Method for producing superabsorbent polymer

Abstract

The present disclosure relates to a method for preparing a superabsorbent polymer. More specifically, the present invention relates to a method for preparing a superabsorbent polymer capable of controlling the occurrence of warpage of a dried product with excellent drying efficiency by controlling drying conditions.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10-2022-0183170, filed on December 23, 2022, and 10-2023-0181011, filed on December 13, 2023, with the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entireties.

[0003] The present disclosure relates to a method for preparing a superabsorbent polymer. More specifically, it relates to a method for preparing a superabsorbent polymer capable of controlling the warping of a dried product with excellent drying efficiency by controlling drying conditions. Background Art

[0004] A superabsorbent polymer (SAP) is a synthetic polymer material capable of absorbing 500 to 1000 times its own weight of moisture. Each manufacturer has named it by different names, such as SAM (superabsorbent material) and AGM (absorbent gel material), etc. Such superabsorbent polymers have started to be practically applied to sanitary products, and now they are widely used in water-retaining soil products for horticulture, water-stopping materials for civil engineering and construction, sheets for raising seedlings, preservatives for the food circulation field, or materials for ointments, etc.

[0005] These superabsorbent polymers have been widely used in the field of sanitary materials such as diapers or sanitary napkins. Superabsorbent polymers are usually contained in such sanitary materials in a state dispersed in pulp. However, in recent years, there have been continuous efforts to provide thinner sanitary materials such as diapers. As part of such efforts, the development of so-called pulp-free diapers, etc., in which the pulp content is reduced or pulp is not used at all, is being actively carried out.

[0006] In the case of the above-mentioned sanitary materials in which the pulp content is reduced or pulp is not used, the superabsorbent polymer is contained in a relatively high proportion, such that the superabsorbent polymer particles are inevitably contained in the sanitary material in a multi-layer form. In order for the entire superabsorbent polymer particles contained in a multi-layer form to more effectively absorb a large amount of liquid such as urine, the superabsorbent polymer basically needs to exhibit excellent absorption performance and a high absorption rate.

[0007] Meanwhile, such superabsorbent polymers are generally prepared by performing the following steps: a step of polymerizing monomers to prepare a hydrogel polymer containing a large amount of moisture; and a step of drying the hydrogel polymer and then pulverizing it into polymer particles having a desired particle size. However, when the hydrogel polymer is dried and then pulverized as described above, a large amount of fine powder is generated, which causes a problem of reducing the physical properties of the finally prepared superabsorbent polymer.

[0008] In addition, in order to reuse the fine powder, the fine powder is usually mixed with water for agglomeration to produce a fine reassembly, and then the fine reassembly is added to processes such as drying / crushing / classification. However, the water used here may cause problems such as an increase in energy use during drying and an increase in the load on the equipment, which may reduce the productivity of superabsorbent polymer manufacturing.

[0009] In addition, the hydrogel polymer polymerized in the method for preparing a superabsorbent polymer has the property of agglomerating with each other, and when made into agglomerated fine particles, the cohesive force increases, resulting in a problem of poor drying during subsequent drying. Specifically, this drying process is usually carried out by applying hot air in a belt dryer equipped with a perforated plate. As the cohesive force of the hydrogel polymer increases, the porosity in the drying layer decreases significantly, thereby increasing the pressure difference of the hot air. Therefore, warping occurs on the outside of the drying layer, making it difficult to carry out drying in large quantities.

[0010] In other words, when the undried rate increases or when the dried product warps, it is difficult to achieve the desired physical properties of the product and defects may occur. Therefore, there is a need to continuously develop technologies that improve drying efficiency without causing these problems. Summary of the Invention

[0011] [Technical Problem]

[0012] Therefore, provided is a method for preparing a superabsorbent polymer, which minimizes warping of the dried product with excellent drying efficiency by controlling drying conditions.

[0013] [Technical Solution]

[0014] To solve the above problems, provided is a method for preparing a superabsorbent polymer, which includes the following steps:

[0015] Polymerizing a monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator to form a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group is crosslinked and polymerized with the internal crosslinking agent (step 1);

[0016] Neutralizing at least some of the acidic groups of the polymer (step 2);

[0017] Micronizing the polymer in the presence of a surfactant (step 3);

[0018] Drying the neutralized and micronized polymer in a fixed-bed dryer to obtain a laminate of dried superabsorbent polymer particles (step 4); and

[0019] Superabsorbent polymer particles are prepared by pulverizing the laminate of the dried superabsorbent polymer particles (Step 5).

[0020] Wherein, Step 4 includes a primary drying step of introducing a downward air flow and a secondary drying step of introducing an upward air flow to the neutralized and micronized polymer, and

[0021] The time of the primary drying is 40 to 60% of the total drying time of Step 4.

[0022] [Beneficial effects]

[0023] According to the method for preparing a superabsorbent polymer of the present disclosure, excellent drying efficiency is achieved by controlling the drying conditions, and thus a superabsorbent polymer that minimizes warping of the dried product can be manufactured.

[0024] According to the method for preparing a superabsorbent polymer of the present disclosure, particles in the shape of fine particle agglomerates are achieved. Therefore, the surface area increases, and thus a superabsorbent polymer that exhibits excellent absorption performance and significantly improved absorption rate can be provided.

[0025] In addition, by having a high molecular weight polymer, a uniform particle size distribution, and a low extractable content (EC), a superabsorbent polymer excellent in absorption properties such as water retention capacity and pressure absorbency, liquid permeability, rewetting characteristics, and absorption rate can be provided. Description of the Drawings

[0026] Figure 1 is a flow chart of a conventional method for preparing a superabsorbent polymer.

[0027] Figure 2 is a cross-sectional photograph of a dried product obtained during the drying process in the methods for preparing superabsorbent polymers of the examples and comparative examples.

[0028] Figure 3 is a drying curve showing the moisture content according to the drying time during the drying process in the methods for preparing superabsorbent polymers of the examples and comparative examples. Detailed Description

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. It will be further understood that when used in this specification, the terms "comprising", "having", or "possessing" specify the presence of the described features, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, steps, components, or combinations thereof.

[0030] Since the present invention can be modified in various ways and has various forms, specific embodiments thereof are shown by way of example and will be described in detail. However, it is not intended to limit the present invention to the specific forms disclosed, and it should be understood that the present invention includes all modifications, equivalents, and substitutions within the spirit and scope of the present invention.

[0031] Since the present invention can be modified in various ways and has various forms, specific embodiments thereof are shown by way of example and will be described in detail. However, it is not intended to limit the present invention to the specific forms disclosed, and it should be understood that the present invention includes all modifications, equivalents, and substitutions within the spirit and scope of the present invention.

[0032] The terms used herein are only intended to refer to specific embodiments and are not intended to limit the present invention. In addition, as used herein, the singular forms also include the plural forms unless the phrase clearly indicates the contrary.

[0033] The term "polymer" in the present disclosure is in a state of polymerization of water-soluble ethylenically unsaturated monomers and can include all moisture content ranges or all particle size ranges.

[0034] In addition, the term "superabsorbent polymer" is used to cover all crosslinked polymers or powder forms of base resins composed of superabsorbent polymer particles in which the crosslinked polymers are pulverized, and depending on the specific situation, the crosslinked polymers or the base resins are further processed, such as drying, pulverizing, grading, surface crosslinking, etc., to make them in a state suitable for commercialization.

[0035] In addition, the terms "fine powder" or "fine particles" refer to particles with a particle size less than 150 μm in superabsorbent polymer particles. The particle size of these polymer particles can be measured according to EDANA (European Disposables and Nonwovens Association) WSP 220.3.

[0036] In addition, the term "chopping" refers to cutting the hydrogel polymer into small pieces in millimeters to improve the drying efficiency, and is distinguished from pulverization that reaches the micron or normal particle level.

[0037] In addition, the term "micronization (micronization)" refers to pulverizing the hydrogel polymer to a particle size of dozens to hundreds of microns and is distinguished from "chopping".

[0038] Hereinafter, the preparation method of the superabsorbent polymer of the present disclosure and the superabsorbent polymer will be described in more detail.

[0039] According to an embodiment of the present disclosure, there is provided a method for preparing a superabsorbent polymer, which includes the following steps:

[0040] A monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator is polymerized to form a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group is crosslinked and polymerized with the internal crosslinking agent (Step 1);

[0041] At least some of the acidic groups of the polymer are neutralized (Step 2);

[0042] The polymer is micronized in the presence of a surfactant (Step 3);

[0043] The neutralized and micronized polymer is dried in a fixed-bed dryer to obtain a laminate of dried superabsorbent polymer particles (Step 4); and

[0044] Superabsorbent polymer particles are prepared by pulverizing the laminate of dried superabsorbent polymer particles (Step 5),

[0045] wherein Step 4 includes a primary drying step of introducing a downward air flow to the neutralized and micronized polymer and a secondary drying step of introducing an upward air flow, and

[0046] The primary drying time is 40 to 60% of the total drying time of Step 4.

