DESCRIPTION

WATER-ABSORBING AGENT HAVING WATER-AB

RESIN AS A MAIN COMPONENT AND PRODUCTIO

OF THE WATER-ABSORBING AGENT

TECHNICAL FIELD

The present invention relates to a water-abs

having a water-absorbent resin as a main comp

production method of the water-absorbing agent

BACKGROUND ART

Recently, in order to absorb body fluids su

blood, and the like , a water-absorbent resin is wi

a mam component of an absorbent structure conc

fluid absorption in sanitary materials (absorbi

such as a disposable diaper, a sanitary

incontinence pad, and the like

Known examples of the water-absorbent resi

crosslinked lsobutylene-maleic acid copolymer, a

polymer of 2-acrylamide-2 -methylpropanesulfoni

acrylic acid, and the like

There has conventionally been nee

water-absorbent resin having the following wate

characteristics (i) a high absorbency, (ii) a

absorption rate, (in) excellent liquid perme

excellent gel strength of a swollen gel, (v) a

absorptive power (absorbing and wicking pro

water is absorbed from a base material containing

liquid, (vi) and the like, with respect to an aq

such as a body fluid

In recent years, a sanitary material such as

diaper has higher performance and a thinner s

amount (g) of the water-absorbent resin use

sanitary material is increased and also a ratio (

the water-absorbent resin is increased with res

whole absorbent structure, thereby making t

material thinner while increasing the absorption

such that a liquid (urine or blood) which

subsequently absorbed cannot permeate into th

structure, so that an absorption amount drops

occurs

Recently, the liquid permeability of the wat

resin attracts attentions and a great numbe

concerning a water-absorbent resin having hi

permeability are reported (for example , see Patent

1 to 7) For example, it is known that partic

distribution greatly contributes to the liquid per

example , see Patent Documents 8 to 1 1 ) , and ther

a technique in which volume of pore in the gel a

by increasing particle diameters so as to enhanc

permeability (for example, see Patent Document

document)

However, there is a problem that if the vol

in the gel are increased by increasing the particl

so as to enhance the liquid permeability, the li

absorbed As a method for solving such a probl

Further, as a method which allows enhance

liquid permeability without crosslinking a sur

water-absorbent resin, there is disclosed a

producing a polymer having high liquid permeabi

absorption capacity (low absorbency) by cro

polymer with use of two types of covalent bond

agents such as a polyvinyl crosslinking ag

crosslinking agent having a hydroxyl group (for

Patent Document 13 and other document)

[Patent Document 1 ]

Pamphlet of International Publication No 95

[Patent Document 2]

Specification of European Patent No 095 19 1

[Patent Document 3]

Specification of European Patent No 064033

[Patent Document 4]

Pamphlet of International Publication No 20

[Patent Document 5]

Pamphlet of International Publication No 98

Specification of USP 5,051,259

[Patent Document 9]

Specification of European Patent No 034924

[Patent Document 10]

Specification of European Patent No 057976

[Patent Document 11]

Specification of European Patent No 062941

[Patent Document 12]

Japanese Unexamined Patent Public

154758/2005 (Tokukai 2005-154758)

[Patent Document 13]

Japanese National Publication of Translated

518150/2003 (Tokuhyo 2003-518150)

DISCLOSURE OF INVENTION

However, the water-absorbent resin w

permeability is enhanced by the conventional

higher liquid permeability but is not sufficiently

view of the entire water-absorption characteristics

Further, according to the method in which

crosslinked with use of two types of cov

crosslinkmg agents such as a polyvinyl crossli

and a crosslinkmg agent having a hydroxyl

possible to achieve the high liquid permeabilit

S possible to produce only a polymer whose absorbe

The present invention was made in view of t

problems, and an object of the present invention

(i) a water-absorbent resin whose liquid per

enhanced without dropping the wate

characteristics such as the absorptive power, th

rate , the absorbency, and the like , and (ii) a wat

agent having the water-absorbent resin , and (in)

method thereof, based on finding of a method fo

the liquid permeability in a manner differen

conventional method

The inventors of the present invention dilige

in view of the foregoing problems As a result o

they polymerized an unsaturated monomer havin

of solely using an internal crosshnkmg agent hav

less functional groups each capable of forming

bond with a carboxyl group or (b) a case of using

crosshnkmg agent together with an internal

agent having two or more polymeπzable ethyle

bonds They first found that the liquid perm

greatly enhanced through the foregoing operati

completing the present invention

In order to solve the foregoing

water-absorbing agent of the present invention i

mam component a water-absorbent resin having a

structure obtained by polymerizing an unsaturat

having a carboxyl group, wherein at least

molecular compound having four or more functi

each capable of forming a covalent bond with

group is introduced into an mside of the wat

resin

Further, the water-absorbing agent may be

as to include as a main component a water-abs

resm is crosslinked with at least a part of t

molecular compound introduced into the in

water-absorbent resin

The water-absorbent resin may be arrange

least a part of the non high molecular compound

any functional group capable of forming a covale

a carboxyl group does not form a bond with t

group of the water-absorbent resin

Note that, in the present invention, a con

which "a non high molecular compound having f

functional groups each capable of forming a co

with a carboxyl group is introduced into an insi

condition under which the non high molecular c

distributed over the whole water-absorbent resin

water-absorbent resin particles, and this is di

surface crosslinking and surface coatin

water-absorbent resin or the water-absorbent res

That is, there has been conventionally known a

which an outermost surface (for example , 0 0 1 to

solvent (for example, 0 1 to 10 weight % of wate

the water-absorbent resin particles) is used at

necessary, so that the compound (surface crossl

or surface coating agent) is unevenly distribut

outermost surface of the water-absorbent resi

thereby causing the compound (surface crosslink

surface coating agent) to be unevenly distribut

outermost surface and causing the compou

crosslinkmg agent or surface coating agent) to

concentration as it is positioned more internally,

compound (surface crosslinkmg agent or sur

agent) does not substantially exist in the in

water-absorbent resin particles In contrast,

invention is characterized in that the non hig

compound is distributed over or crosslinks

water-absorbent resin or the whole water-abs

particles and preferably the non high molecular

substantially evenly distributed over or crosslin

water-absorbent resin (including the mside the

water-absorbing agent, there is included 100 pp

the non high molecular compound in which an

group capable of forming a covalent bond with

group does not form a bond with the carboxyl

water-absorbent resin

It is preferable that a molecular weight of t

molecular compound is not more than 5000 F

preferable that a functional group equivalent w

non high molecular compound is not less than

more than 200 g/ mol

It is preferable that the mside of the wat

resin is further crosslinked with an internal

agent having two or more polymeπzable ethyle

bonds per molecule, and / or an internal crossh

other than the non high molecular compound wh

crosshnkmg agent has two or more functional

molecule Above all, it is preferable that the wat

resin is further subj ected to internal crosshnk

internal crosshnkmg agent having two or more p

whose particle diameter is not less than 1 50 μm a

850 μm is not less than 90 weight % with respe

amount of the water-absorbent resin particles

Further, it is preferable that each of th

groups each capable of forming a covalent b

carboxyl group is a hydroxyl group or an ammo gr

In addition, the water-absorbing agent of

invention further includes a liquid-permeabihty-e

agent Further, it is preferable that in case where

water-absorbing agent is dispersed in 50 ml of a

saline whose temperature is 20 ⁰ C so as t

water-absorbing agent dispersion liquid, a surfac

the water-absorbing agent dispersion liquid is n

55 mN / m

It is preferable to arrange the water-absorb

the present invention so that an absorbency (

water-absorbing agent is greater than 25 g/ g

preferable to arrange the water-absorbing agent of

invention so that a saline flow conductivity (

method includes the steps of (i) polymerizing the

monomer having a carboxyl group and included in

monomer solution in the presence of at least

molecular compound having four or more functi

each capable of forming a covalent bond with

group, so as to obtain a hydropolymer, and (ii)

hydropolymer, obtained in the step (i) , so as to

water-absorbent resin, wherein relative to the

monomer having a carboxyl group, an amount

(mol %) of the non high molecular compound is i

expressed by the following equation ( 1 )

Y< 0 06 / {2- ( l 35X/ 100)} ( 1 )

where X represents a neutralization ratio (m

carboxyl group of the water-absorbent resin, X be

than 45 and not more than 85

It is preferable that the step (i) is suc

unsaturated monomer having a carboxyl group a

in the aqueous monomer solution is polymer

presence of ( 1 ) the non high molecular compound

molecule , so as to obtain the hydropolymer F

more preferable that the step (i) is such that the

monomer having a carboxyl group and inclu

aqueous monomer solution is polymerized in the

( 1 ) the non high molecular compound having f

functional groups each capable of forming a co

with a carboxyl group and (2) an internal crossli

having two or more polymeπzable ethylenical d

per molecule, so as to obtain the hydropolymer

In addition, it is preferable that the method

the present invention for producing the water-abs

further includes the step of (in) crosslinkmg a s

water-absorbent resin with an organic surface

agent and/ or an inorganic surface crosslinkmg ag

Further, it is preferable that the method acc

present invention for producing the water-abso

further includes the step of (iv)

liquid-permeabihty-enhancement agent It is pre

the hquid-permeability-enhancement agent is a w

As described above, the water-absorbing age

to the present invention includes as a main c

water-absorbent resin having a crosslinke

obtained by polymerizing an unsaturated mono

carboxyl group, wherein at least a non hig

compound having four or more functional g

capable of forming a covalent bond with a carbo

introduced into an inside of the water-absorbe

that it is possible to remarkably enhance

permeability compared with a case where

crosslinking agent having three or less functional

capable of forming a covalent bond with a carbo

solely used or a case where an internal crossli

having three or less functional groups and

crosslinking agent having two or more p

ethylenical double bonds are used together with

Also, it is possible to provide the water-absorbent

liquid permeability is enhanced without dr

water-absorption characteristics such as the abso

crosslinking agent (third crosslinking agent) oth

non high molecular compound which internal

agent has two or more functional groups, the

after the polymerization is improved, so that t

characteristics and the water absorbing pro

improved

As described above, the method according to

invention for producing the water-absorbing ag

the arrangement for introducing at least a non hi

compound having four or more functional g

capable of forming a covalent bond with a carbox

an inside of a water-absorbent resin by poly

unsaturated monomer in the presence of th

molecular compound Thus, it is possible to

enhance the liquid permeability compared with a

an internal crosslinking agent having three or les

groups each capable of forming a covalent b

carboxyl group is solely used or a case where

crosslinking agent having three or less functional

BRIEF DESCRIPTION OF DRAWINGS

Fig 1 is a cro ss sectional view schematically

a measuring apparatus used to measure AAP

Fig 2 is a cross sectional view schematically

a measuring apparatus used to measure SFC

BEST MODE FOR CARRYING OUT THE INVENTION

The following explains a water-absorbing

present invention and a method for pro

water-absorbing agent Further, in the presen

assume that values of (a) absorbency (CRC

Retention Capacity) , (b) AAP (Absorbency Agains

(c) absorption rate (FSR Free Swell Rate) , (d)

