【TECHNICAL FIELD】
Cross-reference to Related Application
This application claims the benefit of Korean Patent Applications No. 10-2020-
0183356 filed on December 24, 2020 and No. 10-2021-0185042 filed on December 22,
2021 with the Korean Intellectual Property Office, the disclosures of which are
incorporated herein by reference in their entirety.
The present disclosure relates to a method for preparing a super absorbent
polymer. More specifically, it relates to a method for preparing a super absorbent
polymer capable of improving drying efficiency, reducing a generation amount of refines, and simultaneously improving absorption performance, in particular, absorption
under pressure and permeability of the finally prepared super absorbent polymer by
controlling granulation strength of the extruded fine reassembly.
【BACKGROUND OF ART】
A super absorbent polymer (SAP) is a type of synthetic polymeric material
capable of absorbing 500 to 1000 times its own weight of moisture. Such super
absorbent polymers started to be practically applied in sanitary products, and they are
now being widely used not only for hygiene products such as disposable diapers for
2
children, etc., but also for water retaining soil products for gardening, water stop
materials for the civil engineering and construction, sheets for raising seedling, freshkeeping agents for food distribution fields, materials for poultices, or the like.
An absorption mechanism of the super absorbent polymer is governed by
interaction of penetration pressure due to the difference in electrical attraction caused
by charges of a polymer electrolyte, affinity between water and a polymer electrolyte,
molecular expansion due to repulsion between polymer electrolyte ions, and inhibition of
expansion due to cross-linking. In other words, water absorbency of the super
absorbent polymer depends on the affinity and molecular expansion, and an absorption
rate is largely dependent on the osmotic pressure of the absorbent polymer itself.
Meanwhile, particles having a particle diameter of 150 ㎛ or less, which are
inevitably generated in the preparation of a super absorbent polymer, are called fines,
and it is known that the fines are generated in an amount of about 20 to 30% in the
pulverization or transfer process during the preparation of a super absorbent polymer.
When such fines are included in the super absorbent polymer, they may cause a
reduction in main physical properties of the super absorbent polymer such as
absorption under pressure or water permeability. For this reason, during the
preparation of a super absorbent polymer, particularly in a classification process, the
fines are separated to produce the super absorbent polymer only with the remaining
polymer particles.
According to one known method, the fines separated in the preparation of the
super absorbent polymer are reassembled into large particles by a reassembly process,
3
and then manufactured and used as a super absorbent polymer. As a representative
method of the reassembly method, there is a method of agglomeration by mixing the
fines with water.
As the amount of water used in the reassembly process of the fines increases,
granulation strength of the fine reassembly is improved. However, when an excess of
water is used, the amount of energy used during a drying process of the fine
reassembly increases, resulting in high costs. Furthermore, if moisture in the fine
reassembly is not sufficiently removed during the drying process, problems such as an
increase in the load on the device for preparing a super absorbent polymer may occur.
Conversely, when the amount of water used in the reassembly process is
reduced, cohesive strength is lowered due to the low moisture content in the
reassembly, and as a result, reassembly is not performed properly and the amount of
re-fines which are reduced again into the fines increases. In addition, there is a
problem in that physical properties such as absorbency of the super absorbent polymer
prepared by the reassembly process are not sufficient. Accordingly, a method of
improving the granulation strength and reducing the amount of re-fines by performing an
additional extrusion process on the fine reassembly having a low moisture content is
being used.
Accordingly, the development of a reassembly process of fines capable of
solving the above-mentioned problems is continuously required.
【DETAILED DESCRIPTION OF THE INVENTION】
4
【Technical Problem】
Accordingly, in the present disclosure, there is provided a method for preparing
a super absorbent polymer capable of improving drying efficiency of the reassembly,
reducing a generation amount of re-fines, and simultaneously improving absorption
performance, in particular, absorption under pressure and permeability of the finally
prepared super absorbent polymer by controlling granulation strength of the extruded
fine reassembly.
