【TECHNICAL FIELD】
Cross-reference to Related Application(s)
This application claims the benefit of Korean Patent Applications No.
10-2020-0162890 filed on November 27, 2020 and No. 10-2021-0152460 filed on
November 8, 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 of the same. More specifically, it relates to a super absorbent
polymer having a reduced extractable content without deterioration in absorption
15 performance, and to a preparation method of the super absorbent polymer capable
of producing the above-described super absorbent polymer.
【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. Various
20 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
soil products for gardening, water stop materials for the civil engineering and
25 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,
the super absorbent polymer is generally contained in a state of being spread in the
30 pulp. In recent years, however, continuous efforts have been made to provide
2
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.
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 5 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
absorb a large amount of liquid such as urine, it is necessary for the super absorbent
10 polymer to exhibit high absorption performance as well as fast absorption rate.
Further, the super absorbent polymer should not release the absorbed liquid even
under external pressure, and additionally it should well retain the shape even in a
state where the volume is expanded (swelled) by absorbing liquid, thereby exhibiting
excellent permeability.
15 The super absorbent polymer includes a plurality of hydrophilic moieties on
its surface in order to exhibit high absorption properties for liquids, specifically water.
Therefore, when exposed to air, agglomeration and caking between the super
absorbent polymer particles have occurred by absorbing moisture contained in the
air.
20 Accordingly, there is a continuous demand for the development of a super
absorbent polymer having improved permeability without reducing the absorption
rate while preventing the caking phenomenon between super absorbent polymer
particles, in addition to the improvement of centrifuge retention capacity (CRC) and
absorbency under pressure (AUP), which are physical properties indicating basic
25 absorbency and water retention capacity of the super absorbent polymer.
【DETAILED DESCRIPTION OF THE INVENTION】
【Technical Problem】
Accordingly, the present disclosure relates to a preparation method of a
30 super absorbent polymer with improved permeability and anti-caking efficiency while
3
having a high absorption rate by polymerizing a monomer in the presence of an
encapsulated foaming agent, and adding an additive having a specific structure to
the hydrogel polymer, followed by coarse pulverization.
【Technical Solution】
In order to solve the above problems, according to one 5 embodiment of the
present disclosure, there is provided a super absorbent polymer including
super absorbent polymer particles comprising a cross-linked polymer of a
water-soluble ethylene-based unsaturated monomer having at least partially
neutralized acidic groups and an internal cross-linking agent; and
10 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, and
the super absorbent polymer satisfies the following physical properties of
15 1) an extractable content measured after swelling the super absorbent
polymer for 1 hour according to EDANA WSP 270.2 is 4 wt% or less based on a total
weight of the super absorbent polymer; and
2) BPI (Base Polymer Index) calculated according to the following Equation
1 is 31 or more:
20 [Chemical Formula 1]
in Chemical Formula 1,
A is C5 to C21 alkyl,
B1 is -OCO-, -COO-, or -COOCH(R1)COO-,
25 B2 is -CH2-, -CH2CH2-, -CH(R2)-, -CH=CH-, or -C≡C-,
wherein R1 and R2 are each independently C1 to C4 alkyl,
n is an integer of 1 to 3, and
C is a carboxyl group,
[Equation 1]
4
in Equation 1,
CRC is centrifuge retention capacity measured according to the EDANA
5 WSP 241.3, and
ln (extractable content) is a natural log value of the extractable content.
In addition, there is provided a preparation method of a super absorbent
polymer including
10 a 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 an internal cross-linking agent, an
encapsulated foaming agent, a carboxylic acid-based additive and a polymerization
initiator (Step 1); and
15 a step of drying and pulverizing the hydrogel polymer (Step 2),
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 and a
salt thereof.
20 【ADVANTAGEOUS EFFECTS】
According to the super absorbent polymer and the preparation method
thereof of the present disclosure, the extractable content can be reduced without
deterioration in absorption performance of the super absorbent polymer by including
a carboxylic acid-based additive having a specific structure. In addition, such a
25 carboxylic acid-based additive may be added together with a foaming agent in the
polymerization step to significantly reduce surface tackiness of the hydrogel polymer.
Accordingly, tearing of the polymer is prevented in the chopping step of the hydrogel
polymer, so that the extractable content of the finally prepared super absorbent
polymer is reduced and the absorption performance may not be deteriorated.
