Superabsorbent polymer and method for producing the same

Abstract

To provide a superabsorbent polymer that may continuously and safely exhibit improved bacterial growth inhibition property and deodorization property without deterioration of physical properties of the superabsorbent polymer such as water retention capacity and absorption under pressure, and a method for producing the same.SOLUTION: A superabsorbent polymer comprises a base resin comprising a crosslinked polymer of acrylic acid-based monomers having acid groups, at least a part of the acid groups being neutralized, and an internal crosslinking agent, wherein at least a part of the base resin is surface-treated by a first surface crosslinking agent, and the first surface crosslinking agent is one or more compounds selected from the group consisting of a cationic compound, a terpene-based compound, a phenol-based compound, and a phosphoric acid-based compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Cross-Citation of Related Applications This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0044874 filed on April 13, 2020, and Korean Patent Application No. 10-2021-0047956 filed on April 13, 2021, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a superabsorbent polymer that can sustainably and safely exhibit improved bacterial growth inhibiting properties and deodorizing properties without reducing the physical properties of the superabsorbent polymer, such as water retention capacity and water absorption capacity under pressure, and a method for producing the same. [Background technology]

[0003] Super absorbent polymers (SAPs) are synthetic polymers capable of absorbing 500 to 1,000 times their own weight in water, and different developers have given them different names, such as SAM (Super Absorbency Material) or AGM (Absorbent Gel Material). These super absorbent polymers first came into practical use as sanitary products, and are now widely used in a variety of applications, including sanitary products such as baby diapers, soil water retention agents for gardening, water-stopping materials for civil engineering and construction, seedling sheets, freshness-preserving agents in the food distribution industry, and materials for poultices, as well as electrical insulation.

[0004] However, such superabsorbent polymers are most widely used in sanitary or disposable absorbent products such as baby diapers and adult diapers. Among these, when used in adult diapers, secondary odors caused by bacterial growth can cause significant discomfort to consumers. To address this issue, attempts have been made to incorporate various bacterial growth inhibitors, deodorizing or antibacterial functional ingredients into superabsorbent polymers.

[0005] However, when introducing antibacterial agents that inhibit bacterial growth into superabsorbent polymers, it has not been easy to select and introduce antibacterial components that exhibit excellent bacterial growth inhibition and deodorizing properties, are harmless to the human body, are economical, and do not impair the basic physical properties of the superabsorbent polymer.

[0006] For example, attempts have been made to incorporate antibacterial ingredients containing antibacterial metal ions such as silver, copper, or zinc, such as copper oxide, into superabsorbent polymers. These antibacterial metal ion-containing ingredients can impart deodorizing properties to superabsorbent polymers by destroying the cell walls of microorganisms such as bacteria and killing enzyme-containing bacteria that can cause odors. However, these metal ion-containing ingredients are classified as biocides, which can kill microorganisms that are beneficial to the human body. As a result, when applying these superabsorbent polymers to sanitary products such as baby or adult diapers, the incorporation of these metal ion-containing antibacterial ingredients is avoided as much as possible.

[0007] Meanwhile, conventional methods for incorporating antibacterial agents that inhibit bacterial growth into superabsorbent polymers have mainly involved mixing a small amount of the antibacterial agent into the superabsorbent polymer. However, this method has made it difficult to maintain consistent bacterial growth inhibition over time. Furthermore, this method has drawbacks, such as uneven application and detachment of the antibacterial agent during the mixing process of the superabsorbent polymer and the antibacterial agent, and the need for additional equipment for the mixing process.

[0008] As a result, there is a continuing demand for the development of technologies related to superabsorbent polymers that can exhibit excellent bacterial growth inhibiting properties and deodorizing properties without compromising the basic physical properties of the superabsorbent polymers. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present invention provides a superabsorbent polymer that can continuously and safely exhibit excellent bacterial growth inhibitory properties and deodorizing properties while maintaining excellent basic physical properties such as water retention capacity and water absorption capacity under pressure, and a method for producing the same. [Means for solving the problem]

[0010] According to one embodiment of the present invention, The present invention includes a base resin including an acrylic acid monomer containing an acidic group, at least a portion of which is neutralized, and a crosslinked polymer of an internal crosslinking agent, a superabsorbent resin in which at least a part of the base resin is surface-treated with a first surface cross-linking agent, The first surface cross-linking agent is one or more compounds selected from cationic compounds, terpene-based compounds, phenol-based compounds, and phosphoric acid-based compounds, and the superabsorbent resin is provided.

[0011] According to another embodiment of the present invention, a step of cross-linking and polymerizing an acrylic acid-based monomer containing an acid group, at least a portion of which has been neutralized, in the presence of an internal cross-linking agent to form a hydrogel polymer; drying, grinding, and classifying the hydrogel polymer to form a base resin; and additionally crosslinking the surface of the base resin in the presence of a first surface crosslinking agent; The method for producing a superabsorbent resin as described above is provided, wherein the first surface cross-linking agent is one or more compounds selected from the group consisting of cationic compounds, terpene compounds, phenolic compounds, and phosphoric acid compounds.

[0012] Furthermore, according to yet another embodiment of the present invention, there is provided an article comprising the superabsorbent polymer. [Effects of the Invention]

[0013] The highly water-absorbent polymer of the present invention can exhibit excellent bacterial growth inhibiting properties and deodorizing properties, selectively inhibiting the growth of only bacteria that are harmful to the human body and cause secondary bad odors.

[0014] In addition, the superabsorbent resin can stably exhibit the excellent bacterial growth inhibiting properties and deodorizing properties for a long period of time by surface crosslinking the base resin using a surface crosslinking agent with a specific structure that has excellent antibacterial and deodorizing properties, and can maintain excellent water retention capacity and water absorption capacity under pressure without deterioration of physical properties due to the addition of other antibacterial agents.

[0015] Therefore, the highly water-absorbent polymer can be very suitably applied to various sanitary products, such as not only baby diapers but also adult diapers, where secondary odors are particularly problematic. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the invention. The singular expressions include the plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprise," "include," "comprise," "have," and the like are intended to specify the presence of embodied features, steps, components, or combinations thereof, and should be understood not to preclude the presence or additional possibility of one or more other features, steps, components, or combinations thereof.

[0017] Meanwhile, in the present invention, the alkyl group having 1 to 20 carbon atoms may be a linear, branched, or cyclic alkyl group. Specifically, the alkyl group having 1 to 20 carbon atoms may be a linear alkyl group having 1 to 18 carbon atoms; a linear alkyl group having 1 to 10 carbon atoms; a linear alkyl group having 1 to 5 carbon atoms; a branched or cyclic alkyl group having 3 to 20 carbon atoms; a branched or cyclic alkyl group having 3 to 18 carbon atoms; or a branched or cyclic alkyl group having 3 to 10 carbon atoms. Specific examples include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neo-pentyl group, or a cyclohexyl group.

[0018] While the invention can be modified in various ways and can take various forms, specific embodiments are illustrated and described in detail below, but it should be understood that this is not intended to limit the invention to the particular disclosed form, but rather to include all modifications, equivalents, and alternatives falling within the spirit and technical scope of the invention.

