U.S. patent application number 15/324753 was filed with the patent office on 2017-07-27 for water-absorbent resin and method of producing water-absorbent resin.
The applicant listed for this patent is Sumitomo Seika Chemicals Co. Ltd.. Invention is credited to Tetsuhiro Hinayama, Masahiro Murakami, Hiroki Yabuguchi, Hideki Yokoyama.
Application Number | 20170210831 15/324753 |
Document ID | / |
Family ID | 55063798 |
Filed Date | 2017-07-27 |
United States Patent
Application |
20170210831 |
Kind Code |
A1 |
Hinayama; Tetsuhiro ; et
al. |
July 27, 2017 |
WATER-ABSORBENT RESIN AND METHOD OF PRODUCING WATER-ABSORBENT
RESIN
Abstract
Provided is a water-absorbent resin that increases the
diffusivity of a to-be-absorbed liquid and that makes it possible
to effectively decrease the amount of re-wet. The water-absorbent
resin is obtained by polymerizing a water-soluble ethylenicallyally
unsaturated monomer under the presence of an internal-crosslinking
agent, has the water-absorption capacity of physiological saline
under a load of 4.14 kPa at 120 minutes passed from the start of
water absorption of 20 ml/g or more, and exhibits the degree of
swelling under a load at 30 minutes of 70% or less when the
water-absorption capacity of physiological saline under a load of
4.14 kPa at 120 minutes from the start of water absorption is
designated as the degree of swelling under a load of 100%.
Inventors: |
Hinayama; Tetsuhiro;
(Himeji-shi, JP) ; Murakami; Masahiro;
(Himeji-shi, JP) ; Yabuguchi; Hiroki; (Himeji-shi,
JP) ; Yokoyama; Hideki; (Himeji-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Seika Chemicals Co. Ltd. |
Kako-gun |
|
JP |
|
|
Family ID: |
55063798 |
Appl. No.: |
15/324753 |
Filed: |
November 4, 2014 |
PCT Filed: |
November 4, 2014 |
PCT NO: |
PCT/JP2014/079242 |
371 Date: |
January 9, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 8/14 20130101; A61L
15/60 20130101; A61F 13/49 20130101; A61F 13/15 20130101; B01J
20/267 20130101; A61F 13/53 20130101; C08F 2/32 20130101; A61L
15/24 20130101 |
International
Class: |
C08F 8/14 20060101
C08F008/14; A61L 15/60 20060101 A61L015/60; B01J 20/26 20060101
B01J020/26; A61L 15/24 20060101 A61L015/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2014 |
JP |
2014-143714 |
Oct 31, 2014 |
JP |
2014-223721 |
Claims
1. A method of producing a water-absorbent resin by performing
reversed phase suspension polymerization of a water-soluble
ethylenically unsaturated monomer in the presence of an
internal-crosslinking agent in a hydrocarbon dispersion medium, the
method comprising the steps of: performing polymerization step in
the presence of an azo based compound and a peroxide, and
performing post-crosslinking step of a hydrous gel-like material
obtained from the polymerization using a post-crosslinking
agent.
2). The method of producing a water-absorbent resin according to
claim 1, wherein the azo based compound is at least one selected
from the group consisting of
2,2'-azobis(2-amidinopropane)dihydrochloride,
2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline-2-yl]propane}dihydrochlor-
ide and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropione
amidine]tetrahydrate.
3. The method of producing a water-absorbent resin according to
claim 1, wherein the peroxide is at least one selected from the
group consisting of potassium persulfate, ammonium persulfate,
sodium persulfate and hydrogen peroxide.
4. The method of producing a water-absorbent resin according to
claim 1, wherein the internal-crosslinking agent is at least one
selected from the group consisting of (poly)ethylene glycol
diglycidyl ether, (poly)propylene glycol diglycidyl ether and
(poly)glycerin diglycidyl ether.
5. A water-absorbent resin obtained by polymerizing a water-soluble
ethylenically unsaturated monomer in the presence of an
internal-crosslinking agent, and performing post-crosslinking with
a post-crosslinking agent, wherein a water-absorption capacity of
physiological saline under a load of 4.14 kPa at 120 minutes passed
from the start of water absorption is 20 ml/g or more, and the
degree of swelling under a load at 30 minutes is 70% or less when
the water-absorption capacity of physiological saline under a load
of 4.14 kPa at 120 minutes passed from the start of water
absorption is taken as a degree of swelling under a load of 100%,
and the degree of swelling under a load at a certain time passed is
calculated by the following formula: Degree of swelling under a
load at a certain time passed ( % ) = Water absorption capacity for
physiological saline under a load of 4.14 kPa at a certain time
passed ( ml / g ) Water absorption capacity for physiological
saline under a load of 4.14 kPa at 120 minutes passed ( ml / g )
.times. 100 [ Formula 1 ] ##EQU00006##
6. An absorbent article using an absorbent material comprising the
water-absorbent resin according to claim 5.
7. The method of producing a water-absorbent resin according to
claim 2, wherein the peroxide is at least one selected from the
group consisting of potassium persulfate, ammonium persulfate,
sodium persulfate and hydrogen peroxide.
8. The method of producing a water-absorbent resin according to
claim 2, wherein the internal-crosslinking agent is at least one
selected from the group consisting of (poly)ethylene glycol
diglycidyl ether, (poly)propylene glycol diglycidyl ether and
(poly)glycerin diglycidyl ether.
9. The method of producing a water-absorbent resin according to
claim 3, wherein the internal-crosslinking agent is at least one
selected from the group consisting of (poly)ethylene glycol
diglycidyl ether, (poly)propylene glycol diglycidyl ether and
(poly)glycerin diglycidyl ether.
10. The method of producing a water-absorbent resin according to
claim 7, wherein the internal-crosslinking agent is at least one
selected from the group consisting of (poly)ethylene glycol
diglycidyl ether, (poly)propylene glycol diglycidyl ether and
(poly)glycerin diglycidyl ether.
Description
TECHNICAL FIELD
[0001] The present invention relates to a water-absorbent resin and
a method of producing the water-absorbent resin. More specifically,
the present invention relates to a water-absorbent resin comprising
an absorbent material suitably used for hygienic materials such as
disposable diapers, sanitary napkins and incontinence pads, and
also relates to a method of producing such the water-absorbent
resin.
[0002] BACKGROUND ART
[0003] In recent years, water-absorbent resins have been widely
used in the field of hygienic materials such as disposable diapers,
sanitary napkins and incontinence pads.
[0004] For water-absorbent resins as described above, crosslinked
products of partially neutralized polymers of acrylic acid salt are
preferred because they have many advantages, including the
followings: they have better water absorption performance; their
raw materials such as acrylic acid are easily and industrially
available, and therefore they can be produced with stable quality
and low cost; and they are more resistant to decomposition and
deterioration.
[0005] Preferred properties of water-absorbent resins for hygienic
materials such as sanitary napkins and disposable diapers include a
high water-retention capacity, a better water-absorption rate, a
high water-absorption capacity under a load and the like. However,
for example, since the water-retention capacity and the
water-absorption rate are in a contradictory relationship with the
water-absorption capacity under a load, it is difficult to satisfy
a balance between these properties.
[0006] As technologies to improve the above properties suitably
used for hygienic materials, the followings are known: for example,
a method of performing reversed phase suspension polymerization
using a specific amount of specific macromolecular protective
colloid and surfactant (see Patent Document 1); a method of
performing reversed phase suspension polymerization in two or more
steps (see Patent Document 2); a method of performing reversed
phase suspension polymerization in the presence of
.beta.-1,3-glucans to obtain a water-absorbent resin and further
performing a cross-linking reaction by adding a cross-linking agent
to the water-absorbent resin obtained (see Patent Document 3); a
method of performing reversed phase suspension polymerization using
a specific amount of persulfate (see Patent Document 4); a method
of performing aqueous polymerization in the presence of phosphorous
acid and/or a salt thereof to obtain a water-absorbent resin
precursor, and then mixing the water-absorbent resin precursor with
a surface cross-linking agent followed by heating (see Patent
Document 5).
[0007] However, water-absorbent resins obtained by these methods do
not necessarily satisfy those properties such as the high
water-retention capacity, the high water-absorption capacity under
a load and the better water-absorption rate as described above, and
a room for improvement still remains.
[0008] Further, when a water-absorbent resin showing a relatively
rapid water-absorption rate is used in an absorbent material
comprising a water-absorbent resin, the water-absorbent resin may
locally absorb a to-be-absorbed liquid around a feeding position of
the to-be-absorbed liquid, and the liquid is often blocked because
the water-absorbent resin becomes swollen and denser. Moreover, in
this case, since the diffusibility of the to-be-absorbed liquid
into the absorbent material is prevented by the gelatinized
water-absorbent resin, and the to-be-absorbed liquid may not be
easily distributed throughout the absorbent material, the amount of
re-wet of the to-be-absorbed liquid tends to be larger.
PRIOR ART DOCUMENT
Patent Documents
[0009] Patent Document 1: Japanese Unexamined Patent Application
Publication No. H06-345819
[0010] Patent Document 2: Japanese Unexamined Patent Application
Publication No. H03-227301
[0011] Patent Document 3: Japanese Unexamined Patent Application
Publication No. H08-120013
[0012] Patent Document 4: Japanese Unexamined Patent Application
Publication No. H06-287233
[0013] Patent Document 5: Japanese Unexamined Patent Application
Publication No. H09-124710
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0014] The present invention is proposed in view of these actual
circumstances as described above. An objective of the present
invention is to provide a water-absorbent resin capable of
improving the diffusibility of a to-be-absorbed liquid to
effectively reduce the amount of re-wet when used for an absorbent
material. Another objective of the present invention is to provide
a method of producing the above water-absorbent resin.
