Superabsorbent polymer and preparation method therefor

Abstract

The present invention provides a superabsorbent polymer, a preparation method therefor and an article comprising the superabsorbent polymer, in which a predetermined amount of a specific chelating agent and a metal salt is used in combination and predetermined physical properties of the superabsorbent polymer, which is surface-cross-linked with a base resin, are adjusted within specific ranges, thereby simultaneously improving absorption capacity, gel strength and absorption rate, which are in a trade-off relationship, from among the physical properties of the superabsorbent polymer.

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, in which the absorbent capacity, gel strength, and absorption rate of which are in a trade-off relationship are simultaneously improved by using a combination of a specific chelating agent and a metal salt in a predetermined content range and controlling the specific physical properties of a base resin and a surface-crosslinked absorbent resin to a predetermined range, and an article comprising said absorbent resin.

[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). Such absorbent polymers began to be commercialized for sanitary devices, and are 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 electrical insulation.

[0004] The above-mentioned absorbent resin is widely used in the field of hygiene products such as diapers and sanitary pads. For these applications, it is necessary to exhibit high absorption capacity for moisture and other substances, and the absorbed moisture must not leak out even under external pressure. In addition, it is necessary to maintain its shape well even when swollen after absorbing water, thereby exhibiting excellent permeability.

[0005] In particular, as efforts continue in recent years to provide diapers that exhibit excellent performance while having a thinner thickness and lighter weight, much attention is being focused on providing absorbent resins with improved absorption speed and performance. Along with the aforementioned rapid absorption speed and performance, it is necessary to exhibit gel strength with high long-term stability. As a result, urine is not only uniformly and rapidly dispersed into the absorbent core of the diaper, but skin stability can also be enhanced over a long period.

[0006] However, when attempting to increase gel strength using previously known methods, there was a disadvantage in that the basic absorption rate and absorption performance (under no pressure) of the absorbent resin itself were significantly reduced. For example, conventionally, chelating agents such as EDTA were applied to improve gel strength, but there were limitations in market entry due to insufficient absorption rate and capacity of the absorbent resin. Furthermore, there was a problem where gel strength decreased when attempting to improve absorption rate and capacity. Accordingly, there is a continuous demand for the development of absorbent resins in which absorption capacity, gel strength, and absorption rate are simultaneously improved, despite their trade-off relationship.

[0007] [Prior Art Literature]

[0008] [Patent Literature]

[0009] (Patent Document 001) Korean Registered Patent No. 10-2487977

[0010]

[0011] The present invention is devised to solve the aforementioned problems, and its technical objective is to provide an absorbent resin and a method for manufacturing the same in which the absorption capacity, gel strength, and absorption rate are simultaneously improved by combining a specific chelating agent and a metal salt in a predetermined content range and controlling the surface crosslinking thickness to a specific range according to the difference in physical properties, such as centrifugal retention capacity (CRC), between the base resin (BR) and the final absorbent resin (PD) when manufacturing the absorbent resin.

[0012] 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 absorbency, liquid permeability, and absorption speed, and can continuously provide comfort for a long time.

[0013] Other objects and advantages of the present invention may be more clearly explained by the following detailed description of the invention and claims.

[0014]

[0015] To achieve the above-mentioned technical problem, one aspect of the present invention provides an absorbent resin comprising: a base resin; and a surface cross-linking layer formed on the surface of the base resin; and satisfying the conditions of (i) to (iii) below.

[0016] (i) The gel strength measured after swelling by absorbing 50 g of a 0.9 wt% sodium chloride and 0.005 wt% aqueous solution of ascorbic acid into 0.2 g of absorbent resin is 0.5 N or greater, and

[0017] (ii) The absorption capacity (FSC) measured according to EDANA NWSP 240.0.R2 is 65.0 g / g or higher, and

[0018] (iii) The absorption rate of physiological saline according to the vortex measurement method is 44 seconds or less.

[0019] The above absorbent resin is,

[0020] (i) The gel strength measured after swelling by absorbing 50 g of a 0.9 wt% sodium chloride and 0.005 wt% aqueous solution of ascorbic acid into 0.2 g of absorbent resin is 0.55 N or higher, and

[0021] (ii) The absorption capacity (FSC) according to EDANA NWSP 240.0.R2 is 66.5 g / g or higher, and

[0022] (iii) The absorption rate of physiological saline according to the vortex measurement method may be 43 seconds or less.

[0023] The above absorbent resin may further satisfy at least one of the following conditions (iv) to (vi).

[0024] (iv) The centrifugal retention capacity (CRC) measured according to EDANA NWSP 241.0.R2 is 37.5 g / g or greater, and

[0025] (v) The pressurized absorption capacity (0.7 AUP) for 1 hour at 0.7 psi for physiological saline (0.9 wt% sodium chloride aqueous solution), measured according to the EDANA method NWSP 242.0.R2, is 8.0 g / g or greater, and

[0026] (vi) Permeability is 500 seconds or less.

[0027] The above absorbent resin may include at least one of diethylenetriamine pentaacetic acid (DTPA), ions derived from aluminum sulfate, salts, and decomposition products thereof.

[0028] The above absorbent resin may not contain amino acetate-based chelating agents other than diethylenetriamine pentaacetic acid.

[0029] The above absorbent resin may further include a silica layer formed on the surface cross-linked layer.

[0030] In addition, another aspect of the present invention provides an article comprising the aforementioned absorbent resin.

[0031] 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.

[0032] In addition, another aspect of the present invention is 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 internal crosslinking agent, a polymerization initiator, and diethylenetriamine pentaacetic acid (DTPA); (ii) a step of preparing a base resin powder comprising a crosslinked polymer obtained by drying and grinding the hydrogel polymer; and (iii) a step of preparing an absorbent resin having a surface crosslinked layer formed on the base resin by mixing the base resin powder with a surface crosslinking composition containing aluminum sulfate and a surface crosslinking agent, followed by heat treatment.

[0033] The above diethylenetriamine pentaacetic acid (DTPA) is included in an amount of 100 ppmw to 1,500 ppmw based on 100 parts by weight of the above acrylic acid monomer, and

[0034] The above aluminum sulfate is included in an amount of 0.05 to 0.6 parts by weight based on 100 parts by weight of the base resin, and

[0035] Water retention capacity (CRC) of the base resin prepared in step (ii) above, measured according to EDANA NWSP 241.0.R2 BR ) and the water retention capacity (CRC) of the absorbent resin with the surface cross-linked layer formed in step (iv) above. PD The present invention provides a method for manufacturing an absorbent resin in which the difference of ) is controlled to 15.0 g / g or less.

