【TECHNICAL FIELD】
Cross-reference to Related Application(s)
This application claims the benefit of Korean Patent Applications No.
10-2020-0117132 filed on September 11, 2020 and No. 10-2021-0120214 filed on
September 9, 2021 with the Korean Intellectual Property Office, the disclosures of
10 which are incorporated herein by reference in their entirety.
The present disclosure relates to a super absorbent polymer, and a
preparation method thereof. More specifically, it relates to a super absorbent
polymer prepared such that agglomeration between polymer particles is suppressed,
15 and drying efficiency and uniformity of particle size distribution are improved by
including a carboxylic acid-based additive having a specific structure and
hydrophobic particles.
【BACKGROUND OF ART】
A super absorbent polymer (SAP) is a type of synthetic polymeric material
20 capable of absorbing 500 to 1000 times its own weight of moisture. Various
manufacturers have denominated it with different names, such as SAM (Super
Absorbency Material), AGM (Absorbent Gel Material), and the like. Such super
absorbent polymers started to be practically applied in sanitary products, and they
are now being widely used not only for hygiene products, but also for water retaining
25 soil products for gardening, water stop materials for the civil engineering and
construction, sheets for raising seedling, fresh-keeping agents for food distribution
fields, materials for poultices, or the like.
These super absorbent polymers have been widely used in the field of
hygienic materials such as diapers or sanitary napkins. In such hygienic materials,
30 the super absorbent polymer is generally contained in a state of being spread in the
2
pulp. In recent years, however, continuous efforts have been made to provide
hygienic materials such as diapers having a thinner thickness. As a part of such
efforts, the development of so-called pulpless diapers and the like in which the pulp
content is reduced or pulp is not used at all is being actively advanced.
5 As described above, in the case of hygienic materials in which the pulp
content is reduced or the pulp is not used, a super absorbent polymer is contained at
a relatively high ratio and these super absorbent polymer particles are inevitably
contained in multiple layers in the hygienic materials. In order for the whole super
absorbent polymer particles contained in the multiple layers to more efficiently
10 absorb a large amount of liquid such as urine, it is necessary for the super absorbent
polymer to basically exhibit high absorption performance as well as fast absorption
rate.
Meanwhile, such a super absorbent polymer is generally prepared by the
method including a step of polymerizing a monomer to prepare a hydrogel polymer
15 containing a large amount of moisture, and a step of drying the hydrogel polymer,
and then pulverizing the dried hydrogel polymer into polymer particles having a
desired particle diameter. Representative examples thereof include a method of
aqueous polymerization of neutralized acrylic acid, cutting with a twin-arm kneader,
and drying with hot air; a method of aqueous polymerization of neutralized acrylic
20 acid, cutting the hydrogel with a cutter, and drying the thin film with hot air or a
drum-type dryer; a method of aqueous polymerization of neutralized acrylic acid,
neutralizing and cutting the hydrogel polymer with a cutter, and drying the thin film
with hot air or a drum-type dryer; a method in which a high-concentration aqueous
solution of acrylate is polymerized while removing the moisture generated during
25 polymerization, followed by drying the polymerization gel while heating; and a
method in which neutralized acrylic acid is polymerized by reverse-phase
suspension polymerization, and then, if necessary, a solvent and water are removed
by heating under reduced pressure.
Particularly, in the case of drying with hot air or a drum-type dryer, since the
30 hydrogel polymer has adhesiveness, a phenomenon in which the hydrogel polymers
3
pulverized during drying adhere to each other occurs, so ventilation of hot air for
drying may be deteriorated, thereby lowering drying efficiency.
Accordingly, there is a continuous demand for the development of a
technology capable of manufacturing a super absorbent polymer with improved
5 drying efficiency by preventing agglomeration between hydrogel polymers, in
addition to improving water retention capacity (CRC) representing basic absorption
performance and water-retaining capacity of the super absorbent polymer, and
absorbency under pressure (AUP) representing a property of retaining absorbed
liquid even under external pressure.
10
【DETAILED DESCRIPTION OF THE INVENTION】
【Technical Problem】
The present disclosure specifically relates to a super absorbent polymer
prepared such that agglomeration between pulverized particles is suppressed, and
15 drying efficiency and uniformity of particle size distribution are improved by including
a carboxylic acid-based additive having a specific structure and hydrophobic
particles before drying the hydrogel polymer, and a preparation method thereof.
