Superabsorbent polymer composition and method for producing the same

Abstract

The present invention relates to a superabsorbent polymer composition and a method for producing the same. More specifically, the present invention relates to a superabsorbent polymer composition that has improved deodorizing and antiodor properties by using a combination of specific additives, and that, when applied to products such as diapers, effectively suppresses odors generated from urine, etc. and the growth of bacteria that occurs while the product is being worn, and a method for producing the same.

Description

Technical Field

[0001] Cross-reference of related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0039062 filed on March 29, 2022, and Korean Patent Application No. 10-2023-0038011 filed on March 23, 2023, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a superabsorbent resin composition and a method for producing the same. Specifically, by using a combination of specific additives, the deodorizing power and odor prevention power are improved, and when applied to products such as diapers, the odor generated from urine and the growth of bacteria generated during the wearing of the product are effectively suppressed. The present invention relates to a superabsorbent resin composition and a method for producing the same.

Background Art

[0003] A superabsorbent polymer (SAP) is a synthetic polymer material having a function of absorbing about 500 to 1000 times its own weight of water, and is named differently such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material) for each development company. Such superabsorbent resins have begun to be put into practical use as sanitary products, and currently, in addition to sanitary products such as children's paper diapers, they are widely used as soil moisture retainers for gardening, waterstops for civil engineering and construction, seedling sheets, freshness retainers in the food distribution field, and materials for ships.

[0004] Most often, such superabsorbent polymers are widely used in hygiene products such as diapers and sanitary napkins. In these hygiene products, the superabsorbent polymer is typically contained diffused within the pulp. However, in recent years, efforts have continued to provide thinner diapers and other hygiene products, and as part of this, the development of products with reduced pulp content, or even pulpless diapers, is being actively pursued.

[0005] Thus, in sanitary materials where the pulp content is reduced or pulp is not used, a relatively high proportion of superabsorbent polymers (MSRPs) are present, and these MRPs are inevitably incorporated in multiple layers within the sanitary material. For these multi-layered MRPs to more efficiently absorb liquids such as urine, the MRPs must fundamentally exhibit high water absorption performance and absorption rate. In addition, the absorbed liquid must escape under external pressure, and permeability is also necessary to maintain its original shape well even when swollen after absorbing liquid. Therefore, much research has been conducted, including surface crosslinking, to improve the basic water absorption and water retention capacity of MRPs.

[0006] On the other hand, superabsorbent polymers are used in sanitary products such as diapers and sanitary napkins, and in these cases, there is a problem of reduced usability due to the unpleasant odor of absorbed liquids such as human and pet waste. In addition, there is a problem of odor generation due to accelerated bacterial growth as the wear period progresses.

[0007] In this context, the demand for superabsorbent polymers is gradually increasing, not only for their basic properties of water absorption and retention, but also for their ability to suppress unpleasant odors. Therefore, there is currently a need to manufacture superabsorbent polymers that can effectively deodorize and inhibit bacterial growth. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention provides a superabsorbent polymer composition and a method for producing the same. More specifically, the present invention provides a superabsorbent polymer composition and a method for producing the same that improve deodorizing and odor-preventing properties by using a combination of specific additives, thereby effectively suppressing odors such as urine and bacterial growth when applied to products such as diapers. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides the following superabsorbent polymer compositions: A superabsorbent resin comprising a base resin containing a crosslinked polymer formed by crosslinking an acrylic acid monomer having at least a portion of neutralized acidic groups with an internal crosslinking agent, and a surface crosslinked layer formed on the surface of the base resin, wherein the crosslinked polymer is further crosslinked via a surface crosslinking agent; Aminoacetate-based chelating agents; and Contains cysteine; The aminoacetate-based chelating agent and cysteine ​​are each independently contained within the surface crosslinked layer or on the surface crosslinked layer.

[0010] Furthermore, the present invention provides a method for producing the following superabsorbent polymer composition: Step 1: Crosslinking an acrylic acid monomer having at least a portion of its acidic groups neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrated gel polymer; Step 2: A step in which a base resin is produced containing a crosslinked polymer obtained by drying and grinding the aforementioned water-containing gel polymer; Step 3: Mixing the surface crosslinking composition with the base resin to produce a mixture; and Step 4 includes the step of heat-treating the mixture to produce a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin, The aminoacetate chelating agent and cysteine ​​are each mixed independently in steps 2 to 4 and at least one of the steps before or after them. [Effects of the Invention]

[0011] As described above, the present invention is characterized by providing a superabsorbent polymer composition and a method for producing it that have excellent deodorizing power and suppress the growth of bacteria, thereby suppressing the generation of additional malodors, by using a specific additive in combination with the superabsorbent polymer. [Modes for carrying out the invention]

[0012] The terms used herein are for illustrative purposes only and are not intended to limit the invention.

[0013] A singular expression includes plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes,” “equip,” or “possess” are intended to specify the existence of a feature, stage, component, or combination thereof, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, stages, components, or combinations thereof.

[0014] Terms such as "first," "second," and "third" are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from others.

[0015] As used herein, the terms "polymer" or "polymer" refer to a polymer formed by the polymerization of water-soluble ethylene-based unsaturated monomers, and can encompass all water content ranges or particle size ranges. Among these polymers, those with a water content (moisture content) of approximately 40% by weight or more in their state before drying after polymerization can be called water-containing gel polymers, and particles of such water-containing gel polymers that have been crushed and dried can be called crosslinked polymers.

[0016] Furthermore, the terms "base resin" or "base resin powder" refer to a polymer obtained by drying and pulverizing a polymer formed by polymerizing acrylic acid monomers, and which has not undergone the surface modification or surface crosslinking steps described later.

[0017] Furthermore, the term "superabsorbent resin" or "superabsorbent resin powder" means, depending on the context, a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer (acrylic acid monomer) containing an acidic group and at least a part of which acidic group is neutralized, or a powder (powder) - shaped base resin composed of superabsorbent resin particles obtained by pulverizing the crosslinked polymer, or all products that have been made suitable for commercialization through additional processes such as surface crosslinking, micropowder regranulation, drying, pulverization, classification, etc. with respect to the crosslinked polymer or the base resin are used as including all of them.

[0018] Although the present invention can be modified in various ways and can have various forms, specific embodiments will be exemplified and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and it should be understood that it includes all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0019] Hereinafter, the manufacturing method of the superabsorbent resin and the superabsorbent resin will be described in more detail according to specific embodiments of the invention.

[0020] (Superabsorbent Resin Composition) According to an embodiment of the present invention, a superabsorbent resin composition is provided.

