Preparation method of super absorbent polymer and super absorbent polymer

Abstract

The present invention relates to a method for manufacturing a superabsorbent resin. More specifically, by performing a micronization step under specific conditions, the amount of water-soluble components and fine particles generated is significantly reduced, and the superabsorbent resin exhibits excellent absorption properties.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a superabsorbent resin and to a superabsorbent resin. More specifically, by performing a micronization step under specific conditions, the invention relates to a method for manufacturing a superabsorbent resin and to a superabsorbent resin that exhibits excellent absorption properties while significantly reducing the amount of water-soluble components and fine particles generated. Background Technology

[0003] Super Absorbent Polymer (SAP) is a synthetic polymer material capable of absorbing 500 to 1,000 times its own weight in moisture, and developers name it by different names such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material). The above-mentioned super absorbent polymer began to be commercialized for use in physiological devices, and is now widely used as a material for horticultural soil repair agents, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservation agents in the food distribution sector, and compresses.

[0004] These superabsorbent polymers are widely used in the field of hygiene products, such as diapers and sanitary pads. In the above hygiene products, the superabsorbent polymer is generally contained in a dispersed state within the pulp. However, recently, efforts to provide hygiene products such as thinner diapers have been ongoing, and as part of this, the development of so-called pulpless diapers, in which the pulp content is reduced or no pulp is used at all, is being actively pursued.

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

[0006] Meanwhile, such superabsorbent resins are generally manufactured through a process involving the polymerization of monomers to produce a hydrogel polymer containing a large amount of moisture, followed by the drying of the hydrogel polymer and subsequent grinding into resin particles of a desired size. However, when undergoing the grinding process after drying the hydrogel polymer as described above, a large amount of fine powder is generated, which has been a problem in that it degrades the physical properties of the final superabsorbent resin.

[0007] Furthermore, to reuse such fine powder, it is common practice to mix the fine powder with water to aggregate it and produce a fine powder reassembly, and then feed the reassembly through processes such as drying, grinding, and classification. However, due to the water used in this process, problems such as increased energy consumption during the drying process and heavy load on the equipment may arise, which can reduce the productivity of superabsorbent polymer manufacturing.

[0008] Accordingly, there is a continuous demand for the development of technology capable of manufacturing superabsorbent resins without generating fine particles in order to fundamentally resolve these problems. The problem to be solved

[0010] Accordingly, the present invention aims to provide a method for manufacturing a superabsorbent resin and a superabsorbent resin that can exhibit excellent absorption properties while significantly improving the absorption rate and significantly reducing the amount of fine particles generated during the process by manufacturing particles with a shape in which fine particles are aggregated to increase the surface area. means of solving the problem

[0012] According to one embodiment of the present invention to solve the above problem,

[0013] A step of forming a polymer having acidic groups by cross-linking a water-soluble ethylene-based unsaturated monomer having acidic groups in the presence of an internal cross-linking agent and a polymerization initiator (Step 1);

[0014] A step of preparing water-absorbent superabsorbent resin particles by micronizing a mixture of the above-mentioned polymer having an acidic group and a surfactant (Step 2); and

[0015] The method comprises the step of manufacturing superabsorbent resin particles by drying the above-mentioned function superabsorbent resin particles (step 3); and

[0016] The step of manufacturing the above-mentioned superabsorbent resin particles (step 2) is performed by extruding the mixture into a porous plate having a plurality of holes to atomize it, wherein a neutralizing agent is sprayed into the mixture at the extrusion point of the porous plate, so that at least some of the acidic groups of the polymer having acidic groups within the mixture are neutralized.

[0017] A method for manufacturing a superabsorbent resin is provided.

[0019] In addition, according to one embodiment of the present invention, a superabsorbent resin is provided that is manufactured according to the method for manufacturing a superabsorbent resin described above. Effects of the invention

[0021] According to the method for manufacturing a superabsorbent resin of the present invention, it is possible to manufacture a superabsorbent resin capable of exhibiting excellent absorption properties and significantly improving the absorption rate by implementing particles with an aggregated shape of fine particles, thereby increasing the surface area.

[0022] In addition, by grinding the superabsorbent resin particles from a water-soluble state to the level of normal particles, the amount of fine powder generated during the manufacture of the superabsorbent resin can be significantly reduced.

[0023] In addition, by narrowing the particle size distribution to have a uniform particle size distribution and lowering the water-soluble component (EC) content, it is possible to provide a superabsorbent resin with excellent overall absorption properties, such as water retention capacity and pressurized absorption capacity, as well as absorption rate. Brief explanation of the drawing

[0025] Figure 1 is a flowchart relating to a conventional method for manufacturing a superabsorbent resin. FIG. 2 is a schematic diagram of a micronization device used in a method for manufacturing a superabsorbent resin according to one embodiment of the invention. Specific details for implementing the invention

[0026] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention.

[0027] The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, steps, components, or combinations thereof.

[0028] Terms such as first, second, third, etc. are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from another.

[0029] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0031] (Method for manufacturing superabsorbent resin)

[0032] A method for manufacturing a superabsorbent resin according to one embodiment of the invention comprises: a step of forming a polymer having acidic groups by cross-linking a water-soluble ethylene-based unsaturated monomer having acidic groups in the presence of an internal cross-linking agent and a polymerization initiator (Step 1); a step of manufacturing water-soluble superabsorbent resin particles by micronizing a mixture of the polymer having acidic groups and a surfactant (Step 2); and a step of manufacturing superabsorbent resin particles by drying the water-soluble superabsorbent resin particles (Step 3); wherein the step of manufacturing water-soluble superabsorbent resin particles (Step 2) is performed by micronizing the mixture by discharging it into a porous plate having a plurality of holes, and a neutralizing agent is sprayed into the mixture at the discharge point of the porous plate so that at least some of the acidic groups of the polymer having acidic groups in the mixture are neutralized.

[0034] The terms “polymer” or “polymer” as used in this specification refer to a state in which water-soluble ethylene-based unsaturated monomers are polymerized, and may encompass all moisture content ranges or particle size ranges.

[0035] Additionally, the terms "water-absorbent superabsorbent resin particles" or "superabsorbent resin particles" are used to encompass, depending on the context, a cross-linked polymer in which a water-soluble ethylene-based unsaturated monomer containing acidic groups and at least some of the acidic groups are neutralized is polymerized, or a base resin in the form of particles in which the cross-linked polymer is crushed to form superabsorbent resin particles, or a superabsorbent resin in a state suitable for commercialization after undergoing additional processes, such as surface crosslinking, fine powder reassembly, drying, grinding, classification, etc., with respect to the cross-linked polymer or the base resin.

[0036] In addition, the term "fine" refers to particles among superabsorbent resin particles having a particle size of less than 150 μm. The particle size of these resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0037] In addition, the term "chopping" refers to cutting hydrogel polymers into small, millimeter-sized pieces to increase drying efficiency, and is used to distinguish it from grinding to micrometer or normal particle levels.

[0038] In addition, the term "micronizing" refers to the process of grinding hydrogel polymers to particle sizes of tens to hundreds of micrometers, and is used to distinguish it from "chopping."

[0040] Hydrogel-like polymers obtained by the polymerization reaction of acrylic acid-based monomers are commercially marketed as superabsorbent resins in powder form after undergoing processes such as drying, grinding, classification, and surface crosslinking. Recently, continuous attempts have been made to provide superabsorbent resins that exhibit improved absorption rates.

[0041] The most common method for increasing the absorption rate is to expand the surface area of ​​the superabsorbent resin by forming a porous structure inside the resin. To expand the surface area of ​​the superabsorbent resin, a method is generally adopted in which a porous structure is formed within the base resin powder by proceeding with cross-linking polymerization including a foaming agent in the monomer composition.

[0042] However, the use of foaming agents is accompanied by disadvantages such as a decrease in the various physical properties of superabsorbent resins, such as surface tension, liquid permeability, or bulk density, and an increase in the amount of fine particles generated. Accordingly, there is a continuous demand for the development of technology that can improve the absorption rate of superabsorbent resins without the use of foaming agents.

[0044] Meanwhile, conventional superabsorbent polymers are manufactured by cross-linking a water-soluble ethylene-based unsaturated monomer having at least some neutralized acidic groups in the presence of an internal cross-linking agent and a polymerization initiator to form a hydrogel polymer, drying the formed hydrogel polymer, and then grinding it to a desired particle size. Typically, a chopping process is performed before the drying process to cut the hydrogel polymer into particles of several millimeters in size to facilitate drying and increase the efficiency of the grinding process. However, due to the adhesiveness of the hydrogel polymer during this chopping process, the hydrogel polymer cannot be ground to the micro-sized particle level and remains in an aggregated gel form. When this aggregated gel-type hydrogel polymer is dried, a plate-shaped dried body is formed, and since a multi-stage grinding process is required to grind it to the micro-sized particle level, there has been a problem in that a large amount of fine powder is generated during this process.

[0046] Specifically, FIG. 1 illustrates a flowchart relating to a conventional method for manufacturing a superabsorbent resin. Referring to FIG. 1, a conventional superabsorbent resin has been manufactured by including the following steps.

