Super absorbent polymer

Abstract

The present invention relates to a super absorbent polymer.

Description

superabsorbent resin

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0106890, filed August 9, 2024, and U.S. Patent Application No. 19 / 292,312, filed August 6, 2025, 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] These superabsorbent polymers are widely used in sanitary products, such as diapers and sanitary napkins. Within these sanitary products, the superabsorbent polymers are typically dispersed within pulp. However, recent efforts to provide thinner sanitary products, such as diapers, are ongoing. As part of this effort, the development of so-called pulpless diapers, which contain reduced pulp content or even eliminate pulp altogether, is actively underway.

[0006] In this way, in the case of sanitary materials where the pulp content is reduced or no pulp is used, a relatively high proportion of superabsorbent resin is included, so superabsorbent resin particles are inevitably included in multiple layers within the sanitary material. In order for the entire superabsorbent resin particles included in multiple layers to more efficiently absorb a large amount of liquid such as urine, the superabsorbent resin needs to exhibit not only high absorption performance but also a fast absorption speed. Meanwhile, the most common method for improving such absorption properties is a method of forming a porous structure within the superabsorbent resin to increase the surface area of ​​the superabsorbent resin. In order to increase the surface area of ​​the superabsorbent resin, a method of forming a porous structure within the base resin powder by including a foaming agent in the monomer composition and performing crosslinking polymerization is generally adopted.

[0007] However, the use of a foaming agent has the disadvantage of lowering various properties of the superabsorbent resin, such as surface tension, permeability, or bulk density, and increasing the amount of fine particles generated. Accordingly, there is a continuous demand for the development of a technology that can improve the absorption properties of the superabsorbent resin without the use of a foaming agent.

[0008] Accordingly, there is a continuous demand for the development of superabsorbent resins to fundamentally solve these problems.

[0009] The present invention aims to provide a superabsorbent polymer (SAP) having excellent absorbent properties by appropriately controlling the ratio of various functional groups, such as COOH functional groups and COO- functional groups, present on the surface of the SAP.

[0010] The present invention is a polyacrylic acid (salt)-based superabsorbent resin,

[0011] The above resin contains carbon, oxygen and silicon on the surface,

[0012] A superabsorbent resin is provided in which a spectrum derived from analysis of the above resin surface using FT-IR spectroscopy (Fourier-transform infrared spectroscopy) satisfies the following equation 1.

[0013] [Formula 1]

[0014] X COOH ≤ 2.6

[0015] In the above equation 1,

[0016] X COOH means the value obtained by dividing the integral value of the region corresponding to the COOH functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0017] The superabsorbent polymer of the present invention, when applied to a product, can rapidly absorb bodily fluids and retain large amounts of bodily fluids without leaking them outward. In other words, the superabsorbent polymer of the present invention exhibits excellent absorption performance, particularly excellent initial absorption performance.

[0018] Figure 1 is a diagram showing an FTIR spectrum derived from FT-IR spectroscopy (Fourier-transform infrared spectroscopy) of Example 1.

[0019] Figure 2 is a diagram schematically showing the process of calculating the integral value of a specific functional group.

[0020] 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.

[0021] 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.

[0022] The technical terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Furthermore, the singular forms "a," "an," and "the" as used herein also include the plural forms, unless the context clearly dictates otherwise.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] In this specification, the element symbols used are those described in the periodic table.

[0028] In this specification, 'X A ' means the value obtained by dividing the integral value of the region corresponding to the A functional group in the spectrum showing the main functional group derived from the analysis of the surface of the superabsorbent resin using FT-IR spectroscopy by the integral value of the region corresponding to the CH2 functional group. The resin surface means a region corresponding to a depth of 1 ㎛ to 2 ㎛ based on the outermost layer of the resin.

[0029] The above A functional group is a major functional group present on the resin surface, and includes OH, COO-, COOH, COC, Si-O, etc.

[0030] In addition, the analysis using the above FT-IR spectroscopy (Fourier-transform infrared spectroscopy) derives a spectrum by analyzing a powder-type superabsorbent resin as a sample using the ATR (Diamond) measurement method.

[0031] Next, a baseline was set (baseline correction) based on specific points (BL1, BL2) for each functional group on the resin surface, and then the integral value of the area of ​​another specific point (R1, R2) was obtained. Specific descriptions of BL1, BL2, R1, and R2 are provided in Table 1 below.

[0032] This process was repeated five times for each sample to obtain an average value, and this average value was defined as the integral value of the area corresponding to a specific functional group.

[0033] Next, the value was calculated by dividing the integral value of the region corresponding to the A functional group by the integral value of the region corresponding to the CH2 functional group among the above integral values.

[0034] The final calculated value is X A It means.

[0035] That is, 'X A ' means the relative integral value of the A functional group determined based on the integral value of the region corresponding to the CH2 functional group in the above spectrum.

[0036] Hereinafter, a superabsorbent resin and a method for manufacturing the same according to specific embodiments of the invention will be described in more detail.

