Superabsorbent polymer

Abstract

The present disclosure relates to superabsorbent polymers exhibiting improved rate of absorption and improved absorption performance.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0165504, filed November 24, 2023, and U.S. Patent Application No. 18 / 922,670, filed October 22, 2024, and all disclosures in the foregoing applications are incorporated herein by reference.

[0003] This disclosure relates to superabsorbent polymers exhibiting improved absorption rates and improved absorption properties. Background Technology

[0004] Superabsorbent polymers (SAPs) are synthetic polymer materials capable of absorbing 500 to 1,000 times their own weight in water. They are known by various names depending on the developing company, such as superabsorbent polymers (SAMs) and absorbent gels (AGMs). As described above, such superabsorbent polymers have begun to be commercially used in diapers, hygiene products, etc., and are currently widely used as soil conditioners in horticulture, waterproofing materials in civil engineering or construction, seedling sheets, preservatives in the food distribution sector, and mud dressings.

[0005] These superabsorbent polymers are widely used in hygiene products such as diapers and sanitary napkins. Typically, superabsorbent polymers are contained within the pulp in hygiene products. However, in recent years, there has been an effort to provide hygiene products such as diapers with a thinner thickness, and as part of this effort, so-called pulp-free diapers, in which the pulp content is reduced or even completely eliminated, are being actively developed.

[0006] In the case of sanitary products where the pulp content is reduced or eliminated, a relatively high proportion of superabsorbent polymers is contained, and therefore, the superabsorbent polymer particles are inevitably contained in the sanitary products in a multi-layered manner. For all the superabsorbent polymer particles contained in this multi-layered manner to more effectively absorb large amounts of liquid, such as urine, the superabsorbent polymer needs to exhibit not only substantially high absorbency but also a high absorption rate. Meanwhile, the most common method to improve these absorbency properties includes forming a porous structure within the superabsorbent polymer to increase its surface area. A commonly employed method is to allow the monomer composition to contain a foaming agent to increase the surface area of ​​the superabsorbent polymer, thereby forming a porous structure within the base resin powder during crosslinking and polymerization.

[0007] However, the use of foaming agents has disadvantages such as reduced overall physical properties of superabsorbent polymers, including surface tension, liquid permeability, or bulk density, and increased amount of fine powder produced. Therefore, there is a continued need to develop technologies that can improve the absorption properties of superabsorbent polymers without the use of foaming agents.

[0008] Therefore, there is a continued need to develop technologies that can produce superabsorbent polymers without generating fine powder, thus fundamentally solving these problems. Summary of the Invention

[0009] Technical issues

[0010] This disclosure provides such a superabsorbent polymer by adjusting the sphericity and aspect ratio (A / R) of the particles to predetermined values, which improves the absorption rate while simultaneously improving water retention capacity and absorption performance such as absorption rate under pressure, thereby achieving excellent quality when the polymer is applied to an actual product.

[0011] Technical solution

[0012] According to one aspect of this disclosure, this disclosure provides:

[0013] Superabsorbent polymer, wherein the superabsorbent polymer is a superabsorbent polymer based on polyacrylic acid (salt).

[0014] For all particles, the average roundness calculated according to Expression 1 below is approximately 0.90 or less, and the average aspect ratio (A / R) is approximately 0.70 or greater, where A / R refers to the ratio of the shortest diameter of the particle to the longest diameter of the particle.

[0015] The absorbance per unit pressure (AUP), measured according to EDANA method WSP 242.3 at approximately 2.07 kPa (0.3 psi), is approximately 25 g / g or greater.

[0016] <expression 1>

[0017] Circularity = Circumference of CE particle / Circumference of actual particle

[0018] In expression 1 above,

[0019] The perimeter of a CE particle refers to the circumference of a circle (equivalent circle) that has the same area as the 2D image obtained by taking a 3D image of the particle being measured.

[0020] The actual perimeter of a particle refers to the actual perimeter length of the image obtained by taking a 3D image of the three-dimensional particle to be measured and using it as a 2D image.

[0021] Beneficial effects

[0022] Based on the superabsorbent polymer disclosed herein, a superabsorbent polymer in which the roundness and aspect ratio (A / R) have predetermined values ​​can be provided, thereby achieving excellent quality when the polymer is applied to an actual product.

[0023] In particular, it is possible to provide superabsorbent polymers that, while having a rapid absorption rate, simultaneously improve water retention capacity and absorption performance such as absorption rate under pressure, and thus have a balance of physical properties.

[0024] Furthermore, when applied to hygiene products such as diapers, it can absorb excreted bodily fluids at a high rate and can absorb relatively large amounts, which helps prevent problems such as bodily fluids accumulating inside the hygiene products or leaking to the outside.

[0025] In other words, it is possible to provide such superabsorbent polymers that, when applied to products, can rapidly absorb bodily fluids and retain large amounts of bodily fluids without causing leakage to the outside. Attached Figure Description

[0026] Figure 1 The settings for the sample dispersion unit in the Malvern Panalytical morphologi 4 are shown;

[0027] Figure 2 The lighting settings in the Malvern Panalytical morphologi 4 are shown;

[0028] Figure 3 The settings for optics selection in Malvern Panalytical's morphologi 4 are shown; and

[0029] Figure 4 The settings for the scan region in morphologi 4 from Malvern Panalytical are shown. Detailed Implementation

[0030] According to one example of this disclosure, a superabsorbent polymer is provided, said superabsorbent polymer being a polyacrylic acid (salt)-based superabsorbent polymer.

[0031] For all particles, the average roundness calculated according to Expression 1 below is approximately 0.90 or less, and the average aspect ratio (A / R) is approximately 0.70 or greater, where A / R refers to the ratio of the shortest diameter of the particle to the longest diameter of the particle.

[0032] The absorbance per unit pressure (AUP), measured according to EDANA method WSP 242.3 at approximately 2.07 kPa (0.3 psi), is approximately 25 g / g or greater.

[0033] <expression 1>

[0034] Circularity = Circumference of CE particle / Circumference of actual particle

[0035] In expression 1 above,

[0036] The perimeter of a CE particle refers to the circumference of a circle (equivalent circle) that has the same area as the 2D image obtained by taking a 3D image of the particle being measured.

[0037] The actual perimeter of a particle refers to the actual perimeter length of the image obtained by taking a 3D image of the three-dimensional particle to be measured and using it as a 2D image.

[0038] Invention Embodiments

[0039] In this specification, unless otherwise specified, all technical and scientific terms are used to describe exemplary aspects only and are therefore not intended to limit this disclosure. Singular expressions include plural expressions unless explicitly distinguished in the context. Terms such as “comprising / including,” “equipped,” or “having” are intended to indicate the presence of a implemented feature, quantity, step, constituent element, or combination thereof, and therefore should be understood not to preclude the possibility of the presence or addition of one or more other features, quantities, steps, constituent elements, or combinations thereof.

[0040] Because this disclosure can be modified in various ways and can take many forms, specific aspects will be illustrated and described in detail below. However, this is not intended to limit this disclosure to the specific form disclosed, and it should therefore be understood to include all changes, equivalents, and alternatives within the spirit and technical scope described above.

[0041] The terminology used in this specification is intended to refer only to specific exemplary aspects and is therefore not intended to limit this disclosure. Furthermore, unless the wording explicitly indicates otherwise, the singular forms as used herein include the plural forms.

[0042] As used in this disclosure, the terms "polymer" or "polymer molecule" mean, for example, a polymer or polymer molecule in which water-soluble olefinic unsaturated monomers are polymerized, and may cover those in all ranges of water content or particle diameter.

[0043] Furthermore, depending on the context, the term "superabsorbent polymer" means a crosslinked polymer or a base resin having in powder form in which the crosslinked polymer is made from pulverized particles of a superabsorbent polymer, or is used to encompass all substances that have been made commercially viable by subjecting the crosslinked polymer or base resin to additional processes such as drying, pulverizing, grading, and surface crosslinking.

[0044] Furthermore, the term "fine powder" refers to particles in superabsorbent polymer granules with a diameter of less than approximately 150 μm. The particle diameter of such resin particles can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3.

[0045] In addition, the term "shredding" refers to cutting hydrogel polymers into small fragments at the millimeter level to improve drying efficiency and is used to distinguish them from being pulverized to the micrometer or normal particle level.

[0046] In addition, the term “micronizing / micronization” refers to pulverizing hydrogel polymers into particles with diameters of tens to hundreds of micrometers, and is used to distinguish it from “shredding”.

[0047] The superabsorbent polymers and methods for producing the same according to specific aspects of this disclosure will be described in more detail below.

[0048] I. Superabsorbent polymers based on polyacrylic acid (salt)

[0049] Hydrogel polymers obtained through the polymerization of acrylic acid-based monomers undergo processes such as drying, pulverizing, grading, and surface crosslinking, and are sold as powdered superabsorbent polymers. Recently, continuous efforts have been made to provide superabsorbent polymers with improved absorption rates.

[0050] The most common method to increase the absorption rate includes forming a porous structure within the superabsorbent polymer to increase the surface area of ​​the superabsorbent polymer. A commonly used method is to allow the monomer composition to contain a foaming agent to increase the surface area of ​​the superabsorbent polymer, thereby forming a porous structure within the base resin powder during crosslinking and polymerization.

[0051] However, a problem with the methods in these technologies is that it is difficult to create a sufficient surface area. As a result, during actual urination, unabsorbed bodily fluids flow into the interior of the sanitary product or leak to the outside, causing discomfort to the user.

[0052] To address such problems in the related technology, as described above, the roundness and aspect ratio (A / R) are adjusted to predetermined values, thereby determining that while improving the absorption rate, the water retention capacity and absorption performance such as the absorption rate under pressure can be improved simultaneously, and thus, when the resin is applied to an actual product, excellent quality can be achieved.

[0053] According to one aspect of this disclosure,

[0054] A superabsorbent polymer is provided, wherein the superabsorbent polymer is a polyacrylic acid (salt) based superabsorbent polymer.

[0055] For all particles, the average roundness calculated according to Expression 1 below is approximately 0.90 or less, and the average aspect ratio (A / R) is approximately 0.70 or greater, where A / R refers to the ratio of the shortest diameter of the particle to the longest diameter of the particle.

[0056] The absorbance per unit pressure (AUP), measured according to EDANA method WSP 242.3 at approximately 2.07 kPa (0.3 psi), is approximately 25 g / g or greater.

[0057] <expression 1>

[0058] Circularity = Circumference of CE particle / Circumference of actual particle

[0059] In expression 1 above,

[0060] The perimeter of a CE particle refers to the circumference of a circle (equivalent circle) that has the same area as the 2D image obtained by taking a 3D image of the particle being measured.

[0061] The actual perimeter of a particle refers to the actual perimeter length of the image obtained by taking a 3D image of the three-dimensional particle to be measured and using it as a 2D image.

[0062] The term "all particles" refers to superabsorbent polymer particles for which there are no restrictions on particle size.

[0063] The inventors of this invention have determined that, when each of the roundness and aspect ratio of the superabsorbent polymer particles is adjusted to a predetermined value, the absorption rate of the superabsorbent polymer can be improved, while simultaneously improving water retention capacity and other absorption properties such as absorption rate under pressure, by increasing the specific surface area.

[0064] Specifically, it was determined that by quantifying the shape of superabsorbent polymer particles that affect absorption rate and absorption performance, and then considering roundness as a parameter that allows determination of how close the particles are to perfect spheres and aspect ratio as a parameter that allows determination of particle symmetry, such that each of these parameters has a specific level value, superabsorbent resins can exhibit a high water absorption rate and a balance between improved water retention capacity and improved absorption rate under pressure.

[0065] Circularity is a parameter that allows us to determine how close the superabsorbent polymer particles are to perfect spheres, and it is calculated according to the following expression 1:

[0066] <expression 1>

[0067] Circularity = Circumference of CE particle / Circumference of actual particle

[0068] In expression 1 above,

[0069] The perimeter of a CE particle refers to the circumference of a circle (equivalent circle) that has the same area as the 2D image obtained by taking a 3D image of the particle being measured.

[0070] The actual perimeter of a particle refers to the actual perimeter length of the image obtained by taking a 3D image of the three-dimensional particle to be measured and using it as a 2D image.

[0071] The value of roundness ranges from 0 to 1, where roundness is 1 in the case of a perfect sphere, where roundness close to 1 indicates that the particle is close to a perfect sphere, and where roundness close to 0 indicates that the particle has a very sharp shape, such as a very narrow rod.

[0072] In this case, after the particles are dispersed onto the stage in the measuring instrument by vacuum using any method, the average roundness is measured, and the number of n is ensured to be 200 or greater, and then the average value is obtained as a statistical result.

[0073] Aspect ratio (A / R) is a parameter that allows us to determine the symmetry of particles, and it refers to the ratio of the shortest diameter of a particle to its longest diameter.

[0074] The aspect ratio also has values ​​from 0 to 1, where the aspect ratio is 1 in all cases of axial symmetry (such as in the case of a perfect sphere or cube), where the particle is considered to have a shape close to symmetrical when the aspect ratio is close to 1, and where the particle is considered to have a shape close to asymmetrical when the aspect ratio is close to 0.

[0075] In this case, after the particles are dispersed onto the stage in the measuring instrument by vacuum using any method, the average aspect ratio is similarly measured, and the number of n is ensured to be 200 or greater, and then the average value is obtained as a statistical result.