[0047] Generally, a hydrogel polymer obtained by polymerizing an acrylic monomer is sold as a superabsorbent polymer in powder form after processes such as drying, pulverization, classification, and surface crosslinking.

[0048] When a fixed-bed drying process is employed in the preparation process, the dried superabsorbent polymer is obtained in the form of a laminate, and shrinkage of the hydrogel polymer occurs during the drying process. At this time, depending on the drying conditions, there are differences in the degree of shrinkage of the dried product in the width direction, and as a result, there is a problem that the outside of the dried product warps. This warping of the outside of the dried product causes an imbalance in the pressure difference of the hot air and significantly reduces the drying efficiency, leading to problems such as a longer drying time or insufficient drying inside the dried product.

[0049] As a result of repeated studies to solve this problem, the present inventors confirmed that excellent drying efficiency can be achieved by initially introducing a downward air flow during the drying process to satisfy a predetermined drying time, thus completing the present invention.

[0050] In addition, the present inventors found that when the hydrogel polymer is micronized in the presence of a surfactant before the drying process and the direction of the hot air is controlled during the drying process, warping of the dried laminate is effectively suppressed, and excellent drying efficiency can be achieved even when the drying amount increases, thus completing the present invention.

[0051] Meanwhile, in recent years, there have been continuous attempts to provide superabsorbent polymers that exhibit more improved absorption rates.

[0052] The most common method of increasing the absorption rate is to increase the surface area of the superabsorbent polymer by forming a porous structure in the superabsorbent polymer. To increase the surface area of the superabsorbent polymer, a method is usually selected in which a foaming agent is included in the monomer composition and then cross-linked polymerization is carried out to form a porous structure in the base resin powder.

[0053] However, the disadvantage of using a foaming agent is that it reduces the physical properties of the superabsorbent polymer (such as surface tension, permeability, or bulk density) and increases the generation of fines. Therefore, there is a continuous need to develop a technique that can increase the absorption rate of the superabsorbent polymer without using a foaming agent.

[0054] Meanwhile, superabsorbent polymers are usually prepared by the following process: cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent and a polymerization initiator to form a hydrogel polymer, then drying the formed hydrogel polymer, and subsequently pulverizing it into a desired particle size. At this time, a chopping process of cutting the hydrogel polymer into particles of several millimeters is usually carried out before the drying process to facilitate the drying of the hydrogel polymer and improve the efficiency of the pulverizing process. However, due to the viscosity of the hydrogel polymer during this chopping process, the hydrogel polymer cannot be pulverized into micro-sized particles but becomes agglomerated gels. When the hydrogel polymer in the form of agglomerated gels is dried, a plate-like dried product is formed. To pulverize it into micro-sized particles, a multi-stage pulverizing process is required, so there is a problem of generating many fine particles during this process.

[0055] Specifically, Figure 1 is a flow chart of a conventional preparation method of a superabsorbent polymer. Referring to Figure 1 a superabsorbent polymer is usually prepared by including the following steps.

[0056] (Neutralization) Neutralize at least some acidic groups of the water-soluble ethylenically unsaturated monomer;

[0057] (Polymerization) Form a hydrogel polymer by cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent and a polymerization initiator;

[0058] (Chopping) Chop the hydrogel polymer;

[0059] (Drying) Dry the chopped hydrogel polymer; and

[0060] (Pulverizing / Classification) Pulverize the dried polymer and then classify it into normal particles and fines;

[0061] As described above, the shredded hydrogel polymer has an agglomerated gel shape with a size of about 1 cm to 10 cm. This shredded hydrogel polymer is laminated on a belt made of a perforated plate at the bottom and dried by hot air supplied from the bottom or the top. Since the polymer dried by the above drying method has a plate shape rather than a granular shape, the pulverization and classification steps are carried out by coarse pulverization, then classification, then fine pulverization again, and then classification again, so that the prepared particles become normal particles, that is, particles with a particle size of 150 μm to 850 μm. Since the amount of the fine powder separated in the final classification step is about 20% by weight to about 30% by weight based on the total weight of the final superabsorbent polymer, the separated fine powder is mixed with an appropriate amount of water, reconstituted, and then introduced in the shredding step or before drying for reuse.

[0062] However, when the reconstituted fine powder mixed with water is reinjected into the pulverization or drying process for reusing the fine powder, problems such as an increase in equipment load and / or energy consumption may occur, and the remaining fine powder that is not classified causes deterioration of the physical properties of the superabsorbent polymer.

[0063] Therefore, the present inventors have found that the generation of fine powder in the conventional preparation method is greatly affected by the pulverization process. In addition, it has been confirmed that by adding a surfactant and a neutralizing agent for post-neutralization during the pulverization process of the polymer and pulverizing it finer, that is, micronizing it, while controlling agglomeration and obtaining particles with fine particle agglomeration, the generation of fine powder during the preparation process can be significantly reduced.

[0064] Meanwhile, a method of adding a surfactant has been proposed to reduce the adhesiveness of the hydrogel polymer during the shredding process. However, when a surfactant is added during the shredding process, due to the high water retention capacity of the hydrogel polymer, the surfactant penetrates into the interior of the hydrogel polymer rather than existing at the interface of the hydrogel polymer. Therefore, there is a problem that the surfactant cannot properly play its role.

[0065] The shredded particles are formed into particles with a size of several millimeters to several centimeters. Therefore, compared with the polymer before shredding, the surface area can be increased to a certain extent, but it is difficult to expect an effect of effectively improving the absorption rate. Therefore, in order to improve the absorption rate, a method of increasing the surface area by kneading using increased mechanical force in the shredding step can be considered. However, in this case, due to the viscosity of the polymer, excessive agglomeration occurs, and after shredding, drying, and pulverization, amorphous single particles are formed due to only the unevenness of the particle surface, and excessive kneading or mashing may actually increase the extractable components.

[0066] As a result of repeated studies to solve this problem, it was confirmed that: different from the conventional preparation method of superabsorbent polymers in which polymerization is carried out in a state where the acidic groups of water-soluble ethylenically unsaturated monomers are neutralized, when polymerization is first carried out in a state where the acidic groups are not neutralized to form a polymer, the hydrogel polymer is micronized in the presence of a surfactant, and then the acidic groups of the polymer are neutralized; when the acidic groups of the polymer are neutralized to form a hydrogel polymer, and then the hydrogel polymer is micronized in the presence of a surfactant; or when the acidic groups present in the polymer are neutralized while micronizing, a large amount of surfactant is present on the surface of the polymer, and it can sufficiently play the role of reducing the high adhesiveness of the polymer, preventing excessive aggregation of the polymer, and controlling the aggregation state to the desired level.

[0067] Therefore, by forming the polymer into secondary particles agglomerated from primary particles and then carrying out the pulverization and drying processes under milder conditions, the generation of fines in this process can be significantly reduced.

[0068] In addition, when the polymer is pulverized in the presence of a surfactant, the hydrophobic functional groups contained in the surfactant impart hydrophobicity to the surface of the pulverized superabsorbent polymer particles, thereby reducing the friction between the particles and increasing the bulk density of the superabsorbent polymer. In addition, the hydrophilic functional groups contained in the surfactant can also bind to the superabsorbent polymer particles, so that the surface tension of the polymer is not reduced. Therefore, the superabsorbent polymer prepared according to the above method can have a high bulk density compared to a polymer without using a surfactant, while exhibiting a similar surface tension.

[0069] In addition, when polymerization is first carried out in an unneutralized state to form a polymer, and then the acidic groups present in the polymer are neutralized, a longer-chain polymer can be formed and the crosslinking is incomplete, so the content of extractable components present in a non-crosslinked state can be reduced.

[0070] Extractable components have the property of being easily dissolved when the superabsorbent polymer comes into contact with a liquid. When the content of extractable components is high, most of the dissolved extractable components remain on the surface of the superabsorbent polymer and make the superabsorbent polymer sticky, thereby reducing the permeability. Therefore, it is important to keep the content of extractable components low in terms of permeability.

[0071] According to one embodiment of the present disclosure, since polymerization is carried out in an unneutralized state, the content of extractable components is reduced, so the permeability of the superabsorbent polymer can be improved.

[0072] In addition, the superabsorbent polymer prepared according to an embodiment of the present disclosure may have a uniform particle size distribution, and thus may provide a superabsorbent polymer excellent in absorption properties such as water retention capacity and pressure absorbency, rewetting characteristics, and absorption rate.

[0073] Hereinafter, a method for preparing a superabsorbent polymer according to an embodiment will be described in more detail for each step.