[0019] Hereinafter, the highly water-absorbent polymer and the method for producing the same will be described in more detail with reference to specific embodiments of the invention.

[0020] For reference, the terms "polymer," "macromolecule," or "resin" used herein refer to a polymerized state of acrylic acid-based monomers, and may encompass any range of water content, any range of particle size, and any surface cross-linked or processed state. Among these polymers, polymers in a post-polymerization, pre-drying state with a water content of about 40% by weight or more may be referred to as hydrogel polymers. Furthermore, among these polymers, polymers with a particle size of 150 μm or less may be referred to as "fine powder."

[0021] In the present specification, the term "base resin" or "base resin powder" refers to a polymer obtained by polymerizing an acrylic acid-based monomer and drying and pulverizing it into particles or powder, without undergoing the surface modification or surface crosslinking steps described below.

[0022] The superabsorbent polymer according to one embodiment of the present invention comprises: A superabsorbent resin comprising a base resin including an acrylic acid monomer containing acidic groups, at least a portion of which has been neutralized, and a crosslinked polymer of an internal crosslinking agent, wherein at least a portion of the base resin is surface-treated with a first surface crosslinking agent, wherein the first surface crosslinking agent is one or more compounds selected from the group consisting of cationic compounds, terpene compounds, phenolic compounds, and phosphoric acid compounds.

[0023] In the past, to ensure the antibacterial and deodorizing properties of superabsorbent polymers, metal compounds with antibacterial properties or organic compounds containing cation or alcohol functional groups were introduced as additives. However, in this case, the safety of the superabsorbent polymer was reduced, or basic physical properties such as absorption properties were deteriorated, and there were problems with the durability of the antibacterial properties and the leakage of antibacterial substances.

[0024] In contrast, the present invention incorporates an antibacterial substance into a superabsorbent polymer by forming a surface cross-linked layer on the surface of a base resin using one or more compounds selected from the group consisting of cationic compounds, terpene compounds, alcohol compounds, and phosphate compounds as a surface cross-linking agent. As a result, the superabsorbent polymer exhibits excellent long-lasting bacterial growth inhibition and deodorizing properties, inhibiting the growth of odor-causing bacteria present on human skin, without compromising its basic physical properties, such as water retention and absorbency under pressure. Furthermore, the antibacterial substance is not likely to leak, enhancing safety to the human body. Therefore, the superabsorbent polymer is highly suitable for use in various sanitary products, such as adult diapers, where secondary odors are a particular concern.

[0025] Specifically, a superabsorbent resin according to one embodiment of the present invention includes the steps of: forming a hydrogel polymer by crosslinking and polymerizing an acrylic acid-based monomer containing acidic groups, at least a portion of which is neutralized, in the presence of an internal crosslinking agent; drying, pulverizing, and classifying the hydrogel polymer to form a base resin; and additionally crosslinking a surface of the base resin in the presence of a first surface crosslinking agent, wherein the first surface crosslinking agent is one or more compounds selected from the group consisting of cationic compounds, terpene-based compounds, phenol-based compounds, and phosphate-based compounds.

[0026] The superabsorbent resin can be prepared by a method including the steps of: forming a hydrogel polymer by crosslinking an acrylic acid-based monomer containing an acidic group, at least a portion of which has been neutralized, in the presence of an internal crosslinking agent (Step 1); drying, pulverizing, and classifying the hydrogel polymer to form a base resin (Step 2); and surface-crosslinking the base resin by heat-treating it in the presence of a first surface crosslinking agent (Step 3). Accordingly, according to another embodiment of the present invention, a method for preparing the superabsorbent resin is provided.

[0027] Each stage will be explained in detail below.

[0028] First, step 1 for preparing the superabsorbent resin according to one embodiment of the present invention is a step of forming a hydrogel polymer.

[0029] Specifically, the hydrogel polymer can be prepared by crosslinking an acrylic acid-based monomer, in which at least a portion of the acidic groups have been neutralized, with an internal crosslinking agent. To this end, a monomer composition in a solution state containing an acrylic acid-based monomer, in which at least a portion of the acidic groups have been neutralized, a polymerization initiator, an internal crosslinking agent, and a solvent can be used.

[0030] The acrylic acid monomer is a compound represented by the following Chemical Formula 1:

[0031] [Chemical formula 1] R 1 -COOM 1

[0032] In the above chemical formula 1, R 1 is an alkyl group having 2 to 5 carbon atoms and containing an unsaturated bond, M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0033] Preferably, the acrylic acid monomer includes at least one selected from the group consisting of acrylic acid, methacrylic acid, and their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts.

[0034] The acrylic acid-based monomer may have an acidic group, at least a portion of which may be neutralized. Preferably, the monomer may be partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide. The degree of neutralization of the acrylic acid-based monomer may be 40 mol% or more, or about 45 mol% or more, but may be 95 mol%, 80 mol%, or 75 mol% or less. The range of the degree of neutralization can be adjusted depending on the final properties. However, if the degree of neutralization is too high, the neutralized monomer may precipitate, hindering smooth polymerization. Conversely, if the degree of neutralization is too low, the polymer may not only exhibit significant reductions in absorbency but also exhibit properties similar to elastic rubber, making it difficult to handle.

[0035] The concentration of the acrylic acid-based monomer may be about 20% by weight or more, or about 40% by weight or more, but about 60% by weight or less, or about 50% by weight or less, based on the monomer composition containing the raw materials for the superabsorbent polymer, including the acrylic acid-based monomer with at least a portion of the acidic groups neutralized, a polymerization initiator, and an internal crosslinking agent, and a solvent, and may be an appropriate concentration taking into consideration the polymerization time and reaction conditions, etc. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low, which may cause economic problems. Conversely, if the concentration is too high, processing problems may occur, such as partial precipitation of the monomer or low pulverization efficiency when pulverizing the polymerized hydrogel polymer, and the physical properties of the superabsorbent polymer may be reduced.

[0036] The internal cross-linking agent is used to cross-link the inside of a polymer formed by polymerizing an acrylic acid-based monomer, and is distinguished from a surface cross-linking agent that cross-links the surface of the polymer.

[0037] Specific examples of the internal crosslinking agent include, but are not limited to, one or more selected from polyethylene glycol diacrylate, N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 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, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate.

[0038] The internal cross-linking agent is included in an amount of 0.01 to 1 part by weight per 100 parts by weight of the acrylic acid-based monomer, and can cross-link the polymerized polymer. If the content of the internal cross-linking agent is less than 0.01 part by weight, the improvement effect due to cross-linking is minimal, and if the content of the internal cross-linking agent is more than 1 part by weight, the absorption capacity of the superabsorbent resin may be reduced. More specifically, the internal cross-linking agent may be included in an amount of 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more, but not more than 1 part by weight, 0.5 parts by weight or less, or 0.3 parts by weight or less, per 100 parts by weight of the acrylic acid-based monomer.

[0039] The polymerization initiator used in the polymerization in the method for producing a superabsorbent resin of the present invention is not particularly limited as long as it is one that is generally used in the production of superabsorbent resins.

