U.S. patent application number 10/570965 was filed with the patent office on 2007-03-22 for particulate water absorbing agent with water-absorbing resin as main component.
Invention is credited to Hirotama Fujimaru, Teruyuki Kanto, Kazuki Kimura, Hiroko Ueda, Katsuyuki Wada.
Application Number | 20070066167 10/570965 |
Document ID | / |
Family ID | 34964037 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070066167 |
Kind Code |
A1 |
Wada; Katsuyuki ; et
al. |
March 22, 2007 |
Particulate water absorbing agent with water-absorbing resin as
main component
Abstract
The present invention provides a water absorbing agent which
maintains excellent water absorbing properties for a long time,
even when urine composition of human urine varies depending. A
particulate water absorbing agent comprising a water-absorbing
resin obtained by crosslinking polymerization of an unsaturated
monomer, which exhibits Centrifuge retention capacity in a
physiological saline solution of not lower than 32 g/g, mass median
particle size (D50) of 200 to 400 .mu.m, ratio of particles with
diameter of smaller than 150 .mu.m of 0 to 2% by weight, and
increased extractables by deterioration of 0 to 15% by weight and
extractables for one hour in deterioration test liquid of 0.1 to
30% by weight.
Inventors: |
Wada; Katsuyuki; (Hyogo,
JP) ; Kimura; Kazuki; (Hyogo, JP) ; Ueda;
Hiroko; (Hyogo, JP) ; Kanto; Teruyuki; (Hyogo,
JP) ; Fujimaru; Hirotama; (Osaka, JP) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
34964037 |
Appl. No.: |
10/570965 |
Filed: |
March 29, 2005 |
PCT Filed: |
March 29, 2005 |
PCT NO: |
PCT/JP05/06570 |
371 Date: |
March 7, 2006 |
Current U.S.
Class: |
442/101 |
Current CPC
Class: |
Y10T 428/254 20150115;
Y10T 428/2982 20150115; Y10T 428/2991 20150115; C08J 3/12 20130101;
Y10T 428/2998 20150115; Y10T 442/2344 20150401; C08J 3/245
20130101; Y10T 428/249924 20150401; C08J 2300/14 20130101 |
Class at
Publication: |
442/101 |
International
Class: |
B32B 5/02 20060101
B32B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2004 |
JP |
2004-096083 |
Sep 20, 2004 |
JP |
2004-211856 |
Claims
1. A particulate water absorbing agent comprising a water-absorbing
resin obtained by crosslinking polymerization of an unsaturated
monomer containing an acid group and/or a salt thereof and said
water absorbing agent satisfies the following (a) to (d): (a)
centrifuge retention capacity (CRC) of the water absorbing agent in
a physiological saline solution being in the range not lower than
32 g/g; (b) mass median particle size (D50) of the water absorbing
agent being in the range of 200 to 400 .mu.m; (c) ratio of
particles of the water absorbing agent having diameter of smaller
than 150 .mu.m being in the range of 0 to 2% by weight; and (d)
increased extractables of the water absorbing agent by
deterioration expressed by the following formula of 0 to 15% by
weight and extractables of the water absorbing agent for one hour
in deterioration test liquid of 0.1 to 30% by weight, wherein the
deterioration test solution means a physiological saline solution
containing 0.05% by weight of L-ascorbic acid. Increased
extractables by deterioration (% by weight)=extractables for one
hour in deterioration test liquid (% by weight)-extractables for
one hour in a physiological saline solution (% by weight)
2. A particulate water absorbing agent comprising a water-absorbing
resin obtained by crosslinking polymerization of an unsaturated
monomer containing an acid group and/or a salt thereof and said
water absorbing agent satisfies the following (a) to (c) and (e):
(a) centrifuge retention capacity (CRC) of the water absorbing
agent in a physiological saline solution being in the range of not
lower than 32 g/g; (b) mass median particle size (D50) of the water
absorbing agent being in the range of 200 to 400 .mu.m; (c) ratio
of particles having diameter of smaller than 150 .mu.m being in the
range of 0 to 2% by weight; and (e) increased ratio of extractables
of the water absorbing agent by deterioration expressed by the
following formula of 1 to 4 times, and extractables of the water
absorbing agent for one hour in deterioration test liquid of 0.1 to
30% by weight, wherein the deterioration test solution means a
physiological saline solution containing 0.05% by weight of
L-ascorbic acid. Increased ratio of extractables by
deterioration=extractables for one hour in deterioration test
liquid (% by weight)/extractables for one hour in a physiological
saline solution (% by weight)
3. A particulate water absorbing agent comprising a water-absorbing
resin obtained by crosslinking polymerization of an unsaturated
monomer containing an acid group and/or a salt thereof said water
absorbing agent satisfies the following (a) to (c), (f) and (g):
(a) centrifuge retention capacity (CRC) of the water absorbing
agent in a physiological saline solution being in the range of not
lower than 32 g/g; (b) mass median particle size (D50) of the water
absorbing agent being in the range of 200 to 400 .mu.m; (c) ratio
of particles having diameter of the water absorbing agent of
smaller than 150 .mu.m being in the range of 0 to 2% by weight; (f)
extractables of the water absorbing agent for 16 hours in a
physiological saline solution being in the range of 0.1 to 10% by
weight; and (g) absorbency against pressure at 4.8 kPa (AAP4.8 kPa)
of the absorbent in a physiological saline solution being not lower
than 21 g/g.
4. A particulate water absorbing agent according to claim 1,
wherein a water-absorbing resin is further surface crosslinked.
5. A particulate water absorbing agent according to claim 1,
wherein further (h) 90 to 100% by weight of a particulate water
absorbing agent has diameter in the range of 600 to 150 .mu.m.
6. A particulate water absorbing agent according to claim 1,
wherein the water absorbing agent satisfies further (i) absorbency
against pressure at 1.9 kPa (AAP 1.9 kPa) in a physiological saline
solution being not lower than 20 g/g.
7. A particulate water absorbing agent claim 1, wherein the water
absorbing agent satisfies further (j) absorption speed with vortex
method being not longer than 60 seconds.
8. A particulate water absorbing agent according to claim 1,
wherein the water absorbing agent satisfies further (k) fluidity
after moisture absorption being in the range of 0 to 20% by
weight.
9. A particulate water absorbing agent according to claim 1,
wherein the water absorbing agent satisfies further (l) logarithmic
standard deviation of particle size distribution being in the range
of 0.20 to 0.40.
10. A particulate water absorbing agent according to claim 1, which
further comprises, besides a water-absorbing resin as a main
component, one or more minor components selected from the group
consisting of a chelating agent, a deodorant, a polyvalent metal
salt and an inorganic fine particle.
11. A particulate water absorbing agent according to claim 10,
wherein the chelating agent is one or more agents selected from the
group consisting of aminocarboxylic acid and salt thereof.
12. A particulate water absorbing agent according to claim 10,
wherein the deodorant is a component made from a plant.
13. A particulate water absorbing agent according to claim 10,
wherein the polyvalent metal salt is a polyvalent metal salt of an
organic acid.
14. A particulate water absorbing agent according to claim 10,
wherein the inorganic fine particle is a composite hydrated
oxide.
15. A particulate water absorbing agent according to claim 1,
wherein particle shape of a water-absorbing resin is irregularly
pulverized shape.
16. A particulate water absorbing agent according to claim 1,
wherein the above (d) increased extractables by deterioration is 0
to 12% by weight.
17. A particulate water absorbing agent according to claim 2,
wherein the above (e) increased ratio of extractables by
deterioration is 1 to 3.
18. A particulate water absorbing agent according to claim 1,
wherein the above (g) absorbency against pressure at 4.8 kPa in a
physiological saline solution is not lower than 22 g/g.
19. An absorbing article for excrement, urine or blood, which is
molded by comprising a particulate water absorbing agent according
to claim 1 and hydrophilic fibers.
20. A method for production of a particulate water absorbing agent
according to claim 1, which comprises a step of crosslinking
polymerization of the aqueous solution of an unsaturated monomer
containing non-neutralized acrylic acid and/or salts thereof in the
presence of a crosslinking agent and a chain transfer agent; and a
step of surface crosslinking the water-absorbing resin particle
obtained by the polymerization and satisfied (a) to (c) described
below, (a) centrifuge retention capacity (CRC) of the resin
particle in a physiological saline solution being in the range of
not lower than 32 g/g; (b) mass median particle size (D50) of the
resin particle being in the range of 200 to 400 .mu.m; and (c)
ratio of particles having diameter of the resin particle of smaller
than 150 .mu.m being in the range of 0 to 2% by weight.
21. A method for production of a particulate water absorbing agent
according to claim 1, which comprises a step of crosslinking
polymerization of the aqueous solution of an unsaturated monomer in
concentration of 10 to 30% by weight containing non-neutralized
acrylic acid in the presence of a crosslinking agent; a step of
neutralization after the polymerization; and a step of surface
crosslinking the water-absorbing resin particle obtained by the
neutralization and satisfied (a) to (c) described below, (a)
centrifuge retention capacity (CRC) of the resin particle in a
physiological saline solution being in the range of not lower than
32 g/g; (b) mass median particle size (D50) of the resin particle
being in the range of 200 to 400 .mu.m; and (c) ratio of particles
having diameter of the resin particle of smaller than 150 .mu.m
being in the range of 0 to 2% by weight.
22. A method for production of a particulate water absorbing agent
according to claim 1, which comprises, a step of crosslinking
polymerization of the aqueous solution of an unsaturated monomer
containing non-neutralized acrylic acid and/or salts thereof the
presence of a crosslinking agent; a step of surface crosslinking
the water-absorbing resin particle obtained by the polymerization
and satisfied (a) to (c) described below, (a) centrifuge retention
capacity (CRC) of the resin particle in a physiological saline
solution being in the range of not lower than 32 g/g; (b) mass
median particle size (D50) of the resin particle being in the range
of 200 to 400 .mu.m; (c) ratio of particles having diameter of the
resin particle of smaller than 150 .mu.m being in the range of 0 to
2% by weight; and a step of adding a chelating agent with one or
more timings selected from the group consisting of (i) during
polymerization (ii) after the polymerization and before surface
crosslinking (iii) during surface crosslinking (iv) after surface
crosslinking.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a particulate water
absorbing agent including a water-absorbing resin as a main
component. In particular, it relates to a particulate water
absorbing agent fulfilling superior absorption ability
conventionally not obtained in practical applications as absorbing
articles such as a diaper.
[0003] 2. Description of Related Art
[0004] At present, as component materials in sanitary goods such as
a paper diaper, a sanitary napkin, an incontinence pad, and the
like, a water-absorbing resin to absorb body fluid and hydrophilic
fibers such as pulp are widely used. As the water-absorbing resin,
for example, partially neutralized and crosslinked polyacrylic
acid, hydrolysates of starch-acrylic acid graft polymer, saponified
vinyl acetate-acrylic acid ester copolymers, hydrolysates of
acrylonitrile copolymers or acrylamide copolymers or crosslinked
polymers thereof, crosslinked polymers of cationic monomers, and
the like are used as main raw materials.
[0005] The water-absorbing resin has conventionally been required
to have superior property such as superior liquid absorption amount
or water absorption speed, gel strength and gel permeability in
contact with aqueous liquid such as body fluid, along with water
suction force to suck water from a substrate containing aqueous
liquid. Further, as recent trends, a water-absorbing resin powder
with very narrow particle size distribution or a water-absorbing
resin with high absorption capacity and low water-extractables has
been required and high absorbency against pressure or liquid
permeability under pressure has essentially been required. In
addition to the above needs, such characteristics of gel has also
been required as not to be deteriorated for long term and to retain
absorbing performance even in swollen and gelled state by
absorption of body fluid or urine.
[0006] For example, there are many patent applications on many
parameters specifying various properties of these water-absorbing
resins or water absorbing agents with a water-absorbing resin as a
main component, or on measurement methods thereof (U.S. Reissued
32,649, UK2267094B, U.S. Pat. No. 5,051,259, U.S. Pat. No.
5,419,956, U.S. Pat. No. 6,087,002, EP0629441, EP0707603,
EP0712659, EP1029886, U.S. Pat. No. 5,462,972, U.S. Pat. No.
5,453,323, U.S. Pat. No. 5,797,893, U.S. Pat. No. 6,127,454, U.S.
Pat. No. 6,184,433, U.S. Pat. No. 6,297,335, U.S. Reissued 37,021,
U.S. Pat. No. 5,140,076, U.S. Pat. No. 6,414,214B1, U.S. Pat. No.
5,994,440, U.S. Pat. No. 6,444,744, U.S. Pat. No. 6,194,531,
EP0940148, EP1153656, EP0605215, U.S. Pat. No. 5,147,343, U.S. Pat.
No. 5,149,335, EP0532002, U.S. Pat. No. 5,601,452, U.S. Pat. No.
5,562,646, U.S. Pat. No. 5,669,894, U.S. Pat. No. 6,150,582,
WO02/053198, EP0937739).
[0007] Water-absorbing resins superior in gel strength,
extractables and absorption capacity are proposed in U.S. Reissued
32,649. A water-absorbing resin superior in liquid permeability
under no pressure, absorption speed and absorption capacity is
proposed in UK2267094B. Technology specifying specific particle
size distribution is also proposed in U.S. Pat. No. 5,051,259, U.S.
Pat. No. 5,419,956, U.S. Pat. No. 6,087,002 and EP0629441. Further,
a water-absorbing resin superior in absorbency against pressure
under various loads or many measurement methods therefore are also
proposed and water-absorbing resins with superior absorbency
against pressure alone or in combination with other property are
proposed in EP0707603, EP0712659, EP1029886, U.S. Pat. No.
5,462,972, U.S. Pat. No. 5,453,323, U.S. Pat. No. 5,797,893, U.S.
Pat. No. 6,127,454, U.S. Pat. No. 6,184,433, U.S. Pat. No.
6,297,335 and U.S. Reissued 37,021.
[0008] Water-absorbing resins with little property decrease by
impact are proposed in U.S. Pat. No. 5,140,076 and U.S. Pat. No.
6,414,214B1. A water-absorbing resin with specific powdery dust
amount is proposed in U.S. Pat. No. 5,994,440, and a
water-absorbing resin with less coloring is proposed in U.S. Pat.
No. 6,444,744. Water-absorbing resins superior in gel durability in
an aqueous L-ascorbic acid solution as index of urine resistance or
superior in water absorption ability are proposed in U.S. Pat. No.
6,194,531 and EP0940148. A water-absorbing resin with superior air
permeability is proposed in EP1153656. A water-absorbing resin with
less residual monomers is proposed in EP0605215.
[0009] Further, in U.S. Pat. No. 5,147,343, U.S. Pat. No.
5,149,335, EP0532002, U.S. Pat. No. 5,601,452, U.S. Pat. No.
5,562,646, U.S. Pat. No. 5,669,894, U.S. Pat. No. 6,150,582,
WO02/053198, water-absorbing resins with specific property are
proposed as suitable to water-absorbing articles such as a diaper
having specific property, composition or polymer concentration.
Further, a method for surface crosslinking, while pulverizing at
least a part of resin particles is proposed in EP0937739.
SUMMARY OF THE INVENTION
[0010] Among water-absorbing resins or water absorbing agents which
have been developed based on many properties, as described above,
those targeted to or with specifications of these properties have
also been produced, however, there was a problem that they have not
yet satisfactorily fulfilled performance in practical use such as a
paper diaper, and the like, even if these properties are
controlled.
[0011] Practically sufficient performance has not yet attained even
by controlling or designing such properties as water-absorption
speed, centrifuge retention capacity, absorbency against pressure,
gel strength, durability, extractables and particle size whereas
many water-absorbing resins or water absorbing agents have been
developed and used. Therefore, it is an object of the present
invention to provide a water absorbing agent suitable to practical
use in conventional water absorbing agent substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0012] After studying to solve the problems, it was found that in a
water absorbing agent of the present invention having specific
particle size distribution and absorption capacity, components
contained in urine gradually destruct crosslinked structure of a
water-absorbing resin to make labile to deterioration of the water
absorbing agent and such deterioration caused by urine increases
extractables and changes water-absorption properties.
Conventionally, properties of the water-absorbing resin or the
water absorbing agent measured by a physiological saline solution
(an aqueous solution of 0.9% by weight of NaCl) or various
artificial urine solutions have been proposed, however, urine
components in artificial urine are different in each patent and
composition of practical urine solution itself is not constant but
changes depending on living environment, food practice, age or
seasons and furthermore largely changes every time or by physical
conditions even in the same person. Because absorption properties
of a conventional water-absorbing resin or a water absorbing agent
have been evaluated using single kind of specific absorption liquid
such as a specific physiological saline solution or artificial
urine solution as a urine model, evaluation of the water absorbing
agent responsive to change in urine composition could not suitably
be carried out and thus it was clarified that a conventional water
absorbing agent could not exert sufficient performance in practical
use when extractables of the water absorbing agent changed due to
change in urine composition.
[0013] Therefore, the present invention defined "deterioration
caused by urine" as deterioration of a water absorbing agent
generated by personal difference in urine, or urine compositional
change by seasons or physical conditions of even the same person,
and as indexes of degree of deterioration caused by urine,
"increased extractables by deterioration" and "increased ratio of
extractables by deterioration" were introduced. In the present
invention, increased extractables by deterioration and increased
ratio of extractables by deterioration are defined by the following
formulas. In the present invention, deterioration test liquid means
a physiological saline solution containing 0.05% by weight of
L-ascorbic acid and a physiological saline solution means an
aqueous solution of 0.9% by weight of NaCl, which is used at room
temperature (25.degree. C..+-.2.degree. C.) unless otherwise
specified especially. Measurement methods thereof are as described
in Examples shown later. Increased extractables by deterioration (%
by weight)=extractables for one hour in deterioration test liquid
(% by weight)-extractables for one hour in a physiological saline
solution (% by weight) Increased ratio of extractables by
deterioration=extractables for one hour in deterioration test
liquid (% by weight)/extractables for one hour in a physiological
saline solution (% by weight)
[0014] When extractables increases from the amount before
deterioration, in deterioration test liquid, the extractables tends
to be more easily exuded from an absorbing substrate, which in turn
obstructs diffusion of liquid such as blood and urine into an
absorbing substrate and thus lowers absorption properties. In
addition, significant increase in extractables suggests destruction
of crosslinked structure of the water absorbing agent, making
retention difficult of body fluid such as urine absorbed by the
water absorbing agent and thus absorption performance is lowered.
Such decrease in absorption performance appears as increase in
rewet amount in an absorbing substrate or absorbing articles. It is
thus preferable for "increased extractables by deterioration" and
"increased ratio of extractables by deterioration" to be limited
within specific range to inhibits increase in rewet amount.
[0015] It is also clarified by detailed study on deterioration due
to urine that the deterioration degree tends to depend on surface
area of the water absorbing agent and extractables by the
deterioration significantly increases in the water absorbing agent
with particle size distribution of smaller mass median particle
size, for example, the water absorbing agent with mass median
particle size D50 not larger than 400 .mu.m. Mass median particle
size is an important factor influencing absorption behavior of the
water-absorbing resin or the water absorbing agent and finishing of
absorbing articles such as a diaper, and thus problems cannot be
solved merely by increasing mass median particle size to inhibit
deterioration caused by urine.
[0016] Further, deterioration of the water absorbing agent caused
by urine also correlates to absorption capacity and higher
absorbency significantly increases extractables due to
deterioration caused by urine. Therefore, it is not enough to
increase only absorption capacity of the water-absorbing resin
aiming at improving absorption amount of absorbing articles such as
a diaper, to attain long term durability in practical use.
