Super absorbent polymer

Abstract

The present invention relates to a super absorbent polymer and, more particularly, to a super absorbent polymer which exhibits excellent absorption behavior with respect to low ion concentration water with low electrical conductivity, and in particular, has a fast initial absorption rate and a large maximum absorption capacity.

Description

superabsorbent resin

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0023680, filed February 19, 2024, and U.S. Patent Application No. 18 / 894,676, filed September 24, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a superabsorbent resin, and more particularly, to a superabsorbent resin that exhibits excellent absorption behavior for water with low ion concentration and electrical conductivity, and in particular, has a fast initial absorption rate and a large maximum absorption capacity.

[0004] 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.

[0005] These superabsorbent resins are widely used in sanitary products such as diapers and sanitary pads. For these purposes, they need to exhibit high absorbency for moisture, etc., and the absorbed moisture must not escape even under external pressure, and they need to exhibit excellent initial absorbency.

[0006] Meanwhile, the superabsorbent polymer is typically incorporated into sanitary materials, dispersed within pulp. However, recent efforts to provide sanitary materials such as diapers with thinner thicknesses are ongoing. As part of this effort, development is actively underway for so-called pulpless diapers, which reduce pulp content or even eliminate pulp altogether. This requires the superabsorbent polymer itself to take over the initial, rapid absorption rate previously handled by pulp.

[0007] In this way, in the case of sanitary materials where the pulp content is reduced or no pulp is used, a relatively high proportion of superabsorbent resin is included, so superabsorbent resin particles are inevitably included in multiple layers within the sanitary material. In order for the entire superabsorbent resin particles included in multiple layers to more efficiently absorb a large amount of liquid such as urine, the superabsorbent resin needs to exhibit not only high absorption performance but also a fast absorption speed. Meanwhile, the most common method for improving such absorption properties is a method of forming a porous structure within 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 within the base resin powder by including a foaming agent in the monomer composition and performing crosslinking polymerization is generally adopted.

[0008] However, the use of a foaming agent has the disadvantage of lowering various properties of the superabsorbent resin, such as surface tension, permeability, or bulk density, and increasing the amount of fine particles generated. Accordingly, there is a continuous demand for the development of a technology that can improve the absorption properties of the superabsorbent resin without the use of a foaming agent.

[0009] Accordingly, there is a continuous demand for the development of new superabsorbent resins that have excellent initial absorbency and rapid drying ability when in contact with moisture while being manufactured without generating fine particles to fundamentally solve these problems.

[0010] The present invention aims to provide a superabsorbent resin that has an excellent initial absorption rate and maximum absorption capacity for water with low ion concentration and electrical conductivity, while simultaneously improving absorption performance such as water retention capacity and pressure absorption capacity, thereby enabling the resin to implement excellent quality when applied to actual products.

[0011] In order to solve the above problem, the present invention,

[0012] As a polyacrylic acid (salt)-based superabsorbent resin,

[0013] When the free swelling capacity (g / g) value according to time (s) for water with an electrical conductivity of 100 to 130 μS / cm is modeled by [Equation 1] below, the Se / r value is 3.0 g / g / sec or more.

[0014] We provide super absorbent resins:

[0015] [Formula 1]

[0016]

[0017] In the above equation 1,

[0018] t stands for swelling time (s),

[0019] S t means the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm at a swelling time (s) t,

[0020] S e and r are constants obtained by modeling the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm over time (s) according to [Equation 1].

[0021] The superabsorbent resin according to the present invention exhibits excellent absorption behavior for water with low ion concentration and electrical conductivity, and thus it is possible to provide a superabsorbent resin that can realize excellent quality when applied to an actual product.

[0022] In particular, it is possible to provide a superabsorbent resin with excellent property balance by simultaneously improving absorption performance such as water retention capacity and pressure absorption capacity while improving the initial absorption rate.

[0023] In addition, when applied to sanitary materials such as diapers, it can absorb discharged body fluids at a fast rate and can also absorb relatively large amounts, thereby preventing problems such as body fluids accumulating inside the sanitary material or leaking out.

[0024] That is, it is possible to provide a superabsorbent resin that can quickly absorb body fluids when applied to a product and retain a large amount of body fluids without leaking them out.

[0025] Figure 1 is a graph schematically illustrating the free swelling capacity of a superabsorbent resin over time.

[0026] Figure 2 is a graph modeling the time-dependent absorption behavior of the superabsorbent resin of the example in water with an electrical conductivity of 110 μS / cm according to [Equation 1].

[0027] Figure 3 is a graph modeling the time-dependent absorption behavior of a superabsorbent resin of a comparative example in water with an electrical conductivity of 110 μS / cm according to [Equation 1].

[0028] Figure 4 is a graph that combines the graphs of Figures 2 and 3.

[0029] According to one embodiment of the present invention, as a polyacrylic acid (salt)-based superabsorbent resin,

[0030] When the free swelling capacity (g / g) value according to time (s) for water with an electrical conductivity of 100 to 130 μS / cm is modeled by [Equation 1] below, the Se / r value is 3.0 g / g / sec or more.

[0031] Superabsorbent polymers may be provided:

[0032] [Formula 1]

[0033]

[0034] In the above equation 1,

[0035] t stands for swelling time (s),

[0036] S t means the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm at a swelling time (s) t,

[0037] S e and r are constants obtained by modeling the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm over time (s) according to [Equation 1].

[0038] Unless otherwise defined herein, all technical and scientific terms used herein are used merely to describe exemplary embodiments and are not intended to be limiting of the present invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, it should be understood that terms such as "comprise," "include," or "have" specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0039] 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 scope of the invention.

[0040] The technical terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Furthermore, the singular forms "a," "an," and "the" as used herein also include the plural forms, unless the context clearly dictates otherwise.

[0041] The term "polymer" or "high molecular weight polymer" as used in the specification of the present invention means a polymerized state of a water-soluble ethylenically unsaturated monomer, and may encompass any moisture content range or particle size range.

[0042] In addition, the term "superabsorbent resin" is used to mean, depending on the context, a base resin in powder form made of a crosslinked polymer or superabsorbent resin particles obtained by pulverizing the crosslinked polymer, or to encompass all of the crosslinked polymer or the base resin that have been subjected to additional processes, such as drying, pulverization, classification, surface crosslinking, etc., to make them suitable for commercialization.

[0043] Additionally, the term "fine particles" refers to particles having a particle size of less than 150 μm among superabsorbent resin particles. The particle size of such resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0044] Additionally, the term "chopping" is used to refer to cutting the hydrogel polymer into small pieces on the order of millimeters to increase drying efficiency, as distinguished from grinding to the micrometer or normal particle level.

[0045] Additionally, the term "micronizing" is used to differentiate it from "chopping", as it refers to grinding a hydrogel polymer into particle sizes of tens to hundreds of micrometers.

[0046] Additionally, the term "free swelling" refers to a state in which a superabsorbent polymer can swell without a restraining load when absorbing a specific solution.

[0047] Hereinafter, a superabsorbent resin and a method for manufacturing the same according to specific embodiments of the invention will be described in more detail.

[0048] Ⅰ. Polyacrylic acid (salt)-based superabsorbent resin

[0049] A superabsorbent resin according to one embodiment of the present invention is a polyacrylic acid (salt)-based superabsorbent resin, characterized in that when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm is modeled using the following [Equation 1], the Se / r value is 3.0 g / g / sec or more:

[0050] [Formula 1]

[0051]

[0052] In the above equation 1,

[0053] t stands for swelling time (s),

[0054] S t means the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm at a swelling time (s) t,

[0055] S eand r are constants obtained by modeling the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm over time (s) according to [Equation 1].

[0056]

[0057] Recently, as part of efforts to provide sanitary materials with thinner thickness, the development of products with reduced pulp content within sanitary materials is being actively pursued. Accordingly, the role of initial rapid absorption speed, which has been performed by pulp up to now, is being demanded from the superabsorbent resin itself.

[0058] That is, when superabsorbent resins are used in the sanitary material field, excellent initial absorbency is required to ensure rapid drying ability when in contact with moisture.

[0059] It is known that the absorption behavior of the free-swelling capacity (g / g) of a superabsorbent polymer over time follows the Voigt model equation. That is, if the free-swelling capacity (g / g) value of a superabsorbent polymer is measured over time and the relationship between the free-swelling capacity (g / g) value over time is modeled using a formula, it can be formulated in a form similar to the Voigt model equation.

[0060] The "Voigt model equation" is a model that expresses the behavior of a material (polymer) with viscoelasticity by representing the material as a parallel viscous body (dashpot) and an elastic body (spring), and is a model applied to explain the creep phenomenon such as chain movement or rearrangement of the material (polymer) when stress is applied.

[0061] The Voigt model equation is generally expressed as follows:

[0062]

[0063] If the relationship between the free swelling capacity (g / g) of a superabsorbent resin over time is formulated in the form of a Voigt model equation, there is an advantage in being able to predict absorption characteristics such as the initial absorption rate or maximum absorption capacity of the superabsorbent resin.

[0064] FIG. 1 is a graph schematically illustrating the free swelling capacity of a superabsorbent resin over time. As shown in FIG. 1, the slope of the tangent line when time (t) is 0 is related to the initial absorption rate of the superabsorbent resin, and the free swelling capacity when time (t) is infinite is related to the maximum absorption capacity. Therefore, by formulating the relationship between the free swelling capacity (g / g) value over time of the superabsorbent resin in the form of a Voigt model equation and checking the slope of the tangent line when time (t) is 0 and the free swelling capacity value when time (t) is infinite, one can determine how excellent the initial absorption rate or maximum absorption capacity of the superabsorbent resin is.

[0065] When the free swelling capacity (g / g) over time is formulated in the form of a Voigt model equation using 0.9% saline solution having similar ion concentration and electrical conductivity to urine discharged from the body, there is an advantage in that the absorption characteristics of the superabsorbent resin can be determined when it is actually used in sanitary materials, etc.

[0066] However, in the case of 0.9% saline solution, the ion concentration is high, so the amount absorbed by the superabsorbent resin is small and the absorption rate is relatively slow. Therefore, even if the superabsorbent resin is formulated in the form of a Voigt model equation, there is a drawback that it is difficult to accurately compare the absorption characteristics between superabsorbent resins. In addition, there is a drawback that it is difficult to predict the absorption characteristics of water other than 0.9% saline solution, such as distilled water or tap water with low ion concentrations.

[0067] When the same superabsorbent resin is used, the absorption behavior in water with an electrical conductivity of 100 to 130 μS / cm and the absorption behavior in 0.9% saline water with an electrical conductivity of about 16,100 μS / cm are bound to be different, and accordingly, the initial absorption rate or maximum absorption capacity of 0.9% saline water with an electrical conductivity of about 16,100 μS / cm cannot be used to predict the initial absorption rate or maximum absorption capacity of water with an electrical conductivity of 100 to 130 μS / cm, and vice versa.