[0040] Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator using UV irradiation, depending on the polymerization method. However, even in the photopolymerization method, a certain amount of heat is generated by irradiation with UV rays or the like, and a certain amount of heat is generated as the polymerization reaction, which is an exothermic reaction, progresses, so a thermal polymerization initiator may also be included.

[0041] The photopolymerization initiator can be any compound that can form radicals when exposed to light such as ultraviolet light, and is not limited in its composition.

[0042] The photopolymerization initiator may be at least one selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone. A specific example of an acyl phosphine is commercially available lucirin TPO, i.e., diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide. A wide variety of photoinitiators are described in detail in Reinhold Schwalm's "UV Coatings: Basics, Recent Developments and New Applications" (Elsevier, 2007), p. 115, and are not limited to the above examples.

[0043] The photopolymerization initiator may be included in an amount of 0.001 to 1 part by weight based on 100 parts by weight of the acrylic acid-based monomer. If the amount of the photopolymerization initiator is less than 0.001 part by weight, the polymerization rate may be slow, and if the amount of the photopolymerization initiator is more than 1 part by weight, the molecular weight of the superabsorbent resin may be small, resulting in non-uniform physical properties. More specifically, the photopolymerization initiator may be included in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.1 parts by weight or more, and 0.5 parts by weight or less, or 0.3 parts by weight or less based on 100 parts by weight of the acrylic acid-based monomer.

[0044] In addition, when a thermal polymerization initiator is further included as the polymerization initiator, the thermal polymerization initiator may be at least one selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid. Specific examples of persulfate initiators include sodium persulfate (NaSO), potassium persulfate (KSO), and ammonium persulfate ((NHSO). Examples of azo initiators include 2,2-azobis(2-amidinopropane) dihydrochloride and 2,2-azobis(N,N-dimethylene)isobutyramidine dihydrochloride. dihydrochloride, 2-(carbamoylazo)isobutylonitril, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, and 4,4-azobis-(4-cyanovaleric acid). A wide variety of thermal polymerization initiators are well documented in Odian's "Principle of Polymerization" (Wiley, 1981), p. 203, and are not limited to the examples listed above.

[0045] The thermal polymerization initiator may be included in an amount of 0.001 to 1 part by weight based on 100 parts by weight of the acrylic acid-based monomer. If the amount of the thermal polymerization initiator is less than 0.001 part by weight, additional thermal polymerization hardly occurs, and the effect of adding the thermal polymerization initiator may be minimal. If the amount of the thermal polymerization initiator is more than 1 part by weight, the molecular weight of the superabsorbent resin may be small, resulting in non-uniform physical properties. More specifically, the thermal polymerization initiator may be included in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.1 parts by weight or more, but not more than 0.5 parts by weight, or not more than 0.3 parts by weight based on 100 parts by weight of the acrylic acid-based monomer.

[0046] In addition to the polymerization initiator, one or more additives such as a surfactant, a thickener, a plasticizer, a storage stabilizer, and an antioxidant may be further included as needed during crosslinking polymerization.

[0047] The monomer composition containing the acrylic acid-based monomer, the internal crosslinking agent, the polymerization initiator, and optional additives may be prepared in the form of a solution dissolved in a solvent.

[0048] The solvent may be any solvent capable of dissolving the above-mentioned components, and may be, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide. The solvent may be present in an amount remaining after excluding the above-mentioned components from the total content of the monomer composition.

[0049] On the other hand, the method for forming a hydrogel polymer by photopolymerizing such a monomer composition is not particularly limited as long as it is a commonly used polymerization method.

[0050] Specifically, the photopolymerization can be carried out by irradiating ultraviolet light having an intensity of 5 mW or more, or 10 mW or more, and 30 mW or less, or 20 mW or less, at a temperature of 60° C. or more, or 70° C. or more, and 90° C. or less, or 80° C. or less. Photopolymerization under these conditions can form a crosslinked polymer with better polymerization efficiency.

[0051] Furthermore, when the photopolymerization is carried out, it can be carried out in a reactor equipped with a movable conveyor belt, but the above-mentioned polymerization method is only an example, and the present invention is not limited to the above-mentioned polymerization method.

[0052] Furthermore, when photopolymerization is performed in a reactor equipped with a movable conveyor belt as described above, the resulting hydrogel polymer is typically in the form of a sheet having the width of the belt. The thickness of the polymer sheet varies depending on the concentration and injection rate of the monomer composition injected, but it is preferable to supply the monomer composition so as to obtain a sheet polymer having a thickness of about 0.5 to about 5 cm. Supplying the monomer composition so that the thickness of the sheet polymer is excessively thin is undesirable because of low production efficiency, and if the thickness of the sheet polymer exceeds 5 cm, the polymerization reaction may not occur uniformly throughout the entire thickness due to the excessive thickness.

[0053] The water content of the hydrogel polymer obtained by the above method may be about 40 to about 80 wt% based on the total weight of the hydrogel polymer. Throughout this specification, the term "water content" refers to the water content relative to the total weight of the hydrogel polymer, calculated by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer. Specifically, it is defined as the value calculated by measuring the weight loss due to evaporation of water in the polymer during the drying process by increasing the temperature of the polymer using infrared heating. The drying conditions are as follows: the temperature is increased from room temperature to about 180°C and then maintained at 180°C; the total drying time is set to 20 minutes, including a 5-minute temperature increase step, and the water content is measured.

[0054] Meanwhile, after preparing the hydrogel polymer, a coarse pulverization process may be optionally carried out to pulverize the prepared hydrogel polymer prior to the subsequent drying and pulverization processes.

[0055] The coarse pulverization process is a process for increasing the drying efficiency in the subsequent drying process and controlling the particle size of the final superabsorbent polymer powder. The pulverizer used here is not limited in terms of its configuration, and may specifically include any one selected from the group of pulverizing devices consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a meat chopper, and a disc cutter, but is not limited to the above examples.

[0056] The coarse pulverization step can be carried out so that the particle size of the hydrogel polymer is, for example, about 2 to about 10 mm. Pulverizing the hydrogel polymer to a particle size of less than 2 mm is technically difficult due to the high water content of the hydrogel polymer, and the pulverized particles may aggregate together. On the other hand, pulverizing the hydrogel polymer to a particle size of more than 10 mm results in little increase in the efficiency of the subsequent drying step.

[0057] Next, in step 2, the hydrogel polymer prepared in step 1 is dried, pulverized, and classified to form a base resin.

[0058] The drying method may be selected from any method commonly used in the drying process of hydrogel polymers, without limitation on its structure. Specifically, the drying step may be carried out by hot air supply, infrared radiation, microwave radiation, or ultraviolet radiation.

[0059] Specifically, the drying can be carried out at a temperature of about 150 to about 250°C. If the drying temperature is below 150°C, the drying time will be too long, which may result in a deterioration in the physical properties of the resulting superabsorbent polymer. If the drying temperature exceeds 250°C, only the polymer surface will be excessively dried, which may result in the generation of fine powder in the subsequent pulverization process, which may result in a deterioration in the physical properties of the resulting superabsorbent polymer. Therefore, the drying can preferably be carried out at a temperature of 150°C or higher, or 160°C or higher, and 200°C or lower, or 180°C or lower.

