JP2000093792A - Water absorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a uniform absorbent which is excellent in moisture- absorbed blocking properties, assembly work properties, and absorption properties under pressure and can reduce a return quantity by using a kind of inorganic powder having a specified value or below in pH of dispersion and a specified value or above in specific surface area by a BET method and a water-absorbent resin. SOLUTION: In a water-absorbent resin, preferably, a part of a particle close to the surface is crosslinked, and water absorbency is at least 30 g/g. In inorganic powder which is preferably hydrophobic, pH of the dispersion is 7-10, and the specific surface area is at least 50 m2/g. When the inorganic powder is added to the water-absorbent resin, a dry blend method, a wet mixing method, and others can be employed. Moreover, the blocking percentage of an absorbent which is allowed to stand at 25 deg.C for 1 hr under 90% relative humidity is 20% or below. In this way, the absorbent excellent in moistureproof blocking properties, blending properties, and absorption properties under pressure is produced to be applied to a disposable diaper and others.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a water-absorbing agent and an absorbent article using the water-absorbing agent. More particularly, the present invention relates to a water-absorbing agent, which is excellent in moisture-absorbing blocking resistance, blends with a fiber base material such as pulp, and absorbs under pressure. And a method for producing the same.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been widely used as one of the constituent materials of sanitary materials such as disposable diapers, sanitary napkins and incontinence pads for the purpose of absorbing body fluids.

Examples of the water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, and vinyl acetate-acrylic acid. Saponified ester copolymer, cross-linked carboxymethyl cellulose,
Acrylonitrile polymer or acrylamide polymer hydrolyzate or crosslinked product thereof, crosslinked product of cationic monomer, crosslinked isobutylene-maleic acid copolymer,
A crosslinked product of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid is known.

[0004] Conventionally, the water absorption properties desired for the above-mentioned water-absorbent resin include a high absorption capacity when in contact with an aqueous liquid such as a body fluid, an excellent water absorption rate, a liquid permeability, an absorption capacity under pressure, and the like.
A suction force for sucking water from a base material containing an aqueous liquid has been proposed.

[0005] In recent years, absorbent articles such as disposable diapers have tended to use more water-absorbing resin. That is, in the absorbent layer of an absorbent article such as a disposable diaper, the weight ratio α of the water-absorbent resin to the total amount of the water-absorbent resin and the fiber base (hereinafter sometimes referred to as resin concentration) is 0.3 or more, and further 0.5 or more. It is becoming mainstream. Therefore, when manufacturing various water-absorbent articles such as disposable diapers using the water-absorbent resin, it is necessary to incorporate a large amount of the water-absorbent resin having high hygroscopicity into the fiber base material. Depending on the conditions, the problem that the resin particles are blocked in the middle of a popper or a line or adhere to an apparatus, and a stable production cannot be performed, has become a serious problem.

As a method for solving the blocking property under moisture absorption, a composition in which a water-absorbing resin powder and hydrophobic fine-particle silica are mixed at a specific ratio (Japanese Patent Publication No. 61-17542)
JP-A-59-80459), a composition in which a water-absorbent resin powder is mixed with inorganic powders such as hydrated silicon dioxide, hydrated aluminum dioxide, and hydrated titanium dioxide (JP-A-59-80459). After treating with an activator, a method of mixing an inorganic substance or a high melting point organic compound (Japanese Patent Laid-Open No. 61-69854)
JP-A-9-136966), a method of mixing stearic acid and an inorganic powder with a water-absorbent resin powder (JP-A-63-105064), and a method of treating a water-absorbent resin with a specific silicon-based surfactant (JP-A-9-136966). Is known.

However, the inventors of the present invention have found that when incorporating such a resin having improved blocking properties under moisture absorption into an absorbent article such as a paper diaper having a high resin concentration, the resin and the hydrophilic fiber base such as pulp are used. Poor mixing properties with the material,
There are new problems that it is difficult to obtain an absorber in which both are uniformly mixed, resin that does not adhere to pulp scatters around during machine operation, and that the net at the suction part of the machine is often clogged. I found it to come.

[0008] Further, such a resin having improved blocking properties under moisture absorption is still inferior in some absorption characteristics such as absorption capacity under pressure, and the return amount increases in an absorbent article having a high resin concentration. I also found that there was a tendency.

[0009]

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hydrophilic fiber base material such as pulp which is excellent in blocking property under moisture absorption and which is incorporated into an absorbent article such as a diaper at a high resin concentration. A water-absorbing agent capable of producing a uniform absorber having good workability because of its excellent mixing properties with water and capable of reducing the amount of return even in an absorbent article having a high resin concentration because of its excellent absorption characteristics under pressure, and a method for producing the same. To provide.