[0047] (Neutralization) A step of neutralizing at least some of the acidic groups of a water-soluble ethylene-based unsaturated monomer;

[0048] (Polymerization) A step of forming a hydrogel polymer by cross-linking a water-soluble ethylene-based unsaturated monomer having at least some neutralized acidic groups in the presence of an internal cross-linking agent and a polymerization initiator;

[0049] (Chopping) A step of chopping the above-mentioned hydrogel polymer;

[0050] (Drying) A step of drying the chopped hydrogel polymer; and

[0051] (Grinding / Classification) A step of grinding the above-mentioned dried polymer and classifying it into normal particles and fine powder;

[0052] As described above, the chopped hydrogel polymer has an aggregated gel form with a size of about 1 cm to 10 cm, and this chopped hydrogel polymer is stacked on a belt with a perforated bottom and dried by hot air supplied from the bottom or top. Since the polymer dried by the above drying method exhibits a plate shape rather than a particle shape, the step of classification after grinding has been performed by coarse grinding and classification to ensure that the manufactured particles become normal particles, that is, particles having a particle size of 150 μm to 850 μm, followed by fine grinding and classification. Because the amount of fine powder separated in the final classification step by this manufacturing method is large, amounting to about 20% to about 30% by weight relative to the total weight of the finally manufactured superabsorbent resin, the separated fine powder was reused by mixing it with an appropriate amount of water, reassembling the fine powder, and then feeding it into the chopping step or the drying step.

[0053] However, when the fine powder reassembly mixed with water is reintroduced into the grinding or drying process for the reuse of such fine powder, problems have arisen such as increased equipment load and / or energy consumption, and the remaining fine powder that is not classified has caused a deterioration in the physical properties of the superabsorbent resin.

[0054] Accordingly, the inventors recognized that the amount of fine powder generated in conventional manufacturing methods is significantly influenced by the grinding process. They conceived that by adding a surfactant and a neutralizing agent during the polymer grinding process to post-neutralize the polymer and grind it more finely than before—that is, to micronize it—while simultaneously controlling aggregation to produce particles in the form of aggregated fine particles, the amount of fine powder generated during the manufacturing process can be significantly reduced.

[0056] Meanwhile, a method of adding a surfactant to reduce the tackiness of the hydrogel polymer during the chopping process has been proposed. However, when a surfactant is added during the chopping process, there is a problem in that the surfactant does not perform its role properly because it penetrates into the hydrogel polymer rather than remaining at the interface of the hydrogel polymer due to the high water content of the hydrogel polymer.

[0057] This is because, compared to the polymer before chopping, the chopped particles are formed at the level of a few mm or a few cm, so while the surface area may increase to some extent, it is difficult to expect an effect sufficient to effectively improve the absorption rate. Therefore, to improve the absorption rate, one could consider increasing the surface area by increasing the mechanical force and kneading during the chopping stage; however, in this case, excessive aggregation occurs due to the stickiness characteristic of the polymer, resulting in the formation of amorphous single particles with only rough surfaces after chopping, drying, and grinding, and the water-soluble component may actually increase due to excessive kneading or crushing.

[0058] As a result of repeated research to solve this problem, it was confirmed that, unlike conventional methods for manufacturing superabsorbent polymers where polymerization is performed after neutralizing the acidic groups of water-soluble ethylene-based unsaturated monomers, polymerization is performed first in a state where the acidic groups are not neutralized to form a polymer, and then the water gel polymer is micronized in the presence of a surfactant, or the acidic groups present in the polymer are neutralized simultaneously with micronization, so that the surfactant is present in large quantities on the surface of the polymer, and the high adhesiveness of the polymer is lowered to prevent excessive aggregation of the polymer and to sufficiently perform the role of controlling the aggregation state to a desired level.

[0059] Accordingly, the amount of fine particles generated during the process can be significantly reduced as the polymer is manufactured into secondary particles in which primary particles are aggregated, and the subsequent grinding and drying processes are carried out under milder conditions.

[0061] In addition, when the polymer is micronized in the presence of the surfactant, the hydrophobic functional group portion contained in the surfactant imparts hydrophobicity to the surface of the pulverized superabsorbent resin particles, thereby alleviating inter-particle friction and increasing the apparent density of the superabsorbent resin, while the hydrophilic functional group portion contained in the surfactant also binds to the superabsorbent resin particles, preventing a decrease in the surface tension of the resin. Accordingly, the superabsorbent resin produced according to the above-described manufacturing method can exhibit a surface tension equivalent to that of a resin without a surfactant, while having a higher apparent density value.

[0063] In addition, if polymerization is first performed 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 longer chains, thereby achieving the effect of reducing the content of water-soluble components that exist in an uncrosslinked state due to incomplete crosslinking.

[0064] Since the aforementioned water-soluble components have the property of easily leaching out when the superabsorbent resin comes into contact with liquid, if the content of these components is high, most of the leached components remain on the surface of the superabsorbent resin, making the resin sticky and causing a decrease in liquid permeability. Therefore, it is important to maintain a low content of water-soluble components in terms of liquid permeability.

[0066] Meanwhile, when using a micronizer that was conventionally used in the chopping step, there was a problem in that it was difficult to neutralize the acidic groups present in the polymer simultaneously with micronization as described above. Accordingly, the inventors introduced a micronization device with a new structure including a spray nozzle for a neutralizing agent, thereby making it easy to perform a process of neutralizing the acidic groups of an unneutralized polymer to form a hydrogel polymer, and then micronizing the hydrogel polymer in the presence of a surfactant, or neutralizing the acidic groups present in the polymer simultaneously with micronization or before and after micronization.

[0068] According to one embodiment of the present invention, as polymerization is performed in an unneutralized state, the content of the water-soluble component is lowered, and accordingly, the permeability of the superabsorbent resin can be improved.

[0069] In addition, the superabsorbent resin manufactured according to one embodiment of the present invention may have a uniform particle size distribution, and accordingly, can provide a superabsorbent resin with excellent absorption properties such as water retention capacity, pressurized absorption capacity, and absorption rate.

[0071] Hereinafter, the method for manufacturing a superabsorbent resin of one embodiment will be described in more detail step by step.

[0073] (Step 1: Polymerization Step)

[0074] A method for manufacturing a superabsorbent resin according to one embodiment of the invention comprises the step (step 1) of cross-linking a water-soluble ethylene-based unsaturated monomer having an acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a polymer having an acidic group.

[0075] The above step is to form a polymer by thermally polymerizing or photopolymerizing a monomer composition comprising a monomer mixture containing a water-soluble ethylene-based unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator.

[0077] The above-mentioned water-soluble ethylene-based unsaturated monomer having an acidic group may be any monomer commonly used in the manufacture of superabsorbent resins. As a non-limiting example, the above-mentioned water-soluble ethylene-based unsaturated monomer may be a compound represented by the following chemical formula 2:

[0078] [Chemical Formula 2]

[0079] R1-COOM 1

[0080] In the above chemical formula 2,

[0081] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0082] M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0083] Preferably, the monomer may be one or more selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids. It is advantageous to use acrylic acid or its salts as water-soluble ethylene-based unsaturated monomers in this way, as it is possible to obtain a superabsorbent resin with improved absorbency. In addition, the monomer may be anionic monomers of maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth)acrylamide-2-methylpropanesulfonic acid, and salts thereof; One or more selected from the group consisting of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, or polyethylene glycol (meth)acrylate; nonionic hydrophilic containing monomers of (meth)acrylate; and amino group containing unsaturated monomers of (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide and their quaternaries may be used.

[0085] Here, the water-soluble ethylene-based unsaturated monomer has acidic groups. As previously explained, in the manufacture of conventional superabsorbent resins, a monomer in which at least some of the acidic groups were neutralized by a neutralizing agent was cross-linked to form a hydrogel polymer. Specifically, at least some of the acidic groups of the water-soluble ethylene-based unsaturated monomer having acidic groups were neutralized in the step of mixing an internal crosslinking agent, a polymerization initiator, and a neutralizing agent.

[0086] However, according to one embodiment of the present invention, polymerization is first performed to form a polymer while the acidic group of the water-soluble ethylene-based unsaturated monomer is not neutralized.

[0087] Water-soluble ethylene-based unsaturated monomers (e.g., acrylic acid) in which the acid group is not neutralized are in a liquid state at room temperature and have high miscibility with the solvent (water), existing as a mixed solution in the monomer composition. However, water-soluble ethylene-based unsaturated monomers in which the acid group is neutralized are in a solid state at room temperature and have different solubility depending on the temperature of the solvent (water), and the solubility decreases as the temperature decreases.

[0088] As such, water-soluble ethylene-based unsaturated monomers in a state where the acid groups are not neutralized have higher solubility or miscibility with a solvent (water) than monomers in which the acid groups are neutralized, so they do not precipitate even at low temperatures, and thus are advantageous for long-term polymerization at low temperatures. Accordingly, by performing long-term polymerization using the water-soluble ethylene-based unsaturated monomers in a state where the acid groups are not neutralized, it is possible to stably form a polymer with a higher molecular weight and a uniform molecular weight distribution.

[0089] In addition, since it is possible to form polymers with longer chains, it is possible to achieve the effect of reducing the content of water-soluble components that exist in an uncrosslinked state due to incomplete polymerization or crosslinking.

[0090] In addition, if polymerization is performed first to form a polymer while the acidic groups of the monomer are not neutralized, and then micronized in the presence of a surfactant after neutralization, or if the acidic groups present in the polymer are neutralized simultaneously with micronization, the surfactant can be present in large quantities on the surface of the polymer and sufficiently perform the role of lowering the adhesiveness of the polymer.

[0091] The concentration of the water-soluble ethylene-based unsaturated monomer in the above monomer composition can be appropriately adjusted considering the polymerization time and reaction conditions, and can be about 20 to about 60 weight%, or about 20 to about 40 weight%.

