JP2918808B2 - Absorber and absorbent article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absorbent body and an absorbent article suitably used for sanitary materials such as paper diapers (disposable diapers) and sanitary napkins, so-called incontinence pads.

[0002]

2. Description of the Related Art In recent years, sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, have been used as constituent materials thereof.
BACKGROUND ART Water-absorbing resins for the purpose of absorbing body fluids are widely used.

Examples of the above water-absorbing resin include cross-linked polyacrylic acid partially neutralized products (JP-A-55-84304,
JP-A-55-108407, JP-A-55-133413),
Hydrolyzate of starch-acrylonitrile graft polymer (JP-A-46-43995), neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468), vinyl acetate-acrylate Saponified polymer (JP-A-52
-14689), a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer (JP-A-53-15959) or a crosslinked product thereof, a cross-linked product of a cationic monomer (JP-A-58-154709) And JP-A-58-154710).

[0004] The properties that the above water-absorbent resin should have include excellent water absorption and water absorption speed when in contact with aqueous liquids such as body fluids, gel strength, and suction power for sucking water from a substrate containing the aqueous liquid. Is mentioned. Conventionally, a water-absorbing resin having a plurality of these properties and exhibiting excellent performance (water-absorbing properties) when used in sanitary materials such as disposable diapers and sanitary napkins, or using the water-absorbing resin. Various absorbers and absorbent articles have been proposed.

[0005] Examples of the above-mentioned conventional water-absorbent resin or an absorbent or an absorbent article using the water-absorbent resin include, for example, a water-absorbent resin having a specific gel capacity, shear modulus and extractable polymer content (US Patent No. 4,654,039), a water-absorbing resin having a specified amount of water absorption, a water-absorbing speed, and gel strength;
-185550, JP-A-60-185551, JP-A-60-1
No. 85804), a disposable diaper using a water-absorbing resin having a specific water absorption amount, water absorption speed and gel stability (Japanese Patent Application Laid-Open No. 60-18580).
No. 5), a water-absorbent article provided with a water-absorbent resin having specified water absorption, suction power, and water-soluble component (JP-A-63-21902), water absorption, water absorption under pressure, gel destruction Water-absorbing sanitary articles containing water-absorbing resin with specified strength (Japanese Unexamined Patent Publication No. 63-998
No. 61), a disposable diaper containing a water-absorbent resin having a specified amount of water absorption and a rate of water absorption under pressure (JP-A-2-34167),
Water-absorbing agent containing water-absorbing resin with specified water absorption under pressure and its particle size (European Patent No. 339,461), water-absorbing resin with specified water absorption rate and water absorption under pressure in a short time A water-absorbing agent (European Patent No. 443,627) containing the above, a water-absorbing composite material (European Patent No. 532,002) containing a specific amount or more of a water-absorbing resin having a specified deformation and a wicking index under load and the like are known.

On the other hand, in recent years, hygienic materials such as disposable diapers and sanitary napkins have become more sophisticated and thinner, and the amount of water-absorbing resin used per sanitary material, or mainly water-absorbing resin and hydrophilic properties There is a tendency that the weight% (hereinafter, referred to as resin concentration) of the water-absorbent resin in the absorbent made of the conductive fiber increases. In other words, less hydrophilic fibers with a low bulk specific gravity,
By increasing the amount of the water-absorbing resin which is excellent in water-absorbing property and has a large bulk specific gravity, the ratio of the water-absorbing resin in the absorber is increased, thereby reducing the thickness of the sanitary material without reducing the water absorption.

[0007]

However, as a result of various studies conducted by the present inventors to increase the amount of water absorbed by the sanitary material, for example, to increase the resin concentration in the absorber, it was found that the resin concentration was higher than before. Using the absorber
In addition, it has been found that in order to prevent inconvenience such as leakage of an aqueous liquid from a sanitary material, it is not sufficient to simply control the above-described characteristics such as the amount of water absorption, water absorption speed, gel strength, and suction force. For example, in the case of a water-absorbent resin that has been particularly noticed in recent years and has only a very large amount of water absorption under pressure, when the resin concentration is increased, a phenomenon that the liquid diffusibility in the absorber is extremely reduced occurs. Have a point.

The inventors of the present application have conducted various studies focusing on the water absorption characteristics of an absorber having a higher resin concentration than before, and as a result, have found that a mixture of a known water-absorbent resin and hydrophilic fibers is used as an absorber. When used as a resin, when the resin concentration is low, it exhibits a certain level of water absorption characteristics, but the resin concentration is 40% by weight.
It was found that the liquid diffusivity sharply decreased when the ratio exceeded the limit, and the water absorption per unit weight of the absorber decreased. That is, when a mixture of a known water-absorbent resin and hydrophilic fibers is used as an absorber, the above-described problems occur.

Accordingly, an object of the present invention is to solve the above-mentioned problems. For example, when used for sanitary materials and the like, even if the resin concentration of the water-absorbing resin is increased, the liquid diffusibility and the extremely high liquid diffusivity are always high. An object of the present invention is to provide a water-absorbent resin, an absorbent, and an absorbent article that can exhibit excellent performance (water-absorbing properties) such as maintaining a water absorption amount.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on water-absorbing resins, absorbers and absorbent articles in order to achieve the above object, and as a result, synthesized a specific water-absorbing resin precursor. Heat-treating this water-absorbent resin precursor in the presence of a specific surface cross-linking agent, the water-absorbent resin obtained by the production method, that is, the absorber and the absorbent article containing the water-absorbent resin, Excellent performance not provided by water-absorbent resin (water-absorbing properties), such as maintaining a very high liquid diffusivity and water absorption even when the amount of water-absorbent resin used is high or the resin concentration is high. They have found that they have excellent performance, and have completed the present invention.

That is, in order to solve the above problems, the absorbent according to the first aspect of the present invention comprises 40% by weight of a water-absorbent resin having a diffusion absorption capacity of 25 g / g or more after 60 minutes from the start of absorption. It is characterized by including the above.

According to a second aspect of the present invention, there is provided an absorber according to the first aspect, wherein:
The diffusion absorption capacity after 30 minutes from the start of absorption of the water absorbent resin is
It is characterized by being 15 g / g or more.

