Method for preparing superabsorbent polymer

Abstract

The present invention relates to a method for preparing a superabsorbent polymer and, more specifically, to a method for preparing a superabsorbent polymer, which secures an absorption rate by increasing the amount of a chemical foaming agent used in a polymerization step, while at the same time optimally controlling process conditions to prevent loss of a chemically formed pore structure resulting from the increased amount of the foaming agent during subsequent chopping and pulverizing processes, thereby producing a superabsorbent polymer exhibiting an excellent absorption rate and minimizing the generation of fine dust.

Description

Method for manufacturing superabsorbent resin

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0169689, filed November 29, 2023, and Korean Patent Application No. 10-2024-0174002, filed November 28, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a method for producing a superabsorbent resin, and more particularly, to a method for producing a superabsorbent resin having an excellent absorption rate while minimizing the amount of fine particles generated.

[0004]

[0005] Super absorbent polymer (SAP) is a synthetic polymer material that can absorb 500 to 1,000 times its own weight in water. Different developers call it by different names, such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material). The above super absorbent polymer began to be put to practical use as a sanitary product, and is currently widely used as a soil conditioner for horticulture, a water-stopping material for civil engineering and construction, a sheet for nursery cultivation, a freshness-preserving agent in the food distribution industry, and a material for steaming.

[0006] These superabsorbent polymers are widely used in sanitary products, such as diapers and sanitary napkins. Within these sanitary products, the superabsorbent polymers are typically dispersed within pulp. However, recent efforts to provide thinner sanitary products, such as diapers, are ongoing. As part of this effort, the development of so-called pulpless diapers, which contain reduced pulp content or even eliminate pulp altogether, is actively underway.

[0007] Thus, in sanitary materials with reduced pulp content or no pulp, a relatively high proportion of superabsorbent resin is included, and superabsorbent resin particles are inevitably embedded in multiple layers within the sanitary material. In order for the superabsorbent resin particles embedded in multiple layers to efficiently absorb large amounts of liquids such as urine, the superabsorbent resin must fundamentally exhibit not only high absorption performance but also a rapid absorption rate.

[0008] Meanwhile, the most common method for improving such absorption properties is to form a porous structure inside the superabsorbent resin to increase the surface area of ​​the superabsorbent resin. In order to increase the surface area of ​​the superabsorbent resin, a method of forming a porous structure inside the base resin powder by including a foaming agent in the monomer composition and proceeding with crosslinking polymerization is generally adopted.

[0009] However, when an excessive amount of a foaming agent is used to form a porous structure of the desired degree, various physical properties of the superabsorbent resin, such as surface tension, permeability, or bulk density, are reduced, and in particular, the porous structure is lost during the pulverization process after polymerization, and the amount of fine powder generated increases.

[0010] Accordingly, there is a continuous demand for the development of technologies that can improve the absorption properties of superabsorbent resins while improving the problems associated with the use of foaming agents.

[0011]

[0012] Accordingly, the present invention provides a method for manufacturing a superabsorbent resin having an excellent absorption rate while minimizing the amount of fine particles by optimally controlling process conditions so that the chemical pore structure formed by increasing the amount of a chemical blowing agent is not lost in the subsequent pulverization process while securing an absorption rate by using an increased amount of a chemical blowing agent in the polymerization step.

[0013]

[0014] In order to solve the above problem, the present invention,

[0015] A step (step 1) of forming a functional gel polymer having an acid group by polymerizing a monomer mixture comprising an acrylic acid monomer having at least a partially neutralized acid group and a capsular blowing agent;

[0016] A step (step 2) of chopping the above functional gel polymer so that the average particle diameter, defined as the average of the major axis length and minor axis length of the particles, is 20 mm to 30 mm;

[0017] A step of drying the above chopped functional gel polymer (step 3); and

[0018] The above dried functional gel polymer, having a median particle diameter (D 50 ) to a size of 300 ㎛ to 400 ㎛, thereby manufacturing a base resin (step 4);

[0019] The above capsule-type foaming agent contains 3,000 ppmw or more of the total acrylic acid monomer content.

[0020] A method for producing a superabsorbent resin is provided.

[0021]

[0022] According to the method for producing a superabsorbent resin of the present invention, by increasing the amount of a chemical foaming agent in the polymerization step to secure an absorption rate, and by optimizing the process conditions so that the chemical pore structure formed by increasing the amount of the foaming agent is not lost in the subsequent pulverization process, a superabsorbent resin having an excellent absorption rate and minimizing the amount of fine particles can be produced.

[0023]

[0024] Figures 1 and 2 show SEM images of base resin particles manufactured according to examples and comparative examples.

[0025]

[0026] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the invention.

[0027] Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise," "include," or "have" are intended to indicate the presence of a feature, step, component, or combination thereof, but should be understood not to preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0028] The terms first, second, third, etc. are used to describe various components and are used only for the purpose of distinguishing one component from another.

[0029] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0030] The term "polymer" or "high molecular weight polymer" as used herein refers to a polymerized state of a water-soluble ethylenically unsaturated monomer, and may encompass any moisture content range or particle size range. Among the polymers, a polymer having a moisture content (moisture content) of about 40 wt% or more before polymerization and drying may be referred to as a hydrogel polymer, and particles of such hydrogel polymer that are pulverized and dried may be referred to as a crosslinked polymer.

[0031] In addition, the term "crosslinked polymer" used in this specification means a crosslinked polymerization of a water-soluble ethylenically unsaturated monomer in which at least a portion of the acidic groups are neutralized, and the "base resin powder" means a material containing such a crosslinked polymer.

[0032] In addition, the term "superabsorbent resin" is used to mean a base resin powder in the form of a powder composed of a crosslinked polymer polymerized with a water-soluble ethylenically unsaturated monomer in which at least a portion of the acidic groups are neutralized, or superabsorbent resin particles in which the crosslinked polymer is pulverized, or a product made suitable for commercialization by subjecting the crosslinked polymer or the base resin to an additional process, such as surface crosslinking, fine powder reassembly, drying, pulverization, classification, etc.

