Absorbent resin and preparation method therefor

Abstract

The present invention can provide a polyacrylic acid (salt)-based absorbent resin, a preparation method therefor, and an article comprising the absorbent resin, the polyacrylic acid (salt)-based absorbent resin having an improved absorption rate and a reduced amount of fine particles generated relative to the achieved absorption rate, the improved absorption rate being due to the formation of appropriate pores in the absorbent resin as a result of using an encapsulated foaming agent, having a controlled average particle size in a predetermined range, during the preparation of a base resin.

Description

Absorbent resin and method for manufacturing the same

[0001] The present invention relates to a polyacrylic acid (salt)-based absorbent resin and a method for manufacturing the same, and an article comprising said absorbent resin, wherein the average pore size within the absorbent resin is controlled by using an encapsulated foaming agent having an average particle size controlled to a predetermined range during the manufacture of the base resin, thereby improving various physical properties including the absorption rate and reducing the amount of fine particles generated relative to the achieved fast absorption rate.

[0002]

[0003] Super Absorbent Polymer (SAP) is a synthetic polymer material capable of absorbing 500 to 1,000 times its own weight in moisture, and developers name it by different names such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material). The above-mentioned super absorbent polymer began to be commercialized for sanitary devices, and is now widely used in various fields, including sanitary products such as children's disposable diapers, soil conditioners for horticulture, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservation agents in the food distribution sector, materials for compresses, and even in the field of electrical insulation.

[0004] The aforementioned superabsorbent polymer is widely used in the field of hygiene products, such as diapers and sanitary pads. For these applications, high absorption capacity for moisture, pressurized absorption capacity (which prevents absorbed moisture from escaping even under external pressure), and a rapid absorption rate are required. However, in order for the superabsorbent polymer to simultaneously improve high absorption capacity and pressurized absorption capacity, it is necessary to control the amount of fine particles generated during the manufacturing of the base resin to be minimal.

[0005] Meanwhile, although technology using foaming agents to achieve a rapid absorption rate of absorbent resins has been introduced, there is a problem in that when a rapid absorption rate is formed using such foaming agents, the amount of fine particles generated increases in proportion to the increased absorption rate.

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] (Patent Document 1) Republic of Korea Published Patent No. 2018-0003815

[0009]

[0010] The present invention has been devised to solve the aforementioned problems, and its technical objective is to provide an absorbent resin and a method for manufacturing the same, which can achieve a rapid absorption rate of the absorbent resin and simultaneously exhibit a reduction in the amount of fine particles generated by using an encapsulated foaming agent with an average particle size controlled to a predetermined range during the manufacture of the base resin.

[0011] In addition, another technical objective of the present invention is to provide a sanitary article, such as a diaper, that includes the aforementioned absorbent resin, has excellent overall physical properties such as high absorption capacity and a fast absorption rate, and can continuously provide comfort.

[0012] Other objects and advantages of the present invention may be more clearly explained by the following detailed description of the invention and claims.

[0013]

[0014] To achieve the above-mentioned technical objectives, the present invention is a polyacrylic acid (salt)-based absorbent resin comprising a base resin and a surface cross-linking layer formed on the surface of the base resin, and

[0015] Based on 100 parts by weight of total absorbent resin particles, particles with an average particle size of 150 μm or more and less than 300 μm are included in an amount of 25 parts by weight or less, and

[0016] The centrifugal retention capacity (CRC) measured according to EDANA WSP 241.2 is 36.0 g / g or higher, and

[0017] An absorbent resin having an absorption rate of 34 seconds or less for physiological saline according to a vortex measurement method is provided.

[0018] The above absorbent resin may have a pressurized absorption capacity (0.7 AUP) of 10.0 g / g or more for 1 hour at 0.7 psi for physiological saline (0.9 wt% sodium chloride aqueous solution) as measured by the EDANA method WSP 242.3-10.

[0019] The above absorbent resin may have a liquid permeability of 300 seconds or less.

[0020] The above base resin may be formed by crosslinking an acrylic acid-based monomer having at least some neutralized acidic groups and an internal crosslinking agent in the presence of an encapsulated foaming agent having an average particle size (D50) of 4 to 10 μm.

[0021] The above absorbent resin may further include a silica layer formed on the surface cross-linked layer.

[0022] In addition, the present invention provides an article comprising the aforementioned polyacrylic acid (salt)-based absorbent resin.

[0023] The above-mentioned articles may be one or more selected from absorbent articles, sanitary products, soil repair agents, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservatives, poultice materials, and electrical insulators.

[0024] In addition, the present invention provides a method for manufacturing the aforementioned absorbent resin, specifically comprising: (i) a step of forming a hydrogel polymer by crosslinking an acrylic acid monomer having at least a partially neutralized acidic group in the presence of an encapsulated foaming agent having an average particle size (D50) of 4 to 10 μm, an internal crosslinking agent, and a polymerization initiator; (ii) a step of obtaining a base resin powder by drying, grinding, and classifying the hydrogel polymer; and (iii) a step of manufacturing an absorbent resin having a surface crosslinking layer formed on a base resin by mixing a base resin containing 25 parts by weight or less of particles with an average particle size of 150 μm or more and less than 300 μm relative to 100 parts by weight of the obtained base resin powder with a surface crosslinking composition containing a surface crosslinking agent, followed by heat treatment.

[0025] The above-mentioned encapsulated foaming agent comprises a core containing a hydrocarbon; and a shell formed of a thermoplastic resin surrounding the core, and the expansion initiation temperature may be 90 to 100°C.

[0026] The above-mentioned encapsulated foaming agent may be included in an amount of 100 to 3,000 ppmw per 100 parts by weight of the acrylic acid monomer.

[0027] Based on 100% by weight of the total base resin powder ground in step (ii) above, the amount of fine powder having a particle size of less than 150 μm may be 25% by weight or less.

[0028] The above absorbent resin may have a crushing ratio (PR) of 750%·sec or less according to Formula 1 below.

[0029] [Equation 1]

[0030] PR = BR FP ×PD VT ≤ 750

[0031] In the above formula,

[0032] BR FPis the percentage of fine powder generated having a particle size of less than 150 μm relative to 100 weight% of the total base resin powder ground in step (ii) above, and

[0033] PD VT is the absorption rate of the absorbent resin prepared in step (iii) above into physiological saline according to the Vortex measurement method.

[0034] The above absorbent resin may have a foaming efficiency (FE) of 37.0 or less according to Formula 2 below.

[0035] [Equation 2]

[0036] FE = C FA + PD VT ≤ 37.0

[0037] In the above formula,

[0038] C FA is [content of encapsulated foaming agent used in step (i) above (ppmw)] / 1000, and

[0039] PD VT is the absorption rate of the absorbent resin prepared in step (iii) above into physiological saline according to the Vortex measurement method.

[0040] The above manufacturing method may further include (iv) a step of mixing the absorbent resin with a surface cross-linked layer with silica.

[0041] The above silica may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the above absorbent resin.

[0042]

[0043] The absorbent resin (SAP) according to the present invention can simultaneously achieve a rapid vortex absorption rate and excellent absorption capacity after surface crosslinking by forming an appropriate pore structure through the application of an encapsulated foaming agent with an average particle size controlled to a predetermined range. In addition, it can exhibit an effect of reducing the amount of fine particles generated during the manufacture of the base resin.

[0044] Accordingly, when the above absorbent resin is applied to sanitary products such as diapers, it is possible to secure an improved absorption speed while maintaining excellent basic absorption capacity, and continuously provide comfort.

[0045] The effects according to the present invention are not limited to those exemplified above, and a wider variety of effects are included in this specification.

[0046]

[0047] The present invention will be described in 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 40 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, the terms "super absorbent polymer" or "super absorbent polymer particles" are used to encompass, depending on the context, 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 super absorbent polymer particles, or a state suitable for commercialization made by further processing of the super cross-linked polymer or base resin, such as surface cross-linking, fine powder reassembly, drying, grinding, classification, etc.