【Technical Solution】
According to one embodiment of the present disclosure, there is provided a
method for preparing a super absorbent polymer, including: preparing a hydrogel
polymer by polymerizing a monomer composition comprising a water-soluble ethylenebased unsaturated monomer having at least partially neutralized acidic groups and a
polymerization initiator; drying and pulverizing the hydrogel polymer, and performing
classification into fines having a particle diameter of less than 150 ㎛ and normal
particles having a particle diameter of 150 to 850 ㎛; preparing a fine reassembly by
mixing the fines with water and a polycarboxylic acid-based copolymer, followed by
reassembling; preparing an extruded fine reassembly by extruding the fine reassembly
while adding water, followed by drying, pulverization and classification; and mixing the
extruded fine reassembly with the normal particles, and then performing a surface
cross-linking reaction by adding a surface cross-linking agent; wherein 30 to 80 parts by
5
weight of water are used based on 100 parts by weight of the fines in the preparation of
the fine reassembly, and 15 to 30 parts by weight of water are used based on the fine
reassembly in the preparation of the extruded fine reassembly.
【ADVANTAGEOUS EFFECTS】
The method for preparing a super absorbent polymer according to the present
disclosure can improve drying efficiency of the extruded fine reassembly, reduce a
generation amount of re-fines, and simultaneously improve absorption performance, in
particular, absorption under pressure and permeability of the finally prepared super
absorbent polymer by controlling granulation strength of the extruded fine reassembly
prepared in the preparation of the super absorbent polymer.
【BRIEF DESCRIPTION OF THE DRAWINGS】
FIG. 1 is a graph showing a change in moisture content over time during a
process for drying the extruded fine reassemblies of Example 1 and Comparative
Example 2 in Experimental Example 1.
FIG. 2 is a photograph of the extruded fine reassembly prepared in Example 2
observed with a scanning electron microscope in Experimental Example 4.
FIG. 3 is a photograph of the extruded fine reassembly prepared in Comparative
Example 3 observed with a scanning electron microscope in Experimental Example 4.
【DETAILED DESCRIPTION OF THE EMBODIMENTS】
6
The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of the invention. The singular
forms are intended to include the plural forms as well, unless the context clearly
indicates otherwise. In the present disclosure, the terms “include”, “comprise”, or
“have” specify the presence of stated features, steps, components, or combinations
thereof, but do not preclude the presence or addition of one or more other features,
steps, components, or combinations thereof.
As the present invention can be variously modified and have various forms,
specific embodiments thereof are shown by way of examples and will be described in
detail. However, it is not intended to limit the present invention to the particular form
disclosed and it should be understood that the present invention includes all
modifications, equivalents, and replacements within the idea and technical scope of the
present invention.
Hereinafter, the method for preparing a super absorbent polymer according to a
specific embodiment of the present invention will be described in more detail.
In the present disclosure, fine particles having a particle diameter of a
predetermined particle size or less, i.e., about less than 150 ㎛, are referred to as a
super absorbent polymer fine powder, a SAP fine powder or a fine powder (fines), and
particles having a particle diameter of 150 ㎛ to 850 ㎛ are referred to as normal
particles. The fines may be generated during the polymerization process, the drying
process, or the pulverization step of the dried polymer. When the fines are included in
7
final products, it is difficult to handle, and physical properties may be deteriorated, for
example, gel blocking phenomenon may occur. Therefore, it is preferable to exclude
the fines from the final products, or to reuse the fines to become normal particles. For
example, a reassembly process in which the fines are aggregated to have a normal
particle size may be performed. In general, in order to increase cohesive strength in
the reassembly process, the fines are aggregated in a wet state. If the moisture
content of the fines is increased, cohesive strength of the fines increases, but a
reassembled mass may be generated in the reassembly process, which may cause
problems during operation of the process. If the moisture content is reduced, the
reassembly process is easy, but cohesive strength of the reassembly is not sufficient,
which may cause a generation of re-fines after reassembly. In addition, the fine
reassembly obtained in this way has lower physical properties such as centrifuge
retention capacity (CRC) and absorption under pressure (AUP) than normal particles,
which may lead to a decrease in the quality of the super absorbent polymer.