[0074] (Preparation of Superabsorbent Polymer)

[0075] Step 1: Polymerization step

[0076] First, a monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator is polymerized to form a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group is crosslinked and polymerized with the internal crosslinking agent.

[0077] The above steps may include a step of preparing a monomer composition by mixing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator, and a step of polymerizing the monomer composition to form a polymer.

[0078] The water-soluble ethylenically unsaturated monomer may be any monomer commonly used for preparing a superabsorbent polymer. Specifically, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Chemical Formula 1:

[0079] [Chemical Formula 1]

[0080] R-COOM'

[0081] In Chemical Formula 1,

[0082] R is a C2 to C5 alkyl group having an unsaturated bond, and

[0083] M’ is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0084] Preferably, the monomer may be at least one selected from the group consisting of (meth)acrylic acid and monovalent (alkali) metal salts, divalent metal salts, ammonium salts, and organic amine salts of the acid.

[0085] When using (meth)acrylic acid and / or its salts as water-soluble ethylenically unsaturated monomers, it is beneficial to obtain superabsorbent polymers with improved absorption properties. Additionally, as monomers, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethane sulfonic acid, 2-(meth)acryloylpropane sulfonic acid, 2-(meth)acrylamide-2-methylpropane sulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, and (N,N)-dimethylaminopropyl (meth)acrylamide, etc. can be used.

[0086] Here, the water-soluble ethylenically unsaturated monomer has an acidic group. As described above, in the conventional method, a hydrogel polymer is formed by crosslinking polymerization of monomers in which at least some of the acidic groups are neutralized by a neutralizing agent. Specifically, in the step of mixing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, a polymerization initiator, and a neutralizing agent, at least some of the acidic groups of the water-soluble ethylenically unsaturated monomer are neutralized.

[0087] However, according to one embodiment of the present disclosure, polymerization is first carried out in a state where the acidic groups of the water-soluble ethylenically unsaturated monomer are not neutralized to form a polymer.

[0088] The water-soluble ethylenically unsaturated monomer in a state where the acidic groups are not neutralized (such as acrylic acid) is in a liquid state at room temperature and has high miscibility with a solvent (water), so it exists in the monomer composition in the form of a mixed solution. However, the water-soluble ethylenically unsaturated monomer in which the acidic groups are neutralized is in a solid state at room temperature, has different solubilities depending on the temperature of the solvent (water), and has a lower solubility at a lower temperature.

[0089] Compared with the monomer in which the acidic groups are neutralized, the water-soluble ethylenically unsaturated monomer in which the acidic groups are not neutralized has higher solubility or miscibility with the solvent (water), so it will not precipitate even at low temperatures. Therefore, it is beneficial for long-term polymerization at low temperatures. Therefore, by using a water-soluble ethylenically unsaturated monomer in which the acidic groups are not neutralized for long-term polymerization, a polymer with a higher molecular weight and a uniform molecular weight distribution can be stably formed.

[0090] In addition, long-chain polymers can be formed, thereby achieving the effect of reducing the content of extractable components present in a non-crosslinked state due to incomplete polymerization or crosslinking.

[0091] In addition, when polymerization is first carried out to form a polymer in a state where the acidic groups of the monomers are not neutralized, and then micronization is carried out in the presence of a surfactant after neutralization; micronization is carried out in the presence of a surfactant and then neutralization is carried out; or the acidic groups present in the polymer are neutralized while micronization is being carried out, a large amount of surfactant can be present on the surface of the polymer to sufficiently reduce the adhesiveness of the polymer.

[0092] Considering the polymerization time and reaction conditions, the concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition can be about 20 to 60% by weight, or about 20 to 40% by weight.

[0093] As used herein, the term "internal crosslinking agent" is a term used to distinguish it from a surface crosslinking agent that is commonly used to crosslink the surface of superabsorbent polymer particles, and is used to form a polymer having a crosslinked structure by introducing crosslinks between the unsaturated bonds of the above-mentioned water-soluble ethylenically unsaturated monomers.

[0094] Crosslinking in the above steps is carried out both on the surface and inside, but when the surface crosslinking process of the superabsorbent polymer particles is carried out, the surface of the finally prepared superabsorbent polymer particles can have a structure newly crosslinked by the surface crosslinking agent, and the inside of the particles can maintain the structure crosslinked by the internal crosslinking agent.

[0095] According to one embodiment of the present disclosure, the internal crosslinking agent can include any one or more of polyfunctional acrylate compounds, polyfunctional allyl compounds, or polyfunctional vinyl compounds.

[0096] Non-limiting examples of polyfunctional acrylate compounds can include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate, etc., and these can be used alone or in combination of two or more.

[0097] Non-limiting examples of the polyfunctional allyl compounds may include ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, propylene glycol diallyl ether, tripropylene glycol diallyl ether, polypropylene glycol diallyl ether, 1,4-butanediol diallyl ether, butylene glycol diallyl ether, hexanediol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, dipentaerythritol diallyl ether, dipentaerythritol triallyl ether, dipentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, glycerol diallyl ether, and glycerol triallyl ether, etc., and these may be used alone or in combination of two or more.

[0098] Non-limiting examples of the polyfunctional vinyl compounds may include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, tripropylene glycol divinyl ether, polypropylene glycol divinyl ether, butanediol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, pentaerythritol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol divinyl ether, dipentaerythritol trivinyl ether, dipentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, trimethylolpropane divinyl ether, trimethylolpropane trivinyl ether, glycerol divinyl ether, and glycerol trivinyl ether, etc., and these may be used alone or in combination of two or more. Preferably, pentaerythritol triallyl ether may be used.

[0099] In the above polyfunctional allyl compounds or polyfunctional vinyl compounds, two or more unsaturated groups contained in the molecule bind to the unsaturated bond of the water-soluble ethylenically unsaturated monomer or the unsaturated bond of another internal crosslinking agent, thereby forming a crosslinked structure during the polymerization process. In addition, different from the acrylate compounds containing an ester bond (-(C=O)O-) in the molecule, even during the neutralization process after the above polymerization reaction, the crosslinking can be maintained more stably.

[0100] Therefore, the gel strength of the final superabsorbent polymer can be improved, the process stability can be improved during the discharge process after polymerization, and the amount of extractable components can be minimized.

[0101] The crosslinking polymerization of a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent can be carried out in the presence of a polymerization initiator, a thickener, a plasticizer, a storage stabilizer, an antioxidant, etc. as necessary.

[0102] In the monomer composition, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer, the amount of the internal crosslinking agent used can be 0.01 to 5 parts by weight. For example, the amount of the internal crosslinking agent used can be 0.01 part by weight or more, 0.05 part by weight or more, or 0.1 part by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.7 part by weight or less. When the content of the internal crosslinking agent is too low, crosslinking cannot occur sufficiently, making it difficult to achieve a strength higher than an appropriate level. When the content of the internal crosslinking agent is too high, the internal crosslinking density increases, making it difficult to achieve the required water retention capacity.

[0103] The polymer formed using such an internal crosslinking agent has a three-dimensional network structure in which the main chain formed by the polymerization of the water-soluble ethylenically unsaturated monomer is crosslinked by the internal crosslinking agent. When the polymer has a three-dimensional network structure in this way, the centrifugal retention capacity and pressure absorbency, which are various physical properties as a superabsorbent polymer, can be significantly improved compared to a polymer having a two-dimensional linear structure that is not additionally crosslinked by the internal crosslinking agent.

[0104] According to an embodiment of the present disclosure, the step of forming a polymer by polymerizing the monomer composition can be carried out in a batch reactor.

[0105] In the conventional preparation method of a superabsorbent polymer composition, according to the energy source of the polymerization, the polymerization method is roughly divided into thermal polymerization and photopolymerization. In the case of thermal polymerization, it is usually carried out in a reactor equipped with a stirring shaft (such as a kneader). In the case of photopolymerization, it can be carried out in a reactor equipped with a movable conveyor belt or in a container having a flat bottom.

[0106] Meanwhile, in the above polymerization method, since the polymerization reaction time is usually short (for example, 1 hour or less), a polymer having a wide molecular weight distribution and a small molecular weight is formed.

[0107] Meanwhile, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or in a container having a flat bottom, a hydrogel polymer in the form of a sheet having a width can usually be obtained. At this time, the thickness of the polymer sheet can vary according to the concentration and injection rate or amount of the monomer composition to be injected, and can be about 0.5 to about 5 cm.

[0108] When the monomer composition is supplied such that the thickness of the polymer sheet is too thin, the production efficiency may be low, which is undesirable. When the polymer thickness on the sheet is excessively increased for productivity, the polymerization reaction cannot occur uniformly throughout the thickness, making it difficult to form a high-quality polymer.

[0109] In addition, the polymerization in a reactor equipped with a conveyor belt and a stirring shaft is carried out continuously by supplying a new monomer composition into the reactor while the polymerization product is moving. Therefore, polymers with different degrees of polymerization are mixed. Thus, it is difficult to achieve uniform polymerization throughout the monomer composition, and the overall physical properties may deteriorate.

