Method for preparing super absorbent polymer

Abstract

The present invention relates to a method for preparing a super absorbent polymer. More specifically, the present invention relates to a method for preparing a super absorbent polymer capable of further improving process stability in a subsequent coarse-crushing process and drying efficiency in a drying process, by including a specific thermally degradable internal crosslinking agent in a polymerization step, thereby enabling the preparation of a super absorbent polymer having excellent absorption properties.

Description

Method for manufacturing superabsorbent resin

[0001] Cross-citation with related application(s)

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0191808 dated December 19, 2024, Korean Patent Application No. 10-2024-0191809 dated December 19, 2024, and Korean Patent Application No. 10-2025-0198140 dated December 12, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of the specification.

[0003] The present invention relates to a method for manufacturing a superabsorbent resin. More specifically, by including a specific thermally decomposable internal crosslinking agent in the polymerization step, the process stability in the subsequent coarse grinding process and the drying efficiency in the drying process can be further improved, thereby enabling the production of a superabsorbent resin with excellent absorption properties.

[0004] Super Absorbent Polymer (SAP) is a synthetic polymer material capable of absorbing 500 to 1,000 times its own weight in moisture, and developers name it by different names such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material). The above-mentioned super absorbent polymer began to be commercialized for sanitary devices, and is now widely used as a material for horticultural soil repair agents, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservation agents in the food distribution sector, and for compresses, in addition to sanitary products such as children's disposable diapers.

[0005] In most cases, these superabsorbent polymers are widely used in the field of hygiene products, such as diapers and sanitary pads. For these applications, it is necessary to exhibit high absorption capacity for moisture and other substances, as well as excellent pressure-resistant absorption performance, such as preventing absorbed moisture from escaping even under external pressure.

[0006] In addition, when the aforementioned superabsorbent polymer is incorporated into hygiene materials such as diapers, it is necessary to diffuse urine and other fluids as widely as possible even in an environment where they are pressurized by the user's body weight. Through this, the absorption performance and absorption speed of the hygiene material can be further improved by fully utilizing the superabsorbent polymer particles contained across the entire surface area of ​​the absorbent layer. Furthermore, due to these diffusion characteristics under pressure, the rewetting properties of the diaper, which prevent urine and other fluids that have been absorbed by the superabsorbent polymer from leaking out again, can be further enhanced, and the leakage prevention properties of the diaper can also be improved.

[0007] Previously, attempts were made to improve the characteristics of widely dispersing the aforementioned urine by modifying the design of hygiene products, such as diapers. For example, methods to improve the diffusion characteristics of the urine, etc., have been attempted by introducing an Acquisition Distribution Layer (ADL) into the hygiene product or by utilizing absorption channels.

[0008] However, the improvement in diffusion characteristics resulting from design changes to the sanitary material itself was insufficient. Furthermore, as sanitary materials have recently become thinner and the content of superabsorbent polymers within them has relatively increased, the improvement in diffusion characteristics through design changes to the sanitary material itself has reached its limit, and there is a growing need to improve the diffusion characteristics of the superabsorbent polymers themselves under pressure.

[0009]

[0010] The present invention aims to provide a method for manufacturing a superabsorbent resin that includes a specific thermally decomposable internal crosslinking agent during the polymerization step, thereby further improving process stability in the subsequent coarse grinding process and drying efficiency in the drying process, and consequently achieving excellent water retention and pressure absorption capacity, while simultaneously having a rapid absorption rate.

[0011]

[0012] To solve the above problem, the present invention provides the following method for manufacturing a superabsorbent resin:

[0013] A step of forming a hydrogel polymer by polymerizing a monomer mixture comprising an acrylic acid-based monomer having at least some neutralized acidic groups and a thermally degradable internal crosslinking agent;

[0014] A step of forming base resin particles by coarsely grinding, drying, grinding, and classifying the above-mentioned hydrogel polymer; and

[0015] The method includes the step of heat-treating the base resin particles in the presence of a surface crosslinking agent to crosslink a portion of the surface of the base resin particles.

[0016] Here, the pyrolytic internal crosslinking agent is an aliphatic cyclic epoxy compound containing ester bonds within the molecule or an epoxy compound containing disulfide bonds within the molecule.

[0017]

[0018] As described above, the present invention achieves process stability in the subsequent coarse grinding process by including a specific pyrolytic internal crosslinking agent in the polymerization step to achieve an appropriate degree of internal crosslinking, and the pyrolytic internal crosslinking agent is easily decomposed in the drying process, so that the finally manufactured absorbent resin can achieve excellent water retention capacity and pressure absorption capacity, and can achieve a fast absorption rate.

[0019]

[0020] Figure 1 shows the classification criteria for pore distribution analysis for base resin particles prepared in the examples and comparative examples.

[0021]

[0022] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention.

[0023] The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, steps, components, or combinations thereof.

[0024] Terms such as first, second, third, etc. are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from another.

[0025] The terms "polymer" or "polymer" used in this specification refer to a state in which water-soluble ethylene-based unsaturated monomers are polymerized, and may encompass all ranges of moisture content or particle size. Among the polymers, a polymer having a moisture content (water content) of about 40 weight% or more in the state before drying after polymerization may be referred to as a hydrogel polymer, and particles obtained by grinding and drying such hydrogel polymers may be referred to as a cross-linked polymer.

[0026] Furthermore, the terms “base resin” or “base resin particles” refer to a polymer formed by drying and grinding a polymer of acrylic acid-based monomers into particle or powder form, and refer to a polymer in a state where the surface modification or surface crosslinking steps described below have not been performed.

[0027] Additionally, the terms "superabsorbent resin" or "superabsorbent resin particles" are used to encompass, depending on the context, a cross-linked polymer formed by polymerizing a water-soluble ethylene-based unsaturated monomer (acrylic acid-based monomer) containing acidic groups and having at least some of the acidic groups neutralized, or a base resin in the form of a powder made of superabsorbent resin particles formed by grinding the cross-linked polymer, or a state suitable for commercialization made by undergoing additional processes, such as surface cross-linking, fine powder reassembly, drying, grinding, classification, etc., with respect to the cross-linked polymer or the base resin.

[0028] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0029] Hereinafter, a method for manufacturing a superabsorbent resin and a superabsorbent resin will be described in more detail according to specific embodiments of the invention.

[0030]

[0031] (Method for manufacturing superabsorbent resin)

[0032] A method for manufacturing a superabsorbent resin according to one embodiment of the invention comprises the steps of: polymerizing a monomer mixture comprising an acrylic acid-based monomer having at least a portion of neutralized acidic groups and a pyrolytic internal crosslinking agent to form a hydrogel polymer; coarsely grinding, drying, grinding, and classifying the hydrogel polymer to form base resin particles; and heat-treating the base resin particles in the presence of a surface crosslinking agent to crosslink a portion of the surface of the base resin particles, wherein the pyrolytic internal crosslinking agent is an aliphatic cyclic epoxy compound containing ester bonds within the molecule or an epoxy compound containing disulfide bonds within the molecule.

[0033]

[0034] Superabsorbent polymers are widely used in the field of hygiene products, such as diapers and sanitary pads. Depending on the requirements of these products, they need to exhibit high absorption capacity for moisture, excellent pressure-resistant absorption performance that prevents absorbed moisture from escaping even under external pressure, and a rapid absorption rate to improve user comfort.

[0035] To improve the above absorption properties, a method was proposed in which the content of the internal crosslinking agent is reduced during polymerization for the manufacture of superabsorbents, and the hole size of the chopper is controlled more finely during the coarse grinding process after polymerization to coarsely grind the hydrogel polymer having a small particle size. However, while the absorption rate can be improved when the hole size is reduced during the coarse grinding process, there was a problem in that process stability was reduced due to the increased load on the chopper during the coarse grinding process itself. In particular, when the content of the internal crosslinking agent is reduced, the internal crosslinking degree of the polymer is insufficient, causing the polymer to be crushed during the coarse grinding process, and the adhesiveness increases, resulting in the subsequent drying process not being performed uniformly and the pressure absorption capacity of the product actually decreasing.

[0036] To solve these problems, the inventors introduced a thermally degradable internal crosslinking agent of a specific structure. Specifically, it was confirmed that when a polymer is formed using an aliphatic cyclic epoxy compound containing an ester bond within the molecule or an epoxy compound containing a disulfide bond within the molecule as an internal crosslinking agent, the appropriate degree of internal crosslinking is obtained, so that the load on the chopper does not increase or the absorption properties do not deteriorate even when the hole size of the chopper is reduced during the coarse grinding process. In addition, the thermally degradable internal crosslinking agent is easily decomposed during the subsequent drying process, enabling excellent water retention capacity, pressurized absorption capacity, and a fast absorption rate.

[0037]

[0038] (Step 1: Polymerization Step)

[0039] A method for manufacturing a superabsorbent resin according to one embodiment of the invention comprises the step of polymerizing a monomer mixture comprising an acrylic acid-based monomer having at least some neutralized acidic groups and a thermally degradable internal crosslinking agent to form a hydrogel polymer.

[0040] The polymerization step is a step of forming a hydrogel polymer by photopolymerizing and / or thermally polymerizing a monomer composition comprising an acrylic acid-based monomer having at least some neutralized acidic groups in the presence of an internal crosslinking agent.

