Super absorbent polymer

Abstract

The present invention relates to a polyacrylic acid (salt)-based super absorbent polymer (SAP), which exhibits excellent physical crosslinking and chemical crosslinking by adjusting the normalized strength of the super absorbent polymer to have a predetermined range, while having excellent physical property balance.

Description

superabsorbent resin

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0058658, filed May 2, 2024, and U.S. Patent Application No. 18 / 985,220, filed December 18, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a superabsorbent resin exhibiting improved absorption speed and absorption performance.

[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] The superabsorbent polymer described above has a significant impact on its properties due to the crosslinking structure within the polymer. This crosslinking structure is formed through both chemical and physical crosslinking. Specifically, while superabsorbent polymers possess chemical crosslinking, they also possess physical crosslinking, such as chain entanglement, dangling chains, and interpenetrating networks, in which polymer chains are physically intertwined.

[0006] Among these, chemical crosslinking can determine the degree of crosslinking reaction of superabsorbent resin, and understanding the degree of chemical crosslinking is necessary to understand the initial properties of superabsorbent resin.

[0007] In particular, superabsorbent polymers are widely used in sanitary products such as diapers and sanitary pads. Therefore, they require not only high absorption performance but also a rapid absorption rate. In other words, the initial properties of superabsorbent polymers are crucial in these fields.

[0008] In addition, development of so-called pulpless products, in which the pulp content is reduced or even no pulp is used at all, is being actively pursued to provide products with thinner thicknesses.

[0009] As a result, the product contains a relatively high proportion of superabsorbent polymer, and superabsorbent polymer particles are inevitably incorporated into multiple layers within the product. Furthermore, to ensure that the superabsorbent polymer can absorb large amounts of liquids such as water, saline solution, and urine, its absorbent properties must be enhanced to ensure both high absorption performance and rapid absorption rates.

[0010] For this purpose, a method of forming a porous structure within the base resin powder by including a foaming agent in the monomer composition and proceeding with crosslinking polymerization to increase the surface area of ​​the superabsorbent resin is generally used.

[0011] However, the use of a foaming agent resulted in a decline in the physical properties of the superabsorbent resin, such as surface tension, permeability, and bulk density. This made it difficult to maintain its shape in a swollen state. Furthermore, this resulted in an increase in the amount of fine particles generated.

[0012] Conversely, in order to improve the permeability of a superabsorbent resin, when the crosslinking density of the superabsorbent resin is controlled to be high, there is a problem in that the water retention capacity, which is a basic property of the superabsorbent resin, is reduced because it is difficult for moisture to be absorbed between the dense crosslinking structures.

[0013] Accordingly, there is a continuous demand for the development of superabsorbent resins to improve their initial properties and fundamentally solve problems such as permeability.

[0014] The present invention aims to provide a superabsorbent polymer (SAP) having excellent physical and chemical crosslinking properties and a superior balance of physical properties by controlling the normalization strength of the SAP to be within a certain range. In particular, the present invention aims to provide a superabsorbent polymer having excellent absorbency under pressure and liquid permeability.

[0015] The present invention is a polyacrylic acid (salt)-based superabsorbent resin,

[0016] The TD-NMR analysis results of the above superabsorbent resin provide a superabsorbent resin satisfying the following equation 1.

[0017] [Formula 1]

[0018] 2.5(%) ≤ N t=0.1 (%) ≤ 3.5(%)

[0019] In the above equation 1,

[0020] N t=0.1 refers to the normalized intensity measured at a signal acquisition time of 0.1 ms.

[0021] The superabsorbent polymer of the present invention exhibits excellent pressure absorbency and liquid permeability, and when applied to a product, it can rapidly absorb body fluids and retain large amounts of body fluids without leaking them outward. In other words, the superabsorbent polymer of the present invention has excellent physical property balance.

[0022] Figure 1 shows the setting values ​​of the Sample Dispersion Unit in Malvern Panalytical's morphologi 4.

[0023] Figure 2 shows the illumination setting values ​​in Malvern Panalytical's morphologi 4.

[0024] Figure 3 shows the Optics Selection setting values ​​in Malvern Panalytical's morphologi 4.

[0025] Figure 4 shows the Scan Area setting values ​​in Malvern Panalytical's morphologi 4.

[0026] 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 the terms "comprises," "includes," or "has" indicate 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.

[0027] 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.

[0028] 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 "singular" and "in" also include plural forms, unless the context clearly dictates otherwise.

[0029] The term "polymer" or "high molecular weight polymer" as used herein means a polymerized state of a water-soluble ethylenically unsaturated monomer, and may encompass any moisture content range or particle size range.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In this specification, the element symbols used are those described in the periodic table.

[0034] Hereinafter, a superabsorbent resin and a method for manufacturing the same according to specific embodiments of the invention will be described in more detail.

[0035] I. Polyacrylic acid (salt)-based superabsorbent resin

[0036] The superabsorbent resin of the present invention is a polyacrylic acid (salt)-based superabsorbent resin, and is characterized in that the TD-NMR analysis result of the superabsorbent resin satisfies the above formula 1.

[0037] N in the above equation 1 t=0.1 refers to the normalized intensity measured at a signal acquisition time of 0.1 ms. Here, the normalized intensity refers to the result obtained when the peak intensity is normalized by the method described below after performing TD-NMR analysis on the superabsorbent resin under specific conditions.

[0038] Specifically, the method for deriving the normalized century is as follows.

[0039] - Step 1) Drying (pretreatment) of superabsorbent resin

[0040] The superabsorbent resin is dried at approximately 100°C for approximately 12 hours.

[0041] - Step 2) Sealing (sampling) of dried superabsorbent resin

[0042] ① Add approximately 50 mg of dried superabsorbent resin to a 10 mm NMR tube.

[0043] ② Seal the above tube with parafilm and proceed with sampling for TD-NMR analysis.

[0044] - Step 3) TD-NMR analysis

[0045] ① Superabsorbent resin is injected, and the sampled tube is stabilized at approximately 40°C for approximately 1 hour through sealing treatment.

[0046] ② After stabilization, TD-NMR analysis is performed on the superabsorbent resin under the following measurement conditions to derive the analysis results in which the x-axis represents the signal acquisition time and the y-axis represents the peak intensity.

[0047] At this time, the TD-NMR analysis equipment including the NMR tube can be Bruker TD-NMR the minispec mq20, but is not limited thereto, and equipment commonly used in the relevant field can be used.

[0048] <Measurement conditions>

[0049] 1) Temperature: 40℃

[0050] 2) Nuclides: 1 H

[0051] 3) Method: sc-lc-co

[0052] 4) Delay time: 3 seconds

[0053] 5) Number of scans: 1024

[0054] 6) Receiver gain: Use the automatic value measured by the device for each sample.

[0055] - Step 4) Normalization

[0056] The analysis results derived from step 3 were analyzed through TD-NMR. 1 This refers to the peak intensity observed as a result of free induction decay (FID), which is manifested by the decay of the H signal. The intensity is observed sequentially over time. The time at which the intensity is observed corresponds to the signal acquisition time.

[0057] Among them, the remaining centuries are normalized based on the first century (I1). Specifically, when the first century (I1) is set as 100, the relative sizes of the other centuries are calculated.

[0058] For example, the intensity that appears nth is normalized by calculating it using the following formula A.

[0059] [Formula A]

[0060] N(%) = (In / I1) x 100(%)

[0061] In the above formula A

[0062] N stands for the normalized century of the nth century,

[0063] I n Through TD-NMR analysis 1 It means the intensity of the nth occurrence as a result of observing the FID that appears as the decay of the H signal,

[0064] I1 was analyzed by TD-NMR. 1 It refers to the intensity that appears for the first time when observing the FID that appears as the decay of the H signal.

[0065] In the above process, the pretreatment of drying the superabsorbent resin at approximately 100℃ for approximately 12 hours is performed to measure the mobility of the superabsorbent resin without being affected by the moisture content. In TD-NMR analysis, the water component contained in the superabsorbent resin is a substance that greatly affects the result value. For example, the T1 relaxation time, which is one of the result values ​​derived from TD-NMR measurement, is affected by the surrounding substances, and water is known to be a substance that takes a long time for T2 relaxation. Therefore, the pretreatment process is performed to understand the characteristics of the superabsorbent resin itself.

[0066] Superabsorbent polymers (SAPs) are manufactured by cross-linking a polymer backbone composed of carbon atoms to form a network structure, and then attaching water-loving ionic molecules to this network structure. Alternatively, the ionic molecules themselves are polymerized into the polymer backbone, forming cross-links. This process can be defined as chemical cross-linking.

[0067] In addition to chemical crosslinking, superabsorbent polymers may also exhibit physical crosslinking, such as chain entanglement and dangling chains. These physical crosslinking properties also influence the network structure of superabsorbent polymers. In other words, chemical and physical crosslinking affect the absorption performance, such as water retention capacity and pressurized absorption capacity, as well as liquid permeability, of superabsorbent polymers.

[0068] At this time, the process of increasing the permeability of the superabsorbent resin can lead to a problem of reduced absorption performance. In other words, permeability and absorption performance are in a trade-off relationship, and thus, optimization of both permeability and absorption performance is necessary to provide an excellent superabsorbent resin.