[0110] However, according to one embodiment of the present disclosure, since the polymerization is carried out in a batch reactor in a fixed-bed manner, the risk of mixing polymers with different degrees of polymerization is very small. Thus, a polymer with uniform quality can be obtained.

[0111] In addition, the polymerization step is carried out in a batch reactor having a predetermined volume, and compared with the polymerization carried out continuously in a reactor equipped with a conveyor belt, the polymerization reaction takes a longer time, for example, more than 3 hours. Although the polymerization time is long as described above, since the polymerization is carried out on an unneutralized water-soluble ethylenically unsaturated monomer, the monomer is not easily precipitated. Therefore, it is beneficial to carry out long-term polymerization.

[0112] Meanwhile, when the polymerization in the batch reactor of the present disclosure uses a thermal polymerization method, a thermal polymerization initiator is used as the polymerization initiator.

[0113] In addition, one or more initiators selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used as the thermal polymerization initiator. Specifically, sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), etc. can be used as examples of persulfate initiators; and 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethyl) isobutamidine dihydrochloride, 2-(carbamoylazo)isobutylonitril, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, and 4,4-azobis-(4-cyanovaleric acid) etc. can be used as examples of azo initiators. More various thermal polymerization initiators are well disclosed on page 203 of "Principle of Polymerization (Wiley, 1981)" written by Odian, and the present disclosure is not limited thereto.

[0114] Based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer, the amount of the polymerization initiator used can be 2 parts by weight or less. When the concentration of the polymerization initiator is too low, the polymerization rate may become slow, and a large amount of residual monomer may be extracted from the final product. On the contrary, when the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network become shorter, resulting in an increase in the extractable content and a decrease in the pressure absorbency, thereby reducing the physical properties of the polymer.

[0115] Meanwhile, in one embodiment of the present disclosure, the polymerization can be initiated by adding a reducing agent that forms a redox pair with the initiator.

[0116] Specifically, when the initiator and the reducing agent are added to the polymer solution, they react with each other to form free radicals.

[0117] Since the formed free radicals react with the monomer, and the reactivity of the redox reaction between the initiator and the reducing agent is high, even if only a small amount of the initiator and the reducing agent are added, the polymerization is initiated, so there is no need to increase the process temperature. Therefore, the polymerization can be carried out at a low temperature, and the change in the physical properties of the polymer solution can be minimized.

[0118] The polymerization reaction using the redox reaction can occur smoothly even at a temperature around room temperature (25 °C) or below. For example, the polymerization reaction can be carried out at a temperature of 5 °C or higher and 25 °C or lower, or 5 °C or higher and 20 °C or lower.

[0119] In one embodiment of the present disclosure, when a persulfate-based initiator is used as the initiator, the reducing agent can be at least one selected from the group consisting of sodium metabisulfite (Na2S2O5), tetramethylethylenediamine (TMEDA), a mixture of ferrous sulfate (II) and EDTA (FeSO4 / EDTA), sodium formaldehyde sulfoxylate, and disodium 2-hydroxy-2-sulfonatoacetate.

[0120] In one example, potassium persulfate is used as the initiator and disodium 2-hydroxy-2-sulfonatoacetate is used as the reducing agent; ammonium persulfate is used as the initiator and tetramethylethylenediamine is used as the reducing agent; or sodium persulfate is used as the initiator and sodium formaldehyde sulfoxylate is used as the reducing agent.

[0121] In another embodiment of the present disclosure, when a hydrogen peroxide-based oxidant is used as the initiator, the reducing agent can be at least one selected from the group consisting of ascorbic acid, sucrose, sodium sulfite (Na2SO3), sodium metabisulfite (Na2S2O5), tetramethylethylenediamine (TMEDA), a mixture of ferrous sulfate (II) and EDTA (FeSO4 / EDTA), sodium formaldehyde sulfoxylate, disodium 2-hydroxy-2-sulfonatoacetate, and disodium 2-hydroxy-2-sulfiteacetate.

[0122] When necessary, the monomer composition may further contain additives such as thickeners, plasticizers, storage stabilizers, antioxidants, and surfactants. Here, each additive may be a commonly used component in the art without particular limitation, as long as it does not impair the effects of the present invention, and the surfactant used in Step 3 described later (the compound represented by Chemical Formula 2 or its salt) may also be used as the surfactant.

[0123] In addition, the monomer composition containing monomers may be, for example, in the form of a solution dissolved in a solvent such as water, and the solid content in the monomer composition in solution form, that is, the concentrations of monomers, internal crosslinking agents, and polymerization initiators, may be appropriately adjusted in consideration of the polymerization time and reaction conditions. For example, the solid content in the monomer composition may be 10 to 80% by weight, 15 to 60% by weight, or 30 to 50% by weight.

[0124] At this time, any solvent capable of dissolving the above components can be used without limitation. For example, the solvent may be at least one selected from water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide.

[0125] Since the polymer obtained in this way is polymerized using unneutralized ethylenically unsaturated monomers, a polymer having a high molecular weight and a uniform molecular weight distribution can be formed, and the content of extractable components can be reduced.

[0126] The polymer obtained in this way is a hydrogel polymer and may have a water content of 30 to 80% by weight. For example, the water content of the polymer may be 30% by weight or more, 45% by weight or more, or 50% by weight or more, and 80% by weight or less, or 70% by weight or less.

[0127] When the water content of the polymer is too low, it may not be effectively pulverized because it is difficult to ensure an appropriate surface area in the subsequent pulverization step. When the water content of the polymer is too high, it may be difficult to pulverize the polymer to the required particle size because the pressure applied in the subsequent pulverization step increases.

[0128] At this time, the "water content rate" in the present disclosure is the content of water in the total weight of the polymer, which refers to the value obtained by subtracting the weight of the dried polymer from the weight of the polymer. Specifically, the water content rate is defined as the value calculated by measuring the weight loss caused by the evaporation of water from the polymer during the process of raising the temperature of the polymer in the form of fragments by infrared heating and drying it. At this time, the drying conditions for measuring the water content rate are as follows: the temperature is raised to about 180 °C and maintained at 180 °C, and the total drying time is 40 minutes, including a heating step of 5 minutes.

[0129] Step 2: Neutralization step, and Step 3: Micronization step

[0130] Next, a step of neutralizing at least some of the acidic groups of the polymer (step 2) is carried out.

[0131] Here, a basic material capable of neutralizing acidic groups, such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide, can be used as a neutralizing agent.

[0132] In addition, the degree of neutralization (which refers to the degree to which the acidic groups contained in the polymer are neutralized by the neutralizing agent) can preferably be 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to 75 mol%. The range of the degree of neutralization can vary according to the final physical properties. When the degree of neutralization is too high, the absorbency of the superabsorbent polymer may decrease, and the carboxyl concentration on the particle surface is too low, making it difficult to properly carry out surface crosslinking in the subsequent process, resulting in a decrease in pressure absorbency or liquid permeability. On the contrary, when the degree of neutralization is too low, not only does the absorbency of the polymer deteriorate, but also properties that are difficult to handle, such as the properties of elastic rubber, are imparted to the polymer.

[0133] Simultaneously with step 2, or before or after step 2, a step of micronizing the polymer in the presence of a surfactant (step 3) is carried out.

[0134] The above step is a step of micronizing the polymer in the presence of a surfactant, and is a step in which the hydrogel polymer is not cut into millimeters, but is simultaneously cut into dozens to hundreds of micrometers and agglomerated. That is, this is a step of preparing secondary agglomerated particles in which primary particles cut into dozens to hundreds of micrometers are agglomerated by imparting appropriate adhesiveness to the hydrogel polymer. The water-containing superabsorbent polymer particles (which are the secondary agglomerated particles prepared in this step) have a normal particle size distribution and a greatly increased surface area, thereby significantly improving the absorption rate.

[0135] As described above, after mixing the polymer and the surfactant, the polymer is micronized in the presence of the surfactant, so that water-containing superabsorbent polymer particles ( = neutralized and micronized polymer) in the form of secondary agglomerated particles in which the superabsorbent polymer particles and the surfactant are mixed, then cut and agglomerated can be prepared.

[0136] Here, the "aqueous superabsorbent polymer particles" refer to particles having a water content of about 30% by weight or more, and are prepared by cutting the polymer into particles and then agglomerating them without a drying process. Accordingly, they can have a water content of 30 to 80% by weight similar to that of the polymer.