5
【DETAILED DESCRIPTION OF THE EMBODIMENTS】
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, 5 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
addition of one or more other features, steps, components, or combinations thereof.
10 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
15 the present invention.
Hereinafter, the preparation method of a super absorbent polymer and the
super absorbent polymer will be described in more detail according to specific
embodiments of the present invention.
The terminologies are used merely to refer to specific embodiments, and
20 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.
The terminology “polymer” in the present disclosure is in a state in which a
25 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 30 wt% or more after
polymerization and before drying may be referred to as a hydrogel polymer, and
particles in which the hydrogel polymer is pulverized and dried may be referred to as
30 a cross-linked polymer.
6
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
groups is polymerized and cross-linked by an internal cross-linking agent.
In addition, the terminology "super absorbent 5 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
polymer particles in which the cross-linked polymer is pulverized, and the
10 cross-linked polymer or the base resin further processed, for example, drying,
pulverization, classification, surface cross-linking, etc., to be in a state suitable for
commercialization, depending on the context. Accordingly, the terminology "super
absorbent polymer " may be interpreted as encompassing a composition including a
super absorbent polymer, that is, a plurality of super absorbent polymer particles.
15 In addition, the terminology "normal super absorbent polymer particles"
refers to particles having a particle diameter of 150 ㎛ to 850 ㎛ among super
absorbent polymer particles.
In addition, the terminology "fine powder" refers to particles having a
particle diameter of less than 150 ㎛ among super absorbent polymer particles.
20 In addition, the terminology "chopping" refers to cutting the hydrogel
polymer into small pieces to increase drying efficiency, and is used separately from
pulverization to a normal particle size.
Super absorbent polymers are conventionally prepared by drying a
25 hydrogel polymer obtained by polymerizing monomers and then pulverizing it to a
desired particle size. At this time, in order to facilitate drying of the hydrogel
polymer and increase an efficiency of the pulverization process, a process of
chopping or cutting the hydrogel polymer is performed before the drying process.
However, since the surface of the generally prepared hydrogel polymer is sticky, it is
30 difficult to perform the chopping to a uniform size, so that there has been a problem
7
that the efficiency of chopping is reduced and tearing of the polymer occurs in the
chopping step. In particular, in order to improve the absorption rate by increasing
the specific surface area of the super absorbent polymer, a foaming agent was used
together during polymerization. In this case, since the light was not sufficiently
irradiated to the inside of the monomer composition by 5 the foaming agent, the
tackiness of the hydrogel polymer was increased due to some of the monomer that
did not undergo polymerization, which became a further problem.
Moreover, the polymer adhered to a part of the polymerizer belt due to the
surface tackiness of the hydrogel polymer, and accordingly, polymerization occurred
10 unevenly due to the residue remaining on the part of the polymerizer belt, which also
caused a problem that the polymerizer had to be maintained more frequently.
In the case of the super absorbent polymer produced with the tearing of the
polymer in the chopping step, the polymer structure of some cross-linked polymers
could not be maintained after polymerization, so that the extractable content of the
15 final super absorbent polymer was increased, and general physical properties such
as water retention capacity could also be lowered.
Accordingly, the present inventors have completed the present invention by
confirming that when a carboxylic acid-based additive having a specific structure is
20 included, the extractable content can be reduced without deterioration in the
absorption performance of the super absorbent polymer. In particular, when the
carboxylic acid-based additive is added together with a foaming agent in the
polymerization step, the carboxylic acid-based additive is adsorbed to the inside
and/or surface of the polymerized hydrogel polymer without participating in the
25 polymerization reaction, and the carboxylic acid-based additive adsorbed on the
surface may impart hydrophobicity to the surface of the hydrogel polymer.
Accordingly, the surface tackiness of the hydrogel polymer can be significantly
reduced, and tearing of the polymer in the chopping step is prevented, so that the
extractable content of the final super absorbent polymer is reduced without
30 deterioration in absorption performance.
