Highly water-absorbent resin composition and method for producing the same

Abstract

The present invention relates to a superabsorbent polymer composition and a method for producing the same, and more specifically, to a method for producing a superabsorbent polymer composition which contains an additive having a specific structure and can suppress aggregation of a hydrogel polymer during a pulverization step and improve the pulverization step performance.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0147025, filed October 29, 2021, and Korean Patent Application No. 10-2022-0140642, filed October 27, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a superabsorbent polymer composition and a method for producing the same, and more specifically to a method for producing a superabsorbent polymer composition that contains an additive having a specific structure and that can suppress aggregation of a hydrogel polymer during a pulverization step and improve the pulverization processability. [Background technology]

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

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

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

[0006] On the other hand, such superabsorbent resins are generally produced by polymerizing monomers to produce a hydrogel polymer containing a large amount of water, and then crushing the hydrogel polymer into resin particles having a desired particle size after coarsely crushing and drying. In particular, during the process of coarsely crushing the hydrogel polymer, the coarsely crushed hydrogel polymer tends to aggregate or clump together, making it difficult to crush.

[0007] Therefore, in addition to improving the water retention capacity (CRC), which is a physical property that indicates the basic water absorption and water retention of superabsorbent polymers, and the absorbent capacity under pressure (AUP), which indicates the ability to retain absorbed liquid even under external pressure, there is a continuous demand for the development of technology that can increase the water absorption speed of superabsorbent polymers and technology that can improve the pulverization process during processing. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, the present invention relates to a method for producing a superabsorbent polymer composition which contains an additive having a specific structure and which can suppress aggregation of the hydrogel polymer during the pulverization step and improve the pulverization processability. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides: Superabsorbent resin particles containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent; and A superabsorbent polymer composition is provided, which comprises an additive represented by the following chemical formula 1:

[0010] [ka]

[0011] In the above Chemical Formula 1, A1, A2 and A3 each independently represent a single bond, a carbonyl,

[0012] [ka]

[0013] and one or more of these is a carbonyl or

[0014] [ka]

[0015] wherein m1, m2, and m3 each independently represent an integer of 1 to 8;

[0016] [ka]

[0017] are each linked to adjacent oxygen atoms,

[0018] [ka]

[0019] are linked to adjacent R1, R2 and R3, respectively; R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer of 1 to 9.

[0020] The present invention also provides a step of cross-linking a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a polymer (step 1); neutralizing at least a portion of the acidic groups of the polymer (Step 2); Step 3: atomizing the polymer in the presence of an additive represented by the following formula 1 to produce base resin particles; and drying the base resin particles (Step 4); A method for producing a superabsorbent polymer composition is provided, comprising:

[0021] [ka]

[0022] In the above Chemical Formula 1, A1, A2 and A3 each independently represent a single bond, a carbonyl,

[0023] [ka]

[0024] and one or more of these is a carbonyl or

[0025] [ka]

[0026] wherein m1, m2, and m3 each independently represent an integer of 1 to 8;

[0027] [ka]

[0028] are each linked to adjacent oxygen atoms,

[0029] [ka]

[0030] are linked to adjacent R1, R2 and R3, respectively; R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer of 1 to 9. [Effects of the Invention]

[0031] According to the superabsorbent polymer composition and the method for producing the same of the present invention, the addition of an additive having a specific structure during the pulverization process of the hydrogel polymer suppresses aggregation of the hydrogel polymer particles, thereby improving the pulverization processability and thereby improving the water absorption performance and water absorption rate of the superabsorbent polymer. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a flowchart showing a conventional method for producing a highly water-absorbent resin. [Figure 2] 1 is a photograph showing examples of evaluation items in the evaluation of particle aggregation properties. DETAILED DESCRIPTION OF THE INVENTION

[0033] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise. It should be understood that the terms "comprise," "comprise," or "have" used in this specification are intended to specify the presence of embodied features, steps, components, or combinations thereof, and do not preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0034] Although the present invention can be embodied in various forms through various modifications, specific embodiments are described in detail below by way of example, but it should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0035] Hereinafter, the method for producing a superabsorbent polymer and the superabsorbent polymer will be described in more detail with reference to specific embodiments of the invention.

[0036] Prior to this, the terminology used herein is for the purpose of referring to particular embodiments only and is not intended to limit the present invention, and the singular forms used herein also include the plural forms unless the language clearly dictates otherwise.

[0037] The term "polymer" or "macromolecule" as used in the present specification refers to a polymerized state of a water-soluble ethylenically unsaturated monomer, and can encompass any range of water content or particle size. Among the polymers, a polymer having a water content (moisture content) of about 40% by weight or more in a state after polymerization and before drying can be called a hydrogel polymer, and particles of such a hydrogel polymer that have been crushed and dried can be called a crosslinked polymer.

[0038] In addition, the term "superabsorbent resin particles" refers to a particulate material containing a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing acidic groups and at least a portion of the acidic groups being neutralized, and crosslinking the polymer with an internal crosslinking agent.

[0039] Furthermore, depending on the context, the term "superabsorbent polymer" may refer to a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing acidic groups and at least a portion of which has been neutralized, or to a powder-like base resin composed of superabsorbent polymer particles obtained by pulverizing the crosslinked polymer, or to a product made suitable for commercialization by subjecting the crosslinked polymer or base resin to additional processes, such as surface crosslinking, pulverization, drying, pulverization, classification, etc. Accordingly, the term "superabsorbent polymer composition" is interpreted as including a composition containing a superabsorbent polymer, i.e., a plurality of superabsorbent polymer particles.

[0040] The term "fine powder" refers to superabsorbent resin particles having a particle size of less than 150 μm. The particle size of such resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3 method.

[0041] The term "chopping" refers to cutting the hydrogel polymer into millimeter-sized pieces to improve drying efficiency, as opposed to grinding to micrometer or regular particle sizes.

[0042] Furthermore, the term "micronizing" refers to pulverizing a hydrogel polymer into particles of several tens to several hundreds of micrometers, and is used to distinguish it from "chopping."

[0043] Conventional superabsorbent polymers are manufactured by crosslinking a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer, drying the formed hydrogel polymer, and then pulverizing it to a desired particle size. To facilitate drying of the hydrogel polymer and increase the efficiency of the pulverization process, a chopping process is typically performed before the drying process to cut the hydrogel polymer into particles several millimeters in size. However, due to the stickiness of the hydrogel polymer, the hydrogel polymer remains in an aggregated gel state rather than being pulverized to micro-sized particles. Drying this aggregated gel-like hydrogel polymer results in the formation of a plate-like dried body. To pulverize this into micro-sized particles, multiple pulverization processes are required, which creates the problem of generating a large amount of fine powder.

[0044] Specifically, a flow chart of a conventional method for producing a superabsorbent polymer is shown in Figure 1. Referring to Figure 1, a conventional superabsorbent polymer has been produced through the following steps:

[0045] (neutralizing) neutralizing at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer; (Polymerization) A step of cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a hydrogel polymer; (chopping) chopping the hydrogel polymer; (Drying) drying the chopped hydrogel polymer; and (Crushing / Classification) Crushing the dried polymer and classifying it into normal particles and fine powder;

[0046] As described above, the chopped hydrogel polymer has an agglomerated gel shape with a size of about 1 cm to 10 cm. The chopped hydrogel polymer is stacked on a belt with a perforated bottom and dried by hot air supplied from the bottom or top. Because the polymer dried in this drying method exhibits a plate-like shape rather than a granular shape, the crushing and classification step has been performed by first coarsely crushing and classifying the polymer to produce normal particles, i.e., particles with a diameter of 150 μm to 850 μm, followed by fine crushing and classification again. In this manufacturing method, the amount of fine powder separated in the final classification step is large, about 10 wt% to about 20 wt% of the total weight of the final superabsorbent polymer. Therefore, the separated fine powder is mixed with an appropriate amount of water, re-granulated, and then reused by being added to the chopping step or pre-drying step.

[0047] However, such reuse of fine powder has caused problems such as an increase in the load on the equipment and / or the amount of energy used when the regranulated fine powder mixed with water is reintroduced into a crushing or drying process, and the fine powder remaining unclassified has caused a deterioration in the physical properties of the superabsorbent polymer.

[0048] Therefore, the inventors recognized that in conventional manufacturing methods, the amount of fine powder generated is greatly affected by the pulverization process, and focused on the fact that the amount of fine powder generated during the manufacturing process can be significantly reduced by adding a surfactant in the chopping process (atomization process) to pulverize the material finer than before, while simultaneously controlling aggregation to produce particles in the form of aggregated fine particles.

[0049] On the other hand, when a surfactant is added to a neutralized hydrogel polymer, the surfactant penetrates into the hydrogel polymer rather than existing at the interface of the hydrogel polymer due to the high water content of the neutralized hydrogel polymer, which can cause the surfactant to fail to perform its role properly.

[0050] As a result of extensive research to solve this problem, it was found that, unlike conventional methods for producing superabsorbent polymers, polymerization is first carried out in a state where the acidic groups of a water-soluble ethylenically unsaturated monomer are neutralized, to form a polymer, and the hydrogel polymer is then atomized in the presence of a surfactant and the acidic groups of the polymer are neutralized. Alternatively, the acidic groups of the polymer are neutralized to form a hydrogel polymer, and the hydrogel polymer is then atomized in the presence of a surfactant, or the acidic groups present in the polymer are neutralized simultaneously with atomization. This allows the surfactant to be present in large amounts on the surface of the polymer, reducing the high viscosity of the polymer and preventing excessive aggregation of the polymer, thereby fully fulfilling its role of adjusting the aggregation state to a desired level.

[0051] As a result, the polymer is prepared into secondary particles in the form of agglomerated primary particles, and the subsequent pulverization and drying processes are carried out under milder conditions, thereby significantly reducing the amount of fine powder generated during the process.

[0052] Furthermore, when a polymer is pulverized in the presence of an additive having the specific structure of Chemical Formula 1, the hydrophobic functional groups contained in the additive impart hydrophobicity to the surfaces of the pulverized superabsorbent resin particles, reducing interparticle friction and increasing the apparent density of the superabsorbent resin, while the hydrophilic functional groups contained in the additive also bind to the superabsorbent resin particles, preventing a decrease in the surface tension of the resin. As a result, the superabsorbent resin produced by the above-described production method has a higher apparent density while exhibiting the same level of surface tension as a resin without such an additive.