According to a third aspect of the present invention, there is provided an absorbent body according to the first or second aspect, wherein the absorbent fiber comprises a hydrophilic fiber, and comprises a water-absorbent resin and the hydrophilic fiber. It is characterized in that the amount of the water-absorbing resin relative to the total amount is 50% by weight or more.

According to a fourth aspect of the present invention, there is provided an absorbent article comprising an absorbent layer including the absorbent body according to any one of the first to third aspects, wherein the absorbent layer has a liquid permeability. And a sheet having liquid impermeability.

In order to solve the above-mentioned problems, the water-absorbent resin of the invention according to claim 5 has a diffusion absorption capacity of 15 g / g or more after 30 minutes from the start of absorption, and has a diffusion absorption capacity of 60 g or more after 60 minutes. It is characterized in that the absorption capacity is 25 g / g or more.

In order to solve the above-mentioned problems, the water-absorbent resin of the invention according to claim 6 has a diffusion absorption capacity of 15 g / g or more 20 minutes after the start of absorption, and a diffusion capacity of 60 minutes after the start of absorption. It is characterized by an absorption capacity of 30 g / g or more.

According to a seventh aspect of the present invention, there is provided a method for producing a water-absorbent resin, wherein the average particle size is 200 μm.
Within the scope of m to 600 .mu.m, a particle size ratio of 5 wt% or less of particles less than 106 [mu] m, the water-absorbing resin precursor having a carboxyl group, capable of reacting with the carboxyl group, the solubility parameter is 12.5 (cal / cm ³ ) ^1/2 or more first surface crosslinking agent,
And, by performing a heat treatment in the presence of a second surface crosslinking agent having a solubility parameter of less than 12.5 (cal / cm ³ ) ^1/2 ,
Water absorption with a diffusion absorption capacity of 25 g / g or more after 60 minutes from the start
It is characterized by obtaining a conductive resin .

Hereinafter, the present invention will be described in detail. The diffusion absorption capacity in the present invention, the basis weight of the water-absorbent resin is high, and taking into account the diffusion force of the aqueous liquid in a state where the resin particles are in close contact with each other by external force, to evaluate the water absorption of the absorber Are new physical property values. The above-mentioned diffusion absorption capacity is calculated from a measured value after a predetermined time from the start of absorption, for example, 60 minutes after measurement under a predetermined condition. Diffuse absorption
The method of measuring the magnification will be described in detail.

(A) Diffusion Absorption Ratio First, a measuring device used for measuring the diffusion absorption ratio is described below.
A brief description is given below with reference to FIGS.

As shown in FIG. 1, the measuring device comprises a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have. The container 2 has an opening 2a at the top and an opening 2b at the side surface thereof.
The outside air suction pipe 3 is fitted into the opening a, and the conduit 4 is attached to the opening 2b. The container 2 contains a predetermined amount of physiological saline 12. The lower end of the outside air suction pipe 3 is submerged in the physiological saline 12. The glass filter 6 is formed to have a diameter of 70 mm. And
The container 2 and the glass filter 6 are in communication with each other by a conduit 4. The glass filter 6 is fixed at a position slightly higher than the lower end of the outside air suction pipe 3.

As shown in FIG. 2, the measuring section 5 includes a filter paper 7, a sheet 8, a support cylinder 9, a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11. doing. Then, the measuring unit 5 places the filter paper 7, the sheet 8, and the support cylinder 9 (that is, the wire mesh 10) on the glass filter 6 in this order, and also, inside the support cylinder 9, that is, the wire mesh 1.
The weight 11 is placed on the zero. Sheet 8
It is made of polyethylene terephthalate (PET), and is formed in a 0.1 mm-thick donut shape having an opening with a diameter of 18 mm at the center. The support cylinder 9 has an inner diameter of 60 mm. The wire mesh 10 is made of stainless steel, and is formed in 400 mesh (mesh size 38 μm). Then, a predetermined amount of the water-absorbing resin is evenly spread on the wire mesh 10. The weight of the weight 11 is adjusted so that a load of 20 g / cm ² can be uniformly applied to the wire netting 10, that is, the water-absorbing resin.

The diffusion absorption capacity was measured using the measuring device having the above-mentioned configuration. The measuring method will be described below.

First, predetermined preparation operations such as putting a predetermined amount of physiological saline 12 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, and the sheet 8 was placed on the filter paper 7 such that the opening was located at the center of the glass filter 6. On the other hand, in parallel with these placing operations, 1.5 g of a water-absorbent resin (preferably, a water-absorbent resin whose particle diameter has been previously adjusted to 300 μm to 500 μm by an operation such as classification, etc.) 1.5 g) was evenly dispersed, and a weight 11 was placed on the water absorbent resin.

Next, the wire cylinder 10, that is, the support cylinder 9 on which the water-absorbent resin and the weight 11 are placed is placed on the sheet 8 such that the center of the support cylinder 9 coincides with the center of the glass filter 6. .

The weight W of the physiological saline 12 absorbed by the water-absorbent resin for 20 minutes, 30 minutes, or 60 minutes after the support cylinder 9 is placed on the sheet 8
₂ (g) was measured using the balance 1. As shown in FIG. 3, after passing through the opening of the sheet 8, the physiological saline 12 diffuses almost uniformly in the lateral direction of the water-absorbing resin.
Water was absorbed by the water absorbent resin.

Then, based on the above weight W ₂ , the following equation was obtained: 30 minutes after the start of water absorption, according to the following formula: diffusion absorption capacity (g / g) = weight W ₂ (g) / weight of water-absorbent resin (g). After or after 60 minutes, the diffusion absorption capacity (g / g) was calculated.

The new characteristics of the water-absorbent resin can be evaluated by the diffusion absorption capacity. That is, the diffusion absorption capacity determines how uniformly and quickly the water-absorbent resin can diffuse the aqueous liquid in the direction of the resin layer (hereinafter, referred to as the lateral direction). Can be evaluated. The liquid diffusivity (liquid diffusion capacity and liquid transfer capacity) of the aqueous liquid in the lateral direction is a particularly important factor in absorbing a large amount of the aqueous liquid. Then, from the results of the above evaluation, for example, the absorbent composed mainly of the water-absorbent resin and the hydrophilic fiber, in particular, the water-absorbent resin in the absorbent having a high weight percent (hereinafter referred to as resin concentration) of the water-absorbent resin is high. Water absorption behavior can be easily predicted. The structure of the absorber will be described later.