[0076] While roundness and aspect ratio are similar in that the shape of superabsorbent polymer particles is quantified, they are parameters with different meanings to each other.

[0077] In other words, even when particles have the same roundness value, the aspect ratio value may vary depending on the symmetry of the particles, the degree of surface roughness, etc., and when the shape of the particles changes, both the roundness value and the aspect ratio value may be different, or only one of them may be different.

[0078] Therefore, in order for superabsorbent polymers to exhibit a high water absorption rate and a balance between improved water retention capacity and improved absorption rate under pressure, both roundness and aspect ratio need to meet specific levels.

[0079] These parameters can be measured using several commercial instruments that quantify and analyze particle morphology using particle-based image analysis. For example, the parameters above can be measured using the Malvern Panalytical morphologi 4, and specifically, can be measured according to the following four steps, which will be described in more detail in the experimental examples described below.

[0080] 1) Sample preparation: Prepare the superabsorbent polymer particles to be measured. In this case, the particles with a specific diameter are classified for about 10 minutes using a classifier from Retsch GmbH at an amplitude of about 1.0, with the aim of measuring the roundness and aspect ratio (A / R) of particles with a specific range of particle diameters.

[0081] In this case, the particle diameter of the superabsorbent polymer particles can be measured according to the European Disposable Goods and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0082] 2) Image acquisition: Place the prepared sample on the stage in the device and then scan it at a magnification of about 2.5 times to obtain images of individual particles.

[0083] 3) Image processing: For the acquired images, the circle equivalent diameter (CE diameter), shortest diameter, longest diameter, and actual particle circumference are measured in the images of each particle. The images are obtained by taking 2D images of the three-dimensional particles to be measured.

[0084] 4) Based on the data from the analysis of each particle, shape data values ​​for all particles contained in the sample were obtained. For the aforementioned superabsorbent polymer, the average roundness of all measured particles was approximately 0.90 or less, and the average aspect ratio (A / R) was approximately 0.70 or greater.

[0085] When the average sphericity of all particles of the superabsorbent polymer exceeds approximately 0.90, the particle shape approaches a perfect sphere, thus reducing the specific surface area, which may decrease the absorption rate of the superabsorbent polymer. When the average aspect ratio is less than approximately 0.70, there may be a problem of deteriorated absorption performance.

[0086] Specifically, for example, the average sphericity of all particles of the superabsorbent polymer can be about 0.90 or less, about 0.89 or less, about 0.88 or less, about 0.87 or less, or about 0.86 or less, while being about 0.70 or greater, about 0.71 or greater, about 0.72 or greater, or about 0.73 or greater.

[0087] When the average sphericity is small, i.e., when the particle shape deviates from a perfect sphere and has a sharp shape, the particles can be considered to have an increased specific surface area. However, simply increasing the specific surface area may lead to problems such as deterioration of water retention capacity and absorption performance, such as the absorption rate under pressure.

[0088] Therefore, in order to simultaneously improve absorption rate and absorption performance and achieve an excellent balance of physical properties, the average sphericity of all particles of the superabsorbent polymer is about 0.70 or greater.

[0089] The average aspect ratio of all particles of the superabsorbent polymer can be about 0.85 or less, about 0.84 or less, about 0.83 or less, about 0.82 or less, about 0.81 or less, or about 0.80 or less, while being about 0.70 or greater.

[0090] Due to the asymmetry of the particles when the average aspect ratio is small, the particles can be considered to have an increased specific surface area. However, similarly, simply increasing the specific surface area may lead to problems such as deterioration of water retention capacity and absorption performance, such as the absorption rate under pressure.

[0091] Therefore, in order to simultaneously improve absorption rate and absorption performance and achieve an excellent balance of physical properties, the average aspect ratio of all particles in the superabsorbent polymer is about 0.70 or greater.

[0092] Furthermore, the superabsorbent polymer particles according to this disclosure are such that, for all particles subjected to measurement, the average sphericity satisfies a value of about 0.90 or less, and at the same time, the average aspect ratio satisfies a value of about 0.70 or greater.

[0093] As mentioned above, when the particle shapes differ, both the roundness value and the aspect ratio can be different, or only one of them can be different. However, when both values ​​meet certain levels, the specific surface area of ​​the particles increases, and thus the particle asymmetry also increases. Therefore, the absorption rate and absorption performance of superabsorbent polymers can be improved simultaneously, enabling the realization of superabsorbent polymers with a balance of physical properties.

[0094] On the other hand, as mentioned above, roundness is the ratio of the perimeter of the CE particle to the perimeter of the actual particle, and it can be expressed as high sensitivity circularity (HS circularity) by squaring the value of roundness as shown in the following expression 2, so as to more sensitively indicate the change in the relationship between the perimeter of the actual particle and the perimeter of the CE particle.

[0095] <expression2>

[0096] HS roundness = (circumference of CE particles) 2 / (Actual particle perimeter) 2

[0097] In Expression 2 above, the perimeter of the CE particle and the perimeter of the actual particle are as described above.

[0098] High sensitivity roundness (HS roundness) is a parameter that allows us to determine how close a particle is to a perfect sphere, where the HS roundness value also has a range of 0 to 1. This means that when the HS roundness is close to 1, the particle is close to a sphere, and when the HS roundness is close to 0, the particle has a sharp shape.

[0099] However, HS roundness is obtained by squaring the value of roundness, and it can represent a calculated value that depends on the difference in particle shape, and is therefore maximized.

[0100] Specifically, the average HS roundness of all particles of the superabsorbent polymer can be about 0.80 or less, about 0.79 or less, about 0.78 or less, about 0.77 or less, about 0.76 or less, about 0.75 or less, or about 0.74 or less, while being about 0.50 or greater, about 0.51 or greater, about 0.52 or greater, about 0.53 or greater, or about 0.54 or greater.

[0101] On the other hand, the ratio of the roundness of particles with a diameter of about 300 μm to about 600 μm to the roundness of all particles can be about 0.90 or greater, about 0.93 or greater, or 0.95 or greater.

[0102] Circularity can be measured by separating particles with diameters from approximately 300 μm to approximately 600 μm in the superabsorbent polymer from other particles. In this case, the ratio of the circularity of particles with diameters from approximately 300 μm to approximately 600 μm to the circularity of all particles can be calculated. This means that when the ratio of the circularity of particles with diameters from approximately 300 μm to approximately 600 μm to the circularity of all particles is close to 1, regardless of the particle diameter, the particles in the superabsorbent polymer have a similar closeness to perfect spheres.

[0103] The average circle equivalent diameter (CE diameter) of superabsorbent polymers can be from about 220 μm to about 400 μm.

[0104] CE diameter refers to the diameter of a circle having the same area as a two-dimensional image of the three-dimensional particle being measured, and the size of the particle can be indicated by the CE diameter.

[0105] However, since particles with different shapes can have the same CE diameter value, in addition to CE diameter, the shape of the particles can also be expected to be indicated by the roundness and aspect ratio of the particles.

[0106] The average CE diameter of the superabsorbent polymer can be about 400 μm or less, about 350 μm or less, about 330 μm or less, about 320 μm or less, or about 310 μm or less, while also being about 220 μm or more, about 230 μm or more, or about 240 μm or more.

[0107] When the average CE diameter of the superabsorbent polymer is less than about 220 μm, the amount of fine powder produced may increase due to the large number of micronized particles, and there is a risk that the absorption properties may deteriorate. Furthermore, when the CE diameter exceeds about 400 μm, there may be a problem with a reduced absorption rate. Therefore, the average CE diameter of the superabsorbent polymer can be within the above-mentioned range.

[0108] In this case, after the particles are dispersed onto the stage in the measuring instrument by any method using vacuum, the average diameter of the CE is measured, and the number of n is ensured to be 200 or greater. The average value is then obtained as a statistical result.

[0109] Furthermore, the superabsorbent polymer produced according to one aspect of this disclosure can have a uniform particle diameter distribution, thereby being configured to provide a superabsorbent polymer with excellent overall absorption properties such as water retention capacity and absorbency under pressure, as well as excellent rewetting properties.

[0110] The superabsorbent polymer according to one aspect of this disclosure has a high absorption rate and a low fine powder content, and can have the same or higher levels of water retention capacity (CRC) and absorbance under pressure (AUP) as overall absorption characteristics compared with superabsorbent polymers produced according to methods in the related art.

[0111] Furthermore, the sphericity of the particles can have similar values, independent of particle size, and the content of water-soluble components (EC) is reduced, thus providing a superabsorbent polymer with excellent liquid permeability and rewetting properties.

[0112] Specifically, in the superabsorbent polymers according to this disclosure, the water retention capacity (CRC) measured according to the EDANA method WSP 241.3 can have values ​​in the range of about 50 g / g or less, about 45 g / g or less, or about 40 g / g or less, while being about 33 g / g or more, about 34 g / g or more, or about 35 g / g or more.

[0113] Furthermore, according to the superabsorbent polymer of this disclosure, the absorbance rate (AUP) at a pressure of about 2.07 kPa (0.3 psi) as measured according to the EDANA method WSP 242.3 can have values ​​in the range of about 45 g / g or less, about 42 g / g or less, or about 40 g / g or less, while being 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.

[0114] Furthermore, in the superabsorbent polymers according to this disclosure, the effective absorbent capacity (EFFC) calculated according to the following expression 3 can be about 40 g / g or less, about 39 g / g or less, about 38 g / g or less, about 37 g / g or less, or about 36 g / g or less, while being about 30 g / g or more, about 31 g / g or more, about 32 g / g or more, or about 33 g / g or more.

[0115] <expression 3>

[0116] Effective Absorbable Capacity (EFFC) = {Water Retention Capacity (CRC) + Absorption Rate at Pressure of Approximately 2.07 kPa (0.3 psi) (AUP)} / 2.

[0117] Effective absorbable capacity (EFFC) is the arithmetic mean of water retention capacity (CRC) and absorbance rate (AUP) at a pressure of approximately 2.07 kPa (0.3 psi), which can be calculated from the measured CRC and AUP.

[0118] Furthermore, in the superabsorbent polymers according to this disclosure, the content of the water-soluble component, measured according to EDANA method WSP 270.3 after swelling for approximately 1 hour, can be 5% by weight or less, about 4.8% by weight or less, about 4.5% by weight or less, about 4.3% by weight or less, about 4% by weight or less, or about 3.9% by weight or less. The lower the content of the water-soluble component, the better. Theoretically, its lower limit is 0% by weight; however, it can be, for example, about 0.1% by weight or more, or about 1% by weight or more.

[0119] In the superabsorbent polymers according to this disclosure, the vortex time can be 40 seconds or less, wherein the vortex time is measured at approximately 24.0°C by a vortex measurement method. The vortex measurement method is described in detail in the following examples.

[0120] More specifically, the vortex time can be approximately 40 seconds or less, approximately 35 seconds or less, approximately 33 seconds or less, or approximately 30 seconds or less. Furthermore, a smaller vortex time is preferable. Theoretically, the lower limit for the vortex time is 0 seconds; however, it can be, for example, approximately 10 seconds or more, approximately 15 seconds or more, or approximately 20 seconds or more.

[0121] The methods for measuring the water retention capacity, pressure absorption rate, and absorption rate of superabsorbent polymers will be described in more detail in the experimental examples described later.

[0122] Furthermore, when approximately 1 g of the superabsorbent polymer according to this disclosure is swollen with water having a conductivity of approximately 110 µS / cm for approximately 1 minute, the maximum capacity of water that can be retained in the superabsorbent polymer (free swelling capacity) can be approximately 230 g or less, approximately 225 g or less, approximately 220 g or less, or approximately 215 g or less, while being approximately 170 g or more, approximately 175 g or more, approximately 180 g or more, or approximately 185 g or more.

[0123] The method used to measure the absorption capacity in water with a conductivity of approximately 110 µS / cm will be described in more detail in the section on experimental examples, which will be described later.

[0124] On the other hand, the values ​​of roundness and aspect ratio according to this disclosure can be achieved by adjusting the composition / content of the superabsorbent polymer, the manufacturing process conditions of the superabsorbent polymer, etc.

[0125] The roundness and aspect ratio can be controlled to have values ​​within a specific range by adjusting the following: for example, the type and content of the monomer composition; the type and content of the crosslinking agent during polymerization; or the type, amount and time of the surfactant; the type, amount and time of the neutralizing agent; and the type, speed, orifice size and number of micronization steps of the micronization device in the neutralization and micronization steps.

[0126] This will be described in more detail in Part II. Production Methods of Superabsorbent Polymers.

[0127] The components that make up the superabsorbent polymer will be described in more detail below.

[0128] According to one aspect of this disclosure, a polyacrylic acid (salt)-based superabsorbent polymer comprises a base resin powder comprising a crosslinked polymer of a water-soluble olefinically unsaturated monomer having an acidic group and an internal crosslinking agent. The crosslinked polymer can be formed by polymerizing a monomer composition comprising components such as monomers, internal crosslinking agents, and polymerization initiators.

[0129] Here, the water-soluble olefinically unsaturated monomer can be any monomer commonly used in the production of superabsorbent polymers. As a non-limiting example, the water-soluble olefinically unsaturated monomer can be a compound represented by Formula 1:

[0130] [Chemical Formula 1]

[0131]

[0132] In chemical formula 1,

[0133] R is a hydrocarbon group containing 2 to 5 carbon atoms and an unsaturated bond, and

[0134] M' can be a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0135] In some respects, the monomer may be one or more selected from (meth)acrylic acid and monovalent (alkali) metal salts, divalent metal salts, ammonium salts and organic amine salts of these acids.

