more preferably a monovalent salt. Among these inorganic reducing agents, oxygen-containing reducing inorganic compounds listed below, that is, inorganic reducing agents in which sulfur or phosphorus is combined with oxygen, among them oxygen-containing reducing inorganic salts are preferable. These inorganic reducing agents may be inorganic reducing agents having a reducing inorganic atom, preferably a reducing sulfur atom or phosphorus atom, in an organic compound such as an alkyl group or a hydroxyalkyl group.

As the inorganic reducing agent having a reducing sulfur atom or a reducing phosphorus atom used in the present invention, the most stable oxidation number of the sulfur atom is +6 (positive hexavalent), and the oxidation of the phosphorus atom. The number is +5 (positive pentavalent), but generally, each atom having an oxidation number of less than that has reducibility, and a + 4-valent sulfur compound (for example, sulfite, bisulfite, pyrosulfite), + Trivalent sulfur compounds (e.g. dithionite), + divalent sulfur compounds (e.g. sulfoxylate), + tetravalent phosphorus compounds (e.g. hypophosphate), + trivalent phosphorus compounds (e.g. suboxide) Phosphates, pyrophosphites), +1 valent phosphorus compounds (eg hypophosphites) are used. In these reducing inorganic compounds, the reducing sulfur atom or the reducing phosphorus atom may be substituted with an organic substance.

The inorganic compound containing a sulfur atom, which is an inorganic reducing agent, is not particularly limited, but examples thereof include sulfites such as sodium sulfite, potassium sulfite, calcium sulfite, zinc sulfite, and ammonium sulfite; Bisulfites such as calcium hydrogen and ammonium bisulfite; pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite and ammonium pyrosulfite; sodium dithionite, potassium dithionite, ammonium dithionite, dithione Dithionites such as calcium oxide and zinc dithionite; Trithionates such as potassium trithionate and sodium trithionate; Tethionates such as potassium tetrathionate and sodium tetrathionate; Thiosulfate Sodium, potassium thiosulfate, ammonium thiosulfate Thiosulfates such beam; sodium nitrite, potassium nitrite, calcium nitrite, include nitrites such as zinc nitrite, the inorganic compound containing a phosphorus atom, sodium hypophosphite, and the like. Examples of the organic compound containing a sulfur atom as an inorganic reducing agent include 2-hydroxy-2-sulfinate acetic acid, sodium formaldehydesulfoxylate, formamidinesulfinic acid, and tris (2-carboxyethyl) phosphine thioglycolate. Examples include hydrochloride (TCEP) and tributylphosphine (TBP). Of these, sulfites, hydrogen sulfites, pyrosulfites, and dithionites are preferred. Sodium sulfite, sodium hydrogen sulfite, potassium pyrosulfite, sodium dithionite, 2-hydroxy-2-sulfinate acetate, -Hydroxy-2-sulfonatoacetic acid and / or salts thereof are more preferred. Preferred salts are alkali metal and alkaline earth metal salts, with Li, Na and K being preferred, and sodium salt being particularly preferred. 2-Hydroxy-2-sulfinate acetic acid (salt) may be used in combination with 2-hydroxy-2-sulfonatoacetic acid (salt).

As a preferred inorganic reducing agent, 2-hydroxy-2-sulfinate acetic acid is an inorganic reducing agent of the present invention because it has a reducing sulfur atom as a sulfinate group, and BRUGGOLITE (available from Brueggemann Chemical, Heilbron, Germany) R) FF7, available from 50-60 wt% 2-hydroxy-2-sulfinate acetic acid disodium salt, 30-35 wt% sodium sulfite (Na ₂ SO ₃ ) and 2-hydroxy-2-sulfonate It can be obtained as BRUGGOLITE® FF6 containing 10-15% by weight of disodium acetate.

The phosphorus compound includes an organic phosphorus compound or an inorganic phosphorus compound, preferably a water-soluble phosphorus compound. Furthermore, an inorganic phosphorus compound is preferable from the viewpoint of the physical properties of the obtained water-absorbing agent, for example, the water absorption capacity under pressure, and particularly the suppression of a decrease in surface tension.

Particularly preferred phosphorus compounds are water-soluble inorganic phosphorus compounds. Specifically, phosphoric acid, phosphorous acid, hypophosphorous acid, triphosphoric acid, tripolyphosphoric acid and salts thereof (for example, monohydrogen phosphate disodium salt) And particularly preferable compounds are phosphoric acid (salt) having no reducing property from the viewpoint of the water absorption property of the water-absorbing agent. Preferred salts include water-soluble monovalent salts, that is, alkali metal salts such as sodium salts and potassium salts, ammonium salts, and amine salts. Among the salts, from the viewpoint of the effect of preventing coloration with time, it is most preferable to exhibit an acidity of pH 7 or lower. Phosphoric acid, dihydrogen phosphate monosodium salt, dihydrogen phosphate monopotassium salt, dihydrogen phosphate 1 Ammonium salt.

The above phosphorus compounds may be used alone or in combination of two or more.

The amount of the coloring inhibitor or urine resistance improver used is preferably 0 to 3 parts by mass, more preferably 0.001 to 1 part by mass, and more preferably 0.05 to 0. 5 parts by mass is particularly preferred.

The anti-coloring agent or urine resistance (weather resistance) improver can be added to the monomer, water-containing gel, dry polymer, water-absorbing resin particles, etc., but is preferably added after the polymerization step. In particular, since the inorganic or organic reducing agent is consumed in the polymerization step, it is preferably added after the polymerization step, further after the drying step, particularly at least partly after the surface crosslinking step.

In a preferred embodiment, an anti-coloring agent or a urine resistance (weather resistance) improver is added in the step (2-1) of preparing the acrylic acid (salt) monomer aqueous solution. Or (2-8) the water absorption obtained in the surface crosslinking step performed after the surface crosslinking step and (2-10) before the step of mixing the water absorbent resin particles and the water-insoluble inorganic particles. Add to resin particles.

In addition, although the usage-amount of the various additives added at each manufacturing process becomes content in the obtained water-absorbing agent, each additive in a water-absorbing agent is a residual monomer and a water-soluble component. In the same manner as in quantification, water can be extracted from the water-absorbing agent with physiological saline and quantified appropriately by liquid chromatography, ion chromatography, or the like.

As described above, it is preferable to use a water-absorbing agent containing a chelating agent. However, at least a part of the chelating agent is (2-1) the step of preparing the acrylic acid (salt) monomer aqueous solution, or (2 -2) It is preferably added in the aqueous solution polymerization step, and more preferably added to the acrylic acid (salt) monomer aqueous solution at least in step (2-1). In this case, the addition amount of the chelating agent is preferably 0.1 to 3.0% by mass with respect to the acrylic acid (salt) monomer.

Addition of chelating agent, inorganic reducing agent, α-hydroxycarboxylic acid and phosphorus compound does not require a solvent and may be added directly to the water-absorbent resin particles after surface cross-linking. (Dry blend). However, from the viewpoint of fixation to the water-absorbent resin particles, the compound is preferably added as a solution, more preferably as an aqueous solution or an aqueous solution. In that case, water, the mixed solvent of an organic solvent, and water are used for a solvent. The amount is preferably 0.01 to 10 parts by weight, more preferably 0.05 to 30 parts by weight, and still more preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the water-absorbent resin particles. The concentration of the aqueous solution is preferably about 1 to 50% by mass. Further, a surfactant or the like may be used if necessary. The solvent may be dried if necessary.

Water-soluble polysiloxanes described in International Publication No. 2009/093708 and primary to tertiary amine compounds described in International Publication No. 2008/108343 (US Patent Application Publication No. 2008/221229) are also preferably used as additives. I can do it.

