Method for producing superabsorbent polymer and superabsorbent polymer

Abstract

The present invention relates to a method for producing a superabsorbent polymer, more specifically, to a method for producing a superabsorbent polymer in which the amount of water-soluble components and fine powder generated is significantly reduced and which exhibits excellent water absorption properties.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0079644, filed June 18, 2021, and Korean Patent Application No. 10-2022-0074251, filed June 17, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for producing a superabsorbent polymer and the superabsorbent polymer. More specifically, the present invention relates to a method for producing a superabsorbent polymer and the superabsorbent polymer, which significantly reduces the amount of water-soluble components and fine powder generated and exhibits excellent water absorption properties. [Background technology]

[0003] Super absorbent polymers (SAPs) are synthetic polymers capable of absorbing 500 to 1,000 times their own weight in water, and each developer has their own name for them, such as SAM (Super Absorbency Material) or AGM (Absorbent Gel Material). These super absorbent polymers first came into practical use as sanitary products, and are now widely used in a variety of applications, including soil water retention agents for horticulture, waterproofing agents for civil engineering and construction, seedling sheets, freshness preservatives in the food distribution industry, and adhesive patches.

[0004] Such superabsorbent polymers are widely used in the field of sanitary materials, such as diapers and sanitary napkins. In these sanitary materials, the superabsorbent polymer is generally contained in a dispersed state within the pulp. However, in recent years, efforts have been made to provide thinner sanitary materials, such as diapers. As part of these efforts, the pulp content has been reduced, or even a step further, the development of so-called pulpless diapers, which do not use pulp at all, has been actively pursued.

[0005] In this way, in the case of sanitary materials with a reduced pulp content or no pulp used, the superabsorbent polymer is contained at a relatively high ratio, and the superabsorbent polymer particles are inevitably contained in multiple layers within the sanitary material. In order for the overall superabsorbent polymer particles contained in such multiple layers to more efficiently absorb a large amount of liquid such as urine, the superabsorbent polymer basically needs to exhibit not only high water absorption performance but also a fast water absorption speed.

[0006] Generally, such superabsorbent polymers are produced by polymerizing monomers to produce a hydrogel polymer containing a large amount of water, and then drying and pulverizing the hydrogel polymer into resin particles having a desired particle size. However, when the hydrogel polymer is dried and then pulverized, a large amount of fine powder is generated, which reduces the physical properties of the resulting superabsorbent polymer.

[0007] In order to reuse such fine powder, it is common to mix the fine powder with water to agglomerate it, produce a regranulated fine powder, and then add the regranulated fine powder produced through processes such as drying, pulverization, and classification. However, the water used in this process increases energy consumption during the drying process, causing problems such as a heavy load on the equipment, which can reduce the productivity of the superabsorbent polymer production.

[0008] Therefore, there is a continuing demand for the development of a technology that can produce highly water-absorbent resins without generating fine powder, so as to fundamentally solve these problems. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present invention provides a method for producing a superabsorbent polymer that can produce particles in the form of agglomerated fine particles to increase the surface area, thereby significantly improving the water absorption rate, significantly reducing the amount of fine powder generated during the process, and exhibiting excellent water absorption properties, and also provides a superabsorbent polymer. [Means for solving the problem]

[0010] In order to solve the above problem, according to one embodiment of the present invention, a step (step 1) of polymerizing a monomer composition including 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 and the internal crosslinking agent are crosslinked and polymerized; neutralizing at least a portion of the acidic groups of the polymer (Step 2); granulating the polymer in the presence of a surfactant (Step 3); drying the neutralized and granulated polymer to produce dry superabsorbent polymer particles (Step 4); and and (5) grinding the dried superabsorbent resin particles to produce superabsorbent resin particles. A method for producing a highly water-absorbent resin is provided.

[0011] According to another embodiment of the present invention, The present invention comprises a polymer obtained by crosslinking a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent, wherein at least a portion of the acidic groups of the polymer are neutralized, and the polymer is additionally crosslinked via a surface crosslinking agent to form a surface crosslinked layer on the polymer; The water absorption speed (vortex time) is 30 seconds or less, A highly water-absorbent resin is produced in which the water-soluble component is 5% by weight or less as measured after swelling for 1 hour according to EDANA method WSP270.3. [Effects of the Invention]

[0012] According to the method for producing a superabsorbent polymer of the present invention, it is possible to produce a superabsorbent polymer that has a particle shape in which fine particles are aggregated, thereby increasing the surface area and significantly improving the water absorption rate, thereby exhibiting excellent water absorption properties.

[0013] Furthermore, by pulverizing the polymer after uniformly drying it using a fluidized drying method, the amount of fine powder generated during the production of the highly water-absorbent resin can be significantly reduced.

[0014] Furthermore, by having a high molecular weight polymer, a uniform particle size distribution, and a low content of water-soluble components (EC), it is possible to provide a superabsorbent resin that is excellent in all of the following properties: water retention capacity, water absorption capacity under pressure, liquid permeability, rewet properties, and water absorption speed. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart showing a conventional method for producing a highly water-absorbent resin. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise. It should be understood that the terms "comprise," "comprise," or "have" used in this specification are intended to specify the presence of embodied features, steps, components, or combinations thereof, and do not preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0017] Although the present invention can be embodied in various forms and with various modifications, specific embodiments are described in detail below by way of example, but it should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0018] Although the present invention can be embodied in various forms and with various modifications, specific embodiments are described in detail below by way of example, but it should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0019] Hereinafter, a method for producing a superabsorbent polymer and the superabsorbent polymer according to a specific embodiment of the invention will be described in more detail.

[0020] Prior to this, the terminology used herein is for the purpose of referring to particular embodiments only and is not intended to limit the present invention, and the singular forms used herein also include the plural forms unless the context clearly dictates otherwise.

[0021] According to one embodiment of the invention, a step (step 1) of polymerizing a monomer composition including 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 and the internal crosslinking agent are crosslinked and polymerized; neutralizing at least a portion of the acidic groups of the polymer (Step 2); granulating the polymer in the presence of a surfactant (Step 3); drying the neutralized and granulated polymer to produce dry superabsorbent polymer particles (Step 4); and and (5) grinding the dried superabsorbent resin particles to produce superabsorbent resin particles. A method for making a superabsorbent polymer is provided.

[0022] The term "polymer" or "macromolecule" used in the present specification means a polymerized state of water-soluble ethylenically unsaturated monomers, and can encompass any range of moisture content or particle size.

[0023] Furthermore, the term "superabsorbent polymer" may refer to a crosslinked polymer or a powder-type base resin consisting of superabsorbent polymer particles obtained by pulverizing the crosslinked polymer, depending on the context, or may refer to the crosslinked polymer or base resin that has been subjected to additional processes, such as drying, pulverization, classification, surface crosslinking, etc., to be in a state suitable for commercialization.

[0024] Furthermore, the term "fine powder" refers to superabsorbent resin particles having a particle size of less than 150 μm, which can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3 method.

[0025] The term "chopping" refers to cutting the hydrogel polymer into millimeter-sized pieces to improve drying efficiency, as opposed to grinding to micrometer or regular particle levels.

[0026] Furthermore, the term "micronizing" refers to the grinding of a hydrogel polymer into particles of several tens to several hundreds of micrometers, and is used to distinguish it from "chopping."

[0027] The hydrogel polymer obtained by the polymerization reaction of acrylic acid monomers is commercially available as a powdered product called a superabsorbent resin after undergoing processes such as drying, pulverization, classification, and surface cross-linking. Recently, attempts have been made to provide a superabsorbent resin that exhibits an even faster water absorption rate.

[0028] The most common method for increasing the water absorption rate is to form a porous structure inside the superabsorbent resin to increase the surface area of the superabsorbent resin. In order to increase the surface area of the superabsorbent resin, a commonly used method is to include a foaming agent in the monomer composition and cause cross-linking polymerization to occur, thereby forming a porous structure in the base resin powder.

[0029] However, the use of a foaming agent is accompanied by the disadvantages that various physical properties of the superabsorbent resin, such as surface tension, liquid permeability, or volume density, decrease and the amount of fine powder generated increases. For this reason, there is a continuing demand for the development of a technology that can improve the water absorption rate of a superabsorbent resin without using a foaming agent.

