Superabsorbent polymer and method for producing same

Abstract

Provided are a superabsorbent polymer and a method for preparing the same, and more particularly, a superabsorbent polymer and a method for preparing the same, the superabsorbent polymer has improved absorption rate under pressure, liquid permeability, and gel strength at the same time by containing a specific chelating compound inside base polymer particles and containing a modified organosilicon compound in a surface cross-linked layer of the base polymer particles.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application is based on and claims priority to Korean Patent Application Nos. 10-2023-0131047 and 10-2024-0123329, filed on September 27, 2023 and September 10, 2024, respectively, the disclosures of which are incorporated herein by reference in their entireties.

[0003] The present invention relates to a superabsorbent polymer and a method for preparing the same. More particularly, the present invention relates to a superabsorbent polymer and a method for preparing the same, which has its under-pressure absorbency, liquid permeability, and gel strength simultaneously improved by including a specific chelating compound inside a base polymer particle and including a modified silicone compound in a surface crosslinking layer of the base polymer. BACKGROUND

[0004] A superabsorbent polymer (SAP) is a synthetic polymer material capable of absorbing 500 to 1,000 times its own weight of moisture. Various manufacturers name it differently, such as SAM (Super Absorbency Material), AGM (Absorbent Gel Material), etc. Since such superabsorbent polymers have been practically used in hygiene products, they are now widely used in water-retaining soil products for gardening, water-stopping materials for civil engineering and construction, sheet materials for seedling raising, preservatives for food distribution fields, materials for poultices, etc.

[0005] In most cases, these superabsorbent polymers are widely used in the field of hygiene materials, such as diapers or sanitary napkins, etc. Within the hygiene materials, the superabsorbent polymers are generally distributed throughout the pulp. However, there have been recent efforts to provide hygiene materials such as thinner diapers, and as part of the efforts, diapers with reduced pulp content are being actively developed, and there are diapers without pulp (so-called pulp-free diapers).

[0006] As described above, such hygiene materials with reduced or no pulp contain superabsorbent polymers at a relatively high ratio, and superabsorbent polymer particles are inevitably contained as multiple layers in the hygiene materials. In order for all the superabsorbent polymer particles contained as multiple layers to more effectively absorb a large amount of liquid such as urine, etc., the superabsorbent polymers essentially need to exhibit high absorbency as well as high absorbency.

[0007] Further, when the superabsorbent polymer is contained in a sanitary material such as a diaper or the like, it is required to spread urine as widely as possible even in an environment pressurized by the weight of a user. Thereby, by making full use of the superabsorbent polymer particles contained in the entire area of the absorbent layer of the sanitary material, it is possible to further improve the absorption performance and the absorption rate of the sanitary material. Further, due to such a spreading property under pressure, it is possible to further improve the rewet property of the diaper, which prevents urine that has been absorbed by the superabsorbent polymer from seeping out again. Further, it is possible to improve the leakage suppression property of the diaper.

[0008] Previously, attempts have been made to improve the wide spreading property of urine by changing the design of a sanitary material such as a diaper or the like. For example, attempts have been made to improve the spreading property of urine by introducing an acquisition distribution layer (ADL) into the sanitary material or by applying an absorption channel or the like.

[0009] However, the improvement in the spreading property by such a design change of the sanitary material is not sufficient. Further, recently, due to the sanitary material becoming thinner and the content of the superabsorbent polymer in the sanitary material relatively increasing, there is a limitation in improving the spreading property by the design change of the sanitary material itself. There is an increasing need to improve the spreading property under pressure of the superabsorbent polymer itself.

[0010] Due to these technical needs, there is an increasing need to develop a superabsorbent polymer in which the liquid permeability under pressure directly related to the spreading property under pressure can be further improved, thereby further improving the rewet property and the leakage suppression property of a sanitary material such as a diaper or the like. SUMMARY

[0011] TECHNICAL PROBLEM

[0012] Therefore, provided is a superabsorbent polymer and a method for producing the same, in which the pressure absorption rate, the liquid permeability, and the gel strength are simultaneously improved by containing a specific chelate compound inside a base polymer particle and containing a modified silicone compound in a surface crosslinked layer of the base polymer.

[0013] TECHNICAL SOLUTION

[0014] To solve the above problems, provided is a superabsorbent polymer, which comprises:

[0015] a base polymer particle comprising a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized is crosslinked in the presence of a metal chelate based on an aminocarboxylic acid; and

[0016] a surface crosslinked layer formed by additionally crosslinking a crosslinked polymer on a part of the surface of the base polymer particles via a surface crosslinking agent,

[0017] wherein at least one of the inside or the surface of the surface crosslinked layer comprises a modified organosilicon compound,

[0018] the modified organosilicon compound has a polysiloxane backbone, and

[0019] at least one of the side chains or the terminal end of the polysiloxane comprises one or more carboxylic acid groups or polyether groups.

[0020] Further, according to another exemplary embodiment of the present application, there is provided a method of preparing the above-described superabsorbent polymer, the method comprising the steps of:

[0021] forming an aqueous gel polymer by crosslinking a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized in the presence of an aminocarboxylic acid-based metal chelating agent (step 1);

[0022] forming base polymer particles by drying, pulverizing, and size-sorting the aqueous gel polymer (step 2);

[0023] preparing a surface crosslinking mixture by mixing the base polymer particles with a surface crosslinking composition (step 3); and

[0024] forming a surface crosslinked layer on a part of the surface of the base polymer particles by heat-treating the surface crosslinking mixture (step 4),

[0025] wherein a modified organosilicon compound is added to at least one of step 3 and step 4 or after step 4,

[0026] the modified organosilicon compound has a polysiloxane backbone, and

[0027] at least one of the side chains or the terminal end of the polysiloxane comprises one or more carboxylic acid groups or polyether groups.