(2-10) Step of mixing water-absorbing resin particles and water-insoluble inorganic particles Next, the water-absorbing resin particles and water-insoluble inorganic particles obtained by the above series of operations are mixed. The water-absorbing resin particles to which the water-insoluble inorganic particles are added may be surface-crosslinked or may not be surface-crosslinked. In addition, the water-insoluble inorganic particles may be mixed with a water-absorbing agent particle (hereinafter referred to as “water-absorbing agent”) containing water-absorbing resin particles or other additives. Furthermore, the mixing of the water-insoluble inorganic particles may be performed by mixing the water-absorbing resin particles or the water-absorbing agent, the water-insoluble inorganic particles, and the hydrophilic fibers when the absorbent article is manufactured as described later. That is, it is also preferable that the step of mixing the water-absorbing resin particles and the water-insoluble inorganic particles is a step of manufacturing the absorbent body by mixing the water-absorbing resin particles, the water-insoluble inorganic particles, and the hydrophilic fibers. Hereinafter, the water absorbent resin particles or the water absorbent may be referred to as “water absorbent resin particles / water absorbent”.

Addition of water-insoluble inorganic particles ensures the fluidity of the water-absorbent resin particles / water-absorbing agent used in the absorbent article. Moreover, the absorption amount of an absorbent article can be improved by adding water-insoluble inorganic particles.

Also, as described above, the water-absorbent resin particles / water-absorbing agent may lose fluidity when producing absorbent articles by storage after production. Such water-absorbing resin particles / water-absorbing agent that have lost its fluidity are mixed with water-insoluble inorganic particles, preferably by forming an absorbent body, while maintaining the performance of the water-absorbing resin particles / water-absorbing agent. Since the fluidity of the agent is restored, productivity is improved.

Therefore, the water-insoluble inorganic particles may be added immediately after the production of the water-absorbing resin particles / water-absorbing agent, or the water-absorbing resin particles / water-absorbing agent may be added after storage for a certain period.

As the water-absorbing resin particles / water-absorbing agent to be added, water-absorbing resin particles / water-absorbing agent having a 2000 μm sieve transmittance after moisture absorption of 50% by mass or less (lower limit 0% by mass) is preferably used. By adding water-insoluble inorganic particles to such water-absorbing resin particles / water-absorbing agent, the fluidity of the water-absorbing resin particles / water-absorbing agent is not easily lowered even when stored in a moisture-absorbing environment such as high humidity conditions. . In addition, the water-absorbent resin particles / water-absorbing agent having a 2000 μm sieve permeability after moisture absorption exceeding 50% by mass is difficult to obtain the effects of the present invention. In a more preferred form, the 2000 μm sieve transmittance after moisture absorption of the water absorbent resin particles / water absorbent is preferably 30% by mass or less, more preferably 15% by mass or less.

In addition, as described above, the water-absorbing resin particles / water-absorbing agent that has lost its fluidity are mixed with water-insoluble inorganic particles, and an absorbent body is preferably formed, so that the water-absorbing property is maintained while maintaining the performance. The fluidity of the resin particles / water absorbent can be recovered. For this reason, the suitable addition time of the water-insoluble inorganic particles is, for example, a form in which the water-insoluble inorganic particles are added in a state where the water-absorbing resin particles / water-absorbing agent absorbs moisture after storage for a certain period of time. The moisture absorption state of the water-absorbent resin particles / water-absorbing agent can be determined using a sieve transmittance of 2000 μm as an index. That is, when the water-absorbing resin particles / water-absorbing agent absorbs moisture, the water-absorbing resin particles / water-absorbing agent are aggregated and coarsened, so that the sieve permeability is lowered. One preferred embodiment of the present invention is a form in which water-insoluble particles are mixed with water-absorbing resin particles / water-absorbing agent having a 2000 μm sieve permeability of preferably 50% by mass or less (lower limit 0% by mass). In a more preferred form, the 2000 μm sieve permeability of the water-absorbing agent is more preferably 30% by mass or less, and further preferably 15% by mass or less.

The 2000 μm sieve transmittance and the 2000 μm sieve transmittance after moisture absorption are values measured by the methods described in the following examples.

As described in the above (Particle Size Distribution) column and the following (4-4) Particle Size column, the water-absorbent resin particles and the water-absorbing agent have a mass average particle size (D50) and a particle size distribution from the viewpoint of improving water absorption performance. Is preferably controlled. Even if the mass average particle size (D50) and the particle size distribution are controlled within a suitable range, for example, the particle size distribution is shifted to the larger particle size distribution due to moisture absorption during storage. By adding water-insoluble inorganic particles to the water-absorbing resin particles / water-absorbing agent shifted to the larger particle size distribution, the fluidity lost due to the coarsening of the particle diameter can be recovered. Therefore, in a preferred embodiment of the present invention, a step of obtaining water-absorbing resin particles or a water-absorbing agent having a particle diameter of 95% by mass or more and a particle size of 150 μm or more and less than 850 μm, and a 2000 μm sieve permeability with time is obtained. It is a manufacturing method of an absorptive article which has the process of mixing the water-absorbent resin particles or water-absorbing agent which became 50 mass% or less, and water-insoluble inorganic particles. Here, the time elapsed in “time elapsed” is not uniquely determined because it largely varies depending on the humidity in the storage environment, for example. In the above embodiment, the 2000 μm sieve transmittance of the mixture of the water-absorbent resin particles or water-absorbing agent and the water-insoluble inorganic particles is preferably more than 50% by mass, more preferably 75% by mass or more, More preferably, it is 80 mass% or more.

The present invention also provides a method for recovering the fluidity of water-absorbing resin particles or a water-absorbing agent, comprising mixing water-absorbing resin particles or a water-absorbing agent having a 2000 μm sieve permeability decrease with time and water-insoluble inorganic particles. . At this time, the water-absorbing resin particles or the water-absorbing agent before adding the water-insoluble inorganic particles has a 2000 μm sieve transmittance, and the water-absorbing resin particles or the water-absorbing agent and the water-insoluble inorganic particles after the water-insoluble inorganic particles are added. Of the latter, the latter is preferably 20% by mass or more, preferably 30% by mass or more, and preferably 50% by mass or more.

(Water-insoluble inorganic particles)
Water-insoluble inorganic particles include multi-component metal compounds such as hydrotalcite, silicon dioxide (silica), titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, metal phosphates (for example, calcium phosphates such as tricalcium phosphate , Barium phosphate, aluminum phosphate), metal borates (eg, titanium borate, aluminum borate, iron borate, magnesium borate, manganese borate, calcium borate), silicic acid or salts thereof, clay, diatomaceous earth, Zeolite, bentonite, kaolin, activated clay and the like can be mentioned. Among them, the water-insoluble inorganic particles preferably contain at least one selected from a multi-component metal compound, silicon dioxide, talc, and tricalcium phosphate because the effects of the present invention are remarkably obtained, and water absorption performance is maintained. As it is, the fluidity of the water-absorbing water-absorbing resin particles or the water-absorbing agent is more recovered, and therefore it is more preferable to include at least one selected from multi-component metal compounds, tricalcium phosphate, and silicon dioxide, and multi-component metal compounds. More preferably.

The volume average particle diameter of the water-insoluble inorganic particles is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. The volume average particle size is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. By being more than the said minimum, the fall of workability | operativity at the time of an addition process can be suppressed, and sufficient performance can be obtained. The volume average particle diameter of the water-insoluble inorganic particles can be measured by a “laser diffraction scattering method” (for example, measured by Nikkiso Co., Ltd., trade name: Microtrac MT3000II particle size analyzer).

The surface treatment of the water-insoluble inorganic particles may be performed. Specific examples of the surface treatment agent for the surface treatment include the following multi-metal compound surface treatment agents.

Commercially available water-insoluble inorganic particles can also be used. Examples of the silica include Aerosil 50, Aerosil 200, Aerosil 200CF (all manufactured by Nippon Aerosil Co., Ltd.), and the like. Examples of the talc include, for example, MAICRO ACE series SG-95, SG-2000, NANO ACE series D-1000. , D-800, D-600 (all manufactured by Nippon Talc Co., Ltd.) and the like.