[0053] Furthermore, if polymerization is first carried out in an unneutralized state to form a polymer, and then the acidic groups present in the polymer are neutralized, it is possible to form a polymer with a longer chain, and the content of water-soluble components present in an uncrosslinked state due to incomplete crosslinking can be reduced.

[0054] Since the water-soluble components tend to be easily dissolved when the superabsorbent polymer comes into contact with a liquid, if the content of the water-soluble components is high, the dissolved water-soluble components remain on the surface of most of the superabsorbent polymer, making the superabsorbent polymer sticky and reducing its liquid permeability. Therefore, it is important to maintain a low content of the water-soluble components in terms of liquid permeability.

[0055] In summary, the present inventors have confirmed that when a polymer is pulverized after mixing with an additive having a specific structure represented by the following chemical formula 1, aggregation between pulverized hydrogel polymer particles is suppressed, improving the pulverization process efficiency, and have thus completed the present invention. In particular, the particles contained in the superabsorbent polymer composition produced by the above production method are characterized by exhibiting an improved water absorption rate compared to when the additive is not used.

[0056] [ka]

[0057] In the above Chemical Formula 1, A1, A2 and A3 each independently represent a single bond, a carbonyl,

[0058] [ka]

[0059] and one or more of these is a carbonyl or

[0060] [ka]

[0061] wherein m1, m2, and m3 each independently represent an integer of 1 to 8;

[0062] [ka]

[0063] are each linked to adjacent oxygen atoms,

[0064] [ka]

[0065] are linked to adjacent R1, R2 and R3, respectively; R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer of 1 to 9.

[0066] Specifically, the additive represented by the following Chemical Formula 1 has both a hydrophobic functional group and a hydrophilic functional group. Meanwhile, the water-soluble ethylenically unsaturated monomer has an acid group (-COOH) and / or a neutralized acid group (-COO - ), the surface of the polymer produced by polymerization contains acidic groups (-COOH) that remain without participating in the polymerization and / or neutralized acidic groups (-COO - ) present in a large amount. Therefore, when the additive is mixed with the polymer, the hydrophilic functional groups of the additive are adsorbed to at least a portion of the hydrophilic portions present on the surface of the polymer, and the surface of the polymer to which the additive is adsorbed exhibits hydrophobicity due to the hydrophobic functional groups located at the other end of the additive. This makes it possible to suppress aggregation between the pulverized hydrogel polymer particles.

[0067] Hereinafter, the superabsorbent polymer composition of one embodiment will be described in detail with respect to each component.

[0068] (Super absorbent resin composition) According to one embodiment of the present invention, there is provided a superabsorbent polymer composition comprising superabsorbent polymer particles containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent; and an additive represented by the following Chemical Formula 1:

[0069] [ka]

[0070] In the above Chemical Formula 1, A1, A2 and A3 each independently represent a single bond, a carbonyl,

[0071] [ka]

[0072] and one or more of these is a carbonyl or

[0073] [ka]

[0074] wherein m1, m2, and m3 each independently represent an integer of 1 to 8;

[0075] [ka]

[0076] are each linked to adjacent oxygen atoms,

[0077] [ka]

[0078] are linked to adjacent R1, R2 and R3, respectively; R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer of 1 to 9.

[0079] In one embodiment, the superabsorbent polymer composition includes superabsorbent polymer particles containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent, wherein the crosslinked polymer is formed by crosslinking the water-soluble ethylenically unsaturated monomer having an acidic group in the presence of the internal crosslinking agent, and has a three-dimensional network structure in which the main chain formed by polymerization of the monomer is crosslinked by the internal crosslinking agent.

[0080] In other words, a superabsorbent polymer composition according to one embodiment includes superabsorbent polymer particles containing a crosslinked polymer formed between a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent. When the crosslinked polymer has a three-dimensional network structure in which the main chain formed by polymerization of the monomer is crosslinked by the internal crosslinking agent, the water retention capacity and water absorption capacity under pressure, which are various physical properties of the superabsorbent polymer, can be significantly improved compared to when the crosslinked polymer has a two-dimensional linear structure that is not additionally crosslinked by the internal crosslinking agent.

[0081] The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the production of superabsorbent resins. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Chemical Formula 2:

[0082] [Chemical formula 2] R-COOM'

[0083] In the above Chemical Formula 2, R is an alkyl group having 2 to 5 carbon atoms and containing an unsaturated bond, M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

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

[0085] In this way, when (meth)acrylic acid and / or its salt is used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent resin with improved water absorption. Other examples of the monomer that can be used include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, and (N,N)-dimethylaminopropyl (meth)acrylamide.

[0086] Here, the water-soluble ethylenically unsaturated monomer has an acidic group, and at least a portion of the acidic group is neutralized with a neutralizing agent in a neutralization step described below. In this case, the neutralizing agent is a basic substance capable of neutralizing the acidic group, such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide, which will be described in more detail in the preparation method section described below.

[0087] In addition, the term "internal cross-linking agent" used herein is a term used to distinguish it from a surface cross-linking agent for cross-linking the surface of superabsorbent resin particles, which will be described later, and serves to cross-link the unsaturated bonds of the water-soluble ethylenically unsaturated monomers described above to polymerize them. The cross-linking in this step is performed regardless of whether it is on the surface or inside, but when the surface cross-linking process of superabsorbent resin particles described later is performed, the surface of the superabsorbent resin particles produced finally has a structure cross-linked by the surface cross-linking agent, and the inside has a structure cross-linked by the internal cross-linking agent.

[0088] The internal crosslinking agent may be any compound that can introduce crosslinks during polymerization of the water-soluble ethylenically unsaturated monomer. Non-limiting examples of the internal crosslinking agent include N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and hexanediol di(meth)acrylate. Polyfunctional crosslinkers such as triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, pentaerythritol triallyl ether, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate can be used alone or in combination, but are not limited thereto. Of these, pentaerythritol triallyl ether is preferably used.

[0089] The crosslinking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of such an internal crosslinking agent is carried out by thermal polymerization, photopolymerization or hybrid polymerization in the presence of a polymerization initiator and, if necessary, a thickener, a plasticizer, a storage stabilizer, an antioxidant, etc., the details of which will be described later.

[0090] The highly water-absorbent resin particles may have a particle size of about 150 to about 850 μm, which can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3 method.

[0091] The superabsorbent polymer composition also contains an additive represented by Chemical Formula 1. The additive is mixed with the polymer as described above to facilitate the atomization (chopping) step without agglomeration.

[0092] The additive represented by Chemical Formula 1 is a nonionic surfactant and has excellent surface adsorption performance due to hydrogen bonding with unneutralized polymers, making it suitable for achieving the desired aggregation control effect. In contrast, in the case of anionic surfactants rather than nonionic surfactants, when mixed with polymers neutralized with neutralizing agents such as NaOH or Na2SO4, they are adsorbed via Na+ ions ionized to the carboxyl group substituents of the polymer, and when mixed with unneutralized polymers, there is a problem in that their adsorption efficiency to the polymer is relatively reduced due to competition with the anions of the carboxyl group substituents of the polymer.

[0093] Specifically, in the additive represented by the chemical formula 1, the hydrophobic functional groups are the terminal functional groups R1, R2, and R3 (if they are not hydrogen), and the hydrophilic functional groups are the glycerol-derived portion in the chain and the terminal hydroxyl group (A n is a single bond and R n is hydrogen, n=1 to 3), and the glycerol-derived portion and the terminal hydroxyl group are hydrophilic functional groups that improve the adsorption performance on the polymer surface, thereby effectively suppressing the aggregation of superabsorbent resin particles.

[0094] In Formula 1, the hydrophobic functional groups R1, R2, and R3 (when not hydrogen) are each independently a straight-chain or branched-chain alkyl having 6 to 18 carbon atoms, or a straight-chain or branched-chain alkenyl having 6 to 18 carbon atoms. If the R1, R2, and R3 (when not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, the chain length is too short to effectively control the aggregation of the milled particles. If the R1, R2, and R3 (when not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the additive is reduced, preventing effective mixing with the polymer, and the cost of the additive increases, resulting in a high unit cost of the composition.

[0095] Preferably, R1, R2, and R3 are hydrogen, or when they are straight-chain or branched alkyl having 6 to 18 carbon atoms, they may be 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl, or when they are straight-chain or branched alkenyl having 6 to 18 carbon atoms, they may be 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-dekenyl, 2-undekenyl, 2-dodekenyl, 2-tridekenyl, 2-tetradekenyl, 2-pentadekenyl, 2-hexadekenyl, 2-heptadekenyl, or 2-octadekenyl.

[0096] The additive may be selected from compounds represented by the following formulas 1-1 to 1-14:

[0097] [ka] [ka] [ka]

[0098] The additives are contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the total content of the additives relative to the monomer in the composition is too low, the additives may have little effect in controlling aggregation, resulting in superabsorbent resin particles that are not pulverized to the desired particle size. If the total content of the additives is too high, the balance between the water retention capacity and the water absorption capacity under pressure, which are the physical properties of the superabsorbent resin, may be impaired.

[0099] The content of the additive in the superabsorbent polymer composition can be measured by first adding 1 g of the superabsorbent polymer composition to 1 ml of distilled water, mixing thoroughly for 1 hour until swelling occurs, filtering the mixture to extract only the solution, and then performing HPLC analysis to analyze the content of the additive dissolved in the solution.

[0100] More specifically, the additive is included in an amount of 0.01 parts by weight or more, 0.02 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, or 0.5 parts by weight or more, and 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, or 2 parts by weight or less, relative to 100 parts by weight of the water-soluble ethylenically unsaturated monomer.