[0060] On the other hand, the drying time can be about 20 to about 90 minutes, taking into consideration process efficiency, but is not limited to this.

[0061] The water content of the polymer after such a drying step may be about 5 to about 10% by weight.

[0062] After the drying step, a pulverization step is carried out.

[0063] The pulverization process can be carried out so that the particle size of the polymer powder, i.e., the base resin, is about 150 to about 850 μm. Specific examples of the pulverizer used to pulverize to such a particle size include a pin mill, hammer mill, screw mill, roll mill, disc mill, and jog mill, but the present invention is not limited to these examples.

[0064] After the pulverization step, the pulverized polymer powder may be further classified according to particle size in order to control the properties of the superabsorbent resin to be manufactured as a final product.

[0065] Preferably, polymers having particle sizes of about 150 to about 850 μm are classified, and only polymers having such particle sizes are used as the base resin, which can be subjected to a surface cross-linking reaction step to produce a product.

[0066] The base resin obtained as a result of the above process may be in the form of a powder containing a crosslinked polymer obtained by crosslinking an acrylic acid-based monomer and an internal crosslinking agent. Specifically, the base resin may be in the form of a powder having a particle size of 150 to 850 μm.

[0067] Next, in step 3, the base resin prepared in step 2 is surface-crosslinked by heat-treating it in the presence of a first surface crosslinking agent and, optionally, a second surface crosslinking agent.

[0068] The surface cross-linking is a step of increasing the cross-link density near the surface of the base resin relative to the cross-link density inside the particle. Generally, a surface cross-linking agent is applied to the surface of the base resin. Therefore, this reaction occurs mainly on the surface of the base resin, which improves the cross-linking property on the surface of the particle without substantially affecting the inside of the particle. Therefore, the surface-cross-linked base resin has a higher degree of cross-linking near the surface than inside.

[0069] The surface cross-linking step is carried out using a surface cross-linking liquid containing the first surface cross-linking agent.

[0070] The first surface cross-linking agent used in the preparation of the superabsorbent resin according to one embodiment of the present invention may be a compound that has antibacterial properties and a functional group capable of bonding to a carboxylic acid group of the base resin. Alternatively, the first surface cross-linking agent may be prepared by introducing one or more functional groups capable of bonding to a carboxylic acid group into an antibacterial compound that does not have a functional group capable of bonding to a carboxylic acid group. As a result, a surface cross-linked layer having antibacterial properties can be formed on the surface of the base resin.

[0071] In the first surface crosslinking agent, the functional group that forms crosslinking polymerization with the carboxyl group may be specifically a hydroxyl group, an epoxy group, a carbonate group, a metal salt, an amine group, or the like, and the first surface crosslinking agent may include any one or two or more functional groups among these.

[0072] In addition, the first surface cross-linking agent used in the preparation of the superabsorbent polymer according to one embodiment of the present invention is preferably a hydrophilic compound to prevent the inherent absorption properties of the superabsorbent polymer from decreasing. However, the first surface cross-linking agent may also be a hydrophobic compound, and the content may be adjusted depending on the degree of hydrophobicity to minimize the decrease in absorption properties and impart antibacterial properties.

[0073] The compound that can be used as such a first surface crosslinking agent may be one or more compounds selected from cationic compounds, terpene compounds, phenolic compounds, and phosphoric acid compounds. These compounds exhibit excellent antibacterial properties, and at the same time, form covalent bonds with carboxyl groups on the surface of the base resin, thereby being stably contained in the surface crosslinked layer, and there is no risk of problems caused by elution of the antibacterial agent.

[0074] Specifically, the cationic compound may be a guanidine-based compound.

[0075] The terpene-based compound may be specifically a menthol-based compound or a citronellol-based compound, and any one or a mixture of two or more thereof may be used.

[0076] In addition, the phosphoric acid-based compound may be specifically a phosphonic acid-based compound such as phosphoric acid, phosphonic acid, or amino phosphonic acid, or a phosphinic acid-based compound such as phosphinic acid, bis(aminomethyl)phosphinic acid, or bis(hydroxymethyl)phosphinic acid.

[0077] According to one embodiment of the present invention, a cationic compound may be used as the first surface cross-linking agent, and among the cationic compounds, a guanidine-based compound may be more preferably used.

[0078] Examples of usable guanidine compounds include guanidine, guanidine carbonate, and guanidine hydrochloride, with guanidine carbonate being preferred.

[0079] According to another embodiment of the present invention, the first surface cross-linking agent may be a terpene-based compound, and more preferably, menthol or citronellol.

[0080] According to one embodiment of the present invention, the first surface cross-linking agent may be a phenolic compound such as gallic acid, tannic acid, coumaric acid, caffeic acid, ferulic acid, or protocatechuic acid, and more preferably gallic acid.

[0081] The first surface cross-linking agent is incorporated into the superabsorbent resin by being cross-linked with the base resin and introduced into the surface cross-linked layer. Therefore, by appropriately controlling the content of the first surface cross-linking agent, it is possible to enhance the antibacterial and deodorizing properties of the superabsorbent resin without reducing its absorption properties.

[0082] Specifically, the superabsorbent resin according to one embodiment of the present invention may include the first surface cross-linking agent in an amount of 0.01 to 10 parts by weight relative to 100 parts by weight of the base resin. More specifically, the first surface cross-linking agent may be included in an amount of 0.01 parts by weight or more, or 0.1 parts by weight or more, or 0.5 parts by weight or more, and 10 parts by weight or less, or 5 parts by weight or less, or 3 parts by weight or less, or 2 parts by weight or less, relative to 100 parts by weight of the base resin.

[0083] When the first surface cross-linking agent is contained in the above content range, the superabsorbent resin can continuously and stably exhibit excellent antibacterial and deodorizing properties without the risk of deterioration in the physical properties of the superabsorbent resin.

[0084] Meanwhile, the superabsorbent resin according to one embodiment of the present invention may further include a second surface cross-linking agent during surface treatment to improve the inherent absorption properties of the superabsorbent resin. The second surface cross-linking agent is distinguished from the first surface cross-linking agent in that it does not have an antibacterial functional group.

[0085] In addition, in a preferred example of the present invention, in order to exhibit improved bacterial growth inhibiting properties and deodorizing properties without deteriorating the physical properties of the superabsorbent resin, such as water retention capacity and water absorption capacity under pressure, both the first and second surface crosslinking agents are contained.

[0086] The second surface cross-linking agent is not limited in its structure as long as it is a compound capable of reacting with the functional group of the polymer. Preferably, in order to improve the properties of the resulting superabsorbent resin, the second surface cross-linking agent may be one or more selected from the group consisting of polyhydric alcohol compounds, epoxy compounds, polyamine compounds, haloepoxy compounds, condensation products of haloepoxy compounds, oxazoline compounds, mono-, di-, or polyoxazolidinone compounds, cyclic urea compounds, polyvalent metal salts, and alkylene carbonate compounds.

