Superabsorbent polymer and method for producing same

Abstract

The present invention provides a superabsorbent polymer and a method for preparing the same, and more particularly, the present invention relates to a method for preparing a superabsorbent polymer by using a specific deodorant to improve deodorization capability without deteriorating inherent physical properties of the superabsorbent polymer, the present invention relates to a superabsorbent polymer, and more particularly, to a superabsorbent polymer which effectively suppresses odor generated by urine and the like when applied to a product such as a diaper, and to a method for preparing the same.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application is based on Korean Patent Application Nos. 10-2023-0019560 and 10-2024-0020382, filed on February 14, 2023 and February 13, 2024, respectively, and claims the priority thereof, the entire disclosures of which are incorporated herein by reference.

[0003] The present invention relates to a superabsorbent polymer and a method for preparing the same. In particular, the present invention relates to a superabsorbent polymer that uses a specific deodorant to improve the deodorizing ability without deteriorating the inherent physical properties of the superabsorbent polymer, thereby effectively suppressing odors generated from urine, etc. when applied to products such as diapers, and also relates to a method for preparing the same. Background Art

[0004] A superabsorbent polymer (SAP) is a synthetic polymer material capable of absorbing 500 to 1000 times its own weight of moisture. Each manufacturer has named it by different names, such as SAM (Super Absorbency Material), AGM (Absorbent Gel Material), etc. Initially, this superabsorbent polymer began to be practically applied to sanitary products, and now they are widely used not only in sanitary products such as disposable diapers for children, but also in water-retaining soil products for gardening, water-stopping materials for civil engineering and construction, seedling sheets, preservatives in the food circulation field, hot compress materials, etc.

[0005] In most cases, these superabsorbent polymers have been widely used in the field of sanitary materials such as diapers or sanitary napkins. Inside the sanitary materials, the superabsorbent polymers are usually distributed throughout the pulp. However, recently, there have been continuous efforts to provide sanitary materials such as diapers with a thinner thickness, and as part of this, diapers with a reduced pulp content are being actively developed, and furthermore, pulp-free diapers, i.e., so-called pulp-free diapers.

[0006] As described above, these pulp-reduced or pulp-free sanitary materials contain superabsorbent polymers in a relatively high proportion, and the superabsorbent polymer particles are inevitably included in the sanitary material as multiple layers. In order to enable the entire superabsorbent polymer particles included as multiple layers to more effectively absorb a large amount of liquid (such as urine, etc.), it is necessary for the superabsorbent polymer to basically exhibit high absorption performance and high absorption rate. In addition, the superabsorbent polymer should not release the absorbed liquid even under external pressure. In addition, even when in a swollen state by absorbing liquid, liquid permeability is required to maintain its original shape. Therefore, in order to improve the basic water absorption rate and water retention capacity of the superabsorbent polymer, a large amount of research is being carried out, such as surface crosslinking, etc.

[0007] Meanwhile, superabsorbent polymers can be used in sanitary materials such as diapers, sanitary napkins, etc. In this case, due to the odor of the absorbed liquid (such as human and pet excreta), there may be a problem of reduced usability.

[0008] Therefore, not only is the demand for the absorption capacity and absorption rate as the basic physical properties of the superabsorbent polymer increasing, but also the demand for odor suppression is increasing. Therefore, it is necessary to prepare a superabsorbent polymer that can effectively suppress odor. Summary of the Invention

[0009] Technical Problem

[0010] Therefore, there is provided a superabsorbent polymer that uses a specific deodorant to improve the deodorizing ability without deteriorating the inherent physical properties of the superabsorbent polymer, thereby effectively suppressing the odor generated by urine, etc. when applied to products such as diapers. The present invention also relates to a method for preparing the same.

[0011] Technical Solution

[0012] To achieve the above object, according to an embodiment of the present invention, there is provided a method for preparing a superabsorbent polymer, the method comprising the following steps:

[0013] Polymerizing a monomer composition containing an acrylic monomer having at least partially neutralized acidic groups, an internal crosslinking agent, and a polymerization initiator to form a hydrogel polymer (step 1);

[0014] Drying, pulverizing, and classifying the hydrogel polymer to form a base resin (step 2);

[0015] Mixing the base resin with a deodorant (step 3); and

[0016] Performing a surface crosslinking reaction on the mixture of the base resin and the deodorant in the presence of a surface crosslinking solution containing a surface crosslinking agent (step 4),

[0017] Among them, the deodorant includes metal-organic frameworks (MOF) or ion exchange resins.

[0018] According to another embodiment of the present invention, a superabsorbent polymer is provided, which comprises:

[0019] A base resin composite, which comprises: a base resin obtained by polymerizing an acrylic monomer having at least partially neutralized acidic groups with an internal crosslinking agent, and at least part of a deodorant loaded on the polymer chains of the base resin; and

[0020] A surface crosslinked layer formed on the surface of the base resin,

[0021] Among them, the deodorant includes metal-organic frameworks (MOF) or ion exchange resins.

[0022] Beneficial effects

[0023] As described above, the present invention uses metal-organic frameworks (MOF) or ion exchange resins as deodorants to improve the deodorizing ability without deteriorating the inherent physical properties of the superabsorbent polymer, so that the odor generated by urine, etc. is effectively suppressed when applied to products such as diapers. Specific embodiments

[0024] The terms used in this specification are only for explaining exemplary embodiments and are not intended to limit the present invention.

[0025] Singular expressions may include plural expressions unless otherwise stated in the context. It must be understood that the terms "comprising", "equipped with" or "having" in this specification are only used to specify the existence of effective features, steps, components or combinations thereof, and do not preclude the existence or addition of one or more different features, steps, components or combinations thereof in advance.

[0026] The terms "first", "second", "third", etc. are used to describe various components, and these terms are only used to distinguish a specific component from other components.

[0027] As used herein, the term "polymer" refers to the polymerized state of acrylic monomers and may include all ranges of water content or particle size. Among the above polymers, in the state before drying after polymerization, a polymer having a water content (moisture content) of about 40% by weight or more can be called a hydrogel polymer, and particles obtained by crushing and drying such a hydrogel polymer can be called crosslinked polymers.

[0028] In addition, the term "base resin" or "base resin powder" refers to particles or powder prepared by drying and pulverizing a polymer of an acrylic monomer, and represents a polymer without undergoing surface modification or surface crosslinking steps as described later.