[0021] The superabsorbent resin composition includes a base resin containing a crosslinked polymer obtained by crosslinking and polymerizing an acrylic acid monomer having an acidic group at least partially neutralized with an internal crosslinking agent, and a surface crosslinking layer formed on the surface of the base resin, in which the crosslinked polymer is additionally crosslinked via a surface crosslinking agent; an aminoacetate - based chelating agent; and cysteine; and the aminoacetate - based chelating agent and cysteine are each independently included inside or on the surface of the surface crosslinking layer.

[0022] Superabsorbent polymers are widely used in hygiene products such as diapers and sanitary napkins, but in actual use, the unpleasant odor from human and pet waste can reduce the user experience. Furthermore, as time passes, the absorbed liquids in the product can accelerate bacterial growth, leading to additional unpleasant odors.

[0023] Traditionally, when using deodorizing substances in products to reduce unpleasant odors, it was necessary to use them excessively to achieve the desired level of deodorizing power. This resulted in a significant decrease in water absorption properties and an increase in product costs.

[0024] Therefore, the inventors have discovered that by using a combination of specific additives, it is possible to effectively control malodorous odors caused by various factors without reducing the basic physical properties of superabsorbent polymers, namely their water absorption and water retention capabilities, and thus have completed the present invention.

[0025] Specifically, according to the present invention, when the product is applied, it is possible to effectively control both primary malodors caused by odor-generating substances contained in bodily fluids, urine, etc., and secondary malodors caused by bacterial growth. Furthermore, by using the combination of the two additives, it is possible to achieve excellent deodorizing and odor-preventing power with relatively small amounts, making it economical, and is particularly preferable because it does not reduce water absorption properties.

[0026] The aminoacetate-based chelating agent is an ingredient that can effectively suppress the growth of bacteria such as E. coli that are generated by odor-causing substances. As the product is worn for an extended period, the growth of bacteria accelerates due to odor-causing substances remaining in the product, resulting in additional odors. However, the aminoacetate-based chelating agent can effectively reduce the generation of additional odors by suppressing the growth of such bacteria.

[0027] In particular, aminoacetate chelating agents are divalent cations that form salt crosslinks between cell membrane components, and can effectively suppress bacterial growth by disrupting the bacterial cell membrane.

[0028] The aminoacetate chelating agent may include, for example, one or more selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), L-glutamic acid diacetic acid (GLDA), methylglycine diacetic acid (MGDA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethanol diglycinate (EDG), diethylenetriaminepentaacetic acid (DTPA), and salts thereof.

[0029] The aminoacetate-based chelating agent is included in an amount of 0.01 to 3 parts by weight per 100 parts by weight of the base resin, preferably in an amount of 0.025 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 2.5 parts by weight or less, 2.0 parts by weight or less, 1.5 parts by weight or less, or 0.01 to 2.5 parts by weight, 0.01 to 2.0 parts by weight, 0.025 to 3.0 parts by weight, 0.025 to 2.5 parts by weight, 0.05 to 2.5 parts by weight, 0.05 to 2.0 parts by weight, 0.1 to 2.5 parts by weight, or 0.1 to 2.0 parts by weight.

[0030] When used within the aforementioned content range, the chelating agent can effectively suppress bacteria without reducing the water-absorbing properties, significantly improving the deodorizing and odor-preventing capabilities of the superabsorbent resin. The chelating agent can be used in the form of a salt mixed with an aqueous solution; therefore, the aforementioned content range is based on the solid content. On the other hand, if the chelating agent is included in small amounts, the desired level of bacterial suppression may not be achieved, and if it is included in excess, the inherent properties of the superabsorbent resin may decrease.

[0031] The aforementioned cysteine ​​can reduce odors by chemically reacting with odor-causing substances. Odor-causing substances generally have small molecular weights, and reacting with cysteine ​​can reduce or eliminate the odor, effectively suppressing it. In particular, cysteine ​​is effective in reducing the odors generated by aldehydes and ketone compounds. On the other hand, when using similar amino acids such as methionine, some deodorizing effect can be observed, but the main functional groups are different, and even when the same amount is applied to SAP, the water absorption properties and deodorizing effect may be significantly lower compared to cysteine.

[0032] The cysteine ​​is present in an amount of 0.01 to 3 parts by weight per 100 parts by weight of the base resin, preferably 0.025 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 2.5 parts by weight or less, 2.0 parts by weight or less, 1.5 parts by weight or less, or 0.01 to 2.5 parts by weight, 0.01 to 2.0 parts by weight, 0.025 to 3.0 parts by weight, 0.025 to 2.5 parts by weight, 0.05 to 2.5 parts by weight, 0.05 to 2.0 parts by weight, 0.1 to 2.5 parts by weight, or 0.1 to 2.0 parts by weight.

[0033] When used within the aforementioned content range, the generation of unpleasant odors can be effectively suppressed without reducing the water-absorbing properties, and the deodorizing and odor-preventing capabilities of the superabsorbent resin can be significantly improved. The cysteine ​​can be used in the form of a salt mixed with an aqueous solution, and therefore, the aforementioned content range is based on the solid content. On the other hand, if the cysteine ​​is included in small amounts, the deodorizing properties will not be achieved, and if it is included in excess, the inherent properties of the superabsorbent resin will be reduced, and process problems may occur due to incomplete dissolution.

[0034] The base resin comprises a crosslinked polymer obtained by crosslinking an acrylic acid monomer having at least a portion of neutralized acidic groups with an internal crosslinking agent.

[0035] The acrylic acid monomer may be any monomer commonly used in the production of superabsorbent polymers. Specifically, the acrylic acid monomer may be a compound represented by the following chemical formula 1:

[0036] [Chemical formula 1] R 1 -COOM 1

[0037] In the above chemical formula 1, R 1 This is an alkyl group with 2 to 5 carbon atoms that contains an unsaturated bond. M 1 This is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0038] Preferably, the acrylic acid monomer comprises acrylic acid, methacrylic acid, and one or more selected from the group consisting of monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof.

[0039] The acrylic acid monomer may have an acidic group, and at least a portion of the acidic group may be neutralized. Preferably, the monomer may be partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide.

[0040] At this time, the degree of neutralization of the monomer may be 40-95 mol%, 40-80 mol%, or 45-75 mol%. The range of the degree of neutralization varies depending on the final physical properties, but if the degree of neutralization is excessively high, the neutralized monomer will precipitate, making polymerization difficult. Conversely, if the degree of neutralization is excessively low, not only will the water absorption capacity of the polymer decrease significantly, but it may also exhibit properties similar to elastic rubber, making it difficult to handle.