[0033]

[0034] (Method for producing superabsorbent resin)

[0035] A method for manufacturing a superabsorbent resin according to one embodiment of the invention comprises the steps of: polymerizing a monomer mixture including an acrylic acid-based monomer having at least a partially neutralized acidic group and a capsule-type blowing agent to form a hydrogel polymer having an acidic group (step 1); chopping the hydrogel polymer so that the average particle diameter defined as the average of the major axis length and minor axis length of the particles is 20 mm to 30 mm (step 2); drying the chopped hydrogel polymer (step 3); and drying the dried hydrogel polymer so that the median particle diameter (D 50 ) to a size of 300 ㎛ to 400 ㎛ to manufacture a base resin (step 4);

[0036]

[0037] In order for superabsorbent polymers to achieve the level of excellent absorbency properties required for actual product application, a method of increasing the surface area of ​​the superabsorbent polymer by forming a porous structure within the polymer is used. Specifically, a blowing agent is included in the monomer composition and a polymerization step is performed, thereby forming a porous structure within the polymer. However, if an excessive amount of the blowing agent is used to form the desired porous structure, various physical properties of the superabsorbent polymer, such as surface tension, liquid permeability, or bulk density, deteriorate. In particular, even if a porous structure is formed during the polymerization step, the porous structure is lost during the pulverization process after polymerization, and during this process, the amount of fine powder generated significantly increases and the absorption rate is inhibited.

[0038] Accordingly, the inventors of the present invention discovered that the desired properties can be realized by using a capsule-type foaming agent in the polymerization step, but using it in an amount exceeding 3,000 ppmw compared to the amount normally used, thereby securing an absorption rate, and optimizing the chopping and grinding process conditions so that the chemical pore structure resulting from the increase in the amount of the foaming agent is not lost in the subsequent grinding process, thereby completing the present invention.

[0039]

[0040] Hereinafter, a method for manufacturing a superabsorbent resin according to a specific embodiment of the invention will be described in more detail for each step.

[0041]

[0042] (Step 1: Polymerization stage)

[0043] First, a method for manufacturing a superabsorbent resin according to one embodiment of the invention includes a step (step 1) of polymerizing a monomer mixture including an acrylic acid-based monomer having at least a partially neutralized acidic group and a capsule-type blowing agent to form a hydrogel polymer having an acidic group.

[0044] The above step is a step of forming a functional gel polymer by thermally polymerizing or photopolymerizing a monomer mixture including an acrylic acid monomer having an acidic group and a monomer composition including an internal crosslinking agent and / or a polymerization initiator, etc.

[0045]

[0046] The acrylic acid monomer may be any monomer commonly used in the production of superabsorbent resins. As a non-limiting example, the acrylic acid monomer may be a compound represented by the following chemical formula 1:

[0047] [Chemical Formula 1]

[0048] R1-COOM 1

[0049] In the above chemical formula 1,

[0050] R1 is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

[0051] M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0052] Preferably, the monomer may be at least one 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. When acrylic acid or a salt thereof is used as the acrylic acid-based monomer, a superabsorbent resin with improved absorbency can be obtained, which is advantageous. In addition, examples of the monomer include anionic monomers of maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethane sulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth)acrylamide-2-methyl propane sulfonic acid, and salts thereof; Nonionic hydrophilic monomers containing (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol (meth)acrylate; and amino group-containing unsaturated monomers containing (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide and quaternary compounds thereof may be used.

[0053] Here, the acrylic acid monomer has an acidic group, and at least a portion of the acidic group is neutralized. Preferably, the monomer partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide can be used.

[0054] The neutralization step of the acid group can be carried out by mixing with a neutralizing agent capable of neutralizing the acid group, and examples of the neutralizing agent include basic substances such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc.

[0055] 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, and conversely, if the degree of neutralization is excessively low, not only will the absorbency of the polymer be significantly reduced, but it may also exhibit properties like elastic rubber that are difficult to handle.

[0056]

[0057] The above-mentioned capsule-type foaming agent is a component that generates bubbles during the polymerization stage to form appropriate pores in the hydrogel polymer, thereby increasing the surface area of ​​the hydrogel polymer, and thereby improving the absorption rate of the resin.

[0058] The above-mentioned capsule-type foaming agent may have a core-shell structure including a core containing a hydrocarbon and a shell made of a thermoplastic resin formed on the core.

[0059] The above hydrocarbon may be at least one 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, and the thermoplastic resin may be a polymer formed from at least one monomer selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide and vinylidene halide.

[0060] Commercially available capsule-type blowing agents include, but are not limited to, F-36D (Asahi Kasei Corporation) and MS-140DS (Dongjin Semichem).

[0061] The above-mentioned capsule-type foaming agent is included in an amount of 3,000 ppmw or more based on the total content of acrylic acid-based monomers, which is an excessive amount compared to conventional foaming agents, and enables the formation of pores of the desired degree in the hydrogel polymer. On the other hand, even if the amount of the foaming agent is increased to form a large number of pore structures of the desired degree, there is a problem that a large amount of the pore structures are lost in the subsequent pulverization process, and a large amount of fine powder is generated during this process. The present invention optimizes the subsequent chopping and pulverization conditions, thereby minimizing the loss of the pore structures formed in the polymerization step, and thus further improving the absorption rate.