[0087] Specific examples of the polyhydric alcohol compound include one or more selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, and glycerol.

[0088] In addition, as the epoxy compound, ethylene glycol diglycidyl epoxide, ethylene glycol diglycidyl ether, glycidol, etc. can be used, and as the polyamine compound, one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamidepolyamine can be used.

[0089] The haloepoxy compound may be epichlorohydrin, epibromohydrin, or α-methylepichlorohydrin, while the mono-, di-, or polyoxazolidinone compound may be, for example, 2-oxazolidinone.

[0090] The alkylene carbonate compound may be an alkylene carbonate having 2 to 6 carbon atoms, such as ethylene carbonate or propylene carbonate, which may be used alone or in combination of two or more alkylene carbonates having different carbon numbers.

[0091] As the polyvalent metal salt, specifically, sulfates or carboxylates containing a metal such as aluminum can be used, and among these, aluminum sulfate is more preferably used.

[0092] The second surface cross-linking agent can be added in an amount of 0.001 to 5 parts by weight relative to 100 parts by weight of the base resin. For example, the second surface cross-linking agent can be used in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.1 parts by weight or more, and 3 parts by weight or less, or 2 parts by weight or less, or 1 part by weight or less, or 0.3 parts by weight or less, relative to 100 parts by weight of the base resin. By adjusting the content of the second surface cross-linking agent within the above range, a superabsorbent resin exhibiting various physical properties, such as excellent absorption performance and liquid permeability, can be produced.

[0093] There is no limitation on the constitution of a method for mixing the first and second surface crosslinking agents with a base resin. A method in which the first and second surface crosslinking agents and the base resin are placed in a reaction tank and mixed, a method in which the first and second surface crosslinking agents are sprayed onto a base resin, a method in which the base resin and the first and second surface crosslinking agents are continuously supplied to a continuously operated mixer and mixed, etc. can be used.

[0094] As a result, a surface cross-linked layer is formed on the base resin by additionally cross-linking at least a part of the base resin via the first surface cross-linking agent or the first and second surface cross-linking agents. Preferably, a surface cross-linked layer can be formed on the base resin by uniformly cross-linking the entire surface of the base resin via the first surface cross-linking agent or the first and second surface cross-linking agents.

[0095] Therefore, according to one embodiment of the present invention, the superabsorbent resin may have a core-shell structure in which the base resin serves as a core and the core is surrounded by a surface cross-linked layer in the form of a shell. More specifically, the superabsorbent resin may have a core-shell structure in which the surface cross-linked layer in the form of a shell formed by a first surface cross-linking agent or a surface cross-linked layer in the form of a shell formed by first and second surface cross-linking agents.

[0096] According to another embodiment of the present invention, the superabsorbent resin may have a sea-island structure in which the base resin serves as a core and discontinuous surface cross-linked structures are located on the core in the form of islands. More specifically, the superabsorbent resin may have a sea-island structure in which the base resin serves as a core and the surface cross-linked structures formed by a first surface cross-linking agent are located on the core in the form of discontinuous islands, or the surface cross-linked structures formed by the first and second surface cross-linking agents are located on the core in the form of discontinuous islands.

[0097] In addition to the first and second surface crosslinking agents, water and alcohol may be mixed together and added in the form of the surface crosslinking solution. Adding water and alcohol has the advantage of enabling the first and second surface crosslinking agents to be uniformly dispersed in the base resin. The amount of water and alcohol added is preferably about 5 to about 12 parts by weight per 100 parts by weight of the base resin, in order to induce uniform dispersion of the first and second surface crosslinking agents, prevent clumping of the base resin, and optimize the surface penetration depth of the crosslinking agents.

[0098] The surface cross-linking reaction is carried out by heating the base resin containing the first and second surface cross-linking agents at a temperature of about 150 to about 220°C for about 15 to about 100 minutes. If the cross-linking reaction temperature is less than 150°C, the surface cross-linking reaction may not occur sufficiently, while if it exceeds 220°C, the surface cross-linking reaction may occur excessively. If the cross-linking reaction time is too short, less than 15 minutes, the cross-linking reaction may not occur sufficiently. If the cross-linking reaction time exceeds 100 minutes, the cross-linking reaction may occur excessively, resulting in an excessive increase in the cross-link density on the particle surface and a decrease in physical properties. More specifically, the cross-linking reaction may be carried out by heating at a temperature of 150°C or higher, or 160°C or higher, and 220°C or lower, or 200°C or lower, for 20 minutes or more, or 40 minutes or more, and 70 minutes or less, or 60 minutes or less.

[0099] The heating means for the additional crosslinking reaction is not particularly limited. Heating can be achieved by supplying a heat medium or by directly supplying a heat source. Usable heat mediums include heated fluids such as steam, hot air, and hot oil, but the present invention is not limited to these. The temperature of the supplied heat medium can be appropriately selected taking into account the heat medium, heating rate, and target temperature. Directly supplied heat sources include electrical heating and gas heating, but the present invention is not limited to these examples.

[0100] Through the above manufacturing process, a superabsorbent resin can be manufactured and provided.

[0101] The superabsorbent resin thus produced comprises a base resin comprising a crosslinked polymer of an acrylic acid-based monomer containing acidic groups, at least a portion of which has been neutralized, and an internal crosslinking agent; and a surface crosslinked layer formed on the base resin by additional crosslinking of the base resin via a first surface crosslinking agent or first and second surface crosslinking agents. By incorporating antibacterial-derived units into the surface crosslinked layer of the base resin, the superabsorbent resin can sustainably and safely exhibit improved bacterial growth inhibition and deodorizing properties without compromising its physical properties, such as water retention and pressure absorption. Furthermore, because the antibacterial agent is physically or chemically firmly fixed or bound to the base resin, unlike conventional cases where an antibacterial agent is simply mixed with a superabsorbent resin, uneven application, detachment, or separation during transportation of the antibacterial agent does not occur. The antibacterial component is uniformly distributed throughout the resin, allowing the antibacterial agent to stably exhibit excellent bacterial growth inhibition and deodorizing properties for a long period of time.

[0102] When the superabsorbent polymer is a superabsorbent polymer in which at least a portion of the base resin has been surface-treated with a first surface crosslinking agent, the centrifuge retention capacity (CRC) measured by EDANA method WSP 241.3 may be in the range of about 28 g / g or more, or about 29 g / g or more, or about 30 g / g or more, and about 60 g / g or less, or about 55 g / g or less, or about 50 g / g or less, or about 40 g / g or less, or about 38 g / g or less, or about 35 g / g or less.

[0103] In addition, when the superabsorbent resin is a superabsorbent resin in which at least a portion of the base resin is surface-treated with a first surface crosslinking agent, the absorbency under pressure (AUP) at 0.7 psi measured by EDANA method WSP 242.3 may be in the range of about 8 g / g or more, or 10 g / g or more, or about 20 g / g or more, or about 23 g / g or more, or about 25 g / g or more, but about 37 g / g or less, or about 35 g / g or less, or about 32 g / g or less.