[0068] Therefore, in order to realize a superabsorbent resin having excellent physical property balance by simultaneously improving the initial absorption rate and maximum free absorption capacity, it can be said that determining the absorption performance and absorption rate in water having an electrical conductivity of 100 to 130 μS / cm is independent of using 0.9% salt water having an electrical conductivity of about 16,100 μS / cm.

[0069] Accordingly, the inventors of the present invention measured the absorption behavior of a superabsorbent resin, in particular, the free swelling capacity (g / g) over time, using water having an electrical conductivity of 100 to 130 μS / cm, which has a lower ion concentration and electrical conductivity than 0.9% saline water, that is, an electrical conductivity of about 1 / 100 of 0.9% saline water, and formulated the free swelling capacity (g / g) over time for water having an electrical conductivity of 100 to 130 μS / cm in the form of a Voigt model equation.

[0070] When the free swelling capacity (g / g) of a superabsorbent resin over time in water with an electrical conductivity of 100 to 130 μS / cm is modeled according to the Voigt model equation, it is expressed as shown in [Equation 1] below.

[0071] [Formula 1]

[0072]

[0073] In the above equation 1,

[0074] t stands for swelling time (s),

[0075] S t means the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm at a swelling time (s) t,

[0076] S e and r are constants obtained by modeling the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm over time (s) according to [Equation 1].

[0077] S above e And the r value varies depending on the absorption characteristics of the superabsorbent resin.

[0078] Figure 1 is a graph schematically illustrating the absorption capacity of a superabsorbent resin over time.

[0079] As shown in Figure 1, the slope of the tangent line at a specific time (t) indicates the absorption rate at that specific time interval, so the slope of the tangent line when t is 0 can be said to indicate the initial absorption rate.

[0080] Since the slope of the tangent line when t is 0 is Se / r, it can be seen that the Se / r value is related to the initial absorption rate in water with an electrical conductivity of 100 to 130 μS / cm.

[0081] Also, as t increases (t approaches infinity), the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm remains constant (S e ) and it can be seen that it converges to S e It can be seen that the value is related to the maximum absorption capacity in water with an electrical conductivity of 100 to 130 μS / cm.

[0082] The superabsorbent resin according to the present invention has a large Se / r value related to the initial absorption rate for water having an electrical conductivity of 100 to 130 μS / cm, and a S value related to the maximum absorption capacity in water having an electrical conductivity of 100 to 130 μS / cm. e It has the characteristic of being of great value.

[0083] Therefore, it can be seen that the superabsorbent resin according to the present invention has excellent initial absorption rate and maximum absorption capacity for water having an electrical conductivity of 100 to 130 μS / cm.

[0084] Meanwhile, FIG. 2 is a graph modeling the time-dependent absorption behavior of the superabsorbent resin of the embodiment in water with an electrical conductivity of 110 μS / cm according to [Equation 1], and FIG. 3 is a graph modeling the time-dependent absorption behavior of the superabsorbent resin of the comparative example in water with an electrical conductivity of 110 μS / cm according to [Equation 1]. As shown in FIGS. 2 and 3, when the free swelling capacity values ​​of the superabsorbent resin in water with an electrical conductivity of 110 μS / cm according to time are indicated by dots, it can be confirmed that the formula according to [Equation 1] is satisfied.

[0085] Specifically, the superabsorbent resin of the present invention is a polyacrylic acid (salt)-based superabsorbent resin, and when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm is modeled using the above [Formula 1], the Se / r value may be 3.0 g / g / sec or more, or 3.3 g / g / sec or more, 3.5 g / g / sec or more, or 3.7 g / g / sec or more.

[0086] As described above, when the superabsorbent resin is used in the field of sanitary materials such as diapers and sanitary pads, it is required to have a rapid drying ability upon contact with moisture and an excellent initial absorbency. However, if the superabsorbent resin has a Se / r value of [Formula 1] of less than 3.0 g / g / sec, immediate absorption of water does not occur, which may cause discomfort upon contact with the skin.

[0087] Meanwhile, the superabsorbent resin of the present invention may have a Se value of 310 g / g or more, 320 g / g or more, or 330 g / g or more when modeling the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm using the above [Equation 1].

[0088] As described above, the Se value is related to the maximum absorption capacity for water having an electrical conductivity of 100 to 130 μS / cm. If the Se value is less than 310 g / g, the water retention capacity, which is a general property of the superabsorbent resin, may significantly decrease.

[0089] Meanwhile, in the above [Formula 1], t means swelling time (s), and theoretically, t can be infinite, and specifically, it can be 1800 seconds or more, and for example, it can be 0 to 1800 seconds.

[0090] Also, S t is the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm at a swelling time (s) t, and the specific free swelling capacity is different depending on the time, but S of the superabsorbent resin of the present invention t The values ​​can be 20 g / g or more, 25 g / g or more, or 30 g / g or more at 10 seconds, and S at 20 seconds t may be 40 g / g or more, 45 g / g or more, or 50 g / g or more, and S at 30 seconds t may be 70 g / g or more, 75 g / g or more, or 80 g / g or more, and S at 60 secondst may be 140 g / g or more, 150 g / g or more, or 160 g / g or more, and S at 120 seconds t may be 200 g / g or more, 220 g / g or more, or 240 g / g or more, and S at 300 s t may be 280 g / g or more, 290 g / g or more, or 300 g / g or more, and S at 600 s t may be 305 g / g or more, 310 g / g or more, or 315 g / g or more, and S at 1800 s t may be 315 g / g or more, 320 g / g or more, or 325 g / g or more. S t The larger the value, the more water with an electrical conductivity of 100 to 130 μS / cm can be seen to be absorbed, but for example, S at 1800 s t may be less than 400 g / g.

[0091] The superabsorbent resin of the present invention has a free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm, when modeled using the above [Equation 1], and the Se / r value and Se value are each above a certain value, thereby providing a superabsorbent resin with excellent initial absorption rate and maximum absorption capacity while simultaneously improving absorption performance such as water retention capacity and pressurized absorption capacity, thereby providing a superabsorbent resin with excellent property balance.

[0092] The present inventors investigated the absorption behavior of the superabsorbent resin using water having an electrical conductivity of 100 to 130 μS / cm, which is lower in ion concentration than the 0.9% salt water and is about 1 / 100 of the electrical conductivity of 0.9% salt water (about 16,100 μS / cm). Since there is no significant difference in absorption characteristics in water within the range of 100 to 130 μS / cm in electrical conductivity, water within this range of electrical conductivity can be used, and for example, water having an electrical conductivity of 110 μS / cm can be used.

[0093] In cases where the ion concentration and electrical conductivity are close to 0, such as distilled water, the superabsorbent resin swells excessively, making it difficult to compare the absorption performance between superabsorbent resins, which is not desirable.

[0094] Meanwhile, S was calculated from the free swelling capacity of two different superabsorbent polymers over time in 0.9% saline solution. e Even when the and r values ​​are similar, S calculated through free swelling capacity over time in water with electrical conductivity of 100 to 130 μS / cm e And the r values ​​can vary greatly, because they are affected by the absorption characteristics of the superabsorbent resin itself, such as the degree of crosslinking within the superabsorbent resin.

[0095] For this reason, S was calculated from the free swelling capacity over time in 0.9% saline solution with an electrical conductivity of about 16,100 μS / cm. e and S calculated from the free swelling capacity over time in water with Se / r values ​​and electrical conductivity of 100 to 130 μS / cm. e and Se / r values ​​cannot be directly compared.

[0096] Meanwhile, the superabsorbent resin of the present invention may have a water retention capacity (CRC) measured according to EDANA method WSP 241.3 of about 33 g / g or more, about 34 g / g or more, or about 35 g / g or more, and about 50 g / g or less, about 45 g / g or less, or about 40 g / g or less.

[0097] Additionally, the superabsorbent polymer of the present invention may have an absorbency under pressure (AUP) of about 25 g / g or more, about 27 g / g or more, about 28 g / g or more, about 29 g / g or more, or about 30 g / g or more, and about 45 g / g or less, about 42 g / g or less, or about 40 g / g or less, at 2.07 kPa (0.3 psi) as measured according to EDANA method WSP 242.3.

[0098] The superabsorbent resin of the present invention may have a vortex time of 40 seconds or less as measured by a vortex measurement method at 24.0°C.

[0099] More specifically, the vortex time may be 40 seconds or less, 35 seconds or less, 33 seconds or less, or 30 seconds or less. In addition, the vortex time is better as its value decreases, and the lower limit of the vortex time is theoretically 0 seconds, but may be, for example, 10 seconds or more, 15 seconds or more, or 20 seconds or more.

[0100] The method for measuring the water retention capacity, pressurized absorption capacity and vortex time of the above superabsorbent resin is described in more detail in the experimental examples described below.

[0101] As described above, when the superabsorbent resin according to the present invention models the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm using the above [Equation 1], by controlling the Se / r value to a certain level or higher, absorption characteristics such as water retention capacity (CRC), absorbency under pressure (AUP), and vortex time can be improved at an equivalent level or higher, while the content of water-soluble components (EC) is lowered, thereby simultaneously improving characteristics that are in conflict with absorption characteristics, such as permeability and rewet characteristics.

[0102] Meanwhile, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the superabsorbent resin is modeled using the above [Equation 1], the Se / r value and the Se value can be implemented by adjusting the components / content of the superabsorbent resin, the manufacturing process conditions of the superabsorbent resin, etc.

[0103] For example, by controlling the type and content of the monomer composition in the polymerization process, the type and content of the internal cross-linking agent, the type, amount and timing of injection of the surfactant in the neutralization and atomization steps, the type, amount and timing of injection of the neutralizing agent, the type of atomization device, the rotation speed, the hole size, the number of atomizations, etc., when modeling the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the superabsorbent resin using the above [Equation 1], the Se / r value can be controlled to a certain level or higher.

[0104] This will be explained in more detail in Item II of the method for manufacturing superabsorbent resin.

[0105] Below, each component that makes up the superabsorbent resin will be explained in more detail.

[0106] A polyacrylic acid (salt)-based superabsorbent resin of one embodiment of the invention comprises a base resin comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent. The crosslinked polymer can preferably be formed by polymerizing a monomer composition comprising components such as a monomer, an internal crosslinking agent, and a polymerization initiator.

[0107] Here, the water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the production of superabsorbent resins. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following chemical formula 1:

[0108] [Chemical Formula 1]

[0109] R-COOM'

[0110] In the above chemical formula 1,

[0111] R is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

[0112] M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0113] Preferably, the monomer may be at least one selected from the group consisting of (meth)acrylic acid, and monovalent (alkali) metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids.

[0114] In this way, when (meth)acrylic acid and / or its salt is used as a water-soluble ethylenically unsaturated monomer, a superabsorbent resin with improved absorbency can be obtained, which is advantageous. In addition, as the monomers, 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, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide, etc. can be used.