[0041] The term "internal crosslinking agent" is used to distinguish it from the "surface crosslinking agent" used to crosslink the surface of the base resin, and plays the role of crosslinking and polymerizing the unsaturated bonds of the acrylic monomers described above. Crosslinking in the above stage is performed without distinction between surface and internal crosslinking, but as a result of the surface crosslinking process of the base resin described later, the particle surface of the final superabsorbent polymer consists of a structure crosslinked by the surface crosslinking agent, and the interior consists of a structure crosslinked by the internal crosslinking agent.

[0042] Any compound can be used as the internal crosslinking agent, as long as it enables the introduction of crosslinking bonds during the polymerization of the acrylic acid monomer. As a non-limiting example, the internal crosslinking agent may be a polyfunctional crosslinking agent such as N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triallylamine, allyl(meth)acrylate, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate, used alone or in combination of two or more.

[0043] Such internal crosslinking agents are added to the monomer composition at a concentration of 0.001 to 1% by weight, 0.01 to 0.8% by weight, or 0.1 to 0.7% by weight. In other words, if the concentration of the internal crosslinking agent is excessively low, the water absorption rate of the resin will decrease, and the gel strength may weaken, which is undesirable. Conversely, if the concentration of the internal crosslinking agent is excessively high, the water absorption capacity of the resin will decrease, making it undesirable as a water absorbent.

[0044] In addition, the base resin may contain, as necessary, additives such as thickeners, plasticizers, preservatives, and antioxidants.

[0045] The superabsorbent resin is formed on the surface of the base resin and includes a surface crosslinked layer in which the crosslinked polymer is further crosslinked via a surface crosslinking agent.

[0046] Here, the aminoacetate chelating agent and cysteine ​​are each independently contained within the surface crosslinked layer or on the surface crosslinked layer. This can mean that the aminoacetate chelating agent and cysteine ​​are each independently added after polymerization of the base resin (=before the surface crosslinking step), during the surface crosslinking step, or after the surface crosslinking step, and this will be explained in more detail later in the method for producing the superabsorbent polymer composition.

[0047] The aforementioned surface crosslinked layer is formed by further crosslinking of a crosslinked polymer via a surface crosslinking agent. In this case, the surface crosslinking agent can be any compound that is reactable with the functional groups of the polymer and is commonly used as a surface crosslinking agent for surface crosslinking of superabsorbent resins; there are no special limitations.

[0048] Preferably, in order to improve the properties of the superabsorbent resin produced, one or more of the following can be used as the surface crosslinking agent: polyhydric alcohol compounds; epoxy compounds; polyamine compounds; halo-epoxy compounds; condensation products of halo-epoxy compounds; oxazoline compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyhydric metal salts; and alkylene carbonate compounds.

[0049] Specifically, examples of polyhydric alcohol compounds include one or more selected from the group consisting of mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol.

[0050] Furthermore, as epoxy compounds, ethylene glycol diglycidyl ether and glycidol can be used, and as polyamine compounds, one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamide polyamine can be used.

[0051] Furthermore, as the halo-epoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin can be used. On the other hand, as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone can be used.

[0052] Furthermore, ethylene carbonate and the like can be used as the alkylene carbonate compound. These can be used individually or in combination. On the other hand, in order to improve the efficiency of the surface crosslinking process, one or more polyhydric alcohol compounds having 2 to 10 carbon atoms can be included among these surface crosslinking agents.

[0053] The amount of the surface crosslinking agent added can be appropriately selected depending on the type of surface crosslinking agent added and the reaction conditions, but typically about 0.001 to about 5 parts by weight, preferably about 0.01 to about 3 parts by weight, and more preferably about 0.05 to about 2 parts by weight can be used per 100 parts by weight of polymer.

[0054] If the surface crosslinking agent content is excessively low, the surface crosslinking reaction will hardly occur. However, if it exceeds 5 parts by weight per 100 parts by weight of polymer, excessive surface crosslinking may occur, leading to a decrease in water absorption capacity and physical properties.

[0055] On the other hand, the surface crosslinking agent may additionally contain inorganic substances. Such inorganic substances may be one or more selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate. The inorganic substance can be used in powder or liquid form, and in particular, it can be used as alumina powder, silica-alumina powder, titania powder, or a nanosilica solution. Furthermore, the inorganic substance can be used in an amount of about 0.001 to about 1 part by weight per 100 parts by weight of the base resin.

[0056] Furthermore, the surface crosslinking agent may additionally contain a thickening agent. In this way, by additionally crosslinking the surface of the base resin powder in the presence of a thickening agent, the deterioration of physical properties after grinding can be minimized. Specifically, one or more types selected from polysaccharides and hydroxyl-containing polymers can be used as the thickening agent. Examples of polysaccharides include gum-based thickening agents and cellulose-based thickening agents. Specific examples of the gum-based thickeners include xanthan gum, gum arabic, karaya gum, tragacanth gum, ghatti gum, guar gum, locust bean gum, and psyllium seed gum. Specific examples of the cellulosic thickeners include hydroxypropyl methylcellulose, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose, and methylhydroxypropylcellulose. On the other hand, specific examples of the hydroxy-containing polymers include polyethylene glycol and polyvinyl alcohol.

[0057] According to another embodiment of the invention, the superabsorbent polymer composition may further contain one or more additives selected from the group consisting of metal iodide salts, organic acids, and polyphenols, and the deodorizing and odor-preventing properties can be further improved by the addition of these additives.

[0058] The metal iodide salt may be, for example, in a form in which one or more selected from the group consisting of CuI, NaI, and KI are dissolved together with I2 in water. The metal iodide salt can oxidize malodorous substances and impart deodorizing properties.

[0059] The organic acid may be, for example, one or more selected from the group consisting of citric acid, glutamic acid, ascorbic acid, benzoic acid, and erythorbic acid.

[0060] The polyphenol may be, for example, one or more selected from the group consisting of tannins, anthocyanins, flavonols, isoflavones, catechins, polyquercetins, and caffeic acid.

[0061] Each of the additives is contained independently, preferably in amounts of 0.025 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 2.5 parts by weight or less, 2.0 parts by weight or less, 1.5 parts by weight or less, or 0.01 to 2.5 parts by weight, 0.01 to 2.0 parts by weight, 0.025 to 2.5 parts by weight, 0.05 to 2.5 parts by weight, 0.05 to 2.0 parts by weight, 0.1 to 2.5 parts by weight, or 0.1 to 2.0 parts by weight, per 100 parts by weight of the base resin.

[0062] When used within the aforementioned content range, it is preferable because it can achieve a synergistic effect with cysteine.