[0036] Water retention capacity of base resin measured according to EDANA NWSP 241.0.R2 (CRC BR ) and water retention capacity (CRC) of an absorbent resin with a surface cross-linked layer formed PD The difference in ) may be 13.0 g / g or less.

[0037] The centrifugal retention capacity (CRC) of the base resin measured according to EDANA NWSP 241.0.R2 is 45 to 55 g / g, and the centrifugal retention capacity (CRC) of the absorbent resin may be 37.5 to 47 g / g.

[0038] The weight ratio of the above diethylenetriamine pentaacetic acid (DTPA) and the above aluminum sulfate may be 1:3 to 1:50.

[0039] The above manufacturing method may further include the step of (iv) mixing the absorbent resin with a surface cross-linked layer with silica.

[0040] 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.

[0041]

[0042] The absorbent resin (SAP) according to the present invention can simultaneously improve the absorption capacity, gel strength, and absorption rate characteristics corresponding to the conventional trade-off relationship.

[0043] 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.

[0044] 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.

[0045]

[0046] The present invention will be described in detail below.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Hereinafter, an absorbent resin and a method for manufacturing the same will be described in more detail according to specific embodiments of the invention.

[0056]

[0057] Absorbent resin

[0058] One example of the present invention is an absorbent resin (SAP), which is applied particularly to sanitary products such as infant / adult diapers, and is an absorbent resin in which excellent absorbency, gel strength, and absorption rate are simultaneously optimized.

[0059] Absorption capacity (FSC), one of the key required properties of absorbent resins, refers to the amount of solution (g) that 1g of absorbent resin can absorb without external load. To increase absorption capacity, it is common practice to lower the crosslinking density (degree of crosslinking) of SAP. In other words, if the crosslinking density of the polymer is low, the polymer chain network becomes relatively flexible and loose, allowing water molecules to penetrate easily. This widens the spacing between polymer chains, thereby securing more absorption space. On the other hand, gel strength refers to the strength with which a swollen gel, after absorbing liquid, can withstand external forces (e.g., pressure). SAPs with high crosslinking density retain absorbed moisture well and do not easily leak liquid even under external pressure, thus possessing high gel strength characteristics. As described above, increasing the absorption capacity of the absorbent resin leads to a decrease in gel strength, and conversely, improving gel strength leads to a decrease in absorption capacity; therefore, there have been limitations in simultaneously improving absorption capacity and gel strength, which are in a trade-off relationship. Additionally, the absorption rate is an indicator representing the speed at which SAP particles absorb a liquid (e.g., water) and swell; typical parameters used include vortex time. Generally, a shorter absorption rate indicates faster absorption, while a longer rate indicates slower absorption. Increasing the gel strength of the SAP restricts swelling, thereby slowing down the absorption rate; furthermore, if the absorption capacity of the SAP is too high, gel blocking may occur. This can cause the swollen gel layer to hinder the movement of water molecules into the unswollen interior of the SAP, which can actually lead to a decrease in the absorption rate.

[0060] For example, conventionally, EDTA chelating agents were used to improve gel strength, but in this case, when applied together with polyvalent salts used for surface crosslinking, such as aluminum sulfate, it actually inhibited the gel strength improvement effect, resulting in a deterioration of the physical properties of the absorbent resin.

[0061] Accordingly, the present invention is characterized by combining a specific chelating agent (e.g., DTPA) with excellent metal capture ability and an aluminum sulfate that improves the absorbency of SAP within a predetermined content range, and additionally adjusting the physical properties (e.g., CRC gap) of the base resin (BR) and the absorbent resin (PD) with a surface cross-linked layer formed thereon to a specific range, thereby simultaneously improving the absorbency, gel strength, and absorption rate, which are in a trade-off relationship, to have optimized overall physical properties. When the absorbency, gel strength, and absorption rate of the absorbent resin are simultaneously improved in this way, not only can the amount of absorbent resin (SAP) used in the absorbent article (e.g., diaper) to which it is applied be reduced, but excellent absorbency and the stability of the SAP can also be maintained even when the absorbent article is worn for a long time, thereby enabling comfort for a long time.

[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) The gel strength measured after swelling by absorbing 50 g of an aqueous solution containing 0.9 wt% sodium chloride and 0.005 wt% ascorbic acid (Vitamin C) dissolved in 0.2 g of absorbent resin is 0.5 N or greater, and

[0064] (ii) The absorption capacity (FSC) measured according to EDANA NWSP 240.0.R2 is 65.0 g / g or higher, and

[0065] (iii) The absorption rate of physiological saline according to the vortex measurement method is 44 seconds or less.

[0066] Specifically, in the present invention, a diethylenetriamine pentaacetic acid (DTPA) chelating agent is applied in a specific amount during the polymerization of the base resin, and then an aluminum sulfate is applied in a predetermined amount during the reaction of the surface cross-linking layer, thereby simultaneously satisfying the excellent absorption capacity and gel strength characteristics of the absorbent resin.

[0067] For example, the absorption capacity of the absorbent resin may be 65.0 g / g or more, 66.0 g / g or more, 67.0 g / g or more, 68.0 g / g or more, or 69.0 g / g or more. In this case, the maximum value of the absorption capacity is not particularly limited.

[0068] As another specific example, the gel strength of the absorbent resin may be 0.55 N or more, 0.6 N or more, or 0.7 N or more. In this case, the maximum value of the gel strength is not particularly limited.

[0069] For other specific examples, the absorption rate of the absorbent resin measured according to the Vortex measurement method may be 44 seconds or less, 43 seconds or less, 42 seconds or less, 41 seconds or less, 40 seconds or less, 39 seconds or less, 38 seconds or less, or 37 seconds or less. In this case, the minimum value of the absorption rate is also not specifically limited.

[0070] Generally, the ability of chelating agents applied during base polymerization to capture metal ions varies depending on their type. In the present invention, diethylenetriamine pentaacetic acid (DTPA), which has a strong ability to capture metals, such as iron (Fe) ions, inevitably present in the base resin polymer, is used exclusively, and amino acetate-based chelating agents other than DTPA are not included.

[0071] In this case, if the amount of DTPA is relatively excessive, it may not only capture iron (Fe) ions but also capture metal ions (e.g., aluminum ions) of aluminum sulfate (aluminum sulfate) added during the surface crosslinking reaction to improve the absorption capacity of SAP, thereby causing an inhibitory effect on the absorption capacity of SAP. In addition, if the amount of DTPA is relatively small, gel breakdown may occur due to residual iron (Fe) ions and aluminum (Al) ions, which may lead to a decrease in the gel strength of SAP. Considering the above, the present invention requires controlling the DTPA content to a predetermined range.

