U.S. patent application number 11/526525 was filed with the patent office on 2007-08-30 for absorbent article comprising a primary aqueous-liquid-absorbing agent.
Invention is credited to Holger Beruda, Hiroyuki Ikeuchi, Syaka Machida, Yasue Nakagawa, Shigeru Sakamoto.
Application Number | 20070202772 11/526525 |
Document ID | / |
Family ID | 37499211 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070202772 |
Kind Code |
A1 |
Ikeuchi; Hiroyuki ; et
al. |
August 30, 2007 |
Absorbent article comprising a primary aqueous-liquid-absorbing
agent
Abstract
An absorbent article comprising an absorbent core, which
comprises at least one region comprising an
aqueous-liquid-absorbing agent that contains water-absorbent resin
particles, wherein the water-absorbent resin particles are obtained
by a process including the step of polymerizing a water-soluble
ethylenically unsaturated monomer having a carboxyl group, in the
presence of an internal-crosslinking agent having at least four
functional groups each capable of forming a covalent bond with a
carboxyl group to thereby obtain a hydropolymer that is internally
cross-linked and surface-crosslinked, the aqueous-liquid-absorbing
agent being characterized by exhibiting a water absorption capacity
(CRC) of 5 to 25 g/g and a saline flow conductivity (SFC) of not
less than 1216 cm3s10-7/g.
Inventors: |
Ikeuchi; Hiroyuki;
(Himeji-shi, JP) ; Sakamoto; Shigeru; (Himeji-shi,
JP) ; Machida; Syaka; (Himeji-shi, JP) ;
Nakagawa; Yasue; (Bad Soden, DE) ; Beruda;
Holger; (Schwalbach, DE) |
Correspondence
Address: |
THE PROCTER & GAMBLE COMPANY;INTELLECTUAL PROPERTY DIVISION - WEST BLDG.
WINTON HILL BUSINESS CENTER - BOX 412, 6250 CENTER HILL AVENUE
CINCINNATI
OH
45224
US
|
Family ID: |
37499211 |
Appl. No.: |
11/526525 |
Filed: |
September 25, 2006 |
Current U.S.
Class: |
442/417 ;
442/414 |
Current CPC
Class: |
A61F 13/531 20130101;
A61L 15/60 20130101; Y10T 442/699 20150401; Y10T 442/696 20150401;
A61F 13/15203 20130101 |
Class at
Publication: |
442/417 ;
442/414 |
International
Class: |
D04H 1/00 20060101
D04H001/00; D04H 13/00 20060101 D04H013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2005 |
JP |
2005-289398 |
Claims
1. An absorbent article comprising an absorbent core, which
includes a primary aqueous-liquid-absorbing agent that contains
water-absorbent resin particles, the water-absorbent resin
particles, comprising polymerized water-soluble ethylenically
unsaturated monomers having a carboxyl group, said resin particles
being internally cross-linked and surface-crosslinked, wherein the
primary aqueous-liquid-absorbing agent exhibits a water absorption
capacity (CRC) of 5 to 25 g/g and a saline flow conductivity (SFC)
of not less than 1216.times.10.sup.-7 cm.sup.3 s/g.
2. An absorbent article comprising a primary
aqueous-liquid-absorbing agent exhibiting a water absorption
capacity (CRC) of 5 to 25 g/g and a saline flow conductivity (SFC)
of not less than 1216.times.10.sup.-7 cm.sup.3 s/g, obtained by:
(a) polymerizing a water-soluble ethylenically unsaturated monomer
having a carboxyl group in an aqueous monomer solution including
the water-soluble ethylenically unsaturated monomer having a
carboxyl group, in the presence of an internal-crosslinking agent
having at least four functional groups each capable of forming a
covalent bond with a carboxyl group to thereby obtain a
hydropolymer; (b) drying the hydropolymer obtained in the step (a)
at a temperature of not less than 150.degree. C. to thereby obtain
water-absorbent resin particles; and (c) surface-crosslinking the
water-absorbent resin particles obtained in the step (b), wherein
the amount (Y) (mol %) of the internal-crosslinking agent as used,
relative to the water-soluble ethylenically unsaturated monomer
having a carboxyl group, is expressed by the following equation
(1): Y.gtoreq.-0.06/{2-(2.35X/100)} (1) where X is neutralization
degree (mol %) of a carboxyl group in the water-absorbent resin
particles and is in the range of 45 to 85 mol %.
3. The absorbent article of claim 1, wherein the absorption rate
(modified FSR) of the primary aqueous-liquid-absorbing agent is not
less than 0.1 g/g/s.
4. The absorbent article of claim 2, wherein the primary
aqueous-liquid-absorbing agent has a wet porosity of not less than
20%.
5. The absorbent article of claim 1, wherein the water-absorbing
resin particles comprise agglomerated particles and the primary
aqueous-liquid-absorbing agent is particulate, having at least 90
weight % by weight of particles with a particle diameters in the
range of 150 to 850 .mu.m.
6. The absorbent article of claim 2, wherein said primary
aqueous-liquid-absorbing agent further comprises a
liquid-permeability-enhancing agent, selected from water-soluble
metal compounds and water-soluble polycationic compounds.
7. The absorbent article of claim 1, wherein said water-absorbing
resin particles are internally crosslinked with an
internal-crosslinking agent having at least four functional groups
each capable of forming a covalent bond with the carboxyl
group.
8. The absorbent article of claim 1, further comprising a secondary
aqueous-liquid-absorbing agent, comprising water-absorbing resin
particles, having a SFC of less than 600.times.10.sup.-7 cm.sup.3
s/g, preferably a SFC of between 40.times.10.sup.-7 cm.sup.3 s/g
and 400.times.10.sup.-7 cm.sup.3 s/g.
9. The absorbent article of claim 8, wherein the absorbent core
further comprises an acquisition/storage layer and a storage layer,
whereby said primary aqueous-liquid-absorbing agent is comprised in
at least part of said acquisition/storage layer and whereby said
secondary aqueous-liquid-absorbing agent is comprised in at least
part of said storage region.
10. The absorbent article of claim 1, wherein the absorbent core
includes a layer comprising said primary aqueous-liquid-absorbing
agent and less than 10% by weight of said agent of a fibrous
cellulose material.
11. The absorbent article of claim 1, having a maximum dry caliper
in the crotch region of 4.5 mm or less.
12. The absorbent article of claim 1, wherein the absorbent core
comprises at least said primary aqueous-liquid-absorbing agent and
optionally said secondary aqueous-liquid-absorbing agent, and said
core having one or more regions with an average density greater
than about 0.2 g/cm.sup.3.
13. The absorbent article of claim 2, further comprising a
secondary aqueous-liquid-absorbing agent, comprising
water-absorbing resin particles, having a SFC of less than
600.times.10.sup.-7 cm.sup.3 s/g, preferably a SFC of between
40.times.10.sup.-7 cm.sup.3 s/g and 400.times.10.sup.-7 cm.sup.3
s/g.
14. The absorbent article of claim 2, wherein the absorbent core
includes a layer comprising said primary aqueous-liquid-absorbing
agent and less than 10% by weight of said agent of a fibrous
cellulose material.
15. The absorbent article of claim 2, having a maximum dry caliper
in the crotch region of 4.5 mm or less.
16. The absorbent article of claim 2, wherein the absorbent core
comprises at least said primary aqueous-liquid-absorbing agent and
optionally said secondary aqueous-liquid-absorbing agent, and said
core having one or more regions with an average density greater
than about 0.2 g/cm.sup.3
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an absorbent article, such
as a diaper or adult incontinence article or sanitary napkin,
comprising a primary aqueous-liquid-absorbing agent comprising
resin particles obtained by a process including the step of
polymerizing a water-soluble ethylenically unsaturated monomer
having a carboxyl group, in the presence of an
internal-crosslinking agent having at least four functional groups
each capable of forming a covalent bond with a carboxyl group, the
aqueous-liquid-absorbing agent being characterized by exhibiting a
water absorption capacity (CRC) of 5 to 25 g/g and a saline flow
conductivity (SFC) of not less than 1216 cm3s10-7/g.
BACKGROUND OF THE INVENTION
[0002] There have been continuous investigations to provide
improved absorbent article with so-called super-absorbing resins or
material or water-absorbing material or water-gelling material.
Typically such articles need to that have a high absorption rate,
absorption amount, and retention for aqueous liquids and therefore
the prior art water-absorbing resins are typically being mixed with
or used in addition to fibrous materials such as cellulose fiber,
polyester fiber, polyethylene fiber, and/or polypropylene
fiber.
[0003] In recent years, the ratios of the water-absorbing resins to
fibrous material in the absorbent articles tend to increase with
the increasing needs of the thinning of the sanitary materials such
as diapers. For realization of thinner sanitary materials, it is
desired that the fiber materials are replaced with water-absorbent
resins for further increase in ratio of the water-absorbent resins
in the absorbent structures.
[0004] The water-absorbent resin is inherently excellent in the
performances of absorbing and retaining the aqueous liquid.
However, the fibrous materials are poor in these performances,
particularly the performance of retaining the aqueous liquid, and
have different performances from those of the conventional
water-absorbent resin. As such, as a future water-absorbent resin
that responds to the needs, water-absorbent resins having the
performances of the fibrous materials in the conventional absorbent
structures must be developed. Examples of the performances demanded
to such a water-absorbent resin having the performances of the
fibrous materials include: a performance of rapidly absorbing an
aqueous liquid; a performance of diffusing the aqueous liquid after
having absorbed it; and a performance of being capable of
temporarily retaining the aqueous liquid after having absorbed it.
Therefore, the development of water-absorbent resins having these
performances has been desired.
[0005] The present invention provides absorbent articles comprising
such an improved water-absorbent resin or aqueous-liquid-absorbing
agent, which can be made much thinner or more flexible than
conventional absorbent articles, because the
aqueous-liquid-absorbing agent has the performances of
traditionally used fibrous materials, i.e., the performance of
rapidly absorbing an aqueous liquid; the performance of diffusing
the aqueous liquid after having absorbed it; and the performance of
being capable of temporarily retaining the aqueous liquid after
having absorbed it.
SUMMARY OF THE INVENTION
[0006] The present invention relates to an absorbent article
comprising an absorbent core, which comprises a primary
aqueous-liquid-absorbing agent that contains water-absorbent resin
particles, wherein the water-absorbent resin particles are obtained
by a process including the step of polymerizing a water-soluble
ethylenically unsaturated monomer having a carboxyl group, said
resin particles being internally cross-linked and
surface-crosslinked, whereby the primary aqueous-liquid-absorbing
agent is characterized by exhibiting a water absorption capacity
(CRC) of 5 to 25 g/g and a saline flow conductivity (SFC) of not
less than 1216 cm3s10-7/g, and preferably having an absorption rate
(FSR) of not less than 0.1 g/g/s and/or preferably having a wet
porosity of not less than 20%.
[0007] The absorbent article is preferably a disposable absorbent
article, preferably selected from sanitary napkins, panty-liners,
adult incontinence articles and diapers, including training or
pull-up pants.
[0008] The absorbent article preferably comprises a topsheet,
backsheet and therein between an absorbent core, that may comprise
an acquisition storage layer, in contact with the topsheet, and
there underneath a storage layer, and optionally more absorbent
layers, where one of the layers comprises the primary
aqueous-liquid-absorbing agent herein, said layer comprising less
than 10% by weight (of the primary aqueous-liquid-absorbing agent)
of cellulose fibers (including modified cellulose fibers such as
chemically or mechanically modified cellulose fibers).
[0009] The absorbent core preferably also comprises a secondary
aqueous-liquid absorbing agent, having a SFC of less than 600
cm3s10-7/g, which may comprise in the same or a different layer of
the absorbent core to the primary aqueous-liquid-absorbing agent,
whereby one or more or all of the layers of the care are preferably
substantially free of cellulose-type fibers, e.g., comprising each
less than 10% by weight (by weight of all (i.e., primary or
secondary) liquid-absorbing agents present in said layer) of
cellulose fibers.
