JPH10265582A - Water-absorbing agent and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing agent that has high water absorption times under pressure and excellent water absorption efficiency under pressure and shows excellent water absorption characteristics even in the case that the resin concentration of the water-absorption resin is increased when it is used as a hygienic material and its production. SOLUTION: This water absorption agent has >=30 (g/g) water absorption times and the absorption efficiency represented by the following formula of >=0.7 The absorption efficiency under pressure = (the absorption times at the upper layer after absorption)/(the absorption times at the lower layer after absorption) This agent has 40 or higher absorption times and is produced by heat-treating a water-absorption resin that contains less than 1 pt.wt. of elution components per 100 pts.wt. of the resin in the presence of a surface-crosslinking agent. Or the water absorption resin polymerized in the presence of a water-soluble chain-transfer agent is treated with a hydrophilic aqueous solution, then heat-treated with a surface-crosslinking agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbing agent and a method for producing the same. More specifically, the present invention relates to a water-absorbing resin which exhibits a very high absorption capacity even under pressure, and has a high spray density of a water-absorbing resin. Even when present in a layered manner, the difference in the swelling ratio at each position of the layer shows a uniform swelling behavior with a small difference in swelling ratio, a paper absorbent diaper, a sanitary napkin, a water-absorbing agent suitably used for sanitary materials such as incontinence pads, and the like. It relates to a manufacturing method for providing.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been widely used as one of the constituent materials of sanitary materials such as disposable diapers, sanitary napkins and incontinence pads for the purpose of absorbing body fluids. Examples of the water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, and vinyl acetate-acrylate copolymer. Merged saponified product, crosslinked carboxymethylcellulose, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or crosslinked product thereof, crosslinked product of cationic monomer, crosslinked isobutylene-maleic acid copolymer, 2
A crosslinked product of acrylamide-2-methylpropanesulfonic acid and acrylic acid is known.

[0003] Characteristics that should be provided to the above-mentioned water-absorbent resin include a high absorption capacity, an excellent absorption rate, liquid permeability, gel strength of a swollen gel, and an aqueous liquid in contact with an aqueous liquid such as a body fluid. There is a demand for a suction amount for sucking water from the base material. However, the relationship between these properties does not always show a positive correlation. For example, the higher the absorption capacity, the lower the physical properties such as liquid permeability, gel strength, and absorption rate. Therefore, as a method for improving the water absorbing properties of such a water-absorbent resin in a well-balanced manner, a technique of cross-linking the vicinity of the surface of the water-absorbent resin is known, and various methods have been proposed so far. For example, as a crosslinking agent, a method using a polyhydric alcohol, a method using a polyvalent glycidyl compound, a polyvalent aziridine compound, a polyvalent amine compound, a polyvalent isocyanate compound, a method using glyoxal, a method using a polyvalent metal, a silane cup A method using a ring agent, a method using an epoxy compound and a hydroxy compound,
A method using an alkylene carbonate is known.

In addition, a method of distributing a crosslinking agent more evenly to the surface of a water-absorbent resin at the time of a crosslinking reaction, and a method of adding an inert inorganic powder at the time of adding a crosslinking agent in an attempt to perform uniform surface crosslinking, a method of making a dihydric alcohol exist. A method, a method of making an ether compound present, a method of making a water-soluble polymer present,
A method in which an alkylene oxide adduct of a monohydric alcohol, an organic acid salt, a lactam and the like are present is also known.

Although the balance of various physical properties of the water-absorbing resin is improved by these methods, it is still not enough. Examples of the above-mentioned conventional water-absorbent resin used for an absorbent body in a sanitary article include, for example, a water-absorbent sanitary article containing a water-absorbent resin having a specified amount of water absorption, an amount of water absorption under pressure, and a gel breaking strength (JP-A-63-163). No. 99861), a disposable diaper containing a water-absorbent resin whose water absorption amount and water absorption rate under pressure are specified (Japanese Patent Application Laid-Open No. 2-34167), and a water-absorbent resin whose water absorption amount under pressure and its particle size are specified. Absorbents (European Patent No. 339461), water-absorbing resins containing a specific amount or more of a water-absorbing resin whose water absorption rate and water absorption under pressure in a short time are specified (European Patent No. 443627) and the like are known. However, higher quality is required. Especially in recent years, considering the necessary properties of the water-absorbing resin used in the absorbent in a thin sanitary article that uses a large amount of the water-absorbing resin, the conventional method described above still has a sufficient level of physical properties. It has not reached to the present.

That is, one of the necessary characteristics of a water-absorbent resin used for a thin absorbent body containing a high concentration of the water-absorbent resin is such that a sufficient absorbent capacity can be exerted even when a heavy load is applied during mounting. Under high load (for example, 50g / c
m ² ), the absorption capacity under pressure (hereinafter sometimes referred to as absorption capacity under pressure) can be made relatively high by the surface cross-linking method described above. Insufficient absorption capacity has not been demonstrated.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thin absorbent having a high concentration of a water-absorbing resin. An object of the present invention is to provide a water-absorbing agent capable of exhibiting a high absorption capacity and a method for producing the same.

[0008]

According to the findings of the present inventors, even when a water-absorbing agent having a high absorption capacity under pressure is used, the swelling gel layer is formed when the water-absorbing resin is present at a high concentration and a high spray density. If the difference in the swelling ratio between the upper and lower positions is large and the resin does not swell uniformly to the inherent absorption capacity, the absorbent cannot exhibit sufficient absorption ability.

Therefore, the absorption capacity under pressure is high, and even when the water-absorbing resin is present at a high concentration and a high scatter density, the difference in the swelling capacity due to the vertical position of the swelling gel layer is small, and the absorption capacity of the resin inherently increases. The present inventors have further studied and obtained the present invention in order to obtain a water-absorbing resin having a property capable of uniformly swelling (hereinafter sometimes referred to as absorption efficiency under pressure).

That is, according to the present invention, the absorption capacity under pressure is high and the absorption efficiency under pressure is excellent, and when used for sanitary materials, etc., excellent water absorption characteristics even when the resin concentration of the water absorbent resin is increased. And the water-absorbing ability possessed by the water-absorbent resin can be efficiently exhibited even under a high concentration. The present invention relates to an absorption capacity under pressure of 30 (g / g).
g) or more, wherein the water-absorbing agent is characterized by having an absorption efficiency represented by the following formula of 0.7 or more:

[0011]

(Equation 4)

"The absorption capacity of the lower layer under pressure is 45 (g / g).
g) or more, wherein the water-absorbing agent has an absorption efficiency represented by the following formula of 0.4 or more:

[0013]

(Equation 5)

"The absorption capacity of the lower layer under pressure is 30 (g / g).
g) or more, and the absorption efficiency represented by the following formula is 0.3
In the above range, and the water absorption agent, wherein the absorption efficiency and the absorption capacity of the lower layer satisfy the following formula:

[0015]

(Equation 6)

Absorption efficiency> 1.82-2.93 × 10 ⁻² ×
(Absorption capacity of lower layer) "It is characterized in that a water-absorbing resin having an absorption capacity of 40 times or more and an elution component amount of 1 part by weight or less based on 100 parts by weight of the water-absorbing resin is subjected to heat treatment in the presence of a surface crosslinking agent. A method for producing a water-absorbing agent "," a water-absorbing agent characterized in that a water-absorbent resin polymerized in the presence of a water-soluble chain transfer agent is treated with a hydrophilic solution, and then heat-treated in the presence of a surface crosslinking agent. And a method for producing a water-absorbing agent, comprising: treating a water-absorbent resin having a weight-average molecular weight of an eluted component of 200,000 or less with a hydrophilic solution, followed by heat treatment in the presence of a surface crosslinking agent. ".