[0030] Conventional superabsorbent resins are manufactured by crosslinking a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer, drying the formed hydrogel polymer, and then pulverizing it to a desired particle size. To facilitate drying of the hydrogel polymer and increase the efficiency of the pulverization process, a chopping process is typically performed before the drying process to cut the hydrogel polymer into particles several millimeters in size. However, due to the stickiness of the hydrogel polymer, the hydrogel polymer cannot be pulverized to micro-sized particles during this chopping process, resulting in an aggregated gel. When this aggregated gel-like hydrogel polymer is dried, a plate-like dried body is formed. To pulverize this to micro-sized particles, a multi-stage pulverization process is required to reduce the polymer's stickiness, which results in the generation of a large amount of fine powder.

[0031] Specifically, a flow chart of a conventional method for producing a superabsorbent polymer is shown in Figure 1. Referring to Figure 1, a conventional superabsorbent polymer has been produced through the following steps:

[0032] (neutralizing) neutralizing at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer; (Polymerization) A step of cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a hydrogel polymer; (chopping) chopping the hydrogel polymer; (Drying) drying the chopped hydrogel polymer; and (Crushing / Classification) Crushing the dried polymer and then classifying it into normal particles and fine powder;

[0033] As described above, the chopped hydrogel polymer has an agglomerated gel shape with a size of about 1 cm to 10 cm. This chopped hydrogel polymer is layered on a belt with a perforated bottom and dried by hot air supplied from the bottom or top. Because the polymer dried by this drying method exhibits a plate-like shape rather than a granular shape, the classification step after pulverization has typically been carried out by first coarsely pulverizing and classifying the polymer to produce normal particles, i.e., particles with a diameter of 150 μm to 850 μm, followed by further fine pulverization and classification. In this manufacturing method, the amount of fine powder separated in the final classification step is large, about 20 wt% to about 30 wt% of the total weight of the final superabsorbent polymer. Therefore, the separated fine powder is reused by mixing it with an appropriate amount of water, re-granulating the fine powder, and then adding it to the chopping step or the step before drying.

[0034] However, when the re-granulated fine powder mixed with water for reuse is re-introduced into the crushing or drying process, problems have arisen, such as an increase in the load on the equipment and / or the amount of energy used, and the remaining fine powder that cannot be classified has caused a deterioration in the physical properties of the superabsorbent polymer.

[0035] Therefore, the present inventors recognized that the amount of fine powder generated in conventional manufacturing methods is significantly affected by the pulverization step, and focused on the fact that the amount of fine powder generated during the manufacturing process can be significantly reduced by adding a surfactant and a neutralizing agent in the polymer pulverization step to post-neutralize the polymer, pulverizing it more finely than before, i.e., reducing the particle size, while simultaneously controlling aggregation to produce particles in the form of aggregates of fine particles.

[0036] Meanwhile, a method of adding a surfactant to reduce the stickiness of the hydrogel polymer during the chopping process has been proposed. However, when adding a surfactant during the chopping process, the high water content of the hydrogel polymer causes the surfactant to penetrate into the hydrogel polymer rather than being present at the interface of the hydrogel polymer, which results in the surfactant not being able to perform its function properly.

[0037] This is because chopped particles are formed into particles of several mm or cm in size compared to the polymer before chopping, which can increase the surface area to some extent, but it is difficult to expect an effect that can effectively improve the water absorption rate. Therefore, in order to improve the water absorption rate, it is possible to increase the surface area by increasing the mechanical force during the chopping stage and kneading, but in this case, excessive aggregation occurs due to the stickiness inherent in polymers, and after chopping, drying, and grinding, only the surface of the particles becomes an irregular, amorphous single particle, and excessive kneading or grinding can actually increase the water-soluble components.

[0038] As a result of repeated research to solve this problem, it was found that, unlike conventional methods for producing superabsorbent polymers in which the acidic groups of a water-soluble ethylenically unsaturated monomer are neutralized before polymerization to form a polymer, the polymerization is first carried out in a state in which the acidic groups are not neutralized, and the hydrogel polymer is then granulated in the presence of a surfactant, and the acidic groups of the polymer are then neutralized; or, the acidic groups of the polymer are neutralized to form a hydrogel polymer, and the hydrogel polymer is then granulated in the presence of a surfactant, or, simultaneously with granulation, the acidic groups present in the polymer are neutralized. This allows a large amount of surfactant to be present on the surface of the polymer, thereby reducing the high viscosity of the polymer and preventing excessive aggregation of the polymer, and thereby fully fulfilling the role of adjusting the aggregation state to a desired level.

[0039] As a result, the polymer is produced into secondary particles in the form of agglomerated primary particles, and then the pulverization and drying processes are carried out under milder conditions, thereby significantly reducing the amount of fine powder generated during the process.

[0040] Furthermore, when a polymer is pulverized in the presence of the surfactant, the hydrophobic functional groups contained in the surfactant impart hydrophobicity to the surfaces of the pulverized superabsorbent resin particles, thereby reducing interparticle friction and increasing the apparent density of the superabsorbent resin, while the hydrophilic functional groups contained in the surfactant also bind to the superabsorbent resin particles, preventing a decrease in the surface tension of the resin. As a result, the superabsorbent resin produced by the above-mentioned production method has a higher apparent density value than a resin that does not use a surfactant, while exhibiting the same level of surface tension.

[0041] Furthermore, if polymerization is first carried out in an unneutralized state to form a polymer, and then the acidic groups present in the polymer are neutralized, it is possible to form a polymer with a longer chain, and the content of water-soluble components present in an uncrosslinked state due to incomplete crosslinking can be reduced.

[0042] The water-soluble component has the property of easily dissolving when the superabsorbent polymer comes into contact with a liquid, so if the content of the water-soluble component is high, most of the dissolved water-soluble component remains on the surface of the superabsorbent polymer, making the superabsorbent polymer sticky and reducing liquid permeability. Therefore, from the viewpoint of liquid permeability, it is important to maintain the content of the water-soluble component low.

[0043] According to one embodiment of the present invention, the content of water-soluble components is reduced by carrying out polymerization in an unneutralized state, thereby improving the liquid permeability of the superabsorbent resin.

[0044] In addition, the superabsorbent resin produced according to one embodiment of the present invention may have a uniform particle size distribution, thereby providing a superabsorbent resin with excellent water absorption properties such as water retention capacity, water absorption capacity under pressure, rewet properties, and water absorption speed.

[0045] Hereinafter, each step of the method for producing a highly water-absorbent resin according to one embodiment will be described in more detail.

[0046] Stage 1: Polymerization Stage 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 and the internal crosslinking agent are crosslinked and polymerized.

[0047] The steps include preparing a monomer composition by mixing the water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator, and polymerizing the monomer composition to form a polymer.

[0048] The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the production of superabsorbent resins. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Chemical Formula 1:

[0049] [Chemical formula 1] R-COOM'

[0050] In the above Chemical Formula 1, R is an alkyl group having 2 to 5 carbon atoms and containing an unsaturated bond, M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0051] Preferably, the monomer may be one or more selected from the group consisting of (meth)acrylic acid, and monovalent (alkali) metal salts, divalent metal salts, ammonium salts and organic amine salts of these acids.

[0052] Thus, when (meth)acrylic acid and / or its salt is used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent resin with improved water absorption. Other examples of the monomer that can be used include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamide, N-substituted (meth)acrylates, 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.

[0053] Here, the water-soluble ethylenically unsaturated monomer has an acidic group. As described above, in the conventional production of a superabsorbent resin, a monomer in which at least a portion of the acidic groups have been neutralized with a neutralizing agent is cross-linked to form a hydrogel polymer. Specifically, at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer are neutralized in the step of mixing the water-soluble ethylenically unsaturated monomer having the acidic group, an internal cross-linking agent, a polymerization initiator, and a neutralizing agent.

[0054] However, according to one embodiment of the present invention, the water-soluble ethylenically unsaturated monomer is polymerized first in a state where the acid group is not neutralized to form a polymer.

[0055] A water-soluble ethylenically unsaturated monomer (e.g., acrylic acid) in which the acid group is not neutralized is in a liquid state at room temperature and has high miscibility with the solvent (water), so it exists in the form of a mixed solution in the monomer composition. However, a water-soluble ethylenically unsaturated monomer in which the acid group is neutralized is in a solid state at room temperature and has different solubility depending on the temperature of the solvent (water), with the solubility decreasing as the temperature decreases.