[0093] The term 'internal crosslinking agent' used in this specification is used to distinguish it from the surface crosslinking agent for crosslinking the surface of the superabsorbent resin particles described below, and it serves to form a polymer containing a crosslinked structure by introducing crosslinking between the unsaturated bonds of the water-soluble ethylene-based unsaturated monomers described above.

[0094] The crosslinking in the above step proceeds without distinction between the surface or the interior, but when the surface crosslinking process of the superabsorbent resin particles described later is performed, the surface of the finally manufactured superabsorbent resin particles may include a structure newly crosslinked by the surface crosslinking agent, and the interior of the superabsorbent resin particles may maintain the structure crosslinked by the interior crosslinking agent.

[0095] The above internal crosslinking agent may include one or more of i) a polyfunctional acrylate-based compound, ii) a polyfunctional allyl-based compound, or iii) a polyfunctional vinyl-based compound.

[0096] 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, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, Examples include dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate, and in the present invention, these may be used alone or in a mixture of two or more types.

[0097] 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 trialyl ether, pentaerythritol tetraallyl ether, dipentaerythritol diallyl ether, dipentaerythritol trialyl ether, dipentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, trimethylolpropane diallyl ether, and trimethylolpropane. Examples include trialyl ether, glycerin diallyl ether, and glycerin trialyl ether, and in the present invention, these may be used alone or in a mixture of two or more types.

[0098] 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, and trimethylolpropane trivinyl. Examples include ether, glycerin divinyl ether, and glycerin trivinyl ether, and in the present invention, these may be used alone or in a mixture of two or more types.

[0099] The aforementioned polyfunctional acrylate-based compound can form a cross-linked structure during the polymerization process by having two or more acrylate groups contained within the molecule bond with the unsaturated bonds of water-soluble ethylene-based unsaturated monomers or the unsaturated bonds of other internal cross-linking agents, respectively.

[0100] In addition, the aforementioned polyfunctional allyl compound or polyfunctional vinyl compound can form a cross-linked structure during the polymerization process by having two or more unsaturated groups contained within the molecule bond with the unsaturated bonds of water-soluble ethylene-based unsaturated monomers or the unsaturated bonds of other internal cross-linking agents, respectively, and unlike acrylate compounds containing ester bonds (-(C=O)O-) within the molecule, the cross-linked bond can be stably maintained even during the neutralization process after the aforementioned polymerization reaction.

[0101] Accordingly, the gel strength of the superabsorbent resin being manufactured is increased, and process stability can be improved during the extrusion process after polymerization.

[0102] The total content of the internal crosslinking agent may be used in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. For example, the internal crosslinking agent may be used in an amount of 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, or 0.45 parts 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 parts by weight or less, relative to 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. If the content of the upper internal crosslinking agent is excessively low, crosslinking may not occur sufficiently, making it difficult to achieve strength above an appropriate level; if the content of the upper internal crosslinking agent is excessively high, the internal crosslinking density increases, making it difficult to achieve the desired water retention capacity.

[0103] The polymer formed using such an internal crosslinking agent has a three-dimensional network structure in which the main chains formed by the polymerization of the water-soluble ethylene-based unsaturated monomers are crosslinked by the internal crosslinking agent. In this way, when the polymer has a three-dimensional network structure, the water retention capacity and pressure absorption capacity, which are the general properties of the superabsorbent resin, can be significantly improved compared to the case of a two-dimensional linear structure that is not further crosslinked by the internal crosslinking agent.

[0105] In addition, the monomer composition may include a polymerization initiator commonly used in the manufacture of superabsorbent resins. As a non-limiting example, depending on the polymerization method, a thermal polymerization initiator or a photopolymerization initiator may be used as the polymerization initiator. However, even in the photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation, and since some heat is generated as the polymerization reaction, which is an exothermic reaction, proceeds, a thermal polymerization initiator may be additionally included.

[0106] As the above photopolymerization initiator, for example, one or more compounds selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone may be used. Among these, specific examples of acyl phosphine include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl(2,4,6-trimethylbenzoyl)phenylphosphineate, etc. A wider variety of photoinitiators is well described in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Applications" (Elsevier 2007), p. 115, and is not limited to the examples described above.

[0107] In addition, one or more compounds selected from the group consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid may be used as the thermal polymerization initiator. Specifically, examples of persulfate-based initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8). In addition, azo-based initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutylonitril, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, and 4,4-azobis-(4-cyanovaleric Examples include acid (4,4-azobis-(4-cyanovaleric acid)). A wider variety of thermal polymerization initiators are disclosed on page 203 of Odian's book "Principles of Polymerization" (Wiley, 1981), which can be referenced. As a reference to the above polymerization initiator, as described below, when the polymerization step is carried out in a batch reactor, the above-mentioned thermal polymerization initiator may be used as the polymerization initiator by utilizing a thermal polymerization method.

[0108] This polymerization initiator may be added at a concentration of 0.001 to 1 part by weight per 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. That is, if the concentration of the polymerization initiator is excessively low, the polymerization rate may be slowed down 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 excessively high, the polymer chains forming the network may become shorter, leading to a higher content of water-soluble components and a lower pressurized absorption capacity, which may degrade the physical properties of the resin, which is undesirable.

[0110] Meanwhile, in one embodiment of the present invention, polymerization can be initiated by adding a reducing agent that forms a redox couple with the polymerization initiator.

[0111] Specifically, the polymerization initiator and the reducing agent react with each other to form radicals when added to the polymerization solution.

[0112] The formed radicals react with the monomers, and since the oxidation-reduction reaction between the polymerization initiator and the reducing agent is highly reactive, polymerization is initiated even when only a small amount of the polymerization initiator and reducing agent is added, so there is no need to raise the process temperature, making low-temperature polymerization possible and minimizing changes in the physical properties of the polymer solution.

[0113] The polymerization reaction using the above oxidation-reduction reaction can proceed smoothly even at temperatures near or below room temperature (25°C). For example, the polymerization reaction can be carried out at a temperature between 5°C and 25°C, or between 5°C and 20°C.

[0114] In one embodiment of the present invention, when a persulfate-based initiator is used as the polymerization initiator, one or more reducing agents selected from the group consisting of sodium metabisulfite (Na2S2O5); tetramethyl ethylenediamine (TMEDA); iron(II) sulfate (FeSO4); a mixture of iron(II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinoacteate may be used.

[0115] For example, potassium persulfate may be used as a polymerization initiator and disodium 2-hydroxy-2-sulfinoacetate as a reducing agent; ammonium persulfate may be used as an initiator and tetramethylethylenediamine as a reducing agent; or sodium persulfate may be used as an initiator and sodium formaldehyde sulfoxylate as a reducing agent.

[0116] 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 (Na2SO3) and sodium metabisulfite (Na2S2O5); tetramethyl ethylenediamine (TMEDA); a mixture of iron(II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; disodium 2-hydroxy-2-sulfinoacteate; and disodium 2-hydroxy-2-sulfoacteate.

[0118] In addition, the above monomer composition may further include additives such as thickeners, plasticizers, preservation stabilizers, and antioxidants as needed.

[0120] In addition, this monomer composition can be prepared in the form of a solution in which raw materials such as the aforementioned water-soluble ethylene-based unsaturated monomer, polymerization initiator, and internal crosslinking agent are dissolved in a solvent.

[0121] The solvent that can be used at this time may be any solvent capable of dissolving the aforementioned raw materials, without any limitation in composition. For example, the solvent may be 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, N,N-dimethylacetamide, or a mixture thereof.

[0123] According to one embodiment of the invention, the step of forming a polymer by performing polymerization on the monomer composition can be performed in a batch-type reactor.

[0124] In the conventional method for manufacturing superabsorbent resins, polymerization methods are broadly classified into thermal polymerization and photopolymerization depending on the polymerization energy source. Typically, thermal polymerization can be carried out in a reactor equipped with a stirring shaft, such as a kneader, while photopolymerization can be carried out in a reactor equipped with a movable conveyor belt or in a flat-bottomed container.

[0125] Meanwhile, the polymerization method described above generally results in the formation of a polymer with a broad molecular weight distribution and a small molecular weight, depending on the short polymerization reaction time (e.g., 1 hour or less).

[0126] Meanwhile, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or a flat-bottomed vessel, the form of the hydrogel polymer typically obtained is a sheet-like hydrogel polymer with the width of the belt, and the thickness of the polymer sheet varies depending on the concentration and injection speed or amount of the injected monomer composition, but is typically obtained with a thickness of about 0.5 to about 5 cm.

[0127] However, if the monomer composition is supplied to the extent that the thickness of the polymer on the sheet is excessively thin, the production efficiency is low and is undesirable. If the thickness of the polymer on the sheet is increased for productivity, the polymerization reaction does not occur evenly over the entire thickness, making it difficult to form a high-quality polymer.

[0128] In addition, polymerization in a reactor equipped with a conveyor belt and a stirring shaft is carried out continuously as a new monomer composition is supplied to the reactor while the polymerization product moves, so polymers with different polymerization rates are mixed, and consequently, it is difficult to achieve uniform polymerization throughout the monomer composition, which may lead to a decrease in overall physical properties.

[0129] However, as described above, when polymerization is carried out in a fixed-bed type in a batch reactor according to one embodiment of the invention, there is less risk of polymers with different polymerization rates being mixed, and accordingly, a polymer of uniform quality can be obtained.

[0130] 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 period, for example, 3 hours or more, than when polymerization is carried out continuously in a reactor equipped with a conveyor belt. Despite such a long polymerization reaction time, since polymerization is carried out on water-soluble ethylene-based unsaturated monomers in an unneutralized state, the monomers do not precipitate well even when polymerization is carried out for a long period, and thus it is advantageous to carry out polymerization for a long period.