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the water absorbing agent of the present invention will be described in detail together with a method for producing the same. The present invention firstly obtains a water-absorbent resin having an absorption capacity of a specific value or more and the amount of an eluted component that oozes out from the surface of a swelled gel in an unsaturated state is reduced to a specific value or less, and this water-absorbent resin is coated on the surface. It is based on a new technique such as crosslinking.

It has been known that a water-absorbent resin generally contains an eluting component. However, the amount of the eluting component that oozes out from the surface of the unsaturated swelling gel to the outside of the gel is less than a certain level. No attempt has been made to further surface-crosslink the resin reduced in amount. The most characteristic feature of the water-absorbent resin used in the present invention is that the amount of the eluted component that oozes from the surface of the unsaturated swelled gel to the outside of the gel is reduced to a specific value or less by a specific method and the surface-crosslinking treatment is performed on the water-absorbent resin. It is assumed that.

When the water-absorbent resin is subjected to surface crosslinking treatment, it is possible to improve the absorption capacity under pressure under a high load to a specific level, for example, 30 (g / g) or more, even if the elution component is contained in a specific amount or more. Although possible, it is difficult to obtain a high value of the absorption efficiency under pressure. However, this method has made it possible to obtain, for the first time, a water-absorbing agent excellent in both the absorption capacity under pressure and the absorption efficiency under pressure.

Hereinafter, the present invention will be described in more detail. The water-absorbing resin that can be used in the present invention is one that absorbs and swells a large amount of water, physiological saline, urine, etc. to form a substantially water-insoluble hydrogel, and has an absorption capacity of 40 times in physiological saline described later. As described above, the amount of the eluted component is reduced to 1 part by weight or less based on 100 parts by weight of the water absorbent resin. More preferably, the powder can be handled as a powder having a water content of 10% by weight or less based on the water-absorbing resin, and most preferably a water content of 5% by weight or less.

A typical example is a hydrophilic polymer having a crosslinked structure obtained by polymerizing a hydrophilic monomer containing acrylic acid or a salt thereof as a main component. Such materials include, for example, partially neutralized crosslinked polyacrylic acid polymers, crosslinked and partially neutralized starch-acrylic acid graft polymers, isobutylene-maleic acid copolymers, and vinyl acetate-acrylic acid copolymers. Examples thereof include a saponified product, a hydrolyzate of an acrylamide (co) polymer, and a hydrolyzate of an acrylonitrile polymer. Among them, preferred are polyacrylate crosslinked polymers. As the polyacrylate crosslinked polymer, it is preferable that 50 to 95 mol% of the acid groups in the polymer are neutralized, and it is more preferable that 60 to 90 mol% is neutralized. Examples of the salt include an alkali metal salt, an ammonium salt, an amine salt and the like. This neutralization may be performed with a monomer before polymerization, or with a hydrogel polymer during or after polymerization.

The water-absorbing resin used in the present invention may be obtained by (co) polymerizing a monomer other than the above-mentioned acrylic acid or a salt thereof which is preferably used as a main component of the monomer. Specific examples of other monomers include methacrylic acid, maleic acid, vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, Anionic unsaturated monomers such as-(meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N
-Isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate , Vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, and other nonionic hydrophilic group-containing unsaturated monomers; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl Cationic unsaturated monomers such as (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and quaternary salts thereof, and the like. It can be. The amount of the monomer other than the acrylic acid used is usually 0 to 50 in all the monomers.
It is less than mol%, preferably 0 to 30 mol%, but is not limited thereto.

The cross-linking structure of the water-absorbent resin used in the present invention may be a self-cross-linking type using no cross-linking agent, or an internal cross-linking having two or more polymerizable unsaturated groups or two or more reactive groups. Examples thereof include those having a crosslinked structure obtained by copolymerizing or reacting an internal crosslinking agent, and those having a crosslinked structure obtained by copolymerizing or reacting an internal crosslinking agent are more preferable, but the absorption capacity in physiological saline is 40 times or more. It is necessary to adjust the crosslink density.

Specific examples of these internal crosslinking agents include, for example, N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, tri Methylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate,
Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, Triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether,
Ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol,
Examples thereof include ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate. Further, two or more of these internal crosslinking agents may be used. Above all, it is preferable to use a compound having two or more polymerizable unsaturated groups as an internal crosslinking agent in view of the water absorbing properties of the obtained water-absorbing resin. 0.005 to 3 mol%, more preferably 0.01 to 1.5 mol%.

In the polymerization, starch, cellulose,
A derivative of starch / cellulose, a hydrophilic polymer such as a crosslinked product of polyvinyl alcohol, polyacrylic acid (salt), or polyacrylic acid (salt), or a chain transfer agent such as hypophosphorous acid (salt) may be added. . When polymerizing the above-described monomer containing acrylic acid or a salt thereof as a main component to obtain the water-absorbing resin used in the present invention, bulk polymerization or precipitation polymerization can be performed, From the viewpoint of easy control of polymerization and polymerization, it is preferable to carry out aqueous solution polymerization or reversed-phase suspension polymerization using a monomer as an aqueous solution.

In conducting the polymerization, radical polymerization of potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2'-azobis (2-amidinopropane) dihydrochloride, etc. Initiators, active energy rays such as ultraviolet rays and electron beams, and the like can be used. When an oxidizing radical polymerization initiator is used, redox polymerization may be performed by using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination. The amount of these polymerization initiators used is usually 0.001 to
It is 2 mol%, preferably 0.01 to 0.5 mol%.

The shape of the water-absorbent resin obtained by the above polymerization can be various shapes such as irregular crushed shape, spherical shape, fibrous shape, rod shape, substantially spherical shape, flat shape, etc. The diameter is 200 to 600 μm, more preferably the ratio of particles having a size of 150 μm or less is 10% by weight or less, and further preferably the ratio of particles having a size of 150 μm or less is 5% by weight or less.

In order to achieve the object of the present invention, the water-absorbent resin obtained in this manner is adjusted so that the amount of the eluted component which oozes out from the surface of the unsaturated swelling gel is 1 weight per 100 parts by weight of the water-absorbent resin. Parts or less. A water-absorbent resin having an absorption capacity of 40 times or more in physiological saline usually has an eluting component such as a water-soluble component, and as is well known, a large amount of water or a large amount of physiological saline is used. By saturation swelling, these eluted components are extracted outside the gel. However, even when the water-absorbent resin swells in a non-saturated state under the conditions described below, these eluted components ooze and migrate to the surface of the gel. The amount is not always correlated with the amount extracted at the time of saturation swelling due to the influence of the molecular weight of the compound, the degree of branching, the viscosity, etc., but is usually about 2 to 20 parts by weight based on 100 parts by weight of the water absorbent resin. .
However, the present inventors have found that when the amount of the eluted component is large, the absorption efficiency under pressure does not improve to a certain level or more. In other words, in order to reach the absorption efficiency level under pressure, which is the object of the present invention, the amount of the eluted component that oozes out from the surface of the unsaturated gel of the water-absorbent resin to the outside is determined.
It is essential to reduce the amount to an extremely low level of 1 part by weight or less, preferably 0.5 part by weight or less, more preferably 0.1 part by weight or less with respect to 00 parts by weight.