[0010] The disposable absorbent article herein are preferably very
thin, having preferably a maximum dry caliper in the crotch region
(as measured herein) of 4.5 mm or less.
[0011] The disposable absorbent articles herein comprise preferably
an absorbent core comprising at least said primary
aqueous-liquid-absorbing agent and optionally said secondary
aqueous-liquid-absorbing agent, and said core having one or more
regions with an average density greater than about 0.2 g/cm.sup.3,
or said core as a whole having such a density.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1: A schematic sectional view of a measurement
apparatus as used for measuring the AAP.
[0013] FIG. 2: A schematic sectional view of a measurement
apparatus as used for measuring the SFC.
[0014] FIG. 3: A schematic sectional view of a portion of the
measurement apparatus as used for measuring the SFC.
[0015] FIG. 4: A bottom view of a piston head of the measurement
apparatus as used for measuring the SFC.
DETAILED DESCRIPTION OF THE INVENTION
Absorbent Articles
[0016] "Absorbent article" refers to devices that absorb and
contain liquid, and more specifically, refers to devices that are
placed against or in proximity to the body of the wearer to absorb
and contain the various exudates discharged from the body.
Absorbent articles include but are not limited to diapers (adult
and infant; including training pants), adult incontinence briefs,
diaper holders and liners, sanitary napkins, panty-liners and
tampons.
[0017] "Diaper" refers to an absorbent article generally worn by
infants and incontinent persons about the lower torso.
[0018] "Disposable" is used herein to describe articles that are
generally not intended to be laundered or otherwise restored or
reused (i.e., they are intended to be discarded after a single use
and, preferably, to be recycled, composted or otherwise disposed of
in an environmentally compatible manner).
[0019] "Region", when used herein, as a region of an absorbent core
or layer thereof, means herein an area (with when applicable a
z-direction calliper) of 2 cm.times.2 cm.
[0020] The absorbent articles envisaged herein comprise a
supporting structure and the aqueous-liquid-absorbing agent
described herein.
[0021] A preferred absorbent article herein preferably comprises a
topsheet and a backsheet, described herein below, with therein
between an absorbent core. Said absorbent core may comprise one or
more than one layers, for example a first acquisition/storage
layer, preferably in close contact with the topsheet, and a storage
layer, as described herein below in more detail. The absorbent core
comprises then the primary aqueous-liquid-absorbing agent described
herein, and it may comprise in addition a secondary
aqueous-liquid-absorbing agent with a SFC of less than 600 units as
described herein in more detail.
[0022] The absorbent core comprises preferably very little
cellulose fibres, preferably less than 10% by weight of the total
of primary and if present secondary aqueous-liquid absorbing
agent.
[0023] Thus, an acquisition/storage layer or storage layer or
absorbent core that is "substantially cellulose free" means that
the structure comprises less than 10% (by total weight of all of
the aqueous-liquid absorbing agent or agents, i.e., primary and/or
secondary liquid absorbing agent, present in said layer or core;
more preferably this level is less than 5% or less than 1%, or no
cellulose fibres at all; typically it means that the layer (s) or
core comprises at least about 90% by weight of the layer or core of
aqueous-liquid-absorbing agent or agents, e.g., said primary and or
said secondary aqueous-liquid-absorbing agent.
[0024] A preferred article herein is a diaper or adult incontinent
brief or sanitary napkin, which comprises a chassis, which
comprises an outer covering including a liquid pervious topsheet
and backsheet. The chassis preferably further includes side panels,
(elasticized) leg cuffs and/barrier cuffs, and (elastic) waist
feature. One end portion of the article is configured as a first
waist region of the article. The opposite end portion is configured
as a second waist region. An intermediate portion is configured as
a crotch region, which extends longitudinally between the first and
second waist regions. The crotch region is that portion which, when
the article such as a diaper or adult incontinence brief or
sanitary napkin is worn, is generally positioned between the
wearer's legs. The chassis may also comprise a fastening system,
which may include at least one fastening member and at least one
landing zone.
[0025] For unitary absorbent articles like diapers, the chassis
comprises the main structure of the diaper with other features
added to form the composite diaper structure. While diaper may be
assembled in a variety of well-known configurations, preferred
diaper configurations are described generally in U.S. Pat. Nos.
4,940,464, 5,554,145; 5,569,234; 6,004,306, U.S. patent application
Ser. No. 10/171,249 and in U.S. patent application Ser. No.
10/824,121.
[0026] The absorbent article herein typically comprises an
absorbent core or layer that comprises the primary
aqueous-liquid-absorbing agent described herein. Exemplary
absorbent structures or cores for use herein are described in U.S.
Pat. Nos. 4,610,678; 4,834,735; 5,260,345; 5,387,207; 5,397,316;
and 5,625,222.
[0027] Preferably, the absorbent core comprises at least two
layers: an acquisition/storage layer that provides acquisition
along with temporary distribution and storage of acquired fluids
and optionally permanent storage of a portion thereof and storage
layer, which provides the majority (e.g., more than 60%) of the
storage capacity of the diaper.
[0028] The topsheet is compliant, soft feeling, and non-irritating
to the wearer's skin. It may be liquid pervious, permitting liquids
to readily penetrate through its thickness. A suitable topsheet can
be manufactured from a wide range of materials such as porous
foams, reticulated foams, apertured plastic films, natural fibers
(e.g., wood or cotton fibers), synthetic fibers (e.g., polyester or
polypropylene fibers) or from a combination of natural and
synthetic fibers. In one embodiment, the topsheet is made of a
hydrophobic material to isolate the wearer's skin from liquids in
the absorbent core, and it may then comprise one or more opening to
receive the bodily exudates. Preferably the topsheet comprises a
means to adjust hydrophilicity of the material, like a surfactant.
A preferred topsheet comprises a nonwoven material made using means
well known to those skilled in the fabrics art. Preferably, the
topsheet has a basis weight from about 10 to about 25 g/m.sup.2, a
minimum dry tensile strength of at least about 150 g/cm in the
machine direction and a strikethrough of less than about 3 seconds
according to European Disposables and Nonwovens Association
standard method 150.4-99. One suitable topsheet comprises a
polypropylene spunbonded nonwoven comprises fibers of less than 3
denier having a basis weight of about 18 g/m.sup.2 as is available
from BBA Fiberweb of Simpsonville, S.C.
[0029] The backsheet is preferably joined to the topsheet at least
about a portion of the periphery thereof. The backsheet prevents
exudates absorbed by the absorbent core and contained within the
article from soiling other external articles that may contact the
article, such as bed sheets and clothing. The backsheet is
preferably manufactured from a thin polymer film. In one preferred
embodiment the film is impervious to liquids. Typically, the
backsheet comprises a layer of polyethylene film having a basis
weight between about 10 g/m.sup.2 and about 30 g/m.sup.2, although
other flexible, liquid impervious materials can be used.
Preferably, the film is breathable (e.g., via micropores) so as to
permit vapors to escape from the diaper while still preventing
exudates from passing through the backsheet. Particularly preferred
backsheet materials have a nonwoven laminated to the film layer so
as to make backsheet more "cloth-like". Such a nonwoven layer may
comprise a nonwoven material (e.g., one having a spunbonded or
other suitable structure) with a basis weight between about 15
g/m.sup.2 and about 25 g/m.sup.2. Suitable materials for use as
backsheet are available form Clopay Plastic Products Company of
Mason, Ohio. Additional features for absorbent articles are well
known in the art and are, e.g., described in U.S. Pat. No.
3,860,003 and U.S. Pat. No. 5,151,092.
[0030] The absorbent core may comprises an acquisition layer
underlying the topsheet and then the acquisition/storage layer,
mentioned above, disposed between the acquisition layer and the
remaining component of core, e.g., said storage layer.
[0031] In particularly preferred embodiments, the absorbent core is
narrower in crotch region than it is in either of waist regions.
Preferably, the ratio of the width of core at transverse axis to
the widest lateral width thereof in either of first waist region or
second waist region is less than 0.8, or more preferably less than
about 0.7.
[0032] The absorbent article may comprise a, preferably thin, e.g.,
less than 1 mm thick on average, cellulose containing acquisition
layer, such as chemically stiffened, curled and/or twisted
cellulose. In one embodiment, the absorbent article does not
comprise any acquisition layer comprising more than 10% (by weight
of such layer) of cellulose fibres.
[0033] The acquisition/storage layer, which may be in contact with
the topsheet or an acquisition layer, may be in direct contact with
storage layer, or an intermediate layer may be present, such as a
nonwoven storage layer cover material. The acquisition/storage
layer and/or storage layer may be covered completely or partially
by one or more of such cover materials. One preferred cover
material comprises a spunbonded, a melt-blown and a further
spunbonded layer (i.e., a SMS material). The non-woven materials
are suitably made using synthetic fibers, such as polyethylene,
polyester and, most preferably, polypropylene. Highly preferred are
permanently hydrophilic non-wovens, and in particular nonwovens
with durably hydrophilic coatings. Such hydrophilicity may be
provided by surfactant treatment of the nonwoven. An alternative
material comprises an SMMS-structure or a cellulosic tissue
structure. The cover material may also be substantially free of
cellulose fibers.
[0034] Suitably, acquisition/storage layer has the same surface
area as storage system or smaller. Preferably, acquisition/storage
layer is laterally centered on storage system with the same lateral
width but a shorter longitudinal length than storage system.
Acquisition/storage layer may also be narrower than storage system
while remaining centered thereon. Said another way,
acquisition/storage layer suitably has an area ratio with respect
to storage system of 1.0. Preferably, the area ratio is less than
1.0 (e.g., less than about 0.75), more preferably less than about
0.50.
[0035] The acquisition/storage layer and/or storage system may
comprise each an aqueous-liquid-absorbing agent, typically each
comprise a different aqueous-liquid-absorbing agent and/or a
different mixture of two or more different aqueous-liquid-absorbing
agents. They may comprise an uneven distribution of
aqueous-liquid-absorbing agent(s) basis weight in one or both of
the machine and cross directions.
[0036] In one embodiment, the absorbent core, the
acquisition/storage layer and/or the storage layer thereof is
obtained by stabilising an aqueous-liquid-absorbing agent (of the
invention and/or a different agent) with a fibrous layer of
thermoplastic (adhesive) material, e.g., which allows removal of
some or all of the (absorbent) cellulose fibres that are often
present in the storage layer or core to stabilise the
aqueous-liquid-absorbing agent The core, storage layer and/or
acquisition/storage layer may be substantially cellulose (fibres)
free, as is, for example, also described in aforementioned U.S.
patent application Ser. No. 10/776,839.
[0037] The aqueous-liquid absorbing agent of the storage layer may
have one or more regions with an average basis weight of at least
about 200 g/m.sup.2, or at least at 300 g/m.sup.2. The storage
layer may have one or more regions with an average density greater
than about 0.2 g/cm.sup.3, or preferably at least 0.3 g/cm.sup.3,
or possibly even greater than 0.4 g/cm.sup.3.
[0038] The absorbent articles herein preferably comprise a
secondary aqueous-liquid-absorbing agent that, in contrast to the
primary aqueous-liquid-absorbing agent, has a SFC of less than 600,
preferably less than 400.times.10.sup.7 cm.sup.3s/g or even
preferably less than 200, and typically at least 40.times.10.sup.7
cm.sup.3s/g, or preferably 80.times.10.sup.7 cm.sup.3s/g, or
preferably 100 or even 120.times.10.sup.-7 cm.sup.3s/g. The
secondary aqueous-liquid absorbing agent typically has a CRC of at
least 20 g/g/, preferably at least 25 g/g/ or preferably at least
30 g/g or even preferably at least 35 g/g/.