[0062] When the content of the encapsulated foaming agent is less than 3,000 ppmw, it may be difficult to form a pore structure of the desired degree, and thus the effect of improving the absorption rate may be minimal. Preferably, the content of the encapsulated foaming agent may be 3,000 ppmw or more, 3,100 ppmw or more, 4,000 ppmw or more, 10,000 ppmw or less, 9,000 ppmw or less, 8,000 ppmw or less, 7,000 ppmw or less, or 3,000 ppmw to 10,000 ppmw, 3,000 ppmw to 9,000 ppmw, 4,000 ppmw to 8,000 ppmw, or 4,000 ppmw to 7,000 ppmw. Within the above content range, it is preferable to form an appropriate amount of pores that have an excellent absorption rate while not reducing the gel strength.

[0063]

[0064] Any compound that enables the introduction of crosslinking bonds during polymerization of the acrylic acid monomer may be used as the internal crosslinking agent. As non-limiting examples, the internal cross-linking agent may be N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol(meth)acrylate, polyethylene glycol di(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, Polyfunctional cross-linking agents such as propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, but are not limited thereto. Preferably, among these, ethylene glycol diglycidyl ether may be used.

[0065] In the above monomer composition, such internal crosslinking agent may be used in an amount of 100 ppmw to 10,000 ppmw based on the weight of the acrylic acid-based monomer. By being included in the above content range, sufficient crosslinking can be achieved to realize strength above an appropriate level, and sufficient absorption properties can be realized by introducing an appropriate crosslinking structure. Preferably, it is included in an amount of 100 ppmw or more, 200 ppmw or more, 300 ppmw or more, or 600 ppmw or more, and 10,000 ppmw or less, 9,000 ppmw or less, 7,000 ppmw or less, or 5,000 ppmw or less, and 200 ppmw to 9,000 ppmw, 300 ppmw to 7,000 ppmw, or 600 ppmw to 5,000 ppmw. The above content refers to the mixed content of two or more types of internal cross-linking agents when used.

[0066] If the content of the internal cross-linking agent is too low, cross-linking may not occur sufficiently, making it difficult to achieve strength above an appropriate level. If the content of the internal cross-linking agent is too high, the internal cross-linking density may increase, making it difficult to achieve the desired water retention capacity.

[0067]

[0068] In addition, the monomer composition may further include additives such as a polymerization initiator, a surfactant, a thickener, a plasticizer, a preservation stabilizer, and an antioxidant, as needed.

[0069]

[0070] The polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator, depending on the polymerization method. However, even in the case of a photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation, etc., and a certain amount of heat is also generated as the polymerization reaction, which is an exothermic reaction, progresses, so a thermal polymerization initiator may be additionally included.

[0071] Here, as the photopolymerization initiator, for example, one or more compounds selected from the group consisting of benzoin ether, dialkylacetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and a-aminoketone can be used. As a specific example of the acyl phosphine, commercially available lucirin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide, can be used. For a more detailed description of photopolymerization initiators, see page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Applications" (Elsevier 2007).

[0072] As the above thermal polymerization initiator, one or more compounds selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8). In addition, as azo initiators, 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, 4,4-azobis-(4-cyanovaleric acid) Examples include 4,4-azobis-(4-cyanovaleric acid)). For a more diverse range of thermal polymerization initiators, see page 203 of Odian's book, "Principle of Polymerization (Wiley, 1981)".

[0073] The above polymerization initiator can be used in an amount of 10 ppmw to 10,000 ppmw based on the weight of the acrylic acid monomer. By being included in the above content range, sufficient crosslinking can be achieved to achieve strength above an appropriate level, and sufficient absorption properties can be achieved by introducing an appropriate crosslinking structure. Preferably, it is 50 ppmw or more, 80 ppmw or more, 100 ppmw or more, or 500 ppmw or more, and 10,000 ppmw or less, 9,000 ppmw or less, 7,000 ppmw or less, or 50 ppmw to 5,000 ppmw, 80 ppmw to 5,000 ppmw, or 80 ppmw to 3,000 ppmw. The above content refers to a mixed content when a photopolymerization initiator and a thermal polymerization initiator are used in combination.

[0074] If the concentration of the polymerization initiator is too low, the polymerization rate may slow down and a large amount of residual monomer may be extracted from the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is too high, the polymer chains forming the network may shorten, increasing the content of water-soluble components and lowering the pressure absorption capacity, which may deteriorate the physical properties of the resin, which is undesirable.

[0075]

[0076] Such monomer compositions can be prepared in the form of a solution in which raw materials such as the aforementioned monomer mixture, blowing agent, polymerization initiator, and internal crosslinking agent are dissolved in a solvent.

[0077] At this time, any solvent that can dissolve the above-mentioned raw materials can be used without limitation in its composition. For example, the solvent may include water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof.

[0078]

[0079] In addition, the formation of a hydrogel polymer through polymerization of the monomer composition can be performed using a conventional polymerization method, and the process is not particularly limited. As a non-limiting example, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the type of polymerization energy source. In the case of thermal polymerization, it can be performed in a reactor having a stirring shaft such as a kneader, and in the case of photopolymerization, it can be performed in a reactor equipped with a movable conveyor belt.

[0080] For example, the monomer composition may be introduced into a reactor, such as a kneader, equipped with a stirring shaft, and a hydrogel polymer may be obtained by supplying hot air thereto or heating the reactor to thermally polymerize the polymer. At this time, depending on the shape of the stirring shaft equipped in the reactor, the hydrogel polymer discharged through the reactor outlet may be obtained as particles of several millimeters to several centimeters. Specifically, the hydrogel polymer obtained may be obtained in various forms depending on the concentration and injection speed of the injected monomer composition, and typically, a hydrogel polymer having a weight average particle diameter of 2 to 50 mm may be obtained.

[0081] In addition, as another example, when photopolymerization of the monomer composition is performed in a reactor equipped with a movable conveyor belt, a functional gel polymer in the form of a sheet can be obtained. At this time, the thickness of the sheet can vary depending on the concentration and injection speed of the injected monomer composition, but in order to ensure that the entire sheet can be polymerized evenly while also securing production speed, etc., it is generally preferable to adjust the thickness to 0.5 to 5 cm.