[0056] Such water-soluble ethylenically unsaturated monomers in which the acidic group is not neutralized have higher solubility or miscibility in a solvent (water) than monomers in which the acidic group is neutralized, and do not precipitate even at low temperatures, making them advantageous for long-term polymerization at low temperatures. As a result, long-term polymerization using the water-soluble ethylenically unsaturated monomers in which the acidic group is not neutralized can stably produce polymers with higher molecular weights and more uniform molecular weight distributions.

[0057] Furthermore, it is possible to form a polymer with a longer chain, and the effect of reducing the content of water-soluble components that exist in an uncrosslinked state due to incomplete polymerization or crosslinking can be achieved.

[0058] Furthermore, if polymerization is first carried out in a state where the acidic groups of the monomers are not neutralized to form a polymer, and then the polymer is pulverized in the presence of a surfactant after neutralization, or if the polymer is pulverized in the presence of a surfactant and then neutralized, or if the acidic groups present in the polymer are neutralized simultaneously with pulverization, the surfactant will be present in large amounts on the surface of the polymer, and can fully play a role in reducing the stickiness of the polymer.

[0059] The concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition can be appropriately adjusted in consideration of the polymerization time, reaction conditions, etc., and may be about 20 to about 60% by weight, or about 20 to about 40% by weight.

[0060] The term "internal cross-linking agent" used in this specification is a term used to distinguish it from a surface cross-linking agent for cross-linking the surface of the superabsorbent resin particles described later, and plays a role in introducing cross-linking bonds between unsaturated bonds of the water-soluble ethylenically unsaturated monomer described above to form a polymer containing a cross-linked structure.

[0061] The crosslinking in this step is carried out regardless of whether it is on the surface or inside. However, when a surface crosslinking process of superabsorbent resin particles, which will be described later, is carried out, the surface of the superabsorbent resin particles finally produced may include a structure newly crosslinked by the surface crosslinking agent, and the inside of the superabsorbent resin particles may maintain the structure crosslinked by the internal crosslinking agent.

[0062] According to an embodiment of the present invention, the internal crosslinking agent may include at least one of a multifunctional acrylate-based compound, a multifunctional allyl-based compound, and a multifunctional vinyl-based compound.

[0063] Non-limiting examples of polyfunctional acrylate compounds 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, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, and pentaerythritol. Examples thereof include 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, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate, and these can be used alone or in combination of two or more.

[0064] Non-limiting examples of polyfunctional allyl compounds 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, 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, glycerin diallyl ether, and glycerin triallyl ether. These compounds may be used alone or in combination of two or more.

[0065] Non-limiting examples of polyfunctional vinyl compounds 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, glycerin divinyl ether, and glycerin trivinyl ether. These compounds can be used alone or in combination. Pentaerythritol triallyl ether is preferably used.

[0066] The above-mentioned polyfunctional allyl compounds or polyfunctional vinyl compounds can form a crosslinked structure during the polymerization process by bonding two or more unsaturated groups contained in the molecule with the unsaturated bond of the water-soluble ethylenically unsaturated monomer or the unsaturated bond of another internal crosslinking agent, respectively, and can maintain the crosslinked bond more stably even during the neutralization process after the above-mentioned polymerization reaction, unlike acrylate compounds containing an ester bond (-(C=O)O-) in the molecule.

[0067] This increases the gel strength of the produced superabsorbent resin, improves process stability during the extrusion process after polymerization, and minimizes the amount of water-soluble components.

[0068] The crosslinking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of such an internal crosslinking agent is carried out in the presence of a polymerization initiator, and, if necessary, a thickener, a plasticizer, a storage stabilizer, an antioxidant, etc.

[0069] In the monomer composition, the internal crosslinking agent can be used in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent can be used in an amount of 0.01 part by weight or more, or 0.05 part by weight or more, or 0.1 part by weight or more and 5 parts by weight or less, or 3 parts by weight or less, or 2 parts by weight or less, or 1 part by weight or less, or 0.7 parts by weight or less per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the internal crosslinking agent is too low, crosslinking may not occur sufficiently, making it difficult to achieve an appropriate level of strength. If the content of the internal crosslinking agent is too high, the internal crosslink density may increase, making it difficult to achieve the desired water retention capacity.

[0070] The polymer formed using such an internal crosslinking agent has a three-dimensional network structure in which the main chain formed by polymerization of the water-soluble ethylenically unsaturated monomer is crosslinked by the internal crosslinking agent. When the polymer has such a three-dimensional network structure, the water retention capacity and water absorption capacity under pressure, which are various physical properties of the superabsorbent resin, can be significantly improved compared to when the polymer has a two-dimensional linear structure that is not additionally crosslinked by the internal crosslinking agent.

[0071] According to one embodiment of the present invention, the step of polymerizing the monomer composition to form a polymer is carried out in a batch type reactor.

[0072] In a typical method for producing a superabsorbent resin, polymerization methods are roughly divided into thermal polymerization and photopolymerization depending on the polymerization energy source. Generally, when thermal polymerization is carried out, it is carried out in a reactor having a stirring shaft such as a kneader, and when photopolymerization is carried out, it is carried out in a reactor equipped with a movable conveyor belt or in a vessel with a flat bottom.

[0073] On the other hand, such polymerization methods generally result in a short polymerization reaction time (for example, 1 hour or less), and therefore result in the formation of polymers with a broad molecular weight distribution and a low molecular weight.

[0074] On the other hand, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or a container with a flat bottom, the resulting hydrogel polymer is usually in the form of a sheet having the width of the belt, and the thickness of the polymer sheet varies depending on the concentration and injection speed or amount of the monomer composition injected, but is usually about 0.5 to about 5 cm thick.

[0075] However, if the monomer composition is supplied to such an extent that the thickness of the sheet-like polymer is too thin, the production efficiency is low, which is undesirable, and if the thickness of the sheet-like polymer is increased for productivity reasons, the polymerization reaction does not occur uniformly throughout the entire thickness, making it difficult to form a high-quality polymer.

[0076] In addition, in the polymerization in the reactor having the agitator shaft of the reactor equipped with the conveyor belt, the polymerization is carried out continuously by feeding new monomer composition to the reactor while the polymerization result is moving, so polymers with different polymerization rates are mixed, which makes it difficult to carry out uniform polymerization throughout the monomer composition, and may result in deterioration of overall physical properties.

[0077] However, according to one embodiment of the present invention, the polymerization is carried out in a stationary manner using a batch reactor, which reduces the risk of polymers with different polymerization rates being mixed together, thereby producing polymers with uniform quality.

[0078] In addition, the polymerization step is carried out in a batch reactor having a predetermined volume, and the polymerization reaction is carried out for a longer time, for example, 3 hours or more, than when polymerization is carried out in a continuous reactor equipped with a conveyor belt. Despite this long polymerization reaction time, since the polymerization is carried out on unneutralized water-soluble ethylenically unsaturated monomers, the monomers do not precipitate even when the polymerization is carried out for a long time, and therefore, it is advantageous for long-term polymerization.

[0079] Meanwhile, the polymerization in the batch reactor of the present invention is carried out by using a thermal polymerization method, and thus the polymerization initiator is a thermal polymerization initiator.

[0080] The thermal polymerization initiator may be one or more selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid. Specific examples of persulfate initiators include sodium persulfate (NaSO), potassium persulfate (KSO), and ammonium persulfate ((NHSO). Examples of azo initiators include 2,2-azobis(2-amidinopropane) dihydrochloride and 2,2-azobis(N,N-dimethylene)isobutyramidine dihydrochloride. dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), etc. A wide variety of thermal polymerization initiators are clearly described in Odian's "Principle of Polymerization" (Wiley, 1981), p. 203, and are not limited to the examples mentioned above.

[0081] The polymerization initiator can be used in an amount of 2 parts by weight or less per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, if the concentration of the polymerization initiator is too low, the polymerization rate will be slow and a large amount of residual monomer may be extracted into the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network will be shorter, the content of water-soluble components will be higher, and the physical properties of the resin, such as the water absorption capacity under pressure, will be reduced, which is undesirable.

