Superabsorbent polymer composition and method for producing the same

Abstract

The superabsorbent resin composition and its production method according to the present invention are characterized by having excellent deodorizing power while minimizing the deterioration of the physical properties of the superabsorbent resin by mixing a diester-based compound with the superabsorbent resin.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2023-0020907 dated February 16, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification.

[0002] The present invention relates to a superabsorbent polymer composition and a method for producing the same. Specifically, the present invention relates to a superabsorbent polymer composition with deodorizing properties and a method for producing the same. [Background technology]

[0003] Superabsorbent polymers (SAPs) are synthetic polymers capable of absorbing water up to 500 to 1,000 times their own weight. Each developing company uses a different name for them, such as SAM (Super Absorbency Material) or AGM (Absorbent Gel Material). These superabsorbent polymers began to be used in sanitary products and are now widely used not only in hygiene products such as children's diapers, but also as soil water retention materials for gardening, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservatives in the food distribution sector, and materials for poultices.

[0004] In most cases, such superabsorbent polymers are widely used in hygiene products such as diapers and sanitary napkins. In these hygiene products, the superabsorbent polymer is generally contained diffused within the pulp. However, recently, efforts have been made to provide thinner diapers and other hygiene products, and as part of this, there has been active development of so-called pulpless diapers, which have a reduced pulp content or even no pulp at all.

[0005] Thus, in sanitary materials where the pulp content is reduced or pulp is not used, a relatively high proportion of superabsorbent polymers are included, and these superabsorbent polymer particles are inevitably present in multiple layers within the sanitary material. In order for these multi-layered superabsorbent polymer particles to absorb liquids such as urine more efficiently, the superabsorbent polymers must fundamentally have high water absorption performance and absorption rate. In addition, the absorbed liquid must not escape even under external pressure, and permeability is also necessary to maintain its original shape well even when swollen after absorbing liquid.

[0006] Therefore, much research is being conducted, including surface crosslinking, to improve the basic water absorption and water retention capabilities of superabsorbent polymers.

[0007] However, superabsorbent polymers can be used in sanitary materials, and in this case, there may be a problem of reduced usability due to the unpleasant odor of absorbed liquids such as human and pet excrement. In particular, it is necessary to suppress the unpleasant odor generated from the absorbed liquids.

[0008] Therefore, existing methods have considered adding organic acids or antibacterial substances as deodorizers to superabsorbent polymers to impart deodorizing properties. However, since the malodors generated from absorbed liquids are not limited to ammonia but originate from a variety of substances, it has been difficult to suppress these odors by using only one substance, such as an organic acid or antibacterial substance.

[0009] Therefore, in addition to the basic properties of superabsorbent polymers, such as water absorption and water retention, there is a growing demand for their ability to suppress unpleasant odors. Consequently, there is a real need to manufacture superabsorbent polymers with superior deodorizing properties. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The object of the present invention is to provide a superabsorbent polymer composition having deodorizing properties and a method for producing the same.

[0011] More specifically, an object of the present invention is to provide a superabsorbent resin composition having excellent deodorizing power while minimizing deterioration of the physical properties of the superabsorbent resin and a method for producing the same.

Means for Solving the Problems

[0012] To solve the above problems, the present invention provides the following superabsorbent resin composition.

[0013] A base resin containing a crosslinked polymer obtained by crosslinking and polymerizing an acrylic acid-based 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, wherein the crosslinked polymer is additionally crosslinked through a surface crosslinking agent; and a diester compound represented by Chemical Formula 1, The diester compound is contained separately from or both in the superabsorbent resin within the surface crosslinking layer of the superabsorbent resin.

[0014]

Chemical Formula

[0015] In Chemical Formula 1, n is an integer of 1 to 10, R is C 1-20 linear or branched alkyl.

[0016] Further, the present invention provides a method for producing the following superabsorbent resin composition.

[0017] Crosslinking and polymerizing an acrylic acid-based monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer (Step 1); Producing a base resin containing a crosslinked polymer obtained by drying and pulverizing the hydrogel polymer (Step 2); Mixing a surface crosslinking agent with the base resin to produce a mixture (Step 3); and Step 4 includes the step of heat-treating the mixture to produce a superabsorbent resin in which a surface crosslinked layer is formed on the surface of the base resin, During the surface crosslinking reaction, a diester compound represented by chemical formula 1 is mixed either after or after the surface crosslinking.

[0018] [ka]

[0019] (In the above chemical formula 1, n is an integer from 1 to 10, R is C 1-20 (It is linear or branched alkyl.) [Effects of the Invention]

[0020] As described above, the present invention is characterized by providing a superabsorbent polymer composition and a method for producing it that have excellent water absorption capacity while possessing excellent deodorizing power by applying a diester compound to the superabsorbent polymer. [Modes for carrying out the invention]

[0021] The terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of implemented features, stages, components, or combinations thereof, and should not be understood to preemptively exclude the existence or possibility of adding one or more other features, stages, components, or combinations thereof.

[0022] The present invention can be modified in various ways and may take many forms; specific embodiments are described in detail below. However, this is not intended to limit the present invention to any particular disclosure, but rather should be understood to include all modifications, homogeneous or substitutes that fall within the spirit and technical scope of the present invention.

[0023] The superabsorbent polymer composition and its manufacturing method will be described in more detail below with reference to specific embodiments of the invention.

[0024] Prior to this, the technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. Furthermore, the singular forms used herein also include plural forms unless the wording explicitly indicates otherwise.

[0025] For reference, in this specification, "superabsorbent polymer" may mean the superabsorbent polymer itself, or it may be used to encompass all polymers that have undergone additional processes, such as surface crosslinking, fine powder regranulation, drying, grinding, classification, etc., to make them suitable for commercialization, depending on the context.

