Absorbent resin and preparation method therefor

Abstract

The present invention relates to an absorbent resin and a preparation method therefor. More particularly, the present invention relates to an absorbent resin and a preparation method therefor, the absorbent resin having Hunter Color B of 8 or less, a centrifuge retention capacity (CRC) of 30 g / g or more as measured according to EDANA WSP 241.2, an absorbency under pressure (AUP) of 9 g / g or more at 4826 Pa (0.7 psi) as measured according to EDANA WSP 242.2, and a permeability of 1,000 seconds or less.

Description

Absorbent resin and method for manufacturing the same

[0001] The present invention relates to an absorbent resin and a method for manufacturing the same. More specifically, the invention relates to an absorbent resin having a Hunter Color B of 8 or less, a centrifugal retention capacity (CRC) of 30 g / g or more as measured according to the EDANA method WSP 241.2, an applied absorption capacity (AUP) of 4826 Pa (0.7 psi) of 9 g / g or more as measured according to the EDANA method WSP 242.2, and a permeability of 1,000 seconds or less.

[0002] Absorbent resins are synthetic polymer materials capable of absorbing hundreds of times their own weight in water and are widely used in various industries such as hygiene products, agriculture, civil engineering, construction, and food. In particular, in the field of hygiene products such as diapers and sanitary pads, absorbent resins are used in combination with pulp to play a key role in efficiently absorbing and retaining liquids such as urine.

[0003] Recently, as hygiene products such as diapers become thinner and the demand for 'pulpless' products—which reduce or eliminate pulp content—increases, improving the performance of absorbent resins is becoming increasingly important. In these hygiene products, absorbent resins are used in high proportions, and it is essential that the resin particles be incorporated in multiple layers to efficiently absorb and retain liquids. To achieve this, the absorbent resin must simultaneously satisfy high absorbency and pressurized absorption capacity, which allows it to retain absorbed water even under external pressure.

[0004] However, there was a limitation in that the centrifugal retention capacity (CRC) and pressure absorption capacity (AUP) of absorbent resins are in a mutual trade-off relationship, making it difficult to improve them simultaneously. For example, lowering the crosslinking density can increase the centrifugal retention capacity (CRC), but the gel strength may decrease, which can lower the pressure absorption capacity (AUP); conversely, increasing the crosslinking density improves the pressure absorption capacity (AUP), but causes a problem where the centrifugal retention capacity (CRC) decreases. For this reason, existing absorbent resin manufacturing technologies have shown limitations in simultaneously improving the centrifugal retention capacity (CRC) and pressure absorption capacity (AUP).

[0005]

[0006] In addition, as absorbent resins are widely used in hygiene products such as diapers, the impact of discoloration issues and residual monomer (RM) content on product quality and safety is becoming increasingly important. Discoloration has a negative impact on consumer confidence, and residual monomer (RM) is emerging as a critical issue that must be addressed in terms of product safety and environmental friendliness.

[0007] In conventional technology, sodium persulfate was used as a thermal initiator to reduce residual monomers (RM) in absorbent resins; however, this substance causes problems that impair the color of the absorbent resin. Using sodium persulfate below a certain level improves the color of the absorbent resin but reduces the effectiveness of RM reduction, while using it above a certain level allows for managing RM to below 500 ppm but results in color degradation. In particular, in the field, situations frequently arise where excessive amounts of sodium persulfate must be added to manage RM because the dimer concentration of acrylic acid, a major raw material for absorbent resins, is inconsistent. This problem acts as a factor that simultaneously undermines quality stability and efficiency in the absorbent resin manufacturing process.

[0008]

[0009] Against this backdrop, there is a need for the development of innovative manufacturing technologies that can simultaneously improve the absorption performance (CRC and AUP) and color stability of absorbent resins and minimize residual monomers (RM).

[0010]

[0011] Prior art literature

[0012] [Patent Document 1] Republic of Korea Published Patent No. 10-2022-0088354

[0013] The present invention aims to provide an absorbent resin with stable quality by minimizing residual monomer (RM) while having excellent centrifugal retention capacity (CRC), pressurized absorption capacity (0.7 AUP), permeability, absorption rate, and color stability. In particular, it was confirmed that by optimizing the components and conditions used in the polymerization and post-crosslinking processes, it is possible to manufacture an absorbent resin in which the centrifugal retention capacity is 30 g / g or more, the pressurized absorption capacity is 9 g / g or more, the absorption rate is 80 seconds or less, the permeability is 1000 seconds or less, the Hunter color B value is maintained at 8 or less, and the residual monomer (RM) content is maintained at 500 ppm or less.

[0014] Accordingly, the present invention aims to provide an absorbent resin and a method for manufacturing the same.

[0015]

[0016] However, the problems that this invention seeks to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0017] According to the sun,

[0018] An absorbent resin satisfying (1) to (4) below is provided:

[0019] (1) Hunter Color B must be 8 or less,

[0020] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher,

[0021] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater, and

[0022] (4) Permeability shall be 1000 seconds or less.

[0023] The absorption rate of the above absorbent resin by the (5) vortex method may be 80 seconds or less.

[0024] The content of residual monomers measured according to the EDANA method WSP 210.3 of the above absorbent resin may be 500 ppm or less based on 100 parts by weight of the absorbent resin.

[0025] The above absorbent resin can satisfy (1) to (5) below:

[0026] (1) Hunter Color B is 1 to 7,

[0027] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g,

[0028] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 23 g / g,

[0029] (4) Permeability shall be 50 to 800 seconds, and

[0030] (5) The absorption rate by the vortex method shall be 20 to 75 seconds.

