JPH1143508A - Water absorbing resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water absorbing resin showing an extremely high water absorption ratio under load even in a small particle diameter, a high absorption rate caused by the particle diameter, suitably used for a hygienic article such as a paper diaper, sanitary napkin or incontinent pad. SOLUTION: This water absorbing resin bas 50-200 μm average particle diameter and at least 25 g/g water absorption ratio under load and is obtained, for example, by a process for compounding water absorbing particles with a crosslinking agent containing at least two groups to be reacted with the functional group of the water absorbing resin particles and mixing the mixture of the water absorbing resin particles and the crosslinking agent with an aqueous liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water-absorbing resin and a method for producing the same. More specifically, while exhibiting a very high water absorption capacity under load while having a small particle diameter, and having a large water absorption rate due to the particle diameter,
The present invention relates to a water-absorbent resin suitably used for sanitary materials such as disposable diapers, sanitary napkins and incontinence pads, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been developed which absorb water tens to hundreds of times as much as their own weight. Various water-absorbing resins have been used for applications requiring water absorption and water retention, such as in the field, industrial fields such as dew condensation prevention and cooling materials.

[0003] As such a water-absorbing resin, for example,
Hydrolyzate of starch-acrylonitrile graft polymer (JP-B-49-43395) and neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468)
No.), saponified vinyl acetate-acrylate copolymer (JP-A-52-14689), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (JP-B-53-15959), or a mixture thereof. Cross-linked product, self-cross-linked sodium polyacrylate obtained by reverse phase suspension polymerization (JP-A-53-46389), cross-linked polyacrylic acid partially neutralized product (JP-A-55-84304)
No.) etc. are known.

The performance required of the water-absorbent resin differs depending on the application to be used, but the desired properties of the water-absorbent resin for sanitary materials include an absorption capacity under high pressure when in contact with an aqueous liquid. , Fast absorption rate, large liquid permeability and the like. However, the relationship between these properties does not always show a positive correlation, and it has been difficult to improve these properties at the same time.

[0005] In order to improve the water absorption capacity under a load, a method of crosslinking the vicinity of the surface of the water-absorbent resin particles has been proposed. Although the absorption capacity under load is improved by such a method,
The water absorption rate was low.

When the particle size of the water-absorbing resin is reduced to increase the surface area and improve the water-absorbing speed, the water-absorbing resin tends to swell quickly. However, the water absorption rate was rather slow. In addition, the swollen gel sometimes formed a gel mass having a significantly reduced liquid permeability.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water-absorbent resin and a method for producing the same.

Another object of the present invention is to provide a very high water absorption rate under load while having a small particle diameter and a high water absorption rate due to the particle diameter, and to provide a paper diaper, sanitary napkin, incontinence pad and the like. The present invention relates to a water-absorbent resin suitably used for a sanitary material and a method for producing the same.

[0009]

The above object is achieved by the following (1).
(6).

(1) A water-absorbing resin having an average particle diameter in the range of 50 to 200 μm and having a water absorption capacity under load of at least 35 g / g.

(2) mixing a water-absorbing resin particle and a surface cross-linking agent having at least two groups capable of reacting with a functional group of the water-absorbing resin, or a mixed solution of the cross-linking agent and an organic solvent; A method for producing a water-absorbent resin, comprising a step of mixing an aqueous liquid with a mixture of the water-absorbent resin particles and the surface crosslinking agent.

(3) The water-absorbent resin particles are 212 μm
Through a US standard 70 mesh sieve with openings of 45,
(2) The method for producing a water-absorbent resin according to the above (2), wherein the size of the water-absorbent resin is a size captured by a US standard 325 mesh sieve having an opening of μm.

(4) The method for producing a water-absorbent resin according to the above (2) or (3), wherein the water-absorbent resin particles are spherical.

(5) The method for producing a water absorbent resin according to any one of the above (2) to (4), wherein the surface cross-linking agent contains at least two or more surface cross-linking agents having different reactivities. .

(6) The method for producing a water-absorbent resin according to any one of (2) to (5), wherein the aqueous liquid is water or a mixed solvent of water and a water-soluble organic solvent.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the average particle size is 50 to 2
And the water absorption capacity under load is at least 3
Provide a water-absorbent resin that is 5 g / g. Such a water-absorbent resin, for example, after mixing a water-absorbent resin particles and a cross-linking agent having at least two groups capable of reacting with the functional group of the water-absorbent resin, the water-absorbent resin particles and the cross-linking agent It is obtained by mixing the mixture with an aqueous liquid and then reacting the water-absorbing resin with the crosslinking agent.

The water-absorbent resin particles that can be used in the present invention are those that absorb a large amount of water in water to form a hydrogel and need to have a carboxyl group. Examples of such water-absorbent resin particles include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, and a starch-
Hydrolysis product of acrylic acid graft polymer, vinyl acetate-
Saponified acrylate copolymers, hydrolyzed acrylonitrile copolymers or acrylamide copolymers or cross-linked products thereof, carboxyl group-containing cross-linked polyvinyl alcohol-modified products, cross-linked isobutylene-maleic anhydride copolymers, etc. be able to.