Means for Solving the Problems
[0015] The present inventors conducted extensive studies in order
to solve the problems described above. As a result, the present
inventors have found that a water-absorbent resin obtained by
polymerizing a water-soluble ethylenically unsaturated monomer in
the presence of an internal-crosslinking agent, in which the
water-absorption capacity of physiological saline under a load of
4.14 kPa at 120 minutes passed from the start of water absorption
is 20 ml/g or more, and the degree of swelling under a load at 30
minutes is 70% or less when the water-absorption capacity of
physiological saline under a load of 4.14 kPa at 120 minutes passed
from the start of water absorption is taken as a degree of swelling
under a load of 100% can increase the diffusibility of a
to-be-absorbed liquid in an absorbent material when used in the
absorbent material, enabling effective reduction of the amount of
re-wet. Further, the present inventors have found that these
water-absorbent resins described above can be obtained by a
producing method in which reversed phase suspension polymerization
of a water-soluble ethylenically unsaturated monomer is performed
in a hydrocarbon dispersion medium, the method comprising
performing polymerization in the presence of an azo based compound
and a peroxide. That is, the present invention provides the
followings.
[0016] (1) The present invention provides a method of producing a
water-absorbent resin by performing reversed phase suspension
polymerization of a water-soluble ethylenically unsaturated monomer
in the presence of an internal-crosslinking agent in a hydrocarbon
dispersion medium, the method comprising the steps of: performing
polymerization step in the presence of an azo based compound and a
peroxide; and performing post-crosslinking step of a hydrous
gel-like material obtained from the polymerization using a
post-crosslinking agent.
[0017] (2) The invention also provides the method of producing a
water-absorbent resin according to (1), wherein the azo based
compound is at least one selected from the group consisting of
2,2'-azobis(2-amidinopropane)dihydrochloride,
2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline
2-yl]propane}dihydrochloride and
2,2'-azobis[N-(2-carboxyethyl)-2-methylpropione
amidine]tetrahydrate.
[0018] (3) The present invention also provides the method of
producing a water-absorbent resin according to (1) or (2), wherein
the peroxide is at least one selected from the group consisting of
potassium persulfate, ammonium persulfate, sodium persulfate and
hydrogen peroxide.
[0019] (4) The present invention also provides the method of
producing a water-absorbent resin according to any one of (1) to
(3), wherein the internal-crosslinking agent is at least one
selected from the group consisting of (poly)ethylene glycol
diglycidyl ether, (poly)propylene glycol diglycidyl ether and
(poly)glycerin diglycidyl ether.
[0020] (5) The present invention provides a water-absorbent resin
obtained by performing polymerization of a water-soluble
ethylenically unsaturated monomer in the presence of an
internal-crosslinking agent, and performing post-crosslinking using
a post-crosslinking agent, wherein the water-absorption capacity of
physiological saline under a load of 4.14 kPa at 120 minutes passed
from the start of water absorption is 20 ml/g or more, and the
degree of swelling under a load at 30 minutes is 70% or less when
the water-absorption capacity of physiological saline under a load
of 4.14 kPa at 120 minutes passed from the start of water
absorption is taken as a degree of swelling under a load of 100%.
Note that the degree of swelling under a load at a certain time
passed is calculated by the following formula:
Degree of swelling under a load at a certain time passed ( % ) =
Water absorption capacity for physiological saline under a load of
4.14 kPa at a certain time passed ( ml / g ) Water absorption
capacity for physiological saline under a load of 4.14 kPa at 120
minutes passed ( ml / g ) .times. 100 [ Formula 1 ]
##EQU00001##
[0021] (6) The present invention also provides an absorbent article
using an absorbent material comprising the water-absorbent resin
according to (5).
Effects of the Invention
[0022] The present invention can provide a water-absorbent resin in
which the diffusibility of a to-be-absorbed liquid can be improved
to effectively reduce the amount of re-wet when used for an
absorbent material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows a pattern diagram illustrating the schematic
arrangement of an apparatus for measuring, in a water-absorbent
resin, a water-absorption capacity of physiological saline under a
load of 4.14 kPa.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0024] The present invention will be described in detail below.
1. Method of Producing Water-Absorbent Resin
[0025] The method of producing a water-absorbent resin according to
the present invention is a method of performing reversed phase
suspension polymerization of a water-soluble ethylenically
unsaturated monomer in a hydrocarbon dispersion medium in the
presence of an internal-crosslinking agent, characterized by
comprising the steps of: performing polymerization step in the
presence of an azo based compound and a peroxide; and performing
post-crosslinking step of a hydrous gel-like material obtained from
the polymerization using a post-crosslinking agent.
<Polymerization Step>
[Water-soluble Ethylenically Unsaturated Monomer]
[0026] Water-soluble ethylenically unsaturated monomers include,
for example, (meth)acrylic acid ("(meth)acry" herein refers to both
"acry" and "methacry". The same shall apply hereinafter) and salts
thereof; 2-(meth)acrylamide-2-methylpropanesulfonic acid and salts
thereof; nonionic monomers such as (meth) acrylamide,
N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate,
N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate;
amino group-containing unsaturated monomers such as
N,N-diethylaminoethyl(meth)acrylate,
N,N-diethylaminopropyl(meth)acrylate,
diethylaminopropyl(meth)acrylamide and quaternary compounds
thereof. Among these water-soluble ethylenically unsaturated
monomers, (meth)acrylic acid or salts thereof, (meth)acrylamide,
N,N-dimethylacrylamide are preferred in view of easy industrial
availability, and (meth)acrylic acid and salts thereof are more
preferred. Note that these water-soluble ethylenically unsaturated
monomers may be used alone or in combination of two or more.
[0027] Among these, acrylic acid and salts thereof are widely used
as raw materials for water-absorbent resins, and those materials
may be used in which the aforementioned other water-soluble
ethylenically unsaturated monomers are copolymerized with these
partially neutralized acrylates. In this case, a partially
neutralized acrylate is preferably used as a main water-soluble
ethylenically unsaturated monomer in an amount of 70 to 100 mol %
relative to the total amount of water-soluble ethylenically
unsaturated monomers.
[0028] A water-soluble ethylenically unsaturated monomer is
preferably dispersed in a hydrocarbon dispersion medium in the
state of an aqueous solution, and subjected to reversed phase
suspension polymerization. A water-soluble ethylenically
unsaturated monomer in the form of an aqueous solution can increase
the dispersion efficiency in a hydrocarbon dispersion medium. The
concentration of a water-soluble ethylenically unsaturated monomer
in the aqueous solution is preferably in a range from 20 mass % to
the saturation concentration. Further, the concentration of a
water-soluble ethylenically unsaturated monomer is more preferably
55 mass % or less, further preferably 50 mass % or less and further
more preferably 45 mass % or less. On the other hand, the
concentration of a water-soluble ethylenically unsaturated monomer
is more preferably 25 mass % or more, further preferably 28 mass %
or more, and further more preferably 30 mass % or more.
[0029] When a water-soluble ethylenically unsaturated monomer has
an acid group such as (meth)acrylic acid,
2-(meth)acrylamide-2-methylpropanesulfonic acid, those having the
acid group pre-neutralized with an alkaline neutralizer may be
used, if desired. Such alkaline neutralizers include alkali metal
salts such as sodium hydroxide, sodium carbonate, sodium hydrogen
carbonate, potassium hydroxide, potassium carbonate; ammonia and
the like. Further, these alkaline neutralizers may be used in the
form of an aqueous solution in order to simply neutralization
procedures. Note that the aforementioned alkaline neutralizers may
be used alone or in combination of two or more.
[0030] For the degree of neutralization of a water-soluble
ethylenically unsaturated monomer with an alkaline neutralizer, the
degree of neutralization of all acid groups in the water-soluble
ethylenically unsaturated monomer is preferably 10 to 100 mol %,
more preferably 30 to 90 mol %, further preferably 40 to 85 mol %
and further more preferably 50 to 80 mol %.
[Hydrocarbon Dispersion Media]
[0031] Hydrocarbon dispersion media include, for example, aliphatic
hydrocarbons having 6 to 8 carbon atoms such as n-hexane,
n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane,
3-ethylpentane, n-octane; alicyclic hydrocarbons such as
cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane,
trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane,
trans-1,3-dimethylcyclopentane; aromatic hydrocarbons such as
benzene, toluene, xylene and the like. Among these hydrocarbon
dispersion media, in particular, n-hexane, n-heptane, cyclohexane
are suitably used in view of easy industrial availability, stable
quality and low cost. These hydrocarbon dispersion media may be
used alone or in combination of two or more. Note that examples of
a mixture of hydrocarbon dispersion media include commercially
available products such as EXXSOL heptane (made by ExxonMobil
Corporation: 75 to 85 mass % of heptane and its isomeric
hydrocarbons thereof are contained), which can also produce a
suitable result.
[0032] The used amount of the hydrocarbon dispersion medium is
preferably 100 to 1500 parts by mass relative to 100 parts by mass
of a first-step water-soluble ethylenically unsaturated monomer,
and more preferably 200 to 1400 parts by mass. Note that as
described below, reversed phase suspension polymerization is
performed in one step (single step) or in multiple steps such as
two or more steps, and the first-step polymerization described
above means a polymerization reaction of the first step in
single-step polymerization or multiple-step polymerization (The
same shall apply hereinafter).
[Dispersion Stabilizer]
[0033] A dispersion stabilizer may be used in reversed phase
suspension polymerization in order to improve the dispersion
stability of a water-soluble ethylenically unsaturated monomer in a
hydrocarbon dispersion medium.