[0072] Although the above diethylenetriamine pentaacetic acid (DTPA) is included in the final absorbent resin, a portion of it may be removed by post-processing steps such as washing, filtration, and drying. Accordingly, the DTPA included in the absorbent resin may be reduced to approximately 1 / 4 to 1 / 10 based on the amount of DTPA added during base resin polymerization (e.g., 100 ppmw to 1,500 ppmw relative to 100 parts by weight of acrylic acid) and may remain in the final SAP.

[0073] In addition, the absorbent resin according to the present invention may comprise at least one of diethylenetriamine pentaacetic acid (DTPA) and / or aluminum sulfate, ions derived from said compound, salts, and decomposition products thereof.

[0074] In addition to the aforementioned properties of absorption capacity, gel strength, and absorption rate, the absorbent resin according to the present invention may further satisfy at least one, two or more, or all three of the following conditions (iv) to (vi).

[0075] For example, (iv) the centrifugal retention capacity (CRC) of the absorbent resin may be 37.5 g / g or more, 38.0 g / g or more, or 38.5 g / g or more.

[0076] For other specific examples, (v) the pressurized absorption capacity (0.7 AUP) of the absorbent resin for 1 hour at 0.7 psi for physiological saline (0.9 wt% sodium chloride aqueous solution) may be 8.0 g / g or more, 9.0 g / g or more, 10.0 g / g or more, or 11.0 g / g or more.

[0077] As another specific example, (vi) the permeability of the absorbent resin may be 500 seconds or less, 400 seconds or less, 300 seconds or less, or 250 seconds or less. Preferably, it may be 150 to 250 seconds. At this time, the maximum values ​​of centrifugal retention capacity (CRC) and pressurized absorption capacity (AUP) are not particularly limited.

[0078] The base resin constituting the absorbent resin according to the present invention comprises a crosslinked polymer in which an acrylic acid-based monomer having at least a partially neutralized acidic group is crosslinked with an internal crosslinking agent in the presence of diethylenetriamine pentaacetic acid (DTPA). Here, diethylenetriamine pentaacetic acid may be included in the final absorbent resin, and specifically, may be dispersed within, on the surface of, or both of the base resin.

[0079] 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.

[0080] [Chemical Formula 1]

[0081] R1-COOM1

[0082] In the above chemical formula 1,

[0083] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0084] M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0085] 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.

[0086] 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 76 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.

[0087] 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.

[0088] 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.

[0089] 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 may be used alone or in combination of two or more types.

[0090] 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, and glycerin trialyl ether, and can be used alone or in a mixture of two or more types.

[0091] 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.

[0092] 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. Preferably, pentaerythritol trialyl ether may be used.

[0093] 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, preferably 0.02 to 0.5 parts by weight, more preferably 0.02 to 0.3 parts by weight, and even more preferably 0.03 to 0.15 parts by weight. If the amount of the internal crosslinking agent used 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 amount of the internal crosslinking agent used is excessively high, the internal crosslinking density increases, making it difficult to achieve the desired water retention capacity.

[0094] 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.

[0095] The absorbent resin according to the present invention comprises a surface crosslinking layer formed on the surface of a base resin, wherein the crosslinking polymer is further crosslinked via a surface crosslinking agent.

[0096] Here, since the crosslinking reaction of the surface crosslinking layer is carried out in the presence of aluminum sulfate, the aluminum sulfate is included in the absorbent resin, and specifically, may be included in at least some or all of the interior and surface of the surface crosslinking layer.

[0097] In addition, the aluminum sulfate included in the absorbent resin may exist in an amount substantially equal to the amount of aluminum sulfate added during the surface crosslinking reaction. The aluminum sulfate may be included in an amount of 0.05 to 0.6 parts by weight based on 100 parts by weight of the base resin. For example, the aluminum sulfate may be included in an amount of 0.05 parts by weight or more, 0.06 parts by weight or more, 0.07 parts by weight or more, 0.08 parts by weight or more, 0.09 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, or 0.4 parts by weight or more, or 0.6 parts by weight or less, 0.59 parts by weight or less, 0.58 parts by weight or less, 0.57 parts by weight or less, or 0.56 parts by weight or less, based on 100 parts by weight of the base resin. Examples of the above aluminum sulfate content ranges include 0.05 to 0.6 parts by weight, 0.07 to 0.58 parts by weight, 0.09 to 0.57 parts by weight, 0.1 to 0.55 parts by weight, or 0.1 to 0.5 parts by weight.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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. Non-limiting examples of haloepoxy compounds may include epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin. Meanwhile, non-limiting examples of mono-, di-, or polyoxazolidinone compounds include 2-oxazolidinone. Also, non-limiting 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.

[0102] 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. Accordingly, by appropriately controlling the content of the surface crosslinking agent, it is possible to exhibit an enhanced effect of antibacterial and deodorizing properties without degrading the absorbent properties of the absorbent resin.

[0103] In the present invention, the content of the surface crosslinking agent may be included in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the base resin, preferably 0.01 to 5 parts by weight, more preferably 0.02 to 1 part by weight, and even more preferably 0.03 to 0.1 parts by weight. When the surface crosslinking agent is included within the aforementioned content range, excellent antibacterial and deodorizing properties can be continuously and stably exhibited without concern for deterioration of the physical properties of the absorbent resin.

[0104] 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.

[0105] 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.

[0106] The absorbent resin according to the present invention may further include a silica layer formed on a surface cross-linked layer.

[0107] The physical properties of such a silica layer can affect the liquid permeability, water retention capacity, and absorption rate of the absorbent resin. Specifically, whether the silica surface is hydrophobic or hydrophilic affects the liquid 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.

[0108]

[0109] Method for manufacturing absorbent resin

[0110] Another example of the present invention is a method for manufacturing an absorbent resin (SAP).

[0111] Such absorbent resins can be manufactured according to conventional methods known in the art, except that a specific chelate and a metal salt are used in combination within a predetermined content range during the reaction of the base resin and the surface crosslinking layer, and additionally, the surface crosslinking thickness is controlled within a predetermined range based on the difference in centrifugal retention capacity (CRC) between the base resin (BR) and the final absorbent resin (PD) constituting the absorbent resin.

[0112] 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.

