Super absorbent polymer

Abstract

The present invention provides a super absorbent polymer in which the absorption properties have been improved by constantly controlling the change in storage elastic modulus according to the degree of swelling of the super absorbent polymer. In particular, the present invention relates to a super absorbent polymer that is excellent in terms of liquid permeability and absorption rate.

Description

superabsorbent resin

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0051626, filed April 17, 2024, and U.S. Patent Application No. 18 / 968,679, filed December 4, 2024, the entire contents of which are incorporated herein by reference.

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

[0004] Super absorbent polymer (SAP) is a synthetic polymer material that can absorb 500 to 1,000 times its own weight in water. Different developers call it by different names, such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material). The above super absorbent polymer began to be put to practical use in products such as diapers and hygiene products, 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, and a freshness-preserving agent and material for steaming in the food distribution industry.

[0005] The above-mentioned superabsorbent polymer is typically incorporated into pulp. However, in recent years, to provide thinner products, the pulp content has been reduced, or even the development of so-called pulpless products that do not use pulp at all has been actively pursued.

[0006] As a result, the product contains a relatively high proportion of superabsorbent polymer, and superabsorbent polymer particles are inevitably incorporated into multiple layers within the product. Furthermore, to ensure that the superabsorbent polymer can absorb large amounts of liquids such as water, saline solution, and urine, its absorbent properties must be enhanced to ensure both high absorption performance and rapid absorption rates.

[0007] That is, the superabsorbent resin must have a high ability to absorb moisture (CRC), and once absorbed, the moisture must not escape easily even when pressure is applied (AUP). In addition, when absorbing water, it must have excellent permeability so that the entire resin, not just the parts that come into direct contact, can absorb it well.

[0008] For this purpose, a method of forming a porous structure within the base resin powder by including a foaming agent in the monomer composition and proceeding with crosslinking polymerization to increase the surface area of ​​the superabsorbent resin is generally used.

[0009] However, the use of a foaming agent resulted in a decline in the physical properties of the superabsorbent resin, such as surface tension, permeability, and bulk density. This made it difficult to maintain its shape in a swollen state. Furthermore, this resulted in an increase in the amount of fine particles generated.

[0010] Conversely, in order to improve the permeability of a superabsorbent resin, when the crosslinking density of the superabsorbent resin is controlled to be high, there is a problem in that the water retention capacity, which is a basic property of the superabsorbent resin, is reduced because it is difficult for moisture to be absorbed between the dense crosslinking structures.

[0011] Therefore, it is not easy to develop a superabsorbent resin that has excellent balance in all properties such as absorption capacity, water retention capacity, permeability, and absorption speed, and therefore research to improve the properties of superabsorbent resins is continuously requested.

[0012] The present invention seeks to provide a superabsorbent polymer (SAP) with improved absorbent properties by consistently controlling changes in storage elastic modulus according to the degree of swelling of the SAP. In particular, the present invention seeks to provide a superabsorbent polymer with excellent liquid permeability and absorption rate.

[0013] The present invention is a polyacrylic acid (salt)-based superabsorbent resin,

[0014] The storage modulus (Pa) of the above superabsorbent resin after swelling by 50% is 4,000 Pa or more,

[0015] A superabsorbent resin is provided, wherein the absolute value of the change in storage elastic modulus at 50% and 100% swelling, as derived by the following Equation 1, is 62 or less:

[0016] [Formula 1]

[0017] Change in storage modulus at 50% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 50% swelling)} / 50].

[0018] The present invention provides a superabsorbent polymer (SAP) having excellent balance in absorbency, water retention capacity, liquid permeability, and absorption rate by constantly controlling the change in storage elastic modulus according to the degree of swelling of the SAP.

[0019] According to one embodiment of the present invention, as a polyacrylic acid (salt)-based superabsorbent resin,

[0020] The storage modulus (Pa) of the above superabsorbent resin after swelling by 50% is 4,000 Pa or more,

[0021] A superabsorbent resin can be provided, wherein the absolute value of the change rate of the storage elastic modulus at 50% and 100% swelling, as derived by the following Equation 1, is 62 or less:

[0022] [Formula 1]

[0023] Change in storage modulus at 50% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 50% swelling)} / 50].

[0024] 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.

[0025] 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.

[0026] The technical terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Furthermore, the singular forms "singular" and "in" also include plural forms, unless the context clearly dictates otherwise.

[0027] The term "polymer" or "high molecular weight polymer" as used in the specification of the present invention means a polymerized state of a water-soluble ethylenically unsaturated monomer, and may encompass any moisture content range or particle size range.

[0028] In addition, the term "superabsorbent resin" is used to encompass, depending on the context, a base resin in powder form consisting of a crosslinked polymer, superabsorbent resin particles obtained by pulverizing the crosslinked polymer, or a crosslinked polymer or base resin that has undergone an additional process, such as drying, pulverization, classification, or surface crosslinking, to make it suitable for commercialization.

[0029] Additionally, the term "fine particles" refers to particles having a particle size of less than 150 μm among superabsorbent resin particles. The particle size of such resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0030] 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.

[0031] 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.

[0032] Additionally, the term "free swelling" refers to a state in which a superabsorbent polymer can swell without a restraining load when absorbing a specific solution.

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

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

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

[0036] The superabsorbent resin of the present invention is characterized in that it has a storage elastic modulus of 4,000 Pa or more after 50% swelling, and when the storage elastic modulus according to the degree of swelling (%) is plotted on a graph, the absolute value of the change rate in the storage elastic modulus at 50% and 100% swelling satisfies 62 or less.

[0037] Storage modulus is an indicator of the amount of elastic energy stored in a vibrating sample, and is a measure of how much elasticity an object can maintain against external deformation.

[0038] Through this storage modulus, the stiffness of an elastic object, i.e., a superabsorbent resin as a sample, can be determined, and through this, the pressurized absorption capacity and liquid permeability of the superabsorbent resin can be determined.

[0039] When the storage modulus value is high, it means that the superabsorbent resin particles have excellent strength, and excellent particle strength means that passages through which fluid can flow can be easily formed between particles, so that the pressurized absorbency can be excellent and the liquid permeability can be improved.

[0040] Therefore, the higher the storage modulus value, the better the permeability of the superabsorbent resin.

[0041] Specifically, the method for deriving the storage modulus (Pa) of a polymer resin is as follows.

[0042] - Step 1) Preparation of superabsorbent resin dilution sample

[0043] The superabsorbent resin sample (30-50 Mesh) was sieved, 0.5 g was weighed, and then sufficiently swelled in a 0.9% NaCl solution for more than 1 hour.

[0044] At this time, the degree of swelling was varied. Based on the water retention capacity (CRC) of the superabsorbent resin measured in advance according to EDANA WSP 241.3, the swelling degree when adding the solution equal to the CRC was taken as 100%, and samples were produced that were swollen by 50%, 70%, and 100%.

[0045] - Step 2) Deriving the storage modulus of superabsorbent resin

[0046] The storage modulus of 2.5 g of a swollen superabsorbent resin sample was measured for 60 seconds at an angular frequency of 10 rad / s under a strain of 10% and a temperature of 25°C using a rheometer (TA ARES-G2).

[0047] At this time, the gap was adjusted to 1 mm between two parallel plates, and pressure was applied with a force of 3 N so that the swollen sample could be sufficiently adhered.

[0048] Under these measurement conditions, all resins exhibited a uniform storage modulus for 60 seconds without leaving the linear viscoelastic range, and the values ​​obtained at this time were used to measure the horizontal storage modulus of the sample.

[0049] The storage elastic modulus of the samples in which the superabsorbent resin was swollen by 50%, 70%, and 100%, respectively, was derived using the above method, and the change rate of the storage elastic modulus according to the degree of swelling (%) was calculated according to Equations 1 to 3 below.

[0050] [Formula 1]

[0051] Change in storage modulus at 50% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 50% swelling)} / 50]

[0052] [Formula 2]

[0053] Change in storage modulus at 50% and 70% swelling = [{(storage modulus at 70% swelling)-(storage modulus at 50% swelling)} / 20]

[0054] [Formula 3]

[0055] Change in storage modulus at 70% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 70% swelling)} / 30]

[0056] Until now, the properties of superabsorbent resins have been observed mainly in a dried or fully swollen state, and the properties of the swollen resin have not been observed in detail.

[0057] However, unlike absorbency or water retention capacity, in the case of permeability or absorption rate, the properties when the fluid has been absorbed to a certain extent are more important than the properties before or after the fluid has been absorbed.