In addition, an additive such as polyethylene glycol were conventionally added
to reduce the generation of fines. However, when the fine reassembly is prepared by
using such an additive, less water is usually added, which has a problem in that
granulation strength of the fine reassembly is excessively increased.
As a result of the continuous experimentation by the present inventors, the
present invention has the following characteristics: a polycarboxylic acid-based
copolymer is added in the preparation of a fine reassembly, a process for preparing an
extruded fine reassembly by extrusion is further performed on the fine reassembly after
8
the preparation of the fine reassembly, and granulation strength of the prepared
extruded fine reassembly is adjusted by controlling the amount of water input in the
preparation of the fine reassembly and the extruded fine reassembly. And, the present
inventors have confirmed that drying efficiency can be improved during the subsequent
drying process, a generation amount of re-fines can be reduced, and as a result,
absorption performance, particularly absorption under pressure and permeability, of the
finally prepared super absorbent polymer can be improved.
Therefore, according to one embodiment of the present disclosure, it is possible
to provide a fine reassembling process having various process advantages and a
method for preparing a super absorbent polymer to which the reassembling process is
applied, and thus, a super absorbent polymer exhibiting excellent physical properties
can be manufactured.
Specifically, the method for preparing a super absorbent polymer according to
one embodiment of the present disclosure includes the steps of:
preparing a hydrogel polymer by polymerizing a monomer composition
containing a water-soluble ethylene-based unsaturated monomer having at least
partially neutralized acidic groups and a polymerization initiator (step 1);
drying and pulverizing the hydrogel polymer, and performing classification into
fines having a particle diameter of less than 150 ㎛ and normal particles having a
particle diameter of 150 to 850 ㎛ (step 2);
preparing a fine reassembly by mixing the fines with water and a polycarboxylic
9
acid-based copolymer, followed by reassembling (step 3);
preparing an extruded fine reassembly by extruding the fine reassembly while
adding water, followed by drying, pulverization and classification (step 4); and
mixing the extruded fine reassembly with the normal particles, and then
performing a surface cross-linking reaction by adding a surface cross-linking agent (step
5);
wherein 30 to 80 parts by weight of water are used based on 100 parts by
weight of the fines in the preparation of the fine reassembly, and
15 to 30 parts by weight of water are used based on the fine reassembly in the
preparation of the extruded fine reassembly.
Hereinafter, each step will be described in more detail.
The “polymer” in the present disclosure is in a state in which a water-soluble
ethylene-based unsaturated monomer is polymerized, and may include all moisture
content ranges, all particle diameter ranges, all surface cross-linking states, or
processing states. Among the polymers, a polymer having a moisture content of about
40 wt% or more which is in a state after polymerization and before drying may be
referred to as a hydrogel polymer.
The term “super absorbent polymer” refers to the polymer itself, or includes all
the polymers that have been made suitable for commercialization through additional
processes such as surface cross-linking, fine reassembly, drying, pulverization,
classification, etc., depending on the context.
10
In the preparation method according to one embodiment of the present
disclosure, step 1 is a step of preparing a hydrogel polymer.
The hydrogel polymer may be specifically prepared by polymerizing a monomer
composition containing a water-soluble ethylene-based unsaturated monomer having at
least partially neutralized acidic groups and a polymerization initiator.
The water-soluble ethylene-based unsaturated monomer may be any monomer
commonly used in the preparation of a super absorbent polymer. Specifically, the
water-soluble ethylene-based unsaturated monomer may have acidic groups, and some
of the acidic groups may be neutralized by a neutralizing agent.
For example, as the water-soluble ethylene-based unsaturated monomer, at
least one monomer selected from the group consisting of an anionic monomer and a
salt thereof, a nonionic hydrophilic monomer, and an amino-containing unsaturated
monomer and a quaternary compound thereof may be used.