[0029] In addition, depending on the context, the term "superabsorbent polymer" or "superabsorbent polymer powder" refers to a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer (acrylic monomer) containing at least partially neutralized acidic groups, or a base resin in powder form composed of superabsorbent polymer particles obtained by pulverizing the crosslinked polymer, or is used to cover those suitable for commercialization by further processing (e.g., surface crosslinking, reassembly of fine particles, drying, pulverizing, classification, etc.) of the crosslinked polymer or the base resin.

[0030] The present invention can be modified in various ways and has various forms, and specific exemplary embodiments are illustrated and explained in detail in the following description. However, it is not intended to limit the present invention to specific exemplary embodiments, and it must be understood that the present invention includes every modification, equivalent, or alternative included within the spirit and technical scope of the present invention.

[0031] Hereinafter, a method for preparing a superabsorbent polymer and the superabsorbent polymer will be described in more detail according to specific embodiments of the present invention.

[0032] A method for preparing a superabsorbent polymer according to an embodiment of the present invention includes the following steps:

[0033] By polymerizing a monomer composition containing an acrylic monomer having at least partially neutralized acidic groups, an internal crosslinking agent, and a polymerization initiator to form a hydrogel polymer (step 1);

[0034] By drying, pulverizing, and classifying the hydrogel polymer to form a base resin (step 2);

[0035] Mixing the base resin with a deodorant (step 3); and

[0036] Performing a surface crosslinking reaction on the mixture of the base resin and the deodorant in the presence of a surface crosslinking solution containing a surface crosslinking agent (step 4),

[0037] wherein the deodorant includes a metal-organic framework (MOF) or an ion exchange resin.

[0038] Superabsorbent polymers are used in various sanitary materials such as diapers and sanitary napkins. However, when actually used, their usability may be reduced due to the odor of excrement from humans and pets. In addition, over time during wear, there are the following problems: the growth of bacteria is accelerated due to the liquid absorbed into the product, resulting in the additional generation of odor.

[0039] The problem with deodorizing substances that are usually included in products to reduce odor is that an excessive amount of deodorizing substances must be used to achieve the required level of deodorizing ability. Therefore, the absorption properties are significantly reduced and the cost of the product increases.

[0040] Therefore, the present inventors found that by using a metal-organic framework (MOF) or an ion-exchange resin as a deodorant, and mixing the deodorant with a base resin before surface crosslinking and then performing surface crosslinking, rather than simply mixing the deodorant with the final superabsorbent polymer, it is possible to effectively control the odor generated for various reasons while maintaining whiteness without deteriorating the basic physical properties of the superabsorbent polymer such as water retention capacity, absorption properties (e.g., pressure absorbency and absorption rate), thus completing the present invention.

[0041] Hereinafter, each step of a method for preparing a superabsorbent polymer according to an embodiment of the present invention will be described.

[0042] (Step 1)

[0043] Step 1 is a step of preparing a hydrogel polymer, specifically a step of polymerizing a monomer composition containing an acrylic monomer having at least partially neutralized acidic groups, an internal crosslinking agent, and a polymerization initiator to form a hydrogel polymer.

[0044] The acrylic monomer can be any monomer commonly used for preparing superabsorbent polymers. Specifically, the acrylic monomer can be a compound represented by the following Chemical Formula 1:

[0045] [Chemical Formula 1]

[0046] R 1 -COOM 1

[0047] In Chemical Formula 1, R 1 is a C2-C5 alkyl group containing an unsaturated bond, and

[0048] M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0049] Preferably, the acrylic monomer includes one or more selected from the group consisting of acrylic acid, methacrylic acid, their monovalent metal salts, their divalent metal salts, their ammonium salts, and their organic amine salts.

[0050] The acrylic monomer has acidic groups that can be at least partially neutralized. Preferably, an acrylic monomer partially neutralized with a basic substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. can be used as the monomer.

[0051] In this regard, the degree of neutralization of the monomer can be 40 mol% to 95 mol%, or 40 mol% to 80 mol%, or 45 mol% to 75 mol%. The range of the degree of neutralization can vary depending on the final physical properties. However, when the degree of neutralization is too high, the neutralized monomer precipitates, and thus polymerization may not easily occur. On the contrary, when the degree of neutralization is too low, the absorbency of the polymer is significantly reduced, and in addition, the polymer may exhibit intractable properties similar to those of an elastic rubber.

[0052] "Internal crosslinking agent" is a term used to distinguish it from the "surface crosslinking agent" for crosslinking the surface of the base resin, and the internal crosslinking agent functions to polymerize by crosslinking the unsaturated bonds of the acrylic monomer. Crosslinking in the above steps occurs both on the surface and inside the polymer. However, through the surface crosslinking process of the base resin described below, the particle surface of the finally prepared superabsorbent polymer has a structure crosslinked by the surface crosslinking agent, and its interior has a structure crosslinked by the internal crosslinking agent.

[0053] As the internal crosslinking agent, any compound can be used as long as it can introduce crosslinking bonds during the polymerization process of the acrylic monomer. As non-limiting examples of the internal crosslinking agent, the following polyfunctional crosslinking agents can be used alone or in combination of two or more thereof, 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, 1,4-butanediol di(meth)acrylate, 1,2-butanediol 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, glycerol tri(meth)acrylate, pentaerythritol tetraacrylate, triallylamine, allyl (meth)acrylate, ethylene glycol diglycidyl ether, propylene glycol, glycerol or ethylene carbonate.

[0054] These internal crosslinking agents can be added at a concentration of 0.001 wt% to 1 wt%, or 0.01 wt% to 0.8 wt%, or 0.1 wt% to 0.7 wt% relative to the monomer composition. In other words, when the concentration of the internal crosslinking agent is too low, the absorption rate of the resin may decrease and the gel strength may become weak, which is not preferred. On the contrary, when the concentration of the internal crosslinking agent is too high, the absorption capacity of the resin may decrease, which is not preferred as an absorbent.

[0055] In addition, as needed, the monomer composition may further contain additives such as thickeners, plasticizers, storage stabilizers, and antioxidants.

[0056] In addition, the monomer composition may contain a polymerization initiator commonly used for preparing superabsorbent polymers.

[0057] As the polymerization initiator, a thermal polymerization initiator or a photoinitiator can be used according to the polymerization method. However, even during photopolymerization, a certain amount of heat can be generated by UV irradiation or the like, and a certain amount of heat can also be generated by the polymerization reaction as an exothermic reaction. Therefore, a thermal polymerization initiator can also be included.

[0058] Here, as the photoinitiator, for example, a compound selected from one or more of the group consisting of benzoin ethers, dialkyl acetophenones, hydroxyalkyl ketones, phenyl glyoxylates, benzyl dimethyl ketals, acylphosphines, and α - aminoketones can be used. Among them, specific examples of acylphosphines can include commercially available Lucirin TPO, that is, 2,4,6 - trimethylbenzoyl - trimethylphosphine oxide. More photoinitiators are disclosed on page 115 of "UV Coatings: Basics, Recent Developments and New Application (Elsevier, 2007)" written by Reinhold Schwalm for reference.