【Technical Solution】
20 In order to solve the above problems, there is provided a super absorbent
polymer including
super absorbent polymer particles containing a cross-linked polymer of a
water-soluble ethylene-based unsaturated monomer having at least partially
neutralized acidic groups and a cross-linking agent;
25 hydrophobic particles; and
a carboxylic acid-based additive,
wherein the carboxylic acid-based additive is at least one selected from the
group consisting of a carboxylic acid represented by the following Chemical Formula
1 and a salt thereof:
30 [Chemical Formula 1]
4
in Chemical Formula 1,
A is alkyl having 5 to 21 carbon atoms,
EO is ethylene oxide (-CH2CH2O-),
5 m is an integer of 0 to 8,
B1 is -OCO-, -COO-, or -COOCH(R1)COO-,
wherein R1 is alkyl having 1 to 5 carbon atoms,
B2 is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon
atoms, or alkynylene having 2 to 5 carbon atoms,
10 n is an integer of 1 to 3, and
C is a carboxyl group.
In addition, there is provided a preparation method of a super absorbent
polymer including
15 a first step of forming a hydrogel polymer by cross-linking polymerization of
a water-soluble ethylene-based unsaturated monomer having at least partially
neutralized acidic groups in the presence of a cross-linking agent and a
polymerization initiator;
a second step of mixing the hydrogel polymer with a carboxylic acid-based
20 additive, followed by pulverization;
a third step of mixing the pulverized product prepared in the second step
with hydrophobic particles; and
a fourth step of drying the mixture prepared in the third step,
wherein the carboxylic acid-based additive is at least one selected from the
25 group consisting of a carboxylic acid represented by the Chemical Formula 1 and a
salt thereof.
【ADVANTAGEOUS EFFECTS】
According to the super absorbent polymer of the present disclosure, drying
5
efficiency and uniformity of particle size distribution may be improved by
simultaneously including the carboxylic acid-based additive and the hydrophobic
particles, thereby exhibiting improved absorption performance. In addition, the
super absorbent polymer is pulverized in the presence of the carboxylic acid-based
5 additive, and thus can be pulverized to a desired particle diameter without
re-agglomeration between pulverized particles. Further, the super absorbent
polymer is dried in the presence of the hydrophobic particles to prevent
re-agglomeration between the particles in the drying process, so that the content of
large powder included after the drying process can be significantly reduced.
10
【BRIEF DESCRIPTION OF THE DRAWINGS】
FIG. 1 shows an SEM image of the surface of super absorbent polymer
particles prepared in Example 1.
FIG. 2 shows an SEM image of the surface of super absorbent polymer
15 particles prepared in Example 2.
FIG. 3 shows an SEM image of the surface of super absorbent polymer
particles prepared in Example 3.
FIG. 4 shows an SEM image of the surface of super absorbent polymer
particles prepared in Example 4.
20 FIG. 5 shows an SEM image of the surface of super absorbent polymer
particles prepared in Comparative Example 1.
【DETAILED DESCRIPTION OF THE EMBODIMENTS】
The terminology used herein is for the purpose of describing particular
25 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. It will be further understood that the terms “include”, “have”, or
“possess” when used in this specification, specify the presence of stated features,
steps, components, or combinations thereof, but do not preclude the presence or
30 addition of one or more other features, steps, components, or combinations thereof.
6
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
5 modifications, equivalents, and replacements within the idea and technical scope of
the present invention.
Hereinafter, the super absorbent polymer and the preparation method of the
same will be described in more detail according to specific embodiments of the
present invention.
10 The terminologies are used merely to refer to specific embodiments, and
are not intended to restrict the present disclosure unless it is explicitly expressed.
Singular expressions of the present disclosure may include plural expressions unless
they are differently expressed contextually.
15 The terminology “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, or all particle diameter ranges. Among the
polymers, a polymer having a moisture content of about 40 wt% or more after
polymerization and before drying may be referred to as a hydrogel polymer, and
20 particles in which the hydrogel polymer is pulverized and dried may be referred to as
a cross-linked polymer.