[0131] Meanwhile, as polymerization in a batch reactor as described above utilizes a thermal polymerization method, the aforementioned thermal polymerization initiator may be used.

[0133] (Step 2: Micronization and Neutralization Step)

[0134] Next, the method includes a step (step 2) of manufacturing water-absorbent superabsorbent resin particles by micronizing a mixture of a polymer having acidic groups and a surfactant, wherein a neutralizing agent is sprayed onto the mixture to neutralize at least some of the acidic groups of the polymer having acidic groups within the mixture. More specifically, the step (step 2) of manufacturing water-absorbent superabsorbent resin particles is performed by micronizing the mixture by discharging it into a porous plate having a plurality of holes, and a neutralizing agent is sprayed onto the mixture at the discharge point of the porous plate to neutralize at least some of the acidic groups of the polymer having acidic groups within the mixture.

[0136] The above-mentioned micronization step is a step of micronizing the polymer in the presence of a surfactant, wherein the polymer is not chopped to a millimeter size, but rather a step in which cutting and aggregation into tens to hundreds of micrometers are carried out simultaneously. That is, by imparting appropriate adhesiveness to the polymer, it is a step of producing secondary aggregated particles in the form of aggregated primary particles cut into tens to hundreds of micrometers. The water-absorbent resin particles, which are secondary aggregated particles produced by this step, have a normal particle size distribution and a significantly increased surface area, so the absorption rate can be significantly improved.

[0137] In this way, after mixing the polymer and the surfactant, the polymer is micronized in the presence of the surfactant to produce water-absorbent resin particles in the form of secondary aggregated particles that are fragmented and aggregated while the superabsorbent resin particles and the surfactant are mixed.

[0138] In addition, it is desirable that a neutralizing agent is sprayed during the above-mentioned atomization step, so that the neutralizing agent component acts as a slip agent within the mixture, thereby reducing the load in the atomization process.

[0140] Specifically, as described above, polymerization is first performed to form a polymer that is not in a hydrogel state by performing polymerization without neutralizing the acidic groups of the monomer (Step 1), and a mixture of the polymer having acidic groups and a surfactant is micronized to produce hydrolyzed superabsorbent resin particles (Step 2). This step is performed by micronizing the mixture by extruding it into a porous plate having a plurality of holes, and by spraying a neutralizing agent into the mixture at the extrusion point of the porous plate, at least some of the acidic groups of the polymer having acidic groups within the mixture are neutralized. Accordingly, the surfactant is present in large quantities on the surface of the polymer, thereby lowering the high adhesiveness of the polymer to prevent excessive aggregation of the polymer and sufficiently performing the role of controlling the aggregation state to a desired level. Accordingly, the amount of fine particles generated during the process can be significantly reduced as the polymer is manufactured into secondary particles in the form of aggregated primary particles, and subsequent grinding and drying processes are carried out under milder conditions.

[0141] In addition, if polymerization is performed without neutralizing the acidic groups of the monomer, it is possible to form polymers with longer chains, thereby achieving the effect of reducing the content of water-soluble components that exist in an uncrosslinked state due to incomplete polymerization or crosslinking.

[0143] According to one embodiment of the invention, the step of manufacturing the function superabsorbent resin particles (step 2) comprises: a step of micronizing the mixture (step 2-1); and a step of spraying a neutralizing agent onto the mixture to neutralize at least some of the acidic groups of the polymer having acidic groups in the mixture (step 2-2); wherein steps 2-1 and 2-2 may be performed sequentially, simultaneously, or alternately.

[0144] Meanwhile, to ensure even neutralization of the entire polymer, it may be desirable to leave a certain time difference between the addition of the neutralizing agent and the micronization process.

[0145] The above neutralizing agent is not particularly limited as long as it is a component capable of neutralizing acidic groups, and basic substances such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. may be used.

[0146] In addition, the degree of neutralization, which refers to the extent to which acidic groups included in the polymer are neutralized by the neutralizing agent, may be 50 to 90 mol%, or 60 to 85 mol%, or 65 to 85 mol%, or 65 to 75 mol%. Although the range of the degree of neutralization may vary depending on the final physical properties, if the degree of neutralization is excessively high, the absorption capacity of the superabsorbent resin may decrease, and if the concentration of carboxyl groups on the particle surface is excessively low, surface crosslinking in subsequent processes may be difficult to perform properly, which may result in a decrease in absorption characteristics under pressure or permeability. Conversely, if the degree of neutralization is excessively low, not only is the absorption capacity of the polymer significantly reduced, but it may also exhibit properties similar to elastic rubber, which is difficult to handle.

[0148] According to one embodiment of the invention, the step (step 2) of manufacturing the function superabsorbent resin particles is performed by a micronizing device.

[0149] FIG. 2 is a schematic diagram of a micronizing device used in a method for manufacturing a superabsorbent resin according to one embodiment of the invention, and the details regarding the use of the micronizing device will be explained below with reference to FIG. 2.

[0151] The above-described atomizing device (10) comprises: a body part (100) including a transfer space in which a mixture of a polymer having an acidic group and a surfactant is transferred; a screw member (110) rotatably installed inside the transfer space to move the mixture; a drive motor (200) providing rotational driving force to the screw member; a cutter member (300) installed in the body part (100) and including a porous plate (310) having a plurality of holes formed therein, which grinds the mixture while discharging it to the outside of the body part; and a neutralizing agent spray nozzle (120) installed adjacent to the porous plate inside the body part.

[0152] The neutralizing agent being ground at the above neutralizing agent injection nozzle (120) is introduced adjacent to the porous plate (310), specifically at the discharge point of the porous plate (310), thereby performing a neutralization process and, when the mixture is discharged through the holes of the porous plate, acting as a slip agent within the mixture to reduce the load on the holes. On the other hand, if the neutralizing agent is introduced into the mixture first rather than at the discharge point of the porous plate (310), the adhesiveness of the hydrogel polymer increases, making it difficult to finely pulverize to the desired degree, and the load on the holes increases during discharge. Furthermore, if the polymerization process is performed with a pre-neutralized monomer before the formation of the hydrogel polymer, an additional coarse grinding process is required, which results in a significant increase in the generation of fine powder.

[0153] Here, the discharge point of the porous plate (310) specifically means just before the mixture passes through the porous plate (310), and specifically means the point where the neutralizing agent spray nozzle (120) of FIG. 2 is placed.

[0155] According to one embodiment of the invention, in the atomizing device (10), a neutralizing agent is introduced through the neutralizing agent injection nozzle (120) to the discharge point of the porous plate (310) inside the body part (100) to neutralize at least some of the acidic groups of the polymer having acidic groups in the mixture.

[0156] Specifically, in the above-described atomizing device (10), a neutralizing agent is introduced through the neutralizing agent injection nozzle (120) to the discharge point of the porous plate (310) inside the body part (100), thereby neutralizing at least some of the acidic groups of the polymer having acidic groups in the mixture, while simultaneously pulverizing the mixture as it is discharged to the outside of the body part through the porous plate (310).

[0157] Preferably, the cutter member (300) includes a porous plate (310) and a cutting knife (320) positioned at the outlet side of the body part adjacent to the porous plate (310), and when the mixture is discharged while passing through the porous plate (310), it is crushed and atomized by the cutting knife (320).

[0158] The hole size formed in the porous plate (310) may be 0.1 mm to 30 mm, and preferably 0.5 mm to 25 mm, 1 mm to 20 mm, or 1 mm to 10 mm. By using a porous plate having the above hole size, water-absorbent resin particles having a desired particle size can be manufactured.

[0159] According to one embodiment of the invention, in the micronization device (10), the cutter member (300) may include a plurality of porous plates (310) and a plurality of cutting knives (320). The arrangement order of the plurality of porous plates and the plurality of cutting knives is not particularly limited, and they may be arranged sequentially, arranged intersectingly, arranged continuously, or arranged continuously.

[0160] As described above, by including a plurality of porous plates and cutting knives, multiple atomization steps can be performed within a single atomization device. Meanwhile, a plurality of neutralizing agent spray nozzles may be arranged adjacent to one or more of the plurality of porous plates and cutting knives, and it is preferable to arrange the neutralizing agent spray nozzles adjacent to the porous plates to improve slip properties.

[0161] When the cutter member (300) comprises a plurality of perforated plates and a plurality of cutting knives, for example, a first perforated plate and a first cutting knife and a second perforated plate and a second cutting knife may be arranged sequentially, or a first perforated plate and a first cutting knife, a second perforated plate and a second cutting knife and a third cutting knife may be arranged sequentially, or a first perforated plate and a first cutting knife, a second perforated plate, a third perforated plate and a second cutting knife and a third cutting knife may be arranged sequentially, wherein the perforated plate and cutting knife refer to a configuration arranged adjacently.

[0162] As described above, when the cutter member (300) includes a plurality of porous plates, the size of the holes formed in each porous plate may satisfy the aforementioned range, and they may be the same or different from each other.

[0164] According to one embodiment of the invention, the micronization step (step 2) for manufacturing the function superabsorbent resin particles may be performed multiple times. This may be performed using multiple micronization devices, or using a single micronization device comprising multiple porous plates and / or multiple cutting knives, or some of the multiple micronization devices may comprise multiple porous plates and / or multiple cutting knives. The micronization step may preferably be performed 1 to 6 times or 1 to 4 times.

[0165] Here, in the case of a single atomization device comprising a plurality of porous plates and / or a plurality of cutting knives, the above-described details apply equally, and in this case, a water-absorbent resin having a desired particle size can be manufactured by adjusting the particle size range of the holes of the plurality of porous plates.