[0136] The use of (meth)acrylic acid and / or its salts as water-soluble olefinic unsaturated monomers is advantageous because it yields superabsorbent polymers with improved absorbency. Furthermore, substances that can be used as monomers include: maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide, N-substituted (meth)acrylates, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxy polyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide, etc.

[0137] Water-soluble olefinically unsaturated monomers have acidic groups. On the other hand, in the production of superabsorbent polymers, monomers in which at least some of the aforementioned acidic groups are neutralized by a neutralizing agent are crosslinked and polymerized to form a polymer. However, in this disclosure, the acidic groups can be neutralized after polymer formation, rather than during polymerization. More specific details regarding this will be described in the section concerning the production method of superabsorbent polymers.

[0138] The concentration of water-soluble olefinic unsaturated monomers in the monomer composition can be appropriately adjusted by considering polymerization time and reaction conditions, and can be from about 20% to about 60% by weight, or from about 20% to about 40% by weight.

[0139] The term "internal crosslinking agent" as used in this specification is used to distinguish it from surface crosslinking agents (which will be described later) used to crosslink the surface of superabsorbent polymer particles. Internal crosslinking agents are used to form polymers containing crosslinked structures by introducing crosslinks between the unsaturated bonds of the aforementioned water-soluble olefinic unsaturated monomers.

[0140] The crosslinking in the above steps can occur on the surface or inside without distinction between surface and interior. However, in the case where the surface crosslinking process of the superabsorbent polymer particles described later is carried out, the surface of the final produced superabsorbent polymer particles may contain newly crosslinked structures by the surface crosslinking agent, and the structures crosslinked by the internal crosslinking agent may remain inside the superabsorbent polymer particles.

[0141] According to one aspect of this disclosure, the internal crosslinking agent may include any one or more of a multifunctional acrylate-based compound, a multifunctional allyl-based compound, or a multifunctional vinyl-based compound.

[0142] Non-limiting examples of multifunctional acrylate-based 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, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, and pentaerythritol di(meth)acrylate. Acrylates, pentaerythritol tri(meth)acrylates, pentaerythritol tetra(meth)acrylates, dipentaerythritol di(meth)acrylates, dipentaerythritol tri(meth)acrylates, dipentaerythritol tetra(meth)acrylates, dipentaerythritol penta(meth)acrylates, trimethylolpropane di(meth)acrylates, trimethylolpropane tri(meth)acrylates, glycerol di(meth)acrylates and glycerol tri(meth)acrylates, wherein one of these may be used alone, or a mixture of two or more may be used.

[0143] Non-limiting examples of multifunctional allyl-based 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, butanediol 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, trimethylolpropane triallyl ether, glycerol diallyl ether, and glycerol triallyl ether, wherein one of these may be used alone, or a mixture of two or more may be used.

[0144] Non-limiting examples of multifunctional vinyl-based 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, butanediol 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 trivinyl ether, glycerol divinyl ether, and glycerol trivinyl ether, wherein one of these may be used alone, or a mixture of two or more may be used. In one or more aspects, pentaerythritol triallyl ether may be used.

[0145] In the aforementioned multifunctional allyl-based or vinyl-based compounds, two or more unsaturated groups in the molecule are bonded to the unsaturated bonds of a water-soluble olefinic unsaturated monomer or to the unsaturated bonds of another internal crosslinking agent, thereby forming a crosslinked structure during the polymerization process. Therefore, unlike acrylate-based compounds containing ester bonds (-(C=O)O-) in the molecule, the crosslinking can be maintained more stably even during the neutralization process following the polymerization reaction (which will be described later).

[0146] Therefore, the gel strength of the produced superabsorbent polymer can be improved, the process stability during the discharge process after polymerization can be improved, and the amount of water-soluble components can be minimized.

[0147] The crosslinking and polymerization of water-soluble olefinic unsaturated monomers in the presence of such internal crosslinking agents can be carried out in the presence of polymerization initiators and (as needed) thickeners, plasticizers, storage stabilizers, antioxidants, etc.

[0148] In the monomer composition, the internal crosslinking agent can be used such that its amount is from about 0.01 parts by weight to about 5 parts by weight relative to 100 parts by weight of water-soluble olefinic unsaturated monomer. For example, the internal crosslinking agent can be used such that its amount is about 0.01 parts by weight or more, about 0.05 parts by weight or more, or about 0.1 parts by weight or more, and about 5 parts by weight or less, about 3 parts by weight or less, about 2 parts by weight or less, about 1 part by weight or less, or about 0.7 parts by weight or less, relative to 100 parts by weight of water-soluble olefinic unsaturated monomer. Where the content of the internal crosslinking agent is too low, crosslinking may not proceed sufficiently, making it difficult to achieve an appropriate level or higher of strength; where the content of the internal crosslinking agent is too high, the internal crosslinking density may increase, making it difficult to achieve the desired water retention capacity. In particular, within the above ranges, it is suitable for achieving the roundness and aspect ratio according to the present disclosure within the target range.

[0149] On the other hand, when a low content of internal crosslinking agent is used to manufacture a base resin with high water retention capacity (CRC), the gel strength of the resulting polymer may be reduced, and due to the low gel strength, it may be difficult to operate the shredder during the shredding of the hydrogel polymer. In this case, for the operation of high-speed rotary shredders, the gel strength can be increased by using a mixture of two or more internal crosslinking agents, thereby improving the operational stability of the shredder.

[0150] On the other hand, when a low content of internal crosslinking agent is used to manufacture a base resin with high water retention capacity (CRC), the gel strength of the resulting polymer may be reduced, and due to the low gel strength, it may be difficult to operate the shredder during the shredding of the hydrogel polymer. In this case, for the operation of high-speed rotary shredders, the gel strength can be increased by using a mixture of two or more internal crosslinking agents, thereby improving the operational stability of the shredder.

[0151] In cases where the polymer has a three-dimensional network structure, the overall physical properties of the superabsorbent polymer, including water retention capacity and pressure absorption rate, can be significantly improved compared to a two-dimensional linear structure that has not undergone additional cross-linking through an internal cross-linking agent.

[0152] The polymer is, for example, a polymer obtained by polymerizing a monomer and an internal crosslinking agent in the presence of a polymerization initiator, wherein the type of polymerization initiator is not particularly limited. However, polymerization can be carried out in a batch reactor using a thermal polymerization method, and therefore a thermal polymerization initiator can be used as the polymerization initiator.

[0153] As a thermal polymerization initiator, one or more of the following can be used: persulfate-based initiators, azo-based initiators, and initiators composed of hydrogen peroxide and ascorbic acid. Specifically, examples of persulfate-based initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8), and examples of azo-based initiators include 2,2-azobis(2-amidinepropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, and 4,4-azobis(4-cyanopentanoic acid). Many more different thermal polymerization initiators are fully described on page 203 of the book "Principle of Polymerization" by Odian (Wiley, 1981), and thermal polymerization initiators are not limited to the examples mentioned above.

[0154] A polymerization initiator can be used such that its amount is 2 parts by weight or less relative to 100 parts by weight of water-soluble olefinic unsaturated monomer. That is, if the concentration of the polymerization initiator is too low, the polymerization rate may be slow, and a large amount of residual monomer may be extracted from the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is higher than the above range, the polymer chains constituting the network become shorter. Therefore, the physical properties of the resin may be reduced, i.e., the content of water-soluble components increases, and the absorption rate under pressure decreases, which is also undesirable.

[0155] On the other hand, in one aspect of this disclosure, polymerization can be initiated by adding a reducing agent that forms a redox pair with the above-mentioned polymerization initiator to the monomer composition.

[0156] Specifically, when an initiator and a reducing agent are added to the polymer solution, they react with each other to form free radicals.

[0157] The resulting free radicals react with the monomers, and due to the highly reactive redox reaction between the initiator and the reductant, polymerization is initiated even with only trace amounts of initiator and reductant added. Therefore, there is no need to increase the process temperature, allowing for low-temperature polymerization and minimizing changes in the physical properties of the polymer solution.

[0158] Polymerization reactions utilizing redox reactions can proceed smoothly even at temperatures close to or below ambient temperature (25°C). For example, polymerization reactions can be carried out at temperatures of about 5°C or higher and about 25°C or lower, or about 5°C or higher and about 20°C or lower.

[0159] In one aspect of this disclosure, where a persulfate-based initiator is used as the initiator, the reducing agent used may be selected from one or more of the following: sodium metabisulfite (Na2S2O5); tetramethylethylenediamine (TMEDA); a mixture of ferrous(II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinacetic acid.

[0160] For example, potassium persulfate can be used as an initiator and disodium 2-hydroxy-2-sulfinylacetate can be used as a reducing agent; ammonium persulfate can be used as an initiator and tetramethylethylenediamine can be used as a reducing agent; or sodium persulfate can be used as an initiator and sodium formaldehyde sulfoxylate can be used as a reducing agent.

[0161] In another aspect of this disclosure, where a hydrogen peroxide-based initiator is used as the initiator, the reducing agent may be selected from one or more of the following: ascorbic acid; sucrose; sodium sulfite (Na2SO3); sodium metabisulfite (Na2S2O5); tetramethylethylenediamine (TMEDA); a mixture of ferrous(II) sulfate and EDTA (FeSO4 / EDTA); sodium formaldehyde sulfoxylate; disodium 2-hydroxy-2-sulfinacetic acid; and disodium 2-hydroxy-2-sulfonacetic acid.

[0162] Depending on the requirements, the monomer composition may also contain additives such as thickeners, plasticizers, storage stabilizers and antioxidants.

[0163] Furthermore, the monomer composition containing the monomer can be in a solution dissolved in a solvent (e.g., water). Moreover, the solids content (i.e., the concentrations of the monomer, internal crosslinking agent, and polymerization initiator) in such a solution composition can be appropriately adjusted taking into account the polymerization time and reaction conditions. For example, the solids content in the monomer composition can be from about 10% to about 80% by weight, from about 15% to about 60% by weight, or from about 30% to about 50% by weight.

[0164] In this case, the solvents that can be used are not restricted in their composition, as long as they can dissolve the aforementioned components. For example, a combination of one or more of the following can be used: 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 pentyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, etc.

[0165] Because the polymerization is carried out using olefinically unsaturated monomers in an unneutralized state, the polymers obtained by this method can form polymers with high molecular weight and uniform molecular weight distribution, and because the content of water-soluble components is reduced, they are suitable for achieving target roundness and aspect ratio within an appropriate range.

[0166] In addition, the water content of the polymer can be from about 30% by weight to about 80% by weight. For example, the water content of the polymer can be about 80% by weight or less, about 70% by weight or less, or about 60% by weight or less, while being about 30% by weight or more, about 45% by weight or more, or about 50% by weight or more.

[0167] If the polymer's water content is too low, it may be difficult to ensure an adequate surface area in the subsequent pulverization step, rendering the pulverization ineffective. If the polymer's water content is too high, the increased pressure in the subsequent pulverization step makes it difficult to pulverize to the desired particle size.

[0168] On the other hand, throughout this specification, "water content" refers to the amount of water in the total weight of the polymer, meaning the value obtained by subtracting the weight of the polymer in its dry state from the weight of the polymer itself. Specifically, the water content is defined as a value calculated by measuring the weight loss due to the evaporation of water in the polymer during the drying process of the polymer in its flaky state by raising the temperature via infrared heating. In this case, the drying conditions are as follows: the temperature is raised from room temperature to approximately 180°C, and then the temperature is maintained at approximately 180°C. The total drying time is set to approximately 40 minutes, including approximately 5 minutes for the heating step, and then the water content is measured.

[0169] The superabsorbent polymer according to one aspect of this disclosure comprises: a base resin powder containing a water-soluble olefinic unsaturated monomer having an acidic group and an internal crosslinking agent; and a surface crosslinking layer formed on the base resin powder, wherein the surface crosslinking layer is obtained by further crosslinking the crosslinking polymer via a surface crosslinking agent.

[0170] A surface crosslinking layer is formed on at least a portion of the surface of the base resin powder, and it can be such a layer formed by further crosslinking the crosslinking polymer contained in the base resin powder via a surface crosslinking agent.

[0171] As a surface crosslinking agent, any surface crosslinking agent conventionally used in the production of superabsorbent polymers can be used without any restrictions. For example, surface crosslinking agents include: 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; one or more carbonate-based compounds selected from ethylene carbonate, propylene carbonate, and glyceryl carbonate; and epoxy compounds, such as ethylene glycol diglycidyl ether. Azoline compounds, for example azole ketones; polyamine compounds; monoamines 2-oxazolidinone, dioxazolidinone azole ketones or polyoxinones Azoxyl ketone compounds; cyclic urea compounds; etc.

[0172] Specifically, one or more, two or more, or three or more of the above-mentioned surface crosslinking agents can be used as surface crosslinking agents, such as ethylene carbonate-propylene carbonate (ECPC), propylene glycol and / or glyceryl carbonate.

[0173] A surface crosslinking agent can be used such that its amount relative to 100 parts by weight of superabsorbent polymer particles is from about 0.001 parts by weight to about 5 parts by weight. For example, a surface crosslinking agent can be used such that its content relative to 100 parts by weight of superabsorbent polymer particles is about 0.005 parts by weight or more, about 0.01 parts by weight or more, or about 0.05 parts by weight or more, and about 5 parts by weight or less, about 4 parts by weight or less, or about 3 parts by weight or less. By adjusting the content range of the surface crosslinking agent to the above range, superabsorbent polymers exhibiting excellent overall absorption physical properties can be produced. In particular, within the above range, it is suitable for achieving the sphericity and aspect ratio of the present disclosure within the target range.