As a preferable method for reducing the amount of the eluted components to such a level, a water-absorbent resin obtained by treating the obtained water-absorbent resin with a treatment liquid capable of dissolving the eluted components such as water, an organic solvent, and a mixture of water and an organic solvent. A method of separating these treatment liquids and the water-absorbent resin after repeated contact, for example, a method of polymerizing the water-absorbent resin in the presence of a water-soluble chain transfer agent, and then treating with a hydrophilic solution.

As the organic solvent in the above method, a hydrophobic organic solvent may be used, but methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, t-butyl alcohol Preferred examples include lower alcohols such as acetone; ketones such as acetone; ethers such as dioxane and tetrahydrofuran; amides such as N, N-dimethylformamide; and hydrophilic organic solvents such as sulfoxides such as dimethylsulfoxide. However, in view of the effect of reducing the amount of eluted components, it is preferable to use a mixture of water and an organic solvent as the treatment liquid, and it is more preferable to use water alone as the treatment liquid.

A further preferred embodiment is to select the composition of the treatment liquid so that the water-absorbent resin swells when the treatment liquid is repeatedly brought into contact with the water-absorbent resin. The preferred swelling ratio of the water-absorbing resin during the treatment is about 2 to 500 times, more preferably about 5 to 300 times. The optimum amount of the treatment liquid used in this case varies depending on the type and particle size of the water-absorbent resin, but is usually 0.5 to 10,000, based on 1 part by weight of the solid content of the water-absorbent resin. 000 parts by weight, preferably in the range of 5 to 500,000 parts by weight.

When the water-absorbent resin is brought into contact with the treatment liquid, the contact can be carried out continuously or discontinuously in a batch manner. For example, a method in which the water-absorbent resin is brought into contact with the treatment liquid while stirring if necessary, and then the water-absorbent resin is separated from the treatment liquid by decantation or suction filtration is exemplified. When washing is carried out continuously, the directions of the water-absorbent resin and the treatment liquid are co-current and counter-current are not particularly limited, but co-current is more preferable in view of the effect of reducing the amount of eluted components. In the case of performing a batch process, the number of processes is not particularly limited. These treatment temperatures are from 10C to 100C, preferably from 20C to 60C.
Further, after separation from the processing solution, further drying may be performed if necessary, but care must be taken because the amount of the eluted component once reduced may increase again due to deterioration of the resin or the like.

In the method (1), since the polymerization is carried out in the presence of a water-soluble chain transfer agent, one molecule of the resulting water-absorbing resin is relatively short. Therefore, the amount of the eluted component at the stage when the polymerization is completed is relatively large, but the weight-average molecular weight of the eluted component is small, for example, about 200,000 or less, so that it can be easily removed by treatment with a hydrophilic solution. The water-soluble chain transfer agent used in the present invention is not particularly limited as long as it is soluble in water or a hydrophilic monomer, and thiols, thiolic acids, secondary alcohols, amines, hypophosphorous acid ( Salts) and the like. Specifically, mercaptoethanol, mercaptopropanol, dodecylmercaptan, thioglycolic acid, thiomalic acid, 3-
Mercaptopropionic acid, isopropanol, hypophosphorous acid, formic acid, and salts thereof are used, and one or two or more selected from these groups are used. Due to its effect, hypophosphorous acid such as sodium hypophosphite ( Salts) and thiols.

The amount of the water-soluble chain transfer agent depends on the type and amount of the water-soluble chain transfer agent and the concentration of the aqueous solution of the hydrophilic monomer. %, More preferably 0.005 to 0.3 mol%. In addition to the above, as a method of reducing the amount of the eluted component, a method of subjecting the obtained water-absorbent resin to a heat treatment in the presence of a surface cross-linking agent is also included.

The surface cross-linking agent that can be used to heat-treat the water-absorbing resin thus obtained with a low amount of eluted components in the presence of a surface cross-linking agent reacts with a functional group of the water-absorbing resin such as an acidic group. It has a functional group which can be used, and a known crosslinking agent usually used for the application is exemplified. When the functional group of the water absorbent resin is a carboxyl group, for example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2 , 4-Trimethyl-1,3-pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol , 1,2-cyclohexanedimethanol,
Polyhydric alcohol compounds such as 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene diglycidyl Polyhydric epoxy compounds such as ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentane Min, pentaethylenehexamine, polyallylamine Emissions, polyvalent amine compounds such as polyethyleneimine; 2,4-tolylene diisocyanate,
Polyvalent isocyanate compounds such as hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 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-
Alkylene carbonate compounds such as dioxan-2-one and 4,6-dimethyl-1,3-dioxan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin; zinc , Calcium, magnesium, aluminum, iron, zirconium and other hydroxides and polyvalent metal compounds such as chlorides; and one or more selected from the group consisting of: Preferably, it contains at least one selected from a polyhydric alcohol compound, a polyvalent amine compound, a polyvalent epoxy compound, and an alkylene carbonate compound.

These surface cross-linking agents may be used alone or in combination of two or more. When two or more surface cross-linking agents are used, the surface treatment can be performed in two or more stages, but since the surface treatment tends to reduce the water absorption capacity, two or more surface cross-linking agents are mixed at once. It may be preferable to use them. The amount of the surface cross-linking agent used in the present invention varies depending on the type of the cross-linking agent used and its purpose, but is usually 0.001 to 100 parts by weight of the solid content of the water-absorbent resin of the present invention. The amount is within the range of 10 to 10 parts by weight, preferably 0.01 to 5 parts by weight. If the amount is within this range, a water-absorbing agent excellent in absorption capacity under pressure and absorption efficiency under pressure can be obtained. When the amount of the cross-linking agent exceeds 10 parts by weight, it is not only uneconomical, but also tends to be excessive in achieving an appropriate surface cross-linking effect, and the absorption capacity may be excessively lowered. Conversely, if the amount is less than 0.001 part by weight, the effect of improving the absorption characteristics under pressure may not be obtained.

In the present invention, a device used for mixing the water-absorbing resin and the surface cross-linking agent may be a usual device, for example, a cylindrical mixer, a screw-type mixer, a screw-type extruder, and a turbulator. Riser, Nauter type mixer, V type mixer, ribbon type mixer, double arm type kneader, flow type mixer, air flow type mixer, rotating disk type mixer, roll mixer, tumbling type mixer, etc. The mixing speed may be high or low.

In the present invention, water, steam, or an aqueous liquid composed of water and a hydrophilic organic solvent may be added before or after mixing the water-absorbing resin with the surface cross-linking agent and before performing the cross-linking reaction. Good. If the cross-linking agent reacts with a water-absorbent resin by a covalent bond, such as a polyhydric alcohol, a polyhydric epoxy compound, or an alkylene carbonate compound, the post-addition of water, water vapor, or an aqueous liquid greatly improves the absorption characteristics under pressure. Is preferred. Examples of the hydrophilic organic solvent used in this case 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; acetone and the like. Ketones; ethers such as dioxane and tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethylsulfoxide. The amount of water used in this case varies depending on the type and particle size of the water-absorbent resin, but is usually 10 parts by weight or less, preferably 1 to 100 parts by weight based on the solid content of the water-absorbent resin. The range is 5 parts by weight. Similarly, the amount of the hydrophilic organic solvent used is generally 10 parts by weight or less, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the solid content of the water-absorbent resin.