[0166] In addition, when multiple atomization devices are used, water-absorbent resin particles discharged from the first atomization device are fed back into the second atomization device to perform atomization, and a neutralizing agent is sprayed by a neutralizing agent nozzle inside one or more of the first and second atomization devices so that at least some of the acidic groups of the polymer having acidic groups can be neutralized. At this time, the particle size of the holes in the porous plate included in the first atomization device and the particle size of the holes in the porous plate included in the second atomization device may satisfy the aforementioned range, and they may be the same or different from each other.

[0168] According to one embodiment of the invention, the step of manufacturing the water-absorbent superabsorbent resin particles (step 2) comprises: a step of first micronizing the mixture; and a step of second micronizing the first micronized water-absorbent superabsorbent resin particles so that they have a smaller average particle size, wherein in any one or more of the first micronizing step and the second micronizing step, a neutralizing agent is sprayed so that at least some of the acidic groups of the polymer having acidic groups can be neutralized.

[0169] The above step can be performed using two atomization devices or a single atomization device.

[0170] For example, when the single atomization device described above is used, the atomization step may be performed by including a plurality of porous plates and / or a plurality of cutting knives as described above, and the sizes of the holes formed in the plurality of porous plates may be the same or different from each other.

[0171] In order for the above primary micronized water-absorbent resin particles to be secondary micronized to have a smaller average particle size, the micronizing device may include a first porous plate having a hole size of 1 mm to 6 mm and a second porous plate having a hole size of 0.5 mm to 6 mm. In this case, a first cutting knife may optionally be disposed adjacent to the first porous plate and a second cutting knife may be disposed adjacent to the second porous plate, and additional cutting knives may be included.

[0172] By using two porous plates having the above particle sizes, a first micronization step and a second micronization step are performed, and the second micronization step can be performed so that the water-absorbent resin particles micronized in the first step have a smaller average particle size. In this case, in one or more of the first micronization step and the second micronization step, a neutralizing agent is sprayed so that at least some of the acidic groups of the polymer having acidic groups can be neutralized.

[0174] In this way, when the polymer mixed with the surfactant is neutralized and simultaneously micronized using a micronizing device, the polymer is manufactured into secondary particles in which primary particles are aggregated, and subsequently, the grinding and drying processes are carried out under milder conditions, thereby significantly reducing the amount of fine particles generated during the process.

[0176] The step of manufacturing the above-mentioned water-absorbent superabsorbent resin particles (Step 2) may be micronized so that the average particle size of the water-absorbent superabsorbent resin particles is 50 μm to 600 μm, and preferably, may be micronized so that the average particle size is 100 μm to 500 μm, 150 μm to 450 μm, or 200 μm to 400 μm. By satisfying the above particle size range, the polymer is manufactured into secondary particles in the form of aggregated primary particles, and as the grinding and drying processes are subsequently carried out under milder conditions, the amount of fine powder generated during the process can be significantly reduced.

[0177] In the present invention, the average particle size “Dn” refers to the particle size or particle diameter at the n% point of the cumulative distribution of the number of particles according to particle size. That is, D50 represents the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size, D90 represents the particle size at the 90% point of the cumulative distribution of the number of particles according to particle size, and D10 represents the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. The above Dn can be measured using a laser diffraction method, etc. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution. D10, D50, and D90 can be measured by calculating the particle size at the point where the cumulative distribution of the number of particles according to particle size in the measuring device reaches 10%, 50%, and 90%.

[0179] According to one embodiment of the invention, the surfactant may be one or more selected from the group consisting of a compound represented by Formula 1 and a salt thereof, but is not limited thereto:

[0180] [Chemical Formula 1]

[0181]

[0182] In the above chemical formula 1,

[0183] A1, A2, and A3 each independently, single bond, carbonyl, , or and, provided that one or more of these are carbonyl or and, where, m1, m2 and m3 are each independently integers from 1 to 8, and Each is connected to an adjacent oxygen atom, and It is connected to adjacent R1, R2, and R3, respectively, and

[0184] R1, R2, and R3 are each independently hydrogen, 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, and

[0185] n is an integer from 1 to 9.

[0187] The above surfactant is mixed with the polymer and added so that the micronization (chopping) step can be easily carried out without aggregation.

[0188] The surfactant represented by Chemical Formula 1 above is a nonionic surfactant that exhibits excellent surface adsorption performance due to hydrogen bonding with unneutralized polymers, and is therefore suitable for achieving the desired aggregation control effect. On the other hand, in the case of anionic surfactants rather than nonionic surfactants, when mixed with a polymer neutralized by a neutralizing agent such as NaOH or Na2SO4, adsorption occurs via Na+ ions ionized on the carboxyl group substituents of the polymer, and when mixed with an unneutralized polymer, there is a problem in that the adsorption efficiency for the polymer is relatively reduced due to competition with the anions on the carboxyl group substituents of the polymer.

[0189] Specifically, in the surfactant represented by the above chemical formula 1, the hydrophobic functional group is the terminal functional group R1, R2, or R3 portion (if not hydrogen), and the hydrophilic functional group is the glycerol-derived portion within the chain and the terminal hydroxyl group (A n is a single bond, and at the same time R n In the case where g is hydrogen, n=1~3) is further included, and the glycerol-derived portion and the terminal hydroxyl group serve as hydrophilic functional groups that improve adsorption performance on the polymer surface. Accordingly, the aggregation of superabsorbent resin particles can be effectively suppressed.

[0190] In the above chemical formula 1, the hydrophobic functional groups R1, R2, and R3 (if 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. At this time, if the R1, R2, and R3 (if not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, there is a problem that the aggregation control of the crushed particles is not effectively achieved due to the short chain length, and if the R1, R2, and R3 (if not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the surfactant may be reduced, so it may not be effectively mixed with the polymer, and there may be a problem that the unit cost of the composition increases due to the increase in the cost of the surfactant.

[0191] Preferably, R1, R2, and R3 are hydrogen, or if they are straight-chain or branched-chain alkyls 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-tradecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl; or if they are straight-chain or branched-chain alkenyls having 6 to 18 carbon atoms, they may be 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-dekenyl, 2-undekenyl, 2-dodekenyl, 2-tridecanyl, 2-tetradekenyl, 2-pentadekenyl, 2-hexadekenyl. It may be 2-heptadekenyl or 2-octadekenyl.

[0192] The above surfactant may be selected from compounds represented by the following chemical formulas 1-1 to 1-14:

[0193] [Chemical Formula 1-1]

[0194]

[0195] [Chemical Formula 1-2]

[0196]

[0197] [Chemical Formula 1-3]

[0198]

[0199] [Chemical Formula 1-4]

[0200]

[0201] [Chemical Formula 1-5]

[0202]

[0203] [Chemical Formula 1-6]

[0204]

[0205] [Chemical Formula 1-7]

[0206]

[0207] [Chemical Formula 1-8]

[0208]

[0209] [Chemical Formula 1-9]

[0210]

[0211] [Chemical Formula 1-10]

[0212]

[0213] [Chemical Formula 1-11]

[0214]

[0215] [Chemical Formula 1-12]

[0216]

[0217] [Chemical Formula 1-13]

[0218]

[0219] [Chemical Formula 1-14]

[0220] .

[0222] Meanwhile, the surfactant may 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 in an excessively small amount, it may not be evenly adsorbed onto the surface of the polymer, and re-aggregation of particles may occur after grinding; if the surfactant is used in an excessive amount, the general physical properties of the finally manufactured superabsorbent resin may deteriorate. For example, the surfactant may be used in an amount of 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, per 100 parts by weight of the polymer.

[0223] The method of mixing these surfactants into the polymer is not particularly limited and can be appropriately adopted as long as it allows for even mixing of the surfactants into the polymer. Specifically, the surfactants may be mixed dry, mixed in a solution state after dissolving them in a solvent, or mixed after melting the surfactants.

[0224] For example, the surfactant may be mixed in the form of a solution dissolved in a solvent. At this time, any type of solvent, whether inorganic or organic, can be used without limitation; however, considering the ease of the drying process and the cost of the solvent recovery system, water is the most suitable. Furthermore, the solution may be prepared by mixing the surfactant and the polymer in a reaction vessel, by placing the polymer into a mixer and spraying the solution, or by continuously supplying the polymer and the solution to a continuously operating mixer for mixing.

[0226] Meanwhile, according to one embodiment of the present invention, the step of neutralizing at least some of the acidic groups of the polymer (step 2) and the step of micronizing the polymer in the presence of a surfactant to produce water-absorbent resin particles (step 3) may be performed sequentially or simultaneously.

[0227] 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 micronize the polymer mixed with the surfactant; or, the neutralizing agent and the surfactant may be added simultaneously to the polymer to perform neutralization and micronization. Alternatively, the surfactant may be added first and the neutralizing agent subsequently. Or, the neutralizing agent and the surfactant may be added alternately. Alternatively, the surfactant may be added first to micronize the polymer, followed by the addition of a neutralizing agent to neutralize it, and then an additional surfactant may be added to the neutralized hydrogel polymer to perform an additional micronization process.

[0228] Meanwhile, to ensure even neutralization of the entire polymer, it may be desirable to leave a certain time difference between the addition of the neutralizing agent and the micronization process.

[0229] At least some to a substantial amount of the above surfactant may be present on the surface of the above-mentioned superabsorbent resin particles.

