JP3515679B2 - Water absorbent resin and manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water absorbent resin and a method for producing the same. More specifically, it exhibits a very high water absorption capacity under load despite having a small particle size, and has a large water absorption rate due to the particle size,
The present invention relates to a water-absorbent resin suitable for use in sanitary materials such as paper diapers, sanitary napkins, incontinence pads, etc., and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a water-absorbent resin that absorbs several tens to several hundreds of times its own weight of water has been developed. Various water-absorbent resins have been used for applications requiring water absorption or water retention, such as fields, industrial fields such as dew condensation prevention, and cold insulation materials.

Examples of such water absorbent resin include, for example,
Hydrolyzate of starch-acrylonitrile graft polymer (JP-B-49-43395), neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468)
No.), a saponified product of vinyl acetate-acrylic acid ester copolymer (JP-A No. 52-14689), a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer (JP-B No. 53-15959), or these Crosslinked product, self-crosslinking type sodium polyacrylate obtained by reverse phase suspension polymerization (Japanese Patent Application Laid-Open No. 53-46389), partially neutralized polyacrylic acid crosslinked product (Japanese Patent Application Laid-Open No. 55-84304).
No.) etc. are known.

Although the performance required of the water-absorbent resin differs depending on the intended use, a desired property of the water-absorbent resin for sanitary materials is the absorption capacity under high pressure when contacted with an aqueous liquid. , Fast absorption rate, large liquid permeability and the like. However, the relationship between these characteristics does not always show a positive correlation, and it has been difficult to improve these characteristics at the same time.

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

When the particle size of the water-absorbent resin is reduced in order to increase the water absorption rate by increasing the surface area, the water-absorbent resin tends to swell quickly, but the swollen gel forms mamako or gel blocking. However, the water absorption rate has become slower. In addition, the swollen gel may form gel mass with significantly reduced liquid permeability.

[0007]

SUMMARY OF THE INVENTION Therefore, 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 show a very high water absorption capacity under load despite having a small particle size and a large water absorption rate due to the particle size, and to make paper diapers, sanitary napkins, incontinence pads, etc. The present invention relates to a water absorbent resin preferably used for sanitary materials and a method for producing the same.

[0009]

[Means for Solving the Problems] The above-mentioned object is as follows (1)
~ ( 7 ) is achieved.

(1) Monomer component containing unsaturated carboxylic acid
Of aqueous solution or reverse phase suspension polymerization
Surface of the water-absorbent resin particles having a structure
Water-based resin particles having an average particle size of 50 to 200 μm
Range of 0.7 psi (about 4.8) for artificial urine
Water-absorbent resin particles whose surface has a water absorption capacity under load (60-minute value) of at least 35 g / g ( corresponding to kPa).

(2) Monomer component containing unsaturated carboxylic acid
A water-absorbent resin particle having a cross-linked structure obtained by aqueous solution polymerization or reverse phase suspension polymerization, and a surface cross-linking agent having at least two groups capable of reacting with a functional group of the water-absorbent resin particle , or the cross-linking agent. A step (1) of mixing a mixed solution with an organic solvent, and water or a water-soluble organic solvent for the mixture of the water-absorbent resin particles and the surface-crosslinking agent subsequent to the step (1) The surface further comprises a step (2) of mixing an aqueous liquid consisting of a mixture with a mixture of the step (3) and a step (3) of reacting the water absorbent resin particles with a surface cross-linking agent subsequent to the step (2). A method for producing crosslinked water-absorbent resin particles .

[0012] (3) water-absorbent resin particles having the crosslinked structure, passes the US Standard 70 mesh sieve having an opening of 212 m, a size that is trapped in the US Standard 325 mesh sieve having openings of 45μm The method for producing water-absorbent resin particles according to (2) above.

[0013] (4) water-absorbent resin particles having the crosslinked structure, the manufacturing method of the water-absorbent resin particles according to the spherical (2) or (3).

(5) The surface cross-linking agent comprises at least two kinds of surface cross-linking agents having different reactivity.
~ The method for producing water-absorbent resin particles according to any one of (4).

(6) The aqueous liquid is water or a mixed solvent of water and a water-soluble organic solvent, and is a droplet of 10 to 4000 μm, described in any one of (2) to (5) above. A method for producing water-absorbent resin particles. (7) A body fluid absorbent article using the water-absorbent resin particles as described in (1) above, the surface of which is further crosslinked .