[0101] Meanwhile, at least a portion of the additive may be present on the surface of the superabsorbent resin particles. Here, "at least a portion of the additive is present on the surface of the superabsorbent resin particles" means that at least a portion of the additive is adsorbed or bound to the surface of the superabsorbent resin particles. Specifically, the additives may be physically or chemically adsorbed to the surface of the superabsorbent resin. More specifically, the hydrophilic functional groups of each additive may be physically adsorbed to the hydrophilic portion of the surface of the superabsorbent resin by intermolecular forces such as dipole-dipole interaction. Thus, the hydrophilic portion of each additive may be physically adsorbed to the surface of the superabsorbent resin particles, surrounding the surface, while the hydrophobic portion of each additive may not be adsorbed to the surface of the resin particles, and each additive may be coated on the surface of the resin particles in the form of a type of micelle structure.

[0102] Therefore, when at least a portion of the additive is present on the surface of the superabsorbent resin particles, the aggregation phenomenon between pulverized particles during the preparation process of the superabsorbent resin composition can be more effectively suppressed than when the entire additive of Formula 1 is present inside the superabsorbent resin particles, specifically inside the crosslinked polymer.

[0103] Furthermore, since at least a portion of the additive is present on the surface of the superabsorbent resin particles, the superabsorbent resin composition containing the additive can have an improved water absorption rate compared to a composition that does not contain such an additive.

[0104] On the other hand, when the superabsorbent polymer composition does not further include a surface cross-linked layer described later, it does not include any other hydrophilic additives other than the plurality of superabsorbent polymer particles, the additive, and a hydrolysate of the additive produced by hydrolyzing the additive during the production process of the superabsorbent polymer.

[0105] Specifically, the superabsorbent polymer composition of one embodiment does not contain a compound having many hydroxyl-containing glucose units in the molecule, such as microcrystalline cellulose. For example, if the superabsorbent polymer composition contains microcrystalline cellulose with an average particle size of 1 to 10 μm, such as AVICEL® PH-101, available from FMC Corporation and represented by the following chemical formula 3, the aggregation between the superabsorbent polymer particles is not suppressed due to the large number of hydroxyl groups, and the effects of the above-mentioned additives may not be effectively achieved.

[0106] [ka]

[0107] In addition, one embodiment of the superabsorbent polymer composition does not contain a hydrophilic additive such as polyethylene glycol, polypropylene glycol, poly(ethylene glycol)-poly(propylene glycol) copolymer, polyoxyethylene lauryl ether carboxylic acid, sodium polyoxyethylene lauryl ether carboxylate, lauryl sulfate, or sodium lauryl sulfate. Such additives are not sufficiently adsorbed onto the surface of the crosslinked polymer, and therefore aggregation between superabsorbent polymer particles is not effectively suppressed. Therefore, if the superabsorbent polymer composition contains such a hydrophilic additive instead of the additive of Formula 1, aggregation between particles is not suppressed after pulverization of the crosslinked polymer, and the superabsorbent polymer composition contains a large amount of fine powder and exhibits low water retention capacity and low apparent density.

[0108] Meanwhile, the superabsorbent polymer composition may further include a surface cross-linked layer formed by additionally cross-linking the cross-linked polymer via a surface cross-linking agent on at least a portion of the surface of the superabsorbent polymer particle. This is for increasing the surface cross-linking density of the superabsorbent polymer particle. When the superabsorbent polymer particle further includes a surface cross-linked layer as described above, the particle has a structure in which the cross-linking density is higher at the outside than at the inside.

[0109] The surface cross-linking agent may be any surface cross-linking agent that has been conventionally used in the manufacture of superabsorbent resins, without any particular limitation. For example, the surface cross-linking agent may include one or more polyols selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, and glycerol; one or more carbonate compounds selected from the group consisting of ethylene carbonate, propylene carbonate, and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; mono-, di-, or polyoxazolidinone compounds; or cyclic urea compounds.

[0110] Specifically, one or more, two or more, or three or more of the above-mentioned surface cross-linking agents can be used as the surface cross-linking agent. For example, propylene glycol, ethylene carbonate, and propylene carbonate can be used.

[0111] The superabsorbent polymer composition may have a water absorption rate (vortex time) at 24.0°C measured by a vortex method of 30 seconds or less, 27 seconds or less, 25 seconds or less, 20 seconds or less, 15 seconds or less, or 12 seconds or less. The lower the value, the better the water absorption rate. Theoretically, the lower limit of the water absorption rate is 0 seconds, but it may be, for example, 5 seconds or more, 8 seconds or more, or 10 seconds or more. The method for measuring the water absorption rate of the superabsorbent polymer will be described in more detail in the experimental examples below.

[0112] The superabsorbent polymer composition may have a centrifugal retention capacity (CRC) measured by EDANA method WSP241.3 of 39 g / g or more, or 40 g / g or more, and 50 g / g or less, or 48 g / g or less, or 45 g / g or less. The method for measuring the water retention capacity will be described in more detail in the experimental examples below.

[0113] Furthermore, the superabsorbent polymer composition may have an absorbency under pressure (AUP) at 0.7 psi measured by EDANA method WSP242.3 of 24.0 g / g or more, 25.0 g / g or more, 26.0 g / g or more, or 24.3 g / g or more, and may have an AUP of 30 g / g or less, 28.0 g / g or less, or 26.0 g / g or less. The method for measuring the absorbency under pressure will be described in more detail in the experimental examples below.

[0114] (Method of producing superabsorbent resin composition) On the other hand, the superabsorbent resin composition a step of cross-linking a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a polymer (step 1); neutralizing at least a portion of the acidic groups of the polymer (Step 2); Step 3: atomizing the polymer in the presence of an additive represented by the following formula 1 to produce base resin particles; and and drying the base resin particles (Step 4):

[0115] [ka]

[0116] In the above Chemical Formula 1, A1, A2 and A3 each independently represent a single bond, a carbonyl,

[0117] [ka]

[0118] and one or more of these is a carbonyl or

[0119] [ka]

[0120] wherein m1, m2, and m3 each independently represent an integer of 1 to 8;

[0121] [ka]

[0122] are each linked to adjacent oxygen atoms,

[0123] [ka]

[0124] are linked to adjacent R1, R2 and R3, respectively; R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms; n is an integer of 1 to 9.

[0125] Hereinafter, each step of the method for producing a highly water-absorbent resin according to one embodiment will be described in more detail.

[0126] (Stage 1) In one embodiment of the method for preparing a superabsorbent resin, first, a water-soluble ethylenically unsaturated monomer having an acidic group is cross-linked and polymerized in the presence of an internal cross-linking agent and a polymerization initiator to form a hydrogel polymer.

[0127] The step includes preparing a monomer composition by mixing the water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator, and thermally or photopolymerizing the monomer composition to form a polymer. Here, the description of the water-soluble ethylenically unsaturated monomer and the internal crosslinking agent is as described above.

[0128] Here, the water-soluble ethylenically unsaturated monomer has an acidic group. As described above, in the conventional production of a superabsorbent resin, a monomer in which at least a portion of the acidic groups have been neutralized with a neutralizing agent is cross-linked to form a hydrogel polymer. Specifically, at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer are neutralized in the step of mixing the water-soluble ethylenically unsaturated monomer having the acidic group, an internal cross-linking agent, a polymerization initiator, and a neutralizing agent.

[0129] However, according to one embodiment of the present invention, the water-soluble ethylenically unsaturated monomer is polymerized first in a state where the acid group is not neutralized to form a polymer.

[0130] A water-soluble ethylenically unsaturated monomer (e.g., acrylic acid) in which the acid group is not neutralized is in a liquid state at room temperature and has high miscibility with the solvent (water), so it exists in the form of a mixed solution in the monomer composition. However, a water-soluble ethylenically unsaturated monomer in which the acid group is neutralized is in a solid state at room temperature and has different solubility depending on the temperature of the solvent (water), with the solubility decreasing as the temperature decreases.

[0131] Such water-soluble ethylenically unsaturated monomers in which the acidic group is not neutralized have higher solubility or miscibility in a solvent (water) than monomers in which the acidic group is neutralized, and do not precipitate even at low temperatures, making them advantageous for long-term polymerization at low temperatures. As a result, long-term polymerization using the water-soluble ethylenically unsaturated monomers in which the acidic group is not neutralized can stably produce polymers having higher molecular weights and more uniform molecular weight distributions.

[0132] Furthermore, it is possible to form a polymer with a longer chain, and the effect of reducing the content of water-soluble components that exist in an uncrosslinked state due to incomplete polymerization or crosslinking can be achieved.

[0133] Furthermore, when the acidic groups of the monomers are not neutralized, polymerization is first performed to form a polymer, and the polymer is then neutralized and then micronized in the presence of the additive of Formula 1, or when the acidic groups present in the polymer are neutralized in the presence of the additive of Formula 1, or when the acidic groups present in the polymer are neutralized simultaneously with micronization, the additive of Formula 1 is present in a large amount on the surface of the polymer, and can sufficiently play a role in reducing the stickiness of the polymer.

[0134] The type of the water-soluble ethylenically unsaturated monomer in the monomer composition is the same as that described for the superabsorbent polymer composition. The concentration of the water-soluble ethylenically unsaturated monomer can be appropriately adjusted in consideration of the polymerization time and reaction conditions, and may be about 20 to about 60 wt %, or about 20 to about 40 wt %.

[0135] The same applies to the type of the internal crosslinking agent in the monomer composition as described above for the superabsorbent polymer composition. The content of the internal crosslinking agent can be 0.01 to 5 parts by weight per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent can be used in an amount of 0.01 part by weight or more, 0.05 part by weight or more, or 0.1 part by weight or more and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.7 parts by weight or less per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the internal crosslinking agent is too low, crosslinking may not occur sufficiently, making it difficult to achieve an appropriate level of strength. If the content of the internal crosslinking agent is too high, the internal crosslink density may increase, making it difficult to achieve the desired water retention capacity.

[0136] The polymerization initiator can be appropriately selected depending on the polymerization method, and a thermal polymerization initiator can be used when a thermal polymerization method is used, a photopolymerization initiator can be used when a photopolymerization method is used, and both a thermal polymerization initiator and a photopolymerization initiator can be used when a hybrid polymerization method (a method using both heat and light) is used. However, even in the photopolymerization method, a certain amount of heat is generated by light irradiation such as ultraviolet irradiation, and a certain amount of heat is also generated as the polymerization reaction, which is an exothermic reaction, progresses, so a thermal polymerization initiator may also be used.