[0082] Meanwhile, in one embodiment of the present invention, polymerization can be initiated by adding a reducing agent that forms a redox couple with the initiator.

[0083] Specifically, when the initiator and the reducing agent are added to the polymer solution, they react with each other to form radicals.

[0084] The formed radicals react with the monomer, and the oxidation-reduction reaction between the initiator and the reducing agent is highly reactive, so polymerization can be initiated even with only a small amount of initiator and reducing agent added. This allows low-temperature polymerization without the need to increase the process temperature, and minimizes changes in the physical properties of the polymer solution.

[0085] The polymerization reaction using the oxidation-reduction reaction can occur smoothly at or below room temperature (25°C). For example, the polymerization reaction is carried out at a temperature of 5°C to 25°C or 5°C to 20°C.

[0086] In one embodiment of the present invention, when a persulfate initiator is used as the initiator, the reducing agent can be at least one selected from the group consisting of sodium metabisulfite (NaSO); tetramethylethylenediamine (TMEDA); a mixture of iron (II) sulfate and EDTA (FeSO / EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinoacetate.

[0087] For example, potassium persulfate can be used as the initiator and disodium 2-hydroxy-2-sulfinoacetate as the reducing agent; ammonium persulfate can be used as the initiator and tetramethylethylenediamine as the reducing agent; or sodium persulfate can be used as the initiator and sodium formaldehyde sulfoxylate as the reducing agent.

[0088] In another embodiment of the present invention, when a hydrogen peroxide-based initiator is used as the initiator, the reducing agent may be one or more selected from the group consisting of ascorbic acid; sucrose; sodium sulfite (NaSO), sodium metabisulfite (NaSO); tetramethylethylenediamine (TMEDA); a mixture of iron (II) sulfate and EDTA (FeSO / EDTA); sodium formaldehyde sulfoxylate; disodium 2-hydroxy-2-sulfinoacetate; and disodium 2-hydroxy-2-sulfoacteate.

[0089] The monomer composition may further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

[0090] The monomer composition containing the monomer may be in a solution state dissolved in a solvent such as water, and the solid content in the monomer composition in such a solution state, i.e., the concentrations of the monomer, internal crosslinking agent, and polymerization initiator, can be appropriately adjusted in consideration of the polymerization time, reaction conditions, etc. For example, the solid content in the monomer composition may be 10 to 80 wt %, 15 to 60 wt %, or 30 to 50 wt %.

[0091] The solvent that can be used in this case is not limited in composition as long as it can dissolve the above-mentioned components, and for example, one or more solvents 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 can be used in combination.

[0092] The polymer obtained by this method is obtained by polymerizing an unneutralized ethylenically unsaturated monomer, and as described above, it is possible to form a polymer having a high molecular weight and a uniform molecular weight distribution, and the content of water-soluble components can be reduced.

[0093] The polymer obtained by such a method may be in a hydrogel polymer state with a water content of 30 to 80% by weight. For example, the water content of the polymer may be 30% by weight or more, or 45% by weight or more, or 50% by weight or more, and 80% by weight or less, or 70% by weight or less, or 60% by weight or less.

[0094] If the water content of the polymer is too low, it may be difficult to secure an adequate surface area in the subsequent pulverization step, and the polymer may not be effectively pulverized. If the water content of the polymer is too high, the pressure applied in the subsequent pulverization step may increase, making it difficult to pulverize the polymer to a desired particle size.

[0095] Throughout this specification, the term "moisture content" refers to the amount of water in a polymer relative to its total weight, calculated by subtracting the weight of the polymer in a dry state from the weight of the polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of water in the polymer during the drying process of raising the temperature of a crumb-state polymer using infrared heating. The drying conditions are to raise the temperature from room temperature to about 180°C and then maintain it at 180°C, and the total drying time is set to 40 minutes, including 5 minutes for the temperature rise step, and the moisture content is measured.

[0096] Stage 2: Neutralization Stage and Stage 3: Granulation Stage Next, a step (step 2) is carried out in which at least some of the acid groups of the polymer are neutralized.

[0097] In this case, the neutralizing agent may be a basic substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide, which can neutralize the acidic group.

[0098] Furthermore, the degree of neutralization, which refers to the degree to which the acidic groups contained in the polymer are neutralized by the neutralizing agent, may 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 varies depending on the final physical properties. However, if the degree of neutralization is too high, the water absorption capacity of the superabsorbent polymer may decrease, and the concentration of carboxyl groups on the particle surface may be too low, making it difficult to properly perform surface cross-linking in subsequent processes, resulting in reduced water absorption properties or liquid permeability under pressure. Conversely, if the degree of neutralization is too low, not only will the water absorption capacity of the polymer be significantly reduced, but it may also exhibit properties similar to elastic rubber, making it difficult to handle.

[0099] Simultaneously with, before or after step 2, a step of granulating the polymer in the presence of a surfactant is carried out (step 3).

[0100] This step involves pulverizing the polymer in the presence of a surfactant, not by chopping the polymer into millimeter-sized particles, but by simultaneously chopping and aggregating the polymer into particles of tens to hundreds of micrometers. That is, this step involves imparting appropriate adhesiveness to the polymer to produce secondary agglomerated particles formed by aggregating primary particles chopped into particles of tens to hundreds of micrometers. The resulting secondary agglomerated particles have a normal particle size distribution and a significantly increased surface area, resulting in significantly improved water absorption speed.

[0101] After mixing the polymer and surfactant in this manner, the polymer is pulverized in the presence of the surfactant to produce hydrous superabsorbent resin particles in the form of secondary agglomerated particles in which the superabsorbent resin particles and surfactant are chopped and agglomerated in a mixed state.

[0102] Here, "water-containing superabsorbent resin particles" are particles with a water content (moisture content) of about 30% by weight or more, and are formed by chopping and agglomerating a polymer into particles without a drying process, so they can have a moisture content of 30 to 80% by weight, similar to the polymer.

[0103] According to one embodiment of the present invention, the surfactant may be a compound represented by the following Chemical Formula 2 or a salt thereof, but the present invention is not limited thereto:

[0104] [ka]

[0105] In the above Chemical Formula 2, A1, A2 and A3 each independently represent a single bond, a carbonyl,

[0106] [ka]

[0107] and one or more of these is a carbonyl or

[0108] [ka]

[0109] wherein m1, m2, and m3 each independently represent an integer of 1 to 8;

[0110] [ka]

[0111] are each linked to an adjacent oxygen atom,

[0112] [ka]

[0113] are connected to adjacent R1, R2 and R3, respectively, R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer of 1 to 9.

[0114] The surfactant is added so that the particle size reduction step can be easily carried out without agglomeration by mixing with the polymer.

[0115] The surfactant represented by Chemical Formula 2 is a nonionic surfactant and has excellent surface adsorption performance due to hydrogen bonding even with unneutralized polymers, making it suitable for achieving the desired aggregation control effect. On the other hand, in the case of an anionic surfactant that is not a nonionic surfactant, when it is mixed with a polymer neutralized with a neutralizing agent such as NaOH or Na2SO4, the ionized Na is attached to the carboxyl group substituent of the polymer. +When the compound is adsorbed via ions and mixed with an unneutralized polymer, there is a problem that the adsorption efficiency to the polymer is relatively reduced due to competition with the anions of the carboxyl group substituents of the polymer.

[0116] Specifically, in the surfactant represented by the chemical formula 2, the hydrophobic functional groups are the terminal functional groups R1, R2, and R3 (if they are not hydrogen), and the hydrophilic functional groups are the glycerol-derived portion in the chain and the terminal hydroxyl group (A n is a single bond and R n is hydrogen, n=1 to 3), and the glycerol-derived portion and the terminal hydroxyl group are hydrophilic functional groups that improve the adsorption performance on the polymer surface, thereby effectively suppressing the aggregation of superabsorbent resin particles.

[0117] In Formula 2, the hydrophobic functional groups R1, R2, and R3 (when not hydrogen) are each independently a straight-chain or branched-chain alkyl having 6 to 18 carbon atoms or a straight-chain or branched-chain alkenyl having 6 to 18 carbon atoms. If the R1, R2, and R3 (when not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, the chain length is too short, which can cause problems in that aggregation of the milled particles is not effectively controlled. If the R1, R2, and R3 (when not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the surfactant is reduced, which can prevent effective mixing with the polymer, and the unit cost of the composition can increase due to increased surfactant costs.