In addition, the terminology "super absorbent polymer particle" refers to a
particulate material containing a cross-linked polymer in which a water-soluble
ethylene-based unsaturated monomer having at least partially neutralized acidic
25 groups is polymerized and cross-linked by an internal cross-linking agent.
In addition, the terminology "super absorbent polymer" is used to
encompass all of a cross-linked polymer in which a water-soluble ethylene-based
unsaturated monomer having at least partially neutralized acidic groups is
polymerized or a base resin in the form of powder consisting of super absorbent
30 polymer particles in which the cross-linked polymer is pulverized, and the
7
cross-linked polymer or the base resin further processed, for example, surface
cross-linking, fine powder reassembly, drying, pulverization, classification, etc., to be
in a state suitable for commercialization, depending on the context. Accordingly,
the terminology "super absorbent polymer" may be interpreted as including a
5 plurality of super absorbent polymer particles.
In addition, the terminology “large powder” refers to particles having a
particle diameter greater than about 850 ㎛, and the terminology “fine powder” refers
to particles having a particle diameter of less than about 150 ㎛, and they may be
measured in accordance with EDANA (European Disposables and Nonwovens
10 Association) WSP 220.3.
When the dried polymer was pulverized in the pulverizing step essentially
required preparing super absorbent polymer particles having a desired particle
diameter during the manufacturing process of the super absorbent polymer, a large
15 amount of fine powder was generated, which deteriorated physical properties.
However, a non-dried hydrogel polymer could be coarse-pulverized to have a
particle diameter of approximately 1 to 10 mm, but it was impossible to pulverize the
non-dried hydrogel polymer to have a particle diameter of less than 1 mm due to
agglomeration of pulverized particles.
20
In addition, in the process of drying the coarsely pulverized hydrogel
polymer, agglomeration of the pulverized particles exhibiting adhesiveness occurs,
and accordingly, hot air cannot sufficiently pass between the hydrogel polymers. As
a result, some of the polymer becomes in an uneven dry state, making it difficult to
25 pulverize the super absorbent polymer particles to have a uniform particle size
distribution in the subsequent pulverization process, and some of the polymer
becomes overheated, causing a problem in that absorption performance of the super
absorbent polymer particles is finally deteriorated.
30 Therefore, the present inventors have confirmed that pulverizing the
8
hydrogel polymer in the presence of the carboxylic acid-based additive can be
performed such that pulverized particles have a desired particle diameter without
agglomeration, and additionally adding hydrophobic particles before the drying
process not only prevents re-agglomeration during drying, but also increases drying
5 efficiency, so that a super absorbent polymer with a uniform particle size distribution
and a significantly reduced content of large powder after the drying process can be
prepared, thereby completing the present invention. In particular, the super
absorbent polymer has a relatively uniform particle size distribution of the produced
super absorbent particles (base resin) compared to the case in which the carboxylic
10 acid-based additive and the hydrophobic particles are not included. Accordingly,
the efficiency of surface cross-linking and post-processing of the particles after
drying is increased, and when applied as a diaper absorbent, physical properties
such as absorption performance (CRC, AUP) and moisture blocking resistance are
superior and reproducible.

【Claim 1】
A super absorbent polymer comprising
super absorbent polymer particles containing a cross-linked polymer of a
5 water-soluble ethylene-based unsaturated monomer having at least partially
neutralized acidic groups and a cross-linking agent;
hydrophobic particles; and
a carboxylic acid-based additive,
wherein the carboxylic acid-based additive is at least one selected from the
10 group consisting of a carboxylic acid represented by the following Chemical Formula
1 and a salt thereof:
[Chemical Formula 1]
in Chemical Formula 1,
15 A is alkyl having 5 to 21 carbon atoms,
EO is ethylene oxide (-CH2CH2O-),
m is an integer of 0 to 8,
B1 is -OCO-, -COO-, or -COOCH(R1)COO-,
wherein R1 is alkyl having 1 to 5 carbon atoms,
20 B2 is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon
atoms, or alkynylene having 2 to 5 carbon atoms,
n is an integer of 1 to 3, and
C is a carboxyl group.
25 【Claim 2】
The super absorbent polymer of Claim 1,
wherein at least some of the hydrophobic particles are present on a surface
of the super absorbent polymer particles.