[0011]

DISCLOSURE OF THE INVENTION The present inventors provide a water absorbing agent,
The results of intensive studies from the viewpoint of excellent blocking properties under moisture absorption and excellent mixing properties with hydrophilic fiber base materials such as pulp when incorporating high resin concentration into absorbent articles such as diapers and excellent absorption properties under pressure. The inventors have found that the above object can be achieved when a water-absorbent resin and a specific inorganic powder are combined, and have completed the present invention.

That is, the water absorbing agent according to the first aspect of the present invention
It is characterized by being a water-absorbing agent comprising an inorganic powder having a pH of 7 to 10 and a specific surface area of 50 m2 / g or more by a BET method and a water-absorbing resin.

According to a fifth aspect of the present invention, there is provided a method for producing a water-absorbing agent, wherein the dispersion has a pH of 7 or more and 10 or less and a specific surface area by a BET method of 50 m2 / g or more before mixing the inorganic powder and the water-absorbing resin. Alternatively, an aqueous liquid is added after mixing.

The water-absorbing agent according to claim 6 has a blocking ratio of not more than 20% when left for 1 hour at 25 ° C. and a relative humidity of 90%, and has an absorption capacity under pressure of 30 (g / g).
g) It is characterized by being a water-absorbing agent which is not less than g).

The absorbent article according to the invention of claim 7 is an absorbent article comprising an absorbent layer containing a water-absorbent resin and a fiber base material, a liquid-permeable top sheet, and a liquid-impermeable back sheet. And a water-absorbing resin containing a water-absorbing agent having a blocking rate of 20% or less and an absorption capacity under pressure of 30 (g / g) or more when left at 25 ° C. and a relative humidity of 90% for 1 hour. The weight ratio α of the water absorbent resin to the total amount of the fiber base is 0.3
It is characterized by the above.

The water absorbing agent according to the invention of claim 8 is a water absorbing agent comprising an inorganic powder having a cationic group and a water absorbing resin having an anionic group.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The water-absorbing resin which can be used in the present invention is not particularly limited, but it is preferable that the particles are further crosslinked in the vicinity of the surface and have an absorption capacity under pressure of 30 (g / g) or more. When the value of the absorbency against pressure is less than 30 (g / g), even when the moisture absorption blocking property and the mixing property with pulp or the like are improved, the amount of return when the absorbent article is obtained may not be reduced.
Such a water-absorbent resin is generally obtained by a production method of subjecting a water-absorbent resin precursor to a surface crosslinking treatment under specific conditions.

The water-absorbing resin precursor is synthesized, for example, by aqueous solution polymerization or reverse phase suspension polymerization. Specific examples of the water-absorbent resin precursor include, for example, a crosslinked product of partially neutralized polyacrylic acid, a hydrolyzate of starch-acrylonitrile graft polymer, a neutralized product of starch-acrylic acid graft polymer, and acetic acid. Saponified vinyl-acrylate copolymer, hydrolyzate of acrylonitrile polymer or acrylamide polymer or cross-linked thereof, carboxyl group-containing cross-linked polyvinyl alcohol modified product, cross-linked isobutylene-maleic anhydride copolymer, etc. Can be

The above-mentioned water-absorbing resin precursor is, for example, an unsaturated carboxylic acid such as (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, β-acryloyloxypropionic acid or the like. After polymerizing or copolymerizing one or more types of monomers selected from neutralized products of the above, the polymer is subjected to operations such as pulverization and classification as necessary to adjust the polymer to a predetermined average particle size. can get. Among the above monomers, those having an anionic group such as (meth) acrylic acid and neutralized products thereof are more preferable in view of affinity with inorganic particles.

Further, the water-absorbing resin precursor may be a copolymer of the above monomer and another monomer copolymerizable with the monomer. As the other monomer, specifically,
For example, vinyl sulfonic acid, styrene sulfonic acid, 2-
(Meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2-
Anionic unsaturated monomers such as (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, N
-N-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) ) Nonionic hydrophilic group-containing unsaturated monomers such as acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N-dimethylaminoethyl ( (Meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof And cationic unsaturated monomers such.

It is essential that the interior of the water-absorbent resin precursor is crosslinked by reacting or copolymerizing with a crosslinking agent having a plurality of polymerizable unsaturated groups or a plurality of reactive groups. Specific examples of the crosslinking agent include N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylolpropane. Di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meta) ) Acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol Chole diglycidyl ether, glycerol diglycidyl ether,
Ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol,
Ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate and the like can be mentioned. These crosslinking agents may be used alone or as a mixture of two or more. Among the compounds exemplified above, it is more preferable to use a compound having a plurality of polymerizable unsaturated groups as a crosslinking agent.

The amount of the crosslinking agent used is preferably in the range of 0.01 mol% to 2 mol% based on the total amount of the above monomers,
More preferably, it is in the range of 3 mol% to 0.2 mol%.