(Surfactant)
[0034] A surfactant can be used as the dispersion stabilizer. As
surfactants, the followings may be used: for example, sucrose fatty
acid ester, polyglycerin fatty acid, sorbitan fatty acid ester,
polyoxyethylene sorbitan fatty acid ester, polyoxyethylene
glycerine fatty acid ester, sorbitol fatty acid ester,
polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl
ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor
oil, polyoxyethylene hydrogenated castor oil, alkyl allyl
formaldehyde condensed polyoxyethylene ether, polyoxyethylene
polyoxypropylene block copolymer, polyoxyethylene polyoxy propyl
alkyl ether, polyethylene glycol fatty acid ester, alkyl glucoside,
N-alkyl gluconamide, polyoxyethylene fatty acid amide,
polyoxyethylene alkylamine, phosphate ester of polyoxyethylene
alkyl ether, phosphate ester of polyoxyethylene alkyl aryl ether
and the like. Among these surfactants, in particular, sorbitan
fatty acid ester, polyglycerin fatty acid ester, and sucrose fatty
acid ester are preferably used in view of dispersion stability of
monomers. These surfactants may be used alone or in combination of
two or more.
[0035] The used amount of the surfactant is preferably 0.1 to 30
parts by mass relative to 100 parts by mass of a first-step
water-soluble ethylenically unsaturated monomer, and more
preferably 0.3 to 20 parts by mass.
(Polymeric Dispersion Agent)
[0036] Further, a polymeric dispersion agent may also be used,
along with a surfactant described above, as a dispersion
stabilizer. Polymeric dispersion agents include, for example,
maleic anhydride modified polyethylene, maleic anhydride modified
polypropylene, maleic anhydride modified ethylene-propylene
copolymer, maleic anhydride modified EPDM
(ethylene-propylene-diene-terpolymer), maleic anhydride modified
polybutadiene, maleic anhydride-ethylene copolymer, maleic
anhydride-propylene copolymer, maleic anhydride-ethylene-propylene
copolymer, maleic anhydride-butadiene copolymer, polyethylene,
polypropylene, ethylene-propylene copolymer, oxidized polyethylene,
oxidized polypropylene, oxidized ethylene-propylene copolymer,
ethylene-acrylate copolymer, ethyl cellulose, ethyl hydroxyethyl
cellulose and the like. Among these polymeric dispersion agents,
particularly in view of dispersion stability of monomers, maleic
anhydride modified polyethylene, maleic anhydride modified
polypropylene, maleic anhydride modified ethylene-propylene
copolymer, maleic anhydride-ethylene copolymer, maleic
anhydride-propylene copolymer, maleic anhydride-ethylene-propylene
copolymer, polyethylene, polypropylene, ethylene-propylene
copolymer, oxidized polyethylene, oxidized polypropylene, oxidized
ethylene-propylene copolymer are preferably used. These polymeric
dispersion agents may be used alone or in combination of two or
more.
[0037] The used amount of the polymeric dispersion agent is
preferably 0.1 to 30 parts by mass relative to 100 parts by mass of
a first-step water-soluble ethylenically unsaturated monomer, and
more preferably 0.3 to 20 parts by mass.
[Internal-crosslinking Agent]
[0038] The internal-crosslinking agents include, for example,
unsaturated polyesters obtained by allowing polyols, for example,
diols and triols such as (poly)ethylene glycol ("(poly)" means that
the prefix "poly" is optional. The same shall apply hereinafter.),
(poly)propylene glycol, 1,4-butanediol, trimethylolpropane,
(poly)glycerin to react with unsaturated acids such as
(meth)acrylic acid, maleic acid, fumaric acid; bisacrylamides such
as N,N-methylenebisacrylamide; di(meth)acrylic acid esters or
tri(meth)acrylic acid esters obtained by allowing polyepoxide to
react with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters
obtained by allowing polyisocyanate such as tolylene diisocyanate,
hexamethylene diisocyanate to react with (meth)acrylic acid
hydroxyethyl; compounds having two or more polymerizable
unsaturated groups, for example, allylated starch, allylated
cellulose, diallyl phthalate, N,N',N''-triallylisocyanate,
divinylbenzene and the like; polyglycidyl compounds, for example,
diglycidyl compounds such as (poly)ethylene glycol diglycidyl
ether, (poly)propylene glycol diglycidyl ether, (poly)glycerin
diglycidyl ether, triglycidyl compounds and the like; epihalohydrin
compounds such as epichlorohydrin, epibromhydrin, .alpha.-methyl
epichlorohydrin; compounds having two or more reactive functional
groups, for example, isocyanate compounds such as 2,4-tolylene
diisocyanate, hexamethylene diisocyanate; oxetane compounds such as
3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol,
3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol,
3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol. Among these
internal-crosslinking agents, polyglycidyl compounds is preferably
used, and diglycidyl compounds are more preferably used, and
(poly)ethylene glycol diglycidyl ether, (poly)propylene glycol
diglycidyl ether, (poly)glycerin diglycidyl ether are further
preferably used. These internal-crosslinking agents may be used
alone or in combination of two or more.
[0039] The used amount of the internal-crosslinking agent is
preferably 0.000001 to 0.02 mol relative to 1 mol of a
water-soluble ethylenically unsaturated monomer, more preferably
0.00001 to 0.01 mol, further preferably 0.00001 to 0.005 mol and
further more preferably 0.00005 to 0.002 mol.
[Azo based compound and peroxide]
[0040] In the method of producing a water-absorbent resin according
to the present invention, the phrase "in the presence of an azo
based compound and a peroxide" does not necessarily means that the
azo based compound and the peroxide are coexistent at the beginning
of a polymerization reaction, but means that one compound is
present before a monomer conversion ratio by radical cleavage due
to the other compound becomes 10% or more. However, the both are
preferably present in an aqueous solution containing a monomer
before the start of the polymerization reaction. Further, an azo
based compound and a peroxide may be added to a polymerization
reaction system via different flow channels or may be sequentially
added to the polymerization reaction system via the same flow
channel. Note that an azo based compound and a peroxide to be used
may be in the form of powder or an aqueous solution.
(Azo Based Compound)
[0041] Azo based compounds include, for example, those azo based
compounds such as 1-{(1-cyano-1-methylethyl)azo}formamide,
2,2'-azobis[2-(N-phenyl amidino)propane]dihydrochloride,
2,2'-azobis{2-[N-(4-chlorophenyl)amidino]propane}dihydrochloride,
2,2'-azobis{2-[N-(4-hydroxyphenyl)amidino]propane}dihydrochloride,
2,2'-azobis[2-(N-benzyl amidino)propane]dihydrochloride,
2,2'-azobis[2-(N-allyl amidino)propane]dihydrochloride,
2,2'-azobis(2-amidinopropane)dihydrochloride,
2,2'-azobis{2-[N-(2-hydroxyethyl)amidino]propane}dihydrochloride,
2,2'-azobis[2-(5-methyl-2-imidazoline-2-yl)propane]dihydrochloride,
2,2'-azobis[2-(2-imidazoline-2-yl)propane]dihydrochloride,
2,2'-azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepine-2-yl)propane]dihydroch-
loride,
2,2'-azobis[2-(5-hydroxy-3,4,5,6-tetrahydro-pyrimidine-2-yl)propan-
e]dihydrochloride,
2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline-2-yl]propane}dihydrochlor-
ide, 2,2'-azobis[2-(2-imidazoline-2-yl)propane],
2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamid-
e},
2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide},
2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],
2,2'-azobis(2-methylpropionamide)dihydrochloride,
4,4'-azobis-4-cyanovaleinic acid,
2,2'-azobis[2-(hydroxymethyl)propionitrile],
2,2'-azobis[2-(2-imidazoline-2-yl)propane]disulfate dihydrate,
2,2'-azobis[N-(2-carboxyethyl)-2-methylpropione
amidine]tetrahydrate,
2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]. Among these,
2,2'-azobis(2-amidinopropane)dihydrochloride,
2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline-2-yl]propane}dihydrochlor-
ide, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropione
amidine]tetrahydrate are preferred. These azo based compounds may
be used alone or in combination of two or more.
(Peroxide)
[0042] Peroxides include, for example, persulfates such as
potassium persulfate, ammonium persulfate, sodium persulfate;
peroxides such as methyl ethyl ketone peroxide, methyl isobutyl
ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide,
t-butyl peroxyacetate, t-butyl peroxy isobutyrate, t-butyl peroxy
pivalate, hydrogen peroxide. Among these peroxides, potassium
persulfate, ammonium persulfate, sodium persulfate, hydrogen
peroxide are preferably used, and further, potassium persulfate,
ammonium persulfate, sodium persulfate are more preferably used.
These peroxides may be used alone or in combination of two or
more.
(Used Amount and Used Proportion of Azo Based Compound and
Peroxide)
[0043] The used amount of an azo based compound and a peroxide is
preferably 0.00005 mol or more relative to 1 mol of a water soluble
ethylenically unsaturated monomer, more preferably 0.0001 mol or
more. Further, the used amount is preferably 0.005 mol or less
relative to 1 mol of a water-soluble ethylenically unsaturated
monomer, and more preferably 0.001 mol or less.
[0044] For the used proportion of an azo based compound and a
peroxide, the proportion of the azo based compound is preferably 40
mass % or more relative to the total used amount of the azo based
compound and the peroxide, more preferably 50 mass % or more,
further preferably 60 mass % or more and further more preferably 70
mass %. On the other hand, the proportion of an azo based compound
is preferably 95 mass % or less relative to the total used amount
of the azo based compound and the peroxide, more preferably 90 mass
% or less, further preferably 85 mass % and further more preferably
80 mass % or less. Further, the range of the mass ratio (azo based
compound: peroxide) is preferably 8:12 to 19:1.
[Other Components]
[0045] In the method of producing a water-absorbent resin according
to the present invention, other components may be added to a
water-soluble ethylenically unsaturated monomer to perform reversed
phase suspension polymerization, if desired. As other components,
chain transfer agents, thickeners, other various additives and the
like may be added.
(Chain Transfer Agent)
[0046] For example, a water-soluble ethylenically unsaturated
monomer may be polymerized in the presence of a chain transfer
agent in order to control the water-absorption performance of the
water-absorbent resin.
