Method for producing superabsorbent resin and superabsorbent resin

Abstract

The present invention relates to a method for producing a superabsorbent polymer, more specifically, to a method for producing a superabsorbent polymer that exhibits excellent absorption properties by significantly reducing the amount of water-soluble components and fine powder generated by performing a microparticulation step under specific conditions.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2021 - 0079644 filed on June 18, 2021, Korean Patent Application No. 10 - 2021 - 0080232 filed on June 21, 2021, and Korean Patent Application No. 10 - 2022 - 0074721 filed on June 20, 2022, and all the contents disclosed in the documents of the Korean patent applications are included as part of this specification.

[0002] The present invention relates to a method for manufacturing a superabsorbent resin and a superabsorbent resin. More specifically, the present invention relates to a method for manufacturing a superabsorbent resin and a superabsorbent resin in which the amount of water - soluble components and fine powder is significantly reduced by performing an atomization step under specific conditions, and which exhibits excellent absorption properties.

Background Art

[0003] A superabsorbent polymer (SAP) is a synthetic polymer material having a function of absorbing about 500 to 1000 times its own weight of water, and is named differently such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material) for each developing company. Such superabsorbent resins began to be put into practical use in sanitary products and are now widely used as materials for soil moisture retainers for horticulture, water - stop materials for civil engineering and construction, seedling - raising sheets, freshness retainers in the food distribution field, and wet compresses.

[0004] Such superabsorbent resins are mainly widely used in the field of sanitary materials such as diapers and sanitary napkins. Inside the sanitary materials, it is common for the superabsorbent resin to be contained in a state of being diffused in pulp. However, in recent years, efforts have continued to provide sanitary materials such as thinner diapers, and as part of this, the pulp content has been reduced, or further, the development of so - called pulpless diapers in which pulp is not used at all has been actively progressing.

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

[0006] On the other hand, such superabsorbent resins are generally produced through a stage of polymerizing monomers to produce a water-containing gel polymer containing a large amount of water and a stage of grinding the water-containing gel polymer into resin particles having a desired particle size after drying. However, when the process of grinding is carried out after drying the water-containing gel polymer as described above, a large amount of fine powder is generated, and there is a problem of deteriorating the physical properties of the finally produced superabsorbent resin.

[0007] Also, for the reuse of such fine powder, it is normal to mix the fine powder with water and aggregate it to produce regranulated fine powder, and then input the regranulated fine powder produced through processes such as drying / grinding / classification. However, at this time, problems such as an increase in the energy consumption during the drying process and an increase in the load on the equipment may occur due to the water used, and the productivity of the production of superabsorbent resin may decrease.

[0008] Therefore, in order to fundamentally solve such problems, the development of a technology capable of producing superabsorbent resin without generating fine powder has been continuously demanded. Summary of the Invention Problems to be Solved by the Invention

[0009] The present invention provides a method for producing a superabsorbent resin and a superabsorbent resin, which can significantly improve the absorption rate by producing particles in which fine particles are aggregated to increase the surface area, significantly reduce the amount of fine powder generated during the process, and exhibit excellent absorption physical properties. Means for Solving the Problems

[0010] According to one embodiment of the present invention for solving the above problems, crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal crosslinking agent and a polymerization initiator to form a polymer having an acidic group (Step 1); atomizing a mixture of the polymer having an acidic group and a surfactant to produce water-containing superabsorbent resin particles (Step 2); and drying the water-containing superabsorbent resin particles to produce superabsorbent resin particles (Step 3); including the step of producing the water-containing superabsorbent resin particles (Step 2) is performed by discharging the mixture onto a porous plate having a plurality of holes formed therein for atomization, and a neutralizing agent is injected into the mixture at the discharge point of the porous plate, and at least a part of the acidic groups of the polymer having an acidic group in the mixture is neutralized, and a method for producing a superabsorbent resin is provided.

[0011] Also, according to one embodiment of the present invention, a superabsorbent resin produced by the method for producing a superabsorbent resin described above is provided.

Advantages of the Invention

[0012] According to the method for producing a superabsorbent resin of the present invention, it is possible to produce a superabsorbent resin that can realize particles in a shape in which submicroparticles are aggregated, increase the surface area, and thus significantly improve the absorption rate and exhibit excellent absorption physical properties.

[0013] Also, by pulverizing from the state of water-containing superabsorbent resin particles to the normal particle level, the amount of fine powder generated during the production of the superabsorbent resin can be significantly reduced.

[0014] Also, it is possible to provide a superabsorbent resin having a narrow particle size distribution, a uniform particle size distribution, and excellent absorption physical properties such as water retention ability and pressure absorption ability, and absorption rate by reducing the content of water-soluble components (EC).

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] The terms used in this specification are used merely to explain exemplary embodiments and are not intended to limit the present invention.

[0017] Singular expressions include plural expressions unless the context clearly indicates a different meaning. In this specification, terms such as "including," "comprising," or "having" are used to specify the presence of implemented features, steps, components, or combinations thereof, and it should be understood that they do not preclude the presence or addition of one or more other features, steps, components, or combinations thereof in advance.

[0018] Terms such as first, second, third, etc. are used to describe various components, and these terms are used only for the purpose of distinguishing one component from another.

[0019] The present invention can be subjected to various modifications and can have various forms, and specific embodiments will be exemplified and described in detail below. However, this is not to limit the present invention to a specific disclosed form, and it should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0020] (Method for Manufacturing a Superabsorbent Resin) A method for producing a superabsorbent resin according to an embodiment of the present invention includes a step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal crosslinking agent and a polymerization initiator to form a polymer having an acidic group (step 1); a step of atomizing a mixture of the polymer having an acidic group and a surfactant to produce water-containing superabsorbent resin particles (step 2); and a step of drying the water-containing superabsorbent resin particles to produce superabsorbent resin particles (step 3). The step of producing the water-containing superabsorbent resin particles (step 2) is performed by discharging the mixture onto a porous plate having a plurality of holes formed therein for atomization, and a neutralizing agent is sprayed onto the mixture at the discharge point of the porous plate, and at least a part of the acidic groups of the polymer having an acidic group in the mixture is neutralized.

[0021] As used in the specification of the present invention, the term "polymer" or "macromolecule" means a state in which a water-soluble ethylenically unsaturated monomer is polymerized, and can include all moisture content ranges or particle size ranges.

[0022] Also, the term "water-containing superabsorbent resin particles" or "superabsorbent resin particles" means, depending on the context, a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer containing an acidic group and at least a part of which acidic groups are neutralized is polymerized, or particulate base resin composed of superabsorbent resin particles obtained by pulverizing the crosslinked polymer, or all superabsorbent resins in a state suitable for commercialization through additional processes such as surface crosslinking, micropowder regranulation, drying, pulverization, classification, etc. with respect to the crosslinked polymer and the base resin.

[0023] Also, the term "micropowder" means particles having a particle size of less than 150 μm among superabsorbent resin particles. The particle size of such resin particles can be measured by the method of European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3.

[0024] Also, the term "chopping" refers to cutting a water-containing gel polymer into millimeter-sized pieces to increase drying efficiency, and is used distinctively from grinding to the normal particle level.

[0025] Also, the term "micronizing, micronization" refers to grinding a water-containing gel polymer to a particle size of several tens to several hundreds of micrometers, and is used distinctively from "chopping".

[0026] The water-containing gel polymer obtained by the polymerization reaction of an acrylic acid-based monomer is commercially available as a superabsorbent resin, which is a powdery product through processes such as drying, grinding, classification, and surface crosslinking. Recently, attempts have been continuously made to provide a superabsorbent resin with an improved absorption rate.

[0027] As the most common method for increasing the absorption rate, there is a method of forming a porous structure inside the superabsorbent resin to increase the surface area of the superabsorbent resin. However, in order to increase the surface area of the superabsorbent resin, a method of forming a porous structure inside the base resin powder by including a foaming agent in the monomer composition and performing crosslinking polymerization is generally adopted.

[0028] However, the use of a foaming agent causes disadvantages such as a decrease in various physical properties of the superabsorbent resin, such as surface tension, liquid permeability, or bulk density, and an increase in the amount of fine powder generation. Therefore, there is a need to develop a technology that can improve the absorption rate of the superabsorbent resin without using a foaming agent.

[0029] On the one hand, conventionally, superabsorbent polymers are produced by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer. After drying the thus formed hydrogel polymer, it is pulverized to a desired particle size. At this time, usually, in order to facilitate the drying of the hydrogel polymer and enhance the efficiency of the pulverization process, a chopping process of cutting the hydrogel polymer into particles of several millimeters in size is performed before the drying process. However, due to the adhesiveness of the hydrogel polymer in such a chopping process, the hydrogel polymer cannot be pulverized to the particle level of micro size and becomes an aggregated gel state. When such an aggregated gel-like hydrogel polymer is dried, a tubular dried body is formed, and in order to pulverize this to the micro-size particle level, a multi-stage pulverization process has to be passed through, so there is a problem that a large amount of fine powder is generated in this process.

[0030] Specifically, FIG. 1 shows a flowchart regarding a conventional method for producing a superabsorbent polymer. Referring to FIG. 1, conventionally, superabsorbent polymers have been produced including the following steps. (Neutralization) A step of neutralizing at least a part of the acidic groups of the water-soluble ethylenically unsaturated monomer; (Polymerization) A step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer; (Chopping) A step of chopping the hydrogel polymer; (Drying) A step of drying the chopped hydrogel polymer; and (Pulverization / Classification) A step of classifying the dried polymer into normal particles and fine powder after pulverization.