[0059] As the thermal polymerization initiator, a compound selected from one or more of the group consisting of persulfate initiators, azo initiators, hydroperoxides, and ascorbic acid can be used. Specifically, examples of sulfate initiators can be sodium persulfate (Na 2 S 2 O 8 ), potassium persulfate (K 2 S 2 O 8 ), ammonium persulfate ((NH 4 ) 2 S 2 O 8) and the like. In addition, examples of the azo initiator may be 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N-dimethyl) isobutylamidine dihydrochloride, 2-(carbamoylazo) isobutyronitrile, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 4,4'-azobis(4-cyanovaleric acid), etc. More kinds of thermal polymerization initiators are disclosed on page 203 of "Principle of Polymerization (Wiley, 1981)" written by Odian for reference.

[0060] These polymerization initiators can be added at a concentration of 0.001 wt% to 1 wt%, or 0.005 wt% to 0.1 wt% relative to the monomer composition. In other words, when the concentration of the polymerization initiator is too low, the polymerization rate may become slow, and a large amount of the monomer remaining in the final product can be extracted, which is not preferred. On the contrary, when the concentration of the polymerization initiator is too high, the polymer chains forming the network become shorter, so the content of the water-soluble component increases, and the physical properties of the resin may deteriorate (for example, the pressure absorption rate decreases), which is not preferred.

[0061] In addition, such a monomer composition can be prepared in the form of a solution in which raw materials (such as the above-mentioned acrylic monomers, polymerization initiators, internal cross-linking agents, foaming agents, etc.) are dissolved in a solvent.

[0062] In this regard, as the applicable solvent, any solvent can be used without limitation to the composition as long as it can dissolve the above-mentioned raw materials. For example, as the solvent, 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, ethylene glycol methyl ether acetate, N,N-dimethylacetamide or a mixture thereof can be used.

[0063] The formation of the hydrogel polymer by polymerization of the monomer composition can be carried out by a conventional polymerization method, and this process is not particularly limited.

[0064] As a non-limiting example, the polymerization method can be classified into thermal polymerization and photopolymerization according to the polymerization energy source. When thermal polymerization is carried out, it can be carried out in a reactor of a kneader equipped with a stirring shaft. When photopolymerization is carried out, it can be carried out in a reactor equipped with a movable conveyor belt.

[0065] For example, a monomer composition is injected into a reactor such as a kneader equipped with a stirring shaft, and thermal polymerization is carried out by supplying hot air thereto or by heating the reactor to obtain a hydrogel polymer. In this regard, depending on the type of stirring shaft equipped in the reactor, a hydrogel polymer in the form of particles with a particle size of several centimeters or several millimeters can be obtained from the outlet of the reactor. Specifically, the hydrogel polymer can be obtained in various forms according to the concentration of the monomer composition fed thereto, the feeding rate, etc., and generally, a hydrogel polymer with a (weight average) particle size of 2 mm to 50 mm can be obtained.

[0066] Also for example, when the monomer composition is subjected to photopolymerization in a reactor equipped with a movable conveyor belt, a sheet-type hydrogel polymer can be obtained. In this regard, the thickness of the sheet can vary according to the concentration of the monomer composition fed thereto and the feeding rate. Preferably, the thickness of the sheet is controlled to be 0.5 cm to 10 cm to ensure the production speed while uniformly polymerizing the entire sheet.

[0067] Therefore, the hydrogel polymer obtained by this method can exhibit a water content of 40 wt% to 80 wt%. Here, the water content refers to the weight of water relative to the total weight of the hydrogel polymer, which can be a value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer. Specifically, the water content can be defined as a value calculated by measuring the weight loss caused by the evaporation of water in the polymer during the process of drying the polymer by raising its temperature through infrared heating. At this time, the drying conditions can be set as follows: the temperature is raised from room temperature to 180 °C, and then the temperature is maintained at 180 °C, and the total drying time is set to 20 minutes, including 5 minutes for the temperature-raising step.

[0068] (Step 2)

[0069] Step 2 of the present invention is a step of drying, pulverizing, and classifying the hydrogel polymer prepared in Step 1 to form a base resin powder.

[0070] Before drying the hydrogel polymer, a step of coarsely pulverizing it can also be included. Hereinafter, for the sake of distinction from the pulverization after drying, for convenience, the term "coarse pulverization" is used herein to refer to the pulverization before drying.

[0071] The pulverizer for pulverization can specifically include any one selected from the group consisting of: vertical pulverizers, turbo cutters, turbo grinders, rotary cutters, cutting mills, disk mills, pulverizing crushers, crushers, shredders, and disk cutters, but is not limited to the above examples.

[0072] At this time, a coarse crushing step can be carried out so that the particle size of the hydrogel polymer is about 2 mm to about 10 mm. Since the water content of the hydrogel polymer is relatively high, it is technically not easy to crush the hydrogel polymer into particles with a particle size less than 2 mm, and agglomeration may occur between the crushed particles. On the contrary, when the hydrogel polymer is crushed into particles with a particle size greater than 10 mm, the effect of improving the efficiency in the subsequent drying step may be poor.

[0073] Drying can be carried out at a temperature of 120°C to 250°C, 140°C to 200°C or 150°C to 190°C. At this time, the drying temperature can be defined as the temperature of the heating medium supplied for drying during the drying process or the internal temperature of the drying reactor containing the heating medium and the polymer. When the drying temperature is low and the drying time is long, the process efficiency is reduced. To prevent this, the drying temperature is preferably above 120°C. In addition, when the drying temperature is higher than the required temperature, the surface of the hydrogel polymer may be over-dried, which will increase the generation of fine powder in the subsequent crushing step, and the physical properties of the final resin may deteriorate. To prevent this, the drying temperature is preferably below 250°C.

[0074] At this time, the drying time in the drying step is not particularly limited, but considering the process efficiency and physical properties of the resin, it can be adjusted to 20 minutes to 90 minutes at the drying temperature.

[0075] Drying can be carried out using a common medium. For example, it can be carried out by supplying hot air, infrared irradiation, microwave irradiation or ultraviolet irradiation to the crushed hydrogel polymer.

[0076] In addition, it is preferable to carry out drying so that the water content of the dried polymer can be 0.1 wt% to 10 wt%. In other words, when the water content of the dried polymer is less than 0.1 wt%, over-drying may increase the production cost and may cause degradation of the cross-linked polymer, which is not preferable. In addition, when the water content of the dried polymer is greater than 10 wt%, defects may occur in the subsequent process, which is not preferable.