[0037] I. Polyacrylic acid (salt)-based superabsorbent resin

[0038] The superabsorbent resin of the present invention is a polyacrylic acid (salt)-based superabsorbent resin, and the ratio of various functional groups, such as COOH functional groups and COO- functional groups, present on the surface of the superabsorbent resin is controlled by appropriately controlling various process conditions during the manufacturing process of the resin.

[0039] Controlling process conditions means, for example, adjusting the type or content of additives in the surface crosslinking process, or adjusting the polymerization and grinding process conditions. Through this, the ratio of COOH functional groups present on the surface of the superabsorbent resin can be adjusted so that it satisfies Equation 1 below.

[0040] [Formula 1]

[0041] X COOH ≤ 2.6

[0042] In the above equation 1,

[0043] X COOH means the value obtained by dividing the integral value of the region corresponding to the COOH functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0044] 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.

[0045] Furthermore, the properties of superabsorbent resins can be improved by forming a surface cross-linking layer through a surface cross-linking process. The surface of the superabsorbent resin contains carbon, oxygen, and silicon as major components. Key functional groups present on the surface include COOH functional groups and COO functional groups.

[0046] The content of COOH functional groups present on the resin surface may vary depending on conditions such as the neutralization process or surface cross-linking process. Specifically, it may be controlled by the degree of neutralization during the neutralization process of the resin, and the content of these functional groups may be controlled by the type of surface cross-linking agent, reaction temperature, reaction time, etc. during the surface cross-linking process, as each functional group combines with or disappears.

[0047] The content of COOH functional groups on the resin surface can affect the network structure of superabsorbent polymers, thereby influencing their absorption characteristics. Specifically, COOH functional groups exist in the form of organic acids and are relatively less prone to ionic dissociation than COO functional groups, which are partially neutralized and exist in salt form. As a result, electrostatic repulsion is reduced during the initial absorption of water into the superabsorbent polymer, and the rate of polymer chain separation is slowed. This is one of the factors that slows the water absorption rate of the superabsorbent polymer.

[0048] However, in the case of the COOH functional group existing in the form of an organic acid, it can act as an acid catalyst during surface reaction, thereby facilitating the surface reaction and helping to improve the pressurized properties.

[0049] In other words, if there are many COOH functional groups, the absorption rate is slow, but the surface reaction is good, which is advantageous for the pressurized properties, and if there are few COOH functional groups, the absorption rate is fast, but the surface reaction is insufficient, which has a negative effect on the pressurized properties. For this reason, the content of COOH functional groups can affect the absorption rate and pressurized properties of the superabsorbent polymer, and it is important to have an appropriate content to balance the absorption rate and pressurized properties.

[0050] In the present invention, for the above reasons, the contents of various functional groups such as COOH and COO were measured as relative values ​​based on the CH2 functional group, and the inventors of the present invention confirmed that the ratio of these functional groups based on the CH2 functional group affects the absorption characteristics of the superabsorbent resin.

[0051] Specifically, as described above, it was confirmed that the ratio of COOH functional groups based on the CH2 functional group can affect the absorption characteristics of the superabsorbent resin, and when the ratio of various functional groups based on the CH2 functional group satisfies the above equation 1 and equations 2 to 6 below, it was confirmed that the absorption characteristics of the superabsorbent resin are improved.

[0052] In the present invention, the reason why various functional groups are divided by the area integral value of CH2 group is due to the characteristics of the manufacturing method of superabsorbent resin. The main characteristic of the manufacturing method of superabsorbent resin, which is manufactured by radical polymerization of organic acids and neutralized salts of said organic acids, is that it is manufactured by radical polymerization of acrylic acid and sodium acrylate in particular. Due to this characteristic, the polymer backbone of the superabsorbent resin is composed of repeating units of CH2-CH, and a structure is formed in which various functional groups are bonded with COOH functional groups and COO functional groups as pendant groups to CH. Therefore, if the ratio of each functional group is expressed based on the CH2 (functional) group, the ratio of each functional group can be calculated relative to the polymer backbone content of the superabsorbent resin. For this reason, the ratio of functional groups was obtained by dividing various functional groups by the area integral value of CH2 group, and the relationship between the ratios was confirmed as described above.

[0053] In one embodiment of the present invention, X of the above formula 1 COOH may be less than or equal to 2.6, or less than or equal to 2.5.

[0054] In one embodiment of the present invention, the resin can satisfy the following equation 2.

[0055] [Formula 2]

[0056] X COO + X COOH ≤ 18

[0057] In the above equation 2,

[0058] X COOmeans the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group and the symmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0059] In one embodiment of the present invention, the resin can satisfy the following equation 3.

[0060] [Formula 3]

[0061] X COOH / X COO ≤ 0.17

[0062] In the above equation 3,

[0063] X COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group and the symmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0064] In one embodiment of the present invention, the resin can satisfy the following equation 4.

[0065] [Formula 4]

[0066] X COOH / X Asym.COO ≤ 0.22

[0067] In the above equation 4,

[0068] X Asym.COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0069] In one embodiment of the present invention, the resin can satisfy the following equation 5.