[0026] Furthermore, in the specification of this invention, "base resin" or "base resin powder" refers to a polymer obtained by drying and pulverizing a polymer in which acrylic acid monomers have been polymerized, in the form of particles or powder, and which has not undergone the surface modification or surface crosslinking steps described later.

[0027] (Super absorbent resin composition) According to one embodiment of the present invention, a superabsorbent polymer composition is provided.

[0028] The superabsorbent resin composition comprises 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 superabsorbent resin containing a surface crosslinked layer formed on the surface of the base resin, wherein the crosslinked polymer is further crosslinked via a surface crosslinking agent; and a diester compound. The diester compound is contained in the surface crosslinked layer of the superabsorbent resin, either separately from the superabsorbent resin or in combination with it.

[0029] 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 2.

[0030] [Chemical formula 2] R 1 -COOM 1

[0031] In the aforementioned chemical formula 2, 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.

[0032] 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.

[0033] 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.

[0034] 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 may vary depending on the final physical properties, but if the degree of neutralization is excessively high, the neutralized monomer may 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.

[0035] On the other hand, the polymerization of the acrylic acid monomer is carried out in the presence of a crosslinking agent ("internal crosslinking agent") in order to improve the physical properties of the resin. The crosslinking agent is used to internally crosslink the water-containing gel polymer and can be used separately from the "surface crosslinking agent" described later.

[0036] 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.

[0037] Such internal crosslinking agents can be 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 may 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 may decrease, making it undesirable as a water absorbent.

[0038] In addition, the base resin may further contain additives such as plasticizers, preservatives, and antioxidants, as needed.

[0039] 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 is a surface crosslinking agent commonly used for surface crosslinking of superabsorbent resins, and is not limited to any compound that can react with the functional groups of the polymer.

[0040] 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; haloepoxy compounds; condensation products of haloepoxy compounds; oxazoline compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyhydric metal salts; and alkylene carbonate compounds.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Furthermore, ethylene carbonate and the like can be used as alkylene carbonate compounds. 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.

[0045] The amount of the surface crosslinking agent added can be appropriately selected depending on the specific 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.

[0046] 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.

[0047] On the other hand, the surface crosslinking agent may additionally contain inorganic substances. Such inorganic substances can 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 is particularly useful in the form of alumina powder, silica-alumina powder, titania powder, or nanosilica solution. Furthermore, the inorganic substance can be used in an amount of approximately 0.001 to approximately 1 part by weight per 100 parts by weight of the base resin.

[0048] The superabsorbent polymer composition of one embodiment of the present invention may contain a diester compound as a deodorizing substance. Since the ester and hydrophobic functional groups of the diester compound have an affinity for malodorous substances, when the superabsorbent polymer composition containing the diester compound is applied to a sanitary product, it has the effect of removing the malodorous odor of the liquid absorbed by the sanitary product. The diester compound of one embodiment of the present invention may be represented by the following chemical formula 1.

[0049] [ka]

[0050] In the aforementioned chemical formula 1, n can be an integer from 1 to 10, specifically an integer from 2 to 4.

[0051] R is C 1-20 It can be a linear or branched alkyl group. Specifically, R is C 3-4 It can be a linear or branched alkyl group. For example, R may be isopropyl or isobutyl.

[0052] The aforementioned diester compound may be contained within the surface crosslinked layer of the superabsorbent polymer, either separately from or in combination with the superabsorbent polymer. The presence of the diester compound separately from the superabsorbent polymer could mean that the diester compound is mixed with the superabsorbent polymer in which the surface crosslinked layer is formed, resulting in the diester compound being present on the outer surface of the surface crosslinked layer rather than inside it.

[0053] The diester compound may include one or more selected from the group consisting of diisopropyl adipate, diisobutyl succinate, diisobutyl glutarate, and diisobutyl adipate. Specifically, the diester compound may include one or more selected from the group consisting of diisopropyl adipate, diisobutyl succinate, and diisobutyl adipate.

[0054] The diester compound may be included in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. Specifically, the diester compound may be included in an amount of 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, or 0.4 parts by weight or more to 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, 1.0 part by weight or less, or 0.5 parts by weight or less per 100 parts by weight of the base resin.

[0055] In order to achieve the level of deodorizing ability to be attained in this invention while maintaining the inherent water-absorbing properties of the superabsorbent polymer, it is preferable that the diester compound, which is the deodorizing substance, is included within the aforementioned content range.

[0056] The superabsorbent polymer composition may further contain one or more additives selected from the group consisting of chelating agents, iodine compounds, and organic acids.

[0057] The superabsorbent polymer composition may contain a chelating agent. In the case of a hygiene product containing a superabsorbent polymer composition, bacteria originating from the skin or other sources may come into contact with the absorbed liquid, and the proliferation of these bacteria may generate additional unpleasant odors. A chelating agent can suppress the growth of such bacteria.

[0058] The chelating agent may include an aminoacetate-based chelating agent. Specifically, the aminoacetate-based chelating agent may include 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. More specifically, the chelating agent may be ethylenediaminetetraacetic acid (EDTA).

[0059] In particular, aminoacetate-based chelating agents are ingredients that can effectively suppress the growth of bacteria such as E. coli that are produced by odor-causing substances. As time passes while wearing a product, the growth of bacteria accelerates due to odor-causing substances remaining in the product, resulting in additional odors. However, the aminoacetate-based chelating agents can suppress the growth of such bacteria and effectively reduce the generation of additional odors.

[0060] In particular, aminoacetate chelating agents can effectively suppress bacterial growth by capturing polyvalent metal components necessary for cell membrane growth.

[0061] The chelating agent may be included in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the base resin. Specifically, the chelating agent may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more, or 0.6 parts by weight or more to 2.0 parts by weight or less, 1.5 parts by weight or less, or 1.0 part by weight or less per 100 parts by weight of the base resin.