The multi-component metal compound is a multi-component metal compound containing two kinds of bivalent and trivalent metal cations and a hydroxyl group.

Examples of the divalent metal cation include Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Ni ²⁺ , Co ²⁺ and Cu ²⁺ , and Mg ²⁺ is preferable from the viewpoint of heat resistance and the like. Examples of the trivalent metal cation include Al ³⁺ , Fe ³⁺ and Mn ³⁺ , and Al ³⁺ is preferable from the viewpoint of heat resistance and the like. Accordingly, in a preferred embodiment of the multi-component metal compound, the divalent metal cation is a magnesium cation and the trivalent metal cation is an aluminum cation.

The multi-component metal compound has the general formula (1) [M ₁ ²⁺ _1-x M ₂ ³⁺ _x (OH ⁻ ) ₂ ] ^{x +} · [(A ⁿ⁻ ) _{x / n} · mH ₂ O] ^x− (M ₁ ²⁺ is divalent metal cation, M ₂ ³⁺ is a trivalent metal cation, a ^{n-hydrotalcite} which n-valent anion, H 2 _O is known as the structure of the lamellar compound represented by representing the water) It is preferable to have such a structure.

Further, in the ratio of the divalent metal cation to the trivalent metal cation in the general formula (1), x is preferably in the range of 0.2 to 0.75, more preferably in the range of 0.25 to 0.7. A range of 0.25 to 0.5 is more preferable. Examples of the anion include OH ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ , Fe (CN) ₆ ³⁻ , CH ₃ COO ⁻ , oxalate ion or Examples thereof include salicinate ions, but carbonate anions are preferred. M is a real number larger than 0, and preferably 0 <m ≦ 10.

The shape of the multi-component metal compound is not particularly limited, but is preferably spherical (including powder). The multi-component metal compound preferably has a constant particle size, and the volume average particle size is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 1 μm or less. When the particle diameter is not more than the above upper limit, the amount of addition for obtaining a sufficient effect is not excessively increased, and there is little possibility of impairing the water absorption performance of the obtained water absorbing agent. The volume average particle size is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. By being more than the said minimum, the fall of workability | operativity at the time of an addition process can be suppressed, and sufficient performance can be obtained. Moreover, the measurement of the average particle diameter of the multi-component metal compound adhering to the surface of the water-absorbent resin particles can be performed by a measuring method using SEM (scanning electron microscope).

Furthermore, an organic compound may be intercalated between the layers, and a surface treatment may be performed to improve the mixing property with the water-absorbent resin particles.

Preferred structural formulas of the multi-element metal compound include Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O, Mg ₄ Al ₂ (OH) ₁₂ CO ₃ .3H ₂ O, and the like. Specific examples include DHT-4H and DHT-6 manufactured by Kyowa Chemical Industry Co., Ltd., STABIACE HT-1-NC and STABIACE HT-P manufactured by Sakai Chemical Industry Co., Ltd.

The multi-component metal compound may or may not be surface-treated, but a multi-component metal compound that is not surface-treated is more preferable. Specific examples of the surface treatment agent used for the surface treatment include the following (a) to (j).

(A) Higher fatty acids such as stearic acid, oleic acid, erucic acid, palmitic acid and lauric acid.

(B) Metal salts such as lithium salt, sodium salt and potassium salt of (a) above.

(C) Higher alcohol sulfates such as stearyl alcohol and oleyl alcohol, polyethylene glycol ether sulfates, amide bond sulfates, ether bond sulfonates, ester bond sulfonates, amide bond alkylaryl sulfonates, ethers Anionic surfactants such as bonded alkylaryl sulfonates.

(D) Mono- or diesters such as orthophosphoric acid and oleyl alcohol, stearyl alcohol, or mixtures thereof, and their acid forms or phosphate esters such as alkali metal salts or amine salts.

(E) Silane coupling agents such as vinylethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltris (2-methoxyethoxy) silane, and γ-aminopropyltrimethoxysilane.

(F) Titanium coupling agents such as isopropyl triisostearoyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, isopropyl tridecylbenzenesulfonyl titanate, and the like.

(G) Alkaline coupling agents such as acetoalkoxyaluminum diisopropylate.

(H) Ethanolamines such as monoethanolamine, diethanolamine or triethanolamine.

(I) n-propanolamines such as n-propanolamine, di-n-propanolamine or tri-n-propanolamine.

(J) Isopropanolamines such as monoisopropanolamine, diisopropanolamine or triisopropanolamine.

Of these, ethanolamines such as monoethanolamine, diethanolamine and triethanolamine are preferred.

(Addition amount)
According to the above Japanese translation of PCT publication No. 2003-525105 (International Publication No. WO 01/30290), polyacrylic acid having 30% or more of free acid groups and layered double hydroxide anionic soil dechlorinate the solution containing the electrolyte. , Trying to improve the performance of the water-absorbing agent. For this reason, the layered double hydroxide anionic soil disclosed in JP-T-2003-525105 (International Publication No. 01/30290) needs to be contained at least as much as polyacrylic acid.

On the other hand, the addition amount of the water-insoluble inorganic particles in the present invention improves the absorption amount of the absorbent article and is excellent in the balance between the absorption amount and the return amount, with respect to 100% by mass of the water-absorbent resin particles. The content is 0.01 mass% or more and less than 10 mass%, preferably 0.1 to 5 mass%.

In the preferred embodiment of the present invention described above, in the form in which water-insoluble inorganic particles are added to the water-absorbing resin particles having a sieve permeability of 2000 μm of 50% by mass or less, the effect of restoring fluidity can be further obtained. Therefore, the addition amount of the water-insoluble inorganic particles is preferably 0.1 to 5% by mass, more preferably 0.1 to 4.5% by mass with respect to 100% by mass of the water-absorbing resin particles. More preferably, the content is 0.1 to 4% by mass, and particularly preferably 0.15 to 3.5% by mass.

(Addition / mixing method)
The mixing method of the water-insoluble inorganic particles and the water-absorbing resin particles / water-absorbing agent is not particularly limited, but dry mixing is preferable. The “dry mixing” means mixing in a state where there is no liquid substance other than the liquid substance absorbed or retained by the water-insoluble inorganic particles and the water-absorbing resin particles used in this step. Specifically, the liquid substance is further added to the water-insoluble inorganic particles and the water-absorbent resin particles having the drying residue, moisture absorption moisture, the surface cross-linking agent or the solvent added in the surface cross-linking agent addition step, and the like. The form which mixes without is included.

In order to sufficiently obtain the effect of adding water-insoluble inorganic particles, it is preferable to mix well after the addition, and specific mixing conditions may be appropriately determined according to the apparatus used, the processing amount, and the like. For example, a method of stirring and mixing at a rotational speed of 300 rpm for about 30 seconds to 1 minute using a Redige mixer or a method of stirring and mixing at a rotational speed of 60 rpm for 20 minutes to 1 hour using a paddle type stirring device can be used. Further, a method of mixing while applying vibration or a method of adding water-absorbing resin particles while stirring may be used.

(2-11) Molding into Absorbent Article The absorbent article is not particularly limited, and preferably includes a paper diaper, a sanitary napkin, a so-called incontinence pad, and the like. In particular, the absorbent article is preferably a high-concentration paper diaper (one paper diaper using a large amount of water-absorbing resin particles or water-absorbing agent).

The absorbent article preferably includes an absorber, and may further include a top sheet having liquid permeability and a back sheet having liquid impermeability. The liquid-permeable sheet (hereinafter referred to as a liquid-permeable sheet) is made of a material having a property of transmitting an aqueous liquid. Examples of the material of the liquid permeable sheet include nonwoven fabrics, woven fabrics, and porous synthetic resin films made of polyethylene, polypropylene, polyester, polyamide, and the like. The liquid-impermeable sheet (hereinafter referred to as a liquid-impermeable sheet) is made of a material having a property of not transmitting an aqueous liquid. Examples of the material of the liquid-impermeable sheet include synthetic resin films made of polyethylene, polypropylene, ethylene vinyl acetate, polyvinyl chloride, etc .; films made of composite materials of these synthetic resins and nonwoven fabrics; And a film made of a composite material. Note that the liquid-impermeable sheet may have a property of allowing vapor to pass therethrough.