[0070] [Formula 5]

[0071] X Asym.COO / X Sym.COO ≤ 4.75

[0072] In the above equation 5,

[0073] X Asym.COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum,

[0074] X Sym.COO means the value obtained by dividing the integral value of the region corresponding to the symmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0075] In the present specification, the COO- functional group includes a symmetric COO- functional group and an asymmetric COO- functional group.

[0076] In one embodiment of the present invention, X of the above formula 2 COO + X COOH may be 18 or less, or 17.5 or less. In addition, X in the above formula 2 COO + X COOH can be 8 or more, or 9 or more.

[0077] In one embodiment of the present invention, the X COO may be 16 or less, or 15 or less.

[0078] In one embodiment of the present invention, the X Asym.COO may be less than or equal to 13, or less than or equal to 12.5.

[0079] In one embodiment of the present invention, the X Sym.COO may be less than or equal to 3, or less than or equal to 2.9.

[0080] In one embodiment of the present invention, the resin is X OH may be 20 or less, or 19 or less. The above X OHmeans the value obtained by dividing the integral value of the region corresponding to the OH functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0081] The surface of the above resin contains carbon, oxygen and silicon.

[0082] Additionally, in one embodiment of the present invention, the surface of the resin may further include one or more elements selected from the group consisting of sodium, nitrogen, aluminum, and sulfur.

[0083] In one embodiment of the present invention, the resin can satisfy the following equation 6.

[0084] [Formula 6]

[0085] X C-O-C + X Si-O ≤ 14

[0086] In the above equation 6,

[0087] X C-O-C means the value obtained by dividing the integral value of the region corresponding to the COC functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum,

[0088] X Si-O means the value obtained by dividing the integral value of the region corresponding to the Si-O functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

[0089] In one embodiment of the present invention, X of the above formula 6 C-O-C + X Si-O may be 14 or less, 13 or less, or 12 or less. In addition, X in the above formula 6 C-O-C + X Si-O can be 3 or more, or 4 or more.

[0090] In the case of the COC functional group and the Si-O functional group, it is difficult to separately confirm the ratio of the COC and Si-O functional groups because the COC peak and the Si-O peak overlap, and if the above equation 6 is satisfied, the superabsorbent resin can have better pressurization properties and liquid permeability.

[0091] First, as can be seen in the reaction formula below, in the case of the COC functional group, the more functional groups there are as by-products generated through the surface cross-linking reaction, the more the surface cross-linking reaction occurred.

[0092]

[0093] However, if the surface crosslinking reaction is excessive, the surface hydrophobicity increases, which adversely affects the absorption rate and the water retention capacity of the superabsorbent resin. On the other hand, if the surface crosslinking reaction is too low, it may be difficult to secure pressurized properties. Therefore, it is desirable for the surface crosslinking reaction to occur at an appropriate level, and the presence of COC functional groups in an appropriate ratio can indicate that an appropriate level of surface crosslinking reaction has occurred.

[0094] In addition, in the case of the Si-O functional group, the ratio may change depending on the content of silica, which is a functional group related to silica that functions as a permeability improver and an anti-agglomeration agent of a superabsorbent resin.

[0095] At this time, if too much silica is added, the pressure properties may deteriorate and dust generation may become severe. On the other hand, if too little silica is added, the superabsorbent resin may clump severely in a humid environment and its liquid permeability may decrease.

[0096] For this reason, the ratio of COC functional groups and Si-O functional groups can affect the surface network structure of the superabsorbent polymer, thereby affecting the pressurized properties and liquid permeability of the superabsorbent polymer. When the ratio of COC and Si-O functional groups on the surface of the superabsorbent polymer satisfies Equation 6, the superabsorbent polymer can have better pressurized properties and liquid permeability.

[0097] In one embodiment of the present invention, the resin can satisfy at least one of the above formulas 1 to 6. In addition, the resin can satisfy all of the above formulas 1 to 6.

[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 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.

[0100] “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.

[0101] 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.

[0102] 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.

[0103] For this reason, it is possible to determine whether the superabsorbent resin has excellent performance in terms of crosslinking through the content of the dissolved water-soluble component.

[0104] That is, if surface crosslinking progresses uniformly, the amount of water-soluble components that are eluted through the surface can be reduced, which means that the superabsorbent resin has excellent performance in terms of crosslinking.

[0105] The superabsorbent resin according to the present invention has a ratio of COOH functional groups, which are one of the main functional groups present on the surface, satisfying the above formula 1, which means that the surface crosslinking of the superabsorbent resin has progressed uniformly. As a result, the superabsorbent resin according to the present invention can reduce the content of eluted water-soluble components, and the content of eluted water-soluble components can satisfy the above range.

[0106] In addition, when the COO functional group, which is another major functional group present on the surface, satisfies at least one of the above formulas 2 to 5 in relation to the COOH functional group, this means that surface crosslinking has progressed more uniformly, and as a result, the amount of water-soluble components eluted from the superabsorbent resin can be reduced.