[0069] Therefore, in order to optimize permeability and absorption performance, which are in a trade-off relationship, it is important to control the degree of physical cross-linking and chemical cross-linking within a certain range.

[0070] The superabsorbent resin according to the present invention is characterized in that, among the normalized intensities measured by the above-described method, the normalized intensity measured at a signal acquisition time of 0.1 ms satisfies 2.5% or more and 3.5% or less.

[0071] In addition, the superabsorbent resin according to the present invention satisfies the normalized intensity measured at a signal acquisition time of 0.1 ms among the normalized intensities above, being 2.5% or more and 2.6% or more.

[0072] N in the above equation 1 t=0.1 refers to the normalized intensity measured at a signal acquisition time of 0.1 ms among multiple normalized intensities.

[0073] The reason why the normalized intensity at a signal acquisition time of 0.1 ms in the present invention was measured is because that time period is the point at which the peak intensity of the FID reaches a plateau. In other words, the signal acquisition time of 0.1 ms in Equation 1 has technical significance in that it is a time period in which the characteristics of the superabsorbent resin alone can be identified after eliminating various variables occurring during analysis.

[0074] T2 relaxation, which can be confirmed during TD-NMR analysis, refers to the phenomenon in which the spins inside the atoms are dephased when the radio frequency is cut off after applying a radio frequency to the molecule to make the spins inside the atoms transversely magnetized and in phase. At this time, the signal measured when the radio frequency is cut off is called FID, and the size of the measured FID decreases over time. The degree of transverse magnetization can be determined using the measured FID signal. Here, the size of the degree of transverse magnetization refers to the intensity. The T2 relaxation time refers to the time when the magnitude of the degree of transverse magnetization decreases to 37% of the magnitude of the maximum degree of transverse magnetization. Since the T2 relaxation time is not affected by the strength of the external magnetic field, the properties of the material itself can be identified through it.

[0075] T2 relaxation time (T2 relaxation time) is a numerical value that can be used to determine how dense a molecule is, and can be measured using a time domain NMR (TD NMR) device. The more rigid the molecule, the smaller (faster) the T2 relaxation time is measured. On the other hand, the less dense and flexible the molecule, the larger (slower) the T2 relaxation time is measured. This can be used to determine the relative rigidity of a molecule.

[0076] That is, when the normalized intensity is obtained from the TD-NMR analysis results using the method described above, the degree of crosslinking of the superabsorbent resin can be indirectly predicted.

[0077] At the same time, the inventors of the present invention confirmed that a superabsorbent resin having excellent permeability and excellent absorption performance can be provided when the normalization intensity satisfies the range of the above equation 1.

[0078] To satisfy this requirement, the inventors of the present invention adjusted the manufacturing process conditions of the superabsorbent resin. For example, the process conditions were adjusted, such as adjusting the type or content of additives in the surface crosslinking process or adjusting the polymerization and grinding process conditions, so that the superabsorbent resin of the present invention satisfied Equation 1.

[0079] In one embodiment of the present invention, the superabsorbent resin may have an average value of convexity calculated by Equation 2 below for all particles of 0.94 or less.

[0080] [Formula 2]

[0081] M c = L s / L

[0082] In the above equation 2,

[0083] M c is convexity,

[0084] L s refers to the length of an elastic band when it is assumed that the 3D image of the 3D particle to be measured is surrounded by an imaginary elastic band that stretches around the contour of the captured 2D image.

[0085] L represents the actual circumference of the image captured as a 2D image of the 3D image of the 3D particle to be measured.

[0086] The above convexity is a parameter for measuring the particle outline and surface roughness of the particle with a value of 0 to 1. The closer the convexity is to 1, the more the particle can be seen as having a very smooth outline, and the closer the convexity is to 0, the more the particle can be seen as having a rough or uneven outline.

[0087] At this time, the average value of the convexity is measured after being randomly scattered on the stage by vacuum within the measuring device, and a statistical result is derived by securing n of 200 or more and averaging them.

[0088] In one embodiment of the present invention, the average value of the convexity of all particles of the superabsorbent resin may be 0.80 or more, or 0.83 or more, or 0.85 or more, or 0.87 or more, and 0.94 or less, or 0.93 or less, or 0.92 or less.

[0089] In one embodiment of the present invention, the superabsorbent resin may have an average CE diameter (Circle Equivalent diameter) of 220 ㎛ to 400 ㎛.

[0090] The above CE diameter refers to the diameter of a circle having the same area as an image obtained by capturing a 3D image of a particle as a 2D image, and the size of the particle can be expressed through the CE diameter. The average value of the CE diameter of the above superabsorbent resin may be 220 ㎛ or more, or 230 ㎛ or more, or 240 ㎛ or more, and 400 ㎛ or less, or 350 ㎛ or less, or 330 ㎛ or less, or 320 ㎛ or less, or 310 ㎛ or less.

[0091] Additionally, convexity and CE diameter can be measured using several commercial instruments that quantify and analyze particle morphology based on image analysis of the particles. For example, these parameters can be measured using the Malvern Panalytical Morphologi 4, which is specifically measured through the following four steps, which are described in more detail in the experimental examples below.

[0092] 1) Sample Preparation: Prepare the superabsorbent resin particles to be measured. When measuring the convexity of particles with a specific particle size range, prepare the sample by classifying the particles with the specific particle size using a Retsch classifier at 1.0 amplitude for 10 minutes.

[0093] At this time, the particle size of the superabsorbent resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0094] 2) Image acquisition: After setting the prepared sample on the stage within the equipment, scan it at 2.5x magnification to acquire images of individual particles.

[0095] 3) Image processing: For the acquired images, the 3D image of the 3D particle for each particle is captured as a 2D image, and parameter values ​​such as CE diameter (Circle Equivalent diameter), shortest diameter, longest diameter, actual particle perimeter, and convex hull perimeter are measured.

[0096] 4) Based on the data analyzed for each particle, a distribution map for the parameters for all particles included in the sample is derived.

[0097] In one embodiment of the present invention, the superabsorbent polymer may have a gel strength of 0.7N or more, 0.8N or more, or 0.9N or more after swelling the superabsorbent polymer with 50ml of saline solution containing 0.005% ASC. In addition, the gel strength may be 1.5N or less, 1.4N or less, 1.3N or less, 1.2N or less, 1.1N or less, or 1.0N or less. By having such a high gel strength, it is possible to reduce surface crosslinking damage and prevent deterioration of physical properties. In addition, even if the superabsorbent polymer absorbs water and its volume increases, it can maintain its shape well, and as a result, it can exhibit improved absorbency and liquid permeability. The method for measuring the gel strength of the superabsorbent polymer will be described in more detail in the experimental examples section described below.

[0098] In one embodiment of the present invention, the superabsorbent resin may have a water-soluble component content of 10 wt% or less, or 9.5 wt% or less, or 9 wt% or less, based on the total weight of the superabsorbent resin, as measured after being freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 30 minutes.

[0099] In addition, in one embodiment of the present invention, the superabsorbent resin may have a water-soluble component of 5 wt% or less, or 4.8 wt% or less, or 4.5 wt% or less, or 4.3 wt% or less, or 4 wt% or less, or 3.9 wt% or less, based on the total weight of the superabsorbent resin, as measured after swelling for 1 hour according to the method of EDANA method WSP 270.3. The lower the value of the content of the water-soluble component, the better, and the lower limit is theoretically 0 wt%, but may be, for example, 0.1 wt% or more, or 1 wt% or more.

[0100] In addition, in one embodiment of the present invention, the superabsorbent resin may have a water-soluble component content measured after being freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 3 hours, of 17 wt% or less, or 16 wt% or less, or 15 wt% or less, based on the total weight of the superabsorbent resin.

[0101] “Extractable contents” refers to a polymeric compound that is not crosslinked during the manufacturing process of a superabsorbent resin. This may occur when crosslinking is incomplete during polymerization of the superabsorbent resin, or when the crosslinking agent is decomposed or the main molecular chain is broken during the chopping or drying process.

[0102] The above-mentioned water-soluble components may be eluted when the superabsorbent resin is exposed to liquid, and most of the eluted water-soluble components remain on the surface of the superabsorbent resin. This may cause the surface of the superabsorbent resin to become sticky and its liquid permeability may be reduced. This may cause discomfort when the superabsorbent resin is used in actual products.

[0103] That is, problems related to the crosslinking of superabsorbent polymers can be identified by measuring the content of water-soluble components eluted from the superabsorbent polymer solution. In other words, since the content of water-soluble components is closely related to the interchain crosslinking structure within the superabsorbent polymer, a high content of eluted water-soluble components indicates that the interchain crosslinking structure within the superabsorbent polymer is incomplete.

[0104] Superabsorbent polymers are widely used in sanitary products such as diapers, and the amount of dissolved components is evaluated using 0.9% saline solution, which has a similar ion concentration and electrical conductivity to urine discharged from the body.

[0105] However, superabsorbent polymers are widely used in various applications, including as horticultural soil conditioners, water-retaining materials for civil engineering and construction, nursery sheets, and freshness-preserving agents and steaming agents in food distribution. In these applications, excellent absorption behavior of water-soluble components in water with an electrical conductivity of 100 to 130 μS / cm is required.