[0137] According to one embodiment of the present disclosure, the surfactant may be a compound represented by the following Chemical Formula 2 or a salt thereof, but the present disclosure is not limited thereto:

[0138] [Chemical Formula 2]

[0139]

[0140] In Chemical Formula 2,

[0141] A1, A2, and A3 are each independently a single bond, a carbonyl group, provided that at least one of these is a carbonyl group or wherein m1, m2, and m3 are each independently an integer from 1 to 8, each is connected to an adjacent oxygen atom, and -* is respectively connected to adjacent R1, R2, and R3,

[0142] R1, R2, and R3 are each independently hydrogen, a C6 to C18 straight-chain or branched alkyl group, or a C6 to C18 straight-chain or branched alkenyl group, and

[0143] n is an integer from 1 to 9.

[0144] The surfactant is mixed with the polymer and added such that the micronization step can be easily performed without agglomeration.

[0145] The surfactant represented by Chemical Formula 2 is a nonionic surfactant and has excellent surface adsorption properties even when hydrogen-bonded to an unneutralized polymer, and thus is suitable for achieving the desired agglomeration control effect. On the other hand, for anionic surfactants other than nonionic surfactants, when mixed with a polymer neutralized with a neutralizing agent such as NaOH or Na2SO4, it is adsorbed by Na+ ions ionized at the carboxyl substituents of the polymer. When mixed with an unneutralized polymer, there is a problem in that the adsorption efficiency of the polymer is relatively reduced due to competition with anions of the carboxyl substituents of the polymer.

[0146] Specifically, in the surfactant represented by Chemical Formula 2, the hydrophobic functional groups are the terminal functional groups of R1, R2, and R3 (if not hydrogen), and the hydrophilic functional groups include the glycerol-derived part in the chain and the terminal hydroxyl group (when A n is a single bond and R nWhen it is hydrogen, n = 1 to 3). Here, the glycerol-derived moiety and the terminal hydroxyl group are hydrophilic functional groups and serve to improve the adsorption performance to the polymer surface. Therefore, agglomeration of the superabsorbent polymer particles can be effectively suppressed.

[0147] In Chemical Formula 2, the hydrophobic functional groups of R1, R2, and R3 (if not hydrogen) are each independently a C6 to C18 linear or branched alkyl group or a C6 to C18 linear or branched alkenyl group. At this time, when R1, R2, and R3 (if not hydrogen) are alkyl or alkenyl groups having less than 6 carbon atoms, there is a problem that the chain length is too short to effectively control the agglomeration of the pulverized particles. When R1, R2, and R3 (if not hydrogen) are alkyl or alkenyl groups having more than 18 carbon atoms, there may be a problem that the mobility of the surfactant is reduced and it may not be effectively mixed with the polymer, and due to the increase in the cost of the surfactant, the unit price of the composition increases.

[0148] Preferably, R1, R2, and R3 are hydrogen, a C6 to C18 linear or branched alkyl group such as 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, or n-octadecyl, or a C6 to C18 linear or branched alkenyl group such as 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-decenyl, 2-undecenyl, 2-dodecenyl, 2-tridecenyl, 2-tetradecenyl, 2-pentadecenyl, 2-hexadecenyl, 2-heptadecenyl, or 2-octadecenyl.

[0149] The surfactant may be selected from the compounds represented by the following Chemical Formulas 2-1 to 2-14:

[0150] [Chemical Formula 2-1]

[0151]

[0152] [Chemical Formula 2-2]

[0153]

[0154] [Chemical Formula 2-3]

[0155]

[0156] [Chemical Formula 2-4]

[0157]

[0158] [Chemical Formula 2-5]

[0159]

[0160] [Chemical formula 2-6]

[0161]

[0162] [Chemical formula 2-7]

[0163]

[0164] [Chemical formula 2-8]

[0165]

[0166] [Chemical formula 2-9]

[0167]

[0168] [Chemical formula 2-10]

[0169]

[0170] [Chemical formula 2-11]

[0171]

[0172] [Chemical formula 2-12]

[0173]

[0174] [Chemical formula 2-13]

[0175]

[0176] [Chemical formula 2-14]

[0177]

[0178] Meanwhile, based on 100 parts by weight of the polymer, the amount of the surfactant used can be from 0.01 to 10 parts by weight. When too little surfactant is used, it may not be evenly adsorbed on the surface of the polymer, resulting in re-agglomeration of the particles after pulverization. When too much surfactant is used, the overall physical properties of the final superabsorbent polymer may deteriorate. For example, based on 100 parts by weight of the polymer, the amount of the surfactant used can be 0.01 parts by weight or more, 0.015 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less.

[0179] The method of mixing the surfactant with the polymer is not particularly limited and can be appropriately selected as long as it is a method capable of uniformly mixing the additive with the polymer. Specifically, the surfactant can be dry-blended, dissolved in a solvent and then mixed in a solution state, or melted and then mixed.

[0180] For example, the surfactant can be mixed in the form of a solution dissolved in a solvent. At this time, all types of solvents including inorganic solvents and organic solvents can be used without limitation, but considering the ease of the drying process and the cost of the solvent recovery system, water is the most suitable. In addition, methods such as adding a surfactant in solution form and a polymer to a reaction tank for mixing, spraying the solution after adding the polymer in a mixer, or continuously supplying the polymer and the solution to a continuously operating mixer for mixing can be used.

[0181] Meanwhile, according to an embodiment of the present disclosure, the step of neutralizing at least some acidic groups of the polymer (step 2) and the step of micronizing the polymer in the presence of a surfactant (step 3) can be carried out sequentially, alternately, or simultaneously.

[0182] In other words, a neutralizing agent can be added to the polymer to first neutralize the acidic groups, and then a surfactant can be added to the neutralized polymer to micronize the polymer mixed with the surfactant (carried out in the order of step 2 -> step 3). Alternatively, the polymer can be neutralized and micronized by simultaneously adding a neutralizing agent and a surfactant to the polymer (step 2 and step 3 are carried out simultaneously). Alternatively, the surfactant can be added first, and then the neutralizing agent can be added (carried out in the order of step 3 -> step 2). Alternatively, the neutralizing agent and the surfactant can be added alternately. Alternatively, the surfactant can be added first for micronization, then the neutralizing agent can be added to neutralize the product, and then additional surfactant can be added to the neutralized hydrogel polymer to further carry out the micronization process.

[0183] Meanwhile, in order to uniformly neutralize the entire polymer, it may be desirable to leave a certain time interval between the addition of the neutralizing agent and the micronization process.

[0184] At least some or a large amount of the surfactant may be present on the surface of the water-absorbent polymer particles.

[0185] Here, "at least some or a large amount of surfactant is present on the surface of the aqueous superabsorbent polymer particles" means that at least some or a large amount of surfactant is adsorbed or bound to the surface of the aqueous superabsorbent polymer particles. Specifically, the surfactant can be physically or chemically adsorbed on the surface of the superabsorbent polymer. More specifically, the hydrophilic functional groups of the surfactant can be physically adsorbed on the hydrophilic part of the surface of the superabsorbent polymer through intermolecular forces such as dipole-dipole interactions. In this way, each hydrophilic part of the surfactant is physically adsorbed on the surface of the superabsorbent polymer particle, thereby surrounding the surface, and each hydrophobic part of the surfactant is not adsorbed on the surface of the polymer particle. Therefore, each surfactant can be coated on the surface of the polymer particle in the form of a micelle structure. This is because the surfactant is added in the micronization step after the polymer is formed, rather than during the polymerization of the water-soluble ethylenically unsaturated monomer. In this case, compared with the case where the surfactant is added during the polymerization process and the surfactant is present inside the polymer, its function as a surfactant can be fully exerted, and pulverization and agglomeration occur simultaneously, so that particles with a large surface area can be obtained in the form of fine particle agglomerates.

[0186] According to one embodiment of the present disclosure, the step of micronizing the polymer to prepare the aqueous superabsorbent polymer particles can be carried out more than twice.

[0187] According to one embodiment of the present disclosure, the micronization step is carried out using a micronization device, and the micronization device may include: a main body including a transfer space in which the polymer is transferred; a screw member rotatably installed inside the transfer space to move the polymer; a drive motor that provides a rotational driving force to the screw member; a cutter member installed in the main body to pulverize the polymer; and a perforated plate having a plurality of holes and capable of discharging the polymer pulverized by the cutter member to the outside of the main body. Here, the size of the holes provided in the perforated plate of the micronization device may be 1 mm to 20 mm, 5 mm to 15 mm, or 5 mm to 12 mm.

[0188] When micronizing the polymer mixed with the surfactant while controlling agglomeration using the micronization device, a smaller particle size distribution is achieved, and then the drying and pulverization processes can be carried out under milder conditions, thereby preventing the generation of fine particles and improving the physical properties of the superabsorbent polymer.

[0189] Step 4: Drying step

[0190] Next, a step (step 4) of drying the neutralized and micronized polymer in a fixed-bed dryer to obtain a laminate of dry superabsorbent polymer particles is carried out.