[0063] On the other hand, if the metal iodide salt is present in excess, there is a problem that the inherent physical properties of the superabsorbent polymer will deteriorate, and the amount of residue supplied as a solution during the process may increase, potentially leading to a decrease in deodorizing power. The metal iodide salt is mixed with the superabsorbent polymer in an aqueous solution with water as the solvent, and is present in the superabsorbent polymer in a state where it is physically incorporated into the polymer after being mixed. The metal iodide salt solution may be a solution with a solid content concentration of 1% or less.

[0064] On the other hand, each of the additives is independently contained within the surface crosslinked layer or on the surface crosslinked layer. This can mean that each of the additives is independently added after polymerization of the base resin (= before the surface crosslinking step), during the surface crosslinking step, or after the surface crosslinking step, and this will be explained in more detail later in the method for producing the superabsorbent polymer composition.

[0065] (Method for producing superabsorbent polymer compositions) According to one embodiment of the present invention, a method for producing a superabsorbent polymer composition is provided.

[0066] The method for producing the aforementioned superabsorbent resin composition is as follows: The process includes the steps of: crosslinking an acrylic acid monomer having at least a portion of neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a water-containing gel polymer (Step 1); producing a base resin containing the crosslinked polymer obtained by drying and grinding the water-containing gel polymer (Step 2); mixing a surface crosslinking composition with the base resin to produce a mixture (Step 3); and heat-treating the mixture to produce a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin (Step 4), wherein the aminoacetate chelating agent and cysteine ​​are each independently mixed in at least one of the steps 2 to 4 and the steps before and after them.

[0067] The method for producing the superabsorbent polymer composition described above, by using a combination of an aminoacetate chelating agent and cysteine, can effectively control malodorous odors caused by various factors without reducing the basic properties of the superabsorbent polymer, namely its water absorption and water retention capacity. The aminoacetate chelating agent and cysteine ​​described above are all equally applicable.

[0068] On the one hand, "mixed in stage A" means that the target mixture is additionally mixed while stage A is being performed, and can mean that it is mixed in one or more separate steps to achieve the desired content ratio at that stage. On the other hand, "mixed before or after stage A" means that the mixture is additionally mixed before stage A is performed or after stage A is completed.

[0069] More specifically, the aminoacetate chelating agent and cysteine ​​are mixed independently in at least one of the steps 2 to 4 and the steps before and after them, which can mean that they are mixed during the surface crosslinking step, before the surface crosslinking step, or after the surface crosslinking step is completed, and are mixed in one or more of these steps. The two additives are contained inside or on the surface of the surface crosslinked layer, thereby having excellent deodorizing power through reaction with odor-generating substances, and can effectively suppress the growth of bacteria and the generation of additional malodors. On the other hand, if the two additives are mixed in the polymerization step, it may be difficult to achieve the desired effect.

[0070] More preferably, the aminoacetate chelating agent is mixed in step 2 or after step 4. More specifically, if the chelating agent is included in the step of producing the base resin from the polymerized water-containing gel polymer (step 2), this may mean that it is mixed with the base resin and then added and mixed in the drying and grinding steps. In this case, the chelating agent is contained within the surface crosslinked layer formed in the surface crosslinking step. Alternatively, if the chelating agent is mixed after the surface crosslinking step (step 4), this may mean that it is mixed together with the superabsorbent resin on which the surface crosslinked layer is formed. In this case, the chelating agent is contained on the surface of the surface crosslinked layer formed in the surface crosslinking step.

[0071] More preferably, the cysteine ​​is mixed after step 4. Specifically, when the cysteine ​​is mixed after the surface crosslinking step (step 4), it means that it is mixed together with the superabsorbent resin on which the surface crosslinked layer is formed. In this case, the chelating agent is contained on the surface of the surface crosslinked layer formed in the surface crosslinking step. When the cysteine ​​is included after the surface crosslinking step (step 4), it may be advantageous in that its presence on the surface of the superabsorbent resin increases the contact area with malodorous substances, thereby improving deodorizing power.

[0072] According to one embodiment of the invention, the method for producing the superabsorbent resin may further include one or more additives selected from the group consisting of metal iodide salts, organic acids, and polyphenols, and the additive components are applicable in the same manner as described above.

[0073] The additive is mixed in at least one of the steps 2 to 4 and the steps before and after them, which can mean that it is mixed during the surface crosslinking step, before the surface crosslinking step, or after the surface crosslinking step is completed, and is mixed in one or more of these steps. This allows the additive to be contained inside or on the surface of the surface crosslinking layer, which can more effectively suppress the generation of malodorous odors.

[0074] More preferably, if the additive is included after the surface crosslinking step (step 4), it may mean that it is mixed together with the superabsorbent resin on which the surface crosslinked layer is formed. In this case, the presence of the additive on the surface of the surface crosslinked layer formed in the surface crosslinking step increases the contact area with malodorous odors, which may be advantageous in that the deodorizing power is improved.

[0075] The present invention will be described in detail below, step by step.

[0076] (Stage 1) Step 1 is a step of producing a hydrated gel polymer, and specifically, is a step of crosslinking polymerizing a monomer composition containing an acrylic acid monomer having at least a portion of neutralized acidic groups to form a hydrated gel polymer.

[0077] The acrylic acid monomer may be any monomer commonly used in the production of superabsorbent polymers. Specifically, all of the above-mentioned provisions apply equally to the acrylic acid monomer.

[0078] Furthermore, the monomer composition contains polymerization initiators commonly used in the production of superabsorbent polymers.

[0079] Depending on the polymerization method, thermal polymerization initiators or photopolymerization initiators may be used as the polymerization initiator. However, even with photopolymerization, a certain amount of heat is generated by ultraviolet irradiation, and a certain amount of heat is also generated by the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator may be additionally included.

[0080] As the aforementioned photopolymerization initiator, one or more compounds selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone can be used. Among these, a specific example of acyl phosphine is the commercially available lucirin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide. A wider variety of photopolymerization initiators are disclosed on page 115 of "UV Coatings: Basics, Recent Developments and New Application" by Reinhold Schwalm (Elsevier, 2007), which can be referenced.

[0081] As the thermal polymerization initiator, one or more compounds selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, examples of persulfate initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8). Furthermore, azo-based initiators include 2,2-azobis(2-amidinopropane)dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, and 4,4-azobis-(4-cyanovaleric acid). Examples include acids. A wider variety of thermal polymerization initiators are disclosed on page 203 of Odian's "Principle of Polymerization (Wiley, 1981)," which can be consulted.