[0031] The above absorbent resin can satisfy (1) to (5) below:

[0032] (1) Hunter Color B is 1 to 6.5,

[0033] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g,

[0034] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 22 g / g,

[0035] (4) Permeability shall be 50 to 750 seconds, and

[0036] (5) The absorption rate by the vortex method shall be 25 to 75 seconds.

[0037]

[0038] Another aspect of the present invention is

[0039] (S1) A polymerization process of mixing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with sodium persulfate and hydrogen peroxide (H2O2), and

[0040] (S2) A method for manufacturing an absorbent resin satisfying (1) to (4) below is provided, comprising a post-crosslinking process in which the polymer obtained from the above polymerization process is mixed with an epoxy-based surface crosslinking agent and a discoloration inhibitor:

[0041] (1) Hunter Color B must be 8 or less,

[0042] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher,

[0043] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater, and

[0044] (4) Permeability shall be 1000 seconds or less.

[0045] In the above step (S1), the amount of sodium persulfate added may be 1,000 to 2,500 ppm based on 100 parts by weight of water-soluble ethylene-based unsaturated monomer.

[0046] In the above (S1) step, the amount of hydrogen peroxide added may be 100 or more to less than 500 ppm based on 100 parts by weight of water-soluble ethylene-based unsaturated monomer.

[0047] The amount of surface crosslinking agent added in step (S2) above may be 0.01 to 0.30 parts by weight based on 100 parts by weight of the polymer obtained in step (S1).

[0048] The amount of anti-discoloration agent added in step (S2) above may be 0.01 parts by weight or more and less than 0.1 parts by weight based on 100 parts by weight of the polymer obtained in step (S1).

[0049] In the above (S2) step, the post-crosslinking process can be performed at a temperature of 150°C or lower.

[0050] The absorbent resin according to the present invention can provide the following effects.

[0051] (1) The absorbent resin of the present invention has a centrifugal retention capacity (CRC) of 30 g / g or more and a pressurized absorption capacity (0.7 AUP) of 9 g / g or more, thereby securing superior absorption performance compared to existing products.

[0052] (2) The absorbent resin of the present invention has an absorption rate of 80 seconds or less and maintains a permeability of 1000 seconds or less, providing appropriate liquid absorption and permeability in an actual usage environment.

[0053] (3) The absorbent resin according to the present invention maintains a Hunter color B value of 8 or less, so that the absorbent resin can maintain an excellent appearance without discoloration.

[0054] (4) The absorbent resin according to the present invention can ensure product stability by maintaining the content of residual monomer (RM) at 500 ppm or less, thereby satisfying conditions suitable for use in sanitary materials.

[0055] Therefore, the present invention provides an absorbent resin with stable quality that simultaneously satisfies high performance and color stability, making it highly applicable in various industrial fields.

[0056]

[0057] Meanwhile, the scope of the present invention is not limited by the effects described above.

[0058] The present invention will be described in more detail below.

[0059] All terms used in this specification (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains, unless otherwise defined. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0060] Throughout this specification, when a part is described as “comprising” a certain component, it should be understood as an open-ended term implying the possibility of including additional components rather than excluding other components, unless specifically stated otherwise.

[0061] Additionally, as used herein, “preferred” and “preferably” refer to embodiments of the invention that may provide certain advantages under certain conditions. However, other embodiments may also be preferred under the same or different conditions. Furthermore, the mention of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

[0062] Terms such as first, second, third, etc. are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from another.

[0063] The terms “polymer” or “polymer” as used in this specification refer to a state in which water-soluble ethylene-based unsaturated monomers are polymerized, and may encompass all moisture content ranges or particle size ranges. Among the polymers, a polymer having a moisture content (water content) of about 35 weight% or more in the state before drying after polymerization may be referred to as a hydrogel polymer, and particles obtained by grinding and drying such hydrogel polymers may be referred to as a cross-linked polymer.

[0064] The terms “base resin” or “base resin powder” as used in this specification refer to a polymer formed by drying and grinding a polymer of an acrylic acid monomer into a particle or powder form, and refers to a polymer in a state where the surface modification or surface crosslinking steps described below have not been performed.

[0065] The terms “absorbent resin” or “absorbent resin powder” as used in this specification refer, depending on the context, to a cross-linked polymer in which a water-soluble ethylene-based unsaturated monomer (acrylic acid-based monomer) containing acidic groups and at least some of said acidic groups is neutralized, or to a base resin in the form of a powder made of said cross-linked polymer and said absorbent resin particles that have been ground, or to encompass all of the cross-linked polymer or said base resin that have been made into a state suitable for commercialization through additional processes, such as surface cross-linking, fine powder reassembly, drying, grinding, classification, etc.

[0066] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0067] Hereinafter, an absorbent resin having high performance and color stability and a method for manufacturing the same will be described in more detail according to a specific aspect of the invention.

[0068]

[0069] 1. Absorbent resin

[0070] One aspect of the present invention is

[0071] An absorbent resin satisfying (1) to (4) below is provided:

[0072] (1) Hunter Color B must be 8 or less,

[0073] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher,

[0074] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater, and

[0075] (4) Permeability shall be 1000 seconds or less.

[0076] The Hunter Color B of the absorbent resin may be 8 or less. Specifically, the Hunter Color B of the absorbent resin may be 8 or less, 7.9 or less, 7.8 or less, 7.7 or less, 7.6 or less, 7.5 or less, 7.4 or less, 7.3 or less, 7.2 or less, 7.1 or less, 7.0 or less, 6.9 or less, 6.8 or less, 6.7 or less, 6.6 or less, 6.5 or less, 6.4 or less, 6.3 or less, or 6.2 or less. There is no specific limit on the lower limit of the Hunter Color B of the absorbent resin, but it may typically be 1 or more. For example, the Hunter color B of the absorbent resin may be 1 to 8, 1 to 7.9, 1 to 7.8, 1 to 7.7, 1 to 7.6, 1 to 7.5, 1 to 7.4, 1 to 7.3, 1 to 7.2, 1 to 7.1, 1 to 7.0, 1 to 6.9, 1 to 6.8, 1 to 6.7, 1 to 6.6, 1 to 6.5, 1 to 6.4, 1 to 6.3, or 1 to 6.2. If the value of the Hunter color B of the absorbent resin exceeds 8, it appears yellow to yellowish-brown even to the naked eye, suggesting the possibility of residual impurities or oxidation, which may lead to a decrease in absorption performance and storage stability issues. The above Hunter color B can be measured using a colorimeter (Color Quest II, Hunter Lab Co.).