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has an average particle size of 50 to 2
The water absorption capacity under load is at least 3
5 g / g and a water-absorbent resin (intake whose surface is further cross-linked
Aqueous resin particles) (hereinafter, also simply referred to as water absorbent resin) are provided. Such water-absorbent resin particles , for example, after mixing the water-absorbent resin particles and a crosslinking 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 crosslinking agent It can be obtained by mixing the mixture of 1) with an aqueous liquid, and then reacting the water-absorbent resin with the cross-linking 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 must have a carboxyl group. Examples of such water-absorbent resin particles include crosslinked polyacrylic acid partially neutralized products, hydrolyzates of starch-acrylonitrile graft polymer, starch-
Hydrolyzate of acrylic acid graft polymer, vinyl acetate-
Saponified acrylic ester copolymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or crosslinked products thereof, carboxyl group-containing crosslinked polyvinyl alcohol modified product, crosslinked isobutylene-maleic anhydride copolymer and the like. be able to.

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

The water-absorbent resin particles that can be used in the present invention may be polymerized by using other monomers in combination with the above unsaturated carboxylic acid, if necessary. Specifically, anionic properties such as 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid. Monomers or their alkali metal salts or ammonium salts such as lithium, sodium and potassium; (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, 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. In addition, an amount that does not extremely hinder 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 carboxyl groups contained in the water absorbent resin particles is not particularly limited, but 100 g of the water absorbent resin particles
Therefore, it is preferable that the carboxyl group is present in an amount of 0.01 equivalent or more. For example, the ratio of unneutralized polyacrylic acid is preferably in the range of 1 to 60 mol%, and 10
It is more desirable to be in the range of 50 mol%.

Further, the water-absorbent resin particles are copolymerized with a very small amount of an internal cross-linking agent having two or more polymerizable unsaturated groups or two or more reactive groups, as compared with the self-cross-linking type which does not use a cross-linking agent. Alternatively, a reacted product is preferable. 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, trimethylolpropane di (meth) allyl ether, triallylamine, tetraallyloxyethane, glycerol propoxytriacrylate; 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, sorbit, sorbitan, glucose, mannitol, mannitan, sucrose, glucose, etc. Polyhydric alcohols; polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin, 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,
Hydroxides, halides, carbonates, oxides, borax and other borate salts of metals of Groups 2A, 3B and 8 of the periodic table such as aluminum chloride, zinc chloride and nickel chloride, and polyvalent aluminum isopropylate Examples thereof include metal compounds. One or more of these may 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 cross-linking agent used is 0.005 to 2 mol%, more preferably 0.01 to 2 mol% based on the monomer components.
It is 1 mol%.

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

The water-absorbent resin particles obtained by these polymerization methods may have various shapes such as irregular crushed shape, spherical shape, fibrous shape, rod shape, substantially spherical shape, and scale shape, which are preferably used in the present invention.

The average particle diameter of the water-absorbent resin particles used in the present invention is preferably 50 to 200 μm, particularly preferably 75 to 180 μm. If the average particle size is smaller than 50 μm,
The secondary cross-linking associated with the surface treatment causes excessive cross-linking, resulting in a water-absorbent resin having a low water absorption capacity under load.
Further, if the average particle diameter is larger than 200 μm, the water absorption rate of the water absorbent resin obtained will be inferior.

Such water-absorbent resin particles are, for example, 2
It passes through a US standard 70 mesh screen with a 12 μm opening and is captured on a US standard 325 mesh screen with a 45 μm opening.

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 irregular crushed particles, the water-absorbent resin of the present invention is obtained by the following steps.

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

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

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

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

When the water-absorbent resin particles are spherical or substantially spherical, the water-absorbent resin of the present invention is subjected to surface cross-linking by using, for example, two kinds of surface cross-linking agents having different reactivity 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-. 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, polyamidepolyamine; epichlorohydrin, epibromhydrin , Α-
Haloepoxy compounds such as methylepichlorohydrin; Condensates of the above polyvalent amine compounds and the above haloepoxy compounds; Polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and 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, 4
-Methyl-1,3-dioxolan-2-one, 4,5-
Dimethyl-1,3-dioxolan-2-one, 4,4-
Dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one , 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxane-
Examples thereof include alkylene carbonate compounds such as 2-one and 1,3-dioxoban-2-one; however, they are not particularly limited.