[0174] Furthermore, the surface crosslinking layer can be formed by adding inorganic materials to the surface crosslinking agent. That is, the surface crosslinking layer can be formed by further crosslinking the surface of the base resin powder in the presence of the surface crosslinking agent and inorganic materials.

[0175] As such inorganic materials, one or more inorganic materials selected from silica, clay, alumina, silica-alumina composites, titanium dioxide, zinc oxide, and aluminum sulfate can be used. The inorganic materials can be used in powder or liquid form, and particularly, they can be used as alumina powder, silica-alumina powder, titanium dioxide powder, or nano-silica solution. Furthermore, inorganic materials can be used such that their content is from about 0.001 parts by weight to about 1 part by weight relative to 100 parts by weight of superabsorbent polymer particles.

[0176] As described above, by adjusting the roundness and aspect ratio of the parameters for this application within a specific range, the superabsorbent polymer comprising a base resin powder and a surface cross-linked layer formed on the base resin powder can absorb excreted bodily fluids at a high rate, and furthermore, when applied to hygiene products such as diapers, it allows for the absorption of relatively large amounts in the early stages, which makes it possible to prevent problems such as the accumulation of bodily fluids inside the hygiene product or leakage to its exterior.

[0177] II. Production method of superabsorbent polymer

[0178] On the other hand, superabsorbent polymers in related technologies are produced by crosslinking and polymerizing water-soluble olefinic unsaturated monomers having at least some neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer. The hydrogel polymer formed in this way is then dried, and the dried hydrogel polymer is pulverized to a desired particle size. In this case, to promote the drying of the hydrogel polymer and to improve the efficiency of the pulverization process, a shredding process is typically performed before the drying process, in which the hydrogel polymer is cut into particles of a few millimeters in size. However, during such shredding, due to the adhesiveness of the hydrogel polymer, it cannot be pulverized to the level of micron-sized particles and remains in the form of aggregated gels. When such aggregated hydrogel polymers in the form of aggregated gels are dried, a plate-like dried body is formed. To pulverize the plate-like dried body to the level of micron-sized particles, a multi-step pulverization process is required to reduce the adhesiveness of the polymer, which therefore causes the problem of generating many fine powders in the process.

[0179] Specifically, the superabsorbent polymers in the relevant technology are produced by the following steps.

[0180] (Neutralization) The step of neutralizing at least some of the acidic groups in a water-soluble olefinic unsaturated monomer;

[0181] (Polymerization) The step of crosslinking and polymerizing a water-soluble olefinic unsaturated monomer having at least some of its neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer;

[0182] (Chopping) The step of chopping the hydrogel polymer;

[0183] (Drying) The step of drying the shredded hydrogel polymer; and

[0184] (Grinding / Grading) The step of grinding the dried polymer and then grading it into normal particles and fine powder.

[0185] As described above, the shredded hydrogel polymer has the form of aggregated gel with a size of about 1 cm to about 10 cm, and such shredded hydrogel polymer is laminated on a belt having a bottom composed of a porous plate, and dried by hot air supplied from below or above. Since the polymer dried by the above drying method has a plate-like shape rather than a granular shape, a grading step is performed after pulverization, thus having a grading step after coarse pulverization and a re-grading step after pulverization, so that the produced particles are normal particles, that is, particles with a particle diameter of about 150 μm to about 850 μm. Since the amount of fine powder separated in the final grading step by such a production method is as high as about 20% to about 30% by weight relative to the total weight of the finally produced superabsorbent polymer, the separated fine powder is reused in a method in which the separated fine powder is mixed with an appropriate amount of water to make it fine powder again, and then loaded into the shredding step or pre-drying step.

[0186] However, the practice of re-powdering the fine powder mixed with water and then reloading it into the pulverizing or drying process for reuse causes problems such as increased equipment load and / or energy consumption, as well as deterioration of the physical properties of the superabsorbent polymer due to the retention of ungraded fine powder.

[0187] As a result of repeated research to solve this problem, it was determined that instead of polymerizing in a state where the acidic groups of the water-soluble olefinic unsaturated monomers are neutralized, as in conventional production methods for superabsorbent polymers, polymerization is first carried out in a state where the acidic groups are not neutralized to form a polymer, and the hydrogel polymer is micronized in the presence of a surfactant, and then the acidic groups of the polymer are neutralized; or in a state where the acidic groups of the polymer are neutralized to form a hydrogel polymer, and then the hydrogel polymer is micronized in the presence of a surfactant; or in a state where the acidic groups present in the polymer are simultaneously neutralized and micronized, a large amount of surfactant is present on the surface of the polymer, and the high adhesiveness of the polymer is reduced, thereby preventing excessive aggregation of the polymer, and thus the surfactant can be fully used to adjust the cohesive state to the desired level.

[0188] In this case, where ultrafine pulverization is performed by applying high-intensity mechanical shear force during the micronization step, aggregated hydrogel particles with micropores can be formed.

[0189] The hydrogel polymer produced by ultrafine grinding via the application of high-intensity mechanical shear force is produced in the form of particles with stable micropores of about 100 μm or smaller. Since the grinding and drying processes are carried out under relatively mild conditions, this allows for a further reduction in the amount of fine powder generated during the process.

[0190] Furthermore, by using an ultrafine pulverization process with high-intensity mechanical shear force, the absorption rate can be improved by forming micropores in the hydrogel polymer, even without the use of a separate foaming agent in the polymerization step. Therefore, the roundness and aspect ratio (A / R) of the aforementioned superabsorbent polymers according to various aspects of this disclosure can be easily controlled within target ranges.

[0191] On the other hand, the hydrogel micronization process can be carried out in the presence of surfactants. By using surfactants in the micronization step, particle aggregation can be effectively controlled, thereby reducing the load on the equipment and enabling further improvements in productivity.

[0192] Furthermore, in cases where polymerization is first carried out in an unneutralized state to form a polymer, and then the acidic groups present in the polymer are neutralized, long-chain polymers can be formed, which makes it possible to reduce the content of water-soluble components that exist in an uncrosslinked state due to incomplete crosslinking.

[0193] Water-soluble components tend to elute when the superabsorbent polymer comes into contact with a liquid. Therefore, when the content of the water-soluble component is high, most of the eluted water-soluble component remains on the surface of the superabsorbent polymer, making the polymer sticky and reducing liquid permeability. Therefore, maintaining a low content of the water-soluble component is important for improving liquid permeability.

[0194] According to one aspect of this disclosure, since polymerization is carried out in an unneutralized state, the content of water-soluble components is reduced, and thus the liquid permeability of the superabsorbent polymer can be improved, which makes it easy to control the roundness and aspect ratio within the target range.

[0195] The method for producing a superabsorbent polymer according to one aspect of this disclosure will be described in more detail below, step by step.

[0196] Step 1: Aggregation Step

[0197] First, a monomer composition comprising a water-soluble olefinic unsaturated monomer having acidic groups and an internal crosslinking agent is polymerized to produce a base resin powder comprising a polymer obtained by crosslinking and polymerizing a water-soluble olefinic unsaturated monomer having acidic groups and an internal crosslinking agent.

[0198] This step can consist of a step of mixing a water-soluble olefinic unsaturated monomer with acidic groups, an internal crosslinking agent, and a polymerization initiator to prepare a monomer composition, and a step of polymerizing the monomer composition to form a polymer.

[0199] Here, all the contents described in Part I regarding the superabsorbent polymers described above can be applied in the same manner for the content of each component.

[0200] On the other hand, water-soluble olefinic unsaturated monomers have acidic groups. As previously described, in the production of superabsorbent polymers in related technologies, monomers in which at least some of the aforementioned acidic groups are neutralized by a neutralizing agent are crosslinked and polymerized to form a polymer. Specifically, in the step of mixing the water-soluble olefinic unsaturated monomer having acidic groups, an internal crosslinking agent, a polymerization initiator, and a neutralizing agent, at least some of the acidic groups of the water-soluble olefinic unsaturated monomer are neutralized.

[0201] However, according to one aspect of this disclosure, polymerization is first carried out in a state in which the acidic groups of the water-soluble olefinic unsaturated monomer are not neutralized, and then a polymer is formed.

[0202] Water-soluble olefinic unsaturated monomers (e.g., acrylic acid) with unneutralized acidic groups are liquid at room temperature, highly miscible with the solvent (water), and thus exist as a mixed solution in the monomer composition. However, water-soluble olefinic unsaturated monomers with neutralized acidic groups are solid at room temperature, exhibiting different solubilities depending on the temperature of the solvent (water), with lower temperatures resulting in lower solubility.

[0203] Water-soluble olefinic unsaturated monomers with unneutralized acidic groups exhibit higher solubility or miscibility in solvents (water) compared to monomers with neutralized acidic groups. Consequently, they do not precipitate even at low temperatures, thus favoring long-term polymerization at low temperatures. Therefore, by using water-soluble olefinic unsaturated monomers with unneutralized acidic groups for long-term polymerization, polymers with higher molecular weights and more uniform molecular weight distributions can be stably formed.

[0204] Furthermore, long-chain polymers can be formed, which allows for a reduction in the content of water-soluble components that exist in an uncrosslinked state due to incomplete polymerization or crosslinking. Therefore, it is suitable for achieving the sphericity and aspect ratio of the aforementioned superabsorbent polymers according to various aspects of this disclosure within the target range.

[0205] Furthermore, in cases where polymerization is first carried out in such a state where the acidic groups of the monomers are not neutralized to form a polymer, and after neutralization, micronization is carried out in the presence of a surfactant, or in cases where micronization is carried out in the presence of a surfactant followed by neutralization, or where the acidic groups present in the polymer are simultaneously neutralized and micronized, a large amount of surfactant is present on the surface of the polymer, and the surfactant can be fully used to reduce the adhesiveness of the polymer.

[0206] According to one aspect of this disclosure, the step of polymerizing the monomer composition to form a polymer can be carried out in a batch reactor for about 1 hour or longer.

[0207] In general production methods of superabsorbent polymers, polymerization methods are broadly classified into thermal polymerization and photopolymerization, depending on the energy source used for polymerization. Typically, thermal polymerization can be carried out in a reactor with a stirring shaft, such as a kneader, while photopolymerization can be carried out in a flat-bottomed container.

[0208] On the other hand, in cases where polymerization is carried out as continuous polymerization, for example, in cases where polymerization takes place in a reactor equipped with a conveyor belt, polymerization is carried out continuously by supplying new monomer compositions to the reactor while the polymerized product is being moved, resulting in a mixture of polymers with different polymerization rates. Therefore, it is difficult to achieve uniform polymerization throughout the monomer composition, which may lead to a decrease in overall physical properties.

[0209] However, according to one aspect of this disclosure, since polymerization is carried out in a fixed-bed manner in a batch reactor, the risk of mixing polymers with different polymerization rates is small, and therefore, polymers with uniform quality can be obtained.

[0210] Furthermore, the polymerization step is carried out in a batch reactor with a predetermined volume, and the polymerization reaction proceeds for a longer time than in the case of continuous polymerization in a reactor equipped with a conveyor belt, for example, 1 hour or longer, 3 hours or longer, or 6 hours or longer. Despite such a long polymerization reaction time as described above, the monomers are unlikely to precipitate even during long polymerization periods because the unneutralized water-soluble olefinic unsaturated monomers are polymerized, thus favoring long-term polymerization.

[0211] On the other hand, since the polymerization in the batch reactor in this disclosure uses a thermal polymerization method, a thermal polymerization initiator is used as the polymerization initiator, and the description of the corresponding components is as described above.

[0212] Steps 2 and 3: Micronization and Neutralization Steps

[0213] Next, a step (step 2) is provided to micronize the hydrogel polymer in the presence of a surfactant to produce a mixture comprising the micronized hydrogel polymer.

[0214] The micronization step is a step of micronizing a polymer in the presence of a surfactant, wherein the polymer is micronized to a size of tens to hundreds of micrometers and simultaneously aggregated, rather than cutting the polymer into millimeter-sized particles.

[0215] In other words, it is a step in producing secondary aggregated particles, which have the shape of primary particles aggregated to a size of tens to hundreds of micrometers by imparting appropriate adhesiveness to the polymer. The aqueous superabsorbent polymer particles produced in such a step, as secondary aggregated particles, have a significantly increased surface area while maintaining a normal particle size distribution, which can significantly improve the absorption rate.

[0216] On the other hand, in the case of ultrafine pulverization by applying high-intensity mechanical shear force in the micronization step at a rotation speed of about 500 rpm to about 4,000 rpm, aggregated hydrogel particles with micropores can be formed.

[0217] In this case, due to the application of high-intensity mechanical shear force during ultrafine grinding at speeds of approximately 500 rpm to approximately 4,000 rpm, micropores of 100 μm or smaller are readily formed in the polymer. However, this results in increased surface roughness, and the total surface area of ​​the polymer increases significantly due to the pores formed both inside and outside the polymer particles. Since the micropores form in a stable form compared to the pores formed using a foaming agent in the polymerization step, the degree of fine powder production due to pores in subsequent processes can be significantly reduced. In the superabsorbent polymer particles produced by such a step, the surface area is greatly increased, which can significantly improve the absorption rate. Therefore, it is suitable for achieving the sphericity and aspect ratio of the aforementioned superabsorbent polymers according to various aspects of this disclosure within the target range.