Such water-absorbent resin particles generally contain unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, β-hydroxyacrylic acid, β-acrylic acid. It is obtained by polymerizing a monomer component essentially containing at least one selected from oxypropionic acid and neutralized products thereof. Preferred monomer components are acrylic acid,
Methacrylic acid and their neutralized products.

The water-absorbent resin particles that can be used in the present invention may be polymerized by using another monomer in combination with the above-mentioned unsaturated carboxylic acid, if necessary. Specifically, anionic compounds such as 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid Monomers and their alkali metal salts such as lithium, sodium and potassium, and ammonium salts; (meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, Nonionic hydrophilic group-containing monomers such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone, and N-vinylacetamide; N, N-dimethylaminoethyl (meth) acrylate; N-dimethyl Minopuropiru (meth) acrylate, N, N-dimethylaminopropyl (meth) and an amino group-containing unsaturated monomers and quaternized products thereof and the like of acrylamide. Further, in an amount that does not extremely impair the hydrophilicity of the obtained polymer, for example, methyl (meth) acrylate,
Acrylic esters such as ethyl (meth) acrylate and butyl (meth) acrylate, and hydrophobic monomers such as vinyl acetate and vinyl propionate may be used.

The amount of the carboxyl group contained in the water-absorbent resin particles is not particularly limited.
It is preferable that a carboxyl group is present in an amount of 0.01 equivalent or more. For example, the ratio of the unneutralized polyacrylic acid is preferably in the range of 1 to 60 mol%,
More preferably, it is in the range of ５０50 mol%.

The water-absorbing resin particles are copolymerized with a small amount of an internal cross-linking agent having two or more polymerizable unsaturated groups or two or more reactive groups, rather than a self-cross-linking type without using a cross-linking agent. Alternatively, a reaction product is desirable. For example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane di (meth)
Acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, N, N'-methylenebis (meth) acrylamide,
Compounds having two or more ethylenically unsaturated groups in one molecule such as triallyl isocyanurate, triallyl cyanurate, trimethylolpropanedi (meth) allyl ether, triallylamine, tetraallyloxyethane, glycerolpropoxytriacrylate; ethylene glycol , Diethylene glycol, triethylene glycol,
Polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, neopentyl alcohol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitan, sucrose, glucose, etc. Polyhydric alcohols; polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; polyaldehydes such as glutaraldehyde and glyoxal Polyamines such as ethylenediamine; calcium hydroxide, calcium chloride, calcium carbonate, calcium oxide, borax chloride Neshiumu, magnesium oxide,
Polyvalents such as hydroxides, halides, carbonates, oxides, borates such as borax, and aluminum isopropylate of metals of Groups 2A, 3B and 8 of the periodic table such as aluminum chloride, zinc chloride and nickel chloride. Metal compounds and the like. One or more of these can be used in consideration of reactivity, but it is most preferable to use a compound having two or more ethylenically unsaturated groups in one molecule as a crosslinking agent. The amount of the crosslinking agent to be used is 0.005 to 2 mol%, more preferably 0.01 to 2 mol%, based on the monomer component.
1 mol%.

When the above monomers are polymerized to obtain the water-absorbent resin particles of the present invention, bulk polymerization or precipitation polymerization can be carried out, but from the viewpoint of performance and ease of control of polymerization, It is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization using the monomer as an aqueous solution.

The shape of the water-absorbent resin particles obtained by these polymerization methods may be any of various shapes such as irregularly crushed, spherical, fibrous, rod-like, substantially spherical, and scale-like shapes.

The average particle size of the water-absorbing resin particles used in the present invention is preferably in the range of 50 to 200 μm, particularly preferably 75 to 180 μm. When the average particle size is smaller than 50 μm,
Excessive cross-linking is caused by secondary cross-linking accompanying the surface treatment, and the resulting water-absorbent resin has a low water absorption capacity under load.
On the other hand, if the average particle size is larger than 200 μm, the resulting water-absorbing resin will have a poor water absorption rate.

Such water-absorbent resin particles include, for example, 2
It passes through a US standard 70 mesh sieve with 12 μm openings and is captured by a US standard 325 mesh sieve with 45 μm openings.

In the present invention, the surface of the water-absorbent resin particles is crosslinked by a specific method. When the water-absorbent resin particles are irregularly crushed particles, the water-absorbent resin of the present invention is obtained by the following steps.

(1) A step of mixing the water-absorbing resin particles with a surface cross-linking agent having at least two groups capable of reacting with the functional groups of the water-absorbing resin particles.

(2) A step of mixing an aqueous liquid with a mixture of the water-absorbent resin particles and a surface crosslinking agent.

(3) a step of reacting the water-absorbent resin particles with a surface crosslinking agent.