In the present invention, after mixing the water-absorbing resin and the surface cross-linking agent, a heat treatment is further performed as necessary depending on the type of the cross-linking agent to cross-link the vicinity of the surface of the water-absorbing resin. When the heat treatment is performed in the present invention, the treatment temperature is preferably about 60 ° C. or more and 230 ° C. or less. When the heat treatment temperature is lower than 60 ° C., the heat treatment takes a long time to cause a decrease in productivity. In addition, uniform crosslinking is not achieved, and a resin having high water absorption under pressure which is the object of the present invention is obtained. May not be possible. On the other hand, when the temperature exceeds 230 ° C., the reduced amount of the eluted component increases, and it may be difficult to improve the absorption efficiency under pressure. Although depending on the type of the crosslinking agent used, the heat treatment temperature is more preferably 80 to 200 ° C., and further preferably 120 to 18 ° C.
It is in the range of 0 ° C.

The heat treatment can be carried out using a usual dryer or heating furnace, for example, a groove-type mixing dryer, a rotary dryer, a desk dryer, a fluidized-bed dryer, a gas-flow dryer, and an infrared dryer. Etc. can be exemplified. As described above, as a method for obtaining a water-absorbing agent excellent in both the absorption capacity under pressure and the absorption efficiency under pressure of the present invention, bleeding outward from the surface of a swelling gel having an absorption capacity of a specific value or more and being in an unsaturated state. First, a water-absorbent resin in which the amount of the eluted component to be discharged is reduced to a specific value or less was obtained, and a method for producing a water-absorbent resin of the present invention is not limited thereto. . For example, it can be obtained by a method in which the vicinity of the surface of a particle having a specific particle size range is crosslinked by a specific method to have a specific crosslinking density gradient. Hereinafter, this method will be described.

That is, the water-absorbing agent according to the present invention is preferably prepared by adjusting the water-absorbing resin obtained by aqueous solution polymerization by an operation such as classification so that the particle size is substantially in the range of 106 μm to less than 500 μm. It can also be obtained by performing a heat treatment in the presence of two or more types of surface crosslinking agents having different solubility parameter ranges. Here, “substantially 106 μm or more and less than 500 μm” means that the weight% of the particles present in the particle size range of 106 μm or more and less than 500 μm in the entire particles of the water-absorbent resin is a large part of the whole. . Preferably, 9
0% by weight or more, more preferably 95% by weight or more.

The water-absorbent resin may be granulated into a predetermined shape, or may be in various shapes such as a spherical shape, a scale-like shape, an irregular crushed shape, and a granular shape. Further, the water-absorbing resin may be primary particles, or may be a granulated primary particle. If the particle size is not substantially 106 μm or more and less than 500 μm, it is difficult to obtain a water absorbing agent having excellent performance such as absorption efficiency under pressure.

By using acrylic acid as a monomer as the above-mentioned water-absorbing resin and using a water-absorbing resin obtained by post-neutralizing a polymerized gel, the absorption capacity under pressure, the absorption efficiency and the lower layer can be further improved. A water-absorbing agent having excellent absorption capacity can be obtained. The above-mentioned solubility parameter is a value generally used as a factor indicating the polarity of a compound. In the present invention, as the above-mentioned solubility parameter, the Polymer Handbook, 3rd edition (WILEY INTERSCIENCE
The value of the solubility parameter δ [(cal / cm ³ ) ^1/2 ] of the solvent described on pages 527 to 539) is applied. In addition, regarding the solubility parameter of the solvent not described in the above page, 52 of the polymer handbook.
A value derived by substituting the Hoy's cohesive energy constant described in page 525 into the Small's equation described in page 4 is applied.

The two or more surface cross-linking agents having different solubility parameter ranges are as follows: the first surface cross-linking agent has a solubility parameter (SP value) of 12.5 to 15.0 [(cal / c
m ³ ) ^1/2 ] and can react with a carboxyl group;
The second surface crosslinking agent has a solubility parameter of 12.5
It can react with a carboxyl group at less than [(cal / cm ³ ) ^1/2 ]. The reason why a water absorbing agent having excellent absorption capacity and absorption efficiency under pressure can be obtained by combining the first surface crosslinking agent and the second surface crosslinking agent having different solubility parameters from each other is not clear, but the water absorbing resin of the crosslinking agent is not known. This is probably because the penetration into the surface and the thickness of the crosslinks are controlled.

As the first surface cross-linking agent, specifically, ethylene glycol, propylene glycol,
Examples include ethylene carbonate and propylene carbonate, and one or more selected from these groups can be used. Also, as the second surface crosslinking agent,
Specifically, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl Ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, diethylene triamine, triethylene tetramine, epichlorohydrin, etc., and one or two selected from these groups. More than one species can be used.

Although the first surface cross-linking agent and the second surface cross-linking agent can be used separately, it is preferable to use them at the same time because they are simple and convenient. The amount of the surface cross-linking agent used depends on the compound used, the combination thereof, etc.
The amount of the first surface cross-linking agent is 0.0
1 to 5 parts by weight, the amount of the second surface crosslinking agent used is 0.001 to
The amount is preferably in the range of 1 part by weight, the amount of the first surface crosslinking agent used is 0.1 to 2 parts by weight, and the amount of the second surface crosslinking agent used is 0.0.
The content is more preferably in the range of from 0.5 to 0.5 parts by weight. If the amount of the surface cross-linking agent is too large, it becomes uneconomical and is not preferred. If the amount of the surface crosslinking agent is too small,
In improving the absorption efficiency of the water-absorbent resin under pressure, the improvement effect is difficult to obtain, which is not preferable.

When mixing the water-absorbing resin and the surface crosslinking agent, it is preferable to use water as a solvent. The amount of water used depends on the type and particle size of the water-absorbent resin, but is preferably more than 0 and 20 parts by weight or less, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the solid content of the water-absorbent resin. Is more preferably within the range of parts. In addition, when mixing the water-absorbing resin and the surface crosslinking agent, a hydrophilic organic solvent may be used as a solvent, if necessary. Examples of the above hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol; ketones such as acetone; dioxane And amides such as N, N'-dimethylformamide; and sulfoxides such as dimethylsulfoxide. The amount of the hydrophilic organic solvent used depends on the type and particle size of the water-absorbing resin, but is preferably 20 parts by weight or less, and more preferably 0.1 part by weight or less, based on 100 parts by weight of the solid content of the water-absorbing resin. More preferably, it is in the range of parts by weight.

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

The mixing device used for mixing the water-absorbing resin and the surface cross-linking agent preferably has a large mixing force in order to mix the two uniformly and reliably. Examples of the above mixing device include a cylindrical mixer, a double-walled conical mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a fluidized-type rotary desk mixer, a gas-flow mixer. A machine, a double-arm kneader, an internal mixer, a pulverizing kneader, a rotary mixer, a screw extruder and the like are suitable.

After mixing the water-absorbing resin and the surface crosslinking agent,
A heat treatment is performed to crosslink the vicinity of the surface of the water absorbent resin.
The temperature of the heat treatment depends on the surface cross-linking agent used, but is generally 90 ° C. or more and 250 ° C. or less. When the treatment temperature is lower than 90 ° C., a uniform crosslinked structure is not formed, and therefore, it is not possible to obtain a water-absorbing agent excellent in performance such as diffusion absorption capacity, which is not preferable. When the treatment temperature exceeds 250 ° C., the water absorbing agent is deteriorated, and the performance of the water absorbing agent is reduced, which is not preferable. More preferably, it is 160 ° C. or more and 250 ° C. or less.