[0077] Subsequently, the dried hydrogel polymer can be crushed. This is a step to optimize the surface area of the base resin powder and the superabsorbent polymer. Crushing can be carried out so that the particle size of the crushed polymer is 150 μm to 850 μm.

[0078] In this regard, applicable crushers can include conventional crushers, such as needle mills, hammer mills, screw mills, roller mills, disk mills or slow mills, etc.

[0079] In addition, in order to manage the physical properties of the superabsorbent polymer that will ultimately be commercialized, a step of selectively classifying particles having a particle size of 150 μm to 850 μm from the polymer particles obtained through the pulverization step may also be performed.

[0080] Through the above classification step, a base resin powder can be obtained. The particle size of the base resin powder may be 150 μm to 850 μm, and the content of fine powder having a particle size less than 150 μm may be 2% by weight or less or 1% by weight or less.

[0081] (Step 3)

[0082] Step 3 of the present invention is a step of mixing a base resin with a metal-organic framework (MOF) or an ion exchange resin as a deodorant.

[0083] A metal-organic framework (MOF), also known as a metal-organic structure, is an organic-inorganic composite material in which metal ions or ion clusters are coordinated with organic ligands to form a primary, secondary, or tertiary structure, and various MOFs can be prepared according to the selection of metal ions and organic ligands.

[0084] The characteristics of MOF are that it is porous, with empty spaces existing inside the structure, and the pore size, porosity, three-dimensional structure, surface area, etc. can be designed differently according to the types and bonding methods of the metal ions and organic ligands constituting the MOF.

[0085] Due to this porosity, MOF has an adsorption property for various organic compounds. In particular, compared with widely known zeolites or activated carbon, MOF has excellent adsorption properties for various substances, and thus has attracted attention as a next-generation functional adsorbent. In addition, MOF is not easily deformed at high temperatures and has a strong skeleton, so it has excellent chemical and thermal stability. In addition, some MOFs are known to have antibacterial properties against microorganisms.

[0086] Meanwhile, the inventors of the present invention have confirmed that when this MOF is included in a superabsorbent polymer, it is harmless to the human body, does not impair the inherent properties of the superabsorbent polymer, and has excellent deodorizing ability to inhibit various odorous substances.

[0087] According to an exemplary embodiment of the present invention, the MOF may include one or more metal ions selected from the group consisting of Zn, Ti, Co, Al, and Zr, and one or more organic ligands selected from the group consisting of imidazole, alkylimidazole, alkoxyimidazole, terephthalic acid, and aminoterephthalic acid.

[0088] According to an exemplary embodiment of the present invention, the MOF may include, for example, one selected from the group consisting of Zn-MOF (ZIF-8, (Zn 2++2-methylimidazole)), Zn-MOF (ZIF-67, (Co 2+ +2-methylimidazole)), Ti-MOF (Tn 2+ +2-methylimidazole), NH 2 -UiO-66 (Zr 4+ +2-aminoterephthalic acid) and NH 2 -MIL-101 (Al 3+ +2-aminoterephthalic acid), or one or more of the group consisting of, but the present invention is not limited thereto.

[0089] It has also been confirmed that when the ion exchange resin is included in the superabsorbent polymer, it is harmless to the human body, does not impair the inherent properties of the superabsorbent polymer, and has excellent deodorizing ability to inhibit various odorous substances.

[0090] According to an exemplary embodiment of the present invention, for the ion exchange resin, a hydrophobic ion exchange resin is generally preferred, which is beneficial for removing hydrophobic odorous components. For example, polystyrene-divinylbenzene resins, polymethacrylate-divinylbenzene resins, or polyacrylate-divinylbenzene resins can be used. More specifically, for example, the ion exchange resin may include one or more selected from the group consisting of commercially available Amberlite XAD, Samyang Trilite, Samyang DIAION, etc., but the present invention is not limited thereto.

[0091] Relative to 100 parts by weight of the base resin, the content of the deodorant can be 1 part by weight to 10 parts by weight, respectively. Specifically, relative to 100 parts by weight of the base resin, the content of the MOF or the ion exchange resin can be 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more, and 10 parts by weight or less. When the deodorant is used within the above content range, the deodorizing ability of the superabsorbent polymer can be further improved without deteriorating the absorption properties.

[0092] Meanwhile, when a MOF or an ion exchange resin is simply mixed with the final superabsorbent polymer after surface crosslinking by post-treatment, there is a problem in that the deodorizing effect cannot be maintained for a long time because it is easily desorbed from the superabsorbent polymer. On the contrary, according to an embodiment of the present invention, a base resin is mixed with a deodorant before surface crosslinking, and then surface crosslinking is performed. Thus, its binding state is maintained and it is not easily desorbed until the product is completed into articles such as diapers, and when wetted by urine that causes an odor, the resin swells and the deodorant is desorbed, and then the deodorant is widely distributed, thereby exerting deodorizing ability. Therefore, the deodorizing effect of effectively controlling odors caused by various reasons will be maintained for a long time while maintaining white color without deteriorating the basic physical properties of the superabsorbent polymer such as water retention capacity, absorption properties (such as pressure absorption rate and absorption rate).

[0093] On the other hand, it has been observed that when a deodorant is mixed with a hydrogel before preparing the base resin, there is a problem of loss of deodorizing ability. For example, the pores in the deodorant are blocked by moisture due to a large amount of moisture present on the surface of the hydrogel. Therefore, preferably, the MOF or ion exchange resin as the deodorant is mixed with a base resin that is not in a hydrogel state but has been dried to a water content of 10% or less.

[0094] (Step 4)

[0095] Step 4 of the present invention is a step of performing a surface crosslinking reaction on the mixture of the base resin and the deodorant obtained in Step 3 in the presence of a surface crosslinking solution containing a surface crosslinking agent.

[0096] Through Step 4, a surface crosslinked layer is formed on the surface of the base resin particles.

[0097] The formation of the surface crosslinked layer can be carried out by common methods for increasing the surface crosslinking density of polymer particles. For example, it can be carried out by a method of mixing the pulverized polymer with a surface crosslinking solution containing a surface crosslinking agent and then performing a heat treatment on it to carry out a crosslinking reaction.