[0115] The above-mentioned water-soluble ethylenically unsaturated monomer has acidic groups. Meanwhile, in the production of superabsorbent resins, a monomer in which at least a portion of the acidic groups are neutralized by a neutralizing agent is crosslinked and polymerized to form a polymer. However, in the present invention, the acidic groups are preferably not neutralized during polymerization, but can be neutralized after the polymer is formed. More specific details regarding this will be described in the section on the production method of superabsorbent resins.

[0116] The concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition may be appropriately adjusted in consideration of polymerization time, reaction conditions, etc., and may be about 20 to about 60 wt%, or about 20 to about 40 wt%.

[0117] The term 'internal crosslinking agent' used in this specification is a term used to distinguish it from a surface crosslinking agent for crosslinking the surface of superabsorbent resin particles described later, and it plays a role in forming a polymer including a crosslinked structure by introducing crosslinking bonds between unsaturated bonds of the water-soluble ethylenically unsaturated monomers described above.

[0118] The crosslinking in the above step is carried out without distinction between the surface and the interior, but when the surface crosslinking process of the superabsorbent resin particles described later is carried out, the surface of the finally manufactured superabsorbent resin particles may include a structure newly crosslinked by the surface crosslinking agent, and the interior of the superabsorbent resin particles may maintain the structure crosslinked by the internal crosslinking agent.

[0119] According to one embodiment of the present invention, the internal crosslinking agent may include at least one of a multifunctional acrylate compound, a multifunctional allyl compound, or a multifunctional vinyl compound.

[0120] Non-limiting examples of multifunctional acrylate compounds include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol Examples thereof include tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate, and these may be used alone or in combination of two or more.

[0121] Non-limiting examples of polyfunctional allyl compounds include ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, propylene glycol diallyl ether, tripropylene glycol diallyl ether, polypropylene glycol diallyl ether, butanediol diallyl ether, butylene glycol diallyl ether, hexanediol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, dipentaerythritol diallyl ether, dipentaerythritol triallyl ether, dipentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, trimethylolpropane diallyl ether, Examples include trimethylolpropane triallyl ether, glycerin diallyl ether, and glycerin triallyl ether, and they can be used alone or in combination of two or more.

[0122] Non-limiting examples of polyfunctional vinyl compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, tripropylene glycol divinyl ether, polypropylene glycol divinyl ether, butanediol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, pentaerythritol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol divinyl ether, dipentaerythritol trivinyl ether, dipentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, trimethylolpropane divinyl ether, trimethylolpropane Examples thereof include trivinyl ether, glycerin divinyl ether, and glycerin trivinyl ether, and these may be used singly or in combination of two or more. Preferably, pentaerythritol triallyl ether may be used.

[0123] The above-described multifunctional allyl compound or multifunctional vinyl compound can form a cross-linked structure during the polymerization process by having two or more unsaturated groups included in the molecule bond with the unsaturated bonds of water-soluble ethylenically unsaturated monomers or the unsaturated bonds of other internal cross-linking agents, and unlike an acrylate compound including an ester bond (-(C=O)O-) in the molecule, the cross-linked bond can be more stably maintained even during the neutralization process after the polymerization reaction described below.

[0124] Accordingly, the gel strength of the superabsorbent resin being manufactured can be increased, process stability can be improved during the discharging process after polymerization, and the amount of water-soluble components can be minimized.

[0125] Crosslinking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of such an internal crosslinking agent can be carried out in the presence of a polymerization initiator, a thickener if necessary, a plasticizer, a preservative stabilizer, an antioxidant, etc.

[0126] In the monomer composition, the internal cross-linking agent may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal cross-linking agent may be used in an amount of 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.7 parts by weight or less, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the internal cross-linking agent is too low, cross-linking may not occur sufficiently, making it difficult to achieve a strength higher than an appropriate level, and if the content of the internal cross-linking agent is too high, the internal cross-linking density may increase, making it difficult to achieve a desired water retention capacity. In particular, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the superabsorbent resin of the present invention within the above range is modeled using the above [Formula 1], it is suitable for implementing the Se / r value within the desired range.

[0127] Meanwhile, when a small amount of internal cross-linking agent is used to ensure that the base resin has a high centrifugal retention capacity (CRC), the gel strength of the formed polymer may be reduced, and the low gel strength may make it difficult to operate a shredder or the like when cutting the hydrogel polymer. In this case, by mixing two or more types of internal cross-linking agents and using them to operate a high-speed rotary shredder or the like, the gel strength can be increased, thereby improving the operational stability of the shredder or the like.

[0128] The above-formed functional gel polymer can change the shape of the particles depending on the degree of internal crosslinking, and the polymer formed using such an internal crosslinking agent can have a three-dimensional network structure in which the main chains formed by polymerizing the water-soluble ethylenically unsaturated monomers are crosslinked by the internal crosslinking agent.

[0129] In this way, when the polymer has a three-dimensional network structure, the overall properties of the superabsorbent resin, such as water retention capacity and pressure absorption capacity, can be significantly improved compared to the case of a two-dimensional linear structure that is not further crosslinked by an internal crosslinking agent.

[0130] The above polymer is a polymer in which a monomer and an internal crosslinking agent are polymerized in the presence of a polymerization initiator. The type of the polymerization initiator is not particularly limited, but preferably, the polymerization can be performed using a thermal polymerization method in a batch reactor, and accordingly, a thermal polymerization initiator can be used as the polymerization initiator.

[0131] As the above thermal polymerization initiator, one or more selected from the group of initiators consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, examples of persulfate initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8), and examples of azo initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutylonitril, Examples include 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), etc. A more diverse range of thermal polymerization initiators is well described in Odian's book, 'Principle of Polymerization (Wiley, 1981), p203, and is not limited to the examples described above.

[0132] Such polymerization initiator may be used in an amount of 2 parts by weight or less relative to 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, if the concentration of the polymerization initiator is excessively low, the polymerization rate may be slowed and a large amount of residual monomer may be extracted from the final product, which is not preferable. Conversely, if the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network may become shorter, which may increase the content of water-soluble components and lower the pressure absorbency, thereby deteriorating the physical properties of the resin, which is not preferable.

[0133] Meanwhile, in one embodiment of the present invention, polymerization can be initiated by adding the aforementioned polymerization initiator and a reducing agent forming a redox couple together to the monomer composition.

[0134] Specifically, the initiator and reducing agent react with each other to form radicals when introduced into a polymer solution.

[0135] The formed radicals react with the monomer, and since the oxidation-reduction reaction between the initiator and reducing agent is highly reactive, polymerization is initiated even when only a small amount of initiator and reducing agent is added, so there is no need to increase the process temperature, low-temperature polymerization is possible, and changes in the physical properties of the polymer solution can be minimized.

[0136] The polymerization reaction utilizing the above oxidation-reduction reaction can occur smoothly even at temperatures near room temperature (25°C) or lower. For example, the polymerization reaction can be performed at a temperature of 5°C or higher and 25°C or lower, or 5°C or higher and 20°C or lower.

[0137] In one embodiment of the present invention, when a persulfate-based initiator is used as the initiator, the reducing agent may be at least one selected from the group consisting of sodium metabisulfite (Na2S2O5); tetramethyl ethylenediamine (TMEDA); a mixture of iron (II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinoacetate.

[0138] For example, potassium persulfate may be used as the initiator and disodium 2-hydroxy-2-sulfinoacetate may be used as the reducing agent; ammonium persulfate may be used as the initiator and tetramethylethylenediamine may be used as the reducing agent; or sodium persulfate may be used as the initiator and sodium formaldehyde sulfoxylate may be used as the reducing agent.

[0139] In another embodiment of the present invention, when a hydrogen peroxide-based initiator is used as the initiator, the reducing agent may be at least one selected from the group consisting of ascorbic acid; sucrose; sodium sulfite (Na2SO3), sodium metabisulfite (Na2S2O5); tetramethyl ethylenediamine (TMEDA); a mixture of iron (II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; disodium 2-hydroxy-2-sulfinoacteate; and disodium 2-hydroxy-2-sulfoacteate.

[0140] The above monomer composition may further include additives such as a thickener, a plasticizer, a preservative stabilizer, and an antioxidant, as needed.

[0141] And, the monomer composition including the monomer may be in a solution state dissolved in a solvent such as water, for example, and the solid content in the monomer composition in the solution state, i.e., the concentration of the monomer, internal crosslinking agent, and polymerization initiator, may be appropriately adjusted in consideration of the polymerization time, reaction conditions, etc. For example, the solid content in the monomer composition may be 10 to 80 wt%, 15 to 60 wt%, or 30 to 50 wt%.

[0142] The solvent that can be used at this time can be used without limitation in its composition as long as it can dissolve the above-mentioned components, and for example, one or more selected from water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide can be used in combination.

[0143] The polymer obtained by this method can form a polymer having a high molecular weight and a uniform molecular weight distribution by polymerizing using an ethylenically unsaturated monomer in an unsaturated state, and the content of water-soluble components is reduced, so that when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm, which is the target value, is modeled using the above [Formula 1], it is suitable for implementing the Se / r value in an appropriate range.

[0144] Additionally, the polymer may have a moisture content of 30 to 80 wt%. For example, the moisture content of the polymer may be at least 30 wt%, at least 45 wt%, or at least 50 wt%, but at most 80 wt%, at most 70 wt%, or at most 60 wt%.

[0145] If the moisture content of the polymer is too low, it may be difficult to secure an appropriate surface area in the subsequent grinding step, and thus the polymer may not be effectively ground. If the moisture content of the polymer is too high, the pressure applied in the subsequent grinding step may increase, making it difficult to grind to the desired particle size.

[0146] Meanwhile, throughout this specification, "moisture content" refers to the moisture content in relation to the total polymer weight, which is the value obtained by subtracting the weight of the polymer in a dry state from the weight of the polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to moisture evaporation in the polymer during the drying process by increasing the temperature of the polymer in a crumbly state through infrared heating. At this time, the drying conditions are such that the temperature is increased from room temperature to about 180°C and then maintained at 180°C, and the total drying time is set to 40 minutes, including 5 minutes for the temperature increase step, to measure the moisture content.

[0147] A superabsorbent resin according to one embodiment of the invention comprises a base resin powder comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group as described above and an internal crosslinking agent; and a surface crosslinked layer formed on the base resin powder by further crosslinking the crosslinked polymer via a surface crosslinking agent.

[0148] The above surface cross-linking layer is formed on at least a portion of the surface of the base resin powder, and may be formed by additional cross-linking of a cross-linking polymer included in the base resin powder via a surface cross-linking agent.

[0149] As the surface cross-linking agent, 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, propylene carbonate, and glycerol carbonate; an epoxy compound such as ethylene glycol diglycidyl ether; an oxazoline compound such as oxazolidinone; a polyamine compound; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; etc.

[0150] Specifically, one or more, two or more, or three or more of the surface cross-linking agents described above may be used as the surface cross-linking agent, for example, ethylene carbonate-propylene carbonate (ECPC), propylene glycol, and / or glycerol carbonate may be used.