[0047] Chain transfer agents include, for example, thiols such as
ethanethiol, propanethiol, dodecanethiol; thiolic acids such as
thioglycolic acid, thiomalic acid, dimethyldithiocarbamic acid,
diethyldithiocarbamic acid or salts thereof; secondary alcohols
such as isopropanol; phosphorous acid compounds, for example,
phosphorous acid, normal salts of phosphorous acid such as disodium
phosphite, dipotassium phosphite, diammonium phosphite, acid salts
of phosphorous acid such as sodium hydrogen phosphite, potassium
hydrogen phosphite, ammonium hydrogen phosphite, and the like;
phosphoric acid compound, for example, phosphoric acid, normal
salts of phosphoric acid such as sodium phosphate, potassium
phosphate, ammonium phosphate, acid salts of phosphoric acid such
as sodium dihydrogen phosphate, potassium dihydrogen phosphate,
ammonium dihydrogen phosphate, disodium hydrogen phosphate,
dipotassium hydrogen phosphate, diammonium hydrogen phosphate, and
the like; hypophosphorous acid compounds, for example,
hypophosphorous acid, hypophosphites such as sodium hypophosphite,
potassium phosphinate, ammonium hypophosphorous; pyrophosphoric
acid, tripolyphosphoric acid, polyphosphoric acid and salts
thereof; trimethyl phosphate, nitrilo trimethylene triphosphonic
acid and the like. These chain transfer agents may be used alone or
in combination of two or more. Further, chain transfer agents may
be used as hydrates thereof.
[0048] The used amount of a chain transfer agent is preferably
0.00001 to 0.0005 mol relative to 1 mol of a water-soluble
ethylenically unsaturated monomers, more preferably 0.000025 to
0.00012 mol.
(Thickener)
[0049] Further, a thickener may be added to an aqueous solution
containing a water-soluble ethylenically unsaturated monomer to
perform reversed phase suspension polymerization. By adding a
thickener to adjust the viscosity of an aqueous solution as
described above, the median particle diameter obtained by reversed
phase suspension polymerization may also be controlled.
[0050] As a thickener, for example, hydroxyethyl cellulose,
hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose,
polyacrylic acid, (partially) neutralized polyacrylic acid,
polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin,
sodium alginate, polyvinyl alcohol, polyvinyl pyrrolidone,
polyethylene oxide and the like can be used. Note that the
following tends to be observed: in a case where the stirring speeds
at the time of polymerization are the same, the higher is the
viscosity of an aqueous solution of a water-soluble ethylenically
unsaturated monomer, the larger is the median particle diameter of
the resulting particles.
[Reversed Phase Suspension Polymerization]
[0051] When performing reversed phase suspension polymerization, an
aqueous monomer solution containing a water-soluble ethylenically
unsaturated monomer is dispersed in a hydrocarbon dispersion
medium, for example, in the presence of a dispersion stabilizer.
When doing this, a dispersion stabilizer (a surfactant and/or a
polymeric dispersion agent) may be added either before or after the
aqueous monomer solution is dispersed as long as they are added
before the start of a polymerization reaction.
[0052] In particular, in a view of easy reduction of the amount of
a residual hydrocarbon dispersion medium in the resulting
water-absorbent resin, it is preferred that polymerization is
performed after an aqueous monomer solution is dispersed in a
hydrocarbon dispersion medium in which a polymeric dispersion agent
has been dispersed, and then a surfactant is further dispersed.
[0053] In the method of producing a water-absorbent resin according
to the present invention, reversed phase suspension polymerization
can be performed as described above in a single step or multiple
steps such as two or more steps. Further, in view of increasing
productivity, it is more preferably performed in 2 to 3 steps.
[0054] In a case where reversed phase suspension polymerization is
performed in multiple steps such as two or more steps, after the
first-step reversed phase suspension polymerization is performed, a
water-soluble ethylenically unsaturated monomer may be added to the
reaction mixture obtained in the first-step polymerization
reaction, and mixed to perform a second-step reversed phase
suspension polymerization as in the first step. In a case of
reversed phase suspension polymerization at each step of the second
step and later steps, reversed phase suspension polymerization is
preferably performed by adding, in addition to a water-soluble
ethylenically unsaturated monomer, an internal-crosslinking agent,
an azo compound and a peroxide described above within the
aforementioned range of the molar ratio of each component relative
to the water-soluble ethylenically unsaturated monomer on the basis
of the amount of the water-soluble ethylenically unsaturated
monomer to be added in the reversed phase suspension polymerization
in each step of the second step and later steps. Note that in the
method of producing a water-absorbent resin according to the
present invention, polymerization is also preferably performed in
the presence of an azo based compound and a peroxide in
polymerization of the second step and later steps.
[0055] The reaction temperature for a polymerization reaction is
preferably 20 to 110.degree. C., more preferably 40 to 90.degree.
C. from the viewpoint that economy may be improved by allowing
rapid progress of a polymerization to reduce a polymerization time,
and polymerization heat may be easily removed to perform a smooth
reaction. Further, the reaction time is preferably 0.5 to 4
hours.
<Post-Crosslinking Step>
[0056] Next, in the method of producing a water-absorbent resin
according to the present invention, post-crosslinking of a hydrous
gel-like material obtained by polymerizing a water soluble
ethylenically unsaturated monomer which has an
internal-crosslinking structure is performed using a
post-crosslinking agent (post-crosslinking reaction). This
post-crosslinking reaction is preferably performed in the presence
of a post-crosslinking agent after the polymerization of a water
soluble ethylenically unsaturated monomer. By performing a
post-crosslinking reaction of a hydrous gel-like material having an
internal-crosslinking structure after the polymerization to
increase a crosslinking density near a surface of a water-absorbent
resin as described above, a water-absorbent resin can be obtained
which has various enhanced properties such as a water-absorption
capacity under a load and a water-absorption rate.
[0057] Post-crosslinking agents can include those compounds having
two or more reactive functional groups. They include, for example,
polyols such as ethylene glycol, propylene glycol, 1,4-butanediol,
trimethylolpropane, glycerin, polyoxyethylene glycol,
polyoxypropylene glycol, polyglycerin; polyglycidyl compounds such
as (poly)ethylene glycol diglycidyl ether, (poly)glycerin
diglycidyl ether, (poly)glycerin triglycidyl ether,
trimethylolpropane triglycidyl ether, (poly)propylene glycol
polyglycidyl ether, (poly)glycerol polyglycidyl ether; haloepoxy
compounds such as epichlorohydrin, epibromhydrin, a-methyl
epichlorohydrin; isocyanate compounds such as 2,4-tolylene
diisocyanate, hexamethylene diisocyanate; oxetane compounds such as
3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol,
3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol,
3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; oxazoline
compounds such as 1,2-ethylenebisoxazoline; carbonate compounds
such as ethylene carbonate; hydroxyalkylamide compounds such as
bis[N,N-di(.beta.-hydroxyethyl)]adipamide. Among these
post-crosslinking agents, preferred are polyglycidyl compounds such
as (poly)ethylene glycol diglycidyl ether, (poly)glycerin
diglycidyl ether, (poly)glycerol triglycidyl ether,
trimethylolpropane triglycidyl ether, (poly)propylene glycol
polyglycidyl ether, (poly)glycerol polyglycidyl ether. These
post-crosslinking agents may be used alone or in combination of two
or more.
[0058] The used amount of a post-crosslinking agent is preferably
0.00001 to 0.01 mol relative to 1 mol of the total amount of a
water-soluble ethylenically unsaturated monomer used for
polymerization, more preferably 0.00005 to 0.005 mol and further
preferably 0.0001 to 0.002 mol.
[0059] As a method of adding a post-crosslinking agent, the
post-crosslinking agent may be added as it is or as an aqueous
solution. A post-crosslinking agent may also be added as a solution
in which a hydrophilic organic solvent is used as a solvent, if
desired. Hydrophilic organic solvents include, for example, lower
alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol,
isopropyl alcohol; ketones such as acetone, methyl ethyl ketone;
ethers such as diethyl ether, dioxane, tetrahydrofuran; amides such
as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide.
These hydrophilic organic solvents may be used alone or in
combination of two or more, or may be used as a mixed solvent with
water.
[0060] A post-crosslinking agent may be added after the
polymerization reaction of water-soluble ethylenically unsaturated
monomer has been almost completed, and it is preferably added in
the presence of water in the range of 1 to 400 parts by mass
relative to 100 parts by mass of a water-soluble ethylenically
unsaturated monomer, more preferably added in the presence of water
in the range of 5 to 200 parts by mass, further preferably added in
the presence of water in the range of 10 to 100 parts by mass and
further more preferably added in the presence of water in the range
of 20 to 60 parts by mass. Note that the amount of water means the
total amount of a water content in a reaction system and a water
content used if desired when adding a post-crosslinking agent.
[0061] The reaction temperature in the post-crosslinking reaction,
but it is preferably 50 to 250.degree. C., more preferably 60 to
180.degree. C., further preferably 60 to 140.degree. C. and further
more preferably 70 to 120.degree. C. Further, the reaction time for
the post-crosslinking reaction is preferably for 1 to 300 minutes,
and more preferably for 5 to 200 minutes.
<Drying Step>
[0062] The method of producing a water-absorbent resin according to
the present invention may comprise a drying step of removing water,
a hydrocarbon dispersion medium and the like using distillation by
applying energy such as heat from the outside after performing the
aforementioned reversed phase suspension polymerization. When
performing dehydration of a hydrous gel after reversed phase
suspension polymerization, a system in which the hydrous gel is
dispersed in a hydrocarbon dispersion medium is heated to
temporarily evaporate water and the hydrocarbon dispersion medium
from the system by azeotropic distillation. At this time, only the
hydrocarbon dispersion medium evaporated is allowed to return into
the system, enabling continuous azeotropic distillation. In that
case, the temperature in the system during the drying treatment is
maintained at or below the azeotropic temperature with the
hydrocarbon dispersion medium. Therefore this is preferred in view
of that, for example, the resin is less susceptible to
deterioration. Water and the hydrocarbon dispersion medium is
continuously evaporated away to obtain particles of a
water-absorbent resin. By controlling processing conditions of this
drying step after polymerization to adjust the amount of dehydrated
water, various properties of the resulting water-absorbent resin
can be controlled.