[0062] When used within the aforementioned content range, the water-absorbing properties, which are an inherent property of the superabsorbent polymer, can be effectively suppressed, thereby significantly improving the deodorizing power of the superabsorbent polymer.

[0063] The chelating agent can be used in the form of a salt mixed in an aqueous solution, and the content range is based on the solid content.

[0064] The superabsorbent polymer composition may contain an iodine-based compound. The iodine-based compound may be a metal iodide salt. The metal iodide salt may be added to the manufacturing process in the form of one or more selected from the group consisting of CuI, NaI, and KI, and I2 dissolved together in water, or in the form of a powder obtained by drying an aqueous solution. Like diester compounds, metal iodide salts can also be added to superabsorbent polymers to impart deodorizing properties. Metal iodide salts remove odors by oxidizing malodorous substances, and are effective against most malodorous substances in a general sense.

[0065] The iodine-based compound may be included in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. Specifically, the chelating agent may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more, or 0.6 parts by weight or more to 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, or 1.0 part by weight or less per 100 parts by weight of the base resin.

[0066] The superabsorbent polymer composition may contain an organic acid. The organic acid may be one or more selected from the group consisting of citric acid, acetic acid, formic acid, fumaric acid, lactic acid, and propionic acid. Specifically, the organic acid may be citric acid. The organic acid can exhibit deodorizing properties in the superabsorbent polymer, similar to diester compounds.

[0067] The organic acid may be included in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. Specifically, the chelating agent may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more, or 0.6 parts by weight or more to 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, or 1.0 part by weight or less per 100 parts by weight of the base resin.

[0068] (Method for producing superabsorbent polymer compositions) According to one embodiment of the present invention, a method for producing a superabsorbent polymer composition is provided.

[0069] 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); crushing the water-containing gel polymer and drying it to produce a base resin containing the crosslinked polymer (Step 2); mixing a surface crosslinking agent with the base resin to produce a mixture (Step 3); and heat-treating the mixture to produce a superabsorbent resin in which a surface crosslinked layer is formed on the surface of the base resin (Step 4). During the surface crosslinking reaction, a diester compound can be mixed either after or after the surface crosslinking.

[0070] The method for producing superabsorbent polymers broadly includes the steps of polymerizing acrylic acid monomers to produce a water-containing gel polymer and pulverizing it. In addition, a method of crosslinking the surface of the produced superabsorbent polymer is used to improve various physical properties of the superabsorbent polymer.

[0071] The present invention provides a superabsorbent resin composition having deodorizing properties by mixing a diester compound with the surface-crosslinked superabsorbent resin.

[0072] On the other hand, "mixed in Step A" in the present invention means that it is additionally mixed into the target mixture during the execution of Step A, and may mean that it is divided and mixed one or more times so as to match the target content ratio at this stage. On the other hand, "mixed before and after Step A" means that it is additionally mixed before Step A is carried out or after Step A is completed.

[0073] Hereinafter, the present invention will be described in detail for each step.

[0074] (Step 1) The above-mentioned Step 1 is a step of producing a hydrogel polymer. Specifically, it is a step of crosslinking and polymerizing a monomer composition containing an acrylic acid-based monomer having an acidic group at least partially neutralized to form a hydrogel polymer.

[0075] The acrylic acid-based monomer can be any monomer usually used in the production of a superabsorbent resin. Specifically, the acrylic acid-based monomer can be a compound represented by the following Chemical Formula 2.

[0076] [Chemical Formula 2] R 1 -COOM 1

[0077] In the above Chemical Formula 2, R 1 is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond, M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt.

[0078] Preferably, the acrylic acid-based monomer contains one or more selected from the group consisting of acrylic acid, methacrylic acid, and their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts.

[0079] 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.

[0080] 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 may vary depending on the final physical properties, but if the degree of neutralization is excessively high, the neutralized monomer may 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.

[0081] The monomer composition may contain polymerization initiators commonly used in the production of superabsorbent polymers.

[0082] As the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator can be used depending on the polymerization method. However, even with a photopolymerization method, 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 added in addition.

[0083] As the aforementioned photopolymerization initiator, for example, one or more compounds selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone can be used. A specific example of acyl phosphine among these is the commercial lucirin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide. A wider variety of photopolymerization initiators are disclosed on page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application" (Elsevier, 2007), which can be consulted.

[0084] As the thermal polymerization initiator, one or more compounds selected from the group of initiators consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, examples of persulfate initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), 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)isobutylonitrile, 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 book "Principle of Polymerization" (Wiley, 1981), which can be consulted.

[0085] Such polymerization initiators can be 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 may 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 become shorter, the content of water-soluble components increases, and the physical properties of the resin may deteriorate, such as a decrease in pressure absorption capacity, which is also undesirable.

[0086] On the other hand, polymerization of the monomer composition is carried out in the presence of a crosslinking agent ("internal crosslinking agent") in order to improve the physical properties of the resin obtained by polymerization of the acrylic acid monomer. The crosslinking agent is used to internally crosslink the water-containing gel polymer and can be used separately from the "surface crosslinking agent" described later.

[0087] Any compound that enables the introduction of crosslinking bonds during the polymerization of the acrylic acid monomer can be used as the internal crosslinking agent. 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.

[0088] Such internal crosslinking agents can be 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 may 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 may decrease, making it undesirable as a water absorbent.

[0089] Furthermore, the crosslinking polymerization of the monomer composition can be 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 can decompose during the crosslinking polymerization reaction to generate gas, thereby forming 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 within the superabsorbent resin, further improving the water absorption rate of the superabsorbent resin.

[0090] As non-restrictive 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.

[0091] 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.

[0092] In addition, the monomer composition may further contain additives such as plasticizers, preservatives, and antioxidants, as needed.