[0151] This surface cross-linking agent can be used in an amount of about 0.001 to about 5 parts by weight per 100 parts by weight of the superabsorbent resin particles. For example, the surface cross-linking agent can be used in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.05 parts by weight or more, and 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less, per 100 parts by weight of the superabsorbent resin particles. By adjusting the content range of the surface cross-linking agent within the above-described range, a superabsorbent resin exhibiting excellent overall absorption properties can be manufactured. In particular, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the present invention is modeled using the above [Equation 1] within the above range, it is suitable for implementing the Se / r value within the target range.

[0152] Additionally, the surface cross-linking layer can be formed by adding an inorganic substance to the surface cross-linking agent. That is, in the presence of the surface cross-linking agent and the inorganic substance, the surface of the base resin powder can be further cross-linked to form a surface cross-linking layer.

[0153] As such inorganic materials, one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate can be used. The inorganic material can be used in powder or liquid form, and in particular, can be used as alumina powder, silica-alumina powder, titania powder, or nano silica solution. In addition, the inorganic material can be used in an amount of about 0.001 to about 1 part by weight based on 100 parts by weight of superabsorbent resin particles.

[0154] As described above, the superabsorbent resin including the base resin powder and the surface cross-linking layer formed on the base resin powder is allowed to swell freely in water having an electrical conductivity of 100 to 130 μS / cm, which is the parameter of the present invention, for 1 hour, and then the content of the water-soluble component measured is adjusted to a specific range, so that when applied to sanitary materials such as diapers, the discharged body fluid can be absorbed at a rapid rate, and also, a relatively large amount can be absorbed initially, so that problems such as body fluid accumulating inside the sanitary material or leaking out can not occur.

[0155] Ⅱ. Manufacturing method of superabsorbent resin

[0156] Meanwhile, conventional superabsorbent polymers are manufactured by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer, drying the hydrogel polymer formed in this manner, and then pulverizing it to a desired particle size. In this case, a chopping process is typically performed before the drying process to cut the hydrogel polymer into particles several millimeters in size in order to facilitate drying of the hydrogel polymer and increase the efficiency of the pulverization process. However, in this chopping process, due to the adhesiveness of the hydrogel polymer, the hydrogel polymer cannot be pulverized to a micro-sized particle level, but instead becomes an aggregated gel. When this aggregated gel-type hydrogel polymer is dried, a plate-shaped dried body is formed, and in order to pulverize it to a micro-sized particle level, it must go through a multi-stage pulverization process that lowers the adhesiveness of the polymer. This process has been problematic in that a lot of fine dust is generated.

[0157] Specifically, conventional superabsorbent resins have been manufactured by including the following steps.

[0158] (Neutralization) A step of neutralizing at least a portion of the acidic groups of a water-soluble ethylenically unsaturated monomer;

[0159] (Polymerization) A step of forming a hydrogel polymer by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a portion of neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator;

[0160] (Chopping) A step of chopping the above functional gel polymer;

[0161] (dry) drying the chopped functional gel polymer; and

[0162] (Crushing / classification) A step of crushing the dried polymer and then classifying it into normal particles and fine powder;

[0163] As described above, the chopped hydrogel polymer has a coagulated gel form with a size of about 1 cm to 10 cm, and the chopped hydrogel polymer is laminated on a belt having a perforated bottom and dried by hot air supplied from the bottom or the top. Since the polymer dried by the drying method has a plate shape rather than a particle shape, the step of classifying after grinding has been performed by coarsely grinding and then classifying, and then finely grinding and then classifying again so that the manufactured particles become normal particles, that is, particles having a particle size of 150 ㎛ to 850 ㎛. Since the amount of fine powder separated in the final classification step by this manufacturing method is large, about 20 wt% to about 30 wt% based on the total weight of the finally manufactured superabsorbent resin, the separated fine powder is mixed with an appropriate amount of water, reassembled into fine powder, and then reused by adding it to the chopping step or the step before drying.

[0164] However, when the fine powder reassembly mixed with water is re-introduced into the crushing or drying process for reuse of such fine powder, problems such as increased device load and / or energy consumption have occurred, and the fine powder remaining without being classified has caused a deterioration in the properties of the superabsorbent resin.

[0165] To solve this problem, as a result of repeated research, it was confirmed that, instead of performing polymerization in a state where the acidic groups of a water-soluble ethylenically unsaturated monomer are neutralized, as in the conventional method for producing superabsorbent resins, polymerization is first performed in a state where the acidic groups are not neutralized to form a polymer, and then the hydrogel polymer is micronized in the presence of a surfactant and then the acidic groups of the polymer are neutralized, or the hydrogel polymer is formed by neutralizing the acidic groups of the polymer and then the hydrogel polymer is micronized in the presence of a surfactant, or the acidic groups present in the polymer are neutralized simultaneously with the micronization, so that the surfactant is present in a large amount on the surface of the polymer and can sufficiently play a role in lowering the high adhesiveness of the polymer, preventing the polymer from excessively agglomerating, and controlling the agglomeration state to a desired level.

[0166] At this time, when a high-intensity mechanical shear force is applied to the above-mentioned micronization step to perform ultra-fine grinding, coagulated functional gel particles having finer pores can be formed.

[0167] The functional gel polymer manufactured by applying the above high-intensity mechanical shear force and ultra-fine grinding is manufactured in the form of particles having stable micropores of 100㎛ or less, and as the grinding and drying process is carried out under milder conditions thereafter, the amount of fine powder generated during the process can be further reduced.

[0168] In addition, the ultra-fine grinding process using the high-intensity mechanical shear force can form micropores in the hydrogel polymer without using a separate foaming agent in the polymerization step, thereby improving the absorption rate. Accordingly, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the present invention is modeled using the above-mentioned [Equation 1], it is easy to control the Se / r value within the desired range.

[0169] Meanwhile, preferably, the above-mentioned functional gel micronization process can be conducted in the presence of a surfactant. By using a surfactant in the micronization step, particle aggregation can be effectively controlled, thereby reducing the load on the device and further improving productivity.

[0170] In addition, by first performing polymerization in an uncrosslinked state to form a polymer and then neutralizing the acidic groups present in the polymer, it is possible to form a polymer with a longer chain, and thus achieve the effect of reducing the content of water-soluble components that exist in an uncrosslinked state due to incomplete crosslinking.

[0171] Since the above-mentioned water-soluble component has the property of easily dissolving when the superabsorbent resin comes into contact with a liquid, when the content of the water-soluble component is high, most of the dissolved water-soluble component remains on the surface of the superabsorbent resin, making the superabsorbent resin sticky and causing a decrease in liquid permeability. Therefore, it is important to keep the content of the water-soluble component low from the perspective of liquid permeability.

[0172] According to one embodiment of the present invention, by performing polymerization in an unsaturated state, the content of water-soluble components is reduced, thereby improving the permeability of the superabsorbent resin. Accordingly, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm is modeled using the above [Formula 1], it was confirmed that it is easy to control the Se / r value within the desired range.

[0173] Hereinafter, each step of the method for manufacturing a superabsorbent resin according to an embodiment will be described in more detail.

[0174] Step 1: Polymerization Step

[0175] First, polymerization is performed on a monomer composition including a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent, thereby producing a base resin powder including a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group and the internal crosslinking agent are crosslinked.

[0176] The above step may be comprised of a step of preparing a monomer composition by mixing the water-soluble ethylenically unsaturated monomer having the acidic group, an internal crosslinking agent, and a polymerization initiator, and a step of polymerizing the monomer composition to form a polymer.

[0177] Here, the contents of each component can be equally applied to the contents described in the superabsorbent resin of the above-mentioned item Ⅰ.

[0178] Meanwhile, the water-soluble ethylenically unsaturated monomer has an acidic group. As explained above, in the production of conventional superabsorbent resins, a monomer in which at least a portion of the acidic groups are neutralized by a neutralizing agent is crosslinked and polymerized to form a polymer. Specifically, in the step of mixing the water-soluble ethylenically unsaturated monomer having the acidic group, an internal crosslinking agent, a polymerization initiator, and a neutralizing agent, at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer are neutralized.

[0179] However, according to one embodiment of the present invention, polymerization is first performed in a state where the acidic group of the water-soluble ethylenically unsaturated monomer is not neutralized to form a polymer.

[0180] Water-soluble ethylenically unsaturated monomers (e.g., acrylic acid) whose acid groups are not neutralized are liquid at room temperature and have high miscibility with the solvent (water), so they exist as a mixed solution in the monomer composition. However, water-soluble ethylenically unsaturated monomers whose acid groups are neutralized are solid at room temperature and have different solubility depending on the temperature of the solvent (water), with the solubility decreasing at lower temperatures.

[0181] In this way, a water-soluble ethylenically unsaturated monomer in which the acidic groups are not neutralized has a higher solubility or miscibility in a solvent (water) than a monomer in which the acidic groups are neutralized, and thus does not precipitate even at low temperatures, and is therefore advantageous for long-term polymerization at low temperatures. Accordingly, a water-soluble ethylenically unsaturated monomer in which the acidic groups are not neutralized can be used for long-term polymerization to stably form a polymer having a higher molecular weight and a uniform molecular weight distribution.

[0182] In addition, since the formation of a polymer with a longer chain is possible, the effect of reducing the content of water-soluble components that exist in a non-crosslinked state due to incomplete polymerization or crosslinking can be achieved, and accordingly, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the present invention described above is modeled by the above [Formula 1], it is suitable for implementing the Se / r value in the desired range.

[0183] In addition, if polymerization is first performed in a state where the acidic groups of the monomer are not neutralized to form a polymer, and then the polymer is micronized in the presence of a surfactant after neutralization, or the polymer is micronized in the presence of a surfactant and then neutralized, or the acidic groups present in the polymer are neutralized simultaneously with the micronization, the surfactant can sufficiently play a role in reducing the adhesiveness of the polymer by being present in large quantities on the surface of the polymer.

[0184] According to one embodiment of the present invention, the step of performing polymerization on the monomer composition to form a polymer can be performed for 1 hour or more in a batch type reactor.

[0185] In the manufacturing method of a typical superabsorbent resin, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source. When thermal polymerization is performed, it can be performed in a reactor with a stirring shaft such as a kneader, and when photopolymerization is performed, it can be performed in a flat-bottomed container.

[0186] Meanwhile, when the polymerization is performed as a continuous polymerization, for example, when the polymerization is performed in a reactor having a reactor stirring shaft equipped with a conveyor belt, a new monomer composition is supplied to the reactor as the polymerization product moves, so that polymerization is performed continuously, and thus polymers having different polymerization rates are mixed, and accordingly, it is difficult to achieve even polymerization throughout the monomer composition, which may result in a deterioration of the overall physical properties.

[0187] However, according to one embodiment of the present invention, since polymerization is carried out in a static manner in a batch reactor, there is less concern that polymers with different polymerization rates will be mixed, and thus a polymer with consistent quality can be obtained.