[0082]

[0083] The typical moisture content of the hydrogel polymer obtained by the above method may be 40 to 80 wt%. Meanwhile, the "moisture content" refers to the content of moisture relative to the total weight of the hydrogel polymer, which is the value obtained by subtracting the weight of the dry polymer from the weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during the drying process by increasing the temperature of the polymer through infrared heating. At this time, the drying condition is maintained at about 180°C for about 40 minutes at room temperature to measure the moisture content.

[0084]

[0085] The functional gel polymer obtained by the above method includes a plurality of pores having a diameter of about 5 μm to 400 μm on the surface of the functional gel polymer when the pore distribution on the surface of the functional gel polymer is analyzed by SEM image analysis. In addition, the pore area fraction defined as the ratio of the area of ​​the plurality of pores to the total area of ​​the functional gel polymer derived by SEM image analysis may be 75 to 97%. The specific method for measuring the pore distribution and area fraction will be described in more detail in the experimental examples described below.

[0086] As described above, a chemical blowing agent is used in an amount of 3000 ppmw or more in the polymerization step, so that a chemical pore structure is appropriately formed within the polymer, and these are optimized for subsequent chopping and grinding conditions to minimize the loss of the pore structure, thereby producing a superabsorbent resin having an excellent absorption rate while minimizing the amount of fine particles generated.

[0087]

[0088] (Step 2: Chopping Stage)

[0089] Next, a step (step 2) of chopping the functional gel polymer of step 1 is included. The polymer formed using an excessive amount of a capsular foaming agent in the polymerization step of step 1 includes a plurality of pore structures. In the present invention, a process of chopping under specific conditions prior to drying and grinding is performed so that the pore structures are not lost, thereby allowing the grinding process to proceed more mildly.

[0090]

[0091] In the above step 2, the functional gel polymer is chopped so that the average particle size, defined as the average of the major axis length and minor axis length of the particles, is 20 mm to 30 mm.

[0092] Specifically, the diameter is chopping process is performed to have a relatively large particle size, which, together with the control of the subsequent grinding process conditions, enables the implementation of an appropriate particle size distribution while minimizing the loss of the pore structure formed in the polymerization step, thereby significantly reducing the amount of fine powder generated. In addition, by performing the chopping process under the above conditions before the drying step, not only does the drying efficiency increase, but also the loss of the pore structure in the grinding process after the drying process can be more effectively controlled.

[0093] The average particle diameter of the polymer was calculated by selecting a sample from among the chopped particles, averaging the lengths of the major and minor axes of the selected sample particles, and measuring the arithmetic mean of these values ​​as the average particle diameter. The specific measurement method will be described in the experimental examples described below.

[0094] If the average particle size of the functional gel polymer after the above chopping is less than 20 mm, the pore structure formed by increasing the amount of foaming agent may be lost, reducing the effect of improving the absorption rate. If it exceeds 30 mm, the efficiency of the subsequent drying process may be significantly reduced, and aggregates may be formed, making it difficult to perform the drying process smoothly.

[0095] Preferably, the average particle diameter of the functional gel polymer after the chopping may be 20 to 28 mm, 20.2 to 27.5 mm, and is more suitable for implementing the aforementioned effect within the above range.

[0096] According to one embodiment of the invention, the chopping process is performed by passing the functional gel polymer through a chopper die having a plurality of holes having a diameter of 16 mm to 24 mm. When performed using such a chopper die, chopping into a polymer having the above-described average particle size range is easy, and thus, it is suitable for improving the desired physical properties and enhancing the efficiency of the drying process.

[0097]

[0098] (Step 3: Drying Stage)

[0099] Next, a method for manufacturing a superabsorbent resin according to one embodiment of the invention includes a step (step 3) of drying the chopped functional gel polymer.

[0100] At this time, the drying temperature of the drying step may be 150 to 250°C. If the drying temperature is less than 150°C, the drying time may be excessively long and there is a concern that the properties of the superabsorbent resin ultimately formed may deteriorate. If the drying temperature exceeds 250°C, only the polymer surface may be excessively dried, which may cause fine powder to be generated in the subsequent pulverization process and there is a concern that the properties of the superabsorbent resin ultimately formed may deteriorate. Therefore, the drying may preferably be performed at a temperature of 150 to 200°C, and more preferably at a temperature of 150 to 190°C.

[0101] In terms of drying time, it can be carried out for 20 to 90 minutes, taking into account process efficiency, etc., but is not limited thereto.

[0102]

[0103] Meanwhile, the drying step can be performed as a multi-stage process within the above-mentioned temperature range.

[0104] The drying method of the above-mentioned drying step can be selected and used without limitation in its composition, as long as it is a method commonly used in the drying process of functional gel polymers. Specifically, the drying step can be performed using methods such as hot air supply, infrared irradiation, ultrashort wave irradiation, or ultraviolet irradiation. In the case of hot air supply, it can be performed using a method using an oven capable of vertical air flow transfer.

[0105]

[0106] The moisture content of the polymer after such a drying step may be about 0.1 to about 10 wt%.

[0107]

[0108] (Step 4: Grinding Stage)

[0109] Next, the method includes a step of producing a base resin by crushing the dried functional gel polymer (step 4).

[0110] Step 4 above is to dry the functional gel polymer to obtain a median particle size (D 50 ) is ground to 300 ㎛ to 400 ㎛ to prepare a base resin.

[0111] Specifically, as described above, a chopping process is performed before the drying process to obtain a relatively large particle size, and at the same time, the pulverization process is simultaneously controlled within the above-described range, thereby enabling an appropriate particle size distribution to be realized while minimizing the loss of the pore structure formed in the polymerization step, thereby significantly reducing the amount of fine powder generated.