[0031] As described above, the chopped water-containing gel polymer will have a gel-like form aggregated to a size of about 1 cm to 10 cm. Such a chopped water-containing gel polymer is laminated on a belt with a perforated plate as the floor and dried by hot air supplied from below or above. Since the polymer dried by the above drying method exhibits a plate shape that is not particulate, the classification step after pulverization is performed after coarse pulverization so that the particles to be produced become normal particles, that is, particles having a particle size of 150 μm to 850 μm, and then classified again after fine pulverization. By such a manufacturing method, the amount of fine powder separated in the final classification step is large, about 20% by weight to about 30% by weight with respect to the total weight of the finally produced superabsorbent resin. Therefore, after mixing the separated fine powder with an appropriate amount of water and performing fine powder regranulation, it is reused by the method of charging it into the chopping step or the step before drying.

[0032] However, when the fine powder regranulated body mixed with water for such reuse of fine powder is recharged into the pulverization or drying process, problems such as an increase in equipment load and / or energy consumption occur, and the physical properties of the superabsorbent resin are deteriorated by the fine powder that cannot be classified and remains.

[0033] Therefore, the present inventor grasped the fact that in the conventional manufacturing method, the amount of fine powder generated is greatly affected by the pulverization process, and by adding a surfactant and a neutralizing agent in the polymer pulverization process to post-neutralize the polymer, while pulverizing more finely than before, that is, atomizing, and at the same time controlling aggregation, the present inventor focused on the fact that the amount of fine powder generated during the manufacturing process can be significantly reduced by producing particles in a form in which the submicron particles are aggregated.

[0034] On the other hand, a method of adding a surfactant has been proposed to reduce the adhesiveness of the water-containing gel polymer in the chopping process. However, when a surfactant is added in the chopping process, due to the high water content of the water-containing gel polymer, the surfactant penetrates into the interior of the water-containing gel polymer rather than existing at the interface of the water-containing gel polymer, and there is a problem that the surfactant cannot perform its role correctly.

[0035] Since the chopped particles can increase the surface area to some extent because particles on the order of several millimeters or several centimeters are formed compared to the polymer before chopping, it is difficult to expect an effect that effectively improves the absorption rate. To improve the absorption rate, a method of increasing the surface area by further increasing the mechanical force and kneading at the chopping stage can be considered. In this case, however, due to the adhesiveness peculiar to the polymer, excessive aggregation occurs, and after chopping, drying, and pulverization, only amorphous single particles with uneven surfaces are formed, and excessive kneading or pulverization may increase the water-soluble components instead.

[0036] As a result of repeated research to solve this problem, instead of polymerizing in a state where the acidic groups of water-soluble ethylenically unsaturated monomers are neutralized as in the usual method for producing superabsorbent resins, polymerization is first carried out in a state where the acidic groups are not neutralized to form a polymer, and then the hydrogel polymer is atomized in the presence of a surfactant, or the acidic groups of the polymer are neutralized, or after neutralizing the acidic groups of the polymer to form a hydrogel polymer, the hydrogel polymer is atomized in the presence of a surfactant, or the acidic groups present in the polymer are neutralized simultaneously with atomization. It was confirmed that a large amount of surfactant is present on the surface of the polymer, which can sufficiently play a role in reducing the high adhesiveness of the polymer and preventing excessive aggregation of the polymer, and can adjust the aggregation state to a desired level.

[0037] Thereby, the polymer is produced as secondary particles in which primary particles are aggregated, and then, as the pulverization and drying processes proceed under milder conditions, the amount of fine powder generated during the process can be significantly reduced.

[0038] In addition, when the polymer is atomized in the presence of the surfactant, the hydrophobic functional group portion contained in the surfactant imparts hydrophobicity to the surface of the superabsorbent resin particles obtained by pulverization, thereby relaxing the frictional force between the particles and increasing the apparent density of the superabsorbent resin. At the same time, the hydrophilic functional group portion contained in the surfactant can also bind to the superabsorbent resin particles so that the surface tension of the resin is not decreased. As a result, the superabsorbent resin produced by the above-described production method can have a higher apparent density value while exhibiting the same level of surface tension as the resin without using a surfactant.

[0039] Further, when polymerization is first carried out in an unneutralized state to form a polymer and then the acidic groups present in the polymer are neutralized, it is possible to form a polymer having a longer chain and achieve the effect of reducing the content of the water-soluble component present in a state where crosslinking is incomplete and not crosslinked.

[0040] Since the water-soluble component has the property of being easily eluted when the superabsorbent resin comes into contact with a liquid, when the content of the water-soluble component is high, the eluted water-soluble component will remain on most of the surface of the superabsorbent resin, making the superabsorbent resin sticky and causing a decrease in liquid permeability. Therefore, it is important to keep the content of the water-soluble component low from the aspect of liquid permeability.

[0041] On the other hand, when using a micronizer conventionally used in the chopping step, there was a problem that it was difficult to neutralize the acidic groups present in the polymer simultaneously with atomization as described above. In contrast, the present inventor introduced a new structure atomizing device including a neutralizing agent injection nozzle, neutralized the acidic groups of the unneutralized polymer to form a water-containing gel polymer, and then atomized the water-containing gel polymer in the presence of a surfactant, or made it possible to easily perform the step of neutralizing the acidic groups present in the polymer simultaneously with or before and after atomization.

[0042] According to one embodiment of the present invention, by performing polymerization in an unneutralized state, the content of the water-soluble component is reduced, and thereby the liquid permeability of the superabsorbent resin can be improved.

[0043] Moreover, the superabsorbent resin produced according to an embodiment of the present invention can have a uniform particle size distribution, thereby providing a superabsorbent resin excellent in various absorption physical properties such as water retention ability and pressure absorption ability, and absorption rate.

[0044] Hereinafter, the manufacturing method of the superabsorbent resin of one embodiment will be specifically described step by step.

[0045] (Step 1: Polymerization step) The manufacturing method of the superabsorbent resin according to an embodiment of the invention includes a step (step 1) of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal crosslinking agent and a polymerization initiator to form a polymer having an acidic group.

[0046] The step is a step of thermally polymerizing or photopolymerizing a monomer mixture containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator to form a polymer.

[0047] The water-soluble ethylenically unsaturated monomer having an acidic group can be any monomer commonly used in the production of superabsorbent resins. As a non-limiting example, the water-soluble ethylenically unsaturated monomer can be a compound represented by the following chemical formula 2:

[0048] [Chemical formula 2] R1-COOM 1

[0049] In the chemical formula 2, R1 is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond, M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0050] Preferably, the monomer can be at least one 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. When acrylic acid or its salt is used as the water-soluble ethylenically unsaturated monomer in this way, a superabsorbent resin with improved water absorption can be obtained, which is advantageous. In addition, as the monomer, 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 anionic monomers and their salts, (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; and (N,N)-dimethylaminoethyl (meth)acrylate, or (N,N)-dimethylaminopropyl (meth)acrylamide amino group-containing unsaturated monomers and their quaternized products; one or more selected from the group consisting of can be used.

[0051] Here, the water-soluble ethylenically unsaturated monomer has an acidic group. As described above, in the production of conventional superabsorbent resins, a monomer in which at least a part of the acidic groups is neutralized by a neutralizing agent is crosslinked and polymerized to form a hydrogel polymer. Specifically, in the step of mixing the water-soluble ethylenically unsaturated monomer having the acidic group, the internal crosslinking agent, the polymerization initiator, and the neutralizing agent, at least a part of the acidic groups of the water-soluble ethylenically unsaturated monomer is neutralized.

[0052] However, according to one embodiment of the present invention, polymerization is first carried out in a state where the acidic groups of the water-soluble ethylenically unsaturated monomer are not neutralized to form a polymer.

[0053] Water-soluble ethylenically unsaturated monomers in a state where the acidic groups are not neutralized (e.g., acrylic acid) are in a liquid state at room temperature, highly miscible with the solvent (water), and exist in a mixed solution state in the monomer composition. However, water-soluble ethylenically unsaturated monomers with neutralized acidic groups are in a solid state at room temperature, have different solubilities depending on the temperature of the solvent (water), and the solubility decreases as the temperature gets lower.

[0054] Thus, water-soluble ethylenically unsaturated monomers in a state where the acidic groups are not neutralized have a higher solubility or miscibility with the solvent (water) than monomers with neutralized acidic groups and do not precipitate even at low temperatures, which is advantageous for polymerization at low temperatures for a long time. Thereby, it is possible to stably form a polymer having a higher molecular weight and a uniform molecular weight distribution by performing polymerization for a long time using the water-soluble ethylenically unsaturated monomer in a state where the acidic groups are not neutralized.

[0055] Also, it is possible to form polymers with longer chains and achieve the effect of reducing the content of water-soluble components that exist in an incompletely polymerized and non-crosslinked state due to incomplete polymerization or crosslinking.

[0056] Furthermore, if polymerization is first carried out to form a polymer with the acidic groups of the monomer not neutralized in this way, and then atomized in the presence of a surfactant after neutralization, or the acidic groups present in the polymer are neutralized simultaneously with atomization, the surfactant can be present in a large amount on the surface of the polymer and can sufficiently play a role in reducing the adhesiveness of the polymer.

[0057] The concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition can be appropriately adjusted in consideration of the polymerization time, reaction conditions, etc., and can be about 20 to about 60% by weight, or about 20 to about 40% by weight.

[0058] The term "internal crosslinking agent" used in this specification is a term used to distinguish it from the surface crosslinking agent for crosslinking the surface of the superabsorbent resin particles described later, and it plays a role of introducing a crosslinking bond between the unsaturated bonds of the water-soluble ethylenic unsaturated monomer described above to form a polymer containing a crosslinked structure.