[0055] In addition, the term "fine powder" refers to particles in the polymer with a particle size of less than 150 μm, and can encompass all particles generated in all processes of the absorbent resin, such as the polymerization process, drying process, grinding process of the dried polymer, or surface crosslinking process, regardless of the stage in which the fine powder is generated or whether surface crosslinking occurs.

[0056] 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.

[0057] Hereinafter, absorbent resin particles and a method for manufacturing the same will be described in more detail according to specific embodiments of the invention.

[0058] Absorbent resin

[0059] One example of the present invention is a superabsorbent polymer (SAP) applied to sanitary products such as infant / adult diapers, more specifically, a polyacrylic acid (salt)-based absorbent polymer in which a pore structure of appropriate size is uniformly formed within the absorbent polymer and a rapid absorption rate can be achieved through such pores.

[0060] Fine particles of superabsorbent polymer (SAP) are generally generated during the grinding (fine grinding) and pulverization process stages of dried polymers. These polymer fine particles move within the manufacturing equipment before use, causing a decrease in manufacturing yield, and also lead to a deterioration in the physical properties of the superabsorbent polymer due to gel blocking after manufacturing. Additionally, while a rapid absorption rate of the superabsorbent polymer can be achieved through the introduction of a foaming agent, this results in a problem where the amount of fine particles generated increases in proportion to the increase in the absorption rate.

[0061] Accordingly, the present invention is characterized by using a foaming agent when manufacturing a base resin, wherein the foaming agent is an encapsulated foaming agent having an average particle size controlled to a predetermined range. Through this, the present invention forms appropriate and uniform pores within the absorbent resin, and achieves excellent absorption capacity and a rapid absorption rate of the absorbent resin. Furthermore, the present invention can secure an effect of reducing the amount of fine particles generated relative to the rapid absorption rate (vortex) achieved by introducing the foaming agent.

[0062] In one specific example, the absorbent resin is a polyacrylic acid (salt)-based absorbent resin comprising a base resin and a surface cross-linking layer formed on the surface of the base resin, and satisfies the conditions of (i) to (iii) below.

[0063] (i) Based on 100 parts by weight of total absorbent resin particles, particles with an average particle size of 150 μm or more and less than 300 μm are included in an amount of 25 parts by weight or less, and

[0064] (ii) The centrifugal retention capacity (CRC) measured according to EDANA WSP 241.2 is 36.0 g / g or higher, and

[0065] (iii) The absorption rate of physiological saline according to the vortex measurement method is 34 seconds or less.

[0066] Specifically, in the present invention, an encapsulated foaming agent having an average particle size of 4 to 10 μm is adopted during the cross-linking polymerization of the base resin, and by applying it while controlling its content, the average pore size formed in the final absorbent resin can be uniformly controlled, and the overall physical properties of the SAP, including a fast absorption rate and excellent absorption capacity, can be improved.

[0067] In addition, conventionally, methods to reduce the particle size of absorbent resin powder were adopted to achieve a fast absorption rate. However, when the particle size of the absorbent resin powder is reduced in this way, there is a risk that process problems, such as adhesion and flowability issues, may occur during the manufacturing process of the absorbent resin or during the process of absorbent articles (e.g., diapers) that utilize the absorbent resin. Accordingly, in the present invention, by limiting the content of fine particles (e.g., average particle size of 150 μm or more and less than 300 μm) relative to the total absorbent resin particles to a specific range or lower, it is possible to secure a fast absorption rate of the absorbent resin while minimizing the aforementioned process problems caused by reducing the particle size.

[0068] Based on 100 parts by weight of total absorbent resin particles, the absorbent resin may contain 25 parts by weight or less of particles with an average particle size of 150 μm or more and less than 300 μm, specifically 10 to 25 parts by weight. For example, the absorbent resin particles with an average particle size of 150 μm or more and less than 300 μm may be included in an amount of 10 parts by weight or more, 11 parts by weight or more, 12 parts by weight or more, 13 parts by weight or more, 14 parts by weight or more, 15 parts by weight or more, 16 parts by weight or more, 17 parts by weight or more, 18 parts by weight or more, 19 parts by weight or more, or 20 parts by weight or more, or 25 parts by weight or less, 24 parts by weight or less, 23 parts by weight or less, or 22 parts by weight or less, based on 100 parts by weight of total absorbent resin particles. For example, the content of the absorbent resin particles with an average particle size of 150 μm or more and less than 300 μm may be 10 to 25 parts by weight, 11 to 25 parts by weight, 12 to 25 parts by weight, 13 to 25 parts by weight, 14 to 25 parts by weight, 15 to 25 parts by weight, 16 to 25 parts by weight, 17 to 25 parts by weight, 18 to 25 parts by weight, 19 to 25 parts by weight, or 20 to 25 parts by weight.

[0069] Here, the particle size ratio of particles with an average particle size of 150 μm or more and less than 300 μm can be controlled during the manufacture of the base resin, or it is also possible to control the particle size ratio of the absorbent resin after surface crosslinking.

[0070] As another example, the absorbent resin may have a centrifugal retention capacity (CRC) of 36.0 g / g or more, 36.1 g / g or more, or 36.2 g / g or more as measured according to EDANA WSP 241.2. In this case, the maximum value of the centrifugal retention capacity of the absorbent resin is not particularly limited.

[0071] As another example, the absorption rate of the absorbent resin in physiological saline according to the Vortex measurement method may be 34 seconds or less, 33.9 seconds or less, 33.8 seconds or less, 33.7 seconds or less, 33.6 seconds or less, 33.5 seconds or less, 33.4 seconds or less, 33.3 seconds or less, 33.2 seconds or less, 33.1 seconds or less, or 33 seconds or less. In this case, the minimum value of the absorption rate is not specifically limited. Here, Vortex refers to the time at which the liquid vortex disappears due to rapid absorption when the absorbent resin is added to physiological saline and stirred, and among the required physical properties of the absorbent resin, the absorption rate is used as Vortex.

[0072] In addition to the particle content having a predetermined particle size, centrifugal retention capacity, and absorption rate in the absorbent resin described above, the absorbent resin according to the present invention may further satisfy at least one of the following conditions (iv) and (v), and preferably satisfies both conditions (iv) and (v).

[0073] For example, (iv) the pressurized absorption capacity (0.7 AUP) of the absorbent resin for 1 hour at 0.7 psi with respect to physiological saline (0.9 wt% sodium chloride aqueous solution), measured according to the EDANA method WSP 242.3-10, may be 10.0 g / g or more, 11.0 g / g or more, 12.0 g / g or more, 13.0 g / g or more, or 14.0 g / g or more. In this case, the maximum value of the pressurized absorption capacity is not particularly limited.

[0074] As another example, (v) the permeability of the absorbent resin may be 300 seconds or less, 290 seconds or less, 280 seconds or less, 270 seconds or less, 260 seconds or less, 250 seconds or less, or 240 seconds or less. Here, the minimum value of permeability is not specifically limited.

[0075] The polyacrylic acid (salt)-based absorbent resin according to the present invention comprises a base resin and a surface crosslinking layer formed on the surface of the base resin, wherein the base resin comprises a crosslinked polymer formed by crosslinking an acrylic acid-based monomer having at least a partially neutralized acidic group and an internal crosslinking agent in the presence of an encapsulated foaming agent having an average particle size (D50) of 4 to 10 μm. The encapsulated foaming agent is composed of a core containing a hydrocarbon and a polymer shell surrounding the core, wherein through foaming, the hydrocarbon in the core is vaporized, and the polymer shell remains within the absorbent resin to form a uniform and fine pore structure.

[0076] The above acrylic acid-based monomer may be any monomer commonly used in the manufacture of absorbent resins. Specifically, the above acrylic acid-based monomer may be a compound represented by the following chemical formula 1.

[0077] [Chemical Formula 1]

[0078] R1-COOM1

[0079] In the above chemical formula 1,

[0080] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0081] M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0082] Preferably, the acrylic acid monomer comprises one or more selected from the group consisting of acrylic acid, methacrylic acid, and their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts.