[0104] When the superabsorbent resin is a resin in which at least a portion of the base resin is surface-treated with a first surface crosslinking agent and a second surface crosslinking agent, the centrifuge retention capacity (CRC) measured by EDANA method WSP 241.3 can be in the range of about 28 g / g or more, about 29 g / g or more, or about 30 g / g or more, and about 40 g / g or less, about 38 g / g or less, or about 35 g / g or less.

[0105] In addition, when the superabsorbent resin is a resin in which at least a portion of the base resin is surface-treated with a first surface crosslinking agent and a second surface crosslinking agent, the superabsorbent resin may have a water absorbency under pressure (AUP) at 0.7 psi measured by EDANA method WSP 242.3 of about 20 g / g or more, or about 23 g / g or more, or about 25 g / g or more, and about 37 g / g or less, or about 35 g / g or less, or about 32 g / g or less.

[0106] Therefore, such a highly absorbent polymer can be preferably contained and used in various sanitary products, such as disposable diapers for babies, adult diapers, and sanitary napkins, and is particularly preferably applicable to adult diapers, where secondary odors caused by bacterial growth are particularly problematic.

[0107] Such a sanitary product may have the same structure as a normal sanitary product, except that the highly water-absorbent polymer of one embodiment is contained in the absorbent body.

[0108] In addition to sanitary goods, such highly water-absorbent polymers can be used in a variety of products, such as water-absorbent products, soil repair agents, water-stopping materials for civil engineering and construction, seedling sheets, freshness-preserving agents, materials for wetting, electrical insulators, oral and dental products, cosmetic or skin products.

[0109] The present invention will be described in more detail with reference to the following examples, but the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. [Example]

[0110] <Example> Manufacturing of superabsorbent polymers Example 1 518 g of acrylic acid, 1.2 g of polyethylene glycol (400) diacrylate, and 0.04 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide were dissolved in a 3 L glass vessel equipped with a stirrer, nitrogen injector, and thermometer. 822.2 g of 24.5% sodium hydroxide solution was then added and nitrogen was continuously injected to prepare a water-soluble unsaturated monomer aqueous solution. The water-soluble unsaturated monomer aqueous solution was cooled to 40°C, and 15.54 g of 4% sodium persulfate aqueous solution was added. The solution was then placed in a stainless steel vessel measuring 250 mm wide, 250 mm long, and 30 mm high, and irradiated with ultraviolet light (irradiation dose: 10 mV / cm) for 60 seconds in a UV chamber at 80°C. 2 ) and aged for 2 minutes to obtain a hydrogel polymer. The obtained hydrogel polymer was crushed to a size of 2 mm x 2 mm, and the resulting gel-type resin was spread to a thickness of approximately 30 mm on stainless steel wire gauze with a pore size of 600 μm and dried in a hot air oven at 185°C for 32 minutes. The dried polymer thus obtained was crushed using a crusher and classified using a standard ASTM mesh sieve to obtain a base resin with a particle size of 150 to 850 μm.

[0111] A surface cross-linking solution containing 4.4 parts by weight of water, 0.3 parts by weight of ethylene carbonate, 0.075 parts by weight of a polycarboxylate surfactant, 0.3 parts by weight of aluminum sulfate, and 0.5 parts by weight of guanidine carbonate was sprayed and mixed into 100 parts by weight of the base resin, and the mixture was placed in a vessel equipped with a stirrer and a double jacket and subjected to a surface cross-linking reaction at 180°C for 70 minutes. The surface-treated powder was then classified using a standard ASTM mesh sieve to obtain a superabsorbent resin powder having a particle size of 150 to 850 μm.

[0112] Example 2 A base resin was prepared in the same manner as in Example 1, and then surface cross-linking was carried out in the same manner as in Example 1 using a surface cross-linking solution containing 100 parts by weight of the base resin, 4.4 parts by weight of water, 0.3 parts by weight of ethylene carbonate, 0.075 parts by weight of a polycarboxylate surfactant, 0.3 parts by weight of aluminum sulfate, and 0.5 parts by weight of menthol. All subsequent processes were carried out in the same manner as in Example 1 to obtain a superabsorbent resin powder.

[0113] Example 3 A base resin was prepared in the same manner as in Example 1, and then surface cross-linking was carried out in the same manner as in Example 1 using a surface cross-linking solution containing 100 parts by weight of the base resin, 4.4 parts by weight of water, 0.3 parts by weight of ethylene carbonate, 0.075 parts by weight of a polycarboxylate surfactant, 0.3 parts by weight of aluminum sulfate, and 0.5 parts by weight of gallic acid. All subsequent processes were carried out in the same manner as in Example 1 to obtain a superabsorbent resin powder.

[0114] Example 4 A base resin was prepared in the same manner as in Example 1, and then surface cross-linking was carried out in the same manner as in Example 1 using a surface cross-linking solution containing 100 parts by weight of the base resin, 4.4 parts by weight of water, 0.3 parts by weight of ethylene carbonate, 0.075 parts by weight of a polycarboxylate surfactant, 0.3 parts by weight of aluminum sulfate, and 0.5 parts by weight of citronellol. All subsequent processes were carried out in the same manner as in Example 1 to obtain a superabsorbent resin powder.

[0115] Example 5 A base resin was prepared in the same manner as in Example 1, and then surface cross-linking was carried out in the same manner as in Example 1 using a surface cross-linking solution containing 100 parts by weight of the base resin, 4.4 parts by weight of water, 0.3 parts by weight of ethylene carbonate, 0.075 parts by weight of a polycarboxylate surfactant, 0.3 parts by weight of aluminum sulfate, and 2 parts by weight of phosphoric acid. All subsequent processes were carried out in the same manner as in Example 1 to obtain a superabsorbent resin powder.

[0116] Example 6 A base resin was prepared in the same manner as in Example 1, and then surface cross-linking was carried out in the same manner as in Example 1 using a surface cross-linking solution containing 4.4 parts by weight of water, 0.075 parts by weight of polycarboxylate surfactant, 0.3 parts by weight of aluminum sulfate, and 2 parts by weight of phosphoric acid to 100 parts by weight of the base resin. All subsequent processes were carried out in the same manner as in Example 1 to obtain a superabsorbent resin powder.

[0117] Comparative Example 1 A base resin was prepared in the same manner as in Example 1, and then surface crosslinking was carried out in the same manner as in Example 1 using a surface crosslinking solution containing 100 parts by weight of the base resin, 4.4 parts by weight of water, 0.3 parts by weight of ethylene carbonate, 0.075 parts by weight of a polycarboxylate surfactant, and 0.3 parts by weight of aluminum sulfate.

[0118] Thereafter, the surface-treated powder was classified using a standard mesh sieve according to ASTM standards to obtain a highly water-absorbent resin powder having a particle size of 150 to 850 μm.

[0119] Comparative Example 2 100 parts by weight of the superabsorbent resin powder prepared by the method of Comparative Example 1 was dry-mixed with 0.5 parts by weight of guanidine carbonate at 25°C without a solvent using a Vortex mixer (Vortex-Genie 2 mixer, Scientific Industries).