[0059] The crosslinking at the above stage is carried out without distinction between the surface and the inside. However, when the surface crosslinking step of the superabsorbent resin particles described later is carried out, the surface of the finally produced superabsorbent resin particles can include a structure newly crosslinked by the surface crosslinking agent, and the inside of the superabsorbent resin particles can maintain the structure crosslinked by the internal crosslinking agent as it is.

[0060] The internal crosslinking agent can include one or more of i) a polyfunctional acrylate-based compound, ii) a polyfunctional allyl-based compound, or iii) a polyfunctional vinyl-based compound.

[0061] 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, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate, etc. These can be used alone or in a mixture of two or more.

[0062] Non-limiting examples of multifunctional allyl compounds include ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, propylene glycol diallyl ether, tripropylene glycol diallyl ether, polypropylene glycol diallyl ether, butanediol diallyl ether, butylene glycol diallyl ether, hexanediol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, dipentaerythritol diallyl ether, dipentaerythritol triallyl ether, dipentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, glycerin diallyl ether, and glycerin triallyl ether, etc. They can be used alone or in admixture of two or more kinds.

[0063] Non-limiting examples of the polyfunctional vinyl-based compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, tripropylene glycol divinyl ether, polypropylene glycol divinyl ether, butanediol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, pentaerythritol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol divinyl ether, dipentaerythritol trivinyl ether, dipentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, trimethylolpropane divinyl ether, trimethylolpropane trivinyl ether, glycerin divinyl ether, and glycerin trivinyl ether, etc. These can be used alone or in combination of two or more kinds.

[0064] In the above-mentioned polyfunctional acrylate-based compounds, two or more acrylate groups contained in the molecule can each bind to the unsaturated bond of the water-soluble ethylene-based unsaturated monomer or the unsaturated bond of another internal cross-linking agent to form a cross-linked structure during the polymerization process.

[0065] In addition, in the above-mentioned polyfunctional allyl-based compounds or polyfunctional vinyl-based compounds, two or more unsaturated groups contained in the molecule can each bind to the unsaturated bond of the water-soluble ethylene-based unsaturated monomer or the unsaturated bond of another internal cross-linking agent to form a cross-linked structure during the polymerization process. Different from the acrylate-based compounds containing an ester bond (-(C=O)O-) in the molecule, the cross-linking bond can be stably maintained even during the neutralization process after the above-mentioned polymerization reaction.

[0066] Thereby, the gel strength of the produced superabsorbent resin can be increased, and the process stability can be improved during the discharging process after polymerization.

[0067] The total content of the internal crosslinking agent can be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent can be used in an amount of 0.01 part by weight or more, or 0.05 part by weight or more, or 0.1 part by weight or more, 0.45 part by weight or more, 5 parts by weight or less, or 3 parts by weight or less, or 2 parts by weight or less, or 1 part by weight or less, or 0.7 part by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. When the content of the upper internal crosslinking agent is excessively low, crosslinking is not sufficiently carried out, and it is difficult to achieve a strength above an appropriate level. When the content of the upper internal crosslinking agent is excessively high, the internal crosslinking density becomes high, and it is difficult to achieve the desired water retention ability.

[0068] The polymer formed by using such an internal crosslinking agent has a three-dimensional network structure in which the main chain formed by polymerizing the water-soluble ethylenically unsaturated monomer is crosslinked by the internal crosslinking agent. Thus, when the polymer has a three-dimensional network structure, the water retention ability and the pressure absorption ability, which are various physical properties of the superabsorbent resin, can be significantly improved as compared with the case where it has a two-dimensional linear structure that is not additionally crosslinked by the internal crosslinking agent.

[0069] In addition, the monomer composition can contain a polymerization initiator generally used in the production of superabsorbent resins. As a non-limiting example, as the polymerization initiator, a thermal polymerization initiator or a photo-polymerization initiator can be used depending on the polymerization method. However, even in the photo-polymerization method, a certain amount of heat is generated by ultraviolet irradiation or the like, and a certain amount of heat is generated by the progress of the polymerization reaction, which is an exothermic reaction. Therefore, a thermal polymerization initiator can be additionally contained.

[0070] As the photopolymerization initiator, for example, one or more compounds selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, Benzyl Dimethyl Ketal, acyl phosphine, and α-aminoketone can be used. On the one hand, 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)phenylphosphinate, and the like. Regarding more diverse photoinitiators, they are well described in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)", p115, and are not limited to the above-mentioned examples.

[0071] As the thermal polymerization initiator, one or more selected from the group of initiators consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, examples of persulfate initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), and the like. Examples of azo initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), and the like. More diverse thermal polymerization initiators are clearly shown in "Principle of Polymerization (Wiley, 1981)", p203 by Odian, and are not limited to the above-mentioned examples. For reference, as described later, when the polymerization step is carried out in a batch reactor, the above-mentioned thermal polymerization initiator can be used as the polymerization initiator by utilizing the thermal polymerization method.

[0072] Such a polymerization initiator can be added at a concentration of 0.001 to 1 part by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, when the concentration of the polymerization initiator is excessively low, the polymerization rate becomes slow, and a large amount of residual monomer may be extracted into the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is excessively high, the polymer chains forming the network become short, the content of the water-soluble component increases, and the pressure absorption capacity decreases, etc., and the physical properties of the resin may deteriorate, which is not preferable.

[0073] On the other hand, in one embodiment of the present invention, polymerization can be initiated by charging together with a reducing agent that forms a redox couple with the initiator.

[0074] Specifically, when the initiator and the reducing agent are charged into the polymer solution, they react with each other to form radicals.

[0075] The formed radicals will react with the monomer. Since the oxidation-reduction reaction between the initiator and the reducing agent is highly reactive, polymerization can be initiated even when only a small amount of the initiator and the reducing agent are charged, and it is not necessary to raise the process temperature. Low-temperature polymerization is possible, and changes in the physical properties of the polymer solution can be minimized.

[0076] The polymerization reaction using the oxidation-reduction reaction can occur smoothly even at a temperature around room temperature (25°C) or lower. As an example, the polymerization reaction can be carried out at a temperature of 5°C or higher and 25°C or lower, or 5°C or higher and 20°C or lower.

[0077] In one embodiment of the present invention, when a persulfate-based initiator is used as the initiator, the reducing agent can be one or more selected from the group consisting of sodium metabisulfite (Na2S2O5); tetramethylethylenediamine (TMEDA); iron(II) sulfate (FeSO4), a mixture of iron(II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinoacetate.

[0078] As an example, potassium persulfate can be used as the initiator and disodium 2-hydroxy-2-sulfinoacetate can be used as the reducing agent; ammonium persulfate can be used as the initiator and tetramethylethylenediamine can be used as the reducing agent; or sodium persulfate can be used as the initiator and sodium formaldehyde sulfoxylate can be used as the reducing agent.

[0079] In another embodiment of the present invention, when a hydrogen peroxide-based initiator is used as the initiator, the reducing agent can be one or more selected from the group consisting of ascorbic acid, sucrose, sodium sulfite (Na2SO3), sodium metabisulfite (Na2S2O5), tetramethylethylenediamine (TMEDA), a mixture of iron(II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate, disodium 2-hydroxy-2-sulfinoacetate, and disodium 2-hydroxy-2-sulfoacetate.

[0080] In addition, the monomer composition can further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant as needed.

[0081] And such a monomer composition can be prepared in the form of a solution in which raw material substances such as the above-described water-soluble ethylenically unsaturated monomer, polymerization initiator, and internal cross-linking agent are dissolved in a solvent.

[0082] At this time, the solvent that can be used can be used without limitation of its composition as long as it can dissolve the above-described components. For example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide, or a mixture thereof, etc. can be used.

[0083] According to an embodiment of the present invention, the step of polymerizing the monomer composition to form a polymer can be carried out in a batch type reactor.

[0084] In the usual method for producing a superabsorbent resin, the polymerization method is roughly divided into thermal polymerization and photopolymerization depending on the polymerization energy source. Usually, when performing thermal polymerization, it can be carried out in a reactor having a stirring shaft such as a kneader, and when performing photopolymerization, it can be carried out in a reactor equipped with a movable conveyor belt or in a container with a flat bottom.

[0085] On the other hand, since such a polymerization method is generally carried out with a short polymerization reaction time (for example, about 1 hour or less), a polymer having a small molecular weight and a broad molecular weight distribution is formed.

[0086] On the one hand, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or in a container with a flat bottom, the usually obtained form of the hydrogel polymer is a sheet-shaped hydrogel polymer having the width of the belt. The thickness of the polymer sheet varies depending on the concentration and injection rate or injection amount of the monomer composition to be injected, but is usually obtained with a thickness of about 0.5 to about 5 cm.

[0087] However, when supplying the monomer composition, the thinner the thickness of the sheet-shaped polymer, the lower the production efficiency, which is not preferable. When increasing the thickness of the sheet-shaped polymer for productivity, the polymerization reaction is not uniformly carried out over the entire thickness, making it difficult to form a high-quality polymer.

[0088] Also, in the polymerization in a reactor having a stirrer shaft of the reactor equipped with the conveyor belt, since the polymerization product moves while a new monomer composition is supplied to the reactor and the polymerization is carried out continuously, polymers with different polymerization rates are mixed, making it difficult to carry out uniform polymerization throughout the entire monomer composition and potentially causing a decrease in overall physical properties.

[0089] However, according to one embodiment of the present invention, in a batch reactor, since polymerization is carried out in a fixed-bed type, there is little risk of mixing polymers with different polymerization rates, and thus a polymer having uniform quality can be obtained.

[0090] Also, the polymerization step is carried out in a batch reactor having a predetermined volume, and the polymerization reaction is carried out for a longer time, for example, for 3 hours or more, than when polymerization is carried out continuously in a reactor equipped with a conveyor belt. Despite the long polymerization reaction time as described above, since polymerization is carried out on a water-soluble ethylenically unsaturated monomer in an unneutralized state, the monomer is not easily precipitated even during long-term polymerization, which is advantageous for carrying out long-term polymerization.