[0041] In the present invention, by using a pyrolytic internal crosslinking agent having a specific structure, the process stability in the subsequent coarse grinding process and the drying efficiency in the drying process can be further improved, and a superabsorbent resin with excellent absorption properties can be manufactured.

[0042]

[0043] First, a monomer mixture is prepared comprising an acrylic acid-based monomer having at least some neutralized acidic groups and an internal crosslinking agent. The monomer mixture may further include a polymerization initiator for polymerization.

[0044] The above acrylic acid-based monomer may be any monomer commonly used in the manufacture of superabsorbent resins. As a non-limiting example, the above acrylic acid-based monomer may be a compound represented by the following chemical formula 1:

[0045] [Chemical Formula 1]

[0046] R1-COOM1

[0047] In the above chemical formula 1,

[0048] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0049] M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0050] Preferably, the acrylic acid-based monomer may be one or more selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids. Using such an acrylic acid-based monomer is advantageous because it allows for obtaining a superabsorbent resin with improved absorbency. In addition, the monomer may be an anionic monomer of maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth)acrylamide-2-methylpropanesulfonic acid, and a salt thereof; One or more selected from the group consisting of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, or polyethylene glycol (meth)acrylate; nonionic hydrophilic containing monomers of (meth)acrylate; and amino group containing unsaturated monomers of (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide and their quaternaries may be used.

[0051] Here, the acrylic acid monomer has an acidic group, and at least a portion of the acidic group is partially neutralized using a neutralizing solution. At this time, as the neutralizing agent included in the neutralizing solution, a basic substance capable of neutralizing the acidic group, such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide, may be used.

[0052] At this time, the degree of neutralization of the monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is excessively high, the neutralized monomer may precipitate, making it difficult for polymerization to proceed smoothly; conversely, if the degree of neutralization is excessively low, not only is the absorbency of the polymer significantly reduced, but it may also exhibit properties such as elastic rubber that are difficult to handle.

[0053]

[0054] The term "internal crosslinking agent" used in this specification is used to distinguish it from a "surface crosslinking agent" used to crosslink the surface of the base resin, and it serves to polymerize by crosslinking the unsaturated bonds of the aforementioned acrylic acid-based monomers. Although the crosslinking in the above step proceeds without distinction between the surface and the interior, due to the surface crosslinking process of the base resin described later, the surface of the particles of the finally manufactured superabsorbent resin is composed of a structure crosslinked by the surface crosslinking agent, and the interior is composed of a structure crosslinked by the internal crosslinking agent.

[0055] The above-mentioned pyrolytic internal crosslinking agent is an aliphatic cyclic epoxy compound containing ester bonds within the molecule or an epoxy compound containing disulfide bonds within the molecule, wherein at least one ester bond and one disulfide bond are included within each molecule.

[0056] When manufacturing a polymer using the above-mentioned thermally degradable internal crosslinking agent, strength exceeding an appropriate level can be achieved through sufficient crosslinking, thereby enabling excellent water retention and pressure absorption capabilities. Specifically, the ester bonds (-COO-) and disulfide bonds (-SS-) of the thermally degradable crosslinking agent compound are easily decomposed by heat during the drying stage, and through hydrolysis, the degree of internal crosslinking is reduced to an appropriate level, allowing the final absorbent resin to achieve an excellent absorption rate.

[0057] On the other hand, when an aromatic epoxy compound containing an ester bond is used as an internal crosslinking agent (e.g., diglycidyl phthalate ester), the thermal decomposition effect may be slightly reduced due to the structural characteristics of the aromatic ring. Additionally, when an aliphatic linear epoxy compound containing an ester bond is used as an internal crosslinking agent (e.g., diglycidyl adipate), the uniform crosslinking effect may be slightly reduced due to decreased water solubility in the neutralization solution. Furthermore, since both aromatic and aliphatic linear epoxy compounds exhibit lower polarity compared to aliphatic cyclic epoxy compounds, a problem may arise where solubility decreases even when the same surfactant and organic solvent are added for water dissolution.

[0058]

[0059] The above-mentioned pyrolytic internal crosslinking agent may be one or more selected from the group consisting of bis(3,4-epoxycyclohexylmethyl)adipate, diglycidyl 1,2-cyclohexanedicarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and bis(4-glycidyloxyphenyl)disulfide, and preferably, bis(4-glycidyloxyphenyl)disulfide or diglycidyl 1,2-cyclohexanedicarboxylate may be used.

[0060] The above-mentioned pyrolytic internal crosslinking agent can be used in an amount of 100 ppmw to 10,000 ppmw relative to the weight of the acrylic acid-based monomer. By including it within the above content range, strength above an appropriate level can be achieved through sufficient crosslinking, and sufficient water retention capacity can be achieved through the introduction of an appropriate crosslinking structure. Preferably, it may be 300 ppmw or more, 500 ppmw or more, 600 ppmw or more, 700 ppmw or more, 800 ppmw or more, 8,500 ppmw or less, 7,500 ppmw or less, 500 ppmw to 9,000 ppmw, 500 ppmw to 8,500 ppmw, 500 ppmw to 7,000 ppmw, 500 ppmw to 5,000 ppmw, 500 ppmw to 4,000 ppmw, 500 ppmw to 3,000 ppmw, 500 ppmw to 2,000 ppmw, or 700 ppmw to 2,000 ppmw. If the content of the aforementioned pyrolytic internal crosslinking agent is excessively low, crosslinking may not occur sufficiently, making it difficult to achieve strength above an appropriate level; conversely, if the content of the aforementioned pyrolytic internal crosslinking agent is excessively high, the internal crosslinking density increases, making it difficult to achieve the desired water retention capacity. Furthermore, when included within the above content range, the stability of the subsequent coarse grinding process is excellent, and drying efficiency is superior.

[0061]

[0062] According to one embodiment of the invention, in addition to the pyrolytic internal crosslinking agent, an additional internal crosslinking agent component may be optionally used, and these may be components different from the aforementioned pyrolytic internal crosslinking agent.

[0063] The above internal crosslinking agent may be a polyfunctional component, for example, 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, One or more selected from the group consisting of glycerin and ethylene carbonate may be used. Preferably, polyethylene glycol di(meth)acrylate and propylene glycol di(meth)acrylate may be used.

[0064] The above additional internal crosslinking agent can be used in an amount of 100 ppmw to 10,000 ppmw relative to the weight of the acrylic acid monomer, and by including it within the above content range, it is possible to achieve strength above an appropriate level through sufficient crosslinking, and sufficient water retention capacity can be achieved through the introduction of an appropriate crosslinking structure.

[0065]

[0066] As the polymerization initiator mentioned above, a thermal polymerization initiator or a photopolymerization initiator may be used depending on the polymerization method. However, even in the photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation, and since a certain amount of heat is generated as the polymerization reaction, which is an exothermic reaction, proceeds, a thermal polymerization initiator may be additionally included.

[0067] Here, as the photopolymerization initiator, one or more compounds selected from the group consisting of, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone may be used. Among these, as a specific example of acyl phosphine, commercially available lucirin TPO, namely 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide and diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide may be used. A wider variety of photopolymerization initiators is disclosed on page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application" (Elsevier 2007), which can be referenced.

[0068] In addition, one or more compounds selected from the group consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid may be used as the thermal polymerization initiator. Specifically, examples of persulfate-based initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8). In addition, azo-based initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutylonitril, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, and 4,4-azobis-(4-cyanovaleric Examples include acid (4,4-azobis-(4-cyanovaleric acid)). A wider variety of thermal polymerization initiators are disclosed on page 203 of Odian's book "Principles of Polymerization" (Wiley, 1981), which can be referenced.

[0069] This polymerization initiator may be used at a concentration of 10 ppmw to 10,000 ppmw relative to the weight of the acrylic acid-based monomer. Preferably, it may be 10 ppmw or more, 30 ppmw or more, 50 ppmw or more, 10,000 ppmw or less, 5,000 ppmw or less, or 3,000 ppmw or less, or 30 ppmw to 5,000 ppmw, 50 ppmw to 3,000 ppmw, or 80 ppmw to 2,500 ppmw. If the concentration of the polymerization initiator is excessively low, the polymerization rate may slow down and a large amount of residual monomer may be extracted into the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is excessively high, the polymer chains forming the network may become shorter, leading to a higher content of water-soluble components and a lower pressurized absorption capacity, which may degrade the physical properties of the resin, which is undesirable. The content of the polymerization initiator mentioned above refers to the mixed content when a photopolymerization initiator and a thermal polymerization initiator are used together.

[0070]

[0071] According to one embodiment of the invention, a foaming agent may be further included in the polymerization step.

[0072] The above-mentioned foaming agent plays a role in increasing the surface area by forming pores within the hydrogel polymer through foaming during polymerization. Any compound known in the art capable of generating bubbles during the polymerization stage may be used as the foaming agent without limitation; for example, carbonate-based foaming agents or encapsulated foaming agents may be used.

[0073] The above foaming agent may use carbonates, for example, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium bicarbonate, magnesium bicarbonate, or magnesium carbonate.