[0063] In the drying step, the drying treatment may be performed by
distillation under ordinary pressure or under a reduced pressure.
Further, the drying treatment may be performed under a gas flow of
nitrogen and the like in view of increased drying efficiency. When
performing the drying treatment under ordinary pressure, a drying
temperature is preferably 70 to 250.degree. C., more preferably 80
to 180.degree. C., further preferably 80 to 140.degree. C. and
further more preferably 90 to 130.degree. C. Further, when
performing the drying treatment under reduced pressure, a drying
temperature is preferably 40 to 160.degree. C., more preferably 50
to 110.degree. C.
[0064] Note that in a case where post-crosslinking step is
performed with a post-crosslinking agent after monomers are
polymerized by reversed phase suspension polymerization, the drying
step is performed by distillation as described above after the
post-crosslinking step. Alternatively, the post-crosslinking step
and the drying step may be performed simultaneously.
[0065] Further, if desired, various additives such as chelating
agents, reducing agents, oxidizing agents, antibacterial agents,
deodorizing agents may be added to a water-absorbent resin after
polymerization, during or after drying.
2. Water-Absorbent Resin
[0066] Next, the water-absorbent resin according to the present
invention will be described. The water-absorbent resin according to
the present invention can be obtained by polymerizing a
water-soluble ethylenically unsaturated monomer in the presence of
an internal-crosslinking agent, and performing post-crosslinking
with a post-crosslinking agent, and characterized by that the
water-absorption capacity of physiological saline under a load of
4.14 kPa at 120 minutes passed from the start of water absorption
is 20 ml/g or more.
[0067] For the water-absorbent resin according to the present
invention, the water-absorption capacity of physiological saline
under a load of 4.14 kPa at 120 minutes passed from the start of
water absorption is 20 ml/g or more, preferably 22 ml/g or more,
more preferably 24 ml/g, and further preferably 26 ml/g. Further
the water-absorption capacity of physiological saline under a load
of 4.14 kPa at 120 minutes passed from the start of water
absorption is preferably 50 ml/g or less, and more preferably 40
ml/g or less.
[0068] Furthermore, the water-absorbent resin according to the
present invention is characterized by that the degree of swelling
under a load at 30 minutes is 70% or less. Note that the degree of
swelling under a load after a certain time has passed means a
proportion of [the water-absorption capacity of physiological
saline under a load of 4.14 kPa after a certain time has passed
(for example, after 30 minutes)] relative to [the water-absorption
capacity of physiological saline under a load of 4.14 kPa at 120
minutes passed from the start of water absorption], and may be
calculated by the following formula.
Degree of swelling under a load at a certain time passed ( % ) =
Water absorption capacity for physiological saline under a load of
4.14 kPa at a certain time passed ( ml / g ) Water absorption
capacity for physiological saline under a load of 4.14 kPa at 120
minutes passed ( ml / g ) .times. 100 [ Formula 2 ]
##EQU00002##
[0069] A water-absorbent resin showing a degree of swelling under a
load at 30 minutes of 70% or less means that it will slowly absorb
a liquid (to-be-absorbed liquid) under a load over a long time
period at a predetermined water-absorption capacity. The degree of
swelling under a load at 30 minutes is preferably 65% or less, more
preferably 60% or less, and further preferably 55% or less. On the
other hand, the degree of swelling under a load at 30 minutes is
preferably 15% or more, more preferably is 20% or more, and further
preferably 25% or more, and further more preferably 30% or
more.
[0070] Further, the degree of swelling under a load at 240 minutes
is preferably 110% or more in order to further enhance effects when
used for an absorbent material.
[0071] Further, for the water-absorbent resin according to the
present invention, the water-retention capacity of physiological
saline after 120 minutes is preferably 30 to 60 g/g, more
preferably 35 to 55 g/g, further preferably 37 to 53 g/g and
further more preferably 40 to 50 g/g. Note that a water-retention
capacity of physiological saline represents a degree of a liquid
absorption capacity of a water-absorbent resin per unit mass.
[0072] Moreover, for the water-absorbent resin according to the
present invention, the water-retention degree of swelling after 15
minutes is preferably less than 95%. Here, the water-retention
degree of swelling after a certain time has passed is a proportion
of particles of [the water-retention capacity of physiological
saline after a certain time has passed (for example, after 15
minutes)] relative to [the water-retention capacity of
physiological saline after 120 minutes], and may be calculated by
the following formula.
Water - retention d egree of swelling at a certain time passed ( %
) = Water - retention capacity for physiological saline at a
certain time passed ( g / g ) Water - retention capacity for
physiological saline at 120 minutes passed ( g / g ) .times. 100 [
Formula 3 ] ##EQU00003##
[0073] Further, the water-absorbent resin according to the present
invention preferably has a median particle diameter of 200 to 600
.mu.m, more preferably 250 to 500 .mu.m, further preferably 300 to
450 .mu.m and further more preferably 300 to 400 .mu.m.
[0074] Further, in the water-absorbent resin according to the
present invention, the mass proportion of particles from 150 to 850
.mu.m relative to the whole proportion is preferably 85 mass % or
more, and more preferably 90 mass % or more. Further, the mass
proportion of particles from 300 to 400 .mu.m relative to the whole
proportion is preferably 20 mass % or more, more preferably 25 mass
% or more, and further preferably 30 mass % or more.
[0075] Note that particles of water-absorbent resin may be in a
form where each comprises a single particle, or may be in a form
where fine particles (primary particles) are agglomerated
(secondary particles). Forms of the primary particles include a
substantially spherical form, an irregular fractured form, a
plate-like form and the like. When primary particles are
manufactured by reversed phase suspension polymerization, they
include a substantially spherical single particle form having a
smooth surface such as a true spherical shape, an elliptically
spherical shape. Then, the flowability as powder is high because
primary particles in such forms have a smooth surface. Further,
agglomerated particles are not easily destroyed upon impact, and
thus a water-absorbent resin having high particle strength can be
formed because agglomerated particles tend to be more densely
packed.
[0076] The water-retention capacity of physiological saline, the
water-absorption capacity of physiological saline under a load of
4.14 kPa and the median particle diameter of the aforementioned
water-absorbent resin can either be evaluated by the evaluation
test methods described in Examples below.
[0077] Note that an additive may be blended depending on the
purposes in order to provide various preferred properties on the
resulting water-absorbent resin. Such additives include inorganic
powders, surfactants, oxidizing agents, reducing agents, metal
chelating agents, radical chain inhibitors, anti-oxidizing agents,
antibacterial agents, deodorizing agents and the like. For example,
the flowability of a water-absorbent resin can be improved by
adding 0.05 to 5 parts by mass of amorphous silica as an inorganic
powder relative to 100 parts by mass of the water-absorbent
resin.
3. Absorbent Material and Absorbent Article
[0078] The water-absorbent resin according to the present invention
may form an absorbent material for use in, for example, hygienic
materials such as sanitary goods and disposable diapers, and may
suitably be used in absorbent articles comprising absorbent
materials.
[0079] Here, an absorbent material in which a water-absorbent resin
is used comprises, for example, the water-absorbent resin and a
hydrophilic fiber. The structures of the absorbent material include
a dispersion mixture obtained by mixing a water-absorbent resin and
a hydrophilic fiber to give a uniform composition, a sandwich
structure in which a water-absorbent resin is sandwiched between
layered hydrophilic fibers, a structure in which a water-absorbent
resin and a hydrophilic fiber is wrapped in tissue, and the like.
Note that other components, for example, adhesive binder such as
thermal adhesive synthetic fibers, hot melt adhesives, adhesive
emulsions for increasing the shape retention capability of an
absorbent material may be included in the absorbent material.
[0080] The content of a water-absorbent resin in an absorbent
material is preferably 5 to 95 mass %, more preferably 20 to 90
mass % and further preferably 30 to 80 mass %.
[0081] Hydrophilic fibers include cellulose fibers prepared from
wood such as cotton-like pulp, mechanical pulp, chemical pulp,
semi-chemical pulp; artificial cellulose fibers such as rayon,
acetate; fibers comprising synthetic resin such as hydrophilized
polyamide, polyester and polyolefine.
[0082] Moreover, an absorbent material in which a water-absorbent
resin is used can be held between a liquid permeable sheet (a top
sheet) through which a liquid can permeate and a liquid impermeable
sheet (a back sheet) through which a liquid cannot permeate to give
an absorbent article. The liquid permeable sheet is arranged on the
side to be in contact with the body while the liquid impermeable
sheet is arranged opposite to the side to be in contact with the
body.
[0083] Liquid permeable sheets include nonwoven of an air through
type, a span bond type, a chemical bond type, a needle punch type
and the like comprising fiber such as polyethylene, polypropylene,
polyester, etc. and porous synthetic resin sheets and the like.
Further, liquid impermeable sheets include synthetic resin films
comprising a resin such as polyethylene, polypropylene, polyvinyl
chloride and the like.
EXAMPLES
4. Example
[0084] Hereafter, the present invention will be described in detail
with reference to Examples and Comparative Examples. However, the
present invention shall not in any way be limited to the following
Examples and the like.
<4-1. Method for Evaluation Test>
[Evaluation Test of Water-Absorbent Resin]
[0085] Water-absorbent resins obtained from Examples 1, 2 and 3 and
Comparative Examples 1 and 2 below were subjected to various tests
described below for evaluation. In the followings, each evaluation
test method will be described.