[0107] In other words, if any one or more of the above equations 2 to 5 is satisfied, the superabsorbent resin may have better performance in terms of crosslinking.

[0108] 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.

[0109] 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 addition to sanitary products. In these applications, excellent absorption behavior in water with an electrical conductivity of 100 to 130 μS / cm is required.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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 33 g / g or more, or 34 g / g or more, or 35 g / g or more. In addition, the water retention capacity measured according to the same method may be 50 g / g or less, or 45 g / g or less, or 40 g / g or less.

[0118] In addition, in one embodiment of the present invention, the superabsorbent polymer may have an absorbency under pressure (AUP) of 25 g / g or more, or 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.

[0119] In addition, in one embodiment of the present invention, the superabsorbent resin may have an effective absorbency (EFFC) calculated by Equation 7 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 7 below 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.

[0120] [Formula 7]

[0121] EFFC = (CRC + AUP) / 2

[0122] In the above equation 7,

[0123] CRC is the water retention capacity (unit: g / g) measured according to the method of EDANA method WSP 241.3,

[0124] AUP is the absorbency under pressure (g / g) measured under 0.3 psi according to EDANA method WSP 242.3.

[0125] 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, as measured after swelling for 1 hour according to the method of EDANA method WSP 270.3. The content of the water-soluble component is better as the value is smaller, and the lower limit is theoretically 0 wt%, but may be, for example, 0.1 wt% or more, or 1 wt% or more.

[0126] 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.

[0127] More specifically, the absorption rate (vortex time) may be 40 seconds or less, or 38 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.

[0128] 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.

[0129] 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 swollen in water having an electrical conductivity of 100 to 130 μS / cm for 1 minute, of 130 g / g or more, or 135 g / g or more, or 150 g / g or more, or 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.

[0130] 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.

[0131] 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.

[0132] 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 satisfying any one of the above formulas 1 to 6.

[0133] For example, in the polymerization process, the type and content of the monomer composition, the type and content of the internal cross-linking agent, the type, amount and timing of introduction of the surfactant in the neutralization and atomization steps, the type, amount and timing of introduction of the neutralizing agent, the type of atomization device, the rotation speed, the hole size, the number of atomizations, etc. can be controlled to satisfy at least one of the above formulas 1 to 6.

[0134] Below, each component that makes up the superabsorbent resin will be explained in more detail.

[0135] 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 / or a salt thereof 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.

[0136] 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:

[0137] [Chemical Formula 1]

[0138] R-COOM'

[0139] In the above chemical formula 1,

[0140] R is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

[0141] M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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%.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] Therefore, as described above, it is necessary to minimize the amount of extractable contents of the superabsorbent resin.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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 too 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.

[0164] 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.

[0165] Specifically, the initiator and reducing agent react with each other to form radicals when introduced into a polymer solution.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] The above monomer composition may further include additives such as a thickener, a plasticizer, a preservation stabilizer, and an antioxidant, as needed.

[0172] 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%.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] Ⅱ. Manufacturing method of superabsorbent resin

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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, in the polymerization process, the type and content of the monomer composition, 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, rotation speed, hole size, number of atomizations, the components and content of the surface cross-linking solution, etc., thereby controlling the ratio of functional groups present on the surface of the superabsorbent resin as in the present invention.

[0195] In particular, the ratio of functional groups present on the surface of the superabsorbent resin can be controlled as in the present invention by adjusting the amount of neutralizing agent added in the neutralization step, applying the ultra-fine chain process as a micronization method, or adjusting the components and content of the surface cross-linking agent in the surface cross-linking step. The ultra-fine chain process and adjusting the components and content of the surface cross-linking agent will be described later.

[0196] Hereinafter, each step of the method for manufacturing a superabsorbent resin according to an embodiment will be described in more detail.

[0197] Step 1: Polymerization Step

[0198] 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.

[0199] 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.

[0200] Here, the contents of each component can be equally applied to the contents described in the superabsorbent resin of the aforementioned item Ⅰ.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] Steps 2 and 3: Atomization and neutralization steps

[0213] Next, the method includes a step (step 2) of producing a mixture including the micronized functional gel polymer by micronizing the functional gel polymer in the presence of a surfactant.

[0214] 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.

[0215] 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.

[0216] Meanwhile, when a high-intensity mechanical shear force is applied in the above-mentioned micronization step and ultra-fine grinding is performed at a rotation speed of 500 rpm to 4,000 rpm, coagulated functional gel particles having finer pores can be formed.

[0217] 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.

[0218] 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.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] The surfactant may be selected from compounds represented by the following chemical formulas 2-1 to 2-14, but is not limited thereto:

[0225] [Chemical Formula 2-1]

[0226]

[0227] [Chemical Formula 2-2]

[0228]

[0229] [Chemical Formula 2-3]

[0230]

[0231] [Chemical Formula 2-4]

[0232]

[0233] [Chemical Formula 2-5]

[0234]

[0235] [Chemical Formula 2-6]

[0236]

[0237] [Chemical Formula 2-7]

[0238]

[0239] [Chemical Formula 2-8]

[0240]

[0241] [Chemical Formula 2-9]

[0242]

[0243] [Chemical Formula 2-10]

[0244]

[0245] [Chemical Formula 2-11]

[0246]

[0247] [Chemical Formula 2-12]

[0248]

[0249] [Chemical Formula 2-13]

[0250]

[0251] [Chemical Formula 2-14]

[0252] .