[0074] In addition, a thermally expandable microcapsule foaming agent having a core-shell structure may be used as the encapsulated foaming agent. More specifically, the encapsulated foaming agent has a core-shell structure comprising a core containing a hydrocarbon and a shell made of a thermoplastic resin formed on the core. Specifically, the hydrocarbon constituting the core is a liquid hydrocarbon with a low boiling point that easily vaporizes upon heating. Therefore, when heat is applied to the encapsulated foaming agent, the thermoplastic resin forming the shell softens while the liquid hydrocarbon in the core vaporizes; as the pressure inside the capsule increases, it expands, thereby forming bubbles of a size larger than the original size.

[0075] The hydrocarbon constituting the core of the encapsulated blowing agent may be one or more selected from the group consisting of n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso-heptane, cycloheptane, n-octane, iso-octane, and cyclooctane. Among these, hydrocarbons having 3 to 5 carbon atoms (n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane) are suitable for forming pores of the size described above, and iso-butane may be the most suitable.

[0076] In addition, the thermoplastic resin constituting the shell of the encapsulated foaming agent may be a polymer formed from one or more monomers selected from the group consisting of (meth)acrylate-based compounds, (meth)acrylonitrile-based compounds, aromatic vinyl compounds, vinyl acetate compounds, and vinyl halogenated compounds.

[0077] In addition, this encapsulated foaming agent has a structure comprising a core containing a hydrocarbon and a shell formed of a thermoplastic resin surrounding the core, and has an average diameter of 5 to 30 μm before expansion and a maximum expansion ratio in air of 5 to 15 times.

[0078] In addition, it is preferable to use the foaming agent at a concentration of 15,000 ppmw or less relative to the weight of the acrylic acid-based monomer. If the amount of the foaming agent used exceeds 15,000 ppmw, the pores become too numerous, which may cause the gel strength of the superabsorbent resin to decrease and the density to decrease, potentially leading to problems with distribution and storage. Furthermore, it is preferable to use the foaming agent at a concentration of 500 ppmw or more, 1,000 ppmw or more, or 5,000 ppmw or more relative to the weight of the water-soluble ethylene-based unsaturated monomer.

[0079]

[0080] In addition, the above monomer composition may further include additives such as surfactants, thickeners, plasticizers, preservative stabilizers, foam stabilizers, and antioxidants as needed.

[0081]

[0082] The surfactant used in the above polymerization step induces uniform dispersion of the foaming agent when used together with the foaming agent, thereby preventing a decrease in gel strength or density due to uniform foaming during foaming. The type of surfactant is not particularly limited, and ingredients commonly used in the field may be applied without special restrictions.

[0083] In addition, it is preferable to use the surfactant at a concentration of 300 ppmw or less relative to the weight of the acrylic acid-based monomer. In addition, it is preferable to use the surfactant at a concentration of 100 ppmw or more, or 150 ppmw or more relative to the weight of the acrylic acid-based monomer.

[0084]

[0085] In addition, this monomer composition can be prepared in the form of a solution in which raw materials such as the aforementioned monomer, internal crosslinking agent, foaming agent, and initiator are dissolved in a solvent.

[0086] The solvent that can be used at this time may be any solvent capable of dissolving the aforementioned raw materials, without any limitation in composition. For example, the solvent may be water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or a mixture thereof.

[0087]

[0088] The step of forming a hydrogel polymer through the polymerization of the above monomer composition can be carried out by a conventional polymerization method, and the process is not particularly limited. As a non-limiting example, it may be carried out in a reactor equipped with a movable conveyor belt.

[0089] Specifically, when photopolymerization is carried out on the monomer composition in a reactor equipped with a movable conveyor belt, a sheet-shaped hydrogel polymer can be obtained. At this time, the thickness of the sheet may vary depending on the concentration and injection speed of the injected monomer composition, but in order to ensure that the entire sheet is polymerized evenly while also securing the production speed, it is generally preferable to control the thickness to 0.5 to 10 cm.

[0090] The moisture content of the hydrogel polymer obtained by such a method may typically be 40% to 80% by weight. Meanwhile, throughout this specification, "moisture content" refers to the amount of water contained in 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 a value calculated by measuring the weight loss due to water evaporation in the polymer during the drying process in which the temperature of the polymer is raised by infrared heating. At this time, the drying conditions are set such that the temperature is raised from room temperature to 180°C and then maintained at 180°C, with the total drying time set to 20 minutes, including a 5-minute temperature raising step, to measure the moisture content.

[0091]

[0092] (Step 2: Base Resin Manufacturing Step)

[0093] Next, the method includes the step of coarsely grinding, drying, grinding, and classifying the above-mentioned hydrogel polymer to form base resin particles.

[0094]

[0095] First, a step of coarsely grinding the obtained hydrogel polymer is performed before the drying process to increase drying efficiency and further improve the absorption capacity and absorption rate of the final resin.

[0096] In the case of a hydrogel polymer polymerized using the aforementioned pyrolytic internal crosslinking agent, it possesses an appropriate degree of internal crosslinking. Consequently, the coarse grinding step allows for easy grinding to the desired degree without process load, thereby further improving drying efficiency. For example, even if the grinding conditions are finer during the coarse grinding step, phenomena such as the hydrogel polymer being crushed or the ground polymers aggregating are minimized. Consequently, the desired absorption properties can be enhanced while maintaining process stability.

[0097]

[0098] Meanwhile, the grinder used in the above-mentioned coarse grinding step is not limited in its configuration, but specifically, it may include any one selected from the group of grinding machines 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 chopper, and a disc cutter, and preferably, a chopper may be used.

[0099] When the above coarse grinding step is performed using a chopper, preferably, the coarse grinding step can be performed using a chopper comprising a porous plate having a hole size of 16 mm or less and an opening ratio of 60% or less. While reducing the hole size in the coarse grinding process can improve the absorption rate, there is a problem in that the process stability is reduced due to the increased chopper load in the coarse grinding process itself caused by phenomena such as the hydrogel polymer being crushed or the ground polymers aggregating with each other. However, it is desirable that such problems do not occur when the hydrogel polymer is manufactured using a pyrolytic internal crosslinking agent. Accordingly, it is possible to achieve the desired absorption properties, particularly a fast pressurized absorption rate, while maintaining process stability.

[0100] Meanwhile, if a porous plate is used in the above coarse grinding step where the hole size exceeds 16 mm and the opening ratio exceeds 60%, the size of the crumb may be large, the drying efficiency may decrease, and both the absorption rate and the pressure absorption capacity may decrease.

[0101] The hole size is preferably 16 mm or less, 13 mm or less, 12 mm or less, 10 mm or less, 9 mm or less, 8 mm or less, or 7 mm or less, or 5 mm or more, 7 mm or more, or 8 mm or more, or 5 mm to 16 mm. In addition, the opening ratio is preferably 65% ​​or less, 60% or less, 50% or less, 30% or more, 35% or more, or 30 to 65% or 35 to 60%.

[0102] According to one embodiment of the invention, the coarse grinding step may be performed at a chopper load of 35 to 55 A, and preferably at 37 A to 53 A.

[0103] If the current value of the above chopper load becomes excessively high, it may be difficult to perform the process easily. The above chopper load value of 35 A to 55 A is a range in which the coarse grinding process can be performed easily, meaning that there is substantially no process load. As described above, the hydrogel polymer polymerized using a specific pyrolytic crosslinking agent can maintain an appropriate chopper load by ensuring that the hydrogel polymer is not crushed or remains in the chopper during the coarse grinding process.

[0104] Specifically, the above chopper load refers to the power value input to achieve a constant driving Hz of the chopper drive shaft while the polymer is crushed within the chopper, and specifically, it can be measured at 60 Hz at 65 ℃. A more specific measurement method will be explained in more detail in the experimental example section described later.

[0105]

[0106] According to one embodiment of the invention, in the coarse grinding step, the bulk density (Crumb B / D) of the crumb particles among the coarsely ground hydrogel polymer that are not filtered by a 9.50 mm mesh sieve according to ASTM E11 is 0.70 kg / m³ 3 It may be greater than, and preferably, 0.70 kg / m² 3 up to 0.85 kg / m² 3 , or 0.73 kg / m² 3 Up to 0.83 kg / m² 3It may be possible. If the above Crumb B / D value falls outside the above range and has a small value, process stability is reduced, and clumping of Crumb occurs in the dryer, causing an excessive number of hot air passages, making uniform drying impossible and potentially leading to a decrease in drying efficiency. As mentioned above, a hydrogel polymer polymerized using a specific thermally decomposable crosslinking agent is desirable because it ensures process stability by preventing the hydrogel polymer from being crushed or the crushed polymers from aggregating with each other during the coarse grinding process.

[0107] Specifically, the above Crumb B / D refers to the bulk density measured by feeding 1,000g of Crumb particles that were not filtered by a 9.50 mm mesh sieve into a cylindrical cylinder with an inner diameter of 8 cm and a volume of 1,000 ml after classifying the coarsely ground hydrogel polymer with a sieve according to ASTM E11 at a strength of 1.5 mplitude for at least 5 minutes, and a more specific measurement method will be explained in more detail in the experimental example section described later.

[0108]

[0109] Next, the method includes the step of drying and grinding the above-mentioned coarsely ground hydrogel polymer to form base resin particles.