Flow Conductivity, (e) particle diameter, (f)

standard deviation (σζ) of particle diameter dist

Bulk density, (h) extractable component conte

content or moisture content, (j) surface tensi

amount of unreacted non high molecular compoun

The water-absorbing agent according to

invention contains, as a main component, a wat

resin obtained by polymerizing an unsaturate

having a carboxyl group, wherein the water-abs

has a crosslinked structure, and at least

molecular compound having four or more functi

each capable of forming a covalent bond with

group is introduced into an inside of the wat

resin (preferably is evenly introduced

water-absorbent resin) It is preferable that th

molecular compound introduced in the ms

water-absorbent resm forms a bond with the car

of the water-absorbent resin, and it is more pre

the non high molecular compound crosslinks the i

water-absorbent resin Note that, at least a part

high molecular compound may be such that an

group capable of forming a covalent bond with

group is contained in the water-absorbent re

forming a bond with the carboxyl grou

water-absorbent resin is regarded as one of t

which at least the non high molecular compound

or more functional groups each capable of formin

bond with a carboxyl group is introduced into an

water-absorbent resin

Note that, in the present invention, the

molecular compound" means a compound other

molecular compound The "high molecular compo

a compound obtained by polymerization or means

existing compound, having same structural part

formed, whose molecular weight (weight-averag

weight) is greater than 5000

The water-absorbing agent in the presen

refers to an agent for absorption and solidificatio

liquids, which agent comprises the water-absorb

the main component and, if necessary, further

small amount of additive and/ or water The "wat

resin as the mam component" herein refers to 50

more water-absorbent resin content relative to

regarded as the water-absorbing agent of

invention As a component other than the wat

resin in the water-absorbing agent, usually

contained as its main component, and further

below-mentioned additive is used Note that,

liquid is free from especial limitation if it con

Examples of the aqueous liquid include water,

excrement, waste liquids, moisture , steam, ice ,

water and organic and / or inorganic solvents , rai

underground water However, preferably, the wat

agent of the present invention is used as a

absorption and solidification of urine , particul

urine

The following will describe ( 1 - 1 ) Water-abs

contained in the water-absorbing agent of

invention, ( 1 -2) Components other than the wat

resin, ( 1 -3) Shape and particle diamet

water-absorbent resin and water-absorbing

Water-absorbing characteristics of the water-abs

unsaturated monomer having a carboxyl group, a

crosslinked structure , wherein at least a non hig

compound having four or more functional g

capable of forming a covalent bond with a carbo

introduced into an inside of the water-absorben

the non high molecular compound preferably fo

with a carboxyl group in the water-absorbent res

preferably crosslinks the mside of the water-abso

Also , at least a part of the non high molecular co

be such that any functional group capable o

covalent bond with a carboxyl group is conta

water-absorbent resin without forming a bon

carboxyl group of the water-absorbent resin

condition under which "at least a part of th

molecular compound may be such that any func

capable of forming a covalent bond with a carbo

contained in the water-absorbent resin withou

bond with the carboxyl group of the water-abso

means also a condition under which an entire a

water-insoluble crosslinked polymer Generally

"water- swellable ' means absorbing a large quant

e g ion exchanged water of essentially not less t

more preferably not less than 1 0 times, still mor

not less than 20 times, particularly preferably

times self weight of the water-absorbent resin Al

said that the "water- swellable" crosslinked polym

having " absorbency in ion exchanged water" of no

more preferably not less than 10, still more pr

less than 20 , particularly preferably 50 to 1 000

the " absorbency in ion exchanged water" is obt

same manner as the below-mentioned water absor

measurement method, except for measuring in io

water and using a water-absorbent resin or wat

agent of 0 02Og as an object to be measured

The term "water-insoluble" means

uncrosslinked extractable component content (

polymer) of preferably 0 to 50 weight %, more pr

more than 25 weight % , still more preferably no

unsaturated monomer having a carboxyl group>

In the present invention , favorably us

water-absorbent resin is a water-absorbent resin

polymerizing an unsaturated monomer having

group, and having a crosslinked structure In

invention, also a monomer which becomes a car

after polymerization due to hydrolysis, e g , ac

regarded as the water- soluble unsaturated mono

carboxyl group However, it is preferable

unsaturated monomer having a carboxyl group at

polymerization

Examples of the water-absorbent resin

polymerizing an unsaturated monomer having

group include polymers obtained by polym

crosslinkmg carboxyl-group containing

monomers having a carboxyl group such as (meth)

maleic anhydride, maleic acid, fumaric acid, cr

itaconic acid, and cmnamic acid, and / or

(neutrahzer) , hydrolyzed graft poly

of two or more substances among the above

Above all, the water-absorbent resin is p

water-absorbent resin including a crosslinked pol

(salt) polymer obtained by polymerizing a monom

acrylic acid and / or its salt as a main component

The crosslinked polyacrylic acid (salt) pol

present invention is a polymer which is

polymerizing a monomer (excluding crosslin

containing acrylic acid and/ or its salt in an

preferably 50 to 100 mol % , more preferably 70 to

still more preferably 90 to 100 mol % , relative t

amount of the monomer, and has a crosslinked

its inside

In addition, 45 to 85 mol % of the carboxyl

water-absorbent resin are preferably neutralized

In other words, the carboxyl group of the wat

resin preferably has a neutralization ratio of 45 t

more preferably 50 to 85 mol %, still more prefera

mol %, particularly preferably 60 to 75 mol % As

polymerization, or may be carried out in these thr

Note that, a neutralization ratio of a carbo

the water-absorbent resin can be obtained by calc

(i) the amount of unsaturated monomer

not-yet-neutrahzed carboxyl group and (ii) the tot

bases as used for neutralization before the pol

during the polymerization, and / or after the pol

Alternatively, as mentioned below, the neutrali

may be obtained by titration of an extractable

content in the water-absorbent resin

The water-absorbent resin preferably used in

invention may, if necessary, realized by a copoly

by copolymerizing another monomer j ointly

water-soluble unsaturated monomer having a car

(if crosslinked polyacrylic acid (salt) polymer,

and/ or its salt) used as the main component

Specific examples of the above other mono

water-soluble or hydrophobic unsaturated mono

methacrylic acid, maleic anhydride, maleic acid, f

2-hydroxyethyl (meth)acrylate , methoxypolyeth

(meth) acrylate, polyethylene glycol (meth) acrylate,

and lauryl (meth) acrylate

When the water-absorbent resin is the

polyacrylic acid (salt) polymer, in case of usin

other than acrylic acid (salt) , the amount of thes

used as monomers other than acrylic acid (salt)