[0058] In particular, checking the properties of superabsorbent resin particles in a somewhat swollen state as well as in a dry or fully swollen state, such as storage modulus, helps to more accurately determine the absorption characteristics of the superabsorbent resin.

[0059] Accordingly, the inventors of the present invention observed the storage elastic modulus according to the degree of swelling by paying attention to the properties of the swollen resin, and found that when the storage elastic modulus in the intermediate swelling state has a value within a certain range and the storage elastic modulus in the late or fully swollen state does not decrease significantly compared to the storage elastic modulus in the intermediate swelling state (i.e., when it shows a gradual decrease to a certain level), the superabsorbent resin can have excellent absorption performance such as water retention capacity, permeability, and absorption speed in a balanced manner.

[0060] Specifically, the present invention was completed by discovering that when the storage elastic modulus at 50% swelling, which is a medium-swelling state, has a specific numerical range and the storage elastic moduli at 70% and 100% swelling do not show a large difference compared to the storage elastic modulus at 50% swelling, that is, when the storage elastic modulus at 70% and 100% swelling is maintained at a certain level, excellent absorption properties are exhibited.

[0061] At this time, the storage elastic modulus at 50% swelling means that the superabsorbent resin has absorbed only 50% of the saline solution that it can hold, the storage elastic modulus at 70% swelling means that the superabsorbent resin has absorbed only 70% of the saline solution that it can hold, and the storage elastic modulus at 100% swelling means that the superabsorbent resin has absorbed 100% of the saline solution that it can hold.

[0062] The strength of the superabsorbent resin particles in the intermediate state in which the superabsorbent resin has absorbed the fluid can be confirmed through the storage modulus at 50% swelling, the strength of the superabsorbent resin particles in the later state in which the superabsorbent resin has absorbed the fluid can be confirmed through the storage modulus at 70% swelling, and the strength of the superabsorbent resin particles in the state in which the superabsorbent resin has completely absorbed the fluid can be confirmed through the storage modulus at 100% swelling.

[0063] A high storage modulus indicates superior strength of the superabsorbent resin particles. Furthermore, superior particle strength facilitates the formation of fluid-permeable passages between particles, resulting in superior liquid permeability. Therefore, a superabsorbent resin with a high storage modulus is preferable in terms of liquid permeability.

[0064] However, if the permeability of a superabsorbent polymer is excessively high, its absorption performance may deteriorate. In other words, permeability and absorption performance are in a trade-off relationship, and thus, optimizing both permeability and absorption performance is necessary to provide superior superabsorbent polymers.

[0065] In particular, if the storage modulus of the superabsorbent polymer is too small in a moderately swollen state, the strength of the particles due to fluid absorption may become too small, which may result in poor physical properties such as liquid permeability. On the other hand, if the storage modulus is too large, the strength of the particles may remain large despite fluid absorption, which may result in excessive liquid permeability. Therefore, it is desirable from the perspective of absorption performance that the storage modulus in a 50% swollen state be within a certain range.

[0066] Therefore, it is desirable for the storage elastic modulus, which is related to the permeability, to be within an appropriate range during the swelling process in terms of the absorption performance of the superabsorbent resin.

[0067] The superabsorbent resin according to the present invention has a storage elastic modulus of 4,000 Pa or more after 50% swelling, and the absolute value of the change rate of the storage elastic modulus at 50% and 100% swelling, derived by the following equation, is a specific value of 62 or less.

[0068] [Formula 1]

[0069] Change in storage modulus at 50% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 50% swelling)} / 50]

[0070] The superabsorbent resin of the present invention may have an absolute value of change in storage elastic modulus at 50% and 100% swelling of 62 or less, 61 or less, 60 or less, or 59 or less.

[0071] In the case where there is no change at all in the storage elastic modulus at 50% and 100% swelling, the lower limit of the absolute value of the rate of change in the storage elastic modulus is theoretically 0, but may be, for example, 10 or more, 15 or more, or 20 or more.

[0072] The superabsorbent resin of the present invention may have an absolute value of the change rate of the storage elastic modulus at 50% and 70% swelling derived by the following Equation 2 of 70 or less, 65 or less, 60 or less, or 58 or less.

[0073] [Formula 2]

[0074] Change in storage modulus at 50% and 70% swelling = [{(storage modulus at 70% swelling)-(storage modulus at 50% swelling)} / 20]

[0075] Similarly, if there is no change at all in the storage modulus at 50% and 70% swelling, the lower limit of the absolute value of the rate of change in the storage modulus is theoretically 0, but may be, for example, 10 or more, 15 or more, or 20 or more.

[0076] The superabsorbent resin of the present invention may have an absolute value of the rate of change in storage elastic modulus at 70% and 100% swelling derived by the following equation 3 of 70 or less, 68 or less, 65 or less, or 63 or less.

[0077] [Formula 3]

[0078] Change in storage modulus at 70% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 70% swelling)} / 30]

[0079] Similarly, if there is no change at all in the storage modulus at 70% and 100% swelling, the lower limit of the absolute value of the rate of change in the storage modulus is theoretically 0, but may be, for example, 10 or more, 15 or more, or 20 or more.

[0080] In one embodiment of the present invention, the superabsorbent resin may have a storage elastic modulus value at 50% swelling of 4,000 Pa or more, 4,100 Pa or more, 4,200 Pa or more, or 4,300 Pa or more.

[0081] In one embodiment of the present invention, the superabsorbent resin may have a storage elastic modulus value at 50% swelling of 6,000 Pa or less, 5,500 Pa or less, 5,000 Pa or less, or 4,900 Pa or less.

[0082] In one embodiment of the present invention, the superabsorbent resin can satisfy a range in which the storage elastic modulus value at 70% swelling is 3,000 Pa or more, 3,200 Pa or more, 3,400 Pa or more, or 3,600 Pa or more, and at the same time 5,000 Pa or less, 4,500 Pa or less, 4,000 Pa or less, or 3,800 Pa or less.

[0083] In one embodiment of the present invention, the superabsorbent resin can satisfy a range in which the storage elastic modulus value at 100% swelling is 1,500 Pa or more, 1,600 Pa or more, 1,700 Pa or more, or 1,800 Pa or more, and at the same time 3,000 Pa or less, 2,950 Pa or less, 2,900 Pa or less, or 2,850 Pa or less.

[0084] The superabsorbent resin of the present invention has a storage modulus at the intermediate swelling stage of a predetermined value compared to conventional superabsorbent resins, so that both permeability and water retention capacity can be excellent, and even at the late and complete swelling stage, the decrease in storage modulus due to swelling is not great, so that both permeability and water retention capacity can be appropriately maintained, and even when some fluid is absorbed, the absorption rate does not decrease significantly, so that an excellent absorption rate can be maintained from the early to mid to late absorption stages.

[0085] The superabsorbent resin of the present invention has a storage elastic modulus in a medium-term state of fluid absorption, and the decrease in the storage elastic modulus of the resin is not large as it moves from the medium-term state of fluid absorption to the late-term state, and satisfies a specific range. This can be seen as meaning that the absorption rate and amount of fluid in the medium-term state are large, while the absorption rate and amount do not change significantly as time passes.

[0086] The superabsorbent polymer of the present invention may have a water retention capacity (CRC) measured according to EDANA method WSP 241.3 of about 33 g / g or more, about 34 g / g or more, or about 35 g / g or more, and about 50 g / g or less, about 45 g / g or less, or about 40 g / g or less.

[0087] Additionally, the superabsorbent polymer of the present invention may have an absorbency under pressure (AUP) of about 25 g / g or more, about 27 g / g or more, about 28 g / g or more, about 29 g / g or more, or about 30 g / g or more, and about 45 g / g or less, about 42 g / g or less, or about 40 g / g or less, at 2.07 kPa (0.3 psi) as measured according to EDANA method WSP 242.3.

[0088] The superabsorbent resin of the present invention may have a vortex time of 40 seconds or less as measured by a vortex measurement method at 24.0°C.

[0089] More specifically, the vortex time may be 40 seconds or less, 35 seconds or less, 33 seconds or less, or 30 seconds or less. In addition, the vortex time is better as its value decreases, and the lower limit of the vortex time is theoretically 0 seconds, but may be, for example, 10 seconds or more, 15 seconds or more, or 20 seconds or more.

[0090] The method for measuring the water retention capacity, pressurized absorption capacity and vortex time of the above superabsorbent resin is described in more detail in the experimental examples described below.

[0091] In one embodiment of the present invention, the superabsorbent resin may have a permeability of 3 ml / min or more, as calculated by the following Equation 4. More preferably, the permeability may be 3.5 ml / min or more, 4 ml / min or more, 4.5 ml / min or more, or 5 ml / min or more, and 7 ml / min or less, 6.8 ml / min or less, 6.6 ml / min or less, or 6.4 ml / min or less.