[0110] First, a drying step is performed on the above-mentioned coarsely ground hydrogel polymer. As previously described, the hydrogel polymer possesses an appropriate degree of internal crosslinking due to the pyrolytic internal crosslinking agent used in the polymerization step, allowing the coarse grinding process to be performed smoothly without process load. Accordingly, the hydrogel polymer having a relatively small particle size is effectively dried in the drying step, thereby enabling the realization of the desired excellent absorption properties. Meanwhile, in the drying step, the pyrolytic internal crosslinking agent used in the polymerization step is decomposed; specifically, the degree of internal crosslinking is reduced to an appropriate level through hydrolysis, which can improve the properties of the base resin. Consequently, the final absorbent resin can achieve excellent absorption properties, particularly an absorption rate.

[0111]

[0112] At this time, the drying temperature of the above drying step may be 150 to 250 ℃. If the drying temperature is less than 150 ℃, the drying time may become excessively long and there is a risk that the physical properties of the finally formed superabsorbent resin may deteriorate; if the drying temperature exceeds 250 ℃, only the surface of the polymer may be dried excessively, which may result in fine powder being generated during the subsequent grinding process and there is a risk that the physical properties of the finally formed superabsorbent resin may deteriorate. Therefore, preferably, the drying may be carried out at a temperature of 150 to 200 ℃, and more preferably at a temperature of 150 to 190 ℃.

[0113] In the case of drying time, it may be carried out for 20 to 90 minutes, taking into account process efficiency, but is not limited thereto.

[0114] Meanwhile, the above drying step can be performed as a multi-stage process within the aforementioned temperature range.

[0115] The drying method of the above drying step can also be selected and used without limitation in its composition, as long as it is a method commonly used for drying hydrogel polymers. Specifically, the drying step can be carried out by methods such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. In the case of hot air supply, it can be performed by using an oven capable of transferring airflow vertically.

[0116] The moisture content of the polymer after such a drying step may be about 0.1 to about 10 weight%.

[0117]

[0118] Next, a step of grinding the dried polymer obtained through such a drying step is performed.

[0119] The polymer powder obtained after the grinding step may have a particle size of 150 to 850 μm. Specifically, the grinder used to grind to such a particle size may be a pin mill, hammer mill, screw mill, roll mill, disc mill, or jog mill, but is not limited to the examples described above.

[0120]

[0121] In addition, to manage the physical properties of the superabsorbent resin produced as a final product after such a grinding step, a separate process may be performed to classify the base resin particles obtained after grinding according to particle size.

[0122] Preferably, base resin particles with a particle size of 150 μm to 850 μm can be classified, and a product can be produced by undergoing a surface crosslinking reaction step only for base resin particles having such a particle size. More specifically, the classified base resin particles have a particle size of 150 μm to 850 μm, may contain 50 weight% or more of particles with a particle size of 300 μm to 600 μm, and may contain less than 3 weight% of fine particles with a particle size of less than 150 μm.

[0123]

[0124] The base resin prepared by coarsely grinding, drying, grinding, and classifying the above-mentioned hydrogel polymer has a surface area of ​​35 mm² relative to its actual volume. -1 It can satisfy the ideal.

[0125] Here, surface area relative to actual volume refers to the value obtained by dividing the total surface area of ​​the base resin particles by the total volume of the base resin particles within a specific reference volume.

[0126] The above value is 35 mm -1 By satisfying the above values, curvature is appropriately formed on the surface of the base resin particles, thereby increasing the surface area. This forms absorption pathways for various fluids, enabling the realization of excellent absorption properties, particularly a rapid pressurized absorption rate. Preferably, the surface area relative to the actual volume is 35 to 55 mm² -1 It can be, more preferably 35 to 50 mm -1 or 35 to 48 mm -1 It may be. The surface area relative to the actual volume of the above base resin is 35 mm -1 If it is less than that, a sufficient absorption pathway is not formed to the desired extent, and the absorption properties of the final superabsorbent resin may be slightly degraded.

[0127] The surface area relative to the actual volume mentioned above can be derived using a 3D X-ray microscope (XRM). In the case of an XRM, a cross-sectional image is obtained by rotating the sample and irradiating it with X-rays, and three-dimensional data can be obtained based on this. This is called 3D reconstruction. Conversely, a two-dimensional (2D) cross-sectional image can be extracted from the obtained three-dimensional (3D) data, noise can be removed, and the measurement target can be separated and converted back into three-dimensional (3D) volume data. When the measurement target is separated from the XRM 2D cross-sectional image and converted back into a three-dimensional volume, the measurement target can be observed precisely in a three-dimensional form. In this way, when using an XRM, the resin to be measured can be analyzed in either a three-dimensional or two-dimensional form.

[0128] The surface area relative to actual volume will be explained in more detail in the experimental examples described later.

[0129] Meanwhile, the surface area relative to the actual volume of the base resin particles can be achieved by controlling the manufacturing process conditions of the base resin particles. For example, the components, content, and polymerization process conditions used in the polymerization step can be controlled; using the aforementioned specific thermally decomposable crosslinking agent is suitable for controlling the surface area properties. At the same time, this can be achieved by controlling the coarse grinding, grinding, and drying conditions within an appropriate range during the manufacturing step of the base resin particles.

[0130]

[0131] (Step 3: Surface crosslinking step)

[0132] Next, the method includes the step of heat-treating the base resin particles in the presence of a surface crosslinking agent to crosslink a portion of the surface of the base resin particles.

[0133] The above surface crosslinking step induces a crosslinking reaction on the surface of the base resin particles in the presence of a surface crosslinking composition containing a surface crosslinking agent, wherein the unsaturated bonds of the acrylic acid-based monomers remaining on the surface without being crosslinked are crosslinked by the surface crosslinking agent, thereby forming a superabsorbent resin with a high surface crosslinking density.

[0134] Specifically, a surface crosslinking layer can be formed by a heat treatment process in the presence of a surface crosslinking agent. Since the surface crosslinking density, i.e., the external crosslinking density, increases during the heat treatment process while the internal crosslinking density remains unchanged, the superabsorbent resin with the manufactured surface crosslinking layer has a structure in which the external crosslinking density is higher than the internal one.

[0135]

[0136] In the above surface crosslinking step, a surface crosslinking agent composition comprising an alcohol-based solvent and water in addition to the surface crosslinking agent may be used.

[0137] Meanwhile, any crosslinking agent component that has been conventionally used in the manufacture of superabsorbent resins may be used as the surface crosslinking agent included in the above surface crosslinking agent composition without any particular restrictions. For example, the above surface crosslinking agent may be one or more polyols selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, and glycerol; one or more carbonate-based compounds selected from the group consisting of ethylene carbonate and propylene carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; It may include oxazolidinone compounds; mono-, di-, or polyoxazolidinone compounds; or cyclic urea compounds; etc. Preferably, the same as the internal crosslinking agent described above may be used, and for example, diglycidyl ether compounds of alkylene glycols such as propylene glycol and ethylene glycol diglycidyl ether may be used.

[0138] Such a surface crosslinking agent may be used in an amount of 0.001 to 2 parts by weight per 100 parts by weight of base resin particles. Preferably, it may be used in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, and in an amount of 0.5 parts by weight or less, or 0.3 parts by weight or less. By adjusting the content range of the surface crosslinking agent to the range described above, a superabsorbent resin exhibiting excellent absorption performance and various physical properties such as liquid permeability can be manufactured.

[0139]

[0140] Meanwhile, the above-mentioned surface crosslinking agent is added to the base resin particles in the form of a surface crosslinking agent composition containing it, and there are no specific limitations on the composition of the method of adding such a surface crosslinking agent composition. For example, methods such as placing both the surface crosslinking agent composition and the base resin particles into a reaction vessel and mixing them, spraying the surface crosslinking agent composition onto the base resin particles, or continuously supplying the base resin particles and the surface crosslinking agent composition to a continuously operated mixer for mixing may be used.

[0141] In addition, the surface crosslinking agent composition may further include water and / or a hydrophilic organic solvent as a medium. This provides the advantage that the surface crosslinking agent, etc., can be evenly dispersed on the base resin. At this time, the content of water and the hydrophilic organic solvent can be applied by adjusting the addition ratio to 100 parts by weight of the base resin powder for the purpose of inducing even dissolution / dispersion of the surface crosslinking agent, preventing clumping of the base resin particles, and optimizing the surface penetration depth of the surface crosslinking agent.

[0142]

[0143] The above surface crosslinking step can be carried out by heat treating at a temperature of 110°C to 200°C or 110°C to 150°C for at least 30 minutes. More specifically, the surface crosslinking reaction can be carried out by heat treating at the above-mentioned temperature as the maximum reaction temperature for 20 to 80 minutes or 20 to 70 minutes.

[0144] By satisfying these surface crosslinking process conditions (in particular, temperature increase conditions and reaction conditions at the maximum reaction temperature), a superabsorbent resin that appropriately satisfies physical properties such as superior pressurized liquid permeability can be manufactured.

[0145] The means for raising the temperature for the surface crosslinking reaction are not particularly limited. Heating can be achieved by supplying a heat medium or by directly supplying a heat source. In this case, types of heat mediums that can be used include heated fluids such as steam, hot air, and hot oil, but are not limited thereto. Furthermore, the temperature of the supplied heat medium can be appropriately selected considering the medium type, the heating rate, and the target temperature. Meanwhile, directly supplied heat sources include heating via electricity and heating via gas, but are not limited to the examples described above.