At the start of the polymerization, for example, potassium persulfate, ammonium persulfate, sodium persulfate,
t-butyl hydroperoxide, hydrogen peroxide, 2,
A radical polymerization initiator such as 2′-azobis (2-amidinopropane) dihydrochloride or an active energy ray such as an ultraviolet ray or an electron beam can be used. When an oxidizing radical polymerization initiator is used, redox polymerization may be performed using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination. The amount of these polymerization initiators used is preferably in the range of 0.001 mol% to 2 mol%, more preferably in the range of 0.01 mol% to 0.5 mol%.

It is also preferable to use a method in which a foaming agent such as a carbonate or an azo compound, an inert gas, or the like is added to the monomer during polymerization, and the resulting water-absorbent resin precursor has a porous structure to adjust the specific surface area. .

The water-absorbent resin precursor may be granulated in a predetermined shape, or may be in various shapes such as a sphere, a scale, an irregular crushed shape, and a granular shape. Further, the water absorbing resin precursor may be primary particles,
Granules of secondary particles may be used.

The above-mentioned water-absorbent resin precursor preferably has an average particle diameter in the range of 150 μm to 600 μm, more preferably an average particle diameter in the range of 200 μm to 400 μm.

The above water-absorbent resin precursor generally has a low absorption capacity under pressure. Therefore, by using a surface cross-linking agent, the cross-link density near the surface of the water-absorbent resin precursor is made higher than that inside. Is preferred. That is, by crosslinking the vicinity of the surface of the water-absorbing resin precursor using the specific surface cross-linking agent, a water-absorbing resin that can be preferably used in the present invention can be obtained.

That is, the water-absorbent resin according to the present invention is preferably a water-absorbent resin precursor obtained by the above-mentioned aqueous solution polymerization, that is, having an average particle diameter in the range of 150 μm to 600 μm.
More preferably, those obtained by adjusting by polymerization, classification and the like so that the average particle diameter is in the range of 200 μm to 400 μm are heat-treated in the presence of a surface cross-linking agent, and then subjected to a specific pressure. It is obtained by processing so as to have an absorption capacity value.

The above-mentioned surface cross-linking agent has a functional group of the water-absorbent resin precursor, for example, a functional group capable of reacting with an acidic group. You.

When the functional group of the water absorbent resin precursor is, for example, a carboxyl group, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, dipropylene glycol , 2,2,4-trimethyl-1,3-pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4
-Butanediol, 1,5-pentanediol, 1,6
-Hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine,
Polyhydric alcohol compounds such as polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol poly Polyhydric epoxy compounds such as glycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol; and polyepoxy compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine, and polyethyleneimine Divalent amine compound; 2,4-tolylene diisocyanate, hex Polyvalent isocyanate compounds such as diisocyanate; 1,2-ethylene-bis polyvalent oxazoline compound of oxazoline and the like; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolane -
2-one, 4,5-dimethyl-1,3-dioxolane-
2-one, 4,4-dimethyl-1,3-dioxolane-
2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2
-One, 1,3-dioxan-2-one, 4-methyl-
1,3-dioxan-2-one, 4,6-dimethyl-
Alkylene carbonate compounds such as 1,3-dioxan-2-one and 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin; zinc, calcium Polyhydric metal compounds such as hydroxides and chlorides of magnesium, aluminum, iron, zirconium and the like; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane; One or two or more types can be exemplified.

In order to obtain an excellent blending property with pulp, it is preferable to use a polyhydric alcohol compound as a surface cross-linking agent, and more preferable to use a polyhydric alcohol present on the particle surface. is there. Its abundance is 0.
0001-5 parts by weight, more preferably 0.01-1 part by weight.
The polyhydric alcohol may be added to the surface of the particles as a dispersing aid or a hydrophilizing agent for the surface cross-linking agent in addition to the surface treating agent.

The amount of the surface cross-linking agent used depends on the compound to be used and the combination thereof, but is preferably in the range of 0.001 to 5 parts by weight based on 100 parts by weight of the solid content of the water-absorbing resin precursor. , 0.01 to 2 parts by weight. By using the above surface cross-linking agent, the water-absorbing resin precursor, that is, the cross-linking density near the surface of the water-absorbing resin can be higher than the inside, and the value of the absorption capacity under pressure necessary for the resin of the present invention can be increased. You can have what you have. If the amount of the surface cross-linking agent exceeds 5 parts by weight, not only is it uneconomical, but also because the amount of the surface cross-linking agent becomes excessive in forming the optimum cross-linked structure in the water absorbent resin, the absorption capacity is increased. Is undesirably reduced. In addition, the amount of the surface crosslinking agent used is 0.001
When the amount is less than part by weight, the value of the absorbency against pressure of the water-absorbent resin may not be easily improved.