The absorber is a member that absorbs an aqueous liquid such as a body fluid among members constituting the absorbent article. More preferably, the absorbent body includes water-absorbing resin particles or water-absorbing agent and water-insoluble inorganic particles, and is obtained by mixing water-absorbing resin particles or water-absorbing agent, water-insoluble inorganic particles and hydrophilic fibers.

Water-absorbing resin particles / water-absorbing agent and water-insoluble inorganic particles are powders. An absorbent body can be obtained by molding such powdery water absorbent resin particles / water absorbent and water-insoluble inorganic particles together with any other absorbent material.

The shape of the absorber is not particularly limited, but is preferably processed into a sheet shape, a cylindrical shape, a film shape, and a fiber shape, and more preferably a sheet shape (also called a web shape).

Other hydrophilic materials include hydrophilic fibers. The hydrophilic fiber can carry the water-absorbing resin particles / water-absorbing agent, and can also serve to prevent gel blocking that prevents water-permeable resin particles / water-absorbing agents from contacting each other. Is preferable. When the absorber includes, for example, water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles, and hydrophilic fibers, the structure of the absorber includes, for example, water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles and Structure in which hydrophilic fibers are uniformly mixed; water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles and hydrophilic fibers are uniformly mixed to form a layer, and the layered hydrophilic fibers are laminated thereon Structure: Water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles and hydrophilic fibers are uniformly mixed to form a layer, and the water-absorbing resin particles / water-absorbing agent are formed between the layered hydrophilic fibers. The structure etc. which were pinched are mentioned. In addition, a configuration in which water-absorbing resin particles / water-absorbing agent are sandwiched between hydrophilic fibers formed in layers may be used. Further, the absorbent body may be formed in a sheet shape by blending a specific amount of water with the water-absorbing resin particles / water-absorbing agent and the water-insoluble inorganic particles. In addition, the structure of an absorber is not limited to said structure.

The mixing step of the water-absorbing resin particles / water-absorbing agent and the water-insoluble inorganic particles may be performed at the same time as the mixing step with the hydrophilic fibers. Thus, by mixing the water-insoluble inorganic particles at the time of manufacturing the absorber, even when the water-absorbing resin particles / water-absorbing agent absorbs moisture by storage or the like before manufacturing the absorber, the water-absorbing resin particles / The fluidity can be recovered while maintaining the water absorption performance of the water absorbing agent, and the productivity is improved. That is, one embodiment of the method for producing an absorbent article of the present invention includes a step of producing an absorbent body by mixing water-absorbing resin particles or a water-absorbing agent, water-insoluble inorganic particles, and hydrophilic fibers. The mixing method is not particularly limited. A form in which water-absorbing resin particles / water-absorbing agent and water-insoluble inorganic particles are mixed in advance, and then hydrophilic fibers are added and mixed; water-absorbing resin particles / water-absorbing agent and hydrophilic fibers in advance. After mixing, water-insoluble inorganic particles are added and mixed; water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles and hydrophilic fibers are added together and mixed. Since the effect of recovering the fluidity of the water-absorbing resin / water-absorbing agent can be obtained more efficiently by adding the water-insoluble inorganic particles, the water-absorbing resin particles / water-absorbing agent and the water-insoluble inorganic particles are mixed in advance and then hydrophilic. A form in which fibers are added and mixed, or a form in which water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles and hydrophilic fibers are added and mixed together is preferable.

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

Further, when the ratio of the fiber material such as hydrophilic fiber in the absorbent body is relatively small, the absorbent body, that is, the hydrophilic fibers may be bonded using an adhesive binder. By adhering the hydrophilic fibers to each other, the strength and shape retention of the absorber can be improved before and during use of the absorber. Examples of the adhesive binder include heat-bonded fibers such as polyolefin fibers such as polyethylene, polypropylene, ethylene-propylene copolymer, and 1-butene-ethylene copolymer, and adhesive emulsions. These adhesive binders may be used alone or in combination of two or more. The mass ratio between the hydrophilic fiber and the adhesive binder is preferably within the range of 50/50 to 99/1, more preferably within the range of 70/30 to 95/5, and within the range of 80/20 to 95/5. Is more preferable.

The content (core concentration) of the water-absorbing resin particles / water-absorbing agent and water-insoluble inorganic particles in the absorber is preferably in the range of 20 to 100% by mass. That is, a preferred embodiment of the present invention includes a step of producing an absorbent body by mixing water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles, and pulp. In the method for producing an absorbent article, the total amount (core concentration) of the resin particles / water-absorbing agent and water-insoluble inorganic particles is preferably 20 to 100% by mass. More preferably, it is 25 mass% or more, More preferably, it is 30 mass% or more. By being in such a range, the absorption performance and flow characteristics of the absorber are maintained. Further, in the absorbent body, the upper limit of the content (core concentration) of the water-absorbing resin particles / water-absorbing agent and water-insoluble inorganic particles is preferably 100% by mass, for example, when the hydrophilic fibers are included, The upper limit is preferably 90% by mass or less, and preferably 80% by mass or less. Further, within the above range, the ratio of the water-insoluble inorganic particles to 100% by mass of the water-absorbent resin particles is 0.01% by mass or more and less than 10% by mass. By being in such a range, the absorption amount of the absorbent article is further improved, and the balance between the absorption amount and the return amount is excellent. From the viewpoint of reducing the return amount of the absorbent article, the content of the water-insoluble inorganic particles with respect to 100% by mass of the water-absorbent resin particles is preferably 1 to 5% by mass, and more preferably 1 to 3% by mass. . Further, within the above range, the amount of the water-insoluble inorganic particles in the absorbent body is not particularly limited, but is usually about 0.1 to 10% by mass, and the absorption amount of the absorbent article is further improved. Since the amount of return becomes smaller, it is preferably 0.1 to 5% by mass.

The method for producing such an absorber is not particularly limited. For example, water-absorbing resin particles / water-absorbing agent, water-insoluble inorganic particles and hydrophilic fibers are dry-mixed using a mixer such as a mixer, and the resulting mixture is For example, after forming into a web form by air papermaking etc., the method of compressing and manufacturing as needed is mentioned. An absorbent body has a density 0.001 ~ 0.50g / cm ^3, more preferably 0.001 ~ 0.05g / cm ^3, a basis weight of 0.01 ~ 0.20 g / cm ^2, more preferably 0.01 It is preferably compression molded in a range of ˜0.15 g / cm ² .

Furthermore, the method for producing the final absorbent article is not particularly limited. For example, the absorbent body is composed of a liquid-permeable base material (surface sheet) and a liquid-impermeable base material (back sheet). It is sufficient to make an absorbent article, for example, a paper diaper or a sanitary napkin, by sandwiching, and if necessary, equipped with an elastic member, a diffusion layer, an adhesive tape or the like.

[4] Physical properties of water-absorbing resin particles and water-absorbing agent (4-1) AAP (water absorption capacity under pressure)
The water-absorbent resin particles and the water-absorbing agent preferably have a predetermined AAP. As an example of means for achieving the surface cross-linking after polymerization, the water absorption capacity (AAP) with respect to a 0.9% by mass sodium chloride aqueous solution under a pressure of 2.06 kPa is preferably 20 g / g or more, more preferably 25 g / g. g or more, more preferably 30 g / g or more. In addition, although AAP is so preferable that it is high, from a viewpoint of balance with other physical properties (for example, CRC), as an upper limit, Preferably it is 50 g / g or less, More preferably, it is 40 g / g or less, More preferably, it is 35 g / g or less, Most preferably, it is 33 g / g or less. AAP can be controlled by surface crosslinking and CRC.