[0113] One specific embodiment of the above manufacturing method comprises: (i) a first step of crosslinking an acrylic acid monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent, a polymerization initiator, and diethylenetriamine pentaacetic acid (DTPA) to form a hydrogel polymer; (ii) a second step of preparing a base resin powder comprising a crosslinked polymer obtained by drying and grinding the hydrogel polymer; and (iii) a third step of preparing an absorbent resin having a surface crosslinking layer formed on the base resin by mixing the base resin powder with a surface crosslinking composition containing aluminum sulfate and a surface crosslinking agent, followed by heat treatment; wherein the content of diethylenetriamine pentaacetic acid (DTPA) and aluminum sulfate, and the water retention capacity (CRC) of the base resin BR ) and water retention capacity of surface-crosslinked absorbent resin (CRC PD It can be configured by adjusting the difference of ) to a specific range.

[0114] Specifically, the diethylenetriamine pentaacetic acid (DTPA) is included in an amount of 100 ppmw to 1,500 ppmw based on 100 parts by weight of the acrylic acid monomer, the aluminum sulfate is included in an amount of 0.05 to 0.6 parts by weight based on 100 parts by weight of the base resin, and the water retention capacity (CRC) of the base resin prepared in step (ii) BR ) and the water retention capacity (CRC) of the absorbent resin with the surface cross-linked layer formed in step (iv) above. PD The difference of ) is precisely controlled to 15.0 g / g or less for each.

[0115] The following is a more detailed explanation of each step.

[0116] (i) Preparation step of hydrogel polymer

[0117] 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, an internal crosslinking agent, and DTPA.

[0118] 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 subject to all the aforementioned details.

[0119] In addition, DTPA is a chelating agent having a strong ability to capture metal ions, such as iron, that may be included in the absorbent resin. The content of such diethylenetriamine pentaacetic acid (DTPA) may be 100 ppmw to 1,500 ppmw based on 100 parts by weight of the acrylic acid monomer. For example, diethylenetriamine pentaacetic acid (DTPA) may be 100 ppmw or more, 110 ppmw or more, 120 ppmw or more, 130 ppmw or more, 140 ppmw or more, 150 ppmw or more, 160 ppmw or more, 170 ppmw or more, 180 ppmw or more, 190 ppmw or more, 200 ppmw or more, 210 ppmw or more, 220 ppmw or more, 230 ppmw or more, 240 ppmw or more, or 250 ppmw or more, or 1500 ppmw or less, 1400 ppmw or less, 1300 ppmw or less, 1200 ppmw or less, 1100 ppmw or less, or 1000 ppmw or less. Examples of the above-mentioned diethylenetriamine pentaacetic acid (DTPA) content ranges may be 100 to 1,500 ppmw, 110 to 1,400 ppmw, 120 to 1,400 ppmw, 130 to 1,300 ppmw, 140 to 1,250 ppmw, 150 to 1,200 ppmw, and 200 to 1,000 ppmw. If the DPTA content is lower than the aforementioned ranges, inhibition of gel strength may occur.

[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] In addition, the cross-linking polymerization of the monomer composition may be carried out in the presence of a blowing agent, depending on the necessity and extent of improving the absorption rate. Such a blowing agent decomposes during the cross-linking polymerization reaction process to generate gas, thereby forming pores within the hydrogel polymer. When such a blowing agent is used additionally, a more developed porous structure is formed within the absorbent resin, which can further improve the absorption rate of the absorbent resin.

[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. In addition, specific examples of commercially available blowing agents include encapsulated blowing agents such as F-36D and MS140DS. However, it is not specifically limited thereto.

[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 stage

[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 be subjected to a step of selectively classifying particles having a particle size of 150 to 850 μm.

[0142] 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.

[0143] (iii) Preparation of mixture and formation of surface cross-linking layer

[0144] 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 prepared in the second step and then heat-treating the mixture.

[0145] The surface crosslinking composition used in the third step above includes aluminum sulfate and a surface crosslinking agent capable of increasing the absorption capacity of the absorbent resin.

[0146] Such aluminum sulfate may be included in an amount of 0.05 to 0.6 parts by weight based on 100 parts by weight of the base resin. For example, the aluminum sulfate may be included in an amount of 0.05 parts by weight or more, 0.06 parts by weight or more, 0.07 parts by weight or more, 0.08 parts by weight or more, 0.09 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, or 0.4 parts by weight or more, or 0.6 parts by weight or less, 0.59 parts by weight or less, 0.58 parts by weight or less, 0.57 parts by weight or less, or 0.56 parts by weight or less, based on 100 parts by weight of the base resin. Examples of the above aluminum sulfate content ranges include 0.05 to 0.6 parts by weight, 0.07 to 0.58 parts by weight, 0.09 to 0.57 parts by weight, 0.1 to 0.55 parts by weight, or 0.1 to 0.5 parts by weight. If the content of the aluminum sulfate is smaller than the aforementioned range, the effect of improving absorption capacity may be negligible, and if the content of the aluminum sulfate is excessive compared to the aforementioned range, the AUP decreases and no additional improvement effect on absorption capacity is observed.

[0147] Meanwhile, in order to achieve a synergistic effect on the absorption capacity and gel strength characteristics of the absorbent resin, it is appropriate to control the weight ratio of diethylenetriamine pentaacetic acid (DTPA) added during the polymerization of the base resin and aluminum sulfate added during the surface cross-linking layer reaction to a predetermined range. For example, the weight ratio of diethylenetriamine pentaacetic acid (DTPA) and aluminum sulfate can be controlled to 1:3 to 1:50. Examples of the weight ratio range of diethylenetriamine pentaacetic acid (DTPA) and aluminum sulfate may be 1:4 to 1:45, 1:5 to 1:40, 1:6 to 1:35, 1:7 to 1:30, 1:7 to 1:28, 1:8 to 1:25, 1:9 to 1:22, or 1:10 to 1:20.

[0148] Furthermore, the surface crosslinking agent is not particularly limited as long as it is a compound capable of reacting with the functional groups of the polymer, and is a surface crosslinking agent generally used for the surface crosslinking of absorbent resins. Since the aforementioned details apply equally to such surface crosslinking agents and aluminum sulfate, 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] In particular, the present invention is further characterized by controlling these properties within a predetermined range, based on the observation that the penetration depth of the surface crosslinking composition (surface crosslinking liquid) and the dispersibility of the crosslinking agent vary depending on the ratio of water, organic solvent, and additive during the surface crosslinking reaction, thereby affecting the physical properties of the final absorbent resin.

[0156] For example, in the surface crosslinking reaction, the weight ratio of water:organic solvent:additive may be 8 to 20:3 to 10:1, specifically 9 to 18:3 to 8:1, and preferably 10 to 15:4 to 6:1.