[0137] The photopolymerization initiator can be any compound capable of forming radicals by exposure to light such as ultraviolet light, and is not limited in its composition.

[0138] The photopolymerization initiator may be, for example, one or more selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone. Specific examples of acyl phosphines include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate. A wide variety of photoinitiators are described in detail in Reinhold Schwalm, "UV Coatings: Basics, Recent Developments and New Applications" (Elsevier, 2007), p. 115, and are not limited to the above examples.

[0139] The thermal polymerization initiator may be one or more selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid. Specific examples of persulfate initiators include sodium persulfate (NaSO), potassium persulfate (KSO), and ammonium persulfate ((NHSO). Examples of azo initiators include 2,2-azobis(2-amidinopropane) dihydrochloride and 2,2-azobis(N,N-dimethylene)isobutyramidine dihydrochloride. dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), etc. A wide variety of thermal polymerization initiators are clearly described in Odian, "Principle of Polymerization" (Wiley, 1981), p. 203, and are not limited to the examples mentioned above.

[0140] The polymerization initiator can be used in an amount of 2 parts by weight or less per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, if the concentration of the polymerization initiator is too low, the polymerization rate will be slow and a large amount of residual monomer may be extracted into the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network will be shorter, the content of water-soluble components will be higher, and the physical properties of the resin, such as the water absorption capacity under pressure, will be reduced, which is undesirable.

[0141] The monomer composition may further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

[0142] The monomer composition containing the monomer may be in a solution state, for example, dissolved in a solvent such as water, and the solid content in such a solution state of the monomer composition, i.e., the concentrations of the monomer, internal crosslinking agent, and polymerization initiator, can be appropriately adjusted in consideration of the polymerization time, reaction conditions, etc. For example, the solid content in the monomer composition may be 10 to 80 wt %, 15 to 60 wt %, or 30 to 50 wt %.

[0143] When the monomer composition has a solid content within this range, it may be advantageous to utilize the gel effect phenomenon that occurs in the polymerization reaction of a high-concentration aqueous solution to eliminate the need to remove unreacted monomers after polymerization, while also being able to control the pulverization efficiency during pulverization of the polymer, as described below.

[0144] The solvent that can be used in this case is not limited in composition as long as it can dissolve the above-mentioned components, and for example, one or more solvents selected from water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide can be used in combination.

[0145] According to one embodiment of the present invention, the step of polymerizing the monomer composition to form a polymer is carried out in a batch type reactor.

[0146] In a typical method for producing a superabsorbent polymer composition, polymerization methods are roughly divided into thermal polymerization and photopolymerization depending on the polymerization energy source. Generally, when thermal polymerization is carried out, it is carried out in a reactor having a stirring shaft such as a kneader, and when photopolymerization is carried out, it is carried out in a reactor equipped with a movable conveyor belt or in a vessel with a flat bottom.

[0147] On the other hand, such polymerization methods generally have short polymerization reaction times (eg, 1 hour or less), so that the molecular weight of the polymer is not high and a polymer having a broad molecular weight distribution is formed.

[0148] On the other hand, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or a container with a flat bottom, the resulting hydrogel polymer is usually in the form of a sheet having the width of the belt. The thickness of the polymer sheet varies depending on the concentration and injection rate or amount of the monomer composition injected, but is usually about 0.5 to about 5 cm thick.

[0149] However, if the thickness of the sheet-like polymer is too thin, the production efficiency will be low when supplying the monomer composition, which is not preferable, and if the thickness of the sheet-like polymer is increased for productivity reasons, the polymerization reaction will not occur uniformly throughout the entire thickness, making it difficult to form a high-quality polymer.

[0150] In addition, in the polymerization in the reactor having a reactor agitator equipped with a conveyor belt, the polymerization is carried out continuously by feeding new monomer composition to the reactor while the polymerization result is moving, so polymers with different polymerization rates are mixed, which makes it difficult to carry out uniform polymerization throughout the monomer composition, and may result in deterioration of overall physical properties.

[0151] However, according to one embodiment of the present invention, polymerization is carried out in a stationary manner using a batch reactor, which reduces the risk of polymers with different polymerization rates being mixed together, thereby producing polymers with uniform quality.

[0152] In addition, the polymerization step is carried out in a batch reactor having a predetermined volume, and the polymerization reaction is carried out for a longer time, for example, 3 hours or more, than in a continuous polymerization using a reactor equipped with a conveyor belt. Despite this long polymerization reaction time, since the polymerization is carried out on an unneutralized water-soluble ethylenically unsaturated monomer, the monomer does not precipitate even during long-term polymerization, and therefore, it is advantageous for long-term polymerization.

[0153] Meanwhile, the polymerization in the batch reactor of the present invention is carried out using a thermal polymerization method, and the polymerization initiator may be a thermal polymerization initiator among the above-mentioned initiators.

[0154] Meanwhile, in one embodiment of the present invention, polymerization can be initiated by adding a reducing agent that forms a redox couple with the initiator.

[0155] Specifically, when the initiator and the reducing agent are added to the polymer solution, they react with each other to form radicals.

[0156] The formed radicals react with the monomer, and the oxidation-reduction reaction between the initiator and the reducing agent is highly reactive, so polymerization can be initiated even with only a small amount of initiator and reducing agent added. This eliminates the need to increase the process temperature, allowing low-temperature polymerization and minimizing changes in the physical properties of the polymer solution.

[0157] The polymerization reaction using the oxidation-reduction reaction can occur smoothly at or below room temperature (25°C). For example, the polymerization reaction is carried out at a temperature of 5°C to 25°C or 5°C to 20°C.

[0158] In one embodiment of the present invention, when a persulfate initiator is used as the initiator, the reducing agent can be at least one selected from the group consisting of sodium metabisulfite (NaSO); tetramethylethylenediamine (TMEDA); a mixture of iron (II) sulfate and EDTA (FeSO / EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinoacetate.

[0159] For example, potassium persulfate can be used as the initiator and disodium 2-hydroxy-2-sulfinoacetate as the reducing agent; ammonium persulfate can be used as the initiator and tetramethylethylenediamine as the reducing agent; or sodium persulfate can be used as the initiator and sodium formaldehyde sulfoxylate as the reducing agent.

[0160] In another embodiment of the present invention, when a hydrogen peroxide-based initiator is used as the initiator, the reducing agent may be one or more selected from the group consisting of ascorbic acid; sucrose; sodium sulfite (NaSO), sodium metabisulfite (NaSO); tetramethylethylenediamine (TMEDA); a mixture of iron (II) sulfate and EDTA (FeSO / EDTA); sodium formaldehyde sulfoxylate; disodium 2-hydroxy-2-sulfinoacetate; and disodium 2-hydroxy-2-sulfoacetate.

[0161] The polymer obtained by such a method can form a polymer having a high molecular weight and a uniform molecular weight distribution by polymerizing an unneutralized ethylenically unsaturated monomer, as described above, and the content of water-soluble components can be reduced.

[0162] The polymer obtained by such a method may be in the form of a hydrogel polymer and have a water content of 30 to 80% by weight. For example, the water content of the polymer may be 30% by weight or more, 45% by weight or more, or 50% by weight or more, and 80% by weight or less, 70% by weight or less, or 60% by weight or less.

[0163] If the water content of the polymer is too low, it may be difficult to secure an adequate surface area in the subsequent pulverization step, resulting in ineffective pulverization. If the water content of the polymer is too high, it may be difficult to pulverize the polymer to the desired particle size due to increased pressure in the subsequent pulverization step.

[0164] Throughout this specification, the term "moisture content" refers to the amount of water in a polymer relative to its total weight, calculated by subtracting the weight of the polymer in a dry state from the weight of the polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of water in the polymer during the drying process of raising the temperature of a crumb-state polymer using infrared heating. The drying conditions are to raise the temperature from room temperature to about 180°C and then maintain it at 180°C, and the total drying time is set to 40 minutes, including 5 minutes for the temperature rise step, and the moisture content is measured.

[0165] (Stage 2 and Stage 3) Next, a step (Step 2) of neutralizing at least a portion of the acid groups of the polymer is carried out, and a step (Step 3) of micronizing the polymer in the presence of the additive represented by Chemical Formula 1 to produce base resin particles is carried out.

[0166] First, the neutralizing agent used in step 2 may be a basic substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide that can neutralize acidic groups.

[0167] Furthermore, the degree of neutralization, which refers to the degree to which the acidic groups contained in the polymer are neutralized by the neutralizing agent, may be 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to 75 mol%. The range of the degree of neutralization varies depending on the final physical properties, but if the degree of neutralization is too high, the water absorption capacity of the superabsorbent polymer may decrease, and the concentration of carboxyl groups on the particle surface may be too low, making it difficult to properly perform surface cross-linking in subsequent processes, resulting in reduced water absorption properties or liquid permeability under pressure. Conversely, if the degree of neutralization is too low, not only will the water absorption capacity of the polymer be significantly reduced, but it may also exhibit properties similar to elastic rubber, making it difficult to handle.

[0168] Next, the polymer is atomized in the presence of the additive represented by Chemical Formula 1 to prepare base resin particles (Step 3).

[0169] Here, Steps 2 and 3 are carried out sequentially, simultaneously, or alternately. That is, simultaneously with Step 2, or before or after Step 2, a step of atomizing the polymer in the presence of a surfactant (Step 3) is carried out.

[0170] This step involves atomizing the polymer in the presence of the additive of Formula 1, where the polymer is not chopped into millimeter-sized particles but is simultaneously chopped into particles of tens to hundreds of micrometers and aggregated. That is, this step involves imparting appropriate adhesiveness to the polymer to produce secondary aggregate particles formed by aggregation of primary particles chopped into particles of tens to hundreds of micrometers. The base resin particles, which are secondary aggregate particles produced in this step, have a normal particle size distribution and a significantly increased surface area, resulting in a significantly improved water absorption rate.