[0039] The secondary aqueous-liquid absorbing agent may be present
at a higher level by weight than the primary aqueous-liquid
absorbing agent.
[0040] The secondary aqueous-liquid absorbing agent may be mixed
with the primary liquid absorbing agent, or it may be present in a
separate region or layer; typically it is al least present in an
s-called storage layer.
[0041] The primary aqueous-liquid absorbing agent described herein
is preferably comprised by at least by an acquisition/storage layer
of the absorbent article.
[0042] Because an acquisition/storage layer may be substantially
free of cellulosic fibres, it may have a higher density than
components of an absorbent core used by the prior art for similar
purposes. Suitably, an acquisition/storage layer, comprising the
primary aqueous-liquid-absorbing agent herein, may have one or more
regions with an average density greater than about 0.3 g/cm.sup.3,
or possibly even greater than 0.4 g/cm.sup.3.
[0043] The absorbent article herein is preferably very thin, having
an absorbent core with a maximum dry calliper in the crotch region
of less than about 4.5 mm, preferably less than 4.0 mm, or even
preferably less than 3.5 mm, or even less than 3.0 mm. This is
measured by dividing the crotch regions in areas of 2 cm.times.2
cm, and measuring the calliper per region. The absorbent article
preferably is also very thin, having preferably a maximum dry
caliper of less than about 5.5 mm, preferably less than 5.0 mm, or
even preferably less than 4.5 mm, or even less than 4.0, as
measured in the crotch region as set out above.
[0044] A suitable storage layer may be produced using the method
described in the aforementioned U.S. patent application Ser. No.
10/776,839; a suitable acquisition/storage layer may be produced as
described in U.S. patent application Ser. No. 10/776,839, a laydown
drum is provided with a series of "pockets" having a shape and
volume substantially defined by the desired shape and volume of
acquisition/storage layer.
Primary Aqueous-Liquid-Absorbing Agent
[0045] The absorbent articles of the invention comprise at least a
primary aqueous-liquid-absorbing agent exhibiting a water
absorption capacity (CRC) of 5 to 25 g/g and a saline flow
conductivity (SFC) of not less than 1216 cm3s10-7/g, as claimed
herein, and as is measured the CRC and SFC method described herein,
said agent typically obtainable by a process comprising the steps
of: (a) polymerizing a water-soluble ethylenically unsaturated
monomer having a carboxyl group in an aqueous monomer solution
including the water-soluble ethylenically unsaturated monomer
having a carboxyl group, in the presence of an
internal-crosslinking agent having at least four functional groups
each capable of forming a covalent bond with a carboxyl group to
thereby obtain a hydropolymer; (b) drying the hydropolymer obtained
in the step (a) at a temperature of not less than 150.degree. C. to
thereby obtain water-absorbent resin particles; and (c)
surface-crosslinking the water-absorbent resin particles obtained
in the step (b), wherein the amount (Y) (mol %) of the
intemal-crosslinking agent as used, relative to the water-soluble
ethylenically unsaturated monomer having a carboxyl group, is
expressed by the following equation (1):
Y.gtoreq.0.06/{2-(2.35X/100)} . . . (1) where X is neutralization
degree (mol %) of a carboxyl group in the water-absorbent resin
particles and is in the range of 45 to 85 mol %.
[0046] The process for producing a primary aqueous-liquid-absorbing
agent of the articles of the present invention, favorably further
comprises the step of pulverizing the obtained hydropolymer or the
obtained water-absorbent resin particles at least before or after
the step (b) and/or an agglomeration step, because he
water-absorbent resin particles are preferably agglomerate
particles.
[0047] In the present invention, the water-absorbent resin refers
to a hydrogel-formable, water-swellable, and water-insoluble
crosslinked polymer.
[0048] The CRC upper limit value is preferably 18 g/g, or 16 g/g,
especially or 14 g/g, or 12 g/g. The CRC lower limit value is 5
g/g, more preferably 9 g/g, still more favorably 10 g/g.
[0049] The SFC as measured by the method herein is preferably not
less than 1300 cm3s10-7/g, or not less than 1400 cm3s10-7/g, or not
less than 1450 cm3s10-7/g, or not less than 1500 cm3s10-7/g, or not
less than 1600 cm3s10-7/g. Its upper limit value is not
particularly limited, but the upper limit value is favorably not
more than 4000 cm3s10-7/g.
[0050] The primary aqueous-liquid-absorbing agent herein favorably
exhibits an absorption rate (modified FSR) of not less than 0.1
g/g/s, more favorably not less than 0.15 g/g/s, still more
favorably not less than 0.2 g/g/s, especially favorably not less
than 0.25 g/g/s, most favorably not less than 0.3 g/g/s. Its upper
limit value is not particularly limited, but is favorably not more
than 5 g/g/s, more favorably not more than 2 g/g/s, still more
favorably not more than 1 g/g/s.
[0051] The primary aqueous-liquid-absorbing agent herein favorably
exhibits a wet porosity of not less than 20%, more favorably not
less than 30%, still more favorably not less than 35%, especially
favorably not less than 40%. Its upper limit value is not
particularly limited, but is favorably not more than 60%, more
favorably not more than 50%.
[0052] The primary aqueous-liquid-absorbing agent herein may
exhibit absorbency against pressure (AAP) in the range of favorably
5 to 25 g/g, more favorably 11 to 22 g/g.
[0053] The primary aqueous-liquid-absorbing agent herein may have
an extractable component content in the range of favorably 0 to 15
weight %, more favorably 0 to 10 weight %, still more favorably 0
to 8 weight %.
[0054] The primary aqueous-liquid-absorbing agent may be made by a
process including the step of subjecting the water-absorbent resin
particles to treatment for liquid permeability enhancement before
or after the step (c) above. The treatment for liquid permeability
enhancement may be carried out by adding a
liquid-permeability-enhancing agent. The
liquid-permeability-enhancing agent is favorably at least one
member selected from among water-soluble multivalent metal
compounds and water-soluble polycationic compounds.
[0055] The primary aqueous-liquid-absorbing agent of the articles
herein is an aqueous-liquid-absorbing agent containing
water-absorbent resin particles as essential components being
internally crosslinked and being surface-crosslinked, and
comprising polymerized water-soluble ethylenically unsaturated
monomers, the aqueous-liquid-absorbing agent being characterized by
exhibiting a water absorption capacity (CRC) of 5 to 25 g/g and a
saline flow conductivity (SFC) of not less than 1216
cm3s10-7/g.
[0056] Preferably, the absorbent article also comprises a secondary
aqueous-liquid-absorbing agent, having a different performance,
e.g., and suitable a different chemistry, as described above. This
agent may be made by the method described herein, but typically
having different crosslinking levels, surface-crosslinking levels
and/or different chemistry, e.g., of the cross-linking
compounds.
[0057] The primary aqueous-liquid-absorbing agent herein has
preferably an absorption rate (modified FSR) of not less than 0.1
g/g/s, and on the other hand, that, in order for the above primary
aqueous-liquid-absorbing agent to have the aqueous-liquid-retaining
ability capable of further temporarily retaining the aqueous-liquid
after having quickly absorbed it, the above
aqueous-liquid-absorbing agent favorably exhibit a wet porosity of
not less than 20%, the wet porosity being an index of proportion of
the volume of pore in a gel layer formed in an
aqueous-liquid-absorbing agent swollen (wetted) under load,
relative to the volume of the gel layer.
[0058] Note that as the wet porosity is higher, the primary
aqueous-liquid-absorbing agent is able to absorb the aqueous-liquid
at one go, retain the aqueous-liquid temporarily quickly, and then
diffuse the temporally retained aqueous-liquid because of a large
pore there between. Also, it can be said that the wet porosity is
an index of the amount of liquid that can be retained between gels
other than the aqueous-liquid which is absorbed by the water
absorbent resin and exists in the gel. Therefore, as the wet
porosity is higher, the primary aqueous-liquid-absorbing agent can
retain still more aqueous-liquid therebetween, in addition to the
liquid having been absorbed therein, after having absorbing the
aqueous-liquid.
[0059] The "water-absorbent resin particles as the main components"
herein refer to 50 weight % or more water-absorbent resin particles
content relative to the entire primary aqueous-liquid-absorbing
agent. The water-absorbent resin particles content is favorably in
the range of 60 to 100 weight %, more favorably 70 to 100 weight %,
still more favorably 80 to 100 weight %, yet more favorably 90 to
100 weight %, relative to the entire aqueous-liquid-absorbing
agent.
[0060] The primary aqueous-liquid-absorbing agent comprises
preferably only low levels or no uncrosslinked extractable
component, e.g., 0 to 50 weight %, more favorably not higher than
25 weight %, still more favorably not higher than 20 weight % by
weight of the water-absorbent resin.
[0061] Specific examples of the hydrogel-formable, water-swellable,
and water-insoluble crosslinked polymer or its particles include:
partially-neutralized and crosslinked polymers of poly(acrylic
acids) (e.g., U.S. Pat. No. 4,625,001, U.S. Pat. No. 4,654,039,
U.S. Pat. No. 5,250,640, U.S. Pat. No. 5,275,773, EP 0456136);
crosslinked and partially-neutralized graft polymers of
starch-acrylic acid (U.S. Pat. No. 4,076,663); copolymers of
isobutylene-maleic acid (U.S. Pat. No. 4,389,513); saponified
copolymers of vinyl acetate-acrylic acid (U.S. Pat. No. 4,124,748);
hydrolyzed (co)polymers of acrylamide (U.S. Pat. No. 3,959,569);
and hydrolyzed polymers of acrylonitrile (U.S. Pat. No.
3,935,099).
[0062] The water-absorbent resin particles that can be used herein
are favorably of 100% particulate shape. Examples of the
particulate shape includes: a spherical shape; a shape of an
agglomerate of spheres; a shape like a flattened sphere; an
irregularly pulverized shape; a shape of an agglomerate of
irregularly pulverized materials; and a foamed shape having pores.
Incidentally, in the present invention, the water-absorbent resin
particles may be referred to simply as water-absorbent resin.
[0063] In the case where the primary aqueous-liquid-absorbing agent
used in the present invention is particulate, the particle
diameters and particle diameter distribution of this agent are free
of especial limitation. However, for still more exerting the
effects of the present invention, it is favorable that the
weight-average particle diameter of this agent is in the range of
150 to 850 .mu.m, more favorably 150 to 600 .mu.m, more favorably
150 to 500 .mu.m, more favorably 200 to 400 .mu.m, still more
favorably 250 to 380 .mu.m, and also it is favorable that the
logarithmic standard deviation (.quadrature. .quadrature.) of this
agent is favorably in the range of 0.1 to 0.45, more favorably 0.2
to 0.45, still more favorably 0.25 to 0.40, yet more favorably 0.30
to 0.35. Examples of the water-absorbent resin particles and
aqueous-liquid-absorbing agent herein having a favorable
combination of weight-average particle diameter (D50) and
logarithmic standard deviation (.quadrature. .quadrature.) of
particle diameter distribution includes: those having a
weight-average particle diameter (D50) of not less than 200 .mu.m
and less than 400 .mu.m, and a logarithmic standard deviation
(.quadrature. .quadrature.) of particle diameter distribution of
not less than 0.20 and not more than 0.45 (those having a small
average particle diameter and narrow particle diameter
distribution); and those having a weight-average particle diameter
(D50) of not less than 400 .mu.m and not more than 750 .mu.m, and a
logarithmic standard deviation (.quadrature. .quadrature.) of
particle diameter distribution of not less than 0.20 and not more
than 0.45 (those having a large average particle diameter and
narrow particle diameter distribution).
[0064] It may be preferred that this agent includes particles
having particle diameters in the range of 150 to 850 .mu.m in an
amount of not smaller than 90 to 100 weight %. Further, it is more
favorable that this agent includes particles having particle
diameters in the range of 150 to 600 .mu.m in an amount of not
smaller than 90 to 100 weight %, particularly favorably not smaller
than 95 to 100 weight %. Further, it is more favorable that this
agent includes particles having particle diameters in the range of
150 to 500 .mu.m in an amount of not smaller than 90 to 100 weight
%, particularly favorably not smaller than 95 to 100 weight %.