[0157] Here, the organic solvent can be any solvent used in the surface crosslinking reaction without limitation. Specifically, it may be a conventional alcohol known in the art, and more specifically, methanol. In addition, the additive is aluminum sulfate (Al-S). As long as the aforementioned weight ratio is satisfied, the amounts of water, organic solvent, and additive used are not particularly limited and can be appropriately changed within the conventional range known in the art depending on the conditions of the surface crosslinking reaction.

[0158] 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.

[0159] 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.

[0160] In addition to the use of the aforementioned combination of specific chelates and metal salts and the control of specific content, the present invention is differentiated from conventional absorbent resins in that the thickness of the surface crosslinking layer is controlled within a predetermined range based on the difference in physical properties, such as centrifugal retention capacity (CRC), between the base resin (BR) and the final absorbent resin (PD).

[0161] Specifically, the centrifugal retention capacity (CRC) of the base resin measured according to EDANA NWSP 241.0.R2 BR ) and the centrifugal retention capacity (CRC) of absorbent resin PD The difference ) may be greater than 0 g / g, 1 g / g or more, 2 g / g or more, 3 g / g or more, 4 g / g or more, 5 g / g or more, 6 g / g or more, 7 g / g or more, 8 g / g or more, 9 g / g or more, or 10 g / g or more, or 15.0 g / g or less, 14.0 g / g or less, 13.0 g / g or less, 12.5 g / g or less, 12.0 g / g or less, or 11.9 g / g or less. In this case, if the difference in centrifugal retention capacity between the base resin and the absorbent resin deviates from the aforementioned values, a decrease in the absorption capacity of the absorbent resin may result. For example, the centrifugal retention capacity (CRC) of the base resin BR) may be 45 to 55 g / g, specifically 47 to 54 g / g, and more specifically 49 to 53 g / g. In addition, the centrifugal retention capacity (CRC) of the absorbent resin PD ) is 37.5 to 47 g / g, specifically 38 to 46 g / g, and more specifically 37 to 45 g / g.

[0162] (iv) Silica layer formation step

[0163] If necessary, the present invention may further include a step of mixing an absorbent resin with a surface cross-linked layer with silica.

[0164] 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, specifically 0.03 to 3 parts by weight, more specifically 0.05 to 1 part by weight.

[0165]

[0166] <Items>

[0167] Another example of the present invention is an article comprising the aforementioned absorbent resin.

[0168] The aforementioned absorbent resin may be preferably included in or used in various sanitary products, for example, children's disposable diapers, adult diapers, or sanitary pads, and may be particularly preferably applied to children's / adult diapers where absorbency, odor, and skin safety are issues when worn for a long time.

[0169] These sanitary products may include the composition of conventional sanitary products, except that an absorbent resin of one embodiment is included in the absorbent body.

[0170] 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.

[0171] 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.

[0172]

[0173] [Example 1]

[0174] 100 g acrylic acid (LG Chem), 0.1 g ethylene glycol diglycidyl ether (Kolon Corporation) as a crosslinking agent (0.1 parts by weight per 100 parts by weight of acrylic acid monomer), 0.15 g sodium persulfate (SPS, Daejeong Chemical) as a thermal initiator (0.15 parts by weight per 100 parts by weight of acrylic acid monomer), 300 ppmw DTPA (Merck Ltd. Korea) as a chelating agent (0.075 parts by weight per 100 parts by weight of acrylic acid monomer), 0.008 g benzoin ether (Rainbow Chemical, manufacturer to be specified) as a UV initiator (0.008 parts by weight per 100 parts by weight of acrylic acid monomer), 124 g caustic soda (NaOH, LG Chem) (per 100 parts by weight of acrylic acid monomer A monomer aqueous solution composition (monomer composition, degree of neutralization 70 mol%) was prepared by mixing 124 parts by weight) and 47 g of water (4 parts by weight relative to 100 parts by weight of acrylic acid monomer). The monomer aqueous solution composition was fed into the feed section of a polymerization reactor equipped with a continuously moving conveyor belt, and then ultraviolet light was irradiated using a UV irradiation device while maintaining the polymerization atmosphere temperature at 80°C (irradiation dose: 10 mW / cm²). 2 A hydrogel polymer was prepared by carrying out UV polymerization for 2 minutes.

[0175] The above-mentioned hydrogel polymer was transferred to a meat chopper and cut into pieces ranging from 2 mm to 10 mm. At this time, the moisture content of the cut hydrogel polymer was 50 wt%. Subsequently, the hydrogel polymer was dried in a hot air dryer at a temperature of 180°C for 30 minutes, and the dried hydrogel polymer was ground using a pin mill grinder. Then, the polymer with a particle size (particle diameter) of 150 μm to 850 μm was classified using a sieve to produce a base resin.

[0176] Subsequently, a surface crosslinking solution (6 parts by weight of water, 3 parts by weight of methanol, 0.05 parts by weight of ethylene glycol diglycidyl ether (EX-810), 0.1 parts by weight of aluminum sulfate 18 hydrate (Al-S), and 0.07 parts by weight of silica (Aerosil A200)) was evenly mixed with 100 parts by weight of the prepared base resin.

[0177] Next, the above mixture was subjected to a surface crosslinking reaction at 130°C for 30 minutes. After the surface treatment was completed, an absorbent resin with an average particle size of 150 to 850 μm was obtained using a sieve. In the absorbent resin obtained in this way, the content of particles with an average particle size of less than 150 μm was less than 2%.

[0178]

[0179] [Examples 2 to 5]

[0180] Absorbent resins of Examples 2 to 5 were prepared by performing the same procedure as Example 1, except that the type and content of the chelating agent and the conditions of surface crosslinking were changed as shown in Table 1 below.

[0181] Base Resin Polymerization Surface Crosslinking Reaction Other Additives Chelating Agent Inorganic Material Type Content (ppmw) Type Content (parts by weight) Type Content (parts by weight) Time of Addition Example 1 DTPA300Al-S0.1 Silica 0.07 After surface crosslinking Example 2 DTPA300Al-S0.5 Silica 0.07 Example 3 DTPA300Al-S0.5 Silica 0.07 Example 4 DTPA300Al-S0.5 --- Example 5 DTPA1,000Al-S0.5 Silica 0.07 After surface crosslinking Comparative Example 1 EDTA1,000-- Silica 0.07 Comparative Example 2 EDTA1,000Al-S0.5 Silica 0.07 Comparative Example 3 DTPA300-- Silica 0.07 Comparative Example 4DTPA300Al-S0.7 Silica 0.07 Comparative Example 5DTPA50Al-S0.5 Silica 0.07 Comparative Example 6DTPA2,000Al-S0.5 Silica 0.07

[0182]

[0183] [Comparative Examples 1 to 6]

[0184] Absorbent resins of Comparative Examples 1 to 6 were prepared by performing the same procedure as Example 1, except that the type and content of the chelating agent and the conditions of surface crosslinking were changed as shown in Table 1 above.