[0028] Advantages

[0029] There is provided a superabsorbent polymer and a method of preparing the same, the superabsorbent polymer having simultaneously improved under-pressure absorbency, liquid permeability, and gel strength by including a specific chelating compound inside base polymer particles and a modified organosilicon compound in a surface crosslinked layer of the base polymer. DETAILED DESCRIPTION

[0030] The terms used in the present specification are merely used to describe exemplary embodiments and are not intended to limit the present application.

[0031] The singular expression can include the plural expression unless the singular expression is differently expressed in the context. It must be understood that the terms "include", "comprise" or "have" in the present specification are merely intended to denote presence of features, steps, components, or combinations thereof, and do not preclude presence or addition of one or more different features, steps, components, or combinations thereof.

[0032] The terms "first", "second", "third", and the like are used to describe various components, and the terms are used only for distinguishing a certain component from other components.

[0033] The present application can be modified variously and has various forms, and specific exemplary embodiments are illustrated and described in detail in the following description. However, it is not intended to limit the present application to the specific exemplary embodiments, and it must be understood that the present application includes every modification, equivalent or alternative included in the spirit and technical scope of the present application.

[0034] As used herein, the term "polymer" means a polymerization state of a water-soluble ethylenically unsaturated monomer, and can encompass polymers of all water content ranges or particle size ranges. Among the polymers, those having a water content of about 40% by weight or more after polymerization and before drying can be referred to as a water-containing gel polymer. Particles obtained by pulverizing and drying the water-containing gel polymer can be referred to as a crosslinked polymer.

[0035] In addition, the term "crosslinked polymer" means those obtained by crosslinking polymerization of a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent, and "base polymer particles" means a material containing such a crosslinked polymer.

[0036] In addition, the term "superabsorbent polymer" means, depending on the context, a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized, or a base polymer particle obtained by drying the crosslinked polymer, or to encompass those suitable for commercialization made by additional processes of the crosslinked polymer or base polymer (e.g., surface crosslinking, reassembly of fine particles, drying, pulverization, size sorting, etc.).

[0037] In addition, the term "superabsorbent polymer particle" means a particulate material containing a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized and crosslinking it by an internal crosslinking agent.

[0038] (superabsorbent polymer)

[0039] The superabsorbent polymer according to one embodiment of the present application includes: base polymer particles including a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having an at least partially neutralized acidic group is crosslinked in the presence of an amino carboxylic acid-based metal chelating agent; and a surface crosslinked layer formed by additionally crosslinking the crosslinked polymer on a part of the surface of the base polymer particles via a surface crosslinking agent, wherein at least one of the inside or the surface of the surface crosslinked layer includes a modified organosilicon compound, the modified organosilicon compound having a polysiloxane main chain, and at least one of the side chains or the terminal ends of the polysiloxane includes one or more carboxylic acid groups or polyether groups.

[0040] Recently, with respect to superabsorbent polymers, improvement in not only the basic absorption property but also the rewet property of preventing repermeation of absorbed urine when a sanitary material such as a diaper or the like is actually used has become an important measure for evaluating product quality. In order to improve the above rewet property, all properties such as the absorption under pressure, the liquid permeability, the gel strength, and the like are required to satisfy an appropriate level or more, but due to their trade-off relationship, there is a problem in that it is difficult to simultaneously improve all three properties.

[0041] Accordingly, the present inventors found that when a specific chelating agent is used in the step of forming a water-containing gel polymer, the chelating agent is introduced into the inside of the base polymer particles, thereby preventing gel degradation and maintaining the gel strength, and when a modified organosilicon compound is used in the step of forming a surface crosslinked layer, the modified organosilicon compound is introduced into at least one of the inside or the surface of the surface crosslinked layer, thereby improving the liquid permeability without using a large amount of a liquid permeability improving compound, thereby achieving the effect of improving the liquid permeability without reducing the effect of the chelating agent, and as a result, it is possible to simultaneously improve the absorption under pressure, the liquid permeability, and the gel strength of the absorbent polymer, thereby completing the present application.

[0042] Hereinafter, each component of the superabsorbent polymer according to one embodiment of the present application will be described in detail.

[0043] The superabsorbent polymer according to one embodiment of the present application includes base polymer particles including a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having an at least partially neutralized acidic group is crosslinked in the presence of an amino carboxylic acid-based metal chelating agent. The base polymer particles can refer to a particle type material including the crosslinked polymer of the water-soluble ethylenically unsaturated monomer.

[0044] The amino carboxylic acid-based metal chelating agent captures metal ions included in the base polymer that cause gel deterioration, thereby preventing gel deterioration and improving gel strength. In particular, when used together with the modified silicone compound included in the surface crosslinking layer, it enables the amount of metal compound, which is generally used to improve liquid permeability, to be minimized, thereby achieving the effect of improving liquid permeability while not reducing gel strength. Ultimately, the under-pressure absorbency, liquid permeability, and gel strength of the absorbent resin can be improved at the same time, and the rewet characteristics can be improved, thereby further enhancing the quality of a product in which the polymer is applied.