[0230] Here, the meaning that the surfactant is present on the surface of the water-absorbent superabsorbent resin particles implies that at least some or a significant amount of the surfactant is adsorbed or bound to the surface of the water-absorbent superabsorbent resin particles. Specifically, the surfactant may be physically or chemically adsorbed to the surface of the superabsorbent resin. More specifically, the hydrophilic functional group 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 is physically adsorbed to the surface of the superabsorbent resin particles and surrounds the surface, while the hydrophobic portion of the surfactant is not adsorbed to the surface of the resin particles, so that the resin particles may be coated with the surfactant in the form of a micelle structure. This is because the surfactant is introduced during the micronization stage after polymer formation, rather than during the polymerization process of the water-soluble ethylene-based unsaturated monomer. Compared to cases where the surfactant is introduced during the polymerization process and exists within the polymer, the surfactant can faithfully perform its role as a surfactant, and pulverization and aggregation occur simultaneously, allowing for the acquisition of particles with a large surface area in the form of aggregated fine particles.

[0232] The water-absorbent resin particles obtained by this method may have a water content of 50 to 80 weight%. For example, the water content may be 55 weight% or more, or 75 weight% or less.

[0233] Meanwhile, throughout this specification, "moisture content" refers to the amount of water contained relative to the total weight of the superabsorbent polymer particles, and is the value obtained by subtracting the weight of the polymer in a dry state from the weight of the superabsorbent polymer particles. Specifically, it is defined as a value calculated by measuring the weight loss due to water evaporation in the superabsorbent polymer particles during the drying process in which the temperature of the polymer in a crumb state is raised through infrared heating. At this time, the drying conditions are set such that the temperature is raised from room temperature to approximately 180°C and then maintained at 180°C, with the total drying time set to 40 minutes, including a 5-minute temperature raising step, to measure the moisture content.

[0235] The above-mentioned water-absorbent resin particles may have a particle size at the level of normal particles, that is, a particle diameter of 150 μm to 850 μm. Specifically, the above-mentioned water-absorbent resin particles may contain 89 wt% or more, 90 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, or 95 wt% or more of water-absorbent resin particles having a particle diameter of 150 μm to 850 μm relative to the total weight. The particle diameter of these resin particles may be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method. Alternatively, considering that no additional grinding process is performed after the drying and surface crosslinking processes when manufacturing the superabsorbent resin composition, the content of superabsorbent resin particles having a particle size of 150 μm to 850 μm in the above-mentioned superabsorbent resin particles can be considered to be almost identical to the content of superabsorbent resin particles having a particle size of 150 μm to 850 μm in the finally manufactured superabsorbent resin particles.

[0237] (Step 3: Drying Step)

[0238] Next, the method includes a step (step 3) of drying the above-mentioned superabsorbent resin particles to produce superabsorbent resin particles. This step involves drying the moisture of the superabsorbent resin particles, which are obtained by neutralizing at least some of the acidic groups of the polymer and micronizing the polymer in the presence of a surfactant.

[0239] Preferably, the above step can be performed by drying in a moving type.

[0241] In a conventional method for manufacturing a superabsorbent resin, the drying step is generally performed until the moisture content of the superabsorbent resin particles becomes less than 10 weight%. However, the present invention is performed by controlling the aggregation of the shredded moisture superabsorbent resin by performing a shredding step in the presence of a surfactant, so that the moisture content of the superabsorbent resin particles being dried becomes 10 weight% to 20 weight%, preferably 10 weight% to 15 weight%, but is not limited thereto.

[0242] Accordingly, it has the advantage of exhibiting a high water content, which can fundamentally prevent the generation of fine particles. In addition, it is desirable as it can improve the absorption rate of the final superabsorbent resin.

[0243] To this end, the drying step is performed using a moving type drying method at a relatively low temperature. This moving type drying is distinguished from fixed-bed type drying by the presence or absence of material flow during drying; it is desirable as it prevents aggregation among the finely chopped water-absorbent resin particles within the pulverized material to be dried and enables the drying to be completed within a short period of time.

[0244] Specifically, the aforementioned moving-type drying refers to a method of drying a material while mechanically stirring it. In this case, the direction in which the hot air passes through the material may be the same as or different from the direction of circulation of the material. Alternatively, the material may circulate inside the dryer, and the material may be dried by passing a heat transfer fluid through a separate pipe outside the dryer. Meanwhile, fixed-bed type drying refers to a method of drying in which the material to be dried is stationary on a surface, such as a perforated steel plate, and hot air passes through the material from bottom to top.

[0246] The step of drying the above-mentioned superabsorbent resin particles (step 3) can be performed using a commonly used fluidized dryer without special limitations, for example, a horizontal-type mixer, a rotary kiln, a paddle dryer, or a steam tube dryer.

[0248] The step of drying the above-mentioned superabsorbent resin particles (step 3) can be performed at a relatively low temperature of 150°C or lower, preferably at 100°C to 150°C, 100°C to 130°C, or 105°C to 115°C, and even if performed at a low temperature as above, superabsorbent resin particles having the desired particle size and physical properties without the desired aggregation can be produced.

[0249] Meanwhile, the above drying temperature may be the internal operating temperature at which the material to be dried is introduced into the fluidized drying device used, and this may be controlled by passing a heat transfer fluid (heat transfer oil) through a separate pipe outside the dryer, but is not limited thereto.

[0251] The step of drying the above-mentioned superabsorbent resin particles (step 3) can be performed for 30 to 80 minutes, or for 30 to 60 minutes or 40 to 50 minutes, and even if the drying step is performed for a short time at a relatively low temperature, superabsorbent resin particles having the desired particle size and physical properties can be produced because there is less aggregation between the chopped hydrogel polymer resin particles in the crushed material to be dried.

[0253] (Additional steps)

[0254] Subsequently, the method for manufacturing a superabsorbent resin according to one embodiment of the invention may further include the step of crushing and classifying the superabsorbent resin particles as needed.

[0255] Specifically, the grinding step can be performed by grinding the dried superabsorbent resin particles to have a particle size at the level of normal particles, i.e., a particle diameter of 150 μm to 850 μm.

[0256] The grinder used for this purpose may specifically be a vertical pulverizer, turbo cutter, turbo grinder, rotary cutter mill, cutter mill, disc mill, shred crusher, crusher, chopper, or disc cutter, but is not limited to the examples described above.

[0257] Alternatively, a grinder such as a pin mill, hammer mill, screw mill, roll mill, disc mill, or jog mill may be used, but is not limited to the examples described above.

[0258] Meanwhile, in the manufacturing method of the present invention, superabsorbent resin particles with a smaller particle size distribution than in the conventional chopping step can be realized in the micronization step, and since the moisture content after drying is maintained relatively high at 10 weight% or more when moving-type drying is performed, even if grinding is performed under mild conditions with less grinding force, a superabsorbent resin with a very high content of normal particle sizes of 150 μm to 850 μm can be formed, and the fine particle generation ratio can be significantly reduced.

[0260] The superabsorbent resin particles manufactured as described above may contain 80% or more by weight, 85% or more by weight, 89% or more by weight, 90% or more by weight, 92% or more by weight, 93% or more by weight, 94% or more by weight, or 95% or more by weight of superabsorbent resin particles having a particle size of 150 μm to 850 μm relative to the total weight. The particle size of these resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0261] In addition, the superabsorbent resin particles may contain fine particles having a particle size of less than 150 μm relative to the total weight in an amount of about 20 wt% or less, or about 18 wt% or less, or about 15 wt% or less, or about 13 wt% or less, or about 12 wt% or less, or about 111 wt% or less, or about 10 wt% or less, or about 9 wt% or less, or about 8 wt% or less, or about 5 wt% or less. This is in contrast to having more than about 20 wt% to about 30 wt% of fine particles when manufacturing a superabsorbent resin according to a conventional manufacturing method.

[0263] Next, a method for manufacturing a superabsorbent resin according to one embodiment of the invention may include the step of manufacturing final superabsorbent resin particles by thermally crosslinking the surface of the superabsorbent resin particles in the presence of surface crosslinking.

[0264] The above surface crosslinking step induces a crosslinking reaction on the surface of the base resin powder in the presence of a surface crosslinking agent, so that the unsaturated bonds of the water-soluble ethylene-based unsaturated monomers remaining on the surface without being crosslinked are crosslinked by the surface crosslinking agent, thereby forming a superabsorbent resin with a high surface crosslinking density.

[0265] Specifically, a surface crosslinking layer can be formed through a heat treatment process in the presence of a surface crosslinking agent. During the heat treatment process, the surface crosslinking density, i.e., the external crosslinking density, increases, while the internal crosslinking density remains unchanged. Consequently, the superabsorbent resin with the manufactured surface crosslinking layer has a structure in which the external crosslinking density is higher than the internal one.

[0266] The above surface crosslinking process can be performed at a temperature of about 80°C to about 250°C. More specifically, the above surface crosslinking process can be performed 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-described surface crosslinking process conditions are satisfied, the surface of the superabsorbent resin particles is sufficiently crosslinked, and the pressure absorption capacity can be increased.

[0267] By satisfying these surface crosslinking process conditions (in particular, temperature increase conditions and reaction conditions at the maximum reaction temperature), a superabsorbent resin that appropriately satisfies physical properties such as superior absorption rate can be manufactured.

[0268] The means for raising the temperature for the surface crosslinking reaction are not particularly limited. Heating can be achieved by supplying a heat medium or by directly supplying a heat source. In this case, types of heat mediums that can be used include heated fluids such as steam, hot air, and hot oil, but are not limited thereto. Furthermore, the temperature of the supplied heat medium can be appropriately selected considering the medium type, the heating rate, and the target temperature. Meanwhile, directly supplied heat sources include heating via electricity and heating via gas, but are not limited to the examples described above.