[0091] On the other hand, in the polymerization in the batch reactor of the present invention, by utilizing a thermal polymerization method, the polymerization initiator described above can be used as the thermal polymerization initiator.

[0092] (Step 2: Atomization and Neutralization Step) Next, it includes the step (Step 2) of atomizing a mixture of a polymer having an acidic group and a surfactant to produce water-containing superabsorbent resin particles, where a neutralizing agent is injected into the mixture, and at least some of the acidic groups of the polymer having an acidic group in the mixture are neutralized. More specifically, the step (Step 2) of producing the water-containing superabsorbent resin particles is performed by discharging the mixture onto a porous plate having a plurality of holes formed therein for atomization, and a neutralizing agent is injected into the mixture at the discharge point of the porous plate, and at least some of the acidic groups of the polymer having an acidic group in the mixture are neutralized.

[0093] The atomization step is a step of atomizing the polymer in the presence of a surfactant. Instead of chopping the polymer into millimeter-sized pieces, shredding and aggregation are simultaneously performed at a size of several tens to several hundreds of micrometers. That is, it is a step of producing secondary aggregated particles in a shape where primary particles shredded at a size of several tens to several hundreds of micrometers are aggregated by imparting appropriate adhesiveness to the polymer. The water-containing superabsorbent resin particles, which are secondary aggregated particles produced in such a step, have a normal particle size distribution, a significantly increased surface area, and can have a significantly improved absorption rate.

[0094] In this way, after mixing the polymer and the surfactant, the polymer can be atomized in the presence of the surfactant to produce water-containing superabsorbent resin particles in the form of secondary aggregated particles that are shredded and aggregated in a state where the superabsorbent resin particles and the surfactant are mixed.

[0095] Also, it is preferable that a neutralizing agent is injected in the atomization step because the neutralizing agent component serves as a slipping agent in the mixture, and the load in the atomization process can be reduced.

[0096] Specifically, as described above, polymerization is first carried out in a state where the acidic groups of the monomers are not neutralized to form a polymer that is not in the form of a hydrogel (step 1). The step of atomizing a mixture of the polymer having the acidic groups and a surfactant to produce hydrogel superabsorbent resin particles (step 2) is carried out by a method of discharging the mixture onto a perforated plate having a plurality of holes for atomization, and by injecting a neutralizing agent into the mixture at the discharge point of the perforated plate, at least a part of the acidic groups of the polymer having acidic groups in the mixture is neutralized. Thereby, a large amount of the surfactant is present on the surface of the polymer, reducing the high adhesiveness of the polymer, preventing the polymer from aggregating excessively, and sufficiently performing the role of being able to adjust the aggregation state to a desired level. Thereby, after the polymer is produced into secondary particles in a form in which primary particles are aggregated, the pulverization and drying steps are carried out under milder conditions, so that the amount of fine powder generated during the steps can be significantly reduced.

[0097] In addition, when polymerization is carried out in a state where the acidic groups of the monomers are not neutralized, it is possible to form a polymer with a longer chain, and an effect of reducing the content of water-soluble components that exist in an incompletely polymerized and crosslinked state without being crosslinked can be achieved.

[0098] According to an embodiment of the invention, the step of producing the hydrogel superabsorbent resin particles (step 2) includes a step of atomizing the mixture (step 2-1); and a step of injecting a neutralizing agent into the mixture to neutralize at least a part of the acidic groups of the polymer having acidic groups in the mixture (step 2-2); The step 2-1 and the step 2-2 can be carried out sequentially, simultaneously or alternately.

[0099] On the other hand, in order to achieve uniform neutralization of the entire polymer, it may be preferable to set a certain time difference between the input of the neutralizing agent and the atomization step.

[0100] The neutralizing agent is not particularly limited as long as it can neutralize acidic groups, and basic substances such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide can be used.

[0101] Among the acidic groups contained in the polymer, the degree of neutralization, which refers to the degree of neutralization by the neutralizing agent, can be 50 to 90 mol%, or 60 to 85 mol%, or 65 to 85 mol%, or 65 to 75 mol%. The range of the degree of neutralization varies depending on the final physical properties. If the degree of neutralization is excessively high, the absorption capacity of the superabsorbent resin may decrease, the concentration of carboxyl groups on the particle surface is excessively low, and surface cross-linking in subsequent processes may not be properly carried out, which may reduce the absorption characteristics under pressure or the liquid permeability. Conversely, if the degree of neutralization is excessively low, not only does the absorption power of the polymer significantly decrease, but it may also exhibit properties similar to those of elastic rubber, which are difficult to handle.

[0102] According to one embodiment of the invention, the step of producing the water-containing superabsorbent resin particles (step 2) is carried out by an atomizing device.

[0103] FIG. 2 is a schematic diagram showing an atomizing device used in a method for producing a superabsorbent resin according to one embodiment of the invention. Hereinafter, the content of using the atomizing device will be described with reference to the content of FIG. 2.

[0104] The atomizing device 10 includes a body portion 100 including a transfer space inside which a mixture of a polymer having the 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 a rotational driving force to the screw member; a cutter member 300 including a perforated plate 310 installed in the body portion 100 and having a plurality of holes formed therein, for pulverizing while discharging the mixture to the outside of the body portion; and a neutralizing agent injection nozzle 120 provided adjacent to the perforated plate inside the body portion.

[0105] The neutralizing agent sprayed by the neutralizing agent injection nozzle 120 is adjacent to the perforated plate 310. Specifically, when it is introduced at the discharge point of the perforated plate 310, while performing the neutralization process, when the mixture is discharged through the holes of the perforated plate, it serves as a slip agent in the mixture and can reduce the load on the holes. On the other hand, when the neutralizing agent is introduced into the mixture that is not at the discharge point of the perforated plate 310 first, the adhesiveness of the water-containing gel polymer may increase, making it difficult to atomize to the desired degree, and the load on the holes during discharge may increase. Also, when the polymerization process is performed on the monomer that has been neutralized prior to the formation of the water-containing gel polymer, an additional coarse pulverization process is required, resulting in a significant increase in the generation of fine powder.

[0106] Here, the discharge point of the perforated plate 310 can specifically mean immediately before the mixture passes through the perforated plate 310, and specifically, it can mean the point where the neutralizing agent injection nozzle 120 in FIG. 2 is arranged.

[0107] According to an embodiment of the invention, in the atomizing device 10, the neutralizing agent is introduced through the neutralizing agent injection nozzle 120 to the discharge point of the perforated plate 310 inside the body portion 100, and at least a part of the acidic groups of the polymer having acidic groups in the mixture will be neutralized.

[0108] Specifically, in the atomizing device 10, the neutralizing agent is introduced through the neutralizing agent injection nozzle 120 to the discharge point of the perforated plate 310 inside the body portion 100, neutralizing at least a part of the acidic groups of the polymer having acidic groups in the mixture, and at the same time, the mixture is pulverized while being discharged to the outside of the body portion through the perforated plate 310.

[0109] Preferably, the cutter member 300 includes a cutting knife 320 that is adjacent to the perforated plate 310 and the perforated plate 310 and is arranged on the outlet side of the body portion. When the mixture is discharged while passing through the perforated plate 310, it is pulverized and atomized by the cutting knife 320.

[0110] The size of the holes formed in the porous plate 310 can be from 0.1 mm to 30 mm, preferably from 0.5 mm to 25 mm, from 1 mm to 20 mm, or from 1 mm to 10 mm. By using the porous plate having the size of the holes, water-containing superabsorbent resin particles having a desired particle size can be produced.

[0111] According to an embodiment of the invention, in the atomizing 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 sequentially arranged, arranged to cross each other, a plurality of porous plates may be continuously arranged, or a plurality of cutting knives may be continuously arranged.

[0112] By including a plurality of porous plates and cutting knives as described above, atomization can be performed multiple times within a single atomizing device. On the other hand, a plurality of neutralizer injection nozzles are arranged so as to be adjacent to any one or more of the plurality of porous plates and cutting knives, and it is preferable that the neutralizer injection nozzles are arranged so as to be adjacent to the porous plate from the aspect of improving slipperiness.

[0113] When the cutter member 300 includes a plurality of porous plates and a plurality of cutting knives, for example, the first porous plate - the first cutting knife, the second porous plate - the second cutting knife may be sequentially arranged, or the first porous plate - the first cutting knife, the second porous plate - the second cutting knife, the third cutting knife may be sequentially arranged, or the first porous plate - the first cutting knife, the second porous plate, the third porous plate - the second cutting knife, the third cutting knife may be sequentially arranged, where the porous plate - cutting knife means a configuration where they are arranged adjacent to each other.

[0114] When the cutter member 300 includes a plurality of perforated plates as described above, the sizes of the holes formed in each perforated plate can satisfy the range described above, and these can be the same as or different from each other.

[0115] According to an embodiment of the invention, the atomization step (step 2) of producing the water-containing superabsorbent resin particles can be carried out a plurality of times, which can be carried out using a plurality of atomization devices, or using a single atomization device including a plurality of perforated plates and / or a plurality of cutting knives, or some of the plurality of atomization devices can include a plurality of perforated plates and / or a plurality of cutting knives. The atomization step can preferably be carried out 1 to 6 times or 1 to 4 times.

[0116] Here, in the case of a single atomization device including a plurality of perforated plates and / or a plurality of cutting knives, the above-described content is equally applicable. At this time, the particle size range of the holes of the plurality of perforated plates can be adjusted to produce a water-containing superabsorbent resin having a desired particle size.