(1) Water-Retention Capacity of Physiological Saline
[0086] A cotton bag (cotton broadcloth No. 60, horizontal 100
mm.times.vertical 200 mm) into which 2.0 g of a water-absorbent
resin was weighed out was placed into a 500 mL beaker. To the
cotton bag containing the water-absorbent resin, 500g of 0.9 mass %
aqueous sodium chloride (physiological saline) was poured in one
portion so that lumps were not formed. The upper part of the cotton
bag was then closed with a rubber band, and stood for a
predetermined time to allow the water-absorbent resin to swell.
When a predetermined time has passed, the cotton bag was dehydrated
for 1 minute using a dehydrator (made by KOKUSAN Co., Ltd., Product
number: H-122) configured such that the centrifugal force would be
167 G. Then the mass Wa (g) of the cotton bag containing swollen
gel after dehydration was measured. Similar procedures were
performed without adding a water-absorbent resin, and the empty
mass Wb (g) of the wet cotton bag was measured, and a
water-retention capacity was calculated by the following formula.
Note that in this Example, the water-absorbent resin was allowed to
swell for each standing time of 15 minutes, 30 minutes, 60 minutes,
120 minutes, and a water-retention capacity was measured after each
standing time.
Water-retention capacity of physiological saline (g/g)=[Wa-Wb]
(g)/mass (g) of water-absorbent resin
(2) Water-Absorption Capacity of Physiological Saline Under a Load
of 4.14 kPa
[0087] A water-absorption capacity of physiological saline under a
load of 4.14 kPa of a water-absorbent resin was measured using a
measurement apparatus X. A schematic arrangement of the measurement
apparatus X is shown in FIG. 1.
[0088] The measurement apparatus X shown in FIG. 1 comprises a
buret part 1, a conduit 2, a measurement stage 3, a measurement
part 4 placed on the measurement stage 3. In the buret part 1, a
rubber stopper 14 is connected to the upper part of a buret 10, and
an air introducing pipe 11 and a cock 12 is connected to the lower
part of the buret 10. Further, a cock 13 is attached to the upper
part of the air introducing pipe 11. A conduit 2 connects the buret
part 1 and the measurement stage 3. The diameter of the conduit 2
is 6 mm. The measurement stage 3 has a hole with a diameter of 2 mm
at the center, to which the conduit 2 is connected. The measurement
part 4 is provided with a cylinder 40 and a nylon mesh 41 patched
on the bottom of the cylinder 40, as well as a weight 42. The inner
diameter of the cylinder 40 is 2.0 cm. The nylon mesh 41 is formed
as 200 mesh (75 .mu.m openings). Further, it is configured such
that a predetermined amount of a water-absorbent resin 5 is
uniformly distributed on the nylon mesh 41. The weight 42 has a
diameter of 1.9 cm and a mass of 119.6 g. The weight 42 is to be
placed on the water-absorbent resin 5 to uniformly apply a load of
4.14 kPa to the water-absorbent resin 5.
[0089] Using the measurement apparatus X having a structure as
described above, first, the cock 12 and the cock 13 at the buret
part 1 were closed, and then physiological saline adjusted to
25.degree. C. was introduced into the buret 10 from the top.
Subsequently, the top of the buret was plugged with the rubber
stopper 14, and then the cock 12 and the cock 13 at the buret part
1 were opened. Next, the height of the measurement stage 3 was
adjusted so that the tip of the conduit 2 at the center of the
measurement stage 3 is leveled with the air inlet of the air
introducing pipe 11.
[0090] Meanwhile, 0.10 g of the water-absorbent resin 5 was
uniformly distributed on the nylon mesh 41 in the cylinder 40, and
then the weight 42 was placed on that water-absorbent resin 5. The
measurement part 4 was arranged so that its center coincided with
the conduit inlet at the center of the measurement stage 3.
[0091] The amount of reduced physiological saline in the buret 10
(the amount of physiological saline absorbed by the water-absorbent
resin 5) We (mL) was continuously measured from the time point when
the water-absorbent resin 5 started to absorb water. At each
passing time of 30 minutes, 60 minutes, 120 minutes, and 240
minutes from the start of water absorption, a water-absorption
capacity of physiological saline under a load of 4.14 kPa of the
water-absorbent resin was calculated by the following formula.
Water-absorption capacity of physiological saline under a load of
4.14 kPa (mL/g)=We/0.10 (g)
(3) Median Particle Diameter (Particle Size Distribution)
[0092] JIS standard sieves were combined in the following order
from the top: a sieve of 850 .mu.m openings, a sieve of 600 .mu.m
openings, a sieve of 500 .mu.m openings, a sieve of 400 .mu.m
openings, a sieve of 300 .mu.m openings, a sieve of 250 .mu.m
openings, a sieve 150 .mu.m openings and a receiving tray.
[0093] A water-absorbent resin in an amount of 50 g was introduced
on the top of the combined sieves, and then shaken for 20 minutes
using a ro-tap shaker for classification. After classification, the
mass of the water-absorbent resin which remained in each sieve was
calculated as a mass proportion of particles relative to the total
mass to obtain a particle size distribution. By integrating the
amount on each sieve from the one having the largest particle
diameter in this particle size distribution, the relationship
between the sieve openings and the integrated value of the mass
proportion of particles of the water-absorbent resin which remained
in the sieves was plotted on logarithmic probability paper. By
connecting the plots on the probability paper with a straight line,
a particle diameter corresponding to 50 mass % in the integrated
mass proportion of particles is taken as the median particle
diameter.
[0094] Note that the mass proportion of particles from 300 to 400
.mu.m in the total water-absorbent resin is a mass proportion of
particles of a water-absorbent resin which remained in the sieve
with 300 .mu.m openings relative to the whole proportion in the
aforementioned measurements. Similarly, the mass proportion of
particles from 150 to 850 .mu.m in the total water-absorbent resin
is a value obtained by summing the mass proportion of particles of
the water-absorbent resin which remained in sieves with openings of
150 .mu.m, 250 .mu.m, 300 .mu.m, 400 .mu.m, 500 .mu.m, and 600
.mu.m.
[Evaluation Test of Absorbent Material and Absorbent Article in
which Water-Absorbent Resin is Used] (1) Production of Absorbent
material and Absorbent Article
[0095] Using 10 g of a water-absorbent resin and 10 g of crushed
pulp (made by Rayonier, Rayfloc) were uniformly mixed by air
papermaking to manufacture a sheet-like absorbent material core
with a size of 40 cm.times.12 cm. Next, while the absorbent
material core was placed between two tissue papers, which had the
same size as the absorbent material core and a basis weight of 16
g/m2, the absorbent material core was all over pressed with a load
of 196 kPa for 30 seconds to prepare an absorber absorbent
material. Further, the absorbent article was prepared by arranging
a polyethylene-polypropylene air-through porous liquid permeable
sheet on the upper surface of the absorbent material, the sheet
having a basis weight of 22 g/m.sup.2 and the same size as the
absorbent material, and arranging a polyethylene impermeable sheet
of the same size and the same basis weight on the lower surface of
the absorbent material.
(2) Preparation of Test Liquid
[0096] An appropriate amount of distilled water was introduced into
a 10 L container, and 60 g of sodium chloride, 1.8 g of calcium
chloride dihydrate and 3.6 g of magnesium chloride hexahydrate were
added and dissolved. Subsequently, 0.15 g of polyoxyethylene
nonylphenyl ether was added, and additional distilled water was
further added to give a total mass of 6000 g. Further, coloring was
performed with a small amount of Blue No. 1 to prepare a test
liquid.
(3) Permeation Time
[0097] First, the absorbent article was first placed on a
horizontal stage. On the center portion of the absorbent article, a
measurement apparatus incorporating a liquid pouring cylinder
having an inside diameter of 3 cm was placed, and 50 mL of the test
liquid was poured into the cylinder at a time and a stopwatch was
used to measure the time until the test liquid was made to
disappear completely, with the result that the time was assumed to
be the first permeation time (in seconds).
[0098] Then, the cylinder described above was removed, the
absorbent article was stored in the present state and both when 30
minutes had elapsed and when 60 minutes had elapsed since the start
of the first round of the pouring of the test liquid, the
measurement apparatus was used in the position as in the first
round, and the same operation was performed, with the result that
the second and third permeation times (in seconds) were
measured.
[0099] The total time of the first to third rounds was assumed to
be the total permeation time. It is said that as the permeation
time is shorter, the absorbent article was more preferable.
(4) Amount of Re-wet
[0100] At 120 minutes after the state of the first round of the
pouring of the test liquid in the measurement of the permeation
time described above, in the vicinity of the position on the
absorbent article where the test liquid was poured, filter paper 10
cm square whose mass (Wd (g), about 50 g) was previously measured
was put, and thereon, a weight having a bottom surface of 10
cm.times.10 cm and a mass of 5 kg was placed. The load was placed
for 5 minutes, and the mass (We (g)) of the filter paper was
measured, with the result that the increased mass was assumed to be
the re-wet amount (g). It is said that as the re-wet amount was
decreased, the absorbent article was more preferable.
Amount of re-wet (g)=We-Wd
(5) Diffusion Length
[0101] Within 5 minutes after the measurement of the re-wet amount
described above, the dimension (cm) of spread of the absorbent
article in the longitudinal direction into which the test liquid is
penetrated was measured. Note that values below the decimal point
were rounded off.
4-2. Examples and Comparative Example
Example 1
[0102] A 2L cylindrical round-bottom separable flask with an inner
diameter of 110 mm was prepared which was equipped with a reflux
condenser, a dropping funnel, a nitrogen gas-introducing tube and
stirrer having stirring blades compound of two sets of 4 inclined
paddle blades with a blade diameter of 50 mm. To this flask, 300 g
of n-heptane was introduced as a hydrocarbon dispersion medium, and
0.74 g of maleic anhydride modified ethylene-propylene copolymer
(made by Mitsui Chemicals, Inc., High Wax 1105A) as a polymeric
dispersion agent was added, and heat-dissolved with stirring, and
then cooled to 50.degree. C.