The above heat treatment can be carried out using a usual dryer or heating furnace. Examples of the dryer include a groove-type mixing dryer, a rotary dryer, a desk dryer, a fluidized-bed dryer, a flash dryer, and an infrared dryer. The water-absorbing agent of the present invention thus obtained has an absorption capacity under pressure of 30 (g / g) or more and an absorption efficiency under pressure defined by the absorption capacity ratio in the height direction of the swollen gel in the measurement. Is not less than 0.7 and / or the absorption capacity of the lower layer under pressure close to the liquid absorption part of the swollen gel after the measurement is 45 (g / g) or more, and the absorption efficiency under the pressure is not more than 45 (g / g). It is 0.4 or more. The ratio of the absorption capacity in the height direction of the swollen gel is defined as the ratio of the gel between the layer near the contact portion with the liquid and the layer farthest from the liquid without directly contacting the liquid when the gel swells in a layer under pressure. The ratio of the absorption capacity, defined in the present invention as the ratio of the absorption capacity of the upper gel far from the liquid absorption part to the absorption capacity of the lower gel near the liquid absorption part after the measurement of the absorption capacity under pressure described below is performed This is also called absorption efficiency under pressure. Conventionally known water-absorbent resin has a high absorption capacity under pressure, but the absorption efficiency under pressure defined by the absorption capacity ratio in the height direction of the swollen gel is only about 0.5-0.6 at most. Was.
The water-absorbing agent of the present invention exhibits an unprecedented high value such as an absorption efficiency under pressure of 0.70 or more, preferably 0.75 or more, which is defined by an absorption capacity ratio in the height direction of the swollen gel, and The absorption capacity under pressure is as high as 30 (g / g) or more, preferably 35 (g / g) or more.

Further, conventionally known water-absorbing resins usually have an absorption capacity of the lower layer under pressure of only about 35 to 40 (g / g) at most, and none of them have a capacity of more than 45 (g / g). The water absorbing agent of the present invention exhibits a very high absorption capacity of the lower layer of 45 (g / g) or more under this pressurization. The absorption capacity under rolling is also increased.

The present invention also provides a water-absorbing agent having a high absorption capacity under pressure as a whole and a water-absorbing agent defined from the relationship between the absorption capacity of the lower layer under pressure and the absorption efficiency under pressure. That is, when the relationship between the absorption capacity of the lower layer under pressure and the absorption efficiency under pressure satisfies the following: absorption efficiency> 1.82-2.93 × 10 ⁻² × (absorption capacity of lower layer), The absorption capacity under pressure is high. However, if the absorption capacity of the lower layer is too low, the overall absorption capacity will be low even if the absorption efficiency is high. Therefore, the lower limit of the absorption capacity of the lower layer is set to 30 (g / g). If the absorption ratio is low, the overall absorption ratio will be low even if the absorption ratio of the lower layer is high, so the lower limit of the absorption efficiency was set to 0.3.

The water-absorbing agent of the present invention has excellent absorption characteristics under pressure, has a small difference in swelling ratio depending on the vertical position of the swelling gel layer, and has a characteristic of being able to swell uniformly to the inherent absorption capacity of the resin. It can be used very efficiently. Therefore, a thin absorbent article (for example, a disposable diaper) containing the water absorbing agent of the present invention at a high concentration of a water absorbing resin.
Even when applied to, it exhibits excellent absorption capacity and absorption efficiency under high load, so that the amount of absorption up to leakage is improved.

[0055]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the present invention,
Various properties of the water absorbing agent were measured by the following methods. (A) Absorption capacity 0.2 g of a water-absorbing agent was uniformly placed in a nonwoven fabric bag (60 mm × 60 mm) and immersed in a 0.9% by weight aqueous sodium chloride solution (physiological saline). After 60 minutes, the bag is pulled up and drained at 250 G for 3 minutes using a centrifuge, and then the weight of the bag W ₁ (g)
Was measured. The same operation was performed without using a water absorbing agent, and the weight W ₀ (g) at that time was measured. Then, from these weights W ₁ and W ₀ , the following formula: Absorption capacity (g / g) = (weight W ₁ (g) −weight W ₀ (g)) /
The absorption capacity (g / g) was calculated according to the weight (g) of the water absorbing agent. (B) Absorption Capacity Under Pressure First, a measuring apparatus used for measuring the absorption capacity under pressure will be briefly described below with reference to FIG.

As shown in FIG. 1, the measuring device is a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have. The container 2 has an opening 2a at the top and an opening 2b at the side surface thereof.
The outside air suction pipe 3 is fitted into the opening a, and the conduit 4 is attached to the opening 2b. Further, a predetermined amount of artificial urine 11 (composition: sodium sulfate 0.2% by weight, potassium chloride 0.2% by weight, magnesium chloride hexahydrate 0.05
% Aqueous solution of 0.025% by weight of calcium chloride dihydrate, 0.085% by weight of ammonium dihydrogen phosphate and 0.015% by weight of diammonium hydrogen phosphate). The lower end of the outside air suction pipe 3 is submerged in the artificial urine 11. The glass filter 6 has a diameter of 70 mm. The container 2 and the glass filter 6 are in communication with each other by the conduit 4. The upper part of the glass filter 6 is fixed at a position slightly higher than the lower end of the outside air suction pipe 3.

The measuring section 5 includes a filter paper 7 and a support cylinder 8.
And a wire mesh 9 attached to the bottom of the support cylinder 8, and a weight 10. Then, the measuring unit 5 places the filter paper 7 and the support cylinder 8 (that is, the wire mesh 9) on the glass filter 6 in this order, and places the weight 10 inside the support cylinder 8, that is, on the wire mesh 9. It has been. Support cylinder 8
Has an inner diameter of 60 mm. The wire mesh 9 is made of stainless steel and is formed in a 400 mesh (mesh size 38 μm). Then, a predetermined amount of the water-absorbing agent is evenly spread on the wire mesh 9. The weight of the weight 10 is adjusted so that a load of 50 g / cm ² can be uniformly applied to the wire mesh 9, that is, the water absorbing agent.

The absorption capacity under pressure was measured using the measuring apparatus having the above-mentioned structure. The measuring method will be described below. First, predetermined preparation operations such as putting a predetermined amount of artificial urine 11 into the container 2 and fitting the outside air suction pipe 3 into the container 2 were performed. Next, the filter paper 7 was placed on the glass filter 6. On the other hand, in parallel with these placing operations, 0.9 g of the water-absorbing agent was evenly sprayed on the inside of the support cylinder, that is, on the wire mesh 9, and the weight 10 was placed on the water-absorbing agent.

Next, the wire mesh 9, that is, the support cylinder 8 on which the water absorbing agent and the weight 10 were placed was placed on the filter paper 7. The weight W ₂ (g) of the artificial urine 11 absorbed by the water-absorbing agent was measured using the balance 1 over a period of 60 minutes after the support cylinder 8 was placed on the filter paper 7. Then, from the above weight W ₂ , the absorption under pressure 60 minutes after the start of absorption according to the following equation: absorption capacity under pressure (g / g) = weight W ₂ (g) / weight of water absorbing agent (g) Magnification (g /
g) was calculated. (C) Absorption efficiency under pressure Immediately after measuring the absorption capacity under pressure, a water-absorbing agent (swelled gel) that absorbs and swells artificial urine inside the support cylinder 8
The measuring unit 5 is removed from the measuring device for the absorption capacity under pressure (that is, the filter paper 7) while the weight 10 is placed in the presence of the filter 10 and 10 pieces of 90 mm diameter filter paper (No. 2 manufactured by Advantech Toyo Co., Ltd.) Place it on the stack for 2 minutes,
After removing the artificial urine (interstitial artificial urine not absorbed by the water-absorbing agent) present inside the support cylinder and between the swollen gel particles, the weight W is kept in a state where the swelling gel is present inside the support cylinder and the weight 10 is placed. ₃ (g) was measured. The weight W ₄ (g) and weight 1 of the support cylinder 8 measured in advance
The weight W ₅ (g) of 0 was subtracted from W ₃ (g), and the weight W ₆ (g) of the swollen gel after removing the interstitial artificial urine was determined.