In the above-mentioned prior application, there are many documents which evaluate the amount of water absorption under pressure. However, the conventional evaluation of the water absorption is performed only in a direction perpendicular to the resin layer direction (hereinafter, referred to as a vertical direction). For this reason, it is hardly evaluated how uniformly and quickly the aqueous liquid diffuses in the lateral direction. Therefore, from the results of the conventional evaluation described above, for example, in a disposable diaper or the like using an absorber having a high resin concentration, the water absorption behavior of the absorber cannot be accurately predicted.

The absorbent of the present invention contains 40% by weight of a water-absorbent resin having a diffusion absorption capacity of 25 g / g or more after 60 minutes from the start of absorption.
Or more, more preferably 50% by weight or more, still more preferably
It contains at least 60% by weight, most preferably at least 70% by weight. A water-absorbent resin with a diffusion absorption capacity of less than 25 g / g after 60 minutes from the start of absorption has poor lateral liquid diffusivity in an absorber with a high resin concentration (high concentration), and the absorption capacity of the absorber is low. Become smaller. The diffusion absorption capacity 60 minutes after the start of absorption is 28
g / g or more is more preferable, 30 g / g or more is more preferable, and 32 g / g or more is most preferable. In addition, the diffusion absorption
Even if it contains more than 25 g / g of water-absorbent resin, the ratio is 40
When the amount of the absorber is less than the weight%, the effect may be hardly remarkably exhibited. In the present invention, the diffusion absorption capacity is defined as a measured value after a predetermined time from the start of absorption in the measurement under predetermined conditions.In addition to the above diffusion absorption capacity, further, 20 minutes after the start of absorption Alternatively, a water-absorbent resin having a diffusion absorption capacity of 15 g / g or more calculated from the measured value after 30 minutes is more preferable.

That is, it is more preferable that the water-absorbent resin has a diffusion absorption capacity of 15 g / g or more after 30 minutes from the start of absorption and a diffusion absorption capacity of 25 g / g or more after 60 minutes. , The diffusion absorption capacity after 20 minutes from the start of absorption is 15 g / g or more,
And it is more preferable that the diffusion absorption capacity after 60 minutes is 25 g / g or more, and the diffusion absorption capacity after 20 minutes from the start of absorption is
15 g / g or more, and the diffusion absorption capacity after 60 minutes is 28 g
/ g or more is more preferable, the diffusion absorption capacity after 20 minutes from the start of absorption is 15 g / g or more, and the diffusion absorption capacity after 60 minutes is most preferably 30 g / g or more. . A water-absorbent resin having a diffusion absorption capacity of less than 15 g / g after 30 minutes from the start of absorption may have poor lateral liquid diffusivity, which may cause a decrease in the absorbency of the absorber.

The absorbent of the present invention may contain hydrophilic fibers, if necessary, in addition to the water absorbent resin. When the absorber is made of, for example, a water-absorbent resin and hydrophilic fibers, the structure of the absorber may be, for example, a structure in which a water-absorbent resin and hydrophilic fibers are uniformly mixed, or a layered hydrophilic material. A structure in which a water-absorbent resin is sandwiched between fibers, a structure in which a water-absorbent resin and hydrophilic fibers are uniformly mixed and formed into a layer, and a layer in which the layer-formed hydrophilic fibers are laminated, a water-absorbent resin and A hydrophilic fiber is uniformly mixed to form a layer, and
A configuration in which a water-absorbing resin is sandwiched between hydrophilic fibers formed in a layer shape and the like can be given. Further, the absorber may have a structure in which a specific amount of water is mixed with the water-absorbing resin to form the water-absorbing resin into a sheet. still,
The configuration of the absorber is not limited to the configuration described above.

Examples of the above-mentioned hydrophilic fibers include cellulose fibers such as mechanical pulp, chemical pulp, semi-chemical pulp and dissolved pulp obtained from wood, and artificial cellulose fibers such as rayon and acetate. Among the fibers exemplified above, cellulose fibers are preferred. In addition, hydrophilic fibers, polyamide and polyester,
It may contain synthetic fibers such as polyolefin.
In addition, the hydrophilic fiber is not limited to the fiber exemplified above.

Of the above-mentioned constitutions, a constitution in which the water-absorbent resin and the hydrophilic fiber are uniformly mixed so that the ratio of the water-absorbent resin in the absorber is 40% by weight or more is more preferable. The water-absorbent resin and the hydrophilic fibers are uniformly mixed so that the amount of the water-absorbent resin with respect to the total amount of the hydrophilic fibers is 50% by weight or more, preferably 60% by weight or more, and more preferably 70% by weight or more. A mixed configuration is more preferred. With these configurations, the absorber can sufficiently exhibit its water absorbing properties. Note that the higher the resin concentration in the absorber, the more remarkable the characteristics of the absorber of the present invention appear.

When the ratio of the hydrophilic fibers in the absorber is relatively small, the absorbers, that is, the hydrophilic fibers may be bonded to each other using an adhesive binder. By adhering the hydrophilic fibers to each other, the strength and shape retention of the absorber before and during use of the absorber can be increased.

Examples of the adhesive binder include heat-fusible fibers such as polyolefin fibers such as polyethylene, polypropylene, ethylene-propylene copolymer and 1-butene-ethylene copolymer, and emulsions having adhesive properties. . These adhesive binders may be used alone or as a mixture of two or more. The weight ratio between the hydrophilic fiber and the adhesive binder is 50 / 50-99.
/ 1, preferably in the range of 70/30 to 95/5, and more preferably in the range of 80/20 to 95/5.

The water-absorbent resin according to the present invention can be obtained by a production method comprising synthesizing a specific water-absorbent resin precursor and heat-treating the water-absorbent resin precursor in the presence of a specific surface crosslinking agent. Can be The above water-absorbent resin precursor has an average particle diameter in the range of 200 μm to 600 μm and a particle diameter of 1 μm.
The proportion of particles smaller than 06 μm is 10% by weight or less, and
It is a resin having a carboxyl group that forms a hydrogel by absorbing a large amount of water. The water absorbing resin precursor is synthesized, for example, by aqueous solution polymerization. Specific examples of the water-absorbent resin precursor include, for example, a crosslinked product of partially neutralized polyacrylic acid, a hydrolyzate of starch-acrylonitrile graft polymer, a neutralized product of starch-acrylic acid graft polymer, and acetic acid. Saponified vinyl-acrylate copolymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or cross-linked product thereof, carboxyl group-containing cross-linked polyvinyl alcohol-modified product, cross-linked isobutylene-maleic anhydride copolymer, etc. Is mentioned.