[0065] The water-absorbent resin particles herein are obtained by a
process including the step of polymerizing a water-soluble
ethylenically unsaturated monomer having a carboxyl group, and
having a crosslinked structure.
[0066] Examples of water-absorbent resin particles obtained by a
process including the step of polymerizing a water-soluble
ethylenically unsaturated monomer having a carboxyl group include:
polymers obtained by polymerizing and crosslinking carboxyl-group
containing unsaturated monomers having a carboxyl group such as
(meth)acrylic acid, maleic anhydride, maleic acid, fumaric acid,
crotonic acid, itaconic acid, and cinnamic acid, and/or their salts
(neutralizer); hydrolyzed graft polymers of starch-acrylonitrile;
graft polymers of starch-acrylic acid; saponified copolymers of
vinyl acetate-acrylate acid; hydrolyzed or crosslinked
acrylonitrile copolymers or acrylamide copolymers; denatured
carboxyl-group containing crosslinked polyvinyl alcohol;
crosslinked copolymers of isobutylene-maleic anhydride; or either
one or a combination of two or more substances among the above
substances. Above all, the water-absorbent resin particles are
water-absorbent resin particles including a crosslinked polyacrylic
acid (salt) polymer obtained by a process including the step of
polymerizing a monomer including acrylic acid and/or its salt as a
main component.
[0067] The crosslinked polyacrylic acid (salt) polymer useful
herein is a polymer which is obtained by a process including the
step of polymerizing a monomer (excluding cross-linking agent)
containing acrylic acid and/or its salt in an amount of favorably
50 to 100 mol %, more favorably 70 to 100 mol %, still more
favorably 90 to 100 mol %, and has a crosslinked structure in its
inside. In addition, 45 to 85 mol % of the carboxyl group in the
water-absorbent resin particles are favorably neutralized to form
salt. In other words, the carboxyl group of the water-absorbent
resin particles preferably has a neutralization degree of 45 to 85
mol %, more favorably 50 to 85 mol %, still more favorably 55 to 80
mol %, especially favorably 60 to 75 mol %. As examples of the
salt, there can be cited at least one of such as: alkaline metal
(e.g., sodium, potassium, lithium) salts, ammonium salts, and amine
salts. The neutralization of the carboxyl group for forming the
salt may be carried out in a monomer state before the
polymerization, or may be carried out in a polymer state on the way
of or after the polymerization, or may be carried out both in these
states.
[0068] Incidentally, a neutralization degree of a carboxyl group in
the water-absorbent resin particles can be obtained by calculation
from (i) the amount of water-soluble ethylenically unsaturated
monomer having a not-yet-neutralized carboxyl group and (ii) the
total amount of bases as used for neutralization before the
polymerization, during the polymerization, and/or after the
polymerization. Alternatively, as mentioned below, the
neutralization degree may be obtained by titration of an
extractable component content in the water-absorbent resin
particles.
[0069] The water-absorbent resin particles favorably used in the
present invention may, if necessary, realized by a copolymer
obtained by copolymerizing another monomer jointly with the
water-soluble ethylenically unsaturated monomer having a carboxyl
group (if crosslinked polyacrylic acid (salt) polymer, acrylic acid
and/or its salt) used as the main component.
[0070] Specific examples of the above other monomer include:
anionic unsaturated monomers (e.g., methacrylic acid, maleic acid,
vinylsulfonic acid, styrenesulfonic acid,
2-(meth)acrylamido-2-methylpropanesulfonic acid,
2-(meth)acryloylethanesulfonic acid,
2-(meth)acryloylpropanesulfonic acid) and their salts;
nonionic-hydrophilic-group-containing unsaturated monomers (e.g.,
acrylamide, methacrylamide, N-ethyl(meth)acrylamide,
N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide,
N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol
(meth)acrylate, polyethylene glycol mono(meth)acrylate,
vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine,
N-acryloylpyrrolidine, N-vinylacetamide); and cationic unsaturated
monomers (e.g., N,N-dimethylaminoethyl (meth)acrylate,
N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl
(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylamide, and their
quaternary salts). The amount of these monomers used as monomers
other than acrylic acid and/or its salt is favorably in the range
of 0 to 30 mol %, more favorably 0 to 10 mol %, of the entire
monomers.
[0071] The water-absorbent resin particles, usable in the present
invention, have a crosslinked structure in their inside and
surface, i.e., they are internally cross-linked. As to methods for
introducing the internal crosslinked structure into the
water-absorbent resin particles as used in the present invention,
examples thereof include: a method in which the introduction is
carried out by self-crosslinking without any crosslinking agent;
and a method in which the introduction is carried out by
copolymerization or reaction with an internal-crosslinking agent
having at least two polymerizable ethylenical double bonds and/or
at least two functional groups per molecule. The functional groups
are highly reactive groups in a molecule and includes a
covalent-bondable functional group and an ion-bondable functional
group. For still more exerting the effects of the present
invention, it is favorable that the water-absorbent resin particles
usable in the present invention are surface-crosslinked ones.
[0072] The primary aqueous-liquid-absorbing agent herein may
contain small amount of additive and/or water, if necessary. The
primary aqueous-liquid-absorbing agent of the present invention
favorably contains a liquid-permeability-enhancing agent as the
additive. Especially, in the case where the primary
aqueous-liquid-absorbing agent includes water-absorbent resin
particles not subjected to treatment for liquid permeability
enhancement as main components, it is very favorable that it
further includes a liquid-permeability-enhancing agent. On the
other hand, in the case where the primary aqueous-liquid-absorbing
agent includes water-absorbent resin particles subjected to
treatment for liquid permeability enhancement, the primary
aqueous-liquid-absorbing agent according to the present invention
may be realized by only the water-absorbent resin particles. The
liquid-permeability-enhancing agent herein refers to an agent that
enhances the SFC.
[0073] Examples of the liquid-permeability-enhancing agent include:
water-soluble multivalent metal compounds (e.g., aluminum sulfate,
potassium alum, ammonium alum, sodium alum, (poly)aluminum
chloride, and their hydrates); water-soluble polycationic compounds
(e.g., polyethylenimine, polyvinylamine, polyallylamine); and
water-insoluble inorganic fine particles (e.g., silica, alumina,
bentonite). These may be used either alone respectively or in
combinations with each other. Above all, water-soluble multivalent
metal salts (e.g., aluminum sulfate, potassium alum) are favorable
in point of enhancing the saline flow conductivity (SFC) more than
that in a case of adding no water-soluble multivalent metal
salts.
[0074] The liquid-permeability-enhancing agent is used in an amount
of favorably 0.001 to 10 weight %, more favorably 0.01 to 5 weight
%, relative to the water-absorbent resin particles.
[0075] Note that, the liquid-permeability-enhancing agent is not
limited if it enhances liquid permeability, but preferably a
substance which forms no covalent bonds with functional groups on
the surface of the water-absorbent resin particles.
[0076] Examples of the another additive include: deodorizer,
antimicrobial agent, fragrant material, blowing agent, pigment,
dye, plasticizer, adhesive, surfactant, oxidizer, reducer, water,
salts, chelating agent, bactericidal agent, hydrophilic polymer
such as polyethyleneglycol, paraffin, hydrophobic polymer,
thermoplastic resin such as polyethylene and polypropylene, and
thermosetting resin such as polyester resin and urea resin. For
example, the primary aqueous-liquid-absorbing agent according to
the present invention may further include said other additive of
the order of 0 to 10 weight %, relative to the water-absorbent
resin particles.
[0077] Process for producing the primary aqueous-liquid-absorbing
agent according to the present invention.
[0078] The process for producing a primary aqueous-liquid-absorbing
agent herein includes, for example, at least the following
steps:
[0079] (2-1) polymerizing a water-soluble ethylenically unsaturated
monomer having a carboxyl group in an aqueous monomer solution
including the water-soluble ethylenically unsaturated monomer
having a carboxyl group, in the presence of an
internal-crosslinking agent having at least four functional groups
each capable of forming a covalent bond with a carboxyl group to
thereby obtain a hydropolymer;
[0080] (2-3) drying the hydropolymer obtained in the step (2-1) at
a temperature of not less than 150.degree. C. to thereby obtain
water-absorbent resin particles; and
[0081] (2-5) surface-crosslinking the water-absorbent resin
particles obtained in the step (2-3).
[0082] In addition, the process for a primary
aqueous-liquid-absorbing agent according to the present invention
may further include at least one of the following steps:
[0083] (2-2) before the step (2-1), further preparing an aqueous
monomer solution including a water-soluble ethylenically
unsaturated monomer having a carboxyl group and an
internal-crosslinking agent having at least four functional groups
each capable of forming a covalent bond with the carboxyl
group;
[0084] (2-4) pulverizing the obtained hydropolymer or the obtained
water-absorbent resin particles at least before or after the step
(2-3);
[0085] (2-6) subjecting the water-absorbent resin particles to
treatment for liquid permeability enhancement before or after the
step (2-5).
[0086] The water-soluble ethylenically unsaturated monomer having a
carboxyl group in an aqueous monomer solution including the
water-soluble ethylenically unsaturated monomer having a carboxyl
group, is polymerized in the presence of at least one
internal-crosslinking agent to obtain a hydropolymer. As the
internal-crosslinking agent, used is an internal-crosslinking agent
having at least four functional groups each capable of forming a
covalent bond with the carboxyl group of the water-soluble
ethylenically unsaturated monomer. The water-soluble ethylenically
unsaturated monomer having a carboxyl group is as described above.
Other monomers may also be added in the polymerization process
step.
[0087] Also, in this step, polymerization reaction is carried out
in the presence of at least one inner-crosslinking agent. As the
inner-crosslinking agent, at least an inner-crosslinking agent
having at least four functional groups each of which forms a
covalent bond with the carboxyl group of the water-soluble
ethylenically unsaturated monomer is favorably used. This increases
a saline flow conductivity (SFC) of the obtained water-absorbent
resin particles, as compared with those obtained with a single use
of (a) an internal-crosslinking agent having three or less
functional groups each capable of forming a covalent bond with the
carboxyl group of the water-soluble ethylenically unsaturated
monomer or those obtained with the use of (b) an
internal-crosslinking agent having at least two polymerizable
ethylenical double bonds jointly with the internal-crosslinking
agent (a).
[0088] The functional groups each capable of forming a covalent
bond with a carboxyl group of the water-soluble ethylenically
unsaturated monomer having the carboxyl group, are not particularly
limited if they are functional groups which form bonds with the
carboxyl group. Examples of the functional groups include: hydroxyl
group, amino group, epoxy group, oxetane group, ethyleneimine group
(aziridine group), isocyanate group, oxazoline, cyclocarbonate,
cyclocarbonate, oxazolidinone, cyclic urea, azithidinium salt and
chlorohydrin.
[0089] Therefore, examples of the internal-crosslinking agent
having at least four functional groups each capable of forming a
covalent bond with a carboxyl group include: an
internal-crosslinking agent having at least four hydroxyl groups;
an internal-crosslinking agent having at least four amino groups;
an internal-crosslinking agent having at least four epoxy groups;
an internal-crosslinking agent having at least four oxetane groups;
an internal-crosslinking agent having at least four ethyleneimine
groups (aziridine groups); an internal-crosslinking agent having at
least four isocyanate groups; an internal-crosslinking agent having
at least four oxazolines; an internal-crosslinking agent having at
least four cyclocarbonates; an internal-crosslinking agent having
at least four oxazolidinones; an internal-crosslinking agent having
at least four cyclic ureas; an internal-crosslinking agent having
at least four azithidinium salts; an internal-crosslinking agent
having at least four chlorohydrins; and an internal-crosslinking
agent having at least two kinds of functional groups selected from
among hydroxyl group, amino group, epoxy group, oxetane group,
ethyleneimine group (aziridine group), isocyanate group, oxazoline,
cyclocarbonate, oxazolidinone, cyclic urea, azithidinium salt and
chlorohydrin, wherein a combined total number of groups in the
selected functional groups is at least four. Above all, the
internal-crosslinking agent having at least four functional groups
each capable of forming a covalent bond with a carboxyl group is
more favorably the internal-crosslinking agent having at least four
hydroxyl groups. Incidentally, in the case where the
internal-crosslinking agent has a plurality of kinds of groups, a
ratio between the groups is not particularly limited.