[0188] In addition, the polymerization step is performed in a batch reactor having a predetermined volume, and the polymerization reaction is performed for a longer period of time, for example, 1 hour or more, 3 hours or more, or 6 hours or more, than when polymerization is performed continuously in a reactor equipped with a conveyor belt. Despite the long polymerization reaction time as described above, since the polymerization is performed on a water-soluble ethylenically unsaturated monomer in an unneutralized state, the monomer does not precipitate easily even if the polymerization is performed for a long period of time, and therefore, it is advantageous for long-term polymerization.

[0189] Meanwhile, since polymerization in the batch reactor of the present invention utilizes a thermal polymerization method, the polymerization initiator uses a thermal polymerization initiator, and the description of the corresponding component is as described above.

[0190] Steps 2 and 3: Atomization and neutralization steps

[0191] Next, a step (step 2) is included in which the functional gel polymer is micronized in the presence of a surfactant to prepare a mixture including the micronized functional gel polymer.

[0192] The above-mentioned micronization step is a step of micronizing the polymer in the presence of a surfactant, and is a step in which micronization and agglomeration into sizes of tens to hundreds of micrometers occur simultaneously, rather than chopping the polymer into sizes of millimeters.

[0193] That is, this is a step for manufacturing secondary aggregated particles in the form of aggregated primary particles that are finely divided into tens to hundreds of micrometers in size by imparting appropriate adhesiveness to the polymer. The secondary aggregated particles, which are hydrophilic superabsorbent resin particles manufactured through this step, have a normal particle size distribution while significantly increasing their surface area, which can significantly improve their absorption rate.

[0194] Meanwhile, when a high-intensity mechanical shear force is applied in the above-mentioned micronization step to perform ultra-fine grinding at a rotation speed of 500 rpm to 4,000 rpm, coagulated functional gel particles having finer pores can be formed.

[0195] At this time, when ultra-fine grinding is performed at a rotation speed of 500 rpm to 4,000 rpm, a high-strength mechanical shear force is applied, so that micropores of 100 μm or less are easily formed in the polymer, thereby increasing the surface roughness, and significantly increasing the total surface area of ​​the polymer due to the pores formed inside and outside the polymer particles. Since the micropores are formed in a stable form compared to the pores formed using a foaming agent in the polymerization step, the degree of fine powder generation due to the pores in the subsequent process can be significantly reduced. The superabsorbent resin particles manufactured by this step have a significantly increased surface area, so that the absorption rate can be significantly improved, and accordingly, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the present invention described above is modeled by the above [Formula 1], it is suitable for implementing the Se / r value within the target range.

[0196] The above ultra-fine grinding process is performed at a rotation speed of 500 rpm to 4,000 rpm. If the rotation speed of the process is less than 500 rpm, it is difficult to form sufficient pores to the desired degree, so it is difficult to expect a fast absorption speed and it is difficult to secure the desired level of productivity. In addition, if it exceeds 4,000 rpm, the polymer chains may be damaged due to excessive shear force, and accordingly, the water-soluble component may increase, and the overall physical properties of the manufactured superabsorbent resin may be somewhat deteriorated. Preferably, the above ultra-fine grinding process can be performed at 1,000 rpm to 3,500 rpm, or 2,000 rpm to 3,000 rpm. In this range, it is easy to form the desired micropores without the above-mentioned problems.

[0197] According to one embodiment of the present invention, the atomization step is performed by an atomization device, and the atomization device may include a body part including a transport space into which a polymer is transported; a screw member rotatably installed inside the transport space to move the polymer; a driving motor providing a rotational driving force to the screw member; a cutter member installed in the body part to pulverize the polymer; and a porous plate having a plurality of holes formed therein, which discharges the polymer pulverized by the cutter member to the outside of the body part.

[0198] At this time, the hole size provided in the porous plate of the atomization device may be 1 mm to 25 mm, 5 mm to 20 mm, or 5 mm to 15 mm.

[0199] In this way, when the polymer mixed with the surfactant is atomized while controlling agglomeration using a micronizing device, a smaller particle size distribution is realized, so that subsequent drying and grinding processes can be performed under milder conditions, thereby preventing the generation of fine particles and improving the properties of the superabsorbent resin. In addition, if ultra-fine grinding is performed, the absorption rate can be improved by simultaneously forming appropriate micropores on the surface of the polymer and increasing the surface area.

[0200] The above atomization step may be performed one or more times, preferably one to six times, one to four times, or one to three times. This may be performed using a plurality of atomization devices, a single atomization device comprising a plurality of porous plates and / or a plurality of cutter members, or some of the plurality of atomization devices may comprise a plurality of porous plates and / or a plurality of cutter members.

[0201] According to one embodiment of the present invention, a surfactant may be additionally used in the atomization step, whereby agglomeration between polymer particles can be effectively controlled, thereby reducing the load on the equipment used in the pulverization process and further improving productivity.

[0202] Preferably, the surfactant may be a compound represented by the following chemical formula 2 or a salt thereof, but the present invention is not limited thereto:

[0203] [Chemical Formula 2]

[0204]

[0205] In the above chemical formula 2,

[0206] A1, A2 and A3 are each independently a single bond, carbonyl, , or and, provided that at least one of these is carbonyl or , wherein, m1, m2 and m3 are each independently an integer from 1 to 8, are each connected to an adjacent oxygen atom, are connected to adjacent R1, R2 and R3 respectively,

[0207] R1, R2 and R3 are each independently hydrogen, straight or branched chain alkyl having 6 to 18 carbon atoms or straight or branched chain alkenyl having 6 to 18 carbon atoms,

[0208] n is an integer from 1 to 9.

[0209] The above surfactant is added so that the atomization step can be easily achieved without agglomeration by mixing with the polymer.

[0210] The surfactant represented by the above chemical formula 2 is a nonionic surfactant, and has excellent surface adsorption performance by hydrogen bonding even with a polymer that is not neutralized, and is therefore suitable for implementing the desired coagulation control effect. On the other hand, in the case of anionic surfactants, not nonionic surfactants, when mixed with a polymer that has been neutralized with a neutralizing agent such as NaOH or Na2SO4, the Na ionized in the carboxyl group substituent of the polymer + It is adsorbed through ions, and when mixed with an unsaturated polymer, there is a problem that the adsorption efficiency for the polymer is relatively reduced due to competition with the anion of the carboxyl group substituent of the polymer.

[0211] Specifically, in the surfactant represented by the above chemical formula 2, the hydrophobic functional group is the terminal functional group R1, R2, R3 portion (if not hydrogen), and the hydrophilic functional group is the glycerol-derived portion in the chain and the terminal hydroxyl group (A n is a single bond, and at the same time R n When the polymer is hydrogen, n=1~3) is further included, and the glycerol-derived portion and the terminal hydroxyl group serve as hydrophilic functional groups to improve the adsorption performance on the polymer surface. Accordingly, the aggregation of superabsorbent resin particles can be effectively suppressed.

[0212] In the above chemical formula 2, the hydrophobic functional groups R1, R2, and R3 (if not hydrogen) are each independently a straight-chain or branched alkyl having 6 to 18 carbon atoms or a straight-chain or branched alkenyl having 6 to 18 carbon atoms. In this case, if the R1, R2, and R3 portions (if not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, there is a problem that the agglomeration control of the pulverized particles is not effectively performed due to the short chain length, and if the R1, R2, and R3 portions (if not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the surfactant may be reduced so that it may not be effectively mixed with the polymer, and there may be a problem that the unit price of the composition increases due to the increase in the cost of the surfactant.

[0213] Preferably, R1, R2, R3 may be hydrogen, or, if it is a straight-chain or branched alkyl having 6 to 18 carbon atoms, 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl, or, if it is a straight-chain or branched alkenyl having 6 to 18 carbon atoms, 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-dekenyl, 2-undekenyl, 2-dodekenyl, 2-tridekenyl, 2-tetradekenyl, 2-pentadekenyl, 2-hexadekenyl, It can be 2-heptadekenyl or 2-octadekenyl.

[0214] The above surfactant may be selected from compounds represented by the following chemical formulas 2-1 to 2-14:

[0215] [Chemical Formula 2-1]

[0216]

[0217] [Chemical Formula 2-2]

[0218]

[0219] [Chemical Formula 2-3]

[0220]

[0221]

[0222] [Chemical Formula 2-4]

[0223]

[0224] [Chemical Formula 2-5]

[0225]

[0226] [Chemical Formula 2-6]

[0227]

[0228] [Chemical Formula 2-7]

[0229]

[0230] [Chemical Formula 2-8]

[0231]

[0232] [Chemical Formula 2-9]

[0233]

[0234] [Chemical Formula 2-10]

[0235]

[0236] [Chemical Formula 2-11]

[0237]

[0238] [Chemical Formula 2-12]

[0239]

[0240] [Chemical Formula 2-13]

[0241]

[0242] [Chemical Formula 2-14]

[0243] .

[0244] Meanwhile, the amount of the surfactant used is not particularly limited, but may be used in an amount of 0.06 g to 0.48 g per 1,000 g of the functional gel polymer depending on the need for securing productivity or the load condition of the device.

[0245] If the surfactant is used in an excessively small amount, the surfactant may not be evenly adsorbed on the polymer surface, resulting in re-agglomeration of particles after grinding, or absorption performance, such as water retention capacity and absorbency under pressure, may deteriorate due to the surfactant sharing a large amount with the polymer. On the other hand, if the surfactant is used in an excessive amount, the overall physical properties of the final superabsorbent resin may deteriorate due to a decrease in surface tension.

[0246] Therefore, for example, the surfactant may be used in an amount of 0.06 g or more, 0.1 g or more, or 0.2 g or more, and 0.48 g or less, 0.45 g or less, or 0.4 g or less per 1,000 g of the functional gel polymer, and accordingly, it is easy to control the content of the water-soluble component measured after freely swelling in water having an electrical conductivity of 100 to 130 μS / cm for 1 hour within a desired range.

[0247] The method for mixing these surfactants into the polymer is not particularly limited, and any method capable of evenly mixing them into the polymer may be appropriately employed. Specifically, the surfactants may be mixed dry, dissolved in a solvent and then mixed in a solution state, or melted and then mixed.

[0248] For example, the surfactant may be mixed in a solution state dissolved in a solvent. Any type of solvent, whether inorganic or organic, may be used, but water is most suitable considering the ease of the drying process and the cost of the solvent recovery system. Furthermore, the solution may be prepared by mixing the surfactant and polymer in a reactor, placing the polymer in a mixer and spraying the solution, or continuously supplying the polymer and solution to a continuously operating mixer for mixing.

[0249] Meanwhile, when the surfactant is mixed in a solution state dissolved in water, it can be used by diluting it into an aqueous solution having a concentration of about 0.01% to 10%.

[0250] For example, if the surfactant is to be used at 0.1 g per 1,000 g of the hydrogel polymer, 100 g of an aqueous solution having a concentration of 0.1%, in which 0.1 g of the surfactant is dissolved in 99.9 g of water, may be used. Alternatively, 10 g of an aqueous solution having a concentration of 1%, in which 0.1 g of the surfactant is dissolved in 9.9 g of water, may be used.