The above-mentioned water-absorbent resin precursors include, for example, unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, β-acryloyloxypropionic acid and the like. After polymerizing or copolymerizing one or more monomers selected from neutralized products of the above, the polymer is subjected to operations such as pulverization and classification as necessary to adjust the average particle size to the above. can get. Among the above monomers, (meth) acrylic acid and their neutralized products are more preferable.

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

The content of the carboxyl group in the water-absorbing resin precursor is not particularly limited, but it is preferable that the carboxyl group is present in an amount of 0.01 equivalent or more per 100 g of the water-absorbing resin precursor. When the water-absorbent resin precursor is, for example, a crosslinked product of a partially neutralized polyacrylic acid, the ratio of the unneutralized polyacrylic acid in the crosslinked product is in the range of 1 mol% to 60 mol%. Desirable, 10 mol%
More preferably, it is in the range of 5050 mol%.

The interior of the water absorbing resin precursor is preferably crosslinked by reacting or copolymerizing with a crosslinking agent having a plurality of polymerizable unsaturated groups or a plurality of reactive groups. Further, the water-absorbing resin precursor may be a self-crosslinking type that does not require a crosslinking agent. Specific examples of the crosslinking agent include N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylolpropane. Di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth)
Acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol di Glycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate and the like can be mentioned. These crosslinking agents may be used alone or as a mixture of two or more. Among the compounds exemplified above, it is more preferable to use a compound having a plurality of polymerizable unsaturated groups as a crosslinking agent.

The amount of the cross-linking agent used is preferably in the range of 0.005 mol% to 2 mol%, and
More preferably, it is in the range of 05 mol% to 1 mol%. If the amount of the crosslinking agent used is less than 0.005 mol%, or if it is more than 2 mol%, the diffusion / absorption capacity of the water-absorbing resin is undesirably reduced.

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

The above-mentioned water-absorbent resin precursor has a diffusion absorption capacity that does not satisfy the preferred range in the present invention.
For this reason, it is necessary to use a specific surface cross-linking agent to make the cross-linking density near the surface of the water-absorbent resin precursor higher than that inside. That is, by crosslinking the vicinity of the surface of the water-absorbent resin precursor using the specific surface cross-linking agent, the water-absorbent resin according to the present invention can be obtained.

That is, the water-absorbent resin according to the present invention has a water-absorbent resin precursor obtained by the above-described aqueous solution polymerization, that is, an average particle diameter in the range of 200 μm to 600 μm, and a particle diameter of less than 106 μm. After adjusting by such operations as classification so that the ratio of particles is 10% by weight or less, the water-absorbent resin precursor is subjected to heat treatment in the presence of two or more surface cross-linking agents having different solubility parameter ranges. can get. The water-absorbent resin, that is, the water-absorbent resin precursor, may be granulated into a predetermined shape, or may be various shapes such as a sphere, a scale, an irregular crushed shape, and a granular shape. Further, the water-absorbing resin precursor may be a primary particle or a granulated primary particle. still,
When the average particle size is out of the range of 200 to 600 μm,
If the proportion of particles having a particle size of less than 106 μm exceeds 10% by weight, it may not be possible to obtain a water-absorbing resin having excellent properties such as diffusion absorption capacity.

The above surface cross-linking agent is obtained by combining a first surface cross-linking agent and a second surface cross-linking agent having different solubility parameters (SP values). The above-mentioned solubility parameter is a value generally used as a factor indicating the polarity of a compound. In the present invention, the above-mentioned solubility parameters are compared with the Polymer Handbook, 3rd edition (WI
The value of the solubility parameter δ (cal / cm ³ ) ^1/2 of the solvent described on pages 527 to 539 is applied. Further, regarding the solubility parameters of the solvents not described in the above-mentioned page, the small-sized equation described in page 524 of the polymer handbook is used.
The value derived by substituting Hoy's cohesive energy constant described on page 25 will be applied.

The first surface cross-linking agent is preferably a compound capable of reacting with a carboxyl group and having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more, more preferably 13.0 (cal / cm ³ ) ^1/2 or more. Compounds are more preferred. Examples of the first surface cross-linking agent include ethylene glycol, propylene glycol, glycerin, pentaerythritol, sorbitol, ethylene carbonate (1,3-dioxolan-2-one),
Propylene carbonate (4-methyl-1,3-dioxolan-2-one) and the like, but are not limited to these compounds. These first surface cross-linking agents may be used alone or in combination of two or more.

The second surface crosslinking agent is preferably a compound capable of reacting with a carboxyl group and having a solubility parameter of less than 12.5 (cal / cm ³ ) ^1/2 , and 9.5 (cal / cm ³ ) ^{1/2 to} 12.0 (cal / c
Compounds in the range m ³ ) ^1/2 are more preferred. As the second surface cross-linking agent, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol,
1,3-butanediol, 1,4-butanediol,
1,5-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2,5-hexanediol, trimethylolpropane, diethanolamine,
Triethanolamine, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylenediamine, diethylenetriamine, triethyleneamine Ethylenetetramine, 2,4-tolylenediisocyanate, hexamethylenediisocyanate, 4,5-dimethyl-1,3-dioxolan-2-one, epichlorohydrin, epibromohydrin, and the like, but are not limited to these compounds. It is not something to be done. These second surface cross-linking agents may be used alone or in combination of two or more.

In the present invention, as the surface cross-linking agent, one or more compounds selected from the group of the first surface cross-linking agents, and one or two types selected from the group of the second surface cross-linking agents It is necessary to use the above compounds in combination. When only one or two or more first surface cross-linking agents are used, or when only one or two or more second surface cross-linking agents are used, water absorption having excellent performance such as diffusion absorption capacity There is a possibility that resin cannot be obtained.