[0092] [Formula 4]

[0093] Perm = [20 mL / T1 (sec)] x 60 sec

[0094] In the above equation 4,

[0095] Perm is the permeability of superabsorbent resin,

[0096] T1 means the time (seconds) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin under a pressure of 2.07 kPa (0.3 psi) after placing 0.2 g of superabsorbent resin in a cylinder, pouring saline solution (0.9 wt% sodium chloride aqueous solution) so that the superabsorbent resin is completely submerged, and the superabsorbent resin is swelled for 30 minutes.

[0097] The above permeability refers to the mobility of the solution within the superabsorbent resin, and a higher value means better permeability.

[0098] That is, the superabsorbent resin according to the present invention may have a T1 of 400 seconds or less. More preferably, the T1 may be 300 seconds or less, 250 seconds or less, or 200 seconds or less. The smaller the value, the better. The theoretical lower limit of the T1 is 0 seconds. However, for example, it may be 3 seconds or more, 5 seconds or more, or 10 seconds or more.

[0099] "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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] However, superabsorbent polymers are widely used in various applications, including as horticultural soil conditioners, water-retaining materials for civil engineering and construction, nursery sheets, and freshness-preserving agents and steaming agents in food distribution. In these applications, excellent absorption behavior of water-soluble components in water with an electrical conductivity of 100 to 130 μS / cm is required.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] Accordingly, the inventors of the present invention sought to develop a superabsorbent resin having an excellent absorption rate and absorption capacity for water having an electrical conductivity of 100 to 130 μS / cm, which has a lower ion concentration and electrical conductivity than 0.9% saline water, that is, an electrical conductivity of about 1 / 100 of 0.9% saline water, and implemented this by constantly controlling the change in storage elastic modulus according to the degree of swelling of the superabsorbent resin.

[0111] Since there is no significant difference in absorption characteristics for water within the range of 100 to 130 μS / cm in electrical conductivity, water within this range in electrical conductivity can be used. For example, water with an electrical conductivity of 110 μS / cm can be used.

[0112] In one embodiment of the present invention, the content of a water-soluble component measured after the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 1 hour may be 15 wt% or less, 14 wt% or less, 13 wt% or less, or 12 wt% or less based on the total weight of the superabsorbent resin. In addition, the lower the value of the water-soluble component, the better, and the lower limit is theoretically 0 wt%, but may be, for example, 1 wt% or more, 2 wt% or more, or 3 wt% or more.

[0113] When the amount of the water-soluble component dissolved in water having an electrical conductivity of 100 to 130 μS / cm is below a certain level, the conflicting properties of absorption characteristics and liquid permeability are simultaneously improved, so that a superabsorbent resin having an excellent balance of physical properties can be realized. However, if the content of the water-soluble component measured after the superabsorbent resin is freely swelled for 1 hour in water having an electrical conductivity of 100 to 130 μS / cm exceeds 15 wt% with respect to the total weight of the superabsorbent resin, the polymer chain cross-linking characteristics cannot be said to be excellent, and when the superabsorbent resin comes into contact with the skin in a swollen state, it may cause discomfort or damage the skin, etc.

[0114] In one embodiment of the present invention, the superabsorbent resin may have a water-soluble component content of 25 wt% or less, 23 wt% or less, 21 wt% or less, or 19 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 16 hours. Similarly, the water-soluble component content is better as the value thereof decreases, and the lower limit is theoretically 0 wt%, but may be, for example, 1 wt% or more, 2 wt% or more, or 3 wt% or more.

[0115] The amount of water-soluble components eluted after freely swelling the above superabsorbent resin for 16 hours means the total content of water-soluble components contained in the above superabsorbent resin.

[0116] If the content of the water-soluble component measured after the superabsorbent resin is allowed to swell freely in water having an electrical conductivity of 100 to 130 μS / cm for 16 hours exceeds 25 wt% with respect to the total weight of the superabsorbent resin, crosslinking may be incomplete during polymerization of the superabsorbent resin, and thus the overall physical properties of the superabsorbent resin, such as water retention capacity and pressure absorption capacity, may significantly deteriorate.

[0117] The superabsorbent resin of the present invention can control the amount of dissolved components in water having an electrical conductivity of 100 to 130 μS / cm to a certain level or less by having excellent internal cross-linking properties, and accordingly, the overall physical properties of the superabsorbent resin, such as water retention capacity, pressure absorption capacity, and absorption speed, can also be improved.

[0118] Specifically, the superabsorbent resin of the present invention may have a maximum capacity of water that the superabsorbent resin can hold (Free Swell Capacity) of 70 g or more, 75 g or more, or 80 g or more when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 30 seconds.

[0119] The maximum capacity of water that the superabsorbent resin can hold (Free Swell Capacity) can be seen as the greater the value, the more water with an electrical conductivity of 100 to 130 μS / cm can be absorbed. However, for example, the maximum capacity of water that the superabsorbent resin can hold in 30 seconds may be 200 g or less, 180 g or less, or 150 g or less.

[0120] In addition, the superabsorbent resin of the present invention may have a maximum capacity of water that the superabsorbent resin can hold (Free Swell Capacity) of 200 g or more, 220 g or more, or 240 g or more when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 120 seconds.

[0121] Likewise, the maximum capacity of water that the superabsorbent resin can hold (Free Swell Capacity) can be seen as absorbing more water having an electrical conductivity of 100 to 130 μS / cm as the value increases. However, for example, the maximum capacity of water that the superabsorbent resin can hold at 120 seconds may be 400 g or less, 350 g or less, or 320 g or less.

[0122] When the above-mentioned superabsorbent resin is used in the field of sanitary materials such as diapers or sanitary pads, it is required to have a rapid drying ability when in contact with moisture and to have excellent initial absorbency. In order to evaluate the initial absorbency of the above-mentioned superabsorbent resin, the maximum absorbency at 30 seconds and 120 seconds was measured, and it was confirmed that the superabsorbent resin according to the present invention has excellent initial absorbency.

[0123] Specifically, the maximum capacity of water that a superabsorbent resin can hold when freely swollen for 30 seconds refers to the absorption capacity in the ultra-initial stage when the superabsorbent resin immediately absorbs water having an electrical conductivity of 100 to 130 μS / cm, and the maximum capacity of water that a superabsorbent resin can hold when freely swollen for 120 seconds refers to the absorption capacity in the initial stage when the superabsorbent resin encounters water having an electrical conductivity of 100 to 130 μS / cm. At this time, the distinction between the ultra-initial stage and the initial stage is relative, and is an arbitrarily divided section for comparing the initial absorption capacities of the superabsorbent resins.

[0124] The above superabsorbent resin has an absorption capacity of 70 g / g or more when freely swelled for 30 seconds in water having an electrical conductivity of 100 to 130 μS / cm, confirming that it absorbs water immediately, and has an absorption capacity of 200 g / g or more when freely swelled for 120 seconds, confirming that it has excellent initial absorption capacity.

[0125] 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.

[0126] The superabsorbent resin of the present invention may have an average absorption rate of 2.5 g / g / sec or more, 2.6 g / g / sec or more, or 2.7 g / g / sec or more when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm at 0 to 30 seconds.

[0127] The above average absorption rate is better the higher the value, and there is no theoretical upper limit to the above average rate. However, for example, when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm, the average absorption rate at 0 to 30 seconds may be 10 g / g / sec or less, 9 g / g / sec or less, or 8 g / g / sec or less.

[0128] In addition, when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm, the average absorption rate at 30 to 120 seconds may be 1.4 g / g / sec or more, 1.5 g / g / sec or more, or 1.6 g / g / sec or more.

[0129] Likewise, the average absorption rate is better the higher the value, and there is no theoretical upper limit to the average rate. However, for example, when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm, the average absorption rate at 30 to 120 seconds may be 8 g / g / sec or less, 7 g / g / sec or less, or 6 g / g / sec or less.

[0130] Similarly, in order to evaluate the initial absorption capacity of the superabsorbent resin, the absorption section for water having an electrical conductivity of 100 to 130 μS / cm was divided into 0 to 30 seconds and 30 to 120 seconds, and the average absorption rate in each section was measured.

[0131] The superabsorbent resin has an average absorption rate of 2.7 g / g / sec or more in 0 to 30 seconds when freely swollen in water having an electrical conductivity of 100 to 130 μS / cm, confirming that absorption occurs very immediately upon contact with water. The superabsorbent resin has an excellent initial absorption rate, confirming that the average absorption rate of 1.5 g / g / sec or more in 30 to 120 seconds is confirming that the average absorption rate of 1.5 g / g / sec or more in 30 to 120 seconds.