[0191] This step is a step of drying the moisture in the aqueous superabsorbent polymer obtained by neutralizing at least some acidic groups of the polymer and micronizing the polymer in the presence of a surfactant.

[0192] At this time, the drying step can be carried out using a fixed-bed dryer, and the difference between the fixed-bed method and the mobile method lies in whether the material moves during the drying process.

[0193] Fixed-bed drying refers to a method in which the material to be dried is fixed on a floor such as a porous iron plate through which air can pass, and hot air is dried from the bottom to the top through the material. Mobile drying refers to a method in which drying is carried out while mechanically agitating the material to be dried. At this time, the direction of the hot air passing through the material can be the same as or different from the circulation direction of the material. Alternatively, the material can be circulated inside the dryer, and the heat transfer fluid is passed through a separate pipe outside the dryer for drying.

[0194] When applying fixed-bed drying, the dried superabsorbent polymer is obtained in the form of a laminate. In this case, due to the increase in the cohesive force of the hydrogel polymer, the porosity in the dried laminate is significantly reduced. As a result, the pressure difference of the hot air increases, leading to the problem of external warping of the dried product. In addition, when the amount of the dried product increases, there are problems such as significantly reduced drying efficiency, such as insufficient drying inside the dried product.

[0195] In the present disclosure, a downward air flow is initially introduced and carried out to meet a predetermined drying time. Therefore, the occurrence of warping of the dried laminate can be effectively suppressed, and excellent drying efficiency can be achieved even when the drying amount increases.

[0196] More specifically, the drying step is carried out by changing the direction of the hot air, including primary drying by a downward air flow and secondary drying by an upward air flow. In addition, the primary process is carried out for 40 to 60% of the total drying time, as described below.

[0197] The downward air flow refers to injecting hot air from top to bottom relative to the drying object, and the upward air flow refers to injecting hot air from bottom to top relative to the drying object. In other words, the directions of the hot air of the upward air flow and the downward air flow are opposite to each other. The angle of the direction can vary according to the conditions of the hot air dryer used, but generally, the angle difference between the upward air flow and the downward air flow is 180° ± 5°.

[0198] When performing the drying process under the above conditions, the constant rate period can be rapidly converted into the falling-rate drying period, that is, the falling-rate drying period can be relatively increased to achieve excellent drying efficiency. When the falling-rate period increases, a uniform drying degree can be achieved for the upper layer, the middle layer, and the lower layer of the superabsorbent polymer laminate. In addition, by using an initial downward air flow for drying, warping of the dried product can be minimized.

[0199] Figure 3 It is a drying curve showing the moisture content according to the drying time during the drying process in the preparation methods of superabsorbent polymers of the examples and comparative examples in the experimental examples of the present disclosure to be described later. As can be seen from the above figure, when the drying conditions of the present disclosure are satisfied, the constant rate period is relatively rapidly converted into the falling-rate period, and the falling-rate period increases.

[0200] According to an embodiment of the present disclosure, the fixed-bed dryer used in the drying step (step 4) may be a belt dryer.

[0201] Specifically, the drying process is carried out by adding the neutralized and micronized polymer to be dried to the perforated plate of the fixed-bed dryer. Therefore, the downward air flow means that hot air is injected from above the polymer placed on the perforated plate downward, and the upward air flow means that hot air is injected from below the perforated plate upward.

[0202] When drying is performed once by injecting a downward air flow as described above and then drying is performed a second time by injecting an upward air flow, warping of the polymer laminate is prevented, and the hot air uniformly passes through the polymer laminate. As a result, the drying efficiency is improved, and a uniform drying degree can be achieved for the upper layer, the middle layer, and the lower layer of the dried superabsorbent polymer laminate.

[0203] In particular, when the running time of the first drying by the downward air flow is 40% to 60% of the total drying time, a uniform drying degree of the superabsorbent polymer laminate can be achieved without non-drying. When the running time of the first drying by the downward air flow is less than 40%, non-drying of the upper layer and warping of the lower layer may occur. When the running time exceeds 60%, non-drying of the lower layer may occur, and a uniform drying degree cannot be achieved. Preferably, the first drying by the downward air flow can be carried out for 40% to 50% of the total drying time.

[0204] The drying step (step 4) can preferably be carried out by reducing the initial temperature from 180 °C to 230 °C to 100 °C to 120 °C, more preferably by reducing the initial temperature from 200 °C to 220 °C to 100 °C to 110 °C. When carried out within the above temperature range, the superabsorbent polymer laminate can be dried without warping. Therefore, the drying efficiency is improved, and a uniform drying degree can be achieved in the upper, middle, and lower layers of the dried superabsorbent polymer laminate. At the same time, if the drying step is carried out by raising the temperature, the drying time can be shortened, but it may be somewhat difficult to produce a dried product with a relatively high water content. In addition, the middle layer of the superabsorbent polymer laminate may not be sufficiently dried to the required degree, so the uniformity of the dried superabsorbent polymer laminate may be slightly deteriorated.

[0205] The drying time of the drying step (step 4) can be appropriately controlled according to the required drying amount and the capacity of the dryer under the above temperature and wind direction conditions.

[0206] Assuming that polymers of the same drying amount are formed into the same laminate height, excellent drying efficiency can be achieved in a relatively short time compared to conventional methods. In particular, the upper, middle, and lower layers of the polymer laminate can all be dried to a uniform degree, and the occurrence of warping can also be effectively suppressed.

[0207] The average water content of the laminate of the dried superabsorbent polymer particles obtained by carrying out the drying step (step 4) can be 4 wt% to 9 wt%, preferably 4.5 wt% to 8.5 wt%. Here, the "average water content" of the laminate can be obtained through the following process: dividing the laminate sample into three layers with uniform height: the upper layer, the middle layer, and the lower layer, measuring the water content of the polymer in each layer, and then calculating their arithmetic mean. The above measurement is carried out three times on the same object, and the arithmetic mean is taken as the average water content.

[0208] In addition, the "water content" in the present disclosure refers to the content of water in the total weight of the polymer powder, which means the value obtained by subtracting the weight of the dried polymer from the weight of the polymer powder. Specifically, the water content is defined as the value calculated by measuring the weight loss due to the evaporation of water from the polymer powder during the process of raising the temperature of the polymer by infrared heating and drying it. This will be explained in more detail in the experimental examples described later.

[0209] At the same time, the standard deviation of the water content at each lamination position (upper, middle, lower) of the laminate of the dried superabsorbent polymer particles obtained by carrying out the drying step (step 4) can be 0.1 to 1.5, preferably 0.5 to 1.5.

[0210] That is, when adjusting the drying conditions, the drying efficiency is improved, and the upper, middle, and lower layers of the dried superabsorbent polymer laminate can all be dried to a uniform degree, and the occurrence of warping can also be effectively suppressed.

[0211] Step 5: Grinding step

[0212] Subsequently, a step of preparing superabsorbent polymer particles by pulverizing the laminate of the dried superabsorbent polymer particles is performed.

[0213] Specifically, the pulverization step can be performed so that the laminate of the dried superabsorbent polymer particles has a normal particle size, that is, a particle size of 150 μm to 850 μm.

[0214] The pulverizer used for this purpose can be a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutting mill, a rotary mill, a disk mill, a shredder crusher, a crusher, a chopper, or a disk cutter, but the present disclosure is not limited thereto.

[0215] Alternatively, a needle mill, a hammer mill, a screw mill, a roll mill, a disk mill, or a jogmill can be used as the pulverizer, but the present disclosure is not limited thereto.

[0216] Meanwhile, in the micronization step of the preparation method of the present disclosure, superabsorbent polymer particles having a smaller particle size distribution than in the conventional chopping step can be provided, and when performing mobile drying, the moisture content after drying remains relatively high, being 10% by weight or more. Therefore, even when pulverizing with a smaller force under mild conditions, superabsorbent polymers with a very high content of normal particles having a particle size of 150 μm to 850 μm can be formed, thereby greatly reducing the generation of fine powder.

[0217] The superabsorbent polymer particles prepared as described above may include 80% by weight or more, 85% by weight or more, 89% by weight or more, 90% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, or 95% by weight or more of superabsorbent polymer particles (which are normal particles) having a particle size of 150 μm to 850 μm based on the total weight. The particle size of these polymer particles can be measured according to EDANA (European Disposables and Nonwovens Association) WSP 220.3.

[0218] In addition, the superabsorbent polymer particles may include fines having a particle size of less than 150 μm in an amount of about 20 wt% or less, about 18 wt% or less, about 15 wt% or less, about 13 wt% or less, about 12 wt% or less, about 11 wt% or less, about 10 wt% or less, about 9 wt% or less, about 8 wt% or less, or about 5 wt% or less based on the total weight. This is in contrast to superabsorbent polymers prepared according to conventional preparation methods, which have fines in an amount of greater than about 20 wt% to about 30 wt%.