[0083] The above acrylic acid-based monomer has acidic groups, and at least some of the acidic groups may be neutralized. Specifically, the monomer may be partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide. In this case, the degree of neutralization of the monomer may be 40 to 95 mol%, or 50 to 80 mol%, or 60 to 75 mol%. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is excessively high, the neutralized monomer may precipitate, making it difficult for polymerization to proceed smoothly; conversely, if the degree of neutralization is excessively low, not only is the absorption capacity of the polymer significantly reduced, but it may also exhibit properties such as elastic rubber, which is difficult to handle.

[0084] The term "internal crosslinker" is used to distinguish it from the "surface crosslinker" described later, which crosslinks the surface of the base resin; it serves to polymerize the unsaturated bonds of the acrylic monomers. Although the crosslinking in the above step proceeds without distinction between the surface and the interior, due to the surface crosslinking process of the base resin described later, the surface of the particles of the finally manufactured absorbent resin is composed of a structure crosslinked by the surface crosslinker, while the interior is composed of a structure crosslinked by the internal crosslinker.

[0085] The above internal crosslinking agent may include one or more of the following: a polyfunctional acrylate compound, a polyfunctional allyl compound, a polyfunctional glycidyl ether compound, or a polyfunctional vinyl compound known in the field.

[0086] Non-limiting examples of available polyfunctional acrylate compounds include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate, and dipentaerythritol. Examples include tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate, and these can be used individually or in combination of two or more types.

[0087] Also, non-limiting examples of available polyfunctional allyl compounds include ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, propylene glycol diallyl ether, tripropylene glycol diallyl ether, polypropylene glycol diallyl ether, butanediol diallyl ether, butylene glycol diallyl ether, hexanediol diallyl ether, pentaerythritol diallyl ether, pentaerythritol trialyl ether, pentaerythritol tetraallyl ether, dipentaerythritol diallyl ether, dipentaerythritol trialyl ether, dipentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, trimethylolpropane diallyl ether, Examples include trimethylolpropane trialyl ether, glycerin diallyl ether, glycerin trialyl ether, etc., and can be used alone or in a mixture of two or more. Preferably,

[0088] In addition, non-limiting examples of usable polyfunctional glycidyl ether compounds include ethyleneglycol diglycidyl ether, polyethyleneglycol diglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether, and these can be used individually or in a mixture of two or more. Specifically, ethyleneglycol diglycidyl ether can be used.

[0089] Also, non-limiting examples of available polyfunctional vinyl compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, tripropylene glycol divinyl ether, polypropylene glycol divinyl ether, butanediol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, pentaerythritol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol divinyl ether, dipentaerythritol trivinyl ether, dipentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, trimethylolpropane divinyl ether, Examples include trimethylolpropane trivinyl ether, glycerin divinyl ether, and glycerin trivinyl ether, and these can be used alone or in a mixture of two or more.

[0090] In the present invention, the amount of internal crosslinking agent used is not particularly limited and can be appropriately adjusted within a range known in the art. For example, the internal crosslinking agent may be included in an amount of 0.01 to 1 part by weight per 100 parts by weight of the acrylic acid monomer composition, and specifically, in an amount of 0.03 to 0.15 parts by weight. If the concentration of the internal crosslinking agent is excessively low, crosslinking may not occur sufficiently, making it difficult to achieve strength above an appropriate level and significantly reducing drying efficiency. In addition, if the concentration of the internal crosslinking agent is excessively high, the internal crosslinking density increases, making it difficult to achieve the desired water retention capacity.

[0091] The cross-linking polymerization of acrylic acid monomers in the presence of such internal cross-linking agents can be carried out in the presence of a polymerization initiator, and optionally a thickener, plasticizer, preservative stabilizer, antioxidant, etc.

[0092] The absorbent resin according to the present invention is formed on the surface of a base resin and comprises a surface crosslinked layer in which the crosslinked polymer is further crosslinked via a surface crosslinking agent.

[0093] The above surface crosslinked layer is formed by additionally crosslinking a crosslinked polymer via a surface crosslinking agent. In this case, the surface crosslinking agent is a surface crosslinking agent generally used for surface crosslinking of absorbent resins, and is not particularly limited as long as it is a compound capable of reacting with the functional groups of the polymer.

[0094] Non-limiting examples of usable surface crosslinkers include one or more selected from the group consisting of monofunctional or polyfunctional glycidyl ether compounds; polyhydric alcohol compounds; epoxy compounds; polyamine compounds; haloepoxy compounds; condensation products of haloepoxy compounds; oxazolidinone compounds; mono-, di-, or polyoxazolidinone compounds; cyclic urea compounds; polyhydric metal salts; and alkylene carbonate compounds. The surface crosslinker may be the same as or different from the internal crosslinker described above without limitation.

[0095] Non-limiting examples of usable glycidyl ether-based compounds include ethyleneglycol diglycidyl ether, polyethyleneglycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, etc., and these can be used alone or in a mixture of two or more. Specifically, ethyleneglycol diglycidyl ether can be used.

[0096] In addition, non-limiting examples of usable polyhydric alcohol compounds may include one or more selected from the group consisting of mono-, di-, tri-, tetra-, or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol. In addition, non-limiting examples of haloepoxy compounds may include epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin. In addition, examples of mono-, di-, or polyoxazolidinone compounds may include 2-oxazolidinone, etc. In addition, examples of alkylene carbonate compounds include ethylene carbonate. These may be used individually or in combination with each other. Meanwhile, to increase the efficiency of the surface crosslinking process, at least one polyhydric alcohol compound having 2 to 10 carbon atoms may be included among these surface crosslinking agents.

[0097] The above-mentioned surface crosslinking agent is incorporated into the absorbent resin by crosslinking polymerizing with the base resin and introducing it into the surface crosslinking layer. The content of this surface crosslinking agent may be 0.01 to 10 parts by weight per 100 parts by weight of the base resin, specifically 0.03 to 0.1 parts by weight. When the surface crosslinking agent is included within the aforementioned content range, the pressure characteristics during surface crosslinking can be improved.

[0098] Meanwhile, the surface crosslinking layer may additionally include conventional inorganic materials known in the art. Non-limiting examples of usable inorganic materials include one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate. These inorganic materials may be used in powder or liquid form, and in particular, may be used as alumina powder, silica-alumina powder, titania powder, or nano-silica solution. These inorganic materials may be used in an amount of about 0.001 to about 1 weight part per 100 weight parts of base resin, but are not particularly limited thereto.

[0099] In addition, the surface crosslinking agent may further include a thickening agent. By further crosslinking the surface of the base resin powder in the presence of a thickening agent in this way, the degradation of physical properties can be minimized even after grinding. As usable thickening agents, one or more selected from polysaccharides and hydroxy-containing polymers may be used. As polysaccharides, gum-based thickening agents and cellulose-based thickening agents may be used. Specific examples of gum-based thickeners include xanthan gum, arabic gum, karaya gum, tragacanth gum, ghatti gum, guar gum, locust bean gum, and psyllium seed gum, and specific examples of cellulose-based thickeners include hydroxypropylmethylcellulose, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose, and methylhydroxypropylcellulose.

[0100] The absorbent resin according to the present invention may further include a silica layer formed on a surface cross-linked layer.

[0101] The physical properties of such a silica layer can affect the permeability, water retention capacity, and absorption rate of the absorbent resin; specifically, whether the silica surface is hydrophobic or hydrophilic affects the permeability, water content, and binding strength of the silica to the absorbent resin. Therefore, controlling these properties can further improve the aforementioned effects. Hydrophilic fumed silica may be used as the silica, for example, with a BET value of 175 to 225 m 2 / g, and the pH may be 3.7 to 4.5. However, it is not limited thereto.

[0102] Method for manufacturing absorbent resin

[0103] Another example of the present invention is a method for manufacturing a polyacrylic acid (salt)-based absorbent resin (SAP).

[0104] Such absorbent resins can be manufactured according to conventional methods known in the art, except for applying an encapsulated foaming agent with an average particle size controlled to a predetermined range and controlling its content when manufacturing the base resin.

[0105] The method for manufacturing an absorbent resin according to the present invention is described below. However, the method is not limited to the following, and the steps of each process may be modified or selectively combined as needed.