[0132] The method for measuring the average absorption rate by section in water having an electrical conductivity value of 100 to 130 μS / cm will be described in more detail in the experimental example section described below.

[0133] In one embodiment of the present invention, the superabsorbent polymer may have a gel strength of 0.7N or more, 0.8N or more, or 0.9N or more after swelling the superabsorbent polymer with 50ml of saline solution containing 0.005% ASC. In addition, the gel strength may be 1.5N or less, 1.4N or less, 1.3N or less, 1.2N or less, 1.1N or less, or 1.0N or less. By having such a high gel strength, the amount of fine particles generated due to crushing and damage to surface crosslinking can be reduced, thereby preventing deterioration of physical properties. In addition, even if the superabsorbent polymer absorbs water and increases in volume, the shape can be well maintained, and as a result, improved absorbency and liquid permeability can be exhibited. The method for measuring the gel strength of the superabsorbent polymer will be described in more detail in the experimental examples section described below.

[0134] 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 in which the change in storage elastic modulus according to the degree of swelling is constant.

[0135] 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, amount and timing of introduction of the atomization device, the rotation speed, the hole size, the number of atomizations, etc. can be controlled to have a constant value for the change in the storage elastic modulus according to the degree of swelling.

[0136] Below, each component that makes up the superabsorbent resin will be explained in more detail.

[0137] A polyacrylic acid (salt)-based superabsorbent resin of one embodiment of the invention comprises a base resin comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent. The crosslinked polymer can preferably be formed by polymerizing a monomer composition comprising components such as a monomer, an internal crosslinking agent, and a polymerization initiator.

[0138] 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:

[0139] [Chemical Formula 1]

[0140] R-COOM'

[0141] In the above chemical formula 1,

[0142] R is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

[0143] M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0144] 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.

[0145] 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.

[0146] The above-mentioned water-soluble ethylenically unsaturated monomer has acidic groups. 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.

[0147] 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%.

[0148] The term 'internal crosslinking agent' used in this specification is a term used to distinguish it from a surface crosslinking agent for performing a crosslinking reaction on the surface of superabsorbent resin particles described below, and it serves to form a polymer including a crosslinked structure by introducing crosslinking bonds between unsaturated bonds of the water-soluble ethylenically unsaturated monomers described above.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] Accordingly, the gel strength of the superabsorbent resin being manufactured can be increased, process stability can be improved during the discharging process after polymerization, and the amount of water-soluble components can be minimized.

[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 preservative 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, 0.05 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.7 parts by weight or less, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the internal cross-linking agent is too low, cross-linking may not occur sufficiently, making it difficult to achieve a strength higher than an appropriate level, and if the content of the internal cross-linking agent is too high, the internal cross-linking density may increase, making it difficult to achieve a desired water retention capacity. In particular, the superabsorbent polymer according to the present invention is suitable for implementing a change in storage elastic modulus according to the degree of swelling to have a constant value within the above range.

[0158] When a low content 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 for the operation of 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 properties of the superabsorbent resin, such as water retention capacity and pressure absorption capacity, can be significantly improved compared to the case of a two-dimensional linear structure that is not further crosslinked by an internal crosslinking agent.

[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 excessively low, the polymerization rate may be slowed and a large amount of residual monomer may be extracted from the final product, which is not preferable. Conversely, if the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network may become shorter, which may increase the content of water-soluble components and lower the pressure absorbency, thereby deteriorating the physical properties of the resin, which is not preferable.

[0164] 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 a temperature 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 preservative 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%, 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 by this method can form a polymer with a high molecular weight and uniform molecular weight distribution by polymerizing it using an ethylenically unsaturated monomer in an unsaturated state. This reduces the content of water-soluble components, thereby improving the performance of the superabsorbent resin.

[0175] Additionally, the polymer may have a moisture content of 30 to 80 wt%. For example, the moisture content of the polymer may be at least 30 wt%, at least 45 wt%, or at least 50 wt%, but at most 80 wt%, at most 70 wt%, or at most 60 wt%.

[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] Throughout this specification, "moisture content" refers to the moisture content in relation to the total weight of the polymer, 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 approximately 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; 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, ethylene carbonate-propylene carbonate (ECPC), propylene glycol, and / or glycerol carbonate may be used.

[0182] Such a surface cross-linking agent may be used in an amount of about 0.001 to about 5 parts by weight based on 100 parts by weight of the superabsorbent resin particles. For example, the surface cross-linking agent may be used in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.05 parts by weight or more, and 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less 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. In particular, the superabsorbent resin of the present invention is suitable for implementing a change in storage elastic modulus according to the degree of swelling to have a constant value within the above range.

[0183] 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.

[0184] As such inorganic materials, one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate can be used. The inorganic material can be used in powder or liquid form, and in particular, can be used as alumina powder, silica-alumina powder, titania powder, or nano silica solution. In addition, the inorganic material can be used in an amount of about 0.001 to about 1 part by weight based on 100 parts by weight of superabsorbent resin particles.

[0185] 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.

[0186] Ⅱ. Manufacturing method of superabsorbent resin

[0187] 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.

[0188] 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 deteriorated the properties of the superabsorbent polymer.

[0189] 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.

[0190] 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 the atomization device, the rotation speed, the hole size, the number of atomizations, the components and content of the surface cross-linking solution, etc., can be controlled so that the change in the storage elastic modulus according to the degree of swelling of the superabsorbent resin has a constant value.

[0191] In particular, when carrying out a polymerization process, atomization method, and a surface cross-linking process in the manufacturing process of a superabsorbent resin, the change in storage elastic modulus according to the degree of swelling of the superabsorbent resin can be controlled to have a constant value by controlling the neutralization time and polymerization conditions, whether to apply an ultra-fine chain process, controlling the components and content of the surface cross-linking solution, controlling the hole size, or controlling the number of atomizations.

[0192] Hereinafter, each step of the method for manufacturing a superabsorbent resin according to an embodiment will be described in more detail.

[0193] Step 1: Polymerization stage

[0194] 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.

[0195] 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.

[0196] Here, the contents of each component can be equally applied to the contents described in the superabsorbent resin of the aforementioned item Ⅰ.

[0197] The above-described water-soluble ethylenically unsaturated monomer has an acidic group. As previously explained, in the production of conventional superabsorbent resins, a monomer in which at least a portion of the acidic groups are neutralized by a neutralizing agent is crosslinked and polymerized to form a polymer. Specifically, in the step of mixing the water-soluble ethylenically unsaturated monomer having the acidic group, an internal crosslinking agent, a polymerization initiator, and a neutralizing agent, at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer are neutralized.

[0198] However, according to one embodiment of the present invention, polymerization is first performed in a state where the acidic group of the water-soluble ethylenically unsaturated monomer is not neutralized to form a polymer.

[0199] 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.

[0200] 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.

[0201] In addition, since it is possible to form a polymer with a longer chain, it is possible to achieve the effect of reducing the content of water-soluble components that exist in a non-crosslinked state due to incomplete polymerization or crosslinking, and accordingly, it is suitable for implementing a superabsorbent resin in which the change in storage elastic modulus according to the degree of swelling has a constant value.

[0202] In addition, if polymerization is first performed in a state where the acidic groups of the monomer are not neutralized to form a polymer, and then the polymer is micronized in the presence of a surfactant after neutralization, or the polymer is micronized in the presence of a surfactant and then neutralized, or the acidic groups present in the polymer are neutralized simultaneously with the micronization, the surfactant can sufficiently play a role in reducing the adhesiveness of the polymer by being present in large quantities on the surface of the polymer.

[0203] 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.

[0204] 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.

[0205] When the above polymerization is performed as a continuous polymerization, for example, when the polymerization is performed in a reactor 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 entire monomer composition, which may result in a deterioration of the overall physical properties.

[0206] 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.

[0207] 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.

[0208] 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 components is as described above.

[0209] Steps 2 and 3: Atomization and neutralization steps

[0210] Next, a step (step 2) is included in which the functional gel polymer is micronized in the presence of a surfactant to prepare a mixture including the micronized functional gel polymer.

[0211] 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.

[0212] 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.

[0213] When 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, aggregated hydrogel particles having finer pores can be formed.

[0214] 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, the superabsorbent resin of the present invention is suitable for implementing a change in storage elastic modulus according to the degree of swelling to have a constant value.

[0215] 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.

[0216] 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.

[0217] At this time, the hole size provided in the porous plate of the atomization device may be 1 mm to 25 mm, 5 mm to 20 mm, or 5 mm to 15 mm.