8
Herein, the carboxylic acid-based additive added to the hydrogel polymer is
at least one compound selected from the group consisting of the carboxylic acid
represented by the Chemical Formula 1 and a salt thereof, and has a hydrophobic
functional group and a hydrophilic functional group at the 5 same time. Meanwhile,
since the water-soluble ethylene-based unsaturated monomer contains an acidic
group (-COOH) and/or a neutralized acidic group (-COO-), a large amount of
hydrophilic moiety is present on a surface of the hydrogel polymer prepared by
polymerization due to the acidic group (-COOH) and/or the neutralized acidic group
10 (-COO-) remaining without participating in polymerization. Therefore, a hydrophilic
functional group of the additive is adsorbed to at least some part of the hydrophilic
moiety present on the surface of the hydrogel polymer, and the surface of the
polymer to which the additive is adsorbed becomes hydrophobic by a hydrophobic
functional group located at the other end of the additive. Accordingly, the surface of
15 the hydrogel polymer may exhibit hydrophobicity, thereby reducing the surface
tackiness.
More specifically, in the carboxylic acid-based additive, the hydrophobic
functional group is a C5 to C21 alkyl group (part A), and the hydrophilic functional
group is part C, specifically, a carboxyl group (COOH) or a carboxylate group
20 (-COO-) in the case of a salt. The hydrophobic functional group and the hydrophilic
functional group are respectively located at both ends of the additive. In particular,
the carboxylic acid-based additive further includes part (B1-B2) in addition to part A
and part C at both ends, and the part (B1-B2) improves adsorption performance with
respect to the polymer surface, which may be insufficient only with the part C.
25 Accordingly, the additive having the structure of Chemical Formula 1 has excellent
adsorption performance with respect to the polymer surface exhibiting hydrophilicity
compared to the compound having an A-C structure without the part (B1-B2).
Further, the compound having an A-C structure without the part (B1-B2)
does not exhibit hydrophilicity enough to be dissolved in the monomer composition in
30 which the solvent is water, and thus cannot be added to the monomer composition.
9
Hereinafter, the super absorbent polymer and the preparation method of the
same according to an exemplary embodiment will be described in more detail.
5 Super absorbent polymer
According to one embodiment of the present disclosure, there is provided a
super absorbent polymer including
super absorbent polymer particles comprising a cross-linked polymer of a
water-soluble ethylene-based unsaturated monomer having at least partially
10 neutralized acidic groups and an internal cross-linking agent; 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 Chemical Formula 1 and a
salt thereof, and
15 the super absorbent polymer satisfies the following physical properties of
1) an extractable content measured after swelling the super absorbent
polymer for 1 hour according to EDANA WSP 270.2 is 4 wt% or less based on a total
weight of the super absorbent polymer; and
2) BPI (Base Polymer Index) calculated according to the Equation 1 is 31 or
20 more.

【Claim 1】
A super absorbent polymer comprising
super absorbent polymer particles comprising a cross-linked polymer of a
water-soluble ethylene-based unsaturated monomer 5 having at least partially
neutralized acidic groups and an internal cross-linking agent; 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
10 1 and a salt thereof, and
the super absorbent polymer satisfies the following physical properties of
1) an extractable content measured after swelling the super absorbent
polymer for 1 hour according to EDANA WSP 270.2 is 4 wt% or less based on a total
weight of the super absorbent polymer; and
15 2) BPI (Base Polymer Index) calculated according to the following Equation
1 is 31 or more:
[Chemical Formula 1]
20 in Chemical Formula 1,
A is C5 to C21 alkyl,
B1 is -OCO-, -COO-, or -COOCH(R1)COO-,
B2 is -CH2-, -CH2CH2-, -CH(R2)-, -CH=CH-, or -C≡C-,
wherein R1 and R2 are each independently C1 to C4 alkyl,
25 n is an integer of 1 to 3, and
C is a carboxyl group,
[Equation 1]
56
in Equation 1,
CRC is centrifuge retention capacity measured according to the EDANA
WSP 241.3, and
ln (extractable content) is a natural log value 5 of the extractable content.
【Claim 2】
The super absorbent polymer of Claim 1,
wherein in Chemical Formula 1,
10 A is -C6H13, -C11H23, -C12H25, -C17H35, or -C18H37.
【Claim 3】
The super absorbent polymer of Claim 1,
wherein in Chemical Formula 1,
15 B1 is , or ,
wherein * is a bonding site with a neighboring atom.
【Claim 4】
The super absorbent polymer of Claim 1,
20 wherein in Chemical Formula 1,
B2 is , , or ,
57
wherein * is a bonding site with a neighboring atom.