[0106] An example of the above manufacturing method may comprise: (i) a first step of forming a hydrogel polymer by crosslinking an acrylic acid monomer having at least some neutralized acidic groups in the presence of an encapsulated foaming agent having an average particle size (D50) of 4 to 10 μm, an internal crosslinking agent, and a polymerization initiator; (ii) a second step of obtaining a base resin powder by drying, grinding, and classifying the hydrogel polymer; and (iii) a third step of producing an absorbent resin having a surface crosslinking layer formed on the base resin by mixing a surface crosslinking composition containing a surface crosslinking agent with a base resin containing 25 parts by weight or less of particles with an average particle size of 150 μm or more and less than 300 μm per 100 parts by weight of the obtained base resin powder, and then heat treating the mixture.

[0107] The following is a more detailed explanation of each step.

[0108] (i) Preparation step of hydrogel polymer

[0109] The first step above is a step of preparing a hydrogel polymer, specifically a step of forming a hydrogel polymer by crosslinking a monomer composition comprising an acrylic acid-based monomer having at least some neutralized acidic groups and an internal crosslinking agent in the presence of an encapsulated foaming agent having an average particle size of 10 μm or less.

[0110] Blowing agents play a role in forming pores within the hydrogel polymer through foaming within the monomer mixture during polymerization, thereby increasing the surface area of ​​the hydrogel polymer. Conventionally, carbonate-based inorganic blowing agents were used, or even when encapsulated blowing agents were used, blowing agents with an average particle size exceeding 10 μm (e.g., 12-13 μm) were mainly used. In particular, conventionally, the method of increasing the amount of blowing agent was mainly used to achieve a rapid vortex; however, as the amount of blowing agent increased, the amount of fine particles increased during the manufacturing process, leading to a decrease in manufacturing yield and / or a deterioration in the physical properties of the absorbent resin.

[0111] In contrast, the present invention is differentiated from the prior art in that it simultaneously improves the trade-off relationship between a fast vortex and a small amount of fine particles by using an encapsulated foaming agent having an average particle size (D50) of 4 to 10 μm as a foaming agent in the monomer composition. Specifically, when foaming using a foaming agent in the manufacturing process of an absorbent resin (SAP), the amount of fine particles generated is proportional to the vortex. For example, the higher the amount of fine particles generated, the faster the absorption speed (e.g., reduced vortex time), and the lower the amount of fine particles generated, the slower the absorption speed (e.g., increased vortex time). In the present invention, by controlling and applying the average particle size and content of the encapsulated foaming agent, a fast vortex of 34 seconds or less is achieved, and at the same time, the amount of fine particles having a particle size of less than 150 μm generated during the classification process relative to the achieved vortex can be relatively reduced (see Table 1 below).

[0112] The encapsulated foaming agent has an average particle size (D50) prior to foaming, specifically an average diameter measured before expansion, of 4 to 10 μm. Specifically, it may be 4.0 μm or more, 4.5 μm or more, 5.0 μm or more, 5.5 μm or more, 6.0 μm or more, 6.5 μm or more, 7.0 μm or more, 7.5 μm or more, or 8.0 μm or more, or 10.0 μm or less, 9.5 μm or less, or 9.0 μm or less. For example, the average particle size (D50) of the encapsulated foaming agent may be 4 to 10 μm, 5 to 10 μm, 5.5 to 9.5 μm, or 6 to 9 μm. When using a foaming agent of the aforementioned diameter, the amount of fine powder generated during the manufacturing process can be reduced. In addition, the absorbent resin can be made to contain a high content of absorbent resin particles having a developed porous structure and pores of a predetermined size that are uniformly controlled within the absorbent resin.

[0113] The above-described encapsulated foaming agent may have a structure comprising a core containing a hydrocarbon; and a shell formed of a thermoplastic resin surrounding the core. Since such an encapsulated foaming agent can be expanded to a desired size, it is used in the manufacture of absorbent resins, making it easy to control the amount of fine particles generated.

[0114] The hydrocarbon constituting the core of the encapsulated foaming agent may be one or more selected from the group consisting of n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso-heptane, cycloheptane, n-octane, iso-octane, and cyclooctane. Among these, hydrocarbons having 3 to 5 carbon atoms (n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane) are suitable for forming pores of the size described above.

[0115] In addition, the thermoplastic resin constituting the shell of the encapsulated foaming agent may be a polymer formed from one or more monomers selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halides, and vinylidenes halides. Among these, a copolymer of (meth)acrylate and (meth)acrylonitrile is suitable for forming pores of the size described above.

[0116] In addition to the aforementioned average particle size, it is more advantageous in terms of controlling the amount of fine particles generated for the encapsulated foaming agent to simultaneously control at least one of the expansion initiation temperature, maximum expansion size, and / or moisture content.

[0117] For one specific example, the encapsulated foaming agent may have an expansion initiation temperature of 90 to 100°C, specifically 91 to 99°C, and more specifically 92 to 98°C. Additionally, the maximum foaming temperature (Tmax) of the encapsulated foaming agent may be 110 to 120°C, specifically 110.5 to 119.5°C, and more specifically 111 to 119°C. Here, the expansion initiation temperature (Ts) and the maximum foaming temperature (Tmax) of the encapsulated foaming agent are assumed to be measured by a TMA (Thermomechanical Analyzer). Furthermore, the moisture content of the encapsulated foaming agent may be less than 2%, specifically 1.99% or less, and more specifically 1.95% or less. Here, the moisture content of the encapsulated foaming agent can be measured by analyzing the heat loss at a temperature below the expansion initiation temperature of the foaming agent using a conventional convection oven in the field, and can also be analyzed using a moisture meter, which is an analytical instrument.

[0118] The above-mentioned encapsulated foaming agent may be included in an amount of 100 to 3,000 ppmw per 100 parts by weight of the above-mentioned acrylic acid monomer, preferably 200 to 3,000 ppmw, more preferably 300 to 3,000 ppmw, and even more preferably 500 to 3,000 ppmw. Within the aforementioned content range, a base resin and an absorbent resin satisfying the above-mentioned pore characteristics and general physical properties can be appropriately obtained.

[0119] The acrylic acid-based monomer included in the monomer composition according to the present invention may be any monomer commonly used in the manufacture of absorbent resins. Specifically, the acrylic acid-based monomer may be applied in the same manner as described above.

[0120] The above monomer composition may include a polymerization initiator commonly used in the manufacture of absorbent resins. Depending on the polymerization method, a thermal polymerization initiator or a photopolymerization initiator may be used as such a polymerization initiator. However, even in the photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation, and since a certain amount of heat is also generated as the polymerization reaction, which is an exothermic reaction, proceeds, a thermal polymerization initiator may be additionally included.

[0121] Non-limiting examples of usable photopolymerization initiators include one or more compounds selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone. Additionally, as thermal polymerization initiators, one or more compounds selected from the group consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid may be used.

[0122] The amount of the polymerization initiator used is not particularly limited and, for example, may be added at a concentration of 0.001 to 1 weight% or 0.005 to 0.1 weight% relative to the monomer composition. That is, if the concentration of the polymerization initiator is excessively low, the polymerization rate may slow down and a large amount of residual monomer may be extracted into the final product, which is undesirable. Conversely, if the concentration of the polymerization initiator is excessively high, the polymer chains forming the network become shorter, which may lead to a deterioration in the physical properties of the resin, such as an increase in the content of water-soluble components and a decrease in pressure absorption capacity.

[0123] Meanwhile, the polymerization of the monomer composition is carried out in the presence of an internal crosslinking agent to improve the physical properties of the resin produced by the polymerization of acrylic acid-based monomers. The aforementioned internal crosslinking agent may be applied in the same manner as described above.

[0124] If necessary, the monomer composition may further include a conventional foaming agent known in the art that is different from the aforementioned encapsulated foaming agent.

[0125] Non-limiting examples of available blowing agents include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, magnesium carbonate, azodicarbonamide (ADCA), dinitrosopentamethylene tetramine (DPT), p,p'-oxybis(benzenesulfonyl hydrazide) (OBSH), p-toluenesulfonyl hydrazide (TSH), and sucrose stearate. It may include one or more compounds selected from the group consisting of sucrose palmitate and sucrose laurate.