Specifically, the water-absorbing resin particles and the water-absorbing agent of the present invention preferably have a water absorption capacity (AAP) of 20 g / g or more with respect to a 0.9% by mass sodium chloride aqueous solution under a pressure of 2.06 kPa. .

(4-2) CRC (absorption capacity under no pressure)
The water absorption capacity (CRC) of the water-absorbing resin particles and the water-absorbing agent is preferably 25 g / g or more, more preferably 30 g / g or more, and still more preferably 33 g / g or more. If the water absorption capacity under no pressure is low, the efficiency when used for absorbent articles such as paper diapers is deteriorated. In addition, although CRC is so preferable that it is high, from a viewpoint of balance with other physical properties (for example, AAP), as an upper limit, Preferably it is 60 g / g or less, More preferably, it is 50 g / g or less, More preferably, it is 45 g / g or less. Is done. The CRC can be controlled by the crosslinking density during polymerization or surface crosslinking.

(4-3) Solid Content The solid content of the water-absorbent resin particles and the water-absorbing agent is a value calculated by the method described in the examples, preferably 85 to 99% by mass, more preferably 88 to 98% by mass, More preferably, it is 90 to 95% by mass. When the solid content is less than 85% by weight, the water absorption capacity under no pressure and the water absorption capacity under pressure are lowered, which is not preferable. When the solid content is higher than 98% by weight, the reduction in water absorption under pressure due to mechanical damage due to conveyance or the like is large, which is not preferable.

(4-4) Particle size Although there is no particular limitation on the particle size and particle size distribution of the water-absorbent resin particles (particularly before the surface cross-linking step) and the water-absorbing agent used in the present invention, the final surface cross-linking agent is added and mixed After sizing, it is preferable to adjust the size within the following range (specified by sieve classification).

The upper limit of the particle diameter is less than 1 mm, and it is preferable to obtain water-absorbing resin particles and a water-absorbing agent with the following particle diameter. When a large amount of particles of 1 mm or more, particularly 850 μm or more, the coarse particles not only cause discomfort to the wearer when used in a thin absorbent article, but also the water content of the absorbent article. A permeable material, a so-called back sheet, is damaged due to scratches, which may cause leakage of urine or the like in actual use, which is not preferable. Therefore, it is preferable that the number of particles of 850 μm or more is smaller, preferably 0 to 5% by mass, more preferably 0 to 3% by mass, still more preferably 0 to 1% by mass, and particularly preferably substantially free of particles. .

On the other hand, on the fine particle side, the proportion of particles having a particle diameter of less than 150 μm is preferably 0 to 3% by mass, more preferably 0 to 2% by mass, and further preferably 0 to 1.5% by mass. preferable. When there are many water-absorbing resin particles and water-absorbing agent fine particles, dust tends to increase, moisture-absorbing fluidity decreases, and physical properties such as AAP and liquid permeability tend to decrease.

Furthermore, while maintaining the above range, the particle size distribution of the water-absorbent resin particles and the water-absorbing agent is preferably included in a range of 150 μm or more and less than 850 μm, and preferably 95% by mass or more, and 98% by mass or more. More preferably, 99% by mass or more is further included, and it is most preferable that substantially the entire amount is included in the range.

In the present invention, the water-absorbent resin particles and the water-absorbing agent that have undergone the above-described steps preferably have a mass average particle diameter (D50) defined by standard sieve classification of 600 μm or less, and 550 to 200 μm for improving performance. Is more preferably in the range of 500 to 250 μm, and most preferably in the range of 450 to 300 μm. The proportion of particles having a particle size of less than 300 μm is preferably 10% by mass or more, more preferably in the range of 10 to 50% by mass, and still more preferably in the range of 10 to 30% by mass. .

The particle size can be appropriately controlled by performing pulverization and classification (before and / or after the surface cross-linking step), granulation, the fine powder collecting step, and the like.

When deviating from these ranges, it may not be possible to obtain well-balanced water-absorbing resin particles and water-absorbing agents having excellent liquid permeability while maintaining a desired water absorption ratio. In particular, particles having a particle size of less than 150 μm not only lower the liquid permeability, but may have an adverse effect due to dust generation or the like in the manufacturing work environment of absorbent articles using water-absorbent resin particles or water-absorbing agents as raw materials. Therefore, it is preferable that the amount be as small as possible.

(4-5) Shape The shape of the water-absorbing resin particles and the water-absorbing agent is not particularly limited, and examples thereof include a sheet shape, a fiber shape, a powder shape, a gel shape, and the like. It is preferably in the form of particles. Here, the “indefinite shape” refers to the shape of particles obtained by pulverizing a hydrogel or a dry polymer. The particles may be a granulated product or primary particles.

[5] Examples Hereinafter, the present invention will be described according to examples. However, the present invention is not limited to the examples and should not be construed. Various physical properties described in claims and examples of the present invention were determined according to the following measuring methods (5-1) to (5-5). Unless otherwise specified, each step in each example is performed at a substantially normal pressure (within ± 5% of atmospheric pressure, more preferably within ± 1%). In the same step, intentional pressurization or depressurization is performed. It was carried out without adding a pressure change due to.

(5-1) CRC (Water absorption capacity without pressure)
The CRC of the water-absorbing resin particles and the water-absorbing agent is based on ERT441.2-0.2 and is 0.90% by mass sodium chloride aqueous solution (hereinafter sometimes referred to as “physiological saline”). The water absorption capacity (CRC) (unit: g / g) for 30 minutes was determined under no pressure.

(5-2) AAP (Water absorption capacity under pressure)
AAP (water absorption capacity under pressure) of the water-absorbent resin particles and the water-absorbing agent was performed according to ERT442.2-02.

That is, 0.900 g (mass W3 [g]) of water-absorbing resin particles or water-absorbing agent was put into a measuring apparatus, and the mass of the measuring apparatus set (W4 [g]) was measured. Next, a 0.90 mass% sodium chloride aqueous solution was absorbed into the water absorbent resin particles or the water absorbent under a pressure of 2.06 kPa. After 1 hour, the mass (W5 [g]) of the measuring device set was measured. From the obtained W3 [g], W4 [g], and W5 [g], AAP (water absorption capacity under pressure) was calculated according to the following formula 1.

(Formula 1) AAP (g / g) = (W5-W4) / W3
(5-3) 2000 μm sieve passage rate Water-absorbent resin particles or water-absorbing agent (hereinafter referred to as “powder” in (5-3) and (5-4)) is a JIS standard sieve having an opening of 2000 μm (JIS Z8801-1 (2000)), record the amount of powder remaining on the sieve and the amount of powder that has passed through the sieve, and determine the ratio of the powder that has passed through the sieve to the total mass of 100% by mass. , 2000 μm sieve passage rate (unit: mass%).

(5-4) Permeability of 2000 μm sieve after moisture absorption About 30 g of powder is spread evenly on a cabinet-size SUS bat (size: 170 mm × 210 mm × 30 mm), and using a small environment tester SH-641 manufactured by ESPEC And 30 minutes at a temperature of 25 ° C. and a relative humidity of 90% RH.

The obtained moisture-absorbed powder is dropped onto a JIS standard sieve (JIS Z8801-1 (2000)) having an opening of 2000 μm, and the amount of powder remaining on the sieve and the powder passing through the sieve is recorded. The ratio of the powder that passed through the sieve with respect to 100% by mass of the total amount of the powder was determined and used as the passing rate of 2000 μm sieve after moisture absorption (unit: mass%).

[Production Example 1]
5500 g of sodium acrylate aqueous solution with a neutralization rate of 75 mol% (monomer concentration 35 mass%) and 0.38 g of trimethylolpropane triacrylate (molecular weight 296) as an internal crosslinking agent (0.006 mol% to monomer) Was dissolved to prepare a monomer aqueous solution (a), followed by deaeration for 30 minutes in a nitrogen gas atmosphere.