[0082] Such polymerization initiators are added to the monomer composition at a concentration of 0.001 to 1% by weight, or 0.005 to 0.1% by weight. In other words, if the concentration of the polymerization initiator is excessively low, the polymerization rate will slow down, and a large amount of residual monomer may be extracted into the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is excessively high, the polymer chains forming the network will become shorter, increasing the content of water-soluble components, and the physical properties of the resin may deteriorate, such as a decrease in pressurized water absorption capacity, which is also undesirable.

[0083] On the other hand, polymerization of the monomer composition is carried out in the presence of an internal crosslinking agent in order to improve the physical properties of the resin obtained by polymerization of the acrylic acid monomer. The internal crosslinking agent can be the same as described above.

[0084] Furthermore, the crosslinking polymerization of the monomer composition is carried out in the presence of a blowing agent, depending on the need and degree of improvement in the water absorption rate. Such a blowing agent decomposes during the crosslinking polymerization reaction to generate gas, which can form pores within the water-containing gel polymer. As a result, when such a blowing agent is used in addition, a more developed porous structure is formed in the superabsorbent resin, further improving the water absorption rate of the superabsorbent resin.

[0085] As non-limiting examples, the foaming agents include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, magnesium carbonate, azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), p,p'-oxybis(benzenesulfonyl hydrazide) (OBSH), p-toluenesulfonyl hydrazide (TSH), and sucrose stearate. It may contain one or more compounds selected from the group consisting of stearate, sucrose palmitate, and sucrose laurate.

[0086] The foaming agent can be present in the monomer composition in an amount of 1,000 to 4,000 ppmw, more specifically, in an amount of 1,000 ppm or more, or 1,100 ppmw or more, or 1,200 ppmw or more; and 4,000 ppmw or less, or 3,500 ppmw or less, or 3,000 ppmw or less.

[0087] In addition, the monomer composition may further contain additives such as thickeners, plasticizers, preservatives, and antioxidants, as needed.

[0088] Such monomer compositions are prepared in the form of solutions in which the aforementioned acrylic acid monomers, polymerization initiators, internal crosslinking agents, and blowing agents are dissolved in a solvent.

[0089] At this time, any solvent that can dissolve the aforementioned raw materials can be used without any limitations on its composition. For example, the solvent can be water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof.

[0090] The formation of the hydrated gel polymer by polymerization of the monomer composition is carried out by a conventional polymerization method, and the process is not particularly limited.

[0091] As a non-restrictive example, the polymerization method can be broadly divided into thermal polymerization and photopolymerization depending on the type of polymerization energy source. Thermal polymerization is carried out in a reactor with a stirring shaft such as a kneader, while photopolymerization is carried out in a reactor equipped with a movable conveyor belt.

[0092] As an example, a hydrated gel polymer can be obtained by introducing the monomer composition into a reactor such as a kneader equipped with a stirring shaft, and then thermal polymerization by supplying hot air or heating the reactor. At this time, depending on the configuration of the stirring shaft equipped in the reactor, the hydrated gel polymer discharged from the reactor outlet will be obtained as particles ranging from several millimeters to several centimeters in size. Specifically, the obtained hydrated gel polymer can be obtained in various forms depending on the concentration and injection rate of the monomer composition injected, but typically, a hydrated gel polymer with a (weight average) particle size of 2 to 50 mm is obtained.

[0093] As another example, when photopolymerization of the monomer composition is carried out in a reactor equipped with a movable conveyor belt, a sheet-like hydrated gel polymer is obtained. In this case, the thickness of the sheet varies depending on the concentration and injection rate of the monomer composition being injected, but it is usually preferably adjusted to a thickness of 0.5 to 10 cm in order to ensure uniform polymerization throughout the sheet while also securing the production rate.

[0094] The water-containing gel polymer formed by this method can exhibit a water content of 40-80% by weight. Here, the water content is the weight of water in relation to the total weight of the water-containing gel polymer, and may also be the value obtained by subtracting the weight of the dry polymer from the weight of the water-containing gel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to water evaporation in the polymer during the drying process in which the polymer temperature is raised by infrared heating. At this time, the drying conditions are set to raise the temperature from room temperature to approximately 180°C and then maintain it at 180°C, with a total drying time of 20 minutes, including a 5-minute temperature rise stage.

[0095] (Stage 2) Step 2 of the present invention is the step of drying and pulverizing the water-containing gel polymer produced in Step 1 to produce a base resin.

[0096] Specifically, in the aforementioned stage, it is possible not only to increase the drying efficiency of the water-containing gel polymer but also to influence the morphology of the superabsorbent polymer, thereby affecting various physical properties of the superabsorbent polymer, including the water absorption rate. In particular, in order to improve the water absorption rate of the superabsorbent polymer, the present invention may further include a step of coarse grinding the water-containing gel polymer before drying. Hereinafter, in order to distinguish it from grinding after drying, the term "coarse grinding" will be used in this specification for convenience to refer to grinding before drying.

[0097] The pulverizer used for the aforementioned pulverization is not limited in its configuration, but may include, specifically, any one selected from the group of pulverizing equipment consisting of a vertical pulverizer, turbo cutter, turbo grinder, rotary cutter mill, cutter mill, disc mill, shred crusher, crusher, chopper, and disc cutter, but is not limited to the examples given above.

[0098] At this stage, the coarse grinding step can be performed to grind the water-containing gel polymer to a particle size of approximately 2 mm to 10 mm. Grinding to a particle size of less than 2 mm is technically difficult due to the high water content of the water-containing gel polymer, and the grinding particles may also aggregate with each other. On the other hand, grinding to a particle size of more than 10 mm may only slightly increase the efficiency of the subsequent drying step.

[0099] The drying is carried out at temperatures of 120-250°C, 140-200°C, or 150-190°C. In this case, the drying temperature is defined as the temperature of the heat transfer medium supplied for drying, or the temperature inside the drying reactor containing the heat transfer medium and polymer during the drying process. If the drying temperature is low and the drying time is long, the process efficiency decreases, so to prevent this, it is preferable that the drying temperature be 120°C or higher. Also, if the drying temperature is excessively high, the surface of the water-containing gel polymer may dry excessively, leading to the generation of a large amount of fine powder in the subsequent grinding stage and potentially degrading the physical properties of the final resin, so to prevent this, it is preferable that the drying temperature be 250°C or lower.

[0100] At this time, the drying time in the drying stage is not particularly limited, but it can be adjusted to 20 to 90 minutes at the drying temperature, taking into consideration process efficiency and the physical properties of the resin.

[0101] The drying is carried out using a conventional medium, for example, by supplying hot air to the pulverized water-containing gel polymer, irradiating it with infrared light, irradiating it with ultra-high frequency light, or irradiating it with ultraviolet light.