[0270] Meanwhile, as the surface crosslinking agent included in the above surface crosslinking agent composition, any surface crosslinking agent conventionally used in the manufacture of superabsorbent resins may be used without any particular restrictions. For example, the above surface crosslinking agent may be 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-based compounds selected from the group consisting of ethylene carbonate and propylene carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; It may include mono-, di-, or polyoxazolidinone compounds; or cyclic urea compounds; etc. Preferably, the same as the internal crosslinking agent described above may be used, and for example, alkylene glycol diglycidyl ether compounds such as ethylene glycol diglycidyl ether may be used.

[0271] In the above surface crosslinking step, a surface crosslinking agent composition comprising an alcohol-based solvent and water in addition to the surface crosslinking agent may be used.

[0272] Such a surface crosslinking agent may be used in an amount of 0.001 to 2 parts by weight per 100 parts by weight of superabsorbent resin particles. Preferably, the amount may be 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, and may be used in an amount of 0.5 parts by weight or less, or 0.3 parts by weight or less. By adjusting the content range of the surface crosslinking agent to the range described above, a superabsorbent resin exhibiting excellent absorption performance and various physical properties such as liquid permeability can be manufactured.

[0274] Meanwhile, the above-mentioned surface crosslinking agent is added to superabsorbent resin particles in the form of a surface crosslinking agent composition containing it, and there are no specific limitations on the composition of the method of adding such a surface crosslinking agent composition. For example, methods such as placing the surface crosslinking agent composition and the superabsorbent resin particles into a reaction vessel and mixing them, spraying the surface crosslinking agent composition onto the superabsorbent resin particles, or continuously supplying and mixing the superabsorbent resin particles and the surface crosslinking agent composition into a continuously operated mixer may be used.

[0275] In addition, the surface crosslinking agent composition may further include water and / or a hydrophilic organic solvent as a medium. This provides the advantage that the surface crosslinking agent, etc., can be evenly dispersed on the base resin powder. At this time, the content of water and the hydrophilic organic solvent can be applied by adjusting the addition ratio to 100 parts by weight of superabsorbent resin particles for the purpose of inducing even dissolution / dispersion of the surface crosslinking agent, preventing clumping of the base resin powder, and optimizing the surface penetration depth of the surface crosslinking agent.

[0277] Meanwhile, in order to further improve liquid permeability and other properties, the method for manufacturing a superabsorbent resin according to one embodiment of the invention may further use aluminum salts, such as aluminum sulfate salts, and other various polyvalent metal salts during surface crosslinking. Such polyvalent metal salts may be included on the surface crosslinking layer of the finally manufactured superabsorbent resin.

[0279] 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 process may further include one or more steps of: a cooling step of cooling the superabsorbent resin particles having the surface cross-linked layer formed thereon; a watering 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 watering step, and the post-treatment step may be performed sequentially or simultaneously.

[0280] The additives introduced in the above post-treatment step may include permeability enhancers, anti-caking agents, fluidity enhancers, and antioxidants, but the present invention is not limited thereto.

[0281] By selectively performing the above cooling step, water hydration step, and post-treatment step, the water content of the final superabsorbent resin can be improved, and a higher quality superabsorbent resin product can be manufactured.

[0283] In addition, according to one embodiment of the present invention, a process of crushing and classifying the dried superabsorbent resin particles (or additionally surface-crosslinked superabsorbent resin particles or superabsorbent resin particles that have undergone an additional hydration process, etc.) may be further performed.

[0284] The grinder used for this purpose may specifically be a vertical pulverizer, turbo cutter, turbo grinder, rotary cutter mill, cutter mill, disc mill, shred crusher, crusher, chopper, or disc cutter, but is not limited to the examples described above.

[0285] Alternatively, a grinder such as a pin mill, hammer mill, screw mill, roll mill, disc mill, or jog mill may be used, but is not limited to the examples described above.

[0286] The superabsorbent resin particles manufactured as described above may contain 80% or more by weight, 85% or more by weight, 89% or more by weight, 90% or more by weight, 92% or more by weight, 93% or more by weight, 94% or more by weight, or 95% or more by weight of superabsorbent resin particles having a particle size of 150 μm to 850 μm relative to the total weight. The particle size of these resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0288] According to another embodiment of the present invention, a superabsorbent resin manufactured by the above manufacturing method is provided.

[0289] The superabsorbent resin produced by the above manufacturing method achieves a high water content without a separate additional water addition process or additive input process, thereby having a low fine particle content. It can provide a superabsorbent resin with excellent absorption speed and other properties, such as water retention capacity (CRC) and pressure absorption capacity (AUP), which are equivalent to or higher than those of superabsorbent resins produced by conventional methods, while simultaneously having a lower water-soluble component (EC) content.

[0291] The operation and effects of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0293] [Examples and Comparative Examples]

[0294] Example 1

[0295] (Step 1) 1000g of acrylic acid, 3.5g of pentaerythritol trialyl ether as an internal crosslinking agent, and 2260g of water were mixed in a 5L glass container equipped with a stirrer and a thermometer, and stirred while maintaining the temperature at 5℃. Nitrogen was introduced into the glass container containing the mixture at 1000cc / min for 1 hour to replace the atmosphere with nitrogen. Next, 13g of a 0.3% aqueous hydrogen peroxide solution, 15g of a 1% aqueous ascorbic acid solution, and 30g of a 2% aqueous 2,2'-azobis-(2-amidinopropane) dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 15g of a 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the temperature of the mixture reached 85℃, the polymer was obtained by polymerizing at 90±2℃ for about 3 hours.

[0297] (Step 2) A mixture of 1,000 g of the obtained polymer and 1 g of Glycerol Monolaurate as a surfactant was passed once through a first micronization device equipped with a porous plate having a plurality of holes with a hole size of 6 mm to perform a first micronization process.

[0298] Next, the second, third, and fourth micronization processes were performed by repeatedly feeding the porous plate, which includes a plurality of holes with a hole size of 4 mm, into a second micronization device a total of three times.

[0299] In the above second atomization process, 232g of a 50% NaOH aqueous solution was introduced through a neutralizing agent nozzle placed adjacent to the porous plate, and the neutralization process was performed along with the atomization.

[0300] In the above third atomization process, 37.5g of a 15% aqueous Na2SO4 solution was introduced through a neutralizing agent nozzle placed adjacent to the porous plate, and the atomization process was performed.

[0301] Finally, in the fourth micronization process, the micronization process was performed without adding a neutralizing agent or surfactant to obtain water-absorbent resin particles.

[0302] The degree of neutralization of the above-mentioned superabsorbent resin particles was 70 mol%.

[0304] (Step 3) Afterward, 1,000 g of the above-mentioned superabsorbent resin particles were fed into a rotary mixer fluid dryer rotating at 100 rpm. Drying was performed for 60 minutes while maintaining the internal temperature of the dryer at 105°C to obtain resin particles. The obtained particles were then subjected to a two-stage roll mill (roll mill, (GRAN-U-LIZER TM The material was ground using a sieve to obtain particles with a particle size of 150 μm to 850 μm. The ground material was then selectively recovered using a classifier to obtain only the superabsorbent resin particles with a particle size of 150 μm to 850 μm.

[0305] The water content of the above superabsorbent resin particles was 13 wt%.

[0307] Comparative Example 1

[0308] In step 2 of Example 1, 232 g of 50% NaOH was added to a mixture of 1,000 g of polymer and 1 g of surfactant Glycerol Monolaurate to neutralize it, and the neutralized mixture was passed once through a first micronization device equipped with a porous plate having a plurality of holes with a hole size of 6 mm to perform a first micronization process, a second micronization process was performed without adding a neutralizing agent or surfactant, a third micronization process was performed by adding 37.5 g of a 15% Na2SO4 aqueous solution, and a fourth micronization process was performed without adding a neutralizing agent or surfactant to obtain water-absorbent resin particles.

[0309] The degree of neutralization of the above-mentioned superabsorbent resin particles was 70 mol%.

[0310] Subsequently, 1,000 g of the above-mentioned superabsorbent resin particles were fed into a rotary mixer fluid dryer rotating at 100 rpm. Drying was performed for 60 minutes while maintaining the internal temperature of the dryer at 105°C to obtain resin particles. The obtained particles were then subjected to a two-stage roll mill (GRAN-U-LIZER TM The material was ground using a sieve to obtain particles with a particle size of 150 μm to 850 μm. The ground material was then selectively recovered using a classifier to obtain only the superabsorbent resin particles with a particle size of 150 μm to 850 μm.

[0311] The water content of the above superabsorbent resin particles was 12 wt%.

[0313] Comparative Example 2

[0314] A monomer composition was prepared by mixing 100g of acrylic acid, 140g of 31.5 wt% caustic soda (NaOH), 0.30g of polyethylene glycol diacrylate, 0.12g of sodium persulfate as a thermal polymerization initiator, 0.01g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator, and 40g of water, placed in a square reaction vessel measuring 30cm by 30cm, and 10mW / cm² 2 A hydrogel polymer was prepared by polymerizing the polymer for 60 seconds by irradiating with ultraviolet light having an intensity.

[0315] 1 g of the surfactant Glycerol Monolaurate was mixed with 1,000 g of the obtained hydrogel polymer. The mixture was atomized four times using a micronizing device, and 1,000 g of the hydrogel superabsorbent resin particles were fed into a rotary mixer fluid dryer rotating at 100 rpm. The resin particles were obtained by drying for 60 minutes while maintaining the internal temperature of the dryer at 105°C. The obtained particles were then subjected to a two-stage roll mill (GRAN-U-LIZER TMThe material was ground using a sieve to obtain particles with a particle size of 150 μm to 850 μm. The ground material was then selectively recovered using a classifier to obtain only the superabsorbent resin particles with a particle size of 150 μm to 850 μm.