Next, the monomer aqueous solution (a) is charged into a reactor having a lid on a double-armed jacketed stainless steel kneader having two sigma type blades with an internal volume of 10 L, and the liquid temperature is set to 30 ° C. While maintaining, nitrogen gas was blown into the reactor, and nitrogen substitution was performed so that the dissolved oxygen in the system was 1 ppm or less.

Subsequently, 24.6 g of a 10% by mass sodium persulfate aqueous solution and 21.8 g of a 0.2% by mass L-ascorbic acid aqueous solution were separately added while stirring the monomer aqueous solution (a). Polymerization started after about 1 minute. The resulting hydrogel crosslinked polymer (a) was polymerized at 30 to 90 ° C. while pulverizing the gel, and after 60 minutes from the start of polymerization, the hydrogel crosslinked polymer (a) was taken out from the reactor. The obtained hydrogel crosslinked polymer (a) had a diameter of about 5 mm.

The finely divided hydrogel crosslinked polymer (a) is spread on a wire mesh having an opening of 300 μm (50 mesh), dried with hot air at 180 ° C. for 45 minutes, pulverized with a roll mill, and further has an opening of 850 μm. Classification was performed with a 150 μm JIS standard sieve. By this series of operations, water-absorbing resin particles (a) which are irregularly crushed water-absorbing resins (solid content: 4.0% by mass) were obtained. The water-absorbent resin particles (a) had a CRC (water absorption capacity under no pressure) of 53.0 g / g.

Next, the water-absorbent resin particles (a) were transferred to a rotary mixer manufactured by Ledige, Germany, and 100 parts by mass of the water-absorbent resin particles (a) were mixed with ethylene glycol diglycidyl ether (trade name; Denacol EX-810 / Nagase). From Chemtex Co., Ltd.) 0.025 parts by mass, ethylene carbonate (melting point 36 ° C.) 0.3 parts by mass, 1,2-propanediol (melting point −59 ° C.) 0.5 parts by mass, and water 3.0 parts by mass The resulting surface cross-linking agent aqueous solution (a) was uniformly mixed and heat-treated at 175 ° C. for 40 minutes. Thereafter, the particle size was adjusted by passing through a JIS standard sieve having an opening of 850 μm to obtain water-absorbing resin particles (surface-crosslinked water-absorbing resin) (a-1) having a cross-linked surface. The water-absorbent resin particles (a-1) were indefinite, and the proportion of particles having a particle size of 150 μm or more and less than 850 μm was 95% by mass or more.

[Production Example 2]
291 g of acrylic acid and 0.32 g of polyethylene glycol diacrylate (molecular weight 523) as an internal cross-linking agent in a polypropylene container having an inner diameter of 80 mm and a capacity of 1 liter covered with polystyrene foam as a heat insulating material (0.015 mol relative to acrylic acid) %), 1.80 g of 1.0% by mass of diethylenetriaminepentaacetic acid / pentasodium aqueous solution, and 1.60 g of acrylic acid solution of 1% by mass of Irgacure (registered trademark) 184 were added. Separately, a solution (II) was prepared by mixing 247 g of a 48.5 mass% aqueous sodium hydroxide solution and 255 g of ion-exchanged water adjusted to 50 ° C. Subsequently, using a magnetic stirrer having a length of 5 cm, 800 r. p. m. The monomer aqueous solution (b) was obtained by quickly adding and mixing the solution (II) to the solution (I) stirred in step (b). The aqueous monomer solution (b) rose to about 100 ° C. due to heat of neutralization and heat of dissolution. The neutralization rate of acrylic acid was 73.5 mol%.

Next, after adding 1.8 g of a 3 mass% sodium persulfate aqueous solution to the monomer aqueous solution (b) and stirring for about 1 second, a stainless steel bat-type container with Teflon (registered trademark) attached to the inner surface immediately Poured in an open system. In addition, the monomer aqueous solution was poured into a stainless bat-shaped container and simultaneously irradiated with ultraviolet rays.

Polymerization started soon after the monomer aqueous solution (b) was poured into the vat-shaped container (the temperature at the start of polymerization was 98 ° C.), and the polymerization reached a peak temperature within about 1 minute. After 3 minutes, the irradiation of ultraviolet rays was stopped, and the hydrogel crosslinked polymer (b) was taken out. These series of operations were performed in a system open to the atmosphere.

The obtained hydrogel crosslinked polymer (b) was gel pulverized with a meat chopper (MEAT-CHOPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 6.4 mm, hole number: 38, die thickness: 8 mm). As a result, a finely divided particulate hydrous gel (b) was obtained (mass average particle diameter; 1000 μm).

This finely divided particulate hydrous gel (b) is spread on a 50 mesh (mesh opening 300 μm) wire mesh, dried with hot air at 180 ° C., the dried polymer (b) is pulverized with a roll mill, and further opened with a mesh opening 850 μm. And a JIS standard sieve having a mesh size of 150 μm, water-absorbent resin particles (b) which are irregularly crushed water-absorbent resins (solid content 96 mass%) were obtained. The water absorbent resin particles (b) had a CRC (water absorption capacity under no pressure) of 47.3 g / g.

Next, the water-absorbent resin particles (b) were transferred to a rotary mixer manufactured by Ledige, Germany, and 0.015 parts by mass of ethylene glycol diglycidyl ether and propylene glycol 1 with respect to 100 parts by mass of the water-absorbent resin particles (b). A surface cross-linking agent aqueous solution (b) consisting of 0.0 part by mass and 3.0 parts by mass of water was uniformly mixed and heat-treated at 100 ° C. for 45 minutes. Thereafter, the particle size was adjusted by passing through a JIS standard sieve having an opening of 850 μm to obtain water-absorbing resin particles (surface-crosslinked water-absorbing resin) (b-1) having a cross-linked surface. The water-absorbent resin particles (b-1) were indefinite, and the proportion of particles having a particle diameter of 150 μm or more and less than 850 μm was 95% by mass or more.

[Comparative Example 1-1]
The water absorbent resin particles (a-1) obtained in Production Example 1 were used as they were.

Further, the water absorbent resin particles (a-1) described in Production Example 1 were subjected to moisture absorption treatment under the following conditions. That is, about 30 g of the water-absorbing resin particles (a-1) were uniformly spread on a cabinet-size SUS bat (size: 170 mm × 210 mm × 30 mm), and the temperature was set at 25 ° C. using a small environmental tester SH-641 manufactured by ESPEC. Moisture absorption was performed for 30 minutes under the conditions of ° C. and relative humidity of 90% RH. Using the water-absorbent resin particles (a-1) after moisture absorption, the passing rate of 2000 μm sieve was measured. Table 1 shows the physical properties of the water-absorbent resin particles (a-1) and the passing rate of 2000 μm after the moisture absorption treatment.

[Comparative Example 1-2]
The water absorbent resin particles (b-1) obtained in Production Example 2 were used as they were.

Further, the water absorption resin particles (b-1) described in Production Example 2 were subjected to the same moisture absorption treatment as in Comparative Example 1-1. Using the water-absorbent resin particles (b-1) after moisture absorption, the passing rate of 2000 μm sieve was measured. Table 1 shows the physical properties of the water-absorbent resin particles (b-1) and the passing rate of 2000 μm after the moisture absorption treatment.

[Example 1-1]
100 parts by weight of the water-absorbent resin particles (a-1) obtained in Production Example 1 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and hydrotalcite (product name: DHT) as water-insoluble inorganic particles. −6, manufactured by Kyowa Chemical Industry Co., Ltd., Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O [x = 0.25, m = 0.50 of the general formula (1)], volume average particle size 0. 5 μm) 0.1 part by mass was added to a 225 g mayonnaise bottle and mixed for 3 minutes with a test disperser manufactured by Toyo Seiki Seisakusho. Table 1 shows the 2000 µm sieve passing rate of the obtained mixture and the physical properties of the 2000 µm sieve passing particles (the physical properties of the 2000 µm sieve passing particles are the columns of physical properties after addition of moisture-absorbing / water-insoluble inorganic particles in Table 1). The physical properties (CRC, AAP) of the water-absorbent resin particles (a-1) obtained in Production Example 1 are shown in the physical properties before moisture absorption column of Table 1.