When mixing the water-absorbing resin precursor and the surface crosslinking agent, it is preferable to use water as a solvent. The amount of water used depends on the type and particle size of the water-absorbing resin precursor, but is 0% based on 100 parts by weight of the solid content of the water-absorbing resin precursor.
And preferably not more than 20 parts by weight, more preferably in the range of 0.5 to 10 parts by weight.

When mixing the water-absorbing resin precursor and the surface cross-linking agent, a hydrophilic organic solvent may be used as a solvent, if necessary. As the above hydrophilic organic solvent,
For example, lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol; ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, Propylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentadiol, polypropylene glycol, 2-butene-1,4-diol, 1,4-butanediol, , 5
Polyhydric alcohol compounds such as -pentanediol and 1,6-hexanediol; ketones such as acetone; ethers such as dioxane and tetrahydrofuran; amides such as N, N-dimethylformamide; sulfoxides such as dimethylsulfoxide. No. The amount of the hydrophilic organic solvent used depends on the type and particle size of the water-absorbent resin precursor, but is preferably 20% by weight based on 100 parts by weight of the solid content of the water-absorbent resin precursor.
It is preferably not more than 0.1 parts by weight, more preferably 0.1 to 10 parts by weight.

When mixing the water-absorbing resin precursor and the surface cross-linking agent, for example, after dispersing the water-absorbing resin precursor in the above-mentioned hydrophilic organic solvent, the surface cross-linking agent is mixed. However, the mixing method is not particularly limited. Among various mixing methods, a method in which a surface cross-linking agent dissolved in water and / or a hydrophilic organic solvent, if necessary, is directly sprayed or dropped onto the water-absorbent resin precursor and mixed. In the case of mixing using water, fine powder insoluble in water, a surfactant or the like may be allowed to coexist.

The mixing device used for mixing the water-absorbing resin precursor and the surface crosslinking agent preferably has a large mixing force in order to mix the two uniformly and reliably. As the mixing device, for example, a cylindrical mixer,
Double wall conical mixer, V-shaped mixer, ribbon mixer,
Suitable examples include a screw mixer, a fluid-type furnace rotary desk mixer, an airflow mixer, a double-arm kneader, an internal mixer, a pulverizing kneader, a rotary mixer, and a screw extruder.

After mixing the water-absorbent resin precursor and the surface cross-linking agent, a heat treatment is performed to crosslink the vicinity of the surface of the water-absorbent resin precursor. The temperature of the heat treatment depends on the surface cross-linking agent used, but is preferably from 40 ° C. to 250 ° C. When the treatment temperature is lower than 40 ° C., a uniform crosslinked structure is not formed, and therefore, it may not be possible to obtain a water-absorbent resin having an absorption capacity under pressure within a preferable range. Processing temperature
If the temperature exceeds 250 ° C., the water-absorbent resin may be deteriorated, and the performance of the water-absorbent resin may be reduced.

The above heat treatment can be carried out using a usual dryer or heating furnace. Examples of the dryer include a groove-type mixing dryer, a rotary dryer, a desk dryer, a fluidized-bed dryer, a flash dryer, and an infrared dryer.

The water-absorbing resin which can be used in the present invention preferably has an absorption capacity under pressure of 25 (g / g) or more, more preferably 30 (g / g) or more, even more preferably 32 (g / g) or more. The cross-linking agent, the mixing method, the heating temperature, the treatment time and the like are controlled so as to be as follows.

The water absorbing agent of the present invention can be obtained by adding an inorganic powder having a pH of 7 to 10 and a specific surface area by a BET method of 50 m 2 / g or more to the water absorbing resin obtained as described above.

The dispersion of the present invention is defined as a dispersion in which 4% by weight of a dispersion (here, an inorganic powder) is dispersed in a solution having a water: methanol ratio of 1: 1.

The inorganic powder that can be used in the present invention includes:
The dispersion has a pH of 7 or more and 10 or less and a specific surface area of 50 m2 / g or more by a BET method, and preferably has hydrophobicity.

Examples of such a functional group include cationic groups such as amino groups and quaternary amino groups as functional groups on the surface of powders of silicon oxide, aluminum oxide, titanium oxide, etc. produced by a dry method or a wet method. It can be obtained by adding a hydrophobic group if necessary. Preferably, the specific surface area by the BET method manufactured by a dry method is 50 m2 / g or more.

The inorganic powder preferably has an average particle size of 1 μm.
It is preferred that:

The amount of the inorganic powder used is not particularly limited, but is generally 0.0001 to 100 parts by weight of the water absorbent resin.
A range of 10 parts by weight is preferred. If the amount is less than 0.001, the effect of improving blocking resistance may not be observed. If the amount exceeds 10 parts by weight, the mixing properties with pulp may be significantly reduced. Preferably 0.005-
It is in the range of 0.5 parts by weight.