[0253] According to one embodiment of the present invention, the surfactant may be, but is not limited to, glycerol monolaurate (GML).

[0254] 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 productivity or device load conditions.

[0255] 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.

[0256] 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.

[0257] 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.

[0258] 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.

[0259] 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%.

[0260] 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.

[0261] 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.

[0262] 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.

[0263] 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.

[0264] 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.

[0265] 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.

[0266] 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.

[0267] 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.

[0268] 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] Step 4: Drying

[0273] Next, a step (step 4) is performed to dry the above-mentioned micronized and neutralized polymer to prepare a base resin powder.

[0274] 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.

[0275] 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.

[0276] The above step 4 can be performed in a fixed-bed type drying method, a moving type drying method, or a combination thereof.

[0277] According to one embodiment of the invention, step 4 can be performed by static drying.

[0278] 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.

[0279] 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 direction of hot air from bottom to top, warping of the plate-like dried body during drying was prevented, thereby preventing hot air from leaking out. In addition, the drying temperature was changed section by section so that the upper, middle, and lower layers within the dried body could be dried uniformly with a moisture content deviation of less than 5%.

[0280] 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.

[0281] 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.

[0282] According to one embodiment of the invention, step 4 may be performed by fluid drying.

[0283] 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.

[0284] 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.

[0285] 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.

[0286] Step 5: Grinding Stage

[0287] Next, a step of grinding the dried base resin powder is performed.

[0288] 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.

[0289] 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.

[0290] 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.

[0291] 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.

[0292] 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.

[0293] 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.

[0294] Additive injection stage

[0295] 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).

[0296] 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.

[0297] 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.

[0298] 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.

[0299] 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.

[0300] Classification stage

[0301] 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.

[0302] Step 6: Surface cross-linking step

[0303] 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.

[0304] 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.

[0305] 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.

[0306] 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.

[0307] The temperature raising means for the above surface crosslinking reaction is not particularly limited.

[0308] 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.

[0309] Post-processing step

[0310] 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.

[0311] 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.

[0312] Additionally, after the above-mentioned singer step, a further maturation step can be performed.

[0313] 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.

[0314] 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.

[0315] 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.

[0316] 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.

[0317] <Example>

[0318] 1) Example 1

[0319] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0320] 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.

[0321] (Steps 2 and 3: Atomization and Neutralization Steps)

[0322] 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 chopper (F-150 / Karl Schnell) mounted inside the cylindrical grinder. Subsequently, the hydrogel polymer was further extruded at a rotation speed of 2,600 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.

[0323] At this time, 475 g of 32% NaOH aqueous solution was added for the first pass through the perforated plate, and 42.8 g of 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.

[0324] (Step 4: Drying Stage)

[0325] 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.

[0326] 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.

[0327] (Step 5: Crushing and Classification Stage)

[0328] 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.

[0329] (Step 6: Surface cross-linking step)

[0330] 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.

[0331] 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.

[0332] Specifically, within the surface crosslinking reactor, the base resin powder underwent a surface crosslinking reaction at 140°C for 50 minutes.

[0333] 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.

[0334] 2) Example 2

[0335] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0336] A functional gel polymer was prepared using the same method as in Example 1.

[0337] (Steps 2 and 3: Atomization and Neutralization Steps)

[0338] In Example 1, superabsorbent resin particles were obtained in the same manner as in Example 1, except that instead of adding 475 g of a 32% NaOH aqueous solution per pass through the porous plate in Example 1, 410 g of a 32% NaOH aqueous solution was added.

[0339] (Step 4: Drying Stage)

[0340] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0341] (Step 5: Crushing and Classification Stage)

[0342] 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.

[0343] (Step 6: Surface cross-linking step)

[0344] 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.

[0345] 3) Example 3

[0346] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0347] A functional gel polymer was prepared using the same method as in Example 1.

[0348] (Steps 2 and 3: Atomization and Neutralization Steps)

[0349] In Example 1, superabsorbent resin particles were obtained in the same manner as in Example 1, except that instead of adding 475 g of 32% NaOH aqueous solution per pass through the porous plate in Example 1, 400 g of 32% NaOH aqueous solution was added.

[0350] (Step 4: Drying Stage)

[0351] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0352] (Step 5: Crushing and Classification Stage)

[0353] 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.

[0354] (Step 6: Surface cross-linking step)

[0355] 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.

[0356] 4) Example 4

[0357] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0358] A functional gel polymer was prepared using the same method as in Example 1.

[0359] (Steps 2 and 3: Atomization and Neutralization Steps)

[0360] 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 1,200 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 2,500 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 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.