[0098] The surface crosslinking step can be carried out at a temperature of about 80°C to about 250°C. More specifically, the surface crosslinking process can be carried out at a temperature of about 100°C to about 220°C, or about 110°C to about 200°C, or about 120°C to about 190°C for about 10 minutes to about 2 hours, or about 20 minutes to about 60 minutes. When the crosslinking reaction temperature is lower than 160°C or the reaction time is too short, the surface crosslinking reaction cannot occur normally, and thus the permeability may decrease. When the temperature is higher than 200°C or the reaction time is too long, there may be a problem that the water retention capacity may decrease.

[0099] The heating device for the surface crosslinking reaction is not particularly limited. Heating can be carried out by providing a heating medium or by directly providing a heat source. In this regard, the types of applicable heating media can be steam, hot air, hot fluid (such as hot oil), etc., but the present invention is not limited thereto. Considering the device of the heating medium, the heating rate, and the heating target temperature, the temperature of the heating medium to be provided can be appropriately selected. At the same time, as the heat source to be directly provided, an electric heating method or a gas heating method can be used, but the present invention is not limited to the above examples.

[0100] The surface crosslinking solution contains a surface crosslinking agent, which is a surface crosslinking agent commonly used for the surface crosslinking of superabsorbent polymers. There is no particular limitation as long as it is a compound capable of reacting with the functional groups of the polymer.

[0101] Preferably, in order to improve the properties of the superabsorbent polymer to be prepared, as the surface crosslinking agent, one or more selected from the group consisting of polyhydric alcohols; epoxy compounds; polyamine compounds; halogenated epoxy compounds; condensation products of halogenated epoxy compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; and alkylene carbonate compounds can be used.

[0102] Specifically, as examples of the polyhydric alcohol compound, 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 can be used.

[0103] In addition, as the epoxy compound, ethylene glycol diglycidyl ether and glycidol can be used, and as the polyamine compound, one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamide polyamine can be used.

[0104] In addition, as the halogenated epoxy compound, epichlorohydrin, epibromohydrin, and α-methyl epichlorohydrin can be used. At the same time, as the mono-, di- or polyoxazolidinone compound, for example, 2-oxazolidinone can be used.

[0105] In addition, as the alkylene carbonate compound, ethylene carbonate can be used, etc. These compounds can be used alone or in combination. At the same time, in order to improve the efficiency of the surface crosslinking process, among these surface crosslinking agents, it is preferable to contain one or more C2 to C10 polyhydric alcohol compounds.

[0106] The content of the surface crosslinking agent to be added can be appropriately selected according to the type of the surface crosslinking agent or reaction conditions. However, generally, the amount thereof can be 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 based on 100 parts by weight of the polymer.

[0107] Based on 100 parts by weight of the polymer, when the content of the surface crosslinking agent is too small, the surface crosslinking reaction may hardly occur. When the content exceeds 5 parts by weight, the absorption capacity and physical properties may deteriorate due to the excessive progress of the surface crosslinking reaction.

[0108] Meanwhile, the surface crosslinking solution may further include an inorganic material. As such an inorganic material, one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composite, titanium dioxide, zinc oxide, and aluminum sulfate can be used. The inorganic material can be used in the form of powder or liquid, particularly in the form of alumina powder, silica-alumina powder, titanium dioxide powder, or nano-silica solution. In addition, the amount of the inorganic material can be about 0.001 to about 1 part by weight based on 100 parts by weight of the base resin.

[0109] In the surface crosslinking solution, water can be used as a solvent. In this regard, the content of water can be appropriately controlled to cause uniform dispersion of the surface crosslinking agent and the deodorant, thereby preventing the agglomeration of the base resin powder and optimizing the surface penetration depth of the crosslinking agent at the same time.

[0110] When the surface crosslinking reaction is carried out during the physical mixing of the base resin and the deodorant, the base resin swells due to the surface crosslinking solution, and some deodorant particles can be physically attached to the base resin. In other words, at least part of the deodorant particles adhere and are loaded in the polymer chains of the base resin. As a result, they remain in a bound state and are not easily separated until the subsequent process (such as the surface crosslinking step) or product (such as a diaper, etc.) is completed. When wetted by urine that causes odor, the resin swells and the deodorant is desorbed, and then the deodorant is widely distributed, thereby exerting the deodorizing ability.

[0111] Meanwhile, according to an embodiment of the present invention, a chelating agent or an organic acid can be further mixed during or after the surface crosslinking step to improve the deodorizing ability.

[0112] The 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), hydroxyethyl ethylenediamine triacetic acid (HEDTA), ethanol diglycine (EDG), diethylenetriaminepentaacetic acid (DTPA), and salts thereof. More specifically, the chelating agent may be ethylenediaminetetraacetic acid (EDTA) or L-glutamic acid diacetic acid (GLDA).

[0113] 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.

[0114] Relative to 100 parts by weight of the base resin, the contents of the chelating agent and the organic acid may each independently be from 0.1 part by weight to 2 parts by weight. Specifically, relative to 100 parts by weight of the base resin, the content is 0.1 part by weight or more, 0.3 part by weight or more, 0.5 part by weight or more, 0.7 part by weight or more, or 1 part by weight or more, and is 2 parts by weight or less, 1.7 parts by weight or less, 1.5 parts by weight or less, or 1.3 parts by weight or less. When used within the above content ranges, the deodorizing ability of the superabsorbent polymer can be further improved without deteriorating the absorption properties.

[0115] The chelating agent can be mixed with an aqueous solution in the form of a salt and then used, so the above content range is based on the solid content.

[0116] According to another aspect of the present invention, the superabsorbent polymer includes a base resin composite, which includes: a base resin obtained by polymerizing an acrylic monomer having at least partially neutralized acidic groups with an internal crosslinking agent, at least a part of a deodorant loaded on the polymer chains of the base resin; and

[0117] a surface crosslinked layer formed on the surface of the base resin,

[0118] wherein the deodorant includes a metal-organic framework (MOF) or an ion exchange resin.

[0119] As a result of mixing the base resin with the deodorant (metal-organic framework (MOF) or ion exchange resin) and then performing a surface crosslinking reaction, the base resin composite is in a state where, while the base resin and the deodorant are physically mixed, a part of the deodorant particles are adhered by surface crosslinking and loaded in the base resin chains. Therefore, it remains in an adhesive state and is not easily separated until the subsequent process or product (such as a diaper, etc.) is completed, and when wetted by urine that causes odor, the superabsorbent polymer swells and the deodorant is desorbed, and then the deodorant is widely distributed, thereby exerting the deodorizing ability.

[0120] Regarding the base resin, the raw materials including acrylic monomers and internal crosslinking agents used in the base resin and the preparation method are as described in the preparation method of the superabsorbent polymer.

[0121] In addition, the types, contents, and characteristics of the deodorant are as described in the preparation method of the superabsorbent polymer.