As a method for adding the inorganic powder, a known mixer can be used so that a desired amount of the inorganic powder is added to the water-absorbing resin. Examples of such a mixing device include a cylindrical mixer, a double-walled conical mixer, a V-shaped mixer, a ribbon-type mixer, a screw-type mixer, a fluidized-type rotary desk-type mixer, and an air-flow type. Blender, double-arm kneader, internal mixer, pulverizing kneader,
Rotary mixers, screw-type extruders and the like are suitable.

When the inorganic powder is added to the water absorbent resin, a dry blending method, a wet mixing method, or the like can be employed.
In the case of the wet mixing method, water, an aqueous liquid or various organic solvents are added to the water-absorbent resin, and then the inorganic powder is added. Direct spraying or dripping on resin, etc.
A method of adding water, an aqueous liquid, various organic solvents, and the like to the water-absorbent resin after adding the inorganic powder, and the like can be exemplified. Preferably, an aqueous liquid is added before and / or after mixing the inorganic powder and the water-absorbing resin.

It is also possible to adopt a method of adding an inorganic powder during the polymerization of the water-absorbing resin or a method of adding the inorganic powder to the gel after polymerization. In this case, however, the inorganic powder is uniformly present on the particle surface. However, there is a possibility that the effect corresponding to the used amount may not be obtained without performing the above.

When the water-absorbent resin and the inorganic powder are mixed in the present invention, the amount of water, steam, or an aqueous liquid composed of water and a hydrophilic organic solvent used as required depends on the type and particle size of the water-absorbent resin. The optimum amount is different, but in the case of water, it is usually 10 parts by weight or less, preferably 1 to 5 parts by weight, based on 100 parts by weight of the solid content of the water absorbent resin. Similarly, the amount of the hydrophilic organic solvent used is generally 10 parts by weight or less, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the solid content of the water-absorbent resin.

The water absorbing agent obtained by the above production method is
A water-absorbing agent having a blocking ratio of 20% or less when left at 25 ° C. and a relative humidity of 90% for 1 hour. More preferably, the absorption capacity under pressure is 30 (g / g) or more. If the blocking ratio exceeds 20%, depending on the working environment and climatic conditions, the resin particles may block each other in the middle of the popper or the line, and stable production may not be performed. Preferably, the blocking rate is 10% or less. Further, if the absorption capacity under pressure is less than 30 (g / g), even if the moisture absorption blocking property and the mixing property with pulp and the like are improved, the return amount when the absorbent article is formed may not be reduced, which is not preferable. . Preferably, the absorption capacity under pressure is 32 (g / g) or more. The water-absorbing agent obtained by the above production method is a water-absorbing agent comprising an inorganic powder having a cationic group and a water-absorbing resin having an anionic group, and is preferably left at 25 ° C. and 90% relative humidity for 1 hour. The blocking rate at the time of performing is not more than 20%.

The absorbent article of the present invention is an absorbent article comprising an absorbent layer containing a water-absorbent resin and a fiber base, a liquid-permeable top sheet, and a liquid-impermeable back sheet. The blocking rate when left for 1 hour under the condition of 90% relative humidity is 20% or less, and the absorption capacity under pressure is
The weight ratio α of the water-absorbing resin to the total amount of the water-absorbing resin and the fibrous base material containing the water-absorbing agent of 30 (g / g) or more is 0.3 or more.

When the weight ratio α of the water-absorbent resin to the total amount of the water-absorbent resin and the fiber base is less than 0.3, the amount of the water-absorbent resin used is small, and the distribution of the polymer is relatively uniform regardless of the type of the resin. In this case, the absorbent article is bulky and has a large amount of return.

According to the present invention, under the conditions of 25 ° C. and 90% relative humidity, 1
By using a water-absorbing agent having a blocking ratio of 20% or less and an absorption capacity under pressure of 30 (g / g) or more when left for a period of time, the water-absorbing resin and the fibrous base material in the total amount thereof are used. Even when the weight ratio α is a high resin concentration of 0.3 or more, it is possible to manufacture an absorber in which fibers and resin are uniformly blended with good workability.

As described above, the water absorbing agent of the present invention can stably provide an absorbent article having a high resin concentration and exhibiting excellent absorption characteristics. Specific examples of such absorbent articles include hygiene materials such as adult paper diapers, which have been growing rapidly in recent years, diapers for children, sanitary napkins, so-called incontinence pads, and the like, and are particularly limited to these. However, since the water-absorbing agent present in the absorbent article has excellent working properties and mixing properties, and also has excellent absorption properties under pressure, the amount of return of the absorbent article is small, resulting in a dry feeling. The burden on the wearer, the caregiver, etc. can be greatly reduced.