[Example 1-2]
100 parts by weight of the water-absorbent resin particles (a-1) obtained in Production Example 1 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and hydrotalcite (product name: DHT) as water-insoluble inorganic particles. -6, manufactured by Kyowa Chemical Industry Co., Ltd.) 1.0 part by mass was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water-absorbent resin particles (a-1) obtained in Production Example 1 are shown in the column of physical properties before moisture absorption in Table 1.

[Example 1-3]
100 parts by weight of the water-absorbent resin particles (b-1) obtained in Production Example 2 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and silica (product name: Aerosil 200CF, 0.3 parts by mass of Nippon Aerosil Co., Ltd. was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water-absorbent resin particles (b-1) obtained in Production Example 2 are shown in the column of physical properties before moisture absorption in Table 1.

[Example 1-4]
100 parts by mass of the water-absorbing resin particles (a-1) obtained in Production Example 1 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and tricalcium phosphate (Wako Pure Chemical Industries) as water-insoluble inorganic particles. 1.0 part by mass of Kogyo Co., Ltd., CAS No. 7758-87-4) was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water-absorbent resin particles (a-1) obtained in Production Example 1 are shown in the column of physical properties before moisture absorption in Table 1.

[Example 1-5]
100 parts by mass of the water-absorbent resin particles (a-1) obtained in Production Example 1 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and hydrotalcite (product name: HT) as water-insoluble inorganic particles. -1-NC, manufactured by Sakai Chemical Industry Co., Ltd., chemical formula Mg ₄ Al ₂ (OH) ₁₂ CO ₃ .3H ₂ O [x = 0.33 of general formula (1), m = 0.5], volume average particle 0.48 parts by mass was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water-absorbent resin particles (a-1) obtained in Production Example 1 are shown in the column of physical properties before moisture absorption in Table 1.

[Example 1-6]
100 parts by weight of the water-absorbent resin particles (a-1) obtained in Production Example 1 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and hydrotalcite (product name: DHT) as water-insoluble inorganic particles. -4H, manufactured by Kyowa chemical industry Co., Ltd., the chemical formula _{Mg 4.5 Al 2 (OH) 13} CO 3 · 3.5H 2 O [ general formula (1) x = 0.31, m = 0.54], the volume 0.4 parts by mass of average particle diameter 0.4 μm)) was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water-absorbent resin particles (a-1) obtained in Production Example 1 are shown in the column of physical properties before moisture absorption in Table 1.

[Example 1-7]
100 parts by mass of the water-absorbent resin particles (a-1) obtained in Production Example 1 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and hydrotalcite (product name: HT) as water-insoluble inorganic particles. -P, Sakai chemical Industry Co., Ltd., the chemical formula _{Mg 4.5 Al 2 (OH) 13} CO 3 · 3.5H 2 O [x = 0.69 in the general formula (1), m = 0.54] , the volume 0.3 parts by mass) (average particle size 0.45 μm) was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water-absorbent resin particles (a-1) obtained in Production Example 1 are shown in the column of physical properties before moisture absorption in Table 1.

[Example 1-8]
100 parts by weight of the water-absorbent resin particles (b-1) obtained in Production Example 2 were subjected to the same moisture absorption treatment as in Comparative Example 1-1, and talc (product name: SG-2000) as water-insoluble inorganic particles. (Manufactured by Nippon Talc Co., Ltd.) was mixed in the same manner as in Example 1-1. Table 1 shows the 2000 µm sieve passage rate of the obtained mixture and the physical properties of the 2000 µm sieve passed particles. The physical properties of the water absorbent resin particles (b-1) obtained in Production Example 1 are shown in the physical properties before moisture absorption column of Table 1.

From the above results, in Examples 1-1 to 8 in which water-insoluble inorganic particles were added to the water-absorbent resin particles, compared with Comparative Examples 1-1 and 1-2 in which no water-insoluble inorganic particles were added, the sieve permeation It can be seen that the rate is high and aggregation of particles due to moisture absorption is suppressed, that is, fluidity is restored.

[Example 2-1]
40.0 parts by mass of pulverized wood pulp, 58.2 parts by mass of the water-absorbent resin particles (b-1) described in Production Example 2, and hydrotalcite (product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) 1 .8 parts by mass were molded by the method described in (1) Model Absorber a and (2) Model Absorber b, to obtain Model Absorbers (a-1) and (b-1). The total return amount was evaluated using the model absorber (a-1), and the absorption amount was evaluated using the model absorber (b-1). The obtained evaluation results are shown in Table 2-2. The basis weight and density of the model absorbent are shown in Table 2-1. The basis weight and density of the model absorbers a and b are the same.

(Production of absorber)
(1) Model absorber a
A pulverized wood pulp, water-absorbing resin particles, and water-insoluble inorganic particles are placed on a 120 mm × 400 mm web on a 400 mesh (38 μm mesh) wire screen on which water-absorbing paper is placed, using a batch type air paper making device. Air paper making. The basis weight was adjusted by the air papermaking time. Thereafter, the web was pressed under pressure, cut into a size of 100 mm × 100 mm, and molded to obtain a model absorbent body a.

In Examples and Comparative Examples, when the composition ratio of the pulverized wood pulp is 40 parts by mass, the pulp mass is 1.58 g, and when the composition ratio of the pulverized wood pulp is 60 parts by mass, the pulp mass is 3. At 56 g, water-absorbing resin particles and water-insoluble inorganic particles were further mixed at a predetermined ratio.

(2) Model absorber b
The size of 120 mm x 400 mm using a batch type air paper-making device on a 400 mesh (38 μm mesh) wire screen on which water-absorbing paper is loaded with pulverized wood pulp, water-absorbing resin particles, and water-insoluble inorganic particles. Air made on the web. The basis weight was adjusted by the air papermaking time. Thereafter, the web was pressed under pressure, cut into a size of 34 mm × 100 mm, and molded to obtain a model absorber b.

In Examples and Comparative Examples, when the composition ratio of the pulverized wood pulp is 40 parts by mass, the pulp mass is 0.53 g, and when the composition ratio of the pulverized wood pulp is 60 parts by mass, the pulp mass is 1. At 19 g, water-absorbing resin particles and water-insoluble inorganic particles were further mixed at a predetermined ratio.

[Example 2-2]
40.0 parts by mass of pulverized wood pulp, 59.4 parts by mass of the water-absorbent resin particles (b-1) described in Production Example 2, and hydrotalcite (product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) 0 .6 parts by weight were molded by the method described in (1) Model Absorber a and (2) Model Absorber b to obtain Model Absorbers (a-2) and (b-2). The total return amount was evaluated using the model absorber (a-2), and the absorption amount was evaluated using the model absorber (b-2). The obtained evaluation results are shown in Table 2-2. The basis weight and density of the model absorbent are shown in Table 2-1.

[Example 2-3]
60.0 parts by mass of pulverized wood pulp, 39.6 parts by mass of the water-absorbent resin particles (b-1) described in Production Example 2, and hydrotalcite (product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) 0 .4 parts by mass were molded by the method described in (1) Model Absorber a and (2) Model Absorber b to obtain Model Absorbers (a-3) and (b-3). The total return amount was evaluated using the model absorber (a-3), and the absorption amount was evaluated using the model absorber (b-3). The obtained evaluation results are shown in Table 3-2. The basis weight and density of the model absorbent are shown in Table 3-1.

[Example 2-4]
40.0 parts by mass of pulverized wood pulp, 59.4 parts by mass of the water-absorbent resin particles (b-1) described in Production Example 2, tricalcium phosphate (manufactured by Wako Pure Chemical Industries, Ltd., CAS No. 7758-87-) 4) 0.6 parts by mass were molded by the method described in (1) Model Absorber a and (2) Model Absorber b to obtain Model Absorbers (a-4) and (b-4) . The total return amount was evaluated using the model absorber (a-4), and the absorption amount was evaluated using the model absorber (b-4). The obtained evaluation results are shown in Table 2-2. The basis weight and density of the model absorbent are shown in Table 2-1.