59
【Claim 3】
The super absorbent polymer of Claim 1,
wherein the hydrophobic particles are at least one selected from the group
consisting of hydrophobic silicone resin particles, hydrophobic silica particles and
5 hydrophobic clay particles.
【Claim 4】
The super absorbent polymer of Claim 3,
wherein the hydrophobic silicone resin is polyorganosilsesquioxane.
10
【Claim 5】
The super absorbent polymer of Claim 3,
wherein the hydrophobic silica is fumed silica surface-modified by a surface
treatment agent selected from the group consisting of dimethyldichlorosilane (DDS),
15 polydimethylsiloxane (PDMS) and hexamethyldisilazane (HMDS).
【Claim 6】
The super absorbent polymer of Claim 3,
wherein the hydrophobic clay is at least one selected from the group
20 consisting of kaolin, sericite, pyrophyllite, montmorillonite, bentonite and acid clay.
【Claim 7】
The super absorbent polymer of Claim 1,
wherein in Chemical Formula 1,
25 A is -C6H13, -C11H23, -C12H25, -C17H35, or -C18H37.
【Claim 8】
The super absorbent polymer of Claim 1,
wherein in Chemical Formula 1,
60
B1 is , or ,
wherein * is a bonding site with a neighboring atom.
【Claim 9】
5 The super absorbent polymer of Claim 1,
wherein in Chemical Formula 1,
B2 is , , , or
,
wherein * is a bonding site with a neighboring atom.
10
【Claim 10】
The super absorbent polymer of Claim 1,
wherein the carboxylic acid-based additive is at least one selected from the
group consisting of a carboxylic acid represented by the Chemical Formula 1, an
15 alkali metal salt thereof, and an alkaline earth metal salt thereof.
【Claim 11】
The super absorbent polymer of Claim 1,
wherein the carboxylic acid-based additive is any one of compounds
20 represented by the following Chemical Formulae 1-1 to 1-9:
61
5 .
【Claim 12】
A preparation method of a super absorbent polymer, comprising
a first step of forming a hydrogel polymer by cross-linking polymerization of
a water-soluble ethylene-based unsaturated monomer having at least partially
10 neutralized acidic groups in the presence of a cross-linking agent and a
polymerization initiator;
62
a second step of mixing the hydrogel polymer with a carboxylic acid-based
additive, followed by pulverization;
a third step of mixing the pulverized product prepared in the second step
with hydrophobic particles; and
5 a fourth step of drying the mixture prepared in the third step,
wherein the carboxylic acid-based additive is at least one selected from the
group consisting of a carboxylic acid represented by the following Chemical Formula
1 and a salt thereof:
[Chemical Formula 1]
10
in Chemical Formula 1,
A is alkyl having 5 to 21 carbon atoms,
EO is ethylene oxide (-CH2CH2O-),
m is an integer of 0 to 8,
15 B1 is -OCO-, -COO-, or -COOCH(R1)COO-,
wherein R1 is alkyl having 1 to 5 carbon atoms,
B2 is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon
atoms, or alkynylene having 2 to 5 carbon atoms,
n is an integer of 1 to 3, and
20 C is a carboxyl group.
【Claim 13】
The preparation method of a super absorbent polymer of Claim 12,
wherein the carboxylic acid-based additive is used in an amount of 0.01 to
25 10 parts by weight based on 100 parts by weight of the water-soluble ethylene-based
unsaturated monomer.
【Claim 14】
The preparation method of a super absorbent polymer of Claim 12,
63
wherein the carboxylic acid-based additive is mixed in the form of a solution
dissolved in a solvent.
【Claim 15】
5 The preparation method of a super absorbent polymer of Claim 12,
wherein the hydrophobic particles are used in an amount of 0.1 to 10 parts
by weight based on 100 parts by weight of the hydrogel polymer.
【Claim 16】
10 The preparation method of a super absorbent polymer of Claim 12,
wherein the hydrophobic particles are dry-mixed.
【Claim 17】
The preparation method of a super absorbent polymer of Claim 12,
15 wherein the prepared super absorbent polymer contains less than 40 wt%
of large powder having a particle diameter of greater than 850 ㎛ based on a total
weight.