in the range of 0 to 30 mol %, more preferably 0

of the entire monomers As a result, it is possib

improve the water absorbing characteristics of t

water-absorbent resin and water-absorbing age

possible to obtain the water-absorbent resin (wat

agent) at lower cost

<Crosshnked structure>

The water-absorbent resin used in the prese

has a crosslinked structure at least in their i

preferably in their inside and surface

Further, the water-absorbent resin used in

invention is arranged so that at least a non hig

having three or less functional groups each

forming a covalent bond with a carboxyl group

internal crosslmking agent having three or les

groups and an internal crosslmking agent having

polymeπzable ethylenical double bonds togethe

other

As described above, the non high molecula

preferably crosslinks the mside of the water-abso

but there is a case where the non high molecula

forms a bond with the water-absorbent resin but

the internal crosslinked structure or there is a

any functional group capable of forming a covale

the carboxyl group is contained in the water-abs

without forming a bond with the carboxyl gr

water-absorbent resin In case where the in

water-absorbent resin is not crosslinked with t

molecular compound, the water-absorbent resin

present invention is internally crossli

below-mentioned self-crosslmkmg monomer, belo

carboxyl group of the water-absorbent resin Exa

include a hydroxyl group, an amino group , an epo

oxetane group , an ethyleneimine group (aziπdin

isocyanate group, oxazohne , cyclocarbonate, ox

cyclic urea, an azithidinium salt group, and c

Above all, it is more preferable that the function

hydroxyl group, an ammo group, an oxetane grou

cyclocarbonate , oxazohdmone, cyclic urea, or th

result, it is possible to provide a water-absorbing

is excellent in view of the safety

Thus , examples of the non high molecula

having four or more functional groups each

forming a covalent bond with a carboxyl group in

high molecular compound having four or mo

groups, a non high molecular compound having f

ammo groups, a non high molecular compound h

more epoxy groups, a non high molecular comp

four or more oxetane groups, a non high molecula

having four or more ethyleneimine groups (aziπd

high molecular compound having four or more

salts, a non high molecular compound having f

chlorohydπns , and a non high molecular comp

two or more kinds of functional groups selected

hydroxyl group , ammo group , epoxy group, oxe

ethyleneimme group (aziπdme group) , isocya

oxazohne, cyclocarbonate, oxazohdmone , c

azithidinium salt and chlorohydπn, wherein a co

number of groups in the selected functional group

than four Above all, the non high molecular

having four or more functional groups each

forming a covalent bond with a carboxyl gro

preferably the non high molecular compound ha

more kinds of functional groups selected from amo

group, amino group, oxetane group, oxazohne, cy

oxazohdmone, and cyclic urea, wherein a co

number of groups in the selected functional group

than four As a result, it is possible to

water-absorbing agent which is excellent in view o

groups is not particularly limited _t

In addition, the non high molecular co

further have at least one polymeπzable ethyle

bond, ion-bondable functional group, or the like

the non high molecular compound has four or mo

groups each capable of forming a covalent b

carboxyl group

Moreover, the non high molecular compo

particularly limited if it has four or more functi

each capable of forming a covalent bond with

group However, the number of the functional

capable of forming a covalent bond with a carbo

preferably 4 to 50 , more preferably 4 to 20 ,

preferably 4 to 10 , particularly preferably 4 to 6

of carbon atoms of the non high molecular c

preferably 0 5 to 4 times as many as the nu

functional groups each capable of forming a co

with a carboxyl group, more preferably 1 to 2 ti

case where the number of such a functional gr

maltitol, lactitol, or oligosaccharide alcohol, ald

xylose , glucose , gulose, mannose, or idose , and

as fructose or sorbose Examples of the non hig

compound having four or more ammo gro

tπethylenetetramine, tetraethylenepentamm

pentaethylenehexamme Examples of the non hig

compound having hydroxyl group and amino gr

2-ammo-2-hydroxymethyl- l , 3-propanediol

N ,N-bis- (2 -hydroxyethyl) ethylenediamme Thes

molecular compounds having four or more functi

each capable of forming a covalent bond with

group may be used either alone respecti

combinations with each other

Above all, the non high molecular compound

or more functional groups each capable of formin

bond with a carboxyl group is more preferably t

molecular compound having four or more hydr

more preferably sugar alcohol, still more preferabl

xyhtol, or sorbitol, particularly preferably xyhtol

not less than 1 g, still more preferably not less t

pure water of 100 g at a room temperature fr

points that it can be added easily and real

crosslinking

Further, as to the non high molecular comp

four or more functional groups each capable o

covalent bond with a carboxyl group, its molecul

not particularly limited, but preferably not more

more preferably not more than 2000 , still more pr

more than 1000 , particularly preferably not mor

most preferably not more than 200 Still further,

of the molecular weight of the non high molecula

having four or more functional groups each

forming a covalent bond with a carboxyl gr

particularly limited, but preferably 50 , more pr

still more preferably 90 It is not preferabl

molecular weight of the non high molecular c

greater than 5000 or smaller than 50 since

crosslinking is not carried out more efficiently F

covalent bond with a carboxyl group, its funct

equivalent weight is preferably not less than 20 a

than 200 g/ mol, more preferably not less than

more than 100 g/ mol The functional group equiv

refers to a value obtained by dividing the molecul

the non high molecular compound by the

"functional groups each capable of forming a co

with a carboxyl group" in the non high molecula

It is not preferable that the functional group

weight is greater 200 g/ mol or smaller than 20

the internal crosslinking is not efficiently carried

Note that, as to the non high molecular com

of the functional groups may be modified as lon

more free functional groups each of which is

forming a covalent bond with a carboxyl gro

However, in view of the obtained water-absor

hydrophihcity, property, safety, and coloring aft

treatment, it is preferable to use the non hig

compound whose functional groups are not modifi

not necessarily form a covalent bond with a carbo

the water-absorbent resin Part of the functional

be free without forming covalent bond with a car

of the water-absorbent resin Further, part of o

non high molecular compound having four or mor

groups as used may exist without reacting (i e

functional groups forms bonds)

Suppose that a non high molecular compo

four or more functional groups each capable o

covalent bond with a carboxyl group is a non hig

compound A, and that the non high molecular co

which none of the functional groups form a co

with a carboxyl group of the water-absorbent

unreacted compound A The unreacted compoun

extracted from the water-absorbent resin so

quantified by analysis in the Liquid Chromatogr

the other method An extraction method is not

limited and may be selected appropriately from

conventionally known extraction methods For exa

is 0 to 100 weight %, more preferably 10 to 5

relative to the entire amount of the non hig

compound used

Suppose that the non high molecular com

which at least one of the four functional groups

with a carboxyl group is a reacted compound A

compound A can be quantified in the following m

extracting the unreacted compound A in the foreg

the water-absorbent resin is hydrolyzed, and the

point or the reaction point is cut off, and then t

molecular compound contained in the resulta

analyzed in the Gas Chromatography-Mass S

(GC-MS) , the Liquid Chromatography-Mass Spec

the other method

In the water-absorbing agent according to

invention, the unreacted non high molecular comp

functional group has no bond with a carboxyl g

water-absorbent resin corresponds to an entire

partial amount of the non high molecular com

reason thereof is not clearly known Note that, an

of the amount of the unreacted non high molecul

included in the water-absorbing agent is generall

preferably 5000 ppm, more preferably 1000 ppm

In the water-absorbing agent of the presen

the non high molecular compound is introduced i

of the water-absorbent resin That is, the wat

resin is arranged so that (i) its inside has a bond

high molecular compound preferably so as to be

and / or (ii) the unreacted non high molecular c

included therein Here, it is possible to confirm t

high molecular compound having four or mor

groups is introduced into the inside of the wat

resin by comparing the non high molecular com

exists only in the vicinity of the surfa

water-absorbent resin or the water-absorbing ag

non high molecular compound which exists

water-absorbent resin or the water-absorbing

possible to easily obtain the amount of th

ethanol and the like , in accordance WiIh ₁

Chromatography (LC) or a similar method

It is possible to obtain the amount of the un

high molecular compound which exists in the wat

resin or the water-absorbing agent in the follow

For example , the water-absorbent resin

water-absorbing agent is extracted in 0 9 weight

sodium chloride solution, and thereafter the resul

is analyzed in the Liquid Chromatography (LC)

Further, it is possible to easily confirm that

the water-absorbent resin is crosslinked

crosslinked in a uniform manner) with the non hig

compound having four or more functional gro

following manner The water-absorbent res

water-absorbing agent having been heated at

hours with a hot air drier or the like for example i

ground so as to observe the cleaved or ground por

where also the inside thereof is uniformly co

possible to confirm that the inside of the wat

covalent bond with a carboxyl group (first crossli

is introduced into an inside of the water-absorbe

in addition to the internal crosslinking based

crosslinking agent or instead of the internal

agent based on the first crosslinking

water-absorbent resin may have an internal

structure based on an internal crosslinking agen

the non high molecular compound Examples of

crosslinked structure include a structure o

self-crosslmkmg without any crosslinking ag

structure obtained by copolymeπzation or react

internal crosslinking agent having at least

preferably two to four polymeπzable ethylenical d

per molecule (second crosslinking agent) and/ or

crosslinking agent other than high molecular

which internal crosslinking agent has at least

preferably two to four functional groups per mol

crosslinking agent) The functional groups are hi

groups in a molecule and includes a covale

crosshnkmg agent having two or more p

ethylenical double bonds (second crosshnkmg ag

(in) an internal crosshnkmg agent other than t

molecular compound which internal crosshnkm

two or more functional groups (third internal

agent) in combination That is, it is more prefera

two-kind internal crosshnkmg or three-kin

crosshnkmg Further, it is further more prefera

water-absorbent resin used in the present inven

least both ( 1 ) the non high molecular comp

crosshnkmg agent) having four or more functi

each capable of forming a covalent bond with

group and (2) an internal crosshnkmg age

crosshnkmg agent) having two or more p

ethylenical double bonds per molecule, that is, i

more preferable that the water-absorbent resin

present invention has two-kind internal crosshn

This is preferable since the gel strength

polymerization is enhanced, and its handling ch

tπmethylolpropane tπ(meth)acrylate , tπmet

di(meth) acrylate , glycerol tπ(meth)acrylate , glyce

methacrylate, ethylene-oxide-denatured tπmet

tπ(meth)acrylate, pentaerythπtol hexa(meth)acry

cyanurate, tπallyl isocyanurate, tπallyl

triallylamme , and poly(meth)allyloxyalkanes It i

use 0 to 10 mol %, more preferably 0 00 1 mol % t

of each of these polymeπzable crosshnkmg

respect to the unsaturated monomer having a car

in crosshnkmg After the polymerization, the amo

substantially N D (not more than 1 ppm which is

limit) by being used for the crosshnkmg

In addition, besides, as examples of

crosshnkmg agent, i e , an internal crosshnkmg

than the non high molecular compound whi

crosshnkmg agent has two or more functional gro

internal crosshnkmg agent other than the non hig

compound which internal crosshnkmg agent has

covalent-bondable or ionic-bondable functional g

1 ,6-hexanediol, 1 , 2-cyclohexanedimethanol, 1 , 2-c

tπmethylolpropane, 2 -ammoethanol, diet

tπethanolamme, polyoxypropylene , oxyethylene-

block copolymers , multivalent metallic compou

hydroxides and chlorides of zinc, calcium,

aluminum, iron, or zirconium, (polyjethylenegly

ether, glyceroldiglycidyl ether, ethyl

ethylenecarbonate , propylenecarbonate ,

(meth)acrylate, and the like

These internal crosslmkmg agents (t

crosshnkmg agent and the third crosslmkmg ag

used either alone respectively or in combination

other

The water-absorbent resin used in the prese

may be arranged in any manner as long as

molecular compound having four or more functi

each capable of forming a covalent bond with

group is introduced into an mside of the wat

resin However, it is more preferable that its

compound, an epoxy compound, a polyamme c

polyamme condensation product of a haloepoxy co

oxazohne compound, a monooxazohdmone co

dioxazohdinone compound, a polyoxazohdinone c

multivalent metal salt, and an alkylenecarbonate

Specifically, it is possible to use surface crosslin

mentioned in USP 6,228,930, USP 6,071,976, US

and other documents More specific examples the

polyhydric alcohol compounds such as ethyl

diethylene glycol, tπethylene glycol, tetraethy

polyethylene glycol, 1 ,2-propyleneglycol, 1,3-

dipropylene glycol, 2,3,4-tπmethyl- 1 ,3-

polypropylene glycol, glycerol, polyglycerol, 2-but

1,4-butanediol, 1,3-butanediol, 1,5-

1,6-hexanediol, and 1,2-cyclohexanedimetha

compounds such as ethylene glycol diglycidyl

glycidol), polyamme compounds such as ethyl

diethylenetπamine, trie thy le

tetraethylenepentamme, pentaethyle

cyclic urea compounds, and alkylenecarbonate

(USP 5 ,409 , 77 1 ) such as ethylenecarbonate H

surface crosslinking agent is not limited to the

maximize the effect of the present invention, it i

to use at least one of the oxetane comp

Unexammed Patent Publication 2002 / 7247 1 ) , the

compound, and the polyhydric alcohol, and

preferable to use at least either an oxetane comp

three to ten carbon atoms or a polyhydric alcoho

to ten carbon atoms, and it is further more prefer

polyhydric alcohol having three to eight car

Further, it is preferable to use also a method i

surface crosslinking is carried out with a monome

the crosslinking agent (Japanese Patent No

method in which the surface crosslinking is carrie

radical initiator (Japanese Unexammed Patent Pu

992 1 1 / 1988) , and a method in which the surface

is carried out with a radical initiator and a m

2005-004822 1 ) Thus, in case where the wat

possible to obtain a water-absorbent resin havi

more kinds of crosslinked structures including

crosslmkmg and the surface crosslinking

Further, the surface crosslinking agent for

the surface crosslinking may be an inorga

crosslinking agent (fifth crosshkmg agent) More

a preferable example of the inorganic surface

agent (fifth crosshkmg agent) is an inorga

crosslinking agent which will be described in ( 1 -2)