[0218] 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.

[0219] The above atomization step may be performed one or more times, preferably one to six times, one to four times, or one to three times. This may be performed using a plurality of atomization devices, a single atomization device comprising a plurality of porous plates and / or a plurality of cutter elements, or some of the plurality of atomization devices may comprise a plurality of porous plates and / or a plurality of cutter elements.

[0220] 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.

[0221] Preferably, the surfactant may be a compound represented by the following chemical formula 2 or a salt thereof, but the present invention is not limited thereto:

[0222] [Chemical Formula 2]

[0223]

[0224] In the above chemical formula 2,

[0225] A1, A2 and A3 are each independently a single bond, carbonyl, , or and, provided that at least one of these is carbonyl or , wherein, m1, m2 and m3 are each independently an integer from 1 to 8, are each connected to an adjacent oxygen atom, are connected to adjacent R1, R2 and R3 respectively,

[0226] R1, R2 and R3 are each independently hydrogen, straight or branched chain alkyl having 6 to 18 carbon atoms or straight or branched chain alkenyl having 6 to 18 carbon atoms,

[0227] n is an integer from 1 to 9.

[0228] The above surfactant is added so that the atomization step can be easily achieved without agglomeration by mixing with the polymer.

[0229] The surfactant represented by the above chemical formula 2 is a nonionic surfactant, and has excellent surface adsorption performance by hydrogen bonding even with a polymer that is not neutralized, and is therefore suitable for implementing the desired coagulation control effect. On the other hand, in the case of anionic surfactants, not nonionic surfactants, when mixed with a polymer that has been neutralized with a neutralizing agent such as NaOH or Na2SO4, the Na ionized in the carboxyl group substituent of the polymer + It is adsorbed through ions, and when mixed with an unsaturated polymer, there is a problem that the adsorption efficiency for the polymer is relatively reduced due to competition with the anion of the carboxyl group substituent of the polymer.

[0230] Specifically, in the surfactant represented by the above chemical formula 2, the hydrophobic functional group is the terminal functional group R1, R2, R3 portion (if not hydrogen), and the hydrophilic functional group is the glycerol-derived portion in the chain and the terminal hydroxyl group (A n is a single bond, and at the same time R nWhen hydrogen is present, n=1~3) is further included, and the glycerol-derived portion and the terminal hydroxyl group serve as hydrophilic functional groups to improve the adsorption performance on the polymer surface. Accordingly, the aggregation of superabsorbent resin particles can be effectively suppressed.

[0231] In the above chemical formula 2, the hydrophobic functional groups R1, R2, and R3 (if not hydrogen) are each independently a straight-chain or branched alkyl having 6 to 18 carbon atoms or a straight-chain or branched alkenyl having 6 to 18 carbon atoms. In this case, if the R1, R2, and R3 portions (if not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, there is a problem that the agglomeration control of the pulverized particles is not effectively performed due to the short chain length, and if the R1, R2, and R3 portions (if not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the surfactant may be reduced so that it may not be effectively mixed with the polymer, and there may be a problem that the unit price of the composition increases due to the increase in the cost of the surfactant.

[0232] Preferably, R1, R2, R3 may be hydrogen, or, if it is a straight-chain or branched alkyl having 6 to 18 carbon atoms, 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl, or, if it is a straight-chain or branched alkenyl having 6 to 18 carbon atoms, 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-dekenyl, 2-undekenyl, 2-dodekenyl, 2-tridekenyl, 2-tetradekenyl, 2-pentadekenyl, 2-hexadekenyl, It can be 2-heptadekenyl or 2-octadekenyl.

[0233] The surfactant may be selected from compounds represented by the following chemical formulas 2-1 to 2-14, but is not limited thereto:

[0234] [Chemical Formula 2-1]

[0235]

[0236] [Chemical Formula 2-2]

[0237]

[0238] [Chemical Formula 2-3]

[0239]

[0240] [Chemical Formula 2-4]

[0241]

[0242] [Chemical Formula 2-5]

[0243]

[0244] [Chemical Formula 2-6]

[0245]

[0246] [Chemical Formula 2-7]

[0247]

[0248] [Chemical Formula 2-8]

[0249]

[0250] [Chemical Formula 2-9]

[0251]

[0252] [Chemical Formula 2-10]

[0253]

[0254] [Chemical Formula 2-11]

[0255]

[0256] [Chemical Formula 2-12]

[0257]

[0258] [Chemical Formula 2-13]

[0259]

[0260] [Chemical Formula 2-14]

[0261] .

[0262] 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.

[0263] 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.

[0264] Therefore, for example, the surfactant may be used in an amount of 0.06 g or more, 0.1 g or more, or 0.2 g or more, and 0.48 g or less, 0.45 g or less, or 0.4 g or less per 1,000 g of the functional gel polymer. In this case, it is easy to control the change in storage elastic modulus according to the degree of swelling of the superabsorbent resin so that it has a constant value.

[0265] 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.

[0266] 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.

[0267] When the above 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 90%.

[0268] 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] In particular, by adjusting the rotation speed of the screw-type extruder to 150 rpm to 500 rpm, the change in storage elastic modulus according to the degree of swelling of the superabsorbent resin can be controlled to have a constant value.

[0275] 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.

[0276] In addition, the degree of neutralization, which refers to the degree of neutralization of acidic groups contained in the polymer by the neutralizing agent, may be 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to 80 mol%. The range of the degree of neutralization may vary depending on the final physical properties, and the absorption rate and absorption performance may be controlled by controlling the degree of neutralization.

[0277] 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.

[0278] 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.

[0279] Step 4: Drying

[0280] Next, a step (step 4) is performed to dry the above-mentioned micronized and neutralized polymer to prepare a base resin powder.

[0281] 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.

[0282] 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.

[0283] The above step 4 can be performed in a fixed-bed type drying method, a moving type drying method, or a combination thereof.

[0284] According to one embodiment of the invention, step 4 can be performed by static drying.

[0285] 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.

[0286] Since static drying dries in a plate-like shape without particle movement, it is difficult to achieve uniform drying with a simple flow of hot air. Therefore, static drying requires delicate control of hot air and temperature to obtain a uniform, high-moisture content dried body. In the present invention, by changing the hot air direction from downward to upward, warping of the plate-like dried body during drying was prevented, thereby preventing hot air from escaping. In addition, the drying temperature was changed section by section so that the upper, middle, and lower layers within the dried body could be uniformly dried with a moisture content deviation of less than 5%.

[0287] 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.

[0288] In the above-described static drying step, the drying process may be performed at a temperature of about 80°C to 200°C, preferably 90°C to 190°C or 100°C to 180°C. If the drying temperature is lower than 80°C, the drying time may be excessively long, and if the drying temperature is excessively high, exceeding 200°C, a superabsorbent resin having a moisture content lower than the desired moisture content may be obtained. The drying temperature may refer to the temperature of the hot air used or the internal temperature of the device during the drying process.

[0289] According to one embodiment of the invention, step 4 may be performed by fluid drying.

[0290] The fluidized drying method described above refers to a method of drying in which the material is mechanically stirred during the drying process. The direction in which the hot air passes through the material may be the same as or different from the direction in which the material circulates. Alternatively, the material can be dried by circulating the heat-generating fluid (heat-generating oil) within the dryer and passing it through a separate pipe outside the dryer.

[0291] 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.

[0292] 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.

[0293] Step 5: Grinding Stage

[0294] Next, a step of grinding the dried base resin powder is performed.

[0295] 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.

[0296] The crusher used for this purpose may be, specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, or a disc cutter, but is not limited to the examples described above.

[0297] 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.

[0298] In the manufacturing method of the present invention, superabsorbent resin particles having a smaller particle size distribution than in the conventional chopping step can be realized in the micronization step, and since the moisture content after drying is maintained relatively high, even if the pulverization is performed under mild conditions with less pulverizing force, a superabsorbent resin having a very high content of normal particle sizes of 150 ㎛ to 850 ㎛ can be formed, and the fine powder generation ratio can be greatly reduced.

[0299] 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.

[0300] In addition, the superabsorbent resin particles may include fine particles having a particle size of less than 150 μm in an amount of about 20 wt% or less, about 18 wt% or less, about 15 wt% or less, about 13 wt% or less, about 12 wt% or less, about 11 wt% or less, about 10 wt% or less, about 9 wt% or less, about 8 wt% or less, or about 5 wt% or less, relative to the total weight. This is in contrast to having fine particles in an amount of more than about 20 wt% to about 30 wt% when producing a superabsorbent resin according to a conventional manufacturing method.