[0122] In addition, the surface crosslinking agent for forming the surface crosslinked layer and the preparation method are as described in the preparation method of the superabsorbent polymer.

[0123] For example, the MOF contains one or more metal ions selected from the group consisting of Zn, Ti, Co, Al, and Zr, and one or more organic ligands selected from the group consisting of imidazole, alkylimidazole, alkoxyimidazole, terephthalic acid, and aminoterephthalic acid.

[0124] In addition, the ion exchange resin includes polystyrene-divinylbenzene resins, polymethacrylate-divinylbenzene resins, or polyacrylate-divinylbenzene resins.

[0125] In addition, relative to 100 parts by weight of the base resin, the mixing amount of the deodorant can be 1 part by weight to 10 parts by weight.

[0126] The superabsorbent polymer according to an embodiment of the present invention may further contain a chelating agent or an organic acid to improve the deodorizing ability.

[0127] The 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), hydroxyethyl ethylenediamine triacetic acid (HEDTA), ethanol diglycine (EDG), diethylenetriaminepentaacetic acid (DTPA), and salts thereof. More specifically, the chelating agent may be ethylenediaminetetraacetic acid (EDTA) or L-glutamic acid diacetic acid (GLDA).

[0128] 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. In particular, the organic acid may be citric acid.

[0129] Relative to 100 parts by weight of the base resin, the contents of the chelating agent and the organic acid may each independently be 0.1 part by weight to 2 parts by weight. Specifically, relative to 100 parts by weight of the base resin, the content is 0.1 part by weight or more, 0.3 part by weight or more, 0.5 part by weight or more, 0.7 part by weight or more, or 1 part by weight or more, and 2 parts by weight or less, 1.7 parts by weight or less, 1.5 parts by weight or less, or 1.3 parts by weight or less. When used within the above content range, the deodorizing ability of the superabsorbent polymer can be further improved without deteriorating the absorption properties.

[0130] The chelating agent can be mixed with an aqueous solution in the form of a salt and then used. Therefore, the above content ranges are based on the solid content.

[0131] Hereinafter, preferred exemplary embodiments will be provided to better understand the present invention. However, the following exemplary embodiments are provided only for illustrating the present invention, and the present invention is not limited thereto.

[0132] <Example>

[0133] Example 1

[0134] 100 g of acrylic acid, 0.37 g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15 g of sodium persulfate (SPS) as a thermal initiator, 0.008 g of benzoin ether as a UV initiator, 40 g of caustic soda (NaOH) and 127 g of water were mixed to prepare a monomer aqueous solution composition with a monomer concentration of 45.8% by weight. Then, the monomer aqueous solution composition was fed into the feed zone of a polymerization reactor equipped with a continuously moving conveyor belt. Then, while maintaining the polymerization atmosphere temperature at 80 °C, UV was irradiated with a UV irradiation device (irradiation dose: 10 mW / cm 2 ), and UV polymerization was carried out for 2 minutes to prepare a hydrogel polymer.

[0135] The hydrogel polymer was transferred to a meat grinder and cut into 2 mm to 10 mm. At this time, the water content of the chopped hydrogel polymer was 47% by weight. Subsequently, the hydrogel polymer was dried in a hot air dryer at 170 °C for 30 minutes, and the dried hydrogel polymer was pulverized with a needle mill and then classified with a sieve to obtain a polymer with a particle size of 150 μm to 850 μm, thereby preparing a base resin with a water content of 1% by weight or less.

[0136] While stirring in the dry state, 10 parts by weight of Zn-MOF (ZIF-8, Zn 2+ + 2-methylimidazole) as a deodorant was mixed with respect to 100 parts by weight of the base resin prepared as above.

[0137] Thereafter, with respect to 100 parts by weight of the base resin, the mixture mixed with the deodorant was uniformly mixed with a surface crosslinking solution (2.5 parts by weight of water, 0.1 part by weight of ethylene glycol diglycidyl ether (EX-810), 0.1 part by weight of aluminum sulfate octadecahydrate (Al-S) and 0.1 part by weight of silica (Aerosil A200)).

[0138] Next, the mixture was subjected to a surface crosslinking reaction at 140 °C for 30 minutes. After completion of the surface crosslinking reaction, a superabsorbent polymer with a particle size of 150 μm to 850 μm was obtained by classification with a sieve.

[0139] Example 2

[0140] The superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, while stirring in the dry state, 5 parts by weight of Zn-MOF (ZIF-8, Zn 2+ +2-methylimidazole) as a deodorant was mixed with respect to 100 parts by weight of the base resin prepared as above.

[0141] Example 3

[0142] The superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, while stirring in the dry state, 2 parts by weight of Zn-MOF (ZIF-8, Zn 2+ +2-methylimidazole) as a deodorant was mixed with respect to 100 parts by weight of the base resin prepared as above.

[0143] Example 4

[0144] The superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, while stirring in the dry state, 10 parts by weight of Ti-MOF (Tn 2+ +2-methylimidazole) as a deodorant was mixed with respect to 100 parts by weight of the base resin prepared as above.

[0145] Example 5

[0146] The superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, while stirring in the dry state, 10 parts by weight of the ion exchange resin Amberlite XAD4 (purchased from AlFA) was mixed with respect to 100 parts by weight of the base resin prepared as above.

[0147] Example 6

[0148] The base resin was prepared in the same manner as in Example 1.

[0149] While stirring in the dry state, 5 parts by weight of Zn-MOF (ZIF-8, Zn 2+ +2-methylimidazole) as a deodorant was mixed with respect to 100 parts by weight of the base resin prepared as above.

[0150] Thereafter, relative to 100 parts by weight of the base resin, a mixture mixed with a deodorant is uniformly mixed with a surface crosslinking solution (2.5 parts by weight of water, 0.1 part by weight of ethylene glycol diglycidyl ether (EX-810), 0.1 part by weight of aluminum sulfate 18-hydrate (Al-S), and 0.1 part by weight of silica (Aerosil A200)).

[0151] Next, the mixture is subjected to a surface crosslinking reaction at 140 °C for 30 minutes. After the surface treatment, an aqueous solution of citric acid with a content of 5 parts by weight relative to 100 parts by weight of the base resin is prepared and mixed with the superabsorbent polymer by spraying, and then dried at 80 °C for 25 minutes. Then, a superabsorbent polymer with a particle size of 150 μm to 850 μm is obtained by sieving classification.

[0152] Example 7

[0153] The base resin is prepared in the same manner as in Example 1.