[0185]

[0186] [Evaluation of Physical Properties of Absorbent Resins]

[0187] The physical properties of the absorbent resins prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were evaluated as follows, and the results are listed in Table 2 below.

[0188] Unless otherwise indicated, all of the following physical property evaluations were conducted under constant temperature and humidity conditions (23±1℃, relative humidity 50±10%), and physiological saline or brine refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0189] (1) Centrifuge Retention Capacity (CRC)

[0190] 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 NWSP 241.0.R2.

[0191] Specifically, in the absorbent resin compositions obtained through the examples and comparative examples, a base resin was obtained by classifying it through a #30-50 sieve. (At this time, the product resin was not classified.) W0 (g) (about 0.2g) of this resin was uniformly placed into a nonwoven fabric bag and sealed, 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 under conditions of 250g using a centrifuge, and the mass W2 (g) of the bag was measured. In addition, the same operation was performed without using the resin, and the mass W1 (g) was measured.

[0192] Using each obtained mass, the CRC(g / g) was calculated according to Equation 1 below.

[0193] [Equation 1]

[0194] CRC(g / g) = {[W2(g) - W1(g) - W0(g)] / W0(g)}

[0195]

[0196] (2) Calculation of the difference in water retention capacity between base resin and absorbent resin

[0197] The difference in water retention capacity (CRC) between the base resin (abbreviation: BR) and the surface-crosslinked absorbent resin (abbreviation: PD) prepared in the examples and comparative examples was measured and calculated and is listed in Table 2 below.

[0198] Here, water retention capacity (CRC) refers to the amount of water that can be retained by 1g of absorbent resin (SAP) under centrifugation; generally, the CRC of the base resin is high, while the CRC of the surface-crosslinked product is low. Furthermore, when the water content in the surface-crosslinking solution increases during surface crosslinking, the surface-crosslinking solution penetrates deeply into the base resin, and in this case, the CRC of the product decreases even more significantly. Based on these experimental factors and physical property behaviors, the difference in water retention capacity (CRC) between the base resin (BR) and the surface-crosslinked product (PD) can be inferred from the thickness of the surface-crosslinking layer contained in the absorbent resin particles.

[0199]

[0200] (3) Absorption capacity (FSC, Free Swell Capacity, g / g)

[0201] The absorption ratio (absorption capacity) of the absorbent resins of the above examples and comparative examples was measured using the following method. The Free Swelling Capacity (FSC) was measured in accordance with the EDANA Method NWSP 240.0.R2.

[0202] Specifically, resin W0 (g, approx. 0.2 g) of the examples and comparative examples was uniformly placed into a nonwoven fabric bag and sealed, then immersed in 1 L of physiological saline solution consisting of a 0.9 wt% sodium chloride aqueous solution at room temperature. After 30 minutes, the bag was removed, fixed for 10 minutes to drain the water, and the mass W2 (g) of the bag was measured. Additionally, the same operation was performed without using resin, and the mass W1 (g) was measured. Using each obtained mass, FSC (g / g) was calculated according to Equation 2 below. The above measurements were performed a total of two times, and the average value was calculated.

[0203] [Equation 2]

[0204] FSC (g / g) = {[W2(g) - W1(g)-W0(g)] / W0(g)}

[0205]

[0206] (4) Absorbency under Pressure (AUP)

[0207] The pressurized absorption capacity of the absorbent resin compositions of the above examples and comparative examples at 0.7 psi was measured according to the EDANA method NWSP 242.0.R2. The resin used in the CRC measurement was used for this pressurized absorption capacity measurement.

[0208] Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under conditions of room temperature and 50% humidity, an absorbent resin W0 (g) was uniformly sprayed onto the wire mesh, and a piston capable of uniformly applying a load of 0.7 psi was positioned so that its outer diameter was slightly smaller than 25 mm, there was no gap with the inner wall of the cylinder, and its vertical movement was not obstructed. At this time, the weight W3 (g) of the device was measured.

[0209] 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 3 below.

[0210] [Equation 3]

[0211] AUP (g / g) = [W4(g) - W3(g)] / W0(g)

[0212]

[0213] (5) Permeability

[0214] 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).

[0215] 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.

[0216] 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%.

[0217] 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 the following Equation 4.

[0218] [Equation 4]

[0219] Permeability = Permeability (sec) = T S- T0

[0220] T S 0.2g of absorbent resin powder is swollen with a 0.9 wt% saline (NaCl) solution for 30 minutes to prepare a saline-absorbent resin, and 0.9 wt% saline solution is the time taken to permeate the absorbent resin under a pressure of 0.3 psi, and T0 is the time taken to permeate the absorbent resin under a pressure of 0.3 psi without the absorbent resin.

[0221]

[0222] (6) 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 a physiological saline solution consisting of 50 mL of a 0.9 wt% sodium chloride aqueous solution was added to a 100 mL beaker with a flat bottom 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 lowest part 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]

[0226] (7) Gel strength

[0227] 2g of the absorbent resin from the above examples and comparative examples was completely swollen (approximately 1 minute) in 50g of an aqueous solution containing 0.9 wt% sodium chloride (NaCl) and 0.00 wt5% ascorbic acid (Vitamin C). After the gel had absorbed all the solution and swollen, it was left in a convection oven at 40°C for 24 hours, after which analysis was performed. A digital strength meter (Shimpo, FGP-2, Japan) was used to measure the gel strength of the swollen absorbent resin. The analysis conditions were set with a probe movement speed of 500 mm / min and a 1 cm dipping into the swollen gel. The results of the measured gel strength are listed in Table 2 below.