[0301] Additive injection stage

[0302] According to one embodiment of the invention, the step of adding an additive to the atomized and neutralized polymer before the drying step (step 4) may be further included.

[0303] 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 anti-caking agent for recycling the generated fine powder, a fluidity improver, an antioxidant, a neutralizer, a surfactant, etc.

[0304] 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.

[0305] 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.

[0306] 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.

[0307] Classification stage

[0308] 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.

[0309] Surface cross-linking step

[0310] 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.

[0311] The description of the above surface cross-linking agent can be applied equally to all of the above.

[0312] 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.

[0313] 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.

[0314] 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.

[0315] The temperature raising means for the above surface crosslinking reaction is not particularly limited.

[0316] 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.

[0317] Post-processing step

[0318] 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.

[0319] 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.

[0320] Additionally, after the above-mentioned singer step, a further maturation step can be performed.

[0321] 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.

[0322] 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.

[0323] 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.

[0324] The description of the method for producing the superabsorbent resin of the present invention can be applied to the superabsorbent resin of the present invention described above.

[0325] 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.

[0326] <Example>

[0327] Example 1

[0328] (Step 1: Polymer manufacturing step)

[0329] In a 5 L glass vessel equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 4.5 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 3402 g of water were stirred and mixed, and reacted while maintaining the temperature at 5 ° C. The glass vessel containing the mixture was replaced with nitrogen conditions by introducing 1,000 cc / min of nitrogen for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution as a polymerization initiator, 15.0 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane)dihydrochloric acid solution were added, and at the same time, 22.5 g of a 0.01% aqueous iron sulfate solution as a reducing agent was added to initiate polymerization. After the temperature of the above mixture reached 85°C, a polymer was obtained by polymerizing at 90±2°C for about 6 hours.

[0330] (Steps 2 and 3: Atomization and Neutralization Steps)

[0331] 100 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) mounted inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,800 rpm, thereby carrying out a particle formation process.

[0332] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1138 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0333] (Step 4: Drying Stage)

[0334] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically circulating air. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0335] (Step 5: Crushing and Classification Stage)

[0336] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0337] (Surface cross-linking step)

[0338] Next, a surface cross-linking agent aqueous solution containing 4 g of water, 6 g of methanol, 0.15 g of ethylene glycol diglycidyl ether (EJ-1030S), and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0339] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0340] Example 2

[0341] (Step 1: Polymer manufacturing step)

[0342] In a 5 L glass vessel equipped with a stirrer and a thermometer, 1400 g of acrylic acid, 4.9 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 3512 g of water were stirred and mixed, and the reaction was carried out while maintaining the temperature at 5 ℃. The glass vessel containing the mixture was replaced with nitrogen conditions by introducing 1,000 cc / min of nitrogen for 1 hour. Next, 28.0 g of a 0.3% aqueous hydrogen peroxide solution as a polymerization initiator, 14.0 g of a 1% aqueous ascorbic acid solution, and 42.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane)dihydrochloric acid solution were added, and at the same time, 21.0 g of a 0.01% aqueous ferrous sulfate solution as a reducing agent was added to initiate polymerization. After the temperature of the above mixture reached 85°C, a polymer was obtained by polymerizing at 90±2°C for about 6 hours.

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

[0344] 100 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,500 rpm, thereby carrying out a particle formation process.

[0345] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1138 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0346] (Step 4: Drying Stage)

[0347] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically circulating air. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0348] (Step 5: Crushing and Classification Stage)

[0349] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM, MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0350] (Surface cross-linking step)

[0351] Next, a surface cross-linking agent aqueous solution containing 5 g of water, 6 g of methanol, 0.1 g of ethylene glycol diglycidyl ether (EJ-1030S), and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0352] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0353] Example 3

[0354] (Step 1: Polymer manufacturing step)

[0355] In a 5 L glass vessel equipped with a stirrer and a thermometer, 1500 g of acrylic acid, 3.75 g of pentaerythritol triallyl ether (PETTAE) as an internal cross-linking agent, and 3400 g of water were stirred and mixed, and the reaction was carried out while maintaining the temperature at 5 ° C. The glass vessel containing the mixture was replaced with nitrogen conditions by introducing 1,000 cc / min of nitrogen for 1 hour. Next, 30.0 g of a 0.3% aqueous hydrogen peroxide solution as a polymerization initiator, 15.0 g of a 1% aqueous ascorbic acid solution, and 45.0 g of a 2% aqueous 2,2'-azobis-(2-amidinopropane)dihydrochloric acid solution were added, and at the same time, 22.5 g of a 0.01% aqueous iron sulfate solution as a reducing agent was added to initiate polymerization. After the temperature of the above mixture reached 85°C, a polymer was obtained by polymerizing at 90±2°C for about 6 hours.

[0356] (Steps 2 and 3: Atomization and Neutralization Steps)

[0357] 50 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) mounted inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,200 rpm, thereby carrying out a particle formation process.

[0358] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1396 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0359] (Step 4: Drying Stage)

[0360] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically circulating air. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0361] (Step 5: Crushing and Classification Stage)

[0362] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0363] (Surface cross-linking step)

[0364] Next, a surface cross-linking agent aqueous solution containing 3.5 g of water, 6 g of methanol, 0.07 g of ethylene glycol diglycidyl ether (EJ-1030S), and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0365] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0366] Comparative Example 1

[0367] (Step 1: Polymer manufacturing step)

[0368] A polymer was obtained in the same manner as in Example 1 above.

[0369] (Steps 2 and 3: Atomization and Neutralization Steps)

[0370] 597 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,500 rpm, thereby carrying out a particle formation process.

[0371] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1138 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0372] (Step 4: Drying Stage)

[0373] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically circulating air. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0374] (Step 5: Crushing and Classification Stage)

[0375] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0376] (Surface cross-linking step)

[0377] Next, a surface cross-linking agent aqueous solution containing 5.5 g of water, 6 g of methanol, 0.15 g of ethylene glycol diglycidyl ether (EJ-1030S), and 0.3 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0378] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0379] Comparative Example 2

[0380] (Step 1: Polymer manufacturing step)

[0381] A polymer was obtained in the same manner as in Example 1 above.

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

[0383] 100 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Then, using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher, the polymer was pushed out at a rotation speed of 2,000 rpm through a porous plate having multiple 10 mm holes formed therein. Subsequently, the polymer was further pushed out at a rotation speed of 1,000 rpm through a porous plate having multiple 10 mm holes formed therein to obtain a pulverized gel-type hydrogel polymer.

[0384] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1138 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0385] (Step 4: Drying Stage)

[0386] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically circulating air. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

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

[0388] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM, MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0389] (Surface cross-linking step)

[0390] Next, a surface cross-linking agent aqueous solution containing 5.5 g of water, 5 g of methanol, and 0.07 g of ethylene glycol diglycidyl ether (EJ-1030S) per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0391] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0392] Comparative Example 3

[0393] (Step 1: Polymer manufacturing step)

[0394] A polymer was obtained in the same manner as in Example 3 above.

[0395] (Steps 2 and 3: Atomization and Neutralization Steps)

[0396] 150 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 2,500 rpm, thereby carrying out a particle formation process.

[0397] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1138 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0398] (Step 4: Drying Stage)

[0399] 1,000 g of the above-described superabsorbent resin particles were placed in a ventilated belt-type dryer containing a perforated plate capable of vertically circulating air. Hot air at 200°C and 100°C was sequentially flowed from top to bottom for 5 minutes and 10 minutes, respectively, so that the moisture content of the dried superabsorbent resin was approximately 10%, and then hot air at 100°C was flowed from bottom to top for 15 minutes to uniformly dry the polymer.

[0400] (Step 5: Crushing and Classification Stage)

[0401] The above dried body is crushed by a grinder (GRAN-U-LIZER) TM , MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0402] (Surface cross-linking step)

[0403] Next, a surface cross-linking agent aqueous solution containing 5 g of water, 6 g of methanol, 0.15 g of ethylene carbonate, and 0.38 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 185°C for 50 minutes to obtain a surface-cross-linked superabsorbent resin.

[0404] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0405] Comparative Example 4

[0406] (Step 1: Polymer manufacturing step)

[0407] A polymer was obtained in the same manner as in Example 3 above.

[0408] (Steps 2 and 3: Atomization and Neutralization Steps)

[0409] 100 g of a 0.45 wt% aqueous solution of Glycerol Monolaurate (GML) was added to 5,000 g of the polymer obtained in the above step 1. Thereafter, a high-speed rotary shredder (F-150 / Karl Schnell) mounted inside a cylindrical crusher was used to push the polymer through a perforated plate having multiple 10 mm holes at a rotation speed of 1,200 rpm, thereby carrying out a particle formation process.