[0154] Relative to 100 parts by weight of the base resin prepared as above, while stirring in a dry state, 5 parts by weight of Zn-MOF (ZIF-8, Zn 2+ +2-methylimidazole) as a deodorant is mixed.

[0155] Thereafter, relative to 100 parts by weight of the base resin, a mixture mixed with a deodorant is uniformly mixed with a surface crosslinking solution (2.5 parts by weight of water, 0.1 part by weight of ethylene glycol diglycidyl ether (EX-810), 0.1 part by weight of aluminum sulfate 18-hydrate (Al-S), and 0.1 part by weight of silica (Aerosil A200)).

[0156] Next, the mixture is subjected to a surface crosslinking reaction at 140 °C for 30 minutes. After completion of the surface crosslinking reaction, an aqueous solution of EDTA with a content of 5 parts by weight relative to 100 parts by weight of the base resin is prepared and mixed by spraying onto the superabsorbent polymer, and then dried at 80 °C for 25 minutes. Then, a superabsorbent polymer with a particle size of 150 μm to 850 μm is obtained by sieving classification.

[0157] Comparative Example 1

[0158] 100 g of acrylic acid, 0.37 g of N,N'-methylenebisacrylamide as a crosslinking agent, 0.15 g of sodium persulfate (SPS) as a thermal initiator, 0.008 g of benzoin ether as a UV initiator, 40 g of caustic soda (NaOH), and 127 g of water were mixed to prepare an aqueous monomer composition with a monomer concentration of 45.8% by weight. Then, the aqueous monomer composition was fed into the feed zone of a polymerization reactor equipped with a continuously moving conveyor belt. Then, while maintaining the polymerization atmosphere temperature at 80 °C, UV was irradiated with a UV irradiation device (irradiation dose: 10 mW / cm 2 ), and UV polymerization was carried out for 2 minutes to prepare a hydrogel polymer.

[0159] The hydrogel polymer was transferred to a meat grinder and cut into 2 mm to 10 mm. At this time, the water content of the chopped hydrogel polymer was 47% by weight. Subsequently, the hydrogel polymer was dried in a hot air dryer at 170 °C for 30 minutes, and the dried hydrogel polymer was pulverized with a needle mill and then classified with a sieve to obtain a polymer with a particle size of 150 μm to 850 μm, thereby preparing a base resin with a water content of 1% by weight or less.

[0160] Thereafter, a surface crosslinking solution (2.5 parts by weight of water, 0.1 part by weight of ethylene glycol diglycidyl ether (EX-810), 0.1 part by weight of aluminum sulfate octadecahydrate (Al-S), and 0.1 part by weight of silica (Aerosil A200)) was uniformly mixed with respect to 100 parts by weight of the base resin.

[0161] Next, the mixture was subjected to a surface crosslinking reaction at 140 °C for 30 minutes. After completion of the surface crosslinking reaction, a superabsorbent polymer with a particle size of 150 μm to 850 μm was obtained by classification with a sieve.

[0162] Comparative Example 2

[0163] In Comparative Example 1, after completion of the surface crosslinking reaction, an EDTA aqueous solution with a content of 1 part by weight of EDTA with respect to 100 parts by weight of the base resin was prepared and mixed with the superabsorbent polymer by spraying, and then dried at 80 °C for 25 minutes. Then, a superabsorbent polymer with a particle size of 150 μm to 850 μm was obtained by classification with a sieve.

[0164] Comparative Example 3

[0165] In Comparative Example 1, after completion of the surface crosslinking reaction, an aqueous citric acid solution having a citric acid content of 5 parts by weight relative to 100 parts by weight of the base resin was prepared and mixed with the superabsorbent polymer by spraying, followed by drying at 80 °C for 25 minutes. Then, the superabsorbent polymer having a particle size of 150 μm to 850 μm was obtained by classification using a sieve.

[0166] Comparative Example 4

[0167] A superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, 5 parts by weight of volcanic ash as a deodorant was mixed with 100 parts by weight of the base resin prepared as described above while stirring in a dry state.

[0168] Comparative Example 5

[0169] A superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, 10 parts by weight of lithium saponite (XLS) as a deodorant was mixed with 100 parts by weight of the base resin prepared as described above while stirring in a dry state.

[0170] The main features of the examples and comparative examples are summarized in Table 1.

[0171] [Table 1]

[0172]

[0173] (In Table 1, the content of each deodorant and additive is expressed as parts by weight relative to 100 parts by weight of the base resin.)

[0174] Experimental Example

[0175] The respective physical properties of the superabsorbent polymers prepared in the examples and comparative examples were measured by the following methods.

[0176] Unless otherwise specified, all evaluations of the following physical properties were carried out at a constant temperature and humidity (23 ± 1 °C, relative humidity of 50 ± 10%), and the physiological saline or saline solution refers to an aqueous solution of 0.9 wt% sodium chloride (NaCl).

[0177] Furthermore, unless otherwise specified, the evaluation of the physical properties of the superabsorbent polymer was carried out on the resin having a particle size of 150 μm to 850 μm classified by the ASTM standard sieve.

[0178] (1) Centrifugal Retention Capacity (CRC)

[0179] Measure the water retention capacity of the superabsorbent polymers of the examples and comparative examples obtained from the water absorption amount under no load according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP241.3.

[0180] Specifically, the superabsorbent polymer W 0 (g) (about 0.2 g) was evenly placed into a bag made of nonwoven fabric and then sealed. Then, the bag was immersed in a physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was removed from the bag using a centrifuge at 250 G for 3 minutes, and then the weight of the bag W 2 (g) was measured. In addition, the same procedure was carried out without using the resin, and then the obtained weight W 1 (g) was measured.

[0181] Using the corresponding weights thus obtained, calculate the CRC (g / g) according to the following Equation 1.

[0182] [Equation 1]

[0183] CRC (g / g) = {[W 2 (g) - W 1 (g)] / W 0 (g)} - 1

[0184] (2) Pressurized Absorbency (AUP)

[0185] Measure the pressurized absorbency of the superabsorbent polymers of the examples and comparative examples at 0.7 psi according to the EDANA method WSP242.3.

[0186] First, when measuring the pressurized absorbency, use the fractionated polymer used when measuring CRC.

[0187] Specifically, a 400-mesh stainless steel mesh was installed at the bottom of a plastic cylinder with an inner diameter of 25 mm. Under the conditions of room temperature and a humidity of 50%, the superabsorbent polymer W 0 (g) was evenly dispersed on the stainless steel mesh. A piston capable of uniformly providing a load of 0.7 psi was placed thereon, where the outer diameter of the piston was slightly smaller than 25 mm, there was no gap between the inner wall of the cylinder and the piston, and the up and down movement of the cylinder was not disturbed. At this time, the weight W 3 (g) of the measuring device was measured.