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

These surface cross-linking agents may be used alone, or at least two kinds of surface cross-linking agents having different reactivity may be used in combination. When two or more kinds of surface cross-linking agents are used in combination, the water-absorbent resin particles having further excellent water absorption characteristics by combining the first surface cross-linking agent and the second surface cross-linking agent having different solubility parameters (SP values). Can be obtained. In addition, the above-mentioned solubility parameter is a value generally used as a factor showing the breadth of a compound.

The above-mentioned first surface cross-linking agent is a compound having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more, which is capable of reacting with the carboxyl group contained in the water-absorbent resin particles, and is, for example, glycerin or propylene. Glycol, etc. are applicable. The second surface cross-linking agent has a solubility parameter of 1 which is capable of reacting with the carboxyl group of the water absorbent resin particles.
It is a compound of less than 2.5 (cal / cm ³ ) ^1/2 , and examples thereof include ethylene glycol diglycidyl ether.

The amount of the surface-crosslinking agent used with respect to the water-absorbent resin particles depends on the combination of the water-absorbent resin particles and the surface-crosslinking agent, etc., but is 0.01 to 5 relative to 100 parts by weight of the water-absorbent resin particles in a dry state. The amount may be within the range of parts by weight, more preferably within the range of 0.05 to 3 parts by weight. By using the surface cross-linking agent within the above range, it is possible to further improve the water absorption characteristics for body fluids (aqueous liquids) such as urine, sweat and menstrual blood. When 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. Further, when the amount of the surface cross-linking agent used is more than 5 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and it may be difficult to control the cross-linking density to an appropriate value.

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

The above-mentioned solvent is not particularly limited as long as it can dissolve or disperse the surface cross-linking agent. For example, methyl alcohol, ethyl alcohol,
Lower alcohols such as n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, and t-butyl alcohol; ketones such as acetone; dioxane, ethylene oxide (EO) adduct of monohydric alcohol, tetrahydrofuran And the like; amides such as N, N-dimethylformamide and ε-caprolactam; hydrophilic organic solvents such as sulfoxides such as dimethyl sulfoxide are preferably used. These organic solvents may be used alone, or 2
You may use together more than one kind.

The amount of the solvent used for the water-absorbent resin particles and the surface cross-linking agent is as follows.
Depending on the combination of solvents, etc., the water-absorbent resin particles 100
200 parts by weight or less, more preferably 0.
001 to 50 parts by weight, more preferably 0.1
To 50 parts by weight, particularly preferably 0.5 to 20 parts by weight.

The mixing device used for mixing the water-absorbent resin particles and the surface-crosslinking agent preferably has a large mixing force in order to uniformly and surely mix them. As the above-mentioned mixing device, for example, a cylindrical mixer,
Double-wall conical mixer, high speed stirring mixer, V-shaped mixer, ribbon mixer, screw mixer, fluidized furnace rotary desk mixer, airflow mixer, double-arm kneader, internal A mixer, a crushing type kneader, a rotary type mixer, a screw type extruder and the like are suitable.

As described above, by mixing the water-absorbent resin particles and the surface cross-linking agent without using water as a solvent for the surface cross-linking agent, the surface cross-linking agent is uniformly mixed on the surface of the water-absorbent resin particles. You can Further, there are almost no aggregates in the mixture of the water absorbent resin particles and the surface crosslinking agent. As a result, a water absorbent resin having an excellent water absorption capacity under load can be obtained. If 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. Further, the surface treatment of the agglomerate as it is may result in a water absorbent resin having a slow water absorption rate. Further, since the surface treatment agent is excessively added to the agglomerates, surface cross-linking may proceed excessively, resulting in a water absorbent resin having a low water absorption amount. Further, as described later, when the surface cross-linking reaction proceeds while heating with stirring, the agglomerates may be broken into surface cross-linking by stirring and become 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 cross-linking agent is mixed with an 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 mixed more uniformly on the surface of the water absorbent resin. 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. Dioxane, ethylene oxide (EO) adduct of monohydric alcohol, ethers such as tetrahydrofuran;
Examples thereof include amides such as N, N-dimethylformamide and ε-caprolactam; and sulfoxides such as dimethylsulfoxide. The ratio of water and water-soluble organic solvent is 10
It is in the range of 0: 0 to 1:99, preferably 100: 0.
It is in the range of 10:90, more preferably 95: 5.
The range is 20:80. The surface cross-linking agent described above may be contained in the water or a mixed solvent of water and an organic solvent soluble in water.