[0093] Such monomer compositions can be prepared in the form of solutions in which the aforementioned acrylic acid monomers, polymerization initiators, internal crosslinking agents, blowing agents, and other raw materials are dissolved in a solvent.

[0094] 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.

[0095] The formation of the hydrated gel polymer through polymerization of the monomer composition can be carried out by conventional polymerization methods, and the process is not particularly limited.

[0096] As a non-restrictive example, the polymerization method can be broadly classified into thermal polymerization and photopolymerization depending on the type of polymerization energy source. Thermal polymerization can be carried out in a reactor with a stirring shaft, such as a kneader, while photopolymerization can be carried out in a reactor equipped with a movable conveyor belt.

[0097] 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. In this case, depending on the configuration of the stirring shaft in the reactor, the hydrated gel polymer discharged from the reactor outlet may be obtained as particles ranging from several millimeters to several centimeters in size. Specifically, the obtained hydrated gel polymer may 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 particle size of 2 to 50 mm (weight average) can be obtained.

[0098] As another example, when photopolymerization of the monomer composition is carried out in a reactor equipped with a movable conveyor belt, a sheet-type hydrated gel polymer can be obtained. In this case, the thickness of the sheet may vary depending on the concentration and injection rate of the monomer composition being injected, but it is generally preferable to adjust the thickness to 0.5 to 10 cm in order to ensure uniform polymerization of the entire sheet while also securing the production rate.

[0099] The hydrated gel polymer formed by this method can exhibit a water content of 40-80% by weight. Here, water content is the weight of water in the total weight of the hydrated gel polymer, and can be the value obtained by subtracting the weight of the dry polymer from the weight of the hydrated gel polymer. Specifically, it can be defined as the value calculated by measuring the weight loss due to water evaporation in the polymer during the drying process, which involves raising the temperature of the polymer through infrared heating. In this case, the drying conditions involve raising the temperature from room temperature to approximately 180°C and then maintaining it at 180°C, and the total drying time can be set to 20 minutes, including a 5-minute temperature rise stage.

[0100] (Stage 2) Step 2 of the present invention is the step of drying, pulverizing, and classifying the water-containing gel polymer produced in Step 1 to form a base resin powder.

[0101] Specifically, this not only increases the drying efficiency of the water-containing gel polymer but also affects the morphology of the superabsorbent polymer, thereby influencing various physical properties of the superabsorbent polymer, including its water absorption rate. In particular, 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.

[0102] 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.

[0103] At this stage, the coarse grinding step can be performed so that the particle size of the water-containing gel polymer is 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 a phenomenon of aggregation between the ground particles may occur. On the other hand, grinding to a particle size exceeding 10 mm may result in only a slight increase in the efficiency of the subsequent drying step.

[0104] The drying can be carried out at temperatures of 120-250°C, 140-200°C, or 150-190°C. In this case, the drying temperature can be 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 will decrease, so it is preferable that the drying temperature be 120°C or higher to prevent this. Also, if the drying temperature is unnecessarily high, the surface of the water-containing gel polymer may be excessively dried, which may lead to the generation of a large amount of fine powder in the subsequent grinding step, and the physical properties of the final resin may deteriorate, so it is preferable that the drying temperature be 250°C or lower to prevent this.

[0105] 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.

[0106] The drying can be carried out using a conventional medium, but can also be done by methods such as supplying hot air to the pulverized water-containing gel polymer, infrared irradiation, ultra-high frequency irradiation, or ultraviolet irradiation.

[0107] Furthermore, it is preferable that such drying is carried out so that the dried polymer has a moisture content of 0.1 to 10% by weight. In other words, if the moisture content of the dried polymer is less than 0.1% by weight, it is undesirable because excessive drying may increase manufacturing costs and cause degradation of the crosslinked polymer. Conversely, if the moisture content of the dried polymer exceeds 10% by weight, it is undesirable because defects may occur in subsequent processes.

[0108] Next, the dried water-containing gel polymer can be pulverized. This is a step to optimize the surface area of ​​the base resin powder and the superabsorbent polymer. The pulverization can be carried out so that the particle size of the pulverized polymer is 150 to 850 μm.

[0109] In this case, the grinders that can be used include standard types such as pin mills, hammer mills, screw mills, roll mills, disc mills, or jog mills.

[0110] Furthermore, in order to control the physical properties of the superabsorbent polymer that will be commercialized as a final product, a step is performed to selectively classify the polymer particles obtained through the grinding step into particles having a particle size of 150 to 850 μm.

[0111] The base resin powder can be obtained through the above classification steps. Such a base resin powder 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.

[0112] Furthermore, the process may further include a step of mixing zirconium phosphate after drying and pulverizing to obtain a base resin powder. In this case, the zirconium phosphate can be mixed in a pre-dry manner. That is, the zirconium phosphate can be mixed into the base resin as a solid component in a dry physical manner before surface crosslinking. Zirconium phosphate is a substance that can physically adsorb malodorous substances. Therefore, by further mixing zirconium phosphate into the base resin powder, an additional deodorizing effect can be obtained.

[0113] In this case, zirconium phosphate may be included in an amount of 5.0 parts by weight or less per 100 parts by weight of the base resin. Zirconium phosphate is for additional deodorizing power and is not required to be included, but if included, it may be included in amounts of 0.5 parts by weight or more, 0.8 parts by weight or more, 1.0 part by weight or more, 1.3 parts by weight or more, 1.5 parts by weight or more, or 1.8 parts by weight or more and 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, or 2.0 parts by weight or less. If the amount of zirconium phosphate is mixed in too little, there is a problem that the deodorizing effect will be minimal, and if it is included in too much, surface crosslinking may not occur properly, and problems such as a decrease in absorption capacity under pressure may occur.

[0114] (Stage 3) Step 3 of the present invention is the step of mixing a surface crosslinking agent with the base resin powder produced in Step 2.