[0218] The ultrafine grinding process is carried out at speeds from approximately 500 rpm to approximately 4,000 rpm. However, when the speed is less than approximately 500 rpm, it is difficult to form sufficient pores at the target level. Therefore, it is difficult to expect high absorption rates and ensure the target level of productivity. Furthermore, when the speed exceeds approximately 4,000 rpm, the polymer chains may be damaged due to excessive shear forces, and thus the amount of water-soluble components may increase, which may degrade the overall physical properties of the produced superabsorbent polymer. The ultrafine grinding process can be carried out at speeds from approximately 1,000 rpm to approximately 3,500 rpm, or from approximately 2,000 rpm to approximately 3,000 rpm. Within these ranges, the target micropores are easily formed without the aforementioned problems.

[0219] According to one aspect of this disclosure, the micronization step is performed using a micronization apparatus, and the micronization apparatus may include: a main body including a transfer space having an interior into which a polymer is transferred; a screw member rotatably mounted inside the transfer space to move the polymer; a drive motor providing a rotational driving force to the screw member; a cutter member mounted on the main body to pulverize the polymer; and a porous plate having a plurality of holes formed therein, wherein the porous plate discharges the polymer pulverized by the cutter member to the outside of the main body.

[0220] In this case, the pore size provided in the porous plate of the micronization device can be about 1 mm to about 25 mm, about 5 mm to about 20 mm, or about 5 mm to about 15 mm.

[0221] In cases where polymers mixed with surfactants are micronized while agglomeration is controlled using a micronization device, a smaller particle size distribution is achieved, and thus the subsequent drying and pulverizing processes can be carried out under milder conditions. Therefore, the physical properties of superabsorbent polymers can be improved while preventing the generation of fine powder, and in cases where ultrafine pulverization is performed, the absorption rate can be improved by increasing the surface area through the simultaneous formation of appropriate micropores on the polymer surface.

[0222] The micronization step can be performed once or more, and can be performed 1 to 6 times, 1 to 4 times, or 1 to 3 times. This can be done using multiple micronization devices, or it can be done using a single micronization device comprising multiple perforated plates and / or multiple cutter components, wherein some of the multiple micronization devices may include multiple perforated plates and / or multiple cutter components.

[0223] According to one aspect of this disclosure, a surfactant can be additionally used in the micronization step. This effectively controls the aggregation between polymer particles and thus reduces the load on the equipment used in the pulverization process, allowing for further improvements in productivity.

[0224] In some respects, compounds represented by chemical formula 2 or their salts may be used as surfactants; however, this disclosure is not limited thereto:

[0225] [Chemical Formula 2]

[0226]

[0227] In chemical formula 2,

[0228] A1, A2, and A3 are each independently a single bond, a carbonyl group, and... , ,or The condition is that one or more of these are carbonyl groups or Where m1, m2, and m3 are each independent integers from 1 to 8. Connected to the adjacent oxygen atom, Connect to adjacent R1, R2, and R3.

[0229] R1, R2, and R3 are each independently hydrogen, a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms, and

[0230] n is an integer from 1 to 9.

[0231] The surfactant is mixed with the polymer and then added, which allows the micronization step to be carried out easily without aggregation.

[0232] The surfactant represented by Formula 2 is a nonionic surfactant and, due to hydrogen bonding, exhibits excellent surface adsorption properties even with unneutralized polymers, thus making it suitable for achieving targeted aggregation control. On the other hand, in the case of anionic surfactants that are not nonionic surfactants, when mixed with polymers neutralized by neutralizing agents such as NaOH or Na₂SO₄, their adsorption is achieved via Na₂SO₄ ionized by the carboxyl substituents of the polymer. + Ion adsorption, and when mixed with unneutralized polymers, presents a problem where the adsorption efficiency of the polymer is relatively reduced due to competition with anions of the polymer's carboxyl substituents.

[0233] Specifically, in the surfactant represented by Formula 2, the hydrophobic functional group is the terminal functional group R1, R2, or R3 (in the case that it is not hydrogen), and the hydrophilic functional group also includes the glycerol-derived portion in the chain and the terminal hydroxyl group (in which A n It is a single bond and R at the same time n In the case of hydrogen, n = 1 to 3). However, the glycerol-derived partial and terminal hydroxyl groups are hydrophilic functional groups and are used to improve the adsorption properties on the polymer surface. Therefore, the aggregation of superabsorbent polymer particles can be effectively suppressed.

[0234] In Formula 2, the hydrophobic functional groups R1, R2, and R3 (when not hydrogen) are each independently a linear or branched alkyl group having 6 to 18 carbon atoms, or a linear or branched alkenyl group having 6 to 18 carbon atoms. In this case, if the R1, R2, and R3 (when not hydrogen) are alkyl or alkenyl groups having fewer than 6 carbon atoms, the problem is that the short chain length may prevent effective control of particle aggregation. Furthermore, if the R1, R2, and R3 (when not hydrogen) are alkyl or alkenyl groups having more than 18 carbon atoms, the surfactant mobility is reduced, making effective mixing with the polymer impossible. This may also lead to an increase in the unit cost of the composition due to the increased cost of the surfactant.

[0235] In some respects, R1, R2, and R3 can be hydrogen, and when they are linear or branched alkyl groups having 6 to 18 carbon atoms, they can be 2-methylhexyl, n-heptyl, 2-methylheptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecanyl, n-hexadecyl, n-heptadecyl, or n-octadecyl; or when they are linear or branched alkenyl groups having 6 to 18 carbon atoms, they can be 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-decenyl, 2-undecenyl, 2-dodecenyl, 2-tweldecenyl, 2-tetradecenyl, 2-pentadecanenyl, 2-hexadecenyl, 2-heptadecenyl, or 2-octadecenyl.

[0236] Surfactants can be selected from compounds represented by the following chemical formulas 2-1 to 2-14:

[0237] [Chemical Formula 2-1]

[0238]

[0239] [Chemical Formula 2-2]

[0240]

[0241] [Chemical Formula 2-3]

[0242]

[0243] [Chemical Formula 2-4]

[0244]

[0245] [Chemical Formula 2-5]

[0246]

[0247] [Chemical Formula 2-6]

[0248]

[0249] [Chemical Formula 2-7]

[0250]

[0251] [Chemical Formula 2-8]

[0252]

[0253] [Chemical Formula 2-9]

[0254]

[0255] [Chemical Formula 2-10]

[0256]

[0257] [Chemical Formula 2-11]

[0258]

[0259] [Chemical Formula 2-12]

[0260]

[0261] [Chemical Formula 2-13]

[0262]

[0263] [Chemical Formula 2-14]

[0264] .

[0265] On the other hand, there is no particular limitation on the amount of surfactant used; however, based on ensuring productivity or equipment load conditions, the amount of surfactant used can be from about 0.06 g to about 0.48 g per 1,000 g of hydrogel polymer.

[0266] If too little surfactant is used, the surfactant may not be uniformly adsorbed onto the polymer surface, which may lead to particle re-aggregation after pulverization, or the water retention capacity and absorption performance, such as the absorption rate under pressure, may be degraded due to the large amount of surfactant being shared by the polymer. On the other hand, if too much surfactant is used, the overall physical properties of the resulting superabsorbent polymer may be degraded due to the reduced surface tension.

[0267] Therefore, for example, the surfactant can be used in amounts of about 0.06 g or more, about 0.1 g or more, or about 0.2 g or more, and about 0.48 g or less, about 0.45 g or less, or about 0.4 g or less per 1,000 g of hydrogel polymer. Thus, the sphericity and aspect ratio of the superabsorbent polymers described above according to various aspects of this disclosure can be easily controlled to target ranges.

[0268] There are no particular limitations on the method of mixing such surfactants with polymers, as long as it is a method that can be appropriately employed and used to uniformly mix the surfactants with the polymers. Specifically, surfactants can be mixed by dry methods, or mixed in solution after being dissolved in a solvent, or the surfactants can be melted and then mixed.

[0269] In the above, for example, the surfactant can be mixed in a solution state dissolved in a solvent. In this case, any kind of solvent, whether inorganic or organic, can be used without restriction; however, water is most suitable considering the ease of the drying process and the cost of the solvent recovery system. Furthermore, for the solution, methods can be used in which the surfactant and polymer are placed in a reaction vessel and then mixed, or in which the polymer is placed in a mixer and then the solution is sprayed; methods in which the polymer and solution are continuously supplied to a continuously operating mixer and then mixed; and so on.

[0270] On the other hand, when the surfactant is mixed in a solution dissolved in water, it can be used by diluting it into an aqueous solution with a concentration of about 0.01% to about 90%.

[0271] For example, where the surfactant is used at approximately 0.1 g per 1,000 g of hydrogel polymer, a 0.1% aqueous solution of 100 g can be used, obtained by dissolving 0.1 g of surfactant in 99.9 g of water. Alternatively, a 1% aqueous solution of 10 g can be used, obtained by dissolving 0.1 g of surfactant in 9.9 g of water.

[0272] That is, when using the same amount of surfactant, the surfactant can be used as an aqueous solution with the desired concentration by increasing or decreasing the water content, and the concentration can be appropriately adjusted by taking into account the physical properties of the final superabsorbent polymer produced.

[0273] According to one aspect of this disclosure, a step (step 3) is performed to neutralize at least some of the acidic groups of the polymer, wherein the micronization step of step 2 and the neutralization step of step 3 can be performed sequentially, alternately, or simultaneously.

[0274] That is, firstly, acidic groups are neutralized by adding a neutralizing agent to the polymer, and then a surfactant is added to the neutralized polymer to micronize the polymer mixed with the surfactant (as in step 3). (Step 2 can be performed sequentially), or the neutralizer and surfactant can be added to the polymer simultaneously for neutralization and micronization (steps 2 and 3 can be performed simultaneously). Alternatively, the surfactant can be added first, followed by the neutralizer (in step 2). (Step 3 can be performed sequentially). Alternatively, neutralizing agents and surfactants can be added alternately. Alternatively, after first adding surfactants and micronizing, neutralizing agents can be added for neutralization, and then additional surfactants can be added to the neutralized hydrogel polymer to further carry out the micronization process.

[0275] Here, where the neutralization step is performed independently of the micronization step in step 2, it can be carried out in such a way that the additive is added while the polymer is being pulverized. More specifically, a screw extruder comprising a perforated plate with a plurality of holes can be used. Compared to the micronization apparatus used in the micronization step described above, the screw extruder is a device that performs pulverization under mild conditions. The rotational speed can be from about 150 rpm to about 500 rpm, and the perforation of the perforated plate is from about 3 mm to about 25 mm; however, these are not limited to these.

[0276] The rotational speed of the screw extruder and the size of the orifice plate affect the discharge state of the superabsorbent polymer exiting the extruder, and the particle shape of the superabsorbent polymer can be changed according to the discharge state.

[0277] In particular, by adjusting the rotational speed of the screw extruder to about 150 rpm to about 500 rpm, the roundness and aspect ratio of the superabsorbent polymers described above according to various aspects of this disclosure can be controlled within a desired range.

[0278] In this case, alkaline substances that can neutralize acidic groups, such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide, can be used as neutralizing agents.

[0279] Furthermore, the degree of neutralization (which refers to the extent to which the acidic groups contained in the polymer are neutralized by the neutralizing agent) can be about 50 mol% to about 90 mol%, about 60 mol% to about 85 mol%, about 65 mol% to about 85 mol%, or about 65 mol% to about 80 mol%. The range of the degree of neutralization can be varied according to the final physical properties, and the absorption rate and absorption performance can be adjusted by regulating the degree of neutralization.

[0280] In such cases, if the degree of neutralization is too high, the absorption capacity of the superabsorbent polymer may decrease, and the concentration of carboxyl groups on the particle surface may be too low. Therefore, it becomes difficult to properly crosslink the surface in subsequent processes, which could reduce its absorption properties under pressure or its liquid permeability. Conversely, if the degree of neutralization is too low, not only is the polymer's absorption capacity significantly reduced, but it may also exhibit unmanageable properties, such as those of elastic rubber.

[0281] On the other hand, in order to neutralize the entire polymer evenly, a certain time interval can be left between the addition of the neutralizing agent and the micronization process.

[0282] Step 4: Drying Step

[0283] Next, the micronized and neutralized polymer is dried to produce a base resin powder (step 4).

[0284] The above steps are steps of neutralizing at least some of the acidic groups in the polymer and drying the moisture in the base resin powder of the polymer obtained by micronizing the polymer.

[0285] In a typical production method of superabsorbent polymers, during the drying step, the base resin powder is dried such that the water content is from about 4% to about 20% by weight, from about 4% to about 15% by weight, or from about 6% to about 13% by weight. However, this disclosure is not limited thereto.

[0286] Step 4 can be carried out by fixed-bed drying, mobile drying, or a combination thereof.

[0287] According to one aspect of this disclosure, step 4 can be performed by a fixed-bed drying process.

[0288] Fixed-bed drying refers to a method in which hot air is passed through the material from bottom to top to dry the material while it rests on a base plate, such as a perforated iron plate through which air can pass.