[0090] In addition, the internal-crosslinking agent having at least
four functional groups each capable of forming a covalent bond with
a carboxyl group may further have at least one polymerizable
ethylenical double bond, ion-bondable functional group, or the
like.
[0091] Moreover, the internal-crosslinking agent having at least
four functional groups each capable of forming a covalent bond with
a carboxyl group is not particularly limited if it has at least
four functional groups each capable of forming a covalent bond with
a carboxyl group. However, the number of the functional groups each
capable of forming a covalent bond with a carboxyl group is
favorably 4 to 50, more favorably 4 to 20, still more favorably 4
to 10, especially favorably 4 to 6. The number of carbon atoms of
the internal-crosslinking agent is favorably 0.5 to 4 times as many
as the number of the functional groups each capable of forming a
covalent bond with a carboxyl group, more favorably 1 to 2 times.
In the case where the number of such a functional groups is less
than 4 or exceeds 50, the liquid permeability poorly enhances.
[0092] Specifically, examples of the internal-crosslinking agent
having at least four hydroxyl groups include: polyhydric alcohol
such as polyglycerol or pentaerythritol; sugar alcohol such as
erythritol, xylitol, sorbitol, mannitol, maltitol, lactitol, or
oligosaccharide alcohol; aldose such as xylose, glucose, gulose,
mannose, or idose; and ketose such as fructose or sorbose. Examples
of the internal-crosslinking agent having at least four amino
groups include triethylenetetramine, tetraethylenepentamine, and
pentaethylenehexamine. Examples of the internal-crosslinking agent
having hydroxyl group and amino group include
2-amino-2-hydroxymethyl-1, 3-propanediol, and
N,N-bis-(2-hydroxyethyl) ethylenediamine. These
internal-crosslinking agents having at least four functional groups
each capable of forming a covalent bond with a carboxyl group may
be used either alone respectively or in combinations with each
other.
[0093] Above all, the internal-crosslinking agent having at least
four functional groups each capable of forming a covalent bond with
a carboxyl group is more favorably the internal-crosslinking agent
having at least four hydroxyl groups; more favorably sugar alcohol;
still more favorably erythritol, xylitol, or sorbitol; especially
favorably xylitol or sorbitol; most favorably sorbitol. These
substances are favorably in view of their extremely high
safety.
[0094] Further, the internal-crosslinking agent having at least
four functional groups each capable of forming a covalent bond with
a carboxyl group may be either high-molecular weight compound or
low-molecular weight compound, but more favorably low-molecular
weight compound. Its molecular weight is not particularly limited,
but more favorably not more than 5000, more favorably not more than
2000, still more favorably not more than 1000, especially favorably
not more than 500, most favorably not more than 200. Still further,
a lower limit of the molecular weight of the internal-crosslinking
agent having at least four functional groups each capable of
forming a covalent bond with a carboxyl group is not particularly
limited, but favorably 50, more favorably 80, still more favorably
90. The molecular weight of the above internal-crosslinking agent
in the above range is favorably because internal crosslinking is
carried out more efficiently. Further, in the case where polyvinyl
alcohol, starch, or the like is used as an internal-crosslinking
agent, there may occur coloring during drying. Therefore, the
molecular weight is favorably in the above range.
[0095] Furthermore, the internal-crosslinking agent having at least
four functional groups each capable of forming a covalent bond with
a carboxyl group is favorably water-soluble such that it dissolves
in amount of not less than 0.1 g in pure water of 100 g from the
view points that it can be added easily and realize uniform
crosslinking.
[0096] Additionally, other internal-crosslinking agents may be
used. Examples of other internal-crosslinking agents, as described
previously, includes: an internal-crosslinking agent having at
least two polymerizable ethylenical double bonds and/or at least
two functional groups per molecule. Specific examples of these
other internal-crosslinking agents include: copolymerizable
crosslinking agents having at least two polymerizable ethylenical
double bonds, such as N,N'-methylenebis(meth)acrylamide,
(poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol
di(meth)acrylate, trimethylolpropane tri(meth)acrylate,
trimethylolpropane di(meth)acrylate, glycerol tri(meth)acrylate,
glycerol acrylate methacrylate, ethylene-oxide-modified
trimethylolpropane tri(meth)acrylate, pentaerythritol
tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl
cyanurate, triallyl isocyanurate, triallyl phosphate,
triallylamine, tetraallyloxyethane, pentaerythritol triallyl ether,
and poly(meth)allyloxyalkanes. In addition, as examples of
internal-crosslinking agents having a copolymerizable group having
at least two polymerizable ethylenical double bonds and a
covalent-bondable group, there can be cited such as (poly)ethylene
glycol diglycidyl ether, glycerol diglycidyl ether,
ethylenediamine, polyethylenimine, glycidyl (meth)acrylate,
hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and
glycidyl (meth)acrylate.
[0097] As to the amount of usage of this internal-crosslinking
agent having at least four functional groups each of which forms a
covalent bond with a carboxyl group, the amount of usage (Y) (unit:
mol %) of the internal-crosslinking agent having at least four
functional groups each capable of forming a covalent bond with a
carboxyl group, relative to the water-soluble ethylenically
unsaturated monomer, is favorably in the range expressed by the
following equation (1):
Y.gtoreq.0.06/{2-(2.35X/100)} (1).
[0098] In the equation (1) and the below-mentioned equation (2), X
is a neutralization degree (unit: mol %) of a carboxyl group in the
water-absorbent resin particles, and favorably in the range of 0.45
to 0.85. If Y falls outside the range expressed by the equation
(1), internal crosslinking is carried out insufficiently, and thus
a saline flow conductivity (SFC) of the obtained water-absorbent
resin particles increases poorly. In addition, the water absorption
capacity (CRC) exceeds 25 g/g, and there is a possibility that a
primary aqueous-liquid-absorbing agent having target performances
of the present invention cannot be obtained.
[0099] The lower limit of the Y is, when it is Y=Z/{2-(2.35X/100)}
. . . (2), is a value such that it is favorably Z=0.06, more
favorably Z=0.07, still more favorably Z=0.09, especially favorably
Z=0.15.
[0100] The upper limit of the Y is a value such that it is
favorably Z=1.2, more favorably Z=0.6, still more favorably Z=0.3
in the above equation (2). It is unfavorable that the Y is larger
than 1.2/{2-(2.35X/100)}, because a water absorption capacity
becomes too low.
[0101] In the case where the another internal-crosslinking agent is
used, the total amount of the another internal-crosslinking agent
as used is favorably in the range of 0 to 2 mol %, more favorably 0
to 1.5 mol %, still more favorably 0 to 1 mol %, particularly
favorably 0 to 0.5 mol %, relative to the entire monomers
(water-soluble ethylenically unsaturated monomers excluding the
internal-crosslinking agents).
[0102] The above non-high-molecular weight compound and another
internal-crosslinking agent may be added before polymerization of a
monomer or added on the way of the polymerization, so as to exist
at the time of the polymerization.
[0103] The polymerization reaction is preferably an aqueous
solution polymerization in which the monomer is used in the form of
an aqueous solution, optionally exceeding saturation. Such
polymerization methods are disclosed in such as U.S. Pat. No.
4,625,001, U.S. Pat. No. 4,769,427, U.S. Pat. No. 4,873,299, 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. 4,690,996, U.S.
Pat. No. 4,721,647, U.S. Pat. No. 4,738,867, U.S. Pat. No.
4,748,076, and EP 1178059.
[0104] The temperature of the aqueous monomer solution is favorably
in the range of 0 to 100.degree. C., more favorably 10 to
95.degree. C. (The saturated concentration is specified by the
temperature of the aqueous monomer solution at normal
pressures.)
[0105] A polymer obtained in the aforementioned polymerization step
is obtained as a hydropolymer. The obtained hydropolymer is, if
necessary, pulverized in the form of a hydropolymer with water
content of not less than 10% but less than 70%, for example.
Further, the pulverized hydropolymer particles are dried.
Conditions for drying the hydropolymer and pulverized hydropolymer
particles are not particularly limited. However, the drying is
carried out normally in the temperature range of 150 to 250.degree.
C., favorably 150 to 220.degree. C., more favorably 160 to
200.degree. C., still more favorably 180 to 200.degree. C. Drying
at temperatures lower than 150.degree. C. makes less prone to
bringing an internal-crosslinking reaction. As a result of the
drying, the hydropolymer or the pulverized hydropolymer particles
obtained in such a manner that the hydropolymer is pulverized, if
necessary, in the below-mentioned pulverizing step, favorably have
a solid content in the range of 70 to 99.8 weight %, more favorably
80 to 99.7 weight %, still more favorably 90 to 99.5 weight %.
[0106] The process comprises typically a pulverizing step of
pulverizing the obtained hydropolymer or water-absorbent resin
particles before or after the drying step, favorably before and
after the drying step. The resultant hydropolymer obtained in the
polymerization step may be dried as it is. However, favorably, the
resultant hydropolymer is pulverized before the drying step. For
example, the resultant hydropolymer is extruded from a perforated
structure having perforation diameters in the range of 0.3 to 18 mm
to thus pulverize the hydropolymer to thereby form it into
pulverized hydropolymer particles. By such extrusion of the
hydropolymer from the perforated structure having the specific
perforation diameters to thus pulverize the hydropolymer, it
becomes possible to form it into the pulverized hydropolymer
particles which can sufficiently exert the effects of the present
invention. The shape of the perforations is such as a circular,
quadrangular (e.g., square, rectangular), triangular, or hexagonal
shape and is not especially limited. However, favorably, the
hydropolymer is extruded from circular perforations. Incidentally,
the aforementioned perforation diameters are defined as the
diameters given in the case of converting the outer peripheries of
the mesh opening portions into those of the circles.
[0107] The perforation diameters of the perforated structure for
carrying out the extrusion pulverization in order to obtain the
pulverized hydropolymer particles are more favorably in the range
of 0.5 to 16 mm, still more favorably 0.5 to 12 mm, especially
favorably 0.5 to 9.5 mm, most favorably 0.5 to 6.4 mm. In the case
where the perforation diameters of the perforated structure are
smaller than 0.3 mm, there is a possibility that the gel may become
strings, or that the gel cannot be extruded. In the case where the
perforation diameters of the perforated structure are larger than
18 mm, there is a possibility that the effects of the present
invention cannot be exerted. Especially, there is a possibility
that absorption rate (modified FSR) decreases. Examples of the
apparatus for carrying out the extrusion pulverization in order to
obtain the pulverized hydropolymer particles include such as
extrudes the hydropolymer from a perforated plate to thereby
pulverize the hydropolymer. As the extrusion mechanism, there is
used the mechanism of the type which can press-feed the
hydropolymer from its supply inlet to the perforated plate, such as
screw type or rotary roll type. The screw type extruder may be a
single or multiple screw type and may be a type which is used
usually for extrusion molding of edible meat, rubber, and plastic
or used as a pulverizer. Examples thereof include meat choppers and
Dome Gran.
[0108] It is favorable that at least a portion of the
water-absorbent resin particles usable herein are agglomerate
particles. More favorably, these agglomerate particles are those
which are obtained by a process including the step of agglomeration
of particles having particle diameters of smaller than 150 .mu.m.