[0056]

The water-absorbing agent of the present invention has excellent blocking properties under moisture absorption, and has a mixing property with a hydrophilic fiber base such as pulp even when incorporated into an absorbent article such as a diaper at a high resin concentration. It is a novel water-absorbing agent that can produce a uniform absorber with good workability and excellent absorption characteristics such as absorption capacity under pressure, and can reduce the return amount even in absorbent articles with high resin concentration. is there. Although the cause is not clear, since the specific inorganic powder is added to the water-absorbent resin, the affinity between the inorganic powder and the water-absorbent resin particles is improved, and the particle surface can be more efficiently coated. It is presumed that it became possible for the first time to achieve both the so-called contradictory characteristics of anti-moisture absorption and blending with pulp without reducing absorption characteristics such as absorption capacity under pressure.

In addition, the absorbent article of the present invention has excellent working properties and mixing properties because the water-absorbing agent contained therein has excellent absorption properties under pressure. Since the amount is small and the dry feeling is remarkable, it can be used particularly suitably for sanitary materials such as paper diapers, sanitary napkins, incontinence pads for adults, diapers for adults, etc., and can maintain excellent wearing feeling for a long time. It can be.

<Measurement Methods> Various properties of the water-absorbing resin (or water-absorbing agent) in the present invention were measured by the following methods.

(A) Absorption capacity 0.2 g of a water-absorbing resin (or water-absorbing agent) was added to a nonwoven fabric bag (60 m
m × 60 mm) and immersed in a 0.9% by weight aqueous sodium chloride solution (physiological saline). After 60 minutes, the bag was lifted, and after draining with a centrifuge at 250 G for 3 minutes, the weight W1 (g) of the bag was measured. Further, the same operation was performed without using a water absorbing agent, and the weight W0
(G) was measured. Then, from these weights W1 and W0, the following formula: absorption capacity (g / g) = (weight W1 (g) −weight W0 (g)) /
The absorption capacity (g / g) was calculated according to the weight (g) of the water absorbent resin.

(B) Absorption Capacity Under Pressure First, a measuring apparatus used for measuring the absorption capacity under pressure will be briefly described with reference to FIG.

As shown in FIG. 1, the measuring device is a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have. The container 2 has an opening 2a at the top and an opening 2b at the side surface thereof.
The outside air suction pipe 3 is fitted into the opening a, and the conduit 4 is attached to the opening 2b. The container 2 contains a predetermined amount of physiological saline solution 11 (aqueous solution of 0.9% by weight of sodium chloride). The lower end of the outside air suction pipe 3 is submerged in the physiological saline 11. The glass filter 6 has a diameter of 70 mm. The container 2 and the glass filter 6 are in communication with each other by the conduit 4. The upper part of the glass filter 6 is fixed at a position slightly higher than the lower end of the outside air suction pipe 3. The measuring unit 5 includes a filter paper 7, a support cylinder 8, a wire mesh 9 attached to a bottom of the support cylinder 8,
And a weight 10. Then, the measuring unit 5 places the filter paper 7 and the support cylinder 8 (that is, the wire mesh 9) on the glass filter 6 in this order, and places the weight 10 inside the support cylinder 8, that is, on the wire mesh 9. It has been. The support cylinder 8 has an inner diameter of 60 mm. The wire mesh 9 is made of stainless steel and has a mesh size of 400 mesh (mesh size 38 μm).
m). Then, a predetermined amount of a water-absorbing resin (or a water-absorbing agent) is evenly spread on the wire mesh 9. The weight of the weight 10 is adjusted so that a load of 20 g / cm 2 can be uniformly applied to the wire mesh 9, that is, the water-absorbing resin.

The absorption capacity under pressure was measured using the measuring apparatus having the above-mentioned structure. The measuring method will be described below.

First, predetermined preparation operations were performed, such as putting a predetermined amount of physiological saline 11 into the container 2 and fitting the outside air suction pipe 3 into the container 2. Next, the filter paper 7 was placed on the glass filter 6. On the other hand, in parallel with these mounting operations, 0.9 g of a water-absorbing resin (or water-absorbing agent) is evenly spread on the inside of the support cylinder, that is, on the wire mesh 9, and a weight 10 is placed on the water-absorbing resin.
Was placed.

Next, the wire mesh 9, that is, the support cylinder 8 on which the water-absorbent resin and the weight 10 were mounted was placed on the filter paper 7.

Then, the weight W2 (g) of the physiological saline 11 absorbed by the water-absorbent resin was measured using the balance 1 for 60 minutes from the time when the support cylinder 8 was placed on the filter paper 7. Then, from the above weight W2, the absorption capacity under pressure (g) 60 minutes after the start of absorption according to the following equation: absorption capacity under pressure (g / g) = weight W2 (g) / weight of water absorbent resin (g) / g)
Was calculated.