The amount of the surface cross-linking agent used depends on the compound to be used and the combination thereof. However, the amount of the first surface cross-linking agent is preferably 0.1 to 100 parts by weight of the solid content of the water absorbent resin precursor.
01 parts by weight to 5 parts by weight, the amount of the second surface crosslinking agent used is 0.001
Preferably, the amount of the first surface cross-linking agent is in the range of 0.1 to 2 parts by weight, and the amount of the second surface cross-linking agent is in the range of 0.005 to 0.5 parts by weight. preferable. By using the above surface cross-linking agent, the cross-linking density in the vicinity of the surface of the water-absorbent resin precursor, that is, the water-absorbent resin can be made higher than that of the inside. The amount of surface crosslinking agent used
If the amount exceeds 10 parts by weight, not only is it uneconomical, but the amount of the surface cross-linking agent becomes excessive in forming the optimum cross-linked structure in the water-absorbing resin, which is not preferable. If the amount of the surface cross-linking agent used is less than 0.001 part by weight, it is difficult to obtain the effect of improving the performance of the water-absorbent resin, such as the diffusion absorption capacity, and therefore, it is not preferable.

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

When mixing the water-absorbing resin precursor with the surface crosslinking agent, a hydrophilic organic solvent may be used as a solvent, if necessary. As the above hydrophilic organic solvent,
For example, lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol; ketones such as acetone;
Ethers such as dioxane and tetrahydrofuran;
Amides such as N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; and the like. The amount of the hydrophilic organic solvent used depends on the type and particle size of the water-absorbent resin precursor, but is preferably 20 parts by weight or less, and more preferably 0.1 part by weight, based on 100 parts by weight of the solid content of the water-absorbent resin precursor. More preferably, it is within the range of 10 to 10 parts by weight.

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

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

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

The above-mentioned heat treatment can be performed 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-absorbent resin obtained by the above production method has a diffusion absorption capacity of 15 g / g or more 30 minutes after the start of absorption, and a diffusion absorption capacity of 25 g / g or more after 60 minutes. is there. Further, the absorber of the present invention contains the above water-absorbing resin in an amount of 40% by weight or more. For this reason, the absorber has excellent water absorption characteristics as described above. Therefore, for example, when used in absorbent articles, the absorbent retains extremely high liquid diffusivity and water absorption even when the amount of water-absorbent resin used is large or the resin concentration in the absorbent is high. And excellent performance (water absorption properties).

The reason why the absorbent using the water-absorbent resin according to the present invention exhibits very excellent performances such as diffusion absorption capacity is not clear, but the liquid diffusion and liquid transmission of the aqueous liquid in the absorbent are not clear. On the other hand, in the conventional absorber, the absorption is performed by the capillary phenomenon of the hydrophilic fiber, whereas in the absorber according to the present invention, the water absorption having an excellent diffusion absorption capacity obtained by performing a specific surface crosslinking method. It is presumed that the high liquid diffusibility (liquid diffusing ability and liquid transmitting ability) of the water-soluble resin is sufficiently exhibited even in the absorber.

Further, the absorbent article according to the present invention comprises an absorbent layer including the absorbent having the above-described structure sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. And since the said absorbent article has the absorption layer containing the absorber of the said structure, it is provided with the above-mentioned excellent water absorption characteristics. Specific examples of the absorbent article include, but are not particularly limited to, sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads.
Since the absorbent article has excellent water-absorbing properties, for example, when the absorbent article is a paper diaper, it is possible to prevent urine from leaking and to impart a so-called dry feeling.

The above liquid-permeable sheet (hereinafter, referred to as a liquid-permeable sheet) is made of a material having a property of permeating an aqueous liquid. Examples of the material of the liquid-permeable sheet include a nonwoven fabric and a woven fabric; a porous synthetic resin film made of polyethylene, polypropylene, polyester, polyamide, or the like. The sheet having the liquid impermeability (hereinafter, referred to as a liquid impermeable sheet) is made of a material having a property of impermeable to an aqueous liquid. As a material of the liquid impermeable sheet, for example, a synthetic resin film made of polyethylene, polypropylene, ethylene vinyl acetate, polyvinyl chloride, or the like; a film made of a composite material of these synthetic resin and nonwoven fabric; And the like.
The liquid impermeable sheet may have a property of transmitting vapor.

The structure of the absorbing layer is not particularly limited, as long as it has the above-mentioned absorber. Further, the method for producing the absorbing layer is not particularly limited. further,
The method of sandwiching the absorbent layer between the liquid-permeable sheet and the liquid-impermeable sheet, that is, the method for producing the absorbent article is not particularly limited.

In addition, a deodorant, a fragrance,
Various inorganic powders, foaming agents, pigments, dyes, hydrophilic short fibers,
Fertilizers, oxidizing agents, reducing agents, water, salts and the like may be added, thereby giving the absorber or the absorbent article various functions.

[0062]

As described above, the water-absorbing resin having the above-mentioned structure can exhibit excellent performance (water-absorbing properties) such as extremely high liquid diffusivity and water absorption. In addition, the absorbent having the above-described structure exhibits excellent performance such as maintaining a very high liquid diffusivity and water absorption, even when the amount of the water-absorbing resin used is large or the resin concentration in the absorbent is high. be able to. The above-mentioned absorber can be particularly suitably used for an absorbent article such as a disposable diaper or a sanitary napkin, a sanitary material such as a so-called incontinence pad, for which high functionality and thinness are desired. Thereby, an absorbent article exhibiting the above-described excellent performance can be provided.

[0063]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. In addition, various properties of the water absorbent resin and the absorber were measured by the following methods.

(B) Water Absorption Ratio 0.2 g of the water-absorbent resin was uniformly placed in a nonwoven 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 lifted up, and drained at 250 G for 3 minutes using a centrifuge.
₁ (g) was measured. Further, the same operation was performed without using the water-absorbing resin, and the weight W ₀ (g) at that time was measured. Then, from these weights W ₁ · W ₀ , the water absorption capacity (g / g) = (weight W ₁ (g) −weight W ₀ (g)) / weight (g) of the water-absorbent resin is calculated according to the following equation: g / g) was calculated.

(C) Diffusion Absorption Ratio of Absorber First, a measuring device used for measuring the diffusion absorption ratio of the absorber will be briefly described below with reference to FIGS. 4 and 5. For the sake of convenience, the same reference numerals are given to components having the same functions as those of the measuring device used for measuring the diffusion absorption ratio, and description thereof is omitted.