[0115] The surface crosslinking agent used in step 3 includes a surface crosslinking agent, which is a surface crosslinking agent commonly used for surface crosslinking of superabsorbent polymers. It can be any compound that is reactive with the functional groups of the polymer, and there are no special restrictions.

[0116] 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; haloepoxy compounds; condensation products of haloepoxy compounds; oxazoline compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyhydric metal salts; and alkylene carbonate compounds.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] Furthermore, ethylene carbonate and other similar compounds can be used as alkylene carbonate compounds. 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.

[0121] 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.

[0122] 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.

[0123] On the other hand, the surface crosslinking agent may also include an inorganic substance to form a surface crosslinked layer. One or more inorganic substances selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate can be used as such inorganic substances. The inorganic substance can be used in powder or liquid form, and can be used particularly in the form of alumina powder, silica-alumina powder, titania powder, or nanosilica solution. Furthermore, the inorganic substance can be used in an amount of approximately 0.001 to approximately 1 part by weight per 100 parts by weight of the base resin.

[0124] Furthermore, a diester compound can be mixed with a surface crosslinking agent into the base resin. The diester compound can suppress the malodorous odor of the water-absorbing substance and impart deodorizing properties to the superabsorbent resin.

[0125] One embodiment of the diester compound can be represented by the following chemical formula 1.

[0126] [ka]

[0127] In the aforementioned chemical formula 1, n can be an integer from 1 to 10, specifically an integer from 2 to 4.

[0128] R is C 1-20 It can be a linear or branched alkyl group. Specifically, R is C 3-4 It can be a linear or branched alkyl group. For example, R may be isopropyl or isobutyl.

[0129] The diester compound may include one or more selected from the group consisting of diisopropyl adipate, diisobutyl succinate, diisobutyl glutarate, and diisobutyl adipate. Specifically, the diester compound may include one or more selected from the group consisting of diisopropyl adipate, diisobutyl succinate, and diisobutyl adipate.

[0130] The diester compound may be included in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. Specifically, the diester compound may be included in an amount of 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, or 0.4 parts by weight or more to 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, 1.0 part by weight or less, or 0.5 parts by weight or less per 100 parts by weight of the base resin.

[0131] In order to achieve the level of deodorizing ability to be attained in this invention while maintaining the inherent water-absorbing properties of the superabsorbent polymer, it is preferable that the diester compound, which is the deodorizing substance, is included within the aforementioned content range.

[0132] The diester compound can be mixed with the base resin together with the surface crosslinking agent in solution or emulsion form. Alternatively, after adding the surface crosslinking agent, the diester compound in solution or emulsion form can be sprayed and mixed with the base resin. When the diester compound is used in emulsion form, the emulsifier may be a surfactant, particularly a naturally derived surfactant, such as lecithin. In this case, the diester compound may be present within the surface crosslinking layer.

[0133] On the other hand, the method of mixing the surface crosslinking agent with the base resin is not particularly limited and can be appropriately adopted and used as long as it is a method that can uniformly mix them with the base resin.

[0134] For example, methods such as mixing the surface crosslinking agent and the base resin in a reaction vessel, spraying the surface crosslinking agent onto the base resin, or continuously supplying the base resin and surface crosslinking agent to a continuously operating mixer for mixing can be used.

[0135] In this case, the surface crosslinking agent may be an aqueous solution, and if 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 aggregation of the base resin.

[0136] (Stage 4) Step 4 is a step in which the base resin and the surface crosslinking agent are reacted to form an interpenetrating polymer network on the surface of the crosslinked 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 pulverized base resin particles.

[0137] The formation of the surface crosslinking layer can be carried out by conventional methods that increase the crosslinking bond density on the surface of polymer particles. For example, this can be done by mixing a surface crosslinking agent containing a surface crosslinking agent with the pulverized polymer and then heat-treating it to induce a crosslinking reaction.

[0138] Step 4 can be carried out at a temperature of approximately 80°C to approximately 250°C. More specifically, the surface crosslinking step can be 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 exceeds 200°C or the reaction time is excessively long, a problem of reduced water retention capacity may occur.

[0139] The means for raising the temperature for the surface crosslinking reaction are not particularly limited. Heating can be achieved by supplying a heat transfer medium or by directly supplying a heat source. In this case, suitable heat transfer mediums 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 electric heating and gas heating methods, but are not limited to the examples mentioned above.

[0140] Additionally, a diester compound may be mixed with the superabsorbent resin on which the surface crosslinking layer is formed. The type of diester compound, the amount mixed, and the form in which it is mixed are described in step 3. When mixed in this way, the diester compound can exist separately from the superabsorbent resin. In this case, the diester compound is present on the surface of the surface crosslinking layer formed in the surface crosslinking step, which may have the advantage of increasing the contact area with malodorous odors and improving deodorizing power.

[0141] Alternatively, a diester compound can be used together with a surface crosslinking agent to create a surface crosslinked layer, and then the diester compound can be mixed again into the superabsorbent resin after the surface crosslinked layer has been formed. In this case, the compound can be present both within the surface crosslinked layer and separately from the superabsorbent resin.

[0142] Furthermore, one or more additives selected from the group consisting of chelating agents, iodine-based compounds, and organic acids can be further mixed into the superabsorbent resin on which the surface crosslinked layer is formed. Similarly, the presence of the additive on the surface of the surface crosslinked layer formed in the surface crosslinking stage may have the advantage of increasing the contact area with malodorous odors and improving deodorizing power.

[0143] A chelating agent can be mixed with the superabsorbent polymer on which the surface crosslinking layer is formed. In the case of hygiene products containing a superabsorbent polymer composition, bacteria originating from the skin and other sources may come into contact with the absorbed liquid, causing bacterial growth and the generation of additional unpleasant odors. The mixed chelating agent can suppress the growth of such bacteria.