[0146]

[0147] Meanwhile, in order to further improve liquid permeability and other properties, the method for manufacturing a superabsorbent resin according to one embodiment of the invention may further use aluminum salts, such as aluminum sulfate salts, and other various polyvalent metal salts during surface crosslinking. Such polyvalent metal salts may be included on the surface crosslinking layer of the finally manufactured superabsorbent resin.

[0148]

[0149] (Superabsorbent resin)

[0150] According to one embodiment of the invention, a superabsorbent resin is provided according to the method for manufacturing the superabsorbent resin.

[0151]

[0152] The superabsorbent resin may have a particle size of 150 to 850 μm. More specifically, at least 95 weight% of the superabsorbent resin may have a particle size of 150 to 850 μm, may contain at least 50 weight% of particles having a particle size of 300 to 600 μm, and may contain less than 3 weight% of fine particles having a particle size of less than 150 μm.

[0153]

[0154] The above superabsorbent resin exhibits excellent absorption properties, and in particular, has excellent absorption rate, centrifugal retention capacity, and pressurized absorption capacity.

[0155]

[0156] The above superabsorbent resin may have a centrifugal retention capacity (CRC) according to EDANA WSP 241.3 of 28 to 50 g / g, and preferably, 28.5 to 50 g / g, 32 to 50 g / g, 34 to 50 g / g, or 30 to 45 g / g. The specific measurement method thereof will be explained in more detail in the experimental example section described later.

[0157]

[0158] The above superabsorbent resin may have a 0.9 psi pressurized absorption capacity according to the EDANA method WSP 242.3 of 15 to 30 g / g, and preferably, 15 to 28 g / g, 15 to 25 g / g, or 15.5 to 23 g / g. The specific measurement method thereof will be explained in more detail in the experimental examples section described later.

[0159]

[0160] The above superabsorbent resin may have an absorption rate of 40 seconds or less according to the vortex method, preferably 38 seconds or less, or 35 seconds or less. The lower limit of the absorption rate may be 5 seconds or more, 10 seconds or more, 15 seconds or more, or 20 seconds or more. The absorption rate according to the vortex method may be measured in seconds in accordance with the method described in International Patent Publication No. 1987-003208, and the specific measurement method thereof will be explained in more detail in the experimental example section described later.

[0161]

[0162] The above superabsorbent resin may have a permeability of 40 to 120 seconds, preferably 50 to 115 seconds, or 50 to 110 seconds. The permeability is measured by introducing 0.2 g of the superabsorbent resin sample into a column tube with a diameter of 2.5 cm, adding 50 ml of brine to swell it for 30 minutes, and then measuring the time taken for 20 ml of brine to pass through the swollen superabsorbent resin under a pressure of 0.3 psi. Here, the brine refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution, and the specific measurement method thereof will be explained in more detail in the experimental example section described later.

[0163]

[0164] The above superabsorbent resin may have a gel bed permeability (GBP) of 30 darcy or more, preferably 33 darcy or more, or 60 darcy or less, 50 darcy or less, or 55 darcy or less. The specific measurement method thereof will be explained in more detail in the experimental examples section described later.

[0165]

[0166] The above superabsorbent resin may have a Gel-Vacuum AUL (5 min) of 20 g / g or more, and preferably, 20 to 25 g / g or 20 to 23.5 g / g. The specific measurement method thereof will be explained in more detail in the experimental example section described later.

[0167]

[0168] Preferred embodiments are presented below to aid in understanding the invention. However, the following embodiments are merely illustrative of the invention and do not limit the invention to these embodiments.

[0169]

[0170] Examples and Comparative Examples: Preparation of Superabsorbent Resin

[0171] Example 1-1

[0172] (Step 1 - Polymerization Step)

[0173] A monomer aqueous solution composition was prepared by mixing 100 g of acrylic acid, 0.05 g of diglycidyl 1,2-cyclohexanedicarboxylate (DGHP) as an internal crosslinking agent (500 ppmw relative to acrylic acid), 0.008 g of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (IRGACURE 819) as a photoinitiator, 0.2 g of sodium persulfate (SPS) as a thermal initiator, 128 g of 31.5% caustic soda (NaOH), 63.5 g of water, and 0.04 g of a surfactant (calcium stearate).

[0174] After feeding the above monomer aqueous solution composition into the feed section of a polymerization reactor equipped with a continuously moving conveyor belt, ultraviolet rays are irradiated with a UV irradiation device while maintaining the polymerization atmosphere temperature at 80℃ (irradiation dose: 10 mW / cm² 2 A hydrogel polymer was prepared by carrying out UV polymerization for 3 minutes.

[0175] (Step 2 - Base resin manufacturing step) The polymerized sheet was taken out and cut into pieces 3 cm x 3 cm in size, and then a chopping process was performed using a meat chopper containing a porous plate with a hole size of 16 mm and an opening rate of 36% to produce a crumb.

[0176] Next, the above-mentioned coarsely ground hydrogel polymer was placed into an oven capable of vertical airflow transfer, and 195°C hot air was flowed from bottom to top for 15 minutes and from top to bottom for 15 minutes to dry it uniformly. After drying, the moisture content of the dried body was reduced to 2% or less. The obtained dried body was ground using a pin mill grinder. Subsequently, the polymer with a particle size of 150 μm to 850 μm was classified using a sieve to obtain base resin particles.

[0177] After (Step 4 - Surface Crosslinking Step), a surface crosslinking solution (3.5 parts by weight of water, 3.0 parts by weight of co-solvent propylene glycol, 0.11 parts by weight of ethylene glycol diglycidyl ether as a surface crosslinking agent, 0.4 parts by weight of aluminum sulfate 18 hydrate (Al-S), and 0.1 parts by weight of silica (Aerosil A200)) was evenly mixed with 100 parts by weight of the base resin particles prepared above. Next, the surface crosslinking reaction of the mixture was carried out at 140°C for 20 minutes, and then 0.5 parts by weight of silica (Aerosil A200) was mixed as a permeability enhancer to perform the final surface treatment. Subsequently, a superabsorbent resin having an average particle size of 150 to 850 μm was obtained using a sieve. In the superabsorbent resin obtained in this way, the content of particles with an average particle size of less than 150 μm was less than 2%.

[0178]

[0179] Examples 1-2 to 1-7 and Comparative Examples 1-1 to 1-13

[0180] A superabsorbent resin was prepared in the same manner as in Example 1-1, except that the internal crosslinking agent component and content used in the polymerization step of Step 1 and the process conditions of the coarse grinding step of Step 2 were changed as shown in Table 1 below.

[0181] Classification Polymerization Step Coarse Grinding Step Component Content * Hole Size Example 1-1A-1500 16 mm Example 1-2A-1700 16 mm Example 1-3A-11,000 16 mm Example 1-4A-11,500 16 mm Example 1-5A-11,800 16 mm Example 1-6A-11,500 10 mm Example 1-7A-11,500 8 mm Example 1-8A-21,500 16 mm Comparative Example 1-1B-1200 16 mm Comparative Example 1-2B-1300 16 mm Comparative Example 1-3B-1500 16 mm Comparative Example 1-4B-1700 16 mm Comparative Example 1-5B-11,000 16 mm Comparative Example 1-6B-11,500 16 mm Comparative Example 1-7B-21,500 16 mm Comparative Example 1-8B-22,000 16 mm Comparative Example 1-9B-23,000 16 mm Comparative Example 1-10B-24,000 16 mm Comparative Example 1-11B-25,000 16 mm Comparative Example 1-12B-11,500 10 mm Comparative Example 1-13B-11,500 8 mm Comparative Example 1-14B-31,500 16 mm Comparative Example 1-15B-41,500 16 mm Internal crosslinking agent (*ppmw relative to acrylic acid-based monomer) A-1: ​​Diglycidyl 1,2-cyclohexanedicarboxylate (DGHP) A-2: Bis(4-glycidyloxyphenyl)disulfide B-1: Ethylene glycol diglycidyl ether (EGDGE) B-2: Polyethylene glycol diacrylate (PEGDA) B-3: Phthalate diglycidyl ester - Initiation compound of Preceding 1 B-4: Diglycidyl adipate Initiation compound of Preceding 1

[0182] Experimental Example 1

[0183] For the superabsorbent resins prepared in Example 1 and Comparative Example 1 above, each physical property was measured by the following method, and the results are shown in Table 2 below.

[0184]

[0185] (1) Process stability evaluation

[0186] 1) Evaluation of Chopper Load in Coarse Grinding Process

[0187] In the coarse grinding step of the manufacturing steps of the superabsorbent resins of the above examples and comparative examples, a meat chopper equipped with a perforated plate of SL Corporation SMC-22 was used, and while the coarse grinding conditions were performed at 65°C and 60 Hz, the current value obtained by a current measuring device within the meat chopper equipment was determined, and the results are shown in Table 2 below.