[0077] The centrifugal retention capacity (CRC) of the absorbent resin may be 30 g / g or more. Specifically, the centrifugal retention capacity of the absorbent resin may be 30 to 50 g / g, 30 to 49 g / g, 30 to 48 g / g, 30 to 47 g / g, 30 to 46 g / g, or 30 to 45 g / g. The centrifugal retention capacity may be measured according to the method of the EDANA method WSP 241.2.

[0078] The pressure absorption capacity (AUP) of the absorbent resin may be 9 g / g or more. Specifically, the pressure absorption capacity of the absorbent resin may be 9 to 25 g / g, 9 to 24 g / g, 9 to 23 g / g, or 9.5 to 22 g / g. The pressure absorption capacity may be measured according to the EDANA method WSP 242.2.

[0079] The permeability of the absorbent resin may be 1,000 seconds or less. Specifically, the permeability of the absorbent resin may be 50 to 1,000 seconds, 50 to 900 seconds, 50 to 800 seconds, 50 to 750 seconds, or 50 to 700 seconds. If the permeability of the absorbent resin exceeds 1,000 seconds, the absorption process proceeds inefficiently due to slow diffusion of liquid, which may cause discomfort to the user due to a delay in the wet sensation. The above permeability can be measured by T1 - B, where T1 is the time taken for the liquid level to decrease from 40 ml to 20 ml after placing 0.2 ± 0.0005 g of a classified (30# ~ 50#) absorbent resin sample into a chromatography tube with an inner diameter of 20 mm and a glass filter at the bottom, adding 0.9% brine to make the brine volume 50 ml, and leaving it for 30 minutes, and B is the time taken for the liquid level to decrease from 40 ml to 20 ml in the chromatography tube filled with brine.

[0080] The absorption rate of the above absorbent resin by the (5) vortex method may be 80 seconds or less. Specifically, the absorption rate of the above absorbent resin by the vortex method may be 20 to 80 seconds, 20 to 79 seconds, 20 to 78 seconds, 20 to 77 seconds, 20 to 76 seconds, 20 to 75 seconds, 21 to 75 seconds, 22 to 75 seconds, 23 to 75 seconds, 24 to 75 seconds, or 25 to 75 seconds. If the absorption rate of the above absorbent resin by the vortex method exceeds 80 seconds, moisture is not effectively absorbed under external pressure, resulting in a decrease in absorption efficiency and a decrease in the performance of the product. The absorption rate by the above vortex method can be calculated by adding 2 g of absorbent resin to 50 mL of physiological saline at 23 ℃ to 24 ℃, stirring at 600 rpm, and measuring the time in seconds until the vortex disappears.

[0081] The content of residual monomers measured according to the (6) EDANA method WSP 210.3 of the above absorbent resin may be 500 ppm or less based on 100 parts by weight of the absorbent resin. Since a lower content of residual monomers is preferable, the lower limit is not specifically limited, but it may be 100 ppm or more, for example.

[0082] The above absorbent resin can satisfy (1) to (5) below:

[0083] (1) Hunter Color B is 1 to 7,

[0084] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g,

[0085] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 23 g / g,

[0086] (4) Permeability shall be 50 to 800 seconds, and

[0087] (5) The absorption rate by the vortex method shall be 20 to 75 seconds.

[0088] The above absorbent resin can satisfy (1) to (5) below:

[0089] (1) Hunter Color B is 1 to 6.5,

[0090] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g,

[0091] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 22 g / g,

[0092] (4) Permeability shall be 50 to 750 seconds, and

[0093] (5) The absorption rate by the vortex method shall be 25 to 75 seconds.

[0094] An absorbent resin according to one aspect of the present invention exhibits excellent color stability by maintaining a low Hunter Color B value, and can demonstrate stable quality and reliable absorption performance by significantly reducing the residual monomer (RM) content. Furthermore, it exhibits excellent performance in key absorption characteristics such as centrifugal retention capacity (CRC), pressure absorption capacity (AUP), permeability, and absorption rate by the vortex method, thereby providing the ability to efficiently absorb and stably store liquids.

[0095] In particular, improvements in Hunter Color B and RM simultaneously enhance product appearance and quality reliability, and combined with improvements in liquid permeability and absorption speed, can increase the stability of absorption performance while significantly improving overall product quality and user satisfaction.

[0096] The absorbent resin of the present invention having the above-described characteristics can be manufactured by optimizing the components and conditions used in the polymerization and post-crosslinking processes, and its specific composition and manufacturing method are described in detail below.

[0097]

[0098] 2. Method for manufacturing absorbent resin

[0099] Another aspect of the present invention is

[0100] (S1) A polymerization process of mixing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with a thermal initiator and a color improver, and

[0101] (S2) A method for manufacturing an absorbent resin comprising a post-crosslinking process in which the polymer obtained in the above polymerization process is mixed with a surface crosslinking agent and a discoloration inhibitor, and an absorbent resin satisfying (1) to (4) below:

[0102] (1) Hunter Color B must be 8 or less,

[0103] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher,

[0104] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater.

[0105] (4) Permeability shall be 1000 seconds or less.