The process for achieving such a mode that at least a portion of
the water-absorbent resin particles are agglomerate particles is
not especially limited and will do if hitherto publicly known
agglomeration processes are applied thereto. Examples of such
applicable processes include processes in which: warm water and a
fine powder of water-absorbent resin particles are mixed together
and then dried (U.S. Pat. No. 6,228,930); a fine powder of
water-absorbent resin particles is mixed with an aqueous monomer
solution, and then the resultant mixture is polymerized (U.S. Pat.
No. 5,264,495); water is added to a fine powder of water-absorbent
resin particles, and then the resultant mixture is agglomerated
under not less than a specific face pressure (EP 0844270); a fine
powder of water-absorbent resin particles is sufficiently wetted to
thus form an amorphous gel, and then this gel is dried and
pulverized (U.S. Pat. No. 4,950,692); and a fine powder of
water-absorbent resin particles and a polymer gel are mixed
together (U.S. Pat. No. 5,478,879).
[0109] In addition, it is favorable that at least a portion of the
water-absorbent resin particles usable in the present invention are
foamed particles. These foamed particles are favorably those which
are obtained by a process characterized by including the step of
polymerizing the monomer containing an azo initiator or a foaming
agent (e.g., a carbonate) or polymerizing the monomer while it
contains bubbles by causing it to bubble with an inert gas.
[0110] The agglomeration can be carried out at the same time as the
gel pulverization if, as is aforementioned, the hydropolymer
(obtained by polymerizing the aqueous monomer solution which has
the specific monomer concentration and contains the specific
internal-crosslinking agent in the specific amount) is extruded
under the specific conditions (namely, extruded from the perforated
structure having perforation diameters in the range of 0.3 to 18
mm) to thus pulverize the hydropolymer.
[0111] The water-absorbent resin particles or the primary
aqueous-liquid-absorbing agent favorably has a bulk density in the
range of 0.40 to 0.80 g/ml, more favorably 0.45 to 0.75 g/ml, still
more favorably 0.50 to 0.70 g/ml.
[0112] The water-absorbent resin particles are subjected to
surface-crosslinking. The surface-crosslinking step is carried out
in at least one stage selected from among before, simultaneously
with, and after the step of subjecting the water-absorbent resin
particles to the later-described liquid permeability enhancing
treatment step. However, the surface-crosslinking step is favorably
carried out before the liquid permeability enhancing treatment
step.
[0113] Examples of the surface-crosslinking agent usable for the
surface-crosslinking treatment include: organic
surface-crosslinking agents which have at least two functional
groups reactable with a functional group (particularly, a carboxyl
group) of the water-absorbent resin particles; multivalent metal
compounds; and polycations. Examples thereof include: polyhydric
alcohol compounds (e.g., ethylene glycol, diethylene glycol,
propylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, 1,3-propanediol, dipropylene glycol,
2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol,
polyglycerol, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol,
1,2-cyclohexanol, trimethylolpropane, diethanolamine,
triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block
copolymers, pentaerythritol, and sorbitol); epoxy compounds (e.g.,
ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl
ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether,
polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether,
polypropylene glycol diglycidyl ether, and glycidol); polyamine
compounds (e.g., ethylenediamine, diethylenetriamine,
triethylenetetramine, tetraethylenepentamine,
pentaethylenehexamine, and polyethylenimine) and their inorganic or
organic salts (e.g., azetidinium salts); polyisocyanate compounds
(e.g., 2,4-tolylene diisocyanate and hexamethylene diisocyanate);
polyoxazoline compounds (e.g., 1,2-ethylenebisoxazoline); carbonic
acid derivatives (e.g., urea, thiourea, guanidine, dicyandiamide,
2-oxazolidinone); alkylene carbonate compounds (e.g.,
1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one,
4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one,
4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one,
1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one,
4,6-dimethyl-1,3-dioxan-2-one, and 1,3-dioxopan-2-one); haloepoxy
compounds (e.g., epichlorohydrin, epibromohydrin, and
.quadrature.-methylepichlorohydrin) and their polyamine-added
products (e.g., Kymene (registered trademark) produced by
Hercules); silane coupling agents (e.g.,
.quadrature.-glycidoxypropyltrimethoxysilane and
.quadrature.-aminopropyltriethoxysilane); oxetane compounds (e.g.,
3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol,
3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol,
3-ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol,
3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, and
polyoxetane compounds); and multivalent metal compounds (e.g.,
hydroxides and chlorides of such as zinc, calcium, magnesium,
aluminum, iron and zirconium). These surface-crosslinking agents
may be used either alone respectively or in combinations with each
other. Above all, it is more preferable to use a surface
crosslinking agent which forms a covalent bond with a functional
group (carboxyl group) on the surface of the water-absorbent resin
particles because it can enhances the performance of absorbency
against pressure. The polyhydric alcohols are favorable, because
they are high in safety and can enhance the hydrophilicity of
water-absorbent resin particle surfaces. In addition, the use of
the polyhydric alcohols enhances the affinity of water-absorbent
resin particle surfaces to the multivalent metal particles, so that
interactions between the polyhydric alcohol residue and the
multivalent metal surface enable more uniform existence of the
multivalent metal particles on surfaces of the water-absorbent
resin particles.
[0114] Although depending upon compounds as used, their
combination, and others, the amount of the surface-crosslinking
agent, as used, is favorably in the range of not less than 0.001
and not more than 10 weight parts, more favorably in the range of
not less than 0.01 and not more than 5 weight parts, per 100 weight
parts of the water-absorbent resin.
[0115] Although not especially limited, the method for mixing the
water-absorbent resin particles and the surface-crosslinking agent
together can be exemplified by such as: a method in which the
water-absorbent resin particles are immersed into the hydrophilic
organic solvent and then mixed with the surface-crosslinking agent
that is, if necessary, dissolved in water and/or a hydrophilic
organic solvent; and a method in which the surface-crosslinking
agent that is dissolved in water and/or the hydrophilic organic
solvent is spraywise or dropwise added directly to the
water-absorbent resin particles to mix them together. In addition,
in the case where the surface-crosslinking agent solution is
sprayed, the size of liquid droplets being sprayed is favorably in
the range of 1 to 300 .mu.m, more favorably 2 to 200 .mu.m.
[0116] After the mixing of the water-absorbent resin particles and
the surface-crosslinking agent, usually, a heating treatment is
favorably carried out to conduct the crosslinking reaction.
Depending on the surface-crosslinking agent used, the temperature
of the above heating treatment is favorably in the range of 40 to
250.degree. C., more favorably 150 to 250.degree. C. The duration
of the heating treatment is favorably in the range of 1 minute to 2
hours, more favorably 5 minutes to 1 hour.
[0117] The process herein may include a liquid permeability
enhancing treatment step for subjecting the water-absorbent resin
particles to treatment for liquid permeability enhancement. The
liquid permeability enhancing treatment step may be carried out at
any time of before, simultaneously with, or after the
surface-crosslinking step. However, it is favorable that the liquid
permeability enhancing treatment step is carried out after the
surface-crosslinking step and separately therefrom. The treatment
for liquid permeability enhancement is not particularly limited if
it is treatment for enhancing liquid permeability of the
water-absorbent resin particles. However, the treatment for liquid
permeability enhancement is favorably carried out by adding a
liquid-permeability-enhancing agent, as described above.
[0118] It may be dry-blend, or the liquid-permeability-enhancing
agent may be added in the form of an aqueous solution, or the
addition method may be carried out by heat-fusion. The heat-fusion
is a method in which: the heating is carried out at the same time
as or after mixing the multivalent metal hydrate (e.g., aluminum
sulfate, potassium alum, ammonium alum, sodium alum) and the
water-absorbent resin particles together; or the water-absorbent
resin particles having been preheated are mixed with the
multivalent metal compound; whereby the multivalent metal hydrate
is fused and then made to adhere to the water-absorbent resin
particles. If necessary, water may be added before the heating.
Test Methods Used Herein:
Water Absorption Capacity (CRC: Centrifuge Retention Capacity)
[0119] An amount of 0.200 g of water-absorbent resin or
aqueous-liquid-absorbing agent was uniformly placed into a bag (60
mm.times.60 mm) made of nonwoven fabric (trade name: Heatron Paper,
type: GSP-22, produced by Nangoku Pulp Kogyo Co., Ltd.) and then
immersed into a physiological saline solution (hereinafter the
physiological saline solution all refers to a 0.9 weight % aqueous
sodium chloride solution) of which the temperature had been
adjusted to 25.degree. C. After 30 minutes, the bag was pulled up
and then drained of water by a centrifugal force of 250 G with a
centrifugal separator (produced by Kokusan Co., Ltd., centrifugal
separator: model H-122) for 3 minutes, and then the weight W1 (g)
of the bag was measured. In addition, the same procedure as the
above was carried out without the aqueous-liquid-absorbing agent,
and the resultant weight W0 (g) was measured. Then, the CRC (g/g)
was calculated from these W1 and W0 in accordance with the
following equation:
CRC (g/g)=[(W1 (g)-W0 (g))/weight (g) of water-absorbent
resin]-1
Absorbency Against Pressure (AAP)
[0120] The absorbency against pressure (AAP) refers to absorbency
against pressure for a physiological saline solution (0.9 weight %
aqueous sodium chloride solution) under a load of 4.83 kPa in 60
minutes.
[0121] The measurement was carried out with an apparatus as shown
in FIG. 1.
[0122] A stainless metal gauze 101, which was a screen of 400
meshes (mesh opening size: 38 .mu.m), was fused to a bottom of a
plastic supporting cylinder 100 having an inner diameter of 60 mm.
Then, under conditions of a room temperature (23.0.+-.2.0.degree.
C.) and a humidity of 50 RH %, onto the above metal gauze, there
was uniformly spread 0.90 g of aqueous-liquid-absorbing agent 102,
and further thereon, there were mounted a piston 103 and a load 104
in sequence, wherein the piston had an outer diameter of only a
little smaller than 60 mm and made no gap with the inner wall
surface of the supporting cylinder, but was not hindered from
moving up and down, and wherein the piston and the load were
adjusted so that a load of 4.83 kPa (0.7 psi) could uniformly be
applied to the aqueous-liquid-absorbing agent. Then, the weight Wa
(g) of the resultant one set of measurement apparatus was
measured.
[0123] A glass filter plate 106 having a diameter of 90 mm
(produced by Sogo Rikagaku Glass Seisakusho Co., Ltd., pore
diameter: 100 to 120 .mu.m) was mounted inside a Petri dish 105
having a diameter of 150 mm, and then a physiological saline
solution (0.9 weight % aqueous sodium chloride solution) 108 (20 to
25.degree. C.) was added up to the same level as the upside of the
glass filter plate, on which a filter paper 107 having a diameter
of 90 mm (produced by ADVANTEC Toyo Co., Ltd., trade name: (JIS P
3801, No. 2), thickness: 0.26 mm, diameter of captured particles: 5
.mu.m) was then mounted so that its entire surface would be wetted,
and further, an excess of liquid was removed.