[0289] In fixed-bed drying, particles are dried in a plate-like state without moving, making it difficult to achieve uniform drying with simple hot air flow. Therefore, fixed-bed drying requires precise control of hot air and temperature to obtain a dried body with a uniform high moisture content. In this disclosure, a change has been made so that the hot air flows upward instead of downward, which prevents the plate-like dried body from bending during drying and thus prevents hot air leakage. Furthermore, the drying temperature is varied and adjusted for each section so that the top, bottom, left and right sides, as well as the upper, middle, and lower layers inside the dried body, can be dried uniformly with a moisture content deviation of less than about 5%.

[0290] As an apparatus configured to perform drying by a fixed-bed drying method, a belt dryer or the like can be used; however, the apparatus is not limited to this.

[0291] In the case of a fixed-bed drying step, the drying process can be carried out at a temperature of about 80°C to about 200°C, wherein the temperature can be from 90°C to 190°C or from 100°C to 180°C. If the drying temperature is below about 80°C, the drying time may be too long, and if the drying temperature is above about 200°C and therefore too high, a superabsorbent polymer with a water content lower than the target water content may be obtained. Alternatively, the drying temperature can refer to the temperature of the hot air used, or it can refer to the internal temperature of the apparatus during the drying process.

[0292] According to one aspect of this disclosure, step 4 can be performed by a mobile drying process.

[0293] Mobile drying refers to a method of drying the material while simultaneously subjecting it to mechanical agitation during the drying process. In this case, the direction of hot air passing through the material can be the same as or different from the material's circulation direction. Alternatively, the material can be dried by circulating it inside the dryer while the heat transfer fluid (heat transfer fluid) passes through a separate duct outside the dryer.

[0294] As an apparatus configured to perform drying by such a mobile drying method, a horizontal mixer, rotary kiln, paddle dryer, steam tube dryer, commonly used mobile dryer, etc., can be used.

[0295] In the case of a mobile drying step, the drying process can be carried out at a temperature of about 100°C to about 300°C, wherein the temperature can be from 120°C to 280°C or from 150°C to 250°C. If the drying temperature is below about 100°C and therefore too low, the drying time may be too long. If the drying temperature is above about 300°C and therefore too high, the polymer chains of the superabsorbent polymer may be damaged and the overall physical properties may deteriorate; furthermore, a superabsorbent polymer with a water content lower than the desired water content may be obtained.

[0296] Step 5: Crushing Step

[0297] Next, the dried base resin powder is pulverized.

[0298] Specifically, a pulverization step can be performed to pulverize the dry base resin powder to a particle size level at the normal particle size level, that is, a particle diameter of about 150 μm to about 850 μm.

[0299] The shredder used for this purpose can specifically be a vertical shredder, a turbine cutter, a turbine mill, a rotary shredder, a cutter mill, a disc mill, a fragment shredder, a crusher, a chopper, a disc cutter, etc., however, the shredder is not limited to the above examples.

[0300] Alternatively, pin mills, hammer mills, screw mills, roller mills, disc mills, jogging mills, etc., can be used as pulverizers; however, pulverizers are not limited to the examples mentioned above.

[0301] On the other hand, in the production method according to this disclosure, in the micronization step, superabsorbent polymer particles with a small particle size distribution can be obtained compared to a conventional shredding step. Furthermore, even when shredding is performed under mild conditions with a small shredding force, superabsorbent polymers with a very high content and a normal particle size of about 150 μm to about 850 μm can be formed, and since the water content remains relatively high after drying, the rate of fine powder generation can be significantly reduced.

[0302] The superabsorbent polymer granules produced as described above may contain superabsorbent polymer granules (i.e., normal granules) with a particle diameter of about 150 μm to about 850 μm, such that their amount relative to the total weight is about 80% by weight or more, about 85% by weight or more, about 89% by weight or more, about 90% by weight or more, about 92% by weight or more, about 93% by weight or more, about 94% by weight or more, or about 95% by weight or more. The particle diameter of such resin granules can be measured according to the European Disposable Goods and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0303] Furthermore, the superabsorbent polymer particles may contain fine powder with a particle diameter of less than about 150 μm, such that, relative to the total weight, the amount is about 20% by weight or less, about 18% by weight or less, about 15% by weight or less, about 13% by weight or less, about 12% by weight or less, about 11% by weight or less, about 10% by weight or less, about 9% by weight or less, about 8% by weight or less, or about 5% by weight or less. This contrasts with the case where the superabsorbent polymer is produced according to the production method in the related art, where the fine powder comprises more than about 20% by weight to about 30% by weight.

[0304] Additive addition steps

[0305] On the other hand, according to one aspect of this disclosure, prior to the drying step (step 4), a step of adding additives to the micronized and neutralized polymer may also be provided.

[0306] The additive addition process is the process of improving physical properties by using additional additives without compromising the target effect. There are no particular limitations on the types of additives, and examples include, but are not limited to, polymerization initiators for removing residual monomers, liquid permeability improvers for improving absorption properties, fine powder anti-caking agents for recovering the resulting fine powder, flowability improvers, antioxidants, neutralizers, and surfactants.

[0307] The additive addition step can 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 additive addition step can be performed multiple times as needed and can be performed more than once in each step.

[0308] In cases where the additive addition step is performed independently of steps 2 and 3, i.e., where the additive addition step is performed after steps 2 and 3 and before step 4, it can be carried out in such a way that the additive is added while the polymer is being crushed.

[0309] For pulverization, the pulverization step described in step 5 above can typically be applied in the same manner, and in the pulverization step, the additive can be added once or multiple times and mixed with the polymer.

[0310] Grading steps

[0311] Next, after the step of pulverizing the base resin powder (step 5), a step of classifying the pulverized superabsorbent polymer particles according to the particle diameter can also be set.

[0312] Surface crosslinking steps

[0313] Furthermore, after pulverizing (step 5) and / or classifying the base resin powder, a step of forming a surface crosslinking layer on at least a portion of the surface of the base resin particles in the presence of a surface crosslinking agent may be included. Through the above steps, the crosslinked polymer contained in the base resin powder is further crosslinked via the surface crosslinking agent, and thus a surface crosslinking layer can be formed on at least a portion of the surface of the base resin powder.

[0314] In the description of surface crosslinking agents, all of the above can be applied in the same way.

[0315] Furthermore, there are no limitations on the configuration of the method for mixing the surface crosslinking agent with the base resin powder. Methods such as placing the surface crosslinking agent and the composition containing the base resin powder into a reaction vessel and mixing them, or spraying the surface crosslinking agent onto the composition, or continuously supplying the resin composition and the surface crosslinking agent to a continuously operating mixer and then mixing them, can be used.

[0316] When the surface crosslinking agent and the base resin powder are mixed, water and methanol can be mixed together and then added separately. Adding water and methanol has the advantage that the surface crosslinking agent can be uniformly dispersed in the resin composition. In this case, the content of added water and methanol can be appropriately adjusted to induce uniform dispersion of the surface crosslinking agent, prevent aggregation of the resin composition, and simultaneously optimize the surface penetration depth of the crosslinking agent.

[0317] The surface crosslinking process can be carried out at a temperature of about 80°C to about 250°C. More specifically, the surface crosslinking process can be carried out 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 surface crosslinking process conditions are met, the surface of the superabsorbent polymer particles can be fully crosslinked, thereby increasing the absorption rate under pressure.

[0318] There are no particular restrictions on the heating method used for surface crosslinking reactions.

[0319] Heating can be achieved by supplying a heat transfer medium or by directly supplying a heat source. In this case, regarding the type of heat transfer medium that can be used, fluids that raise the temperature, such as steam, hot air, or hot oil, can be used; however, the heat transfer medium is not limited to these. Furthermore, the temperature of the heat transfer medium to be supplied can be appropriately selected by considering the type of heat transfer medium, the heating rate, and the target heating rate. On the other hand, examples of directly supplied heat sources include electric heating and gas heating; however, directly supplied heat sources are not limited to the examples mentioned above.

[0320] Post-processing steps

[0321] According to one aspect of this disclosure, after the step of forming a surface crosslinking layer on at least a portion of the surface of the base resin powder, one or more of the following steps may be performed: a cooling step of cooling the superabsorbent polymer particles on which the surface crosslinking layer has been formed, a water addition step of adding water to the superabsorbent polymer particles on which the surface crosslinking layer has been formed, and a post-treatment step of adding an additive to the superabsorbent polymer particles on which the surface crosslinking layer has been formed. In this case, the cooling step, the water addition step, and the post-treatment step may be performed sequentially or simultaneously.

[0322] Water or brine can be used in the water addition step, and the amount of sieve debris can be controlled by using water or brine. The amount of water used can be appropriately adjusted taking into account the water content of the target final product, and water can be used in amounts such that it is about 0.1% to about 10% by weight, about 0.5% to about 8% by weight, or about 1% to about 5% by weight relative to the absorbent resin, and the amount is not limited thereto.

[0323] In addition, a ripening step can be performed after the water addition step.

[0324] When brine is used in the water addition step, the solution absorption rate is relatively low due to the conductivity of brine, and therefore the brine diffuses uniformly during the curing step, allowing the absorbent resin to absorb evenly. In the curing step, commonly used methods can be applied without particular limitation, and it can be carried out, for example, at about 10 minutes to about 1 hour using a rotary stirring device at about 100°C or lower, about 80°C or lower, or 50°C or lower.

[0325] The additives added in the post-processing step may be surfactants, inorganic salts, liquid permeability improvers, anti-caking agents, flowability improvers, antioxidants, etc., however, this disclosure is not limited to these.

[0326] By selectively performing cooling, water addition, and post-treatment steps, the generation of sieve debris can be controlled, thereby improving the water content of the final superabsorbent polymer and enabling the production of superabsorbent polymer products with higher quality.

[0327] In the following, the effects and functions of some aspects of this disclosure will be described in more detail through specific embodiments. However, these embodiments are presented merely as examples of some aspects of this disclosure, and therefore the scope of this disclosure is not determined by them.

[0328] <Example>

[0329] Example 1

[0330] (Step 1: Polymer production steps)

[0331] In a 5 L glass container equipped with a stirrer and thermometer, 1500 g of acrylic acid, 3.75 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3401 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the above mixture at approximately 1,000 cc / min for approximately 1 hour to purge the glass container under nitrogen conditions. Next, 30.0 g of 0.3% aqueous hydrogen peroxide solution, 15.0 g of 1% aqueous ascorbic acid solution, and 45.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 22.5 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0332] (Steps 2 and 3: Micronization and neutralization steps)

[0333] Add 100 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in step 1. Then, perform a micronization process by extruding the resulting mixture at approximately 2,000 rpm onto a porous plate with multiple holes of approximately 10 mm using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical shredder.

[0334] Subsequently, the recovered hydrogel polymer was extruded three times at 250 rpm through a porous plate with multiple 10 mm orifices using a screw extruder installed inside a cylindrical pulverizer, thus performing another pulverization process. Depending on the steps of the screw extruder, 1383 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to neutralize some of the acidic groups in the polymer, followed by the addition of 100 g of fine powder (another additive addition step) and 157 g of a 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0335] (Step 4: Drying step)

[0336] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0337] (Step 5: Crushing and Grading)

[0338] Use a grinder (GRAN-U-LIZER) TM The MPE (Medium-to-Earth Extraction) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0339] (Surface crosslinking step)

[0340] Next, every 100 g of base resin powder was sprayed with an aqueous solution of a surface crosslinking agent containing 4 g water, 6 g methanol, 0.05 g ethylene glycol diglycidyl ether (EJ-1030S), 0.1 g propylene glycol, and 0.2 g aluminum sulfate, and stirred at room temperature to mix the solution, ensuring a uniform distribution of the surface crosslinking solution on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to initiate a surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 140°C for approximately 40 minutes to obtain a surface-crosslinked superabsorbent polymer.

[0341] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters of approximately 150 μm to approximately 850 μm (water content: 1.8%).

[0342] Example 2

[0343] (Step 1: Polymer production steps)

[0344] The polymer was obtained in the same manner as in Example 1 above, except that 3.0 g of pentaerythritol triallyl ether (PETTAE) and 0.75 g of trimethylolpropane triacrylate (TMPTA) (Miramer M3190, a product from Miwon Specialty Chemical Co., Ltd.) were used instead of 3.75 g of pentaerythritol triallyl ether (PETTAE) as internal crosslinking agents.

[0345] (Steps 2 and 3: Micronization and neutralization steps)

[0346] Aqueous superabsorbent polymer particles (=micronized and neutralized polymer) were produced using the same method as in Example 1, except that the speed of the high-speed rotary shredder was set to approximately 2,500 rpm.

[0347] Subsequently, the steps of drying, pulverizing, grading and surface crosslinking were performed in the same manner as in Example 1, thereby producing a superabsorbent polymer (water content: 1.6%).

[0348] Example 3

[0349] (Post-processing steps)

[0350] The superabsorbent polymer produced in Example 2 was further subjected to a water addition step as follows.

[0351] Each 100 g of the superabsorbent polymer produced in Example 2 is sprayed with 4 g of water and about 0.4 g of an aqueous solution of a polycarboxylic acid-based copolymer and stirred to mix, such that the solution is uniformly distributed on the superabsorbent polymer powder. Subsequently, the mixture is uniformly mixed in a reactor at about 50°C for 20 minutes, thereby producing a superabsorbent polymer (water content: 4.6%).

[0352] Example 4

[0353] (Step 1: Polymer production steps)

[0354] The polymer was obtained in the same manner as in Example 1 above.