As shown in FIG. 4, the measuring device is a balance 1
, Container 2, outside air suction pipe 3, conduit 4, diameter 1
It is composed of a glass filter 6 having a size of 20 mm and a measuring unit 15 mounted on the glass filter 6. As shown in FIG. 5, the measuring unit 15 has the filter paper 7, the sheet 8, the support square tube 19, and the weight 11.
The wire mesh is not provided.

The measuring section 15 has a filter paper 7, a sheet 8, and a support square tube 19 placed in this order on the glass filter 6, and a weight 11 placed inside the support square tube 19. The sheet 8 is made of polyethylene terephthalate, and is formed in a rectangular shape with a thickness of 0.1 mm having a rectangular opening of 12.5 mm × 100 mm at the center. Support square tube 19
Has an inner dimension of 100 mm x 100 mm. Then, an absorber having a predetermined size is placed inside the support square tube 19. Other configurations of the measuring device are the same as those of the measuring device used for measuring the diffusion absorption capacity.

The diffusion absorption capacity of the absorber was measured using the measuring device having the above-mentioned configuration. The measuring method will be described below.

First, the absorber was formed in a size of 100 mm × 100 mm. Further, a predetermined preparation operation was performed. Next, the filter paper 7 was placed on the glass filter 6, and the sheet 8 was placed on the filter paper 7 such that the opening was located at the center of the glass filter 6. Next, the supporting square tube 19 was placed on the sheet 8 such that the center portion thereof coincided with the center portion of the glass filter 6.

Thereafter, the absorber was placed inside the support rectangular tube 19, that is, on the sheet 8, and the weight 11 was placed on the absorber. The operation of placing the absorber and the weight 11 was performed quickly.

Then, the weight W ₃ (g) of the physiological saline 12 absorbed by the absorber for 30 minutes or 60 minutes from the time when the absorber was placed on the sheet 8 was measured using the balance 1. did. In addition, as shown in FIG.
After passing through the opening of the sheet 8, water was absorbed by the absorber while diffusing almost uniformly in the lateral direction in the absorber.

From the above weight W ₃ , 30 minutes after the start of water absorption, according to the following equation: diffusion absorption capacity (g / g) of absorber: weight W ₃ (g) / weight of absorber (g) Alternatively, the diffusion absorption capacity (g / g) of the absorber after 60 minutes was calculated.

Example 1 To 5500 g of a 30% by weight aqueous solution of sodium acrylate (neutralization ratio: 65 mol%) as a monomer, polyethylene glycol diacrylate as a cross-linking agent (average number of moles of ethylene oxide added: 8) 18.49 g was dissolved to obtain 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 inner volume of 10 L and having a capacity of 30 L.
The system was replaced with nitrogen gas while maintaining the temperature at ° C. Subsequently, 2.3 g of ammonium persulfate and L-
When 0.12 g of ascorbic acid was added, polymerization started about 1 minute later. Then, polymerization was carried out at 30 ° C. to 80 ° C., and 60 minutes after the initiation of the polymerization, the hydrogel polymer was taken out.

The resulting 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 is crushed using a vibration mill, and further classified using a 20-mesh wire net to form an amorphous crushed material having an average particle diameter of 360 μm and a particle size of less than 106 μm in which the ratio of particles is 5% by weight. A water-absorbent resin precursor was obtained.

To 100 parts by weight of the obtained water-absorbent resin precursor,
Glycerin as the first surface crosslinking agent (SP value: δ = 16.5
(cal / cm ³ ) ^1/2 ) 1 part by weight and ethylene glycol diglycidyl ether (SP value: δ =
10.2 (cal / cm ³ ) ^1/2 ) A surface cross-linking agent consisting of 0.05 part by weight, 3 parts by weight of water, and 1 part by weight of ethyl alcohol was mixed. The above mixture was heated at 195 ° C. for 40 minutes to obtain a water-absorbing resin. The average particle size of the obtained water-absorbent resin was 360 μm, and the ratio of particles having a particle size of less than 106 μm was 5% by weight. The water absorption capacity and diffusion absorption capacity (hereinafter simply referred to as results) of the water-absorbent resin are also shown in Table 1.

Example 2 3.59 g of trimethylolpropane triacrylate as a crosslinking agent was dissolved in 5500 g of a 39% by weight aqueous solution of sodium acrylate (neutralization ratio: 75 mol%) 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 similar to the reactor of Example 1, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ° C. 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 ° C
Polymerization was carried out at 8080 ° C., 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 is crushed using a vibration mill, and further classified using a 20-mesh wire gauze to form an irregular size crushed powder having an average particle size of 400 μm and a particle size of less than 106 μm in which the ratio of particles is 5% by weight. A water-absorbent resin precursor was obtained.

To 100 parts by weight of the obtained water-absorbent resin precursor,
Ethylene glycol (SP value:
δ = 14.6 (cal / cm ³ ) ^1/2 ) 0.5 part by weight and glycerol polyglycidyl ether (SP
Value: δ = 10.8 (cal / cm ³ ) ^1/2 ) A surface cross-linking agent composed of 0.1 part by weight, 3 parts by weight of water, and 1 part by weight of ethyl alcohol was mixed. The above mixture was heated at 195 ° C. for 40 minutes to obtain a water-absorbing resin. The average particle size of the obtained water-absorbent resin was 400 μm, and the ratio of particles having a particle size of less than 106 μm was 3% by weight. The results of the water-absorbent resin are shown in Table 1.

Example 3 N, N'-methylenebisacrylamide 2.35 as a crosslinking agent was added to 5500 g of a 20% by weight aqueous solution of sodium acrylate.
g was dissolved to obtain 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 similar to the reactor of Example 1, and the reaction solution was
While maintaining the temperature at 30 ° C., the system was replaced with nitrogen gas. Subsequently, 1.5 g of ammonium persulfate and L
-When 0.07 g of ascorbic acid was added, polymerization started about 1 minute later. Then, polymerization is performed at 30 ° C to 80 ° C,
60 minutes after the start of polymerization, sodium carbonate as a neutralizing agent
After further adding 606.7 g and stirring, the hydrogel polymer was taken out.