[0117] Also, when using a plurality of atomization devices, the water-containing superabsorbent resin particles discharged from the first atomization device are put into the second atomization device again for atomization, and in one or more of the first atomization device and the second atomization device, a neutralizing agent is injected by a neutralizing agent nozzle, and at least a part of the acidic groups of the polymer having acidic groups can be neutralized. At this time, the particle size of the holes of the perforated plates contained in the first atomization device and the particle size of the holes of the perforated plates contained in the second atomization device can satisfy the range described above, and these can be the same as or different from each other.

[0118] According to an embodiment of the invention, the step of manufacturing the water-containing superabsorbent resin particles (step 2) includes the step of primary atomization of the mixture; and the step of secondary atomization so that the primary atomized water-containing superabsorbent resin particles have a smaller average particle size. In one or more of the primary atomization step and the secondary atomization step, a neutralizing agent can be injected so that at least some of the acidic groups of the polymer having acidic groups are neutralized.

[0119] The step can be performed using two atomization devices or a single atomization device.

[0120] For example, when the single atomization device is used, the atomization step can be performed including a plurality of perforated plates and / or a plurality of cutting knives as described above, and the sizes of the holes formed in the plurality of perforated plates can be the same or different from each other.

[0121] In order for the primary atomized water-containing superabsorbent resin particles to be secondary atomized so as to have a smaller average particle size, the atomization device can include a first perforated plate with a hole size of 1 mm to 6 mm and a second perforated plate with a hole size of 0.5 mm to 6 mm. In this case, a first cutting knife can be selectively arranged adjacent to the first perforated plate, a second cutting knife can be arranged adjacent to the second perforated plate, and additional cutting knives can be included.

[0122] By using the two perforated plates having the above particle sizes, the primary atomization step and the secondary atomization step are performed, and the secondary atomization step can be performed so that the primary atomized water-containing superabsorbent resin particles have a smaller average particle size. In this case, in one or more of the primary atomization step and the secondary atomization step, a neutralizing agent can be injected so that at least some of the acidic groups of the polymer having acidic groups are neutralized.

[0123] Thus, when the polymer mixed with the surfactant is neutralized and atomized using an atomizing device, after the polymer is produced into secondary particles in a form where primary particles are aggregated, by performing the grinding and drying processes under milder conditions, the amount of fine powder generated during the process can be significantly reduced.

[0124] In the step of producing the water-containing superabsorbent resin particles (step 2), the particles can be atomized so that the average particle diameter of the water-containing superabsorbent resin particles is 50 μm to 600 μm, preferably 100 μm to 500 μm, 150 μm to 450 μm, or 200 μm to 400 μm. By satisfying the particle size range, after the polymer is produced into secondary particles in a form where primary particles are aggregated, by performing the grinding and drying processes under milder conditions, the amount of fine powder generated during the process can be significantly reduced.

[0125] In the present invention, the average particle diameter "Dn" means the particle size or particle diameter at the n% point of the cumulative particle number distribution according to the particle size. That is, D50 represents the particle size at the 50% point of the cumulative particle number distribution according to the particle size, D90 represents the particle size at the 90% point of the cumulative particle number distribution according to the particle size, and D10 indicates the particle size at the 10% point of the cumulative particle number distribution according to the particle size. The Dn can be measured using a laser diffraction method or the like. 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 (for example, Microtrac S3500). When the particles pass through the laser beam, the diffraction pattern difference according to the particle size is measured to calculate the particle size distribution. By calculating the particle sizes at the 10%, 50%, and 90% points of the cumulative particle number distribution according to the particle size in the measuring device, D10, D50, and D90 can be measured.

[0126] According to one embodiment of the invention, the surfactant can be one or more selected from the group consisting of the compound represented by the chemical formula 1 and its salts, but is not limited thereto:

[0127]

Chemical formula

[0128] In the chemical formula 1, A1, A2 and A3 are each independently a single bond, a carbonyl, or,

[0129]

Chemical formula

[0130] wherein one or more of these are carbonyl or,

[0131]

Chemical formula

[0132] where m1, m2 and m3 are each independently an integer from 1 to 8,

[0133]

Chemical formula

[0134] are each connected to the adjacent oxygen atom,

[0135]

Chemical formula

[0136] is connected to the adjacent R1, R2 and R3 respectively, R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl having 6 to 18 carbon atoms, or a linear or branched alkenyl having 6 to 18 carbon atoms, n is an integer from 1 to 9.

[0137] The surfactant is added so that the atomization (chopping) step can be easily performed without aggregation when mixed with the polymer.

[0138] The surfactant represented by Chemical Formula 1 is a nonionic surfactant and has excellent surface adsorption performance with respect to the unneutralized polymer by hydrogen bonding, thereby being suitable for realizing the intended aggregation control effect. On the other hand, in the case of an anionic surfactant that is not a nonionic surfactant, when mixed with a polymer neutralized with a neutralizing agent such as NaOH or Na2SO4, it adsorbs through Na+ ions ionized in the carboxyl group substituents of the polymer, and when mixed with an unneutralized polymer, there is a problem that the adsorption efficiency with respect to the polymer is relatively reduced due to competition with the anions of the carboxyl group substituents of the polymer.

[0139] Specifically, in the surfactant represented by Chemical Formula 1, the hydrophobic functional group is the R1, R2, R3 part (when not hydrogen) which is the terminal functional group, and the hydrophilic functional group is the part derived from glycerol in the chain and the terminal hydroxyl group (A n is a single bond, and at the same time R n is hydrogen, and n = 1 to 3) is further included. The part derived from glycerol and the terminal hydroxyl group are hydrophilic functional groups and play a role in improving the adsorption performance on the polymer surface. Thereby, aggregation of the superabsorbent resin particles can be effectively suppressed.

[0140] In the above Chemical Formula 1, when the R1, R2, and R3 moieties (when not hydrogen) which are hydrophobic functional groups are each independently a linear or branched alkyl having 6 to 18 carbon atoms or a linear or branched alkenyl having 6 to 18 carbon atoms. At this time, when the R1, R2, and R3 moieties (when not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, there is a problem that the control of aggregation of the pulverized particles cannot be effectively carried out due to the short chain length, and when the R1, R2, and R3 moieties (when not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the surfactant may decrease and it may not be effectively mixed with the polymer, and there is a problem that the unit price of the composition increases due to the increase in the cost of the surfactant.

[0141] Preferably, R1, R2, and R3 are hydrogen, or in the case of a linear or branched alkyl having 6 to 18 carbon atoms, they can also be 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl, or in the case of a linear or branched alkenyl having 6 to 18 carbon atoms, they can be 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-decenyl, 2-undecenyl, 2-dodecenyl, 2-tridecenyl, 2-tetradecenyl, 2-pentadecenyl, 2-hexadecenyl, 2-heptadecenyl, or 2-octadecenyl.

[0142] The surfactant can be selected from the compounds represented by the following Chemical Formulas 1-1 to 1-14:

[0143]

Chemical Formula

Chemical Formula

[0144] On the one hand, the surfactant can be used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the polymer. When the amount of the surfactant used is excessively small, it may not be adsorbed evenly on the polymer surface, and the phenomenon of re-aggregation of particles after pulverization may occur. When the amount of the surfactant used is excessively large, various physical properties of the finally produced superabsorbent resin may deteriorate. For example, the surfactant can be used in an amount of 0.01 part by weight or more, 0.015 part by weight or more, or 0.1 part by weight or more, while being 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 based on 100 parts by weight of the polymer.

[0145] The method of mixing such a surfactant with the polymer is not particularly limited as long as it can uniformly mix them with the polymer, and can be appropriately selected and used. Specifically, the surfactant can be mixed dry, mixed in a solution state after being dissolved in a solvent, or mixed after melting the surfactant.

[0146] Among these, for example, the surfactant can be mixed in a solution state dissolved in a solvent. At this time, as the solvent, all types can be used without being limited to inorganic solvents or organic solvents, but considering the ease of the drying process and the cost of the solvent recovery system, water is most appropriate. Also, for the solution, methods such as putting the surfactant and the polymer into a reaction tank and mixing them, spraying the solution into a mixer with the polymer, or continuously supplying and mixing the polymer and the solution to a continuously operating mixer can be used.

[0147] On the one hand, according to an embodiment of the present invention, the step of neutralizing at least a part of the acidic groups of the polymer (step 2) and the step of atomizing the polymer in the presence of a surfactant (step 3) can be carried out sequentially or simultaneously.

[0148] That is, after adding a neutralizing agent to the polymer to neutralize the acidic groups first, a surfactant can be added to the neutralized polymer to atomize the polymer mixed with the surfactant, or the neutralizing agent and the surfactant can be added to the polymer simultaneously to perform neutralization and atomization on the polymer. Alternatively, the surfactant can be added first and then the neutralizing agent. Alternatively, the neutralizing agent and the surfactant can be added alternately in a cross pattern. Alternatively, the surfactant can be added first and atomized, then the neutralizing agent can be added for neutralization, and an additional surfactant can be further added to the neutralized water-containing gel polymer to perform an additional atomization step.

[0149] On the other hand, for uniform neutralization of the entire polymer, it may be preferable to set a certain time difference between the addition of the neutralizing agent and the atomization step.

[0150] At least a part or a considerable amount of the surfactant can be present on the surface of the water-containing superabsorbent resin particles.