[0112] The median particle diameter (D) of the above polymer 50 ) means the particle size at which the cumulative distribution percentage corresponds to 50% when distributed by weight based on the particle size of the crushed particles. Preferably, the median particle size (D 50 ) was classified by vibrating the crushed base resin particles with an amplitude of 1.5 mm / g for 10 minutes using a classifier, and classified into particles of 850 ㎛ or more, 850 to 600 ㎛, 600 to 300 ㎛, 300 to 150 ㎛, and 150 ㎛ or less, and the weight % by size was measured. These were distributed based on weight, and the cumulative distribution percentage refers to the particle size value corresponding to 50%.

[0113] The median particle diameter (D) of the polymer after the above grinding 50 ) is less than 300 ㎛, the pore structure formed by increasing the amount of foaming agent may be lost, reducing the effect of improving the absorption rate, and a problem of increased generation of fine particles may occur. In addition, if it exceeds 400 ㎛, the absorption properties of the final resin may be somewhat deteriorated.

[0114] Preferably, the median particle diameter (D) of the polymer after the grinding 50 ) can be 300 to 350 μm, and is more suitable for implementing the aforementioned effect within the above range.

[0115] According to one embodiment of the invention, the grinding process can produce base resin particles by passing the dried functional gel polymer through a screen having a mesh of 4 mm or more. In this case, the median particle diameter (D) described above 50 ) is easy to manufacture, and thus is suitable for implementing the desired property improvement effect. The specific measurement method thereof will be described in the experimental example described below.

[0116] Preferably, the above-described grinding process is performed using a grinder having a screen mesh of 4 mm or more, and the grinder that can be used at this time is specifically a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog mill, but is not limited to the examples described above.

[0117] Preferably, the crushing in step 4 can be performed by multi-stage crushing.

[0118] For example, the pulverization of step 4 may include a step (step 4-1) of first pulverizing the dried hydrogel polymer by passing it through a screen having a mesh of 4 mm or more; and a step (step 4-2) of second pulverizing hydrogel polymers having a particle size greater than a standard particle size among the first pulverized hydrogel polymers by passing them through a screen having a mesh of less than 4 mm. Here, the standard particle size of the second pulverization step may be 850 μm or less, and a pulverization process may be performed in which only relatively large particles are selected and the pore structure is maintained through mild pulverization while minimizing the amount of fine powder generated.

[0119] As another example, the pulverization of step 4 may include a step (step 4-1) of first pulverizing the dried hydrogel polymer by passing it through a screen having a mesh of 4 mm to 8 mm; and a step (step 4-2) of second pulverizing hydrogel polymers having a particle size larger than a standard particle size among the first pulverized hydrogel polymers by passing them through a screen having a mesh of 1 mm to 3 mm. Here, the standard particle size of the second pulverization step may be 850 μm or less, and a pulverization process may be performed in which only relatively large particles are selected and the pore structure is maintained through mild pulverization while minimizing the amount of fine powder generated.

[0120] According to one embodiment of the invention, when the crushing step is performed by multi-stage crushing, the secondary crushed product may be mixed with the primary crushed product, and the base resin particles may mean a mixture of the primary and secondary crushed products.

[0121]

[0122] When the pore distribution on the surface of the base resin particles is analyzed by SEM image analysis, the functional gel polymer obtained by the above method includes a plurality of pores having a diameter of about 5 μm to 200 μm on the surface of the base resin particles.

[0123] In addition, the pore area fraction, defined as the ratio of the area of ​​multiple pores to the total area of ​​the base resin particles derived from SEM image analysis, may be 60 to 70%. The specific method for measuring the pore distribution and area fraction will be described in more detail in the experimental examples described below. By satisfying the above conditions, it is possible to implement an appropriate particle size distribution while minimizing the loss of the pore structure formed during the polymerization step, thereby significantly reducing the amount of fine particles generated.

[0124] As described above, a chemical blowing agent was used in an amount of 3000 ppmw or more in the polymerization step, so that a chemical pore structure was appropriately formed within the polymer, and the conditions for the chopping and grinding processes described above were optimized to minimize the loss of the pore structure, thereby producing a superabsorbent resin having an excellent absorption rate while minimizing the amount of fine particles generated.

[0125]

[0126] (additional steps)

[0127] Additionally, in order to manage the properties of the final superabsorbent resin product, the above-mentioned grinding process may undergo a separate process of classifying the polymer powder obtained after grinding according to particle size. Preferably, the process may further include a step of classifying into fine powder having a particle size of less than 150 μm and particles having a particle size of 150 μm to 850 μm.

[0128]

[0129] When the above-mentioned crushing step is performed as a multi-stage crushing step, a classification step may be performed on the first crushed polymer, followed by a second crushing step. In addition, a classification process may be performed on the polymer after the second crushing is completed.

[0130] According to one embodiment of the invention, base resin particles can be manufactured through the above grinding and / or classification steps.

[0131]

[0132] Among the base resin particles manufactured according to one embodiment of the invention, particles (fine powder) having a particle size of less than 150 μm may be 30% or less, preferably 29% or less, or 28% or less. The lower limit of the fine powder content may be 0% or more. The method for measuring the particle distribution will be described in more detail in the experimental examples described below.

[0133] In addition, the vortex absorption rate of the base resin particles manufactured according to one embodiment of the invention may be 33 seconds or less, preferably 32 seconds or less, or 30 seconds or less. The lower limit of the vortex absorption rate may be 10 seconds or more, or 15 seconds or more. A specific measurement method thereof will be described in more detail in the experimental examples described below.

[0134] The base resin particles manufactured according to one embodiment of the invention can simultaneously achieve the aforementioned properties of fine particle content and vortex absorption rate. This is achieved by increasing the amount of foaming agent used as described above to secure the absorption rate, while optimizing chopping and grinding conditions so that the chemical pore structure resulting from the increased amount of foaming agent is not lost during the subsequent chopping and grinding processes.