[0103] Meanwhile, 92 g (1.02 mol) of 80 mass % aqueous solution of
acrylic acid was introduced into a 500 mL Erlenmeyer flask, and
102.2 g of 30 mass % aqueous solution of sodium hydroxide was added
dropwise while cooling from the outside to perform 75 mol %
neutralization. Subsequently, 0.092 g of hydroxylethyl cellulose
(made by Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F) as a
thickener, 0.092 g (0.339 mmol) of
2,2'-azobis(2-amidinopropane)dihydrochloride as an azo based
compound, 0.037 g (0.137 mmol) of potassium persulfate as a
peroxide, 0.010 g (0.058 mmol) of ethylene glycol diglycidyl ether
as an internal-crosslinking agent and 43.8 g of ion exchange water
were added and dissolved to prepare an aqueous monomer
solution.
[0104] Then the aqueous monomer solution prepared as described
above was added to a separable flask, and stirred for 10 minutes.
Then, 7.4 g of a surfactant solution in which 0.74 g of HLB3
sucrose stearic acid ester (made by Mitsubishi-Kagaku Foods
Corporation, Ryoto sugar ester S-370) as a surfactant was
heat-dissolved in 6.66 g of n-heptane was further added, and the
atmosphere in the system was thoroughly replaced with nitrogen with
stirring. Then, the flask was immersed into a 70.degree. C. water
bath to raise temperature, and a first-step polymerization was
performed for 60 minutes to obtain a first-step polymerized
slurry.
[0105] Meanwhile, 128.8 g (1.43 mol) of 80 mass % solution of
aqueous acrylic acid was introduced to another 500 mL Erlenmeyer
flask, and 143.1 g of 30 mass % aqueous solution of sodium
hydroxide was added dropwise while cooling from the outside to
perform 75 mol % neutralization. Subsequently, 0.129 g (0.475 mmol)
of 2,2'-azobis(2-amidinopropane)dihydrochloride as an azo based
compound, 0.052 g (0.191 mmol) of potassium persulfate as a
peroxide, 0.012 g (0.067 mmol) of ethylene glycol diglycidyl ether
as an internal-crosslinking agent and 15.9 g of ion exchange water
were added and dissolved to prepare a second-step aqueous monomer
solution.
[0106] After cooling the system in the aforementioned separable
flask to 25.degree. C., all of the second-step aqueous monomer
solution was added to the first-step polymerized slurry, and the
atmosphere in the system was thoroughly replaced with nitrogen.
Then the flask was again immersed into a 70.degree. C. water bath
to raise temperature, and a second-step polymerization was
performed for 30 minutes.
[0107] After the second-step polymerization, the reaction liquid
was heated to 125.degree. C. in an oil bath, and 239 g of water was
removed from the system by refluxing n-heptane in azeotropic
distillation of n-heptane and water. Then, 4.42 g (0.51 mmol) of 2
mass % aqueous solution of ethylene glycol diglycidyl ether was
added as a post-crosslinking agent, and maintained at 80.degree. C.
for 2 hours. Subsequently, drying was performed by evaporating
n-heptane, and then a dried resin was obtained. This dried resin
was mixed with 0.3 mass % of amorphous silica (made by Evonik
Degussa Japan, Inc., Carplex #80), and allowed to pass through a
sieve with 1000 .mu.m openings to obtain 231.2 g of a
water-absorbent resin in a form of agglomerated spherical
particles. This water-absorbent resin was evaluated in accordance
with the various test methods as described above.
[0108] Note that for the water-absorbent resin obtained, the mass
proportion of particles from 150 to 850 .mu.m relative to the whole
proportion was 92 mass %, and the mass proportion of particles from
300 to 400 .mu.m relative to the whole proportion was 32 mass
%.
Example 2
[0109] In Example 2, the same was performed as in Example 1 except
that after the second-step polymerization, 236 g of water was
removed from the system by refluxing n-heptane in azeotropic
distillation of n-heptane and water. Thereby, obtained was 234.1 g
of a water-absorbent resin having a different water-retention
capacity from the water-absorbent resin obtained in Example 1. This
water-absorbent resin was evaluated in accordance with the various
test methods as described above.
[0110] Note that for the water-absorbent resin obtained, the mass
proportion of particles from 150 to 850 .mu.m relative to the whole
proportion was 94 mass %, and the mass proportion of particles from
300 to 400 .mu.m relative to the whole proportion was 36 mass
%.
Example 3
[0111] In Example 3, the same was performed as in Example 1 except
that the addition amount of an internal-crosslinking agent ethylene
glycol diglycidyl ether to be dissolved in the first-step aqueous
monomer solution was 0.020 g (0.116 mmol), and after the
second-step polymerization, 254 g of water was removed from the
system by refluxing n-heptane in azeotropic distillation of
n-heptane and water. Thereby, obtained was 232.9 g of a
water-absorbent resin which differed from the water-absorbent resin
obtained in Example 1 in that a different internal-crosslinking
agent was used. This water-absorbent resin way was evaluated in
accordance with the various test methods as described above.
[0112] Note that for the water-absorbent resin obtained, the mass
proportion of particles from 150 to 850 .mu.m relative to the whole
proportion was 95 mass %, and the mass proportion of particles from
300 to 400 .mu.m relative to the whole proportion was 33 mass
%.
Comparative Example 1
[0113] In Comparative Example 1, reversed phase suspension
polymerization was performed using only a peroxide alone to produce
a water-absorbent resin.
[0114] A 2L cylindrical round-bottom separable flask with an inner
diameter of 110 mm was prepared which was equipped with a reflux
condenser, a dropping funnel, a nitrogen gas-introducing tube and
stirrer having stirring blades compound of two sets of 4 inclined
paddle blades with a blade diameter of 50 mm. To this flask, 300 g
of n-heptane as a hydrocarbon dispersion medium was introduced, and
0.74 g of maleic anhydride modified ethylene-propylene copolymer
(made by Mitsui Chemicals, Inc., High Wax 1105A) as a polymeric
dispersion agent was added, and heat-dissolved with stirring. Then
it was cooled to 50.degree. C.
[0115] Meanwhile, 92 g (1.02 mol) of 80 mass % aqueous solution of
acrylic acid was introduced into a 500 mL Erlenmeyer flask, and
102.2 g of 30 mass % aqueous solution of sodium hydroxide was added
dropwise while cooling from the outside to perform 75 mol %
neutralization. Subsequently, 0.092 g of hydroxylethyl cellulose
(made by Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F) as a
thickener, 0.074 g (0.274 mmol) of potassium persulfate as a
peroxide, 0.010 g (0.058 mmol) of ethylene glycol diglycidyl ether
as an internal-crosslinking agent and 43.8 g of ion exchange water
were added and dissolved to prepare an aqueous monomer
solution.
[0116] Then the aqueous monomer solution prepared as described
above was added to a separable flask, and stirred for 10 minutes.
Then, 7.4 g of a surfactant solution in which 0.74 g of HLB3
sucrose stearic acid ester (made by Mitsubishi-Kagaku Foods
Corporation, Ryoto sugar ester S-370) as surfactant was
heat-dissolved in 6.66 g of n-heptane was further added, and the
atmosphere in the system was thoroughly replaced with nitrogen with
stirring. Then, the flask was immersed into a 70.degree. C. water
bath to raise temperature, and a first-step polymerization was
performed for 60 minutes to obtain a first-step polymerized
slurry.
[0117] Meanwhile, 128.8 g (1.43 mol) of 80 mass % aqueous solution
of acrylic acid was introduced to another 500 mL Erlenmeyer flask,
and 143.1 g of 30 mass % aqueous solution of sodium hydroxide was
added dropwise while cooling from the outside to perform 75 mol %
neutralization. Then, 0.104 g (0.382 mmol) of potassium persulfate
as a peroxide, 0.012 g (0.067 mmol) of ethylene glycol diglycidyl
ether as an internal-crosslinking agent and 15.9 g of ion exchange
water were added and dissolved to prepare a second-step aqueous
monomer solution.
[0118] After cooling the system in the aforementioned separable
flask to 25.degree. C., all of the second-step aqueous monomer
solution was added to the first-step polymerized slurry, and the
atmosphere in the system was thoroughly replaced with nitrogen.
Subsequently, the flask was again immersed into a 70.degree. C.
water bath to raise temperature, and a second-step polymerization
was performed for 30 minutes.
[0119] After the second-step polymerization, the reaction liquid
was heated to 125.degree. C. in an oil bath, and 257 g of water was
removed from the system by refluxing n-heptane in azeotropic
distillation of n-heptane and water. Then, 4.42 g (0.51 mmol) of 2
mass % aqueous solution of ethylene glycol diglycidyl ether was
added as a post-crosslinking agent, and maintained at 80.degree. C.
for 2 hours. Subsequently, drying was performed by evaporating
n-heptane to obtain a dried resin. This dried resin was mixed with
0.3 mass % of amorphous silica (made by Evonik Degussa Japan, Inc.,
Carplex #80), and allowed to pass through a sieve with 1000 .mu.m
openings to obtain 228.2 g of a water-absorbent resin in a form of
agglomerated spherical particles. This water-absorbent resin was
evaluated in accordance with the various test methods as described
above.
[0120] Note that in the resulting water-absorbent resin, the mass
proportion of particles from 150 to 850 .mu.m relative to the whole
proportion was 94 mass %, and the mass proportion of particles from
300 to 400 .mu.m relative to the whole proportion was 33 mass
%.
Comparative Example 2
[0121] In Comparative Example 2, after a predetermined monomer
conversion ratio was achieved in the polymerization performed by
adding an azo based compound, a peroxide was added to perform
reversed phase suspension polymerization for production of a
water-absorbent resin.