[0102] Furthermore, it is preferable that such drying is carried out so that the dried polymer has a water content of 0.1 to 10% by weight. In other words, if the water content of the dried polymer is less than 0.1% by weight, it is undesirable because excessive drying can increase manufacturing costs and degradation of the crosslinked polymer may occur. Also, if the water content of the dried polymer exceeds 10% by weight, it is undesirable because defects may occur in subsequent processes.

[0103] Next, the dried water-containing gel polymer can be pulverized. This is a step to optimize the surface area of ​​the base resin and the superabsorbent polymer. The pulverization is carried out so that the particle size of the pulverized polymer is 150 to 850 μm.

[0104] At this time, standard grinders such as pin mills, hammer mills, screw mills, roll mills, disc mills, and jog mills can be used.

[0105] Furthermore, in order to control the physical properties of the superabsorbent polymer that will be commercialized as a final product, a step can be performed to selectively classify the polymer particles obtained in the grinding step that have a particle size of 150 to 850 μm.

[0106] A base resin can be obtained through the above classification steps. Such a base resin may have a particle size of 150 to 850 μm and may contain 2% or less by weight of fine powder with a particle size of less than 150 μm, or 1% or less by weight.

[0107] On the other hand, as described above, the aminoacetate-based chelating agent is included in the step (step 2) of producing the base resin from the polymerized water-containing gel polymer. In this case, it is advantageous in that it prevents the base resin from clumping, suppresses a decrease in physical properties, and allows for a more uniform distribution of the chelating agent. On the other hand, the method of mixing the aminoacetate-based chelating agent is not particularly limited and may be mixed by simple mixing or by spraying in an aqueous solution.

[0108] (Stages 3 and 4) Step 3 of the present invention is the step of mixing a surface crosslinking composition with the base resin produced in Step 2, and Step 4 is the step of heat-treating the mixture to produce a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin.

[0109] The surface crosslinking composition used in step 3 includes a surface crosslinking agent, and the surface crosslinking agent can be any compound that is reactable with the functional groups of the polymer as a surface crosslinking agent commonly used for surface crosslinking of superabsorbent resins, and there are no special restrictions.

[0110] Preferably, in order to improve the properties of the superabsorbent resin produced, one or more of the following can be used as the surface crosslinking agent: polyhydric alcohol compounds; epoxy compounds; polyamine compounds; halo-epoxy compounds; condensation products of halo-epoxy compounds; oxazoline compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyhydric metal salts; and alkylene carbonate compounds.

[0111] Specifically, examples of polyhydric alcohol compounds include one or more selected from the group consisting of mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol.

[0112] Furthermore, as epoxy compounds, ethylene glycol diglycidyl ether and glycidol can be used, and as polyamine compounds, one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamide polyamine can be used.

[0113] Furthermore, as the halo-epoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin can be used. On the other hand, as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone can be used.

[0114] Furthermore, ethylene carbonate and the like can be used as the alkylene carbonate compound. These can be used individually or in combination. On the other hand, in order to improve the efficiency of the surface crosslinking process, one or more polyhydric alcohol compounds having 2 to 10 carbon atoms can be included among these surface crosslinking agents.

[0115] The amount of the surface crosslinking agent added can be appropriately selected depending on the type of surface crosslinking agent added and the reaction conditions, but typically about 0.001 to about 5 parts by weight, preferably about 0.01 to about 3 parts by weight, and more preferably about 0.05 to about 2 parts by weight can be used per 100 parts by weight of polymer.

[0116] If the surface crosslinking agent content is excessively low, the surface crosslinking reaction will hardly occur. However, if the content exceeds 5 parts by weight per 100 parts by weight of polymer, excessive surface crosslinking may occur, leading to a decrease in water absorption capacity and physical properties.

[0117] On the other hand, the surface crosslinking composition may be further modified by adding an inorganic substance to form a surface crosslinking layer. As such an inorganic substance, one or more substances selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate can be used. The inorganic substance can be used in powder or liquid form, and in particular, it can be used as alumina powder, silica-alumina powder, titania powder, or a nanosilica solution. Furthermore, the inorganic substance can be used in an amount of about 0.001 to about 1 part by weight per 100 parts by weight of the base resin.

[0118] Furthermore, the surface crosslinking composition may additionally contain a thickening agent. By additionally crosslinking the surface of the base resin powder in the presence of a thickening agent, the deterioration of physical properties after grinding can be minimized. Specifically, one or more types selected from polysaccharides and hydroxyl-containing polymers can be used as the thickening agent. Examples of polysaccharides include gum-based thickening agents and cellulose-based thickening agents. Specific examples of the gum-based thickeners include xanthan gum, gum arabic, karaya gum, tragacanth gum, ghatti gum, guar gum, locust bean gum, and psyllium seed gum. Specific examples of the cellulosic thickeners include hydroxypropyl methylcellulose, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose, and methylhydroxypropylcellulose. On the other hand, specific examples of the hydroxy-containing polymers include polyethylene glycol and polyvinyl alcohol.

[0119] On the other hand, the method of mixing the surface crosslinking composition with the base resin is not particularly limited as long as it is a method that can uniformly mix them with the base resin, and can be appropriately adopted and used.

[0120] For example, methods such as mixing the surface crosslinking composition with the base resin in a reaction vessel, spraying the surface crosslinking composition onto the base resin, or continuously supplying the base resin and surface crosslinking composition to a continuously operating mixer for mixing can be used.

[0121] In this case, the surface crosslinking composition may be a solution, and when the solid content in the solution is 1% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or more, or 50% by weight or less, 30% by weight or less, or 20% by weight or less, it is suitable for uniform dispersion in the base resin and can simultaneously prevent the base resin from clumping.

[0122] Next, step 4 is a step in which the mixture is heat-treated to produce a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin. Specifically, this step involves heat-treating the base resin and the surface crosslinking composition to form an interpenetrating polymer network on the surface of the crosslinking polymer contained in the base resin, thereby further improving the physical properties of the superabsorbent resin. Through this surface modification, a surface crosslinking layer is formed on the surface of the crushed base resin particles.

[0123] The formation of the surface crosslinking layer is carried out by a conventional method that increases the crosslinking bond density on the surface of polymer particles, for example, by mixing a surface crosslinking agent composition solution containing a surface crosslinking agent with the pulverized polymer and then heat-treating it to cause a crosslinking reaction.

[0124] Step 4 is carried out at a temperature of approximately 80°C to approximately 250°C. More specifically, the surface crosslinking step is carried out at a temperature of approximately 100°C to approximately 220°C, or approximately 110°C to approximately 200°C, or approximately 120°C to approximately 190°C, for approximately 10 minutes to approximately 2 hours, or approximately 20 minutes to approximately 60 minutes. If the crosslinking reaction temperature is below 160°C or the reaction time is excessively short, the surface crosslinking reaction may not occur properly, resulting in low permeability. If the temperature is above 200°C or the reaction time is excessively long, a problem of reduced water retention capacity may occur.