The aqueous liquid is preferably added as droplets. By directly adding the aqueous liquid in the form of droplets to the surface of the particles, the aqueous liquid can be quickly permeated to the surface of the water absorbent resin as compared with the case of using water vapor or exposing the water absorbent resin to a high humidity atmosphere. . The surface cross-linking agent penetrates into the surface of the water-absorbent resin together with the aqueous liquid, and can form a surface cross-linking layer capable of exhibiting water absorbability even under 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
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, it becomes possible to uniformly control the degree of penetration of the crosslinking agent into the surface of the water absorbent resin particles. Then, it is possible to obtain a water absorbent resin in which the surface cross-linked portion has a uniform thickness. Further, no aggregate of water absorbent resin particles is formed.

As a method for mixing the mixture of the water-absorbent resin particles and the surface cross-linking agent and the aqueous liquid, mechanical mixing can be carried out using the above-mentioned various mixing devices. Aqueous liquid can be uniformly mixed by mechanical mixing.

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

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

The heat treatment can be carried out by using an ordinary dryer or a heating furnace, and a groove type mixing dryer, a rotary dryer, a desk dryer, a fluidized bed dryer, an air flow type dryer and an infrared dryer are used. It is illustrated.

After the heat treatment, if necessary, the heated product is sieved 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 μm, the water absorption capacity under load is 35 g / g or more, exhibiting unprecedented excellent water absorption performance.

Conventionally, the smaller the particle size, the more quickly the water-absorbent resin tends to absorb the liquid to be absorbed, but the swollen gel blocks the capillary space between the particles, significantly reducing the liquid permeability. Since the water-absorbent resin of the present invention has a high water absorption capacity under load of 35 g / g or more, it can hold a capillary space for allowing the liquid to be absorbed between the swollen gels and cause mamko or gel blocking. It is possible to quickly absorb the liquid to be absorbed.

In addition to the above water-absorbent resin, if necessary, deodorant, fragrance, various inorganic powders, foaming agents, pigments, dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, A fertilizer, an oxidizing agent, a reducing agent, water, salts and the like may be added to give various functions to the water absorbent resin.

Examples of the inorganic powder include substances that are inactive to aqueous liquids, such as 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 acid (salt) such as natural zeolite and synthetic zeolite, kaolin, talc, clay,
Examples include bentonite. Among these, 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 measured by the Coulter counter method are further preferable.

The amount of the inorganic powder used with respect to the water absorbent resin is
Depending on the combination of water absorbent resin and 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 method of mixing the water absorbent resin and the inorganic powder is
The method is not particularly limited, and for example, a dry blending method, a wet mixing method, etc. can be adopted, but the dry blending method is preferably used.

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

Examples of the absorbent article include sanitary materials (body fluid absorbent articles) such as paper diapers, sanitary napkins, incontinence pads, wound protection materials and wound healing materials; absorbent articles such as urine for pets; building materials and soil. Materials for civil engineering such as water retention material, water blocking material, packing material, gel water bag, food products such as drip absorbent, freshness retention material, cold insulation material, oil water separation material, dew condensation prevention material,
Examples include various industrial articles such as coagulation materials; agricultural and horticultural articles such as water retaining materials for plants and soil, but are not particularly limited. Note that, for example, a paper diaper is obtained by laminating a back sheet (back surface material) made of a liquid impermeable material, the above water absorbing composition, and a top sheet (surface material) made of a liquid permeable material in this order. They are fixed to each other, and are formed by attaching a gather (elastic portion), a so-called tape fastener or the like to this laminate. The paper diaper also includes pants with a paper diaper that is used when an infant is disciplined to urinate or defecate.

[0057]

EXAMPLES 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 by these Examples. Unless otherwise specified,% in Examples and Comparative Examples means% by weight, and parts mean parts by weight.