The surface crosslinking agent may be sol

may be used in combination with two or m

crosslinking agents Further, a combination of

surface crosslinking agent (fourth crosslinking ag

inorganic crosslinking agent (fifth crosslinking ag

used As a result, in case where the water-absor

crosslinked with the non high molecular com

crosslinking agent) , other internal crosslinking a

crosslinking agent and / or third crosslinking

organic surface crosslinking agent (fourth crosslin

use a water-absorbing agent including as a main

water-absorbent resin having a cro sslinke

obtained by polymerizing an unsaturated mono

carboxyl group, wherein an inside of the wat

resin is crosslinked with a non high molecula

having four or more functional groups each

forming a covalent bond with a carboxyl gro

internal crosslinking agent having two or more p

ethylenical double bonds per molecule , and a su

water-absorbent resin is crosslinked with an org

crosslinking agent and an inorganic surface

agent

Further, as described in Patent Document

the surface of the water-absorbent resin used in

invention may have tetravalent or further multiv

and, if necessary, tπvalent or further multivalen

As a result, the wettability of a particulate wat

resin composition is exhibited

( 1 -2) Components other than the water-absorbent

possible to enhance the liquid permeability In

specification, the liquid-permeabihty-enhance

herein refers to an agent which enhances

water-absorbent resin or water-absorbing agent

SFC of not less than 1 by at least 10

Mixture of the liquid-permeabihty-enhance

with the water-absorbent resin or water-absor

holds a liquid permeation path for the water-abs

or water-absorbing agent after having absorbed

liquid in a physical manner or ionized manne

makes it possible to increase liquid permeability

Examples of the liquid-permeabihty-enhanc

include water-soluble multivalent metal compou

aluminum sulfate, potassium alum, ammonium al

alum, (poly) aluminum chloride, and their

polycationic compounds such as polye

polyvmylamine , polyallylamme , and water-insolub

fine particles such as silica, alumina, and bent

may be used either alone respectively or in combi

multivalent metal salts

The liquid-permeabihty-enhancement agent i

amount of preferably 0 00 1 to 1 0 weight % , mor

0 0 1 to 5 weight %, relative to the water-absorben

Note that, the liquid-permeabihty-enhancem

not limited if it enhances liquid permeability, but

substance which forms no covalent bonds wit

groups on the surface of the water-absorbent resi

Further, the water-absorbing agent accor

present invention may further include, if necess

additive in such a range that water-absorption ch

such as liquid permeability of the water-absorbi

not decrease Examples of the another additi

deodorizer, antimicrobial agent, fragrant mater

agent, pigment, dye, plasticizer, adhe sive,

fertilizer, oxidizer, reducer, water, salts, chel

bactericidal agent, hydrophilic polymer

polyethyleneglycol, paraffin, hydrophobic

thermoplastic resin such as polyethylene and po

invention may include inorganic powder as the ad

is preferable to add the inorganic power in such

water-absorption characteristics such as liquid

of the water-absorbing agent do not decrea

examples of the inorganic powder include metal

as silicon dioxide and titanium oxide, silicate aci

as natural zeolite and synthetic zeolite, kaolin, ta

bentonite Among of them, silicon dioxide and s

are preferable , and silicon dioxide and silicate (

which has an average particle diameter of not mo

μm based on measurement by Coulter Counter

more preferable The amount of the inorganic p

depending on a composition of the water-abso

and/ or water-absorbing agent However, for e

amount of the inorganic powder preferably ra

weight % to 0 5 weight %, more preferably from 0

0 3 weight %, still more preferably from 0 weig

weight %, particularly preferably from 0 weight

weight % , with respect to the water-absorbent res

The shape of the water-absorbent resin

present invention and the water-absorbing a

present invention is not particularly limited

achieving the present invention, it is preferab

shape is particulate , and it is more preferable th

is adjusted to be a specific particle diameter

particle diameter of the water-absorbent resin u

present invention and the water-absorbing a

present invention, an amount of particles wh

diameter is less than 850 μm and not less t

(defined by classification with a sieve JIS Z880 1

preferably not less than 90 weight % and 100 wei

limit) , more preferably not less than 95 weight

preferably not less than 98 weight %, with re

entire amount Further, it is preferable that a

particles whose particle diameter is not less tha

not less than 60 weight % with respect to the en

Note that, the "entire amount" means an entire a

particulate water-absorbent resin in referring to

to 600 μm, still more preferably from 300 μm

particularly preferably from 300 μm to 500

preferably from 350 μm to 450 μm The particle

the water-absorbent resin and the water-absorbin

be adjusted by granulation if required

Further, the particulate shape of the wat

resin or the water-absorbing agent is not particul

Examples of the particulate shape includes a sph

a pulverized shape , an irregular shape, and th

preferable that the particulate shape is an

pulverized shape obtained by carrying out the pul

In addition, the water-absorbent resin or the wat

agent preferably has a bulk density (defined by

1998) in the range of 0 40 to 0 80 g/ ml, more pre

to 0 75 g/ ml, still more preferably 0 60 to 0 73 g/

In the water-absorbent resin or the wat

agent of the present invention, a logarithmi

deviation (σζ) of particle diameter distribution is

the range of 0 1 to 0 45 , more preferably 0 25 t

that is wide to some extent In the case where the

standard deviation (σζ) is less than 0 1 , not onl

performances cannot be obtained, but also

decreases seriously In the case where the

standard deviation (σξ) exceeds 0 45, a partic

distribution becomes too wide , and there is a po

the target performances might not be obtained

In the present invention, the "particle s wh

diameter is not less than 300 μm" refer to parti

been pulverized, which were classified with a J

sieve having a mesh opening size of 300 μm an

the sieve Further, the "particles whose particle

less than 300 μm" refer to particles, having bee

which were classified with a JIS standard sieve h

opening size of 300 μm and passes through the s

applicable to other mesh opening sizes In cas

weight % of particles are classified with a

opening size is 300 μm, the weight-average parti

(D 50) is 300 μm

agent of the present invention

In the water-absorbing agent of the present

is preferable that its absorbency (CRC) is more t

This allows aqueous liquid to be favorably a

retained in using the water-absorbing agent of

invention for a sanitary material such as a diaper

The present invention is to allow enhancement

permeability without dropping the absorbency

provide a water-absorbing agent having

permeability also in case where the absorbency (

than 25 g/ g Of course , the absorbency (CRC)