[0171] In this manner, the polymer and the additive of Formula 1 are mixed, and then the polymer is atomized in the presence of the additive of Formula 1, thereby producing base resin particles in the form of secondary agglomerated particles that are chopped and agglomerated in a state where the superabsorbent resin particles and the surfactant are mixed.

[0172] The description of the additive represented by Chemical Formula 1 can be applied to the superabsorbent polymer composition described above.

[0173] Here, the "base resin particles" are particles with a water content (moisture content) of approximately 30% by weight or more, and are formed by chopping and agglomerating a polymer into particles without a drying process, so that, like the polymer, they can have a moisture content of 30 to 80% by weight, preferably 70 to 80% by weight.

[0174] Meanwhile, the additive of Formula 1 can be used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer used in the crosslinking polymerization to produce the polymer. If too little additive of Formula 1 is used, it may not be evenly adsorbed on the surface of the polymer, which may result in re-agglomeration of particles after pulverization. If too much surfactant is used, the physical properties of the final superabsorbent resin may be degraded. For example, the additive of Formula 1 can be used in an amount of 0.01 part by weight or more, 0.015 parts by weight or more, or 0.1 part by weight or more, but not more than 5 parts by weight, 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 water-soluble ethylenically unsaturated monomer.

[0175] The method of mixing the additive of Formula 1 with the polymer is not particularly limited as long as it can be uniformly mixed with the polymer, and can be appropriately adopted and used. Specifically, the additive of Formula 1 can be mixed dry, dissolved in a solvent and mixed in a solution state, or melted and then mixed.

[0176] For example, the additive of Formula 1 is mixed in a solvent in the form of a solution. Any type of solvent, including inorganic and organic solvents, can be used, but water is the most suitable when considering the ease of the drying process and the cost of the solvent recovery system. The solution can be prepared by mixing the additive of Formula 1 and the polymer in a reaction vessel, by adding the polymer to a mixer and spraying the solution, or by continuously supplying the polymer and the solution to a continuously operating mixer and mixing them.

[0177] Meanwhile, according to one embodiment of the present invention, the steps 2 and 3 are performed sequentially, simultaneously, or alternately.

[0178] That is, a neutralizing agent may be added to a polymer to neutralize the acidic groups first, and then the additive of Formula 1 may be added to the neutralized polymer to atomize the polymer mixed with the additive; alternatively, the neutralizing agent and additive may be added to the polymer simultaneously to neutralize and atomize the polymer. Alternatively, the additive may be added first and then the neutralizing agent. Alternatively, the neutralizing agent and additive may be added alternately. Alternatively, the additive may be added first to atomize the polymer, and then the neutralizing agent may be added to neutralize it, and then an additional additive may be added to the neutralized hydrogel polymer to perform an additional atomization process.

[0179] On the other hand, in order to ensure uniform neutralization of the entire polymer, it is preferable to leave a certain time lag between the addition of the neutralizing agent and the atomization step.

[0180] At least a portion or a substantial amount of the additive of Formula 1 may be present on the surface of the base resin particles.

[0181] Here, the presence of the additive of Formula 1 on the surface of the base resin particles means that at least a portion or a substantial amount of the additive of Formula 1 is adsorbed or bound to the surface of the base resin particles. Specifically, the additive of Formula 1 may be physically or chemically adsorbed to the surface of the base resin particles. More specifically, the hydrophilic functional group of the additive of Formula 1 may be physically adsorbed to the hydrophilic portion of the surface of the base resin particles by intermolecular forces such as dipole-dipole interaction. In this way, the hydrophilic portion of the additive of Formula 1 may be physically adsorbed to the surface of the base resin particles, surrounding the surface, while the hydrophobic portion of the additive of Formula 1 may not be adsorbed to the surface of the base resin particles, and the additive of Formula 1 may be coated on the base resin particles in the form of a micelle structure. This is because the additive of Formula 1 is added not during the polymerization process of the water-soluble ethylenically unsaturated monomer but during the atomization step after polymer formation, and therefore can faithfully function as a surfactant compared to when the additive of Formula 1 is added during the polymerization process and exists inside the polymer, and particles with a large surface area can be obtained in the form of an aggregate of fine particles due to simultaneous pulverization and aggregation.

[0182] According to one embodiment, the step of preparing the base resin particles (Step 3) is carried out using an atomizer.

[0183] The atomization device includes a body portion including a transfer space into which a mixture of a polymer and an additive is transferred, a screw member rotatably installed within the transfer space to move the mixture, a drive motor to provide a rotational driving force to the screw member, and a cutter member installed in the body portion, including a perforated plate having a number of holes formed therein, to pulverize the mixture while discharging it to the outside of the body portion.

[0184] According to one embodiment, said steps 2 and 3 are carried out sequentially, simultaneously or intersectingly, which is carried out using an atomizer.

[0185] In this case, the atomization device further includes a neutralizer injection nozzle provided inside the body portion, and the neutralizer is injected through the neutralizer injection nozzle, so that steps 2 and 3 are performed sequentially, simultaneously, or crosswise.

[0186] Specifically, a neutralizer is injected into the body through the neutralizer injection nozzle to neutralize at least some of the acid groups of the polymer having acid groups in the mixture. Specifically, in the atomization device, a neutralizer is injected into the body through the neutralizer injection nozzle to neutralize at least some of the acid groups of the polymer having acid groups in the mixture, and at the same time, the mixture is pulverized (atomized) while being discharged to the outside of the body through a perforated plate.

[0187] Preferably, the neutralizing agent pulverized by the neutralizing agent injection nozzle is injected adjacent to the perforated plate. In this case, the neutralizing process is carried out and, at the same time, when the mixture is discharged through the holes in the perforated plate, the neutralizing agent acts as a slip agent in the mixture, thereby reducing the load on the holes.

[0188] Preferably, the cutter member of the atomization device includes a perforated plate and a cutting knife disposed adjacent to the perforated plate on the outlet side of the body portion, and after the mixture passes through the perforated plate, it is more effectively crushed and atomized by the cutting knife.

[0189] In the atomization device, the cutter member may include a plurality of perforated plates and a plurality of cutting knives. The arrangement order of the perforated plates and the cutting knives is not particularly limited, and they may be arranged sequentially, crossing each other, or the perforated plates may be arranged consecutively, or the cutting knives may be arranged consecutively.

[0190] By including a plurality of perforated plates and cutting knives as described above, multiple atomizations can be performed within a single atomization device. Meanwhile, a plurality of neutralizing agent spray nozzles may be disposed adjacent to one or more of the perforated plates and cutting knives, and it is preferable that the neutralizing agent spray nozzle be disposed adjacent to the perforated plate in terms of improving slipperiness.

[0191] In the atomization device, the hole size formed in the perforated plate may be 0.1 mm to 30 mm. Preferably, it may be 0.5 mm to 25 mm, 1 mm to 20 mm, or 1 mm to 10 mm. By using a perforated plate having such hole sizes, base resin particles having a desired particle size can be produced. When the cutter member includes multiple perforated plates as described above, the size of the holes formed in each perforated plate satisfies the above-mentioned range, and these holes may be the same or different from each other.

[0192] According to one embodiment of the invention, step 3 may be performed multiple times, using multiple atomizing devices, or a single atomizing device including multiple perforated plates and / or multiple cutting knives, or multiple atomizing devices, some of which may include multiple perforated plates and / or multiple cutting knives. The atomizing step is preferably performed 1 to 6 times or 1 to 4 times. When step 3 is performed multiple times, the additive may be added multiple times.

[0193] In the step (step 3) of atomizing the polymer to prepare base resin particles, the base resin particles can be atomized to an average particle size of 50 μm to 600 μm, preferably 100 μm to 500 μm, 150 μm to 450 μm, or 200 μm to 400 μm. By satisfying this particle size range, the polymer is prepared into secondary particles in the form of agglomerated primary particles, and the subsequent pulverization and drying processes can be carried out under milder conditions, thereby significantly reducing the amount of fine powder generated during the process.

[0194] In the present invention, the average particle size "Dn" refers to the particle size or particle diameter at the n% point in the cumulative particle number distribution by particle size. That is, D50 refers to the particle size at the 50% point in the cumulative particle number distribution by particle size, D90 refers to the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 refers to the particle size at the 10% point in the cumulative particle number distribution by particle size. The Dn can be measured using a laser diffraction method, etc. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500). When the particles pass through a laser beam, the difference in the diffraction pattern according to particle size is measured to calculate the particle size distribution. D10, D50, and D90 can be measured by calculating the particle sizes at the 10%, 50%, and 90% points in the cumulative particle number distribution by particle size in the measurement device.

[0195] (Stage 4) Next, the base resin particles are dried (Step 4), thereby producing a superabsorbent polymer composition containing the superabsorbent polymer particles and the additive represented by Formula 1.

[0196] The drying is carried out so that the moisture content of each of the multiple superabsorbent resin particles contained in the produced superabsorbent resin composition is about 10% by weight or less, specifically about 0.1 to about 10% by weight.

[0197] In this case, the drying of the pulverized material is carried out in a moving type, which is distinguished from fixed-bed type drying by whether or not the material moves during drying.

[0198] In conventional methods for producing superabsorbent polymers, the drying step is generally carried out until the moisture content of the superabsorbent polymer particles is less than 10% by weight. However, in the present invention, aggregation is controlled by carrying out the atomization step in the presence of the additive of Chemical Formula 1, and drying is carried out so that the moisture content of the dried superabsorbent polymer particles is 10% to 20% by weight, preferably 10% to 25% by weight. However, the present invention is not limited thereto. This has the advantage of achieving a high moisture content and fundamentally preventing the generation of fine powder. Furthermore, this is preferable because it can improve the water absorption rate of the final superabsorbent polymer composition.

[0199] For this reason, the drying step is carried out at a relatively low temperature using a moving-type drying method. Such moving-type drying is distinguished from fixed-bed drying by the presence or absence of material movement during drying, and is preferred because it prevents aggregation between the chopped water-containing superabsorbent polymer particles in the pulverized material to be dried and allows drying to be completed within a short period of time.

[0200] For this reason, the drying step is carried out in a moving-type manner at a relatively low temperature. Such moving-type drying is distinguished from fixed-bed drying by the presence or absence of material movement during drying, and is preferred because it prevents aggregation between the finely chopped base resin particles in the pulverized material to be dried and allows drying to be completed in a short time.