[0106]

[0107] (S1) Polymerization process

[0108] The above polymerization process can be carried out by mixing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least some of the acidic group neutralized with a thermal initiator and a color improver.

[0109] Sodium persulfate (Na2S2O8) may be used as the thermal initiator. The amount of sodium persulfate added may be 1,000 to 2,500 ppm based on 100 parts by weight of water-soluble ethylene-based unsaturated monomer. If the amount of sodium persulfate added is less than 1,000 ppm, the efficiency of removing residual monomers decreases, and if the amount of sodium persulfate added exceeds 2,500 ppm, a problem arises in which the color quality of the absorbent resin deteriorates. Therefore, appropriate control of the amount of sodium persulfate added is a key factor that significantly affects the removal of residual monomers and the color quality of the absorbent resin.

[0110] Hydrogen peroxide (H2O2) may be used as the color improving agent. The amount of hydrogen peroxide added may be 50 ppm or more and less than 500 ppm based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. Specifically, the amount of hydrogen peroxide added may be 50 ppm or more, 60 ppm or more, 70 ppm or more, 80 ppm or more, 90 ppm or more, or 100 ppm or more, and less than 500 ppm, 450 ppm or less, 400 ppm or less, 350 ppm or less, 300 ppm or less, 250 ppm or less, 200 ppm or less, or 150 ppm or less. For example, the amount of hydrogen peroxide added may be 50 ppm or more to less than 500 ppm, 50 ppm to 450 ppm, 60 ppm to 400 ppm, 70 ppm to 350 ppm, 80 ppm to 300 ppm, 90 ppm to 250 ppm, 100 ppm to 200 ppm, or 100 ppm to 150 ppm. If the amount of hydrogen peroxide added is less than 50 ppm, the color quality of the absorbent resin deteriorates, and if the amount of hydrogen peroxide added is 500 ppm or more, the content of residual monomers may increase significantly. Therefore, controlling the appropriate amount of hydrogen peroxide added also plays an important role in maintaining a balance between removing residual monomers and maintaining color quality of the absorbent resin.

[0111] The polymerization process may include (S1-1) a step of polymerizing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least some of the acidic group neutralized in the presence of a crosslinking agent, a chelating agent, a thermal initiator, a color improver, and other additives to form a hydrogel polymer, and (S1-2) a step of drying, grinding, and classifying the hydrogel polymer to form a base resin.

[0112] The above-mentioned water-soluble ethylene-based unsaturated monomer may be any monomer commonly used in the manufacture of absorbent resins. For example, the above-mentioned water-soluble ethylene-based unsaturated monomer may be a compound represented by the following chemical formula 1:

[0113] [Chemical Formula 1]

[0114] R1 -COOM 1

[0115] In the above chemical formula 1,

[0116] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0117] M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine base.

[0118] The above monomer may comprise one or more selected from the group consisting of (meth)acrylic acid, and monovalent alkali metal salts, divalent metal salts, ammonium salts, organic amine salts of these acids, 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, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, and (N,N)-dimethylaminopropyl (meth)acrylamide. However, it is not limited thereto. The concentration of the water-soluble ethylene-based unsaturated monomer in the monomer composition can be appropriately adjusted considering the polymerization time and reaction conditions, and preferably, it may be 20 to 90 weight% or 40 to 65 weight%. This concentration range may be advantageous for controlling the grinding efficiency during the grinding of the polymer described later, while eliminating the need to remove unreacted monomers after polymerization by utilizing the gel effect phenomenon that appears in the polymerization reaction of a high-concentration aqueous solution. However, if the concentration of the monomer becomes excessively low, the yield of the absorbent resin may decrease. Conversely, if the concentration of the monomer becomes excessively high, process problems may arise, such as the precipitation of some of the monomer or a decrease in grinding efficiency during the grinding of the polymerized aqueous gel polymer, and the physical properties of the absorbent resin may deteriorate.

[0119] Any compound that enables the introduction of crosslinking bonds during the polymerization of the above-mentioned water-soluble ethylene-based unsaturated monomer can be used as the above-mentioned crosslinking agent (also called an internal crosslinking agent to distinguish it from a surface crosslinking agent for crosslinking the surface of the absorbent resin). For example, the crosslinking agent is selected from the group consisting of N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate. It may include one or more types, but is not limited thereto. The amount of the crosslinking agent added may be 500 to 1500 ppm based on 100 parts by weight of a water-soluble ethylene-based unsaturated monomer. If the amount of the crosslinking agent added is less than 500 ppm, crosslinking may not occur sufficiently, making it difficult to achieve strength above an appropriate level, and if the amount of the crosslinking agent added exceeds 1500 ppm, there is a risk that the physical properties of the absorbent resin may deteriorate due to excessive crosslinking.

[0120] The above chelating agent may include one or more selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), phenolic acid, citric acid, amino acids, and salts thereof, but is not limited thereto. The amount of the chelating agent added may be 100 ppm or more to 15,000 ppm or less based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. If the amount of the chelating agent added exceeds 15,000 ppm, the content of residual monomer in the absorbent resin increases, which may degrade the physical properties and absorption performance of the absorbent resin.

[0121] The above other additives may include one or more selected from the group consisting of neutralizing agents, foam stabilizers, thickeners, plasticizers, preservative stabilizers, and antioxidants, but are not limited thereto.

[0122] As the above neutralizing agent, a basic substance capable of neutralizing acidic groups in the above water-soluble ethylene-based unsaturated monomer may be used. For example, the above basic substance may include one or more selected from the group consisting of sodium hydroxide (or caustic soda), potassium hydroxide, and ammonium hydroxide, but is not limited thereto.