[0017] This indicates that, in a present day with favor of thinner
type absorbing articles, such the water absorbing agent as having
small mass median particle size D50 of not larger than 400 .mu.m,
high absorption capacity and certain limited range of extractables
irrespective of change in urine can be a more superior water
absorbing agent than conventional ones, however, further indicates
that such the water absorbing agent as having small mass median
particle size D50 of not larger than 400 .mu.m, high absorption
capacity and low extractables irrespective of change in urine is
difficult to prepare practically and has thus not been present
before.
[0018] By consideration of the above, the inventors thought of that
the problems could be solved, in the present invention, by making
the water absorbing agent with also superior stability to urine in
specific mass median particle size, by furnishing crosslinked
structure, specific centrifuge retention capacity, specific
particle size distribution and mass median particle size and
further specific ranges of "increased extractables by
deterioration" and "increased ratio of extractables by
deterioration" as a water absorbing agent.
[0019] A first particulate water absorbing agent of the present
invention is:
[0020] a particulate water absorbing agent comprising a
water-absorbing resin obtained by crosslinking polymerization of an
unsaturated monomer containing an acid group and/or a salt thereof
as a main component, and said water absorbing agent satisfies the
following (a) to (d):
[0021] (a) centrifuge retention capacity (CRC) in a physiological
saline solution being in the range of not lower than 32 g/g;
[0022] (b) mass median particle size (D50) being in the range of
200 to 400 .mu.m;
[0023] (c) ratio of particles having diameter of smaller than 150
.mu.m being in the range of 0 to 2% by weight; and
[0024] (d) increased extractables by deterioration expressed by the
above mentioned formula of 0 to 15% by weight and extractables for
one hour in deterioration test liquid of 0.1 to 30% by weight.
[0025] A second particulate water absorbing agent of the present
invention is:
[0026] a particulate water absorbing agent comprising a
water-absorbing resin obtained by crosslinking polymerization of an
unsaturated monomer containing an acid group and/or a salt thereof
as a main component, and said water absorbing agent satisfies the
following (a) to (c) and (e):
[0027] (a) centrifuge retention capacity (CRC) in a physiological
saline solution being in the range of not lower than 32 g/g;
[0028] (b) mass median particle size (D50) being in the range of
200 to 400 .mu.m;
[0029] (c) ratio of particles having diameter of smaller than 150
.mu.m being in the range of 0 to 2% by weight; and
[0030] (e) increased ratio of extractables by deterioration
expressed by the above mentioned formula of 1 to 4 times, and
extractables for one hour in deterioration test liquid of 0.1 to
30% by weight.
[0031] A third particulate water absorbing agent of the present
invention is:
[0032] a particulate water absorbing agent comprising a
water-absorbing resin obtained by crosslinking polymerization of an
unsaturated monomer containing an acid group and/or a salt thereof
as a main component, and said water absorbing agent satisfies the
following (a) to (c), (f) and (g):
[0033] (a) centrifuge retention capacity (CRC) in a physiological
saline solution being in the range of not lower than 32 g/g;
[0034] (b) mass median particle size (D50) being in the range of
200 to 400 .mu.m;
[0035] (c) ratio of particles having diameter of smaller than 150
.mu.m being in the range of 0 to 2% by weight;
[0036] (f) extractables for 16 hours in a physiological saline
solution being in the range of 0.1 to 10% by weight; and
[0037] (g) absorbency against pressure at 4.8 kPa (AAP4. 8 kPa) in
a physiological saline solution being not lower than 21 g/g.
[0038] A method for production of the first particulate water
absorbing agent of the present invention is characterized by
comprising:
[0039] a step of crosslinking polymerization of the aqueous
solution of an unsaturated monomer containing non-neutralized
acrylic acid and/or salts thereof as a main component in the
presence of a crosslinking agent and a chain transfer agent;
and
[0040] a step of surface crosslinking the water-absorbing resin
particle obtained by the polymerization and satisfied (a) to (c)
described below,
[0041] (a) centrifuge retention capacity (CRC) of the resin
particle in a physiological saline solution being in the range of
not lower than 32 g/g;
[0042] (b) mass median particle size (D50) of the resin particle
being in the range of 200 to 400 .mu.m; and
[0043] (c) ratio of particles having diameter of the resin particle
of smaller than 150 .mu.m being in the range of 0 to 2% by
weight.
[0044] A production method of the second particulate water
absorbing agent of the present invention is characterized by
comprising:
[0045] a step of crosslinking polymerization of the aqueous
solution of an unsaturated monomer in concentration of 10 to 30% by
weight containing non-neutralized acrylic acid as a main component
in the presence of a crosslinking agent;
[0046] a step of neutralization after the polymerization; and
[0047] a step of surface crosslinking the water-absorbing resin
particle obtained by the neutralization and satisfied (a) to (c)
described below,
[0048] (a) centrifuge retention capacity (CRC) of the resin
particle in a physiological saline solution being in the range of
not lower than 32 g/g;
[0049] (b) mass median particle size (D50) of the resin particle
being in the range of 200 to 400 .mu.m; and
[0050] (c) ratio of particles having diameter of the resin particle
of smaller than 150 .mu.m being in the range of 0 to 2% by
weight.
[0051] A production method of the third particulate water absorbing
agent of the present invention is characterized by comprising:
[0052] a step of crosslinking polymerization of the aqueous
solution of an unsaturated monomer containing non-neutralized
acrylic acid and/or salts thereof as a main component in the
presence of a crosslinking agent;
[0053] a step of surface crosslinking the water-absorbing resin
particle obtained by the polymerization and satisfied (a) to (c)
described below,
[0054] (a) centrifuge retention capacity (CRC) of the resin
particle in a physiological saline solution being in the range of
not lower than 32 g/g;
[0055] (b) mass median particle size (D50) of the resin particle
being in the range of 200 to 400 .mu.m;
[0056] (c) ratio of particles having diameter of the resin particle
of smaller than 150 .mu.m being in the range of 0 to 2% by weight;
and
[0057] a step of adding a chelating agent with one or more timings
selected from the group consisting of [0058] (i) during
polymerization [0059] (ii) after the polymerization and before
surface crosslinking [0060] (iii) during surface crosslinking
[0061] (iv) after surface crosslinking.
EFFECTS OF THE INVENTION
[0062] Using the particulate water absorbing agent of the present
invention, due to having specific absorption capacity and specific
particle size distribution, in practical application as absorbing
articles such as a diaper, particularly in absorbing ability in
short period, not conventionally obtained performance can be
attained. In particular, rewet amount can be reduced and
improvement effect of dry feeling at diaper surface is
significant.
[0063] Further, due to inhibition of deterioration caused by urine,
it provides superior gel stability and maintains absorbing
performance over long period, therefore it reduces discomfort for
persons wearing absorbing articles.
[0064] In the present invention, because deterioration caused by
urine can be inhibited and simultaneously specific particle size
distribution is provided, size segregation is less and in powder
transfer to produce the particulate water absorbing agent and
produce absorbing articles such as a diaper, superior piston-flow
property is provided and pulsation which is periodical change in
powder feed amount is inhibited. In addition to this, in production
of absorbing articles such as a diaper, mixing is easy between the
particulate water absorbing agent of the present invention and
hydrophilic fibers such as wood crushed pulp, which conveniently
provides homogeneous composition.
Best Embodiments to Practice the Invention
[0065] Raw materials used for the water-absorbing resin and the
water absorbing agent of the present invention and reaction
conditions will be explained below. In the present invention, the
followings are values obtained by methods described in Examples
shown later: (a) centrifuge retention capacity (CRC) in a
physiological saline solution, (b) mass median particle size (D50),
(d) increased extractables by deterioration, (e) increased ratio of
extractables by deterioration, (f) extractables for 16 hours in a
physiological saline solution, (g) absorbency against pressure at
4.8 kPa (AAP4.8 kPa) in a physiological saline solution, (i)
absorbency against pressure at 1.9 kPa (AAP1.9 kPa) in a
physiological saline solution, (j) absorption speed with vortex
method in a physiological saline solution, (k) fluidity after
moisture absorption, (l) logarithmic standard deviation of particle
size distribution and extractables for one hour in deterioration
test liquid.
[0066] (1) A Water-Absorbing Resin
[0067] A water-absorbing resin of the present invention means a
crosslinked polymer which can form hydrogel and is water swelling
and non-dissolving in water, for example, water swelling indicates
one absorbing large quantity of water in ion exchanged water, such
as essentially 5 times or more own weight and preferably 50 to 1000
times. Non-dissolving in water means one with extractables in water
in 1 hour of not higher than 50% by weight and in the range
described later. Measurement methods thereof are specified in
Examples.
[0068] As the water-absorbing resin in the present invention, to
attain objectives of the present invention, a water-absorbing resin
obtained by crosslinking polymerization of an unsaturated monomer
containing an acid group and/or salts thereof is essentially used
and preferably (partially) neutralized polymer of polyacrylic acid
obtained by polymerizing and crosslinking of an unsaturated monomer
mainly composed of acrylic acid and/or salts thereof is used. Any
water-absorbing resin may be used as long as it has crosslinked
polymerized structure and it may be the water-absorbing resin
obtained by crosslinking reaction with a crosslinking agent after
polymerization of an unsaturated monomer containing an acid group
and/or salts thereof.
[0069] (2) A Water Absorbing Agent and a Method for Production
Thereof
[0070] A water absorbing agent in the present invention is a
solidifying agent made of the water-absorbing resin as a main
component, to absorb aqueous liquid. Aqueous liquid is not limited
to water but also includes water containing substance without
especially limited, such as urine, blood, excrement, waste liquid,
humidity or steam, ice, a mixture of water and organic solvents or
inorganic solvents, rain water and underground water, preferably
urine and particularly preferably human urine. In the present
invention, the water-absorbing resin may be used as it is as the
water absorbing agent and additives or water may be contained
optionally. Content of the water-absorbing resin in the water
absorbing agent is 70 to 100% by weight of the water absorbing
agent, preferably 80 to 100% by weight and further preferably 90 to
100% by weight. As other components contained, generally water is
used as a main or essential component and further additives
described later are used.
[0071] A water absorbing agent of the present invention can be
obtained, for example, by the following production methods 1 to 3,
although a method for production is not limited as long as it
provides one satisfying the properties.
[0072] Production method 1: A method for crosslinking
polymerization of an aqueous solution of an unsaturated monomer
containing non-neutralized acrylic acid and/or salts thereof as a
main component in the presence of a crosslinking agent and a chain
transfer agent, followed by adjustment to specific particle size
distribution and further surface crosslinking of thus obtained
water-absorbing resin particles with specific absorption
capacity.
[0073] Production method 2: A method for crosslinking
polymerization of an aqueous solution of specific concentration of
an unsaturated monomer containing non-neutralized acrylic acid as a
main component in the presence of a crosslinking agent, followed by
neutralization, adjustment to specific particle size distribution
and further surface crosslinking of thus obtained water-absorbing
resin particles with specific absorption capacity.
[0074] Production method 3: A method for crosslinking
polymerization of an aqueous solution of an unsaturated monomer
containing non-neutralized acrylic acid and/or salts thereof as a
main component in the presence of a crosslinking agent, followed by
adjustment to specific particle size distribution and further
surface crosslinking of thus obtained water-absorbing resin
particles with specific absorption capacity, wherein a chelating
agent is added with one or more timings selected from the group
consisting of [0075] (i) during polymerization [0076] (ii) after
the polymerization and before surface crosslinking [0077] (iii)
during surface crosslinking [0078] (iv) after surface
crosslinking.
[0079] A production method for the water absorbing agent of the
present invention and further the water absorbing agent of the
present invention are explained below sequentially.
[0080] (3) An Unsaturated Monomer
[0081] As an unsaturated monomer composing the water-absorbing
resin (herein after abbreviated simply as a monomer), acrylic acid
and/or salt thereof is used as a main component, and they may be
used alone or in combination with other monomers to obtain the
water-absorbing resin. Such other monomers include, an aqueous or
hydrophobic unsaturated monomer such as methacrylic acid, maleic
anhydride, maleic acid, fumaric acid, crotonic acid, itaconic acid,
vinylsulfonic acid, 2-(meth)acrylamide-2-methylpropane sulfonic
acid, (meth)acryloxyalkane sulfonic acid and its alkali metal salt,
ammonium salt, N-vinyl-2-pyrrolidone, N-vinylacetamide,
(meth)acrylamide, N-isopropyl(meth)acrylamide,
N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl (meth)acrylate,
methoxypolyethyleneglycol(meth)acrylate,
polyethyleneglycol(meth)acrylate, isobutylene,
lauryl(meth)acrylate, etc. They may be used alone or in combination
of two or more kinds.
[0082] When monomers other than acrylic acid (salts) are used in
combination, to attain objectives of the present invention, use
ratio of the monomer other than acrylic acid (salt thereof) is
preferably 0 to 30% by mole based on total amount of acrylic acid
and salts thereof, more preferably 0 to 10% by mole and most
preferably 0 to 5% by mole.
[0083] When an unsaturated monomer containing an acid group is used
as a monomer, salts thereof include alkali metal salts, alkaline
earth metal salts and ammonium salts, in view of performance,
industrial availability and safety of the water-absorbing resin
obtained, sodium salts and potassium salts are preferable. An
unsaturated monomer containing an acid group such as acrylic acid
is preferably neutralized at the acid group in view of property and
pH and neutralization ratio of the acid group is usually 20 to 100%
bymole, preferably 30 to 95% by mole and more preferably 40 to 80%
by mole. Neutralization of the acid group maybe performed in an
aqueous solution containing a monomer or may be performed after
obtaining a polymer as shown in the production method 2 or they may
be used in combination.
[0084] (4) An Internal Crosslinking Agent
[0085] A water-absorbing resin used in the present invention is a
crosslinked polymer and crosslinked structure may be formed as
self-crosslinked type without using a crosslinkable monomer or an
internal crosslinking agent such as so called a crosslinkable
monomer may be used. In view of property, it is preferable to
copolymerize or react with an internal crosslinking agent having
not less than 2 polymerizable unsaturated groups or not less than 2
reactable groups in a molecule. A water absorbing agent becomes
insoluble to water due to being a crosslinked polymer.
[0086] Specific examples of these internal crosslinking agents
include, for example, N,N'-methylenebis(meth)acrylamide,
(poly)ethyleneglycol di(meth)acrylate, (poly)propyleneglycol
di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerine
tri(meth)acrylate, glycerine acrylate methacrylate, ethylene oxide
modified trimethylolpropane tri(meth)acrylate, pentaerythritol
tetra(meth)acrylate, triallyl cyanurate, triallyl isocyanurate,
triallyl phosphate, triallylamine, poly(meth)allyloxyalkane,
(poly)ethyleneglycol diglycidyl ether, glycerol diglycidyl ether,
ethyleneglycol, polyethyleneglycol, propyleneglycol, glycerine,
pentaerythritol, ethylenediamine, ethylene carbonate, propylene
carbonate, polyethyleneimine, glycidyl (meth)acrylate, etc.
[0087] These internal crosslinking agents may be used alone or in a
mixture of two or more kinds, as appropriate. These internal
crosslinking agents may be added as a whole into a reaction system
or in portion wise. When at least one kind or not less than 2 kinds
of internal crosslinking agents are used, in consideration of
absorption properties of the water-absorbing resin or the water
absorbing agent finally obtained, it is preferable to use
essentially a compound having not less than two polymerizable
unsaturated groups, in polymerization.
[0088] Using amount of these internal crosslinking agents is
preferably in the range of 0.001 to 2% by mole based on the
unsaturated monomer (excluding the internal crosslinking agents),
more preferably 0.005 to 0.5% by mole, further preferably 0.01 to
0.2% by mole and particularly preferably 0.03 to 0.15% by mole. The
using amounts of the internal crosslinking agents less than 0.001%
by mole and over 2% by mole may not provide sufficient absorption
properties. The using amount of the internal crosslinking agents
less than the range does not sufficiently form crosslinked
structure, which increases extractables in a physiological saline
solution or extractables in deterioration test liquid described
later, increased extractables by deterioration, increased ratio of
extractables by deterioration and "extractables for 16 hours" and
thus not preferable. On the other hand, the using amount of the
internal crosslinking agents over the range reduces the
extractables, however, induces reduced absorption capacity of the
water-absorbing resin or the water absorbing agent, which in turn
lowers absorption capacity of absorbing articles such as a diaper,
and thus not preferable.
[0089] When crosslinked structure is introduced inside a polymer by
using the internal crosslinking agent, the internal crosslinking
agent may be added to a reaction system before, during or after
polymerization of the monomer or after neutralization.
[0090] (5) A Polymerization Initiator
[0091] An initiator used in polymerization of a monomer to obtain
the water-absorbing resin used in the present invention includes a
radical polymerization initiator such as potassium persulfate,
ammonium persulfate, sodium persulfate, potassium peracetate,
sodium peracetate, potassium percarbonate, sodium percarbonate,
tert-butyl hydroperoxide, hydrogen peroxide,
2,2'-azobis(2-amidinopropane)dihydrochloride: photopolymerization
initiators such as 2-hydroxy-2-methyl-1-phenylpropane-1-one. Using
amount of the polymerization initiator is, in view of property,
0.001 to 2% by mole, preferably 0.01 to 0.1% by mole (based on
total monomers). When the using amount of the polymerization
initiator is less than 0.001% by mole, unreacted residual monomers
increase, while, the amount of the polymerization initiator is over
2% by mole, polymerization control becomes difficult and thus not
preferable.
[0092] (6) A Polymerization Method
[0093] In the present invention, bulk polymerization or
precipitation polymerization may be carried out, however, in view
of property, aqueous solution polymerization or reversed phase
suspension polymerization by preparation of an aqueous solution of
the monomer is preferable. Monomer concentration in the aqueous
solution (hereinafter referred to as a monomer aqueous solution),
when an aqueous solution of the monomer is prepared, is determined
by temperature of the aqueous solution or the monomer and not
especially limited, however, preferably 10 to 70% by weight, and
further preferably 20 to 60% by weight. When aqueous solution
polymerization is carried out, a solvent other than water may also
be used, if necessary, and solvent type used in combination is not
especially limited. Crushing may be carried out after
polymerization, if necessary.
[0094] Polymerization is started using the polymerization
initiator. An activated energy ray such as UV ray, electron beam or
.gamma.-ray may be used other than the polymerization initiator as
it is or in combination with the polymerization initiator.
Polymerization temperature depends on type of the polymerization
initiator used, however, is preferably in the range of 15 to
130.degree. C. and more preferably in the range of 20 to
120.degree. C.
[0095] Reversed phase polymerization is a method for polymerization
by suspending a monomer aqueous solution in a hydrophobic organic
solvent, and described, for example, in U.S. Pat. No. 4,093,776,
U.S. Pat. No. 4,367,323, U.S. Pat. No. 4,446,261, U.S. Pat. No.
4,683,274, U.S. Pat. No. 5,244,735, etc. Aqueous solution
polymerization is the method for polymerization of a monomer
aqueous solution without using a dispersing solvent, and described,
for example, in U.S. Pat. No. 4,625,001, U.S. Pat. No. 4,873,299,
U.S. Pat. No. 4,286,082, U.S. Pat. No. 4,973,632, U.S. Pat. No.
4,985,518, U.S. Pat. No. 5,124,416, U.S. Pat. No. 5,250,640, U.S.