Further, the surface-treated water-absorbent resin may be further surface-treated, or a surface-treating agent may be added while sufficiently loosening the water-absorbent resin particles, or the surface-treated water may be heated while sufficiently loosening the particles. Can be obtained by The temperature of the particles is 20-80 ° C, preferably 30-6
It can also be obtained by adding a surface treating agent while controlling at 0 ° C., and then performing a surface treatment. When the temperature of the particles is out of the above range, the particles mixed with the surface treating agent tend to aggregate, and as a result, the water absorption capacity under load may be low.

When the water-absorbent resin particles are spherical or substantially spherical, the water-absorbent resin of the present invention may be subjected to surface crosslinking using, for example, two types of surface crosslinking agents having different reactivities in addition to the above steps. Is obtained by

Examples of the surface cross-linking agent include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl glycol. 1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene
1,4-diol, 1,4-butanediol, 1,5-
Pentanediol, 1,6-hexanediol, 1,2
-Cyclohexanedimethanol, 1,2-cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene,
Oxyethylene-oxypropylene block copolymer,
Polyhydric alcohol compounds such as pentaerythritol and sorbitol; ethylene glycol diglycidyl ether;
Polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether,
Epoxy compounds such as polypropylene glycol diglycidyl ether and glycidol; polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and polyamidepolyamine; epichlorohydrin, epibromohydrin , Α-
Haloepoxy compounds such as methyl epichlorohydrin; condensates of the above polyvalent amine compounds and the above haloepoxy compounds; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate, hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one,
-Methyl-1,3-dioxolan-2-one, 4,5-
Dimethyl-1,3-dioxolan-2-one, 4,4-
Dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one , 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxane-
Alkylene carbonate compounds such as 2-one and 1,3-dioxoban-2-one; and the like, but are not particularly limited.

Among the surface cross-linking agents exemplified above, polyhydric alcohol compounds, epoxy compounds, polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, and alkylene carbonate compounds are more preferable.

These surface cross-linking agents may be used alone, or at least two or more surface cross-linking agents having different reactivities may be used in combination. When two or more surface cross-linking agents are used in combination, the first surface cross-linking agent and the second surface cross-linking agent having different solubility parameters (SP values) are combined, so that the water-absorbing resin particles having even more excellent water-absorbing properties are obtained. Can be obtained. The above-mentioned solubility parameter is a value generally used as a factor indicating the breadth of a compound.

The first surface cross-linking agent is a compound capable of reacting with the carboxyl group of the water-absorbent resin particles and having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more, such as glycerin or propylene. Glycol and the like correspond. The second surface cross-linking agent has a solubility parameter of 1 which can react with a carboxyl group of the water-absorbent resin particles.
It is a compound of less than 2.5 (cal / cm ³ ) ^1/2 , such as ethylene glycol diglycidyl ether.

The amount of the surface crosslinking agent used with respect to the water-absorbing resin particles depends on the combination of the water-absorbing resin particles and the surface crosslinking agent. It may be in the range of parts by weight, more preferably in the range of 0.05 to 3 parts by weight. By using the surface cross-linking agent within the above range, the water absorbing properties for body fluids (aqueous liquids) such as urine, sweat, menstrual blood, etc. can be further improved. If the amount of the surface cross-linking agent used is less than 0.01 parts by weight, the cross-linking density near the surface of the water-absorbent resin particles can hardly be increased. If the amount of the surface cross-linking agent is more than 5 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and may make it difficult to control the cross-linking density to an appropriate value.

The treatment method for treating the water-absorbent resin particles with a surface crosslinking agent is not particularly limited. For example, (a) a method of mixing the water-absorbing resin particles and the surface cross-linking agent without a solvent, (b) dispersing the water-absorbing resin particles in a hydrophobic solvent such as cyclohexane or pentane, and then mixing the surface cross-linking agent. And (c) dissolving or dispersing the surface crosslinking agent in a solvent, and then spraying or dropping the solution or dispersion onto the water-absorbent resin particles and mixing.

The solvent is not particularly limited as long as it can dissolve or disperse the surface cross-linking agent. Examples thereof include methyl alcohol, ethyl alcohol,
Lower alcohols such as n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, t-butyl alcohol; ketones such as acetone; dioxane; ethylene oxide (EO) adduct of monohydric alcohol, tetrahydrofuran Ethers such as N, N-dimethylformamide and ε-caprolactam; and hydrophilic organic solvents such as sulfoxides such as dimethylsulfoxide are preferably used. These organic solvents may be used alone,
More than one type may be used in combination.

The amount of the solvent used for the water-absorbing resin particles and the surface cross-linking agent depends on the water-absorbing resin particles, the surface cross-linking agent
Depending on the combination of solvents, etc., the water-absorbent resin particles 100
200 parts by weight or less, more preferably 0.1 part by weight based on parts by weight.
001 to 50 parts by weight, more preferably 0.1 to 50 parts by weight.
The amount may be in the range of from 50 to 50 parts by weight, particularly preferably in the range of from 0.5 to 20 parts by weight.