[0188] Place a glass filter with a diameter of 90 mm and a thickness of 5 mm in a petri dish with a diameter of 150 mm, and then pour a physiological saline solution composed of 0.9% by weight of sodium chloride until the surface level of the physiological saline solution becomes the same as the upper surface of the glass filter. Place a filter paper with a diameter of 90 mm on the glass filter. Install the measuring device on the filter paper to absorb the liquid under load for 1 hour. After 1 hour, lift the measuring device and then measure the weight W 4 (g). Calculate the pressure absorption rate (g / g) using the obtained weight according to the following Equation 2.

[0189] [Equation 2]

[0190] AUP (g / g) = [W 4 (g) - W 3 (g)] / W 0 (g)

[0191] (3) Deodorizing ability (adsorbent tube test)

[0192] Select guaiacol as a phenolic compound, dimethyl trisulfide as a sulfur compound, and 3-methylbutyraldehyde as an aldehyde compound as odoriferous substances, and use the adsorbent tube test to test the deodorizing ability.

[0193] - Adsorbent tube test method: Put 1 g of superabsorbent polymer into a 500 mL glass bottle, and then inject 25 mL of the odoriferous substance. Thereafter, age for 3 hours in a thermostatic chamber and collect for 20 minutes. At this time, the temperature of the thermostatic chamber is 35 °C, and the N 2 flow rate is 250 mL / min. Push out the odor and adsorb it to the connected adsorbent tube (TENAX / GR), and collect the same sample twice. Analyze the collection results by GC to confirm the results.

[0194] - Deodorizing ability (%) = (amount of odor of the reference sample (sample of Comparative Example 1) measured by GC - amount of odor of the sample measured by GC) / amount of odor of the reference sample (sample of Comparative Example 1) measured by GC × 100 (%)

[0195] (4) Color test

[0196] The color test is carried out as follows: Weigh 5 g of superabsorbent polymer on an aluminum tray, spread it thinly in the same way, and measure it using a color difference meter Labscan XE (product of Hunter Lab). The measured values are output as three parameters: L, a, and b. Substitute these values into the following equation to calculate the color evaluation value (WI; whiteness index). At this time, the higher the WI value, the closer the color is to white.

[0197]

[0198] The experimental results are shown in Table 2. The deodorizing ability values in Table 2 show the deodorizing efficiency relative to Comparative Example 1, and the higher the deodorizing efficiency, the higher the numerical value.

[0199] [Table 2]

[0200]

[0201] Referring to Table 2, the superabsorbent polymer prepared by mixing with MOF or ion exchange resin as a deodorant before surface crosslinking according to the preparation method of the present invention equally exhibits excellent deodorizing ability against phenols, sulfides and aldehyde compounds which are the main causes of odors, and also exhibits excellent color characteristics.

[0202] It was confirmed that Comparative Examples 2, 3 and 5 using common deodorants (EDTA, organic acids or hectorite) exhibited poor deodorizing ability, and Comparative Example 4 using volcanic ash as a deodorizing adsorbent had poor color characteristics and was not suitable for application to diapers.

Claims

1. A method for preparing a superabsorbent polymer, the method comprising the following steps: Step 1: forming a hydrogel polymer by polymerizing a monomer composition comprising an acrylic monomer having an acidic group that is at least partially neutralized, an internal crosslinking agent, and a polymerization initiator; Step 2: Drying, crushing and classifying the hydrogel polymer to form a base resin; Step 3: mixing the base resin with a deodorant; as well as Step 4: subjecting the mixture of the base resin and the deodorant to a surface crosslinking reaction in the presence of a surface crosslinking solution containing a surface crosslinking agent, Wherein, the deodorant comprises a metal organic framework (MOF) or an ion exchange resin.

2. The method of claim 1, wherein: The MOF comprises one or more metal ions selected from the group consisting of Zn, Ti, Co, Al and Zr, and one or more organic ligands selected from the group consisting of imidazole, alkylimidazole, alkoxyimidazole, terephthalic acid and aminoterephthalic acid.

3. The method of claim 1, wherein: The ion exchange resin includes polystyrene-divinylbenzene resin, polymethacrylate-divinylbenzene resin or polyacrylate-divinylbenzene resin.

4. The method of claim 1, wherein: The deodorant is mixed in an amount of 1 to 10 parts by weight relative to 100 parts by weight of the base resin.

5. The method of claim 1, wherein: A chelating agent or an organic acid is further mixed in step 4 or thereafter.

6. The method of claim 5, wherein: The chelating agent includes 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 diglycine (EDG), diethylenetriaminepentaacetic acid (DTPA) and salts thereof.

7. The method of claim 5, wherein: The organic acid includes one or more selected from the group consisting of citric acid, acetic acid, formic acid, fumaric acid, lactic acid and propionic acid.

8. The method of claim 5, wherein: The mixing amount of the chelating agent or the organic acid is independently 0.1 to 5 parts by weight relative to 100 parts by weight of the base resin.

9. A superabsorbent polymer, comprising: A base resin composite comprising: a base resin in which an acrylic monomer having an at least partially neutralized acidic group is polymerized with an internal crosslinking agent, and at least a portion of a deodorant supported on a polymer chain of the base resin; and forming a surface cross-linked layer on the surface of the base resin, in, The deodorant includes a metal organic framework (MOF) or an ion exchange resin.

10. The superabsorbent polymer according to claim 9, wherein The MOF comprises one or more metal ions selected from the group consisting of Zn, Ti, Co, Al and Zr, and one or more organic ligands selected from the group consisting of imidazole, alkylimidazole, alkoxyimidazole, terephthalic acid and aminoterephthalic acid.

11. The superabsorbent polymer according to claim 9, wherein The ion exchange resin includes polystyrene-divinylbenzene resin, polymethacrylate-divinylbenzene resin or polyacrylate-divinylbenzene resin.

12. The superabsorbent polymer according to claim 9, wherein The deodorant is mixed in an amount of 1 to 10 parts by weight relative to 100 parts by weight of the base resin.

13. The superabsorbent polymer of claim 9, further comprising a chelating agent or an organic acid.

14. The superabsorbent polymer according to claim 13, wherein The chelating agent includes 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 diglycine acid (EDG), diethylenetriaminepentaacetic acid (DTPA) and salts thereof.

15. The superabsorbent polymer according to claim 13, wherein The organic acid includes one or more selected from the group consisting of citric acid, acetic acid, formic acid, fumaric acid, lactic acid and propionic acid.

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