Specifically, as the water-soluble ethylene-based unsaturated monomer, at least
one selected from the group consisting of an anionic monomer of (meth)acrylic acid,
maleic anhydride, fumalic acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic
acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropane sulfonic acid, or 2-
(meth)acrylamide-2-methyl propane sulfonic acid, and a salt thereof; a nonionic
hydrophilic monomer of (meth)acrylamide, N-substituted (meth)acrylate, 2-
hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,
methoxypolyethyleneglycol(meth)acrylate, or polyethyleneglycol(meth)acrylate; and an
11
amino-containing unsaturated monomer of (N,N)-dimethylaminoethyl(meth)acrylate or
(N,N)-dimethylaminopropyl(meth)acrylamide, and a quaternary compound thereof may
be used.
More Specifically, acrylic acid or a salt thereof, for example, acrylic acid or an
alkali metal salt thereof such as sodium salt, may be used. By using the monomer, it
becomes possible to prepare a super absorbent polymer having superior physical
properties.
In addition, the water-soluble ethylene-based unsaturated monomer may be
used by neutralizing some of the acid groups with a neutralizing agent. As such, when
a water-soluble ethylene-based unsaturated monomer having at least partially
neutralized acidic groups is used, the prepared polymer has water retention properties
and absorbs surrounding water to form a hydrogel polymer having a moisture content of
40 wt% or more.
At this time, a basic material such as sodium hydroxide, potassium hydroxide,
ammonium hydroxide, etc. that can neutralize an acidic group in the water-soluble
ethylene-based unsaturated monomer may be used as the neutralizing agent.
In addition, the amount of the neutralizing agent may be appropriately
determined in consideration of the degree of neutralization of the water-soluble
ethylene-based unsaturated monomer or the degree of neutralization in the hydrogel
polymer. For example, a degree of neutralization of the water-soluble ethylene-based
unsaturated monomer may be 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to
12
75 mol%, wherein the degree of neutralization refers to the degree to which the acidic
groups contained in the water-soluble ethylene-based unsaturated monomer are
neutralized by the neutralizing agent. The range of the degree of neutralization may
vary depending on the final physical properties. An excessively high degree of
neutralization causes the neutralized monomers to be precipitated, and thus
polymerization may not readily occur. On the contrary, an excessively low degree of
neutralization not only deteriorates absorbency of the polymer, but also gives the
polymer hard-to-handle properties, such as those of an elastic rubber.
In addition, a concentration of the water-soluble ethylene-based unsaturated
monomer may be about 20 to 60 wt%, or about 40 to 50 wt% based on the monomer
composition containing the raw materials of the super absorbent polymer and the
solvent, and properly controlled in consideration of polymerization time and reaction
conditions. When the concentration of the monomer is excessively low, the yield of the
super absorbent polymer is low and there may be a problem in economic efficiency. In
contrast, when the concentration is excessively high, it may cause problems in
processes in that some of the monomer may be extracted or the pulverization efficiency
of the polymerized hydrogel polymer may be lowered in the pulverization process, and
thus physical properties of the super absorbent polymer may be deteriorated.
In the preparation method according to the present disclosure, the
polymerization initiator is not particularly limited as long as it is generally used in the
preparation of a super absorbent polymer.
Specifically, the polymerization initiator may be an initiator for thermal
13
polymerization or an initiator for photopolymerization by UV radiation according to the
polymerization method. However, even when the photopolymerization method is
applied thereto, a certain amount heat is generated by UV radiation and the like, and
some heat occurs as the polymerization reaction, an exothermal reaction, progresses.
Therefore, the composition may additionally include the thermal polymerization initiator.
The polymerization initiator may be used in an amount of 0.001 to 2 wt% based
on a total weight of the monomer composition. When the concentration of the
polymerization initiator is excessively low, the polymerization rate may become slow,
and a large amount of residual monomers may be extracted from the final product.
Conversely, when the concentration of the polymerization initiator is higher than the
above range, polymer chains forming a network are shortened, so that the content of
extractable components increases and absorption under pressure decreases, thereby
lowering physical properties of the polymer.
More specifically, any compound which can form a radical by light such as UV
rays may be used as the photopolymerization initiator without limitation.