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

(1) Water absorption of 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 the artificial urine shown below. After 60 minutes, the tea bag type bag was pulled up and drained at 250 G for 3 minutes using a centrifuge, and then the weight W ₁ (g) of the bag was measured.
The same operation was performed without using the water absorbent resin, and the weight W ₀ (g) at that time was measured. And these weights W
_{From 1} and W ₀ , the water absorption amount (g / g) was calculated according to the following equation: Water absorption amount (g / g) = (W ₁ −W ₀ ) / weight of water absorbent resin (g).

The composition of the above artificial urine and the blending amount thereof are as follows.

Composition of artificial urine Blending 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 device shown in FIG.
As shown in FIG. 1, the measuring device includes a balance 1, a container 2 having a predetermined volume 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 at the top and an opening 2b at the side. Opening 2
The outside air suction pipe 3 is fitted in a, and the opening 2b
A conduit 4 is attached to the. Further, 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 intake pipe 3
Are provided to maintain the pressure in the container 2 at approximately atmospheric pressure. The glass filter 6 has a diameter of 55 mm. The container 2 and the glass filter 6 are in communication with each other by a conduit 4 made of silicone resin. The position and height of the glass filter 6 with respect to the container 2 are fixed. The measuring unit 5 is composed of a filter paper 7, a supporting cylinder 9, and a wire netting 1 attached to the bottom of the supporting cylinder 9.
It has 0 and a weight 11. The measuring unit 5 includes a filter paper 7, a supporting cylinder 9 (that is, a wire net 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 net 10, that is, the height of the contact surface between the wire net 10 and the water-absorbent resin 15 is the lower end surface 3 of the outside air intake pipe 3.
It is set to be equal to the height of a. Wire mesh 10
A predetermined amount of water-absorbent resin is evenly dispersed on the top. The weight 11 is less than the weight of the wire net 10, that is, the water absorbent resin 15.
Its 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 device having the above structure. The measuring method will be described below.

A predetermined amount of artificial urine 12 is placed in the container 2. A predetermined preparatory 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. Further, in parallel with the placement, 0.9 g of the water-absorbent resin was evenly dispersed inside the support cylinder 9, that is, on the metal net 10, and the weight 11 was placed on the water-absorbent resin 15. Then, on the filter paper 7, the metal net 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 central portion thereof coincided with the central portion of the glass filter 6. Next, from the time when the supporting cylinder 9 was placed on the filter paper 7, the weight of the artificial urine absorbed by the water absorbent resin 15 was calculated from the measured value of the balance 1 over time for 60 minutes. Further, the same operation was performed without using the water-absorbent resin 15, and the weight of artificial urine absorbed by the filter paper 7 other than the water-absorbent resin was determined from the measured value of the balance 1 and used as a blank value. The water absorption under load was calculated from the following formula.

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 cylinder with inner diameter of 58 mm and depth of 25 mm 1.0 g of the water-absorbent resin was put in the polypropylene container. Next, 20 g of artificial urine was poured into the container. Then, the time from when the artificial urine was poured to when the artificial urine was completely absorbed by the water absorbent resin and disappeared was measured. The measurement was repeated 3 times, and the average value thereof was taken as the water absorption rate (second).

(4) Water-soluble component amount 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 then filtered with a filter paper. Then, the obtained filtrate was titrated by colloid titration to determine the amount (%) of water-soluble component in the water absorbent resin.

(5) Average particle size of water-absorbent resin The openings (300 μm, 250 μm, 212 μm) shown below.
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 a log probability paper, and the particle size corresponding to R = 50% was taken as the average particle size. .

Example 1 A monomer aqueous solution containing 441 g of acrylic acid, 4668 g of 37% sodium acrylate aqueous solution, 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. After the air, the internal volume 1
The reactor was fed with 0 liter of a stainless steel double-arm kneader with a jacket having two sigma-type blades and a lid, and the reaction system was further replaced with nitrogen while maintaining the temperature of the monomer at 30 ° C.

Then, 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 with stirring. Polymerization started after 1 minute, and after 15 minutes, the peak temperature in the reaction system reached 78 ° C. The stirring was continued, and the hydrogel polymer was taken out 35 minutes after the polymerization was started.

16 parts of the obtained hydrogel polymer fine granules were prepared.
It was dried with hot air at 0 ° C. for 60 minutes. The dried product was crushed 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 the 106 μm sieve.