[0126] If necessary, the monomer composition may further include additives such as thickeners, plasticizers, preservation stabilizers, and antioxidants.

[0127] In addition, this monomer composition can be prepared in the form of a solution in which raw materials such as the aforementioned acrylic acid-based monomer, polymerization initiator, internal crosslinking agent, DTPA, and foaming agent are dissolved in a solvent.

[0128] The solvent is not particularly limited as long as it is capable of dissolving the aforementioned raw materials. Non-limiting examples of usable solvents include 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, N,N-dimethylacetamide, or mixtures thereof.

[0129] The formation of a hydrogel polymer through the polymerization of the above monomer composition can be carried out by conventional polymerization methods, and the process is not particularly limited.

[0130] These polymerization methods are broadly classified into thermal polymerization and photopolymerization depending on the type of polymerization energy source. Thermal polymerization can be carried out in a reactor equipped with a stirring shaft, such as a kneader, while photopolymerization can be carried out in a reactor equipped with a movable conveyor belt. For example, a hydrogel polymer can be obtained by introducing the monomer composition into a reactor, such as a kneader equipped with a stirring shaft, and then supplying hot air or heating the reactor to perform thermal polymerization. At this time, depending on the shape of the stirring shaft equipped in the reactor, the hydrogel polymer discharged through the reactor outlet can be obtained as particles ranging from several millimeters to several centimeters. Specifically, the obtained hydrogel polymer can be obtained in various forms depending on the concentration and injection speed of the injected monomer composition, but typically, a hydrogel polymer with a (weight average) particle size of 2 to 50 mm can be obtained.

[0131] In addition, as another example, when photopolymerization of the monomer composition is carried out in a reactor equipped with a movable conveyor belt, a sheet-shaped hydrogel polymer can be obtained. In this case, the thickness of the sheet may vary depending on the concentration and injection speed of the injected monomer composition, but in order to ensure that the entire sheet is polymerized evenly while also securing the production speed, it is generally preferable to adjust the thickness to 0.5 to 10 cm.

[0132] The hydrogel polymer formed by this method may exhibit a water content of 40 to 80 weight percent. Here, the water content is the weight of water in the total weight of the hydrogel polymer, and may be the value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer. Specifically, it may be defined as a value calculated by measuring the weight loss due to water evaporation in the polymer during the drying process in which the temperature of the polymer is raised through infrared heating. At this time, the drying conditions may be set such that the temperature is raised from room temperature to approximately 180°C and then maintained at 180°C, and the total drying time may be set to 20 minutes, including a 5-minute temperature raising step.

[0133] (ii) Base resin manufacturing step

[0134] The second step above is a step of preparing a base resin by drying and grinding the hydrogel polymer prepared in the first step described above.

[0135] In the second step above, in order to not only increase the drying efficiency of the hydrogel polymer but also improve the absorption rate of the absorbent resin, a step of coarse grinding the hydrogel polymer before drying may be further included. In the present invention, the term 'coarse grinding' is used for convenience to refer to grinding before drying in order to distinguish it from grinding after drying.

[0136] The grinder used for coarse grinding is not particularly limited, and specifically, any one selected from the group of grinding machines consisting of a vertical pulverizer, turbo cutter, turbo grinder, rotary cutter mill, cutter mill, disc mill, shred crusher, crusher, chopper, and disc cutter may be used. This coarse grinding step can grind the hydrogel polymer to a particle size of about 2 mm to about 10 mm.

[0137] The drying process may be carried out according to methods and conditions known in the art, for example, at a temperature of 120 to 250°C, 140 to 200°C, or 150 to 190°C. In addition, the drying time is not particularly limited, but can be adjusted to 20 to 90 minutes at the above drying temperature, taking into account process efficiency and the physical properties of the resin.

[0138] The above drying process can be carried out using a conventional medium, for example, through methods such as supplying hot air to the pulverized hydrogel polymer, infrared irradiation, microwave irradiation, or ultraviolet irradiation.

[0139] In addition, the drying process is preferably performed so that the dried polymer has a moisture content of 0.1 to 10 weight%. That is, if the moisture content of the dried polymer is less than 0.1 weight%, it is undesirable as it may lead to increased manufacturing costs due to excessive drying and degradation of the cross-linked polymer. In addition, if the moisture content of the dried polymer exceeds 10 weight%, it is undesirable as defects may occur in subsequent processes.

[0140] Next, the dried hydrogel polymer can be ground, which is a step to optimize the surface area of ​​the base resin and the absorbent resin. This grinding can be performed so that the particle size of the ground polymer is 150 to 850 μm. Conventional grinders such as pin mills, hammer mills, screw mills, roll mills, disc mills, and jog mills can be used at this time.

[0141] In addition, to control the physical properties of the absorbent resin that is finalized, the polymer particles obtained through the grinding step may undergo a classification step to separate fine particles with a particle size of less than 150 μm and normal particles with a particle size of 150 μm or more and 850 μm or less, thereby obtaining base resin powder.

[0142] In this case, by using an encapsulated foaming agent with an average particle size of 4 to 10 μm, the amount of fine powder having a particle size of less than 150 μm relative to 100% of the total ground base resin powder can be controlled to 25% or less, specifically 24.5% or less, more specifically 24% or less.

[0143] If necessary, the present invention may further include the step of reassembling the classified fine powder to form a reassembled body having a particle size of 150 to 850 μm. Such reassembly process is not particularly limited and can be performed using conventional processes known in the art.

[0144] A base resin can be obtained by going through the aforementioned drying, grinding, and classification steps. This base resin may have a particle size of 150 to 850 μm and may contain 2 weight% or less, or 1 weight% or less, of fine powder having a particle size of less than 150 μm.

[0145] (iii) Surface cross-linking layer formation step

[0146] The third step is to produce an absorbent resin in which a surface crosslinking layer is formed on the surface of the base resin by mixing a surface crosslinking composition with the base resin obtained in the second step and then heat-treating the mixture.

[0147] At this time, in the present invention, surface crosslinking is performed after adjusting the amount of particles with an average particle size of 150 μm or more and less than 300 μm to be 25 parts by weight or less, preferably 10 to 25 parts by weight, and more preferably 15 to 25 parts by weight, relative to 100 parts by weight of the obtained base resin powder. For example, surface crosslinking can be performed by mixing a first base resin (BR1) having a particle size of 600-850 μm based on the particle size (particle size) of the base resin obtained by classification, a second base resin (BR2) having a particle size of 300 μm or more and less than 600 μm, and a third base resin (BR3) having a particle size of 150 μm or more and less than 300 μm in a predetermined ratio. At this time, the mixing ratio of the first base resin (BR1), the second base resin (BR2), and the third base resin (BR3) may be, for example, BR1 : BR2 : BR3 = 10 to 25 : 50 to 80 : 10 to 25 by weight.

[0148] Surface crosslinking agents are generally used for surface crosslinking of absorbent resins and are not particularly limited as long as they are compounds capable of reacting with the functional groups of the polymer. Since the aforementioned details apply equally to such surface crosslinking agents, a separate explanation is omitted.

[0149] The above surface crosslinking composition may additionally include an inorganic material to perform the step of forming a surface crosslinking layer.

[0150] One or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate may be used as such inorganic materials. The inorganic materials may be used in powder or liquid form, and in particular, may be used as alumina powder, silica-alumina powder, titania powder, or nano-silica solution. Additionally, the inorganic materials may be used in an amount of about 0.001 to about 1 part by weight per 100 parts by weight of base resin.

[0151] In addition, the surface crosslinking composition may further include a thickening agent. By further crosslinking the surface of the base resin powder in the presence of such a thickening agent, the degradation of physical properties can be minimized even after grinding.

[0152] Meanwhile, the method of mixing the surface crosslinking composition with the base resin is not particularly limited and can be appropriately adopted as long as it allows for even mixing of the two into the base resin. Possible mixing methods include a method of adding the surface crosslinking composition to a base resin reaction vessel and mixing, a method of spraying the surface crosslinking composition onto the base resin, and a method of continuously supplying the base resin and the surface crosslinking composition to a continuously operated mixer to mix them.

[0153] At this time, the surface crosslinking composition may be a solution, and if the content of solids in the solution is 1% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or more, 50% by weight or less, 30% by weight or less, or 20% by weight or less, it is suitable for evenly dispersing in the base resin and at the same time can prevent clumping of the base resin.

[0154] When the aforementioned base resin and surface crosslinking composition are mixed and heat-treated, an interpenetrating polymer network is formed on the surface of the crosslinking polymer contained in the base resin, thereby further improving the physical properties of the absorbent resin. That is, through this surface modification, a surface crosslinking layer is formed on the surface of the pulverized base resin particles.

[0155] The formation of such a surface crosslinking layer can be carried out by conventional methods that increase the crosslinking bond density on the surface of polymer particles. For example, it can be carried out by mixing a surface crosslinking agent composition solution containing a surface crosslinking agent with the pulverized polymer and heat-treating it to induce a crosslinking reaction.

[0156] The heat treatment temperature of the above surface crosslinking process can be performed at a temperature of about 80°C to about 250°C. More specifically, it can be performed at a temperature of about 10°C to about 220°C, or about 110°C to about 200°C, or about 120°C to about 190°C, for about 10 minutes to about 2 hours, or about 20 minutes to about 60 minutes.

[0157] (iv) Silica layer formation step

[0158] If necessary, the present invention may further include a fourth step of mixing the absorbent resin with a surface cross-linked layer with silica.

[0159] Such silica may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the absorbent resin, preferably 0.03 to 3 parts by weight, and more preferably 0.05 to 1 part by weight. However, it is not particularly limited thereto and can be appropriately adjusted within the ordinary range known in the art.

[0160] Meanwhile, in absorbent resins, a fast vortex and a small amount of fine particles are in a trade-off relationship. For example, if the amount of blowing agent is increased to achieve a fast vortex, the amount of fine particles increases during the manufacturing process, and if the amount of blowing agent is reduced, the amount of fine particles generated decreases, but the vortex slows down. Accordingly, conventionally, it was possible to achieve either a fast vortex or a small amount of fine particles, but it was difficult to achieve both simultaneously.

[0161] In contrast, the present invention optimizes the average particle size and content of the encapsulated foaming agent, thereby enabling the simultaneous achievement of a fast vortex and a small amount of fine particles, which correspond to the conventional trade-off relationship. In fact, the present invention can simultaneously achieve a fine particle generation amount of 25 wt% or less and a fast vortex of 34 seconds or less. In order to effectively represent the fine particle generation amount relative to the achieved fast vortex, the present invention newly introduces a pulverizing ratio (PR) represented by the following Equation 1.

[0162] Specifically, the absorbent resin may have a crushing ratio (PR) according to Formula 1 below of 750 %·sec or less, 740 %·sec or less, 730 %·sec or less, 720 %·sec or less, 710 %·sec or less, 700 %·sec or less, 690 %·sec or less, or 680 %·sec or less. In this case, the lower limit of the crushing ratio is not specifically limited.

[0163] [Equation 1]

[0164] PR = BR FP ×PD VT ≤ 750

[0165] In the above formula,

[0166] BR FP is a percentage of fine powder having a particle size of less than 150 μm based on 100 weight% of the base resin powder ground in step (ii) above, and

[0167] PD VT is the absorption rate of the absorbent resin prepared in step (iii) above into physiological saline according to the Vortex measurement method.

[0168] The crushing ratio (PR) newly introduced in the present invention is the value obtained by multiplying the amount of fine particles generated during the manufacture of the absorbent resin by the vortex velocity of the manufactured absorbent resin. Since the aforementioned crushing ratio (PR) can only have a low value when simultaneously satisfying the trade-off relationship between low fine particle generation and a fast vortex, it is a novel evaluation parameter that is differentiated from the prior art. In this case, the lower limit of the crushing ratio is not specifically restricted.

[0169] In addition, the present invention allows for the production of an absorbent resin with a uniformly formed pore structure suitable for securing a rapid vortex by using an encapsulated foaming agent having an average particle size controlled to a specific range and controlling its content. In particular, the present invention utilizes an encapsulated foaming agent with an average particle size of 4-10 μm to achieve a synergistic effect on the rapid vortex compared to a control group using the same weight of foaming agent with an average particle size exceeding 10 μm. To represent the relationship between the realized rapid vortex and the content of the foaming agent, the present invention newly introduces a foaming efficiency (FE) represented by the following Equation 2.

[0170] Specifically, the absorbent resin may have a foaming efficiency (FE) according to Formula 2 below of 37.0 or less, 36.0 or less, 35.0 or less, 34.0 or less, 33.8 or less, or 33.5 or less. In this case, the lower limit of the foaming efficiency is not specifically limited.

[0171] [Equation 2]

[0172] FE = C FA + PD VT ≤ 37.0

[0173] In the above formula,

[0174] CFA is [content of encapsulated foaming agent used in step (i) above (ppmw)] / 1000, and

[0175] PD VT is the absorption rate of the absorbent resin prepared in step (iii) above into physiological saline according to the Vortex measurement method.

[0176] <Items>

[0177] Another example of the present invention is an article comprising the aforementioned absorbent resin.

[0178] The aforementioned absorbent resin may be preferably included in or used in various sanitary products, for example, children's paper diapers, adult diapers, or sanitary pads, and may be particularly preferably applied to children's / adult diapers where a fast absorption rate is required.

[0179] These sanitary products may comprise the composition of conventional sanitary products, except that the absorbent body contains a polyacrylic acid (salt)-based absorbent resin according to the present invention.

[0180] In addition, the above absorbent resin can be used without limitation in various other products besides sanitary products, for example, absorbent articles, soil repair agents, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservatives, poultice materials, electrical insulators, oral and dental products, cosmetic or skin products.

[0181] The present invention will be described in detail below through examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited by the following examples.

[0182]

[0183] [Preparation Example]

[0184] As an encapsulated foaming agent used in the example, encapsulated foaming agent A (Dongjin Semichem, MS-140DSS) was prepared, wherein the core is iso-pentane and the shell is composed of a copolymer of acrylonitrile, methacrylonitrile, and methyl methacrylate, and the content of the core is 25% by weight relative to 100% by weight of the total encapsulated foaming agent.

[0185] The diameter of the encapsulated foaming agent A was measured using a laser diffraction particle size analyzer (Malvern, Mastersizer 3000+). After measurement, the D50 value (diameter of the particle corresponding to the 50% cumulative distribution) was calculated as the average particle size. The average particle size of the encapsulated foaming agent A was 8.5 μm, and the particle distribution values ​​were D10 (diameter of the particle corresponding to the 10% cumulative distribution): 2.6 μm, D50: 8.5 μm, and D90 (diameter of the particle corresponding to the 90% cumulative distribution): 38.7 μm. Here, the D10, D50, and D90 values ​​represent the particle sizes (μm) corresponding to the 10%, 50%, and 90%, respectively, based on the particle size cumulative distribution curve generated from the laser diffraction particle size analysis.

[0186] In addition, the onset temperature of expansion (Ts) and the maximum expansion temperature (Tmax) of encapsulated foaming agent A were measured using a thermomechanical analyzer (TMA, Mettler Toledo SDTA 2+). The analysis was performed under heating conditions ranging from 50 to 300°C at a rate of 5 to 20°C / min. As measured above, the onset temperature of expansion of the encapsulated foaming agent was 95°C, and the maximum expansion temperature was 110-120°C. Furthermore, the moisture content of encapsulated foaming agent A was less than 2%.

[0187]

[0188] [Example 1]

[0189] 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 660 g of a 31.5% caustic soda solution was added to prepare an aqueous solution of a water-soluble unsaturated monomer (degree of neutralization: 75 mol%; solid content: 43.5 wt%). 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 (60 cm by width, 60 cm by length) containing 1600 ppmw of sodium persulfate (relative to 100 parts by weight of acrylic acid), which is a thermal polymerization initiator, 500 ppmw of the encapsulated foaming agent A of the above preparation example (average particle size before expansion: 8.5 μm, expansion initiation temperature: 95°C), relative to 100 parts by weight of acrylic acid, and 200 ppmw of SDS (relative to 100 parts by weight of acrylic acid), and then irradiated with ultraviolet light for 1 minute (irradiation dose: 10 mV / cm² 2 UV polymerization was performed to obtain a hydrogel-like polymer sheet.

[0190] The obtained hydrogel polymer sheet was passed through a chopper with a hole size of 16 mm to produce a crumb.

[0191] Next, the above-mentioned crumb was dried in an oven capable of vertical airflow transfer. The drying was performed in multiple stages; specifically, using an air flow oven, the process was carried out at 170°C for 30 minutes (up flow 5 min - down flow 5 min - up flow 5 min - down flow 5 min - up flow 5 min - down flow 5 min). The dried polymer obtained through the drying process was ground using a 1 mm Fitz Mill grinder (Fitz mill, Fritsch, Pulverisette 19) and classified using a standard sieve (Sieve cassette 1 mm trapezoidal perforation) conforming to ASTM standards to obtain a base resin having a particle size of 150 to 850 μm. At this time, the weight ratio of the base resin with a particle size of less than 150 μm removed by classification relative to 100 wt% of the total ground base resin powder was defined as the 'amount of fine powder generated,' and the amount of fine powder generated in the base resin of Example 1 was 20 wt%.

[0192] Subsequently, based on the particle size (particle size) of the base resin obtained by classification, the base resin was classified into a first base resin (BR1) having a particle size of 600-850 μm, a second base resin (BR2) having a particle size of 300 μm or more and less than 600 μm, and a third base resin (BR3) having a particle size of 150 μm or more and less than 300 μm, respectively, and surface crosslinking was carried out after adjusting the weight ratio of BR1 : BR2 : BR3 = 10 : 70 : 20. A surface treatment solution comprising 6 parts by weight of water, 3 parts by weight of methanol, 0.3 parts by weight of aluminum sulfate, and 0.05 parts by weight of ethylene glycol diglycidyl ether (EGDGE) was evenly mixed with 100 parts by weight of the prepared base resin, supplied to a surface crosslinking reactor, and the surface crosslinking reaction of the base resin was carried out at 130°C for 40 minutes. After surface crosslinking, 0.07 parts by weight of fumed silica were mixed to obtain the absorbent resin of Example 1.

[0193]

[0194] [Examples 2-5]

[0195] Absorbent resin particles of Examples 2 to 5 were prepared by performing the same procedure as Example 1, except that the content of encapsulated foaming agent A was changed as shown in Table 1 below.

[0196]

[0197] [Comparative Examples 1 to 3]

[0198] Absorbent resins of Comparative Examples 1 to 3 were prepared by performing the same procedure as Example 1 above, except that encapsulated foaming agent B (Dongjin Semichem, MS-140DS, average particle size before expansion: 15 μm, expansion start temperature: 90℃, maximum foaming temperature: 115-130℃) was used instead of encapsulated foaming agent A, and the content was changed as shown in Table 1 below.

[0199]

[0200] [Physical Property Evaluation]

[0201] The physical properties of the absorbent resin particles prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated as follows, and the results are listed in Table 1 below.

[0202] (1) Centrifuge Retention Capacity (CRC)

[0203] The water retention capacity of the absorbent resin compositions of the above examples and comparative examples was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.2.

[0204] Specifically, absorbent resin W0 (g) (about 0.2g) obtained through the examples and comparative examples, respectively, was uniformly placed into a nonwoven fabric bag and sealed, and then immersed in physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was drained from the bag for 3 minutes using a centrifuge under conditions of 250g, and the mass W2 (g) of the bag was measured. In addition, the same operation was performed without using resin, and the mass W1 (g) at that time was measured.

[0205] Using each obtained mass, the CRC(g / g) was calculated according to Equation 3 below.

[0206] [Equation 3]

[0207] CRC (g / g) = {[W2(g) - W1(g) - W0(g)] / W0(g)}

[0208] (2) Absorbency under Pressure (AUP)

[0209] The absorbent resin compositions of the above examples and comparative examples were measured for 0.7 psi under pressure (AUP) according to the European Disposables and Nonwovens Association (EDANA) standard EDANA method WSP 242.3-10.

[0210] First, a stainless steel 400 mesh wire mesh was installed on the bottom of a plastic cylinder with an inner diameter of 60 mm. Under conditions of room temperature and 50% humidity, a superabsorbent resin W0 (g) was uniformly spread over the wire mesh, and a piston capable of uniformly applying a load of 0.7 psi was positioned slightly smaller than 60 mm in outer diameter, with no gap between it and the inner wall of the cylinder, and so that its vertical movement was not obstructed. At this time, the weight W3 (g) of the device was measured.

[0211] A glass filter with a diameter of 90 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 0.9 wt% sodium chloride was placed at the same level as the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of it. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted, and its weight W4 (g) was measured. Using each obtained mass, the pressurized absorption capacity (g / g) was calculated according to Equation 4 below.

[0212] [Equation 4]

[0213] AUP (g / g) = [W4(g) - W3(g)] / W0(g)

[0214] (3) Permeability

[0215] Permeability was measured under a 0.3 psi load using a 0.9% saline solution by the method described in the literature (Buchholz, FL and Graham, AT, "Modern Superabsorbent Polymer Technology," John Wiley & Sons (1998), page 161).

[0216] More specifically, 0.2 g of particles having a particle size of 300 to 600 μm among the absorbent resins prepared in the examples and comparative examples were taken and placed into a cylinder (Φ20 mm). At this time, one end of the cylinder includes a stopcock and an upper limit and a lower limit are marked, wherein the upper limit of the cylinder is marked at the position when 40 mL of (saline) solution is filled and the lower limit is marked at the position when 20 mL of (saline) solution is filled.

[0217] 50 g of 0.9% saline solution (NaCl) was added to the cylinder with the stopcock closed and left for 30 minutes. Next, if necessary, additional saline solution was added until the level of the saline solution reached the upper limit of the cylinder. Next, a load of 0.3 psi was applied to the cylinder containing the saline-absorbing resin and left for 1 minute. Afterward, the stopcock located at the bottom of the cylinder was opened, and the time it took for the 0.9% saline solution to pass from the upper limit marked on the cylinder to the lower limit was measured. All measurements were performed at a temperature of 24±1°C and a relative humidity of 50±10%.

[0218] For each absorbent resin sample (TS) and a control group (T0) without the addition of absorbent resin, the time taken to pass from the upper limit to the lower limit was measured, and then the permeability was calculated according to Equation 5 below.

[0219] [Equation 5]

[0220] Permeability = Permeability (sec) = T S - T0

[0221] T S 0.2g of absorbent resin powder is swollen with a 0.9 wt% saline (NaCl) solution for 30 minutes to prepare an absorbent resin that has absorbed saline, and 0.9 wt% saline solution is the time it takes to permeate the absorbent resin under a pressure of 0.3 psi, and T0 is the time it takes to permeate the absorbent resin without absorbent resin under a pressure of 0.3 psi.

[0222] (4) Absorption rate (Vortex time)

[0223] The absorption rate (vortex time) of the absorbent resins obtained in the above examples and comparative examples was measured in the following manner.

[0224] First, ① 50 mL of 0.9% saline solution was added to a 100 mL flat-bottomed beaker using a 100 mL mass cylinder. ② Next, the beaker was placed in the center of a magnetic stirrer, and a magnetic bar (diameter 8 mm, length 30 mm) was inserted into the beaker. ③ Subsequently, the stirrer was operated to stir the magnetic bar at 600 rpm, ensuring that the bottom of the vortex generated by stirring touched the top of the magnetic bar. ④ After confirming that the temperature of the saline solution in the beaker reached 24.0℃, 2 ± 0.01 g of the absorbent resin sample was added while simultaneously starting a stopwatch. The time in seconds until the vortex disappeared and the liquid surface became completely horizontal was measured and recorded as the absorption rate.

[0225] (5) Pulverizing ratio (PR)

[0226] For the absorbent resins obtained in the above examples and comparative examples, the pulverizing ratio (PR) according to Formula 1 below was calculated and listed in Table 1 below.

[0227] [Equation 1]

[0228] PR = BR FP ×PD VT ≤ 750

[0229] In the above formula,

[0230] BR FP The percentage of fine powder generated having a particle size of less than 150 μm relative to 100 weight% of the total ground base resin powder during the manufacture of the silver base resin (BR FP It means ), PD VT is the absorption rate (Vortex time) of the manufactured absorbent resin in physiological saline.

[0231] (6) Foaming efficiency

[0232] For the absorbent resins obtained in the above examples and comparative examples, the foaming efficiency (FE) according to Formula 2 below was calculated and listed in Table 1 below.

[0233] [Equation 2]

[0234] FE = C FA + PD VT ≤ 37.0

[0235] In the above formula,

[0236] C FA is [content of encapsulated foaming agent (ppmw)] / 1000, and

[0237] PD VT is the absorption rate (Vortex time) of the manufactured absorbent resin in physiological saline.

[0238] Absorbent resin fragmentation ratio (PR = BR) after crosslinking of the encapsulated foaming agent-based resin surface FP ХPD VT Foaming efficiency (FE = C)(%·sec) FA + PD VT )(No unit) Type Average particle size before expansion (㎛) Content (ppmw) Fine particle generation amount (BR FP, wt%)CRC(g / g)AUP(g / g)Liquid permeability(sec)Vortex(PD VT, sec) Example 1 A8.5 500 203 7.0 21.0 1 203 36 60 33.5 Example 2 A8.5 1000 203 8.4 17.2 10 23 26 40 33.0 Example 3 A8.5 1500 223 7.8 15.8 15 530 660 31.5 Example 4 A8.5 2000 243 6.4 15.6 15 62 76 48 29.0 Example 5 A8.5 3000 243 6.2 14.0 240 25 600 28.0 Comparative Example 1 B15 1000 203 7.3 21.2 70 39 78 0 40 Comparative Example 2 B15 1500 223 7.9 21.0 80 39 85 8 40.5 Comparative Example 3B1530002638.617.91083593638.0

[0239] As described in Table 1 above, in Comparative Examples 1 to 3 using encapsulated foaming agent with an average particle size exceeding 10 μm, it was found that the absorption rate (Vortex) of the absorbent resin was reduced compared to Examples 2-3 and 5 using the same amount of foaming agent.

[0240] In contrast, Examples 1 to 5, which use an encapsulated foaming agent having an average particle size of 10 μm or less in a predetermined amount, not only exhibited a rapid absorption rate effect of the final absorbent resin but also demonstrated significantly superior performance compared to Comparative Examples 1 to 3 in terms of fracture ratio (PR) and foaming efficiency (FE) characteristics. Furthermore, when manufacturing the base resin, the amount of fine powder generated was similar to or reduced compared to Comparative Examples 1-3.

[0241] It was confirmed that by controlling the average particle size of the encapsulated foaming agent, pores of an appropriate size (e.g., pore size, porosity, and / or continuous / conserved pore structure, etc.) relative to the particle size of the absorbent resin were uniformly formed, thereby achieving a fast absorption rate (Vortex). In addition, it was found that by controlling the average particle size and content of the encapsulated foaming agent, the reduction in pore surface area lost as fine powder due to the cutting of foaming edges during the manufacturing process was minimal, and the amount of fine powder generated itself was reduced.

[0242] From the above results, it was found that the present invention, by optimizing the average particle size (D50) and content of the encapsulated foaming agent, significantly improves the absorption rate (Vortex) of the absorbent resin while exhibiting a relatively small amount of fine particles compared to the level of absorption rate. In addition, the main absorption capacity (e.g., CRC, AUP) of the absorbent resin secured physical properties equivalent to or greater than those of the comparative example using an encapsulated foaming agent with an average particle size exceeding 10 μm, and although the liquid permeability was slightly lower compared to the comparative example, it was still maintained within the conventional range of physical properties of the absorbent resin.

Claims

1. A polyacrylic acid (salt)-based absorbent resin comprising a base resin and a surface cross-linked layer formed on the surface of the base resin, and Based on 100 parts by weight of total absorbent resin particles, particles with an average particle size of 150 μm or more and less than 300 μm are included in an amount of 25 parts by weight or less, and The centrifugal retention capacity (CRC) measured according to EDANA WSP 241.2 is 36.0 g / g or higher, and Absorbent resin having an absorption rate of 34 seconds or less in physiological saline according to the vortex measurement method.

2. In Paragraph 1, An absorbent resin having a pressurized absorption capacity (0.7 AUP) of 10.0 g / g or more for 1 hour at 0.7 psi for physiological saline (0.9 wt% sodium chloride aqueous solution) as measured according to the EDANA method WSP 242.3-10.

3. In Paragraph 1, Absorbent resin with a permeability of 300 seconds or less.

4. In Paragraph 1, The above base resin is, Average particle size of 4 to 10 μm (D 50 An absorbent resin formed by crosslinking an acrylic acid-based monomer having at least some neutralized acidic groups and an internal crosslinking agent in the presence of an encapsulated foaming agent having ).

5. In Paragraph 1, The above absorbent resin further comprises a silica layer formed on the surface cross-linked layer.

6. An article comprising an absorbent resin as described in any one of paragraphs 1 through 5.

7. In Paragraph 6, The above article is one or more selected from absorbent articles, sanitary products, soil repair agents, waterproofing materials for civil engineering and construction, seedling sheets, freshness preservatives, poultice materials, and electrical insulators.

8. (i) A step of forming a hydrogel polymer by crosslinking an acrylic acid monomer having at least some of neutralized acidic groups in the presence of an encapsulated foaming agent having an average particle size (D50) of 4 to 10 μm, an internal crosslinking agent, and a polymerization initiator; (ii) a step of drying, grinding, and classifying the above-mentioned hydrogel polymer to obtain a base resin powder; and (iii) a step of preparing an absorbent resin having a surface crosslinking layer formed on the base resin by mixing a base resin containing 25 parts by weight or less of particles with an average particle size of 150 μm or more and less than 300 μm relative to 100 parts by weight of the obtained base resin powder with a surface crosslinking composition containing a surface crosslinking agent, and then heat-treating the mixture; A method for manufacturing a polyacrylic acid (salt)-based absorbent resin comprising 9. In Paragraph 8, The above-mentioned encapsulated foaming agent is, A core containing hydrocarbons; and It includes a shell formed of a thermoplastic resin surrounding the above-mentioned core, and A manufacturing method having an expansion start temperature of 90 to 100℃.

10. In Paragraph 8, A method of manufacturing in which the above-mentioned encapsulated foaming agent is included in an amount of 100 to 3,000 ppmw per 100 parts by weight of the above-mentioned acrylic acid monomer.

11. In Paragraph 8, A manufacturing method in which the amount of fine powder having a particle size of less than 150 μm generated relative to 100 wt% of the total base resin powder ground in step (ii) is 25 wt% or less.

12. In Paragraph 8, A manufacturing method for the above absorbent resin having a crushing ratio (PR) of 750 %·sec or less according to Formula 1 below: [Equation 1] PR = BR FP ×PD VT ≤ 750 In the above formula, BR FP is the percentage of fine powder generated having a particle size of less than 150 μm relative to 100 weight% of the total base resin powder ground in step (ii) above, and PD VT is the absorption rate of the absorbent resin prepared in step (iii) above into physiological saline according to the Vortex measurement method.

13. In Paragraph 8, A manufacturing method for the above absorbent resin having a foaming efficiency (FE) of 37.0 or less according to Formula 2 below: [Equation 2] FE = C FA + PD VT ≤ 37.0 In the above formula, C FA is [content of encapsulated foaming agent used in step (i) above (ppmw)] / 1000, and PD VT is the absorption rate of the absorbent resin prepared in step (iii) above into physiological saline according to the Vortex measurement method.

14. In Paragraph 8, The above manufacturing method is, (iv) A manufacturing method further comprising the step of mixing an absorbent resin with a surface cross-linked layer with silica.

15. In Paragraph 14, A manufacturing method in which the above silica is included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the above absorbent resin.