[0123] The above foam stabilizer may include one or more selected from the group consisting of sodium dodecyl sulfate, calcium stearate, oleth carboxylic acid, sodium dodecanoate, and oleyl phosphate, but is not limited thereto.

[0124] The above-mentioned thickener may include one or more selected from the group consisting of hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, polyacrylic acid, polyacrylic acid (partially) neutralized, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene oxide, but is not limited thereto.

[0125] The monomer composition may be prepared in the form of a solution dissolved in a solvent. For example, the solvent may include one or more selected from the group consisting of water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide, but is not limited thereto.

[0126]

[0127] (S2) Post-crosslinking process

[0128] The above post-crosslinking process can be performed by mixing the polymer obtained from the polymerization process with a surface crosslinking agent and an anti-discoloration agent.

[0129] An epoxy-based surface crosslinking agent may be used as the surface crosslinking agent. For example, the epoxy-based surface crosslinking agent may include one or more selected from the group consisting of ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, hexahydrophthalic anhydride diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, and N,N-diglycidylaniline, but is not limited thereto. When the epoxy-based surface crosslinking agent is used, the pressure absorption capacity (AUP) and liquid permeability of the absorbent resin tend to be improved. On the other hand, when non-epoxy surface crosslinking agents are used, the AUP tends to be relatively lower and liquid permeability may also tend to be slower. Therefore, the performance of absorbent resins can be improved more efficiently by applying epoxy surface crosslinking agents.

[0130] The amount of the surface crosslinking agent added may be 0.01 parts by weight or more to 0.30 parts by weight or less, 0.01 parts by weight or more to 0.20 parts by weight or less, or 0.01 parts by weight or more to 0.15 parts by weight or less, based on 100 parts by weight of the polymer. If the amount of the surface crosslinking agent added exceeds 0.30 parts by weight based on 100 parts by weight of the polymer, there is a risk that the physical properties of the absorbent resin will deteriorate due to excessive surface crosslinking.

[0131] The above anti-discoloration agent may include one or more selected from the group consisting of disodium alpha-sulfoglycolate, laurylphosphonic acid, stearylphosphonic acid, and disodium salt of 2-hydroxy-2-sulfonatoacetic acid, but is not limited thereto. The amount of the above anti-discoloration agent added may be 0.01 parts by weight or more to less than 0.10 parts by weight, 0.01 parts by weight or more to 0.07 parts by weight or less, 0.01 parts by weight or more to 0.05 parts by weight or less, or 0.01 parts by weight or more to 0.03 parts by weight or less, based on 100 parts by weight of the polymer. If the amount of the above anti-discoloration agent added is 0.10 parts by weight or more based on 100 parts by weight of the polymer, the pressure absorption capacity (AUP) and liquid permeability of the absorbent resin may decrease, and the absorption characteristics may deteriorate.

[0132] The above post-crosslinking process may be performed at a temperature of 150 ℃ or lower. Specifically, the above post-crosslinking process may be performed at a temperature of 150 ℃ or lower, 145 ℃ or lower, 140 ℃ or lower, 135 ℃ or lower, or 130 ℃ or lower. For example, the above post-crosslinking process may be performed at a temperature of 110 to 150 ℃, 110 to 145 ℃, 110 to 140 ℃, 110 to 135 ℃, or 110 to 130 ℃. The above post-crosslinking process may be performed for a time of 10 minutes or more and less than 60 minutes. Specifically, the above post-crosslinking process may be performed for 10 minutes or more but less than 60 minutes, 10 minutes to 55 minutes, 10 minutes to 50 minutes, 10 minutes to 45 minutes, 10 minutes to 40 minutes, 10 minutes to 35 minutes, or 10 minutes to 30 minutes. Since the post-crosslinking process of the present invention is performed in a short time under the above-defined temperature and time conditions, thermal degradation and discoloration are suppressed compared to a long-term high-temperature heating process, and there is an advantage of improved process reproducibility and product uniformity.

[0133] The above other additives may include one or more selected from the group consisting of reducing agents, inorganic fillers, and thickeners, but are not limited thereto.

[0134] The above reducing agent may include one or more selected from the group consisting of sodium bisulfite, sodium metabisulfite (Na2S2O5), sodium hydrosulfite, sodium thiosulfate, and sodium formaldehyde sulfoxylate, but is not limited thereto.

[0135] The above-mentioned inorganic filler may include one or more selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and silicate, but is not limited thereto.

[0136] Polysaccharides, hydroxyl-containing polymers, or combinations thereof may be used as the above-mentioned thickening agent. For example, the above-mentioned thickener may include one or more selected from the group consisting of xanthan gum, arabic gum, karaya gum, tragacanth gum, ghatti gum, guar gum, locust bean gum, psyllium seed gum, hydroxypropylmethylcellulose, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose, and methylhydroxypropylcellulose, but is not limited thereto.

[0137] The absorbent resin produced by the above manufacturing method can satisfy (1) to (5) below:

[0138] (1) Hunter Color B must be 8 or less,

[0139] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher,

[0140] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater.

[0141] (4) Permeability shall be 1000 seconds or less, and

[0142] (5) The absorption rate by the vortex method shall be 80 seconds or less.

[0143] The absorbent resin produced by the above manufacturing method can satisfy (1) to (5) below:

[0144] (1) Hunter Color B is 1 to 7,

[0145] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g,

[0146] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 23 g / g,

[0147] (4) Permeability shall be 50 to 800 seconds, and

[0148] (5) The absorption rate by the vortex method shall be 20 to 75 seconds.

[0149] The absorbent resin produced by the above manufacturing method can satisfy (1) to (5) below:

[0150] (1) Hunter Color B is 1 to 6.5,

[0151] (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g,

[0152] (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 22 g / g,

[0153] (4) Permeability shall be 50 to 750 seconds, and

[0154] (5) The absorption rate by the vortex method shall be 25 to 75 seconds.