(C) Blocking ratio 5 g of a water-absorbing resin (or water-absorbing agent) was evenly sprayed on the bottom of an aluminum cup having a diameter of 52 mm at the bottom and a height of 22 mm, and was previously adjusted to 25 ° C. and 90% relative humidity. Put quickly in a moisturizer and leave for 1 hour. Thereafter, the water-absorbing agent that has absorbed the moisture is passed through a standard sieve having a diameter of 7.5 cm and an opening of 2000 μm (10 mesh). After applying light vibration, measure the weight (W1) of the block-shaped water absorbing agent remaining on the net without passing through the sieve and the weight (W0) of the water absorbing agent passed through the sieve. The blocking ratio is calculated based on the following equation.

Blocking ratio (%) = W1 / (W1 + W0) × 100 (d) Return amount of absorbent article 50 parts by weight of a water-absorbent resin (or water-absorbing agent) and 50 parts by weight of ground wood pulp were mixed. . The resulting mixture is then:
A web having a size of 100 mm × 100 mm was formed on a wire screen formed into a 400 mesh (mesh size of 38 μm) by air-making using a batch-type air-making apparatus. Further, the web was pressed at a pressure of 2 kg / cm2 for 5 seconds to obtain an absorbent having a basis weight of about 360 g / m2.

Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impermeable polypropylene, the above-described absorber, and a top sheet (liquid-permeable sheet) made of liquid-permeable polypropylene were placed in this order. By mounting, an absorbent article was obtained. The weight of this absorbent article is 3.6
g.

An artificial urine (2.0 g of KCl, 2.0 g of Na 2 SO 4, 0.8 g of NH 4 H 2 PO in 1 L of ion exchange water)
4, 0.15 g (NH4) 2HPO4, 0.19 g CaCl2, 0.23 g MgCl2
10 g of the kitchen towel was folded in four, placed on a top sheet on the upper surface, and a load of 10 kg was applied for 1 minute to check the return amount.

(E) Blending property with pulp 50 parts by weight of a water-absorbing resin (or water-absorbing agent) is added to a mixer charged with 50 parts by weight of pulp, and after the whole amount is added, the mixture is further stirred for 1 minute. At that time, the blendability of the pulp and the water-absorbing resin (or water-absorbing agent) was evaluated as follows.

◎: Good blending property (no separated resin) ：: Some resin separated from pulp ×: Many resin separated from pulp

[0072]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Reference Example 1 1.70 parts by weight of trimethylolpropane triacrylate was dissolved in 5500 parts by weight (monomer concentration: 38%) of an aqueous solution of sodium acrylate having a neutralization ratio of 75 mol% to prepare a reaction solution. Next, the reaction solution was degassed under a nitrogen gas atmosphere for 30 minutes. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader having an internal volume of 10 L and having two sigma-type blades, and the reaction solution was maintained at 30 ° C. while maintaining the system under nitrogen. The gas was replaced. Subsequently, while stirring the reaction solution,
When 2.46 parts by weight of sodium persulfate and 0.10 part by weight of L-ascorbic acid were added, polymerization started about 1 minute later. Then, polymerization was carried out at 30 ° C. to 80 ° C., and after 60 minutes from the start of the polymerization, the hydrogel polymer was taken out. The obtained hydrogel polymer was finely divided into a diameter of about 5 mm. The finely divided hydrogel polymer was spread on a 50-mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Then
The dried product was pulverized using a vibration mill, and further classified with a 20-mesh wire net to obtain an irregularly crushed water-absorbent resin precursor (A) having an average particle size of 330 μm.

[0074] 100 parts by weight of the obtained water-absorbent resin precursor (A) is composed of 1 part by weight of propylene glycol, 0.05 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water, and 1 part by weight of isopropyl alcohol. The surface crosslinking agent was mixed. The mixture was heated at 210 ° C. for 40 minutes to obtain a water-absorbent resin (1). The absorption capacity of this water absorbent resin (1) is 31 (g / g), and the absorption capacity under pressure is 3
It was 3 (g / g).

Reference Example 2 100 parts by weight of the water-absorbent resin precursor (A) was mixed with 0.1 parts of ethylene glycol diglycidyl ether.
Parts by weight, a surface crosslinking agent consisting of 4.5 parts by weight of water and 1.5 parts by weight of isopropyl alcohol were mixed. The above mixture
Water-absorbent resin by heat treatment at 200 ° C for 35 minutes (2)
I got This water absorbent resin (2) has an absorption capacity of 32 (g / g),
The absorbency against pressure was 31 (g / g).

Example 1 100% by weight of the water-absorbent resin (1) obtained in Reference Example 1 was used as an inorganic powder and a 4% dispersion of pH 7.5 to
9.5, cationic hydrophobic silicon dioxide with a specific surface area of 145 ± 15 m2 / g by BET method (manufactured by Nippon Aerosil Co., Ltd.)
RA200HS) in an amount of 0.05 part by weight to obtain a water absorbing agent (1).
Table 1 summarizes various physical properties of the water absorbing agent (1).