more than 25 g/ g as long as the absorbency is not

g/ g However, in view of the performance for ab

retaining the aqueous liquid, the absorbenc

preferably not less than 25 g/ g and not more t

more preferably not less than 26 g/ g and not m

g/ g, particularly preferably not less than 27 g/ g a

than 35 g/ g, most preferably not less than 28

more than 35 g/ g It is not preferable that the

(CRC) varies depending on a type of the monom

the crosslinking agent, and a similar conditi

absorbency (CRC) can be controlled by adjusting

of the non high molecular compound (first crossli

having four or more functional groups each

forming a covalent bond with a carboxyl group an

of the crosslinking agent (second crosslinking a

two or more polymeπzable ethylenical double bon

adjusting the amount of the non high molecula

used therein, it is necessary to consider a neutral

of the carboxyl group since the bond of th

molecular compound and the carboxyl group dep

neutralization ratio of the carboxyl grou

water-absorbent resin In consideration of the n

ratio, the amount of the non high molecular com

is required so that the absorbency (CRC) exceeds

be represented as a relational expression with re

neutralization ratio

That is, an amount (Y) (mol %) of the non hi

The water-absorbing agent of the prese

exhibits a saline flow conductivity (SFC an

evaluating the liquid permeability) of not

30cm ³ s 10 ⁷ /g, preferably not less than 40cm ³ s

preferably not less than 45cm ³ s 10 ⁷ /g, still mor

not less than 50cm ³ s 10 ⁷ /g, particularly prefera

than 55cm ³ s 10 ⁷ /g, most preferably not

60cm ³ s 10 ⁷ /g Its upper limit value is not

limited, but the upper limit value is preferably no

400cm ³ s 10 ⁷ /g, more preferably not

300cm ³ s 10 ⁷ /g, still more preferably not

200cm ³ s 10 ⁷ /g In case where the saline flow

(SFC) is less than 30cm ³ s 10 ⁷ /g, this may

example, the following disadvantage an aqueo

such as urine is hardly diffused in an absorbent s

that the aqueous solution is hardly absorb

absorbent structure, which results in leakage

Note that, the "liquid permeability" in

invention means the water-absorbing age

In the water-absorbing agent of the present

is preferable that its absorbency against pressure

less than 15 g/ g This allows aqueous liquid to

absorbed and retained in using the water-absorb

the present invention for a sanitary material such

and the like The present invention is to allow enh

the liquid permeability without dropping the abs

is to provide a water-absorbing agent having

permeability also in case where the absorbe

pressure (AAP) is more than 15 g/ g Of

absorbency against pressure (AAP) may be not m

g/ g as long as the absorbency against pressure

less than 5 g/ g However, in view of the perf

absorbing and retaining the aqueous liquid, the

against pressure (AAP) is preferably not less than

not more than 30 g/ g, more preferably not less

and not more than 30 g/ g, particularly prefera

than 20 g/ g and not more than 28 g/ g It is no

that the absorbency against pressure (AAP) is sm

absorbent structure and/ or the sanitary mat

results in the blocking This raises problems suc

skin eruption, and the like on the occasion of t

use in a disposable diaper

In the water-absorbing agent of the presen

an absorption rate (FSR) is preferably not les

g/ g/ s, more preferably not less than 0 1 g/ g/ s

preferably not less than 0 15 g/ g/ s, particularl

not less than 0 17 g/ g/ s An upper limit th

particularly limited but is preferably not more tha

more preferably not more than 3 0 g/ g/ s In cas

absorption rate (FSR) is smaller than 0 05 g/ g/ s,

sufficiently absorbed and leaks on the occasion o

a diaper for example

Further, the water-absorbing agent of

invention preferably has a solid content in the ra

99 8 weight %, more preferably 80 to 99 5 weight

preferably 85 to 99 weight % , particularly prefera

weight % In case where the solid content is sma

dispersion liquid obtained by dispersing 0 5

water-absorbing agent in 50 ml of physiologic

preferably not less than 55 mN / m, more prefera

than 60 mN / m, still more preferably not less tha

particularly preferably not less than 68 m

preferably not less than 70 mN / m Further, an u

the surface tension of the water-absorbing agen

liquid is not particularly limited but is preferabl

more preferably 80 mN/ m, still more preferably

is not preferable that the surface tension is lo

mN / m since the liquid diffusing ability drop

water-absorbing agent is used in a sanitary mate

a diaper

( 1 -5) Usage of the water-absorbing agent of

invention

The water-absorbing agent of the present

superior in water-absorption characteristics suc

permeability and absorbency Th

absorption/ solidification agent (absorption/ g

particulate shape is combined with a hydrophilic

molded so as to be used as an absorbent str

respect to a total weight of the water-absorbing a

hydrophilic fiber, an amount (core concentrat

water-absorbing agent contained in the absorbe

preferably ranges from 20 to 1 00 weight %, mor

from 30( to 100 weight % , still more preferably fro

weight %, particularly preferably from 50 to 1 00

case where the core concentration is less than 20

is difficult to make use of properties of the wat

agent

The absorbent structure is preferably o

carrying out compression molding so that its de

from 0 06 to 0 50 g/ cc, its basic weight ranges f

0 20 g/ cm ² Note that, examples of the fiber b

include hydrophilic fibers such as crushed wood

hnter or crosslinked cellulose fiber, rayon, co

wool, acetate, vmylon, and the like It is prefera

out an air-laid process with respect to these mate

(2) Method according to the present invention for

water-absorbing agent

The method according to the present i

producing a water-absorbing agent is not particu

as long as the method allows production of a wat

agent including, as a mam component, a wat

resin having a crosslinked structure obtained by

an unsaturated monomer having a carboxyl group

least a non high molecular compound having f

functional groups each capable of forming a co

with a carboxyl group is introduced into an

water-absorbent resin

The method according to the present i

producing the water-absorbing agent may be arra

manner as long as, for example , the method inclu

(2- 1 ) a polymerization step in which the

monomer having a carboxyl group and included in

monomer solution is polymerized in the presenc

the non high molecular compound having fo

compound is dissolved in a large amount of

weight is 1 to 300 times , more preferably, 3 to 3

large as a weight of the water-absorbent resin

may be absorbed by a dried water-absorbent

hydrogel of the water-absorbent resin, and th

molecular compound may be kneaded into the hy

water-absorbent resin by a kneader or a me

Preferably, the non high molecular compound is

in the polymerization step as described above,

possible to uniformly introduce the non hig

compound into the whole water-absorbent resin

any arrangement may be made as long as th

molecular compound is introduced into the m

water-absorbent resin, and distribution of th

molecular compound in the inside of the wat

resm may be such that a micro domain i

distributed or may be such that the non hig

compound is uniformly introduced at a molecular

all, it is more preferable that the non hig

high molecular compound is prepared before carr

polymerization step, (2-4) a pulverization step i

hydropolymer or the water-absorbent resin

pulverized at least before or after the drying s

surface crosslinking step in which a surf

water-absorbent resin is crosshnked, and

liquid-permeabihty-enhancement agent adding st

a liquid-permeabihty-enhancement agent is

respective steps are described as follows

(2- 1 ) Polymerization step

In the present step, the unsaturated mono

carboxyl group and included in a aqueous mono

is polymerized in the presence of at least th

molecular compound having four or more functi

each capable of forming a covalent bond with

group, so as to obtain a hydropolymer

As to an amount of usage of the non hig

compound having four or more functional g

capable of forming a covalent bond with a carboxy

Y < 006/{2-(2 35X/100)} (1)

In the equation (1), X is a neutralization rati

a carboxyl group in the water-absorbent resin, an

in the range of 45 mol % to 85 mol %

As to the unsaturated monomer having a car

the description of (1-1) is applicable

Further, in the present step, in combinati

unsaturated monomer having a carboxyl g

monomer described in (1-1) may be copolymeπzed

In case of copolymeπzing other monomer, t

monomer solution including the unsaturated mon

a carboxyl group may further contain othe

described in (1-1) in addition to the unsaturat

having a carboxyl group Hereinafter, a monomer

the aqueous monomer solution is referred to

monomer That is, hereinafter, (a) the unsaturat

having a carboxyl group in case where other mo

used or (b) the unsaturated monomer having a ca

and other monomer in case where other monome

water-absorbent resin

The amount of the non high molecular comp

four or more functional groups each capable o

covalent bond with a carboxyl group (first crossli

is as described above For example, when the ne

ratio of the carboxyl group in the water-absorben

mol %, the amount is preferably less than 0 064

respect to the unsaturated monomer having a car

For example, when the neutralization ratio of t

group in the water-absorbent resin is 85 m

preferable that the amount is preferably less tha

with respect to the unsaturated monomer having

group

Further, a lower limit of the amount of t

molecular compound having four or more functi

each capable of forming a covalent bond with

group is preferably 0 00 1 mol %, more preferably

still more preferably 0 005 mol % , particularly pre

mol %, most preferably 0 02 mol %, with res

of the non high molecular compound deviates fro

defined by the foregoing equation ( 1 ) , the absor

drops Thus, such amount is not preferable

Further, the monomer of the aqueous mono

may be polymerized in the presence of ( 1 ) th

molecular compound and (2) the internal crossl

(second crosslmkmg agent) having two or more p

ethylenical double bonds de scribed in ( 1 - 1 )

internal crosslmkmg agent (third crosslmkmg

than the high molecular compound whic

crosslmkmg agent has two or more functional gro

that the monomer is further internally crosslmk

internal crosslmkmg agents (the second crossl

and/ or the third crosslmkmg agent) other than t

molecular compound A ratio of an amount

crosslmkmg agent and an amount of the second

agent and / or the third crosslmkmg agent whic

together [(amount of the first crosslmkmg agent)

the second crosslmkmg agent and / or the third

carboxyl group (excluding the crosshnkmg agen

amount of these internal crosshnkmg agents oth

non high molecular compound (second crossh

and/ or third crosshnkmg agent) is preferably not

and not more than 1 0 mol %, more preferably not

and not more than 0 5 mol % , still more prefera

than 0 and not more than 0 2 mol % , particularl

not less than 0 005 mol % and not more than 0 1

preferably not less than 0 0 1 mol % and less tha

In case where the total amount of the internal

agent other than the non high molecular compo

than 1 0 mol %, the absorbency (CRC) drops

amount is not preferable

Above all, it is preferable to additionally use

crosshnkmg agent (second crosshnkmg agent) h

more polymeπzable ethylenical double bonds as ot

crosshnkmg agent Further, the polymeπzable

agent (second crosshnkmg agent) is used for c

Thus, after the polymerization, the amount i

molecular compound having four or more functi

each capable of forming a covalent bond with

group and the internal crosshnkmg age

crosslinkmg agent) having two or more p

ethylenical double bonds so as to obtain a hydrop

that, in case of using as the internal crosshnkm

the internal crosshnkmg agent based on the co

the internal crosshnkmg is carried out by being h

drying step or the surface crosshnkmg step Furt

of using as the internal crosshnkmg agent

crosshnkmg agent having two or more p

ethylenical double bonds, the internal crosshnk

out in the polymerization step Thus, the

structure is formed in the polymerization step

second crosshnkmg agent together, so that it is

obtain a hydrogel which is hard to some exte

polymerization step, in other words, it is possibl

after the polymerization step, a hydrogel whose ge

improved Therefore , the handling characteris

water-absorbent resin accordingly, it is possible

properties, such as a water absorption rate and

the resultant water-absorbent resin

In this way, in case of using the internal

agent which is the non high molecular compound

or more functional groups each capable of formin

bond with a carboxyl group and the internal

agent having two or more polymeπzable ethyle

bonds, it is preferable that the amount of

crosslinking agent which is the non high molecul

having four or more functional groups each

forming a covalent bond with a carboxyl group i

aforementioned range Further, with respe

unsaturated monomer having a carboxyl group (e

crosslinking agent) , the amount of the internal

agent having two or more polymeπzable ethyle

bonds is preferably not less than 0 and not mo

mol % , more preferably not less than 0 and not m

mol %, still more preferably not less than 0 a

Note that, the non high molecular compoun

internal crosshnkmg agent may be added befor

polymerization of the monomer as long as they

time of polymerization of the monomer Fur

internal crosshnkmg agents may be added to

system in a single dose or several doses

In the present step, as an initiator used in

the monomer, it is possible to use radical po

initiators such as potassium persulfate, ammoniu

sodium persulfate , potassium peracetate , sodium

potassium percarbonate, sodium percarbona

hydroperoxide, hydrogen peroxide,

2 ,2 ' -azobis(2 -amidmopropane) dihy

photopolymeπzation initiators suc

2-hydroxy-2-methyl- 1 -phenyl-ρropane- l -one, a

initiators In view of properties of the

water-absorbent resin, the amount of these po

initiators as used is in the range of 0 00 1 t

preferably 0 0 1 to 0 1 mol % (relative to the entir

Further, in polymerizing the monomer in

step, it is possible to carry out bulk polym

precipitation polymerization However, in view of

the resultant water-absorbent resin, it is prefera

out aqueous solution polymerization or rev

suspension polymerization in which the monome

the form of an aqueous solution The concentr

monomer contained in the aqueous solutio

monomer solution) in the case where the monome

the form of the aqueous solution is determined d

temperature of the aqueous solution and a

monomer, so that the concentration is not particu

However, for example, in case of carryin

polymerization (neutralization polymerization)