[0144] The chelating agent may include an aminoacetate-based chelating agent. Specifically, the aminoacetate-based chelating agent may include 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. More specifically, the chelating agent may be ethylenediaminetetraacetic acid (EDTA).

[0145] In particular, aminoacetate-based chelating agents are ingredients that can effectively suppress the growth of bacteria such as E. coli that are produced by odor-causing substances. As time passes while wearing a product, the growth of bacteria accelerates due to odor-causing substances remaining in the product, resulting in additional odors. However, the aminoacetate-based chelating agents can effectively reduce the generation of additional odors by suppressing the growth of such bacteria.

[0146] In particular, aminoacetate chelating agents are divalent cations that form salt structures between the components of the cell membrane, and can effectively suppress bacterial growth by disrupting the bacterial cell membrane.

[0147] The chelating agent may be mixed in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the base resin. Specifically, the amount of the chelating agent may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more, or 0.6 parts by weight or more to 2.0 parts by weight or less, 1.5 parts by weight or less, or 1.0 part by weight or less per 100 parts by weight of the base resin.

[0148] When mixed within the aforementioned content range, the water-absorbing properties, which are an inherent property of the superabsorbent polymer, can be effectively suppressed, thereby significantly improving the deodorizing power of the superabsorbent polymer.

[0149] The chelating agent can be used in the form of a salt, mixed in an aqueous solution, and the content range is based on the solid content.

[0150] An iodine-based compound can be mixed with the superabsorbent resin on which the surface crosslinking layer is formed. The iodine-based compound may be a metal iodide salt. The metal iodide salt can be added to the manufacturing process in the form of one or more selected from the group consisting of CuI, NaI, and KI, and I2 dissolved together in water, or in the form of a powder obtained by drying an aqueous solution. Like diester compounds, metal iodide salts can also be added to superabsorbent resins to impart deodorizing properties. Metal iodide salts remove odors by oxidizing malodorous substances, and are effective on most malodorous substances in a general sense.

[0151] The iodine-based compound may be mixed in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. Specifically, the chelating agent may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more, or 0.6 parts by weight or more to 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, or 1.0 part by weight or less per 100 parts by weight of the base resin.

[0152] An organic acid can be mixed with the superabsorbent resin on which the surface crosslinking layer is formed. The organic acid may be one or more selected from the group consisting of citric acid, acetic acid, formic acid, fumaric acid, lactic acid, and propionic acid. Specifically, the organic acid may be citric acid. The organic acid can exhibit deodorizing effects in the superabsorbent resin, similar to diester compounds.

[0153] The organic acid may be mixed in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. Specifically, the chelating agent may be 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more, or 0.6 parts by weight or more to 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, or 1.0 part by weight or less per 100 parts by weight of the base resin.

[0154] When a superabsorbent polymer with a surface cross-linked layer is added with a deodorizing substance and, if necessary, additives in an aqueous solution, an additional drying step can be performed later.

[0155] The following are preferred embodiments for understanding the invention. However, these embodiments are merely illustrative and do not limit the invention to them.

[0156] Comparative Example 1 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0157] The aforementioned water-containing gel polymer was transferred to a meat chopper and cut into pieces ranging from 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 170°C for 30 minutes, and the dried water-containing gel polymer was pulverized in a pin mill. Next, the polymer, ranging in size from 150 μm to 850 μm, was classified using a sieve to produce a base resin.

[0158] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0159] Comparative Example 2 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0160] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0161] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0162] Subsequently, the surface-crosslinked superabsorbent polymer was mixed by chopping (hole size 16 mm) while spraying an EDTA aqueous solution (EDTA concentration 40%). At this time, the EDTA was mixed to 0.6 parts by weight based on 100 parts by weight of the base resin. After that, a drying step was carried out at 80°C for 25 minutes.

[0163] Comparative Example 3 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0164] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0165] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0166] Subsequently, the surface-crosslinked superabsorbent polymer was mixed by chopping (hole size 16 mm) while spraying an EDTA aqueous solution (EDTA concentration 40%) onto it. At this time, the EDTA was mixed to a ratio of 1.0 part by weight to 100 parts by weight of the base resin. After that, a drying step was carried out at 80°C for 25 minutes.

[0167] Comparative Example 4 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0168] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0169] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0170] Subsequently, a cyclodextrin aqueous solution (cyclodextrin concentration 10%) was sprayed onto the surface-crosslinked superabsorbent polymer while chopping (hole size 16 mm) to mix it. At this time, the cyclodextrin was mixed to a ratio of 0.5 parts by weight per 100 parts by weight of the base resin. After that, a drying step was carried out at 80°C for 25 minutes.

[0171] Comparative Example 5 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0172] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0173] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0174] Subsequently, the surface-crosslinked superabsorbent polymer was mixed by chopping (hole size 16 mm) while spraying it with a citric acid aqueous solution (citric acid concentration 20%). At this time, the citric acid was mixed to a ratio of 1.0 part by weight to 100 parts by weight of the base resin. After that, a drying step was carried out at 80°C for 25 minutes.

[0175] Comparative Example 6 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0176] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0177] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0178] Subsequently, the surface-crosslinked superabsorbent polymer was mixed by chopping (hole size 16 mm) while spraying it with a citric acid aqueous solution (citric acid concentration 20%). At this time, the citric acid was mixed to 5.0 parts by weight based on 100 parts by weight of the base resin. After that, a drying step was carried out at 80°C for 25 minutes.

[0179] Example 1 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0180] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0181] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0182] Subsequently, a diisopropyl adipate emulsion (20% diisopropyl adipate concentration) and an EDTA aqueous solution (40% EDTA concentration) were mixed by spraying them onto the surface-crosslinked superabsorbent polymer using lecithin as an emulsifier, and by chopping (hole size 16 mm). At this time, the diisopropyl adipate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin, and the EDTA was mixed to 0.6 parts by weight based on 100 parts by weight of the base resin.