[0201] Specifically, moving-type drying refers to a method of drying materials while mechanically stirring them. The direction in which the hot air passes through the materials may be the same as or different from the direction in which the materials circulate. Alternatively, the materials may be circulated inside the dryer, and a heat transfer fluid (heat medium flow) may be passed through a separate pipe outside the dryer to dry the materials. Fixed-bed drying refers to a method in which the materials to be dried are placed on a perforated iron plate or other perforated plate that allows air to pass through, and hot air passes through the materials from bottom to top.

[0202] The step of drying the base resin particles (step 4) may be carried out using any commonly used fluidized bed dryer without any particular limitation, for example, a fluidized bed dryer such as a horizontal-type mixer, a rotary kiln, a paddle dryer, or a steam tube dryer.

[0203] The drying step (Step 4) is carried out at a relatively low temperature of 150°C or less, preferably 100°C to 150°C, 100°C to 130°C, or 105°C to 115°C. Even when the drying step is carried out at such a low temperature, it is possible to produce superabsorbent resin particles having the desired particle size and physical properties without the desired aggregation.

[0204] Meanwhile, the drying temperature may be an internal driving temperature of the fluidized-bed dryer to which the material to be dried is fed, or it may be adjusted by passing a heat transfer fluid (heat medium flow) through a separate pipe outside the dryer, but is not limited thereto.

[0205] The drying step (Step 4) is carried out for 30 to 80 minutes, 30 to 60 minutes, or 40 to 50 minutes. Since there is little aggregation between the finely chopped polymer resin particles in the pulverized material to be dried, even if the drying step is carried out at a relatively low temperature for a short time, it is possible to produce superabsorbent resin particles having the desired particle size and physical properties.

[0206] (Additional stage) Hereinafter, the method for preparing a superabsorbent polymer composition according to an embodiment of the present invention may further include the step of pulverizing and classifying the superabsorbent polymer particles, if necessary.

[0207] Specifically, the pulverization step is performed by pulverizing the dried superabsorbent resin particles to have a particle size of normal particle level, that is, a particle size of 150 μm to 850 μm.

[0208] To this end, the crusher used may be, 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, but is not limited to the above examples.

[0209] Alternatively, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like may be used as the pulverizer, but the pulverizer is not limited to the above examples.

[0210] On the other hand, in the manufacturing method of the present invention, it is possible to realize superabsorbent resin particles with a smaller particle size distribution in the atomization step than in the conventional chopping step, and when fluidized-type drying is performed, the moisture content after drying is maintained relatively high at 10% by weight or more. Therefore, even if the grinding is performed under mild conditions with less grinding force, it is possible to form a superabsorbent resin with a very high content of normal particle sizes of 150 μm to 850 μm, and the rate of fine powder generation can be significantly reduced.

[0211] The superabsorbent resin particles prepared as described above may contain 80% by weight or more, 85% by weight or more, 89% by weight or more, 90% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, or 95% by weight or more of superabsorbent resin particles having a particle size of 150 μm to 850 μm, i.e., normal particles, based on the total weight. The particle size of such resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3 method.

[0212] The superabsorbent resin particles may contain less than about 20% by weight, less than about 18% by weight, less than about 15% by weight, less than about 13% by weight, less than about 10% by weight, specifically less than about 5% by weight, and more specifically less than about 3% by weight of fine powder having a particle size of less than 150 μm, relative to the total weight. This is in contrast to superabsorbent resins produced by conventional manufacturing methods, which contain more than about 20% to about 30% by weight of fine powder.

[0213] Next, a method for preparing a superabsorbent resin according to an embodiment of the present invention may include a step of thermally crosslinking the surface of the base resin powder in the presence of a surface crosslinker to prepare superabsorbent resin particles.

[0214] The surface cross-linking step induces a cross-linking reaction on the surface of the base resin powder in the presence of a surface cross-linking agent, and unsaturated bonds of the water-soluble ethylenically unsaturated monomer that remain uncross-linked on the surface are cross-linked by the surface cross-linking agent, thereby forming a superabsorbent resin with a high surface cross-linking density.

[0215] Specifically, in the presence of a surface cross-linking agent, a surface cross-linked layer is formed in a heat treatment process, and the heat treatment process increases the surface cross-link density, i.e., the external cross-link density, while leaving the internal cross-link density unchanged. As a result, the superabsorbent resin having a surface cross-linked layer formed thereon has a structure in which the external cross-link density is higher than the internal cross-link density.

[0216] The surface cross-linking step is carried out at a temperature of about 80°C to about 250°C. More specifically, the surface cross-linking step is carried out at a temperature of about 100°C to about 220°C, or about 120°C to about 200°C, for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. When the above-mentioned surface cross-linking step conditions are satisfied, the surfaces of the superabsorbent resin particles are sufficiently cross-linked, thereby increasing the water absorption capacity under pressure.

[0217] By satisfying these surface cross-linking process conditions (particularly, the temperature rise conditions and the reaction conditions at the maximum reaction temperature), a highly water-absorbent resin having excellent physical properties such as excellent water absorption rate can be produced.

[0218] The temperature raising means for the surface crosslinking reaction is not particularly limited. Heating can be achieved by supplying a heat medium or directly supplying a heat source. At this time, the type of heat medium that can be used may be a heated fluid such as steam, hot air, or hot oil, but is not limited to these. The temperature of the heat medium to be supplied can be appropriately selected in consideration of the heat medium means, the temperature raising rate, and the target temperature. On the other hand, examples of the heat source that can be directly supplied include, but are not limited to, electric heating and gas heating methods.

[0219] Meanwhile, the surface cross-linking agent contained in the surface cross-linking agent composition may be any surface cross-linking agent that has been conventionally used in the production of superabsorbent resins, without any particular limitation. For example, the surface cross-linking agent may include one or more polyols selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, and glycerol; one or more carbonate compounds selected from the group consisting of ethylene carbonate and propylene 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. Preferably, the same internal crosslinking agent as described above can be used, for example, a diglycidyl ether compound of alkylene glycol such as ethylene glycol diglycidyl ether.

[0220] In the surface cross-linking step, a surface cross-linking agent composition containing an alcohol-based solvent and water in addition to a surface cross-linking agent may be used.

[0221] Such a surface cross-linking agent can be used in an amount of 0.001 to 2 parts by weight per 100 parts by weight of superabsorbent resin particles. Preferably, the amount is 0.005 part by weight or more, 0.01 part by weight or more, or 0.02 part by weight or more, and 0.5 part by weight or less, or 0.3 part by weight or less. By adjusting the content of the surface cross-linking agent within the above-mentioned range, a superabsorbent resin exhibiting various physical properties such as excellent water absorption performance and liquid permeability can be produced.

[0222] On the other hand, the surface cross-linking agent is added to the superabsorbent resin particles in the form of a surface cross-linking agent composition containing the same, and the method for adding such a surface cross-linking agent composition is not particularly limited in terms of its constitution. For example, a method in which the surface cross-linking agent composition and the superabsorbent resin particles are mixed in a reaction tank, a method in which the surface cross-linking agent composition is sprayed onto the superabsorbent resin particles, a method in which the superabsorbent resin particles and the surface cross-linking agent composition are continuously supplied to a continuously operating mixer and mixed therewith, etc. can be used.

[0223] The surface cross-linking agent composition may further include water and / or a hydrophilic organic solvent as a medium. This has the advantage that the surface cross-linking agent can be uniformly dispersed on the base resin powder. At this time, the content of water and the hydrophilic organic solvent can be adjusted by adjusting the addition ratio with respect to 100 parts by weight of the superabsorbent resin particles in order to induce uniform dissolution / dispersion of the surface cross-linking agent and prevent agglomeration of the base resin powder, while optimizing the surface penetration depth of the surface cross-linking agent.

[0224] Meanwhile, in the method for producing a superabsorbent resin according to an embodiment of the present invention, various polyvalent metal salts, such as aluminum salts such as aluminum sulfate, may be further used during surface cross-linking to further improve liquid permeability, etc. Such polyvalent metal salts are contained on the surface cross-linked layer of the final superabsorbent resin.

[0225] According to one embodiment of the present invention, after the step of forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent resin particles, the method further includes one or more of the following steps: a cooling step of cooling the superabsorbent resin particles having the surface cross-linked layer formed thereon, a hydration step of adding water to the superabsorbent resin particles having the surface cross-linked layer formed thereon, and a post-treatment step of adding an additive to the superabsorbent resin particles having the surface cross-linked layer formed thereon. In this case, the cooling step, the hydration step, and the post-treatment step may be performed sequentially or simultaneously.

[0226] The additives added in the post-treatment step may be, but are not limited to, a liquid permeability improver, an anti-caking agent, a flowability improver, an antioxidant, etc.

[0227] By selectively carrying out the cooling step, the hydration step, and the post-treatment step, the moisture content of the final superabsorbent polymer can be improved, and a higher quality superabsorbent polymer product can be produced.

[0228] According to another embodiment of the present invention, there is provided a superabsorbent polymer composition produced by the above-mentioned production method.

[0229] The superabsorbent polymer composition produced by the above production method achieves a high water content without the need for a separate additional water addition process or additive addition process, and therefore has a low fine powder content. The water retention capacity (CRC) and absorbency under pressure (AUP), which are water absorption properties, are at the same level or higher than those of superabsorbent polymers produced by conventional methods. At the same time, the low content of water-soluble components (EC) makes it possible to provide a superabsorbent polymer that is excellent in all aspects, such as water absorption speed.

[0230] The functions and effects of the present invention will be further described below through specific examples of the present invention, but these examples are presented only as examples of the present invention and do not define the scope of the invention.