unsaturated monomer having a carboxyl g

monomer has been neutralized in advance , the c

ranges preferably from 10 to 70 mass %, more pre

20 to 60 mass % Further, in carrying out t

solution polymerization, a solvent other than w

ultraviolet rays, electron beams, and y rays m

used or may be used in combination with the afo

polymerization initiators Temperature in in

polymerization depends on a type of the po

initiator used, but its upper limit preferably ran

to 130 ⁰ C, more preferably from 20 to 120 ⁰ C

Note that, the reversed-phase suspension po

is a polymerization method which causes t

monomer solution to be suspended in a hydroph

solvent Such polymerization method is disclosed

USP 4,093,776, USP 4,367,323, USP 4,44

4,683,274, and USP 5,244,735 for example T

solution polymerization is a polymerization m

causes the aqueous monomer solution to be

without using any dispersion solvent Such po

method is disclosed in such as USP 4,625,001, US

USP 4,286,082, USP 4,973,632, USP 4,98

5,124,416, USP 5,250,640, USP 5,264,495, USP

USP 5,380,808, EP 0811636, EP 0955086, EP 09

carboxyl group which monomer has been ne

advance However, as other polymerization me

possible to adopt a so-called acid polymerization

neutralization method in which polymerization is

by using, as a main component, the unsaturat

having a carboxyl group which monomer ha

neutralized, particularly, by using, as a main

acrylic acid which has not been neutralized, and

group is neutralized after the polymerization

In such acid polymerization / subsequent ne

method, the aqueous monomer solution contai

main component the acrylic acid which has

neutralized and having a specific concentration i

to crosslmkmg polymerization in the presence of

crosslinking agent and then is neutralized, and t

is adjusted so as to have a specific particle diame

thus obtained crosslinked polymer having the spe

diameter and water absorbency is further subj ecte

crosslinking

preferably from 90 to 100 mol %, particularly pr

mol % , relative to a total acrylic acid Then,

compound, particularly, alkaline metal compound

the thus obtained crosslinked polymer so that

crosslinked polymer is monovalent salt, particula

metal salt, thereby obtaining a water-absorbent r

the present invention

Note that, as in the foregoing polymerizati

the acid polymerization/ subsequent neutralizat

allows use of "other monomer" as necessary in

with the unsaturated monomer having a carb

Further, details of types and amounts of the "othe

"the non high molecular compound having fo

functional groups each capable of forming a co

with a carboxyl group" , "other internal crosslin

and "polymerization initiator" are the same

aforementioned polymerization methods

Note that, the non high molecular compoun

internal crosslinking agent may be added before o

neutralized Examples of an alkaline metal compo

neutralize the carboxyl group of the thus obtained

polymer so that part of the crosslinked polymer t

metal salt include alkaline metal hydroxi

hydroxide , potassium hydroxide , lithium hydroxi

like) , alkaline metal carbonate (sodium carbon

hydrogencarbonate, and the like) , and a similar

Further, it is possible to use amines such as

alkanolamme, ammonium carbonate, and a simila

In view of performance of the resultant water-abso

industrial availability, and the safety, it is prefe

sodium salt or potassium salt In

polymerization/ subsequent neutralization method

45 to 85 mol % , more preferably 50 to 85 mol

preferably 55 to 80 mol %, particularly preferab

mol % of the carboxyl group in the crosslinked

neutralized with the alkaline metal compound to

into alkaline metal salt In case where the poly

carried out by using a solvent, an example of the

or a meat chopper Further, in obtaining the wat

agent of the present invention, a neutralization

preferably ranges from 50 to 100 ⁰ C , more prefer

to 90 ⁰ C As to the neutralization, a first n

coefficient (defined as a neutralization degree of 2

recited in claim 1 of USP 6, 187 , 872 is preferably

as to be uniform

<Method for adding a chain transfer agent>

In the method of the present invention for p

water-absorbing agent, a chain transfer agent ma

the time of the polymerization In the presence of

monomer, the non high molecular compound ha

more functional groups each capable of formin

bond with a carboxyl group, other internal crossh

and the polymerization initiator, but also a w

chain transfer agent, the polymerization is car

that it is possible to obtain the water-absorbing

high water absorbing ability and excellent st

respect to urine in case where the water-abso

secondary alcohols, amines, hypophosphites , a

Specifically, one kind or two or more kinds sele

group made up of mercaptoethanol, merca

dodecylmercaptan, thioglycols, thiomali

3-mercaptopropionic acid, isopropanol, sodium hy

formic acid, and salts thereof In view of the effect

preferable to use hypophosphite such

hypophosphite

An amount of the water-soluble chain tra

depends on a type of the water- soluble chain t

monomer concentration of the aqueous monomer s

the amount is 0 00 1 to 1 mol %, preferably 0 05 t

with respect to the entire monomer In case where

is less than 0 00 1 mol % , the amount of t

crosslinkmg agent used in the present invention

crosslmkmg density, which drops the absorbency

amount is not preferable In case where the amou

mol %, a water- soluble content increases, whic

stability Thus, such amount is not preferable

high molecular compound having four or mor

groups each capable of forming a covalent b

carboxyl group , before the polymerization step

The aqueous monomer solution includes at

unsaturated monomer having a carboxyl group a

high molecular compound having four or mor

groups each capable of forming a covalent b

carboxyl group Additionally, the aqueous mono

may include other monomer described in ( 1 - 1 )

Further, as other internal crosslinking

aqueous monomer solution may include t

crosslinking agent having two or more p

ethylenical double bonds and/ or other internal

agent having two or more functional groups

(2-3) Drying step

A polymer obtained in the aforementioned po

step is obtained as a hydropolymer Th

hydropolymer is, if necessary, pulverized in th

hydropolymer with water content of not less than

temperatures higher than 250 ⁰ C might cause t

water-absorbent resin to be colored Note that, in

oil or steam is used as a heat medium,

temperature is a temperature of the heat medi

other hand, in case where electron beam irradiat

means is used for drying without using the heat

drying temperature is a temperature of the materi

be dried) Alternatively, the drying temperatu

changed stepwise The duration of the dryi

determined to obtain a target water content, dep

surface area and water content of the hydropoly

type of a drying oven For example, the duration o

is in the range of 10 to 180 minutes, more pref

120 minutes Note that, in the present inv

crosslinked polymer having been dried is refer

water-absorbent resin

The water content of the water-absorbent res

the present invention is not particularly limit

water-absorbent resin is particles (powder) sho

may cause a trouble in the production, m

impossible to pulverize the water-absorbent resi

make it impossible to control for specific parti

distribution

As a drying method as used, various kinds

can be adopted so as to obtain a target water cont

heat drying, hot-air drying, reduced-pressure dryi

drying, microwave drying, dehydration by azeot

hydrophobic organic solvent, high-temperature

means of high-temperature steam The drying m

particularly limited

A shape of the water-absorbent resin obta

above method is not particularly limited as l

water-absorbent resin can be treated as powder

the shape is generally such as spherical shape , fi

bar shape, approximately spherical shape ,

irregular shape, granulated particle shape , partic

perforated structure , and similar shape Ho

preferable to use a water-absorbent resin

water-absorbent resin is pulverized before or afte

step, preferably before and after the drying step

In case of pulverizing the resultant h

obtained before the drying step, the resultant hyd

extruded from the perforated structure whose

diameter is preferably 0 3 to 22mm, more pref

20mm, still more preferably 5 to 18mm so as to be

thereby obtaining pulverized hydropolymer p

such extrusion of the hydropolymer from the

structure having the specific perforation diamet

pulverize the hydropolymer, it becomes possible

into the pulverized hydropolymer particles

sufficiently exert the effects of the present inv

shape of the perforations is such as a circular, q

(e g square, rectangular) , triangular, or hexagona

is not particularly limited However, pref

hydropolymer is extruded from circular perfor

that, the aforementioned perforation diameters ar

the diameters given in the case of convertin

extrusion mechanism, there is used the mecha

type which can press-feed the hydropolymer fro

inlet to the perforated plate , such as screw type o

type The screw type extruder may be a single

screw type and may be a type which is used

extrusion molding of edible meat, rubber, and pla

as a pulverizer Examples thereof include meat c

Dome Gran

It is preferable that the water-absorbent res

the present invention is particulate water-abso

particles, and it is preferable that at least

particles is granulated particles More prefer

granulated particles are those which are obtai

granulation of particles having particle diameter

than 150 μm The process for achieving such a

least part of the water-absorbent resin p

granulated particles is not particularly limited a

hitherto publicly known granulation processes

thereto Examples of such applicable proces

particles, and then the resultant mixture is gran

not less than a specific face pressure (EP 0844

powder of water-absorbent resin particles is

wetted to thus form an amorphous gel, and the

dried and pulverized (USP 4 ,950 ,692) , and a fin

water-absorbent resin particles and a polymer g

together (USP 5 ,478 ,879)

In addition, it is preferable that at least

water-absorbent resin particles usable in t

invention are foamed particles These foamed

preferably those which are obtained by

characterized by including the step of poly

monomer containing an azo initiator or a foaming

carbonate) or polymerizing the monomer while

bubbles by causing it to bubble with an inert gas

It is preferable that the water-absorbent

aqueous-hquid-absorbent resin of the present inv

bulk density within the range described in ( 1 -3)

granulated particles so as not deviate from the ra

rate , the absorbency, and the saline flow conducti

Conditions for pulverizing the hydropoly

pulverized hydropolymer particles (preferably,

dried it) are not especially limited However, f

hitherto known pulverizers (e g roll mills, hamm

usable The shape obtained by the pulverization i

an irregularly pulverized shape and, more

particles of a granulated shape having a large

are partly contained

The water-absorbent resin particles usa

present invention are, for example, further proces

as classification, whereby the weight-avera

diameter and the logarithmic standard deviati

adjusted in the range described in ( 1 -3)

water-absorbent resin particle s usable in t

invention, it is possible to further exhibit the e

present invention by adjusting the weight-aver

diameter and the logarithmic standard deviation

manner

the classification, it is difficult to completely rem

whose particle diameter is not more than 150 μ

order to obtain the water-absorbent resin part

water-absorbing agent having a desired particle di

preferable to suitably chose a type of the sieve to

For still more exerting the effects of

invention, the water-absorbent resin particles u

present invention include particles having particl

in the range of 1 50 to 850 μm preferably in an a

to 1 00 weight %, more preferably in an amount

weight % In case where particles of smaller tha

particle diameter are included in a large amount

possibility that the liquid permeability may be s

result in failure to sufficiently exert the effects of

invention In case where particles of larger than

particle diameter are included in a large amount

possibility that, on the occasion of the practi

example , an unpleasant feeling may be given to h

during the contact therewith

out in at least one stage selected from am

simultaneously with, and after the step of su

water-absorbent resin particles to the later-desc

permeability enhancing treatment step

As the surface crosslmkmg agent usable in

invention, it is possible to use the surface crossl

described in ( 1 - 1 )