[0135]

[0136] Meanwhile, after manufacturing base resin particles through the above-described classification process, a step of surface crosslinking the base resin powder by heat-treating it in the presence of a surface crosslinking agent may be further included.

[0137] The above surface cross-linking step induces a cross-linking reaction on the surface of the base resin powder in the presence of a surface cross-linking agent, so that the unsaturated bonds of the water-soluble ethylenically unsaturated monomer remaining on the surface without being cross-linked are cross-linked by the surface cross-linking agent, thereby forming a superabsorbent resin with a high surface cross-linking density.

[0138] Specifically, a surface cross-linking layer can be formed by a heat treatment process in the presence of a surface cross-linking agent, and the heat treatment process increases the surface cross-linking density, i.e., the external cross-linking density, while the internal cross-linking density does not change, so the manufactured superabsorbent resin having a surface cross-linking layer formed has a structure in which the external cross-linking density is higher than the internal cross-linking density.

[0139]

[0140] In the above surface crosslinking step, a surface crosslinking agent composition containing an alcohol-based solvent and water in addition to a surface crosslinking agent can be used.

[0141] Meanwhile, as the surface cross-linking agent included in the surface cross-linking agent composition, any surface cross-linking agent that has been conventionally used in the production of superabsorbent resins can be used without particular limitation. For example, the surface cross-linking agent may be at least one polyol 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; at least one carbonate compound selected from the group consisting of ethylene carbonate and propylene carbonate; an epoxy compound such as ethylene glycol diglycidyl ether; an oxazoline compound such as oxazolidinone; a polyamine compound; It may include an oxazoline compound; a mono-, di- or polyoxazolidinone compound; or a cyclic urea compound; etc. Preferably, the same internal crosslinking agent as described above may be used, and for example, a diglycidyl ether compound of an alkylene glycol such as ethylene glycol diglycidyl ether may be used.

[0142] Such surface cross-linking agents may be used in an amount of 0.001 to 2 parts by weight per 100 parts by weight of the base resin powder. Preferably, the amount is 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, and 0.5 parts by weight or less, or 0.3 parts by weight or less. By adjusting the content range of the surface cross-linking agent within the above-described range, a superabsorbent resin exhibiting excellent absorption performance, liquid permeability, and other physical properties can be manufactured.

[0143]

[0144] Meanwhile, the surface cross-linking agent is added to the base resin powder in the form of a surface cross-linking agent composition containing the surface cross-linking agent. There is no particular limitation on the composition of the method for adding the surface cross-linking agent composition. For example, a method of mixing the surface cross-linking agent composition and the base resin powder in a reaction tank, a method of spraying the surface cross-linking agent composition onto the base resin powder, a method of continuously supplying the base resin powder and the surface cross-linking agent composition to a continuously operating mixer, and a method of mixing them may be used.

[0145] In addition, the surface cross-linking agent composition may further include water and / or a hydrophilic organic solvent as a medium. This has the advantage that the surface cross-linking agent, etc. can be evenly dispersed on the base resin powder. At this time, the content of water and hydrophilic organic solvent can be applied by adjusting the addition ratio with respect to 100 parts by weight of the base resin powder for the purpose of inducing even dissolution / dispersion of the surface cross-linking agent, preventing clumping of the base resin powder, and optimizing the surface penetration depth of the surface cross-linking agent.

[0146]

[0147] The above surface crosslinking step can be performed by heat treatment at a temperature of 110°C to 200°C, or 110°C to 150°C, for 30 minutes or more. More specifically, the surface crosslinking reaction can be performed by heat treatment at the above-described temperature as the highest reaction temperature for 30 to 80 minutes, or 40 to 70 minutes.

[0148] By satisfying these surface cross-linking process conditions (particularly, temperature-elevation conditions and reaction conditions at the highest reaction temperature), a superabsorbent resin that appropriately satisfies physical properties such as superior pressure permeability can be manufactured.

[0149] The means for increasing the temperature for the surface crosslinking reaction is not particularly limited. Heating can be achieved by supplying a heat medium or directly supplying a heat source. Usable heat mediums include, but are not limited to, heated fluids such as steam, hot air, and hot oil. Furthermore, the temperature of the supplied heat medium can be appropriately selected considering the means of the heat medium, the heating rate, and the target temperature. Meanwhile, directly supplied heat sources include, but are not limited to, heating via electricity or gas.

[0150]

[0151] Meanwhile, the method for manufacturing a superabsorbent resin according to one embodiment of the invention may further use various polyvalent metal salts, such as aluminum sulfate salt, during surface crosslinking to further improve permeability, etc. Such polyvalent metal salts may be included on the surface crosslinking layer of the finally manufactured superabsorbent resin.

[0152]

[0153] (superabsorbent resin)

[0154] According to one embodiment of the invention, a superabsorbent resin is provided, which comprises base resin particles manufactured according to the method for manufacturing the superabsorbent resin. According to the method for manufacturing the superabsorbent resin according to the embodiment described above, a superabsorbent resin having excellent absorbent properties can be manufactured.

[0155]

[0156] Hereinafter, the functions and effects of the invention will be described in more detail through specific examples. However, these examples are provided merely as examples of the invention and do not define the scope of the invention.