[0151] Here, the meaning that the surfactant is present on the surface of the water-containing superabsorbent resin particles means that at least a part or a considerable amount of the surfactant is adsorbed or bound to the surface of the water-containing superabsorbent resin particles. Specifically, the surfactant can be physically or chemically adsorbed on the surface of the superabsorbent resin. More specifically, the hydrophilic functional group of the surfactant can be physically adsorbed on the hydrophilic part of the superabsorbent resin surface by intermolecular forces such as dipole-dipole interaction. In this way, the hydrophilic part of the surfactant physically adsorbs on the surface of the superabsorbent resin particles and wraps the surface, and the hydrophobic part of the surfactant does not adsorb on the surface of the resin particles, so the resin particles can be coated with the surfactant in the form of a kind of micelle structure. This is because the surfactant is not added during the polymerization process of the water-soluble ethylenically unsaturated monomer, but is added at the atomization stage after polymer formation. Compared with the case where the surfactant is added during the polymerization process and the surfactant is present inside the polymer, the surfactant can faithfully perform its role as a surfactant, and pulverization and aggregation are carried out simultaneously, and particles with a large surface area in the form of aggregated fine particles can be obtained.

[0152] The water-containing superabsorbent resin particles obtained by such a method can have a water content of 50 to 80% by weight. For example, the water content can be 55% by weight or more, or 75% by weight or less.

[0153] On the other hand, throughout this specification, the "water content" means the content of water in the total weight of the water-containing superabsorbent resin particles, and is the value obtained by subtracting the weight of the polymer in the dry state from the weight of the water-containing superabsorbent resin particles. Specifically, it is defined as the value calculated by measuring the weight loss due to the evaporation of water in the water-containing superabsorbent resin particles during the process of drying by raising the temperature of the polymer in the crumb state through infrared heating. At this time, the drying conditions are to raise the temperature from room temperature to about 180°C and then maintain it at 180°C. The total drying time is set to 40 minutes including 5 minutes for the temperature rise stage, and the water content is measured.

[0154] The water-containing superabsorbent resin particles can have a particle size at the normal particle level, that is, a particle diameter of 150 μm to 850 μm. Specifically, the water-containing superabsorbent resin particles can contain 89% by weight or more, 90% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, or 95% by weight or more of water-containing superabsorbent resin particles having a particle diameter of 150 μm to 850 μm with respect to the total weight. The particle diameter of such resin particles can be measured by the method of European Disposables and Nonwovens Association (EDANA) standard EDANAWSP220.3. Alternatively, when considering the point that no additional pulverization process is performed after the drying and surface crosslinking processes during the production of the superabsorbent resin composition, the content of the water-containing superabsorbent resin particles having a particle diameter of 150 μm to 850 μm in the water-containing superabsorbent resin particles can be regarded as almost the same as the content of the superabsorbent resin particles having a particle diameter of 150 μm to 850 μm in the finally produced superabsorbent resin particles.

[0155] (Step 3: Drying step) Next, the step of drying the water-containing superabsorbent resin particles to produce superabsorbent resin particles (Step 3) is included. The step is a step of drying the moisture of the water-containing superabsorbent resin particles, which are polymers obtained by neutralizing at least a part of the acidic groups of the polymer and atomizing the polymer in the presence of a surfactant.

[0156] Preferably, the step can be carried out by a method of drying in a moving type.

[0157] In the conventional method for producing a superabsorbent resin, the drying step is generally carried out until the water content of the superabsorbent resin particles becomes less than 10% by weight. However, in the present invention, by performing the shredding step in the presence of a surfactant, the aggregation of the shredded water-containing superabsorbent resin is controlled, and the drying is carried out so that the water content of the superabsorbent resin particles to be dried becomes 10% by weight to 20% by weight, preferably 10% by weight to 15% by weight, but is not limited thereto.

[0158] Thus, there is an advantage that it is possible to fundamentally prevent the generation of fine powder by showing a high water content. Further, it is preferable that the absorption rate of the final superabsorbent resin can be improved.

[0159] For this reason, the drying stage is carried out by a method of drying in a relatively low temperature and in a moving type. Such moving type drying is classified according to the presence / absence of the flow of the substance during drying from the fixed-bed type drying, and it is preferable that it can prevent the aggregation phenomenon between the shredded water-containing superabsorbent resin particles in the pulverized material to be dried and can complete the drying within a short time.

[0160] Specifically, the moving type drying refers to a method of drying while mechanically stirring the drying body. At this time, the direction in which the hot air passes through the substance can be the same as or different from the circulation direction of the substance. Alternatively, the substance can be circulated inside the dryer and the substance can be dried by passing a heat transfer fluid (heat medium oil) through a separate pipe outside the dryer. On the other hand, the fixed-bed type drying refers to a method of drying by passing hot air from the bottom to the top through the substance to be dried in a state where the substance is stopped on a floor such as a porous iron plate through which air can pass.

[0161] The step of drying the water-containing superabsorbent resin particles (step 3) can be carried out using a generally used fluidized dryer without special restrictions, for example, a horizontal-type mixer, a rotary kiln, a paddle dryer, a steam tube dryer, etc. A fluidized dryer such as this can be used.

[0162] The step of drying the water-containing superabsorbent resin particles (step 3) can be carried out 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. Even when carried out at a low temperature as described above, superabsorbent resin particles having the desired particle size and physical properties can be produced without the desired aggregation.

[0163] On the other hand, the drying temperature can be the internal driving temperature at which the building of the fluidized drying apparatus used is introduced, and this can be adjusted by passing a heat transfer medium fluid (heat medium oil) through a separate pipe outside the dryer, but is not limited thereto.

[0164] The step of drying the water-containing superabsorbent resin particles (step 3) can be carried out for 30 minutes to 80 minutes, 30 minutes to 60 minutes, or 40 minutes to 50 minutes. Even when the drying step is carried out for a short time at a relatively low temperature with less aggregation between the shredded water-containing gel polymer resin particles in the pulverized material to be dried, superabsorbent resin particles having the desired particle size and physical properties can be produced.

[0165] (Additional step) Thereafter, the method for producing a superabsorbent resin according to an embodiment of the invention can further include a step of pulverizing and classifying the superabsorbent resin particles as necessary.

[0166] Specifically, the pulverizing step can be carried out by pulverizing the dried superabsorbent resin particles to have a particle size at the normal particle level, that is, a particle size of 150 μm to 850 μm.

[0167] The crushers used for this purpose are specifically, for example, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper or a disc cutter, etc., and are not limited to the above-mentioned examples.

[0168] Alternatively, as the crusher, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill or a jog mill, etc. can also be used, and are not limited to the above-mentioned examples.

[0169] On the other hand, in the manufacturing method of the present invention, in the atomization stage, superabsorbent resin particles with a smaller particle size distribution than in the conventional chopping stage can be realized. When performing moving type drying, since the moisture content after drying is relatively high and maintained at 10% by weight or more, even if pulverization is performed under mild conditions with less pulverizing force, a superabsorbent resin with a very high content of normal particles having a particle size of 150 μm to 850 μm can be formed, and the fine powder generation ratio can be greatly reduced.

[0170] The superabsorbent resin particles produced as described above can contain 80% by weight or more, 85% by weight or more, 89% by weight or more, 90% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, or 95% by weight or more of superabsorbent resin particles having a particle size of 150 μm to 850 μm with respect to the total weight, that is, normal particles. The particle size of such resin particles can be measured by the method of European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3.

[0171] Further, the superabsorbent resin particles can contain fine powder having a particle size of less than 150 μm in an amount of about 20% by weight or less, or about 18% by weight or less, or about 15% by weight or less, or about 13% by weight or less, or about 12% by weight or less, or about 11% by weight or less, or about 10% by weight or less, or about 9% by weight or less, or about 8% by weight or less, or about 5% by weight or less, based on the total weight. This is in contrast to the case of producing a superabsorbent resin by a conventional production method, which has about 20% by weight to about 30% of fine powder.

[0172] Next, a method for producing a superabsorbent resin according to an embodiment of the invention can include a step of thermally crosslinking the surface of the superabsorbent resin particles in the presence of surface crosslinking to produce final superabsorbent resin particles.

[0173] In the surface crosslinking step, by inducing a crosslinking reaction on the surface of the base resin powder in the presence of a surface crosslinking agent, the unsaturated bonds of the water-soluble ethylenic unsaturated monomer remaining on the surface without being crosslinked are crosslinked by the surface crosslinking agent, so that a superabsorbent resin with a high surface crosslinking density is formed.

[0174] Specifically, in the presence of a surface crosslinking agent, a surface crosslinking layer can be formed in a heat treatment step. In the heat treatment step, the surface crosslinking density, that is, the external crosslinking density increases, but the internal crosslinking density does not change, and the produced superabsorbent resin with a surface crosslinking layer formed has a structure with a higher crosslinking density on the outside than on the inside.

[0175] The surface crosslinking step can be carried out at a temperature of about 80°C to about 250°C. More specifically, the surface crosslinking step can be carried out at a temperature of about 100°C to about 220°C, or about 120°C to about 200°C, for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. When the above-described surface crosslinking step conditions are satisfied, the surface of the superabsorbent resin particles can be sufficiently crosslinked and the pressure absorption capacity can be increased.

[0176] By satisfying such surface crosslinking process conditions (particularly, temperature increase conditions and reaction conditions at the maximum reaction temperature), a superabsorbent resin that appropriately satisfies physical properties such as a more excellent absorption rate can be produced.

[0177] The means for increasing the temperature for the surface crosslinking reaction is not particularly limited. A heat medium can be supplied, or heating can be performed by directly supplying a heat source. At this time, as the type of heat medium that can be used, heated fluids such as steam, hot air, and hot oil can be used, but it is not limited thereto, and the temperature of the supplied heat medium can be appropriately selected in consideration of the means of the heat medium, the temperature increase rate, and the target temperature for temperature increase. On the other hand, as the heat source directly supplied, there are heating methods through electricity and heating methods through gas, but it is not limited to the above-described examples.