[0120] Comparative Example 3 100 parts by weight of the highly water-absorbent resin powder produced by the method of Comparative Example 1 was dry-mixed with 0.5 parts by weight of menthol in the same manner as in Comparative Example 2.

[0121] Comparative Example 4 100 parts by weight of the highly water-absorbent resin powder produced by the method of Comparative Example 1 was dry-mixed with 0.5 parts by weight of gallic acid in the same manner as in Comparative Example 2.

[0122] Comparative Example 5 100 parts by weight of the highly water-absorbent resin powder produced by the method of Comparative Example 1 was dry-mixed with 0.5 parts by weight of citronellol in the same manner as in Comparative Example 2.

[0123] Comparative Example 6 100 parts by weight of the highly water-absorbent resin powder produced by the method of Comparative Example 1 was dry-mixed with 2 parts by weight of phosphoric acid in the same manner as in Comparative Example 2.

[0124] <Experimental Example> The properties of the superabsorbent resins prepared in the above Examples and Comparative Examples were evaluated by the following methods.

[0125] Unless otherwise specified, all of the following physical property evaluations were performed at constant temperature and humidity (23±1°C, relative humidity 50±10%), and saline or salt water refers to a 0.9 wt% aqueous sodium chloride (NaCl) solution.

[0126] (1)Centrifuge Retention Capacity (CRC) The water retention capacity of each resin was measured by the absorbency under no load using EDANA WSP 241.3.

[0127] Specifically, a quantity of superabsorbent resin W0 (g) (approximately 0.2 g) was evenly placed in a nonwoven fabric envelope, sealed, and then immersed in saline (0.9 wt%) at room temperature. After 30 minutes, the envelope was centrifuged at 250 G for 3 minutes to remove water, and the mass of the envelope W2 (g) was measured. The same procedure was repeated without the resin, and the mass W1 (g) was then measured. The centrifugal water retention capacity (CRC) (g / g) was calculated using the obtained masses according to the following formula:

[0128] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0129] (2) Absorption Under Pressure (AUP) The water absorption capacity of each resin at a pressure of 0.7 psi was measured by EDANA method WSP 242.3.

[0130] Specifically, a 400-mesh stainless steel iron net was attached to the bottom of a plastic cylinder with an inner diameter of 60 mm. Under conditions of room temperature and 50% humidity, 0.90 g of superabsorbent resin W0 (g) was evenly spread on the iron net, and a piston capable of applying a uniform load of 0.7 psi to the resin was slightly smaller than the outer diameter of 60 mm, with no gap between it and the inner wall of the cylinder to prevent interference with its up-and-down movement. The weight of the device, W3 (g), was then measured.

[0131] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a Petri dish with a diameter of 150 mm, and physiological saline solution composed of 0.9 wt% sodium chloride was placed at the same level as the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of the glass filter. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for 1 hour. After 1 hour, the measuring device was removed and its weight W4 (g) was measured.

[0132] The obtained masses were used to calculate the water absorption capacity under pressure (AUP) (g / g) according to the following formula.

[0133] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0134] (3) Bacteria growth inhibition performance test 1 50ml of artificial urine inoculated with Proteus mirabilis (ATCC 29906) at 3000 CFU / ml was cultured in an incubator at 37°C for 16 hours. The artificial urine immediately after inoculation and after 16 hours served as controls. These samples were thoroughly washed with 150ml of saline and cultured on Nutrient Broth Agar (BD DIFCO) plates to measure the CFU (Colony Forming Unit; CFU / ml), which was then used to calculate the physical properties of the control group.

[0135] More specifically, 2 g of each of the superabsorbent resins of Examples 1 to 4 and Comparative Examples 1 to 5 was added to 50 ml of artificial urine inoculated with Proteus mirabilis (ATCC 29906) at 3,000 CFU / ml, and the mixture was shaken for 1 minute to ensure uniform mixing. This mixture was then cultured in an incubator at 37°C for 16 hours. After 16 hours of culture, the artificial urine was thoroughly washed with 150 ml of saline and cultured on a nutrient broth agar plate to measure the CFU (Colony Forming Unit; CFU / ml).

[0136] The results of these measurements were calculated as the growth rate of the bacteria Proteus mirabilis (ATCC 29906) represented by the following formula 1, and the bacterial growth inhibitory properties of each Example and Comparative Example were evaluated based on this:

[0137] Proteus mirabilis, the strain used to measure bacterial growth rate, secretes urease, which breaks down urea in urine and produces ammonia, which causes bad odors. Therefore, the antibacterial and deodorizing effects of superabsorbent polymers can be appropriately evaluated based on the growth rate of Proteus mirabilis. However, excessive inhibition of Proteus mirabilis growth for the sake of deodorizing effects can kill other beneficial bacteria in the body, causing problems such as skin rashes, so an appropriate level of growth inhibition is necessary.

[0138] [Formula 1] Bacterial growth rate (%) = [CFU(16h)] / [CFU(0h)] x 100

[0139] In the above formula 1, CFU (0h) indicates the number of bacteria (Proteus mirabilis; ATCC29906) initially inoculated into the superabsorbent polymer per unit volume of artificial urine (3000 CFU / ml), and CFU (16h) indicates the number of bacteria proliferated per unit volume of artificial urine (CFU / ml) when the superabsorbent polymer was maintained at 37°C for 16 hours.

[0140] The physical properties of the examples and comparative examples are shown in Table 1 below.

[0141] [Table 1]

[0142] Referring to Table 1, it can be seen that in Examples 1 to 3, in which surface cross-linking was performed using the first surface cross-linking agent of the present invention, excellent bacterial growth inhibitory properties were exhibited without any reduction in absorption properties.

[0143] In Comparative Examples 2 to 4, in which the same compound was dry-mixed with a surface-crosslinked superabsorbent polymer, the bacterial growth rate was lower than in Comparative Example 1, in which no antibacterial compound was added, but was about 20% higher than in Examples 1 to 3. Therefore, it can be experimentally confirmed that, when a specific antibacterial compound is used as a surface crosslinking agent for surface crosslinking as in the present invention, superior bacterial growth inhibition properties and deodorizing properties are stably exhibited for a long period of time compared to when the compound is simply mixed with a superabsorbent polymer.

[0144] (4) Bacteria growth inhibition performance test 2 50ml of artificial urine inoculated with Proteus mirabilis (CCUG 4637) at 3000 CFU / ml was cultured in an incubator at 35°C for 12 hours. The artificial urine immediately after inoculation and after 12 hours served as controls. These samples were thoroughly washed with 150ml of saline and cultured on Nutrient Broth Agar (BD DIFCO) plates to measure the CFU (Colony Forming Unit; CFU / ml), which was used to calculate the physical properties of the control group.

[0145] More specifically, 2 g of each of the superabsorbent resins of Examples 5-6 and Comparative Examples 1, 6-7 was added to 50 ml of artificial urine inoculated with Proteus mirabilis (CCUG 4637) at 3000 CFU / ml and shaken for 1 minute to ensure uniform mixing. This was then cultured in an incubator at 35°C for 12 hours. After 12 hours of culture, the artificial urine was thoroughly washed with 150 ml of saline and cultured on a nutrient broth agar plate to measure the CFU (Colony Forming Unit; CFU / ml).