[0045] The above amino carboxylic acid-based metal chelating agent can be, for example, at least one selected from the group consisting of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, trans-1,2-diaminocyclohexanetetraacetic acid, and metal salts thereof, and is preferably ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and alkali metal salts thereof.

[0046] The amino carboxylic acid-based metal chelating agent can be included in an amount of 50 ppmw to 5,000 ppmw with respect to the water-soluble ethylenically unsaturated monomer, and the above content range is suitable for achieving the above-mentioned effects. Preferably, it can be included in an amount of 100 ppmw to 2,000 ppmw, 200 ppmw to 1,500 ppmw, or 300 ppmw to 1,000 ppmw.

[0047] The crosslinked polymer is an aqueous gel polymer formed by crosslinking a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized in the presence of the amino carboxylic acid-based metal chelating agent, and its polymerization method will be described in more detail in the description of the method of preparing a superabsorbent polymer.

[0048] The water-soluble ethylenically unsaturated monomer can be any monomer commonly used in the preparation of a superabsorbent polymer. Non-limiting examples of the water-soluble ethylenically unsaturated monomer can be compounds represented by the following Chemical Formula 1:

[0049] [Chemical Formula 1]

[0050] R1-COOM 1

[0051] In Chemical Formula 1,

[0052] R1 is a hydrocarbon group including an unsaturated bond and having 2 to 5 carbon atoms, and

[0053] M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0054] Preferably, the monomer can include one or more selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof. As described, when acrylic acid or a salt thereof is used as the water-soluble ethylenically unsaturated monomer, it is advantageous in terms of obtaining a superabsorbent polymer having improved absorbency. In addition, the monomer can include one or more selected from the group consisting of anionic monomers such as maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloyl ethanesulfonic acid, 2-methacryloyl ethanesulfonic acid, 2-(meth)acryloyl propanesulfonic acid, or 2-(meth)acrylamido-2-methylpropanesulfonic acid, and salts thereof; nonionic hydrophilic monomers such as (meth)acrylamide, N-substituted (meth)acrylic acid ester, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, or polyethylene glycol (meth)acrylate; and amino-containing unsaturated monomers such as (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide, and quaternary compounds thereof.

[0055] Here, the water-soluble ethylenically unsaturated monomer can have an acidic group, wherein at least a portion of the acidic group can be partially neutralized with a neutralizing solution. The type of the neutralizing solution is not particularly limited, and any basic component commonly used in the art can be used.

[0056] In this regard, the neutralization degree of the monomer can be 40 mol% to 95 mol%, or 40 mol% to 80 mol%, or 45 mol% to 75 mol%. The range of the neutralization degree can vary depending on the final physical properties. A too high neutralization degree causes the neutralized monomer to precipitate, and thus polymerization can not be easily performed. Conversely, a too low neutralization degree not only greatly deteriorates the absorbency of the polymer, but also imparts a characteristic of the polymer that is difficult to handle, such as that of an elastic rubber.

[0057] Next, the superabsorbent polymer according to one embodiment of the present application includes a surface crosslinked layer formed by additionally crosslinking a crosslinked polymer via a surface crosslinking agent on a portion of the surface of the base polymer particles. Here, at least one of the inside or the surface of the surface crosslinked layer contains a modified organosilicon compound.

[0058] The modified organosilicon compound is contained in the surface crosslinked layer, which enables the amount of use of a metal compound, which is generally used to improve the liquid permeability, to be minimized, thereby improving the liquid permeability without reducing the gel strength. In particular, in addition to the effect of improving the gel strength by the chelating agent contained in the inside of the base polymer, it simultaneously improves the absorbency under pressure, the liquid permeability, and the gel strength of the absorbent polymer, and finally improves the rewet characteristics, thereby further improving the quality of a product in which the polymer is applied.

[0059] The modified organosilicon compound has a polysiloxane backbone, wherein at least one of a side chain or a terminal end of the polysiloxane includes one or more carboxylic acid groups or polyether groups. In other words, the modified organosilicon compound means a carboxyl-modified organosilicon compound or a polyether-modified organosilicon compound.

[0060] The polysiloxane backbone can generally mean a polymer having a backbone composed of silicon and oxygen, and the carboxylic acid groups or polyether groups in the side chain or terminal end of the polysiloxane can impart water solubility to the compound.

[0061] The modified organosilicon compound can be included in an amount of 0.001 parts by weight to 0.1 parts by weight with respect to the base polymer particles, and the above content range is suitable to achieve the above-mentioned effects. Preferably, it can be included in an amount of 0.0015 parts by weight to 0.07 parts by weight, 0.003 parts by weight to 0.005 parts by weight.

[0062] As used herein, the term "surface crosslinking agent" is used to distinguish it from an "internal crosslinking agent" used in the step of polymerizing the base polymer, and refers to what is described in the following method of preparing a polymer. Crosslinking occurs both on the surface and inside. However, through the surface crosslinking process of the base polymer, the surface of the particles of the superabsorbent polymer finally prepared has a structure crosslinked by the surface crosslinking agent, and its inside has a structure crosslinked by the internal crosslinking agent.

[0063] The surface crosslinking agent can include one or more selected from the group consisting of: a polyol; an epoxy compound; a polyamine compound; a halogenated epoxy compound; a condensation product of a halogenated epoxy compound; an oxazoline compound; a mono an oxazolidone, di an oxazolidone or poly an oxazolidone compound; a cyclic urea compound; a polyvalent metal salt; and an alkylene carbonate compound.