[0106] That is, even if 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% salt water with an electrical conductivity of approximately 16,100 μS / cm are bound to be different.

[0107] The content of water-soluble components is closely related to the interchain cross-linking structure within the superabsorbent resin. When 0.9% saline solution is used, the volume of swelling of the superabsorbent resin is small, so the amount of water-soluble components eluted is small. However, when water with an electrical conductivity of 100 to 130 μS / cm is used, the superabsorbent resin swells more, so the amount of water-soluble components eluted increases due to the separation of the chains within the superabsorbent resin. Therefore, the correlation between the interchain cross-linking structure within the superabsorbent resin and the absorption behavior can be more accurately identified.

[0108] For example, even if two different superabsorbent resins have the same content of water-soluble components in 0.9% saline water, the content of water-soluble components in water having an electrical conductivity of 100 to 130 μS / cm can vary greatly depending on the crosslinking characteristics, because the degree of crosslinking within the superabsorbent resin affects the content of water-soluble components.

[0109] For this reason, the experimental results on the release amount and absorption characteristics of water-soluble components after free swelling using 0.9% saline water having an electrical conductivity of about 16,100 μS / cm cannot be directly compared with the experimental results after free swelling using water having an electrical conductivity of 100 to 130 μS / cm as in the present invention.

[0110] That is, 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 solution with an electrical conductivity of about 16,100 μS / cm are bound to be different, and accordingly, the content of water-soluble components after free swelling in water with an electrical conductivity of 100 to 130 μS / cm for 1 hour cannot be used to predict the content of water-soluble components after free swelling in 0.9% saline solution with an electrical conductivity of about 16,100 μS / cm, and vice versa.

[0111] Therefore, in order to realize a highly absorbent material with excellent property balance by simultaneously improving absorption characteristics and permeability, it can be said that determining the amount of dissolved components, absorption performance, and absorption rate in water with an electrical conductivity of 100 to 130 μS / cm is independent of using 0.9% saline water with an electrical conductivity of about 16,100 μS / cm.

[0112] The method for measuring the content (weight%) of water-soluble components in water having an electrical conductivity value of 100 to 130 μS / cm will be described in more detail in the experimental examples section described below.

[0113] In one embodiment of the present invention, the superabsorbent polymer may have a water retention capacity (CRC) measured according to EDANA method WSP 241.3 of 30 g / g or more, or 31 g / g or more, or 32 g / g or more, or 33 g / g or more, or 34 g / g or more, or 35 g / g or more. In addition, the water retention capacity measured by the same method may be 50 g / g or less, or 45 g / g or less, or 40 g / g or less.

[0114] In addition, in one embodiment of the present invention, the superabsorbent resin may have an absorbency under pressure (AUP) of 28 g / g or more, or 29 g / g or more, or 30 g / g or more, measured under 0.3 psi according to EDANA method WSP 242.3. In addition, the absorbency under pressure measured by the same method may be 45 g / g or less, or 42 g / g or less, or 40 g / g or less.

[0115] In addition, in one embodiment of the present invention, the superabsorbent resin may have an effective absorbency (EFFC) calculated by Equation 3 below of 30 g / g or more, or 31 g / g or more, or 32 g / g or more, or 33 g / g or more. In addition, the effective absorbency (EFFC) calculated by Equation 3 may be 40 g / g or less, or 39 g / g or less, or 38 g / g or less, or 37 g / g or less, or 36 g / g or less.

[0116] [Formula 3]

[0117] EFFC = (CRC + AUP) / 2

[0118] In the above equation 3,

[0119] CRC is the water retention capacity (unit: g / g) measured according to the method of EDANA method WSP 241.3,

[0120] AUP is the absorbency under pressure (g / g) measured under 0.3 psi according to EDANA method WSP 242.3.

[0121] In one embodiment of the present invention, the superabsorbent resin may have an absorption rate (vortex time) of 40 seconds or less as measured by a vortex measurement method at 24.0°C.

[0122] More specifically, the absorption rate (vortex time) may be 40 seconds or less, or 35 seconds or less, or 33 seconds or less, or 30 seconds or less. In addition, the absorption rate is better as the value thereof decreases, and the lower limit of the absorption rate is theoretically 0 seconds, but may be, for example, 10 seconds or more, or 15 seconds or more, or 20 seconds or more.

[0123] The method for measuring the water retention capacity, pressure absorption capacity, and absorption rate of the above superabsorbent resin is explained in more detail in the experimental examples described below.

[0124] In addition, the superabsorbent resin of the present invention may have a maximum capacity of water (Free Swell Capacity) that the superabsorbent resin can hold when the superabsorbent resin is swelled in water having an electrical conductivity of 100 to 130 μS / cm for 1 minute, of 135 g / g or more, 138 g / g or more, 140 g / g or more, 150 g / g or more, 160 g / g or more, 170 g / g or more, or 175 g / g or more, or 180 g / g or more, or 185 g / g or more, and 230 g / g or less, or 225 g / g or less, or 220 g / g or less. This is a value showing the absorption capacity of the superabsorbent resin.

[0125] As described above, even 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% salt water with an electrical conductivity of approximately 16,100 μS / cm are bound to be different.

[0126] That is, it can be said that not only the content of water-soluble components but also the absorption capacity, such as the maximum capacity of water, has an independent meaning when using water with an electrical conductivity value of 100 to 130 μS / cm and when using 0.9% salt water with an electrical conductivity of about 16,100 μS / cm.

[0127] The present inventors determined the maximum capacity of water that a superabsorbent polymer can hold by using water having an electrical conductivity of 100 to 130 μS / cm at 24°C, 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 at 24°C of about 16,100 μS / cm, and in one embodiment, water having an electrical conductivity of 110 μS / cm at 24°C was used. In the case of water within the range of 100 to 130 μS / cm in electrical conductivity, there is no significant difference in absorption characteristics according to electrical conductivity.

[0128] Accordingly, the inventors of the present invention sought to develop a superabsorbent resin having an excellent absorption rate and absorption capacity for 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 implemented this by manufacturing the superabsorbent resin so that it satisfies the above normalized strength.

[0129] The method for measuring the absorption capacity in water having an electrical conductivity value of 100 to 130 μS / cm will be described in more detail in the experimental examples section described below.

[0130] In one embodiment of the present invention, the superabsorbent resin may have a permeability of 65 ml or more, as calculated by the following equation 4. More preferably, the permeability may be 70 ml or more, 75 ml or more, or 80 ml or more.

[0131] [Formula 4]

[0132] Perm = [20 mL / T1 (sec)] x 60 sec

[0133] In the above equation 4,

[0134] Perm is permeable,

[0135] T1 means the time (seconds) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin under a pressure of 0.3 psi after 0.2 g of superabsorbent resin was placed in a cylinder, saline solution (0.9 wt% sodium chloride aqueous solution) was poured so that the superabsorbent resin was completely submerged, and the superabsorbent resin was swelled for 30 minutes.

[0136] Meanwhile, the permeability refers to the mobility of the solution within the superabsorbent resin, and a higher value indicates better permeability. That is, there is no theoretical upper limit to the permeability, but it may be, for example, 400 ml or less, or 240 ml or less, or 180 ml or less.

[0137] That is, the superabsorbent resin according to the present invention may have a T1 of 18 seconds or less. More preferably, the T1 may be 17 seconds or less, 16 seconds or less, or 15 seconds or less. The smaller the value, the better. The theoretical lower limit of the T1 is 0 seconds. However, for example, it may be 3 seconds or more, or 5 seconds or more, or 10 seconds or more.

[0138] Meanwhile, the superabsorbent resin according to the present invention can be produced by appropriately controlling manufacturing process conditions, such as the components / content of the superabsorbent resin, polymerization process conditions of the superabsorbent resin, or crushing process conditions. That is, by controlling these process conditions, it is possible to produce a superabsorbent resin that satisfies the above normalized strength.

[0139] For example, the above normalization intensity can be controlled to be satisfied by adjusting 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, rotation speed, hole size, number of atomizations, etc.

[0140] Below, each component that makes up the superabsorbent resin will be explained in more detail.

[0141] 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.

[0142] 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:

[0143] [Chemical Formula 1]

[0144] R-COOM'

[0145] In the above chemical formula 1,

[0146] R is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

[0147] M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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%.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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 extractable contents can be minimized.

[0160] As described above, water-soluble components are primarily eluted when superabsorbent polymers absorb liquid and swell. A high content of eluted water-soluble components indicates poor cross-linking properties within the superabsorbent polymer. Furthermore, since most of the eluted water-soluble components remain on the surface of the superabsorbent polymer, this can reduce permeability and cause discomfort when applied to actual products.

[0161] Therefore, as described above, it is necessary to minimize the amount of extractable contents of the superabsorbent resin.

[0162] 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 preservation stabilizer, an antioxidant, etc.

[0163] In the above monomer composition, such 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, or 0.05 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, or 3 parts by weight or less, or 2 parts by weight or less, or 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 upper 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.

[0164] 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.