[0219] Additional step

[0220] After the superabsorbent polymer particles are pulverized, a step of classifying the pulverized superabsorbent polymer particles according to particle size may be further included.

[0221] Furthermore, after the superabsorbent polymer particles are pulverized and / or classified, a step of forming a surface crosslinked layer on at least a part of the surface of the superabsorbent polymer particles in the presence of a surface crosslinking agent may be further included. Through the above steps, the crosslinked polymer contained in the superabsorbent polymer particles can be further crosslinked by the surface crosslinking agent, thereby forming a surface crosslinked layer on at least a part of the surface of the superabsorbent polymer particles.

[0222] As the surface crosslinking agent, any crosslinking agent conventionally used for preparing superabsorbent polymers can be used without any particular limitation. Examples of the surface crosslinking agent may include at least one polyol selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, and glycerol; at least one carbonate compound selected from the group consisting of ethylene carbonate, propylene carbonate, and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di-, or poly-oxazolidinone compounds; and cyclic urea compounds, etc.

[0223] Specifically, as the surface crosslinking agent, one or more, two or more, or three or more of the above surface crosslinking agents can be used. For example, ethylene carbonate - propylene carbonate (ECPC), propylene glycol, and / or glycerol carbonate can be used.

[0224] Based on 100 parts by weight of the superabsorbent polymer particles, the amount of the surface crosslinking agent used can be from 0.001 to 5 parts by weight. For example, the amount used can be above 0.005 parts by weight, above 0.01 parts by weight, or above 0.05 parts by weight, and below 5 parts by weight, below 4 parts by weight, or below 3 parts by weight. When the content range of the surface crosslinking agent is adjusted within the above range, a superabsorbent polymer exhibiting excellent various physical properties can be prepared.

[0225] In addition, besides the surface crosslinking agent, the step of forming the surface crosslinked layer can be carried out by adding an inorganic material. That is, in the presence of the surface crosslinking agent and the inorganic material, the step of further crosslinking the surface of the superabsorbent polymer particles to form the surface crosslinked layer can be carried out.

[0226] As the inorganic material, at least one inorganic material selected from the group consisting of silica, clay, alumina, silica-alumina composite, titanium dioxide, zinc oxide, and aluminum sulfate can be used. The inorganic material can be used in the form of powder or in the form of liquid, and in particular, alumina powder, silica-alumina powder, titanium dioxide powder, or nano-silica solution can be used. In addition, based on 100 parts by weight of the superabsorbent polymer particles, the amount of the inorganic material used can be about 0.001 to about 1 part by weight.

[0227] In addition, the method of mixing the surface crosslinking agent with the superabsorbent polymer is not particularly limited. For example, a method of adding the surface crosslinking agent and the superabsorbent polymer composition into a reactor for mixing, a method of spraying the surface crosslinking agent onto the superabsorbent polymer composition, or a method of mixing the superabsorbent polymer composition and the surface crosslinking agent while continuously feeding them into a continuously operating mixer can be used.

[0228] When mixing the surface crosslinking agent and the superabsorbent polymer composition, water and methanol can be further mixed therewith. When water and methanol are added thereto, there is an advantage that the surface crosslinking agent can be uniformly dispersed in the superabsorbent polymer composition. At this time, for the purpose of inducing the uniform dispersion of the surface crosslinking agent, preventing the agglomeration phenomenon of the superabsorbent polymer composition, and optimizing the surface penetration depth of the crosslinking agent, the addition amounts of water and methanol can be appropriately controlled.

[0229] The surface crosslinking process can be carried out at a temperature of about 80 °C to about 250 °C. More specifically, the surface crosslinking process can be carried out at a temperature of about 100 °C to about 220 °C, or about 120 °C to about 200 °C for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. When the above surface crosslinking process conditions are satisfied, the surface of the superabsorbent polymer particles is sufficiently crosslinked, thereby increasing the pressure absorbency.

[0230] The heating means for the surface crosslinking reaction is not particularly limited. Heat medium can be supplied thereto or heat source can be directly supplied thereto. At this time, the available heat medium can be a heating fluid such as steam, hot air, and hot oil, etc., but the present invention is not limited thereto. In addition, the temperature of the heat medium supplied thereto can be appropriately selected in consideration of the means of the heat medium, the heating rate, and the target temperature of heating. Meanwhile, as the heat source directly supplied, an electric heater or a gas heater can be used, but the present disclosure is not limited thereto.

[0231] According to an embodiment of the present disclosure, after forming a surface crosslinking layer on at least a part of the surface of the superabsorbent polymer particles, at least one of a cooling step of cooling the superabsorbent polymer particles on which the surface crosslinking layer is formed, a hydration step of adding water to the superabsorbent polymer particles on which the surface crosslinking layer is formed, and a post-treatment step of adding an additive to the superabsorbent polymer particles on which the surface crosslinking layer is formed can be further performed. At this time, the cooling step, the hydration step, and the post-treatment step can be performed sequentially or simultaneously.

[0232] The additives added in the post-treatment step can include a permeability enhancer, an anti-caking agent, a fluidity enhancer, an antioxidant, etc., but the present disclosure is not limited thereto.

[0233] When the cooling step, the hydration step, and the post-treatment step are optionally performed, the moisture content of the final superabsorbent polymer can be improved and a high-quality superabsorbent polymer product can be manufactured.

[0234] (Superabsorbent polymer)

[0235] Meanwhile, according to an embodiment of the present invention, a superabsorbent polymer according to the above preparation method can be provided.

[0236] The superabsorbent polymer has excellent other physical properties, and at the same time, due to excellent drying efficiency, warping on the outside is effectively suppressed, thereby improving the quality of the final product.

[0237] The superabsorbent polymer can have a particle size of 150 to 850 μm. More specifically, the base resin powder and the superabsorbent polymer including the same can contain at least 95% by weight of particles having a particle size of 150 to 850 μm, more than 50% by weight of particles having a particle size of 300 to 600 μm, and less than 3% by weight of fine powder having a particle size of less than 150 μm.

[0238] Hereinafter, the functions and effects of the present invention will be described in more detail through specific examples. However, these examples are for illustrative purposes only, and the present invention is not intended to be limited by these examples.

[0239] <Example>

[0240] Example 1

[0241] (Step 1: Preparation of Polymer)

[0242] In a 10 L glass container equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 5.0 g of pentaerythritol triallyl ether as an internal crosslinking agent, and 3406 g of water were stirred and mixed, and stirring was carried out while maintaining the temperature at 5 °C. The glass container containing the mixture was replaced with a nitrogen condition by flowing nitrogen at 1000 cc / min for 1 hour. Thereafter, 20.0 g of a 0.3% hydrogen peroxide aqueous solution, 22.5 g of a 1% ascorbic acid aqueous solution, and 45.0 g of a 2% 2,2'-azobis-(2-amidinopropane) dihydrochloride aqueous solution were added as polymerization initiators, and at the same time, 22.5 g of a 0.01% iron sulfate aqueous solution was added as a reducing agent to initiate polymerization. After the temperature of the mixture reached 85 °C, polymerization was carried out at 90 ± 2 °C for about 6 hours to obtain a polymer.

[0243] (Steps 2 and 3: Neutralization and Micronization)

[0244] While rotating a micronizer (F200, Karl Schnell) equipped with a perforated plate having a plurality of holes with a hole size of 10 mm at 1500 rpm, 5000 g of the obtained polymer was added and micronized into primary particles having a particle size of several tens to several hundreds of micrometers. At this time, 299 g of a 0.45 w% glycerol monolaurate (GML) aqueous solution was added to prevent excessive agglomeration.

[0245] Then, while rotating a meat grinder (a screw cutter equipped with a perforated plate having a plurality of holes with a hole size of 6 mm) at 500 rpm, the micronized polymer was added thereto to prepare secondary agglomerated particles. Here, the process of preparing secondary agglomerated particles was repeated three times. At this time, 1252 g of a 50% NaOH aqueous solution was added in the first pass to neutralize some acidic groups of the polymer. 157.8 g of a 10% Na2SO3 aqueous solution was added in the second pass to neutralize some acidic groups of the polymer. In the third pass, water-containing superabsorbent polymer particles were prepared by passing them through without adding any additives.

[0246] (Step 4: Drying)

[0247] 1472 g of water-containing superabsorbent polymer particles were added to a belt dryer equipped with a perforated plate that can change the wind direction up and down, with a width of 200 mm, a length of 200 mm, and a thickness of 1 mm. The water-containing superabsorbent polymer particles were placed on the perforated plate and dried by first injecting a downward air flow from above the perforated plate for 20 minutes and then injecting an upward air flow from below the perforated plate for 30 minutes. At the same time, the temperature of the hot air in the dryer was maintained at 200 °C for 5 minutes. Then, the temperature was lowered to 100 °C and dried for 45 minutes to obtain a laminate of dried superabsorbent polymer particles.