The mixing device used for mixing the water-absorbent resin particles and the surface cross-linking agent preferably has a large mixing force in order to uniformly and surely mix them. As the mixing device, for example, a cylindrical mixer,
Double wall cone type mixer, high speed stirring type mixer, V-shaped mixer, ribbon type mixer, screw type mixer, fluidized furnace rotary desk type mixer, air flow type mixer, double arm type kneader, inside A mixer, a pulverizing kneader, a rotary mixer, a screw extruder and the like are suitable.

As described above, by mixing the water-absorbing resin particles with the surface crosslinking agent without using water as the solvent for the surface crosslinking agent, the surface crosslinking agent is uniformly mixed with the surface of the water-absorbing resin particles. Can be. Also, there is almost no aggregate in the mixture of the water-absorbent resin particles and the surface crosslinking agent. As a result, it is possible to obtain a water-absorbent resin having an excellent water absorption capacity under load. When aggregates are formed in the mixture of the water-absorbent resin particles and the surface cross-linking agent, it becomes difficult to uniformly mix the surface cross-linking agent on the surface of the water-absorbent resin particles. In addition, if the agglomerate is subjected to surface treatment as it is, it may become a water-absorbing resin having a low water absorption rate. Further, since the surface treatment agent is excessively added to the aggregate, there is a possibility that the surface cross-linking proceeds excessively and the water-absorbent resin has a low water absorption. In addition, when the surface cross-linking reaction proceeds while heating with stirring, as described later, the agglomerates may break down the surface cross-links due to the stirring, resulting in a water-absorbent resin having a low water absorption capacity under load.

The mixture of the water-absorbent resin particles thus obtained and the surface crosslinking agent is mixed with the aqueous liquid. Examples of the aqueous liquid include water or a mixed solvent of water and an organic solvent soluble in water. By using a mixed solvent of water and an organic solvent soluble in water as the aqueous liquid, water can be more uniformly mixed on the surface of the water-absorbing resin. Examples of water-soluble organic solvents include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol and t-butyl alcohol; ketones such as acetone. Ethers such as dioxane, ethylene oxide (EO) adduct of monohydric alcohol, and tetrahydrofuran;
Examples include amides such as N, N-dimethylformamide and ε-caprolactam; and sulfoxides such as dimethyl sulfoxide. The ratio of water and water-soluble organic solvent is 10
0: 0 to 1:99, preferably 100: 0.
10:90, more preferably 95: 5
20:80. The water or a mixed solvent of water and an organic solvent soluble in water may contain the surface cross-linking agent described above.

The aqueous liquid is preferably added as droplets. By adding the aqueous liquid directly to the particle surface in the form of droplets, the aqueous liquid can be quickly penetrated to the surface of the water-absorbent resin as compared with the case where the water-absorbent resin is exposed to water vapor or a high humidity atmosphere. . Then, the surface cross-linking agent permeates the surface of the water-absorbent resin together with the aqueous liquid, and can form a surface cross-linked layer capable of exhibiting water absorption even under a load. The size of the droplet can be appropriately set depending on the type and amount of the aqueous liquid, the shape and particle size of the water-absorbent resin particles,
It is generally in the range of 10 to 4000 μm, preferably 5 to
It is in the range of 0 to 1000 μm.

By adding water after mixing the crosslinking agent,
Water can be uniformly mixed on the surface of the water-absorbent resin particles. As a result, the degree of penetration of the crosslinking agent into the surface of the water-absorbent resin particles can be controlled uniformly. Then, a water-absorbing resin having a uniform thickness at the surface cross-linked portion can be obtained. In addition, no aggregate of the water-absorbing resin particles is generated.

As a method of mixing the mixture of the water-absorbent resin particles and the surface cross-linking agent with the aqueous liquid, mechanical mixing can be performed using the above-described various mixing devices. The aqueous liquid can be uniformly mixed by mechanical mixing.

When the surface cross-linking is carried out by the above-mentioned surface cross-linking agent, a heat treatment is carried out, if necessary, depending on the type of the surface cross-linking agent to cross-link the vicinity of the surface of the water-absorbent resin particles. By performing the secondary crosslinking, it is possible to obtain water-absorbent resin particles having an excellent absorption capacity under pressure.

The treatment temperature and treatment time for treating the water-absorbent resin particles with the surface cross-linking agent may be appropriately selected according to the combination of the water-absorbent resin particles and the surface cross-linking agent, the desired crosslinking density, and the like. Although not particularly limited, for example, the treatment temperature is 0 to 250 ° C., particularly 80 to 22 ° C.
A temperature in the range of 0 ° C. is preferred.

The heat treatment can be carried out using a usual dryer or heating furnace, and includes a groove-type mixing dryer, a rotary dryer, a desk dryer, a fluidized-bed dryer, a gas-flow dryer and an infrared dryer. Is exemplified.

After the heat treatment, the heated product is optionally sieved with a sieve to obtain the water-absorbent resin of the present invention. The water-absorbent resin of the present invention includes not only single particles but also granules thereof.