[0165] 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.

[0166] In this way, when the polymer has a three-dimensional network structure, the overall physical properties of the superabsorbent resin, such as water retention capacity and pressure absorption capacity, can be significantly improved compared to the case where the polymer has a two-dimensional linear structure that is not further crosslinked by an internal crosslinking agent.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] Specifically, the initiator and reducing agent react with each other to form radicals when introduced into a polymer solution.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] The above monomer composition may further include additives such as a thickener, a plasticizer, a preservation stabilizer, and an antioxidant, as needed.

[0178] 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%, or 15 to 60 wt%, or 30 to 50 wt%.

[0179] 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.

[0180] The polymer obtained in this way 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.

[0181] Additionally, the polymer may have a moisture content of 30 to 80 wt%. For example, the moisture content of the polymer may be 30 wt% or more, or 45 wt% or more, or 50 wt% or more, and 80 wt% or less, or 70 wt% or less, or 60 wt% or less.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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; It may include oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; etc.

[0187] 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, two types of propylene glycol and ethylene glycol diglycidyl ether may be used, or ethylene carbonate-propylene carbonate (ECPC), propylene glycol and / or glycerol carbonate may be used.

[0188] Such surface cross-linking agent may be used in an amount of 0.001 to 0.5 parts by weight per 100 parts by weight of the superabsorbent resin particles. In this case, 100 parts by weight of the superabsorbent resin particles is based on a dried state. In addition, the content refers to the total amount of the surface cross-linking agent used.

[0189] For example, the surface cross-linking agent may be used in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.05 parts by weight or more, based on 100 parts by weight of the superabsorbent resin particles. In addition, the surface cross-linking agent may be used in an amount of 0.5 parts by weight or less, or 0.4 parts by weight or less, or 0.2 parts by weight or less, based on 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.

[0190] 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.

[0191] 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. In addition, the inorganic material can be used in an amount of 0.001 to 1 part by weight based on 100 parts by weight of the superabsorbent resin particles. In this case, 100 parts by weight of the superabsorbent resin particles is based on a dried state. In addition, the content refers to the total amount of the inorganic material used.

[0192] For example, the inorganic material may be used in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.05 parts by weight or more, based on 100 parts by weight of the superabsorbent resin particles. In addition, the inorganic material may be used in an amount of 0.5 parts by weight or less, or 0.4 parts by weight or less, or 0.2 parts by weight or less, based on 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.

[0193] 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.

[0194] In addition, when mixing the surface crosslinking agent and base resin powder, a surfactant may be additionally mixed and added. Examples of the surfactant include sucrose stearate. The surfactant may also perform the function of inducing even dispersion of the surface crosslinking agent and preventing clumping of the resin composition.

[0195] As described above, a superabsorbent resin including a base resin powder and a surface cross-linking layer formed on the base resin powder can absorb body fluid or water at a high rate, and can also absorb a relatively large amount initially, thereby preventing problems such as body fluid or water not being absorbed but pooling or leaking out.

[0196] Ⅱ. Manufacturing method of superabsorbent resin

[0197] 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. Typically, a chopping process is 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.

[0198] To address this issue, a method has been used to reuse the separated fine particles by mixing them with an appropriate amount of water, reassembling the fine particles, and then adding them to the chopping or pre-drying step. However, this process of reusing the fine particles has led to problems such as increased equipment load and / or energy consumption. Furthermore, even after reuse, the remaining fine particles, which were not classified, have resulted in a deterioration of the physical properties of the superabsorbent polymer.

[0199] 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.

[0200] Meanwhile, the superabsorbent resin according to the present invention can be implemented by controlling the resin components and content, polymerization conditions, or grinding process conditions, etc. For example, the superabsorbent resin can be controlled to satisfy the above Equation 1 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 the surfactant in the neutralization and atomization steps, the type, amount, and timing of the neutralizing agent, the type of atomization device, the rotation speed, the hole size, the number of atomizations, the components and content of the surface cross-linking solution, etc.

[0201] In particular, the superabsorbent resin can be controlled to satisfy the above formula 1 by controlling the amount of neutralizing agent added in the neutralization step, applying the ultra-fine chain process as a micronization method, or controlling the components and content of the surface cross-linking solution in the surface cross-linking step. The ultra-fine chain process and controlling the components and content of the surface cross-linking solution will be described later.

[0202] Hereinafter, each step of the method for manufacturing a superabsorbent resin according to an embodiment will be described in more detail.

[0203] Step 1: Polymerization Step

[0204] 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.

[0205] 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.

[0206] Here, the contents of each component can be equally applied to the contents described in the superabsorbent resin of the aforementioned item Ⅰ.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] In addition, since the formation of a polymer with a longer chain is possible, the effect of reducing the content of a water-soluble component that exists in a non-crosslinked state due to incomplete polymerization or crosslinking can be achieved, and accordingly, it is suitable for implementing the content of a water-soluble component measured after freely swelling for 1 hour in water having an electrical conductivity of 100 to 130 μS / cm of the present invention described above within the target range.

[0211] 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 after neutralization, the polymer is micronized in the presence of a surfactant, or 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.

[0212] 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.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] 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.

[0217] 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.

[0218] Steps 2 and 3: Atomization and neutralization steps

[0219] 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.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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, it is suitable for implementing the content of the water-soluble component measured after freely swelling for 1 hour in water having an electrical conductivity of 100 to 130 μS / cm of the present invention described above within the target range.

[0224] 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, making it difficult to expect a fast absorption speed and securing 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, which may slightly deteriorate the overall physical properties of the manufactured superabsorbent resin. 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. Within this range, it is easy to form the desired micropores without the aforementioned problems.

[0225] 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.

[0226] At this time, the hole size provided in the porous plate of the atomization device may be 1 mm to 25 mm, or 5 mm to 20 mm, or 5 mm to 15 mm.

[0227] 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.

[0228] 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, or 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.

[0229] 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.

[0230] The surfactant may be selected from compounds represented by the following chemical formulas 2-1 to 2-14, but is not limited thereto:

[0231] [Chemical Formula 2-1]

[0232]

[0233] [Chemical Formula 2-2]

[0234]

[0235] [Chemical Formula 2-3]

[0236]

[0237] [Chemical Formula 2-4]

[0238]

[0239] [Chemical Formula 2-5]

[0240]

[0241] [Chemical Formula 2-6]

[0242]

[0243] [Chemical Formula 2-7]

[0244]

[0245] [Chemical Formula 2-8]

[0246]

[0247] [Chemical Formula 2-9]

[0248]

[0249] [Chemical Formula 2-10]

[0250]

[0251] [Chemical Formula 2-11]

[0252]

[0253] [Chemical Formula 2-12]

[0254]

[0255] [Chemical Formula 2-13]

[0256]

[0257] [Chemical Formula 2-14]

[0258] .

[0259] According to one embodiment of the present invention, the surfactant may be, but is not limited to, glycerol monolaurate (GML).

[0260] 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.

[0261] 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.

[0262] Therefore, for example, the surfactant may be used in an amount of 0.06 g or more, or 0.1 g or more, or 0.2 g or more, and 0.48 g or less, or 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 for 1 hour in water having an electrical conductivity of 100 to 130 μS / cm of the present invention described above within a desired range.

[0263] 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.

[0264] 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.

[0265] 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%.

[0266] 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.

[0267] 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.

[0268] 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] 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.

[0273] In particular, by adjusting the rotation speed of the screw-type extruder to 150 rpm to 500 rpm, the content of the water-soluble component measured after freely swelling for 1 hour in water having an electrical conductivity of 100 to 130 μS / cm of the present invention can be controlled to a desired range.

[0274] 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.

[0275] 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%, or 60 to 85 mol%, or 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.

[0276] 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.

[0277] 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.

[0278] Step 4: Drying

[0279] Next, a step (step 4) is performed to dry the above-mentioned micronized and neutralized polymer to prepare a base resin powder.

[0280] 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.

[0281] 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.

[0282] The above step 4 can be performed in a fixed-bed type drying method, a moving type drying method, or a combination thereof.

[0283] According to one embodiment of the invention, step 4 can be performed by static drying.

[0284] 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.

[0285] 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%.

[0286] 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.

[0287] In the above-described static drying step, the drying process can 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.

[0288] According to one embodiment of the invention, step 4 may be performed by fluid drying.

[0289] The fluidized drying method described above refers to a drying method in which the material is mechanically stirred during drying. 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 may be dried by circulating it within the dryer and passing the heat-generating fluid (heat-generating oil) through a separate pipe outside the dryer.

[0290] 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.

[0291] 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.

[0292] Step 5: Grinding Stage

[0293] Next, a step of grinding the dried base resin powder is performed.

[0294] 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.

[0295] The pulverizer 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.

[0296] 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.

[0297] 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 pulverization force, a superabsorbent resin having a very high content of normal particle sizes of 150 ㎛ to 850 ㎛ can be formed, and the fine powder generation ratio can be greatly reduced.

[0298] 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.

[0299] In addition, the superabsorbent resin particles may contain fine particles having a particle size of less than 150 μm in an amount of about 20 wt% or less, or about 18 wt% or less, or about 15 wt% or less, or about 13 wt% or less, or about 12 wt% or less, or about 111 wt% or less, or about 10 wt% or less, or about 9 wt% or less, or 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 production method.