[0361] At this time, 350 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.

[0362] (Step 4: Drying Stage)

[0363] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0364] (Step 5: Crushing and Classification Stage)

[0365] 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.

[0366] (Step 6: Surface cross-linking step)

[0367] 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.

[0368] 5) Comparative Example 1

[0369] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0370] A functional gel polymer was prepared using the same method as in Example 1.

[0371] (Steps 2 and 3: Atomization and Neutralization Steps)

[0372] 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.

[0373] (Step 4: Drying Stage)

[0374] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0375] (Step 5: Crushing and Classification Stage)

[0376] 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.

[0377] (Step 6: Surface cross-linking step)

[0378] 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.

[0379] 6) Comparative Example 2

[0380] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0381] A functional gel polymer was prepared using the same method as in Example 1.

[0382] (Steps 2 and 3: Atomization and Neutralization Steps)

[0383] 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 2,800 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 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.

[0384] At this time, 330 g of 32% NaOH aqueous solution was added for the first pass through the perforated plate, and 42.8 g of 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.

[0385] (Step 4: Drying Stage)

[0386] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0387] (Step 5: Crushing and Classification Stage)

[0388] 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.

[0389] (Step 6: Surface cross-linking step)

[0390] 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.

[0391] 7) Comparative Example 3

[0392] (Step 1: Polymerization step - Manufacturing step of functional gel polymer)

[0393] A functional gel polymer was prepared using the same method as in Example 1.

[0394] (Steps 2 and 3: Atomization and Neutralization Steps)

[0395] 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 2,800 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 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.

[0396] 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.

[0397] (Step 4: Drying Stage)

[0398] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0399] (Step 5: Crushing and Classification Stage)

[0400] 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.

[0401] (Step 6: Surface cross-linking step)

[0402] 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.

[0403] 8) Comparative Example 4

[0404] 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).

[0405] Specifically, the manufacturing process of Comparative Example 4 was as follows.

[0406] (Neutralization and polymerization)

[0407] 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.

[0408] (Chopping)

[0409] 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.

[0410] (dry)

[0411] 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.

[0412] (crushing / classifying)

[0413] 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.

[0414] (Surface cross-linking step)

[0415] 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.

[0416] 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

[0417] The substances A to G in Table 1 above are as follows, and in Table 1 above, '-' means a component not included in the surface cross-linking agent solution, and the unit of each number is g.

[0418] A: Water

[0419] B: Methanol

[0420] C: Ethylene glycol diglycidyl ether

[0421] D: Propylene glycol

[0422] E: Aluminum sulfate

[0423] F: Sucrose stearate

[0424] G: Silica

[0425] Table 1 above indicates the amount of material used per 100g of the base resin powder.

[0426] <Experimental Example 1> - FT-IR spectroscopy (Fourier-transform infrared spectroscopy) analysis

[0427] The superabsorbent resins manufactured in the above examples and comparative examples were each analyzed using FT-IR spectroscopy (Fourier-transform infrared spectroscopy).

[0428] Specifically, the superabsorbent resins of the examples and comparative examples were manufactured in powder form for use as samples. Subsequently, the superabsorbent resins were analyzed using the atomic target laser (ATR) (Diamond) measurement method. Through this, a spectrum capable of analyzing functional groups in a region corresponding to a depth of 1 μm to 2 μm from the outermost layer of the resin surface was derived.

[0429] Figure 1 is a diagram showing an FTIR spectrum derived from FT-IR spectroscopy (Fourier-transform infrared spectroscopy) of Example 1.

[0430] Next, as shown in Fig. 2, a baseline is set based on BL1 and BL2 for each functional group in the FTIR spectrum, and the integral values ​​of the R1 and R2 regions are calculated to calculate the integral value of a specific functional group.

[0431] Specifically, for each functional group, a baseline was set (baseline correction) based on a specific point (BL1, BL2) in Table 2 below, and then the integral value of the area of ​​another specific point (R1, R2) in Table 2 below was obtained. The values ​​of the specific points (BL1, BL2) and (R1, R2) in Table 2 below are determined according to the functional group.

[0432] O-HCOOHAsym. COO-CH2Sym. COO-COC, Si-OBL1 (cm -1 )370017751775148014801265BL2(cm -1 )30001480148013601360880R1(cm -1 )360017401620147014251235R2(cm -1 )306516501510143513751000

[0433] That is, as can be confirmed in Table 2 above, the region corresponding to the COOH functional group in the FTIR spectrum is 1740 cm, which is the wavenumber range of R1 to R2. -1 ~ 1650 cm -1 , and the integral value of the region corresponding to the COOH functional group is 1740 cm -1 ~ 1650 cm -1 It means the integral value in .

[0434] Similarly, in the FTIR spectrum, the region corresponding to the CH2 functional group is 1470 cm, which is the wavenumber range of R1 to R2. -1 ~ 1435 cm -1 , and the integral value of the region corresponding to the CH2 functional group is 1470 cm -1 ~ 1435 cm -1 It means the integral value in .