[0251] That is, when using the same amount of surfactant, the water content can be increased or decreased to create an aqueous solution having a desired concentration, and the concentration can be appropriately adjusted in consideration of the properties of the superabsorbent resin to be ultimately manufactured.

[0252] Meanwhile, if the surfactant is hydrophobic and has very low solubility in water, it can be used by dry mixing the surfactant into the polymer, or by dispersing the surfactant in water. For example, if it is dry mixed in powder form and dispersed into the polymer, the degree of dispersion is very weak, so it can be used by dispersing it in water and evenly spreading it on the surface.

[0253] According to one embodiment of the invention, a step of neutralizing at least a portion of the acidic groups of the polymer (step 3) is performed, wherein the atomizing step of step 2 and the neutralizing step of step 3 described above may be performed sequentially, alternately, or simultaneously.

[0254] That is, a neutralizing agent may be added to the polymer to first neutralize the acidic groups, and then a surfactant may be added to the neutralized polymer to micronize the polymer mixed with the surfactant (performed in the order of Step 3->Step 2), or the neutralizing agent and the surfactant may be added to the polymer simultaneously to neutralize and micronize the polymer (perform Steps 2 and 3 simultaneously). Alternatively, the surfactant may be added first and the neutralizing agent may be added later (performed in the order of Step 2->Step 3). Alternatively, the neutralizing agent and the surfactant may be added alternately in a cross-sectional manner. Alternatively, the surfactant may be added first to micronize, the neutralizing agent may be added to neutralize, and then an additional surfactant may be added to the neutralized hydrogel polymer to further perform the micronization process.

[0255] Here, if the neutralization step is performed independently from the atomization step of step 2, it can be performed in a manner in which the additive is added while pulverizing the polymer at the same time. More specifically, a screw-type extruder including a porous plate having a plurality of holes formed therein can be used. The screw-type extruder is a device that performs pulverization under milder conditions compared to the atomization device used in the atomization step described above, and the rotation speed can be about 150 rpm to 500 rpm, and the holes of the porous plate can be about 3 mm to 25 mm, but are not limited thereto.

[0256] The rotation speed of the screw-type extruder and the size of the perforated plate holes affect the discharge state of the superabsorbent resin discharged from the extruder, and the particle shape of the superabsorbent resin may change depending on the discharge state.

[0257] In particular, by controlling the rotation speed of the screw-type extruder to 150 rpm to 500 rpm, when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm of the above-described present invention is modeled using the above [Formula 1], the Se / r value can be controlled to a desired range.

[0258] At this time, a basic substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide that can neutralize acid groups can be used as a neutralizing agent.

[0259] In addition, the degree of neutralization, which refers to the degree of neutralization of acidic groups contained in the polymer by the neutralizing agent, may be 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to 80 mol%. The range of the degree of neutralization may vary depending on the final physical properties, and the absorption rate and absorption performance may be controlled by controlling the degree of neutralization.

[0260] At this time, if the degree of neutralization is excessively high, the absorption capacity of the superabsorbent resin may decrease, and if the concentration of carboxyl groups on the particle surface is excessively low, it may be difficult to properly perform surface cross-linking in subsequent processes, which may reduce the pressure-absorbent properties or liquid permeability. Conversely, if the degree of neutralization is excessively low, not only will the polymer's absorption capacity significantly decrease, but it may also exhibit properties similar to elastic rubber that are difficult to handle.

[0261] Meanwhile, it may be desirable to leave a certain time gap between the introduction of the neutralizing agent and the atomization process to ensure even neutralization of the entire polymer.

[0262] Step 4: Drying

[0263] Next, a step (step 4) is performed to dry the above-mentioned micronized and neutralized polymer to prepare a base resin powder.

[0264] The above step is a step of drying the moisture in the base resin powder, which is a polymer obtained by neutralizing at least a portion of the acidic groups of the polymer and pulverizing the polymer.

[0265] In a conventional method for manufacturing a superabsorbent resin, the drying step is performed so that the moisture content of the base resin powder is about 4 to 20 wt%, about 4 to about 15 wt%, or about 6 to about 13 wt%. However, the present invention is not limited thereto.

[0266] The above step 4 can be performed in a fixed-bed type drying method, a moving type drying method, or a combination thereof.

[0267] According to one embodiment of the invention, step 4 can be performed by static drying.

[0268] The above-mentioned static drying method refers to a method in which the material to be dried is placed on a perforated iron plate or other permeable floor, and hot air is passed through the material from below to dry it.

[0269] Since static drying dries in a plate-like shape without particle movement, it is difficult to achieve uniform drying with a simple flow of hot air. Therefore, static drying requires delicate control of hot air and temperature to obtain a uniform, high-moisture content dried body. In the present invention, by changing the hot air direction from downward to upward, warping of the plate-like dried body during drying was prevented, thereby preventing hot air from escaping. In addition, the drying temperature was changed section by section so that the upper, middle, and lower layers within the dried body could be uniformly dried with a moisture content deviation of less than 5%.

[0270] As a device capable of drying using the above-mentioned political drying method, a belt-type dryer may be used, but is not limited thereto.

[0271] In the above-described static drying step, the drying process may be performed at a temperature of about 80°C to 200°C, preferably 90°C to 190°C or 100°C to 180°C. If the drying temperature is lower than 80°C, the drying time may be excessively long, and if the drying temperature is excessively high, exceeding 200°C, a superabsorbent resin having a moisture content lower than the desired moisture content may be obtained. Meanwhile, the drying temperature may refer to the temperature of the hot air used or the internal temperature of the device during the drying process.

[0272] According to one embodiment of the invention, step 4 may be performed by fluid drying.

[0273] The fluidized drying method described above refers to a method of drying in which the material is mechanically stirred during the drying process. The direction in which the hot air passes through the material may be the same as or different from the direction in which the material circulates. Alternatively, the material can be dried by circulating the heat-generating fluid (heat-generating oil) within the dryer and passing it through a separate pipe outside the dryer.

[0274] Devices capable of drying using this fluid drying method include a horizontal-type mixer, a rotary kiln, a paddle dryer, a steam tube dryer, or a generally used fluid dryer.

[0275] In the case of the above-mentioned fluid drying step, the drying process can be performed at a temperature of about 100°C to 300°C, preferably 120°C to 280°C or 150°C to 250°C. If the drying temperature is too low, such as below 100°C, the drying time may be too long, and if the drying temperature is too high, such as exceeding 300°C, the superabsorbent resin polymer chain may be damaged, resulting in a decline in overall physical properties and a superabsorbent resin having a moisture content lower than the desired moisture content may be obtained.

[0276] Step 5: Grinding Stage

[0277] Next, a step of grinding the dried base resin powder is performed.

[0278] Specifically, the above grinding step can be performed by grinding the dry base resin powder to have a particle size of a normal particle level, i.e., a particle size of 150 μm to 850 μm.

[0279] The crusher used for this purpose may be, specifically, 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, or a disc cutter, but is not limited to the examples described above.

[0280] Alternatively, a grinder such as a pin mill, hammer mill, screw mill, roll mill, disc mill or jog mill may be used, but is not limited to the examples described above.

[0281] Meanwhile, in the manufacturing method of the present invention, superabsorbent resin particles having a smaller particle size distribution than in the conventional chopping step can be realized in the micronization step, and since the moisture content after drying is maintained relatively high, even if the pulverization is performed under mild conditions with less pulverizing force, a superabsorbent resin having a very high content of normal particle size of 150 ㎛ to 850 ㎛ can be formed, and the fine powder generation ratio can be greatly reduced.

[0282] The superabsorbent resin particles manufactured as described above may contain superabsorbent resin particles having a particle size of 150 ㎛ to 850 ㎛, i.e., normal particles, in an amount of 80 wt% or more, 85 wt% or more, 89 wt% or more, 90 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, or 95 wt% or more, based on the total weight. The particle size of these resin particles may be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0283] In addition, the superabsorbent resin particles may include fine particles having a particle size of less than 150 μm in an amount of about 20 wt% or less, about 18 wt% or less, about 15 wt% or less, about 13 wt% or less, about 12 wt% or less, about 11 wt% or less, about 10 wt% or less, about 9 wt% or less, about 8 wt% or less, or about 5 wt% or less, relative to the total weight. This is in contrast to having fine particles in an amount of more than about 20 wt% to about 30 wt% when producing a superabsorbent resin according to a conventional manufacturing method.

[0284] Additive injection stage

[0285] Meanwhile, according to one embodiment of the invention, a step of adding an additive to the atomized and neutralized polymer may be further included before the drying step (step 4).

[0286] The above additive injection process is a process for improving properties by using additional additives within a range that does not impede the desired effect, and the types of the additives are not particularly limited, and examples thereof include, but are not limited to, a polymerization initiator for removing residual monomers, a permeability improver for improving absorption properties, a fine powder for recycling the fine powder generated, an anti-caking agent, a fluidity improver, an antioxidant, a neutralizer, a surfactant, etc.

[0287] The above additive injection step may be performed simultaneously with step 2, simultaneously with step 3, after steps 2 and 3, or in at least one or more of these steps. The above additive injection step may be performed multiple times as needed, and may also be performed at least once in each step.

[0288] If the above additive injection step is performed independently from steps 2 and 3, i.e., after steps 2 and 3 and before step 4, it can be performed in such a way that the additive is injected simultaneously with the polymer being crushed.

[0289] The above grinding can be applied in the same manner as the grinding step of step 5 described above, and the additive can be added once or multiple times in the grinding step and mixed with the polymer.

[0290] Classification stage

[0291] Next, after the step of crushing the base resin powder (step 5), a step of classifying the crushed superabsorbent resin particles according to particle size may be further included.

[0292] Surface cross-linking step

[0293] In addition, a step of forming a surface cross-linking layer on at least a portion of the surface of the base resin particles may be further included in the presence of a surface cross-linking agent after the base resin powder has been pulverized (step 5) and / or classified. By this step, the cross-linking polymer contained in the base resin powder may be further cross-linked via the surface cross-linking agent, thereby forming a surface cross-linking layer on at least a portion of the surface of the base resin powder.

[0294] The description of the above surface cross-linking agent can be applied equally to all of the above.

[0295] In addition, there is no limitation on the composition of the method for mixing the surface cross-linking agent with the base resin powder. For example, a method of mixing a composition containing the surface cross-linking agent and the base resin powder by placing them in a reaction tank, a method of spraying the surface cross-linking agent onto the composition, a method of continuously supplying the resin composition and the surface cross-linking agent to a continuously operating mixer, and the like can be used.

[0296] When mixing the surface crosslinking agent and base resin powder, water and methanol may be additionally mixed and added. Adding water and methanol has the advantage of ensuring that the surface crosslinking agent is evenly dispersed throughout the resin composition. The amount of water and methanol added can be appropriately adjusted to ensure even dispersion of the surface crosslinking agent, prevent clumping of the resin composition, and optimize the depth of surface penetration of the crosslinking agent.