[0300] Additive injection stage

[0301] 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).

[0302] 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.

[0303] 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.

[0304] 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.

[0305] 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.

[0306] Classification stage

[0307] 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.

[0308] Step 6: Surface cross-linking step

[0309] 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.

[0310] The description of the surface cross-linking agent described above can be applied equally to all of the aforementioned contents. Furthermore, the description of the water, methanol, and surfactant added when mixing the surface cross-linking agent and base resin powder can be applied equally to all of the aforementioned contents.

[0311] 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.

[0312] 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.

[0313] The temperature raising means for the above surface crosslinking reaction is not particularly limited.

[0314] 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.

[0315] Post-processing step

[0316] 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.

[0317] 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.

[0318] Additionally, after the above-mentioned singer step, a further maturation step can be performed.

[0319] 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.

[0320] 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.

[0321] 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.

[0322] 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.

[0323] <Example>

[0324] 1) Example 1

[0325] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0326] In a 2 L glass vessel equipped with a stirrer and a thermometer, 1,000 g of acrylic acid, 2.5 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 2,260 g of water were mixed with stirring. The reaction temperature was maintained at 5°C. 1,000 cc / min of nitrogen was introduced into the glass vessel containing the mixture for 1 hour to replace the inside of the glass vessel with nitrogen. Thereafter, 13.0 g of a 0.3% aqueous hydrogen peroxide solution, 15.0 g of a 1% aqueous ascorbic acid solution, and 30.0 g of a 2% aqueous 2,2'-azobis amidinopropane dihydrochloride solution were introduced as polymerization initiators. Simultaneously, 15.0 g of a 0.01% aqueous ferrous sulfate solution, as a reducing agent, was added and mixed to initiate polymerization. A polymerization reaction was initiated in the above mixture, and after the temperature of the polymer reached 85°C, a functional gel polymer was manufactured by polymerizing in an oven at 90±2°C for about 6 hours.

[0327] (Steps 2 and 3: Atomization and Neutralization Steps)

[0328] 1,000 g of the hydrogel polymer obtained in Step 1 and 0.1 g of glycerol monolaurate (GML) were dissolved in water at 60°C or higher and fed into a cylindrical grinder in the form of an aqueous solution. Thereafter, the hydrogel polymer was extruded at a rotation speed of 1,600 rpm through a porous plate having multiple holes of 10 mm in diameter using a high-speed rotary chopper (F-150 / Karl Schnell) mounted inside the cylindrical grinder. Subsequently, the hydrogel polymer was further extruded at a rotation speed of 2,000 rpm through a porous plate having multiple holes of 10 mm in diameter to obtain a pulverized gel-type hydrogel polymer. Thereafter, the pulverized gel-type hydrogel polymer was extruded three times through a porous plate having multiple holes of 6 mm in diameter using a screw-type extruder mounted inside the cylindrical grinder at a rotation speed of 250 rpm to obtain hydrogel superabsorbent resin particles.

[0329] At this time, 460 g of a 32% NaOH aqueous solution was added for the first pass through the perforated plate, and 42.8 g of a 0.5% Na2S2O8 aqueous solution (SPS aqueous solution) was added for the second pass and pushed through the perforated plate. For the third pass, the solution was passed through the perforated plate without adding any additives.

[0330] (Step 4: Drying Stage)

[0331] The superabsorbent resin particles obtained as a result of the above grinding were placed on a porous plate capable of vertically transferring airflow, and dried at 120°C for 40 minutes using an air-flow oven.

[0332] Hot air of 200°C and 100°C was sequentially flowed from the top to the 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 of 100°C was flowed from the bottom to the top for 15 minutes to uniformly dry the water-absorbent resin particles, thereby obtaining a dried body.

[0333] (Step 5: Crushing and Classification Stage)

[0334] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0335] (Step 6: Surface cross-linking step)

[0336] Next, as described in Table 1 below, for 100 g of the base resin powder, a surface cross-linking agent aqueous solution containing 4 g of water, 6 g of methanol, 0.08 g of ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g of propylene glycol, 0.2 g of aluminum sulfate, and 0.1 g of silica particles (Aerosil 200) was added and mixed. At this time, the surface cross-linking agent aqueous solution was mixed so as to be evenly distributed on the superabsorbent resin powder.

[0337] Next, the base resin powder mixed with the surface cross-linking solution was placed in a surface cross-linking reactor, and a surface cross-linking reaction was performed to obtain a surface-cross-linked superabsorbent resin.

[0338] Specifically, within the surface crosslinking reactor, the base resin powder underwent a surface crosslinking reaction at 140°C for 50 minutes.

[0339] After the above surface cross-linking step, a superabsorbent resin having a particle size of 150 μm to 850 μm was manufactured by classifying it through a standard mesh sieve according to ASTM standards.

[0340] 2) Example 2

[0341] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0342] A functional gel polymer was prepared using the same method as in Example 1.

[0343] (Steps 2 and 3: Atomization and Neutralization Steps)

[0344] In Example 1, superabsorbent resin particles were obtained in the same manner as in Example 1, except that instead of adding 460 g of a 32% NaOH aqueous solution per pass through the porous plate in Example 1, 405 g of a 32% NaOH aqueous solution was added.

[0345] (Step 4: Drying Stage)

[0346] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0347] (Step 5: Crushing and Classification Stage)

[0348] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0349] (Step 6: Surface cross-linking step)

[0350] The superabsorbent resin of Example 2 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1, except that the components and contents of the surface crosslinking agent aqueous solution were prepared as described in Table 1 below.

[0351] 3) Example 3

[0352] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0353] A functional gel polymer was prepared using the same method as in Example 1.

[0354] (Steps 2 and 3: Atomization and Neutralization Steps)

[0355] 1,000 g of the hydrogel polymer obtained in Step 1 and 0.1 g of glycerol monolaurate (GML) were dissolved in water at 60°C or higher and fed into a cylindrical grinder in the form of an aqueous solution. Thereafter, the hydrogel polymer was extruded at a rotation speed of 1,500 rpm through a porous plate having multiple holes of 10 mm in diameter using a high-speed rotary shredder (F-150 / Karl Schnell) mounted inside the cylindrical grinder. Subsequently, the hydrogel polymer was further extruded at a rotation speed of 2,500 rpm through a porous plate having multiple holes of 12 mm in diameter to obtain a pulverized gel-type hydrogel polymer. Thereafter, the pulverized gel-type hydrogel polymer was extruded three times through a porous plate having multiple holes of 6 mm in diameter using a screw-type extruder mounted inside the cylindrical grinder at a rotation speed of 250 rpm to obtain hydrogel superabsorbent resin particles.

[0356] At this time, 400 g of a 32% NaOH aqueous solution was added for the first pass through the perforated plate, and 42.8 g of a 0.5% Na2S2O8 aqueous solution (SPS aqueous solution) was added for the second pass and pushed through the perforated plate. For the third pass, the solution was passed through the perforated plate without adding any additives.

[0357] (Step 4: Drying Stage)

[0358] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0359] (Step 5: Crushing and Classification Stage)

[0360] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0361] (Step 6: Surface cross-linking step)

[0362] The superabsorbent resin of Example 3 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1, except that the components and contents of the surface crosslinking agent aqueous solution were prepared as described in Table 1 below.

[0363] 4) Example 4

[0364] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0365] A functional gel polymer was prepared using the same method as in Example 1.

[0366] (Steps 2 and 3: Atomization and Neutralization Steps)

[0367] 1,000 g of the hydrogel polymer obtained in Step 1 and 0.1 g of glycerol monolaurate (GML) were dissolved in water at 60°C or higher and fed into a cylindrical grinder in the form of an aqueous solution. Thereafter, the hydrogel polymer was extruded at a rotation speed of 1,200 rpm through a porous plate having multiple holes of 8 mm in diameter using a high-speed rotary chopper (F-150 / Karl Schnell) mounted inside the cylindrical grinder. Subsequently, the hydrogel polymer was further extruded at a rotation speed of 2,800 rpm through a porous plate having multiple holes of 10 mm in diameter to obtain a pulverized gel-type hydrogel polymer. Thereafter, the pulverized gel-type hydrogel polymer was extruded three times through a porous plate having multiple holes of 6 mm in diameter using a screw-type extruder mounted inside the cylindrical grinder at a rotation speed of 250 rpm to obtain hydrogel superabsorbent resin particles.

[0368] At this time, 365 g of a 32% NaOH aqueous solution was injected into the perforated plate once, and 42.8 g of a 0.5% Na2S2O8 aqueous solution (SPS aqueous solution) was injected into the perforated plate twice and pushed out. In the third pass, the solution was passed through the perforated plate without adding any additives.

[0369] (Step 4: Drying Stage)

[0370] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0371] (Step 5: Crushing and Classification Stage)

[0372] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0373] (Step 6: Surface cross-linking step)

[0374] The superabsorbent resin of Example 4 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1, except that the components and contents of the surface crosslinking agent aqueous solution were prepared as described in Table 1 below.