[0146] The results of these measurements were calculated as the proliferation rate of the bacteria Proteus mirabilis (CCUG 4637) as shown in the following formula 2, and the bacterial proliferation inhibitory properties of each example and comparative example were evaluated based on this:

[0147] [Formula 2] Bacterial growth rate (%) = [CFU(12h)] / [CFU(0h)] x 100

[0148] In the above formula 2, CFU (0h) indicates the number of bacteria (Proteus mirabilis; CCUG 4637) initially inoculated into the superabsorbent polymer per unit volume of artificial urine (3000 CFU / ml), and CFU (12h) indicates the number of bacteria proliferated per unit volume of artificial urine (CFU / ml) when the superabsorbent polymer was maintained at 35°C for 12 hours.

[0149] [Table 2]

[0150] Referring to Table 2, it can be seen that excellent bacterial growth inhibitory properties are also exhibited when a phosphorus-based compound is used as the first surface crosslinking agent. Meanwhile, in the case of Example 6, in which surface crosslinking was performed using only the first surface crosslinking agent without using the second surface crosslinking agent, antibacterial performance was similar to that of Example 5, but it was confirmed that there was a difference in the physical properties of the superabsorbent resin.

[0151] Microorganisms present in artificial urine are distributed evenly both inside and outside of superabsorbent polymers, but when the same compound is dry-mixed with a surface-crosslinked superabsorbent polymer, the antibacterial compound is distributed unevenly around the superabsorbent polymer. On the other hand, when the antibacterial compound is distributed evenly on the surface of the superabsorbent polymer through surface crosslinking, it has been confirmed that this increases contact between the microorganisms and the antibacterial compound, resulting in more effective antibacterial performance.

[0152] Comparing the growth rates in Tables 1 and 2, it was confirmed that the Examples in which the microbial compounds were bonded through surface cross-linking had a longer microbial growth inhibitory effect over a longer incubation period of 12 or 16 hours than the Comparative Example in which the microbial compounds were simply mixed without surface treatment.

Claims

1. The present invention includes a base resin including an acrylic acid monomer containing an acidic group, at least a portion of which is neutralized, and a crosslinked polymer of an internal crosslinking agent, a superabsorbent resin in which at least a part of the base resin is surface-treated with a first surface cross-linking agent, The first surface cross-linking agent is a superabsorbent resin that is one or more compounds selected from the group consisting of cationic compounds, terpene-based compounds, phenol-based compounds, and phosphate-based compounds.

2. The superabsorbent resin according to claim 1, wherein the cationic compound is a guanidine-based compound.

3. The superabsorbent polymer according to claim 2, wherein the guanidine compound is guanidine carbonate or guanidine hydrochloride.

4. 2. The superabsorbent resin according to claim 1, wherein the terpene compound is menthol or citronellol.

5. 2. The superabsorbent polymer according to claim 1, wherein the phenol-based compound is gallic acid, tannic acid, coumaric acid, caffeic acid, ferulic acid, or protocatechuic acid.

6. 2. The superabsorbent resin according to claim 1, wherein the phosphate-based compound is phosphoric acid, phosphonic acid, aminophosphonic acid, phosphinic acid, bis(aminomethyl)phosphinic acid, or bis(hydroxymethyl)phosphinic acid.

7. 7. The highly water-absorbent resin according to claim 1, wherein at least a portion of the base resin is surface-treated with a first surface cross-linking agent and a second surface cross-linking agent.

8. 8. The superabsorbent resin according to claim 7, wherein the second surface cross-linking agent comprises one or more selected from the group consisting of polyhydric alcohol-based compounds; epoxy compounds; polyamine compounds; haloepoxy compounds; condensation products of haloepoxy compounds; oxazoline compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; and alkylene carbonate-based compounds.

9. The highly absorbent resin according to any one of claims 1 to 8, wherein the first surface cross-linking agent is contained in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the base resin.

10. The highly absorbent resin according to any one of claims 1 to 6, having a centrifugation retention capacity (CRC) measured by EDANA method WSP 241.3 of 28 g / g to 60 g / g.

11. The highly water-absorbent resin according to any one of claims 1 to 6, having an absorbency under pressure (AUP) of 8 g / g to 37 g / g at 0.7 psi as measured by EDANA method WSP 242.

3.

12. 7. The superabsorbent polymer of claim 1, which inhibits the growth of Proteus mirabilis bacteria.

13. The superabsorbent resin according to any one of claims 1 to 6, wherein the superabsorbent resin has a core-shell structure in which the base resin is a core and a surface cross-linked layer is formed on the core in a shell shape.

14. The highly absorbent resin according to any one of claims 7 to 13, having a centrifugation retention capacity (CRC) measured by EDANA method WSP 241.3 of 28 g / g to 40 g / g.

15. The highly water-absorbent resin according to any one of claims 7 to 14, having an absorbency under pressure (AUP) of 20 g / g to 37 g / g at 0.7 psi as measured by EDANA method WSP 242.

3.

16. 16. The superabsorbent polymer of any one of claims 7, 14 and 15, which inhibits the growth of Proteus mirabilis bacteria.

17. The superabsorbent polymer according to any one of claims 7 and 14 to 16, wherein the superabsorbent polymer has a core-shell structure in which the base resin is a core and a surface cross-linked layer is formed on the core in a shell shape.

18. a step of cross-linking the acrylic acid monomer, which contains an acid group and at least a portion of the acid group has been neutralized, in the presence of an internal cross-linking agent to form a hydrogel polymer; drying, grinding and classifying the hydrogel polymer to form a base resin; and crosslinking the surface of the base resin in the presence of a first surface crosslinking agent; The method for producing a superabsorbent resin, wherein the first surface cross-linking agent is one or more compounds selected from the group consisting of cationic compounds, terpene compounds, phenolic compounds, and phosphoric acid compounds.

19. The method for producing a superabsorbent resin according to claim 18, wherein the step of cross-linking the surface of the base resin is performed at 150 to 220°C.

20. 20. The method for producing a superabsorbent resin according to claim 18 or 19, wherein the step of cross-linking the surface of the base resin additionally includes a second surface cross-linking agent.

21. 21. The method for producing a superabsorbent resin according to claim 20, wherein the second surface cross-linking agent is at least one selected from the group consisting of polyhydric alcohol compounds; epoxy compounds; polyamine compounds; haloepoxy compounds; condensation products of haloepoxy compounds; oxazoline compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; and alkylene carbonate compounds.

22. An article comprising the superabsorbent polymer of any one of claims 1 to 17.

23. The article according to claim 22, wherein the article is one or more selected from the group consisting of absorbent articles, sanitary goods, soil repair agents, water-stopping materials for civil engineering and construction, seedling sheets, freshness-preserving agents, materials for droppings, electrical insulators, oral and dental articles, cosmetic or skin articles.

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