[0118] Preferably, R1, R2, and R3 are hydrogen, or in the case of a straight-chain or branched alkyl having 6 to 18 carbon atoms, they may be 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl, or in the case of a straight-chain or branched alkenyl having 6 to 18 carbon atoms, they may be 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-dekenyl, 2-undekenyl, 2-dodekenyl, 2-tridekenyl, 2-tetradekenyl, 2-pentadekenyl, 2-hexadekenyl, 2-heptadekenyl, or 2-octadekenyl.

[0119] The surfactant is selected from the compounds represented by the following chemical formulas 2-1 to 2-14: [ka] [ka] [ka]

[0120] The surfactant can be used in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the polymer. If the surfactant is used too little, it will not be uniformly adsorbed onto the surface of the polymer, resulting in re-agglomeration of particles after pulverization. If the surfactant is used too much, the properties of the final superabsorbent resin may be degraded. For example, the surfactant can be used in an amount of 0.01 part by weight or more, 0.015 parts 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, or 1 part by weight or less per 100 parts by weight of the polymer.

[0121] The method of mixing such a surfactant with a polymer is not particularly limited as long as it can be uniformly mixed with the polymer, and can be appropriately adopted and used. Specifically, the surfactant can be mixed in a dry state, dissolved in a solvent and then mixed in a solution state, or melted and then mixed.

[0122] For example, the surfactant may be mixed in a solvent in the form of a solution. Any type of solvent, including inorganic and organic solvents, may be used. However, considering the ease of the drying process and the cost of the solvent recovery system, water is the most suitable. The solution may be prepared by mixing the surfactant and polymer in a reaction vessel, by adding the polymer to a mixer and injecting the solution, or by continuously supplying the polymer and solution to a continuously operated mixer and mixing them.

[0123] Meanwhile, according to one embodiment of the present invention, the step of neutralizing at least a portion of the acid groups of the polymer (Step 2) and the step of pulverizing the polymer in the presence of a surfactant (Step 3) are carried out sequentially, alternately, or simultaneously.

[0124] That is, a neutralizing agent may be added to the polymer to neutralize the acidic groups first, and then a surfactant may be added to the neutralized polymer to refine the polymer mixed with the surfactant, or a neutralizing agent and surfactant may be added to the polymer simultaneously to neutralize and refine the polymer. Alternatively, the surfactant may be added first, and then the neutralizing agent may be added later. Alternatively, the neutralizing agent and surfactant may be added alternately. Alternatively, the surfactant may be added first to refine the particles, and then the neutralizing agent may be added to neutralize the particles, and then an additional surfactant may be added to the neutralized hydrogel polymer to perform an additional refinement step.

[0125] On the other hand, in order to ensure uniform neutralization of the entire polymer, it is preferable to leave a certain time lag between the addition of the neutralizing agent and the particle refining step.

[0126] At least a portion or a substantial amount of the surfactant may be present on the surface of the hydrated superabsorbent resin particles.

[0127] Here, the presence of the surfactant on the surface of the hydrated superabsorbent resin particles means that at least a portion or a substantial amount of the surfactant is adsorbed or bound to the surface of the hydrated superabsorbent resin particles. Specifically, the surfactant may be physically or chemically adsorbed to the surface of the superabsorbent resin. More specifically, the hydrophilic functional groups of the surfactant may be physically adsorbed to the hydrophilic portion of the surface of the superabsorbent resin by intermolecular forces such as dipole-dipole interaction. In this way, the hydrophilic portion of the surfactant may be physically adsorbed to the surface of the superabsorbent resin particles, surrounding the surface, while the hydrophobic portion of the surfactant may not be adsorbed to the surface of the resin particles, and the resin particles may be coated with the surfactant in the form of a type of micelle structure. This is because the surfactant is added not during the polymerization process of the water-soluble ethylenically unsaturated monomer, but during the granulation step after polymer formation. This allows the surfactant to faithfully fulfill its role as compared to when the surfactant is added during the polymerization process and exists inside the polymer, and particles with a large surface area can be obtained in the form of aggregated fine particles due to simultaneous pulverization and aggregation.

[0128] According to one embodiment of the present invention, the step of pulverizing the polymer to prepare the water-containing superabsorbent resin particles is carried out two or more times.

[0129] According to one embodiment of the present invention, the pulverization step is performed by a pulverization device, which may include a body having a transfer space into which the polymer is transferred, a screw member rotatably installed within the transfer space to move the polymer, a drive motor providing rotational driving force to the screw member, a cutter member installed in the body to pulverize the polymer, and a perforated plate having a plurality of holes formed therein and discharging the polymer pulverized by the cutter member to the outside of the body. The hole size of the perforated plate of the pulverization device may be 1 mm to 20 mm, 5 mm to 15 mm, or 5 mm to 12 mm.

[0130] In this way, when the polymer mixed with the surfactant is pulverized using a pulverizer while controlling aggregation, a smaller particle size distribution is achieved, and the subsequent drying and pulverization steps can be carried out under milder conditions, thereby preventing the generation of fine powder and improving the physical properties of the superabsorbent resin.

[0131] Stage 4: Drying Next, the hydrated superabsorbent resin particles are dried to produce dried superabsorbent resin particles (Step 4).

[0132] This step involves drying the water content of the hydrated superabsorbent polymer particles, which are polymers obtained by neutralizing at least some of the acid groups of the polymer and pulverizing the polymer in the presence of a surfactant.

[0133] In a typical method for producing a superabsorbent polymer, the drying step is generally carried out until the moisture content of the superabsorbent polymer is less than 10% by weight, but according to one embodiment of the present invention, the superabsorbent polymer is dried to a moisture content of 10% by weight or more, for example, about 10 to about 20% by weight, or about 10 to about 15% by weight, although the present invention is not limited thereto.

[0134] For this reason, the temperature inside the dryer used in the drying step can be relatively low, about 150° C. or less, for example, about 80° C. to about 150° C. If the temperature inside the dryer is too low, the drying time becomes too long, and if the drying temperature is too high, a superabsorbent resin having a moisture content lower than the desired moisture content is obtained.

[0135] In this case, the drying is carried out in a moving type, which is distinguished from stationary drying by whether or not the material moves during drying.

[0136] The moving-type drying method refers to a method of drying materials while mechanically stirring them. In this case, the direction in which the hot air passes through the materials may be the same as or different from the direction in which the materials circulate. Alternatively, the materials may be circulated inside the dryer, and a heat transfer fluid (heat medium flow) may be passed through a separate pipe outside the dryer to dry the materials.

[0137] In contrast, stationary drying is a method in which the material to be dried is placed at the bottom of a perforated iron plate through which air passes, and hot air passes from bottom to top to dry the material.

[0138] Therefore, in this step, it is preferable to dry the hydrated superabsorbent polymer using a fluidized drying method, since this allows for uniform drying to be completed within a short drying time.

[0139] Examples of devices that can be used for drying by this fluidized drying method include a horizontal-type mixer, a rotary kiln, a paddle dryer, a steam tube dryer, or a commonly used fluidized dryer.

[0140] Stage 5: Crushing Stage Next, the dried superabsorbent resin particles are pulverized to prepare superabsorbent resin particles.

[0141] Specifically, the pulverization step is performed by pulverizing the dried superabsorbent resin particles to have a particle size of normal particle level, that is, a particle size of 150 μm to 850 μm.

[0142] The pulverizer used for this purpose may be, specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, or a disc cutter, but is not limited to the above examples.

[0143] Alternatively, the crusher may be a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like, but is not limited to the above examples.

[0144] On the other hand, in the manufacturing method of the present invention, in the granulation step, it is possible to realize superabsorbent resin particles with a smaller particle size distribution than in the conventional chopping step, and when fluidized (moving type) drying is performed, the moisture content after drying is maintained relatively high at 10% by weight or more. Therefore, even if pulverization is performed under mild conditions with less pulverization force, it is possible to form a superabsorbent resin with a very high content of normal particle sizes of 150 μm to 850 μm, and the rate of fine powder generation can be significantly reduced.

[0145] The superabsorbent resin particles prepared as described above may contain 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 resin particles having a particle size of 150 μm to 850 μm, i.e., normal particles, based on the total weight. The particle size of such resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3 method.