Next, the weight 10 is removed from the support cylinder, and the swollen gel inside the support cylinder is removed from above by the weight W ₆ of the swollen gel.
Take out 1/3 weight of (g), top layer of gel, middle layer,
Lower layer. The upper layer of the removed gel was weighed into an aluminum cup, dried at 180 ° C. for 3 hours, and the absorption capacity G ₁ (g / g) of the upper layer of the gel was determined from the weight of the dried product. At this time, the absorption capacity of the gel was calculated assuming that the artificial urine component incorporated in the absorbent was 50%.

The same operation was performed for the lower layer of the gel taken out, and the absorption capacity G ₂ (g / g) of the lower layer of the gel was determined. The absorption efficiency under pressure was calculated according to the following equation. Absorption efficiency under pressure = G ₁ / G ₂ (d) Amount of eluted component The amount of eluted component is measured by a different method depending on the crosslinked polyacrylic acid partially neutralized product and other water-absorbent resins. In the case of a crosslinked product of a partially neutralized polyacrylic acid, a colloid titration method is used, and in the case of other water-absorbing resins, a gravimetric method is used.

* Colloid titration method 1.000 (g) of a water-absorbent resin was added to 25 (g) of a 0.9% by weight aqueous sodium chloride solution to uniformly swell. After 1 hour, the swollen water-absorbent resin was dispersed in 975 g of deionized water, stirred for 1 minute, and filtered with a filter paper. Next, 50 g of the obtained filtrate was placed in a 100 ml beaker, and 1 ml of 0.1 N sodium hydroxide and 1 ml of N / N were added to the filtrate.
200-methyl glycol chitosan aqueous solution was added to 10.00
ml and 4 drops of a 0.1% by weight aqueous solution of toluidine blue were added.

Next, the solution in the above beaker was added to N / 40
Colloidal titration was performed using an aqueous solution of 0-polyvinyl potassium sulfate, and the titration A (ml) was determined as the end point of the titration when the color of the solution changed from blue to magenta. The filtrate 5
The same operation was performed using 50 (g) of deionized water instead of 0 (g), and a blank titration was performed to obtain a titer B (ml). Then, from these titration amounts A and B and the neutralization ratio x (mol%) of the polyacrylic acid supplied to the water absorbent resin,

[0064]

(Equation 7)

The amount of the eluted component (% by weight) was calculated according to the following formula. * Gravimetric method 1.000 (g) of a water-absorbent resin is added to 25 (g) of a 0.9% by weight aqueous solution of sodium chloride to swell uniformly. After 1 hour, the swollen water-absorbent resin was dispersed in 975 g of deionized water, stirred for 1 minute, and filtered with a filter paper. Next, 50 g of the obtained filtrate was dried and the solid content was measured.

[0066]

(Equation 8)

The amount of the eluted component (% by weight) was calculated according to the following. (E) Molecular weight of eluted component Commercially available sodium polyacrylate of known molecular weight (peak molecular weight (Mp): 1100000, 782200, 467300, 392)
600, 272900, 193800, 115000, 28000, 16000, 7500, 2
(950, 1250) The weight average molecular weight of the eluted components sampled by the method (d) was determined by gel permeation chromatography using 12 types as standards. (F) Evaluation with Absorbent Article (Kewpie Doll Test) 75 parts by weight of a water-absorbing agent and 25 parts by weight of ground wood pulp
Dry mixing was performed using a mixer. Then, the obtained mixture was air-formed on a wire screen formed into a 400 mesh (mesh size of 38 μm) using a batch-type air-forming apparatus to obtain 120 mm × 350 mm.
Was formed into a web having a size of Further, the web was pressed at a pressure of 2 kg / cm ² for 5 seconds to obtain an absorbent having a basis weight of about 500 g / m ² .

Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impermeable polypropylene and having a so-called leg gather, the above-described absorber, and a top sheet (liquid-impermeable sheet) made of liquid-permeable polypropylene Sheets) were adhered to each other in this order using a double-sided tape, and two so-called tape fasteners were attached to the adhered product to obtain an absorbent article (that is, a paper diaper). The weight of this absorbent article was 44 g.

Each of the above-mentioned absorbent articles is attached to a so-called Kewpie doll (three 55 cm long and 5 kg weight), and the doll is placed face down. Then, a tube is inserted between the absorbent article and the doll. 70 ml of physiological saline was inject | poured into the position corresponding to the position which performs insertion and urination in the human body at intervals of 20 minutes at one time. Then, when the injected physiological saline was not absorbed by the absorbent article and leaked, the injection operation was terminated, and the number of injections up to this time was measured. Reference Example 1 5500 g of an aqueous solution of sodium acrylate having a neutralization ratio of 75 mol% (monomer concentration: 33% by weight)
In this solution, 3.56 g of polyethylene glycol diacrylate was dissolved to prepare a reaction solution. Next, this reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-armed kneader having two sigma-type blades and having an internal volume of 10 L, and while maintaining the reaction solution at 30 ° C., the system was purged with nitrogen. The gas was replaced. Subsequently, 2.4 g of ammonium persulfate and 0.12 g of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. And 30 ℃ ~ 80 ℃
, And the hydrogel polymer was taken out 60 minutes after the initiation of the polymerization.

The obtained hydrogel polymer was finely divided into a diameter of about 5 mm. The finely divided hydrogel polymer was spread on a 50-mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Next, the dried product was pulverized using a vibration mill, and further subjected to a classification operation to obtain a water-absorbent resin (a) having a particle size of less than 600 μm and not less than 300 μm. Of this,
The absorption capacity was 58 (g / g), and the amount of eluted components was 5.5.
(% By weight). The weight average molecular weight of the eluted component is 3
It was 50,000. Reference Example 2 100-mesh nylon bag (20 ×
30 cm) to the water-absorbent resin (a) 3 obtained in Reference Example 1.
(G) Three bottles were prepared, placed in a pipette washer having an internal volume of about 16 L, and left for 1 day under a flow of 1.6 L / min of deionized water.

After standing, the swollen water-absorbent resin was taken out of the nylon bag, dried with hot air at 80 ° C. for 24 hours, and classified to obtain a water-absorbent resin (b) having a particle size of less than 600 μm and 300 μm or more. However, the absorption capacity was 57
(G / g), the amount of the eluted component was 0.5 (% by weight), and the water content was 5.7 (% by weight). [Reference Example 3] Instead of being left for 1 day under a flow of 1.6 L / min of deionized water of Reference Example 2, 1.6 L / min of deionized water was used.
The water-absorbent resin (c) having a particle size in the range of less than 600 μm and 300 μm or more was obtained in the same manner as in Reference Example 2 except that the resin was allowed to stand for 7 days in a water flow.