Pat. No. 5,264,495, U.S. Pat. No. 5,145,906, U.S. Pat. No.
5,380,808, EP0811636, EP0955086, EP0922717, etc. Monomers or
polymerization initiators exemplified in these polymerization
methods are also applicable to the present invention.
[0096] A water absorbing agent of the present invention has, as
described above, neutralization degree of acid groups of generally
20 to 100% by mole, but in a polymerization process of an
unsaturated monomer, the unsaturated monomer may be polymerized as
not-neutralized state and neutralized after polymerization, or
polymerization may be carried out using the unsaturated monomer
neutralized in advance. Therefore, neutralization degree of the
unsaturated monomer in the monomer aqueous solution may be in any
range of 0 to 100% by mole. Among these, in the production method 1
or the production method 3 may also be neutralization
polymerization and polymerization can be carried out using the
monomer aqueous solution with neutralization degree of 20 to 100%
by mole, preferably 30 to 95% by mole and more preferably 40 to 80%
by mole. Neutralization embodiments include to start polymerization
using the non-neutralized unsaturated monomer, followed by
neutralization in the midst of polymerization; to polymerize using
the unsaturated monomer neutralized in advance to the above range;
and to neutralize further in the midst of polymerization, all of
which providing polymerization of the unsaturated monomer
neutralized finally, and the neutralization degree means value at
the start of polymerization.
[0097] On the other hand, so to speak a method for acid
polymerization, followed by neutralization may be adopted, wherein
the non-neutralized unsaturated monomer containing an acid group,
in particular, non-neutralized acrylic acid as a main component is
polymerized, followed by neutralization of the acid group. This
corresponds to the production method 2. That is, the production
method 2 of the present invention is a method for crosslinking
polymerization of specific concentration of the unsaturated monomer
aqueous solution with non-neutralized acrylic acid as a main
component in the presence of a crosslinking agent, followed by
neutralization, adjustment to specific particle size and further
surface crosslinking of thus obtained water-absorbing resin
particles with specific absorption capacity. In the production
method 2, non-neutralized acrylic acid is a main component and
after crosslinking polymerization using a non-neutralized acrylic
acid monomer in the range of preferably 30 to 100% by mole, more
preferably 90 to 100% by mole and particularly preferably 100% by
mole, followed by the addition of an alkali metal salt for post
neutralization to provide partial alkali metal base to be used as a
water-absorbing resin of the present invention. When the
water-absorbing resin obtained by this polymerization method is
used as a water absorbing agent of the present invention, it is
possible to obtain an absorbing substrate with high absorbing
ability and superior stability to urine. When the non-neutralized
unsaturated monomer is polymerized, using amount of an internal
crosslinking agent tends to be able to increase, although details
are unknown, and deterioration resistance to urine can be improved
by increase in crosslinking density.
[0098] In the present invention, other polymerizable monomers can
be used with acrylic acid, if necessary. Specific other
polymerizable monomers, internal crosslinking agents, types of
polymerization initiators, additives, and the like are the same as
described in the content of the items (3), (4) and (5). In the
production method 2, concentration of the polymerizable monomer,
when a solvent is used, is not especially limited, however, is as
low as generally 5 to 30% by weight and preferably 10 to 30% by
weight and polymerization is preferably carried out in an aqueous
solution at temperature as low as 10 to 25.degree. C.
[0099] Alkali metal compounds used to neutralize an acid group in
the unsaturated monomer containing an acid group or in the polymer
obtained to provide a partial alkali metal base include alkali
metal hydroxide (sodium hydroxide, potassium hydroxide, lithium
hydroxide, etc.), alkali metal carbonate (sodium carbonate,
potassium bicarbonate, etc.), etc. In view of performance,
industrial availability and safety of the water-absorbing resin
obtained, sodium salts and potassium salts are preferable among
them. In the present invention, 50 to 90% by mole, preferably 60 to
80% by mole of acid groups in the polymer are converted to alkali
metal salts by neutralization reaction with an alkali metal
compound.
[0100] In the production method 2, the polymer after polymerization
is essentially neutralized. A method for neutralization of the
polymer with an alkali metal compound includes, when polymerization
is carried out using a solvent, one wherein an aqueous solution of
an alkali metal compound is added, while cutting the gel-like
polymer obtained to small pieces of not larger than about 1
cm.sup.3, followed by further mixing the gel with a kneader or a
meat chopper. Neutralization temperature to obtain the water
absorbing agent of the present invention is 50 to 100.degree. C.,
preferably 60 to 90.degree. C. and neutralization is preferably
performed so that uniformly of not larger than 10 as represented by
the first neutralization index (specified by neutralization degree
of 200 particles) described in claim 1 of U.S. Pat. No.
6,187,872.
[0101] (7) A Chain Transfer Agent
[0102] In the present invention, a chain transfer agent may be used
essentially in polymerization. By polymerization in the presence of
an aqueous chain transfer agent in addition to the unsaturated
monomer, inner crosslinking agent and polymerization initiator, and
when the water-absorbing resin thus obtained is used as the water
absorbing agent of the present invention, an absorbing substrate
with high absorbing ability and superior stability to urine can be
obtained. When the chain transfer agent is used in combination,
using amount of the inner crosslinking agent can be increased and
deterioration resistance to urine can be improved by increase in
crosslinking density. The aqueous chain transfer agent used for
polymerization in the present invention is not especially limited
as long as it dissolves in water or an aqueous ethylenic
unsaturated monomer and includes thiols, thiolates, secondary
alcohols, amines, phosphites, hypophosphites, etc. Specifically,
mercaptoethanol, mercaptopropanol, dodecylmercaptan, thioglycols,
thiomalic acid, 3-mercaptopropionic acid, isopropanol, sodium
phosphite, potassium phosphite, sodium hypophosphite, formic acid
and their salts are used, and one kind or not less than 2 kinds
selected from the group can be used. In view of the effect,
phosphorous compounds, in particular, hypophosphite salts such as
sodium hypophosphite are preferably used.
[0103] Using amount of the aqueous chain transfer agent depends on
kind of the aqueous chain transfer agent and concentration of a
monomer aqueous solution, however, is 0.001 to 1% by mole based on
total monomers and preferably 0.005 to 0.3% by mole. The using
amount less than 0.001% by mole provides high crosslinking density
under using amount of the inner crosslinking agent in the present
invention and too low absorption capacity and thus not preferable.
On the other hand, the using amount over 1% by mole increases water
extractables and lowers stability on the contrary and thus not
preferable. The chain transfer agent may be added by dissolving in
the monomer aqueous solution before polymerization or sequentially
in the midst of polymerization. The aqueous chain transfer agent is
essential in the production method 1 and it may also be used in the
production method 2 and the production method 3.
[0104] (8) Drying
[0105] A crosslinked polymer obtained by the above polymerization
methods is the hydrated gel-like crosslinked polymer, which may be
crushed, if necessary, and further dried. Drying is carried out
generally at temperature range of 60 to 250.degree. C., preferably
100 to 220.degree. C. and more preferably 120 to 200.degree. C. as
heating medium temperature. Drying time depends on surface area and
water content of the polymer and the dryer type and is selected to
obtain objective water content. In the present invention, the
crosslinked polymer after drying is called the water-absorbing
resin.
[0106] Water content of the water-absorbing resin used in the
present invention is not especially limited, however, it is
selected so as to provide a particle exhibiting fluidity even at
room temperature and powder state with water content of more
preferably 0.2 to 30% by weight, further-preferably 0.3 to 15% by
weight and particularly preferably 0.5 to 10% by weight. Too high
water content not only impairs fluidity and thus affects production
but also makes pulverizing of the water-absorbing resin impossible
and may lose control to specific particle size distribution. Water
content of the water-absorbing resin is specified as amount of
water contained in the water-absorbing resin, measured by weight
loss in drying at 180.degree. C. for 3 hours.
[0107] As a drying method used, various methods can be adopted, so
that objective water content is obtained, including heat drying,
hot air drying, reduced pressure drying, infrared ray drying,
microwave drying, dehydration by azeotrope with a hydrophobic
organic solvent and high-humidity drying using high temperature
steam, however, not especially limited.
[0108] Shape of the water-absorbing resin of the present invention
obtained by the above production methods is not especially limited,
as long as it is suitable to be treated as powder and includes
spherical, fibrous, rod, nearly spherical, flat, irregular,
agglomelated particulate, porous-structured particles, however,
irregularly pulverized one obtained by a pulverizing process is
preferably used.
[0109] (9) Pulverizing, Classification and Particle Size Control
and Absorption Capacity
[0110] A water-absorbing resin used in the present invention is
adjusted preferably to have specific particle size to obtain the
particulate water absorbing agent of the present invention.
[0111] Particle diameter of the water-absorbing resin used in the
present invention to obtain the water absorbing agent of the
present invention is usually controlled in small range of 180 to
420 .mu.m, as mass median particle size, preferably 200 to 400
.mu.m, more preferably 225 to 380 .mu.m and particularly preferably
250 to 350 .mu.m, and ratio of particles with diameter of lower
than 150 .mu.m is controlled to be 0 to 3% by weight, preferably 0
to 2% by weight and more preferably 0 to 1% by weight.
[0112] Bulk density (specified by JIS K-3362-1998) of the
water-absorbing resin of the present invention to obtain the water
absorbing agent of the present invention is adjusted to be in the
range of preferably 0.40 to 0.90 g/ml and more preferably 0.50 to
0.80 g/ml. Ratio of particles with diameter of 150 to 600 .mu.m is
preferably 90 to 100% by weight in whole particles, more preferably
95 to 100% by weight and further more preferably 98 to 100% by
weight. Logarithmic standard deviation (.sigma..zeta.) of particle
size distribution is controlled preferably to be 0.20 to 0.50, more
preferably 0.20 to 0.45 and particularly preferably 0.20 to
0.40.
[0113] Particle size may be adjusted, when crosslinked polymer is
produced by reversed phase suspension polymerization, by dispersion
polymerization in particulate state and distribution drying,
however, it is generally adjusted, particularly in an aqueous
solution polymerization, by pulverizing and classification after
drying, while controlling mass median particle size D50 and ratio
of particles having particle diameter of below 150 .mu.m, being
mutually contradictory, and thus adjusting to specific particle
size. For example, in the adjustment to specific particle size to
obtain mass median particle size D50 of not larger than 400 .mu.m
and to reduce content of fine particles with diameter smaller than
150 .mu.m, coarse particles and fine particles may be removed using
a general classifier such as a sieve after the pulverizing. In that
case, the coarse particles to be removed have particle diameter of
preferably 400 .mu.m to 5000 .mu.m, more preferably 400 .mu.m to
2000 .mu.m, further preferably 400 .mu.m to 1000 .mu.m. On the
other hand, the fine particles to be removed by the particle size
adjustment have particle diameter of preferably smaller than 150
.mu.m and more preferably smaller than 200 .mu.m. Thus removed
coarse particles and fine particles may be disposed as they are.
The coarse particles, however, are preferably pulverized again by
the pulverizing process. While, the fine particles removed are
subjected to particle size enlargement process mentioned at the
following item (10) to reduce loss.
[0114] A water-absorbing resin thus obtained in the present
invention is adjusted to have the above particle size and
preferably the centrifuge retention capacity (CRC) in a
physiological saline solution before surface crosslinking is
controlled to be not lower than 32 g/g, more preferably 35 to 70
g/g, further preferably 40 to 65 g/g and particularly preferably 45
to 60 g/g. "The centrifuge retention capacity" can be controlled by
using specific amount of an inner crosslinking agent to an aqueous
solution of an unsaturated monomer or by controlling the
polymerization conditions or drying conditions. A water-absorbing
resin can be used as the water absorbing agent as it is and the
centrifuge retention capacity of the water-absorbing resin is also
required to be not lower than 32 g/g to obtain the water absorbing
agent of the present invention having the centrifuge retention
capacity of not lower than 32 g/g.
[0115] (10) Diameter Enlargement of Fine Particles
[0116] The fine particles removed in pulverizing, classification
and particle size control in the item (9) are regenerated to larger
particles or particulate aggregates to be used as the
water-absorbing resin of the present invention. In this case,
methods described in U.S. Pat. No. 6,228,930, U.S. Pat. No.
5,264,495, U.S. Pat. No. 4,950,692, U.S. Pat. No. 5,478,879 and
EP844270 can be used, and, thus regenerated water-absorbing resin
has substantially porous structure.
[0117] Ratio of the regenerated water-absorbing resin by this
process, contained in the water-absorbing resin of the present
invention is preferably 0 to 50% by weight, more preferably 5 to
40% by weight and most preferably 10 to 30% by weight. The
regenerated water-absorbing resin by this process, when used as the
water-absorbing resin of the present invention, has larger surface
area than a non-regenerated one and provides higher absorption
speed, thus advantageous in view of performance. A water-absorbing
resin with thus enlarged particle diameter is generally subjected
to pulverizing, classification and particle size control after
mixing with the water-absorbing resin obtained by the drying
process (8).
[0118] (11) Surface Crosslinking Treatment
[0119] A water-absorbing resin of the present invention may be, as
represented by the production methods 1 to 3, one with specific
absorption capacity obtained by adjustment to specific particle
size distribution, followed by further surface crosslinking. A
water-absorbing resin used in the present invention has the
centrifuge retention capacity (CRC) lowered by such surface
crosslinking, for example, to generally 50 to 95% of the centrifuge
retention capacity (CRC) before surface crosslinking and further to
60 to 90%. Lowering of the centrifuge retention capacity can be
adjusted by type and amount of the crosslinking agent, reaction
temperature and time, as appropriate.
[0120] A surface crosslinking agent used in the present invention
is not especially limited, however, for example, those exemplified
in U.S. Pat. No. 6,228,930, U.S. Pat. No. 6,071,976, U.S. Pat. No.
6,254,990, and the like can be used and includes, for example,
polyhydric alcohols such as mono, di-, tri-, tetra- or
polyethyleneglycol, monopropyleneglycol, 1,3-propanediol,
dipropyleneglycol, 2,3,4-trimethyl-1,3-pentanediol,
polypropyleneglycol, glycerin, polyglycerin, 2-butene-1,4-diol,
1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,2-cyclohexanedimethanol, etc.; epoxy compounds such as
ethyleneglycol diglycidyl ether, glycidol, etc.; polyvalent amine
compounds such as ethylenediamine, diethylenetriamine,
triethylenetetramine, tetraethylenepentamine,
pentaethylenehexamine, polyethyleneimine, polyamidepolyamine, etc.;
haloepoxy compounds such as epichlorohydrin, epibromohydrin,
.alpha.-methylepichlorohydrin, etc.; condensates of the polyvalent
amine compounds and the haloepoxy compounds; oxazolidinone
compounds such as 2-oxazolidinone, etc.; cyclic urea; alkylene
carbonate compounds such as ethylene carbonate, etc. They may be
used alone or in combination of two or more kinds. To sufficiently
exert effects of the present invention, it is preferable to
essentially use a polyvalent alcohol among these surface
crosslinking agents. As a polyvalent alcohol, one having carbon
atoms of 2 to 10 is preferable and one having carbon atoms of 3 to
8 is more preferable.
[0121] Using amount of the surface crosslinking agent depends on
compounds used or combination thereof, however, is preferably in
the range of 0.001 to 10% by weight based on the water-absorbing
resin and more preferably in the range of 0.01 to 5% by weight.
[0122] In surface crosslinking in the present invention, water is
preferably used as a solvent. In this case, using amount of water
depends on water content of the water-absorbing resin used,
however, is preferably in the range of 0.5 to 20% by weight based
on the water-absorbing resin and more preferably in the range of
0.5 to 10% by weight. A hydrophilic organic solvent other than
water may be used. When a hydrophilic organic solvent is used,
using amount thereof is preferably in the range of 0 to 10% by
weight based on the water-absorbing resin, more preferably in the
range of 0 to 5% by weight and further preferably in the range of 0
to 3% by weight.
[0123] In surface crosslinking in the present invention, the
preferable method is premixing of a surface crosslinking agent in
water and/or a hydrophilic organic solvent, followed by spraying or
drop-wise addition of the solution to the water-absorbing resin and
the spraying method is more preferable. Droplet size to be sprayed
is, as average particle diameter, preferably in the range of 0.1 to
300 .mu.m and more preferably in the range of 0.1 to 200 .mu.m.
[0124] Mixing equipment to be used in mixing the water-absorbing
resin, the crosslinking agent and water or the hydrophilic organic
solvent is preferably one with strong mixing force to uniformly and
surely mix them. Suitable mixing equipment includes, for example, a
cylinder type mixer, a double wall conical mixer, a high speed
agitation type mixer, a V-shaped mixer, a ribbon type mixer, a
screw type mixer, a double-arm kneader, a crushing type kneader, a
rotation type mixer, an air-flow type mixer, a turbulizer, a batch
type Lodige mixer, a continuous type Lodige mixer, etc.
[0125] A water-absorbing resin after the addition of the surface
crosslinking agent is preferably subjected to heat treatment.
Heating temperature (temperature of heating medium or temperature
of material) is preferably in the range of 100 to 250.degree. C.,
more preferably in the range of 150 to 250.degree. C. and heating
time is preferably in the range of 1 minute to 2 hours. A suitable
combination example of heating temperature and heating time is
180.degree. C. for 0.1 to 1.5 hour and 200.degree. C. for 0.1 to 1
hour. A particulate water-absorbing resin can be obtained by these
processes.
[0126] (12) Agglomeration
[0127] A water-absorbing resin used in the present invention may
further be agglomerated in addition to the above processes.
Agglomeration process includes the addition of aqueous liquid to
water-absorbing resin after surface crosslinking treatment, then
the heating with maintaining water content of 1 to 10% by weight,
and further if necessary the adjusting to specific particle size of
obtained water-absorbing resin by Pulverizing and classification
mentioned above.
[0128] In the present invention, agglomerating is preferably
performed by a method for spraying or drop-wisely addition of water
or an aqueous solution dissolved with other additives components to
the water-absorbing resin, and, in particular, a spraying method is
preferable. Droplet size to be sprayed is, as average particle
diameter, preferably in the range of 0.1 to 300 .mu.m and more
preferably in the range of 0.1 to 200 .mu.m. Heat treatment is
performed, in view of agglomerating ratio or agglomerating
strength, by maintaining water content (specified by weight loss in
drying at 180.degree. C. for 3 hours) of the water-absorbing resin,
at 1 to 10% by weight, more preferably at 2 to 8% by weight and
further preferably at 2.5 to 6% by weight. Heating medium such as
hot air can be used in heating and heating temperature (temperature
of heating medium or temperature of material) is preferably in the
range of 40 to 120.degree. C., more preferably in the range of 50
to 100.degree. C. and heating time is preferably in the range of 1
minute to 2 hours. Heating temperature is expressed by temperature
of heating medium in many cases. A suitable combination example of
heating temperature and heating time is 60.degree. C. for 0.1 to
1.5 hour and 100.degree. C. for 0.1 to 1 hour. Heating and the
addition of water may be carried out by the same equipment or by
separate equipment. Heating may be carried out, with stirring or
without stirring, as long as temperature or water content can be
controlled, but heating without stirring is preferable. A more
preferable method is heating of the water-absorbing resin added
with water, and the like by heaping up of 1 to 100 cm, more
preferably 5 to 80 cm and particularly preferably 10 to 70 cm. A
hardened water-absorbing resin can be obtained by heating and the
particulate water-absorbing resin can be obtained by subsequent
crushing and classification.
[0129] As agglomerating equipment to be used, those having strong
mixing force are preferable, including a cylinder type mixer, a
double wall conical mixer, a high speed agitation type mixer, a
V-shaped mixer, a ribbon type mixer, a screw type mixer, a
double-arm kneader, a crashing type kneader, a rotation type mixer,
an air-flow type mixer, a turbulizer, a batch type Lodige mixer, a
continuous type Lodige mixer, etc.
[0130] Water to be added to the water-absorbing resin may contain
other additives such as chelating agents described later,
components made from plants, antimicrobials, aqueous polymers,
inorganic salts, etc. Content of the additives is in the range of
0.001 to 50% by weight in an aqueous solution.
[0131] (13) Addition of a Chelating Agent
[0132] To the particulate water absorbing agent of the present
invention, a chelating agent, in particular, a polyvalent
carboxylic acid and salts thereof can be formulated.
[0133] The production method 3 of the present invention, in
particular, is a method for crosslinking polymerization of an
aqueous solution of an unsaturated monomer with non-neutralized
acrylic acid and/or salts thereof, as main components, in the
presence of a crosslinking agent, followed by adjustment to
specific particle size distribution and further surface
crosslinking of thus obtained water-absorbing resin particles with
specific absorption capacity, wherein the chelating agent is added
during polymerization or, before or after surface crosslinking. By
the addition effect of the chelating agent, it is possible to
inhibit action of a component to deteriorate or destruct
crosslinked structure and thus to produce the water absorbing agent
superior in deterioration resistance to urine.
[0134] The chelating agent used in the water absorbing agent of the
present invention is preferably one with high blocking ability or
chelating ability for Fe or Cu ion, specifically, one with
stability constant for Fe ion of not lower than 10, preferably not
lower than 20, further preferably an aminopolyvalentcarboxylic acid
and salts thereof and particularly preferably aminocarboxylic acid
with not less than 3 carboxyl groups and salts thereof. Among
these, aminocarboxylate salts may be those, wherein a part of the
acid groups contained is neutralized or all acid groups are
neutralized. These polyvalent carboxylic acids specifically include
diethylenetriamine pentaacetic acid, triethylenetetramine
hexaacetic acid, cyclohexane-1,2-diamine tetraacetic acid,
N-hydroxyethyl ethylenediamine triacetic acid, ethyleneglycol
diethylether diamine tetraacetic acid, ethylenediamine tetra
propionic acetic acid, N-alkyl-N'-carboxymethyl aspartic acid,
N-alkenyl-N'-carboxymethyl aspartic acid and alkaline metal salts
thereof; alkaline earth metal salts; ammonium salts or amine salts.
They may be used alone or in combination of two or more kinds.
Among these, diethylenetriamine pentaacetic acid,
triethylenetetramine hexaacetic acid, N-hydroxyethyl
ethylenediamine triacetic acid and salts thereof are most
preferable.
[0135] Using amount of the chelating agent, in particular, the
amino polyvalent carboxylic acid is as small as generally 0.00001
to 10 parts by weight based on 100 weight parts of the
water-absorbing resin, a main component, and preferably 0.0001 to 1
weight parts. The using amount over 10 parts by weight is not only
uneconomical due to failure to get enough effect relative to using
amount but also poses a problem of reducing absorption capacity. On
the other hand, the using amount less than 0.00001 part by weight
does not provide sufficient addition effect.
[0136] In the case of the addition of the chelating agent during
polymerization, the chelating agent may be added to an aqueous
solution of an unsaturated monomer, followed by polymerization or
it may be added in the midst of polymerization, or it may be added
to the gel-like crosslinked polymer or the water-absorbing resin
obtained. To add the chelating agent during surface crosslinking,
surface crosslinking may be performed using a solution containing
the surface crosslinking agent added with the chelating agent.
Further, in the case of adding the chelating agent after surface
crosslinking, it may be added to the water-absorbing resin after
crosslinking. Further in the case of performing the agglomerating
process of the above item (12), water dissolved with the chelating
agent may be sprayed, followed by heating, while maintaining water
content at 1 to 10% by weight, as described above. In the case of
drying after the addition, if necessary, the temperature may be in
the range not impair the effects of the chelating agent and
generally in the range described in agglomerating process of the
item (12). The chelating agent is essential in the production
method 3, however, it may also be used to the water-absorbing resin
obtained in the production method 1 and the production method
2.
[0137] (14) Other Additives
[0138] In the present invention, the following (A) components made
from plants, (B) polyvalent metal salts of organic acids, (C)
inorganic fine particles (including (D) composite hydrated oxides)
may be added as minor components in addition to the chelating
agent, by which various functions can be added to the
water-absorbing resin of the present invention. The addition
methods include, in the case that the additives are solutions, an
embodiment to add as a solution, as a water dispersion or as it is;
while in the case that the additives are powders, non-soluble in
water, an embodiment to add as a water dispersion or as it is; and
in the case that the additives are soluble in water, the same
embodiments as in the case of the solutions.
[0139] Using amount of these (A) to (D) and (E) other additives
depends on objectives or function to be added, however, is usually,
as the amount of one kind of additive, 0 to 10 parts by weight
based on 100 parts by weight of the water-absorbing resin,
preferably 0.001 to 5 parts by weight and further preferably 0. 002
to 3 parts by weight. The using amount less than 0.001 part by
weight usually does not provide sufficient effect or additional
function, while the using amount over 10 part by weight may not get
effect matching to the added amount or may incur lowering of
absorption performance.
[0140] (A) Components Made From Plants
[0141] A water absorbing agent of the present invention can be
added with components made from plants in the amount described
above to fulfill deodorization effect. The components made from
plants to be used in the present invention are preferably at least
one compound selected from polyphenol, flavone, derivatives thereof
and caffeine. It is further preferable that the component made of
plant is at least one kind selected from tannin, tannic acid,
stachyurus praecox, gall or gallic acid.
[0142] Plants containing the components made from plants to be used
in the present invention include, for example, Theaceae plant such
as camellia, Hikasaki plant and Sprague; Gramineae plant such as
rice plant, sasa-bamboo, bamboo, corn, wheet, etc.; and Rubiaceae
plant such as coffee.
[0143] Form of the components made from plants to be used in the
present invention includes plant extract (essential oil), plat
itself (plant-ground powder), plant residue or extract residue as
by-products in production processes from plant processing industry
or foods processing industry, however, not limited thereto.
[0144] (B) A Polyvalent Metal Salt
[0145] A water absorbing agent of the present invention may be
added a polyvalent metal salt, in particular, a polyvalent metal
salt of organic acids in the amount described above to improve
powder fluidity and to maintain the fluidity after moisture
absorption.
[0146] A polyvalent metal salt of an organic acid used and a
methods for mixing the polyvalent metal salts are exemplified in WO
PCT/2004/JP1355, and the polyvalent metal salt of organic acids
used in the present invention, having carbon atoms of not less than
7 in a molecule include polyvalent metal salts of fatty acid,
petroleum acid or polymeric acid, specifically calcium, aluminium,
magnesium or zinc salts. They maybe used alone or in combination of
two or more kinds.
[0147] An organic acid composing the polyvalent metal salt of an
organic acid exemplified are long chain or branched fatty acids
such as caproic acid, octylic acid, octynoic acid, decanoic acid,
lauric acid, myristic acid, palmitic acid, oleic acid, stearic
acid, etc.; petroleum acids such as benzoic acid, myristicinic
acid, naphthenic acid, naphthoic acid, naphthoxyacetic acid, etc.;
polymeric acids such as poly(meth)acrylic acid, polysulfonic acid,
and the like and preferable ones have a carboxyl group in a
molecule and more preferably includes fatty acids such as caproic
acid, octylic acid, octynoic acid, decanoic acid, lauric acid,
myristic acid, palmitic acid, oleic acid, stearic acid, tallow acid
or hydrogenated fatty acid of castor oil, etc. Further preferably,
they are fatty acids without an unsaturated bond in a molecule, for
example, caproic acid, octylic acid, decanoic acid, lauric acid,
myristic acid, palmitic acid, stearic acid. Most preferably, they
are long chain type fatty acids having not less than 12 carbon
atoms in a molecule, without an unsaturated bond in a molecule such
as laulic acid, myristic acid, palmitic acid and stearic acid.
[0148] (C) An Inorganic Fine Particle
[0149] A water absorbing agent of the present invention may be
added an inorganic fine particle, in particular, an inorganic fine
particle of non-dissolving in water to maintain the fluidity after
moisture absorption. Specific inorganic powders to be used in the
present invention include, for example, metal oxides such as
silicon dioxide, titanium oxide, etc.; silica acid (silicate) such
as natural zeolite, synthetic zeolite, etc.; kaolin, talc, clay,
bentonite, etc. They may be used alone or in combination of two or
more kinds. Among these, silicon dioxide and silica acid (silicate
salt) are more preferable and silicon dioxide and silica acid
(silicate salt) with average particle diameter, measured by a
coulter counter method, of 0.001 to 200 .mu.m are further
preferable.
[0150] (D) A Composite Hydrated Oxide
[0151] A water absorbing agent of the present invention may further
be added a composite hydrated oxide containing zinc and silicon or
zinc and aluminum to add superior fluidity after moisture
absorption (powder fluidity after the water-absorbing resin or the
water absorbing agent absorbs moisture) and further superior
deodorization performance.
[0152] (E) Others
[0153] Other additives such as a antimicrobial, an aqueous polymer,
water, an organic fine particle, and the like may be added
arbitrarily, as long as the water absorbing agent of the present
invention can be obtained.
[0154] (15) A Particulate Water Absorbing Agent of the Present
Invention
[0155] A particulate water absorbing agent of the present
invention, obtained by the production methods 1 to 3, as an
example, is a novel water absorbing agent exhibiting novel
performance not conventionally available.
[0156] That is, the first particulate water absorbing agent of the
present invention is:
[0157] a particulate water absorbing agent comprising a
water-absorbing resin obtained by crosslinking polymerization of an
unsaturated monomer containing an acid group and/or a salt thereof
as a main component, and the water absorbing agent satisfies the
following (a) to (d):
[0158] (a) centrifuge retention capacity (CRC) in a physiological
saline solution being in the range of not lower than 32 g/g;
[0159] (b) mass median particle size (D50) being in the range of
200 to 400 .mu.m;
[0160] (c) ratio of particles having diameter of smaller than 150
.mu.m being in the range of 0 to 2% by weight; and
[0161] (d) increased extractables by deterioration expressed by the
mentioned above formula of 0 to 15% by weight and extractables for
one hour in deterioration test liquid of 0.1 to 30% by weight.
[0162] A second particulate water absorbing agent of the present
invention is:
[0163] a particulate water absorbing agent comprising a
water-absorbing resin obtained by crosslinking polymerization of an
unsaturated monomer containing an acid group and/or a salt thereof
as a main component, and the water absorbing agent satisfies the
following (a) to (c) and (e):
[0164] (a) centrifuge retention capacity (CRC) in a physiological
saline solution being in the range of not lower than 32 g/g;
[0165] (b) mass median particle size (D50) being in the range of
200 to 400 .mu.m;
[0166] (c) ratio of particles having diameter of smaller than 150
.mu.m being in the range of 0 to 2% by weight; and
[0167] (e) increased ratio of extractables by deterioration
expressed by the mentioned above formula of 1 to 4 times, and
extractables for one hour in deterioration test liquid of 0.1 to
30% by weight.
[0168] A third particulate water absorbing agent of the present
invention is:
[0169] a particulate water absorbing agent comprising a
water-absorbing resin obtained by crosslinking polymerization of an
unsaturated monomer containing an acid group and/or a salt thereof
as a main component, and the water absorbing agent satisfies the
following (a) to (c), (f) and (g):
[0170] (a) centrifuge retention capacity (CRC) in a physiological
saline solution being in the range of not lower than 32 g/g;
[0171] (b) mass median particle size (D50) being in the range of
200 to 400 .mu.m;
[0172] (c) ratio of particles having diameter of smaller than 150
.mu.m being in the range of 0 to 2% by weight;
[0173] (f) extractables for 16 hours in a physiological saline
solution being in the range of 0.1 to 10% by weight; and
[0174] (g) absorbency against pressure at 4.8 kPa (AAP4.8 kPa) in a
physiological saline solution being not lower than 21 g/g.
[0175] A water absorbing agent of the present invention is
controlled to have (b) mass median particle size (D50) of usually
as narrow range as 180 to 400 .mu.m, preferably 200 to 400 .mu.m,
more preferably 225 to 380 .mu.m and particularly preferably 250 to
350 .mu.m and (c) ratio of particles with diameter of smaller than
150 .mu.m to be 0 to 3% by weight, preferably 0 to 2% by weight and
more preferably 0 to 1% by weight. Particle size adjustment is
preferably carried out before surface crosslinking, however, it may
be adjusted by pulverizing, classification and agglomerating after
surface crosslinking. When particle size distribution is out of
this range, suitable absorption characteristics and high property
can not be obtained in a diaper application. In particular, the
item (b) affects absorption characteristics of the water absorbing
agent in absorbing articles such as a diaper and when mass median
particle size is over 400 .mu.m, surface area per unit weight is
decreased, which reduces contact area between the water absorbing
agent and urine, and the like, therefore longer absorption period
is required to absorb aqueous liquid. On the other hand, when mass
median particle size is smaller than 180 .mu.m, surface area per
unit weight is increased, which shortens absorption period,
however, penetration speed of deteriorated components by urine into
particle inside increase simultaneously, which may accelerates
deterioration speed by urea. Increase in fine particles also
requires regeneration and is not preferable in view of cost.
Furthermore, in continuous production, fine particles with diameter
of smaller than 150 .mu.m, which is out of treatment capacity of
classifier, may generate and make control difficult of ratio of
particles with diameter of smaller than 150 .mu.m.
[0176] When (c) ratio of particles with diameter of smaller than
150 .mu.m is over 3% by weight, it may lower absorption ability due
to gel blocking in absorbing articles, or swollen gel, by absorbing
body fluid in practical application, may directly contact with skin
(gel on skin) of a user, due to fall off of fine particulate
powders before swelling, from inside of absorbing articles to a
surface top sheet. Furthermore, loss by scattering in production of
absorbing articles or bad effects to work environment may happen
and thus not preferable.
[0177] The water absorbing agent of the present invention has the
above particle size distribution and (a) centrifuge retention
capacity (CRC) in a physiological saline solution of not smaller
than 32 g/g, preferably 33 to 75 g/g, more preferably 35 to 70 g/g,
further preferably 40 to 65 g/g and particularly preferably 45 to
60 g/g. When centrifuge retention capacity (CRC) is smaller than 32
g/g, it requires high quantity of the water absorbing agent to
secure desired absorption capacity of absorbing articles and thus
practically not preferable.
[0178] A water absorbing agent of the present invention satisfies
the above characteristics and (d) increased extractables by
deterioration of generally 0 to 15% by weight, more preferably 0 to
12% by weight, further preferably 0 to 10% by weight, particularly
preferably 0 to 8% by weight and most preferably 0 to 5% by weight.
Reason for using a physiological saline solution containing 0.05%
by weight of L-ascorbic acid, as deterioration test liquid in
measurement of "increased extractables by deterioration" is that
deterioration of the water absorbing agent by urine is caused by
L-ascorbic acid contained in urine, and that the osmotic pressure
is matched to that of body fluid. Increased extractables by
deterioration, as shown by the formula, is comparative absolute
amount of extractables increased in deterioration by urine,
therefore the smaller value means less deterioration. In the
present invention, increased extractables by deterioration in the
range of 0 to 15% by weight shows stability of the water absorbing
agent against body fluid such as urine and thus the present
invention has features in the value range itself. When increased
extractables by deterioration is over 15% by weight, stability of
the water absorbing agent against body fluid such as urine is
insufficient and sufficient absorption ability cannot be fulfilled
in long period practical application of absorbing substrate.
[0179] Similarly, (e) increased ratio of extractables by
deterioration of the present invention is usually 1 to 4 times,
preferably 1 to 3 times, more preferably 1 to 2 times, further
preferably 1 to 1.5 times and particularly preferably 1 to 1.3
times. Increased ratio of extractables by deterioration represents
generation ratio of extractables by deterioration and thus the
smaller value means less deterioration by urine. Increased ratio of
extractables by deterioration in the range of 1 to 4 times shows
stability of the water absorbing agent against body fluid such as
urine and when increased ratio of extractables by deterioration is
over 4 times, stability of the water absorbing agent against body
fluid such as urine is insufficient and sufficient absorption
ability cannot be fulfilled in long period practical application of
absorbing substrate.
[0180] Extractables for 1 hour in deterioration test liquid is
preferably not more than 0.1 to 30% by weight, more preferably not
more than 0.2 to 25% by weight, further preferably not more than
0.3 to 22% by weight, particularly preferably not more than 0.4 to
20% by weight and most preferably not more than 0.5 to 18% by
weight. When extractables for 1 hour in deterioration test liquid
is over the range, swollen gel in long period use deteriorates with
time and extractables increases. The extractables is exuded from an
absorbing substrate and may inhibit liquid diffusion of blood or
urine into the absorbing substrate. Attainment of the level lower
than the lower limit is not restricted, however, it is specified in
consideration of production conditions such as cost.
[0181] When the item (d) increased extractables by deterioration
and/or (e) increased ratio of extractables by deterioration are
over the upper limit range, maintaining becomes difficult of body
fluid such as urine absorbed by swollen gel, due to significant
destruction of crosslinked structure of the water absorbing agent,
which may incur increased rewet amount in application such as a
diaper. Moreover, swollen gel with destructed crosslinked structure
is converted to an aqueous polymer, which may cause leak-out of a
fluidized polymer to surface of absorbing articles such as a
diaper. Therefore, it may incur increased uncomfortable feeling to
persons fitting absorbing articles and is not preferable.
[0182] As described above, particle size distribution correlates to
increased extractables by deterioration and increased ratio of
extractables by deterioration, therefore, the water absorbing agent
with (b) mass median particle size D50 adjusted to relatively small
level of not larger than 400 .mu.m, along with inhibited (d)
increased extractables by deterioration and (e) increased ratio of
extractables by deterioration has not been present up to now.
However, in the present invention, by introducing (d) increased
extractables by deterioration and (e) increased ratio of
extractables by deterioration and controlling each to be 0 to 15%
by weight and 1 to 4 times, the water absorbing agent superior in
use feeling and long period absorption properties can be obtained.
Such the water absorbing agent can be produced by the above
described methods, however, as shown by Examples, it can be
produced by methods other than those described above.
[0183] In the present invention, it may be enough that either of
(d) increased extractables by deterioration or (e) increased ratio
of extractables by deterioration is satisfied, however, it is
preferable that both are satisfied simultaneously. In the present
invention, as shown later in a measurement method in Example,
swollen gel obtained by the addition of 1 g of the water absorbing
agent in 25 ml of deterioration test liquid is used based on
consideration of 25 times swelling of a diaper and it was found
that increased extractables by deterioration or increased ratio of
extractables by deterioration correlates to practical use of a
diaper and that a water absorbing agent with specific particle size
distribution, specific absorption capacity and (d) increased
extractables by deterioration or (e) increased ratio of
extractables by deterioration provides a high property diaper,
irrespective of change in urine composition or use period also in
practical application. Evaluation of extractables by dispersing a
water-absorbing resin in far excess amount of a physiological
saline solution at room temperature or property thereof described
in JP-A-8-337726, and the like, has no correlation to practical use
and thus meaningless.