[0146] Furthermore, the superabsorbent resin particles may contain fine powder having a particle size of less than 150 μm in an amount of about 20% by weight or less, about 18% by weight or less, about 15% by weight or less, about 13% by weight or less, about 12% by weight or less, about 11% by weight or less, about 10% by weight or less, about 9% by weight or less, about 8% by weight or less, or about 5% by weight or less, based on the total weight of the superabsorbent resin particles. This is in contrast to the fine powder content of more than about 20% by weight to about 30% by weight when superabsorbent resins are produced by conventional manufacturing methods.

[0147] Additional Stages After the step of pulverizing the superabsorbent resin particles, the method may further include a step of classifying the pulverized superabsorbent resin particles according to particle size.

[0148] The method may further include a step of forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent resin particles in the presence of a surface cross-linking agent after pulverizing and / or classifying the superabsorbent resin particles, whereby the cross-linked polymer contained in the superabsorbent resin particles is additionally cross-linked through the intermediation of the surface cross-linking agent, thereby forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent resin particles.

[0149] The surface cross-linking agent may be any surface cross-linking agent that has been conventionally used in the production of superabsorbent resins, without any particular limitation. For example, the surface cross-linking agent may include one or more polyols 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; one or more carbonate compounds 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; mono-, di-, or polyoxazolidinone compounds; or cyclic urea compounds.

[0150] Specifically, one or more, two or more, or three or more of the above-mentioned surface cross-linking agents can be used as the surface cross-linking agent. For example, ethylene carbonate-propylene carbonate (ECPC), propylene glycol, and / or glycerol carbonate can be used.

[0151] Such a surface cross-linking agent can be used in an amount of about 0.001 to about 5 parts by weight relative to 100 parts by weight of the superabsorbent resin particles. For example, the surface cross-linking agent can be used in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.05 parts by weight or more and 5 parts by weight or less, or 4 parts by weight or less, or 3 parts by weight or less relative to 100 parts by weight of the superabsorbent resin particles. By adjusting the content range of the surface cross-linking agent within the above range, a superabsorbent resin exhibiting excellent water absorption properties can be produced.

[0152] In addition, the step of forming the surface cross-linked layer may be performed by adding an inorganic substance to the surface cross-linking agent, i.e., the surface of the superabsorbent resin particles may be additionally cross-linked in the presence of the surface cross-linking agent and the inorganic substance to form the surface cross-linked layer.

[0153] The inorganic substance may be one or more selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate. The inorganic substance may be used in powder or liquid form, particularly alumina powder, silica-alumina powder, titania powder, or nanosilica solution. The inorganic substance may be used in an amount of about 0.001 to about 1 part by weight per 100 parts by weight of the superabsorbent resin particles.

[0154] Furthermore, there is no limitation on the configuration of the method for mixing the surface cross-linking agent with the superabsorbent polymer composition. For example, a method in which the surface cross-linking agent and the superabsorbent polymer composition are mixed in a reaction tank, a method in which the surface cross-linking agent is sprayed onto the superabsorbent polymer composition, a method in which the superabsorbent polymer composition and the surface cross-linking agent are continuously supplied to a continuously operated mixer and mixed therein, etc. can be used.

[0155] When the surface cross-linking agent and the superabsorbent polymer composition are mixed, water and methanol may be added together. The addition of water and methanol has the advantage of enabling the surface cross-linking agent to be uniformly dispersed in the superabsorbent polymer composition. The amounts of water and methanol added can be appropriately adjusted to induce uniform dispersion of the surface cross-linking agent, prevent clumping of the superabsorbent polymer composition, and optimize the surface penetration depth of the cross-linking agent.

[0156] The surface cross-linking step is carried out at a temperature of about 80°C to about 250°C. More specifically, the surface cross-linking step is 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-mentioned conditions for the surface cross-linking step are satisfied, the surfaces of the superabsorbent resin particles are sufficiently cross-linked, thereby increasing the water absorption capacity under pressure.

[0157] The temperature raising means for the surface crosslinking reaction is not particularly limited. Heating can be performed by supplying a heat medium or directly supplying a heat source. In this case, the type of heat medium that can be used may be a heated fluid such as steam, hot air, or hot oil, but is not limited thereto. The temperature of the heat medium to be supplied may be appropriately selected in consideration of the means of the heat medium, the rate of temperature rise, and the target temperature of temperature rise. Meanwhile, examples of a heat source that can be directly supplied include, but are not limited to, electric heating and gas heating methods.

[0158] According to one embodiment of the present invention, after the step of forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent resin particles, the method further includes one or more steps of: a cooling step of cooling the superabsorbent resin particles having the surface cross-linked layer formed thereon; a hydration step of adding water to the superabsorbent resin particles having the surface cross-linked layer formed thereon; and a post-treatment step of adding an additive to the superabsorbent resin particles having the surface cross-linked layer formed thereon. In this case, the cooling step, the hydration step, and the post-treatment step are performed sequentially or simultaneously.

[0159] The additives added in the post-treatment step may be, but are not limited to, a liquid permeability improver, an anti-caking agent, a flowability improver, an antioxidant, and the like.

[0160] By selectively carrying out the cooling step, the hydration step, and the post-treatment step, the moisture content of the final superabsorbent polymer can be improved, and a higher quality superabsorbent polymer product can be produced.

[0161] The superabsorbent polymer produced by this method has a high water absorption rate and a low fine powder content, and its water absorption properties, such as water retention capacity (CRC) and absorbency under pressure (AUP), are at the same level or higher than those of superabsorbent polymers produced by conventional methods.

[0162] In addition, the particle size distribution can be narrowed to provide a uniform particle size distribution, and the content of water-soluble components (EC) can be reduced, thereby providing a superabsorbent resin with excellent liquid permeability and rewet properties.

[0163] The superabsorbent polymer according to one embodiment comprises: The present invention comprises a polymer obtained by crosslinking a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent, wherein at least a portion of the acidic groups of the polymer are neutralized, and the polymer is additionally crosslinked via a surface crosslinking agent to form a surface crosslinked layer on the polymer; The water absorption speed (vortex time) is 30 seconds or less, The water-soluble component measured after swelling for 1 hour according to EDANA method WSP270.3 is 5% by weight or less.

[0164] As an example, the superabsorbent polymer of the present invention may have a water retention capacity (CRC) measured by EDANA method WSP241.3 of about 30 g / g or more, or about 32 g / g or more, or about 34 g / g or more, or about 35 g / g or more, or about 36 g / g or more, or about 37 g / g or more, and about 50 g / g or less, or about 45 g / g or less, or about 40 g / g or less.

[0165] Furthermore, the superabsorbent polymer of the present invention may have an absorbency under pressure (AUP) at 0.3 psi, measured by EDANA method WSP242.3, of about 25 g / g or more, or about 27 g / g or more, or about 28 g / g or more, or about 29 g / g or more, or about 30 g / g or more, or about 31 g / g or more, and about 40 g / g or less, or about 35 g / g or less, or about 33 g / g or less.

[0166] Furthermore, the superabsorbent polymer of the present invention may have a water absorption rate (vortex time) of 30 seconds or less, or 28 seconds or less, or 27 seconds or less, or 26 seconds or less, or 25 seconds or less, or 24 seconds or less, or 23 seconds or less, or 22 seconds or less, or 21 seconds or less, or 20 seconds or less, or 19 seconds or less, or 18 seconds or less. The smaller the water absorption rate, the better, and the theoretical lower limit of the water absorption rate is 0 seconds, but, for example, the water absorption rate may be about 5 seconds or more, about 10 seconds or more, or about 12 seconds or more.

[0167] The water absorption rate refers to the time (unit: seconds) required for a vortex to disappear due to rapid water absorption when a superabsorbent polymer is added to saline and stirred. The shorter the time, the faster the superabsorbent polymer is considered to have an initial water absorption rate.

[0168] Furthermore, the superabsorbent polymer of the present invention may have a water-soluble component content of 5% by weight or less, or 4.8% by weight or less, or 4.5% by weight or less, or 4.3% by weight or less, or 4% by weight or less, or 3.9% by weight or less, measured after swelling for 1 hour according to EDANA method WSP270.3. The lower the value of the water-soluble component content, the better, and the lower limit is theoretically 0% by weight, but for example, it may be 0.1% by weight or more, or 1% by weight or more.