[0157]

[0158] [Examples and Comparative Examples]

[0159] Example 1

[0160] (Step 1: Polymerization process)

[0161] A monomer solution was prepared by mixing 0.15 parts by weight of EJ-1030S as an internal crosslinking agent and 0.007 parts by weight of IRGACURE 819 as a photoinitiator with 100 parts by weight of acrylic acid. Subsequently, while continuously supplying the monomer solution with a metering pump, 140 parts by weight of a 31 wt% aqueous sodium hydroxide solution was continuously mixed in a line to prepare a monomer solution. After confirming that the temperature of the monomer solution had risen to about 72°C or higher due to the heat of neutralization, it was waited for the temperature to cool to 40°C. When the temperature had cooled to 40°C, 0.31 parts by weight of F36D (3,100 ppmw relative to the acrylic acid monomer) as a solid foaming agent in capsule form was added to the monomer solution. Simultaneously, 5.6 parts by weight of a 4 wt% aqueous sodium persulfate solution was added. The above solution was poured into a Vat-shaped tray (15 cm wide × 15 cm long) installed in a square polymerizer with a photoirradiation device mounted on the top and the interior preheated to 80°C, and photoinitiated by photoirradiation. After UV irradiation for 60 seconds, an additional reaction was performed for 120 seconds to obtain a sheet-shaped functional gel polymer.

[0162] (Step 2: Chopping Process)

[0163] In order to finely pulverize the manufactured functional gel polymer, 100 g of water was evenly sprayed as a lubricant and then the polymer was passed through a chopper die having multiple 16 mm holes to perform a chopping process.

[0164] (Step 3: Drying Process)

[0165] The above chopped functional gel polymer was dried in a dryer capable of vertical airflow. Hot air at 180°C was flowed from bottom to top for 15 minutes, and then again from top to bottom for 15 minutes, to uniformly dry the functional gel polymer so that the moisture content of the dried functional gel polymer was approximately 2% or less.

[0166] (Step 4: Grinding Process)

[0167] The above dried functional gel polymer was pulverized using a Pulverisette 19 device from Fritsch. First, a screen mesh with a spacing of 4 mm was fixed to the bottom of the rotating device, and then the first pulverization was performed.

[0168] Afterwards, the first pulverized dry polymer was classified, and for particles having a particle size of 850㎛ or more, a screen mesh with a gap of 2mm was fixed, and then second pulverization was performed, and the particles were mixed with the first pulverized material to produce base resin particles.

[0169]

[0170] Examples 2 to 5 and Comparative Examples 1 to 11

[0171] Base resin particles were manufactured in the same manner as in Example 1, except that the components and contents used in the polymerization step of Step 1 were used as in Table 1 below, and the conditions for the chopping step of Step 2 and the grinding step of Step 4 were performed as in Table 2 below.

[0172] Here, the chopping step refers to the hole size (mm) of the chopper used, the crushing step refers to the mesh size (mm), and when performed secondarily, it refers to the crushing process being performed on particles of #20 or higher among the first crushed products.

[0173] Classification Crosslinking Polymerization Stage Blowing Agent Content (ppmw) Example 1F36D3,100 Example 2F36D3,100 Example 3F36D3,100 Example 4F36D6,200 Example 5F36D10,000 Comparative Example 1F36D3,100 Comparative Example 2F36D6,200 Comparative Example 3F36D10,000 Comparative Example 4F36D3,100 Comparative Example 5F36D3,100 Comparative Example 6F36D3,100 Comparative Example 7F36D3,100 Comparative Example 8F36D3,100 Comparative Example 9F36D3,100 Comparative Example 10F36D2,000 Comparative Example 11F36D2,000

[0174] Classification step 2: Chopping step Step 4: Grinding step (mm) Average particle size (mm) 1st (mm) 2nd (mm) Median particle size D 50 (㎛) Example 1 1620.242315 Example 2 2021.642334 Example 3 2424.842340 Example 4 2427.142317 Example 5 2426.842350 Comparative Example 1 129.11-283 Comparative Example 2 1212.71-265 Comparative Example 3 1215.11-250 Comparative Example 4 87.21-284 Comparative Example 5 1620.21-280 Comparative Example 6 2021.61-265 Comparative Example 7 2424.81-252 Comparative Example 8 87.242271 Comparative Example 9 129.242278 Comparative Example 10 2416.242284 Comparative Example 111611.242255

[0175] Here, the average particle size of Step 2 was determined by randomly selecting 50 (approximately 10% of the total sample) chopped particles. The hydrogel polymer before the drying step was in the shape of a sphere or an oval, and the average values ​​of the major and minor axis lengths of the selected particles were measured, and the arithmetic average of these was calculated as the average particle size.

[0176] Central entry diameter (D) of step 4 50 ) was used to classify the crushed base resin particles into particles of 850㎛ or more, 850~600㎛, 600~300㎛, 300~150㎛, and 150㎛ or less using a sieve of #20 / #20-30 / #30-50 / #50-100 / #100 while vibrating them at an amplitude of 1.5 mm / g for 10 minutes, and the weight % by size was measured. These were distributed based on weight, and the particle size corresponding to the cumulative distribution percentage of 50% was determined as the median particle size (D 50 ) was calculated.

[0177]

[0178] [Experimental Example]

[0179] The properties of the superabsorbent resin including the base resin particles manufactured in the above examples and comparative examples were evaluated by the following method, and the results are shown in Table 3.

[0180] Unless otherwise specified, all of the following property evaluations were conducted at room temperature (25±1°C), and saline solution or saline refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0181]

[0182] (1) Particle size distribution

[0183] For the base resin particles manufactured according to the examples and comparative examples, a classifier was placed and vibrated for 10 minutes at an amplitude of 1.5 mm / g to classify them into fine powder having a particle size of less than 150 μm and particles having a particle size of 150 μm to 850 μm, and the content of the fine powder having a particle size of less than 150 μm is shown in Table 3 below.

[0184]

[0185] (2) Vortex absorption speed (sec)

[0186] For the base resin particles manufactured according to the examples and comparative examples, 2 g of the base resin particle sample was added to 50 mL of physiological saline solution, and the magnetic bar (particle diameter 8 mm, length 30 mm) was stirred at 600 rpm, and the time until the vortex disappeared was measured in seconds and calculated (refer to International Publication Application No. 1987-003208), and the results are shown in Table 3 below.