[0122] A 2L cylindrical round-bottom separable flask with an inner
diameter of 110 mm was prepared which was equipped with a reflux
condenser, a dropping funnel, a nitrogen gas-introducing tube and
stirrer having stirring blades compound of two sets of 4 inclined
paddle blades with a blade diameter of 50 mm. To this flask, 300 g
of n-heptane as a hydrocarbon dispersion medium was introduced and
0.74 g of maleic anhydride modified ethylene-propylene copolymer
(made by Mitsui Chemicals, Inc., High Wax 1105A) as a polymeric
dispersion agent was added, and heat-dissolved with stirring. Then
it was cooled to 50.degree. C.
[0123] Meanwhile, 184 g (2.04 mol) of 80 mass % aqueous acrylic
acid to a 1000 mL Erlenmeyer flask, and 292.0 g of 21 mass %
aqueous solution of sodium hydroxide was added dropwise while
cooling from the outside to perform 75 mol % neutralization, and
the resulting aqueous monomer solution was evenly aliquoted into
two.
[0124] Subsequently, 0.092 g (0.339 mmol) of
2,2'-azobis(2-amidinopropane)dihydrochloride as an azo based
compound, 0.010 g (0.058 mmol) of ethylene glycol diglycidyl ether
as an internal-crosslinking agent, 0.184 g of hydroxylethyl
cellulose (made by Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F)
as a thickener were added to one aqueous monomer solution, and
dissolved to prepare a aqueous monomer solution.
[0125] Then the aqueous monomer solution prepared as described
above was added to a separable flask, and stirred for 10 minutes.
Then, 7.4 g of a surfactant solution in which 0.74 g of HLB3
sucrose stearic acid ester (made by Mitsubishi-Kagaku Foods
Corporation, Ryoto sugar ester S-370) as a surfactant was
heat-dissolved in 6.66 g of n-heptane was further added, and the
atmosphere in the system was thoroughly replaced with nitrogen with
stirring. Then, the flask was immersed into a 70.degree. C. water
bath to raise temperature, and then a first-step polymerization was
performed for 60 minutes. The system after cooled to 25.degree. C.
was taken as the 50% monomer conversion ratio, and an aqueous
solution in which 0.037 g (0.137 mmol) of potassium persulfate as a
peroxide was dissolved in 1.23 g of ion exchange water was
added.
[0126] As an internal-crosslinking agent, 0.010 g (0.058 mmol) of
ethylene glycol diglycidyl ether was added to the other aqueous
monomer solution, and dissolved to prepare a second-step aqueous
monomer solution.
[0127] All of the second-step aqueous monomer solution was added to
the first-step polymerized slurry after addition of aqueous
solution of potassium persulfate, and the atmosphere in the system
was thoroughly replaced with nitrogen. Subsequently, the flask was
again immersed into a 70.degree. C. water bath to raise
temperature, and a second-step polymerization was performed for 30
minutes.
[0128] After the second-step polymerization, the reaction liquid
was heated to 125.degree. C. in an oil bath, and 237 g of water was
removed from the system by refluxing n-heptane in azeotropic
distillation of n-heptane and water. Then, 4.42 g (0.51 mmol) of 2
mass % aqueous solution of ethylene glycol diglycidyl ether was
added as a post-crosslinking agent, and maintained at 80.degree. C.
for 2 hours. Subsequently, drying was performed by evaporating
n-heptane to obtain a dried resin. This dried resin was mixed with
0.3 mass % of amorphous silica (Evonik Degussa Japan, Inc., Carplex
#80), and allowed to pass through a sieve with 1000 .mu.m openings
to obtain 199.5 g of a water-absorbent resin in a form of
agglomerated spherical particles. This water-absorbent resin was
evaluated in accordance with the various test methods as described
below.
[0129] Note that in the resulting water-absorbent resin, the mass
proportion of particles from 150 to 850 .mu.m relative to the whole
proportion was 93 mass %, and the mass proportion of particles from
300 to 400 .mu.m relative to the whole proportion was 28 mass
%.
<4-3. Evaluation Results>
[Evaluation Results of Water-Absorbent Resin]
[0130] First, shown in Table 1 below are the water-retention
capacities (measured values) of physiological saline after
corresponding standing times when allowed to stand to absorb water
for 15 minutes, 30 minutes, 60 minutes, and 120 minutes, and the
water-retention degrees of swelling (%) which is calculated by the
following formula based on the analytical value of its
water-retention capacity when the water-retention capacity of a
water-absorbent resin after 120 minutes (the 120-minute value)is
taken as a water-retention degree of swelling of 100%. Note that
also shown in Table 1 are evaluation results of the median particle
diameter (.mu.m) of each water-absorbent resin obtained in Examples
and Comparative Examples.
Water - retention d egree of swelling at a certain time passed ( %
) = Water - retention capacity for physiological saline at a
certain time passed ( g / g ) Water - retention capacity for
physiological saline at 120 minutes passed ( g / g ) .times. 100 [
Formula 4 ] ##EQU00004##
TABLE-US-00001 TABLE 1 Degree of swelling at water-retention
capacity(%) Water-retention (When 120- capacity of minute
physiological saline value was taken Median (Measured value) as
100%) particle Passing time (min.) diameter 15 30 60 120 15 30 60
120 (.mu.m) Example 1 40.4 46.0 46.7 47.8 84 96 98 100 342 Example
2 36.0 40.3 41.0 41.7 86 97 98 100 333 Example 3 38.2 39.4 40.0
40.2 95 98 99 100 372 Comparative 39.8 40.1 40.4 40.5 98 99 100 100
360 Example 1 Comparative 45.2 46.3 47.2 47.3 96 98 100 100 324
Example 2
[0131] Next, shown in Table 2 below are a water absorption
capacities (measured values) of physiological saline under a load
of 4.14 kPa of water-absorbent resins at passing times of 30
minutes, 60 minutes, 120 minutes, and 240 minute after the start of
water absorption, and the degrees of swelling under a load(%)which
is calculated by the following formula based on the measured value
of the water-absorption capacity of physiological saline under the
load when a value after 120 minutes (the 120-minute value) for a
water-absorbent resin is taken as a degree of swelling under a load
of 100%. Note that also shown in Table 2 are evaluation results of
the median particle diameter (.mu.m) of each water-absorbent resin
obtained in Examples and Comparative Examples.
Degree of swelling under a load at a certain time passed ( % ) =
Water absorption capacity for physiological saline under a load of
4.14 kPa at a certain time passed ( ml / g ) Water absorption
capacity for physiological saline under a load of 4.14 kPa at 120
minutes passed ( ml / g ) .times. 100 [ Formula 5 ]
##EQU00005##
TABLE-US-00002 TABLE 2 Water-absorption capacity of Degree of
swelling under a physiological saline under a load (%) load of 4.14
kPa (When 120-minute Median (ml/g)( Measured value) value was taken
as 100%) particle Passing time (min.) diameter 30 60 120 180 240 30
60 120 180 240 (.mu.m) Example 1 14.0 20.0 27.0 30.0 33.0 52 74 100
111 122 342 Example 2 15.0 24.0 26.9 29.5 30.5 56 89 100 110 113
333 Example 3 15.0 19.0 22.4 24.5 25.0 67 85 100 109 112 372
Comparative 11.4 15.0 19.2 20.3 23.0 59 78 100 106 120 360 Example
1 Comparative 20.0 23.5 26.8 27.0 28.0 75 88 100 101 104 324
Example 2
[Evaluation Results of Absorbent Articles]
[0132] Next, shown in Table 3 below are evaluation results of the
permeation time, the amount of re-wet, the diffusion length of test
liquid for absorbent articles produced using the water-absorbent
resins obtained from Examples 1 and 2 and Comparative Example 1
described above.
[0133] Note that in a case of Reference Examples to evaluate these
absorbent articles, a water-absorbent resin was collected from a
commercially available absorbent article, and then an absorbent
article was produced in a similar way as described in the sections
describing (1) the method of producing an absorbent material and an
absorbent article, and the permeation time, the amount of re-wet,
the diffusion length of test liquid were measured. For Reference
Example 1, a water-absorbent resin collected from MamyPoko (made by
Unicharm Corporation) was used, and for Reference Example 2, a
water-absorbent resin collected from Refre Pull-on Pants (made by
Livedo Corporation) was used.
TABLE-US-00003 TABLE 3 Performance of water- absorbent resin Water-
Degree Absorbent article absorption of (Production results)
Evaluation results of absorbent articles Water- capacity swelling
Water- Amount retention under a under absorbent Permeation time (s)
of re- Diffusion capacity*.sup.1 load*.sup.2 load*.sup.3 resin Pulp
Thickness First Second Third wet length (gl/g) (ml/g) (%) (g) (g)
(mm) time time time Total (g) (cm) Example 1 47.8 27.0 52 10 10 3
18 18 23 59 7.8 18 Example 2 41.7 26.9 56 10 10 3 18 17 22 57 12.8
19 Example 3 40.5 19.2 59 10 10 3 19 19 28 66 27.9 16 Reference
36.2 12.5 80 10 10 3 18 19 28 65 33.6 17 Example 1 Reference 42.0
16.5 93 10 10 3 19 21 27 67 31.8 16 Example 2 *.sup.1The
water-retention capacity represents 120-minute values for the
water-retention capacity of physiological saline as measured by the
method described in "(1) water-retention capacity of physiological
saline" in the method of evaluation tests. *.sup.2The
water-absorption capacity under a load represents a 120-minute
value of the water-absorption capacity of physiological saline
under a load of 4.14 kPa as measured by the method described in
"(2) water-absorption capacity of physiological saline under a load
of 4.14 kPa" in the method of evaluation tests. *.sup.3The degree
of swelling under a load was calculated from a 30-minute value of
the water-absorption capacity of physiological saline under a load
of 4.14 kPa as measured by the method described in "(2)
Water-absorption capacity of physiological saline under a load of
4.14 kPa" in the method of evaluation tests.
EXPLANATION OF REFERENCE NUMERALS
[0134] X Measurement apparatus
[0135] 1 Buret part
[0136] 2 Conduit
[0137] 3 Measurement stage
[0138] 4 Measurement part
[0139] 5 Water-absorbent resin
* * * * *