[0178] On the other hand, as the surface crosslinking agent contained in the surface crosslinking agent composition, all surface crosslinking agents that have been used in the production of superabsorbent resins from existing ones can be used without any special restrictions. For example, the surface crosslinking agent is 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, propylene carbonate, and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; and the like can be included. Preferably, the same ones as the above-described internal crosslinking agents can be used. For example, alkylene glycol diglycidyl ether-based compounds such as ethylene glycol diglycidyl ether can be used.

[0179] In the surface crosslinking step, a surface crosslinking agent composition containing an alcohol-based solvent and water in addition to the surface crosslinking agent can be used.

[0180] Such a surface crosslinking agent can be used in an amount of about 0.001 to 2 parts by weight based on 100 parts by weight of the superabsorbent resin particles. Preferably, it can be used in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, or in an amount of 0.5 parts by weight or less, 0.3 parts by weight or less. By adjusting the content range of the surface crosslinking agent within the above-mentioned range, a superabsorbent resin exhibiting excellent absorption performance, liquid permeability, and other various physical properties can be produced.

[0181] On the other hand, the surface crosslinking agent is added to the superabsorbent resin particles in the state of a surface crosslinking agent composition containing the same, but there is no special limitation on the configuration of the addition method of such a surface crosslinking agent composition. For example, the surface crosslinking agent composition and the superabsorbent resin particles can be put into a reaction tank and mixed, or the surface crosslinking agent composition water can be sprayed onto the superabsorbent resin particles, or a method of continuously supplying and mixing the superabsorbent resin particles and the surface crosslinking agent composition to a continuously operated mixer can be used.

[0182] And the surface crosslinking agent composition can further contain water and / or a hydrophilic organic solvent as a medium. Thereby, there is an advantage that the surface crosslinking agent and the like can be evenly dispersed on the base resin powder. At this time, the contents of water and the hydrophilic organic solvent can be adjusted according to the addition ratio to 100 parts by weight of the superabsorbent resin particles for the purpose of inducing uniform dissolution / dispersion of the surface crosslinking agent, preventing the aggregation phenomenon of the base resin powder, and at the same time optimizing the surface penetration depth of the surface crosslinking agent.

[0183] On the other hand, in the method for producing a superabsorbent resin according to an embodiment of the invention, for further improvement of liquid permeability and the like, aluminum salts such as aluminum sulfate salts and various other polyvalent metal salts can be further used during surface crosslinking. Such polyvalent metal salts can be contained on the surface crosslinking layer of the finally produced superabsorbent resin.

[0184] According to an embodiment of the present invention, after the step of forming a surface crosslinked layer on at least a part of the surface of the superabsorbent resin particles, a cooling step of cooling the superabsorbent resin particles on which the surface crosslinked layer is formed, a water addition step of introducing water into the superabsorbent resin particles on which the surface crosslinked layer is formed, and a post-treatment step of introducing an additive into the superabsorbent resin particles on which the surface crosslinked layer is formed can be further performed including one or more of these steps. At this time, the cooling step, the water addition step, and the post-treatment step can be performed sequentially or simultaneously.

[0185] Examples of the additive introduced in the post-treatment step include a liquid permeability improver, an anti-caking agent, a fluidity improver, and an antioxidant, but the present invention is not limited thereto.

[0186] By selectively performing the cooling step, the water addition step, and the post-treatment step, the water content of the final superabsorbent resin can be improved, and a higher quality superabsorbent resin product can be manufactured.

[0187] Also, according to an embodiment of the present invention, a step of pulverizing and classifying the dried superabsorbent resin particles (or superabsorbent resin particles additionally surface crosslinked, or superabsorbent resin particles subjected to an additional water addition process, etc.) can be further performed.

[0188] Specific examples of the pulverizer used for this purpose include a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, or a disc cutter, etc., and are not limited to the examples described above.

[0189] Alternatively, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like can be used for the pulverizer, but it is not limited to the above-described examples.

[0190] The superabsorbent resin particles produced as described above can contain superabsorbent resin particles having a particle size of 150 μm to 850 μm with respect to the total weight, that is, 80% by weight or more, 85% by weight or more, 89% by weight or more, 90% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, or 95% by weight or more of normal particles. The particle size of such resin particles can be measured by the method of EDANA WSP220.3 standard of the European Disposables and Nonwovens Association (EDANA).

[0191] According to another embodiment of the present invention, there is provided a superabsorbent resin produced by the above production method.

[0192] The superabsorbent resin produced by the above production method realizes a high moisture content without a separate additional water addition step or additive input step, so that the fine powder content is low, and the water retention ability (CRC) and the pressure absorption ability (AUP), which are various absorption physical properties with respect to the superabsorbent resin produced by the conventional method, are at the same level or higher. At the same time, by reducing the content of water-soluble components (EC), it is possible to provide a superabsorbent resin with excellent absorption rates and the like.

[0193] Hereinafter, the actions and effects of the invention will be described in more detail through specific examples of the invention. However, such examples are merely presented as illustrations of the invention and do not determine the scope of the invention.

[0194] [Examples and Comparative Examples] Example 1 (Step 1) 1000 g of acrylic acid, 3.5 g of pentaerythritol triallyl ether as an internal cross-linking agent, and 2260 g of water were mixed in a 5 L glass container equipped with a stirrer and a thermometer, and stirred while maintaining the temperature at 5°C. 1000 cc / min of nitrogen was introduced into the glass container containing the mixture for 1 hour to replace it under nitrogen conditions. Next, 13 g of a 0.3% hydrogen peroxide aqueous solution, 15 g of a 1% ascorbic acid aqueous solution, and 30 g of a 2% 2,2’-azobis-(2-amidinopropane) dihydrochloride aqueous solution were added as polymerization initiators, and simultaneously 15 g of a 0.01% iron sulfate aqueous solution was added as a reducing agent to initiate polymerization. After the temperature of the mixture reached 85°C, polymerization was carried out at 90 ± 2°C for about 3 hours to obtain a polymer.

[0195] (Step 2) A mixture obtained by mixing 1,000 g of the obtained polymer and 1 g of glycerol monolaurate as a surfactant was passed once through a first atomization device equipped with a perforated plate containing a plurality of holes with a hole size of 6 mm to perform a primary atomization process.

[0196] Next, it was repeatedly charged a total of 3 times into a second atomization device equipped with a perforated plate containing a plurality of holes with a hole size of 4 mm to perform secondary, tertiary, and quaternary atomization processes.

[0197] In the secondary atomization process, 232 g of a 50% NaOH aqueous solution was introduced through a neutralizing agent nozzle arranged adjacent to the perforated plate, and a neutralization process was performed while atomizing.

[0198] In the tertiary atomization process, 37.5 g of a 15% Na2SO4 aqueous solution was introduced through a neutralizing agent nozzle arranged adjacent to the perforated plate to perform an atomization process.

[0199] Finally, in the quaternary atomization process, an atomization process was performed without adding a neutralizing agent or a surfactant to obtain water-containing superabsorbent resin particles.

[0200] The degree of neutralization of the water-containing superabsorbent resin particles was 70 mol%.

[0201] (Step 3) After that, 1,000 g of the water-containing superabsorbent resin particles were put into a rotary mixer fluidized dryer rotating at 100 rpm. Drying was carried out for 60 minutes while maintaining the internal temperature of the dryer at 105°C to obtain resin particles. The obtained particles were ground using a two-roll mill (roll mill, (GRAN-U-LIZERTM, MPE)) to have a particle size of 150 μm to 850 μm. Only the superabsorbent resin particles having a particle size of 150 μm to 850 μm were selectively recovered using a classification sieve.

[0202] The water content of the high-hoop property resin particles was 13 wt%.

[0203] Comparative Example 1 In Step 2 of Example 1, 232 g of 50% NaOH was additionally added to a mixture of 1,000 g of the polymer and 1 g of the surfactant Glycerol Monolaurate for neutralization. The neutralized mixture was passed once through a first atomization device equipped with a perforated plate containing a plurality of holes with a hole size of 6 mm to perform a primary atomization step. In the secondary atomization step, the atomization step was performed without adding a neutralizing agent or a surfactant. In the tertiary atomization step, 37.5 g of a 15% aqueous Na2SO4 solution was added to perform the atomization step. In the quaternary atomization step, the atomization step was performed without adding a neutralizing agent or a surfactant to obtain water-containing superabsorbent resin particles.

[0204] The degree of neutralization of the water-containing superabsorbent resin particles was 70 mol%.

[0205] Thereafter, 1,000 g of the water-containing superabsorbent resin particles were put into a rotary mixer (mixer) fluidized dryer rotating at 100 rpm. The internal temperature of the dryer was maintained at 105°C and drying was performed for 60 minutes to obtain resin particles. The obtained particles were ground using a two-roll mill (roll mill, (GRAN-U-LIZERTM, MPE)) to have a particle size of 150 μm to 850 μm. Only the superabsorbent resin particles having a particle size of 150 μm to 850 μm were selectively recovered using a classification sieve for the ground product.

[0206] The water content of the high-hoop resin particles was 12 wt%.

[0207] Comparative Example 2 100 g of acrylic acid, 140 g of 31.5 wt% caustic soda (NaOH), 0.30 g of polyethylene glycol diacrylate, 0.12 g of sodium persulfate as a thermal polymerization initiator, 0.01 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator, and 40 g of water were mixed to produce a monomer composition, which was placed in a square reaction vessel with a size of 30 cm in width and 30 cm in length, and irradiated with ultraviolet rays having a strength of 10 mW / cm 2 for 60 seconds for a polymerization reaction to produce a water-containing gel polymer.