The absorption capacity was 56 (g / g).
g), the amount of eluted components is 0.1 (% by weight), and the water content is 5.
8 (% by weight). Example 1 Water-absorbent resin (b) 100 obtained in Reference Example 2
Parts by weight, glycerin 0.03 parts by weight, ethylene glycol diglycidyl ether 0.05 parts by weight, water 3 parts by weight,
A surface crosslinking agent consisting of 5 parts by weight of isopropyl alcohol and 0.5 part by weight of lactic acid was mixed. Mix the above mixture at 180 ° C for 2
The water-absorbing agent (1) of the present invention was obtained by heating for 0 minutes. Table 1 shows the absorption capacity of the water absorbing agent (1), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. Example 2 Water-absorbent resin (c) 100 obtained in Reference Example 3
Parts by weight, glycerin 0.03 parts by weight, ethylene glycol diglycidyl ether 0.05 parts by weight, water 3 parts by weight,
A surface crosslinking agent consisting of 5 parts by weight of isopropyl alcohol and 0.5 part by weight of lactic acid was mixed. Mix the above mixture at 120 ° C for 1
The water-absorbing agent (2) of the present invention was obtained by heating for 5 minutes. Table 1 shows the absorption capacity of this water absorbing agent (2), absorption capacity under pressure, absorption capacity of the upper layer, absorption capacity of the lower layer, absorption efficiency under pressure, and the results of the Kewpie doll test. (Comparative Example 1) Water-absorbent resin (a) 100 obtained in Reference Example 1
Parts by weight, glycerin 0.03 parts by weight, ethylene glycol diglycidyl ether 0.05 parts by weight, water 3 parts by weight,
A surface crosslinking agent consisting of 5 parts by weight of isopropyl alcohol and 0.5 part by weight of lactic acid was mixed. Mix the above mixture at 180 ° C for 2
By heating for 0 minutes, a comparative water-absorbing agent (1) of the present invention was obtained. Table 1 shows the absorption capacity of this comparative water-absorbing agent (1), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test.
It described in. (Comparative Example 2) Water-absorbent resin (a) 100 obtained in Reference Example 1
In parts by weight, glycerin 0.7 part by weight, ethylene glycol diglycidyl ether 0.1 part by weight, water 4 parts by weight,
A surface crosslinking agent consisting of 5 parts by weight of isopropyl alcohol and 1 part by weight of lactic acid was mixed. Mix the above mixture at 180 ° C for 50
The comparative water-absorbing agent of the present invention (2)
I got Table 1 shows the absorption capacity of this comparative water-absorbing agent (2), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. Reference Example 4 5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% (monomer concentration 39% by weight)
In this solution, 23.43 g of polyethylene glycol diacrylate and 5.79 g of sodium hypophosphite monohydrate were dissolved to prepare a reaction solution. Next, this reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, the reaction solution was supplied to the reactor described in Reference Example 1, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ° C. Subsequently, while the reaction solution was stirred, 2.4 g of ammonium persulfate and 0.12 g of L-ascorbic acid were added, and polymerization started about 1 minute later. And 30 ℃ ~ 80
Polymerization was carried out at 60 ° C., and 60 minutes after the start of the polymerization, the hydrogel polymer was taken out.

The obtained hydrogel polymer was finely divided into a diameter of about 5 mm. This finely divided hydrogel polymer was spread on a 50-mesh wire mesh,
Hot air drying was performed for 0 minutes. Next, the dried product is pulverized using a vibration mill, and the particle size is further reduced to less than 600 μm by a classification operation.
The water-absorbent resin (d) as the above particles was obtained. It had an absorption capacity of 48 (g / g) and an elution component amount of 11.7.
(% By weight), and the weight-average molecular weight of the eluted component was 120,000.

A 100-mesh nylon bag (20 ×
30 cm) and 3 (g) of the obtained water-absorbent resin (d) were prepared, placed in a pipette washer having an internal volume of about 16 L, and placed under a flow of 1.6 L / min of deionized water. Left for days. After standing, the swollen water-absorbent resin was taken out of the nylon bag, dried with hot air at 80 ° C. for 24 hours, and further classified to obtain a water-absorbent resin (e) having a particle diameter of less than 600 μm and 300 μm or more.

The absorption capacity was 51 (g / g),
The eluted component amount was 0.1 (% by weight). (Example 3) The water-absorbent resin (e) 100 obtained in Reference Example 4
In parts by weight, ethylene glycol diglycidyl ether 0.1
A surface crosslinking agent consisting of 1 part by weight, 1 part by weight of propylene glycol, 3 parts by weight of water, and 2 parts by weight of isopropyl alcohol was mixed. The above mixture was heated at 120 ° C. for 15 minutes to obtain a water absorbing agent (3) of the present invention. Table 1 shows the absorption capacity of the water absorbing agent (3), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. [Reference Example 5] 5500 g of an aqueous solution of sodium acrylate having a neutralization ratio of 75 mol% (monomer concentration: 33% by weight)
4.96 g of polyethylene glycol diacrylate
Was dissolved to obtain a reaction solution. Next, the reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, sigma-type blades
The above-mentioned reaction solution was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ° C. Subsequently, 2.46 g of sodium persulfate and 0.10 g of L-ascorbic acid were stirred while the reaction solution was stirred.
Was added, polymerization started about 1 minute later. Then, polymerization is carried out at 30 ° C. to 80 ° C.
After one minute, the hydrogel polymer was taken out.