The water-absorbent resin of the present invention has an average particle size of 50
Despite being as fine as ~ 200 [mu] m, the water absorption capacity under load is 35 g / g or more, indicating an unprecedented excellent water absorption performance.

Conventionally, as the particle size becomes smaller, the water-absorbing resin tends to absorb the liquid to be absorbed more quickly, but the swollen gel closes the capillary space between the particles, thereby significantly lowering the liquid permeability. Since the water-absorbing resin of the present invention has a high water absorption capacity under load of 35 g / g or more, it is possible to maintain a capillary space for allowing the liquid to be absorbed to pass between the swollen gels, and to cause momako and gel blocking. And the liquid to be absorbed can be quickly absorbed.

The above-mentioned water-absorbing resin may be further added to a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a plasticizer, an adhesive, a surfactant, if necessary. Fertilizers, oxidizing agents, reducing agents, water, salts, and the like may be added to impart various functions to the water-absorbing resin.

Examples of the inorganic powder include substances inert to aqueous liquids and the like, for example, fine particles of various inorganic compounds and fine particles of clay minerals. The inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water. Specifically, for example, metal oxides such as silicon dioxide and titanium oxide, silicic acids (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay,
Bentonite and the like can be mentioned. Among them, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter of 200 μm or less as measured by the Coulter counter method are more preferable.

The amount of the inorganic powder used for the water-absorbent resin is as follows:
Although it depends on the combination of the water-absorbent resin and the inorganic powder,
The amount may be in the range of 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin. The mixing method of the water-absorbent resin and the inorganic powder,
There is no particular limitation, and for example, a dry blending method, a wet mixing method, or the like can be employed. However, it is preferable to employ a dry blending method.

The water-absorbent resin is made into an absorbent article by, for example, compounding (combining) with a fibrous material such as pulp.

Examples of the absorbent articles include sanitary materials (body fluid absorbent articles) such as disposable diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials; absorbent articles such as urine for pets; Materials for civil engineering and construction such as water retention materials, water stop materials, packing materials, gel blisters, etc .; Food products such as drip absorbents, freshness retention materials, cold insulation materials; oil / water separation materials, dew condensation prevention materials,
Various industrial articles such as coagulants; agricultural and horticultural articles such as water retention materials such as plants and soil; and the like are not particularly limited. In addition, for example, a disposable diaper is formed by laminating a back sheet (back surface material) made of a liquid-impermeable material, the above-described water-absorbing composition, and a top sheet (surface material) made of a liquid-permeable material in this order. It is formed by fixing to each other and attaching a gather (elastic portion) or a so-called tape fastener to the laminate. Further, the disposable diaper also includes pants with a disposable diaper used when disciplining urination and defecation for infants.

[0057]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to these Examples. Further,% in Examples and Comparative Examples means% by weight unless otherwise specified, and parts means parts by weight.

The water absorption of the water-absorbent resin, the water absorption capacity under load, the water absorption rate, and the amount of water-soluble components were measured by the following methods.

(1) Amount of water absorbed by water-absorbent resin 0.2 g of water-absorbent resin was added to a tea bag type bag (6 cm × 6 c
m), the opening was heat sealed, and then immersed in artificial urine shown below. After 60 minutes, the tea bag bag was pulled out and drained with a centrifuge at 250 G for 3 minutes, and then the weight W ₁ (g) of the bag was measured.
The same operation was performed without using a water-absorbing resin, and the weight W ₀ (g) at that time was measured. And these weights W
_{From 1} and W ₀ , the water absorption (g / g) was calculated according to the following equation: Water absorption (g / g) = (W ₁ −W ₀ ) / weight (g) of water-absorbing resin.

The composition of the above-mentioned artificial urine and the compounding amount thereof are as follows.

Composition of artificial urine Amount of each composition (% by weight) Sodium sulfate 0.200% Potassium chloride 0.200% Magnesium chloride hexahydrate 0.050% Calcium chloride dihydrate 0.025% Phosphoric acid Ammonium dihydrogen 0.035% Diammonium hydrogen phosphate 0.015% (2) Water absorption capacity under load The water absorption capacity under load was determined using the measuring apparatus shown in FIG.
As shown in FIG. 1, the measuring device includes a balance 1, a container 2 having a predetermined capacity placed on the balance 1, an outside air suction pipe sheet 3,
It comprises a conduit 4, a glass filter 6, and a measuring section 5 mounted on the glass filter 6. The container 2 has an opening 2a on the top and an opening 2b on the side. Opening 2
a is fitted with an outside air suction pipe 3 and has an opening 2b.
Is provided with a conduit 4. The container 2 contains a predetermined amount of artificial urine 12. The lower end of the outside air suction pipe 3 is submerged in the artificial urine 12. Outside air suction pipe 3
Is provided to keep the pressure in the container 2 substantially at atmospheric pressure. The above glass filter 6 is formed to have a diameter of 55 mm. The container 2 and the glass filter 6 communicate with each other by a conduit 4 made of a silicone resin. Further, the position and height of the glass filter 6 with respect to the container 2 are fixed. The measuring unit 5 includes a filter paper 7, a support cylinder 9, and a wire mesh 1 attached to the bottom of the support cylinder 9.
0 and a weight 11. The measuring unit 5 includes a filter paper 7 and a support cylinder 9 (that is, a wire mesh 10) on a glass filter 6.
Are placed in this order. The wire mesh 10 is made of stainless steel, and the size of the mesh is 400 mesh. The height of the upper surface of the wire mesh 10, that is, the height of the contact surface between the wire mesh 10 and the water-absorbent resin 15 is the lower end surface 3 of the outside air suction pipe 3.
It is set to be equal to the height of a. Wire mesh 10
A predetermined amount of the water-absorbing resin is uniformly spread on the top. The weight 11 is set at 0.
The weight is adjusted so that a load of 7 psi can be applied uniformly.