[0316] The water content of the above superabsorbent resin particles was 11 wt%.

[0318] [Experimental Example]

[0319] For the superabsorbent resin prepared in the above example, the physical properties were evaluated in the following manner, and the results are shown in Table 1.

[0320] Unless otherwise indicated, all of the following physical property evaluations were conducted in a constant temperature and humidity (23±1℃, relative humidity 50±10%), and physiological saline or saline refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0322] (1) Moisture content

[0323] The moisture content is the amount of water relative to the total weight of the superabsorbent resin, and was calculated according to the following mathematical formula 2.

[0324] Specifically, the weight loss due to moisture evaporation in the superabsorbent resin was measured and calculated during the drying process in which the temperature of the superabsorbent resin was raised through infrared heating. At this time, the drying conditions were set such that the temperature was raised from room temperature to 180°C and then maintained at 180°C, with the total drying time set to 40 minutes, including a 5-minute temperature raising step. The weight of the superabsorbent resin was measured before and after drying, respectively, and calculated according to the following Equation 1.

[0325] [Mathematical Formula 1]

[0326] Moisture content (weight%) = [(Ao-At) / Ao ]X100

[0327] 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.

[0329] (2) Fine content

[0330] For the superabsorbent resin prepared in the example, it was classified using standard sieves with scales of 850 μm (20 mesh), 600 μm (30 mesh), 300 μm (50 mesh), and 150 μm (100 mesh) according to ASTM standards, and after measuring the weight of fine particles with a size of less than 150 μm, the content of the fine particles was expressed as a percentage based on the total weight of the sample superabsorbent resin particles (weight%).

[0332] (3) Centrifuge Retention Capacity (CRC)

[0333] For the superabsorbent resins prepared in the examples, samples having a particle size of 150 to 850 μm were taken from each superabsorbent resin, and the centrifugal retention capacity (CRC) was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3 under no load.

[0334] Specifically, from the resins obtained through each example, a resin classified by sieve #30-50 was obtained. This resin W0 (g) (approx. 0.2g) was uniformly placed into a nonwoven fabric bag and sealed, after which it was immersed in physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was drained from the bag for 3 minutes using a centrifuge under conditions of 250g, and the mass W2 (g) of the bag was measured. Additionally, the same operation was performed without using the resin, and the mass W1 (g) was measured. Using each obtained mass, the CRC (g / g) was calculated according to the following formula.

[0335] [Mathematical Formula 2]

[0336] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0338] (4) Water-soluble content (EC)

[0339] For 2g of superabsorbent resin, the water-soluble components were measured after swelling for 1 hour according to the EDANA method WSP 270.3.

[0341] (5) Vortex absorption rate (Vortex)

[0342] The absorption rate (vortex time) was measured in seconds according to the method described in International Publication Application No. 1987-003208. When measuring the absorption rate, the resin obtained after the surface crosslinking was used without classification.

[0343] Specifically, 2g of each resin was added to 50 mL of physiological saline at 23℃, and a magnetic bar (diameter 8 mm, length 30 mm) was stirred at 600 rpm, and the time until the vortex disappeared was measured in seconds and calculated.

[0345] division Example 1 Comparative Example 1 Comparative Example 2 Fine content #100 or less (%) 15% 21% 20% CRC (g / g) 43.4 42.6 43.0 EC (g) 4.8 5.6 6.0 Vortex time (sec) 26 32 55 Discharge rate (kg / h) 159 126 130

[0346] As can be seen in Table 1 above, by performing a micronization step and simultaneously neutralizing the polymer under specific conditions, it was confirmed that the superabsorbent resin produced had reduced water-soluble components and fine particles, and excellent absorption properties, particularly the absorption rate, were improved.

[0347] In the case of Comparative Example 1, in which neutralization was performed during the mixing process of adding a surfactant to the polymer before the micronization process, and Comparative Example 2, in which pre-neutralization was performed during the polymerization stage, it was confirmed that the physical properties of the Vortex were degraded due to the aggregation phenomenon of the hydrogel, and the discharge volume was reduced. Explanation of the symbols

[0349] 10: Micronization device 100: Body 110: Screw member 120: Neutralizer spray nozzle 200: Drive motor 300: Cutter member 310: Perforated plate 320: Cutting knife

Claims

Claim 1 A method for manufacturing a superabsorbent resin comprising: a step of cross-linking a water-soluble ethylene-based unsaturated monomer having an acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a polymer having an acidic group (Step 1); a step of micronizing a mixture of the polymer having an acidic group and a surfactant to produce water-soluble superabsorbent resin particles (Step 2); and a step of drying the water-soluble superabsorbent resin particles to produce superabsorbent resin particles (Step 3); wherein the step of manufacturing the water-soluble superabsorbent resin particles (Step 2) is performed by micronizing the mixture by discharging it into a porous plate having a plurality of holes using a micronizing device including a spray nozzle into which a neutralizing agent is sprayed, and the neutralizing agent is sprayed into the mixture by the spray nozzle at the discharge point of the porous plate, so that at least some of the acidic groups of the polymer having an acidic group in the mixture are neutralized. Claim 2 delete Claim 3 A method for manufacturing a superabsorbent resin according to claim 1, wherein the step of manufacturing the function superabsorbent resin particles (step 2) comprises: a step of micronizing the mixture (step 2-1); and a step of spraying a neutralizing agent onto the mixture to neutralize at least some of the acidic groups of the polymer having acidic groups in the mixture (step 2-2); wherein step 2-1 and step 2-2 are performed sequentially, simultaneously, or alternately. Claim 4 A method for manufacturing a superabsorbent resin according to claim 1, wherein the step of manufacturing the function superabsorbent resin particles (step 2) is performed using a micronizing device, and the micronizing device comprises: a body part including a transfer space in which a mixture of a polymer having acidic groups and a surfactant is transferred; a screw member rotatably installed inside the transfer space to move the mixture; a drive motor providing rotational driving force to the screw member; a cutter member installed in the body part and including a porous plate having a plurality of holes formed therein, which grinds the mixture while discharging it to the outside of the body part; and a neutralizing agent spray nozzle installed adjacent to the porous plate inside the body part. Claim 5 A method for manufacturing a superabsorbent resin according to claim 4, wherein in the above-described atomizing device, a neutralizing agent is injected through a neutralizing agent injection nozzle at a discharge point of a porous plate inside a body part to neutralize at least some of the acidic groups of a polymer having acidic groups in a mixture. Claim 6 A method for manufacturing a superabsorbent resin according to claim 4, wherein the cutter member further comprises a cutting knife positioned adjacent to the porous plate and towards the exit side of the body part. Claim 7 A method for manufacturing a superabsorbent resin according to claim 4, wherein the cutter member comprises a plurality of porous plates and a plurality of cutting knives. Claim 8 A method for manufacturing a superabsorbent resin according to claim 4, wherein the hole size formed in the porous plate is 0.1 mm to 30 mm. Claim 9 A method for manufacturing a superabsorbent resin according to claim 1, wherein the step of manufacturing the water-absorbent superabsorbent resin particles (step 2) comprises: a step of first micronizing the mixture; and a step of second micronizing the first micronized water-absorbent superabsorbent resin particles so as to have a smaller average particle size, wherein in any one or more of the first micronizing step and the second micronizing step, a neutralizing agent is sprayed so that the acidic groups of at least some of the polymer having acidic groups are neutralized. Claim 10 A method for manufacturing a superabsorbent resin according to claim 1, wherein at least a portion of the surfactant is present on the surface of the superabsorbent resin particles. Claim 11 In claim 1, the surfactant is one or more selected from the group consisting of a compound represented by the following chemical formula 1 and a salt thereof, Method for manufacturing superabsorbent resin: [Chemical Formula 1] In the above chemical formula 1, A1, A2, and A3 each independently have a single bond, carbonyl, , or and, provided that one or more of these are carbonyl or and, where, m1, m2 and m3 are each independently integers from 1 to 8, and Each is connected to an adjacent oxygen atom, and is connected to adjacent R1, R2 and R3, respectively, and R1, R2 and R3 are each independently hydrogen, 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, and n is an integer from 1 to 9. Claim 12 A method for manufacturing a superabsorbent resin according to claim 1, wherein the step of drying the superabsorbent resin particles (step 3) is performed in a moving type. Claim 13 A method for manufacturing a superabsorbent resin according to claim 1, wherein the step of drying the superabsorbent resin particles (step 3) is performed using a moving type dryer such as a horizontal-type mixer, rotary kiln, paddle dryer, or steam tube dryer. Claim 14 A method for manufacturing a superabsorbent resin according to claim 1, wherein the step of drying the superabsorbent resin particles (step 3) is performed at a temperature of 150°C or lower. Claim 15 A method for manufacturing a superabsorbent resin according to claim 1, wherein the moisture content of the superabsorbent resin particles obtained in the step (step 3) of drying the superabsorbent resin particles is 10% to 20% by weight. Claim 16 A method for manufacturing a superabsorbent resin according to claim 1, further comprising the step (step 5) of crushing and classifying the superabsorbent resin particles. Claim 17 A method for manufacturing a superabsorbent resin according to claim 16, further comprising the step (step 6) of forming a surface cross-linking layer on at least a portion of the surface of the classified superabsorbent resin particles. Claim 18 A superabsorbent resin manufactured by the manufacturing method of claim 1.

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