[0064] Specifically, examples of the polyol can include one or more selected from the group consisting of: monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-buten-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol.

[0065] Further, the epoxy compound can include ethylene glycol diglycidyl ether and glycidol, etc., and the polyamine compound can include one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamide polyamine.

[0066] Further, the halogenated epoxy compound can include epichlorohydrin, epibromohydrin, and a-methyl epichlorohydrin. Meanwhile, the mono azlactone, di azlactone, or poly azlactone compound can be exemplified as 2- azlactone, etc.

[0067] Further, the alkylene carbonate compound can include ethylene carbonate, etc. These compounds can be used alone or in combination thereof. Meanwhile, in order to improve the efficiency of the surface crosslinking process, a polyol compound having 2 to 10 carbon atoms can be included using one or more of these surface crosslinking agents.

[0068] The content of the surface crosslinking agent can be appropriately selected depending on the kind of the surface crosslinking agent to be added or the reaction conditions. However, it can be generally used in an amount of about 0.001 parts by weight to about 5 parts by weight, preferably about 0.01 parts by weight to about 3 parts by weight, more preferably about 0.05 parts by weight to about 2 parts by weight, with respect to 100 parts by weight of the base polymer particles.

[0069] When the content of the surface crosslinking agent is too small, the surface crosslinking reaction can hardly occur, and when the content exceeds 5 parts by weight with respect to 100 parts by weight of the base polymer particles, the absorbency and physical properties can be deteriorated due to excessive progress of the surface crosslinking reaction.

[0070] Regarding the superabsorbent polymer according to one embodiment of the present application, since the above-mentioned metal chelating agent based on aminocarboxylic acid inside the base polymer and the modified organosilicon compound of the surface crosslinking layer are used, the absorbency under pressure, the liquid permeability, and the gel strength can be simultaneously improved.

[0071] Regarding the superabsorbent polymer, the absorbency under centrifuge pressure of 0.7 psi (AUP) according to EDANA method WSP 242.3-10 can be 13.0 g / g or more, preferably 13.1 g / g or more, 13.3 g / g or more, 13.5 g / g or more, 14 g / g or more, 14.2 g / g or more, and 30 g / g or less, 27 g / g or less, or 24 g / g or less, and 13.0 g / g to 30 g / g, 13.5 g / g to 27 g / g, or 14.0 g / g to 24 g / g.

[0072] The more detailed measurement method will be described in the experimental example below.

[0073] The liquid permeability of the superabsorbent polymer determined according to the following Equation 1 can be 180 seconds or less, preferably 150 seconds or less, or 130 seconds or less. The lower limit of the liquid permeability can be 0 seconds or more, 50 seconds or more, or 80 seconds or more.

[0074] [Equation 1]

[0075] Liquid permeability (sec) = T1 - B

[0076] In Equation 1,

[0077] T1 denotes the time taken for the liquid level to drop from 40 ml to 20 ml when 0.2 ± 0.0005 g of a superabsorbent polymer sample is put into a chromatographic column having a glass filter, 50 ml of a saline solution is applied and left for 30 minutes, then a piston having a weight (0.3 psi) is placed and left for 1 minute, and a lower valve is opened, and

[0078] B denotes the time taken for the liquid level to drop from 40 ml to 20 ml when the piston having a weight (0.3 psi) is placed in the chromatographic column filled with the saline solution.

[0079] Here, the saline means a 0.9 wt% sodium chloride (NaCl) aqueous solution, and a more detailed measurement method will be described in the Experimental Example below.

[0080] Further, the gel strength of the superabsorbent polymer measured by immersing 2.5 g of a superabsorbent polymer sample in 50 g of an ascorbic acid aqueous solution and swelling it in an oven at 40°C for 24 hours, and then measuring the swollen superabsorbent polymer using a tensile tester can be 0.70 N or more. Preferably, the gel strength can be 0.75 N or more, 0.80 N or more, or 0.70 N to 2.0 N, 0.75 N to 1.8 N, 0.80 N to 1.5 N.

[0081] Here, the ascorbic acid aqueous solution means a 0.9 wt% sodium chloride (NaCl) and 0.005 wt% ascorbic acid aqueous solution, and a more detailed measurement method will be described in the Experimental Example below.

[0082] Further, the particle size of the superabsorbent polymer can be 150 μm to 850 μm. More specifically, at least 95 wt% or more of the superabsorbent polymer can have a particle size of 150 μm to 850 μm, and can include 50 wt% or more of particles having a particle size of 300 μm to 600 μm and less than 3 wt% of fine particles having a particle size of less than 150 μm.

[0083] (Method for producing superabsorbent polymer)

[0084] The method for producing a superabsorbent polymer according to one embodiment of the present application includes the steps of forming a hydrogel-containing polymer by cross-linking a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized in the presence of an aminocarboxylic acid-based metal chelating agent (Step 1); forming base polymer particles by drying, pulverizing, and size-sorting the hydrogel-containing polymer (Step 2); preparing a surface cross-linking mixture by mixing the base polymer particles with a surface cross-linking composition (Step 3); and forming a surface cross-linking layer on a part of the surface of the base polymer particles by heat-treating the surface cross-linking mixture (Step 4). Here, a modified organosilicon compound is added to at least one of Step 3 and Step 4 or after Step 4. Here, the modified organosilicon compound has a polysiloxane main chain, and at least one of a side chain or a terminal of the polysiloxane contains one or more carboxylic acid groups or polyether groups.