[0169] <Example> Example 1 (Polymer manufacturing stage) In a 10L glass vessel equipped with a stirrer and thermometer, 1500g of acrylic acid, 6.3g of pentaerythritol triallyl ether as an internal crosslinker, and 3387g of water were mixed and stirred while maintaining the temperature at 5°C. Nitrogen was introduced into the glass vessel containing the mixture at 1000cc / min for 1 hour to flush the mixture under nitrogen. Next, 20.1g of 0.3% aqueous hydrogen peroxide solution, 22.5g of 1% aqueous ascorbic acid solution, and 45.0g of 2% aqueous 2,2'-azobis-(2-amidinopropane) dihydrochloride solution were added as polymerization initiators, and 22.3g of 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the mixture reached a temperature of 85°C, the mixture was polymerized at 90±2°C for approximately 3 hours to obtain a polymer.

[0170] (Neutralization and granulation stage) 5000 g of the resulting polymer was added to a Micronizer (F200, Karl Schnell) equipped with a perforated plate containing a large number of 10 mm holes, rotating at 1500 rpm, to pulverize the polymer into primary particles with diameters ranging from several tens to several hundreds of micrometers. At this time, 90 g of a 1.5 wt % aqueous solution of glycerol monolaurate (GML) was added to prevent excessive aggregation.

[0171] The pulverized polymer was then added to a meat chopper, a screw-type chopper equipped with a perforated plate containing a large number of 6mm holes, while rotating at 500 rpm to produce secondary agglomerated particles. This process was repeated three times. During the first pass, 1,904g of 50% NaOH aqueous solution was added to neutralize some of the acidic groups of the polymer. During the second pass, 18.8g of 15% Na2SO4 aqueous solution was added to neutralize some of the acidic groups of the polymer. During the third pass, the mixture was passed without adding any additives to produce hydrated superabsorbent resin particles.

[0172] (Drying stage) 1,000 g of the water-containing superabsorbent resin particles were placed in a rotary kiln fluidized dryer rotating at 120 rpm. Drying was carried out for 60 minutes while maintaining the internal temperature of the dryer at 105°C, yielding a resin powder. The resulting powder was passed through a two-stage roll mill to yield a base resin (BR) powder.

[0173] (Surface cross-linking stage) Next, 100 g of the obtained base resin powder was mixed with 4 g of water, 6 g of methanol, 0.30 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate to prepare a surface cross-linking liquid, which was then mixed for 1 minute. The surface cross-linking reaction was carried out at 140°C for 50 minutes to obtain a surface cross-linked superabsorbent resin.

[0174] Example 2 The same method as in Example 1 was used to produce the hydrated superabsorbent resin particles, except that in the drying step of Example 1, 1,000 g of the hydrated superabsorbent resin particles was placed in a ventilation dryer containing a perforated plate instead of a rotary kiln dryer, and the internal temperature of the dryer was maintained at 140°C while drying was carried out for 40 minutes.

[0175] Example 3 In the neutralization and granulation step of Example 1, 5,000 g of the polymer was introduced into a Micronizer (F200, Karl Schnell) equipped with a perforated plate containing a large number of 10 mm holes, rotating at 1,500 rpm, to granulate the polymer into primary particles with diameters ranging from several tens to several hundreds of micrometers. At this time, 1,904 g of a 50% NaOH aqueous solution was introduced to partially neutralize the acidic groups of the polymer. Subsequently, the neutralized and granulated polymer was introduced into a Micronizer (F200, Karl Schnell) equipped with a perforated plate containing a large number of 10 mm holes, rotating at 1,500 rpm, to produce secondary agglomerated particles. At this time, in order to prevent excessive aggregation, 180 g of a 1.5 wt % aqueous solution of glycerol monolaurate (GML) was added, and 18.8 g of a 15% aqueous solution of Na2SO4 was added to neutralize some of the acidic groups of the polymer. Otherwise, the production was carried out in the same manner as in Example 1.

[0176] Comparative Example (Polymer manufacturing stage) A monomer composition was prepared by mixing 100 g of acrylic acid, 130 g of 31.5 wt % caustic soda (NaOH), 0.15 g of ethylene glycol diglycidyl ether, 0.2 g of sodium persulfate as a thermal polymerization initiator, 0.01 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator, 5 g of capsule-type blowing agent F-36D as a blowing agent, 5 g of sodium dodecyl sulfate as a foam stabilizer, and 45 g of water in a glass reactor.

[0177] The monomer composition was placed in a square reaction vessel measuring 30 cm in width and 30 cm in length, and irradiated with 10 mW / cm 2 The polymer was irradiated with ultraviolet light having an intensity of 1000 kJ / min for 60 seconds to allow the polymerization reaction to proceed, thereby obtaining a hydrogel polymer (water content = 44.3 wt %).

[0178] (Crushing stage) The hydrogel polymer prepared in step 1 was cut into pieces 5 cm wide and 5 cm long, and the hydrogel was crushed using a meat chopper of a screw-type chopper. At this time, the screw-type chopper was equipped with a perforated plate with a number of chopping holes with a hole size of 16 mm.

[0179] (Drying stage) Then, 1,000 g of the pulverized superabsorbent resin hydrogel was placed in a ventilated dryer equipped with a perforated plate. The internal temperature of the dryer was maintained at 180°C, and drying was carried out for 40 minutes to obtain a resin powder. The obtained powder was passed through a two-stage roll mill to obtain a base resin (BR) powder.

[0180] (Crushing and classification stage) The base resin was mixed in a two-stage roll mill (GRAN-U-LIZER TM , MPE) to give particles having a particle size of 150 μm to 850 μm.

[0181] The crushed material was subjected to a classifier to selectively recover only highly water-absorbent resin particles having particle sizes of 150 μm to 850 μm.

[0182] (Surface cross-linking stage) A surface cross-linking liquid prepared by mixing 5 g of water, 5.3 g of propylene glycol, 0.1 g of ethylene glycol diglycidyl ether, and 0.87 g of a 23% aqueous aluminum sulfate solution with 100 g of the obtained superabsorbent resin particles was added and mixed for 2 minutes, and the surface cross-linking reaction was allowed to proceed at 130°C for 50 minutes to prepare a final superabsorbent resin.

[0183] <Experimental Example> The properties of the base resin (abbreviation: BR) and the surface-crosslinked final superabsorbent resin (abbreviation: PD) prepared in the above examples and comparative examples were evaluated by the following methods and are shown in Table 1 below.

[0184] Unless otherwise specified, all of the following physical property evaluations were carried out at constant temperature and humidity (23±1°C, relative humidity 50±10%), and saline or salt water refers to a 0.9 wt% aqueous sodium chloride (NaCl) solution.

[0185] The tap water used for the rewetting property evaluation had an electrical conductivity of 170 to 180 μS / cm when measured using Orion Star A222 (company: Thermo Scientific).

[0186] Furthermore, unless otherwise specified, the evaluation of the physical properties of the base resin was performed on a resin having a particle size of 300 μm to 400 μm classified using an ASTM sieve, and the evaluation of the physical properties of the surface-crosslinked final superabsorbent polymer was performed on a resin having a particle size of 150 μm to 850 μm classified using an ASTM sieve.

[0187] (1)Centrifuge Retention Capacity (CRC) The water retention capacity of the superabsorbent resins of the examples and comparative examples was measured in terms of the absorbency under no load according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP241.3.

[0188] Specifically, the superabsorbent resin W0 (g) (approximately 0.2 g) obtained in each of the Examples and Comparative Examples was uniformly placed in a nonwoven fabric envelope, sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the envelope was centrifuged at 250 G for 3 minutes to remove water, and the mass of the envelope W2 (g) was measured. The same procedure was repeated without the resin, and the mass W1 (g) was then measured.

[0189] Using the obtained masses, the CRC (g / g) was calculated according to the following formula 1.

[0190] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0191] (2) Absorbency under Pressure (AUP) The water absorption capacity of the superabsorbent resins of the above Examples and Comparative Examples at a pressure of 0.3 psi was measured by EDANA method WSP242.3.