[0188]

[0189] 2) Evaluation of Crumb B / D in the Coarse Grinding Process

[0190] During the manufacturing steps of the superabsorbent resins of the above examples and comparative examples, the above-mentioned coarse-ground hydrogel polymer was classified using a sieve according to ASTM E11 at a strength of 1.5 mplitude for at least 5 minutes, and then 1,000 g of crumb particles that were not filtered by a sieve with a mesh of 9.50 mm were placed into a cylindrical cylinder with an inner diameter of 8 cm and a volume of 1,000 ml, and the bulk density was measured according to the mass-to-volume ratio, and the results are shown in Table 2 below.

[0191]

[0192] (2) Evaluation of absorption properties

[0193] 1) Centrifuge Retention Capacity (CRC)

[0194] The water retention capacity of the superabsorbent resins of the above examples and comparative examples based on the absorption ratio under no load was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, and the results are shown in Table 2 below.

[0195] Specifically, from the superabsorbent resins obtained through the examples and comparative examples, a resin classified by a #30-50 sieve was obtained. This resin W0 (g) (about 0.2g) was uniformly placed into a nonwoven fabric bag and sealed, then immersed in physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was drained from the bag for 3 minutes under conditions of 250g using a centrifuge, and the mass W2 (g) of the bag was measured. In addition, the same operation was performed without using the resin, and the mass W1 (g) at that time was measured.

[0196] Using each mass obtained, the CRC(g / g) was calculated according to the following formula 1.

[0197] [Formula 1]

[0198] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0199]

[0200] 2) Absorbency under Load (AUL)

[0201] The pressurized absorption capacity of the superabsorbent resins of the above examples and comparative examples at 0.9 psi was measured according to the EDANA method WSP 242.3, and the results are shown in Table 2 below.

[0202] First, when measuring pressurized absorption capacity, the resin classifier from the above CRC measurement was used.

[0203] Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under conditions of room temperature and 50% humidity, a superabsorbent resin W0 (g) was uniformly spread over the wire mesh, and a piston capable of uniformly applying a load of 0.9 psi was positioned so that its outer diameter was slightly smaller than 25 mm, there was no gap with the inner wall of the cylinder, and its vertical movement was not obstructed. At this time, the weight W3 (g) of the device was measured.

[0204] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed on the inside of a petroleum 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 it. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted, and its weight W4 (g) was measured. Using each obtained mass, the pressurized absorption capacity (g / g) was calculated according to the following formula 2.

[0205] [Formula 2]

[0206] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0207]

[0208] 3) Permeability

[0209] The permeability of the superabsorbent resins of the above examples and comparative examples was measured, and the results are shown in Table 2 below.

[0210] 0.2 g of the above superabsorbent resin sample was placed into a column tube with a diameter of 2.5 cm, and 50 ml of brine was added to swell it for 30 minutes. Then, the time taken for 20 ml of brine to pass through the swollen superabsorbent resin under a pressure of 0.3 psi was measured. Here, brine refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0211]

[0212] 4) Vortex absorption rate

[0213] For the superabsorbent resins prepared in the above examples and comparative examples, particles having a particle size of 150 μm to 850 μm were taken, and the vortex absorption rate was measured according to the following method, and the results are shown in Table 2 below.

[0214] ① First, 50 mL of 0.9% saline solution was added to a 100 mL beaker with a flat bottom using a 100 mL mass cylinder.

[0215] ② Next, the beaker was placed in the center of the magnetic stirrer, and a magnetic bar (diameter 8 mm, length 30 mm) was placed inside the beaker.

[0216] ③ Afterwards, the stirrer was operated so that the magnetic bar stirred at 600 rpm, and the lowest part of the vortex generated by stirring was brought into contact with the top of the magnetic bar.

[0217] ④ After confirming that the temperature of the brine in the beaker reached 24.0℃, 2±0.01 g of superabsorbent resin particles were added while simultaneously starting a stopwatch. The time until the vortex disappeared and the liquid surface became completely horizontal was measured in seconds, and this was defined as the absorption rate.

[0218] Classification Process Stability Absorption Physical Properties Chopper Load (A) Crumb B / D (kg / m²) 3)CRC(g / g)0.9 AUL(g / g)Perm(sec.)Vortex(sec.) Example 1-15 10.734 2.41 5.911140 Example 1-25 10.733 9.81 7.310840 Example 1-34 80.743 7.51 9.89140 Example 1-44 60.773 5.12 2.37937 Example 1-53 70.813 4.22 5.84433 Example 1-64 80.803 4.92 2.55833 Example 1-75 10.833 5.22 2.74931 Example 1-85 00.734 0.11 6.911040 Comparative Example 1-1 Manufacturing Comparative Example 1-2 Manufacture Impossible Comparative Example 1-3 700.6037.210.221344 Comparative Example 1-4 620.6235.416.314844 Comparative Example 1-5 600.6227.819.88944 Comparative Example 1-6 590.6626.724.44044 Comparative Example 1-7 Manufacture Impossible Comparative Example 1-8 780.6440.19.818855 Comparative Example 1-9 780.6636.715.513551 Comparative Example 1-10 640.6833.117.29945 Comparative Example 1-11 570.6831.219.76444 Comparative Example 1-12640.6727.622.64644 Comparative Example 1-13810.6926.921.94443 Comparative Example 1-14690.6135.115.416446 Comparative Example 1-15710.6038.212.717948

[0219] As can be seen in Table 2 above, in the case of examples containing a specific thermally decomposable internal crosslinking agent during the polymerization step, it was confirmed that the process stability in the coarse grinding process was excellent and the physical properties of the final resin were excellent.

[0220] In the case of Comparative Examples 1-3, 1-4, 1-5, and 1-6, the same amount of internal crosslinking agent was used compared to Examples 1-1 to 1-4, but the specific thermally degradable internal crosslinking agent of the present invention was not used; accordingly, it was confirmed that the absorption rate was lowered compared to the Examples. In addition, it was confirmed that the water retention capacity was lowered compared to the Examples, and that the pressure absorption properties were lowered when the water retention capacity was the same.

[0221] In the case of Comparative Examples 1-1, 1-2, and 1-7, it was confirmed that they were not suitable for production as products because the internal crosslinking agent content was low, resulting in a low degree of internal crosslinking, which made the chopping process impossible.

[0222] In the case of Comparative Examples 1-14, it was confirmed that due to the characteristics of aromatic ring compounds, the thermal decomposition efficiency was low, making it difficult to achieve pressurized properties at similar water retention capacity.

[0223] In the case of Comparative Example 1-15, it was confirmed that the balance between water retention capacity and pressurized properties was somewhat reduced because the solubility was low and a uniform crosslinking effect could not be achieved.

[0224]

[0225] Example 2-1

[0226] (Step 1: Polymerization Step)

[0227] A monomer mixture was prepared by mixing 100 parts by weight of acrylic acid with 0.05 parts by weight of diglycidyl 1,2-cyclohexanedicarboxylate (DGHP) as a thermally decomposable internal crosslinking agent and 0.008 parts by weight of IRGACURE 819 as a photoinitiator. Subsequently, while continuously supplying the monomer mixture using a metering pump, 140 parts by weight of a 31 wt% aqueous sodium hydroxide solution were continuously line-mixed. At this time, after confirming that the temperature of the monomer mixture had risen to approximately 72°C or higher due to the heat of neutralization, the process was waited for the temperature to cool to 40°C. When the temperature cooled to 40°C, 0.1 parts by weight of solid F36D (1,000 ppmw relative to the acrylic acid monomer), which is a capsule-type foaming agent, and 0.01 parts by weight of calcium stearate (100 ppmw relative to the acrylic acid monomer), which is a surfactant, were added to the monomer mixture. Simultaneously, 5.6 parts by weight of a 4 wt% sodium persulfate aqueous solution were added. The solution was poured into a Vat-shaped tray (15 cm wide × 15 cm long) installed inside a square polymerization reactor preheated to 80°C and equipped with a light irradiation device on the top, and photoinitiation was performed by light irradiation. After UV irradiation for 60 seconds, the reaction was carried out for an additional 120 seconds to obtain a sheet-shaped hydrogel polymer.

[0228] (Step 2: Base Resin Manufacturing Step)

[0229] After cutting the above sheet-shaped hydrogel polymer into pieces measuring 3 cm x 3 cm, a crumb was prepared by performing a chopping process using a meat chopper containing a porous plate with a hole size of 10 mm and an opening rate of 60%.

[0230] The above-mentioned coarsely ground hydrogel polymer was dried in a dryer capable of vertical airflow transfer. Hot air at 170°C was flowed from bottom to top for 15 minutes and then flowed from top to bottom for another 15 minutes to uniformly dry the hydrogel polymer so that the moisture content of the dried hydrogel polymer was about 1% or less.

[0231] The above dry hydrogel polymer was ground using Fritsch's Pulverisette 19 machine. First, a screen mesh with a spacing of 1 mm was fixed to the bottom of the rotary machine and the grinding was carried out, and the base resin particles were classified through a standard sieve of ASTM standards to obtain base resin particles having a particle size of 150 to 850 μm.

[0232] (Step 3: Surface crosslinking process)

[0233] Next, a surface crosslinking composition was prepared comprising 5 parts by weight of water, 3 parts by weight of propylene glycol, 0.1 parts by weight of aluminum sulfate, and 0.1 parts by weight of ethylene glycol diglycidyl ether (EGDGE) (based on 100 parts by weight of base resin particles).