[0085] (Step 1: Polymerization Step)

[0086] First, included is a step of forming a hydrogel-containing polymer by cross-linking a water-soluble ethylenically unsaturated monomer having an acid group that is at least partially neutralized in the presence of an aminocarboxylic acid-based metal chelating agent (Step 1).

[0087] In the polymerization step, an internal cross-linking agent and a polymerization initiator can be used together with the aminocarboxylic acid-based metal chelating agent, and specifically, the step is a step of forming a hydrogel-containing polymer by performing thermal polymerization or photopolymerization of a monomer composition containing the chelating agent, the internal cross-linking agent, the polymerization initiator, and a monomer mixture. The foregoing description can equally apply to the description of the chelating agent and the monomer.

[0088] As used herein, the term "internal cross-linking agent" is used to distinguish it from a "surface cross-linking agent" used to cross-link the surface of the base polymer particles, and is used to polymerize the above-described water-soluble ethylenically unsaturated monomer by cross-linking the unsaturated bond thereof. The cross-linking in the above step occurs both on the surface and inside. However, through the surface cross-linking process of the base polymer described below, the surface of the superabsorbent polymer particles finally produced has a structure cross-linked by the surface cross-linking agent, and the inside thereof has a structure cross-linked by the internal cross-linking agent.

[0089] As the internal crosslinking agent, a multifunctional component can be used, and for example, one or more selected from the group consisting of N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butane diol di(meth)acrylate, butanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerol tri(meth)acrylate, pentaerythritol tetraacrylate, triallylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerol, and ethylene carbonate can be used. Preferably, ethylene glycol diglycidyl ether can be used.

[0090] The internal crosslinking agent can be used in an amount of 50 ppmw to 1,000 ppmw with respect to the weight of the water-soluble ethylenically unsaturated monomer. When included in the above content range, a proper level or higher of strength can be achieved by sufficient crosslinking, and the introduction of a proper crosslinked structure enables sufficient water retention capacity to be achieved. Preferably, it can be included in an amount of 100 ppmw or more, 200 ppmw or more, 300 ppmw or more, or 600 ppmw or more, and 1,000 ppmw or less, or 800 ppmw or less, and 200 ppmw to 1,000 ppmw, 200 ppmw to 800 ppmw, or 600 ppmw to 800 ppmw. When the content of the internal crosslinking agent is too low, crosslinking does not sufficiently proceed, making it difficult to achieve a proper level or higher of strength, and drying efficiency is significantly reduced, while when the content of the internal crosslinking agent is too high, internal crosslinking density increases, making it difficult to achieve the desired water retention capacity.

[0091] As the polymerization initiator, a thermal polymerization initiator and / or a photopolymerization initiator can be used.

[0092] As a thermal polymerization initiator, one or more compounds selected from the group consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, the persulfate-based initiator can be exemplified by sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), and the like. The azo-based initiator can be exemplified by 2,2-azobis(2-imidazolin-2-ylpropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutylamidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), and the like. More various thermal polymerization initiators are disclosed in "Principle of Polymerization (Wiley, 1981)" by Odian, p. 203, which can be used as a reference.

[0093] Further, as a polymerization initiator, in addition to the above-mentioned thermal polymerization initiator, a photopolymerization initiator can be used.

[0094] The photopolymerization initiator can include, for example, one or more compounds selected from the group consisting of benzoin ethers, dialkyl phenylacetophenones, hydroxyalkyl ketones, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphines, and α-amino ketones. Among them, specific examples of the acyl phosphine can include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, (2,4,6-trimethylbenzoyl)phenyl phosphinic acid ethyl ester, and the like. More various photopolymerization initiators are fully disclosed in "UV Coatings: Basics, Recent Developments and New Application (Elsevier, 2007)" by Reinhold Schwalm, p. 115, but are not limited thereto.

[0095] The polymerization initiator can be included in an amount of 500 ppmw to 10,000 ppmw, preferably, in an amount of 500 ppmw or more, 750 ppmw or more, 800 ppmw or more, or 1,000 ppmw or more, and 10,000 ppmw or less, 8,000 ppmw or less, 7,000 ppmw or less, 5,000 ppmw or less, 3,000 ppmw or less, 1,500 ppmw or less, or 1,000 ppmw or less, and 500 ppmw to 8,000 ppmw, 500 ppmw to 5,000 ppmw, 750 ppmw to 3,000 ppmw, or 800 ppmw to 1,500 ppmw, relative to the weight of the water-soluble ethylenically unsaturated monomer, and within the above ranges, the foregoing effects can be further improved. The content of the polymerization initiator means the content of a mixture thereof when a thermal polymerization initiator and a photopolymerization initiator are used together.

[0096] In addition, the monomer composition can further include additives commonly used in the art, such as a foaming agent, a thickening agent, a plasticizer, a preservative stabilizer, an antioxidant, a surfactant, etc., as necessary.

[0097] The foaming agent causes foaming during polymerization to produce pores inside the aqueous gel polymer, thereby increasing the surface area. As the foaming agent, a carbonate salt such as sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, or magnesium carbonate can be used. As an applicable commercial foaming agent, Encapsulated Foaming Agent F-36D can be used, but is not limited thereto.