[0410] Afterwards, the recovered hydrogel polymer was extruded three times through a perforated plate having multiple 10 mm holes at a rotation speed of 250 rpm using a screw extruder mounted inside a cylindrical crusher to perform an additional crushing process. 1138 g of a 50% NaOH aqueous solution (Step 3: Neutralization Step) was added to each step of the screw extruder to neutralize some of the acidic groups of the polymer, and then 100 g of fine powder (additional additive addition step) and 162 g of a 10% Na2SO4 aqueous solution (additional additive addition step) were added, respectively, to manufacture hydrogel superabsorbent resin particles (=micronized and neutralized polymer).

[0411] (Step 4: Drying Stage)

[0412] The functional superabsorbent resin particles were uniformly dried in the same manner as in Example 1 to obtain a dried product.

[0413] (Step 5: Crushing and Classification Stage)

[0414] The polymer dried in the above step 4 is crushed in a granulator (GRAN-U-LIZER) TM , MPE) and then sieved through a standard mesh sieve of ASTM standards to obtain base resin powder with a size of 150 to 850 μm.

[0415] (Surface cross-linking step)

[0416] Next, a surface cross-linking agent aqueous solution containing 4 g of water, 6 g of methanol, 0.15 g of ethylene glycol diglycidyl ether (EJ-1030S), and 0.2 g of aluminum sulfate per 100 g of the base resin powder was sprayed and stirred at room temperature to evenly distribute the surface cross-linking agent on the superabsorbent resin powder. Subsequently, the base resin powder mixed with the surface cross-linking agent was placed in a surface cross-linking reactor to perform a surface cross-linking reaction. Within this surface cross-linking reactor, the base resin powder underwent a surface cross-linking reaction at about 140°C for 40 minutes to obtain a surface-cross-linked superabsorbent resin.

[0417] After the surface cross-linking step, the surface-cross-linked superabsorbent resin was classified through a standard mesh sieve according to ASTM standards to produce a superabsorbent resin having a particle size of 150 μm to 850 μm.

[0418] Experimental Example 1

[0419] The storage modulus (Pa) according to the degree of swelling (%) of the superabsorbent resin of Example 1 was obtained according to the following steps, and a graph was drawn with the degree of swelling (%) as the x-axis and the storage modulus as the y-axis to calculate the rate of change in the storage modulus according to each section.

[0420] - Step 1) Preparation of superabsorbent resin dilution sample

[0421] The superabsorbent resin sample (30-50 Mesh) was sieved, 0.5 g was weighed, and then sufficiently swelled in a 0.9% NaCl solution for more than 1 hour.

[0422] At this time, the degree of swelling was varied. Based on the water retention capacity (CRC) of the superabsorbent resin measured in advance according to EDANA WSP 241.3, the swelling degree when adding the solution equal to the CRC was taken as 100%, and samples were produced that were swollen by 50%, 70%, and 100%.

[0423] - Step 2) Deriving the storage modulus of superabsorbent resin

[0424] The storage modulus of 2.5 g of a swollen superabsorbent resin sample was measured for 60 seconds at an angular frequency of 10 rad / s under a strain of 10% and a temperature of 25°C using a rheometer (TA ARES-G2).

[0425] At this time, the gap was adjusted to 1 mm between two parallel plates, and pressure was applied with a force of 3 N so that the swollen sample could be sufficiently adhered.

[0426] Under these measurement conditions, all resins exhibited a uniform storage modulus for 60 seconds without leaving the linear viscoelastic range, and the values ​​obtained at this time were used to measure the horizontal storage modulus of the sample.

[0427] The storage elastic modulus of the samples in which the superabsorbent resin was swollen by 50%, 70%, and 100%, respectively, was derived using the above method, and the change rate of the storage elastic modulus according to the degree of swelling (%) was calculated according to Equations 1 to 3 below.

[0428] [Formula 1]

[0429] Change in storage modulus at 50% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 50% swelling)} / 50]

[0430] [Formula 2]

[0431] Change in storage modulus at 50% and 70% swelling = [{(storage modulus at 70% swelling)-(storage modulus at 50% swelling)} / 20]

[0432] [Formula 3]

[0433] Change in storage modulus at 70% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 70% swelling)} / 30]

[0434] Storage modulus (%) according to swelling degree (50%, 70%, 100%) Average 50%~70% change rate Absolute 70%~100% change rate Absolute 50%~100% change rate Absolute value 50% 70% 100% Example 1 43433666 210733.85 51.97 44.72 Example 2 47763728186 152.43 62.22 58.31 Example 3 486337332834 56.50 29.94 40.56 Comparative Example 1 829366753584 80.93 103.0 394.19 Comparative Example 2 73915751385281.98 63.30 70.77 Comparative Example 3 365728672334 39.53 17.75 26.46 Comparative Example 4 39283228273735.00 16.38 23.83

[0435] <Experimental Example 2> - Physical Property Evaluation

[0436] The properties of the superabsorbent resins manufactured in the above examples and comparative examples were evaluated using the following methods and are listed in Tables 2 and 3 below.

[0437] Unless otherwise specified, all of the following property evaluations were conducted under constant temperature and humidity (23±1℃, relative humidity 50±10%), and physiological saline solution or saline refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0438] After the sample to be measured was left under constant temperature and humidity conditions for 24 hours, each property was evaluated.

[0439] (1) Gel strength measurement

[0440] The gel strength of the superabsorbent resins manufactured in the above examples and comparative examples was measured using the following method.

[0441] A saline solution containing 0.005% ASC was prepared using saline and ascorbic acid (ACS). Subsequently, the saline solution containing 0.005% ASC and approximately 2.5 (2.5±0.01 g) of a superabsorbent resin were placed in a 100 ml beaker, mixed, sealed with transparent wrap, and placed in an oven for 24 hours at 40°C to swell. After removing the beaker from the oven, the transparent wrap was removed, and the beaker was left at room temperature for 30 minutes. The gel strength of the superabsorbent resin was measured using a tensile compression tester (manufacturer: Nidec-Shimpo).

[0442] (2) Centrifuge Retention Capacity (CRC, g / g)

[0443] 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.

[0444] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 241.0.

[0445] 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.

[0446] Using each mass obtained, CRC (g / g) was calculated according to the following mathematical formula 1.

[0447] [Mathematical Formula 1]

[0448] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0449] The above measurement was repeated five times, and the average value and standard deviation were calculated.

[0450] (3) Absorbency under Pressure (AUP: Absorbency under Pressure, g / g)

[0451] The pressurized absorption capacity of 2.07 kPa (0.3 psi) of the superabsorbent resins of the above examples and comparative examples was measured according to the EDANA method WSP 242.3.

[0452] Measurements were performed at a temperature of 23±2℃ and a relative humidity of 45±15% as described in EDANA WSP 242.0.

[0453] 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 W3 (g) (0.9 g) was uniformly sprayed on the wire mesh, and a piston capable of uniformly applying a load of 2.07 kPa (0.3 psi) was installed on top of it, with an outer diameter slightly smaller than 25 mm, without a gap with the inner wall of the cylinder, and without impeding up-and-down movement. At this time, the weight W4 (g) of the device was measured.

[0454] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a petri dish with a diameter of 150 mm, and a saline solution consisting of 0.9 wt% sodium chloride was placed so that it was level with the upper surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of it. The measuring device was placed on the filter paper, and the liquid was absorbed under a load for 1 hour. After 1 hour, the measuring device was lifted, and its weight W5 (g) was measured.

[0455] Using each mass obtained, the pressurized absorbency (g / g) was calculated according to the following mathematical formula 2.

[0456] [Equation 2]

[0457] AUP(g / g) = [W5(g) - W4(g)] / W3(g)

[0458] The above measurement was repeated five times, and the average value and standard deviation were calculated.

[0459] (4) Vortex time

[0460] The vortex time of the superabsorbent resins of the above examples and comparative examples was measured by the following method.

[0461] 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.

[0462] 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.

[0463] 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.

[0464] 4) After confirming that the temperature of the brine in the beaker reached 24.0℃, 2±0.01 g of superabsorbent resin sample was added while simultaneously operating the stopwatch, and the time until the vortex disappeared and the liquid surface became completely horizontal was measured in seconds, which was designated as the vortex time.

[0465] (5) Measurement of permeability of superabsorbent resin

[0466] For each resin, the permeability was measured using Equation 4 below.