[0125] The means for raising the temperature for the surface crosslinking reaction are not particularly limited. Heating can be performed by supplying a heat transfer medium or by directly supplying a heat source. In this case, the types of heat transfer mediums that can be used include heated fluids such as steam, hot air, and hot oil, but the present invention is not limited to these, and the temperature of the supplied heat transfer medium can be appropriately selected considering the type of heat transfer medium, the heating rate, and the target temperature. On the other hand, examples of directly supplied heat sources include heating by electricity and heating by gas, but the present invention is not limited to the examples described above.

[0126] On the other hand, as mentioned above, the aminoacetate chelating agent is mixed after the step (step 4) in which the mixture is heat-treated to produce a superabsorbent resin in which a surface crosslinked layer is formed on the surface of the base resin. In this case, it is advantageous in that the possibility of residue generation during process processing after surface crosslinking of cysteine, etc., can be further reduced. On the other hand, the method of mixing the aminoacetate chelating agent is not particularly limited and can be mixed by simple mixing or by spraying in an aqueous solution.

[0127] Furthermore, as described above, cysteine ​​is advantageous in that it is mixed after the step (step 4) in which the mixture is heat-treated to produce a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin, thereby improving deodorizing power by being present on the surface of the superabsorbent resin and increasing the contact area with malodorous odors. On the other hand, the method of mixing cysteine ​​is not particularly limited and can be done by spraying it in an aqueous solution or by dry mixing.

[0128] Furthermore, as described above, one or more additives selected from the group consisting of metal iodide salts, organic acids, and polyphenols may be mixed independently after the step (step 4) in which the mixture is heat-treated to produce a superabsorbent resin in which a surface crosslinked layer is formed on the surface of the base resin. In this case, it is advantageous in that the deodorizing power is improved by increasing the contact area with malodorous odors when the additive is present on the surface of the superabsorbent resin. On the other hand, the additive is not particularly limited and can be mixed by spraying in an aqueous solution or by dry mixing.

[0129] In one embodiment of the invention, after the step of producing a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin as described above (step 4), the process may include a step in which an aminoacetate chelating agent, cysteine, a metal iodide salt, an organic acid, and a polyphenol are mixed in aqueous solution form (post-hydration addition step), in which case a drying step is additionally performed. The drying step can be carried out in the same manner as described above.

[0130] The following are preferred embodiments for understanding the invention. However, these embodiments are merely illustrative and do not limit the invention to them.

[0131] Examples and Comparative Examples: Production of Superabsorbent Polymers Example 1 (Step 1) 100 g of acrylic acid, 0.37 g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15 g of sodium persulfate (SPS) as a thermal initiator, 0.008 g of benzoin ether as a UV initiator, 40 g of caustic soda (NaOH), and 127 g of water were mixed to produce a monomer aqueous solution composition with a monomer concentration of 45.8% by weight. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and while maintaining the polymerization atmosphere temperature at 80°C, ultraviolet light was irradiated using a UV irradiation device (irradiation dose: 10 mW / cm²). 2 A hydrated gel polymer was produced by proceeding with UV polymerization for 2 minutes.

[0132] (Step 2) The water-containing gel polymer was transferred to a meat chopper and cut into pieces of 2 mm to 10 mm. At this time, the water content of the cut water-containing gel polymer was 47% by weight. Next, the water-containing gel polymer was dried in a hot air dryer at a temperature of 170°C for 30 minutes, and the dried water-containing gel polymer was pulverized in a pin mill. Next, the polymer with a particle size (average particle size) of 150 μm to 850 μm was classified using a sieve to produce the base resin.

[0133] (Step 3) Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking solution (2.5 parts by weight of water, 0.1 parts by weight of ethylene glycol diglycidyl ether (EX-810), 0.1 parts by weight of aluminum sulfate 18 hydrate (Al-S), and 0.1 parts by weight of silica (Aerosil A200)).

[0134] (Step 4) Next, the mixture was subjected to a surface crosslinking reaction at 140°C for 30 minutes. After the surface treatment was completed, a superabsorbent resin with an average particle size of 150 to 850 μm was obtained using a sieve. In the superabsorbent resin thus obtained, the content of particles with an average particle size of less than 150 μm was less than 2%.

[0135] In step 2, the aminoacetate chelating agent was dissolved in an aqueous solution to the extent of 0.5 parts by weight of EDTA (based on 100 parts by weight of the base resin), and then mixed with the base resin by spraying.

[0136] Furthermore, in step 4, after the surface crosslinking step, L-cysteine ​​was dissolved in an aqueous solution to a concentration of 0.2 parts by weight (based on 100 parts by weight of the base resin) and mixed with the superabsorbent resin by spraying. Subsequently, a drying step was performed to prepare the superabsorbent resin composition.

[0137] Examples 2-17 and Comparative Examples 1-3 In Example 1, a superabsorbent polymer was produced in the same manner as in Example 1, except that the components and content of the additives were changed as shown in Table 1.

[0138] On the other hand, in Examples 9 to 11, additional additives were sprayed onto the surface-crosslinked superabsorbent resin in aqueous solution form (metal iodide solution (1% concentration, CuI), tannin solution, citric acid solution), and an additional drying step was performed.

[0139] [Table 1A] [Table 1B]

[0140] Experimental example The superabsorbent polymer compositions produced in the above examples and comparative examples were measured for each physical property using the following method.

[0141] (1) Evaluation of water absorption properties 1) Centrifuge Retention Capacity (CRC) The water retention capacity of the superabsorbent polymer compositions of the above examples and comparative examples was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP241.3 based on the water absorption ratio under no load.

[0142] Specifically, the superabsorbent polymer compositions obtained in the examples and comparative examples were classified using a #30-50 sieve to obtain resin. Approximately 0.2 g of this resin W0 (g) was uniformly placed in a nonwoven fabric envelope and sealed. The envelope was then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the envelope was drained for 3 minutes under 250 G conditions using a centrifuge, and the mass W2 (g) of the envelope was measured. The same procedure was also performed without the resin, and the mass W1 (g) at that time was measured.

[0143] Using the obtained masses, the CRC (g / g) was calculated using the following formula 1.

[0144] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0145] 2) Absorbency under Pressure (AUP) The water absorption capacity at 0.7 psi of the superabsorbent polymer compositions of the above examples and comparative examples was measured by the EDANA method WSP242.3.