[0208] 1 g of the surfactant glycerol monolaurate was mixed with 1,000 g of the obtained water-containing gel polymer. The mixture was atomized 4 times using an atomizing device, and 1,000 g of the water-containing superabsorbent resin particles were put into a rotary mixer (mixer) fluidized dryer rotating at 100 rpm. The internal temperature of the dryer was maintained at 105°C and drying was performed for 60 minutes to obtain resin particles. The obtained particles were ground using a two-roll mill (roll mill, (GRAN-U-LIZERTM, MPE)) to have a particle size of 150 μm to 850 μm. Only the superabsorbent resin particles having a particle size of 150 μm to 850 μm were selectively recovered using a classification sieve for the ground product.

[0209] The water content of the high hoop resin particles was 11 wt%.

[0210] [Experimental Example] For the superabsorbent resin produced in the above Example, the physical properties were evaluated by the following method, and the results are shown in Table 1.

[0211] Unless otherwise noted, all of the following physical property evaluations were carried out at a constant temperature and humidity of 23 ± 1 °C and a relative humidity of 50 ± 10%, and physiological saline or brine means a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0212] (1) Water content The water content is the content of water in the total weight of the superabsorbent resin and was calculated by the following formula 2.

[0213] Specifically, in the process of drying by raising the temperature of the superabsorbent resin through infrared heating, the weight loss due to water evaporation in the superabsorbent resin was measured and calculated. At this time, the drying conditions were such that the temperature was raised from room temperature to 180 °C and then maintained at 180 °C, and the total drying time was set to 40 minutes including 5 minutes in the temperature rising stage. The weights of the superabsorbent resin before and after drying were measured respectively and calculated by the following formula 1.

[0214] [Formula 1] Water content (wt%) = [(Ao - At) / Ao] × 100

[0215] 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.

[0216] (2) Fine powder content For the superabsorbent resin produced in the Example, classification was carried out using standard sieves having graduations of 850 μm (20 mesh), 600 μm (30 mesh), 300 μm (50 mesh), and 150 μm (100 mesh) according to ASTM standards. After measuring the weight of the fine powder having a size of less than 150 μm, the content of the fine powder was expressed as a percentage based on the total weight of the sample superabsorbent resin particles (wt%).

[0217] (3) Centrifuge Retention Capacity (CRC) For the superabsorbent resins produced in the examples, samples having a particle size of 150 to 850 μm were taken from each superabsorbent resin, and the centrifuge retention capacity (CRC) based on the absorption ratio under no load was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANAWSP241.3.

[0218] Specifically, resins classified by a #30 - 50 sieve were obtained from the resins respectively obtained through the examples. Such resin W0 (g) (about 0.2 g) was uniformly placed in an envelope made of non-woven fabric and sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, moisture was removed from the envelope for 3 minutes under the condition of 250G using a centrifuge, and the mass W2 (g) of the envelope was measured. Also, after performing the same operation without using the resin, the mass W1 (g) at that time was measured. Using the obtained masses, CRC (g / g) was calculated by the following formula.

[0219] [Equation 2] CRC (g / g) = {[W2 (g) - W1 (g)] / W0 (g)} - 1

[0220] (4) Water Soluble Content (EC) For 2 g of the superabsorbent resin, after swelling for 1 hour by the method of EDANA method WSP270.3, the water-soluble components were measured.

[0221] (5) Vortex Absorption Rate The absorption rate (vortex time) was measured in seconds according to the method described in International Publication No. WO1987 / 003208. When measuring the absorption rate, the resin obtained after the surface crosslinking was used without classification.

[0222] Specifically, 2 g of each resin was placed into 50 mL of physiological saline at 23°C, and a magnetic bar (8 mm in diameter and 30 mm in length) was stirred at 600 rpm, and the time until the vortex disappeared was measured and calculated in seconds.

[0223]

Table 1

[0224] As can be confirmed in Table 1 above, by performing the atomization step and simultaneously neutralizing the polymer under specific conditions, it was confirmed that the superabsorbent resin produced had a reduced amount of water-soluble components and fine powder generation, and excellent absorption properties, particularly an improved absorption rate.

[0225] In the case of Comparative Example 1 where neutralization proceeded in the mixing step of adding a surfactant to the polymer before the atomization step, and Comparative Example 2 where pre-neutralization proceeded in the polymerization step, it was confirmed that in all cases, the physical properties of the Vortex deteriorated due to the aggregation phenomenon of the hydrogel, and the discharge amount decreased.

Explanation of Signs

[0226] 10 Atomization device 100 Body part 110 Screw member 120 Neutralizing agent injection nozzle 200 Driving motor 300 Cutter member 310 Perforated plate 320 Cutting knife

Claims

1. A step (step 1) of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal crosslinking agent and a polymerization initiator to form a polymer having an acidic group; A step (step 2) of atomizing a mixture of the polymer having the acidic group and a surfactant to produce water-containing superabsorbent resin particles; and A step (step 3) of drying the water-containing superabsorbent resin particles to produce superabsorbent resin particles; including The step of producing the water-containing superabsorbent resin particles (step 2) is performed by a method of discharging the mixture onto a perforated plate having a plurality of holes formed therein for atomization, and a neutralizing agent is injected into the mixture at the discharge point of the perforated plate, and at least a part of the acidic groups of the polymer having an acidic group in the mixture are neutralized, The discharge point of the perforated plate is immediately before the mixture passes through the perforated plate, A method for producing a superabsorbent resin.

2. The step of producing the water-containing superabsorbent resin particles (step 2) Is performed using an atomizing device including an injection nozzle into which a neutralizing agent is injected, The injection nozzle is disposed at the discharge point of the perforated plate immediately before the mixture passes through the perforated plate, and the method for producing a superabsorbent resin according to claim 1.

3. The step of producing the water-containing superabsorbent resin particles (step 2) A step of atomizing the mixture (step 2-1); and A step of injecting a neutralizing agent into the mixture to neutralize at least a part of the acidic groups of the polymer having an acidic group in the mixture (step 2-2); including The steps 2-1 and 2-2 are performed sequentially, simultaneously or alternately, and the method for producing a superabsorbent resin according to claim 1.

4. The step of producing the water-containing superabsorbent resin particles (step 2) is performed using an atomizing device, The atomizing device A body part including a transfer space into which a mixture of the polymer having the acidic group and a surfactant is transferred; A screw member rotatably installed inside the transfer space for moving the mixture; A drive motor for providing a rotational driving force to the screw member; A cutter member installed on the body part and including a perforated plate having a plurality of holes formed therein, for pulverizing while discharging the mixture to the outside of the body part; and Including a neutralizing agent injection nozzle provided adjacent to the perforated plate inside the body part, and the method for producing a superabsorbent resin according to claim 1.

5. In the atomizing device, The method for producing a superabsorbent resin according to claim 4, wherein a neutralizing agent is introduced through the neutralizing agent injection nozzle at the discharge point of the perforated plate inside the body portion to neutralize at least a part of the acidic groups of the polymer having acidic groups in the mixture.

6. The method for producing a superabsorbent resin according to claim 4, wherein the cutter member further includes a cutting knife that is adjacent to the perforated plate and is disposed on the outlet side of the body portion.

7. The method for producing a superabsorbent resin according to claim 4, wherein the cutter member includes a plurality of perforated plates and a plurality of cutting knives.

8. The method for producing a superabsorbent resin according to claim 4, wherein the size of the holes formed in the perforated plate is 0.1 mm to 30 mm.

9. The step of producing the water-containing superabsorbent resin particles (step 2) includes a step of primary atomization of the mixture; and a step of secondary atomization so that the water-containing superabsorbent resin particles obtained by the primary atomization have a smaller average particle size, and in at least one of the primary atomization step and the secondary atomization step, a neutralizing agent is injected to neutralize at least a part of the acidic groups of the polymer having acidic groups. The method for producing a superabsorbent resin according to claim 1.

10. The method for producing a superabsorbent resin according to claim 1, wherein at least a part of the surfactant is present on the surface of the water-containing superabsorbent resin particles.

11. The method for producing a superabsorbent resin according to any one of claims 1 to 10, wherein the surfactant is one or more selected from the group consisting of a compound represented by the following chemical formula 1 and its salts: 【Chemical 1】 In the chemical formula 1, A １ 、 A ２ and A ３ each independently represents a single bond, a carbonyl group, [Chemical Formula 2] wherein one or more of these are carbonyl or 【Chemical Formula 3】 wherein m1, m2 and m3 are each independently an integer from 1 to 8, [Chemical Formula 4] are each linked to an adjacent oxygen atom, 【Chemical Formula 5】 is adjacent to R １ , R ２ and R ３ are respectively connected to R １ , R ２ and R ３ are each independently hydrogen, a linear or branched alkyl having 6 to 18 carbon atoms or a linear or branched alkenyl having 6 to 18 carbon atoms, and n is an integer from 1 to 9.

12. The step of drying the water-containing superabsorbent resin particles (step 3) is performed in a moving type. The method for producing a superabsorbent resin according to claim 1.

13. The step of drying the water-containing superabsorbent resin particles (step 3) The method for producing a superabsorbent resin according to claim 1, which is carried out using a moving type dryer such as a horizontal-type mixer, a rotary kiln, a paddle dryer, or a steam tube dryer.

14. The step (step 3) of drying the water-containing superabsorbent resin particles is The method for producing a superabsorbent resin according to claim 1, which is carried out at a temperature of 150 ° C or lower.

15. The method for producing a superabsorbent resin according to claim 1, wherein the water content of the superabsorbent resin particles obtained in the step (step 3) of drying the water-containing superabsorbent resin particles is 10% by weight to 20% by weight.

16. The method for producing a superabsorbent resin according to claim 1, further comprising a step (step 5) of pulverizing and classifying the superabsorbent resin particles.

17. The method for producing a superabsorbent resin according to claim 16, further comprising a step (step 6) of forming a surface crosslinked layer on at least a part of the surface of the classified superabsorbent resin particles.

Images