[0467] [Formula 4]

[0468] Perm = [20 mL / T1 (sec)] x 60 sec

[0469] In the above equation 4,

[0470] Perm is permeable,

[0471] T1 means the time (seconds) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin under a pressure of 2.07 kPa (0.3 psi) after placing 0.2 g of superabsorbent resin in a cylinder, pouring saline solution (0.9 wt% sodium chloride aqueous solution) so that the superabsorbent resin is completely submerged, and the superabsorbent resin is swelled for 30 minutes.

[0472] Specifically, a cylinder and a piston were prepared. The cylinder used had an inner diameter of 20 mm and was equipped with a glass filter and a stopcock at the bottom. The piston used had an outer diameter slightly smaller than 20 mm, a screen that allowed the cylinder to move freely up and down was placed at the bottom, a weight was placed at the top, and the screen and the weight were connected by a rod. A weight capable of applying a pressure of 2.07 kPa (0.3 psi) due to the addition of the piston was installed on the piston.

[0473] With the stopcock of the cylinder locked, 0.2 g of superabsorbent resin was added, and an excess amount of saline solution (0.9 wt% sodium chloride aqueous solution) was poured so that the superabsorbent resin was completely submerged. Then, the superabsorbent resin was allowed to swell for 30 minutes. Thereafter, a piston was added so that a load of 2.07 kPa (0.3 psi) could be uniformly applied to the swollen superabsorbent resin.

[0474] Next, the stopcock of the cylinder was opened, and the time taken for 20 mL of saline solution to pass through the swollen superabsorbent resin was measured in seconds. At this time, by marking the meniscus when the cylinder is filled with 40 mL of saline solution and marking the meniscus when the cylinder is filled with 20 mL of saline solution, the time taken to reach the level corresponding to 40 mL to the level corresponding to 20 mL can be measured, thereby easily measuring T1 in the above calculation formula 1.

[0475] (6) Content of water-soluble components in water with an electrical conductivity of 110 μS / cm

[0476] 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.

[0477] 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, and then placed in 200 mL of water having an electrical conductivity of 110 μS / cm, and allowed to swell freely while stirring at 250 rpm (1 hour / 16 hours), and then the aqueous solution was filtered with filter paper.

[0478] 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 %).

[0479] (7) Absorption capacity in water with an electrical conductivity of 110 μS / cm

[0480] The absorption capacity of the superabsorbent resin of the examples and comparative examples in water with an electrical conductivity of 110 μS / cm was measured by the following method.

[0481] 1) First, 1.0 g(W 11 ) was placed in a non-woven bag (18 cm Х 28 cm) and immersed in 1000 mL of water having an electrical conductivity value of 110 μS / cm at 24°C for (30 s / 120 s).

[0482] 2) After (30 s / 120 s), the bag containing the swollen superabsorbent resin was taken out of water with an electrical conductivity of 110 μS / cm, hung, and left for 1 minute. After that, the mass of the bag (W 13 ) was measured.

[0483] 3) In addition, the mass (W) at that time was measured after performing the same operation without using superabsorbent resin. 12 ) was measured.

[0484] 4) Using each mass thus obtained, the absorption capacity (g / g) in water with an electrical conductivity value of 110 μS / cm (30 seconds / 120 seconds) was calculated according to the following mathematical formula 3.

[0485] [Equation 3]

[0486] Absorption capacity in water with an electrical conductivity of 110 μS / cm = {[W 13 (g) - W 12 (g) - W 11 (g)] / W 11 (g)}

[0487] The results of measuring the absorption capacity in water with an electrical conductivity of 110 μS / cm for the above examples and comparative examples are shown in Table 3 below.

[0488] (8) Average absorption rate by section of water with an electrical conductivity of 110 μS / cm

[0489] Using the results of 30-second absorption capacity and 120-second absorption capacity in water with an electrical conductivity of 110 μS / cm, the average absorption rate in the 0 to 30-second interval and the average absorption rate in the 30 to 120-second interval were calculated.

[0490] The results of measuring the absorption rate according to the swelling section in water with an electrical conductivity of 110 μS / cm for the above examples and comparative examples are shown in Table 3 below.

[0491] Gel strength (N) CRC (g / g) 0.3 AUP (g / g) Vortex time (sec) Liquid permeability (mL / min) Example 10.97 36.5 33.0 235.1 Example 20.92 35.6 31.92 66.4 Example 30.96 37.23 2.125 6.0 Comparative example 10.91 31.2 26.5 372.6 Comparative example 20.98 30.127.34 23.2 Comparative example 30.87 28.6 29.138 1.9 Comparative example 41.0 227.4 25.4 392.8

[0492] Content of water-soluble components in water with an electrical conductivity of 110 μS / cm at 24°C (%) Absorption capacity in water with an electrical conductivity of 110 μS / cm at 24°C (g / g) Absorption rate in water with an electrical conductivity of 110 μS / cm at 24°C (g / g / sec) Swelling time Swelling time (sec) Average swelling range (sec) 1 hr 16 hr 30 sec 120 sec 0~30 sec 30~120 sec Example 19.9 15.6 119 28 6 3.97 1.86 Example 210.0 16.11 122 8 9 3.73 1.97 Example 39.2 14.9 120 29 14.00 1.90 Comparative example 115.4 26.76 7 18 22.23 1.28 Comparative example 217.527.5571861.901.43Comparative example 318.127.9611752.031.27Comparative example 416.326.8661912.201.39

[0493] As can be seen in Tables 1 to 3 above, in the case of the superabsorbent resin of the example in which the change in storage elastic modulus according to the degree of swelling was constantly controlled, it was confirmed that it had excellent physical property balance with excellent absorption performance and liquid permeability, a fast absorption speed, and a certain level of dissolved components.

[0494] The present invention can be applied to superabsorbent resins.

Claims

1. As a polyacrylic acid (salt)-based superabsorbent resin, The storage modulus (Pa) of the above superabsorbent resin after swelling by 50% is 4,000 Pa or more, A superabsorbent resin having an absolute value of change in storage elastic modulus at 50% and 100% swelling derived by Equation 1 below of 62 or less: [Formula 1] Change in storage modulus at 50% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 50% swelling)} / 50].

2. In paragraph 1, A superabsorbent resin having a storage modulus (Pa) of 6,000 Pa or less after swelling the superabsorbent resin by 50%.

3. In paragraph 1, A superabsorbent resin having an absolute value of change in storage elastic modulus at 50% and 70% swelling derived by Equation 2 below of 70 or less: [Formula 2] Change in storage modulus at 50% and 70% swelling = [{(storage modulus at 70% swelling)-(storage modulus at 50% swelling)} / 20].

4. In paragraph 1, A superabsorbent resin having an absolute value of change in storage elastic modulus at 70% and 100% swelling, as derived by Equation 3 below, of 70 or less: [Formula 3] Change in storage modulus at 70% and 100% swelling = [{(storage modulus at 100% swelling)-(storage modulus at 70% swelling)} / 30].

5. In paragraph 1, A superabsorbent resin having a storage modulus (Pa) of 3,000 Pa to 5,000 Pa after swelling the superabsorbent resin by 70%.

6. In paragraph 1, A superabsorbent resin having a storage modulus (Pa) of 1,500 Pa to 3,000 Pa after 100% swelling of the superabsorbent resin.

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

8. In paragraph 1, The above superabsorbent resin is a superabsorbent resin having a permeability of 3 ml / min or more, calculated by the following equation 4: [Formula 4] Perm = [20 mL / T1 (sec)] x 60 sec In the above equation 4, Perm is the permeability of superabsorbent resin, T1 means the time (seconds) taken for 20 mL of saline solution to pass through the swollen superabsorbent resin under a pressure of 2.07 kPa (0.3 psi) after placing 0.2 g of superabsorbent resin in a cylinder, pouring saline solution (0.9 wt% sodium chloride aqueous solution) so that the superabsorbent resin is completely submerged, and the superabsorbent resin is swelled for 30 minutes.

9. In paragraph 1, A superabsorbent resin, wherein when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 30 seconds, the maximum capacity of water that the superabsorbent resin can hold is 70 g or more.

10. In paragraph 1, A superabsorbent resin, wherein when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm for 120 seconds, the maximum capacity of water that the superabsorbent resin can hold is 200 g or more.

11. In paragraph 1, A superabsorbent resin having an average absorption rate of 2.5 g / g / sec or more at 0 to 30 seconds when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm.

12. In paragraph 1, A superabsorbent resin having an average absorption rate of 1.4 g / g / sec or more in 30 to 120 seconds when 1 g of the superabsorbent resin is freely swelled in water having an electrical conductivity of 100 to 130 μS / cm.

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