[0098] In addition, it is preferable that the foaming agent be used in an amount of 1,500 ppmw or less, relative to the weight of the water-soluble ethylenically unsaturated monomer. When the foaming agent is used in an amount greater than 1,500 ppmw, the pores can be excessively increased, and thus the gel strength of the superabsorbent polymer can be reduced and the density can be reduced, causing problems in distribution and storage. In addition, it is preferable that the foaming agent be used in an amount of 500 ppmw or more, or 1,000 ppmw or more, relative to the weight of the water-soluble ethylenically unsaturated monomer.

[0099] In addition, such a monomer composition can be prepared in the form of a solution in which the above-described raw materials including the internal crosslinking agent, the water-soluble ethylenically unsaturated monomer, the polymerization initiator, etc. are dissolved in a solvent.

[0100] In this regard, as the applicable solvent, any solvent can be used without limitation in terms of composition, as long as it is capable of dissolving the above-described raw materials. For example, as the solvent, 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 a mixture thereof can be used.

[0101] The step of forming the hydrogel polymer by polymerization of the monomer composition can be performed by a common polymerization method, and its process is not particularly limited. For non-limiting examples, the polymerization method is roughly classified into thermal polymerization and photopolymerization according to the energy source for polymerization. The thermal polymerization can be performed in a reactor equipped with a stirring shaft such as a kneader. The photopolymerization can be performed in a reactor equipped with a movable conveyor belt.

[0102] For example, the monomer composition is injected into a reactor equipped with a stirring shaft such as a kneader, and the thermal polymerization is performed by supplying hot air thereto or by heating the reactor, thereby obtaining the hydrogel polymer. In this regard, depending on the type of the stirring shaft equipped in the reactor, the hydrogel polymer can be obtained as a pellet having a size of millimeter or centimeter when it is discharged from the outlet of the reactor. Specifically, depending on the concentration, feeding speed, etc. of the monomer composition fed thereto, the hydrogel polymer can be obtained in various forms, and generally the hydrogel polymer having a (weight average) particle size of 2 mm to 50 mm can be obtained.

[0103] For another example, when the monomer composition is subjected to photopolymerization in a reactor equipped with a movable conveyor belt, the hydrogel polymer can be obtained in a sheet type. In this regard, the thickness of the sheet can vary depending on the concentration and feeding speed of the monomer composition fed thereto. In order to secure the production speed while uniformly polymerizing the entire sheet, it is preferable to control the sheet to have a thickness of 0.5 cm to 10 cm.

[0104] The water-containing gel polymer obtained by such a method can exhibit a water content of 40 to 80% by weight. Meanwhile, throughout the present specification, the "water content" means the weight of water with respect to the total weight of the water-containing gel polymer, which can be a value obtained by subtracting the weight of the dried polymer from the weight of the water-containing gel polymer. Specifically, the water content can be defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during a drying process performed by raising the temperature of the polymer via infrared heating. At this time, the water content is measured under drying conditions in which the temperature is raised from room temperature to 180°C, the temperature is then maintained at 180°C, and the total drying time is set to 20 minutes, including 5 minutes of the temperature raising step.

[0105] (Step 2: Step of drying, pulverizing and size sorting)

[0106] Next, the method of preparing a superabsorbent polymer according to one embodiment of the present application includes a step of forming base polymer particles by drying, pulverizing, and size-sorting the prepared water-containing gel polymer (Step 2).

[0107] Specifically, a step of drying the obtained water-containing gel polymer is performed. If necessary, a step of roughly pulverizing (chopping) the water-containing gel polymer can be performed before drying to improve the efficiency of the drying step.

[0108] In this regard, the pulverizer used can include, but is not limited to, any one selected from the group consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a chip breaker, a crusher, a chopper, and a disc cutter, but is not limited thereto.

[0109] In this regard, the step of rough pulverization can be performed such that the particle size of the water-containing gel polymer is 2 to 10 mm. Since the water content is high, it is not easy to pulverize the water-containing gel polymer to a particle size of less than 2 mm in a technical aspect, and the agglomeration phenomenon between the pulverized particles can occur. Conversely, when the polymer is pulverized to a particle size of more than 10 mm, the effect of improving the efficiency of the subsequent drying step can not be satisfactory.

[0110] The water-containing gel polymer as above coarsely pulverized or the water-containing gel polymer immediately after polymerization without the coarsely pulverizing step is subjected to a drying step. In this regard, the drying temperature of the drying step can be 150°C to 250°C. When the drying temperature is lower than 150°C, the drying time becomes excessively long and can deteriorate the physical properties of the finally formed superabsorbent polymer. When the drying temperature is higher than 250°C, only the surface of the polymer is excessively dried, thus fine particles can be generated during the subsequent pulverization process and can deteriorate the physical properties of the finally formed superabsorbent polymer. Preferably, the drying can be performed at a temperature of about 150°C to about 200°C, more preferably at a temperature of about 150°C to about 190°C.

[0111] The drying time can be 20 minutes to 90 minutes in consideration of process efficiency, etc., but is not limited thereto.

[0112] Meanwhile, the drying step can be performed by a multi-stage process within the above temperature range.

[0113] As to the drying method of the drying step, any method can be selected and used without limitation in terms of constitution, as long as it can be commonly used in the process of drying the water-containing gel polymer. Specifically, the drying step can be performed by a method of supplying hot air, irradiating infrared rays, irradiating microwaves, irradiating ultraviolet rays, etc. The hot air supply can be performed by a method of using an oven capable of transferring the amount of air up and down.