Although depending upon compounds as

combination, and others, the amount of t

crosslmkmg agent, as used, is preferably in the

less than 0 00 1 and not more than 10 weig

preferably in the range of not less than 0 0 1 a

than 5 weight % , with respect to the water-absorb

In the present invention, it is preferable to

performing the surface crosslmkmg At this ti

depending on the water content of the water-abs

used, it is general that an amount of water is pr

less than 0 5 weight % and not more than 10 wei

preferably not less than 0 5 weight % and not m

respect to the water-absorbent resin

Further, in addition to the surface crosshnk

is possible to use acidic substances such as

(lactic acid, citric acid, p-toluene-sulfonic acid) a

acid (phosphoric acid, sulfuric acid, sulfurous

substance such as caustic soda and sodium

polyvalent metal such as aluminum sulfate, in an

to 10 weight %, more preferably 0 to 5 weight %,

preferably 0 to 1 weight %, with respe

water-absorbent resin

In case of performing the surface crosshn

present invention , after mixing water and / or the

organic solvent with the surface crosshnkmg agen

the aqueous liquid is preferably sprayed or dropp

the water-absorbent resin, and the aqueous liq

preferably sprayed to the water-absorbent resin

of the sprayed drop, its average particle diamete

ranges from 0 1 to 300 μm, more preferably fro

μm

double-wall circular cone mixer, a high-speed-sti

a V-shaped mixer, a ribbon blender, a scre

double-arm kneader, a pulverizing kneader, a

mixer, an air current mixer, a turbuhzer, a batch

mixer, and a sequential Lodige mixer

It is preferable that the water-absorbent

which the surface crosslinkmg agent has bee

subj ected to a heat-treatment A temperature a

heat-treatment is performed (heat medium tem

material temperature) preferably ranges from 12

more preferably from 1 50 to 250 ⁰ C The dura

heat-treatment preferably ranges from 1 minute t

Preferable examples of a combination of t

temperature and the heating duration are 0 1 to

180 ⁰ C and 0 1 to 1 hour at 200 ⁰ C

An apparatus for performing the heat-treat

particularly limited as long as the apparatus allo

uniformly conducted to the mixture of t

crosslinkmg agent and the water-absorbent resin

electron beam type

(2-6) Liquid permeability enhancing treatment ste

The process for producing an aqueous-hqu

agent according to the present invention prefera

the liquid permeability enhancing treatmen

subj ecting the water-absorbent resin particles t

for liquid permeability enhancement The liquid

enhancing treatment step may be carried out at

before, simultaneously with, or after the surface

step However, for more exerting the effects of

invention, it is preferable that the liquid

enhancing treatment step is carried out after

crosslmkmg step and separately therefrom

The liquid-permeabihty-enhancement age

preferably a water-soluble multivalent metal c

water-soluble polycationic compound, still more

1 water-soluble multivalent metal compound,

preferably at least one compound selected from

groups consisting of compounds having aluminum

over the entire surface of the water-absorbent r

demixmg and other demerits

The liquid-permeabihty-enhancement agent i

amount of preferably 0 00 1 to 1 0 weight % , mor

0 0 1 to 5 weight %, relative to the water-abs

particles

The method for addin

liquid-permeabihty-enhancement agent is not

limited It may be dry-blend,

liquid-permeabihty-enhancement agent may be a

form of an aqueous solution or a dispersion li

addition method may be carried out by heat-fusio

More specifically, the dry-blend is a method

water-absorbent resin particles are uniformly mi

above liquid-permeabihty-enhancement agent (w

and powdery) (e g the multivalent metal co

inorganic fine particles) after having been

pulverized If necessary, after this mixing, w

aqueous polyhydric alcohol solution may furth

or polycationic compound is, the more prefera

addition, after the mixing, heating may be car

necessary The heat-fusion is a method in which

is carried out at the same time as or after

multivalent metal hydrate (e g aluminum sulfate

alum, ammonium alum, sodium alum)

water-absorbent resin particles together,

water-absorbent resin particles having been pr

mixed with the multivalent metal compound,

multivalent metal hydrate is fused and then ma

to the water-absorbent resin particles If nece

may be added before the heating

[Examples]

Hereinafter, the present invention is more

illustrated by the following Examples and

Examples However, the present invention is no

them Hereinafter, for convenience , the units "we

and " liter(s) " may be referred to simply as " part

respectively In addition, the unit ' weight %" may

" "

RH%

Note that, the following statement is m

assumption that the water-absorbent resin or wat

agent is measured and evaluated Thus, in case o

the water-absorbing agent, the measurement is ca

replacing the "water-absorbent resin" descri

measurement method with the "water-absorbin

addition, in case where a commercially

water-absorbent resin or a water-absorbent resi

from a diaper is measured, it is measured

appropriately been dried under a reduced pressur

to 80 ⁰ C for 16 hours) so as to have a solid cont

100 weight %

(a) Absorbency (CRC Centrifuge Retention Capacit

An amount of 0 200 g of water-absorben

uniformly placed into a bag (80 mm x 60 m

nonwoven fabric (trade name Heatron Paper, ty

produced by Nangoku Pulp Kogyo Co , Ltd )

immersed into a physiological saline (here

the weight W i (g) of the bag was measured In a

same procedure as the above was carried out

water-absorbent resin, and the resultant weight

measured Then, the CRC (g/ g) was calculated fr

and Wo in accordance with the following equation

CRC (g/ g) = [(W i (g) - W ₀ (g)) / wei

water-absorbent resin] - 1

(b) Absorbency Against Pressure (AAP)

The absorbency against pressure (AAP) r

absorbency against pressure for a physiological

weight % aqueous sodium chloride solution) und

4 83 kPa in 60 minutes

The measurement was carried out with an a

shown in Fig 1

A stainless metal gauze 10 1 , which was a s

meshes (mesh opening size 38 μm) , was fused to

a plastic supporting cylinder 100 having an inner

60 mm Then, under conditions of a room

(23 0±2 0 ⁰ C) and a humidity of 50 RH%, onto the

the piston and the load were adj usted so that a

kPa (0 7 psi) could uniformly be appli

water-absorbent resin Then, the weight Wa

resultant one set of measurement apparatus was

A glass filter plate 106 having a diamete

(produced by Sogo Rikagaku Glass Seisakusho Co

diameter 100 to 120 μm) was mounted mside a Pe

having a diameter of 150 mm, and then a physiol

(0 9 weight % aqueous sodium chloride solution)

25 ⁰ C) was added up to the same level as the u

glass filter plate , on which a filter paper 10

diameter of 90 mm (produced by ADVANTEC Toy

trade name (JIS P 380 1 , No 2) , thickness 0 26 m

of captured particles 5 μm) was then mounted

entire surface would be wetted, and further, a

liquid was removed

The one set of measurement apparatus was

the above wet filter paper, thereby getting the liq

under the load for a predetermined duration Thi

(AAP) (g/ g) was calculated from the Wa and Wb in

with the following equation

AAP (g/ g) = [Wb (g) - Wa (g) ] / wei

aqueous-hquid-absorbmg agent

(c) Absorption rate (FSR Free Swell Rate)

1 000+0 0005 g of water-absorbent resin

out precisely to the fourth decimal place (unit

water-absorbent resin as weighed out was placed

glass beaker (diameter 32-34 mm, height 50 m

upside of the water-absorbent resin as placed int

was made horizontal If necessary, a treatment

cautiously tapping the beaker may be carried out

surface of the water-absorbent resin horizontal

of physiological saline (0 9 weight % aqueous sodi

solution) , of which the temperature had been

23 0±2 0 ⁰ C , was weighed out into a 50 ml glass

then the weight (unit g) was measured to the fo

place (W i) Then, the physiological saline as weig

carefully and quickly poured into the 25 ml beake

was ended when the upside, which had been

surface of the physiological saline at the start

replaced by the surface of the water-absorbent r

absorbed the physiological saline) as a res

absorption of the physiological saline

water-absorbent resin (unit sec) (t _s ) Next, the

g) of thei physiological saline, which remained atta

50 ml beaker after the pouring of the physiological

measured to the fourth decimal place (W2) The

unit g) of the poured physiological saline was

from the equation (a) below

The water absorption rate (FSR) was calcula

equation (c) below

Equation (a)

W _F (g) = W i (g) - W ₂ (g)

Equation (c)

FSR (g/ g/ s) = W _F / (tβ x WA)

The same measurement was carried out repe

times per one sample The measurement result wa

50959 1 / 1997 (Tokuhyohei 9 -50959 1 )

By using an apparatus shown in Fig 2

absorbent resin (0 900 g) evenly spread in a cont

swollen in a synthesized urine ( 1 ) under a pressu

(2 07 kPa) for 60 minutes, and a height of a gel l

44 was recorded Then, under a pressure of 0 3 p

0 69 mass % sodium chloride solution 33 was

from a tank 3 1 and to pass through the swollen g

constant hydrostatic pressure

By using a computer and a scale , an amou

passing through the gel layer at intervals of 20

recorded for 10 minutes as a time function A flow

the solution passing through the swollen gel

between particles thereof) was determined in ter

dividing an increasing weight (g) by an increasin

time in which a constant hydrostatic pressure a

flow rate had been obtained was set as "t _s " , an

obtained between "t _s " and a ten-minute interval

calculate the flow rate, the flow rate calculated

= (Fs (t=0) x Lo)/(p ^χ AxδP)

Here,

F _s (t=0) a flow rate represented by "g/s"

Lo a height of the gel layer that is represent

p a density (1 003 g/cm ³ ) of NaCl solution

A an area (2827 cm ² ) on the upper side of

of the cell 41

δP a hydrostatic pressure (4920 dyne/cm ²

the gel layer Further, a unit of the saline flow

(SFC) is (cm ³ s 10 ⁷ /g)

In the apparatus shown in Fig 2, a glass t

inserted into the tank 31, and a lower end of th

32 was disposed so that 069 weight % sodi

solution 33 was positioned 5 cm higher than a b

swelling gel 44 in the cell 41 069 mass % sodi

solution 33 contained in the tank 31 was supplie

41 via an L-shaped tube 34 with a cock

container 48 for collecting liquid having passed

glass filter 45 having high permeability was pro

bottom thereof so that the water-absorbent resin

or the swelling gel did not enter into the hole 47

was placed on a table for the cell, and the tab

which is in contact with the cell was positio

stainless metal gauze 43 which did not preven

from passing through

The synthesized urine ( 1 ) was prepared by m

of calcium chloride dihydrate, 2 0 g of potassi

0 5O g of magnesium chloride hexahydrate, 2 0

sulfate, 0 85 g of ammonium dihydrogen phospha

ammonium dihydrogen phosphate, and 994 25

water

(e) Particle diameter

The water absorbent resin having been pul

sieved by using JIS standard sieves respectively

sizes of 850 μm, 7 10 μm, 600 μm, 500 μm, 425

2 12 μm, 150 μm, 45 μm, and the like, and

percentage R was plotted on a logarithmic proba

distribution

The water absorbent resin was sieved b

standard sieves respectively having mesh sizes of

μm, 600 μm, 500 μm, 425 μm, 300 μm, 2 12 μm,

μm, and the like , and a residual percentage R wa

a logarithmic probability paper Note that, in c

water-absorbent resin whose particle diameter

μm, a commercially available JIS standard

opening mesh size exceeds 850 μm Further, as

X l is a particle diameter in case where R=84 1 w

X2 is a particle diameter in case where R= 1 5 9 w

logarithmic standard deviation (σζ) is represen

following equation As a value of σζ is smaller,

diameter distribution is narrower

σζ= 0 5 x In (X2 / X 1 )