[0155] The absorbent resin produced by the manufacturing method according to one aspect of the present invention maintains a stable Hunter color, resulting in excellent product appearance quality and enhanced consumer preference. Furthermore, it exhibits excellent centrifugal retention capacity, allowing it to stably retain a large amount of moisture, and also demonstrates excellent pressurized absorption capacity, enabling stable absorption performance even under pressure. In addition, appropriate liquid permeability is ensured, allowing liquids to be absorbed and dispersed quickly and uniformly, and the absorption rate is also fast, providing rapid absorption responsiveness during use.

[0156] Furthermore, the absorbent resin produced by the manufacturing method according to one aspect of the present invention can minimize leakage or discomfort during product use due to the excellent absorption characteristics described above, and demonstrates stable absorption capacity and shape retention ability even during prolonged use, thereby enhancing the reliability and satisfaction of hygiene products. In addition, these characteristics are expected to contribute to reducing quality variations during the manufacturing process and ensuring consistent performance of the final product.

[0157] Various embodiments are presented below to aid in understanding the invention. The following embodiments are provided merely to facilitate a better understanding of the invention and do not limit the scope of protection of the invention to the following embodiments.

[0158]

[0159] <Example>

[0160] Example 1

[0161] A monomer composition was prepared by mixing 100 g of acrylic acid, 1000 ppm of internal crosslinking agent EJ1030 (ethylene glycol diglycidyl ether), 300 ppm of chelating agent DTPA (diethylenetriamine pentaacetate), 1800 ppm of thermal initiator sodium persulfate (SPS), 100 ppm of color improver (hydrogen peroxide, H2O2), and a 22% aqueous sodium hydroxide solution. The monomer composition was placed in a stainless steel container measuring 250 mm in width, 250 mm in length, and 30 mm in height, and a crosslinking polymerization reaction was carried out by irradiating with ultraviolet light for 60 seconds in a UV chamber at 80°C (irradiation dose: 10 mV / cm²). 2 A crosslinked polymer was obtained by aging for 2 minutes. The obtained crosslinked polymer was cut into pieces approximately 5 cm × 5 cm in size, placed in a chopper, and chopped to obtain a hydrogel polymer. The obtained hydrogel polymer was dried in a 185°C hot air oven for 35 minutes, ground, and then classified through a standard sieve of ASTM specifications to obtain a base resin powder having a particle size of 150 to 850 μm (base resin CRC 35~60 g / g, 1hr E / C <=20%).

[0162] 3.6g of water, 3.8g of methanol, 0.08g of epoxy-based surface crosslinking agent, and other additives including 0.15g of aluminum sulfate (Al-S), 0.01g of inorganic filler (Aerosil200™ manufactured by Evonic Degussa Corporation), 0.05g of reducing agent (SMBS™ manufactured by sigma Aldrich), and 0.03g of anti-discoloration agent (blancolen™ HP manufactured by Bruggemann Chemical) were placed in a mixer and mixed for 30 seconds at 200 rpm to prepare a surface crosslinking solution.

[0163] Based on 100 parts by weight of the base resin prepared above, a surface crosslinking solution was mixed, and a surface crosslinking reaction was carried out at 130°C for 20 minutes. After the surface treatment was completed, an absorbent resin having an average particle size of 150 to 850 μm was obtained using a sieve.

[0164]

[0165] Examples 2 to 4, and Comparative Examples 1 to 8

[0166] An absorbent resin was prepared in the same manner as Example 1 above, except that the composition and conditions listed in Table 1 below were used.

[0167] Classification Post-polymerization crosslinking Internal crosslinking agent (ppm) SPS (ppm) H2O2 (ppm) Surface crosslinking agent Surface crosslinking temperature (°C) Anti-discoloration agent (g) Example 1 1000 1800 100 Epoxy 1300.03 Example 2 1000 1500 150 Epoxy 1300.03 Example 3 600 2000 150 Epoxy 1300.03 Example 4 1400 2000 150 Epoxy 1300.03 Comparative Example 1 1000 1500 - Epoxy 1300.03 Comparative Example 2 1000 1500 150 Epoxy 1800.03 Comparative Example 3 1000 1500 150 Non-epoxy 1800.03 Comparative Example 410001500150 Non-epoxy 1300.03 Comparative Example 510001500150 Epoxy 1300.3 Comparative Example 66002000-Epoxy 1300.03 Comparative Example 714002000-Epoxy 1300.03 Comparative Example 810001500500 Epoxy 1300.03

[0168] The terms listed in Table 1 above are as follows: Epoxy: Ethylene Glycol Diglycidyl Ether (EJ1030S™ Junsei) Non-epoxy: Ethylene carbonate (Sigma Aldrich)

[0169] Anti-discoloration agent: B-HP (blancolen™ HP, Bruggemann Chemical)

[0170]

[0171] <Experimental Example>

[0172] The physical properties of the absorbent resins prepared in the above examples and comparative examples were evaluated in the following manner, and the results are shown in the table below. Unless otherwise indicated, the following physical property evaluations were conducted at a temperature of 23±2 ℃ and a relative humidity of 50±5 %, and physiological saline or saline refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0173]

[0174] 1. Hunter Color B

[0175] The b value was measured using a colorimeter (Color Quest II, Hunter Lab Co.). L, a, and b, measured by the colorimeter, represent coordinate axis values ​​indicating unique colors. L represents whiteness (brightness, lightness) and can range from 0 to 100. An L value closer to 0 indicates black, while a value closer to 100 indicates white. A can take positive or negative values ​​relative to 0; a value greater than 0 indicates a reddish tint, while a value less than 0 indicates a greenish tint. B can also take positive or negative values ​​relative to 0; a value greater than 0 indicates a yellowish tint, while a value less than 0 indicates a blue tint.