[0228] Base Resin CRC BR (g / g)CRC BR -CRC PD Basic physical properties of absorbent resin (PD) CRC PD (g / g) Absorption Capacity (FSC, g / g) AUP (g / g) Permeability (sec) Vortex Time (sec) Gel Strength (N) Example 1 5 1.9 12.2 39.7 6 6.8 12.4 2 38 35 0.89 Example 2 5 1.9 12.1 39.8 6 8.8 12.01 7 4 36 0.76 Example 3 49.9 10.1 39.8 7 0.01 1.1 1 50 34 0.79 Example 4 49.9 10.1 39.7 6 8.01 3.5 20 5 35 0.6 Example 5 5 0.9 11.8 39.1 6 9.01 1.01 39 34 0.79 Comparative Example 154.415.339.163.314.8154390.89 Comparative Example 254.415.139.364.414.4146390.41 Comparative Example 351.812.239.664.113.0198451.1 Comparative Example 451.812.139.769.110.8143340.42 Comparative Example 551.712.239.568.411.2144350.35 Comparative Example 649.312.037.362.713.0166380.77

[0229] As described in Table 2 above, Comparative Examples 1 to 6, which do not include the composition of the present invention, showed a tendency for selective improvement in only one or two of the absorption capacity, gel strength, and absorption rate. For example, in Comparative Example 1, which uses EDTA and does not use aluminum sulfate, and where the difference in water retention capacity between the base resin and the surface cross-linking layer exceeds a specific range, the gel strength was relatively high but the lowest absorption capacity was observed. Furthermore, in Comparative Example 3, which uses DTPA instead of EDTA and does not use aluminum sulfate, the gel strength was excellent, while relatively poor absorption capacity and the slowest absorption rate were exhibited. In particular, Comparative Example 2, which uses both EDTA and aluminum sulfate, actually showed poor physical properties in terms of gel strength. The same pattern was observed in Comparative Examples 4 to 6, which use a combination of a specific chelating agent and a metal salt but are not controlled within a predetermined content range. In contrast, it was confirmed that the absorbent resins prepared in Examples 1 to 5 not only simultaneously improved the absorption capacity, gel strength, and absorption rate, which are in a trade-off relationship, but were also excellent in all aspects of the physical properties of the absorbent resin, such as CRC, AUP, and permeability.

[0230]

[0231] [Example 6]

[0232] After preparing a tissue with a length of 45 cm and a width of 25 cm, 9.0 g of the absorbent resin prepared in Example 1 and 10 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. Next, 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 produced absorbent body sample by heat bonding, and a top sheet made of polypropylene nonwoven fabric was attached to the top in the same manner to complete the absorbent article of Example 6.

[0233]

[0234] [Comparative Example 7]

[0235] The absorbent article of Comparative Example 7 was prepared by carrying out the same method as in Example 6, except that a commercial product (LG Chem, GS-407NR) using EDTA as a chelating agent was used instead of the absorbent resin of Example 1.

[0236]

[0237] [Comparative Example 8]

[0238] The absorbent article of Comparative Example 8 was prepared by carrying out the same method as in Example 6, except that a commercial product (LG Chem, GS-506ND, Vortex 85 sec, FSC 63.5 g / g) not containing a chelating agent was used instead of the absorbent resin of Example 1.

[0239]

[0240] [Evaluation of Physical Properties of Absorbent Articles]

[0241] The physical properties of the absorbent articles prepared in Example 6 and Comparative Examples 7 to 8 were evaluated as follows, and the results are shown in Table 3 below.

[0242] (1) Absorption amount of absorbent article

[0243] The absorption amount (absorption capacity) of the absorbent articles prepared in Example 6 and Comparative Examples 7-8 above was measured using the following method. The absorption capacity of these absorbent articles was measured in accordance with ISO 11948-1.

[0244] Three absorbent items (e.g., diapers) were prepared, and the weight (W1) of each was measured. 2 kg of 0.9 wt% saline solution was poured into an absorbency measuring container, and the three absorbent items were placed in the container with the top sheet facing downward and swollen for 30 minutes. The absorbent items were removed from the container, placed horizontally on a drainage mesh with the top sheet facing downward, and drained for 5 minutes. After placing the tray on a scale and zeroing it, the drained swollen absorbent items were placed on the tray, and the weight (W2) was measured. Subsequently, the absorbency was calculated according to Equation 5 below.

[0245] [Equation 5]

[0246] Absorption capacity of absorbent article (g) = W2 - W1

[0247] (2) Measurement of multiple absorption rates

[0248] After placing the above-manufactured absorbent article on a flat surface, a location for injecting 0.9 wt% saline (aqueous sodium chloride solution) was marked at the center of the absorbent article. Using a circular injection port (870 g), 80 ml of saline was first injected at the injection location within 10 seconds. The time it took for the saline to disappear from the surface of the absorbent article from the moment of injection was recorded (first absorption rate), and the article was left for 5 minutes. That is, a stopwatch was started immediately after the saline was injected into the surface of the absorbent article, and the stopwatch was stopped and recorded when the absorbent article had absorbed all the saline; the elapsed time was recorded as the absorption rate. This process was repeated 5 times under the same conditions, and the average value of the measured times was calculated as the absorption rate for each stage of the absorbent article. After 10 minutes had elapsed from the start of the first saline injection, 80 ml of saline was secondarily injected at the same location as the first saline injection location within 10 seconds. The time it took for the saline to disappear from the moment of injection was recorded (second absorption rate), and the article was left for 5 minutes. After 10 minutes had elapsed from the start of the second saline injection, 80 ml of saline was injected a third time within 10 seconds at the same location as the second saline injection, the time it took for the saline to disappear from the moment of injection was recorded (third absorption rate), and the area was left for 5 minutes. At this time, all procedures were carried out in a constant temperature and humidity room (temperature 23 ± 2℃, relative humidity 45 ± 15%), and the saline used was used under room temperature conditions (temperature 23 ± 2℃).

[0249] (3) Rewetting measurement

[0250] To evaluate the rewetting characteristics under pressurized conditions, the weight (W1, g) of the initial rewetting measurement paper (rewet paper) was measured. Subsequently, the manufactured absorbent article was placed on a flat surface, and a location for injecting 0.9 wt% brine (aqueous sodium chloride solution) was marked at the center of the absorbent article. Using a circular injection port (870 g), 80 ml of brine was injected first at the injection location within 10 seconds. After leaving it for 5 minutes from the time the brine was injected, rewetting measurement paper (rewet paper) was placed on the absorbent article, and a 2.8 kg weight was placed on top of it to apply pressure for 3 minutes to measure the first rewetting amount (rewet), and then left for 2 minutes. The weight (W2) of the rewetting measurement paper (rewet paper) that had absorbed the brine was measured to calculate the amount of brine that seeped from the absorbent article into the rewet paper, and the rewetting amount (Rewet, g) was calculated by the following Equation 6. After 10 minutes had elapsed from the start of the first brine injection, the aforementioned process was repeated to measure the second rewet, and the sample was left for 2 minutes. Afterward, after 10 minutes had elapsed from the start of the second brine injection, the aforementioned process was repeated to measure the third rewet, and the rewets for each stage were summed to calculate the total rewet. All processes were carried out in a constant temperature and humidity room (temperature 23 ± 2℃, relative humidity 45 ± 15%), and the brine used was at room temperature (temperature 23 ± 2℃).