The resulting hydrogel polymer had a neutralization ratio of 75 mol% and had 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 is crushed using a vibration mill, and further classified using a 20-mesh wire net, to form an irregular-sized crushed material having an average particle size of 390 μm and a particle size of less than 106 μm at a ratio of 4% by weight. A water-absorbent resin precursor was obtained.

To 100 parts by weight of the obtained water-absorbing resin precursor,
Propylene glycol (SP) as first surface crosslinking agent
Value: δ = 12.6 (cal / cm ³ ) ^1/2 ) 0.75 parts by weight and propylene glycol diglycidyl ether (SP value: δ = 10.1 (cal / cm ³ ) ^1/2 ) 0.05 as the second surface crosslinking agent A surface crosslinking agent consisting of 3 parts by weight of water, 3 parts by weight of water and 0.75 parts by weight of ethyl alcohol was mixed. The above mixture was heated at 195 ° C. for 40 minutes to obtain a water-absorbing resin. The average particle size of the obtained water-absorbent resin is 390 μm, and the particle size is 106 μm.
The proportion of particles less than 3% by weight. The results of the water-absorbent resin are shown in Table 1.

Comparative Example 1 A reaction solution was prepared by dissolving 7.18 g of trimethylolpropane triacrylate as a crosslinking agent in 5500 g of a 39% by weight aqueous solution of sodium acrylate (neutralization ratio: 75 mol%). Next, this reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere.
Next, the reaction solution was supplied to a reactor similar to the reactor of Example 1, and the system was purged with nitrogen gas while maintaining the reaction solution at 30 ° C. Subsequently, while stirring the reaction solution, 5.0 g of sodium persulfate and 0.25 g of L-ascorbic acid were added, and polymerization started about 1 minute later. And 30 ℃ ~
Polymerization was carried out at 80 ° C., and a hydrogel polymer was taken out 60 minutes after the initiation of the polymerization.

The obtained hydrogel polymer was subdivided 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 is crushed using a vibration mill, and further classified using a 20-mesh wire net to form an amorphous crushed material having an average particle diameter of 360 μm and a particle size of less than 106 μm in which the ratio of particles is 5% by weight. Thus, a comparative water-absorbent resin was obtained. The results of the obtained comparative water absorbent resin are shown in Table 1.

Comparative Example 2 The same reaction and operation as in Comparative Example 1 were carried out except that 18.67 g of N, N′-methylenebisacrylamide was used as a crosslinking agent instead of trimethylolpropane triacrylate in Comparative Example 1. To obtain an amorphous crushed comparative water-absorbent resin having an average particle diameter of 400 μm and a ratio of particles having a particle diameter of less than 106 μm of 3% by weight. The results of the obtained comparative water absorbent resin are shown in Table 1.

Comparative Example 3 A partially neutralized and crosslinked acrylic acid polymer (trade name: Aquaric CA W4; manufactured by Nippon Shokubai Co., Ltd.) was used as a comparative water absorbent resin. The obtained results are shown in Table 1.

Comparative Example 4 A partially neutralized and crosslinked starch-acrylic acid graft polymer (trade name: Sunwet IM3900P; manufactured by Hoechst Celanese Corporation) was used as a comparative water-absorbent resin. The obtained results are shown in Table 1.

Comparative Example 5 A partially neutralized and crosslinked acrylic acid polymer (trade name: DiaWet US2-45Z; manufactured by Mitsubishi Yuka Co., Ltd.) was used as a comparative water absorbent resin. The obtained results are shown in Table 1.

Comparative Example 6 A partially neutralized and crosslinked acrylic acid polymer (trade name: AquaKeep SA-60; manufactured by Sumitomo Seika Co., Ltd.) was used as a comparative water absorbent resin. The obtained results are shown in Table 1.

Comparative Example 7 A water-absorbent resin was taken out of a paper diaper called Mummy Poko (trade name) manufactured by Unicharm Co., Ltd. and used as a comparative water-absorbent resin. The obtained results are shown in Table 1.

[0090]

[Table 1]

Example 4 45 parts by weight of the water-absorbent resin obtained in Example 1 and 55 parts by weight of ground wood pulp as hydrophilic fibers were dry-mixed using a mixer. After the obtained mixture was formed into a web having a size of 100 mm x 100 mm, the web was pressed at a pressure of 2 kg / cm ^2.
Press for 1 minute at a basis weight of about 0.050 g / cm ²
Was obtained. The diffusion absorption capacity (hereinafter, simply referred to as a result) of the obtained absorber is also shown in Table 2.

Example 5 50 parts by weight of the water-absorbent resin obtained in Example 1 and 50 parts by weight of ground wood pulp were dry-mixed using a mixer. The obtained mixture was formed into a web having a size of 100 mm × 100 mm, and the web was pressed at a pressure of 2 kg / cm ² for 1 minute to obtain an absorbent having a basis weight of about 0.047 g / cm ² . The results of the obtained absorber are also shown in Table 2.

Example 6 60 parts by weight of the water-absorbent resin obtained in Example 1 and 40 parts by weight of ground wood pulp were dry-mixed using a mixer. The obtained mixture was formed into a web having a size of 100 mm × 100 mm, and the web was pressed at a pressure of 2 kg / cm ² for 1 minute to obtain an absorbent having a basis weight of about 0.041 g / cm ² . The results of the obtained absorber are also shown in Table 2.

Example 7 75 parts by weight of the water-absorbent resin obtained in Example 1 and 25 parts by weight of ground wood pulp were dry-mixed using a mixer. The obtained mixture was formed into a web having a size of 100 mm × 100 mm, and the web was pressed at a pressure of 2 kg / cm ² for 1 minute to obtain an absorbent having a basis weight of about 0.035 g / cm ² . The results of the obtained absorber are also shown in Table 2.

Examples 8 and 9 In Example 7, except that the water absorbent resins obtained in Examples 2 and 3 were used in place of the water absorbent resin obtained in Example 1, respectively. In the same manner as in Example 7, an absorber was obtained. The results of the obtained absorber are also shown in Table 2.

Comparative Example 8 The procedure of Example 4 was repeated, except that the comparative water absorbent resin obtained in Comparative Example 1 was used instead of the water absorbent resin obtained in Example 1. To obtain a comparative absorber. The results of the obtained comparative absorber are also shown in Table 2.