The amount of water absorption under pressure was measured using the measuring apparatus having the above configuration. The measuring method will be described below.

The container 2 is filled with a predetermined amount of artificial urine 12. A predetermined preparation operation such as fitting the external suction pipe 3 into the container 2 was performed. Next, the filter paper 7 was placed on the glass filter 6. In parallel with the placement, 0.9 g of the water-absorbent resin was evenly sprayed inside the support cylinder 9, that is, on the wire mesh 10, and the weight 11 was placed on the water-absorbent resin 15. Next, on the filter paper 7, the wire cylinder 10, that is, the support cylinder 9 on which the water-absorbent resin 15 and the weight 11 were placed, was placed so that the center part thereof coincided with the center part of the glass filter 6. Next, the weight of the artificial urine absorbed by the water-absorbent resin 15 was obtained from the measured value of the balance 1 over a period of 60 minutes from the time when the support cylinder 9 was placed on the filter paper 7. The same operation was performed without using the water-absorbent resin 15, and the weight of artificial urine other than the water-absorbent resin, for example, the water absorbed by the filter paper 7, was determined from the measured value of the balance 1, and this was used as a blank value. The water absorption under load was determined by the following equation.

Water absorption under load (g / g) = (water absorption after 60 minutes−blank value) / weight of water-absorbent resin (3) Water-absorption rate of water-absorbent resin Cylindrical bottom with inner diameter of 58 mm and depth of 25 mm 1.0 g of a water-absorbent resin was placed in a polypropylene container of No. 1. Next, 20 g of artificial urine was poured into the container. Then, the time from when the artificial urine was poured until the artificial urine was completely absorbed by the water-absorbent resin and disappeared was measured. The measurement was repeated three times, and the average value was taken as the water absorption rate (second).

(4) Amount of Water-Soluble Component of Water Absorbent Resin 0.5 g of the water absorbent resin was dispersed in 1000 ml of deionized water, stirred for 16 hours, and filtered with a filter paper. Then, the obtained filtrate was titrated by colloid titration to determine the amount (%) of a water-soluble component in the water absorbent resin.

(5) Average particle size of water-absorbent resin The following openings (300 μm, 250 μm, 212 μm)
m, 150 μm, 106 μm, 75 μm, 45 μm), the water absorbent resin was classified using a sieve, and the residual percentage R was plotted on log probability paper, and the particle diameter corresponding to R = 50% was taken as the average particle diameter. .

Example 1 A monomer aqueous solution comprising 441 g of acrylic acid, 4668 g of a 37% aqueous solution of sodium acrylate, 6.5 g of polyethylene glycol (n = 8) diacrylate and 1418 g of pure water was prepared, and degassed with nitrogen gas for 30 minutes. Qi, internal volume 1
At 0 liter, the mixture was supplied to a reactor equipped with a jacketed stainless steel double-armed kneader having two sigma-type blades and a lid, and the reaction system was further purged with nitrogen while maintaining the temperature of the monomer at 30 ° C.

Next, while stirring, 34 g of a 10% aqueous solution of sodium persulfate and 1.6 g of a 1% aqueous solution of L-ascorbic acid were added. One minute later, polymerization started, and 15 minutes later, the peak temperature in the reaction system reached 78 ° C. Stirring was further continued, and the hydrogel polymer was taken out 35 minutes after the polymerization was started.

The obtained hydrogel polymer was refined into 16 granules.
Hot air drying was performed at 0 ° C. for 60 minutes. The dried product was pulverized with a roll mill, and further passed through a 212-μm sieve to obtain water-absorbent resin particles (1) having a particle diameter remaining on a 106-μm sieve.

To 100 parts of the water-absorbent resin particles (1), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinker solution consisting of 0.06 parts, 2 parts of propylene glycol and 2 parts of isopropyl alcohol was mixed. An aqueous liquid composed of 6 parts of water and 4 parts of isopropyl alcohol was mixed with the mixture of the water absorbent resin particles (1) and the crosslinking agent. Almost no agglomerates of the water-absorbing resin particles were found.
This was heated at 185 ° C. for 40 minutes to obtain the water absorbent resin (1) of the present invention.

The water-absorbing resin (1) thus obtained has a water absorption of 40
(G / g), water absorption capacity under load is 36.4 (g / g), water absorption rate is 20 seconds, soluble component is 14% and average particle diameter is 1
It was 60 μm.

Example 2 An aqueous monomer solution consisting of 720 g of acrylic acid, 4.8 g of polyethylene glycol (n = 8) diacrylate and 2862 g of pure water was prepared in a 5-liter container, and degassed with nitrogen gas for 30 minutes. Then, the temperature of the monomer was kept at 20 ° C.

Next, 4.8 g of a 5% aqueous 2,2′-azobis (2-amidinopropane) dihydrochloride solution, 8.6 g of a 0.5% aqueous L-ascorbic acid solution and 4 g of a 0.35% aqueous hydrogen peroxide solution Was added and static polymerization was performed. 30
The polymerization started after 1 minute, and the peak temperature in the reaction system reached 70 ° C. after 80 minutes. After further standing for 60 minutes, the hydrogel polymer was taken out. While crushing the hydrogel polymer taken out with a double-arm kneader, sodium carbonate powder 41
2 g was added and neutralized. The crushed hydrogel polymer was taken out, and 5000 g of pure water was added on a vat, and aged until the neutralization was uniform and no color reaction with phenolphthalein was observed. The neutralization ratio of carboxyl groups contained in the hydrogel was 75%. The gel after neutralization was dried at 160 ° C. for 1 hour with a hot air drier. The dried product is pulverized by a roll mill, sieved with a sieve, passed through a 212 μm sieve, and
Thus, water-absorbent resin particles (2) having a particle diameter remaining on a sieve of μm were obtained.

To 100 parts of the water-absorbing resin particles (2), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinking agent solution consisting of 0.1 part, 2 parts of propylene glycol and 2 parts of isopropyl alcohol was mixed. An aqueous liquid composed of 6 parts of water and 4 parts of isopropyl alcohol was mixed with the mixture of the water absorbent resin particles (2) and the crosslinking agent. Almost no agglomerates of the water-absorbing resin particles were found. This was heated at 185 ° C. for 50 minutes to obtain the water absorbent resin (2) of the present invention.

The obtained water-absorbent resin (2) had a water absorption of 4
5.4 (g / g), water absorption capacity under load is 38.7 (g / g)
g), the water absorption rate was 26 seconds, the soluble component was 7%, and the average particle size was 180 μm.

Example 3 In Example 2, the pulverized product was sieved with a sieve, passed through a 212 μm sieve, and water-absorbent resin particles (3) having a particle diameter remaining on the 104 μm sieve were obtained.

To 100 parts of the water-absorbing resin particles (3), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinker solution consisting of 0.125 parts, 2.5 parts of propylene glycol and 2.5 parts of isopropyl alcohol was mixed. An aqueous liquid composed of 7.5 parts of water and 5 parts of isopropyl alcohol was mixed with the mixture of the water absorbent resin particles (3) and the crosslinking agent. Almost no agglomerates of the water-absorbing resin particles were found. This is heated at 185 ° C. for 35 minutes,
The water-absorbent resin (3) of the present invention was obtained.

The water-absorbing resin (3) obtained had a water absorption of 4
2.4 (g / g), water absorption capacity under load is 37.8 (g / g)
g), the water absorption rate was 22 seconds, the soluble component was 8%, and the average particle size was 140 μm.

Example 4 36 g of acrylic acid, 381 g of a 37% aqueous solution of sodium acrylate, N, N'-methylenebisacrylamide 0.1 g
An aqueous monomer solution consisting of 15 g and 173 g of pure water was prepared. 0.24 g of sodium persulfate
And dissolved nitrogen was blown out to expel dissolved oxygen.

In a 2 liter four-neck separable flask equipped with a stirrer, reflux condenser, thermometer, nitrogen gas inlet tube and dropping funnel, 1 liter of cyclohexane and sorbitan monostearate (HLB4.7) 3 as a dispersant were added.
g was added and dissolved, and dissolved oxygen was removed by blowing nitrogen gas.

Next, the monomer aqueous solution was added to the separable flask and dispersed by stirring at 230 rpm. Thereafter, the bath temperature was raised to 65 ° C. to start the polymerization reaction, and then the temperature was maintained at this temperature for 2 hours to complete the polymerization. After the completion of the polymerization, azeotropic dehydration was performed to remove most of the water, followed by filtration. The residue was dried at 100 ° C. overnight under reduced pressure to obtain spherical water-absorbent resin particles (4). Water absorbent resin particles (4)
Was 110 μm.

To 100 parts of the water absorbent resin particles (4), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinking agent solution consisting of 0.05 part, 1 part of propylene glycol and 1 part of isopropyl alcohol was mixed. An aqueous liquid composed of 3 parts of water and 2 parts of isopropyl alcohol was mixed with the mixture of the water absorbent resin particles (4) and the crosslinking agent. Almost no agglomerates of the water-absorbing resin particles were found.
This was heated at 150 ° C. for 10 minutes to obtain a water absorbent resin (4) of the present invention.