[0192] Specifically, a 400-mesh stainless steel wire mesh was attached to the bottom of a plastic cylinder with an inner diameter of 25 mm. At room temperature and 50% humidity, 0.9 g of superabsorbent resin W0 (g) was evenly spread on the wire mesh, and a piston capable of applying a uniform load of 0.3 psi to the mesh was placed slightly smaller than the outer diameter of 25 mm, with no gap between it and the inner wall of the cylinder, ensuring unhindered up-and-down movement. The weight of the device, W3 (g), was then measured.

[0193] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a Petri dish with a diameter of 150 mm, and physiological saline solution containing 0.9 wt% sodium chloride was placed at the same level as the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of the glass filter. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for 1 hour. After 1 hour, the measuring device was lifted and its weight W4 (g) was measured.

[0194] Using the obtained masses, the water absorption capacity under pressure (g / g) was calculated according to the following formula 2.

[0195] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0196] The measurement was repeated five times, and the average value and standard deviation were calculated.

[0197] (3) Moisture content The moisture content is the amount of water relative to the total weight of the superabsorbent resin, and was calculated using the following formula 3.

[0198] Specifically, the weight loss due to evaporation of water in the superabsorbent polymer was measured and calculated during the drying process by increasing the temperature of the superabsorbent polymer using infrared heating. The drying conditions were to increase the temperature from room temperature to 180°C and then maintain it at 180°C, with a total drying time of 40 minutes, including 5 minutes for the temperature increase stage. The weight of the superabsorbent polymer before and after drying was measured and calculated using the following equation 3.

[0199] [Formula 3] Moisture content (wt%)=[(Ao-At) / Ao]×100

[0200] In the above formula, At is the weight of the superabsorbent resin after drying, and Ao is the weight of the superabsorbent resin before drying.

[0201] (4) Water absorption rate (Vortex time) The water absorption rate (vortex time) was measured in seconds according to the method described in WO 1987 / 003208.

[0202] Specifically, 2 g of superabsorbent resin was placed in 50 mL of saline at 23 to 24°C, and the mixture was stirred at 600 rpm with a magnetic bar (diameter 8 mm, length 30 mm), and the time until the vortex disappeared was measured in seconds.

[0203] (5) Water-soluble components (EC, Extractable Contents) The water-soluble components of 2 g of the superabsorbent resin were measured after swelling for 1 hour according to EDANA method WSP270.3.

[0204] (6) Fine powder content The base resin (BR) powders of the examples and comparative examples were classified using standard sieves having ASTM standard sieves with size graduations of 850 μm (#20), 600 μm (#30), 300 μm (#50), and 150 μm (#100). The weight of fine particles having a particle size of less than 150 μm was measured and expressed as a percentage based on the total weight of the base resin powder.

[0205] (7) Long-term rewetting with pressurized tap water (6-hour rewet) (i) 4 g of superabsorbent resin was evenly spread on a petri dish having a diameter of 13 cm, and distributed evenly using a spatula. 200 g of tap water was poured into the dish and allowed to swell. (ii) The superabsorbent resin that had been swollen for 6 hours was placed on 20 sheets of 11 cm diameter filter paper (manufacturer: Whatman, catalog No. 1004-110, pore size 20-25 μm, diameter 11 cm), and pressure was applied to the 11 cm diameter with a 5 kg weight (0.75 psi) for 1 minute. (iii) After applying pressure for 1 minute, the amount of tap water (unit: g) on the filter paper was measured.

[0206] (8)TWFA (Tap Water Free Absorbency, 1 minute water absorption capacity) 1.0 g (W5) of the superabsorbent resin of each of the Examples and Comparative Examples was placed in a nonwoven envelope (15 cm x 15 cm) and immersed in 500 mL of tap water at 24°C for 1 minute. After 1 minute, the envelope was removed from the water and then suspended and left for 1 minute. The mass of the envelope (W6) was then measured. The same procedure was repeated without using the superabsorbent resin, and the resulting mass, W7 (g), was then measured.

[0207] Using the masses thus obtained, TWFA was calculated according to the following formula 5.

[0208] [Formula 5] TWFA={[W6(g)-W7(g)-W5(g)] / W5(g)}

[0209] [Table 1]

[0210] (In Table 1, BR refers to the base resin after the drying step and before the surface cross-linking step, and PD refers to the final superabsorbent polymer product after the surface cross-linking step.)

[0211] Examples 1 to 3 were prepared according to one embodiment of the present invention by polymerizing a water-soluble ethylenically unsaturated monomer in an unneutralized state using a batch polymerization method, and then adding a surfactant and a neutralizing agent to post-neutralize the polymer and pulverize it.

[0212] Referring to Table 1, compared to the conventional comparative example process in which a monomer in which some of the acidic groups had been neutralized first was polymerized, followed by chopping and drying, Examples 1 to 3 showed a significant reduction in the fine powder content of the base resin and a significant reduction in the water-soluble components of the superabsorbent resin after surface crosslinking.

[0213] Comparing Examples 1 and 2, it was found that a base resin with a low fine powder content could be obtained in the post-neutralization and granulation process, but in order to achieve a high vortex water absorption rate, fluidized drying using a rotary dryer in Example 1 was more advantageous than stationary drying in Example 2.

Claims

1. Step 1: carrying out polymerization on a monomer composition including 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 and the internal crosslinking agent are crosslinked and polymerized; neutralizing at least a portion of the acidic groups of the polymer (Step 2); granulating the polymer in the presence of a surfactant (Step 3); drying the neutralized and granulated polymer to produce dry superabsorbent polymer particles (Step 4); and and (5) grinding the dried superabsorbent resin particles to prepare superabsorbent resin particles. The surfactant includes a compound represented by the following Chemical Formula 2 or a salt thereof: The water absorption rate (vortex time) is 27 seconds or less, The water-soluble component measured after swelling for 1 hour according to EDANA method WSP270.3 is 5% by weight or less. A method for producing superabsorbent resin. 【Chemical 1】 In the above Chemical Formula 2, A １ , A ２ and A ３ are each independently a single bond, a carbonyl, 【Chemistry 2】 wherein one or more of these is a carbonyl or 【Chemistry 3】 wherein m1, m2, and m3 each independently represent an integer from 1 to 8; 【Chemistry 4】 are each linked to an adjacent oxygen atom, 【Chemistry 5】 is the adjacent R １ , R ２ and R ３ and R １ , R ２ and R ３ are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer from 1 to 9.

2. The step of forming the polymer is carried out in a batch type reactor. A method for producing the highly water-absorbent resin according to claim 1.

3. Steps 2 and 3 are performed sequentially, alternately, or simultaneously; A method for producing the highly water-absorbent resin according to claim 1.

4. The pulverization step is performed by a pulverization device, which comprises: a body portion including a transfer space into which a polymer is transferred; a screw member rotatably provided within the transfer space to move the polymer; a drive motor for providing a rotational drive force to the screw member; a cutter member provided in the body portion to pulverize the polymer; a perforated plate having a plurality of holes formed therein, which discharges the polymer pulverized by the cutter member to the outside of the body portion, A method for producing the highly water-absorbent resin according to claim 1.

5. The step of drying the neutralized and granulated polymer is carried out in a moving type. A method for producing the highly water-absorbent resin according to claim 1.

6. The fluidized-bed drying is carried out using a horizontal-type mixer, a rotary kiln, a paddle dryer, or a steam tube dryer. A method for producing the highly water-absorbent resin according to claim 5.

7. The step of drying the neutralized and granulated polymer is carried out at a temperature of 150° C. or less. A method for producing the highly water-absorbent resin according to claim 1.

8. The moisture content of the dried superabsorbent resin particles obtained by carrying out step 4 is 10 to 20% by weight. A method for producing the highly water-absorbent resin according to claim 1.

9. At least a portion of the surfactant is present on the surface of the polymer. A method for producing the highly water-absorbent resin according to claim 1.

10. The superabsorbent resin particles contain 20% by weight or less of superabsorbent resin particles having a particle size of less than 150 μm relative to the total weight of the superabsorbent resin particles. A method for producing the highly water-absorbent resin according to claim 1.

11. The method further comprises the step of classifying the superabsorbent resin particles according to particle size. A method for producing the highly water-absorbent resin according to claim 1.

12. The method further comprises forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent resin particles. A method for producing the highly water-absorbent resin according to claim 1 or 11.

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