[0183] Example 2 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0184] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0185] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0186] Subsequently, a diisopropyl adipate emulsion (20% diisopropyl adipate concentration) and a citric acid aqueous solution (20% citric acid concentration) were mixed by spraying them onto the surface-crosslinked superabsorbent polymer using lecithin as an emulsifier, and by chopping (hole size 16 mm). At this time, the diisopropyl adipate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin, and the citric acid was mixed to 0.6 parts by weight based on 100 parts by weight of the base resin.

[0187] Example 3 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0188] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0189] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0190] Subsequently, a diisopropyl adipate emulsion (diisopropyl adipate concentration 20%) using lecithin as an emulsifier was sprayed onto the surface-crosslinked superabsorbent polymer and mixed by chopping (hole size 16 mm). At this time, the diisopropyl adipate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin.

[0191] Example 4 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0192] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0193] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0194] Subsequently, a diisopropyl adipate emulsion (diisopropyl adipate concentration 20%) using lecithin as an emulsifier was sprayed onto the surface-crosslinked superabsorbent resin and mixed by chopping (hole size 16 mm). At this time, the diisopropyl adipate was mixed to a ratio of 1.0 part by weight to 100 parts by weight of the base resin.

[0195] Example 5 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0196] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0197] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0198] Subsequently, a diisobutyl succinate emulsion (diisobutyl succinate concentration 20%) using lecithin as an emulsifier was sprayed onto the surface-crosslinked superabsorbent polymer and mixed by chopping (hole size 16 mm). At this time, the diisobutyl succinate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin.

[0199] Example 6 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0200] The manufactured water-containing gel polymer was in sheet form, and this sheet 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 170°C for 30 minutes, and the dried water-containing gel polymer was pulverized in a pin mill. Next, the polymer, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0201] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0202] Subsequently, a diisobutyl succinate emulsion (diisobutyl succinate concentration 20%) using lecithin as an emulsifier was sprayed onto the surface-crosslinked superabsorbent polymer and mixed by chopping (hole size 16 mm). At this time, the diisobutyl succinate was mixed to a ratio of 1.0 part by weight to 100 parts by weight of the base resin.

[0203] Example 7 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0204] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0205] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0206] Subsequently, a diisobutyl adipate emulsion (diisobutyl adipate concentration 20%) using lecithin as an emulsifier was sprayed onto the surface-crosslinked superabsorbent polymer and mixed by chopping (hole size 16 mm). At this time, the diisobutyl adipate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin.

[0207] Example 8 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0208] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0209] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0210] Subsequently, a diisopropyl adipate emulsion (20% diisopropyl adipate concentration) and a citric acid aqueous solution (20% citric acid concentration) were mixed by spraying them onto the surface-crosslinked superabsorbent polymer using lecithin as an emulsifier, and by chopping (hole size 16 mm). At this time, the diisopropyl adipate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin, and the citric acid was mixed to 5.0 parts by weight based on 100 parts by weight of the base resin.

[0211] Example 9 A monomer aqueous solution composition with a monomer concentration of 45.8% by weight was prepared by mixing 100g of acrylic acid, 0.37g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15g of sodium persulfate (SPS) as a thermal initiator, 0.008g of benzoin ether as a UV initiator, 40g of caustic soda (NaOH), and 127g of water. The monomer aqueous solution composition was then fed into the feed section of a polymerizer equipped with a continuously moving conveyor belt, and the polymerization atmosphere temperature was maintained at 80°C while irradiating with ultraviolet light using a UV irradiation device (irradiation dose: 10mW / cm²). 2 A hydrated gel polymer was produced by UV polymerization for 2 minutes.

[0212] The manufactured water-containing gel polymer was in sheet form, and this sheet 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, which was 150 μm to 850 μm in size, was classified using a sieve to produce the base resin.

[0213] Subsequently, 100 parts by weight of the prepared base resin was uniformly mixed with a surface crosslinking agent (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)), and a surface crosslinking reaction was carried out at 140°C for 30 minutes. After the completion of the surface treatment, a superabsorbent resin with a particle size of 150 to 850 μm was obtained using a sieve.

[0214] Subsequently, a diisopropyl adipate emulsion (20% diisopropyl adipate concentration) and an EDTA aqueous solution (40% EDTA concentration) were mixed by spraying them onto the surface-crosslinked superabsorbent polymer using lecithin as an emulsifier, and by chopping (hole size 16 mm). At this time, the diisopropyl adipate was mixed to 0.5 parts by weight based on 100 parts by weight of the base resin, and the EDTA was mixed to 1.0 part by weight based on 100 parts by weight of the base resin.

[0215] Experimental example The superabsorbent polymer compositions produced in the above examples and comparative examples were measured for each physical property using the following method.

[0216] 1) Odor evaluation Two g of each of the superabsorbent polymers produced in Examples 1-9 and Comparative Examples 1-6 was placed in a 500 mL glass bottle, and then 50 mL of urine was injected. After sealing the glass bottle, it was aged in a constant temperature chamber for 3 hours. The temperature of the constant temperature chamber was 35°C at this time. After aging was complete, the degree of malodor was evaluated by sensory evaluation. A total of nine people evaluated the degree of malodor on a scale of 1 to 5, with a score closer to 1 indicating less malodor and a score closer to 5 indicating stronger malodor. Table 1 shows the average evaluation results of the nine people.

[0217] 2) Centrifuge Retention Capacity (CRC) The water retention capacity of each resin, measured by its water absorption ratio under no load, was determined according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3.

[0218] Specifically, resins were obtained from the resins acquired in the examples and comparative examples, respectively, that were classified into a particle size range of 300 to 600 μm. 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 centrifugated under 250 G conditions for 3 minutes to remove the moisture, and the mass W2 (g) of the envelope was measured. The same procedure was then performed without using resin, and the mass W1 (g) was measured.