[0124] The one set of measurement apparatus was mounted on the
above wet filter paper, thereby getting the liquid absorbed under
the load for a predetermined duration. This absorption duration was
defined as 1 hour from the start of the measurement. Specifically,
1 hour later, the one set of measurement apparatus was removed by
being lifted to measure its weight Wb (g). This measurement of the
weight must be carried out as quickly as possible and so as not to
give any vibration. Then, the absorbency against pressure (AAP)
(g/g) was calculated from the Wa and Wb in accordance with the
following equation:
AAP (g/g)=[Wb (g)-Wa (g)]/weight (g) of aqueous-liquid-absorbing
agent
Absorption Rate (Modified FSR: Free Swell Rate)
[0125] An amount (unit: g) (WA) (calculated from the
below-mentioned equation (a)) of aqueous-liquid-absorbing agent was
weighed out precisely to the fourth decimal place. This
aqueous-liquid-absorbing agent as weighed out was placed into a 25
ml glass beaker (diameter: 32-34 mm, height: 50 mm), when the
upside of the aqueous-liquid-absorbing agent as placed into the
beaker was made horizontal. If necessary, a treatment such as of
cautiously tapping the beaker may be carried out to make the
surface of the aqueous absorbing agent horizontal. Next, 20 ml of
physiological saline solution (0.9 weight % aqueous sodium chloride
solution), of which the temperature had been adjusted to
23.0.+-.2.0.degree. C., was weighed out into a 50 ml glass beaker,
and then the weight (unit: g) was measured to the fourth decimal
place (W1). Then, the physiological saline solution as weighed out
was carefully and quickly poured into the 25 ml beaker containing
the aqueous-liquid-absorbing agent. The time measurement was
started at the same time as when the poured physiological saline
solution contacted with the aqueous-liquid-absorbing agent. Then,
the upside of the physiological saline solution in the beaker into
which the physiological saline solution had been poured was
observed at an angle of about 20.degree. with the eye. Then, the
time measurement was ended when the upside, which had been the
liquid surface of the physiological saline solution at the start,
had been replaced by the surface of the aqueous-liquid-absorbing
agent (having absorbed the physiological saline solution) as a
result of the absorption of the physiological saline solution into
the aqueous-liquid-absorbing agent (unit: sec) (ts). Next, the
weight (unit: g) of the physiological saline solution, which
remained attaching to the 50 ml beaker after the pouring of the
physiological saline solution, was measured to the fourth decimal
place (W2). The weight (WF, unit: g) of the poured physiological
saline solution was determined from the equation (b) below.
[0126] The water absorption rate (modified FSR) was calculated from
the equation (c) below.
WA (g)=20 (g)/(0.75.times.CRC (g/g)) Equation (a):
WF (g)=W1 (g)-W2 (g) Equation (b):
FSR (g/g/s)=WF/(ts.times.WA) Equation (c):
[0127] The same measurement was carried out repeatedly three times
per one sample. The measurement result was defined as the average
value of the three-time-measured values. Saline flow conductivity
(SFC)
(SFC Measurement Apparatus)
[0128] This measurement is to measure the saline flow conductivity
(SFC) of a gel layer formed in an aqueous-liquid-absorbing agent
which has absorbed the physiological saline solution under load and
thereby swollen.
[0129] This measurement of the saline flow conductivity (SFC) uses
Darcy's law and the stationary-flow method (e.g., refer to
"Absorbency", edited by P. K. Chatteijee, Elsevier 1985, pp. 42-43
and Chemical Engineering, Vol. II, 3rd edition, J. M. Coulson and
J. F. Richarson, Pergamon Press, 1978, pp. 125-127).
[0130] An apparatus favorable for this measurement is illustrated
in FIG. 2. This apparatus has a storage tank (202) of about 5 L in
capacity as put on a laboratory jack (203). The storage tank (202)
has an end-open glass tube and a rubber stopper part (200) which
have been provided thereto in order to obtain a function of keeping
the hydrostatic height constant. To the storage tank (202), there
can be added a liquid by removing a rubber stopper part (201). The
storage tank (202) has an liquid outlet therein below the liquid
surface, and a glass tube (204) having a valve (205) is connected
to this outlet. The liquid feed can be controlled by opening and
closing the valve (205). The glass tube (204) is connected to a
flexible tube (210). The other end of the flexible tube (210) is
set so as to feed a liquid to an SFC instrument (206) as
illustrated in its entirety. The SFC instrument (206) was set on a
support (209) having a stainless wire mesh of 1 mm in mesh opening
size. Under the support (209), there is disposed a collection tank
(207) for liquid collection. The collection tank (207) is disposed
on a balance (208). The balance (208) is wired to a computer so
that the mass of the collected liquid can be taken in every
definite time. Incidentally, in FIG. 2, in order to facilitate the
understanding of this drawing figure, the right-hand apparatus
(e.g., SFC instrument 206, collection tank 207, balance 208,
support 209) is illustrated on a scale enlarged in comparison with
the reduced scale of the left-hand apparatus.
[0131] As to FIG. 3, the SFC instrument basically includes: a
cylinder (214) (obtained by processing LEXANR or its equivalent)
having a stainless wire mesh at the bottom; a piston (212)
(obtained by processing LEXANR or its equivalent); a cover (213)
(obtained by processing LEXANR or its equivalent) having an opening
for insertion of the liquid-feeding tube; and a weight (211). The
piston (212) has a piston head (215) through which holes are made
as illustrated in FIG. 3. The holes of the piston head (215) have
the cylindrical structure which is penetrating in upside and
downside directions of the piston head (215) as illustrated in FIG.
4. On the bottom of the piston head (215), there is stuck a wire
mesh (216) of 400 meshes (mesh opening size: 38 .mu.m) (produced by
Weisse & Eschrich, material: SUS 304, mesh opening width: 0.038
mm, wire diameter: 0.025 mm). The piston head (215) has a diameter
only a little smaller than the inner diameter of the cylinder (214)
and has such a size as allows the piston head (215) to smoothly
migrate inside the cylinder (214) without being hindered from
moving up and down. The top end of the shaft of the piston (212) is
processed so that the weight can be set there. The cylinder (214)
has an inner diameter of 6.00 cm (bottom area 28.27 cm2), a wall
thickness of 0.5 cm, and a height of 6.0 cm. On the bottom of the
cylinder (214), there is stuck a wire mesh (216) of 400 meshes
(mesh opening size: 38 .mu.m) (produced by Weisse & Eschrich,
material: SUS 304, mesh opening width: 0.038 mm, wire diameter:
0.025 mm). The cover (213) has a hole of a size only a little
larger than the external form of the shaft of the piston (212) so
that the shaft of the piston (212) can smoothly migrate without
being hindered from moving up and down. In addition, the cover
(213) has the opening for insertion of the liquid-feeding tube. The
total weight of the weight (211) and the piston (212) is adjusted
so that a load of 2.07 kPa (0.3 psi) can be applied to the bottom
of the cylinder.
(SFC Measurement Method)
[0132] First of all, the height (h0: unit=mm, number of significant
figures=4) and weight (W0: unit=g, number of significant figures=4)
of the SFC instrument, including the cylinder (214), the piston
(212), the cover (213), and the weight (211), were measured before
the aqueous-liquid-absorbing agent was placed into it, in other
words, in an empty state. Next, 3.00.+-.0.05 g of
aqueous-liquid-absorbing agent was weighed out (W: unit=g, number
of significant figures=4). The amount of the
aqueous-liquid-absorbing agent being weighed out is favorably
adjusted so that the below-mentioned "d final" will be in the range
of 10 to 20 mm, more preferably 15 to 20 mm. For example, in the
case where the water absorption capacity (CRC) is in the range of 5
to 16 g/g, the amount of the aqueous-liquid-absorbing agent being
weighed out is adjusted to 3.00.+-.0.05 g. In the case where the
water absorption capacity (CRC) is in the range of above 16 to 20
g/g, the amount of the aqueous-liquid-absorbing agent being weighed
out is adjusted to 2.00.+-.0.03 g. In the case where the water
absorption capacity (CRC) is in the range of above 20 to 25 g/g,
the amount of the aqueous-liquid-absorbing agent being weighed out
is adjusted to 1.60.+-.0.03 g.
[0133] For a secondary aqueous liquid absorbing agent herein that
has a water absorption capacity (CRC) above 25 g/g, the amount of
the secondary aqueous liquid-absorbing agent being weight out is
adjusted to 0.9.+-.0.05 g.
[0134] Note that the amount of the aqueous-liquid-absorbing agent
being weighed out is favorably adjusted so that the below-mentioned
"d final" will be in the above range. The weighed-out
aqueous-liquid-absorbing agent was placed on the entire bottom of
the cylinder (214) so as to carefully and uniformly be dispersed
there. Thereafter, the piston (212), the cover (213), and the
weight (211) are set to measure the height (h1: unit=mm) of the SFC
instrument. Next, a physiological saline solution (0.9 weight %
aqueous sodium chloride solution) was added into a Petri dish of at
least 16 cm in diameter and at least 4 cm in height so that the SFC
instrument could be immersed by at least 3 cm from its bottom. A
filter paper of 90 mm in diameter (filter paper produced by
ADVANTEC Co., Ltd.: No. 2) was laid on the inner bottom of the
Petri dish. The SFC instrument containing the
aqueous-liquid-absorbing agent was mounted on the filter paper to
swell the aqueous-liquid-absorbing agent for 60 minutes. After the
aqueous-liquid-absorbing agent had been swollen for 60 minutes in
this way, the SFC instrument was removed from the Petri dish to
measure the height (h2: unit=mm, number of significant figures=4)
and weight (W2: unit=g, number of significant figures=4) of the SFC
instrument. Thereafter, the SFC instrument was moved and set onto
the support (209) of the SFC measurement apparatus, and the
flexible tube (210) was set into the insertion opening. Next, the
valve (205) was opened to thereby start feeding the liquid. After
this start of the liquid feeding, the hydrostatic height in the
cylinder was adjusted so as to be kept at 5 cm until the amount
(indicated by the balance) of the liquid, having passed through the
gel layer and then been collected, reached about 200 g. This
adjustment may be carried out either by adjusting the height of the
laboratory jack (203) or by adjusting the height of the lower
portion of the glass tube as inserted from the upper portion of the
storage tank (202). When the hydrostatic height in the cylinder had
been adjusted so as to be kept at 5 cm, then the weight data of the
liquid, having passed through the gel layer and then been
collected, started to be taken in by the computer as connected with
the balance. The data intake was carried out every 5 sec until 180
sec. However, if the amount of the collected liquid reached not
smaller than 2 kg within 180 sec after the start of the data
intake, then, at that point of time (e.g., 120 sec), the data
intake was ended. After the end of the data intake, the valve (205)
was quickly closed. Thereafter, when the liquid had almost come not
to flow down from the bottom of the cylinder (214) of the SFC
instrument (when the hydrostatic height in the cylinder (214) had
agreed with the height of the gel layer), the height (h3: unit=mm,
number of significant figures=4) of the SFC instrument was
measured. Thereafter, the SFC instrument was moved onto a
cylindrical instrument (having the same inner diameter as of the
cylinder of the SFC instrument) to drip water off for 30 minutes.
This operation is to put the SFC instrument on the cylindrical
instrument to thereby make the dripping-off of water carried out
favorably in a state where the bottom of the wire mesh, on which
the aqueous-liquid-absorbing agent in the cylinder is disposed, is
not in direct contact with anything. After the dripping-off of
water had been carried out for 30 minutes in the above way, the
height (h4: unit=mm, number of significant figures=4) and weight
(W4: unit=g, number of significant figures=4) of the SFC instrument
were measured.
(Calculation of SFC)
[0135] The data as taken in by the computer were plotted on a graph
by indicating the time t (sec) as the X-axis and the weight (g) of
the collected liquid as the Y-axis. The resultant plots were
approximated to a straight line by the method of least squares, and
then the rate (unit: g/s) of this straight line was determined.
[0136] The SFC was determined from the following equation:
SFC(cm3s10-7/g)=(d
final.times.rate)/(Area.times.Density.times.Pressure).times.10,000,000
[0137] wherein: [0138] Area (cm2)=28.27 [0139] Density
(g/cm3)=1.005 (the density of the 0.9 weight % physiological saline
solution at 20.degree. C. is used) [0140] d final
(cm)={(h2-h0)+(h3-h0)}/2/10
Wet Porosity
[0141] The measurement of the wet porosity is carried out
subsequently to the measurement of the saline flow conductivity
(SFC).
[0142] A five-ply filter paper (10 cm.times.10 cm, produced by
Ahlstrom, Grade: 989) was set on a horizontal experimental stand.