For example, the photopolymerization initiator may be one or more compounds
selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl
alkylketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and αaminoketone. Further, as the specific example of acyl phosphine, diphenyl(2,4,6-
trimethylbenzoyl)-phosphine oxide, or commercial lucirin TPO, namely, 2,4,6-trimethylbenzoyl-trimethyl phosphine oxide, may be used. More various photopolymerization
initiators are well disclosed in “UV Coatings: Basics, Recent Developments and New
14
Application (Elsevier, 2007)” written by Reinhold Schwalm, p 115, and the present
disclosure is not limited thereto.
When the photopolymerization initiator is used, a concentration of the
photopolymerization initiator in the monomer composition may be about 0.01 to about
1.0 wt%. When the concentration of the photopolymerization initiator is excessively
low, the polymerization rate may become slow, and when the concentration is
excessively high, the molecular weight of the super absorbent polymer may become low
and properties may be uneven.
Furthermore, as the thermal polymerization initiator, one or more initiators
selected from the group consisting of a persulfate-based initiator, an azo-based initiator,
hydrogen peroxide, and ascorbic acid may be used. Specifically, sodium persulfate
(Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), and the
like may be used as examples of the persulfate-based initiators; and 2,2-azobis-(2-
amidinopropane)dihydrochloride, 2,2-azobis-(N,Ndimethylene)isobutyramidinedihydrochloride, 2-(carbamoylazo)isobutylonitril, 2,2-
azobis-[2-(2-imidazolin-2-yl)propane]dihydrochloride, 4,4-azobis-(4-cyanovaleric acid),
and the like may be used as examples of azo-based initiators. More various thermal
polymerization initiators are well disclosed in “Principle of Polymerization (Wiley,
1981)” written by Odian, p 203, and the present disclosure is not limited thereto.
When the thermal polymerization initiator is used, a concentration of the thermal
polymerization initiator included in the monomer composition may be 0.001 to 0.5 wt%.
When the concentration of the thermal polymerization initiator is excessively low,
15
additional thermal polymerization hardly occurs and there may be less effect of adding
the thermal polymerization initiator. When the concentration of the thermal
polymerization initiator is excessively high, the molecular weight of the super absorbent
polymer may become low and the properties may be uneven.
In the preparation method according to the present disclosure, the monomer
composition may further include an internal cross-linking agent as a raw material of the
super absorbent polymer.
In addition, the terminology 'internal cross-linking agent' used herein is different
from a surface cross-linking agent for cross-linking the surface of the super absorbent
polymer particles to be described later, and the internal cross-linking agent polymerizes
unsaturated bonds of the water-soluble ethylene-based unsaturated monomers by
cross-linking. The cross-linking in the above step proceeds both on the surface and on
the inside, but when the surface cross-linking process of the super absorbent polymer
particles to be described later is in progress, the surface of the particles of the finally
prepared super absorbent polymer has a structure cross-linked by a surface crosslinking agent, and the inside of the particles has a structure cross-linked by the internal
cross-linking agent.
The internal cross-linking agent may be a cross-linking agent having one or
more ethylene-based unsaturated groups in addition to the functional group which may
react with the water-soluble substituents of the water-soluble ethylene-based
unsaturated monomer; or a cross-linking agent having two or more functional groups
which may react with the water-soluble substituents of the monomer and/or the water-
16
soluble substituents formed by hydrolysis of the monomer.
As the specific example of the internal cross-linking agent, a C8-C12
bisacrylamide, bismethacrylamide, a poly(meth)acrylate of C2-C10 polyol, a
poly(meth)allylether of C2-C10 polyol, or the like may be used. More specifically, one
or more agents selected from the group consisting of N,N′-methylenebis(meth)acrylate,
ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, polyethyleneglycol
diacrylate, polypropyleneoxy(meth)acrylate, glycerin diaciylate, glycerin triacrylate,
trimethylol triacrylate, triallylamine, triarylcyanurate, triallylisocyanate,
polyethyleneglycol, diethyleneglycol, and propyleneglycol may be used.