[0234] Subsequently, a surface crosslinking mixture was prepared by mixing 100 parts by weight of base resin particles and 8.2 parts by weight of the surface crosslinking composition prepared above. The surface crosslinking mixture was supplied to a surface crosslinking reactor, and the surface crosslinking reaction of the base resin particles was carried out at 130°C for 40 minutes. Subsequently, 0.1 parts by weight of fumed silica was mixed to obtain a superabsorbent resin. Subsequently, a superabsorbent resin having an average particle size of 150 to 850 μm was obtained using a sieve. In the superabsorbent resin obtained in this way, the content of particles with an average particle size of less than 150 μm was less than 2%.

[0235]

[0236] Examples 2-2 to 2-2 and Comparative Examples 2-1 to 2-5

[0237] A superabsorbent resin was prepared in the same manner as in Example 1, except that the internal crosslinking agent components and content used in the polymerization process of Step 1 were changed as shown in Table 3, and the coarse grinding process conditions of Step 2 were changed.

[0238] Separate Polymerization Step (Internal Crosslinking Agent) Coarse Grinding Step PEG DAD GHP Hole Size (mm) / Opening Ratio (%) Example 2-15,000 5,000 10 / 60 Example 2-25,000 3,000 10 / 60 Example 2-34,000 2,000 10 / 60 Example 2-43,000 2,000 10 / 60 Example 2-52,000 1,500 10 / 60 Example 2-60 7,000 10 / 60 Example 2-70 6,000 10 / 60 Example 2-80 5,000 10 / 60 Example 2-95,000 5,000 8 / 60 Example 2-10 5,000 3,000 8 / 60 Comparative Example 2-17,0000 10 / 60 Comparative Example 2-26,0000 10 / 60 Comparative Example 2-34,0000 10 / 60 Comparative Example 2-42,0000 10 / 60 Comparative Example 2-56,0000 8 / 60 Internal crosslinking agent (*ppmw relative to acrylic acid-based monomer) DGHP: Diglycidyl 1,2-cyclohexanedicarboxylate (DGHP) PEGDA: Polyethylene glycol diacrylate (PEGDA)

[0239] Experimental Example 2

[0240] For the superabsorbent resins prepared in Example 2 and Comparative Example 2 above, each physical property was measured by the following method, and the results are shown in Table 4 below.

[0241]

[0242] 2-1. Analysis of Physical Properties of Base Resin Particles

[0243] (1) Surface area relative to actual volume

[0244] For the base resin particles of Step 2 prepared in the examples and comparative examples, the surface area relative to the actual volume was measured using a 3D X-ray microscope (XRM) according to the following steps, and the results are shown in Table 4 below.

[0245] Step 1) Drying and sampling of base resin particles

[0246] The base resin particles of Step 2 above were sampled into a sampling port of size 1.5cm*1.5cm*1.5cm (width*length*height).

[0247] Step 2) Image Derivation

[0248] Sampled base resin particles were analyzed using an XRM (ZEISS Xradia 620 Versa) under the following conditions to obtain a 3D image of the superabsorbent resin.

[0249] <Condition>

[0250] ■ X-Ray Energy: 70 kV

[0251] ■ Detector: Flat Pane

[0252] ■ Voxel Size: 5 µm

[0253] ■ Measurement time: 0.05 s / frame

[0254] ■ Total images: 4501

[0255] Step 3) Deriving Surface Area to Actual Volume (SSAP / VC)

[0256] (STEP 1) A region of interest (measurement area) was set and cut from the XRM cross-sectional 2D image of the 3D reconstructed base resin particle.

[0257] (STEP 2) Noise was removed by applying Gaussian blur to the cropped 2D cross-sectional image.

[0258] Next, the 2D cross-sectional images were converted into binarized images using Otsu's thresholding method to distinguish between the background image and the base resin particle image. This was applied to all 2D cross-sectional images to obtain 2D cross-sectional images in which the base resin particles were separated.

[0259] (STEP 3) The above multiple 2D cross-sectional images were stacked, and 3D rendering was performed.

[0260] (STEP 4) Volume of total base resin particles (V) from 3D rendered volume data C ) was measured. In addition, considering the connectivity of the 3D rendered image, the surface area of ​​the entire base resin particle (S), excluding the surface area of ​​the closed pore region, was SAP ) was measured. The surface area (S) of the above base resin particles. SAP ) is the volume of the total base resin particles (V C Divided by ) the surface area relative to the actual volume of the base resin particles to be measured (S SAP / V C ) was derived.

[0261]

[0262] (2) Proportion of Entangled Numbers

[0263] For the base resin particles of Step 3 prepared in the examples and comparative examples, the morphology of the particles was quantified based on SEM image analysis to analyze the pore size and pore number ratio, and the results are shown in Table 4 below.

[0264] 1) Sample preparation: A sample with a particle size of 150 μm to 850 μm is prepared by classifying the base resin at 1.0 amplitude for 10 minutes using a particle classifier (such as a Sieve shaker from Retsch). At this time, the particle size of the base resin particles can be measured according to the European Isposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0265] 2) Image acquisition: After setting the prepared sample on the stage within the instrument, an SEM image was acquired by scanning. The value was set to 1 pixel = 1 / 235 mm = 0.00425 mm.

[0266] 3) Image processing: For the acquired SEM images, shape data was classified as follows according to the criteria below (see Fig. 1), and Mask R-CNN[1] was used to automatically classify Flat / Entangled / Bubble / Pore and derive the number.

[0267] ① Flat particles: Flat particles

[0268] ② Entangled particles: Uneven particles like sheared particles or finely reassembled particles

[0269] ③ Bubble: Effervescent bubbles visible around a white rim

[0270] ④ Pore: A pore that appears black

[0271] 4) Measurement of number ratio: Based on the SEM image analysis above, the number ratio of entangled particles was measured, and the results are listed in Table 2 below.

[0272] [Formula 5]

[0273] Ratio of Entangled Counts = ②Entangled Count / (①Flat Count + ②Entangled Count + ③Bubble Count + ④Pore Count) * 100

[0274]

[0275] (3) Centrifuge Retention Capacity (CRC)

[0276] For the base resin particles of Step 3 prepared in the above examples and comparative examples, the water retention capacity based on the absorption ratio under no load was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, and the results are shown in Table 4 below.

[0277] Specifically, from the base resins obtained through the examples and comparative examples, a resin classified by a #30-50 sieve was obtained. This resin W′0 (g) (about 0.2g) was uniformly placed into a nonwoven fabric bag and sealed, then immersed in physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was drained from the bag for 3 minutes using a centrifuge under conditions of 250g, and the mass W′2 (g) of the bag was measured. In addition, the same operation was performed without using the resin, and the mass W′1 (g) was measured.

[0278] Using each obtained mass, the CRC(g / g) was calculated according to the following formula 1-1.

[0279] [Calculation Formula 1-1]

[0280] CRC (g / g) = {[W′2(g) - W′1(g)] / W′0(g)} - 1

[0281]

[0282] 2-2. Analysis of Physical Properties of Superabsorbent Resins

[0283] (1) Centrifuge Retention Capacity (CRC)

[0284] The water retention capacity of the superabsorbent resins prepared in the above examples and comparative examples, based on the absorption ratio under no load, was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, and the results are shown in Table 4 below.

[0285] Specifically, from the superabsorbent resins obtained through the examples and comparative examples, a resin classified by a #30-50 sieve was obtained. This resin W0 (g) (about 0.2g) was uniformly placed into a nonwoven fabric bag and sealed, then immersed in physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was drained from the bag for 3 minutes under conditions of 250g using a centrifuge, and the mass W2 (g) of the bag was measured. In addition, the same operation was performed without using the resin, and the mass W1 (g) at that time was measured.

[0286] Using each mass obtained, the CRC(g / g) was calculated according to the following formula 1.

[0287] [Formula 1]

[0288] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0289]

[0290] (2) Absorbency under Load (AUL)

[0291] The pressurized absorption capacity of the superabsorbent resins prepared in the above examples and comparative examples at 0.9 psi was measured according to the EDANA method WSP 242.3, and the results are shown in Table 4 below.

[0292] First, when measuring pressurized absorption capacity, the resin classifier from the above CRC measurement was used.

[0293] Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under conditions of room temperature and 50% humidity, a superabsorbent resin W0 (g) was uniformly spread over the wire mesh, and a piston capable of uniformly applying a load of 0.9 psi was positioned so that its outer diameter was slightly smaller than 25 mm, there was no gap with the inner wall of the cylinder, and its vertical movement was not obstructed. At this time, the weight W3 (g) of the device was measured.

[0294] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed on the inside of a petroleum 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 it. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted, and its weight W4 (g) was measured. Using each obtained mass, the pressurized absorption capacity (g / g) was calculated according to the following formula 2.

[0295] [Formula 2]

[0296] AUL(g / g) = [W4(g) - W3(g)] / W0(g)

[0297]

[0298] (3) Vortex absorption rate

[0299] For the superabsorbent resins prepared in the above examples and comparative examples, particles having a particle size of 150 μm to 850 μm were taken, and the vortex absorption rate was measured according to the following method, and the results are shown in Table 4 below.

[0300] ① First, 50 mL of 0.9% saline solution was added to a 100 mL beaker with a flat bottom using a 100 mL mass cylinder.