[0231] Example - Preparation of superabsorbent polymer composition Example 1 (Step 1) 1,000 g of acrylic acid, 3.5 g of pentaerythritol triallyl ether as an internal crosslinker, and 2,260 g of water were mixed in a 5 L glass vessel equipped with a stirrer and thermometer and stirred while maintaining the temperature at 5°C. Nitrogen was introduced into the glass vessel containing the mixture at 1,000 cc / min for 1 hour to create a nitrogen atmosphere. Next, 13 g of a 0.3% aqueous hydrogen peroxide solution, 15 g of a 1% aqueous ascorbic acid solution, and 30 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane) dihydrochloride solution were added as polymerization initiators, and 15 g of a 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the mixture reached a temperature of 85°C, the mixture was polymerized at 90±2°C for approximately 3 hours to obtain a polymer. The water content of the polymer was approximately 70 wt%.

[0232] (Steps 2 and 3) 1.19 g of the A-1 compound in Table 1 as an additive of Chemical Formula 1 was dispersed in 52.27 g of water (preparation of a 2 wt% aqueous dispersion), which was then mixed with 1,000 g of the polymer obtained in Step 1.

[0233] The mixture was passed once through a first atomizer equipped with a perforated plate containing a large number of holes with a hole size of 6 mm to carry out a primary atomization process.

[0234] Next, the mixture was repeatedly introduced into a second atomizer equipped with a perforated plate having a number of holes with a hole size of 4 mm three times to carry out the second, third and fourth atomization processes.

[0235] In the secondary atomization step, 400 g of a 32% NaOH aqueous solution was introduced through a neutralizer nozzle disposed adjacent to the perforated plate to carry out atomization and neutralization.

[0236] In the tertiary atomization step, 37.5 g of a 15% aqueous solution of Na2SO4 was added through a neutralizer nozzle disposed adjacent to the perforated plate, and atomization and neutralization steps were carried out.

[0237] Finally, in the fourth atomization step, the atomization step was carried out without adding a neutralizing agent or a surfactant to obtain base resin particles.

[0238] The degree of neutralization of the base resin particles was 70 mol %.

[0239] (Step 4) Then, 1,000 g of the base resin particles were placed in a rotary mixer fluidized dryer rotating at 100 rpm. The internal temperature of the dryer was maintained at 105°C, and drying was carried out for 60 minutes to obtain superabsorbent resin particles. The moisture content of the superabsorbent resin particles was 11 wt%.

[0240] Example 2 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-2 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0241] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 11 wt%.

[0242] Example 3 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-3 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0243] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 11 wt%.

[0244] Example 4 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that compound A-4 in Table 1 was used instead of compound A-1 as the additive of Chemical Formula 1.

[0245] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 11 wt%.

[0246] Example 5 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-5 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0247] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 14 wt%.

[0248] Example 6 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-6 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0249] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 14 wt%.

[0250] Example 7 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-7 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0251] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 11 wt%.

[0252] Example 8 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-8 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0253] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 12 wt%.

[0254] Example 9 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-9 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0255] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 13 wt%.

[0256] Example 10 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-10 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0257] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 11 wt%.

[0258] Example 11 (Step 1) 1,000 g of acrylic acid, 3.5 g of pentaerythritol triallyl ether as an internal crosslinker, and 2,260 g of water were mixed in a 5 L glass vessel equipped with a stirrer and thermometer and stirred while maintaining the temperature at 5°C. Nitrogen was introduced into the glass vessel containing the mixture at 1,000 cc / min for 1 hour to create a nitrogen atmosphere. Next, 13 g of a 0.3% aqueous hydrogen peroxide solution, 15 g of a 1% aqueous ascorbic acid solution, and 30 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane) dihydrochloride solution were added as polymerization initiators, and 15 g of a 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the mixture reached a temperature of 85°C, the mixture was polymerized at 90±2°C for approximately 3 hours to obtain a polymer. The water content of the polymer was approximately 70 wt%.

[0259] (Steps 2 and 3) 0.595 g of the A-1 compound in Table 1 as an additive of Chemical Formula 1 was dispersed in 52.27 g of water (preparation of a 2 wt% aqueous dispersion), which was then mixed with 1,000 g of the polymer obtained in Step 1.

[0260] The mixture was passed once through a first atomizer equipped with a perforated plate containing a large number of holes with a hole size of 6 mm to carry out a primary atomization process.

[0261] Next, the mixture was repeatedly introduced into a second atomizer equipped with a perforated plate having a number of holes with a hole size of 4 mm three times to carry out the second, third and fourth atomization processes.

[0262] In the secondary atomization step, 400 g of a 32% NaOH aqueous solution was introduced through a neutralizer nozzle disposed adjacent to the perforated plate to carry out atomization and neutralization.

[0263] In the tertiary atomization step, 37.5 g of a 15% aqueous solution of Na2SO4 was added through a neutralizer nozzle disposed adjacent to the perforated plate, and atomization and neutralization steps were carried out.

[0264] Finally, in the fourth atomization step, 0.595 g of the A-11 compound in Table 1 was dispersed in 52.27 g of water (preparing a 2 wt% aqueous dispersion) as the additive of Chemical Formula 1, and then this was added to the second atomization device containing the mixture from the third atomization step to prepare base resin particles. The degree of neutralization of the base resin particles was 70 mol%.

[0265] (Step 4) Then, 1,000 g of the base resin particles were placed in a rotary mixer fluidized dryer rotating at 100 rpm. The internal temperature of the dryer was maintained at 105°C, and drying was carried out for 60 minutes to obtain superabsorbent resin particles.

[0266] The final superabsorbent polymer particles after drying in step 4 had a moisture content of 12 wt%.

[0267] Example 12 A superabsorbent polymer composition was prepared in the same manner as in Example 11, except that the A-1 compound was used as the additive of Chemical Formula 1 in the first micronization step, and the A-2 compound in Table 1 was used instead of the A-11 compound as the additive of Chemical Formula 1 in the fourth micronization step.

[0268] The moisture content of the final superabsorbent polymer particles after drying in step 4 was 10 wt%.

[0269] Example 13 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that compound A-12 in Table 1 was used instead of compound A-1 as the additive of Chemical Formula 1.

[0270] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 14 wt%.

[0271] Example 14 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the A-13 compound in Table 1 was used instead of the A-1 compound as the additive of Chemical Formula 1.

[0272] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 14 wt%.

[0273] Example 15 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that 0.595 g of the A-12 compound used in Example 13 and 0.595 g of the A-13 compound used in Example 14 were mixed together to use a total of 1.19 g of the additive of Chemical Formula 1.

[0274] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 13 wt%.

[0275] Example 16 A superabsorbent polymer composition was prepared in the same manner as in Example 13, except that the amount of A-12 as the additive of Chemical Formula 1 was increased to 2.38 g.

[0276] The moisture content of the final superabsorbent polymer particles after stage 4 drying was 12 wt%.

[0277] Comparative Example 1 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the additive of Chemical Formula 1 was not used.

[0278] Comparative Examples 2 to 6, 8 and 9 A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that the additive of Chemical Formula 1 was replaced with an additive listed in Table 1 below.

[0279] Comparative Example 7 In a 3 L glass vessel equipped with a stirrer and a thermometer, 100 g (1.388 mol) of acrylic acid, 0.16 g of an internal crosslinking agent polyethylene glycol diacrylate (Mn=508), 0.008 g of a photopolymerization initiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 0.12 g of a thermal polymerization initiator sodium persulfate, and 123.5 g of a 32% caustic soda solution were mixed at room temperature to prepare a monomer composition (neutralization degree of acrylic acid: 70 mol%, solid content: 45 wt%).

[0280] Thereafter, the monomer composition was supplied at a rate of 500 to 2000 mL / min onto a conveyor belt having a width of 10 cm and a length of 2 m, which was rotating at a speed of 50 cm / min. Simultaneously with the supply of the monomer composition, a 10 mW / cm 2 The polymerization reaction was allowed to proceed for 60 seconds under irradiation with ultraviolet light having an intensity of 10 ...

[0281] Next, the hydrogel polymer obtained by the polymerization reaction was pulverized using a meat chopper without any additives. At this time, the water content of the hydrous superabsorbent resin particles contained in the final pulverized product was 55 wt%.

[0282] Thereafter, the pulverized material was dried using a convection oven capable of airflow transfer between up and down, with hot air at 185°C flowing from bottom to top for 20 minutes, and then again with hot air flowing from top to bottom for 20 minutes, to produce a superabsorbent resin having a final moisture content of 25 wt% after drying.

[0283] [Table 1A] [Table 1B]

[0284] Test Example The superabsorbent polymer compositions prepared in the above Examples and Comparative Examples were evaluated for particle aggregation characteristics, centrifugation retention capacity (CRC), absorbency under pressure (AUP), water absorption rate, and effective water absorption capacity, respectively, using the following methods. The results are shown in Tables 3 and 4 below. Unless otherwise noted, all of the following property evaluations were carried out in a constant temperature and humidity chamber (23±2°C, 45±10% relative humidity), and the measurement data were averaged from three measurements to prevent measurement errors. In addition, in the following property evaluations, saline or salt water refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0285] (1) Evaluation of particle aggregation characteristics (i) 1,000 g of the unneutralized polymer (water content: 70 wt%) of Step 1 produced in each Example and Comparative Example was prepared. (ii) Next, 0.36 g of the additive of Formula 1 or the corresponding comparative compound was dispersed in 17.54 g of water at 80°C (to prepare a 2.04 wt% aqueous dispersion), which was then mixed with 300 g of the polymer obtained in Step 1.

[0286] The additives in step 2 or the corresponding comparative compounds were mixed in the form of an aqueous solution according to the type and content used in each example and comparative example.

[0287] (iii) 300 g of the mixture was placed in a mincer equipped with a perforated plate having 3 mm Ψ holes and a thickness of 5T and pulverized.

[0288] (iv) The pulverized product was subjected to a macroscopic evaluation of aggregation based on the discharge time, discharge amount, and the evaluation criteria in Table 2 below. The results are shown in Table 3.

[0289] In this case, the discharge time means the time (seconds) it takes for 200 g of ground material to be discharged from the mincer, and the discharge time is shortened as the aggregation is reduced.

[0290] The discharge amount means the ratio (wt%) of the content discharged through the outlet to the 300 g of the mixture introduced after the completion of step (iii). As the agglomeration is reduced, the amount of lumps remaining inside the mill decreases, and the discharge amount increases.

[0291] Photographs illustrating the evaluation items of ○ and X in the macroscopic aggregation evaluation are shown in Figure 2(a) and (b), respectively.