[0435] The same explanation can be applied to other functional groups.

[0436] This process was repeated five times for each sample, and the average value was calculated, which was defined as the integral value of the area corresponding to a specific functional group.

[0437] Among them, the integral value of the region corresponding to the CH2 functional group, the integral value of the region corresponding to the OH functional group, the integral value of the region corresponding to the symmetric COO- functional group, the integral value of the region corresponding to the asymmetric COO- functional group, the integral value of the region corresponding to the COOH functional group, and the integral value of the region corresponding to the COC functional group and the Si-O functional group are divided by X OH, X COO , X Asym.COO , X Sym.COO and X C-O-C + X Si-O was saved.

[0438] The results are shown in Table 3 below.

[0439] In addition, the ratio of each functional group calculated by Equations 2 to 4 is shown in Table 4 below.

[0440] X OH X COOH X Asym. COO- X Sym. COO- X C-O-C + X Si-O Example 118.40.812.12.85.6Example 212.72.012.32.76.6Example 314.22.212.32.65.5Example 410.52.512.32.611.0Comparative Example 119.23.212.52.56.2Comparative Example 215.82.812.32.-614.7Comparative Example 312.52.711.92.516.5Comparative Example 49.53.512.53.017.0

[0441] Equation 2(X COO + X COOH )Formula 3(X COOH / X COO )Formula 4(X COOH / X Asym.COO )Formula 5(X Asym.COO / X Sym.CO)Example 115.70.0520.064.26Example 2170.1340.164.64Example 317.10.1460.184.73Example 417.40.1670.24.69Comparative Example 118.20.2120.255.06Comparative Example 217.70.1880.234.79Comparative Example 317.10.1880.234.82Comparative Example 4190.2260.284.17

[0442] <Experimental Example 2> - Content of water-soluble components in water with an electrical conductivity of 110 μS / cm

[0443] The water-soluble components were measured for the superabsorbent resins of the examples and comparative examples. The water-soluble components were measured using the EDANA method WSP 270.2.

[0444] Specifically, 1.0 g of a sample having a particle size of 150 to 850 μm among the superabsorbent resins prepared by the methods according to the examples and comparative examples was placed in a 250 mL Erlenmeyer flask, then placed in 200 mL of water having an electrical conductivity of 110 μS / cm, stirred at 250 rpm for 1 hour to allow free swelling, and then the aqueous solution was filtered with filter paper.

[0445] The filtered solution was first titrated to pH 10 with a 0.1 N caustic soda solution, and then back-titrated to pH 2.7 with a 0.1 N hydrogen chloride solution. The amount of non-crosslinked polymer material required for neutralization was calculated as the soluble component (weight %).

[0446] The measurement results of the water-soluble components of the above examples and comparative examples are shown in Table 5 below.

[0447] Content of water-soluble components (%) Swelling time 0.5 hr (weight %) Swelling time 3 hr (weight %) Example 15.6 10.2 Example 27.2 9.4 Example 36.6 10.4 Example 45.5 9.7 Comparative Example 11.5 13.2 Comparative Example 212.5 17.1 Comparative Example 312.9 21.5 Comparative Example 413.2 21.7

[0448] As can be seen in Table 5 above, the superabsorbent resin of the example was found to have a lower content of water-soluble components than the comparative example. In other words, it can be confirmed that the superabsorbent resin according to the present invention can reduce the content of water-soluble components by controlling the content of functional groups present on the resin surface.

[0449] <Experimental Example 3> - Physical Property Evaluation

[0450] Additionally, the properties of the superabsorbent resins manufactured in the above examples and comparative examples were evaluated using the following method and are listed in Table 6 below.

[0451] 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.

[0452] After the sample to be measured was left under constant temperature and humidity conditions for 24 hours, each property was evaluated.

[0453] (1) Centrifuge Retention Capacity (CRC, g / g)

[0454] 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.

[0455] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 241.0.

[0456] 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.

[0457] Using each mass obtained, CRC (g / g) was calculated according to the following mathematical formula 1.

[0458] [Mathematical Formula 1]

[0459] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0460] The above measurement was repeated five times, and the average value and standard deviation were calculated.

[0461] The results are shown in Table 6 below.

[0462] (2) Absorbency under Pressure (AUP: Absorbency under Pressure, g / g)

[0463] 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.

[0464] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 242.0.

[0465] 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.

[0466] 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.

[0467] Using each mass obtained, the pressurized absorbency (g / g) was calculated according to the following mathematical formula 2.

[0468] [Equation 2]

[0469] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0470] The above measurement was repeated five times, and the average value and standard deviation were calculated.

[0471] The results are shown in Table 6 below.

[0472] (3) Effective absorption capacity (EFFC)

[0473] The measured retention capacity and pressurized absorption capacity were applied to Equation 4 below to calculate the effective absorption capacity (EFFC).