[0375] 5) Comparative Example 1

[0376] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0377] A functional gel polymer was prepared using the same method as in Example 1.

[0378] (Steps 2 and 3: Atomization and Neutralization Steps)

[0379] In Example 1, superabsorbent resin particles were obtained in the same manner as in Example 1, except that 300 g of a 32% NaOH aqueous solution was added instead of 475 g of a 32% NaOH aqueous solution per pass through the porous plate.

[0380] (Step 4: Drying Stage)

[0381] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

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

[0383] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0384] (Step 6: Surface cross-linking step)

[0385] A superabsorbent resin of Comparative Example 1 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1, except that the components and contents of the surface crosslinking agent aqueous solution were prepared as described in Table 1 below.

[0386] 6) Comparative Example 2

[0387] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0388] A functional gel polymer was prepared using the same method as in Example 1.

[0389] (Steps 2 and 3: Atomization and Neutralization Steps)

[0390] 1,000 g of the hydrogel polymer obtained in Step 1 and 0.1 g of glycerol monolaurate (GML) were dissolved in water at 60°C or higher and fed into a cylindrical grinder in the form of an aqueous solution. Thereafter, the hydrogel polymer was pushed out at a rotation speed of 1,400 rpm through a porous plate having multiple holes of 10 mm in diameter using a high-speed rotary chopper (F-150 / Karl Schnell) mounted inside the cylindrical grinder. Subsequently, the hydrogel polymer was further pushed out at a rotation speed of 2,700 rpm through a porous plate having multiple holes of 8 mm in diameter to obtain a pulverized gel-type hydrogel polymer. Thereafter, the pulverized gel-type hydrogel polymer was pushed out three times through a porous plate having multiple holes of 6 mm in diameter using a screw-type extruder mounted inside the cylindrical grinder at a rotation speed of 250 rpm to obtain hydrogel superabsorbent resin particles.

[0391] At this time, 320 g of a 32% NaOH aqueous solution was added for the first pass through the perforated plate, and 42.8 g of a 0.5% Na2S2O8 aqueous solution (SPS aqueous solution) was added for the second pass and pushed through the perforated plate. For the third pass, the solution was passed through the perforated plate without adding any additives.

[0392] (Step 4: Drying Stage)

[0393] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0394] (Step 5: Crushing and Classification Stage)

[0395] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0396] (Step 6: Surface cross-linking step)

[0397] A superabsorbent resin of Comparative Example 2 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1, except that the components and contents of the surface crosslinking agent aqueous solution were prepared as described in Table 1 below.

[0398] 7) Comparative Example 3

[0399] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0400] A functional gel polymer was prepared using the same method as in Example 1.

[0401] (Steps 2 and 3: Atomization and Neutralization Steps)

[0402] 1,000 g of the hydrogel polymer obtained in Step 1 and 0.1 g of glycerol monolaurate (GML) were dissolved in water at 60°C or higher and fed into a cylindrical grinder in the form of an aqueous solution. Thereafter, the hydrogel polymer was pushed out at a rotation speed of 1,750 rpm through a porous plate having multiple holes of 10 mm in diameter using a high-speed rotary chopper (F-150 / Karl Schnell) mounted inside the cylindrical grinder. Subsequently, the hydrogel polymer was further pushed out at a rotation speed of 2,200 rpm through a porous plate having multiple holes of 8 mm in diameter to obtain a pulverized gel-type hydrogel polymer. Thereafter, the pulverized gel-type hydrogel polymer was pushed out three times through a porous plate having multiple holes of 6 mm in diameter using a screw-type extruder mounted inside the cylindrical grinder at a rotation speed of 250 rpm to obtain hydrogel superabsorbent resin particles.

[0403] At this time, 340 g of a 32% NaOH aqueous solution was added for the first pass through the perforated plate, and 42.8 g of a 0.5% Na2S2O8 aqueous solution (SPS aqueous solution) was added for the second pass and pushed through the perforated plate. For the third pass, the solution was passed through the perforated plate without adding any additives.

[0404] (Step 4: Drying Stage)

[0405] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0406] (Step 5: Crushing and Classification Stage)

[0407] The above dried material was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain a base resin powder having a size of 150 to 850 μm.

[0408] (Step 6: Surface cross-linking step)

[0409] A superabsorbent resin of Comparative Example 3 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1, except that the components and contents of the surface crosslinking agent aqueous solution were prepared as described in Table 1 below.

[0410] 8) Comparative Example 4

[0411] Comparative Example 4 is a method for producing a superabsorbent resin, comprising: a step of neutralizing at least a portion of acidic groups of a water-soluble ethylenically unsaturated monomer (neutralization); a step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a portion of the neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer (polymerization); a step of chopping the hydrogel polymer (chopping); a step of drying the chopped hydrogel polymer (drying); a step of pulverizing and then classifying the dried polymer into normal particles and fine particles (pulverization / classification); and a step of forming a surface crosslinking layer on at least a portion of the surface of the normal particles in the presence of a surface crosslinking agent (surface crosslinking).

[0412] Specifically, the manufacturing process of Comparative Example 4 was as follows.

[0413] (Neutralization and polymerization)

[0414] A monomer composition was prepared by mixing 495 g of acrylic acid, 0.4 g of ethylene glycol diglycidyl ether as an internal crosslinking agent, 19.2 g of 1% IGAGURE 819 as a photopolymerization initiator, 0.6 g of F-36D capsule-type foaming agent as a foaming agent, 0.1 g of sodium dodecyl sulfate as a foaming stabilizer, and 292.6 g of water in a 3 L glass container equipped with a stirrer and a thermometer. Subsequently, the monomer solution was continuously supplied using a metering pump, while simultaneously line-mixing 611.1 g of a 32% NaOH aqueous solution to prepare a monomer aqueous solution. At this time, after confirming that the temperature of the monomer aqueous solution had risen to about 72°C or higher due to the heat of neutralization, the temperature was allowed to cool to 40°C. When the temperature was cooled to 40℃, 41.2 g of a 2 wt% sodium persulfate aqueous solution and 21.2 g of a mixed solution of 0.6 g of sodium bicarbonate dissolved in a 1 wt% sodium dodecyl sulfate aqueous solution were added. The mixed solution was placed in a stainless steel vessel measuring 250 mm in width, 250 mm in length, and 30 mm in height, which was installed in a square polymerization reactor with a light irradiation device mounted on the top and the inside preheated to 80℃, and light irradiation was performed to initiate photoinitiation. After light irradiation, it was confirmed that a gel was generated from the surface after about 15 seconds, and a polymerization reaction occurred simultaneously with foaming after about 30 seconds, and a sheet-shaped hydrogel polymer was obtained by reacting for an additional 3 minutes.

[0415] (Chopping)

[0416] The above functional gel polymer was cut into pieces measuring 5 cm in width and 5 cm in length, and the functional gel was pulverized using a screw-type chopper (meat chopper) equipped with a perforated plate containing numerous holes. The rotation speed of the screw-type chopper was 250 rpm, and the hole size of the perforated plate was 10 mm.

[0417] (dry)

[0418] 1,000 g of the above-mentioned pulverized polymer was placed in a ventilated belt-type dryer containing a perforated plate capable of vertical airflow. Hot air at 180°C was flowed upward from downward for 15 minutes so that the moisture content of the dried body was approximately 2%, and then flowed upward from downward for another 15 minutes to uniformly dry the polymer, thereby producing a dried base resin powder.

[0419] (crushing / classifying)

[0420] The above dried base resin powder was ground with a grinder (GRAN-U-LIZERTM, MPE) and then classified with a standard mesh sieve of ASTM standards to obtain superabsorbent resin powder having a size of 150 to 850 μm.

[0421] (Surface cross-linking step)

[0422] A superabsorbent resin of Comparative Example 4 was manufactured by carrying out the surface crosslinking step in the same manner as in Example 1 using the surface crosslinking agent aqueous solution of Example 1.

[0423] ABCDEFG Example 1460.080.10.2-0.1 Example 2460.080.1-0.10.15 Example 3460.10.1-0.070.1 Example 4560.080.10.20.030.25 Comparative Example 1560.10.10.40.030.1 Comparative Example 2560.10.10.10.20.05 Comparative Example 3660.10.1--0.25 Comparative Example 4460.080.10.2-0.1

[0424] The materials A to G of the above Table 1 are as follows, and in the above Table 1, '-' means a component not included in the surface cross-linking agent aqueous solution, and the unit of each number is g. That is, the above Table 1 means the amount of material used per 100 g of the base resin powder.

[0425] A: Water

[0426] B: Methanol

[0427] C: Ethylene glycol diglycidyl ether

[0428] D: Propylene glycol

[0429] E: Aluminum sulfate

[0430] F: Sucrose stearate

[0431] G: Silica

[0432] <Experimental Example 1> - TD-NMR spectroscopy (time-domain nuclear magnetic resonance spectroscopy) analysis

[0433] The normalized strength of the superabsorbent resin of Example 1 was obtained according to steps 1 to 4 below.

[0434] - Step 1) Drying (pretreatment) of superabsorbent resin

[0435] The superabsorbent resin of Example 1 was dried at about 100°C for about 12 hours.