[0248] The drying curve of the water content according to the drying time during the drying process is shown in Figure 3 the

[0249] (Step 5: Crushing and classification)

[0250] The laminate of dried superabsorbent polymer particles was crushed using a two-stage roller mill (GRAN-U-LIZERTM, MPE) to obtain particles with a particle size of 150 μm to 850 μm.

[0251] A classifier was used to selectively recover the crushed material, and only the superabsorbent polymer particles with a particle size of 150 μm to 850 μm were selectively recovered.

[0252] (Step 6: Surface crosslinking)

[0253] Then, a surface crosslinking solution prepared by adding 3 g of water, 4 g of methanol, 0.1 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate was mixed with 100 g of the above-obtained superabsorbent polymer particles for 1 minute, and a surface crosslinking reaction was carried out at 140 °C for 40 minutes to obtain surface-crosslinked superabsorbent polymer.

[0254] Examples 2 to 6 and Comparative Examples 1 to 6

[0255] A superabsorbent polymer was obtained in the same manner as in Example 1, except that the process conditions of the drying step in Example 1 were changed as shown in Table 1 below.

[0256] The drying curve of the water content according to the drying time during the drying process of Comparative Example 2 is shown in Figure 3 the

[0257] In addition, in the case of Comparative Examples 2 to 6, the water content after the drying step was high, so it was difficult to crush into particles, and the subsequent process was not carried out.

[0258] [Table 1]

[0259]

[0260]

[0261] <Experimental Example>

[0262] Experimental Example 1: Evaluation of drying performance

[0263] (1) Measurement of moisture content before drying

[0264] Samples of the water-containing superabsorbent polymer obtained in Step 3 before the drying process were obtained in the Examples and Comparative Examples. Measure its initial weight H0 (g) and the weight H1 (g) after maintaining at 180 °C for 40 minutes by infrared heating, and measure the moisture content according to the following equation and list it in Table 2.

[0265] [Equation 1]

[0266] Moisture content (wt%) = {[H0 (g) - H1 (g)] / H0 (g)} * 100

[0267] (2) Measurement of moisture content after drying

[0268] For the dried superabsorbent polymer particles obtained in Step 4 (before surface crosslinking) in the Examples and Comparative Examples after the drying process, samples were obtained by cutting the dried plate-like laminate into 10 x 10 cm. Based on the cross-section (based on the height of the laminate), the samples were divided into three parts to obtain the upper layer, middle layer, and lower layer, respectively. Samples were taken from the superabsorbent polymer of each layer, and the moisture content of each layer was measured in the same manner as above, and the standard deviation between them was calculated, and the results are listed in Table 2.

[0269] (3) Degree of warping

[0270] For the dried superabsorbent polymer particles obtained in Step 4 (before surface crosslinking) in the Examples and Comparative Examples after the drying process, samples were obtained by cutting the dried plate-like laminate into 10 x 10 cm. The degree of warping of the cross-section of the sample was evaluated according to the following evaluation criteria, and the results are shown in Table 2 below.

[0271] In addition, a cross-sectional photograph of the dried product after the drying step is shown in Figure 2 . Figure 2 (a) is a cross-sectional photograph of the dried laminate after the drying step in Example 1, and (b) is a cross-sectional photograph of the dried laminate after the drying step in Comparative Example 4.

[0272] <Warping evaluation criteria>

[0273] ○: When more than 10% of the floating appears on the outside compared to the thickness of the central part of the dried product;

[0274] △: When the outer part shows a bulge of more than 5% and less than 10% compared to the thickness of the central part of the dried product;

[0275] X: When the outer part shows a bulge of less than 5% compared to the thickness of the central part of the dried product.

[0276] [Table 2]

[0277]

[0278] In the cases of Examples 1 to 6 that satisfy the drying conditions of the present disclosure, it was confirmed that due to the excellent drying efficiency, the overall physical properties of the finally prepared superabsorbent polymer were also excellent.

[0279] In Comparative Example 1, drying was carried out by minimizing the upward air flow at the start of drying, but some warping of the dried product occurred. Although the drying was carried out at a low temperature, due to the reduction in drying efficiency, there were slight differences in the moisture content of each layer in the dried product.

[0280] In Comparative Example 2, drying was carried out by minimizing the upward air flow at the start of drying, and no warping of the dried product occurred. However, although the moisture content of the upper layer and the middle layer was low, sufficient drying was not carried out, resulting in the lower layer not being dried, and there were significant differences in the moisture content of each layer in the dried product.

[0281] Experimental Example 2 - Evaluation of physical properties of superabsorbent polymers

[0282] The physical properties of the superabsorbent polymer obtained in Step 6 after the final surface crosslinking process in the Examples and Comparative Examples were evaluated as follows and are listed in Table 3 below.

[0283] Unless otherwise specified, all procedures were carried out in a thermo-hygrostat chamber (23 ± 1 °C, relative humidity 50 ± 10%), and normal saline or brine refers to an aqueous solution of 0.9 wt% sodium chloride (NaCl).

[0284] [Table 3]

[0285]

[0286] In the cases of Examples 1 to 6 that satisfy the drying conditions of the present disclosure, it was confirmed that the overall physical properties of the finally prepared superabsorbent polymer were excellent and it had excellent drying efficiency.

[0287] In the cases of Comparative Examples 2 to 6, the moisture content after drying was high, so it was difficult to pulverize into particles. Therefore, it was difficult to carry out additional processes and no additional experiments were carried out.

Claims

1. A method for preparing a superabsorbent polymer, comprising the following steps: Step 1: Polymerize a monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator to form a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group is crosslinked and polymerized with the internal crosslinking agent; Step 2: Neutralize at least some of the acidic groups of the polymer; Step 3: Micronize the polymer in the presence of a surfactant; Step 4: Dry the neutralized and micronized polymer in a fixed-bed dryer to obtain a laminate of dry superabsorbent polymer particles; and Step 5: Prepare superabsorbent polymer particles by pulverizing the laminate of dry superabsorbent polymer particles, wherein Step 4 includes a primary drying step of introducing a downward air flow and a secondary drying step of introducing an upward air flow to the neutralized and micronized polymer, and the time of the primary drying is 40% to 60% of the total drying time of Step 4.

2. The method for preparing a superabsorbent polymer according to claim 1, Among them, Step 4 is carried out by reducing the initial drying temperature from 180 °C to 230 °C to 100 °C to 120 °C.

3. The method for preparing a superabsorbent polymer according to claim 1, Among them, The average moisture content of the laminate of the dry superabsorbent polymer particles obtained by carrying out Step 4 is 4% by weight to 9% by weight.

4. The method for preparing a superabsorbent polymer according to claim 1, Among them, The standard deviation of the moisture content at each laminated position of the laminate of the dry superabsorbent polymer particles obtained by carrying out Step 4 is 0.1 to 1.

5.

5. The method for preparing a superabsorbent polymer according to claim 1, Among them, Step 1 of forming the polymer is carried out in a batch reactor.

6. The method for preparing a superabsorbent polymer according to claim 1, Among them, Step 2 and Step 3 are carried out in sequence, alternately, or simultaneously.

7. The method for preparing a superabsorbent polymer according to claim 1, Among them, The micronization step 3 is carried out by a micronization device, and the micronization device includes: A main body containing a transfer space, in which the polymer is transferred; A screw member rotatably installed inside the transfer space to move the polymer; A drive motor that provides a rotational driving force to the screw member; A cutter member installed in the main body to pulverize the polymer; and A perforated plate having a plurality of holes and capable of discharging the polymer pulverized by the cutter member to the outside of the main body.

8. The method for preparing a superabsorbent polymer according to claim 1, Among them, At least some of the surfactant in Step 3 is present on the surface of the polymer.

9. The method for preparing a superabsorbent polymer according to claim 1, Among them, The surfactant in Step 3 includes a compound represented by the following Chemical Formula 2 or a salt thereof: [Chemical Formula 2] In Chemical Formula 2, A1, A2, and A3 are each independently a single bond, a carbonyl group, provided that at least one of these is a carbonyl group or wherein m1, m2, and m3 are each independently an integer from 1 to 8, each is connected to an adjacent oxygen atom, and -* is respectively connected to adjacent R1, R2, and R3, R1, R2, and R3 are each independently hydrogen, a C6 to C18 straight-chain or branched alkyl group, or a C6 to C18 straight-chain or branched alkenyl group, and n is an integer from 1 to 9.

10. The method for preparing a superabsorbent polymer according to claim 1, further comprising the step of classifying the superabsorbent polymer particles according to particle size.

11. The method for preparing a superabsorbent polymer according to claim 1 or claim 10, further comprising the step of forming a surface crosslinked layer on at least a part of the surface of the superabsorbent polymer particles.

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