[0292] [Table 2]

[0293] [Table 3]

[0294] 2, it was confirmed that when an unneutralized polymer and the additive of Chemical Formula 1 of the present invention were added and milled, aggregation between particles after milling was suppressed compared to when no additive was used or when a compound with a mismatched structure was used, resulting in a shorter discharge time and a superior discharge amount. Furthermore, it was confirmed that the additive of Chemical Formula 1 of the present invention reduced the adhesive and cohesive forces of the mixture added to the mixer, and that more than 80% of the discharged material was discharged in the form of 1 cm particles as evaluated by the naked eye.

[0295] (2)Centrifuge Retention Capacity (CRC) The water retention capacity of each resin composition in terms of water absorption capacity under no load was measured in accordance with the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP241.3.

[0296] Specifically, the superabsorbent polymer compositions obtained in the Examples and Comparative Examples were sieved through a #30-50 sieve to obtain resins. W0 (g) (approximately 0.2 g) of this resin was evenly placed in a nonwoven fabric envelope, sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the envelope was centrifuged at 250 G for 3 minutes to remove water, and the mass of the envelope, W2 (g), was measured. The same procedure was repeated without the resin, and the mass, W1 (g), was then measured.

[0297] Using the obtained masses, the CRC (g / g) was calculated according to the following formula 1, and the results are shown in Table 4.

[0298] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0299] (3) Absorbency under Pressure (AUP) The water absorption capacity of the superabsorbent polymer compositions of the above Examples and Comparative Examples at a pressure of 0.7 psi was measured by EDANA method WSP242.3.

[0300] First, when measuring the water absorption capacity under pressure, the resin-classified powder used in the CRC measurement was used.

[0301] Specifically, a stainless steel wire mesh of 400 mesh was attached to the bottom of a plastic cylinder with an inner diameter of 25 mm. Under conditions of room temperature and 50% humidity, a water-absorbent resin composition W0 (g) (0.16 g) was evenly spread on the wire mesh, and a piston capable of uniformly applying a load of 0.7 psi thereon was slightly smaller than the outer diameter of 25 mm, had no gap with the inner wall of the cylinder, and was designed so that up and down movement was not hindered. At this time, the weight W3 (g) of the device was measured.

[0302] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a 150 mm diameter petroleum dish, and physiological saline containing 0.9 wt% sodium chloride was placed at the same level as the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of the glass filter. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for 1 hour. After 1 hour, the measuring device was lifted and its weight W4 (g) was measured.

[0303] Using the obtained masses, the water absorption capacity under pressure (g / g) was calculated according to the following formula 2. The results are shown in Table 4.

[0304] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0305] (4)Surface tension:S / T To measure the surface tension of the superabsorbent polymer compositions of the Examples and Comparative Examples, 0.5 g of each superabsorbent polymer composition was added to 40 mL of 0.9% saline, stirred at 350 rpm for 3 minutes, and then the stirring was stopped to obtain saline containing swollen superabsorbent polymer. The surface tension of each superabsorbent polymer composition was measured using a surface tension meter (product name: Force Tensiometer-K100, manufactured by KRUSS) using the saline as a measurement sample, and the results are shown in Table 4.

[0306] (5) Bulk density (BD) 100 g of the superabsorbent polymer composition of each of the Examples and Comparative Examples was poured through the orifice of a standard flowmeter into a 100 ml container, and the superabsorbent polymer composition was scraped off so that it was level, adjusting the volume of the superabsorbent polymer composition to 100 ml. The weight of the superabsorbent polymer composition alone, excluding the container, was then measured. The weight of the superabsorbent polymer composition alone was then divided by 100 ml, which was the volume of the superabsorbent polymer composition, to determine the apparent density, which corresponds to the weight of the superabsorbent polymer composition per unit volume.

[0307] (6) Amount of fine powder generated The amount of fine powder generated from the superabsorbent polymer compositions of the Examples and Comparative Examples was calculated as the ratio of the weight of resin having a particle size of less than 150 μm to the total weight after passing the produced superabsorbent polymer compositions once through a coarse grinder (under the conditions of 2800 rpm, 0.4 mm clearance, and 1 mm mesh). The results are shown in Table 4.

[0308] (7) Water absorption rate (Vortex time) The water absorption rate (vortex time) of the superabsorbent resin compositions of the Examples and Comparative Examples was measured by the following method, and the results are shown in Table 4.

[0309] (i) First, 50 mL of 0.9% saline was poured into a 100 mL flat-bottomed beaker using a 100 mL mass cylinder. (ii) Next, the beaker was placed in the center of a magnetic stirrer, and a magnetic bar (diameter 8 mm, length 30 mm) was placed in the beaker. (iii) Thereafter, the agitator was operated so that the magnetic bar was stirring at 600 rpm, and the lowest part of the vortex generated by the agitation was brought into contact with the magnetic bar. (iv) After confirming that the temperature of the saltwater in the beaker had reached 24.0°C, 2±0.01 g of a superabsorbent polymer composition sample was added while simultaneously starting a stopwatch. The time until the vortex disappeared and the liquid surface became completely horizontal was measured in seconds, and this was taken as the water absorption rate.

[0310] [Table 4]

[0311] TABLE 4 shows that when a superabsorbent polymer composition is prepared by adding an unneutralized polymer and the additive of Formula 1 of the present invention, aggregation between particles after grinding is suppressed compared to when no additive is used, when a compound with a structurally incompatible additive is used, or when the additive is mixed with a neutralized hydrogel polymer. This makes it possible to prepare a composition containing superabsorbent polymer particles of the desired particle size without an additional grinding process after drying, thereby reducing the amount of fine powder. Therefore, it can be seen that the superabsorbent polymer composition of this example has a significantly faster water absorption rate than the comparative example, and exhibits water retention capacity and pressurized water absorption capacity at the same or higher levels, while also exhibiting a high apparent bulk density without a decrease in surface tension.

Claims

1. Superabsorbent resin particles containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent; and A superabsorbent polymer composition comprising one or more additives selected from the compounds represented by the following Chemical Formulas 1-1 to 1-14: 【Chemical 1】 【Chemistry 2】 【Chemistry 3】

2. The additive is contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. The highly water-absorbent resin composition according to claim 1.

3. The highly water-absorbent resin particles further include a surface cross-linked layer formed by additionally cross-linking the cross-linked polymer via a surface cross-linking agent on at least a part of the surface thereof. The highly water-absorbent resin composition according to claim 1.

4. The superabsorbent resin composition comprises: The water absorption rate (vortex time) at 24.0°C measured by the vortex method is 30 seconds or less. The highly water-absorbent resin composition according to claim 1.

5. The superabsorbent resin composition comprises: The centrifuge retention capacity (CRC) according to EDANA WSP241.3 is 39.0 g / g or more; The highly water-absorbent resin composition according to claim 1.

6. The superabsorbent resin composition comprises: The water absorption capacity under pressure (AUP) at 0.7 psi according to EDANA method WSP242.3 is 24.0 g / g or more; The highly water-absorbent resin composition according to claim 1.

7. Step 1: cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group in the presence of an internal cross-linking agent and a polymerization initiator to form a polymer; neutralizing at least a portion of the acidic groups of the polymer (Step 2); Step 3: preparing base resin particles by atomizing the polymer in the presence of one or more additives selected from the compounds represented by the following Formulas 1-1 to 1-14: drying the base resin particles (Step 4); Method for producing a superabsorbent polymer composition: 【Chemistry 4】 【Chemistry 5】 【Chemistry 6】

8. The step of forming the polymer (step 1) is carried out in a batch type reactor. A method for producing the highly water-absorbent polymer composition according to claim 7.

9. Steps 2 and 3 are performed sequentially, simultaneously, or alternately. A method for producing the highly water-absorbent polymer composition according to claim 7.

10. The additive is contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. A method for producing the highly water-absorbent polymer composition according to claim 7.

11. The step of preparing the base resin particles (step 3) is carried out using an atomizer, The atomization device is a body portion including a transfer space into which a mixture of a polymer and an additive is transferred; a screw member rotatably provided in the transfer space to move the mixture; a drive motor for providing a rotational drive force to the screw member; a cutter member provided in the body portion, the cutter member including a perforated plate having a number of holes formed therein, for discharging the mixture to the outside of the body portion while pulverizing the mixture; A method for producing the highly water-absorbent polymer composition according to claim 7.

12. Steps 2 and 3 are performed sequentially, simultaneously, or alternately; Steps 2 and 3 are carried out using an atomizer; The atomization device is a body portion including a transfer space into which a mixture of a polymer and an additive is transferred; a screw member rotatably provided in the transfer space to move the mixture; a drive motor for providing a rotational drive force to the screw member; a cutter member provided in the body portion, the cutter member including a perforated plate having a plurality of holes formed therein, for discharging the mixture to the outside of the body portion while pulverizing the mixture; and a neutralizer injection nozzle provided inside the body portion. A method for producing the highly water-absorbent polymer composition according to claim 7.

13. In the atomization device, a neutralizing agent is injected into the body through the neutralizing agent injection nozzle to neutralize at least a portion of the acidic groups of the polymer having acidic groups in the mixture; A method for producing the highly water-absorbent polymer composition according to claim 12.

14. The hole size formed in the perforated plate is 0.1 mm to 30 mm. A method for producing the highly water-absorbent polymer composition according to claim 11.

15. The step of drying the base resin particles (step 4) is carried out in a moving type. A method for producing the highly water-absorbent polymer composition according to claim 7.

16. The step of drying the base resin particles (step 4) comprises: It is carried out using a moving type dryer such as a horizontal mixer, a rotary kiln, a paddle dryer, or a steam tube dryer. A method for producing the highly water-absorbent polymer composition according to claim 7.

17. The moisture content of the superabsorbent resin particles obtained in the step (step 4) of drying the base resin particles is 10% by weight to 20% by weight. A method for producing the highly water-absorbent polymer composition according to claim 7.

18. The method further includes forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent resin particles prepared in step 4 in the presence of a surface cross-linking agent. A method for producing the highly water-absorbent polymer composition according to claim 7.

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