This internal cross-linking agent may be included at a concentration of 0.01 to
0.5 wt% based on the monomer composition, so that the polymerized polymer can be
cross-linked. The polymer formed using an internal cross-linking agent has a threedimensional network structure in which main chains formed by polymerization of the
water-soluble ethylene-based unsaturated monomers are cross-linked by the internal
cross-linking agent. When the polymer has a three-dimensional network structure,
water retention capacity and absorption under pressure, which are general physical
properties of the super absorbent polymer, can be significantly improved compared to
the case of having a two-dimensional linear structure that is not further cross-linked by
the internal cross-linking agent. However, when the content of the internal crosslinking agent exceeds 0.5 wt%, the internal cross-linking density increases, and thus it
may be difficult to achieve a desired level of water retention capacity.
17
In the preparation method according to the present disclosure, the monomer
composition may further include an additive such as a thickener, a plasticizer, a
preservation stabilizer, and an antioxidant, if necessary.
The raw materials such as the water-soluble ethylene-based unsaturated
monomer, the photopolymerization initiator, the thermal polymerization initiator, the
internal cross-linking agent, and the additive may be prepared in the form of a monomer
composition solution dissolved in a solvent.
At this time, any solvent which can dissolve the components may be used
without limitation, and for example, one or more solvents selected from water, ethanol,
ethyleneglycol, diethyleneglycol, triethyleneglycol, 1,4-butanediol, propyleneglycol,
ethyleneglycol monobutylether, propyleneglycol monomethylether, propyleneglycol
monomethylether acetate, methylethylketone, acetone, methylamylketone,
cyclohexanone, cyclopentanone, diethyleneglycol monomethylether, diethyleneglycol
ethylether, toluene, xylene, butyrolactone, carbitol, methylcellosolve acetate, N,Ndimethylacetamide, and the like may be used.
The solvent may be included in the monomer composition at a residual quantity
except for the above components.
Meanwhile, the method of preparing the hydrogel polymer by thermal
polymerization or photopolymerization of the monomer composition is not particularly
limited if it is a common polymerization method for preparing a super absorbent polymer.
Specifically, the polymerization method is largely divided into the thermal
polymerization and the photopolymerization according to an energy source of the
18
polymerization. In the case of thermal polymerization, it is generally carried out in a
reactor equipped with an agitation spindle, such as a kneader. In the case of
photopolymerization, it may be carried out in a reactor equipped with a movable
conveyor belt. However, the polymerization method is just an example, and the
present disclosure is not limited thereto.
For example, in the reactor equipped with an agitation spindle such as a
kneader, the hydrogel polymer obtained by thermal polymerization by supplying hot air
or heating the reactor may be discharged to a reactor outlet in the form of several
centimeters to several millimeters depending on a shape of the agitation spindle
provided in the reactor. Specifically, a size of the hydrogel polymer obtained may vary
depending on the concentration and injection rate of the monomer composition to be
injected, and a hydrogel polymer having a weight average particle diameter of 2 to 50
mm may be usually obtained.

【CLAIMS】
【Claim 1】
A method for preparing a super absorbent polymer, comprising:
preparing a hydrogel polymer by polymerizing a monomer composition
comprising a water-soluble ethylene-based unsaturated monomer having at least
partially neutralized acidic groups and a polymerization initiator;
drying and pulverizing the hydrogel polymer, and performing classification into
fines having a particle diameter of less than 150 ㎛ and normal particles having a
particle diameter of 150 to 850 ㎛;
preparing a fine reassembly by mixing the fines with water and a polycarboxylic
acid-based copolymer, followed by reassembling;
preparing an extruded fine reassembly by extruding the fine reassembly while
adding water, followed by drying, pulverization and classification; and
mixing the extruded fine reassembly with the normal particles, and then
performing a surface cross-linking reaction by adding a surface cross-linking agent;
wherein 30 to 80 parts by weight of water are used based on 100 parts by
weight of the fines in the preparation of the fine reassembly, and
15 to 30 parts by weight of water are used based on the fine reassembly in the
preparation of the extruded fine reassembly.