Then, the SFC instrument having been subjected to the dripping-off
of water for 30 minutes was put on the above five-ply filter paper
for 10 minutes. Thereafter, the SFC instrument was moved onto a
separately prepared new five-ply filter paper of the same as the
aforementioned. After 16.+-.2 hours, the height (h5: unit=mm) and
weight (W5: unit=g) of the SFC instrument were measured.
Incidentally, the specifications of the aforementioned filter
papers are described in the EDANA strikethrough test.
[0143] The wet porosity was calculated from the following
equation:
Wet Porosity (unit:
%)=[(W3-W4-0.7)/{h4-h0}.times.28.27]].times.100
Particle Diameters
[0144] Water-absorbent resin particles or aqueous-liquid-absorbing
agents, having been pulverized, were classified with JIS standard
sieves having mesh opening sizes 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, and
45 .mu.m. Then, the percentages R of the residues on these sieves
were plotted on a logarithmic probability paper. Therefrom, the
weight-average particle diameter (D50) was read. Note that in the
case where sizes of the water-absorbent resin particles or
aqueous-liquid-absorbing agents exceed 850 .mu.m, commercial JIS
standard sieves having mesh opening sizes exceeding 850 .mu.m are
used appropriately. Logarithmic standard deviation (.quadrature.
.quadrature.) of particle diameter distribution
[0145] Water-absorbent resin particles or aqueous-liquid-absorbing
agents were classified with JIS standard sieves having mesh opening
sizes 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, and 45 .mu.m. Then, the percentages R
of the residues on these sieves were plotted on a logarithmic
probability paper. Note that in the case where sizes of the
water-absorbent resin particles or aqueous-liquid-absorbing agents
exceed 850 .mu.m, commercial JIS standard sieves having mesh
opening sizes exceeding 850 .mu.m are used appropriately. Thus, if
X1 is defined as a particle diameter when R=84.1 weight %, and if
X2 is defined as a particle diameter when R=15.9 weight %, then the
logarithmic standard deviation (.quadrature. .quadrature.) is shown
by the following equation. The smaller .quadrature. .quadrature.
value shows the narrower particle diameter distribution.
.quadrature. .quadrature.=0.5.times.ln(X2/X1)
[0146] As to the classification method for measuring the particle
diameters and the logarithmic standard deviation (.quadrature.
.quadrature.) of the particle diameter distribution, 10.0 g of
water-absorbent resin particles or aqueous-liquid-absorbing agent
was placed onto JIS standard sieves (having mesh opening sizes 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, and 45 .mu.m) (THE IIDA TESTING SIEVE:
diameter=8 cm) and then classified with a shaking classifier (IIDA
SIEVE SHAKER, TYPE: ES-65 type, SER. No. 0501) for 5 minutes.
Bulk Density
[0147] The bulk density of the water-absorbent resin particles or
aqueous-liquid-absorbing agent was measured by the method as
described in Edana 460.1-99.
Basis Weight
[0148] The basis weight as used herein can be determined with the
"European Disposables and Nonwovens Association" (EDANA) standard
method for Mass per Unit Area (40.3-90).
Caliper
[0149] European Disposables and Nonwovens Association (EDANA)
standard method for Thickness (No 30.5-99) is suitable used herein
to determine the caliper. A suitable apparatus is described in
paragraph 4.1. The specified pressure is 2.1 kPa.
Density
[0150] The density as used herein of a region or layer or core or
article can be determined by divide the basis weight of that
region, layer, core or an article, determined using the Basis
Weight method, by the caliper, determined by the Caliper
method.
Extractable Component Content
[0151] Into a plastic receptacle of 250 ml in capacity having a
lid, 184.3 g of physiological saline solution (0.9 weight % aqueous
sodium chloride solution) was weighed out. Then, 1.00 g of
water-absorbent resin or aqueous-liquid-absorbing agent was added
to this aqueous solution, and they were stirred for 16 hours,
thereby extractable components were extracted from the resin. The
resultant extract liquid was filtrated with a filter paper
(produced by ADVANTEC Toyo Co., Ltd., trade name: (JIS P 3801, No.
2), thickness: 0.26 mm, diameter of captured particles: 5 .mu.m),
and then 50.0 g of the resultant filtrate was weighed out and used
as a measuring solution.
[0152] To begin with, only the physiological saline solution was
firstly titrated with an aqueous 0.1N NaOH solution until the pH
reached 10, and then the resultant solution was titrated with an
aqueous 0.1N HCl solution until the pH reached 2.7, thus obtaining
blank titration amounts ([bNaOH] ml and [bHCl] ml).
[0153] The same titration procedure was carried out also for the
measuring solution, thus obtaining titration amounts ([NaOH] ml and
[HCl] ml).
[0154] For example, if the water-absorbent resin comprised acrylic
acid and its sodium salt in known amounts, the extractable
component content of the water-absorbent resin was calculated from
the average molecular weight of the monomers and the titration
amounts, as obtained from the above procedures, in accordance with
the following equation. In the case of unknown amounts, the average
molecular weight of the monomers was calculated from the
neutralization degree as determined by the titration.
[0155] Extractable component content (weight %)=0.1.times.(average
molecular
weight).times.184.3.times.100.times.([HCl]-[bHCl])/1,000/1.0/50-
.0
Neutralization degree (mol
%)=[1-([NaOH]-[bNaOH])/([HCl]-[bHCl])].times.100
EXAMPLES
Example 1
[0156] In a reactor as formed by lidding a jacketed stainless
twin-arm kneader of 10 liters in capacity having two sigma-type
blades, there was prepared a reaction liquid by dissolving 52.63 g
(0.4 mol %) of polyethylene glycol diacrylate and 18.33 g (0.4 mol
%) of D-sorbitol into 5,367.3 g of aqueous solution of sodium
acrylate having a neutralization degree of 60 mol % (monomer
concentration: about 40 weight %). Next, this reaction liquid was
deaerated under an atmosphere of nitrogen gas for 20 minutes.
Subsequently, 30.19 g of 10 weight % aqueous sodium persulfate
solution and 25.16 g of 0.1 weight % aqueous L-ascorbic acid
solution were added thereto under stirred conditions. As a result,
polymerization started after about 1 minute. Then, the
polymerization was carried out in the range of 20 to 95.degree. C.
while the forming gel was pulverized. Then, the resultant
hydropolymer was got out after 30 minutes from the start of the
polymerization. The resultant hydropolymer was in the form of
divided small pieces having diameters of not larger than about 5
mm.
[0157] The resultant hydropolymer was pulverized and agglomerated
with a screw extruder (produced by Hiraga Kosakusho, Chopper,
MODEL: TB-32, perforation diameter of perforated plate=9.5 mm,
thickness of perforated plate=5.0 mm, number of revolutions of
screw=32.5 rpm), thus obtaining pulverized hydropolymer particles
having been divided into small pieces. Incidentally, the
hydropolymer was supplied at 1300 g/minute.
[0158] The resultant pulverized hydropolymer particles having been
divided into small pieces were spread onto a metal gauze of 50
meshes (opening size: 300 .mu.m) and then dried with hot air of
180.degree. C. for 40 minutes. Next, the dried product was
pulverized with a roll mill and then classified with JIS standard
sieves having a mesh opening size of 600 .mu.m and 150 .mu.m, thus
obtaining a water-absorbent resin (having a solid content of 96
weight parts) of an irregularly pulverized shape, which had a
weight-average particle diameter of 324 .mu.m and a logarithmic
standard deviation (.quadrature. .quadrature.) of 0.32.
[0159] An amount of 500 weight parts of the obtained
water-absorbent resin was placed into Lodige Mixer (produced by
Lodige, type: M5R) and then uniformly spraywise mixed with a
surface-crosslinking agent solution comprising a mixed liquid of
2.4 weight parts of 1,4-butanediol, 3.8 weight parts of propylene
glycol, and 20.0 weight parts of pure water under stirring. Then,
the water-absorbent resin, which had been mixed with the
surface-crosslinking agent solution, was placed into a stainless
reactor (diameter: about 30 cm, height: about 20 cm)
TABLE-US-00001 Aqueous- liquid- Wet Ratio of absorbing SFC CRC FSR
Porosity D50 150 600 .mu.m Examples agents (.times.10-7 cm3 s/g)
(g/g) (g/g/s) (%) (.mu.m) (wt %) 1 (1) 1564 9.1 0.18 41.3 353 98.3
2 (2) 1632 9.2 0.23 41.9 321 98.4
having a stirrer. Then, the reactor was immersed into an oil bath
(of which the temperature had been adjusted to 200.degree. C.) to
carry out heat treatment for surface-crosslinking under stirring
for 35 minutes. After this heat treatment, the resultant
water-absorbent resin was disintegrated to such a degree that it
could pass through a JIS standard sieve having a mesh opening size
of 600 .mu.m. As a result, surface-crosslinked water-absorbent
resin particles were obtained.
[0160] An amount of 100 weight parts of the resultant
surface-crosslinked water-absorbent resin particles was heated to
150.degree. C. and then uniformly mixed with 1.6 weight parts of
potassium alum (potassium aluminum sulfate dodecahydrate) under
stirring for 5 minutes, thus obtaining a primary
aqueous-liquid-absorbing agent (1).
Example 2
[0161] A primary aqueous-liquid-absorbing agent (2) was obtained in
the same way as of Example 1 except that: the perforation diameter
of perforated plate in Example 1 was changed to 6.5 mm. The
physical properties of the primary aqueous-liquid-absorbing agent
(2) are shown in Table 1. Incidentally, the resultant primary
aqueous-liquid-absorbing agent (2) had an extractable component
content of 1.1 weight % and a bulk density of 5.8 g/ml.
Comparative Example 1
[0162] A comparative primary aqueous-liquid-absorbing agent (1) was
obtained in the same way as of Example 1 except that: 52.63 g (0.4
mol %) of polyethylene glycol diacrylate and 18.33 g (0.4 mol %) of
D-sorbitol were replaced with 13.16 g (0.1 mol %) of polyethylene
glycol diacrylate and 13.90 g (0.6 mol %) of glycerine; the
perforation diameter of perforated plate in the screw extruder was
changed to 4.5 mm; and the number of revolutions of screw was
changed to 32.5 rpm.
Comparative Example 2
[0163] A comparative primary aqueous-liquid-absorbing agent (2) was
obtained in the same way as of Example 1 except that: 52.63 g (0.4
mol %) of polyethylene glycol diacrylate and 18.33 g (0.4 mol %) of
D-sorbitol were replaced with 92.11 g (0.7 mol %) of polyethylene
glycol diacrylate alone; the perforation diameter of perforated
plate in the screw extruder was changed to 4.5 mm; the number of
revolutions of screw was changed to 32.5 rpm; a mixture liquid of
2.4 weight parts of 1,4-butanediol, 3.8 weight parts of propylene
glycol, and 20 weight parts of pure water is replaced with a
mixture liquid of 2.3 weight parts of 1,4-butanediol, 4.5 weight
parts of propylene glycol, and 22.5 weight parts of pure water.
TABLE-US-00002 TABLE 2 Comparative aqueous- liquid- Wet Ratio of
Comparative absorbing SFC CRC FSR Porosity D50 150 600 .mu.m
Examples agents (.times.10-7 cm3 s/g) (g/g) (g/g/s) (%) (.mu.m) (wt
%) 1 (1) 953 10.1 0.24 37.3 324 97.5 2 (2) 1000 12.1 0.34 39.0 350
99.9
[0164] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm".
[0165] All documents cited in the Detailed Description of the
Invention are, in relevant part, incorporated herein by reference;
the citation of any document is not to be construed as an admission
that it is prior art with respect to the present invention. To the
extent that any meaning or definition of a term in this written
document conflicts with any meaning or definition of the term in a
document incorporated by reference, the meaning or definition
assigned to the term in this written document shall govern.
[0166] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *