Absorbent polymer and preparation method therefor

Abstract

The present invention relates to an absorbent polymer and a preparation method therefor. More specifically, the present invention relates to an absorbent polymer and a preparation method therefor, the absorbent polymer having centrifuge retention capacity (CRC) of 35 g / g or more measured according to EDANA WSP 241.2, an absorption rate of 35 seconds or less measured by a vortex method, and a tertiary absorption rate of 60 seconds or less in a U-shaped device.

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 present invention relates to an absorbent resin and a method for manufacturing the same, wherein the centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 35 g / g or more, the absorption rate by the vortex method is 35 seconds or less, and the tertiary absorption rate of an absorbent article containing the absorbent resin in a U-shaped device is 60 seconds or less.

[0002] Absorbent polymers are synthetic polymer materials capable of absorbing hundreds of times their own weight in water, and they are widely used in various industries, including agriculture, civil engineering, construction, and food, as well as in hygiene products such as diapers and sanitary pads. In particular, in the hygiene product sector, absorbent polymers are used in conjunction with pulp to play a key role in efficiently absorbing and retaining liquids. Recently, as hygiene materials have become thinner and there is increasing demand for 'pulpless' products that reduce pulp content or use no pulp at all, improving the performance of absorbent polymers has emerged as an important challenge.

[0003]

[0004] The performance of absorbent resins is evaluated based on two key indicators. The first is Vortex Time, which indicates how quickly the resin can absorb liquid using the vortex method, and the second is Centrifuge Retention Capacity (CRC), which indicates how effectively the absorbed liquid can be retained. These two indicators are critical factors determining the functionality and user comfort of hygiene products, and thus, achieving both high absorption rate and excellent CRC simultaneously is required.

[0005]

[0006] Blowing agents play a crucial role in optimizing these performances. By imparting porosity to the internal structure of the absorbent resin, blowing agents provide pathways for liquids to rapidly penetrate into the resin particles. This is essential for increasing the diffusion rate of the liquid and enhancing the initial absorption performance of the absorbent resin. In particular, blowing agents help ensure the liquid is evenly dispersed within the absorbent resin and prevent localized saturation, thereby maintaining stable performance even under repeated absorption conditions. The use of blowing agents can affect not only the absorption rate but also the centrifugal retention capacity (CRC). During the process of forming an internal porous structure, blowing agents can alter the mechanical strength and network structure of the resin. If the amount of blowing agent used is excessive, porosity increases too much, potentially degrading the physical stability of the resin and reducing the CRC. Therefore, blowing agents must be precisely designed not merely to increase porosity, but to provide a rapid absorption rate while maintaining the CRC.

[0007]

[0008] The performance of hygiene materials must be maintained even under repeated absorption conditions. In particular, when hygiene materials are arranged in a U-shape to conform to the user's body curves, liquid tends to concentrate towards the center of the material due to the influence of gravity. In such situations, the tertiary absorption rate is an important indicator for evaluating the ability of hygiene materials to rapidly absorb and disperse liquid even after repeated absorption. Existing research has focused on evaluating absorption performance in a flat state, failing to adequately reflect performance in actual usage environments. Under physical conditions such as a U-shape, central saturation is prone to occur, which can lead to reduced comfort and skin discomfort. Therefore, the design of absorbent resins that consider actual usage environments is required.

[0009]

[0010] Conventional absorbent resin manufacturing technologies have shown limitations in simultaneously improving CRC, absorption rate via the vortex method, and tertiary absorption rate. For example, lowering the crosslinking density increases the CRC but leads to problems such as slower absorption rate and reduced tertiary absorption rate. Conversely, increasing the crosslinking density improves the absorption rate but results in a trade-off where the CRC and repeated absorption performance deteriorate. While it is possible to overcome these trade-offs through the amount of components such as foaming agents and structural design, existing technologies have struggled to optimize them under actual usage conditions.

[0011]

[0012] Therefore, to enhance the performance of absorbent resins, a technical approach is required to simultaneously improve the initial absorption rate, CRC, and repetitive absorption performance (tertiary absorption rate) by optimizing the amount of foaming agent and structural design.

[0013]

[0014] Prior art literature

[0015] [Patent Document 1] Republic of Korea Published Patent No. 10-2022-0088354

[0016] The present invention aims to provide an absorbent resin capable of simultaneously improving centrifugal retention capacity (CRC) and absorption rate by the vortex method, while also improving the tertiary absorption rate. Specifically, it was confirmed that when a capsule foaming agent with a small average particle size is used during the polymerization stage, the CRC is 35 g / g or more, the absorption rate by the vortex method is 35 seconds or less, and the tertiary absorption rate in a U-shaped device is 60 seconds or less, while maintaining a low amount of fine particles.

[0017]

[0018] Accordingly, the present invention aims to provide an absorbent resin capable of exhibiting excellent tertiary absorption performance under actual usage conditions and a method for manufacturing the same.

[0019]

[0020] 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.

[0021] According to the sun,

[0022] An absorbent resin satisfying (1) to (3) below is disclosed:

[0023] (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 35 g / g or higher,

[0024] (2) The absorption rate by the vortex method shall be 35 seconds or less, and

[0025] (3) The tertiary absorption rate of an absorbent article containing an absorbent resin in a U-shaped device shall be 60 seconds or less.

[0026] The absorption rate by the above vortex method may be 25 to 31 seconds.

[0027] In the above U-shaped device, the third absorption rate may be 50 to 55 seconds.

[0028] The above third absorption rate can be determined by measuring the time until the injected aqueous solution is absorbed into the absorbent article by injecting a 0.8 wt% sodium chloride aqueous solution from an injector installed in the device at a rate of 20 ml / sec while the absorbent article containing an absorbent resin is fixed in the center of the U-shaped device, and the time until the injected aqueous solution disappears from the surface of the absorbent article after the first injection of the aqueous solution is called the first absorption rate, the time until the aqueous solution disappears from the surface of the absorbent article after the same amount of aqueous solution is injected a second time under the same conditions as the first injection after 10 minutes have elapsed since the start of the first injection is called the second absorption rate, and the time until the aqueous solution disappears from the surface of the absorbent article after the same amount of aqueous solution is injected a third time under the same conditions as the second injection after 10 minutes have elapsed since the start of the second injection is called the third absorption rate.

[0029] The above absorbent resin can satisfy (1) to (3) below:

[0030] (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 35 to 50 g / g,

[0031] (2) The absorption rate by the vortex method shall be 25 to 30 seconds, and

[0032] (3) The absorption rate in the U-shaped device shall be 50 to 55 seconds.

[0033]

[0034] According to another sun,

[0035] A method for producing a cross-linked absorbent resin is disclosed by polymerizing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with a polymerization initiator and a foaming agent.

[0036] The average particle size of the foaming agent may be 1 to 20 μm, preferably 6 to 10 μm. The foaming initiation temperature of the foaming agent may be 115°C or lower, for example, 100 to 110°C. The maximum foaming temperature of the foaming agent may be 140°C or lower, for example, 125 to 135°C.

[0037] The blowing agent can be used in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer.

[0038] The above polymerization initiator may be used in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the above water-soluble ethylene-based unsaturated monomer.

[0039] During the above polymerization, 0.04 to 0.07 parts by weight of a crosslinking agent may be further included based on 100 parts by weight of a water-soluble ethylene-based unsaturated monomer.

[0040] The absorbent resin according to the present invention maintains a high retention capacity (CRC) even under centrifugal conditions, thereby effectively immobilizing the absorbed liquid. In addition, it maintains an excellent level compared to existing technologies in terms of absorption rate measured by the vortex method, thereby stably providing fast absorption performance. In particular, the absorbent resin of the present invention has the advantage of significantly improving the tertiary absorption rate even in complex structures such as U-shaped devices used in sanitary materials.

[0041] Therefore, the present invention can contribute to maximizing the performance of hygiene materials and increasing user satisfaction.

[0042]

[0043] Meanwhile, the scope of the present invention is not limited by the effects described above.

[0044] Figure 1 shows a micrograph of an absorbent resin prepared according to Example 1.

[0045] Figure 2 shows a micrograph of an absorbent resin prepared according to Comparative Example 1.

[0046] Figure 3 shows a U-shaped device used to evaluate multiple absorption rates according to an experimental example.

[0047] The present invention will be described in more detail below.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Furthermore, the terms "base resin" or "base resin powder" refer to a polymer formed by drying and grinding a polymer of acrylic acid-based monomers into particle or powder form, and refer to a polymer in a state where the surface modification or surface crosslinking steps described below have not been performed.

[0054] Additionally, depending on the context, the terms "absorbent resin" or "absorbent resin powder" refer to a cross-linked polymer formed by polymerizing a water-soluble ethylene-based unsaturated monomer (acrylic acid-based monomer) containing acidic groups and having at least some of the acidic groups neutralized, or a base resin in the form of a powder made of crushed absorbent resin particles from said cross-linked polymer, or are used to encompass all of the cross-linked polymer or said base resin that has been made into a state suitable for commercialization through additional processes, such as surface cross-linking, fine powder reassembly, drying, grinding, classification, etc.

[0055] 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.

[0056] Hereinafter, an absorbent resin for improving multiple absorption rates and a method for manufacturing the same will be described in more detail according to a specific aspect of the invention.

[0057]

[0058] 1. Absorbent resin

[0059] One aspect of the present invention is

[0060] An absorbent resin satisfying (1) to (3) below is provided:

[0061] (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 35 g / g or higher,

[0062] (2) The absorption rate by the vortex method shall be 35 seconds or less, and

[0063] (3) In a U-shaped device, the third absorption rate shall be 60 seconds or less.

[0064] The centrifugal retention capacity (CRC) of the absorbent resin may be 35 g / g or more. Specifically, the centrifugal retention capacity of the absorbent resin may be 35 to 50 g / g, 35 to 49 g / g, 35 to 48 g / g, 35 to 47 g / g, 35 to 46 g / g, 35 to 45 g / g, 35 to 44 g / g, 35 to 43 g / g, 35 to 42 g / g, 35 to 41 g / g, or 35 to 40 g / g. The centrifugal retention capacity may be measured according to the method of the EDANA method WSP 241.2.

[0065] The absorption rate of the absorbent resin by the vortex method may be 35 seconds or less. Specifically, the absorption rate of the absorbent resin by the vortex method may be 25 to 35 seconds, 25 to 34 seconds, 25 to 33 seconds, 25 to 32 seconds, 25 to 31 seconds, or 25 to 30 seconds. The absorption rate of the absorbent resin by the vortex method may preferably be 25 to 31 seconds, and more preferably 25 to 30 seconds. If the absorption rate of the absorbent resin by the vortex method exceeds 35 seconds, moisture is not effectively absorbed under external pressure, leading to a decrease in absorption efficiency and a decline in product performance. The absorption rate by the vortex method can be calculated by adding 2g of absorbent resin to 50 mL of physiological saline solution at 23°C to 24°C, stirring at 600 rpm, and measuring the time in seconds until the vortex disappears.

[0066] In the U-shaped device of the absorbent resin above, the tertiary absorption rate may be 60 seconds or less. Specifically, the tertiary absorption rate may be 45 to 60 seconds, 46 to 58 seconds, 47 to 56 seconds, 48 ​​to 56 seconds, or 50 to 55 seconds. Preferably, the tertiary absorption rate may be 50 to 55 seconds. If the tertiary absorption rate of the absorbent resin exceeds 60 seconds, the absorption efficiency decreases and moisture leakage problems occur, which may reduce the overall quality and effectiveness of the product.

[0067] The above third absorption rate can be determined by measuring the time until the injected aqueous solution is absorbed into the absorbent article by injecting a 0.8 wt% sodium chloride aqueous solution from an injector installed in the device at a rate of 20 ml / sec while the absorbent article containing an absorbent resin is fixed in the center of the U-shaped device, and the time until the injected aqueous solution disappears from the surface of the absorbent article after the first injection of the aqueous solution is called the first absorption rate, the time until the aqueous solution disappears from the surface of the absorbent article after the same amount of aqueous solution is injected a second time under the same conditions as the first injection after 10 minutes have elapsed since the start of the first injection is called the second absorption rate, and the time until the aqueous solution disappears from the surface of the absorbent article after the same amount of aqueous solution is injected a third time under the same conditions as the second injection after 10 minutes have elapsed since the start of the second injection is called the third absorption rate. For example, the above 0.8 wt% sodium chloride aqueous solution comprises 2 wt% urea (NH₂CONH₂), 0.8 wt% sodium chloride (NaCl), 0.023 wt% calcium chloride anhydrate (CaCl₂), and 0.08 wt% magnesium sulfate heptahydrate (MgSO₄·7H₂O) based on 1 L of distilled water, and may additionally contain 0.1 g of food coloring blue No. 1 (3-[N-ethyl-N-[4-[[4-[N-ethyl-N-(3-sulfonatebenzyl)amino]phenyl](2-sulfonatephenyl)methylene]-2,5-cyclohexadienylidene]ammoniomethyl]benzenesulfonate disodium).

[0068] According to one exemplary example, the absorbent resin may satisfy (1) to (3) below:

[0069] (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 35 to 50 g / g,

[0070] (2) The absorption rate by the vortex method shall be 25 to 30 seconds, and

[0071] (3) In a U-shaped device, the third absorption rate shall be 50 to 55 seconds.

[0072]

[0073] 2. Method for manufacturing absorbent resin

[0074] Another aspect of the present invention is

[0075] A method for producing a cross-linked absorbent resin is provided by polymerizing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with a polymerization initiator and a foaming agent.

[0076] According to one exemplary example, the method for manufacturing the absorbent resin is:

[0077] (S1) A polymerization process for mixing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with a polymerization initiator and a foaming agent, and

[0078] (S2) A post-crosslinking process may be included in which the polymer obtained from the above polymerization process is mixed with a surface crosslinking agent.

[0079]

[0080] (S1) Polymerization process

[0081] 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 polymerization initiator and a foaming agent.

[0082] The above polymerization initiator may be appropriately selected depending on the polymerization method. For example, when using a thermal polymerization method, a thermal polymerization initiator may be used, and when using a photopolymerization method, a photopolymerization initiator may be used. When using a hybrid polymerization method (a method using both heat and light), both a thermal polymerization initiator and a photopolymerization initiator may be used. However, even in the photopolymerization method, a certain amount of heat is generated by light irradiation such as ultraviolet irradiation, and since some heat is also generated as the polymerization reaction, which is an exothermic reaction, proceeds, a thermal polymerization initiator may be additionally used. The above photopolymerization initiator may be used without limitation in composition as long as it is a compound capable of forming radicals by light such as ultraviolet light.

[0083] As the above photopolymerization initiator, one or more selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone may be used. Meanwhile, specific examples of acyl phosphine include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl(2,4,6-trimethylbenzoyl)phenylphosphineate, etc. A wider variety of photoinitiators is well described in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Applications" (Elsevier 2007), p. 115, and is not limited to the examples described above.

[0084] As the above thermal polymerization initiator, one or more selected from the group of initiators consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of persulfate-based initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8), while examples of azo-based initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, and 2-(carbamoylazo)isobutylonitrile. Examples include 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride and 4,4-azobis-(4-cyanovaleric acid). A wider variety of thermal polymerization initiators is well described in Odian's book 'Principles of Polymerization' (Wiley, 1981), p. 203, and is not limited to the examples mentioned above.

[0085] The above polymerization initiator may be used in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. If the above polymerization initiator is used in an amount of 0.1 parts by weight per 100 parts by weight of the water-soluble ethylene-based unsaturated monomer, the polymerization rate may be slowed down and a large amount of residual monomer may be extracted in the final product. If it is used in an amount exceeding 2.0 parts by weight, the polymer chains forming the network may become shorter, resulting in a higher content of water-soluble components and a lower pressure absorption capacity, which may degrade the physical properties of the resin.

[0086] In the method for manufacturing an absorbent resin according to the present invention, the foaming agent may be a capsule foaming agent and may have a structure comprising a core containing a hydrocarbon and a shell formed of a thermoplastic resin surrounding the core. Such a capsule foaming agent has different expansion characteristics depending on the components forming the core and the shell, as well as the weight and diameter of each component; by controlling these, it is possible to expand to a desired size and control the porosity of the absorbent resin sheet.

[0087] The average particle size of the blowing agent may be 1 or more and less than 15 μm, 1 to 14 μm, 2 to 14 μm, 3 to 13 μm, 4 to 13 μm, 5 to 12 μm, 5 to 11 μm, or 6 to 10 μm. The average particle size of the blowing agent may preferably be 5 to 11 μm, and more preferably 6 to 10 μm. Here, "average particle size of the blowing agent" refers to the particle size measured in its natural state, that is, before the blowing agent initiates foaming due to the application of heat or other conditions. This indicates that the blowing agent is an important factor in forming an appropriate porous structure during the polymerization process. When a blowing agent with an average particle size of 15 μm or more is used in the manufacturing process of an absorbent resin, excessive initial pores may be formed during the polymerization stage, and there is a possibility that this pore structure may not be sufficiently maintained on the surface or inside the resin during the process of drying and grinding the hydrogel after polymerization. As a result, the structural stability or absorption characteristics of the final absorbent resin may be reduced. Therefore, in the manufacture of the absorbent resin according to the present invention, it is preferable to select and use a foaming agent having an average particle size of 1 or more and less than 15 μm. In particular, when a foaming agent with an average particle size of 6 to 10 μm is used, more stable results can be obtained regarding the structural stability and absorption characteristics of the absorbent resin, and the absorption rate can be improved.

[0088] The foaming initiation temperature of the above-mentioned foaming agent (hereinafter also referred to as the “expansion initiation temperature”) may be 95 to 115°C, preferably 100 to 110°C. Here, “foaming initiation temperature” refers to the temperature at which foaming begins to expand in a manner such as volume expansion when the foaming agent is heated. The foaming initiation temperature can be measured through thermomechanical analysis and can be calculated by analyzing the illustrated temperature-expansion ratio curve.

[0089] The maximum foaming temperature of the foaming agent (hereinafter also referred to as the “maximum expansion temperature”) may be 120 to 140°C, preferably 125 to 140°C. Here, the “maximum foaming temperature” refers to the temperature at which the size of the foaming agent increases as it is heated to a specific temperature, and then begins to decrease due to the softening of the thermoplastic resin and an increase in external pressure when that temperature is exceeded. The maximum foaming temperature can be measured through thermomechanical analysis and can be calculated by analyzing the illustrated temperature-expansion ratio curve.

[0090] The above foaming agent may therefore be a thermo-expandable microcapsule, and the types of foaming agents that can be used in the present invention may include various commercially available products. For example, "FN-80GSD" manufactured by SDI may be used. According to one exemplary embodiment, as the foaming agent, a thermo-expandable microcapsule having an average particle size of 6 to 10 μm, an expansion initiation temperature of 100 to 110°C, and a maximum expansion temperature of 125 to 135°C may be used.

[0091] The blowing agent may be used in an amount of 0.1 to 0.5 parts by weight relative to 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. If the content of the blowing agent is less than 0.1 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer, the porous structure caused by the blowing agent may not be sufficiently formed, which may result in a decrease in the absorption rate. On the other hand, if the blowing agent is used in an amount exceeding 0.5 parts by weight, the mechanical strength of the absorbent resin may be weakened due to the excessive porous structure, and there is a possibility that the network structure may be formed unevenly. This may lead to a decrease in pressurized absorption capacity and retention capacity (CRC), thereby deteriorating the physical properties of the absorbent resin. Therefore, by using the blowing agent in a range of 0.1 to 0.5 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer, the optimal performance and physical properties of the absorbent resin can be maintained.

[0092]

[0093] According to one exemplary embodiment, the polymerization process may include the steps 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 polymerization initiator, a foaming agent, and other additives to form a hydrogel polymer, and drying, grinding, and classifying the hydrogel polymer to form a base resin.

[0094] According to one exemplary embodiment, the water-soluble ethylene-based unsaturated monomer may be any monomer commonly used in the manufacture of absorbent resins. For example, the water-soluble ethylene-based unsaturated monomer may be a compound represented by the following chemical formula 1:

[0095] [Chemical Formula 1]

[0096] R1 -COOM 1

[0097] In the above chemical formula 1,

[0098] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0099] M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine base.

[0100] 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.

[0101] According to one exemplary example, any compound that enables the introduction of crosslinking bonds during the polymerization of the water-soluble ethylene-based unsaturated monomer can be used as the crosslinking agent. 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 0.04 to 0.07 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. If the amount of the crosslinking agent added is less than 0.04 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer, crosslinking may not occur sufficiently, making it difficult to achieve strength above an appropriate level; if the amount of the crosslinking agent added exceeds 0.07 parts by weight, there is a risk that the physical properties of the absorbent resin may deteriorate due to excessive crosslinking.

[0102] According to one exemplary example, the other additives may include one or more selected from the group consisting of chelating agents, neutralizing agents, foam stabilizers, thickeners, plasticizers, preservative stabilizers, and antioxidants, but are not limited thereto.

[0103] 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 above chelating agent added may be 0.01 to 0.15 parts by weight based on 100 parts by weight of water-soluble ethylene-based unsaturated monomer. If the amount of the above chelating agent added exceeds 0.15 parts by weight, the content of residual monomer in the absorbent resin increases, which may degrade the physical properties and absorption performance of the absorbent resin.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108]

[0109] (S2) Post-crosslinking process

[0110] In the method for manufacturing an absorbent resin according to the present invention, the post-crosslinking process may be performed by mixing the polymer obtained from the polymerization process with a surface crosslinking agent.

[0111] In the method for manufacturing an absorbent resin according to the present invention, 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. The amount of the surface crosslinking agent added may be 0.04 to 0.1 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer. If the amount of the surface crosslinking agent added exceeds 0.1 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer, there is a risk that the physical properties of the absorbent resin will deteriorate due to excessive surface crosslinking.

[0112] According to one exemplary example, the other additives may include one or more selected from the group consisting of reducing agents, inorganic fillers, and thickeners, but are not limited thereto.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] The absorbent resin produced by the manufacturing method according to the present invention has excellent centrifugal retention capacity (CRC) and absorption rate by the vortex method, and the absorption rate in a U-shaped device can be improved to 60 seconds or less.

[0117] According to one exemplary example, an absorbent resin produced by the manufacturing method according to the present invention may satisfy (1) to (3) below:

[0118] (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 35 g / g or higher,

[0119] (2) The absorption rate by the vortex method shall be 35 seconds or less,

[0120] (3) In a U-shaped device, the third absorption rate shall be 60 seconds or less.

[0121] According to one exemplary example, an absorbent resin produced by the manufacturing method according to the present invention may satisfy (1) to (3) below:

[0122] (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 35 to 50 g / g,

[0123] (2) The absorption rate by the vortex method shall be 25 to 30 seconds,

[0124] (3) In a U-shaped device, the third absorption rate shall be 50 to 55 seconds.

[0125] 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.

[0126]

[0127] <Example>

[0128] Example 1

[0129] [Manufacture of Base Resin]

[0130] 500 g of acrylic acid, 600 ppmw of ethylene glycol diglycidyl ether (relative to 100 parts by weight of acrylic acid) as an internal crosslinking agent, and 80 ppmw of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (relative to 100 parts by weight of acrylic acid) as a photopolymerization initiator were added and dissolved in a 3 L glass container equipped with a stirrer and a thermometer, and then a 31.5% caustic soda solution was added to prepare an aqueous solution of a water-soluble unsaturated monomer (degree of neutralization: 70~80 mol%).

[0131] When the temperature of the above aqueous solution of the water-soluble unsaturated monomer rises to 40°C due to the heat of neutralization, this mixture is placed in a square container containing 1650 ppmw of sodium persulfate (relative to 100 parts by weight of acrylic acid), a thermal polymerization initiator, and 4000 ppmw of FN-80GSD (SDI Korea Co., Ltd.), a capsule foaming agent (relative to 100 parts by weight of acrylic acid), and then irradiated with ultraviolet rays for 1 to 5 minutes (irradiation dose: 10 mV / cm² 2Photopolymerization was performed by ) and a hydrogel-type polymer sheet was obtained. The obtained hydrogel-type polymer sheet was passed through a chopper with a hole size of 16 mm to produce a crumb.

[0132] Next, the above-mentioned crumb was dried in an oven capable of vertical airflow transfer. The drying was performed in multiple stages; specifically, an air flow oven was used at a temperature of 170°C for approximately 30 minutes. The dried polymer obtained through the drying process was ground using a grinder to obtain a base resin having a particle size of 150 to 850 μm.

[0133] [Surface Treatment of Base Resin]

[0134] A surface treatment solution comprising 5 to 6 parts by weight of water, 0.05 parts by weight of ethylene glycol diglycidyl ether (EGDGE), and 0.05 parts by weight of an aqueous solution of a polycarboxylic acid surfactant was evenly mixed with 100 parts by weight of the base resin prepared above, supplied to a surface crosslinking reactor, and carried out a surface crosslinking reaction of the base resin at 130 to 190 °C for 60 minutes. Subsequently, 0.05 to 0.5 parts by weight of fumed silica was mixed to obtain an absorbent resin. A micrograph of the absorbent resin particles prepared according to Example 1 is shown in Figure 1.

[0135]

[0136] Comparative Example 1

[0137] An absorbent resin was prepared in the same manner as in Example 1, except that MS-140DS from Dongjin Semichem Co., Ltd. was added in an amount of 1500 ppmw instead of the capsule foaming agent FN-80GSD. A micrograph of the absorbent resin particles prepared according to Comparative Example 1 is shown in Figure 2.

[0138]

[0139] The main characteristics of the capsule foaming agents used in Example 1 and Comparative Example 1 above are shown in Table 1 below:

[0140] Type of foaming agent Average particle size (μm) Expansion onset temperature (°C) Maximum expansion temperature (°C) Example 16-10 105 130 Comparative Example 115-25 90 120

[0141] <Experimental Example>

[0142] 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 %.

[0143]

[0144] 1. Centrifugal Retention Capacity (CRC)

[0145] 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. 0.2g) was uniformly placed into a nonwoven bag and sealed, after which it was immersed in a physiological saline solution containing 0.9 wt% sodium chloride. 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 using 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.

[0146] [Formula 1]

[0147] CRC(g / g) = {[W2(g) - W1(g) - W0(g)] / W0(g)}

[0148]

[0149] 2. Absorption rate (Vortex time) by the vortex method

[0150] The absorption rate was measured according to the Japanese standard method (JIS K 7224). Specifically, 50 mL of physiological saline solution (0.9 wt% sodium chloride aqueous solution) at 24°C ± 0.5°C and a magnetic bar (diameter 8 mm, length 31.8 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.

[0151]

[0152] 3. Fine powder content

[0153] The particle size of the absorbent resin was measured, and the content of particles with a particle size of 180 μm or less was measured as the fine content. The fine content was measured using a standard test sieve from Retsch, Germany. The sieve used for measurement was a Sieve #100 (opening size 150 μm) manufactured according to the ASTM E 11 standard, and the mesh material was stainless steel. After accurately weighing 100 to 200 g of absorbent resin powder, the powder was sieved for 5 minutes using a vibratory sieve shaker with the above sieve, and the mass of the particles that passed through the sieve was measured.

[0154]

[0155] 4. Measurement of multiple absorption rates

[0156] After preparing a tissue with a length of 45 cm and a width of 25 cm, 9.9 g of the absorbent resin prepared in the above examples and comparative examples and 8.1 g of crushed wood pulp were uniformly mixed using a mechanical mixer inside a mold with a length of 32 cm and a width of 10 to 12 cm, and the mixture was evenly distributed inside the mold using an automatic distribution device. Then, the tissue containing the mixture was removed from the mold, the absorbent resin / pulp mixture was wrapped in the tissue, and an absorbent body the size of a children's paper diaper was produced by pressing it with a pressure of 10 kPa using a roll-type press with a 0.1 cm spacing. A back sheet made of polyethylene film was attached to the bottom of the sample of the produced absorbent body by a heat-sealing method, and a top sheet made of polypropylene nonwoven fabric was attached to the top in the same manner to complete the absorbent article.

[0157] (1) U-shaped (U-type) device

[0158] A U-shaped device with dimensions of R=80 mm, L1=290 mm and L2=190 mm was used (Fig. 3).

[0159] (2) Artificial urine composition

[0160] Artificial urine was prepared based on 1 L of distilled water, containing 20 g of urea (NH₂CONH₂), 8 g of sodium chloride (NaCl), 0.23 g of calcium chloride anhydrate (CaCl₂), 0.8 g of magnesium sulfate heptahydrate (MgSO₄·7H₂O), and 0.1 g of food coloring Blue No. 1 (3-[N-ethyl-N-[4-[[4-[N-ethyl-N-(3-sulfonatebenzyl)amino]phenyl](2-sulfonatephenyl)methylene]-2,5-cyclohexadienylidene]ammoniomethyl]sodium benzenesulfonate).

[0161] (3) U-type multi-level absorption rate measurement

[0162] An artificial urine injection site was marked near the center of the above-mentioned manufactured absorbent article, and the center was aligned with the center of the U-shaped device. Using a funnel, 80 ml of artificial urine was injected first at the injection site within 10 seconds, maintaining a 10 mm gap between the end of the funnel and the top of the absorbent article. The time from the injection of artificial urine until the artificial urine disappeared from the surface of the absorbent article was recorded (first absorption rate), and the device was left for 5 minutes. That is, the absorption rate was measured by starting a stopwatch immediately after the artificial urine was applied to the surface of the absorbent article, stopping the stopwatch when the absorbent article had completely absorbed the artificial urine, and recording the elapsed time. Subsequently, the device was pressurized with rewet paper for 3 minutes, released the rewet, and left for 2 minutes before measuring the next stage. That is, 10 minutes after the start of the first artificial urine injection, 80 ml of artificial urine was injected secondly within 10 seconds at the same location as the first artificial urine injection site. The time from the moment the artificial urine was injected until it disappeared was recorded (secondary absorption rate), and the sample was left for 5 minutes. Subsequently, the sample was pressurized with rewet paper for 3 minutes, the rewet was removed, and the sample was left for 2 minutes before measuring the next stage. Specifically, 10 minutes after the start of the second artificial urine injection, 80 ml of artificial urine was injected for the third time within 10 seconds at the same location as the second injection, and the time from the moment of injection until it disappeared was recorded (tertiary absorption rate). At this time, the measurements of the first, second, and third absorption rates were each repeated 5 times under identical conditions, and the average value of the measured times was calculated as the absorption rate of the corresponding absorbent material. All these processes were conducted in a constant temperature and humidity room (temperature 23 ± 2℃, relative humidity 45 ± 15%), and the artificial urine used was used under conditions of 24 ℃ ± 1℃.