[0355] (Steps 2 and 3: Micronization and neutralization steps)

[0356] Add 299 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in step 1. Then, perform a micronization process by extruding the resulting mixture at approximately 2,000 rpm onto a porous plate with multiple holes of approximately 10 mm using a high-speed rotary shredder (F-150 / KarlSchnell) installed inside a cylindrical shredder.

[0357] Subsequently, the recovered hydrogel polymer was extruded three times at approximately 150 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder installed inside a cylindrical pulverizer, thus performing another pulverization process. Depending on the steps of the screw extruder, 1383 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to neutralize some of the acidic groups in the polymer, followed by the addition of 100 g of fine powder (another additive addition step) and 157 g of a 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0358] Subsequently, the steps of drying, pulverizing, grading and surface crosslinking were performed in the same manner as in Example 1, thereby producing a superabsorbent polymer (water content: 1.9%).

[0359] Example 5

[0360] (Step 1: Polymer production steps)

[0361] In a 5 L glass container equipped with a stirrer and thermometer, 1500 g of acrylic acid, 3.75 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3401 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at 1,000 cc / min for 1 hour to purge the container under nitrogen conditions. Next, 30.0 g of 0.3% aqueous hydrogen peroxide solution, 15.0 g of 1% aqueous ascorbic acid solution, and 45.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 22.5 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 85°C ± 2°C for approximately 8 hours to obtain the polymer.

[0362] (Steps 2 and 3: Micronization and neutralization steps)

[0363] Add 100 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in step 1. Then, perform a micronization process by extruding the resulting mixture at approximately 1,500 rpm onto a porous plate with multiple holes of approximately 15 mm using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical shredder.

[0364] Subsequently, the recovered hydrogel polymer was extruded three times at approximately 500 rpm through a porous plate with multiple holes of approximately 6 mm each using a screw extruder installed inside a cylindrical pulverizer, thus performing another pulverization process. Depending on the steps of the screw extruder, 1383 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to neutralize some of the acidic groups in the polymer, followed by the addition of 100 g of fine powder (another additive addition step) and 157 g of a 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0365] Subsequently, the steps of drying, pulverizing, grading and surface crosslinking were performed in the same manner as in Example 1, thereby producing a superabsorbent polymer (water content: 1.7%).

[0366] Example 6

[0367] (Step 1: Polymer production steps)

[0368] The polymer was obtained in the same manner as in Example 1 above, except that 3.0 g of pentaerythritol triallyl ether (PETTAE) and 0.75 g of trimethylolpropane triacrylate (TMPTA) (Miramer M3190, a product from MiwonSpecialty Chemical Co., Ltd.) were used instead of 3.75 g of pentaerythritol triallyl ether (PETTAE) as internal crosslinking agents.

[0369] (Steps 2 and 3: Micronization and neutralization steps)

[0370] Add 150 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in step 1. Then, perform a micronization process by extruding the resulting mixture at approximately 3,000 rpm onto a porous plate with multiple holes of approximately 10 mm using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical shredder.

[0371] Subsequently, the recovered hydrogel polymer was extruded three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder installed inside a cylindrical pulverizer, thus performing another pulverization process. Depending on the steps of the screw extruder, 1383 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to neutralize some of the acidic groups in the polymer, followed by the addition of 100 g of fine powder (another additive addition step) and 157 g of a 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0372] Subsequently, the steps of drying, pulverizing, grading and surface crosslinking were performed in the same manner as in Example 1, thereby producing a superabsorbent polymer (water content: 1.8%).

[0373] Comparative Example 1

[0374] (Step 1: Polymer production steps)

[0375] In a 5 L glass container equipped with a stirrer and thermometer, 1500 g of acrylic acid, 5.25 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3404 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the above mixture at approximately 1,000 cc / min for approximately 1 hour to purge the glass container under nitrogen conditions. Next, 30.0 g of 0.3% aqueous hydrogen peroxide solution, 15.0 g of 1% aqueous ascorbic acid solution, and 45.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 22.5 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0376] (Steps 2 and 3: Micronization and neutralization steps)

[0377] The micronization process is carried out by extruding 5,000 g of the polymer obtained in step 1 at a rotation speed of about 2,000 rpm onto a porous plate with multiple holes of about 10 mm in diameter using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical shredder.

[0378] Subsequently, the recovered hydrogel polymer was extruded three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder installed inside a cylindrical pulverizer, thus performing another pulverization process. Depending on the steps of the screw extruder, 1161 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to neutralize some of the acidic groups in the polymer, followed by the addition of 100 g of fine powder (another additive addition step) and 165 g of a 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0379] (Step 4: Drying step)

[0380] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0381] (Step 5: Crushing and Grading)

[0382] Use a grinder (GRAN-U-LIZER) TM The MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0383] (Surface crosslinking step)

[0384] Next, every 100 g of base resin powder was sprayed with an aqueous solution containing 5.5 g water, 6 g methanol, 0.15 g ethylene glycol diglycidyl ether (EJ-1030S), and 0.3 g aluminum sulfate, and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to carry out the surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 140°C for approximately 40 minutes to obtain a surface-crosslinked superabsorbent polymer.

[0385] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0386] Comparative Example 2

[0387] (Step 1: Polymer production steps)

[0388] In a 5 L glass container equipped with a stirrer and thermometer, 1500 g of acrylic acid, 5.25 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3404 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at approximately 1,000 cc / min for approximately 1 hour to purge the container under nitrogen conditions. Next, 30.0 g of 0.3% aqueous hydrogen peroxide solution, 15.0 g of 1% aqueous ascorbic acid solution, and 45.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 22.5 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0389] (Steps 2 and 3: Micronization and neutralization steps)

[0390] Add 597 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in step 1. Then, perform a micronization process by extruding the resulting mixture at approximately 2,000 rpm onto a porous plate with multiple orifices of approximately 10 mm using a high-speed rotary shredder (F-150 / Karl Schnell) installed inside a cylindrical shredder.

[0391] Subsequently, the recovered hydrogel polymer was extruded three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder installed inside a cylindrical pulverizer, thus performing another pulverization process. Depending on the steps of the screw extruder, 1037 g of a 50% NaOH aqueous solution (step 3: neutralization step) was added to neutralize some of the acidic groups in the polymer, followed by the addition of 100 g of fine powder (another additive addition step) and 150 g of a 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0392] (Step 4: Drying step)

[0393] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0394] (Step 5: Crushing and Grading)

[0395] Use a grinder (GRAN-U-LIZER) TM The MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0396] (Surface crosslinking step)

[0397] Next, an aqueous solution of a surface crosslinking agent containing 5.5 g water, 5 g methanol, and 0.07 g ethylene glycol diglycidyl ether (EJ-1030S) was sprayed onto every 100 g of base resin powder and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to carry out the surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 140°C for approximately 40 minutes to obtain a surface-crosslinked superabsorbent polymer.

[0398] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0399] Comparative Example 3

[0400] (Step 1: Polymer production steps)

[0401] In a 5 L glass container equipped with a stirrer and thermometer, 1500 g of acrylic acid, 3.75 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3400 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at approximately 1000 cc / min for 1 hour to purge the container under nitrogen conditions. Next, 30.0 g of 0.3% aqueous hydrogen peroxide solution, 15.0 g of 1% aqueous ascorbic acid solution, and 45.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 22.5 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0402] (Steps 2 and 3: Micronization and neutralization steps)

[0403] Add 100 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in Step 1. Then, perform another pulverization process by extruding the recovered hydrogel polymer three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder mounted inside a cylindrical pulverizer. Depending on the steps of the screw extruder, add 1383 g of 50% NaOH aqueous solution (Step 3: Neutralization step) to neutralize some of the acidic groups in the polymer, then add 100 g of fine powder (another additive addition step) and 162 g of 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0404] (Step 4: Drying step)

[0405] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0406] (Step 5: Crushing and Grading)

[0407] Use a grinder (GRAN-U-LIZER) TMThe MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0408] (Surface crosslinking step)

[0409] Next, an aqueous solution of a surface crosslinking agent containing 3.5 g water, 5 g methanol, and 0.12 g ethylene glycol diglycidyl ether (EJ-1030S) was sprayed onto every 100 g of base resin powder and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to carry out the surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 140°C for approximately 40 minutes to obtain a superabsorbent polymer that had undergone surface crosslinking.

[0410] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0411] Comparative Example 4

[0412] (Step 1: Polymer production steps)

[0413] In a 5 L glass container equipped with a stirrer and thermometer, 1500 g of acrylic acid, 3.0 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3399 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at approximately 1,000 cc / min for approximately 1 hour to purge the container under nitrogen conditions. Next, 30.0 g of 0.3% aqueous hydrogen peroxide solution, 15.0 g of 1% aqueous ascorbic acid solution, and 45.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 22.5 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0414] (Steps 2 and 3: Micronization and neutralization steps)

[0415] Add 100 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in Step 1. Then, perform another pulverization process by extruding the recovered hydrogel polymer three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder mounted inside a cylindrical pulverizer. Depending on the steps of the screw extruder, add 1140 g of 50% NaOH aqueous solution (Step 3: Neutralization step) to neutralize some of the acidic groups in the polymer, then add 100 g of fine powder (another additive addition step) and 162 g of 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0416] (Step 4: Drying step)

[0417] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0418] (Step 5: Crushing and Grading)

[0419] Use a grinder (GRAN-U-LIZER) TM The MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0420] (Surface crosslinking step)

[0421] Next, an aqueous solution of a surface crosslinking agent containing 5 g water, 6 g methanol, 0.15 g ethylene carbonate, and 0.38 g aluminum sulfate was sprayed onto every 100 g of base resin powder and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to initiate a surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 185°C for approximately 50 minutes to obtain a surface-crosslinked superabsorbent polymer.

[0422] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0423] Comparative Example 5

[0424] (Step 1: Polymer production steps)

[0425] In a 5 L glass container equipped with a stirrer and thermometer, 1450 g of acrylic acid, 3.63 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3454 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at approximately 1,000 cc / min for approximately 1 hour to purge the container under nitrogen conditions. Next, 29.0 g of 0.3% aqueous hydrogen peroxide solution, 14.5 g of 1% aqueous ascorbic acid solution, and 43.5 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 21.75 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0426] (Steps 2 and 3: Micronization and neutralization steps)

[0427] Add 96 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in Step 1. Then, perform another pulverization process by extruding the recovered hydrogel polymer three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder mounted inside a cylindrical pulverizer. Depending on the steps of the screw extruder, add 1417 g of 50% NaOH aqueous solution (Step 3: Neutralization step) to neutralize some of the acidic groups in the polymer, then add 100 g of fine powder (another additive addition step) and 159 g of 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0428] (Step 4: Drying step)

[0429] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0430] (Step 5: Crushing and Grading)

[0431] Use a grinder (GRAN-U-LIZER) TM The MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0432] (Surface crosslinking step)

[0433] Next, an aqueous solution of a surface crosslinking agent containing 3.5 g water, 5 g methanol, and 0.1 g ethylene glycol diglycidyl ether (EJ-1030S) was sprayed onto every 100 g of base resin powder and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to carry out the surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 140°C for approximately 40 minutes to obtain a superabsorbent polymer that had undergone surface crosslinking.

[0434] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0435] Comparative Example 6

[0436] (Step 1: Polymer production steps)

[0437] In a 5 L glass container equipped with a stirrer and thermometer, 1400 g of acrylic acid, 2.8 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3506 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at approximately 1,000 cc / min for approximately 1 hour to purge the container under nitrogen conditions. Next, 28.0 g of 0.3% aqueous hydrogen peroxide solution, 14.0 g of 1% aqueous ascorbic acid solution, and 42.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 21.0 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0438] (Steps 2 and 3: Micronization and neutralization steps)

[0439] Add 279 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in Step 1. Then, perform another pulverization process by extruding the recovered hydrogel polymer three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder mounted inside a cylindrical pulverizer. Depending on the steps of the screw extruder, add 1027 g of 50% NaOH aqueous solution (Step 3: Neutralization step) to neutralize some of the acidic groups in the polymer, then add 100 g of fine powder (another additive addition step) and 149 g of 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0440] (Step 4: Drying step)

[0441] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0442] (Step 5: Crushing and Grading)

[0443] Use a grinder (GRAN-U-LIZER) TMThe MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0444] (Surface crosslinking step)

[0445] Next, an aqueous solution of a surface crosslinking agent containing 3.5 g water, 5 g methanol, 0.15 g ethylene carbonate, and 0.2 g aluminum sulfate was sprayed onto every 100 g of base resin powder and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to carry out a surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 185°C for approximately 50 minutes to obtain a surface-crosslinked superabsorbent polymer.

[0446] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0447] Comparative Example 7

[0448] (Step 1: Polymer production steps)

[0449] In a 5 L glass container equipped with a stirrer and thermometer, 1400 g of acrylic acid, 2.8 g of pentaerythritol triallyl ether (PETTAE) as an internal crosslinking agent, and 3506 g of water were stirred and mixed, and then allowed to react while maintaining the temperature at approximately 5°C. Nitrogen gas was introduced into the glass container containing the mixture at approximately 1,000 cc / min for approximately 1 hour to purge the container under nitrogen conditions. Next, 28.0 g of 0.3% aqueous hydrogen peroxide solution, 14.0 g of 1% aqueous ascorbic acid solution, and 42.0 g of 2% aqueous 2,2'-azobis-(2-amidinylpropane)dihydrochloric acid solution were added as polymerization initiators, and simultaneously, 21.0 g of 0.01% aqueous ferrous sulfate solution was added as a reducing agent, thereby initiating polymerization. After the temperature of the mixture reached approximately 85°C, polymerization was carried out at approximately 90°C ± 2°C for approximately 6 hours to obtain the polymer.

[0450] (Steps 2 and 3: Micronization and neutralization steps)

[0451] Add 279 g of 0.45 wt% glyceryl monolaurate (GML) aqueous solution to 5,000 g of the polymer obtained in Step 1. Then, perform another pulverization process by extruding the recovered hydrogel polymer three times at approximately 250 rpm through a porous plate with multiple holes of approximately 10 mm each using a screw extruder mounted inside a cylindrical pulverizer. Depending on the steps of the screw extruder, add 1027 g of 50% NaOH aqueous solution (Step 3: Neutralization step) to neutralize some of the acidic groups in the polymer, then add 100 g of fine powder (another additive addition step) and 149 g of 10% Na2SO4 aqueous solution (another additive addition step) to produce aqueous superabsorbent polymer particles (=micronized and neutralized polymer).

[0452] (Step 4: Drying step)

[0453] 1,000 g of water-containing superabsorbent polymer granules were loaded into a dryer comprising a perforated plate configured to allow airflow in either upward or downward directions. To achieve a water content of approximately 10% in the dried superabsorbent polymer, hot air at approximately 200°C and hot air at approximately 100°C were sequentially circulated from top to bottom for approximately 5 minutes and approximately 10 minutes, respectively, and then hot air at approximately 100°C was circulated from bottom to top again for approximately 15 minutes to uniformly dry the polymer.

[0454] (Step 5: Crushing and Grading)

[0455] Use a grinder (GRAN-U-LIZER) TM The MPE (Medium-to-Earth Expansion) powder is pulverized and dried, and then graded using standard sieves according to ASTM standards to obtain base resin powder with a size of approximately 150 μm to approximately 850 μm.

[0456] (Surface crosslinking step)

[0457] Next, every 100 g of base resin powder was sprayed with an aqueous solution of a surface crosslinking agent containing 4.5 g water, 5 g methanol, 0.1 g ethylene glycol diglycidyl ether (EJ-1030S), and 0.4 g aluminum sulfate, and stirred at room temperature to mix, ensuring the surface crosslinking solution was uniformly distributed on the superabsorbent polymer powder. Subsequently, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor to carry out the surface crosslinking reaction. In this reactor, the surface crosslinking reaction of the base resin powder was carried out at approximately 140°C for approximately 40 minutes to obtain a surface-crosslinked superabsorbent polymer.

[0458] Following the surface crosslinking step, the surface-crosslinked superabsorbent polymer is graded using standard sieves according to ASTM standards to produce superabsorbent polymers with particle diameters ranging from approximately 150 μm to approximately 850 μm.

[0459] <Experimental Example>

[0460] The physical properties of the superabsorbent polymers produced in the above examples and comparative examples were evaluated using the following methods and are listed in Table 1 below.

[0461] Unless otherwise specified, all assessments of the following physical properties were conducted under constant temperature and humidity (23℃±1℃, relative humidity: 50%±10%), and physiological saline or saline means an aqueous solution of approximately 0.9% by weight of sodium chloride (NaCl).

[0462] The sample to be measured is placed under constant temperature and humidity conditions for about 24 hours, and then the various physical properties are evaluated.

[0463] Furthermore, unless otherwise noted, the physical properties of the final superabsorbent polymer that has undergone surface crosslinking were evaluated using resins with particle diameters of approximately 150 μm to approximately 850 μm, sieved according to ASTM standards.

[0464] (1) Measurement of the roundness and aspect ratio of superabsorbent polymer particles

[0465] The roundness and aspect ratio of each superabsorbent polymer of the above examples and comparative examples were measured using a morphologi 4 from Malvern Panalytical according to the following method.

[0466] 1) Sample Preparation: Prepare a 1 g sample of superabsorbent polymer particles to be measured. To measure the roundness and aspect ratio of particles with a diameter of approximately 300 μm to approximately 600 μm, classify the superabsorbent polymer using a particle classifier from Retsch GmbH at an amplitude of approximately 1.0 for approximately 10 minutes to prepare a 1 g sample separated into individual particles with a diameter of approximately 300 μm to approximately 600 μm without damaging the particles. Figure 1 The settings for the sample dispersion unit in this case are shown in the figure.

[0467] 2) Image Acquisition: The prepared sample is placed on the stage in the device and then scanned at approximately 2.5x magnification to obtain images of individual particles. In this case, Figure 2 and Figure 3 The settings for illumination and optical selection are shown in the figure.

[0468] 3) Image Processing: For the acquired images, parameters such as the equivalent diameter of the circle (CE diameter), the shortest diameter, the longest diameter, the actual circumference of the particle, and the circumference of the convex outer surface (convex hull circumference) are measured in the images of each particle. These images are obtained by capturing 2D images of the three-dimensional particles to be measured. In this case, the scanning area settings are as follows: Figure 4 As shown, the measurements were taken without setting a filter value for the particles.

[0469] 4) Based on the data analyzed for each particle, obtain the shape data values ​​of all particles contained in the sample.

[0470] [Table 1]

[0471]

[0472] [Table 2]

[0473]

[0474] (2) Centrifuge retention capacity (CRC, g / g) was measured according to the European Disposable Materials and Nonwovens Association (EDANA) standard EDANA WSP 241.3, which measures the water retention capacity of each superabsorbent polymer in the above examples and comparative examples in terms of absorption rate under no load.

[0475] Measurements were performed at a temperature of approximately 23°C ± 2°C and a relative humidity of approximately 45% ± 15%, as described in EDANA WSP 241.0.

[0476] Specifically, W0 (g) (approximately 0.2 g) of each of the superabsorbent polymers obtained through the examples and comparative examples was uniformly placed in a nonwoven fabric bag, sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After approximately 30 minutes, the water was removed from the bag for 3 minutes using a centrifuge at approximately 250 G, and the mass of the bag, W2 (g), was measured. Furthermore, the same procedure was performed without the use of resin, and the mass W1 (g) at this point was measured.

[0477] Using the obtained masses, calculate CRC (g / g) according to the following mathematical expression 1.

[0478] [Mathematical Expression 1]

[0479] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0480] Repeat the measurement 5 times and determine the mean and standard deviation.

[0481] (3) Absorption rate under pressure (AUP, g / g)

[0482] The absorption rate of each superabsorbent polymer of the above examples and comparative examples at a pressure of about 2.07 kPa (0.3 psi) was measured according to EDANA method WSP 242.3.

[0483] Measurements were performed at a temperature of approximately 23°C ± 2°C and a relative humidity of approximately 45% ± 15%, as described in EDANA WSP 242.0.

[0484] Specifically, a 400-mesh stainless steel wire mesh is installed at the bottom of a plastic cylinder with an inner diameter of approximately 25 mm. Under ambient temperature and approximately 50% humidity conditions, W0 (g) (0.9 g) of superabsorbent polymer is uniformly distributed on the wire mesh, and a piston configured to further uniformly apply a load of approximately 2.07 kPa (0.3 psi) is installed, such that the outer diameter of the piston is slightly less than approximately 25 mm, there is no gap between the piston and the inner wall of the cylinder, and the vertical movement of the piston is not impeded. The weight of the measuring device at this point is W3 (g).

[0485] A glass filter with a diameter of approximately 90 mm and a thickness of approximately 5 mm was placed on the inside of a petri dish with a diameter of approximately 150 mm. Physiological saline solution consisting of approximately 0.9% by weight sodium chloride was added to the same level as the upper surface of the glass filter. A sheet of filter paper with a diameter of approximately 90 mm was placed on top of the filter. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for approximately 1 hour. After approximately 1 hour, the measuring device was lifted and the weight W4 (g) was measured.

[0486] Using the obtained masses, calculate the absorption rate (g / g) under pressure according to the following mathematical expression 2.

[0487] [Mathematical Expression 2]

[0488] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0489] Repeat the measurement 5 times and determine the mean and standard deviation.

[0490] (4) Vortex time

[0491] The vortex time of each superabsorbent polymer in the above examples and comparative examples was measured as follows.

[0492] 1) First, add 50 mL of 0.9% saline solution to a 100 mL beaker with a flat bottom using a 100 mL graduated cylinder.

[0493] 2) Next, place the beaker in the center of the magnetic stirrer and put the round magnetic rod (diameter: 30 mm) into the beaker.

[0494] 3) After that, operate the stirrer so that the magnetic rod stirs at about 600 rpm and the bottom of the vortex generated by stirring touches the top of the magnetic rod.

[0495] 4) After confirming that the temperature of the brine in the beaker has reached approximately 24.0°C, begin adding approximately 2 ± 0.01 g of the superabsorbent polymer sample while simultaneously operating a stopwatch. Then, measure in seconds the time taken until the vortex disappears and the liquid surface becomes completely horizontal, and define the measurement time as the vortex time.

[0496] (5) Absorption capacity in water with a conductivity of approximately 110 µS / cm in one minute (EC 110 µS / cm 1-minute absorption capacity)

[0497] 1.0 g (W5) of each of the superabsorbent polymers of the above examples and comparative examples was placed in a nonwoven fabric bag (18 cm × 28 cm) and immersed in approximately 1000 mL of water with a conductivity of approximately 110 µS / cm at approximately 24°C for approximately 1 minute. After approximately 1 minute, the bag was removed from the distilled water, hung, and left to stand for approximately 1 minute. The mass of the bag was then measured (W7). The same procedure was then performed without the superabsorbent polymer, and the mass at this point was measured (W6). Using the masses obtained in this manner, the absorption capacity (g / g) in water with a conductivity of approximately 110 µS / cm was calculated according to the following mathematical expression 3.

[0498] [Mathematical Expression 3]

[0499] The absorption capacity in water with a conductivity of approximately 110 µS / cm is calculated as: {[W7(g) - W6(g) - W5(g)] / W5(g)}

[0500] [Table 3]

[0501]

[0502] As can be determined in Table 3 above, by controlling the roundness and aspect ratio within a specific range, it is possible to improve the absorption rate while simultaneously improving the centrifugal retention capacity and absorption performance such as the absorption rate under pressure, thus exhibiting a balance of physical properties.

[0503] Industrial applicability

[0504] This invention can be applied to superabsorbent polymers.

Claims

1. A superabsorbent polymer, said superabsorbent polymer being a superabsorbent polymer based on polyacrylic acid (salt), For all particles, the average roundness calculated according to the following expression 1 is 0.90 or less. The average aspect ratio (A / R) is 0.70 or greater, where A / R refers to the ratio of the shortest diameter of the particle to the longest diameter of the particle. According to EDANA method WSP 242.3, the absorbance under pressure (AUP) is 25 g / g or greater at 2.07 kPa (0.3 psi). <expression 1> Circularity = Circumference of the Circular Equivalent (CE) Particle / Circumference of the Actual Particle In expression 1 above, The perimeter of the CE particle refers to the circumference of a circle (equivalent circle) having the same area as the image obtained by capturing a 3D image of the three-dimensional particle being measured as a 2D image (CE perimeter). The actual perimeter of the particle refers to the actual perimeter length (circumference) of the image obtained by taking a 3D image of the three-dimensional particle to be measured as a 2D image.

2. The superabsorbent polymer of claim 1, wherein the average value of the sphericity is 0.70 to 0.90 for all particles.

3. The superabsorbent polymer according to claim 1, wherein the average aspect ratio is 0.70 to 0.85 for all particles.

4. The superabsorbent polymer according to claim 1, For all particles, the average high-sensitivity (HS) roundness calculated according to the following expression 2 is 0.80 or less: <expression2> HS roundness = (circumference of CE particles) 2 / (Actual particle perimeter) 2 .

5. The superabsorbent polymer of claim 1, wherein the average value of the HS roundness is 0.50 to 0.80 for all particles.

6. The superabsorbent polymer according to claim 1, wherein the ratio of the roundness of particles with a diameter of 300 μm to 600 μm in the superabsorbent polymer to the roundness of all particles is 0.9 to 1.

1.

7. The superabsorbent polymer according to claim 1, wherein the average CE diameter of the superabsorbent polymer is from 220 μm to 400 μm.

8. The superabsorbent polymer of claim 1, wherein the superabsorbent polymer has a water retention capacity (CRC) of 33 g / g or greater, wherein the water retention capacity (CRC) is measured according to EDANA method WSP 241.

3.

9. The superabsorbent polymer according to claim 1, The superabsorbent polymer described herein has an effective absorbent capacity (EFFC) of 30 g / g or greater, wherein the effective absorbent capacity (EFFC) is calculated according to the following expression 3: <expression3> Effective Absorbable Capacity (EFFC) = {Water Retention Capacity (CRC) + Absorption Rate at Pressure of 2.07 kPa (0.3 psi) (AUP)} / 2.

10. The superabsorbent polymer of claim 1, wherein the vortex time is 40 seconds or less, wherein the vortex time is measured at 24.0°C by a vortex measurement method.

11. The superabsorbent polymer according to claim 1, wherein when 1 g of the superabsorbent polymer is swollen with water having a conductivity of 110 μS / cm for 1 minute, the maximum capacity of water that can be retained in the superabsorbent polymer (free swelling capacity) is 170 g or greater.

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