With respect 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 part, 2 parts propylene glycol and 2 parts isopropyl alcohol was mixed. An aqueous liquid containing 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. There were almost no aggregates of water-absorbent resin particles.
This was heated at 185 ° C. for 40 minutes to obtain the water absorbent resin (1) of the present invention.

The water absorption of the water absorbent resin (1) thus obtained was 40.
(G / g), water absorption capacity under load 36.4 (g / g), water absorption speed 20 seconds, soluble component 14% and average particle size 1
It was 60 μm.

Example 2 A monomer aqueous solution containing 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. The temperature of the monomer was kept at 20 ° C.

Then, 4.8 g of 5% 2,2'-azobis (2-amidinopropane) dihydrochloride aqueous solution, 8.6 g of 0.5% L-ascorbic acid aqueous solution and 4 g of 0.35% hydrogen peroxide aqueous solution. Was added and static polymerization was carried out. Thirty
Polymerization started after minutes, and after 80 minutes, the peak temperature in the reaction system reached 70 ° C. After standing still for 60 minutes, the hydrogel polymer was taken out. While crushing the taken-out hydrogel polymer with a double-arm kneader, sodium carbonate powder 41
2 g was added to neutralize. The crushed hydrogel polymer was taken out, and 5000 g of pure water was added on a vat, and the mixture was aged until the neutralization was made uniform and no color reaction due to phenolphthalein was observed. The neutralization rate of the carboxyl groups contained in the hydrous gel was 75%. The neutralized gel was dried with a hot air dryer at 160 ° C. for 1 hour. The dried product is crushed with a roll mill, sieved and passed through a 212 μm sieve to give 150
Water-absorbent resin particles (2) having a particle size remaining on the sieve of μm were obtained.

With respect to 100 parts of the water-absorbent resin particles (2), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinker solution consisting of 0.1 part, 2 parts propylene glycol and 2 parts isopropyl alcohol was mixed. An aqueous liquid containing 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. There were almost no aggregates of water-absorbent resin particles. This was heated at 185 ° C. for 50 minutes to obtain the water absorbent resin (2) of the present invention.

The water absorption amount of the resulting water absorbent resin (2) is 4
5.4 (g / g), the 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 The pulverized product in Example 2 was passed through a sieve of 212 μm and passed through a sieve of 212 μm to obtain water-absorbent resin particles (3) having a particle size remaining on the sieve of 104 μm.

With respect to 100 parts of the water absorbent resin particles (3), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinking agent solution consisting of 0.125 parts, 2.5 parts of propylene glycol and 2.5 parts of isopropyl alcohol was mixed. An aqueous liquid containing 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. There were almost no aggregates of water-absorbent resin particles. Heat this at 185 ° C for 35 minutes,
A water absorbent resin (3) of the present invention was obtained.

The water absorption of the water-absorbent resin (3) thus obtained was 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 37% aqueous sodium acrylate solution, N, N'-methylenebisacrylamide of 0.
A monomer aqueous solution consisting of 15 g and pure water 173 g was prepared. 0.24 g of sodium persulfate in this monomer aqueous solution
Was dissolved and nitrogen gas was blown into it to expel dissolved oxygen.

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

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

With respect 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 crosslinker solution consisting of 0.05 parts, 1 part propylene glycol and 1 part isopropyl alcohol was mixed. An aqueous liquid containing 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. There were almost no aggregates of water-absorbent resin particles.
This was heated at 150 ° C. for 10 minutes to obtain the water absorbent resin (4) of the present invention.

The water absorption of the water absorbent resin (4) thus obtained was 39.
(G / g), the water absorption capacity under load was 39.4 (g / g), the water absorption speed was 20 seconds, the soluble component was 18%, and the average particle diameter was 120 μm.

Example 5 Water-absorbent resin particles (5) obtained by sieving the dried product in Example 4 with a sieve and passing through a 104 μm sieve and remaining on the 75 μm sieve.
Got

With respect to 100 parts of the water-absorbent resin particles (5), ethylene glycol diglycidyl ether (trade name: Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.)
A crosslinker solution consisting of 0.05 parts, 1 part propylene glycol and 1 part isopropyl alcohol was mixed. An aqueous liquid containing 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. There were almost no aggregates of water-absorbent resin particles.
This was heated at 150 ° C. for 10 minutes to obtain the water absorbent resin (5) of the present invention.