[Example 2-5]
60.0 parts by mass of pulverized wood pulp, 39.6 parts by mass of the water-absorbent resin particles (b-1) described in Production Example 2, and 0.4 parts by mass of silica (product name: Aerosil 200CF, manufactured by Nippon Aerosil Co., Ltd.) Were molded by the method described in (1) Model Absorber a and (2) Model Absorber b to obtain Model Absorbers (a-5) and (b-5). The total return amount was evaluated using the model absorber (a-5), and the absorption amount was evaluated using the model absorber (b-5). The obtained evaluation results are shown in Table 3-2. The basis weight and density of the model absorbent are shown in Table 3-1.

[Example 2-6]
40.0 parts by mass of pulverized wood pulp, 59.4 parts by mass of the water-absorbent resin particles (b-1) described in Production Example 2, and 0.6 parts by mass of silica (product name: Aerosil 200CF, manufactured by Nippon Aerosil Co., Ltd.) Were molded by the method described in (1) Model Absorber a and (2) Model Absorber b to obtain Model Absorbers (a-6) and (b-6). The total return amount was evaluated using the model absorber (a-6), and the absorption amount was evaluated using the model absorber (b-6). The obtained evaluation results are shown in Table 2-2. The basis weight and density of the model absorbent are shown in Table 2-1.

[Comparative Example 2-1]
40.0 parts by weight of pulverized wood pulp, 54.0 parts by weight of the water-absorbent resin particles (b-1) described in Production Example 2, and hydrotalcite (product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) 6 0.0 parts by weight were molded by the method described in (1) Model Absorber a and (2) Model Absorber b to obtain Model Absorbers (a-7) and (b-7). The total return amount was evaluated using the model absorber (a-7), and the absorption amount was evaluated using the model absorber (b-7). The obtained evaluation results are shown in Table 2-2. The basis weight and density of the model absorbent are shown in Table 2-1.

[Comparative Example 2-2]
40.0 parts by weight of pulverized wood pulp and 60.0 parts by weight of water-absorbent resin particles (b-1) described in Production Example 2 are described in (1) Model Absorber a and (2) Model Absorber b. Molded by the method, model absorbers (a-8) and (b-8) were obtained. The total return amount was evaluated using the model absorber (a-8), and the absorption amount was evaluated using the model absorber (b-8). The obtained evaluation results are shown in Table 2-2. The basis weight and density of the model absorbent are shown in Table 2-1.

(5-5) Absorber performance evaluation (a) Total return (Re-Wet)
The model absorbent body a is provided with a liquid-impermeable back sheet and a polyethylene sheet as a side gather, water-absorbing paper is used as a liquid-permeable top sheet, and is a paper diaper-type model absorbent having an inner diameter of 28 mm and a height. A 100 mm × 100 mm device having a 100 mm cylinder at the center was placed, and weights were evenly placed so as to apply a load of 21 g / cm ² (2.1 kPa) to the model absorber. Next, 25 ml of the test liquid adjusted to 25 ± 3 ° C. was quickly poured into the cylinder. Ten minutes after pouring the test liquid, remove the weight and device from the model absorber, and weigh about 5 g (17 sheets) of filter paper (manufacturer: ADVANTEC, FILTER PAPER, No. 2, 55 mm) to the second decimal place. The weight was recorded (W1 [g]), placed on the center of the model absorber, and a weight was evenly placed on the entire filter paper so that a load of 49 g / cm ² (4.8 kPa) was applied, and left for 2 minutes. After leaving, remove the filter paper and the load from the model absorber, record the weight of the filter paper to 2 digits after the decimal point (W2 [g]), and the amount of liquid absorbed by the filter paper from the change in the weight of the filter paper according to the following formula (2) Was calculated as the first return amount (g).

Expression (2) Return amount [g] = W2−W1
Thereafter, using the model absorber used in the above measurement, the same liquid injection operation and return amount measurement operation were repeated twice, and the second return amount (g) and the third return amount (g) were measured. The total of the three return amounts was taken as the total return amount.

In addition, the filter paper used for the measurement of the return amount was about 8 g (27 sheets) for the second time, and about 10 g (33 sheets) for the third time. The test solution was a 0.9% by mass sodium chloride aqueous solution.

(B) Absorption amount The model absorbent body b, whose total weight (W3 ′ [g]) was measured in advance, was obtained by using a non-woven bag (size: 74 mm × 140 mm, manufacturer: Nankoku Pulp Co., Ltd., paper name: Heaton It was put into paper, product type: GSP-22, and heat-sealed (size of seal inner part (effective part): 64 mm × 130 mm), and then immersed horizontally in 1 L of test liquid adjusted to 25 ± 3 ° C. 30 minutes after soaking, lift the bag by holding both sides of the short side (74mm), fix the one side so that it does not sag, hang it for 10 minutes, drain the bag (W4 ' [G]) was measured.

The same operation was performed without inserting the model absorber, and the weight of the bag at that time (W5 ′ [g]) was measured. The absorption amount [g] of the model absorber was calculated according to the following formula (3). The test solution was a 0.9 mass% sodium chloride aqueous solution.

Formula (3): Absorption amount [g] = W4′−W3′−W5 ′

From the above results, the absorbent articles described in Examples 2-1 to 2-6 had a higher absorption amount than the absorbent articles described in Comparative Examples 2-1 and 2-2. In addition, the absorbent articles described in Examples 2-1 to 2-6 were excellent in the balance between the absorption amount and the return amount.

This application is based on Japanese Patent Application No. 2014-5502 filed on January 15, 2014 and Japanese Patent Application No. 2014-76414 filed on April 2, 2014. , Referenced and incorporated in its entirety.

Claims (10)

1. A method for producing an absorbent article comprising at least water absorbent resin particles and water-insoluble inorganic particles,
   Mixing the water-absorbent resin particles and the water-insoluble inorganic particles so that a ratio of the water-insoluble inorganic particles to 100% by mass of the water-absorbent resin particles is 0.01% by mass or more and less than 10% by mass. A method for producing an absorbent article, comprising:
2. The method for producing an absorbent article according to claim 1, wherein the volume average particle diameter of the water-insoluble inorganic particles is 10 µm or less.
3. The method for producing an absorbent article according to claim 1 or 2, wherein the water-insoluble inorganic particles include at least one selected from a multi-component metal compound, tricalcium phosphate, and silicon dioxide.
4. The method for producing an absorbent article according to claim 3, wherein the multi-element metal compound has a volume average particle diameter of 2 µm or less.
5. The production of the absorbent article according to any one of claims 1 to 4, further comprising a step of producing an absorbent body by mixing the water-absorbent resin particles, the water-insoluble inorganic particles, and hydrophilic fibers. Method.
6. The absorbent article according to any one of claims 1 to 5, wherein a water-absorbing agent containing the water-absorbing resin particles having a sieve passage rate of 2000 µm or less is mixed with water-insoluble inorganic particles. Manufacturing method.
7. The method for producing an absorbent article according to claim 6, wherein a ratio of the water-insoluble inorganic particles to 100% by mass of the water-absorbent resin particles is 0.1 to 5% by mass.
8. It has the process of manufacturing the absorber by mixing the water-absorbent resin particles, the water-insoluble inorganic particles, and pulp, and the total amount of the water-absorbent resin particles and the water-insoluble inorganic particles in the absorber The method for producing an absorbent article according to any one of claims 1 to 6, wherein (core concentration) is 20 to 100% by mass.
9. The method for producing an absorbent article according to claim 8, wherein a ratio of the water-insoluble inorganic particles to 100% by mass of the water-absorbent resin particles is 0.5% by mass or more and less than 10% by mass.
10. The method for producing an absorbent article according to claim 8 or 9, wherein the amount of the water-insoluble inorganic particles in the absorber is 0.1 to 5% by mass.