[0219] The CRC (g / g) was calculated using the following formula 1, based on the obtained masses.

[0220] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0221] 3) Absorbency under Pressure (AUP) The 0.7 psi pressure absorption capacity of the superabsorbent resins of the above examples and comparative examples was measured by the EDANA method WSP 242.3.

[0222] First, when measuring the pressure absorption capacity, the resin-classified powder used for the CRC measurement was used.

[0223] 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 spread on 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 as not to hinder its vertical movement. At this time, the weight W3 (g) of the device was measured.

[0224] 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 composed of 0.9 wt% sodium chloride was poured into it so that it was level with 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 top of the filter paper and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was removed and its weight W4 (g) was measured. The pressurized absorption capacity (g / g) was calculated using the following formula 2, based on the obtained masses.

[0225] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0226] 4) Deodorization rate The deodorization rate was measured using the adsorption tube measurement method. 3-methylbutanal was selected as the aldehyde-based malodorous substance, diacetyl as the ketone-based substance, and dimethyl trisulfide (DMTS) as the sulfur compound-based malodorous substance to test the deodorizing power.

[0227] - Adsorption 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 performed for 20 minutes. At this time, the temperature of the constant temperature chamber was 35°C, and the N2 flow rate was 250 mL / min. The displaced malodorous substance was then adsorbed onto a connected adsorption tube, and this process was repeated twice for the same sample. The collection results were analyzed by GC to confirm the results.

[0228] -Deodorizing power (%) = (Amount of malodor of Reference sample (superabsorbent resin of Comparative Example 1) measured by GC - Amount of malodor of sample measured by GC) / Amount of malodor of Reference sample (superabsorbent resin of Comparative Example 1) measured by GC × 100 (%)

[0229] The results of the odor evaluation, centrifugal separation water retention capacity (CRC), and pressurized absorption capacity (AUP) evaluations are shown in Table 1, and the deodorization rate is shown in Table 2.

[0230] [Table 1]

[0231] [Table 2]

[0232] According to the results in Table 1, it was found that in Examples 1 to 9, while maintaining a similar level of water absorption capacity compared to Comparative Example 1 (which did not contain additives), the deodorizing power was superior.

[0233] Furthermore, in Comparative Examples 2 and 3, where only a chelating agent was used without a diester compound, the deodorizing power tended to be lower compared to the Examples. In Comparative Examples 4 and 5, where cyclodextrin or citric acid was used alone, the deodorizing power was also lower compared to the Examples. In Comparative Example 6, where a large amount of citric acid was used, the deodorizing power was slightly improved compared to the other comparative examples, but it was confirmed that the deodorizing power was still at an inferior level compared to Example 8, which was used together with diisopropyl adipate, a diester compound.

[0234] According to the results in Table 2, it was confirmed that Comparative Examples 1-6 showed significantly lower rates of odor suppression compared to Examples 1-9. In the case of Comparative Example 6, which used a large amount of citric acid, the odor suppression rate was also similarly inferior to that of the other comparative examples.

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; and a diester compound represented by chemical formula 1, The diester compound is contained in the surface crosslinked layer of the superabsorbent resin, either separately from or in combination with the superabsorbent resin. Super absorbent resin composition. 【Chemistry 1】 (In the above chemical formula 1, n is an integer from 1 to 10, R is either isopropyl or isobutyl.

2. The diester compound comprises one or more selected from the group consisting of diisopropyl adipate, diisobutyl succinate, diisobutyl glutarate, and diisobutyl adipate. The superabsorbent polymer composition according to claim 1.

3. The diester compound is contained in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. The superabsorbent polymer composition according to claim 1.

4. The superabsorbent polymer composition further comprises one or more additives selected from the group consisting of chelating agents, iodine compounds, and organic acids. The superabsorbent polymer composition according to claim 1.

5. The chelating agent includes an aminoacetate-based chelating agent. The superabsorbent polymer composition according to claim 4.

6. 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 diglycinic acid (EDG), diethylenetriaminepentaacetic acid (DTPA), and salts thereof. The superabsorbent polymer composition according to claim 5.

7. The aforementioned iodine-based compound is a metal iodide salt. The superabsorbent polymer composition according to claim 4.

8. The aforementioned organic acid is one or more selected from the group consisting of citric acid, acetic acid, formic acid, fumaric acid, lactic acid, and propionic acid. The superabsorbent polymer composition according to claim 4.

9. 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 a surface crosslinking agent 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; During the surface crosslinking reaction, a diester compound represented by chemical formula 1 is mixed either after or after the surface crosslinking. A method for producing a superabsorbent polymer composition. 【Chemistry 2】 (In the above chemical formula 1, n is an integer from 1 to 10, R is either isopropyl or isobutyl.

10. The diester compound comprises one or more selected from the group consisting of diisopropyl adipate, diisobutyl succinate, diisobutyl glutarate, and diisobutyl adipate. A method for producing the superabsorbent polymer composition according to claim 9.

11. The method for producing the superabsorbent resin composition according to claim 9, wherein the diester compound is mixed in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin.

12. After step 4, the superabsorbent resin on which the surface crosslinking layer has been formed, Further mixing in one or more additives selected from the group consisting of chelating agents, iodine compounds, and organic acids. A method for producing the superabsorbent polymer composition according to claim 9.

13. The chelating agent includes an aminoacetate-based chelating agent. A method for producing the superabsorbent polymer composition according to claim 12.

14. The aforementioned iodine-based compound is a metal iodide salt. A method for producing the superabsorbent polymer composition according to claim 12.

15. The aforementioned organic acid is one or more selected from the group consisting of citric acid, acetic acid, formic acid, fumaric acid, lactic acid, and propionic acid. A method for producing the superabsorbent polymer composition according to claim 12.

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