[0114] The water content of the polymer after the drying step can be about 0.1% by weight to about 10% by weight.

[0115] Next, a step of pulverizing the dried polymer obtained by the drying step can be performed.

[0116] The particle size of the polymer obtained after the pulverization step can be 150 μm to 850 μm. The pulverizer for pulverizing to such a particle size can specifically include a pin mill, a hammer mill, a screw-type mill, a roll mill, a disc mill, a point-to-point mill, etc., but the present application is not limited to the above examples.

[0117] In order to control the physical properties of the superabsorbent polymer powder finally commercialized after the pulverization step, the base polymer particles obtained after the pulverization can undergo a separate process of size sorting the particles according to the particle size.

[0118] Preferably, the base polymer particles having a particle size of about 150 μm to about 850 μm are size-sorted, and only the base polymer particles having such a particle size can be subjected to the step of surface crosslinking reaction, and finally commercialized. More specifically, the size-sorted base polymer particles have a particle size of 150 μm to 850 μm, and can contain 50% by weight or more of particles having a particle size of 300 μm to 600 μm and less than 3% by weight of fine particles having a particle size of less than 150 μm.

[0119] (Step 3 and Step 4: Surface Crosslinking Step)

[0120] Next, included are a step of preparing a surface crosslinking mixture by mixing the base polymer particles with a surface crosslinking composition (Step 3), and a step of forming a surface crosslinking layer on a part of the surface of the base polymer particles by subjecting the surface crosslinking mixture to heat treatment (Step 4).

[0121] The surface crosslinking step is to initiate a crosslinking reaction on the surface of the base polymer particles in the presence of the surface crosslinking composition containing the surface crosslinking agent, and the un-crosslinked unsaturated bonds of the water-soluble ethylenically unsaturated monomer remaining on the surface are crosslinked by the surface crosslinking agent, thereby forming a superabsorbent polymer having an increased surface crosslinking density. Specifically, the surface crosslinking layer can be formed by a heat treatment process in the presence of the surface crosslinking agent, and the heat treatment process increases the surface crosslinking density, i.e., the outer crosslinking density, but does not change the inner crosslinking density, and thus the superabsorbent polymer having the prepared surface crosslinking layer has a structure in which the crosslinking density of the outside is higher than that of the inside.

[0122] Here, the modified organosilicon compound is added in at least one of before Step 3 (= the surface crosslinking step), during Step 4 (= the surface crosslinking step), or after Step 4 (= after the surface crosslinking step), and thus the modified organosilicon compound is contained in at least one of the inside or the surface of the surface crosslinking layer.

[0123] In other words, as described above, in the step of forming the aqueous gel polymer, a specific chelating agent is used to introduce the chelating agent into the inside of the base polymer particles, thereby preventing gel degradation and maintaining gel strength. In the step of forming the surface crosslinking layer, a modified organosilicon compound is used to introduce the modified organosilicon compound into at least one of the inside or the surface of the surface crosslinking layer, thereby improving the liquid permeability without using a large amount of a liquid permeability-improving compound, thereby achieving the effect of improving the liquid permeability without reducing the effect of the chelating agent, and thus the under-pressure absorbency, the liquid permeability, and the gel strength of the absorbent polymer can be simultaneously improved.

[0124] First, in the step of preparing the surface crosslinking mixture by mixing the base polymer particles with the surface crosslinking composition (step 3), the surface crosslinking composition contains a surface crosslinking agent for surface crosslinking, and can further contain water and / or a hydrophilic organic solvent.

[0125] The aforementioned description can be equally applied to the components and contents of the surface crosslinking agent contained in the surface crosslinking composition.

[0126] The surface crosslinking composition can contain water and / or a hydrophilic organic solvent as a medium. Thus, the surface crosslinking agent, etc. can be uniformly dispersed in the base polymer particles. In this regard, in order to induce uniform dissolution / dispersion of the surface crosslinking agent, prevent agglomeration of the base polymer particles, and at the same time optimize the surface penetration depth of the surface crosslinking agent, the contents of water and the hydrophilic organic solvent can be determined by controlling the addition ratio with respect to 100 parts by weight of the base polymer particles.

[0127] The surface crosslinking composition can be prepared as a surface crosslinking mixture by mixing with the base polymer particles, and the mixing method thereof is not particularly limited. For example, a method of adding and mixing the surface crosslinking composition and the base polymer particles in a reactor, a method of spraying the surface crosslinking agent composition onto the base polymer particles, a method of mixing them by continuously feeding the base polymer particles and the surface crosslinking agent composition into a continuously operated mixer, etc. can be used.

[0128] Next, included is a step of forming a surface crosslinking layer on a part of the surface of the base polymer particles by heat-treating the surface crosslinking mixture (step 4);

[0129] The step of forming a surface crosslinking layer can be performed by heat-treating at a temperature of 110°C to 200°C or 110°C to 150°C for about 30 minutes or more. More specifically, the above temperature is determined as the maximum reaction temperature, and the surface crosslinking can be performed by heat-treating at the maximum reaction temperature for 30 minutes to 80 minutes or 40 minutes to 70 minutes.

[0130] By satisfying these surface crosslinking process conditions (in particular, the temperature rise condition and the reaction condition at the maximum reaction temperature), a superabsorbent polymer that appropriately satisfies more excellent properties such as the liquid permeability under pressure, etc. can be prepared.