[0176]

[0177] 2. Centrifugal Retention Capacity (CRC)

[0178] The centrifugal water retention capacity (CRC) was measured based on the absorption ratio under no load in accordance with the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.2. Absorbent resin W0 (g, approx. 0.2 g) was uniformly placed into a nonwoven bag and sealed. The bag was then immersed in a physiological saline solution containing 0.9 wt% sodium chloride at room temperature. After 30 minutes, the bag was centrifuged at 250g for 3 minutes to remove water, and the mass W2 (g) of the bag was measured. Additionally, the same procedure was performed without the absorbent resin, and the mass W1 (g) was measured. Using the masses obtained in this way, the CRC (g / g) was calculated according to the following Formula 1 to verify the water retention capacity.

[0179] [Formula 1]

[0180] CRC(g / g) = {[W2(g) - W1(g) - W0(g)] / W0(g)}

[0181]

[0182] 3. Absorbency Under Pressure (AUP)

[0183] The 0.7 psi pressurized absorption capacity of each resin was measured according to the method of the European Disposables and Nonwovens Association standard EDANA WSP 242.2. First, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 60 mm. Under conditions of a temperature of 23±2℃ and a relative humidity of 45%, resins W0 (g, 0.90 g) obtained from the examples and comparative examples were uniformly spread on the wire mesh. A piston capable of uniformly applying a load of 4.82 kPa (0.7 psi) was positioned so that its outer diameter was slightly smaller than 60 mm, there was no gap with the inner wall of the cylinder, and its vertical movement was not obstructed. At this time, the weight W3 (g) of the device was measured. A glass filter with a diameter of 125 mm and a thickness of 5 mm was placed on the inside of a petroleum dish with a diameter of 150 mm, and physiological saline solution composed of 0.90 wt% sodium chloride was placed at the same level as the top surface of the glass filter. The measuring device was placed on the glass filter, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted, and its weight W4 (g) was measured. Using the mass obtained in this way, the AUP (g / g) was calculated according to the following formula 2 to confirm the pressurized absorption capacity.

[0184] [Formula 2]

[0185] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0186]

[0187] 4. Absorption rate (Vortex time) by the vortex method

[0188] The absorption rate was measured in seconds according to the method described in International Publication Application No. 1987-003208. Specifically, 50 mL of physiological saline solution (0.9 wt% sodium chloride aqueous solution) at 23 to 24 ℃ and a magnetic bar (diameter 8 mm, length 30 mm) were placed in a 100 ml beaker and stirred at 600 rpm. 2.0 g of absorbent resin was added to the stirred physiological saline solution, and the absorption rate was calculated by measuring the time in seconds until the vortex disappeared.

[0189]

[0190] 5. Permeability

[0191] Lines were marked on the liquid levels at 20 ml and 40 ml with the piston inserted into the chromatography tube (F20 mm). Subsequently, water was added in reverse to fill the tube to about 10 ml, ensuring no air bubbles formed between the lower glass filter and the stopcock. The tube was then washed 2 to 3 times with saline solution, and 0.9% saline solution was added up to 40 ml or more. The piston was inserted into the chromatography tube, and the lower valve was opened to record the time (B) during which the liquid level decreased from 40 ml to the 20 ml mark. 10 ml of saline solution was left in the chromatography tube, 0.2 ± 0.0005 g of a classified (300 ~ 600 µm) absorbent resin sample was added, and saline solution was added to make the volume 50 ml, after which it was left for 30 minutes. After that, a piston with an additional weight (0.3 psi = 106.26 g) was inserted into the chromatography tube and left for 1 minute. Then, the lower valve of the chromatography tube was opened to record the time (T1) during which the liquid level decreased from 40 ml to the 20 ml mark, and the time (unit: seconds) of T1 - B was calculated.

[0192]

[0193] 6. Residual Monomers (RM, ppm)

[0194] The residual monomer content was measured according to the EDANA WSP 210.3 method. Specifically, 1.000 g of an absorbent resin powder sample with a particle size of 150 to 850 µm and 200 g of a 0.90 wt% aqueous sodium chloride solution were placed in a 250 ml plastic container with a lid and stirred for 1 hour to extract unreacted acrylic acid. The extracted solution was analyzed using HPLC / CAD under the following conditions, and the content of unreacted acrylic acid, which is the residual monomer, was measured (based on the total weight of the absorbent resin, ppm).

[0195] <Analysis Conditions>

[0196] * Mobile bed

[0197] - Mobile phase A: 1000 mL of acetonitrile was filtered through a solvent clarification system to remove impurities.

[0198] - Mobile phase B: 1000 mL of ultrapure water was filtered through a solvent clarification system to remove impurities.

[0199] * HPLC analysis conditions

[0200] - Column: Capcellpak C18 (4.6 mm ID × 50 mm L., 3㎛, ​​Shiseido)

[0201] - Eluent: Mobile Phase A / Mobile Phase B = 75 / 25 (v / v, %)

[0202] - Flow rate: 1mL / min

[0203] - Column temp.: 40 ℃

[0204] - Run time: 15 min

[0205] - Injection Volume: 10 µl

[0206] CAD analysis conditions

[0207] - Gas pressure=232,353 Pa(33.7 psi), Corona=normal

[0208] - Total flow=1.14 mL / min, Flow ratio=0.48

[0209] - The range was measured at 100 pA and then adjusted according to the content.

[0210] (The peak size increases as the amperage goes from 100 pA to 50 pA to 20 pA.)