[0187]

[0188] (3) Pore distribution analysis

[0189] (3)-1. Pore area fraction (Area %)

[0190] In the examples and comparative examples, approximately 5 g of samples of functional gel polymer and base resin particles were prepared. For each sample, SEM images of the sample particle surfaces were obtained at a magnification of approximately 20 to 25 times using JCM-6000, JEOL Ltd.

[0191] For the derived SEM images, the pore area fraction was calculated using ImageJ software according to the following method, and the results are shown in Table 3 below.

[0192] In addition, the rate of change in the pore area fraction of the base resin powder compared to the pore area fraction of the functional gel polymer (change in pore area fraction (%) = pore area fraction of the base resin powder / pore area fraction of the functional gel polymer * 100) was calculated and shown together in Table 3.

[0193] 1) Load image file

[0194] 2) [Image]-[Type]-[8 bit] settings

[0195] 3) [Image]-[Adjust]-[Threshold] settings

[0196] 4) Enter the setting values ​​0 and 160 and click [Apply]

[0197] 5) Measure Area% (background + pore) value through [Measure]

[0198] 6) Measure the Area% (background) value individually using the Wand tool.

[0199] 7) Particle area = 100% - Area% (background)

[0200] 8) Pore area = Area % (background + pore) - Area % (background)

[0201] 9) Final result (pore area fraction, Area %) = pore area / particle area

[0202]

[0203] (3)-2. Visual evaluation of SEM images

[0204] By analyzing SEM images of base resin particles manufactured according to the examples and comparative examples, the pore characteristics according to the increase in the amount of foaming agent and the crushing and pulverizing processes were visually confirmed.

[0205] Specifically, Fig. 1 shows the pore distribution according to the control of chopping process conditions when the same content of capsule-type foaming agent was used, and compares SEM images for Comparative Example 8, Example 1, and Example 3.

[0206] Figure 2 shows the pore distribution according to the multi-stage crushing process, comparing SEM images of Comparative Example 7 and Example 3.

[0207]

[0208] Classification Composite gel polymer base resin powder pore area fraction change rate (%) pore area fraction (Area %) absorption rate (sec) fine powder content (wt%) pore area fraction (Area %) Example 178.73 223.26 2.37 9.16 Example 275.93 122.66 1.08 0.37 Example 376.32 920.16 4.38 4.27 Example 489.82 524.46 4.77 2.05 Example 591.92 327.66 2.26 7.68 Comparative example 174.53 526.54 1.15 5.17 Comparative example 286.93 730.14 5.25 2.01 Comparative example 393.73734.534.436.71Comparative Example 475.94427.345.559.95Comparative Example 579.93626.631.939.92Comparative Example 682.13726.929.836.30Comparative Example 775.03526.644.158.80Comparative Example 874.94222.134.946.60Comparative Example 980.43521.844.955.85Comparative Example 1065.23522.329.845.71Comparative Example 1169.14019.834.149.35

[0209] As can be seen in Table 3 above, even when using a foaming agent in an amount as in the present invention, the chopping and grinding processes are controlled to an optimal range, so that the chemical pore structure formed by increasing the amount of the foaming agent is not lost in the subsequent grinding process, and the process conditions are optimized to produce a superabsorbent resin having an excellent absorption rate while minimizing the amount of fine particles generated.

Claims

1. A step of polymerizing a monomer mixture including an acrylic acid-based monomer having at least a partially neutralized acid group and a capsule-type blowing agent to form a hydrogel polymer having an acid group (step 1); A step (step 2) of chopping the above functional gel polymer so that the average particle size, defined as the average of the major and minor axis lengths of the particles, becomes 20 mm to 30 mm; A step of drying the above chopped functional gel polymer (step 3); and The above dried functional gel polymer has a median particle diameter (D 50 ) is pulverized to 300 ㎛ to 400 ㎛ to manufacture a base resin (step 4); The above capsule-type foaming agent contains 3,000 ppmw or more of the total acrylic acid monomer content. A method for producing a superabsorbent resin.

2. In paragraph 1, The capsule-type foaming agent of the above step 1 contains 3,000 ppmw to 10,000 ppmw of the total content of acrylic acid monomers. A method for producing a superabsorbent resin.

3. In paragraph 1, The capsule-type foaming agent of the above step 1 has a core-shell structure including a core containing a hydrocarbon and a shell made of a thermoplastic resin formed on the core. A method for producing a superabsorbent resin.

4. In paragraph 3, The above hydrocarbon is at least one 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, The thermoplastic resin is a polymer formed from at least one monomer selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, halogenated vinyl, and halogenated vinylidene. A method for producing a superabsorbent resin.

5. In paragraph 1, The chopping in step 2 is performed by passing the functional gel polymer through a chopper die having a plurality of holes having a diameter of 16 mm to 24 mm. A method for producing a superabsorbent resin.

6. In paragraph 1, The crushing in step 4 above is performed by multi-stage crushing. A step (step 4-1) of first crushing the dried functional gel polymer by passing it through a screen having a mesh of 4 mm or more; and A step (step 4-2) of secondarily crushing the functional gel polymer having a particle size greater than or equal to a standard particle size among the first crushed functional gel polymers by passing the functional gel polymer through a screen having a mesh size of less than 4 mm; A method for producing a superabsorbent resin.

7. In paragraph 6, In the second grinding of the above step 4-2, the standard particle size is 850㎛ or more. A method for producing a superabsorbent resin.

8. In paragraph 1, The above base resin particles have a vortex absorption speed of 33 seconds or less. A method for producing a superabsorbent resin.

9. In paragraph 1, Among the above base resin particles, particles having a particle size of less than 150㎛ are 30 wt% or less. A method for producing a superabsorbent resin.

10. In paragraph 1, In the presence of a surface crosslinking agent, a step (step 5) of heat-treating the base resin particles to crosslink a portion of the surface of the base resin particles is further included. A method for producing a superabsorbent resin.

Images