[0436] - Step 2) Swelling (sampling) of dried superabsorbent resin

[0437] ① About 50 mg of the dried superabsorbent resin of Example 1 was placed in a 10 mm NMR tube.

[0438] ② The tube was sealed with parafilm and sampling for TD-NMR analysis was performed.

[0439] -Step 3) TD-NMR analysis

[0440] ① The superabsorbent resin of Example 1 was introduced, and the sampled tube was stabilized at about 40°C for about 1 hour through sealing treatment.

[0441] ② After stabilization, TD-NMR analysis (analysis device: TD-NMR analysis equipment: Bruker TD-NMR the minispec mq20) was performed on the superabsorbent resin of Example 1 under the following measurement conditions. As a result, the analysis results were derived in which the x-axis represents the signal acquisition time and the y-axis represents the peak intensity.

[0442] <Measurement conditions>

[0443] 1) Temperature: 40℃

[0444] 2) Nuclides: 1 H

[0445] 3) Method: sc-lc-co

[0446] 4) Delay time: 3 seconds

[0447] 5) Number of scans: 1024

[0448] 6) Receiver gain: Use the automatic value measured by the device for each sample.

[0449] - Step 4) Normalization

[0450] The analysis results derived from step 3 were analyzed through TD-NMR. 1 This refers to the peak intensity observed as a result of free induction decay (FID), which is manifested by the decay of the H signal. The intensity is observed sequentially over time. The time at which the intensity is observed corresponds to the signal acquisition time.

[0451] Among them, the remaining centuries were normalized based on the first century (I1). Specifically, when the first century (I1) was set as 100, the relative sizes of the other centuries were calculated.

[0452] For example, the century that appears nth is normalized by calculating it using the following formula A.

[0453] [Formula A]

[0454] N(%) = (I n / I1) x 100(%)

[0455] In the above formula A

[0456] N represents the normalized intensity of the nth intensity,

[0457] I nThrough TD-NMR analysis 1 It refers to the third peak intensity observed as a result of observing the FID that appears as the decay of the H signal.

[0458] I1 was analyzed by TD-NMR. 1 It refers to the intensity that appears for the first time when observing the FID that appears as the decay of the H signal.

[0459] Next, the normalized intensity (N) corresponding to a signal acquisition time of 0.1 ms t=0.1- ) was measured.

[0460] The results are shown in Table 2 below.

[0461] In addition, for Examples 2 to 4 and Comparative Examples 1 to 4, the normalized intensity (N) corresponding to a signal acquisition time of 0.1 ms was obtained in the same manner as in Example 1. int, 0.1 ) was measured.

[0462] The results are also shown in Table 2 below.

[0463] N int, 0.1 (%)Example 13.5Example 22.6Example 33.0Example 42.9Comparative Example 13.6Comparative Example 21.9Comparative Example 32.3Comparative Example 43.8

[0464] <Experimental Example 2> Measurement of convexity and CE diameter

[0465] Additionally, the convexity and CE diameter of the superabsorbent resin particles manufactured in the above examples and comparative examples were measured using the following method, and the results are listed in Table 3 below.

[0466] Unless otherwise specified, all of the following property evaluations were conducted under constant temperature and humidity (23±1℃, relative humidity 50±10%), and saline solution or saline refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0467] After the sample to be measured was left under constant temperature and humidity conditions for 24 hours, each property was evaluated.

[0468] For the superabsorbent resins of the above examples and comparative examples, the convexity and CE diameter were measured using a morphologi 4 from Malvern Panalytical using the following method.

[0469] 1) Sample Preparation: A 1 g particle sample of the superabsorbent resin to be measured was prepared. At this time, the superabsorbent resin was classified using a particle classifier from Retsch at 1.0 amplitude for 10 minutes to separate 1 g of the sample into individual particles with a particle size of 300 μm to 600 μm without damage to the particles. The setting values ​​of the Sample Dispersion Unit at this time are as shown in Fig. 1.

[0470] 2) Image acquisition: The prepared sample was placed on the stage within the equipment and scanned at 2.5x magnification to acquire images of individual particles. At this time, the Illunination Setting value and Optics Selection Setting value were as shown in Figures 2 and 3, respectively.

[0471] 3) Image processing: For the acquired images, the parameter values ​​such as the 3D image of the 3D particle for each particle was captured as a 2D image, the CE diameter (Circle Equivalent diameter), the shortest diameter, the longest diameter, the actual particle perimeter, and the convex hull perimeter were measured. At this time, the Scan Area setting value was as shown in Fig. 4, and the particle was measured without setting the Filtering value.

[0472] Among these, the average value of convexity and CE diameter (Circle Equivalent diameter) calculated by the above equation 2 are listed in Table 3 below.

[0473] Convexity Average CE Diameter Average (㎛) Example 10.87245 Example 20.91301 Example 30.88327 Example 40.92303 Comparative Example 10.88284 Comparative Example 20.87245 Comparative Example 30.94325 Comparative Example 40.95450

[0474] <Experimental Example 3> - Physical Property Evaluation

[0475] Additionally, the properties of the superabsorbent resins manufactured in the above examples and comparative examples were evaluated using the following methods and are listed in Tables 4 to 6 below.

[0476] Unless otherwise specified, all of the following property evaluations were conducted under constant temperature and humidity (23±1℃, relative humidity 50±10%), and saline solution or saline refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0477] After the sample to be measured was left under constant temperature and humidity conditions for 24 hours, each physical property was evaluated.

[0478] (1) Gel strength measurement

[0479] The gel strength of the superabsorbent resins manufactured in the above examples and comparative examples was measured using the following method.

[0480] A saline solution containing 0.005% ASC was prepared using saline and ascorbic acid (ACS). Subsequently, the saline solution containing 0.005% ASC and approximately 2.5 (2.5±0.01 g) of a superabsorbent resin were placed in a 100 ml beaker, mixed, sealed with transparent wrap, and placed in an oven for 24 hours at 40°C to swell. After removing the beaker from the oven, the transparent wrap was removed, and the beaker was left at room temperature for 30 minutes. The gel strength of the superabsorbent resin was measured using a tensile compression tester (manufacturer: Nidec-Shimpo).

[0481] The results are shown in Table 4 below.

[0482] (2) Centrifuge Retention Capacity (CRC, g / g)

[0483] 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.

[0484] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 241.0.

[0485] Specifically, the superabsorbent resin W0(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 W2(g) of the bag was measured. In addition, the same operation was performed without using the resin, and the mass W1(g) at that time was measured.

[0486] Using each mass obtained, CRC (g / g) was calculated according to the following mathematical formula 1.

[0487] [Mathematical Formula 1]

[0488] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0489] The above measurement was repeated five times, and the average value and standard deviation were calculated.

[0490] The results are shown in Table 4 below.

[0491] (3) Absorbency under Pressure (AUP: Absorbency under Pressure, g / g)

[0492] The 0.3 psi pressurized absorbency of the superabsorbent resins of the above examples and comparative examples was measured according to EDANA method WSP 242.3.

[0493] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 242.0.

[0494] 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 W0 (g) (0.9 g) was uniformly sprayed on the wire mesh, and a piston capable of uniformly applying a load of 0.3 psi thereon was installed, with an outer diameter slightly smaller than 25 mm, no gap with the inner wall of the cylinder, and unobstructed up-and-down movement. At this time, the weight W3 (g) of the device was measured.

[0495] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a petroleum 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 W4 (g) was measured.

[0496] Using each mass obtained, the pressurized absorbency (g / g) was calculated according to the following mathematical formula 2.

[0497] [Equation 2]

[0498] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0499] The above measurement was repeated five times, and the average value and standard deviation were calculated.

[0500] The results are shown in Table 4 below.

[0501] (4) Effective absorption capacity (EFFC)

[0502] The measured retention capacity and pressurized absorption capacity were applied to Equation 3 below to calculate the effective absorption capacity (EFFC).

[0503] [Formula 3]

[0504] EFFC = (CRC + AUP) / 2

[0505] In the above equation 3,

[0506] CRC is the water retention capacity (unit: g / g) measured according to the method of EDANA method WSP 241.3,

[0507] AUP is the absorbency under pressure (g / g) measured under 0.3 psi according to EDANA method WSP 242.3.

[0508] The results are shown in Table 4 below.

[0509] (5) Absorption speed (Vortex time)

[0510] The absorption rate (vortex time) of the superabsorbent resins of the above examples and comparative examples was measured by the following method.

[0511] 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.

[0512] 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.

[0513] 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.

[0514] ④ After confirming that the temperature of the saline solution 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 taken as the absorption rate.

[0515] The results are shown in Table 4 below.

[0516] (6) Free swelling capacity (FSC) in water with an electrical conductivity value of 110 μS / cm 110 ) and 1 minute absorbency (WFA) 110 )

[0517] For the superabsorbent resin of Example 1 above, the free swelling capacity (FSC) in water having an electrical conductivity value of 110 μS / cm at 24°C was measured using the following method. 110 ) and 1-minute absorbency (WFA) 110 ) was measured. The specific measurement process was as follows.

[0518] ① Put 18cm x 28cm tea bags for broth into each of 8 2L beakers.