The water absorption amount of the water absorbent resin (5) thus obtained was 3
8.8 (g / g), the 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 With respect to 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
Parts, 2 parts of propylene glycol, 6 parts of pure water, and 6 parts of isopropyl alcohol 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) is 38 (g)
/ G), the water absorption capacity under load is 28.5 (g / g), the water absorption speed is 24 seconds, the soluble component is 16%, and the average particle size is 18
It was 0 μm.

Comparative Example 2 With respect to 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 were mixed. 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) is 43.9.
(G / g), the water absorption capacity under load was 32.6 (g / g), the water absorption speed was 27 seconds, the soluble component was 7%, and the average particle diameter was 190 μm.

[0091]

EFFECTS OF THE INVENTION The water-absorbent resin of the present invention has a fine particle size and is excellent in water absorption under load. Therefore, when it is used in a diaper or sanitary cotton, urine can be swiftly and quickly without causing blockage due to swollen gel. Can absorb large amounts.

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

[Brief description of drawings]

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

[Explanation of symbols]

1 scale, 2 containers, 2a top opening, 2b side opening, 3 Outside air intake pipe sheet, 4 conduits, 5 measuring section, 6 glass filters, 7 filter paper, 9 support cylinder, 10 wire mesh, 11 weights, 12 artificial urine, 15 Water absorbent resin.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C08F 20/02 A61F 13/18 307A C08J 3/12 A41B 13/02 D // A61F 13/49 (72) Inventor Kazuki Kimura Hyogo 1 992 Nishioki Okihama, Aboshi-ku, Himeji-shi, Japan Within Nihon Shokubai Co., Ltd. (72) Inventor Yasuhiro Fujita 1 992 Nishioki Okihama, Aboshi-ku, Himeji-shi, Hyogo (56) Reference JP-A-8-157823 ( JP, A) JP-A-1-297430 (JP, A) Special table: 8-509521 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08F 8/00-8/50

Claims (7)

(57) [Claims] 1. A monomer component containing an unsaturated carboxylic acid is treated with water.
Solution polymerization or a water-absorbing resin particles the surface of the water absorbent resin particles are further crosslinked with a crosslinking structure obtained by reversed phase suspension polymerization, average particle size is in the range of 50 to 200 [mu] m, artificial urine 0.7 psi (about 4.8 kP
Water-absorbent resin particles having a further crosslinked surface , which has a water absorption capacity under load ( 60 minutes value ) of at least 35 g / g. 2. A monomer component containing an unsaturated carboxylic acid is added to water.
Solution polymerization or at least two having a surface cross-linking agent or cross-linking agent and an organic group capable of reacting with the functional group of the water-absorbent resin particles and the water-absorbent resin particles having a crosslinked structure obtained by reversed phase suspension polymerization A step (1) of mixing a mixed solution with a solvent; and, after the step (1), water or an organic solvent soluble in water for the mixture of the water absorbent resin particles and the surface cross-linking agent. The surface is further crosslinked, comprising a step (2) of mixing an aqueous liquid consisting of the mixture of 1. and a step (3) of reacting the water-absorbent resin particles with a surface crosslinking agent subsequent to the step (2). Of producing the water-absorbent resin particles thus obtained. 3. A water-absorbent resin particles having the crosslinked structure,
The method for producing water-absorbent resin particles according to claim 2, wherein the water-absorbent resin particles have such a size that they pass through a US standard 70 mesh sieve having an opening of 212 μm and are captured by a US standard 325 mesh sieve having an opening of 45 μm. 4. A water-absorbent resin particles having the crosslinked structure,
The method for producing water-absorbent resin particles according to claim 2, which is spherical. 5. The method for producing water-absorbent resin particles according to claim 2, wherein the surface-crosslinking agent contains at least two kinds of surface-crosslinking agents having different reactivity. 6. The water-absorbent resin particles according to claim 2, wherein the aqueous liquid is water or a mixed solvent of water and a water-soluble organic solvent, and is a droplet of 10 to 4000 μm.
Child manufacturing method. 7. A body fluid absorbent article using the water-absorbent resin particles according to claim 1, the surface of which is further crosslinked .