[0474] [Formula 7]

[0475] EFFC = (CRC + AUP) / 2

[0476] In the above equation 7,

[0477] CRC is the water retention capacity (unit: g / g) measured according to the method of EDANA method WSP 241.3,

[0478] AUP is the absorbency under pressure (g / g) measured under 0.3 psi according to EDANA method WSP 242.3.

[0479] The results are shown in Table 6 below.

[0480] (4) Absorption speed (Vortex time)

[0481] The absorption rate (vortex time) of the superabsorbent resins of the above examples and comparative examples was measured by the following method.

[0482] 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.

[0483] 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.

[0484] 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.

[0485] 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.

[0486] The results are shown in Table 6 below.

[0487] (5) Free swelling capacity (FSC) in water with an electrical conductivity value of 110 μS / cm 110 ) and 1 minute absorbency (WFA) 110 )

[0488] 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.

[0489] ① Put 18cm x 28cm tea bags for broth into each of 8 2L beakers.

[0490] 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).

[0491] 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).

[0492] ④ Put 18cm x 28cm tea bags for broth into each of 8 other 2L beakers.

[0493] 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.

[0494] 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).

[0495] 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.

[0496] 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.

[0497] [Equation 3]

[0498] FSC 110 (g / g) = W a - W s

[0499] 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.

[0500] [Equation 4]

[0501] WFA 110 (g / g) = W2- W1

[0502] 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.

[0503] The results are shown in Tables 6 and 7 below.

[0504] CRC(g / g)0.3AUP(g / g)EFFC(g / g)Vortex time(sec)WFA 110 (g / g) Example 138.831.735.315211 Example 235.533.534.532187 Example 332.728.630.726136 Example 430.729.230.024139 Comparative Example 139.226.933.14285 Comparative Example 237.42732.242119 Comparative Example 340.621.831.245122 Comparative Example 439.926.433.23991

[0505] 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 60 120 300 600 1800 Example 1 5 9 0 1 2 5 2 1 1 2 6 6 3 4 0 3 6 5 3 8 8 Example 2 4 5 8 0 1 1 0 1 8 7 2 5 5 3 0 7 3 2 3 3 2 Example 3 3 6 6 8 1 0 5 1 3 6 3 0 3 1 9 3 2 1 3 8 8 Example 4 3 8 6 9 1 0 8 1 3 9 2 8 0 3 0 6 3 1 7 3 2 6 Comparative Example 1 1 7 3 1 4 8 8 5 2 0 5 2 8 8 3 1 4 3 1 0 Comparative Example 2 2 9 4 9 7 5 1 1 9 1 6 9 2 8 5 3 4 8 3 7 5 Comparative Example 3 3 5 5 0 7 2 1 2 1 8 5 2 6 7 3 1 3 3 7 2 Comparative Example 425355691189260308337

[0506] As can be seen from Tables 6 and 7 above, it was confirmed that the superabsorbent resin according to the embodiment of the present invention can exhibit excellent physical property balance by simultaneously improving absorption performance such as centrifugal retention capacity and pressurized absorption capacity while improving absorption speed.

Claims

1. As a polyacrylic acid (salt)-based superabsorbent resin, The above resin contains carbon, oxygen and silicon on the surface, A superabsorbent resin having a spectrum derived from analysis of the above resin surface using FT-IR spectroscopy (Fourier-transform infrared spectroscopy) that satisfies the following equation 1: [Formula 1] X COOH ≤ 2.6 In the above equation 1, X COOH means the value obtained by dividing the integral value of the region corresponding to the COOH functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

2. In paragraph 1, The above resin is a superabsorbent resin satisfying the following formula 2: [Formula 2] X COO + X COOH ≤ 18 In the above equation 2, X COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group and the symmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

3. In paragraph 1, The above resin is a superabsorbent resin satisfying the following formula 3: [Formula 3] X COOH / X COO ≤ 0.17 In the above equation 3, X COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group and the symmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

4. In paragraph 1, The above resin is a superabsorbent resin satisfying the following formula 4: [Formula 4] X COOH / X Asym.COO ≤ 0.22 In the above equation 4, X Asym.COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

5. In paragraph 1, The above resin is a superabsorbent resin satisfying the following formula 5: [Formula 5] X Asym.COO / X Sym.COO ≤ 4.75 In the above equation 5, X Asym.COO means the value obtained by dividing the integral value of the region corresponding to the asymmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum, X Sym.COO means the value obtained by dividing the integral value of the region corresponding to the symmetric COO- functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

6. In paragraph 1, The above resin is a superabsorbent resin satisfying the following formula 6: [Formula 6] X C-O-C + X Si-O ≤ 14 In the above equation 6, X C-O-C means the value obtained by dividing the integral value of the region corresponding to the COC functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum, X Si-O means the value obtained by dividing the integral value of the region corresponding to the Si-O functional group within the above spectrum by the integral value of the region corresponding to the CH2 functional group within the above spectrum.

7. 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.

8. 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.

9. 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.

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

3.

11. 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 formula 7: [Formula 7] EFFC = (CRC + AUP) / 2 In the above equation 7, 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.

12. 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.

13. 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 130 g / g or more.

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