[0519] ② After pouring 1 L of water having an electrical conductivity value of 110 μS / cm at 24°C into the above beaker, each beaker was left submerged for (10 seconds / 20 seconds / 30 seconds / 60 seconds / 120 seconds / 300 seconds / 600 seconds / 1800 seconds).

[0520] ③ After removing the tea bag for broth from each beaker (10 seconds / 20 seconds / 30 seconds / 60 seconds / 120 seconds / 300 seconds / 600 seconds / 1800 seconds), when water no longer drips from the tea bag for broth, the weight of the tea bag for broth (W a ) was recorded. Among these, the weight measured when no water dripped from the tea bag for broth after 60 seconds (1 minute) was W. 1, It was defined as (Blank value).

[0521] ④ Put 18cm x 28cm tea bags for broth into each of 8 other 2L beakers.

[0522] ⑤ 1g of super absorbent polymer (SAP) of Example 1 was accurately weighed and evenly sprinkled on the bottom of each tea bag for broth.

[0523] ⑥ After pouring 1 L of water having an electrical conductivity value of 110 μS / cm at 24℃ into each beaker, each beaker was left submerged for (10 seconds / 20 seconds / 30 seconds / 60 seconds / 120 seconds / 300 seconds / 600 seconds / 1800 seconds).

[0524] ⑦ After removing the tea bag for broth sprayed with superabsorbent resin from each beaker (10 seconds / 20 seconds / 30 seconds / 60 seconds / 120 seconds / 300 seconds / 600 seconds / 1800 seconds), when the water with an electrical conductivity value of 110 μS / cm no longer falls, the weight of the tea bag for broth sprayed with superabsorbent resin (W s ) was recorded. Among these, the weight measured when no water dripped from the tea bag for broth sprinkled with superabsorbent resin after 60 seconds (1 minute) was defined as W2.

[0525] ⑧ The weight of the tea bag for broth performed in each beaker was applied to the following mathematical equation 3 to obtain the free swelling capacity (FSC) in water with an electrical conductivity value of 110 μS / cm at 24°C. 110 ) was produced.

[0526] [Equation 3]

[0527] FSC 110 (g / g) = W a - W s

[0528] ⑨ The 1-minute absorption capacity (WFA) in water with an electrical conductivity value of 110 μS / cm is calculated using the following mathematical formula 4. 110 ) was calculated. That is, the 1-minute absorption capacity (WFA) in water with an electrical conductivity value of 110 μS / cm 110 ) is the free swelling capacity (FSC) in water with an electrical conductivity of 110 μS / cm at 24°C calculated through a tea bag for broth placed in a beaker for 1 minute. 110 ) means.

[0529] [Equation 4]

[0530] WFA 110 (g / g) = W2- W1

[0531] In addition, experiments were additionally conducted on the superabsorbent resins of Examples 2 to 4 and Comparative Examples 1 to 4 in the same manner as on the superabsorbent resin of Example 1.

[0532] The results are shown in Tables 4 and 5 below.

[0533] (7) Measurement of permeability of superabsorbent resin

[0534] At room temperature (23°C to 25°C), 0.2 g of the superabsorbent resins of the examples and comparative examples were placed in a cylinder with an inner diameter of 20 mm, and physiological saline solution (0.9 wt% sodium chloride aqueous solution) was poured so that the superabsorbent resin was completely submerged, thereby swelling the superabsorbent resin for 30 minutes. Thereafter, a pressure of 0.3 psi was applied using a piston with an outer diameter slightly smaller than 20 mm.

[0535] The time (T1) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin was measured by measuring the decrease in height of the saline solution filled in the cylinder under a pressure of 0.3 psi.

[0536] Next, the permeability of the superabsorbent resin was calculated according to Equation 4 below.

[0537] [Formula 4]

[0538] Perm = [20 mL / T1 (sec)] x 60 sec

[0539] In the above equation 4,

[0540] Perm is permeable,

[0541] T1 means the time (seconds) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin under a pressure of 0.3 psi after 0.2 g of superabsorbent resin was placed in a cylinder, saline solution (0.9 wt% sodium chloride aqueous solution) was poured so that the superabsorbent resin was completely submerged, and the superabsorbent resin was swelled for 30 minutes.

[0542] The results are shown in Table 6 below.

[0543] Gel strength (N) CRC (g / g) 0.3AUP (g / g) EFFCVortex time (sec) WFA 110 (g / g)Example 10.8437.430.934.215216Example 20.9134.23433.437190Example 30.9231.528.830.229138Example 41.3730.829.830.325141Comparative Example 10.7638.126.532.94186Comparative Example 20.6136.426.132.343122Comparative Example 30.7239.521.530.546123Comparative Example 40.674026.533.53890

[0544] Free swelling capacity (FSC) as a function of time in water with an electrical conductivity of 110 μS / cm at 24°C 110 ), (g / g) Swelling time, t (s) 10 20 30 60 1 20 30 0 60 0 1 800 Example 1 5 48 9 1 2 4 2 1 6 2 6 8 3 4 2 3 6 6 3 8 8 Example 2 4 4 8 0 1 0 9 1 9 0 2 5 6 3 0 9 3 2 6 3 3 3 Example 3 3 6 6 9 1 0 4 1 3 8 3 0 5 3 2 0 3 2 3 3 8 9 Example 4 3 7 7 0 1 1 0 1 4 1 2 7 9 3 1 1 3 1 9 3 2 8 Comparative Example 1 1 7 3 2 4 7 8 6 2 0 6 2 9 0 3 1 5 3 1 0 Comparative Example 2 2 9 5 1 7 4 1 2 1 6 8 2 8 9 3 5 2 3 7 4 Comparative Example 3 3 7 5 1 7 0 1 2 3 1 8 8 2 6 3 1 7 3 7 0 Comparative Example 425355690189260308337

[0545] T1(sec) Liquid permeability (mL) of equation 4 Example 110120 Example 27171 Example 311109 Example 41486 Comparative Example 11963 Comparative Example 22060 Comparative Example 32450 Comparative Example 42352

[0546] As can be seen in Tables 3 to 6 above, the superabsorbent resin was measured by TD-NMR and the result normalized to the above formula A was confirmed to exhibit an excellent balance of physical properties such as absorption performance and liquid permeability in the case of the superabsorbent resin of the example satisfying the above formula 1.

Claims

1. As a polyacrylic acid (salt)-based superabsorbent resin, The TD-NMR analysis result of the above superabsorbent resin satisfies the following equation 1: [Formula 1] 2.5(%) ≤ N t=0.1 (%) ≤ 3.5(%) In the above equation 1, N t=0.1 refers to the normalized intensity measured at a signal acquisition time of 0.1 ms.

2. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having an average value of convexity calculated by the following equation 2 for all particles of 0.94 or less: [Formula 2] M c = L s / L In the above equation 2, M c is convexity, L s refers to the length of an elastic band when it is assumed that the 3D image of the 3D particle to be measured is surrounded by an imaginary elastic band that stretches around the contour of the captured 2D image. L represents the actual circumference of the image captured as a 2D image of the 3D image of the 3D particle to be measured.

3. In paragraph 1, The above superabsorbent resin is a superabsorbent resin in which the content of a water-soluble component measured after freely swelling in water having an electrical conductivity of 100 to 130 μS / cm for 30 minutes is 10 wt% or less with respect to the total weight of the superabsorbent resin.

4. In paragraph 1, The above superabsorbent resin is a superabsorbent resin in which the content of a water-soluble component measured after freely swelling for 3 hours in water having an electrical conductivity of 100 to 130 μS / cm is 17 wt% or less with respect to the total weight of the superabsorbent resin.

5. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having an absorbency under pressure (AUP) of 28 g / g or more as measured under 0.3 psi according to EDANA method WSP 242.

3.

6. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having a water retention capacity (CRC) of 30 g / g or more as measured according to the method of EDANA method WSP 241.

3.

7. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having an effective absorbency (EFFC) of 30 g / g or more, calculated by the following equation 3: [Formula 3] EFFC = (CRC + AUP) / 2 In the above equation 3, CRC is the water retention capacity (unit: g / g) measured according to the method of EDANA method WSP 241.3, AUP is the absorbency under pressure (g / g) measured under 0.3 psi according to EDANA method WSP 242.

3.

8. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having an absorption rate (vortex time) of 40 seconds or less as measured by a vortex measurement method at 24.0°C.

9. In paragraph 1, A superabsorbent resin, wherein when the superabsorbent resin is swelled in water having an electrical conductivity of 100 to 130 μS / cm for 1 minute, the maximum capacity of water that the superabsorbent resin can hold (Free Swell Capacity) is 135 g / g or more.

10. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having a permeability of 65 ml or more as calculated by the following formula 4: [Formula 4] Perm = [20 mL / T1 (sec)] x 60 sec In the above equation 4, Perm is permeable, T1 means the time (seconds) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin under a pressure of 0.3 psi after 0.2 g of superabsorbent resin was placed in a cylinder, saline solution (0.9 wt% sodium chloride aqueous solution) was poured so that the superabsorbent resin was completely submerged, and the superabsorbent resin was swelled for 30 minutes.

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