[0301] ② Next, the beaker was placed in the center of the magnetic stirrer, and a magnetic bar (diameter 8 mm, length 30 mm) was placed inside the beaker.

[0302] ③ Afterwards, the stirrer was operated so that the magnetic bar stirred at 600 rpm, and the lowest part of the vortex generated by stirring was brought into contact with the top of the magnetic bar.

[0303] ④ After confirming that the temperature of the brine in the beaker reached 24.0℃, 2±0.01 g of superabsorbent resin particles were added while simultaneously starting a stopwatch. The time until the vortex disappeared and the liquid surface became completely horizontal was measured in seconds, and this was defined as the absorption rate.

[0304]

[0305] (4) Gel Bed Permeability (GBP)

[0306] For the superabsorbent resins prepared in the above examples and comparative examples, the free swelling gel bed permeability (GBP) with respect to physiological saline was measured, and the results are shown in Table 4 below. The gel bed permeability was measured according to the following method described in Korean Patent Application No. 10-2014-7018005.

[0307] The above gel bed permeability is the same as the method described in Korean Patent Application No. 10-2014-7018005 (using the same device) and was measured according to the following formula 3.

[0308] [Formula 3]

[0309] K = [Q×H×Mu] / [A×Rho×P]

[0310] In the above calculation formula 3,

[0311] K is the permeability (cm²), Q is the flow velocity (g / velocity), and,

[0312] H is the height of the sample (cm), Mu is the liquid viscosity (poise) (approximately 1 cps for the test solution used in the test), and

[0313] A is the cross-sectional area (cm²) for liquid flow, and

[0314] Rho is the liquid density (g / cm³) (for the test solution used in the test), and P is the hydrostatic pressure (dynes / cm²) (typically about 3,923 dynes / cm²).

[0315] Hydrostatic pressure is calculated using the following formula 3-1.

[0316] [Formula 3-1]

[0317] P = Rho × g × h

[0318] In the above calculation formula 3-1,

[0319] Rho is the liquid density (g / cm³), and

[0320] g is the acceleration due to gravity, typically 981 cm / sec 2 is,

[0321] h is the fluid height (e.g., 7.8 cm in the case of the permeability test described herein).

[0322]

[0323] (5) 0.3 Gel-Vacuum AUL (0.3 Gel-vac. 5 min)

[0324] For the superabsorbent resins prepared in the above examples and comparative examples, 0.3 Gel-vac (5 min) was measured. A stainless steel 400 mesh screen was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. Then, under room temperature (25 ± 1℃) and 50% humidity, W0 (g) of the superabsorbent resin, for which the Gel-Vacuum AUL of 5 min was to be measured, was uniformly sprayed onto the screen. Subsequently, a piston capable of uniformly applying a load of 0.3 psi was added to the superabsorbent resin. At this time, the piston used was manufactured so that its outer diameter was slightly smaller than 25 mm, so there was no gap with the inner wall of the cylinder, and it could move freely up and down. Then, the weight W5 (g) of the device thus prepared was measured. Subsequently, 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 0.9 wt% physiological saline solution was poured into the Petri dish. At this point, physiological saline was poured until the water level was level with the top surface of the glass filter. Then, a sheet of filter paper with a diameter of 90 mm was placed on the glass filter. Subsequently, the prepared device was placed on the filter paper so that the superabsorbent resin inside the device would swell due to the physiological saline under load. After 5 minutes, the remaining liquid was removed using a vacuum pump. At this time, the unabsorbed residual liquid between the swollen superabsorbent resin particles was removed.

[0325] Subsequently, the weight W6 (g) of the device containing the superabsorbent resin was measured. Using the measured weight, the Gel-Vacuum AUL of 5 minutes was calculated according to the following formula 4, and the results are shown in Table 4 below.

[0326] [Formula 4]

[0327] 5 min Gel-Vacuum AUL(g / g) = [W6(g) - W5(g)] / W0(g)

[0328] In the above calculation formula 4,

[0329] W0(g) is the initial weight (g) of the superabsorbent resin, and

[0330] W5(g) is the total weight of the superabsorbent resin and the weight of the device capable of applying a load to the superabsorbent resin, and

[0331] W6(g) is the total weight of the superabsorbent resin measured after absorbing physiological saline solution into the superabsorbent resin for 5 minutes under a load (0.3 psi) and removing the remaining liquid with a vacuum device, and the total weight of the device capable of applying a load to the superabsorbent resin.

[0332]

[0333] Classification Base Resin Properties Superabsorbent Resin Properties Entangled Ratio (%) Surface Area to Actual Volume (mm²) -1 )CRC(g / g)CRC(g / g)0.9 AUL(g / g)GBP(darcy)Vortex(sec)0.3 Gel-vac @5 min AUL (g / g) Example 2-176.84437.529.520.3552722.6 Example 2-272.14139.230.119.1463121.8 Example 2-368.23741.531.819.4553421.2 Example 2-465.43544.133.618.6383320.7 Example 2-561.43545.334.018.0343420.3 Example 2-669.33940.530.619.8513021.3 Example 2-766.23643.232.719.1433120.9 Example 2-861.43546.734.318.0403320.1 Example 2-977.14636.528.519.3432523.5 Example 2-1076.34838.229.818.4412822.8 Comparative Example 2-153.52832.824.317.8454519.8 Comparative Example 2-251.62634.227.117.6434618.5 Comparative Example 2-350.12239.729.517.2334818.0 Comparative Example 2-449.32046.232.216.7305217.3 Comparative Example 2-558.93232.226.816.8324519.5

[0334] When a hydrogel polymer is prepared using a specific thermally degradable internal crosslinking agent during the polymerization step, the base resin can have an appropriate specific surface area. Consequently, it was confirmed that the final resin achieves an appropriate degree of internal crosslinking, resulting in excellent absorption properties, particularly a rapid pressurized absorption rate, while also exhibiting excellent process stability. Here, a higher entangled ratio in the base resin particles indicates that there are more particles that have received a significant amount of shear from particles with high gel strength in the chopper; in this case, the surface area value relative to the actual volume is higher, which can be improved compared to the absorption rate.

[0335] Meanwhile, in the case of comparative examples using a general internal crosslinking agent without including a pyrolytic internal crosslinking agent, it was confirmed that the absorption rate decreased and the pressure absorption capacity was significantly reduced compared to the examples.

Claims

1. A step of polymerizing a monomer mixture comprising an acrylic acid-based monomer having at least a partially neutralized acidic group and a thermally degradable internal crosslinking agent to form a hydrogel polymer; A step of forming base resin particles by coarsely grinding, drying, grinding, and classifying the above-mentioned hydrogel polymer; and The method includes the step of heat-treating the base resin particles in the presence of a surface crosslinking agent to crosslink a portion of the surface of the base resin particles. The above-mentioned pyrolytic internal crosslinking agent is an aliphatic cyclic epoxy compound containing ester bonds within the molecule or an epoxy compound containing disulfide bonds within the molecule, Method for manufacturing a superabsorbent resin.

2. In Paragraph 1, The above-mentioned pyrolytic internal crosslinking agent is one or more selected from the group consisting of bis(3,4-epoxycyclohexylmethyl)adipate, diglycidyl 1,2-cyclohexanedicarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and bis(4-glycidyloxyphenyl)disulfide, Method for manufacturing a superabsorbent resin.

3. In Paragraph 1, The above-mentioned pyrolytic internal crosslinking agent is included in an amount of 100 ppmw to 10,000 ppmw relative to the weight of the acrylic acid-based monomer, Method for manufacturing a superabsorbent resin.

4. In Paragraph 1, In the above polymerization step, further comprising a foaming agent, Method for manufacturing a superabsorbent resin.

5. In Paragraph 1, The above coarse grinding step is performed by coarsely grinding the hydrogel polymer with a chopper comprising a porous plate having a hole size of 16 mm or less and an opening ratio of 60% or less. Method for manufacturing a superabsorbent resin.

6. In Paragraph 1, The above coarse grinding step is performed at a chopper load of 35 to 55 A, Method for manufacturing a superabsorbent resin.

7. In Paragraph 1, The bulk density of crumb particles among the above coarsely ground hydrogel polymer that were not filtered by a 9.50 mm mesh sieve according to ASTM E11 is 0.7 kg / m³ 3 Lee Sang-in, Method for manufacturing a superabsorbent resin.

8. In Paragraph 1, The above base resin particles have a surface area of ​​35 mm relative to their substantial volume. -1 Lee Sang-in, Method for manufacturing a superabsorbent resin.

9. In Paragraph 1, The above superabsorbent resin has a centrifugal retention capacity of 28 to 50 g / g according to EDANA WSP 241.3, Method for manufacturing a superabsorbent resin.

10. In Paragraph 1, The above superabsorbent resin has a 0.9 psi pressurized absorption capacity of 15 to 30 g / g according to the EDANA method WSP 242.3, Method for manufacturing a superabsorbent resin.

11. In Paragraph 1, The above superabsorbent resin has an absorption rate of 40 seconds or less according to the vortex method, Method for manufacturing a superabsorbent resin.

12. In Paragraph 1, The above superabsorbent resin has a 0.3 psi Gel-Vacuum AUL (5 min) of 20 g / g or more, Method for manufacturing a superabsorbent resin.

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