[0146] First, when measuring the pressurized water absorption capacity, the resin-classified powder used for the CRC measurement was used.

[0147] Specifically, a 400-mesh stainless steel wire mesh was attached to the bottom of a 25mm inner diameter plastic cylinder. Under normal temperature and 50% humidity conditions, a superabsorbent polymer W0 (g) was uniformly scattered onto the wire mesh, and a piston capable of uniformly applying a load of 0.7 psi was placed on top of it. The piston was slightly smaller than the 25mm outer diameter, with no gap between it and the inner wall of the cylinder, so that its vertical movement would not be hindered. At this time, the weight W3 (g) of the device was measured.

[0148] 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 solution consisting of 0.9 wt% sodium chloride was poured into it so that it was 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 that. The measuring device was placed on the filter paper and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted and its weight W4 (g) was measured. Using the obtained masses, the pressurized water absorption capacity (g / g) was calculated using the following formula 2.

[0149] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0150] (2) Evaluation of bacterial inhibition rate The bacterial inhibition rate of the superabsorbent polymer compositions of the above examples and comparative examples was evaluated by the following method.

[0151] Specifically, Escherichia coli (ATCC25922) test bacteria were cultured in LB-Broth for 24 hours. The cultured bacteria were then diluted and injected together with artificial urine into 2g samples of a superabsorbent polymer composition. After culturing at 37°C for 24 hours, the bacteria were extracted and the bacterial count was measured (average value of two samples).

[0152] Bacterial inhibition rate (%) = (1 - ((bacterial amount in sample) / (bacterial amount in Reference sample (sample with no deodorizing effect))) × 100 (%)

[0153] The experimental results for the bacterial inhibition rate are shown in Table 2. The values ​​in Table 2 indicate the deodorization efficiency compared to Comparative Example 1, with higher values ​​indicating higher deodorization efficiency.

[0154] (3) Deodorizing power (odor removal rate) Deodorizing power was measured using an adsorption tube measurement method. The deodorizing power was tested using selected malodorous substances: ketones (Diacetyl), sulfur compounds (Dimethyl Trisulfide), and aldehydes (3-Methyl Butanal).

[0155] - Adsorption tube measurement method: 1 g of superabsorbent polymer was placed in a 500 mL glass bottle, and then 25 mL of malodorous substance was injected. After aging for 3 hours in a constant temperature chamber, collection was carried out for 20 minutes. At this time, the temperature of the constant temperature chamber was 35 degrees Celsius, and the N2 flow rate was set to 250 mL / min. The malodorous substance that drifted in was then adsorbed into the connected adsorption tube, and collection was repeated twice for the same sample. The collection results were analyzed by GC and confirmed.

[0156] -Deodorizing power (%) = (Amount of malodor of the Reference sample (sample with no deodorizing power) measured by GC - Amount of malodor of the sample measured by GC) / Amount of malodor of the Reference sample (sample with no deodorizing power) measured by GC × 100 (%)

[0157] The experimental results for the deodorizing power are shown in Table 2. The values ​​in Table 2 indicate the deodorizing efficiency compared to Comparative Example 1, with higher values ​​indicating higher deodorizing efficiency.

[0158] [Table 2]

[0159] As can be seen from the results in Table 2 above, the superabsorbent polymer compositions according to the embodiments of the present invention, when used in combination with an aminoacetate chelating agent and cysteine, exhibit excellent water absorption properties while simultaneously possessing excellent deodorizing and odor-preventing properties, and can be confirmed to effectively suppress the growth of bacteria that occur during wear of the product.

[0160] In comparative examples where only some of the two additives mentioned above were used, it was confirmed that it was difficult to achieve both bacterial inhibition and deodorizing power simultaneously. In particular, when a metal salt of ricinoleate, which is not an aminoacetate chelating agent, was used in combination with cysteine, the deodorizing power was similar to that of the examples, but the bacterial growth inhibition rate was significantly lower.

Claims

1. A superabsorbent resin comprising a base resin containing a crosslinked polymer formed by crosslinking an acrylic acid monomer having at least a portion of neutralized acidic groups with an internal crosslinking agent, and a surface crosslinked layer formed on the surface of the base resin, wherein the crosslinked polymer is further crosslinked via a surface crosslinking agent; Aminoacetate-based chelating agents; and Contains cysteine; The aminoacetate chelating agent and cysteine ​​are each independently contained within the surface crosslinked layer or on the surface crosslinked layer. The aminoacetate-based chelating agent is present in an amount of 0.01 to 3 parts by weight per 100 parts by weight of the base resin. The cysteine ​​is present in an amount of 0.01 to 3 parts by weight per 100 parts by weight of the base resin. Super absorbent resin composition.

2. The aminoacetate chelating agent comprises one or more selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), L-glutamic acid diacetic acid (GLDA), methylglycine diacetic acid (MGDA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethanol diglycinate (EDG), diethylenetriaminepentaacetic acid (DTPA), and salts thereof. The superabsorbent polymer composition according to claim 1.

3. It further comprises one or more additives selected from the group consisting of metal iodide salts, organic acids, and polyphenols. The superabsorbent polymer composition according to claim 1 or 2.

4. Step 1: Crosslinking an acrylic acid monomer having at least a portion of its acidic groups neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrated gel polymer; Step 2: A step of producing a base resin containing a crosslinked polymer obtained by drying and grinding the aforementioned water-containing gel polymer; Step 3: Mixing the surface crosslinking composition with the base resin to produce a mixture; and Step 4: Heat-treating the mixture to produce a superabsorbent resin in which a surface crosslinking layer is formed on the surface of the base resin; The aminoacetate chelating agent and cysteine ​​are each independently mixed in at least one of the steps 2 to 4 and the steps before and after them. The aminoacetate-based chelating agent is present in an amount of 0.01 to 3 parts by weight per 100 parts by weight of the base resin. The cysteine ​​is present in an amount of 0.01 to 3 parts by weight per 100 parts by weight of the base resin. A method for producing a superabsorbent polymer composition.

5. The aminoacetate chelating agent is mixed in step 2 or after step 4. A method for producing the superabsorbent polymer composition according to claim 4.

6. The cysteine ​​is mixed after step 4. A method for producing the superabsorbent polymer composition according to claim 4.

7. The process further includes mixing one or more additives selected from the group consisting of metal iodide salts, organic acids, and polyphenols. A method for producing the superabsorbent polymer composition according to claim 4.

8. Each of the additives is mixed independently in at least one of the steps 2 to 4 and the steps before and after them. A method for producing the superabsorbent polymer composition according to claim 7.

9. Each of the aforementioned additives is mixed independently after step 4. A method for producing the superabsorbent polymer composition according to claim 7.

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