Comparative Example 9 In the same manner as in Example 5, except that the comparative water absorbent resin obtained in Comparative Example 1 was used instead of the water absorbent resin obtained in Example 1, To obtain a comparative absorber. The results of the obtained comparative absorber are also shown in Table 2.

Comparative Example 10 The procedure of Example 6 was repeated, except that the comparative water-absorbent resin obtained in Comparative Example 1 was used instead of the water-absorbent resin obtained in Example 1. To obtain a comparative absorber. The results of the obtained comparative absorber are also shown in Table 2.

Comparative Examples 11 to 17 In Example 7, the comparative water absorbent resins obtained in Comparative Examples 1 to 7 were respectively used in place of the water absorbent resin obtained in Example 1. Except for the above, a comparative absorber was obtained in the same manner as in Example 7. Table 2 shows the results of the comparative absorber thus obtained.
It is described in accordance with.

[0100]

[Table 2]

Example 10 50 parts by weight of the water-absorbent resin obtained in Example 1 and 50 parts by weight of ground wood pulp were dry-mixed using a mixer. Subsequently, the obtained mixture was sifted with a 400 mesh
μm) by using a batch-type air-paper-making machine to form air on a wire screen of 120 mm ×
It was formed into a web having a size of 400 mm. 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 0.047 g / cm 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-permeable 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 46 g.

The above-mentioned absorbent article is mounted on a so-called Kewpie doll (55 cm in length and 5 kg in weight), and the doll is placed in a prone state. At a position corresponding to the position to be performed, 50 ml of physiological saline was sequentially injected at a time interval of 20 minutes. Then, when the injected physiological saline was not absorbed by the absorbent article and leaked out, the above injection operation was terminated, and the amount of the physiological saline injected up to this time was measured.

After repeating the above measurement four times,
The average of the obtained measured values was determined, and this value was used as the absorption amount.
As a result, the absorbed amount was 250 g.

Comparative Example 18 The procedure of Example 10 was repeated, except that the comparative water absorbent resin obtained in Comparative Example 1 was used instead of the water absorbent resin obtained in Example 1. To obtain a comparative absorbent article. The comparative absorbent article weighed 46 g.

Using the above comparative absorbent article, the same measurement as in Example 10 was repeated four times, and the average of the obtained measured values was determined. This value was taken as the amount of absorption. As a result, the absorbed amount was 225 g.

As is apparent from the results shown in Tables 1 and 2, the water-absorbent resin and the absorber of the present invention have a high diffusion / absorption ratio and have a very high liquid diffusivity. In other words, the difference between the water absorbing properties of the water absorbent resin and the absorbent of the present invention and the water absorbent properties of the comparative water absorbent resin and the absorbent, especially, increases as the resin concentration in the absorbent increases. Recognize. Also, as is clear from the results described in Example 10 and Comparative Example 18,
It can be seen that the absorbent article of the present invention exhibits excellent performance (water absorption properties) such as maintaining a very high absorption (water absorption) as compared with the comparative absorbent article.

[0108]

The above-mentioned water-absorbing resin has excellent performance (water-absorbing properties) such as extremely high liquid diffusivity and water absorption.
Can be shown. In addition, the above-mentioned absorber exhibits excellent performance such as maintaining a very high liquid diffusivity and water absorption even when the amount of the water-absorbing resin used is large or the resin concentration in the absorber is high. This has the effect that it can be performed. The above-mentioned absorber can be particularly suitably used for an absorbent article such as a sanitary material such as a disposable diaper or a sanitary napkin, a so-called incontinence pad, for which high functionality and thinness are desired. Thereby, there is an effect that an absorbent article exhibiting the above-described excellent performance can be provided.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a main part of the measuring device.

FIG. 3 is an explanatory diagram illustrating a diffusion direction of a physiological saline in the measuring device.

FIG. 4 is a schematic cross-sectional view of a measuring device used for measuring a diffusion absorption capacity, which is one of the properties exhibited by the absorber in the present invention.

5 is a sectional view of a main part of the measuring device of FIG.

FIG. 6 is an explanatory diagram illustrating a diffusion direction of a physiological saline in the measuring device of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance 2 Container 3 External air suction pipe 4 Conduit 5 Measuring part 6 Glass filter 7 Filter paper 8 Sheet 9 Support cylinder 10 Wire mesh 11 Weight 12 Physiological saline 15 Measuring part 19 Square prism

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichi Fujino 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo Nippon Shokubai Polymer Research Laboratory Co., Ltd. (1) References JP-A-2-132103 (JP, A) JP-A-6-184320 (JP, A) JP-A-7-88171 (JP, A) Kaihei 8-57310 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B01J 20/26 C08F 8/00

Claims (7)

(57) [Claims] 1. A diffusion absorption capacity of 25 g after 60 minutes from the start of absorption.
An absorber comprising 40% by weight or more of a water-absorbent resin having a weight of at least 40 g / g. 2. The absorbent body according to claim 1, wherein a diffusion absorption capacity 30 minutes after the start of absorption of the water-absorbent resin is 15 g / g or more. 3. The absorber according to claim 1, wherein the absorbent contains hydrophilic fibers and the amount of the water-absorbent resin is at least 50% by weight based on the total amount of the water-absorbent resin and the hydrophilic fibers. . 4. An absorbent layer comprising the absorbent body according to any one of claims 1 to 3, wherein the absorbent layer is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. An absorbent article characterized by the following. 5. The diffusion absorption capacity after 15 minutes from the start of absorption is 15 g.
/ g and a diffusion absorption capacity after 60 minutes of 25 g / g or more. 6. The diffusion absorption capacity after 20 minutes from the start of absorption is 15 g.
/ g and a diffusion absorption capacity after 60 minutes of 30 g / g or more. 7. An average particle diameter in a range of 200 μm to 600 μm.
And the proportion of particles with a particle size of less than 106 μm5% by weight or less
The water-absorbing resin precursor having a carboxyl group
A solubility parameter of 12.5 (c
al / cm^Three)^1/2The above first surface cross-linking agent and solubility parameter
Meter is 12.5 (cal / cm^Three)^1/2The presence of less than the second surface crosslinker
Heat treatment underAs a result, expansion 60 minutes after the start of absorption
Obtain a water-absorbent resin with a scattering capacity of 25 g / g or moreThat
A method for producing a water-absorbent resin.