The obtained hydrogel polymer was finely divided into a diameter of about 5 mm. This finely divided hydrogel polymer was spread on a 50-mesh wire mesh,
Hot air drying was performed for 0 minutes. Next, the dried product is pulverized using a vibration mill, and the particle size is smaller than 500 μm by a classification operation.
A water-absorbent resin (f) having particles of 6 μm or more in 98% by weight of the whole was obtained. [Reference Example 6] Acrylic acid aqueous solution obtained by uniformly mixing 160.0 parts by weight of acrylic acid, 622.5 parts by weight of ion-exchanged water, and 0.342 parts by weight of N, N'-methylenebisacrylamide was used as a cylindrical container. And degassed with nitrogen gas. Then, while maintaining the aqueous acrylic acid solution at 15 ° C., 9.6 weight% aqueous solution of 2,2′-azobis (2-amidinopropane) dihydrochloride (trade name V-50, manufactured by Wako Pure Chemical Industries, Ltd.) And 4.5 parts by weight of a 3.5% by weight aqueous solution of hydrogen peroxide and 4.0 parts by weight of a 1% by weight aqueous solution of L-ascorbic acid were added as polymerization initiators and mixed. Was started and then the static adiabatic polymerization was continued for 1.5 hours. Further, the obtained hydrogel polymer was taken out of the reactor, placed in a kneader having a jacket at 70 ° C., and the blade was stirred for 20 minutes to shred the hydrogel into about 1 to 5 mm. After shredding, the mixture was neutralized with 1024.6 parts by weight of a 6.5% by weight aqueous solution of sodium hydroxide, and the mixture was uniformly neutralized using phenolphthalein as an indicator until the coloration of phenolphthalein was not completely observed. . Further, after the neutralized hydrogel was dried with a hot air drier at 160 ° C. for 1 hour, it was further pulverized with a tabletop pulverizer, and further classified by a classification operation to a particle size of less than 500 μm and 106 μm.
The above particles accounted for 97% by weight of the whole, and a water-absorbent resin (g) having a degree of neutralization of 75 mol% was obtained. [Reference Example 7] Acrylic acid aqueous solution obtained by uniformly mixing 160.0 parts by weight of acrylic acid, 622.5 parts by weight of ion-exchanged water, and 0.342 parts by weight of N, N'-methylenebisacrylamide was used as a cylindrical container. And degassed with nitrogen gas. Then, while maintaining the aqueous acrylic acid solution at 15 ° C., 9.6 weight% aqueous solution of 2,2′-azobis (2-amidinopropane) dihydrochloride (trade name V-50, manufactured by Wako Pure Chemical Industries, Ltd.) And 4.5 parts by weight of a 3.5% by weight aqueous solution of hydrogen peroxide and 4.0 parts by weight of a 1% by weight aqueous solution of L-ascorbic acid were added as polymerization initiators and mixed. Was started and then the static adiabatic polymerization was continued for 1.5 hours. Further, the obtained hydrogel polymer was taken out of the reactor, placed in a kneader having a jacket at 70 ° C., and the blade was stirred for 20 minutes to shred the hydrogel into about 1 to 5 mm. After shredding, the mixture was neutralized with 88.2 parts by weight of sodium carbonate, and was uniformly neutralized using phenolphthalein as an indicator until coloration of phenolphthalein could not be completely observed. Further, after the neutralized hydrogel was dried with a hot air drier at 160 ° C. for 1 hour, it was further pulverized with a tabletop pulverizer, and further classified by a classification operation so that particles having a particle size of less than 500 μm and 106 μm or more accounted for 97% by weight of the whole. A water-absorbent resin (h) having a degree of neutralization of 75 mol% was obtained. Example 4 Water-absorbent resin (f) 10 obtained in Reference Example 5
0 parts by weight, propylene glycol 0.1 parts by weight, glycerol polyglycidyl ether 0.03 parts by weight,
A surface crosslinking agent consisting of 3 parts by weight of water and 1 part by weight of isopropyl alcohol was mixed. Mix the above mixture at 195 ° C. for 5
Heat treatment was performed for 0 minutes to obtain a water absorbing agent (4) of the present invention. Table 1 shows the absorption capacity of the water absorbing agent (4), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. (Example 5) The water-absorbent resin (f) 10 obtained in Reference Example 5
A surface cross-linking agent consisting of 1.0 part by weight of propylene glycol, 0.03 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water, and 1 part by weight of isopropyl alcohol was mixed with 0 parts by weight. 185 ° C of the above mixture
For 35 minutes to obtain a water absorbing agent (5) of the present invention. Table 1 shows the absorption capacity of this water absorbing agent (5), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. (Example 6) Water-absorbent resin (g) 10 obtained in Reference Example 6
A surface cross-linking agent consisting of 1.0 part by weight of propylene glycol, 0.05 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water, and 3 parts by weight of isopropyl alcohol was mixed with 0 parts by weight. 190 ° C of the above mixture
For 50 minutes to obtain a water absorbing agent (6) of the present invention. Table 1 shows the absorption capacity of the water absorbing agent (6), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. (Example 7) The water absorbent resin (h) 10 obtained in Reference Example 7
0 parts by weight, 1 part by weight of ethylene carbonate, 0.03 parts by weight of ethylene glycol diglycidyl ether,
A surface crosslinking agent consisting of 3 parts by weight of water and 1 part by weight of isopropyl alcohol was mixed. The above mixture at 190 ° C. for 5
Heat treatment was performed for 0 minutes to obtain a water absorbing agent (7) of the present invention. Table 1 shows the absorption capacity of the water absorbing agent (7), the absorption capacity under pressure, the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. (Comparative Example 3) Water-absorbent resin (f) 10 obtained in Reference Example 5
A surface cross-linking agent consisting of 0.5 parts by weight of glycerin, 2 parts by weight of water, and 2 parts by weight of isopropyl alcohol was mixed with 0 parts by weight. The above mixture was heated at 190 ° C. for 50 minutes to obtain a comparative water-absorbing agent (3) of the present invention.
Absorption capacity of this comparative water-absorbing agent (3), absorption capacity under pressure,
Table 1 shows the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test. (Comparative Example 4) Water-absorbing resin (h) 10 obtained in Reference Example 7
A surface cross-linking agent composed of 0.5 parts by weight of glycerin, 0.05 parts by weight of glycerol polyglycidyl ether, 3 parts by weight of water, and 1 part by weight of isopropyl alcohol was mixed with 0 parts by weight. The above mixture was heated at 180 ° C. for 20 minutes to obtain a comparative water-absorbing agent (4) of the present invention.
Absorption capacity of this comparative water absorbing agent (4), absorption capacity under pressure,
Table 1 shows the absorption capacity of the upper layer, the absorption capacity of the lower layer, the absorption efficiency under pressure, and the results of the Kewpie doll test.

[0077]

[Table 1]

As is clear from the results shown in Table 1, the water-absorbing agent of the present invention exhibits high absorption efficiency under pressure. Such a water absorbing agent is, as in Examples 1 to 3,
The amount of the eluted component is 1 part by weight or less per 100 parts by weight of the water-absorbent resin. The water-absorbent resin is subjected to a heat treatment in the presence of a surface cross-linking agent, or as in Examples 4 to 7, It was first obtained by performing a heat treatment in the presence of two or more types of surface cross-linking agents having different solubility parameter ranges, after adjusting by classification or the like so as to be within a range of 106 μm or more and less than 500 μm.

[0079]

According to the water absorbing agent of the present invention and the method for producing the same, it is possible to obtain a water absorbing agent having a high absorption capacity under pressure and excellent absorption efficiency under pressure. Therefore, the water-absorbing agent of the present invention can be used in a water-absorbent article such as a disposable diaper or a sanitary napkin obtained by compounding a water-absorbent resin with a fibrous material, for example, 50% by weight (of a fibrous material such as pulp and a water-absorbent resin). When used under high-concentration conditions, such as the ratio to the total), the resin can exhibit sufficient absorption capacity even when a higher load is applied. In addition, the difference in the swelling ratio due to the vertical position of the swelling gel layer is small and the resin originally has Since the resin has the property of uniformly swelling up to the absorption capacity and the entire resin is used very efficiently, the amount of the resin used can be reduced and an even thinner absorbent article can be provided. Further, the water-absorbing agent of the present invention is preferably used for various applications such as a wound protecting material, an absorbent article for body fluids such as a wound healing material, a drip absorbing material for food, a freshness retaining material, a water stopping material, and a soil water retaining material. Can be used.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance 2 Container 3 External air suction pipe 4 Pipe 5 Measurement part 6 Glass filter 7 Filter paper 8 Support cylinder 9 Wire net 10 Weight 11 Artificial urine

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // A61F 13/46 C08J 7/00 301 C08J 7/00 A61F 13/18 307A 301 A41B 13/02 D

Claims (7)

[Claims] 1. A water absorbing agent having an absorption capacity under pressure of 30 (g / g) or more and an absorption efficiency represented by the following formula of 0.7 or more. (Equation 1) 2. The absorption capacity of the lower layer under pressure is 45 (g / g).
g) or more, and the absorption efficiency represented by the following formula is 0.4 or more. (Equation 2) 3. The absorption capacity of the lower layer under pressure is 30 (g / g).
g) or more, and the absorption efficiency represented by the following formula is 0.3
A water-absorbing agent in the above range, wherein the absorption efficiency and the absorption capacity of the lower layer satisfy the following formula. (Equation 3) Absorption efficiency> 1.8-2.93 × 10 ⁻² × (absorption ratio of lower layer) 4. A water-absorbent resin having an absorption capacity of 40 times or more and an elution component amount of 1 part by weight or less based on 100 parts by weight of the water-absorbent resin is subjected to heat treatment in the presence of a surface crosslinking agent. A method for producing a water absorbing agent. 5. The method for producing a water absorbing agent according to claim 4, wherein the water absorbing resin is treated with a hydrophilic solution. 6. A method for producing a water-absorbing agent, comprising: treating a water-absorbent resin polymerized in the presence of a water-soluble chain transfer agent with a hydrophilic solution, followed by heat treatment in the presence of a surface crosslinking agent. 7. A method for producing a water-absorbing agent, comprising: treating a water-absorbent resin having a weight-average molecular weight of eluted components of 200,000 or less with a hydrophilic solution, followed by heat treatment in the presence of a surface crosslinking agent.