[0297] The above surface cross-linking process may be performed at a temperature of about 80°C to about 250°C. More specifically, the surface cross-linking process may be performed at a temperature of about 100°C to about 220°C, or about 120°C to about 200°C, for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. When the above-described surface cross-linking process conditions are met, the surface of the superabsorbent resin particles may be sufficiently cross-linked, thereby increasing the absorbency under pressure.

[0298] The temperature raising means for the above surface crosslinking reaction is not particularly limited.

[0299] Heating can be achieved by supplying a heat medium or directly supplying a heat source. At this time, available 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 heat medium source, heating rate, and target temperature. Meanwhile, directly supplied heat sources include, but are not limited to, heating via electricity or gas.

[0300] Post-processing step

[0301] According to one embodiment of the present invention, after the step of forming a surface cross-linking layer on at least a portion of the surface of the base resin powder, the method may further include at least one of a cooling step of cooling the superabsorbent resin particles on which the surface cross-linking layer has been formed, a watering step of adding water to the superabsorbent resin particles on which the surface cross-linking layer has been formed, and a post-treatment step of adding an additive to the superabsorbent resin particles on which the surface cross-linking layer has been formed. In this case, the cooling step, the watering step, and the post-treatment step may be performed sequentially or simultaneously.

[0302] In the above-described water step, water or brine can be used, thereby controlling the amount of water generated, etc. The amount of water used can be appropriately adjusted in consideration of the moisture content of the desired final product, etc., and preferably, 0.1 to 10 wt%, 0.5 to 8 wt%, or 1 to 5 wt% can be used relative to the absorbent resin, but is not limited thereto.

[0303] Additionally, after the above-mentioned singer step, a further maturation step can be performed.

[0304] When using brine in the above-mentioned water step, the solution absorption rate is relatively low due to the conductivity of the brine, so that the brine is evenly distributed during the maturation step, enabling even absorption into the absorbent resin. The maturation step may be performed using a commonly used method without any particular limitation, and may be performed, for example, using a rotary stirring device, at a temperature of 100°C or lower, 80°C or lower, and preferably 50°C or lower for 10 minutes to 1 hour.

[0305] The additives added in the above post-processing step may include surfactants, inorganic salts, permeability improvers, anti-caking agents, fluidity improvers, and antioxidants, but the present invention is not limited thereto.

[0306] By selectively performing the above cooling step, water step, and post-treatment step, the moisture content of the final superabsorbent resin can be improved by controlling the occurrence of moisture, etc., and a higher quality superabsorbent resin product can be manufactured.

[0307] 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.

[0308] <Example>

[0309] Example 1

[0310] (Step 1: Polymer manufacturing step)

[0311] In a 5L glass container equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 3.0 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, 0.75 g of trimethylolpropane triacrylate (TMPTA) (Miwon Miramer M3190 product), and 3406 g of water were stirred and mixed, and the mixture was allowed to react while maintaining the temperature at 5°C. The glass container containing the mixture was replaced with nitrogen at a rate of 1,000 cc / min for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution, 15.8 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane) dihydrochloric acid solution were added as polymerization initiators, and simultaneously 22.5 g of a 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the temperature of the mixture reached 85°C, polymerization was performed at 90±2°C for about 6 hours to obtain a polymer.

[0312] (Steps 2 and 3: Atomization and Neutralization Steps)

[0313] 20 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) mounted inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,000 rpm, thereby carrying out a particle formation process.

[0314] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 400 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0315] (Step 4: Drying Stage)

[0316] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically transferring airflow. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0317] (Step 5: Crushing and Classification Stage)

[0318] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) was used, and the crusher roll gap was set to 0.12 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0319] (Surface cross-linking step)

[0320] Next, a surface cross-linking agent aqueous solution containing 4 g of water, 6 g of methanol, 0.05 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0321] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0322] Example 2

[0323] (Step 1: Polymer manufacturing step)

[0324] A polymer was obtained in the same manner as in Example 1 above.

[0325] (Steps 2 and 3: Atomization and Neutralization Steps)

[0326] 40 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Then, the polymer was pushed through a porous plate having multiple 10 mm holes at a rotation speed of 2,500 rpm using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher, thereby carrying out a particle formation process.

[0327] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 150 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 400 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0328] (Step 4: Drying Stage)

[0329] The polymer was dried in the same manner as in Example 1.

[0330] (Step 5: Crushing and Classification Stage)

[0331] The base resin powder was obtained by crushing and classifying in the same manner as in Example 1.

[0332] (Surface cross-linking step)

[0333] A surface cross-linked superabsorbent resin was obtained by carrying out a surface cross-linking reaction in the same manner as in Example 1.

[0334] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0335] Example 3

[0336] (Step 1: Polymer manufacturing step)

[0337] A polymer was obtained in the same manner as in Example 1, except that 3.75 g of pentaerythritol triallyl ether (PETTAE) was used instead of 3.0 g of pentaerythritol triallyl ether (PETTAE) and 0.75 g of trimethylolpropane triacrylate (TMPTA) as internal crosslinking agents.

[0338] (Steps 2 and 3: Atomization and Neutralization Steps)

[0339] 40 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,000 rpm, thereby carrying out a particle formation process.

[0340] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 450 g of a 32% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0341] (Step 4: Drying Stage)

[0342] The polymer was dried in the same manner as in Example 1.

[0343] (Step 5: Crushing and Classification Stage)

[0344] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) was used, and the crusher roll gap was set to 0.20 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0345] (Surface cross-linking step)

[0346] A surface cross-linked superabsorbent resin was obtained by carrying out a surface cross-linking reaction in the same manner as in Example 1.

[0347] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0348] Example 4

[0349] (Step 1: Polymer manufacturing step)

[0350] A polymer was obtained in the same manner as in Example 1 above.

[0351] (Steps 2 and 3: Atomization and Neutralization Steps)

[0352] 30 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 1,500 rpm, thereby carrying out a particle formation process.

[0353] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 300 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 400 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0354] (Step 4: Drying Stage)

[0355] The polymer was dried in the same manner as in Example 1.

[0356] (Step 5: Crushing and Classification Stage)

[0357] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM, MPE) was used, and the crusher roll gap was set to 0.18 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0358] (Surface cross-linking step)

[0359] A surface cross-linked superabsorbent resin was obtained by carrying out a surface cross-linking reaction in the same manner as in Example 1.

[0360] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0361] Example 5

[0362] (Step 1: Polymer manufacturing step)

[0363] A polymer was obtained in the same manner as in Example 1, except that 3.75 g of pentaerythritol triallyl ether (PETTAE) was used instead of 3.0 g of pentaerythritol triallyl ether (PETTAE) and 0.75 g of trimethylolpropane triacrylate (TMPTA) as internal crosslinking agents.

[0364] (Steps 2 and 3: Atomization and Neutralization Steps)

[0365] 20 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 1,280 rpm, thereby carrying out a particle formation process.

[0366] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 500 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 350 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0367] (Step 4: Drying Stage)

[0368] The polymer was dried in the same manner as in Example 1.

[0369] (Step 5: Crushing and Classification Stage)

[0370] The base resin powder was obtained by crushing and classifying in the same manner as in Example 1.

[0371] (Surface cross-linking step)

[0372] A surface cross-linked superabsorbent resin was obtained by carrying out a surface cross-linking reaction in the same manner as in Example 1, except that 6 g of water was used per 100 g of base resin powder.

[0373] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0374] Comparative Example 1

[0375] (Step 1: Polymer manufacturing step)

[0376] In a 5 L glass vessel equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 5.0 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 3406 g of water were stirred and mixed, and the mixture was allowed to react while maintaining the temperature at 5°C. The glass vessel containing the mixture was replaced with nitrogen at a rate of 1,000 cc / min for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution, 15.8 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane)dihydrochloric acid solution were added as polymerization initiators, and at the same time, 22.5 g of a 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the temperature of the above mixture reached 85°C, a polymer was obtained by polymerizing at 90±2°C for about 6 hours.

[0377] (Steps 2 and 3: Atomization and Neutralization Steps)

[0378] 20 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 500 rpm, thereby carrying out a particle formation process.

[0379] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 400 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0380] (Step 4: Drying Stage)

[0381] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically transferring airflow. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0382] (Step 5: Crushing and Classification Stage)

[0383] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) was used, and the crusher roll gap was set to 0.12 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0384] (Surface cross-linking step)

[0385] Next, a surface cross-linking agent aqueous solution containing 4 g of water, 6 g of methanol, 0.05 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0386] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0387] Comparative Example 2

[0388] (Step 1: Polymer manufacturing step)

[0389] In a 5 L glass vessel equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 3.0 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 3406 g of water were stirred and mixed, and reacted while maintaining the temperature at 5°C. The glass vessel containing the mixture was replaced with nitrogen conditions by introducing 1,000 cc / min of nitrogen for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution as a polymerization initiator, 15.8 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane)dihydrochloric acid solution were added, and at the same time, 22.5 g of a 0.01% aqueous ferrous sulfate solution as a reducing agent was added to initiate polymerization. After the temperature of the above mixture reached 85°C, a polymer was obtained by polymerizing at 90±2°C for about 6 hours.

[0390] (Steps 2 and 3: Atomization and Neutralization Steps)

[0391] 20 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 500 rpm, thereby carrying out a particle formation process.

[0392] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 380 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0393] (Step 4: Drying Stage)

[0394] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically transferring airflow. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0395] (Step 5: Crushing and Classification Stage)

[0396] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) was used, and the crusher roll gap was set to 0.12 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0397] (Surface cross-linking step)

[0398] Next, a surface cross-linking agent aqueous solution containing 4 g of water, 6 g of methanol, 0.05 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0399] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0400] Comparative Example 3

[0401] (Step 1: Polymer manufacturing step)

[0402] In a 5 L glass vessel equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 2.0 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 3406 g of water were stirred and mixed, and the mixture was allowed to react while maintaining the temperature at 5°C. The glass vessel containing the mixture was replaced with nitrogen conditions by introducing 1,000 cc / min of nitrogen for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution as a polymerization initiator, 15.8 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane)dihydrochloric acid solution were added, and at the same time, 22.5 g of a 0.01% aqueous iron sulfate solution as a reducing agent was added to initiate polymerization. After the temperature of the above mixture reached 85°C, a polymer was obtained by polymerizing at 90±2°C for about 6 hours.

[0403] (Steps 2 and 3: Atomization and Neutralization Steps)

[0404] 20 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 500 rpm, thereby carrying out a particle formation process.