【Claim 5】
The super absorbent polymer of Claim 1,
wherein the carboxylic acid-based additive is at 5 least one selected from the
group consisting of a carboxylic acid represented by the Chemical Formula 1, an
alkali metal salt thereof, and an alkaline earth metal salt thereof.
【Claim 6】
10 The super absorbent polymer of Claim 1,
wherein the carboxylic acid-based additive is any one of the compounds
represented by the following Chemical Formulae 1-1 to 1-7:
58
.
【Claim 7】
A super absorbent polymer,
further comprising a surface cross-linked 5 layer formed by further
cross-linking the cross-linked polymer using a surface cross-linking agent on at least
a part of the surface of the super absorbent polymer particles.
【Claim 8】
10 A preparation method of a super absorbent polymer, comprising
a 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 an internal cross-linking agent, an
encapsulated foaming agent, a carboxylic acid-based additive and a polymerization
15 initiator (Step 1); and
a step of drying and pulverizing the hydrogel polymer (Step 2),
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:
20 [Chemical Formula 1]
in Chemical Formula 1,
A is C5 to C21 alkyl,
B1 is -OCO-, -COO-, or -COOCH(R1)COO-,
25 B2 is -CH2-, -CH2CH2-, -CH(R2)-, -CH=CH-, or -C≡C-,
wherein R1 and R2 are each independently C1 to C4 alkyl,
n is an integer of 1 to 3, and
C is a carboxyl group.
59
【Claim 9】
The preparation method of a super absorbent polymer of Claim 8,
wherein the encapsulated foaming agent has a structure having a core
comprising a hydrocarbon and a shell formed of a thermoplastic resin surrounding
5 the core.
【Claim 10】
The preparation method of a super absorbent polymer of Claim 9,
wherein the hydrocarbon is at least one selected from the group consisting
10 of n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane,
cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso-heptane,
cycloheptane, n-octane, iso-octane and cyclooctane, and
the thermoplastic resin is a polymer formed from at least one monomer
selected from the group consisting of a (meth)acrylate-based compound, a (meth)
15 acrylonitrile-based compound, an aromatic vinyl-based compound, a vinyl
acetate-based compound and a halogenated vinyl-based compound.
【Claim 11】
The preparation method of a super absorbent polymer of Claim 8,
20 wherein the encapsulated foaming agent has an average diameter before
expansion of 5 to 30 ㎛, and a maximum expansion ratio in air of 5 to 15 times.
【Claim 12】
The preparation method of a super absorbent polymer of Claim 8,
25 wherein the encapsulated foaming agent is used in an amount of 0.05 to 1
part by weight based on 100 parts by weight of the water-soluble ethylene-based
unsaturated monomer.
【Claim 13】
30 The preparation method of a super absorbent polymer of Claim 8,
60
wherein the carboxylic acid-based additive is used in an amount of 0.01 to
10 parts by weight based on 100 parts by weight of the water-soluble ethylene-based
unsaturated monomer.
5 【Claim 14】
The preparation method of a super absorbent polymer of Claim 8,
wherein a surface tackiness index (at 25 ℃) of the hydrogel polymer
measured according to the steps of 1) to 4) below is 200 g or less:
1) preparing two specimens in which a hydrogel polymer having a bottom
10 surface (surface in contact with a reaction vessel when preparing a hydrogel
polymer) is cut to a size of 2.5 cm in width * 2.5 cm in length * 2 cm in thickness;
2) fixing each of the prepared two specimens to upper and lower holders of
a texture analyzer, wherein the two specimens are fixed such that the bottom surface
of the specimen protrudes out of each holder by 1 mm;
15 3) attaching the bottom surfaces of the two specimens by approaching the
upper/lower holders to which the two specimens are fixed such that a distance
between the holders becomes 1 mm, and then holding them for 5 seconds; and
4) measuring a maximum force (max force, g) when the parts to which the
two specimens are attached fall off by pulling the upper holder, and taking this as a
20 surface tackiness index.
【Claim 15】
The preparation method of a super absorbent polymer of Claim 8,
further comprising a step of forming a surface cross-linked layer on at least
25 a part of the surface of the prepared super absorbent polymer particles in the
presence of a surface cross-linking agent.