[0184] Extractables for 1 hour in a physiological saline solution
of a water absorbing agent of the present invention is essentially
not higher than 50% by weight, preferably 0.1 to 30% by weight,
more preferably 0.2 to2 5% by weight, further preferably 0.3 to 20%
by weight, further more preferably 0.4 to 15% by weight,
particularly preferably 0.5 to 10% by weight and most preferably 0.
5 to 8% by weight. When extractables for 1 hour is over the upper
limit range, extractables is exuded to absorbing substrate in water
absorption, which may inhibit liquid diffusion of such as blood and
urine to absorbing substrate. Attainment of the level less than
0.1% by weight is generally difficult and does not counterbalance
with cost.
[0185] In the case of a particulate water absorbing agent with
arbitrary level of (d) increased extractables by deterioration or
(e) increased ratio of extractables by deterioration, that is in
the case of the third particulate water absorbing agent, (f)
extractables for 16 hours in a physiological saline solution is 0.1
to 10% by weight, preferably 0.6 to 8% by weight and particularly
0.7 to 5% by weight. When it is over 10% by weight, extractables is
exuded from the absorbing substrate in water absorption, which may
inhibit liquid diffusion of such as blood and urine to the
absorbing substrate. Moreover when deterioration by urine proceeds,
it may be to such proceeding degree as not to maintain crosslinked
structure and thus disadvantageous. Furthermore, (g) Absorbency
Against Pressure at 4.8 kPa (AAP 4.8 kPa) in a physiological saline
solution at 4.8 kPa (about 50 g/cm.sup.2, about 0.7 psi) is
preferably not lower than 21 g/g, more preferably not lower than 22
g/g, further preferably not lower than 23 g/g, particularly
preferably not lower than 24 g/g and most preferably not lower than
25 g/g. When that value is less than 21 g/g, liquid contained in a
water absorbing agent may leak out of a water absorbing agent by
pressure in practical use. It was found out by detailed study on
absorption properties that, even if (d) increased extractables by
deterioration or (e) increased ratio of extractables by
deterioration may not be satisfied, if the requirements (a), (b)
and (c), along with "(f) extractables for 16 hours" and "(g)
Absorbency Against Pressure at 4.8 kPa (AAP4.8 kPa)" are
simultaneously satisfied, performance of the absorbing substrate is
not lowered even in long period absorption state of urine in
practical use. Reason for that is, performance of absorbing
substrate can be maintained in practical use, when extractables for
16 hours of a water absorbing agent before destruction is inhibited
low, even if crosslinked structure is destructed in certain level
by deterioration caused by urine.
[0186] The absorbency against pressure at 4.8 kPa (AAP 4.8 kPa) was
found in increasing tendency with higher amount of an internal
crosslinking agent, when absorption capacity is the same. It is not
clear in detail, however, by consideration of the fact that
increase in the amount of an internal crosslinking agent lowers
deterioration degree by urine, the absorbency against pressure at
4.8 kPa (AAP4.8 kPa) seems to have indirect correlation. That is,
to get desired performance of a water absorbing agent after
deterioration by urine in the absorbing substrate based on
estimation of deterioration by urine, performance of a water
absorbing agent before deterioration is required to be set in the
above range. The upper limit of (g) is not especially restricted,
however, about 40 g/g may be sufficient in certain cases in view of
cost increase due to difficulty in production.
[0187] Even in the third particulate water absorbing agent, it is
preferable to further satisfy (d) increased extractables by
deterioration or (e) increased ratio of extractables by
deterioration.
[0188] (16) Other Properties of a Particulate Water Absorbing Agent
of the Present Invention
[0189] (i) absorbency against pressure at 1.9 kPa (AAP1.9 kPa) in a
physiological saline solution under 1.9 kPa The absorbency against
pressure of a water absorbing agent of the present invention in a
physiological saline solution under load of 1.9 kPa pressure (under
load) is preferably not lower than 20 g/g, more preferably not
lower than 25 g/g, further preferably not lower than 30 g/g and
particularly preferably not lower than 35 g/g. When that value is
less than 20 g/g, effect of the present invention may not be
fulfilled. The upper limit is not especially limited, however,
about 60 g/g may be sufficient in certain cases in view of cost
increase due to difficulty in production.
[0190] (h) Particles with diameter of 150 to 600 .mu.m; (1)
Logarithmic standard deviation
[0191] Bulk density (specified by JIS K-3362) of a water absorbing
agent of the present invention is adjusted to be preferably in the
range of 0.40 to 0.90 g/ml and more preferably 0.50 to 0.80 g/ml.
Ratio of "(h) particles with diameter between 150 and 600 .mu.m" is
preferably 90 to 100% by weight based on total particles, more
preferably 95 to 100% by weight and further preferably 98 to 100%
by weight. (L) Logarithmic standard deviation (.sigma..zeta.) of
particle size distribution is preferably in the range of 0.20 to
0.40, more preferably 0.20 to 0.38 and particularly preferably 0.20
to 0.36. When particles in this range are used in a diaper,
superior property can be obtained.
[0192] (k) Fluidity After Moisture Absorption (Blocking Ratio)
[0193] A water absorbing agent of the present invention is superior
in powder handling characteristics due to having low fluidity after
moisture absorption described later in Example. Fluidity after
moisture absorption is preferably not higher than 0 to 30% by
weight, more preferably 0 to 20% by weight, further preferably 0 to
10% by weight and particularly preferably 0 to 5% by weight.
Fluidity after moisture absorption over 30% by weight provides a
problem such as difficulty in production of a diaper owing to poor
powder fluidity. These fluidity after moisture absorptions can be
attained by using the additives.
[0194] (j) Absorption Speed with Vortex Method
[0195] Absorption speed of the water absorbing agent of the present
invention is shorter than 60 seconds, preferably 1 to 55 seconds
and more preferably 2 to 50 seconds. A water absorbing agent with
absorption speed over 60 seconds may not fulfill sufficient
absorption ability when used in an absorbing substrate such as a
diaper.
[0196] (17) An Absorbing Article
[0197] Applications of the particulate water absorbing agent of the
present invention are not especially limited, however, the water
absorbing agent is used preferably in an absorbing substrate and an
absorbing article.
[0198] The absorbing substrate of the present invention is obtained
using the particulate water absorbing agent. The absorbing
substrate in the present invention means one formed using the
particulate water absorbing agent and hydrophilic fibers as main
components. Content of the water absorbing agent (core
concentration) in the absorbing substrate of the present invention,
based on total weight of the water absorbing agent and hydrophilic
fibers is preferably 20 to 100% by weight, more preferably 30 to
100% by weight and particularly preferably 40 to 100% by
weight.
[0199] Further, an absorbing article of the present invention is
one equipped with the absorbing substrate of the present invention,
a surface sheet with liquid permeability and a back sheet with
liquid non-permeability.
[0200] A method for production of absorbing articles of the present
invention maybe, for example, as follows: Preparation of the
absorbing substrate (absorbing core) by blending or sandwiching
fiber substrates and the water-absorbing agent of the present
invention, followed by sandwiching the absorbing core between the
substrate with liquid permeability (the surface sheet) and the
substrate with liquid non-permeability (the back sheet) and
mounting of elastic parts, diffusion layers, pressure sensitive
adhesive tapes, and the like, if necessary, to fabricate an
absorbing article, in particular, a diaper for a child, a diaper
for an adult or a sanitary napkin. Such absorbing core has density
of 0.06 to 0.50 g/cc and compression molded to have basis weight in
the range of 0.01 to 0.20 g/cm.sup.2. The fiber substrate to be
used is exemplified to be hydrophilic fiber, ground wood pulp, or
cotton linter, crosslinked cellulosic fiber, rayon fiber, cotton
fiber, wool fiber, acetate fiber, vinylon fiber, etc. Preferably
they are used as airlied.
[0201] A water absorbing agent of the present invention is one
exhibiting superior absorption properties. An absorbing article
using this specifically includes, sanitary goods starting from a
paper diaper for an adult, whose growth is significant recently, a
diaper for a child, a sanitary napkin, so to speak a pad for
incontinence, and the like, however, not limited to these. Common
idea is that due to improvement of a water absorbing agent of the
present invention present in an absorbing article so as to obtain
an absorbing article with less rewet and significant dry feeling,
it can significantly reduce loads of person wearing such goods and
nursing staffs.
EXAMPLES
[0202] The present invention will be elucidated specifically with
the following Examples and Comparative Examples, without being
limited to the following Examples.
[0203] Various performances of a water absorbing agent were
measured by the following methods. They were evaluated also by
using a water-absorbing resin instead of a water absorbing agent.
Electrical equipment was always used under conditions of 100 V and
60 Hz in Examples. A water-absorbing resin, a water absorbing agent
and an absorbing article were used under conditions of 25.degree.
C..+-.2.degree. C. and 50% RH (relative humidity), unless
particularly specified. An aqueous solution of 0.90% by weight of
sodium chloride was used as a physiological saline solution.
[0204] A water-absorbing resin and a diaper on the market and a
water-absorbing resin taken out of a diaper which may absorb
moisture on distribution, may be used in a comparison test after
vacuum drying under reduced pressure (for example, for about 16
hours at 60 to 80.degree. C.), as appropriate, to equilibrium
moisture content (2 to 8% by weight, about 5% by weight) of the
water-absorbing resin.
[0205] (a) Centrifuge Retention Capacity (CRC) for a Physiological
Saline Solution
[0206] A water absorbing agent of 0.20 g was uniformly put in a bag
(60 mm.times.85 mm) made of unwoven fabric and immersed in a
physiological saline solution controlled at 25.+-.2.degree. C. The
bag containing the water absorbing agent was taken out of the
saline solution after 30 minutes and subjected to dewatering for 3
minutes at 250 G (250.times.9.81 m/sec.sup.2) using a centrifuge
(Model H-122 small size centrifuge made by Kokusan Corporation) and
then weighed to get weight W2 (g). Weight W1 (g) of the bag was
measured after similar operation without any water absorbing agent.
Centrifuge Retention Capacity (g/g) was calculated from weights W1
and W2 according to the following formula. Centrifuge Retention
Capacity (g/g)=((weight W2(g)-weight W1(g))/weight of water
absorbing agent (g))-1
[0207] (b) Absorbency Against Pressure at 4.8 kPa (AAP4.8 kPa) in a
Physiological Saline Solution
[0208] A water absorbing agent of 0.900 g was uniformly scattered
on a 400-Mesh wire mesh made of stainless steel (mesh size: 38
.mu.m) welded to the bottom end face of a plastic support cylinder
with inner diameter of 60 mm. A piston (cover plate), which has
outer diameter a little smaller than 60 mm, no gap against the
inner surface of the support cylinder and can move up and down
smoothly, was mounted on the water absorbing agent. Total weight W3
(g) of the support cylinder, the water absorbing agent and the
piston was measured. A load adjusted weight to press the water
absorbing agent uniformly at 4.8 kPa (about 50/cm.sup.2, about 0.7
psi) including the weight of the piston was mounted on the piston,
thereby completing a set of measuring apparatus. A glass filter
with diameter of 90 mm and thickness of 5 mm was placed in a Petri
dish with diameter of 150 mm and a physiological saline solution
controlled at 25.+-.2.degree. C. was poured up to the same level as
the upper surface of the glass filter. A sheet of filter paper with
diameter of 9 cm (No. 2 from Toyo Roshi Kaisha Ltd.) was placed on
the surface of the glass filter to be entirely wetted, and then
excess solution over the wetted filter paper was removed.
[0209] The set of the measuring apparatus was placed on the wetted
filter paper and the liquid was absorbed with the water absorbing
agent under load. The liquid level was kept constant by adding the
liquid when the liquid surface became lower than the upper surface
of the filter paper. The set of the measuring apparatus was lifted
up after an hour and weight W4 (g) (the total weight of the support
cylinder, the swollen water absorbing agent and the piston)
excluding the load was measured again. The absorbency against
pressure (AAP 4.8 kPa) (g/g) was calculated from weights W3 and W4
according to the following formula. Absorbency Against Pressure
(g/g)=(weight W4 (g)-weight W3 (g))/weight of a water absorbing
agent (g)
[0210] (c) Absorbency Against Pressure at 1.9 kPa (AAP1.9 kPa) in a
Physiological Saline Solution
[0211] The absorbency against pressure (AAP1.9 kPa) was obtained by
the same operation and calculation as in the above (b) except that
the water absorbing agent was uniformly pressed at 1.9 kPa (about
20 g/cm.sup.2, about 0.3 psi), including the weight of the
piston.
[0212] (d) Mass Median Particle Size (D50), Logarithmic Standard
Deviation (.delta..zeta.) and Percentage by Weight of Particles
Less than 150 .mu.m in Diameter.
[0213] A water absorbing agent was subjected to sieve
classification using JIS standard sieves having mesh opening size
of 850 .mu.m, 710 .mu.m, 600 .mu.m, 500 .mu.m, 425 .mu.m, 300
.mu.m, 212 .mu.m, 150 .mu.m, 106 .mu.m and 45 .mu.m, and percentage
by weight of particles less than 150 .mu.m in diameter was
measured, while oversize percentages R at each particle size were
plotted on a logarithmic probability paper. Particle size
corresponding to R=50% by weight was thus determined as mass median
particle size (D50). Logarithmic standard deviation (.delta..zeta.)
is represented by the following formula, wherein smaller value of
.delta..zeta. means narrower particle-size distribution.
.delta..zeta.=0.5.times.ln (X2/X1) (wherein X1 and X2 are particle
diameters for R=84.1% by weight and R=15.9% by weight,
respectively)
[0214] For sieve classification, a water absorbing agent of 10.00 g
is charged into each of the JIS standard mesh sieves (The IIDA
TESTING SIEVE: inner diameter of 80 mm) and sieved for 5 minutes
using a Ro-tap type sieve shaker (Model ES-65 sieve shaker from
Iida Seisakusho Co., Ltd.).
[0215] Mass median particle size (D50) means particle diameter for
a standard sieve, corresponding to 50% by weight based on the whole
particles, when sieving is carried out by standard sieves with
particular meshes as described in U.S. Pat. No. 5,051,259 etc.
[0216] (e) Extractables (Extractabless in a Physiological Saline
Solution for One Hour and 16 Hours)
[0217] First of all, preparation for measurement of extractabless
in a physiological saline solution for one hour and 16 hours
(hereinafter, referred to as extractables for one hour and
extractables for 16 hours, respectively) will be described. A pH
electrode was calibrated with buffer solutions of pH4.0, pH 7.0 and
pH 10.0. A physiological saline solution of 50 ml, prepared
beforehand for a blank test, was poured into a 100 ml glass beaker
and added in dropwise with a 0.1 mol/L aqueous solution of sodium
hydroxide until pH 10, while stirring with a stirrer chip with
length of 30 mm, to determine titration amount V.sub.ab (ml) of the
aqueous solution of sodium hydroxide for a blank test. The saline
solution was further added in dropwise with a 0.1 mol/L aqueous
solution of hydrochloric acid until pH 2.7, while stirring, to
determine titration amount V.sub.bb (ml) of hydrochloric acid for a
blank test.
[0218] A physiological saline solution of 200 ml, prepared
beforehand, was poured into a 250 ml polypropylene cup with a lid
and added with 1.0 g (=m (g)) of a water absorbing agent obtained
in Examples or Comparative Examples to be described later. The
saline solution was stirred with a stirrer with length of 30 mm and
diameter of 8 mm at 500.+-.50 rpm for one hour or 16 hours to
extract extractables. After stirring for one hour or 16 hours, the
saline solution was filtered with a filter paper (No. 2, made by
Toyo Roshi Kaisha Ltd., retaining particle size of 5 .mu.m
according to JIS P3801), to obtain a filtrate.
[0219] Thus obtained filtrate of 20 ml (recorded as F (ml)) was
poured into a 100 ml glass beaker and added with a physiological
saline solution to obtain 50 ml of a filtrate for titration. When
thus obtained filtrate is less than 20 ml, the total amount of thus
obtained filtrate was recorded as F(ml) and added with a 0.90% by
weight aqueous solution of sodium chloride to obtain 50 ml of a
filtrate for titration.
[0220] Subsequently, the filtrate for titration was added in
dropwise with a 0.1 mol/L aqueous solution of sodium hydroxide,
while stirring with a cylinder-type stirrer with length of 30 mm
and diameter of 8 mm until pH 10, to determine titration amount
V.sub.a (ml) of the aqueous solution of sodium hydroxide. The
filtrate was further added in dropwise with a 0.1 mol/L aqueous
solution of hydrochloric acid, while stirring, until pH 2.7, to
determine titration amount V.sub.b (ml) of the aqueous solution of
hydrochloric acid. Extractables (%) is calculated by the following
formula. Extractables (%)=((W.sub.a+W.sub.b)/m).times.100
[0221] Wherein W.sub.a (g) is relative weight of units having an
acid group of extractables in a water absorbing agent and W.sub.b
(g) is relative weight of units having a carboxylate group
neutralized by an alkali metal of extractables in a water absorbing
agent. Each of them is calculated by the following formulas.
W.sub.a(g)=N.sub.a33 72.times.200/F
W.sub.b(g)=N.sub.b.times.94.times.200/F
[0222] Wherein the value 72 is weight per 1 mole of a repetition
unit in polyacrylic acid, and when a monomer with an acid group
other than acrylic acid is copolymerized, the value is altered to
average weight of a repetition unit including such a monomer. The
value 94 is weight per 1 mole of a repetition unit in polysodium
acrylate and it is altered, as appropriate, when a monomer having
an acid group other than acrylic acid is copolymerized, or when
potassium, lithium, and the like is used instead of sodium as an
alkali metal salt.
[0223] N.sub.a (mol) is number of moles of an acid group of
extractables in a filtrate and N.sub.b (mol) is number of moles of
a carboxylate group neutralized by an alkali metal, of extractables
in a filtrate. Each of them is calculated by the following
formulas. N.sub.a(mol)=(V.sub.a-V.sub.ab)/1000.times.0.1
N.sub.b(mol)=N.sub.1-N.sub.a
[0224] Wherein N.sub.1 (mol) is number of total moles of
extractables in a filtrate to be measured and is calculated by the
following formula.
N.sub.1(mol)=(V.sub.b-V.sub.bb)/1000.times.0.1
[0225] The extractabless calculated by the formulas were
differentiated as extractables for one hour (%) on a filtrate
obtained by stirring a physiological saline solution for one hour,
and extractables for 16 hours (%) on a filtrate obtained by
stirring a physiological saline solution for 16 hours.
[0226] (f) Evaluation of Resistance to Urine (Extractables for One
Hour in Deterioration Test Liquid, Increased Extractables by
Deterioration, Increased Ratio of Extractables by
Deterioration)
[0227] A physiological saline solution prepared beforehand was
added with L-ascorbic acid so as to obtain deterioration test
liquid of 0.05% by weight. Specifically, 0.50 g of L-ascorbic acid
was dissolved in 999.5 g of a physiological saline solution to
prepare deterioration test liquid.
[0228] Deterioration test liquid of 25 ml was poured into a 250 ml
polypropylene cup with a lid and added with 1.0 g of a water
absorbing agent to form swollen gel. After the cup was sealed with
the lid, the swollen gel was left for standing in atmosphere of
37.degree. C. for 16 hours.
[0229] After 16 hours, 175 ml of the physiological saline solution
was added and then extractables after deterioration was extracted
from the hydrated gel by stirring for one hour similarly as in (d)
with a cylinder-type stirrer with length of 30 mm and diameter of 8
mm.
[0230] After extraction by stirring for one hour, the saline
solution was filtered and pH-titrated by the same method as in the
previous item (d) to determine extractables for one hour (%) in
deterioration test liquid using the same formulas as in (d). To
compare absolute amount of increased extractables by deterioration,
for evaluation of resistance to urine, increased extractables by
deterioration (% by weight) was calculated by the following
formula. Increased extractables by deterioration (% by
weight)=extractables for one hour (% by weight) in deterioration
test liquid-extractables for one hour (% by weight) in a
physiological saline solution
[0231] To compare extractables formed by deterioration with
extractables before deterioration, for evaluating resistance to
urine, increased ratio of extractables by deterioration (quotient)
was calculated by the following formula. Increased ratio of
extractables by deterioration=extractables for one hour (% by
weight) in deterioration test liquid/extractables for one hour (%
by weight) in a physiological saline solution
[0232] (g) Evaluation of Absorption Speed (Vortex Method)
[0233] A 0.90% by weight aqueous solution of sodium chloride
(physiological saline solution) of 1,000 parts by weight was added
with 0.02 part by weight of a brilliant blue-FCF, a food additive,
and kept at 30.degree. C. The physiological saline solution of 50
ml was poured into a 100 ml beaker and added with 2.0 g of a water
absorbing agent, while stirring at 600 rpm with a cylinder-type
stirrer with length of 40 mm and diameter of 8 mm, to measure
absorption speed (second). Absorption speed (second) is time
required for the test liquid to completely cover the stirrer chip
as the water absorbing agent absorbs the physiological saline
solution, which was measured according to the standard described in
JIS K 7224 (1996) "Testing method for water absorption speed of
super absorbent resins--Description"
[0234] (h) Fluidity After Moisture Absorption (% by Weight)
[0235] A water absorbing agent of 2 g was uniformly scattered on
the bottom of an aluminum cup with diameter of 52 mm and height of
22 mm and quickly put in a humidity-controllable incubator
(PLATIOOUS LUCIFER PL-2G from ESPEC Corp.) controlled beforehand at
25.degree. C. and 90% relative humidity, and left for standing for
60 minutes. The moisture-absorbed water absorbing agent was
transferred to a JIS standard sieve with diameter of 7.5 cm and
2,000 .mu.m of mesh open when the moisture-absorbed water absorbing
agent was adhered to aluminum cup too rigidly to do so, the water
absorbing agent should be torn off the cup and transferred to the
sieve very carefully not to destroy the block. The transferred
water absorbing agent to the sieve was immediately sieved for 8
seconds using a sieve shaker (IIDA SIEVE SHAKER, TYPE: ES-65, SER.
No. 0501). Weight W5 (g) of the oversize water absorbing agent left
on the sieve and weight W6 (g) of the undersize water absorbing
agent passed through the sieve were measured. Fluidity after
moisture absorption (Blocking ratio) (% by weight) was calculated
by the following formula. The lower fluidity after moisture
absorption means, the better water absorbing agent in fluidity
after moisture absorption and in powder handling nature. Fluidity
after moisture absorption (% by weight)=(weight W5 (g)/(weight W5
(g)+weight W6 (g))).times.100
[0236] (i) Deodorization Test (Evaluation of a Water Absorbing
Agent)
[0237] Urine of 50 m, collected from 20 adults, was poured into a
120 ml polypropylene cup with a lid and added with 2.0 g of a water
absorbing agent to form swollen gel. The urine used was one within
2 hours after excretion. The cup was capped and the swollen gel was
kept at 37.degree. C. The lid was removed after 6 hours from start
of liquid absorption and 20 adult panelists evaluated deodorization
effect by smelling the contents at about 3 cm above the top of the
cup. Each panelist recorded scores according to the 6 grades of the
following evaluation criterion to determine an average score. Urine
without a water absorbing agent was evaluated similarly and graded
as score 5 to be used as evaluation standard. [0238] 0: no odor
[0239] 1: barely perceivable odor [0240] 2: perceivable but
allowable odor [0241] 3: easily perceivable odor [0242] 4: strong
odor [0243] 5: very strong odor
[0244] (j) Performance Evaluation as an Absorbing Substrate (Rewet
Amounts After 10 Minutes and by Deterioration)
[0245] An absorbing substrate for evaluation was prepared to
evaluate a water absorbing agent as an absorbing substrate and
subjected to a rewet test.
[0246] To begin with, a method for preparation of an absorbing
substrate for evaluation is shown below.
[0247] A water absorbing agent to be described later of 1 part by
weight and crushed wood pulp of 2 parts by weight were subjected to
dry mixing using a mixer. Thus obtained mixture was spread on a
wire screen of 400-Mesh (mesh size: 38 .mu.m) to form a web with
diameter of 90 mm. The web was pressed under pressure of 196.14 kPa
(2 kgf/cm.sup.2) for 1 minute to obtain an absorbing substrate for
evaluation with basis weight of 0.05 g/cm.sup.2.
[0248] Subsequently, a method for evaluation of rewet amount after
10 minutes is shown below.
[0249] The absorbing substrate for evaluation was placed on the
bottom of a Petri dish with inner diameter of 90 mm made of
stainless steel and nonwoven fabric with diameter of 90 mm was
placed thereon. Deterioration test liquid of 30 ml used in the item
(f); evaluation of resistance to urine, was then poured over the
nonwoven fabric and subjected to absorption for 10 minutes under
conditions of no load. Subsequently, 30 sheets of filter paper with
diameter of 90 mm (No. 2 from Toyo Roshi Kaisha Ltd.), whose weight
(W7(g)) was measured beforehand, was placed on the nonwoven and the
absorbing substrate. And then, a piston and a load (total weight of
the piston and load was 20 kg) with diameter of 90 mm were placed
on the filter paper so as to press uniformly the absorbing
substrate, the nonwoven and the filter paper. The filter papers
were made to absorb rewet liquid, while pressing for 5 minutes. The
30 sheets of the filter papers were then weighed (W8 (g)) to
calculate rewet amount after 10 minutes. Rewet amount after 10
minutes (g)=W8 (g)-W7 (g)
[0250] A method for evaluation of rewet amount by deterioration is
shown below.
[0251] Deterioration test liquid of 30 ml, prepared beforehand by
processing similarly as above, was poured over the nonwoven fabric
and an absorbing substrate for evaluation, and was absorbed under
condition of no load and left for standing in atmosphere of
37.degree. C. for 16 hours. The Petri dish was put in a sealed
polyethylene bag with size of 140 mm.times.200 mm to prevent
moisture from evaporating during standing.
[0252] After specified time, subsequently, 30 sheets of filter
paper with diameter of 90 mm (No. 2 from Toyo Roshi Kaisha Ltd.),
whose weight (W9(g)) was measured beforehand, was placed on the
nonwoven and the absorbing substrate. And then, a piston and a load
(total weight of the piston and load was 20 kg) with diameter of 90
mm were placed on the filter paper so as to press uniformly the
absorbing substrate, the nonwoven and the filter paper. The filter
papers were made to absorb rewet liquid, while pressing for 5
minutes. The 30 sheets of the filter papers (W10 (g)) were then
weighed to calculate rewet amount by deterioration. Rewet amount by
deterioration (g)=W10 (g)-W9 (g)
Reference Example 1
[0253] Polyethylene glycol diacrylate (average added mole number of
ethylene oxide unit: 9) of 4.3 g was dissolved in 1,500 g of an
aqueous solution of sodium acrylate having neutralization ratio of
75% by mole (monomer concentration: 24% by weight) to make reaction
liquid. Thus obtained reaction liquid was poured into a tray with
length of 320 mm, width of 220 mm and height of 50 mm made of
stainless steel, with the reaction liquid being 17 mm deep. The
stainless steel tray was immersed in a water bath at 30.degree. C.,
after the top of the tray was sealed with a polyethylene film
having a nitrogen gas inlet, an exhaust gas outlet and an inlet of
a polymerization initiator. Nitrogen gas was introduced into the
reaction liquid to purge dissolved oxygen in the liquid, while
controlling the reaction liquid temperature at 30.degree. C.
Subsequently, nitrogen gas continued to be introduced in an upper
space of the reactor, while exhausting from the other side. The
reaction liquid was added with, as polymerization initiators, 5.1 g
of a 10% by weight aqueous solution of
2,2'-azobis(2-amidinopropane)dihydrochloride, 2.5 g of a 10% by
weight aqueous solution of sodium persulfate, 0.4 g of a 1% by
weight aqueous solution of L-ascorbic acid and 2.2 g of a 0.35% by
weight aqueous solution of hydrogen peroxide, and stirred
sufficiently with a magnetic stirrer. As polymerization began in 1
minute after the addition of the polymerization initiators, the
stainless steel tray was intermittently immersed in a water bath at
12.degree. C. by 10 mm in height from the tray bottom to control
polymerization temperature. As peak temperature of polymerization
of 80.degree. C. was attained after 55 minutes from initiation of
polymerization, the tray was immersed in a water bath at 70.degree.
C. up to 10 mm in height from the tray bottom to mature gel and
left for 60 minutes. Thus obtained hydrated gel-like polymer was
crushed by a meat chopper (Model No. 32 meat chopper from Hiraga
Seisakusho Inc.) equipped with a die having bore diameter of 9.5
mm, spread on a wire net of 50-Mesh (mesh size: 300 .mu.m) and
dried with hot air at 160.degree. C. for 60 minutes. Thus dried
material was then pulverized by a roll mill and sieved with wire
meshes with mesh opening sizes of 710 .mu.m and 150 .mu.m to obtain
irregularly pulverized powder of a water-absorbing resin (a).
Centrifuge Retention Capacity (CRC), mass median particle size
(D50), and percentage by weight of particles less than 150 .mu.m in
diameter of thus obtained water-absorbing resin (a) are shown in
Table 1. Water-absorbing resins (b) to (1) obtained in the
following Reference Examples were also evaluated similarly and
results of the evaluation are shown in Table 1.
[0254] Thus obtained powder of a water-absorbing resin (a) of 100
parts by weight was mixed with 3.9 parts by weight of a surface
crosslinking agent composed of 0.55 part by weight of propylene
glycol, 0.35 part by weight of 1,4-butanediol and 3 parts by weight
of water. The mixture was heated at heating medium temperature of
210.degree. C. for 40 minutes to obtain a water-absorbing resin
(1).
Reference Example 2
[0255] Polyethylene glycol diacrylate (average added mole number of
ethylene oxide unit: 9) of 4.0 g was dissolved in 5,500 g of an
aqueous solution of sodium acrylate having neutralization ratio of
75% by mole (monomer concentration: 40% by weight) to make reaction
liquid. Subsequently, a reactor fabricated by attaching a lid to a
10-L twin-arm type kneader made of stainless steel and equipped
with a jacket and two .SIGMA.-shaped agitating blades was supplied
the reaction liquid and the reaction system was purged dissolved
oxygen by introducing with nitrogen gas, while keeping the reaction
liquid at 30.degree. C. The reaction liquid was then added with
29.8 g of a 10% by weight aqueous solution of sodium persulfate and
1.5 g of a 1% by weight aqueous solution of L-ascorbic acid, while
stirring the reaction liquid, resulting in initiation of
polymerization after 1 minute. Peak temperature of polymerization
of 93.degree. C. was attained after 15 minutes from initiation of
polymerization. After 60 minutes from initiation of polymerization,
a hydrated gel-like polymer was taken out, which was in crushed
state to particles with diameter of 1 to 4 mm. The crushed,
hydrated gel-like polymer was spread on a wire net of 50-Mesh (mesh
size: 300 .mu.m) and dried with hot air at 160.degree. C. for 60
minutes. Thus dried material was then pulverized by a roll mill and
sieved with wire meshes with mesh opening sizes of 710 .mu.m and
150 .mu.m to obtain irregularly pulverized powder of a
water-absorbing resin (b).
[0256] Thus obtained powder of a water-absorbing resin (b) of 100
parts by weight was mixed with 3.53 parts by weight of a surface
crosslinking agent composed of 0.5 part by weight of propylene
glycol, 0.03 part by weight of ethylene glycol diglycidyl ether,
0.3 part by weight of 1,4-butanediol and 2.7 parts by weight of
water. The mixture was heated at heating medium temperature of
210.degree. C. for 45 minutes to obtain a water-absorbing resin
(2).
Reference Example 3
[0257] Polyethylene glycol diacrylate (average added mole number of
ethylene oxide unit: 9) of 2.5 g was dissolved in 5,500 g of an
aqueous solution of sodium acrylate having neutralization ratio of
75% by mole (monomer concentration: 38% by weight) to make reaction
liquid. After purging dissolved oxygen similarly as in Reference
Example 2, the reaction liquid was supplied to the reactor of
Reference Example 2 and the reaction system was purged with
nitrogen gas, while keeping the reaction liquid at 30.degree. C.
The reaction liquid was then added with 29.8 g of a 10% by weight
aqueous solution of sodium persulfate and 1.5 g of a 1% by weight
aqueous solution of L-ascorbic acid, while stirring the reaction
liquid, resulting in initiation of polymerization after about 1
minute. Peak temperature of polymerization of 86.degree. C. was
attained after 17 minutes from initiation of polymerization. After
60 minutes from initiation of polymerization, a hydrated gel-like
polymer was taken out, which was in granulated state to particles
with diameter of about 1 to 4 mm. The hydrated gel-like polymer was
dried and pulverized similarly as in Reference Example 2, and
sieved with wire meshes with mesh opening sizes of 710 .mu.m and
150 .mu.m to obtain irregularly pulverized powder of a
water-absorbing resin (c).
[0258] Thus obtained powder of a water-absorbing resin (c) of 100
parts by weight was mixed with 3.53 parts by weight of the surface
crosslinking agent having the same composition as in Reference
Example 2. The mixture was heated at heating medium temperature of
195.degree. C. for 40 minutes to obtain a water-absorbing resin
(3).
Reference Example 4
[0259] Polyethylene glycol diacrylate (average added mole number of
ethylene oxide unit: 9) of 19.6 g and disodium phosphite
pentahydrate of 36.3 g were dissolved in 5,500 g of an aqueous
solution of sodium acrylate having neutralization ratio of 75% by
mole (monomer concentration: 33% by weight) to make reaction
liquid. After purging dissolved oxygen similarly as in Reference
Example 2, the reaction liquid was supplied to the reactor of
Reference Example 2 and the reaction system was purged with
nitrogen gas, while keeping the reaction liquid at 30.degree. C.
The reaction liquid was then added with 20.5 g of a 10% by weight
aqueous solution of sodium persulfate and 1.0 g of a 1% by weight
aqueous solution of L-ascorbic acid, while stirring the reaction
liquid, resulting in initiation of polymerization after about 1
minute. Peak temperature of polymerization of 85.degree. C. was
attained after 17 minutes from initiation of polymerization. After
60 minutes from initiation of polymerization, a hydrated gel-like
polymer was taken out, which was in crushed state to particles with
diameter of about 1 to 4 mm. The hydrated gel-like polymer was
dried and pulverized similarly as in Reference Example 2, and
sieved with wire meshes with mesh opening sizes of 600 .mu.m and
150 .mu.m to obtain irregularly pulverized powder of a
water-absorbing resin (d).
[0260] Thus obtained powder of a water-absorbing resin (d) of 100
parts by weight was mixed with 3.53 parts by weight of the surface
crosslinking agent of the same composition as in Reference Example
2. The mixture was heated at heating medium temperature of
210.degree. C. for 35 minutes to obtain a water-absorbing resin
(4).
Reference Example 5
[0261] Polyethylene glycol diacrylate (average added mole number of
ethylene oxide unit: 9) of 20.0 g and sodium phosphinate of 3.3 g
were dissolved in 5,500 g of an aqueous solution of sodium acrylate
having neutralization ratio of 70% by mole (monomer concentration:
30% by weight) to make reaction liquid. After purging dissolved
oxygen similarly as in Reference Example 2, the reaction liquid was
supplied to the reactor of Reference Example 2 and the reaction
system was purged with nitrogen gas, while keeping the reaction
liquid at 30.degree. C. The reaction liquid was then added with
22.6 g of a 10% by weight aqueous solution of sodium persulfate and
1.1 g of a 1% by weight aqueous solution of L-ascorbic acid, while
stirring the reaction liquid, resulting in initiation of
polymerization after about 1 minute. Peak temperature of
polymerization of 82.degree. C. was attained after 18 minutes from
initiation of polymerization. After 40 minutes from initiation of
polymerization, a hydrated gel-like polymer was taken out, which
was in crushed state to particles with diameter of about 1 to 4 mm.
The hydrated gel-like polymer was dried and pulverized similarly as
in Reference Example 2, and sieved with wire meshes with mesh
opening sizes of 600 .mu.m and 150 .mu.m to obtain irregularly
pulverized powder of a water-absorbing resin (e).
[0262] Thus obtained powder of a water-absorbing resin (e) of 100
parts by weight was mixed with 3.8 parts by weight of a surface
crosslinking agent composed of 0.5 part by weight of propylene
glycol, 0.3 part by weight of 1,3-propanediol and 3 parts by weight
of water. The mixture was heated at heating medium temperature of
195.degree. C. for 40 minutes to obtain a water-absorbing resin
(5).
Reference Example 6
[0263] Tetraallyloxyethane of 1.9 g was dissolved in 1,500 g of an
aqueous solution of acrylic acid (monomer concentration: 20% by
weight) to prepare reaction liquid. Thus obtained reaction liquid
was poured into the tray made of stainless steel of Reference
Example 1, with the reaction liquid being 17 mm deep. The stainless
steel tray was sealed similarly as in Reference Example 1 and
immersed in a water bath at 20.degree. C. Nitrogen gas was
introduced into the reaction liquid to purge dissolved oxygen in
the liquid, while controlling the reaction liquid temperature at
20.degree. C. Subsequently, nitrogen gas continued to be introduced
in an upper space of the reactor, while exhausting from the other
side. The reaction liquid was then added with, as polymerization
initiators, 8.3 g of a 10% by weight aqueous solution of
2,2'-azobis(2-amidinopropane)dihydrochloride, 0.6 g of a 5% by
weight aqueous solution of L-ascorbic acid and 2.1 g of a 3.5% by
weight aqueous solution of hydrogen peroxide, while stirring the
reaction liquid with a magnetic stirrer, resulting in initiation of
polymerization after about 1 minute. Cooling and heating of the
reactant was repeated from the bottom surface of the tray during
the polymerization reaction. Peak temperature of polymerization of
75.degree. C. was attained after 35 minutes from initiation of
polymerization. After 90 minutes from initiation of polymerization,
a hydrated gel-like polymer was taken out. Thus obtained hydrated
gel-like polymer was cut with scissors into squares with sides of
about 5 cm. Thus obtained hydrated gel-like polymer in squares with
sides of about 5 cm was then fed at constant rate to the same meat
chopper as in Reference Example 1, while 702 g of a 22% by weight
aqueous solution of sodium carbonate was added at constant rate for
neutralization. The crushed gel discharged from the meat chopper
was left in atmosphere of about 70.degree. C. until the gel did not
turn red any longer even when phenolphthalein liquid was poured
over the gel. The gel was then dried and pulverized similarly as in
Reference Example 1 and sieved with wire meshes with mesh opening
sizes of 600 .mu.m and 150 .mu.m to obtain irregularly pulverized
powder of a water-absorbing resin (f).
[0264] Thus obtained powder of a water-absorbing resin (f) of 100
parts by weight was mixed with 3.83 parts by weight of a surface
crosslinking agent composed of 0.5 part by weight of propylene
glycol, 0.03 part by weight of ethylene glycol diglycidyl ether,
0.3 part by weight of 1,3-propanediol and 3 parts by weight of
water. The mixture was heated at heating medium temperature of
195.degree. C. for 40 minutes to obtain a water-absorbing resin
(6).
Reference Example 7
[0265] The dried material of the hydrated gel-like polymer obtained
in Reference Example 2 was pulverized by the similar roll mill as
in Reference Example 2, setting pulverizing conditions so as to
obtain finer particles than in Reference Example 2 and sieved with
wire meshes having mesh opening sizes of 425 .mu.m and 150 .mu.m to
obtain irregularly pulverized powder of a water-absorbing resin
(g).
[0266] Thus obtained powder of a water-absorbing resin (g) of 100
parts by weight was mixed with 4.93 parts by weight of a surface
crosslinking agent composed of 1 part by weight of propylene
glycol, 0.03 part by weight of ethylene glycol diglycidyl ether, 3
parts by weight of water and 0.9 part by weight of methanol. The
mixture was heated at heating medium temperature of 210.degree. C.
for 45 minutes to obtain a water-absorbing resin (7).
Reference Example 8
[0267] The dried material of the hydrated gel-like polymer obtained
in Reference Example 3 was pulverized by the similar roll mill as
in Reference Example 3, setting pulverizing conditions so as to
obtain finer particles than in Reference Example 3 and sieved with
wire meshes having mesh opening sizes of 500 .mu.m and 150 .mu.m to
obtain irregularly pulverized powder of a water-absorbing resin
(h).
[0268] Thus obtained powder of a water-absorbing resin (h) of 100
parts by weight was mixed with 3.53 parts by weight of the surface
crosslinking agent of the same composition as in Reference Example
3. The mixture was heated at heating medium temperature of
210.degree. C. for 45 minutes to obtain a water-absorbing resin
(8).
Reference Example 9
[0269] The dried material of the hydrated gel-like polymer obtained
in Reference Example 2 was pulverized by the similar roll mill as
in Reference Example 2, setting pulverizing conditions so as to
obtain coarser particles than in Reference Example 2 and sieved
with wire meshes having mesh opening sizes of 850 .mu.m and 106
.mu.m to obtain irregularly pulverized powder of a water-absorbing
resin (i).
[0270] Thus obtained powder of a water-absorbing resin (i) of 100
parts by weight was mixed with 3.53 parts by weight of the similar
surface crosslinking agent as in Reference Example 2. The mixture
was heated at heating medium temperature of 210.degree. C. for 55
minutes to obtain a water-absorbing resin (9).
Reference Example 10
[0271] The dried material of the hydrated gel-like polymer obtained
in Reference Example 3 was pulverized by the similar roll mill as
in Reference Example 9, setting pulverizing conditions so as to
obtain still coarser particles than in Reference Example 9 and
sieved with wire meshes having mesh opening sizes of a 850 .mu.m
and 150 .mu.m to obtain irregularly pulverized powder of a
water-absorbing resin (j).
[0272] Thus obtained powder of a water-absorbing resin (j) of 100
parts by weight was mixed with 3.53 parts by weight of the similar
surface crosslinking agent as in Reference Example 2. The mixture
was heated at heating medium temperature of 195.degree. C. for 45
minutes to obtain a water-absorbing resin (10).
Reference Example 11
[0273] A water-absorbing resin (11) was obtained by processing
similarly as in Reference Example 4 except that disodium phosphite
pentahydrate was not added as in Reference Example 4.
Example 1
[0274] The water-absorbing resin (1) obtained in Reference Example
1 was used as it is as a water absorbing agent (1). Evaluation
results on centrifuge retention capacity, absorbency against
pressure at 4.8 kPa, extractables for 16 hours in a physiological
saline solution, absorbency against pressure at 1.9 kPa, urine
resistance, absorption speed and particle size distribution of the
water absorbing agent (1) are shown in Tables 2 to 4.
Example 2
[0275] To 100 parts by weight of the water-absorbing resin (2)
obtained in Reference Example 2, 2 parts by weight of a sodium
diethylenetriamine pentaacetate aqueous solution was mixed by
spraying so that content of sodium diethylenetriamine pentaacetate
became 50 ppm to the water-absorbing resin (2). Thus obtained
mixture was cured at 60.degree. C. for 1 hour to obtain a water
absorbing agent (2). The water absorbing agent (2) was evaluated in
the same manner as in Example 1. Results are shown in Tables 2 to
4. By applying the spray mixing process of the aqueous solution and
the curing process, the water absorbing agent (2) obtained was in
agglomelated state.
Example 3
[0276] To 100 parts by weight of the water-absorbing resin (3)
obtained in Reference Example 3, 2 parts by weight of sodium
diethylenetriamine pentaacetate aqueous solution was mixed by
spraying so that content of sodium diethylenetriamine pentaacetate
became 100 ppm to the water-absorbing resin (3). Thus obtained
mixture was cured at 60.degree. C. for 1 hour to obtain a water
absorbing agent (3). The water absorbing agent (3) was evaluated in
the same manner as in Example 1. Results are shown in Tables 2 to
4. By applying the spray mixing process of the aqueous solution and
the curing process, the water absorbing agent (3) obtained was in
agglomerated state.
Example 4
[0277] To 100 parts by weight of the water-absorbing resin (4)
obtained in Reference Example 4, 2 parts by weight of water was
mixed by spraying. Thus obtained mixture was cured at 60.degree. C.
for 1 hour to obtain a water absorbing agent (4). The water
absorbing agent (4) was evaluated in the same manner as in Example
1. Results are shown in Tables 2 to 4. By applying the water spray
mixing process and the curing process, the water absorbing agent
(4) obtained was in agglomerated state.
Example 5
[0278] The same procedures as in Example 4 were repeated except for
using the water-absorbing resin (5) obtained in Reference Example 5
instead of the water-absorbing resin (4) obtained in Reference
Example 4, to obtain a water absorbing agent (5). The water
absorbing agent (5) was evaluated in the same manner as in Example
1. Results are shown in Tables 2 to 4. By applying the water spray
mixing process and the curing process, the water absorbing agent
(5) obtained was in agglomerated state.
Example 6
[0279] The same procedures as in Example 4 were repeated except for
using the water-absorbing resin (6) obtained in Reference Example 6
instead of the water-absorbing resin (4) obtained in Reference
Example 4, to obtain a water absorbing agent (6). The water
absorbing agent (6) was evaluated in the same manner as in Example
1. Results are shown in Tables 2 to 4. By applying the water spray
mixing process and the curing process, the water absorbing agent
(6) obtained was in agglomerated state.
Example 7
[0280] The same procedures as in Example 2 were repeated except for
using the water-absorbing resin (7) obtained in Reference Example 7
instead of the water-absorbing resin (2) obtained in Reference
Example 2, to obtain a water absorbing agent (7). The water
absorbing agent (7) was evaluated in the same manner as in Example
1. Results are shown in Tables 2 to 4. By applying the water spray
mixing process and the curing process, the water absorbing agent
(7) obtained was in agglomerated state.
Example 8
[0281] The same procedures as in Example 3 were repeated except for
using the water-absorbing resin (8) obtained in Reference Example 8
instead of the water-absorbing resin (3) obtained in Reference
Example 3, to obtain a water absorbing agent (8). The water
absorbing agent (8) was evaluated in the same manner as in Example
1. Results are shown in Tables 2 to 4. By applying the water spray
mixing process and the curing process, the water absorbing agent
(8) obtained was in agglomerated state.
Comparative Example 1
[0282] The same procedures as in Example 2 were repeated except for
using the water-absorbing resin (9) obtained in Reference Example 9
instead of the water-absorbing resin (2) obtained in Reference
Example 2, to obtain a comparative water absorbing agent (1). The
comparative water absorbing agent (1) was evaluated in the same
manner as in Example 1. Results are shown in Tables 2 to 4. By
applying the water spray mixing process and the curing process, the
comparative water absorbing agent (1) obtained was in agglomerated
state.
Comparative Example 2
[0283] The same procedures as in Example 3 were repeated except for
using the water-absorbing resin (10) obtained in Reference Example
10 instead of the water-absorbing resin (3) obtained in Reference
Example 3, to obtain a comparative water absorbing agent (2). The
comparative water absorbing agent (2) was evaluated in the same
manner as in Example 1. Results are shown in Tables 2 to 4. By
applying the water spray mixing process and the curing process, the
comparative water absorbing agent (2) obtained was in agglomerated
state.
Comparative Example 3
[0284] The same procedures as in Example 2 were repeated except for
using water instead of the sodium diethylenetriamine pentaacetate
aqueous solution, to obtain a comparative water absorbing agent
(3). The comparative water absorbing agent (3) was evaluated in the
same manner as in Example 1. Results are shown in Tables 2 to 4.
Further, fluidity after moisture absorption was evaluated. Results
are shown in Table 5. By applying the water spray mixing process
and the curing process, the comparative water absorbing agent (3)
obtained was in agglomelated state.
Comparative Example 4
[0285] The same procedures as in Example 3 were repeated except for
using water instead of the sodium diethylenetriamine pentaacetate
aqueous solution, to obtain a comparative water absorbing agent
(4). The comparative water absorbing agent (4) was evaluated in the
same manner as in Example 1. Results are shown in Tables 2 to 4.
Further, fluidity after moisture absorption was evaluated. Results
are shown in Table 5. By applying the water spray mixing process
and the curing process, the comparative water absorbing agent (4)
obtained was in agglomelated state.
Comparative Example 5
[0286] The same procedures as in Example 4 were repeated except for
using the water-absorbing resin (11) obtained in Reference Example
11 instead of the water-absorbing resin (4) obtained in Reference
Example 4, to obtain a comparative water absorbing agent (5). The
comparative water absorbing agent (5) was evaluated in the same
manner as in Example 1. Results are shown in Tables 2 to 4. By
applying the water spray mixing process and the curing process, the
comparative water absorbing agent (5) obtained was in agglomerated
state.
Example 9
[0287] To 100 parts by weight of the water absorbing agent (1)
obtained in Example 1, 0.3 part by weight of fine particulate
aluminum stearate (made by Kanto Chemical Co., Inc.) was added and
mixed (dry blend) to obtain a water absorbing agent (9). From
measurement of particle size distribution of thus obtained a water
absorbing agent (9), little change was found. Namely, mass median
particle size (D50), logarithmic standard deviation (.delta..zeta.)
and percent by weight of particle diameter less than 150 .mu.m
showed the same values as of the water absorbing agent (1) before
mixing. Further, results of urine resistance test and extractables
for 16 hours in a physiological saline solution also showed the
same values as of the water absorbing agent (1) before mixing.
Centrifuge retention capacity, absorbency against pressure at 1.9
kPa, extractables for 16 hours in a physiological saline solution,
urine resistance, absorption speed, absorbency against pressure at
4.8 kPa and fluidity after moisture absorption of the water
absorbing agent (9) were measured. Results are shown in Table
5.
Example 10
[0288] To 100 parts by weight of the water absorbing agent (2)
obtained in Example 2, 0.3 part by weight of fine particulate
silicon dioxide (Trade Name: Aerosil 200 (average particle size of
the primary particle: 12 nm), made by Nippon Aerosil Co., Ltd.) was
added and mixed (dry blend) to obtain a water absorbing agent (10).
From measurement of particle size distribution of thus obtained a
water absorbing agent (10), little change was found. Namely, mass
median particle size (D50), logarithmic standard deviation
(.delta..zeta.) and percent by weight of particle diameter less
than 150 .mu.m showed the same values as of the water absorbing
agent (2) before mixing. Further, results of urine resistance test
and extractables for 16 hours in a physiological saline solution
also showed the same values as of the water absorbing agent (2)
before mixing. The water absorbing agent (10) was evaluated in the
same manner as in Example 9. Results are shown in Table 5.
Example 11
[0289] The same procedures as in Example 10 were repeated except
for using fine particulate aluminum stearate instead of the fine
particulate silicon dioxide to obtain a water absorbing agent (11).
From measurement of particle size distribution of thus obtained a
water absorbing agent (11), little change was found. Namely, mass
median particle size (D50), logarithmic standard deviation
(.delta..zeta.) and percent by weight of particle diameter less
than 150 .mu.m showed the same values as of the water absorbing
agent (2) before mixing. Further, results of urine resistance test
and extractables for 16 hours in a physiological saline solution
also showed the same values as of the water absorbing agent (2)
before mixing. The water absorbing agent (11) was evaluated in the
same manner as in Example 9. Results are shown in Table 5.
Example 12
[0290] The same procedures as in Example 10 were repeated except
for using the water absorbing agent (3) obtained in Example 3
instead of the water absorbing agent (2) obtained in Example 2, to
obtain a water absorbing agent (12). From measurement of particle
size distribution of thus obtained a water absorbing agent (12),
little change was found. Namely, mass median particle size (D50),
logarithmic standard deviation (.delta..zeta.) and percent by
weight of particle diameter less than 150 .mu.m showed the same
values as of the water absorbing agent (3) before mixing. Further,
results of urine resistance test and extractables for 16 hours in a
physiological saline solution also showed the same values as of the
water absorbing agent (3) before mixing. The water absorbing agent
(12) was evaluated in the same manner as in Example 9. Results are
shown in Table 5.
Example 13
[0291] The same procedures as in Example 10 were repeated except
for using the water absorbing agent (3) obtained in Example 3
instead of the water absorbing agent (2) obtained in Example 2 and
fine particulate aluminum stearate instead of the fine particulate
silicon dioxide, to obtain a water absorbing agent (13). From
measurement of particle size distribution of thus obtained a water
absorbing agent (13), little change was found. Namely, mass median
particle size (D50), logarithmic standard deviation (.delta..zeta.)
and percent by weight of particle diameter less than 150 .mu.m
showed the same values as of the water absorbing agent (3) before
mixing. Further, results of urine resistance test and extractables
for 16 hours in a physiological saline solution also showed the
same values as of the water absorbing agent (3) before mixing. The
water absorbing agent (13) was evaluated in the same manner as in
Example 9. Results are shown in Table 5.
Example 14
[0292] To 100 parts by weight of the water absorbing agent (4)
obtained in Example 4, 0.3 part by weight of fine particulate
silicon dioxide (Trade Name: Aerosil 200) was added and mixed (dry
blend) to obtain a water absorbing agent (14). From measurement of
particle size distribution of thus obtained a water absorbing agent
(14), little change was found. Namely, mass median particle size
(D50), logarithmic standard deviation (.delta..zeta.) and percent
by weight of particle diameter less than 150 .mu.m showed the same
values as of the water absorbing agent (4) before mixing. Further,
results of urine resistance test and extractables for 16 hours in a
physiological saline solution also showed the same values as of the
water absorbing agent (4) before mixing. The water absorbing agent
(14) was evaluated in the same manner as in Example 9. Results are
shown in Table 5.
Example 15
[0293] To 100 parts by weight of the water absorbing agent (5)
obtained in Example 5, 0.3 parts by weight of fine particulate
magnesium stearate (made by Kanto Chemical Co., Inc.) was added and
mixed (dry blend), to obtain a water absorbing agent. (15). From
measurement of particle size distribution of Thus obtained a water
absorbing agent (15), little change was found. Namely, mass median
particle size (D50), logarithmic standard deviation (.delta..zeta.)
and percent by weight of particle diameter less than 150 .mu.m
showed the same values as of the water absorbing agent (5) before
mixing. Further, results of urine resistance test and extractables
for 16 hours in a physiological saline solution also showed the
same values as of the water absorbing agent (5) before mixing. The
water absorbing agent (15) was evaluated in the same manner as in
Example 9. Results are shown in Table 5.
Examples 16 to 18
[0294] The same procedures as in Example 10 were repeated except
for using the water absorbing agents (6) to (8) obtained in
Examples 6 to 8 instead of the water absorbing agent (2) obtained
in Example 2 to obtain a water absorbing agents (16) to (18),
respectively. From measurements of particle size distributions of
thus obtained a water absorbing agents (16) to (18), little change
was found in any agent. Namely, mass median particle size (D50),
logarithmic standard deviation (.delta..zeta.) and percent by
weight of particle diameter less than 150 .mu.m of each agent
showed the same values as of the corresponding a water absorbing
agents (6) to (8) before mixing, respectively. Further, results of
urine resistance test and extractables for 16 hours in a
physiological saline solution of each agent also showed the same
values as of the corresponding a water absorbing agent (6) to (8)
before mixing, respectively. The water absorbing agents (16) to
(18) were evaluated in the same manner as in Example 9. Results are
shown in Table 5.
Comparative Examples 6 and 7
[0295] The same procedures as in Example 10 were repeated except
for using the comparative water absorbing agents (1) and (2)
obtained in Comparative Examples 1 and 2 instead of the water
absorbing agent (2) obtained in Example 2, to obtain a comparative
water absorbing agents (6) and (7), respectively. From measurements
of particle size distributions of thus obtained comparative water
absorbing agents (6) and (7), little change was found in any agent.
Namely, mass median particle size (D50), logarithmic standard
deviation (.delta..zeta.) and percent by weight of particle
diameter less than 150 .mu.m of each agent showed the same values
as of the corresponding a water absorbing agents (1) and (2) before
mixing, respectively. Further, results of urine resistance test and
extractables for 16 hours in a physiological saline solution of
each agent also showed the same values as of the, corresponding a
comparative water absorbing agent (1) and (2) before mixing,
respectively. Further, results of urine resistance test and
extractables for 16 hours in a physiological saline solution of
each agent also showed the same values as of the corresponding a
comparative water absorbing agent (1) and (2) before mixing,
respectively. The comparative water absorbing agents (6) and (7)
were evaluated in the same manner as in Example 9. Results are
shown in Table 5.
[0296] Further, fluidity after moisture absorption of the
comparative water absorbing agents (3) and (4) were also measured.
Results are shown in Table 5.
Example 19
[0297] To 100 parts by weight of the water-absorbing resin (2)
obtained in Reference Example 2, 2 parts by weight of an aqueous
solution comprising sodium diethylenetriamine pentaacetate aqueous
solution and a 15% by weight aqueous solution of extract from plant
leaves of Theaceae plant (Trade Name: FS-80MO, Supplier: Shiraimatu
Shinyaku Co., Ltd., Address: 37-1 Ugawa, Mizuguchi-Cho, kouga-Gun,
Shiga-Ken, Japan) (amount of each component was adjusted so that
sodium diethylenetriamine pentaacetate and the 15% by weight
aqueous solution of extract from plant leaves of Theaceae plant
became 50 ppm and 0.1% by weight relative to the water-absorbing
resin (2), respectively) was mixed by spraying. The resultant
mixture was cured at 60.degree. C. for 1 hour to obtain a water
absorbing agent (19). Particle size distribution of thus obtained a
water absorbing agent (19) was the same as in Example 10 wherein
the 15% by weight aqueous solution of extract from plant leaves of
Theaceae plant was not added. Further, centrifuge retention
capacity, absorbency against pressure at 1.9 kPa, deodorization
test, extractables for 16 hours in a physiological saline solution,
urine resistance and absorbency against pressure at 4.8 kPa of the
water absorbing agent (19) were measured. Results are shown in
Table 6.
Example 20
[0298] The same procedures as in Example 10 were repeated except
for using zinc and silicon composite hydrated oxide (Trade Name:
CERATIOX SZ-100, made by Titan Kogyo K. K., weight ratio of Zn and
Si contents: 82/18, average particle size: 0.36 .mu.m) instead of
fine particulate silicon dioxide, to obtain a water absorbing agent
(20). Particle size distribution of thus obtained a water absorbing
agent (20) was the same as of the water absorbing agent (10).
Further, the water absorbing agent (20) was evaluated in the same
manner as the water absorbing agent (19). Results are shown in
Table 6.
Example 21
[0299] The same procedures as in Example 10 were repeated except
for using the water-absorbing resin (3) obtained in Reference
Example 3 instead of the water-absorbing resin (2) obtained in
Reference Example 2, to obtain a water absorbing agent (21).
Particle size distribution of thus obtained a water absorbing agent
(21) was the same as of the water absorbing agent (12). Further,
the water absorbing agent (21) was evaluated in the same manner as
the water absorbing agent (19). Results are shown in Table 6.
Example 22
[0300] The same procedures as in Example 12 were repeated except
for using zinc/silicon composite hydrated oxide (Trade Name:
CERATIOX SZ-100, made by Titan Kogyo K. K., weight ratio of Zn and
Si contents: 82/18, average particle size: 0.36 .mu.m) instead of
fine particulate silicon dioxide to obtain a water absorbing agent
(22). Particle size distribution of thus obtained a water absorbing
agent (22) was the same as of the water absorbing agent (12).
Further, the water absorbing agent (22) was evaluated in the same
manner as the water absorbing agent (19). Results are shown in
Table 6.
[0301] Further, results of deodorization tests of the comparative
water absorbing agents (3) and (4) are shown together in Table
6.
Example 23
[0302] To evaluate an absorbing substrate performance of the water
absorbing agent (2) obtained in Example 2, an absorbing substrate
for evaluation (1) was prepared according to the method (j) for
evaluation of an absorbing substrate performance described above,
to measure rewet amount after 10 min. and rewet amount after
deterioration. Results are shown in Table 7.
Examples 24 to 27
[0303] The same procedures as in Example 23 were repeated except
for using the water absorbing agents (13) and (16) to (18) obtained
in Examples 13 and 16 to 18 instead of the water absorbing agent
(2) used in Example 23, to obtain absorbing substrates for
evaluation (2) to (5), respectively.
[0304] Evaluation results on rewet amounts of thus obtained
absorbing articles (2) to (5) are shown in Table 7.
Comparative Examples 8 to 12
[0305] The same procedures as in Example 23 were repeated except
for using the comparative water absorbing agents (3) to (7)
obtained in Comparative Examples 3 to 7 instead of the water
absorbing agent (2) used in Example 23 to obtain absorbing
substrates for comparative evaluation (1) to (5), respectively.
[0306] Evaluation results on rewet amounts of thus obtained
absorbing substrates for comparative evaluation (1) to (5) are
shown in Table 7.
Example 28
[0307] To 1,500 g of an acrylic acid aqueous solution (monomer
concentration 20%), 3.1 g of N,N'-methylenebisacrylamide was
dissolved to prepare a reaction solution, and the resultant
reaction solution was charged into a stainless steel tray used in
Reference Example 1, so that thickness of the reaction solution
became 17 mm. The stainless steel tray, after sealed in the same
manner as in Reference Example 1, was dipped into a water bath at
20.degree. C., and nitrogen gas was introduced through the reaction
solution to remove dissolved oxygen in the solution, while
adjusting temperature of the reaction solution at 20.degree. C.
After that, nitrogen gas was introduced into the upper space of the
reactor, and kept exhausting from the opposite side. Then, 20.0 g
of a 10% by weight 2,2'-azobis(2-amidinopropane)dihydrochloride
aqueous solution, 18.0 g of a 1% by weight L-ascorbic acid aqueous
solution and 20.0 g of a 3.5% by weight hydrogen peroxide aqueous
solution as polymerization initiators were added, while stirring
the reaction solution with magnetic stirrer, to start
polymerization about 1 minute later. By repeating cooling and
heating from the bottom surface of the bath during the
polymerization reaction, the solution showed peak temperature of
60.degree. C. after 12 minutes from the start of the
polymerization. A hydrated gel-like polymer was taken out after 100
minutes from the start of the polymerization. Thus obtained
hydrated gel-like polymer was cut off into about 5 cm square pieces
with scissors, which were fed into the same meat chopper as used in
Reference Example 1 at constant rate, together with 749 g of a 40%
by weight sodium hydroxide aqueous solution, also being fed at
constant rate, to crush and post-neutralize the gel simultaneously.
The crushed gel discharged from the meat chopper was maintained in
atmosphere at about 70.degree. C. until the gel did not indicate
red color even by the addition of a phenolphthalein indicator,
followed by drying and pulverizing in the same manner as in
Reference Example 1, further classification by metal sieves with
mesh opening size with of 710 .mu.m and 150 .mu.m and to obtain a
water-absorbing resin powder (1) with irregularly pulverized shape.
Centrifuge retention capacity (CRC), mass median particle size
(D50) and percent by weight of particles less than 150 .mu.m (%) of
the water-absorbing resin (1) obtained are shown in Table 1.
[0308] Next, to 100 parts by weight of the water-absorbing resin
powder (1) obtained, 3.53 parts by weight of a surface crosslinking
agent consisting of 0.5 part by weight of propyleneglycol, 0.03
part by weight of ethyleneglycol glycidylether, 0.3 part by weight
of 1,4-butandiol and 2.7 parts by weight of water were mixed. The
mixture was heat treated at 195.degree. C. of heating medium
temperature for 60 minutes to obtain water-absorbing resin
(12).
[0309] Thus obtained water-absorbing resin (12) was used as it is
as a water absorbing agent (23), which was evaluated in the same
manner as in Example 1. Results are shown in Tables 2 to 4.
Example 29
[0310] To 100 parts by weight of the water absorbing agent (23)
obtained in Example 28, 0.1 part by weight of fine particulate
calcium stearate (made by NOF Corp.) was added and mixed (dry
blend) to obtain a water absorbing agent (24). From measurement of
particle size distribution of thus obtained a water absorbing agent
(24), little change was found. Namely, mass median (D50),
logarithmic standard deviation (.delta..zeta.) and percent by
weight of particle diameter less than 150 .mu.m showed the same
values as of the water absorbing agent (23) before mixing. Further,
results of urine resistance test and extractables for 16 hours in a
physiological saline solution also showed the same values as of the
water absorbing agent (23) before mixing. The water absorbing agent
(23) was evaluated in the same manner as in Example 9. Results are
shown in Table 5.
Example 30
[0311] To evaluate absorbing substrate performance of the water
absorbing agent (23) obtained in Example 28, an absorbing substrate
for evaluation (6) was prepared according to the method (j) for
evaluation of the absorbing substrate performance, to measure rewet
amount after 10 minutes and rewet amount after deterioration.
Results are shown in Table 7. TABLE-US-00001 TABLE 1 Ratio of Mass
Median particle Water-Absorbing CRC Particle size smaller than
Resin Powder (g/g) (.mu.m) 150 .mu.m (%) Reference Water-Absorbing
42 370 1.5 Example 1 resin powder (a) Reference Water-Absorbing 45
360 1.5 Example 2 resin powder (b) Reference Water-Absorbing 57 360
1.6 Example 3 resin powder (c) Reference Water-Absorbing 48 310 1.5
Example 4 resin powder (d) Reference Water-Absorbing 52 355 1.7
Example 5 resin powder (e) Reference Water-Absorbing 50 310 1.4
Example 6 resin powder (f) Reference Water-Absorbing 46 225 1.5
Example 7 resin powder (g) Reference Water-Absorbing 57 230 1.6
Example 8 resin powder (h) Reference Water-Absorbing 45 350 5.0
Example 9 resin powder (i) Reference Water-Absorbing 56 495 0.5
Example 10 resin powder (j) Reference Water-Absorbing 32 355 1.5
Example 11 resin powder (k) Example 28 Water-Absorbing 48 370 0.5
resin powder (l) EX.: Example, Comp. EX.: Comparative Example, WA:
Water absorbing agent, Comp. WA: Comparative Water absorbing agent,
CRC: Centrifuge Retention Capacity, AAP: Absorbency Against
Pressure
[0312] TABLE-US-00002 TABLE 2 Not Not Not Not Not Not smaller
smaller smaller smaller smaller smaller than than than than than
than Not Not Not 710 .mu.m 600 .mu.m 500 .mu.m 425 .mu.m 300 .mu.m
212 .mu.m smaller smaller smaller Smaller Smaller Smaller Smaller
Smaller Smaller than 150 .mu.m than 45 .mu.m Smaller Water than
than than than than than than Smaller Smaller than absorbing 850
.mu.m 850 .mu.m 710 .mu.m 600 .mu.m 500 .mu.m 425 .mu.m 300 .mu.m
than 212 .mu.m than 150 .mu.m 45 .mu.m agent (wt %) (Wt %) (Wt %)
(Wt %) (Wt %) (Wt %) (Wt %) (Wt %) (Wt %) (Wt %) EX. 1 WA (1) 0.0
0.0 5.0 15.3 18.3 30.1 20.0 9.8 1.3 0.2 EX. 2 WA (2) 0.0 0.0 2.3
16.3 18.6 33.3 19.9 8.9 0.6 0.1 EX. 3 WA (3) 0.0 0.0 2.3 15.3 19.4
33.5 19.8 8.9 0.8 0.0 EX. 4 WA (4) 0.0 0.0 0.0 1.1 15.6 42.6 28.1
11.3 1.1 0.2 EX. 5 WA (5) 0.0 0.0 0.1 10.6 19.4 46.5 18.2 3.7 1.4
0.1 EX. 6 WA (6) 0.0 0.0 0.0 5.4 17.4 40.9 29.4 5.5 1.1 0.3 EX. 7
WA (7) 0.0 0.0 0.0 0.0 0.6 11.4 59.8 26.8 1.2 0.2 EX. 8 WA (8) 0.0
0.0 0.0 0.0 6.6 11.7 55.8 24.5 1.2 0.2 Comp. Comp. 0.0 1.1 5.5 15.6
13.9 33.7 17.1 9.7 3.3 0.1 EX. 1 WA (1) Comp. Comp. 0.1 4.0 27.2
20.6 10.6 23.0 11.3 2.5 0.6 0.1 EX. 2 WA (2) Comp. Comp. 0.0 0.0
2.8 16.4 18.7 33.5 18.7 9.1 0.7 0.1 EX. 3 WA (3) Comp. Comp. 0.0
0.0 4.2 14.9 19.7 34.5 17.6 8.5 0.5 0.1 EX. 4 WA (4) Comp. Comp.
0.0 0.0 0.0 2.3 15.8 43.1 25.2 12.3 1.0 0.3 EX. 5 WA (5) EX. 28 WA
(23) 0.0 0.0 1.9 13.9 20.5 36.8 18.5 7.6 0.8 0.0 EX.: Example,
Comp. EX.: Comparative Example, WA: Water absorbing agent, Comp.
WA: Comparative Water absorbing agent
[0313] TABLE-US-00003 TABLE 3 mass median particle size Logarithmic
Standard Water absorbing agent D50 (.mu.m) Deviation
(.sigma..zeta.) Example 1 Water absorbing agent 373 0.397 (1)
Example 2 Water absorbing agent 373 0.369 (2) Example 3 Water
absorbing agent 372 0.367 (3) Example 4 Water absorbing agent 321
0.322 (4) Example 5 Water absorbing agent 367 0.281 (5) Example 6
Water absorbing agent 335 0.298 (6) Example 7 Water absorbing agent
238 0.201 (7) Example 8 Water absorbing agent 245 0.241 (8)
Comparative Comparative Water 369 0.423 Example 1 Absorbing Agent
(1) Comparative Comparative 508 0.367 Example 2 Water absorbing
agent (2) Comparative Comparative 376 0.371 Example 3 Water
absorbing agent (3) Comparative Comparative 381 0.361 Example 4
Water absorbing agent (4) Comparative Comparative 326 0.333 Example
5 Water absorbing agent (5) Example 28 Water absorbing agent 375
0.343 (23)
[0314] TABLE-US-00004 TABLE 4 Increased Increased Ratio
Extractables Water AAP at Extractables for Extractables by of
Extractables Absorption AAP at for 1 hour in absorbing CRC 1.9 kPa
16 Hours in Saline Deterioration by speed 4.8 kPa Deterioration
agent (g/g) (g/g) Soln. (%) (%) Deterioration (sec.) (g/g) Test
Liquid (%) EX. 1 WA (1) 33 33 8 14 3.8 45 25 19 EX. 2 WA (2) 35 33
18 2 1.2 46 23 11 EX. 3 WA (3) 43 38 30 2 1.2 42 15 13 EX. 4 WA (4)
37 32 23 14 2.1 42 22 27 EX. 5 WA (5) 41 30 32 13 2.0 44 16 26 EX.
6 WA (6) 45 35 8 9 4.0 43 19 12 EX. 7 WA (7) 35 33 18 5 1.5 32 23
15 EX. 8 WA (8) 45 37 30 3 1.3 29 15 14 Comp. Comp. 35 33 18 3 1.4
48 24 11 EX. 1 WA (1) Comp. Comp. 42 33 30 2 1.2 63 14 12 EX. 2 WA
(2) Comp. Comp. 35 33 18 41 5.6 46 23 50 EX. 3 WA (3) Comp. Comp.
43 34 30 59 6.4 45 15 70 EX. 4 WA (4) Comp. Comp. 29 23 5 13 5.3 50
27 16 EX. 5 WA (5) EX. 28 WA (23) 38 35 2 8 5.0 43 26 10 EX.:
Example, Comp. EX.: Comparative Example, WA: Water absorbing agent,
Comp. WA: Comparative Water absorbing agent CRC: Centrifuge
Retention Capacity, AAP: Absorbency Against Pressure
[0315] TABLE-US-00005 TABLE 5 Increased Fluidity Extractables
Increased Ratio of after Extractables Water AAP at for 16 Hours
Extractables Extractables Absorption moisture AAP at for 1 hour in
absorbing CRC 1.9 kPa in Saline by Deterio- by Speed absorption 4.8
kPa Deterioration agent (g/g) (g/g) Soln. (%) ration (%)
Deterioration (sec.) (%) (g/g) Test Liquid (%) EX. 9 WA (9) 33 33 8
14 3.8 48 0 25 19 EX. 10 WA (10) 35 30 18 2 1.2 40 0 19 11 EX. 11
WA (11) 35 33 18 2 1.2 49 0 23 11 EX. 12 WA (12) 43 29 30 2 1.2 34
0 9 13 EX. 13 WA (13) 43 38 30 2 1.2 45 0 15 13 EX. 14 WA (14) 37
29 23 14 2.1 38 0 15 27 EX. 15 WA (15) 41 30 32 13 2.0 47 0 16 26
EX. 16 WA (16) 45 24 8 9 4.0 35 0 9 3 EX. 17 WA (17) 34 30 18 5 1.5
25 0 18 15 EX. 18 WA (18) 44 28 30 3 1.3 25 0 8 14 Comp. Comp. 35
33 18 41 5.6 46 70 23 50 EX. 3 WA (3) Comp. Comp. 43 34 30 59 6.4
45 50 15 70 EX. 4 WA (4) Comp. Comp. 35 30 18 3 1.4 44 0 17 11 EX.
6 WA (6) Comp. Comp. 42 25 30 2 1.2 60 0 8 12 EX. 7 WA (7) EX. 29
WA(24) 38 35 26 8 5.0 47 0 26 10 EX.: Example, Comp. EX.:
Comparative Example, WA: Water absorbing agent, Comp. WA:
Comparative Water absorbing agent CRC: Centrifuge Retention
Capacity, AAP: Absorbency Against Pressure
[0316] TABLE-US-00006 TABLE 6 Absorbency Increased Absorbency
Centrifuge Against Result of Extractables Increased Ratio of
Against Extractables Water Retention Pressure Deodor- for 16 Hours
Extractables Extractables Pressure for 1 Hour absorbing Capacity at
1.9 kPa ization in Saline by Deterio- by at 4.8 kPa in Saline agent
(g/g) (g/g) Test Soln. (%) ration (%) Deterioration (g/g) Soln. (%)
Ex. 19 WA (19) 33 33 2.5 18 2 1.2 23 11 Ex. 20 WA (20) 35 30 2.6 18
2 1.2 19 11 Ex. 21 WA (21) 43 29 2.6 30 2 1.2 15 13 Ex. 22 WA (22)
43 29 2.7 30 2 1.2 9 13 Comp. Comp. WA (3) 35 33 4.8 18 41 5.6 23
50 Ex. 3 Comp. Comp. WA (4) 43 34 4.9 30 59 6.4 15 70 Ex. 4 EX.:
Example, Comp. EX.: Comparative Example, WA: Water absorbing agent,
Comp. WA: Comparative Water absorbing agent
[0317] TABLE-US-00007 TABLE 7 Absorbing Water absorbing agent Rewet
Amount Rewet Amount Substrate Used after 10 Min. after
Deterioration Example 23 Absorbing Substrate Water absorbing agent
8 6 for Evaluation (1) (2) Example 24 Absorbing Substrate Water
absorbing agent 6 1 for Evaluation (2) (13) Example 25 Absorbing
Substrate Water absorbing agent 4 3 for Evaluation (3) (16) Example
26 Absorbing Substrate Water absorbing agent 8 6 for Evaluation (4)
(17) Example 27 Absorbing Substrate Water absorbing agent 3 1 for
Evaluation (5) (18) Comparative Absorbing Substrate for Comparative
8 17 Example 8 Comparative Evaluation (1) Water absorbing agent (3)
Comparative Absorbing Substrate for Comparative 6 20 Example 9
Comparative Evaluation (1) Water absorbing agent (4) Comparative
Absorbing Substrate for Comparative 12 10 Example 10 Comparative
Evaluation (1) Water absorbing agent (5) Comparative Absorbing
Substrate for Comparative 10* 6 Example 11 Comparative Evaluation
(1) Water absorbing agent (6) Comparative Absorbing Substrate for
Comparative 10 1 Example 12 Comparative Evaluation (1) Water
absorbing agent (7) Example 30 Absorbing Substrate Water absorbing
agent 7 2 for Evaluation (1) (23) *After measurement of rewet
amount after 10 Min., fine gel particles were observed on nonwoven
fabric as gel on skin.
[0318] A particulate water absorbing agent of the present invention
has, as shown in Tables 2 to 4, a well controlled particle size,
high absorption capacity, little difference between extractabless
in physiological saline solutions containing and not containing
L-ascorbic acid, and thereby shows stable high performance,
irrespective of changes in urine compositions (individual
difference, seasonal variation, and the like) and time in use.
[0319] A particulate water absorbing agent of the present invention
is, as shown in Table 5, superior in absorption speed and fluidity
after moisture absorption, and shows high deodorization performance
by adding a deodorant, if necessary, as separately shown in Table
6.
[0320] A particulate water absorbing agent of the present invention
provides, as shown in Table 7, absorbing articles (absorbing
substrates in Table 7) having small rewet amount for any kind of
liquid. Further, a particulate water absorbing agent of the present
invention does not bring about leak-out of fine gel particles from
an absorbing substrate, and thereby provides absorbing articles
(diapers) having stable and high performance, irrespective of
changes in urine compositions (individual difference, seasonal
variation, and the like) and time in use.
INDUSTRIAL APPLICABILITY
[0321] A water-absorbing resin obtained according to the present
invention has well controlled specific particle size distribution
and superior stability against urine, and exerts effect that it can
provide an absorbing substrate having very superior absorbing
performance in comparison with a conventional absorbing substrate,
when used for an absorbing substrate such as a diaper.
* * * * *