[0405] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 500 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 400 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0406] (Step 4: Drying Stage)

[0407] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically transferring airflow. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0408] (Step 5: Crushing and Classification Stage)

[0409] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM, MPE) was used, and the crusher roll gap was set to 0.12 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0410] (Surface cross-linking step)

[0411] Next, a surface cross-linking agent aqueous solution containing 6 g of water, 6 g of methanol, 0.05 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0412] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0413] Comparative Example 4

[0414] (Step 1: Polymer manufacturing step)

[0415] In a 5L glass container equipped with a stirrer and thermometer, 1500g of acrylic acid, 2.5g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, 0.5g of trimethylolpropane triacrylate (TMPTA) (Miwon Miramer M3190 product), and 3406g of water were stirred and mixed, and reacted while maintaining the temperature at 5℃. The glass container containing the mixture was replaced with nitrogen at a rate of 1,000 cc / min for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution, 15.8 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane) dihydrochloric acid solution were added as polymerization initiators, and simultaneously 22.5 g of a 0.01% aqueous iron sulfate solution was added as a reducing agent to initiate polymerization. After the temperature of the mixture reached 85°C, polymerization was performed at 90±2°C for about 6 hours to obtain a polymer.

[0416] (Steps 2 and 3: Atomization and Neutralization Steps)

[0417] 15 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 1,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 500 rpm, thereby carrying out a particle formation process.

[0418] After this, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 400 g of a 32% NaOH aqueous solution (step 3: neutralization step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 35.5 g of a 5% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0419] (Step 4: Drying Stage)

[0420] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically transferring airflow. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0421] (Step 5: Crushing and Classification Stage)

[0422] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) was used, and the crusher roll gap was set to 0.12 mm, and then the base resin powder was sieved through a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0423] (Surface cross-linking step)

[0424] Next, a surface cross-linking agent aqueous solution containing 8 g of water, 6 g of methanol, 0.05 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0425] After the above surface cross-linking process, a superabsorbent resin having a particle size of 150 ㎛ to 850 ㎛ was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0426] <Experimental Example>

[0427] The properties of the superabsorbent resins manufactured in the above examples and comparative examples were evaluated using the following methods and are listed in Table 1 below.

[0428] Unless otherwise specified, all of the following property evaluations were conducted under constant temperature and humidity (23±1℃, relative humidity 50±10%).

[0429] After the sample to be measured was left under constant temperature and humidity conditions for 24 hours, each property was evaluated.

[0430] Additionally, unless otherwise indicated, the property evaluation of the surface-crosslinked final superabsorbent resin was performed on a resin having a particle size of 150 μm to 850 μm classified through an ASTM standard sieve.

[0431] (1) Free swell capacity over time in water with an electrical conductivity of 110 μS / cm

[0432] Free swelling capacity (FSC) over time in water with an electrical conductivity of 110 μS / cm of superabsorbent resins of examples and comparative examples 110 , g / g) was measured using the following method.

[0433] 1) First, 1.0 g (W1) of superabsorbent resin was placed in a non-woven bag (18 cm Х 28 cm) and immersed in 1000 mL of water having an electrical conductivity value of 110 μS / cm at 24°C for (10 sec / 20 sec / 30 sec / 60 sec / 120 sec / 300 sec / 600 sec / 1800 sec) respectively.

[0434] 2) After (10 sec / 20 sec / 30 sec / 60 sec / 120 sec / 300 sec / 600 sec / 1800 sec), the bag containing the swollen superabsorbent resin was taken out of water with an electrical conductivity of 110 μS / cm, hung, and left for 1 minute. Afterwards, the mass (W3) of the bag was measured.

[0435] 3) In addition, the mass (W2) at that time was measured after performing the same operation without using superabsorbent resin.

[0436] 4) Using each mass thus obtained, the free swelling capacity (FSC) over time in water with an electrical conductivity value of 110 μS / cm was calculated according to the following mathematical equation 1. 110 , g / g) was calculated.

[0437] [Mathematical Formula 1]

[0438] Free swelling capacity (FSC) in water with an electrical conductivity value of 110 μS / cm 110 , g / g) = {[W3(g) - W2(g) - W1(g)] / W1(g)}

[0439] Free swelling capacity (FSC) over time in water with an electrical conductivity of 110 μS / cm for the above examples and comparative examples 110 , g / g) measurement results are shown in Table 1 below.

[0440] Free swelling capacity (FSC) as a function of time in water with an electrical conductivity of 110 μS / cm 110, g / g)Swelling time, t (s)102030601203006001800Example 15485121188261339359384Example 25384107171249336363388Example 3305082192303319319328Example 4405994168245320354371Example 55287132182252325334338Comparative Example 1285073136203287310307Comparative Example 2162947104168284346376Comparative Example 3334970106182268314371Comparative Example 4355679117187264306336

[0441] (2) Calculation of Se and Se / r values ​​in water with an electrical conductivity of 110 μS / cm using the Voigt model equation

[0442] Free swelling capacity (FSC) of water with electrical conductivity of 100 to 130 μS / cm as a function of time (s) in Table 1 110 , g / g) value of S t It was modeled using the formula of [Formula 1].

[0443] Specifically, the raw data for the fitting curve was fitted using the Origin program, and then the graph curve values ​​were extracted to obtain the Se and r values.

[0444] The Se / r value was calculated using the Se and r values ​​derived above, and the results are shown in Table 2 below.

[0445] Figures 2 and 3 are graphs modeling the time-dependent absorption behavior in water with an electrical conductivity of 110 μS / cm for the superabsorbent resins of the examples and comparative examples, respectively, according to [Equation 1], and Figure 4 is a graph integrating the graphs of Figures 2 and 3.

[0446] SampleFitted curveS e rS e / rR2(g / g)(s)(g / g / s)Example 1363844.320.988Example 2368973.790.987Example 3330744.460.967Example 43561023.510.994Example 5331724.620.989Comparative Example 13081092.830.999Comparative Example 23712031.830.998Comparative Example 33451712.020.980Comparative Example 43171332.380.984

[0447] (3) Centrifuge Retention Capacity (CRC, g / g)

[0448] The water retention capacity of the superabsorbent resins of the above examples and comparative examples by the absorption rate under no load was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3.

[0449] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 241.0.

[0450] Specifically, the superabsorbent resin W4 (g) (approximately 0.2 g) obtained through each of the examples and comparative examples was uniformly placed in a nonwoven bag, sealed, and then immersed in a physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, water was removed from the bag for 3 minutes using a centrifuge at 250 G, and the mass W6 (g) of the bag was measured. In addition, the same operation was performed without using the resin, and the mass W5 (g) at that time was measured.

[0451] Using each mass obtained, CRC (g / g) was calculated according to the following mathematical formula 2.

[0452] [Equation 2]

[0453] CRC (g / g) = {[W6(g) - W5(g)] / W4(g)} - 1

[0454] (4) Absorbency under Pressure (AUP: Absorbency under Pressure, g / g)

[0455] The pressurized absorption capacity of 2.07 kPa (0.3 psi) of the superabsorbent resins of the above examples and comparative examples was measured according to the EDANA method WSP 242.3.

[0456] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 242.0.

[0457] Specifically, a 400-mesh stainless steel wire mesh was installed on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under conditions of room temperature and 50% humidity, superabsorbent resin W7 (g) (0.9 g) was uniformly sprayed on the wire mesh, and a piston capable of uniformly applying a load of 2.07 kPa (0.3 psi) was installed thereon, with an outer diameter slightly smaller than 25 mm, without a gap with the inner wall of the cylinder, and without impeding up-and-down movement. At this time, the weight W8 (g) of the device was measured.

[0458] 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 a saline solution consisting of 0.9 wt% sodium chloride was placed so that it was level with the upper 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 a load for 1 hour. After 1 hour, the measuring device was lifted, and its weight W9 (g) was measured.

[0459] Using each mass obtained, the pressurized absorbency (g / g) was calculated according to the following mathematical formula 3.

[0460] [Equation 3]

[0461] AUP(g / g) = [W9(g) - W8(g)] / W7(g)

[0462] (5) Vortex time

[0463] The vortex time of the superabsorbent resins of the above examples and comparative examples was measured by the following method.

[0464] 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.

[0465] ② Next, the beaker was placed in the center of the magnetic stirrer, and a circular magnetic bar (diameter 30 mm) was placed inside the beaker.

[0466] ③ Afterwards, the stirrer was operated so that the magnetic bar stirred at 600 rpm, and the lowest part of the vortex created by stirring was made to touch the top of the magnetic bar.

[0467] ④ After confirming that the temperature of the brine in the beaker reached 24.0℃, 2±0.01 g of superabsorbent resin sample was added while simultaneously operating the stopwatch, and the time until the vortex disappeared and the liquid surface became completely horizontal was measured in seconds, which was designated as the vortex time.

[0468] CRC(g / g)0.3AUP(g / g)Vortex time(sec)Example 137.632.119Example 237.732.326Example 335.233.528Example 437.132.527Example 536.032.227Comparative Example 132.528.427Comparative Example 238.825.639Comparative Example 340.622.243Comparative Example 437.527.141

[0469] As can be seen in Table 3 above, in the case of the present invention, by controlling the initial absorption rate (Se / r) for water with an electrical conductivity of 100 to 130 μS / cm calculated through the Voigt model equation to a certain level or higher, it was confirmed that the absorption rate can be improved while simultaneously improving absorption performance such as water retention capacity and pressurized absorption capacity, thereby exhibiting an excellent balance of physical properties.

[0470] The present invention can be applied to superabsorbent resins.

Claims

1. As a polyacrylic acid (salt)-based superabsorbent resin, When the free swelling capacity (g / g) value according to time (s) for water with an electrical conductivity of 100 to 130 μS / cm is modeled by [Equation 1] below, the Se / r value is 3.0 g / g / sec or more. Superabsorbent resin: [Formula 1] In the above equation 1, t stands for swelling time (s), S t means the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm at a swelling time (s) t, S e and r are constants obtained by modeling the free swelling capacity (g / g) of water with an electrical conductivity of 100 to 130 μS / cm over time (s) according to [Equation 1].

2. In paragraph 1, A superabsorbent resin having a Se value of 310 g / g or more when the free swelling capacity (g / g) value according to time (s) for water having an electrical conductivity of 100 to 130 μS / cm is modeled using the above [Equation 1].

3. In paragraph 1, Superabsorbent resin having a Se / r value of 3.7 g / g / sec or more.

4. In paragraph 2, Superabsorbent resin with a Se value of 330 g / g or more.

5. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having a water retention capacity (CRC) of 33 g / g or more as measured according to the method of EDANA method WSP 241.

3.

6. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having an absorbency under pressure (AUP) of 25 g / g or more as measured under 2.07 kPa (0.3 psi) according to EDANA method WSP 242.

3.

7. In paragraph 1, A superabsorbent resin having a vortex time of 40 seconds or less as measured by a vortex measurement method at 24.0°C.

8. In paragraph 1, The above polyacrylic acid (salt)-based superabsorbent resin is a superabsorbent resin comprising a base resin powder including a water-soluble ethylenically unsaturated monomer having an acidic group and a crosslinked polymer of an internal crosslinking agent.

9. In paragraph 8, The above polyacrylic acid (salt)-based superabsorbent resin is a superabsorbent resin comprising a surface crosslinking layer formed on the base resin powder by further crosslinking the crosslinked polymer using a surface crosslinking agent.

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