The water-absorbing resin (4) obtained had a water absorption of 39.
(G / g), the water absorption capacity under load was 39.4 (g / g), the water absorption rate was 20 seconds, the soluble component was 18%, and the average particle size was 120 μm.

Example 5 The dried product was sieved with a sieve in Example 4, passed through a 104 μm sieve, and remained on a 75 μm sieve. (5)
I got

To 100 parts of the water-absorbing resin particles (5), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinking agent solution consisting of 0.05 part, 1 part of propylene glycol and 1 part of isopropyl alcohol was mixed. An aqueous liquid composed of 3 parts of water and 2 parts of isopropyl alcohol was mixed with the mixture of the water absorbent resin particles (5) and the crosslinking agent. Almost no agglomerates of the water-absorbing resin particles were found.
This was heated at 150 ° C. for 10 minutes to obtain a water absorbent resin (5) of the present invention.

The water-absorbing resin (5) thus obtained had a water absorption of 3
8.8 (g / g), water absorption capacity under load is 39.8 (g / g)
g), the water absorption rate was 9 seconds, and the soluble component was 18%.

Comparative Example 1 100 parts of the water absorbent resin particles (1) obtained in Example 1
Ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.) 0.06
, Propylene glycol 2 parts, pure water 6 parts and isopropyl alcohol 6 parts were added and mixed. The proportion of aggregates in the mixture was 10%. This was heated at 185 ° C. for 40 minutes and sieved with a 300 μm sieve to obtain a comparative water absorbent resin (1).

The water absorption of the comparative water absorbent resin (1) was 38 (g).
/ G), a water absorption capacity under load of 28.5 (g / g), a water absorption rate of 24 seconds, a soluble component of 16%, and an average particle size of 18
It was 0 μm.

Comparative Example 2 100 parts of the water absorbent resin particles (2) obtained in Example 2
Ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.) 0.1
Parts, 2 parts of propylene glycol, 6 parts of water, and 6 parts of isopropyl alcohol. The ratio of aggregates of the water-absorbent resin particles in the mixture was about 15%. This mixture was heated at 185 ° C. for 50 minutes to obtain a comparative water absorbent resin (2).

The water absorption of the comparative water absorbent resin (2) was 43.9.
(G / g), the water absorption capacity under load was 32.6 (g / g), the water absorption rate was 27 seconds, the soluble component was 7%, and the average particle size was 190 μm.

[0091]

The water-absorbent resin of the present invention has a fine particle size and is excellent in water absorbency under load. Therefore, when used in a diaper or a menstrual cotton, urine can be quickly and without being blocked by a swollen gel. Can be absorbed in large quantities.

Further, according to the production method of the present invention, it is possible to easily obtain a water-absorbing resin having a high water-absorbing speed and excellent water-absorbing properties under load.

[Brief description of the drawings]

FIG. 1 is an apparatus for measuring a water absorption capacity under load.

[Explanation of symbols]

 Reference Signs List 1 balance, 2 container, 2a top opening, 2b side opening, 3 outside air suction pipe sheet, 4 conduit, 5 measuring unit, 6 glass filter, 7 filter paper, 9 support cylinder, 10 wire mesh, 11 weight, 12 Artificial urine, 15 water absorbent resin.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C08J 3/12 A61F 13/18 307A // A61F 13/46 A41B 13/02 D (72) Inventor Kazuki Kimura Himeji-shi, Hyogo Nippon Shokubai Co., Ltd., 992 Nishioki, Nippon Shokubai Co., Ltd. (72) Inventor Yasuhiro Fujita 992 Nishioki, Koshihama, Aboshi-ku, Himeji-shi, Hyogo

Claims (6)

[Claims] 1. A water-absorbent resin having an average particle diameter in the range of 50 to 200 μm and a water absorption capacity under load of at least 35 g / g. 2. A step of mixing a water-absorbent resin particle and a surface cross-linking agent having at least two groups capable of reacting with a functional group of the water-absorbent resin, or a mixed solution of the cross-linking agent and an organic solvent; A method for producing a water-absorbent resin, comprising a step of mixing a mixture of the water-absorbent resin particles and the surface crosslinking agent with an aqueous liquid. 3. The method of claim 2, wherein said water-absorbent resin particles are sized to pass through a U.S. standard 70 mesh sieve having an opening of 212 μm and to be captured by a U.S. standard 325 mesh sieve having an opening of 45 μm. A method for producing the water-absorbent resin according to the above. 4. The method for producing a water-absorbent resin according to claim 2, wherein the water-absorbent resin particles are spherical. 5. The method for producing a water-absorbent resin according to claim 2, wherein the surface cross-linking agent contains at least two or more surface cross-linking agents having different reactivities. 6. The method according to claim 2, wherein the aqueous liquid is water or a mixed solvent of water and a water-soluble organic solvent.