[0211]

[0212] Classification Hunter B (Color) CRC(g / g) 0.7 AUP(g / g) Vortex(s) Permeability(s) RM(ppm) Example 1 4.8 37.9 21.7 69 98488 Example 2 4.7 37.7 20 6410 1380 Example 3 6.0 45 9.5 30 700 491 Example 4 6.2 30.5 19 30 145 488 Comparative Example 1 8.4 37.8 19 68 96519 Comparative Example 2 8.9 38 18.7 69 100 590 Comparative Example 3 9.1 38.1 23.1 75 855 20 Comparative Example 4 45.4 38.1 8.5 6310 12519 Comparative Example 5 3.6 38.2 15 67100 1499 Comparative Example 69.845.19.331699477 Comparative Example 710.230.718.729180478 Comparative Example 82.938.520.5651001000

[0213] According to Table 2, the absorbent resins according to Examples 1 to 4 of the present invention were confirmed to exhibit excellent characteristics, satisfying centrifugal retention capacity of 30 g / g or more, pressurized absorption capacity of 9 g / g or more, absorption rate of 80 seconds or less, and liquid permeability of 1000 seconds or less, with a Hunter color B of 8 or less and a residual monomer content of 500 ppm or less. On the other hand, Comparative Examples 1, 6, and 7, in which hydrogen peroxide was not added during the polymerization step, showed an increase in Hunter color B to 8.4, 9.8, and 10.2, respectively, and Comparative Example 8, in which hydrogen peroxide was added at a concentration of 500 ppm or more, showed a residual monomer content that increased by more than 2 times compared to the examples. Comparative Example 2, in which surface crosslinking was performed at 180°C during the post-crosslinking step, showed a significant increase in Hunter color B to 8.9, and Comparative Example 3, in which surface crosslinking was performed at 180°C using a non-epoxy surface crosslinking agent, showed a further increase in Hunter color B to 9.1, resulting in significant discoloration compared to Examples 1 and 2.

[0214] Meanwhile, in the case of Comparative Example 4, which used a non-epoxy surface crosslinking agent in the post-crosslinking step, and Comparative Example 5, which used 0.1 parts by weight or more of a discoloration inhibitor, the Hunter color B was maintained at 8 or lower, but it was confirmed that the pressurized absorption capacity was significantly reduced and the permeability was significantly increased compared to Example 2.

[0215]

[0216] Accordingly, it was confirmed that the absorbent resins according to Examples 1 to 4 of the present invention exhibit all major physical properties, including Hunter color, centrifugal retention capacity, pressurized absorption capacity, absorption rate, and liquid permeability, in a balanced and excellent manner, and that safety and stability are ensured due to the low residual monomer content. In particular, by applying optimized polymerization and post-crosslinking conditions, discoloration and performance degradation can be minimized, and various effects that consumers can experience, such as leakage prevention, rapid liquid absorption, and shape stability during long-term use, can also be expected. In conclusion, the absorbent resins of the present invention are significantly superior in terms of appearance quality, absorption performance, safety, and ease of use, and can exhibit excellent effects as sanitary products.

[0217]

[0218] Specific parts of the present invention have been described in detail above. It is evident to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the invention. Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.

Claims

Absorbent resin satisfying (1) to (4) below: (1) Hunter Color B must be 8 or less, (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher, (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater, and (4) Permeability shall be 1000 seconds or less. In paragraph 1, The absorption rate of the above absorbent resin by the (5) vortex method is 80 seconds or less, wherein the absorption rate by the vortex method is calculated by adding 2g of absorbent resin to 50 mL of physiological saline solution at 23°C to 24°C and stirring at 600 rpm, and measuring the time in seconds until the vortex disappears. In paragraph 1, Absorbent resin satisfying (1) to (5) below: (1) Hunter Color B is 1 to 7, (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g, (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 23 g / g, (4) Permeability shall be 50 to 800 seconds, and (5) The absorption rate by the vortex method shall be 20 to 75 seconds. In paragraph 1, Absorbent resin satisfying (1) to (5) below: (1) Hunter Color B is 1 to 6.5, (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 30 to 45 g / g, (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 to 22 g / g, (4) Permeability shall be 50 to 750 seconds, and (5) The absorption rate by the vortex method shall be 25 to 75 seconds. (S1) A polymerization process of mixing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with sodium persulfate and hydrogen peroxide (H2O2), and (S2) A post-crosslinking process in which the polymer obtained from the above polymerization process is mixed with an epoxy-based surface crosslinking agent and a discoloration inhibitor, A method for manufacturing an absorbent resin comprising and satisfying the following (1) to (4): (1) Hunter Color B must be 8 or less, (2) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 30 g / g or higher, (3) The pressure absorption capacity (AUP) at 4826 Pa (0.7 psi) measured according to the EDANA method WSP 242.2 shall be 9 g / g or greater, and (4) Permeability shall be 1000 seconds or less. In paragraph 5, A method for manufacturing an absorbent resin, wherein the amount of sodium persulfate added in step (S1) above is 1000 to 2500 ppm based on 100 parts by weight of a water-soluble ethylene-based unsaturated monomer. In paragraph 5, A method for manufacturing an absorbent resin, wherein the amount of hydrogen peroxide added in step (S1) above is 100 or more to less than 500 ppm based on 100 parts by weight of a water-soluble ethylene-based unsaturated monomer. In paragraph 5, A method for manufacturing an absorbent resin, wherein the amount of surface crosslinking agent added in step (S2) is 0.01 to 0.30 parts by weight based on 100 parts by weight of the polymer obtained in step (S1). In paragraph 5, A method for manufacturing an absorbent resin, wherein the amount of discoloration inhibitor added in step (S1) is 0.01 or more to less than 0.10 parts by weight based on 100 parts by weight of the polymer obtained in step (S1). In paragraph 5, A method for manufacturing an absorbent resin, wherein the post-crosslinking process in the above (S2) step is performed at a temperature of 150°C or lower.