[0251] [Equation 6]

[0252] Re-wetting amount (g) = W2(g) - W1(g)

[0253] In the above Equation 6,

[0254] W1(g) is the initial weight of the rewetting paper, and W2(g) is the weight of the rewetting paper that absorbs the brine seeping out of the absorbent article by injecting 80 g of 0.9 wt% brine into the absorbent article under no pressure and applying pressure with a 2.8 kg weight for 3 minutes.

[0255] Physical properties of absorbent articles Absorption amount (g) 1st 2nd 3rd Total Rewet (g) Absorption rate (s) Rewet (g) Absorption rate (s) Rewet (g) Absorption rate (s) Rewet (g) Example 68 45 270.24 568.24 6717.54 26 Comparative Example 77 93 270.23 5511.89 6526.06 38 Comparative Example 88 30 290.18 809.55 8423.14 33

[0256] The absorption capacity of the absorbent resin and the absorption amount of the absorbent article are in a proportional relationship. As shown in Table 3 above, the absorbent article prepared in Example 6 exhibited a higher absorption amount than Comparative Examples 7-8, which did not contain the composition of the present invention.

[0257] In addition, regarding the absorption rate, while Example 6 and Comparative Example 7 showed similar trends by order, Comparative Example 8 showed slow absorption rates in the second and third orders, exhibiting relatively poor absorption rate characteristics.

[0258] In addition, regarding the amount of rewetting, it was confirmed that the absorbent article of Example 6 had significantly lower secondary and tertiary rewetting amounts than Comparative Examples 7-8, indicating less salt water discharge from the absorbent article.

[0259] Accordingly, it was found that the absorbent article prepared in Example 6 simultaneously achieved excellent absorption, low re-wetting amount, and stable absorption rate when compared to commercial products Comparative Examples 7 and 8, resulting in improved overall physical properties.

[0260] From the above results, it was confirmed that the absorbent resin of the present invention can simultaneously improve absorbency, gel strength, and absorption rate, which are in a trade-off relationship, and accordingly, can reduce the amount of SAP used in diapers to meet the demands of thinning absorbent articles (e.g., the diaper market), and can also continuously provide comfort by maintaining excellent absorbency and the stability of SAP even when the absorbent article (e.g., diaper) is worn for a long time.

Claims

1. 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 Absorbent resin satisfying the conditions of (i) to (iii) below: (i) The gel strength measured after swelling by absorbing 50 g of a 0.9 wt% sodium chloride and 0.005 wt% aqueous solution of ascorbic acid into 0.2 g of absorbent resin is 0.5 N or greater, and (ii) The absorption capacity (FSC) according to EDANA NWSP 240.0.R2 is 65.0 g / g or higher, and (iii) The absorption rate of physiological saline according to the vortex measurement method is 44 seconds or less.

2. In Paragraph 1, The above absorbent resin is, (i) The gel strength measured after swelling by absorbing 50 g of a 0.9 wt% sodium chloride and 0.005 wt% aqueous solution of ascorbic acid into 0.2 g of absorbent resin is 0.55 N or higher, and (i) The absorption capacity (FSC) according to EDANA NWSP 240.0.R2 is 66.5 g / g or higher, and (iii) Absorbent resin having an absorption rate of 43 seconds or less in physiological saline according to the vortex measurement method.

3. In Paragraph 1, The above absorbent resin is an absorbent resin that further satisfies at least one of the following conditions (iv) to (vi): (iv) The centrifugal retention capacity (CRC) measured according to EDANA NWSP 241.0.R2 is 37.5 g / g or greater, and (v) The pressurized absorption capacity (0.7 AUP) for 1 hour at 0.7 psi for physiological saline (0.9 wt% sodium chloride aqueous solution), measured according to the EDANA method NWSP 242.0.R2, is 8.0 g / g or greater, and (vi) Permeability is 500 seconds or less.

4. In Paragraph 1, The above absorbent resin is an absorbent resin comprising at least one of diethylenetriamine pentaacetic acid (DTPA), ions derived from aluminum sulfate, salts, and decomposition products thereof.

5. In Paragraph 1, The above absorbent resin is an absorbent resin that does not contain an amino acetate-based chelating agent other than diethylenetriamine pentaacetic acid.

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

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

8. In Paragraph 7, 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.

9. (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 internal crosslinking agent, a polymerization initiator, and diethylenetriamine pentaacetic acid (DTPA); (ii) a step of preparing a base resin powder comprising a cross-linked polymer obtained by drying and grinding the above-mentioned hydrogel polymer; and (iii) a step of preparing an absorbent resin having a surface crosslinking layer formed on the base resin by mixing the above base resin powder with a surface crosslinking composition containing aluminum sulfate and a surface crosslinking agent, and then heat-treating the mixture; wherein The above diethylenetriamine pentaacetic acid (DTPA) is included in an amount of 100 ppmw to 1,500 ppmw based on 100 parts by weight of the above acrylic acid monomer, and The above aluminum sulfate is included in an amount of 0.05 to 0.6 parts by weight based on 100 parts by weight of the base resin, and Water retention capacity (CRC) of the base resin prepared in step (ii) above, measured according to EDANA NWSP 241.0.R2 BR ) and the water retention capacity (CRC) of the absorbent resin with the surface cross-linked layer formed in step (iv) above. PD A method for manufacturing an absorbent resin in which the difference of ) is controlled to 15.0 g / g or less.

10. In Paragraph 9, Water retention capacity (CRC) of the base resin prepared in step (ii) above, measured according to EDANA NWSP 241.0.R2 BR ) and the water retention capacity (CRC) of the absorbent resin with the surface cross-linked layer formed in step (iv) above. PD A manufacturing method in which the difference of ) is 13.0 g / g or less.

11. In Paragraph 9, The centrifugal retention capacity (CRC) of the base resin measured according to EDANA NWSP 241.0.R2 is 45 to 55 g / g, and A method for manufacturing the above absorbent resin, wherein the centrifugal retention capacity (CRC) is 37.5 to 47 g / g.

12. In Paragraph 9, A method for manufacturing in which the weight ratio of the above diethylenetriamine pentaacetic acid (DTPA) and the above aluminum sulfate is 1:3 to 1:

50.

13. In Paragraph 9, 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.

14. In Paragraph 13, 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.