Classification in measuring (e) the particle di

(f) the logarithmic standard deviation (σζ) of

diameter distribution was performed as follows 1

water absorbent resin particles or the water abs

(g) Bulk density

The bulk density of the water-absorbent re

was measured in accordance with a method d

edana 460 1 -99

(h) Extractable Component Content

184 3 g of a pysiological saline (0 90 w

aqueous sodium chloride solution) was measure

into a 250 ml plastic container having a cove

aqueous solution, 1 00 g of a water absorben

added, and the solution was stirred for 16 hours

an extractable component of the water absorben

extracted The extract solution was filtered throug

filter paper (product of ADVANTEC Toyo Kaisha, L

name JIS P380 1 , No 2 , thickness 0 26 mm,

retained particles 5 μm) , thereby obtaining a filt

of the filtrate was measured, and used as a

solution

First, only the physiological saline was titrat

a 0 I N NaOH aqueous solution, until pH of the p

([NaOH]ml and [HCl]ml)

For example, in case of a water-abso

including a known amount of acrylic acid and its

an extractable component content in the wat

resin was calculated, in accordance with t

equation, from an average molecular mass of t

and the, titration amounts obtained by the foregoi

In case of an unknown amount, the average molec

the monomer was calculated by using a neutral

calculated by the titration

Extractable component (wt %) = 0 1 x (avera

mass) x 1843 x 100 x ([HCl]-[bHCl])/ 1000/ 1 0/50

Neutralization ratio (mol %) = (l-([NaO

/([HClHbHCl])) x 100

(i) Solid content or water content

1 000 g of a water-absorbent resin was wei

the third decimal place, and was placed in an al

(diameter 52 mm), and was heated for three

windless oven at 180 ⁰ C Then, a solid content

Water content (wt %) = {(weight of sample

been dried - weight of dried samplej / weight of sa

not been dried} * 100

(j) Surface Tension

50 ml of physiological saline whose temp

been adjusted to 20 ⁰ C was poured into a 100 ml

had been sufficiently rinsed First, a surface te

physiological saline was measured by using a

(K I l automatic tensiometer, product of KRUS

measurement, the surface tension needs to be wi

of 7 1 to 75 mN / m Next, a sufficiently rinsed fl

whose length was 25 mm and 0 5 g of the wat

agent were put into the beaker containing the

saline whose temperature had been adjusted to

were stirred for 4 minutes under a condition of

minutes later, the stirring operation was stopp

water-absorbing agent containing water was

Thereafter, a surface tension of a supernatant

measured by performing the same operation agai

1 g of water-absorbing agent was put into

physiological saline (09 mass % aqueous sodi

solution), and the mixture was stirred with a m

by using a stirrer chip whose length was 30 mm

under a condition of 300 r p m The stirred

saline was filtered An extract obtained as a

analyzed by Liquid Chromatography and was qua

analytical curve which had been prepared in ad

that, the analytical curve was prepared by analyzi

prepared so as to have known amounts of about

200, 500, 1000, 2000, and 5000 ppm As an anal

Shodex SUGAR SHlOIl (product of Showa Denk

used

[Example 1]

(Operation 1-1)

In a polypropylene-made container of 80

diameter and 1 liter in capacity as covered with

foam being a heat insulator, a solution (A) was

mixing 293 g (4 1 mol) of acrylic acid, 0215 g (

(Registered Trademark) 1 84 together, and a solu

prepared by mixing (i) a mixture solution of 23

weight % of aqueous sodium hydroxide solution

ion-exchanged water of which the temperatur

adjusted to 50 ⁰ C with (ii) 0 20 g (0 04 mol % wit

the unsaturated monomer having a carboxyl

meso-erithπtol together The solution (B) was q

to the solution (A) being stirred with a magnetic s

length was 5 cm under a condition of 800 r p m

together, thus obtaining an aqueous monomer sol

to the aqueous monomer solution (C) , its liquid

rose to about 100 ⁰ C due to the neutralization h

dissolution heat Note that, a neutralization rati

acid was 70 mol %

Next, 1 1 g of 3 weight % aqueous sodiu

solution was added to this aqueous monomer s

Immediately after stirring carried out for about 1

resultant mixture was poured into a stainles

container having an inner surface as coated

solution (C) into the vat, polymerization

temperature of the polymerization reached its

about 1 minute After 3 minutes, the ultraviole

was stopped, and then the resultant hydropoly

out Note that, a series of these operations were c

an open system of the atmosphere

(Operation 1 -2)

The resultant hydropolymer was pulverized

chopper (MEAT-CHOPPER, Type 12VR-400KSOX,

Iizuka Kogyo Co , Ltd , die perforation diameter =

number of perforations = 38 , die thickness = 8

obtaining hydropolymer particles having been

small pieces

(Operation 1 -3)

The resultant pulverized hydropolymer part

been divided into small pieces were spread onto a

of 50 meshes (opening size 300 μm) and then dr

air of 180 ⁰ C Next, the dried product was pulve

roll mill and then classified with JIS standard sie

cro sslmkmg agent solution comprising a mixed

weight part of 1 , 4-butanediol, 0 6 weight part

glycol, and 3 0 weight parts of pure water

water-absorbent resin, which had been mixed wit

crosslmkmg agent solution, was heat-treated

crosslmkmg with a heating apparatus having a j

temperature 2 10 ⁰ C) for 35 minutes Afte

treatment, the resultant water-absorbent

disintegrated to such a degree that they could pa

JIS standard sieve having a mesh opening size of

a result, surface-crosslmked water-absorbent r

obtained The water-absorbent resin ( 1 ) was

water-absorbing agent ( 1 ) Table 1 shows prope

water-absorbing agent ( 1 )

Note that, an amount of unreacted meso-erit

water-absorbing agent analyzed by usi

Chromatography was 280 ppm with respe

water-absorbing agent

Table 1

Ex Example

C-Ex Comparative Example

W-A agent Water-absorbing agent

C-W-A agent Comparative water-absorbing agent

^* 4 (g/ g)

* 5 (g/ g/ s)

[Example 2 ]

The same operations as in Example 1 were

except that 0 20 g (0 04 mol % with resp

unsaturated monomer having a carboxyl group) of

crosslmkmg agent meso-eπthπtol was changed

(0 04 mol % with respect to the unsaturated mon

a carboxyl group) of xylitol, thereby o

surface-crosshnked water-absorbent resin

water-absorbent resin (2) was used as a wat

agent (2) Table 1 shows properties of the wat

agent (2)

Note that, an amount of unreacted xyl

water-absorbing agent analyzed by usi

Chromatography was 460 ppm with respe

water-absorbing agent

[Examples 3 to 5]

The same operations as in Example 1 were

water-absorbent resins (3) to (5) were

water-absorbing agents (3) to (5) Table 1 shows

the water-absorbing agents (3) to (5) Note that,

4, and 5 were slightly different from Exampl

heat-treatment duration The heat-treatment d

Examples 3 , 4 , and 5 were respectively 25

minutes, and 40 minutes

In Example 5 , an amount of unreacted sor

water-absorbing agent analyzed by usi

Chromatography was 280 ppm with respe

water-absorbing agent

[Example 6]

The same operations as in Example 1 were

except that 0 20 g (0 04 mol % with resp

unsaturated monomer having a carboxyl group) of

crosslinking agent meso-erithπtol was changed

(0 04 mol % with respect to the unsaturated mon

a carboxyl group) of D - sorbit

polyethyleneglycoldiacrylate serving as othe

Note that, an amount of unreacted sorb

water-absorbing agent analyzed by usi

Chromatography was 250 ppm with respe

water-absorbing agent

[Comparative Example 1 ]

The same operations as in Example 1 were

except that 1 10 g (0 05 mol % with resp

unsaturated monomer having a carbox

polyethyleneglycoldiacrylate was solely used as

crosslinkmg agent and meso-eπthπtol was not u

obtaining a comparative water-absorbent resi

comparative water-absorbent resin ( 1 ) was

comparative water-absorbing agent ( 1 ) Tabl

properties of the comparative water-absorbing age

[Comparative Examples 2 and 3]

The same operations as in Example 1 were

except that 0 20 g (0 04 mol % with resp

unsaturated monomer having a carboxyl group) of

crosslinkmg agent meso-erithπtol was changed

and (3) were used as comparative water-absorbin

and (3) Table 1 shows properties of the

water-absorbing agents (2) and (3)

[Comparative Examples 4 and 5]

The same operations as in Example 1 were

except that 0 20 g (0 04 mol % with resp

unsaturated monomer having a carboxyl group) of

crosshnkmg agent meso-erithπtol was changed

(0 04 mol % with respect to the unsaturated mon

a carboxyl group) of glycerin (polyethylenegly

serving as other internal crosshnkmg agent was

Example 1 ) , thereby obtaining surface

comparative water-absorbent resins (4) and

comparative water-absorbent resins (4) and (5) w

comparative water-absorbing agents (4) and (

shows properties of the comparative water-absor

(4) and (5)

In Comparative Example 4 , an amount o

glycerin in the water-absorbing agent analyze

which a liquid-permeabihty-enhancement agent

Table 2 shows properties of the water-absorbing a

(Operation 1 - 5)

1 weight part of aluminum sulfate hydrate

tetradecane hydrate obtained from Sumitomo C

Ltd ) was uniformly mixed with 100 weight

surface-crosshnked water-absorbent resin (

obtaining a water-absorbing agent (7) Tabl

properties of the water-absorbing agent (7)

- I l l -

Table 2

Ex Example

C-Ex Comparative Example

W-A agent Water-absorbing agent

C-W-A agent Comparative water-absorbing agent

^* 4 (g/ g)

*5 (g/ g/ s)

[Examples 8 to 12]

The same operations as in Example 7 were

except that the water-absorbent resm ( 1 ) was ch

water-absorbent resins (2) to (6) obtained in Exa

thereby obtaining water-absorbing agents (8) to (

liquid-permeabihty-enhancement agents were ad

shows properties of the water-absorbing agents (8

[Comparative Examples 6 to 10]

The same operations as in Example 7 were

except that the water-absorbent resm ( 1) was ch

comparative water-absorbent resins ( 1 ) to (5)

Comparative Examples 1 to 5 , thereby obtaining

water-absorbing agents (6) to ( 10)

liquid-permeabihty-enhancement agents were ad

shows properties of the comparative water-abso

(6) to ( 10)

The invention being thus described, it will

INDUSTRIAL APPLICABILITY

The pre sent invention relates to a water-abs

whose liquid permeability has been enhan

production method thereof If the water-absorbi

used for sanitary materials such as a disposable

water-absorbing agent exhibits higher liquid

than that of a conventional water absorbent st

allows improvement in terms of problems s

absorbency and leakage which are caused by gel b

Further, the water-absorbing agent accor

present invention is widely applicable not only to

materials but also to conventional usag

water-absorbent resin, e g , agriculture / horticu

water proofing agent, civil engineering and const

food products

Therefore, the present invention is applicable

sanitary material production industry, horticultu

civil engineering and construction industry, food

industry, which respectively produce the foregoin