Example 2 After adding 1 part by weight of water to 100 parts by weight of the water absorbent resin (2) obtained in Reference Example 2,
Inorganic powder similar to (RA200HS manufactured by Nippon Aerosil Co., Ltd.) 0.1
The parts by weight were mixed to obtain a water absorbing agent (2). Table 1 summarizes the physical properties of the water absorbing agent (2).

Comparative Example 1 The water absorbing resin (1) obtained in Reference Example 1 was used as a comparative water absorbing agent (1). Table 1 similarly summarizes various physical properties of the comparative water-absorbing agent (1).

Comparative Example 2 The water absorbent resin (2) obtained in Reference Example 2 was used as a comparative water absorbent (2). Table 1 similarly summarizes various physical properties of the comparative water-absorbing agent (2).

[Comparative Example 3] Aerosil R972 manufactured by Nippon Aerosil Co., Ltd. as hydrophobic fine particle silicon dioxide was used as an inorganic powder in 100 parts by weight of the water absorbent resin (1) obtained in Reference Example 1.
(PH 4.0 ~ 5.5 of 4% dispersion, specific surface area 110 ± 2 by BET method)
0m2 / g) of 0.05 part by weight to obtain a comparative water absorbing agent (3). Table 1 similarly summarizes various physical properties of the comparative water-absorbing agent (3).

Comparative Example 4 The amount of the inorganic powder used in Comparative Example 3 was changed to 0.1 part by weight to obtain a comparative water absorbing agent (4). Table 1 summarizes various physical properties of the comparative water-absorbing agent (4).

Comparative Example 5 The inorganic powder used in Example 2 was finely divided silicon dioxide, Aerosil R202, manufactured by Nippon Aerosil Co., Ltd. (pH 4 to 4% dispersion, specific surface area by BET method 100 ± 20 m 2 / g). Perform the same operation except for changing to
A comparative water absorbing agent (5) was obtained. Table 1 summarizes various physical properties of the comparative water absorbing agent (5).

[Comparative Example 6] Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. (4%) was used as inorganic powder in 100 parts by weight of the water-absorbent resin (1) obtained in Reference Example 1.
Dispersion pH 4-6, specific surface area by BET method 200 ± 25m2 / g)
0.5 parts by weight were mixed to obtain a comparative water absorbing agent (6). Table 1 summarizes various physical properties of the comparative water absorbing agent (6).

[0084]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a measuring device used for measuring an absorption capacity under pressure, which is one of the properties exhibited by a water absorbing agent (water absorbing resin).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance 2 Container 3 External air suction pipe 4 Conduit 5 Measurement part 6 Glass filter 7 Filter paper 8 Support cylinder 9 Wire mesh 10 Weight 11 Physiological saline

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 41/12 C08J 3/20 Z C08J 3/20 A61F 13/18 307B F-term (reference) 4C003 AA23 AA24 4F070 AA02 AA03 AA28 AA29 AA32 AA34 AA35 AA37 AB13 AB21 AC13 AC23 AD06 AD10 AE30 FA01 4G066 AA10D AA22B AB06D AB07A AB07D AB23A AE06B BA03 BA05 BA26 BA36 BA38 CA43 DA11 FA08 FA21 FA37 FA40

Claims (9)

[Claims] 1. A water-absorbing agent comprising an inorganic powder having a pH of 7 to 10 and a specific surface area by a BET method of 50 m2 / g or more, and a water-absorbing resin. 2. The water-absorbing agent according to claim 1, wherein the inorganic powder exhibits hydrophobicity. 3. The water-absorbing agent according to claim 1, wherein the inorganic powder contains silicon dioxide as a main component. 4. The water absorbing agent according to claim 1, wherein the water absorbing resin has a polyhydric alcohol on a surface portion. 5. An aqueous liquid is added before and / or after mixing a water-absorbent resin with an inorganic powder having a pH of 7 to 10 and a specific surface area by a BET method of 50 m2 / g or more by a BET method. Method for producing a water absorbing agent. 6. A water-absorbing agent having a blocking ratio of 20% or less when left at 25 ° C. and a relative humidity of 90% for 1 hour and an absorption capacity under pressure of 30 (g / g) or more. 7. An absorbent article comprising an absorbent layer containing a water-absorbent resin and a fibrous base material, a liquid-permeable top sheet, and a liquid-impermeable back sheet, wherein the absorbent article has a temperature of 25 ° C. and a relative humidity of 90%. The water-absorbing resin contains a water-absorbing agent that has a blocking rate of 20% or less and an absorption capacity under pressure of 30 (g / g) or more when left for 1 hour under the condition, and the total amount of the water-absorbing resin and the fiber base material. Is an absorbent article characterized by having a weight ratio α of 0.3 or more. 8. A water absorbing agent comprising an inorganic powder having a cationic group and a water absorbing resin having an anionic group. 9. The water-absorbing agent according to claim 8, which has a blocking ratio of not more than 20% when left for 1 hour at 25 ° C. and 90% relative humidity.