61
【Claim 2】
The method for preparing a super absorbent polymer of Claim 1,
wherein a total amount of water used in the preparation of the fine reassembly
and the extruded fine reassembly is smaller than a total weight of the fines used in the
preparation of the fine reassembly.
【Claim 3】
The method for preparing a super absorbent polymer of Claim 1,
wherein the polycarboxylic acid-based copolymer is a copolymer comprising at
least one of a repeating unit represented by the following Chemical Formula 1-a and a
repeating unit represented by the following Chemical Formula 1-b:
[Chemical Formula 1-a]
[Chemical Formula 1-b]
62
wherein, in the Chemical Formulae 1-a and 1-b,
R1
, R2 and R3 are each independently hydrogen or a C1 to C6 alkyl group,
RO is a C2 to C4 oxyalkylene group,
M1
is hydrogen, or a monovalent metal or non-metal ion,
X is -COO-, a C1 to C5 alkyloxy group, or a C1 to C5 alkyldioxy group,
m is an integer of 1 to 100,
n is an integer of 1 to 1000, and
p is an integer of 1 to 150, and when p is 2 or more, two or more repeating -ROare the same as or different from each other.
【Claim 4】
The method for preparing a super absorbent polymer of Claim 1,
wherein the polycarboxylic acid-based copolymer is a copolymer comprising a
repeating unit derived from methoxy polyethylene glycol monomethacrylate and a
repeating unit derived from (meth)acrylic acid.
63
【Claim 5】
The method for preparing a super absorbent polymer of Claim 1,
wherein the polycarboxylic acid-based copolymer has a weight average
molecular weight of 500 to 1,000,000 g/mol.
【Claim 6】
The method for preparing a super absorbent polymer of Claim 1,
wherein the polycarboxylic acid-based copolymer is added in an amount of 0.01
to 5 parts by weight based on 100 parts by weight of the fines.
【Claim 7】
The method for preparing a super absorbent polymer of Claim 1,
wherein the mixing of the fines with water and the polycarboxylic acid-based
copolymer is performed at a mixing speed of 300 to 2000 rpm.
【Claim 8】
The method for preparing a super absorbent polymer of Claim 1,
wherein the extrusion is performed at a speed of 80 to 150 rpm using an
extruder provided with an outlet having a hole diameter of 10 to 20 mm.
64
【Claim 9】
The method for preparing a super absorbent polymer of Claim 1,
wherein the drying is performed at a temperature of 120 to 220 ℃ for 30 to 120
minutes in the preparation of the extruded fine reassembly.
【Claim 10】
The method for preparing a super absorbent polymer of Claim 1,
wherein an amount of re-fines having a particle diameter of less than 150 ㎛
based on a total weight of the extruded fine reassembly is 20 wt% or less in the
preparation of the extruded fine reassembly.
【Claim 11】
The method for preparing a super absorbent polymer of Claim 1,
wherein the extruded fine reassembly satisfies the following conditions of a1) to
a3):
a1) moisture content: 1 to 5 wt% based on a total weight of the extruded fine
reassembly,
a2) centrifuge retention capacity measured according to EDANA WSP 241.3: 30
to 50 g/g, and
a3) absorption rate according to JIS K 7224: 30 to 50 seconds.
65
【Claim 12】
The method for preparing a super absorbent polymer of Claim 1,
wherein the extruded fine reassembly and the normal particles are mixed in a
weight ratio of 10:90 to 90:10.
【Claim 13】
The method for preparing a super absorbent polymer of Claim 1,
wherein the super absorbent polymer satisfies the following conditions of b1) to
b4):
b1) centrifuge retention capacity measured according to EDANA WSP 241.3: 30
to 40 g/g,
b2) absorption under pressure of the super absorbent polymer to 0.9 wt%
aqueous solution of sodium chloride at 0.7 psi for 1 hour measured according to
EDANA WSP 242.3: 17 to 25 g/g;
b3) permeability: 20 to 400 seconds, and
b4) absorption rate according to JIS K 7224: 40 to 60 seconds.