[0163]

[0164] Classification Absorbent Resin Physical Properties Absorbent Article Multi-stage Absorption Rate (sec) CRC (g / g) Vortex (s) Fine Powder (g) 1st 2nd 3rd Example 138.42997222953 Comparative Example 137.63899242767

[0165] According to Table 1, the absorbent resin prepared in Comparative Example 1 had a centrifugal retention capacity of 37.6 g / g, an absorption rate of 38 seconds, and a fine content of 99 g, and the absorbent article prepared using this exhibited a tertiary absorption rate of 67 seconds. In contrast, the absorbent resin prepared according to Example 1 of the present invention was found to have a centrifugal retention capacity of 35 g / g or more, an absorption rate of 35 seconds or less, and a fine content of 97 g, while exhibiting a tertiary absorption rate of 60 seconds or less. From these results, it is determined that the blowing agent used in Example 1 exhibits characteristics advantageous for maintaining physical stability in terms of suppressing fine generation while simultaneously improving the absorption performance of the absorbent resin. In particular, even under conditions where the amount of blowing agent used increased up to 4,000 ppmw, the negative impact on the amount of fine generation and CRC was minimal, and accordingly, the initial absorption rate and tertiary absorption rate of the absorbent resin showed a tendency to be significantly improved compared to the existing Comparative Example. Therefore, it can be seen that the foaming agent presented in the present invention is suitable for application to absorbent articles, particularly to sanitary materials where the tertiary absorption rate is important.

[0166]

[0167] 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

1. An absorbent resin satisfying (1) to (3) below: (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 35 g / g or higher, (2) The absorption rate by the vortex method shall be 35 seconds or less, and (3) The third absorption rate of the absorbent article containing the absorbent resin in the U-shaped device shall be 60 seconds or less.

2. In Paragraph 1, An absorbent resin having an absorption rate of 25 to 31 seconds by the above vortex method.

3. In Paragraph 1, An absorbent resin having a third absorption rate of 50 to 55 seconds in the above U-shaped device.

4. In Paragraph 1, The above third absorption rate is determined by measuring the time until the injected aqueous solution is absorbed into the absorbent article by fixing the absorbent article containing the absorbent resin in the center of the U-shaped device and injecting a 0.8 wt% sodium chloride aqueous solution from an injector installed in the device at a rate of 20 ml / sec, wherein the time until the injected aqueous solution disappears from the surface of the absorbent article after the first injection of the aqueous solution is defined as the first absorption rate, the time until the aqueous solution disappears from the surface of the absorbent article after the same amount of aqueous solution is injected a second time under the same conditions as the first injection 10 minutes after the start of the first injection is defined as the second absorption rate, and the time until the aqueous solution disappears from the surface of the absorbent article after the same amount of aqueous solution is injected a third time under the same conditions as the second injection 10 minutes after the start of the second injection is defined as the third absorption rate.

5. In Paragraph 1, Absorbent resin satisfying (1) to (3) below: (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 is 35 to 50 g / g, (2) The absorption rate by the vortex method shall be 25 to 30 seconds, and (3) The third absorption rate of the absorbent article containing the absorbent resin in the U-shaped device shall be 50 to 55 seconds.

6. A method for producing a cross-linked absorbent resin by polymerizing a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized with a polymerization initiator and a foaming agent, wherein A method for manufacturing an absorbent resin that satisfies (1) to (3) below, wherein the average particle size of the foaming agent is 1 to 20 μm: (1) The centrifugal retention capacity (CRC) measured according to the EDANA method WSP 241.2 must be 35 g / g or higher, (2) The absorption rate by the vortex method shall be 35 seconds or less, and (3) In a U-shaped device, the third absorption rate shall be 60 seconds or less.

7. In Paragraph 6, A method for manufacturing an absorbent resin, wherein the average particle size of the foaming agent is 6 to 10 μm.

8. In Paragraph 6, A method for manufacturing an absorbent resin, wherein the blowing agent is used in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer.

9. In Paragraph 6, A method for manufacturing an absorbent resin, wherein the above polymerization initiator is used in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the above water-soluble ethylene-based unsaturated monomer.

10. In Paragraph 6, A method for manufacturing an absorbent resin, further comprising 0.04 to 0.07 parts by weight of a crosslinking agent based on 100 parts by weight of a water-soluble ethylene-based unsaturated monomer during the polymerization.

Images