[0131] The means for elevating the temperature for the surface crosslinking reaction is not particularly limited. The heating can be performed by providing a heating medium or by directly providing a heat source. In this regard, the kind of the applicable heating medium can include steam, hot air, a hot fluid such as hot oil, etc., but is not limited thereto. The temperature of the heating medium provided can be appropriately selected in consideration of the manner of the heating medium, the heating rate, and the target temperature of the heating. Meanwhile, as the heat source directly provided, an electric heater or a gas heater can be used, but is not limited to these examples.

[0132] According to one embodiment of the present application, in the step of preparing the surface crosslinking mixture (step 3), a modified organosilicon compound can also be included, and thus the modified organosilicon compound can be included in the interior and / or on the surface of the surface crosslinking layer. The foregoing description can equally apply to the components and contents of the modified organosilicon compound.

[0133] According to one embodiment of the present application, in the step of forming the surface crosslinking layer by heat treatment (step 4), a modified organosilicon compound can also be included, and thus the modified organosilicon compound can be included in the interior and / or on the surface of the surface crosslinking layer. The foregoing description can equally apply to the components and contents of the modified organosilicon compound.

[0134] According to one embodiment of the present application, after the step of forming the surface crosslinking layer by heat treatment (step 4), a modified organosilicon compound can also be included, and thus the modified organosilicon compound can be included on the surface of the surface crosslinking layer. The foregoing description can equally apply to the components and contents of the modified organosilicon compound.

[0135] The process after the step of forming the surface crosslinking layer by heat treatment (step 4) is not particularly limited, but can be performed together with the post-treatment process (e.g., a cooling process, a hydration process, and a process of injecting an additive) commonly applied in the art, but is not limited thereto.

[0136] According to one embodiment of the present application, in at least one of the step of preparing the surface crosslinking mixture (step 3) or the step of forming the surface crosslinking layer by heat treatment (step 4) or after the step of forming the surface crosslinking layer by heat treatment (step 4), a modified organosilicon compound can also be included, and thus the modified organosilicon compound can be included in the interior and / or on the surface of the surface crosslinking layer. The foregoing description can equally apply to the components and contents of the modified organosilicon compound.

[0137] Hereinafter, the effects and advantages of the present application will be described in more detail with reference to specific exemplary embodiments of the present application. However, these exemplary embodiments are provided only for exemplification of the present application, and the scope of the present application is not limited thereto.

[0138] [Examples and Comparative Examples]

[0139] Example 1

[0140] (Step 1: polymerization step)

[0141] Into a 3 L glass container equipped with a stirrer and a thermometer, 500 g of acrylic acid, 800 ppmw (relative to 100 parts by weight of acrylic acid) of ethylene glycol diglycidyl ether as an internal crosslinking agent, and 80 ppmw (relative to 100 parts by weight of acrylic acid) of diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide as a photopolymerization initiator were introduced and dissolved, and then 627 g of a 31.5% sodium hydroxide solution was added to prepare an aqueous solution of water-soluble unsaturated monomers (degree of neutralization: 70 mol%; total solid content: 44.9% by weight). After the temperature of the aqueous solution of water-soluble unsaturated monomers was increased due to heat of neutralization and became 40°C, the mixed solution was put into a square container (60 cm wide, 60 cm high) containing 1,000 ppmw (relative to 100 parts by weight of acrylic acid) of sodium persulfate as a thermal polymerization initiator, 800 ppmw (relative to 100 parts by weight of acrylic acid) of a capsule blowing agent F36D, 800 ppmw (relative to 100 parts by weight of acrylic acid) of sodium dodecyl sulfate, and 300 ppmw (relative to 100 parts by weight of acrylic acid) of DTPA-5Na as a chelating agent, and then UV irradiation (irradiation dose: 10 mW / cm2) was performed for 1 minute to perform UV polymerization, thereby obtaining a water-containing gel polymer sheet. 2

[0142] (Step 2: step of performing drying, pulverization, and size sorting)

[0143] The obtained water-containing gel polymer sheet was passed through a chopper having a hole size of 16 mm to prepare a crumb.

[0144] Next, the crumb was dried in an oven capable of transferring the air volume up and down. The drying was performed by multiple stages, and specifically, it was performed using an air flow oven at 170°C for 30 minutes (upward flow for 5 minutes - downward flow for 5 minutes - upward flow for 5 minutes - downward flow for 5 minutes - upward flow for 5 minutes - downward flow for 5 minutes). The dry polymer obtained by the drying process was pulverized with a pulverizer, and then size sorted by an ASTM standard sieve to obtain base polymer particles having a particle size of 150 μm to 850 μm.

[0145] (Steps 3 and 4: surface crosslinking step)

[0146] ​First, a surface crosslinking composition containing 6 parts by weight of water, 3 parts by weight of methanol, 0.1 parts by weight of aluminum sulfate, 0.05 parts by weight of ethylene glycol diglycidyl ether (EGDGE) was prepared (with respect to 100 parts by weight of base polymer particles).

[0147] Thereafter, a surface crosslinking mixture in which 100 parts by weight of base polymer particles, 9.15 parts by weight of the prepared surface crosslinking composition, and 0.005 parts by weight of a carboxyl-modified organosilicon compound (with respect to 100 parts by weight of base polymer particles) were uniformly mixed was prepared.

[0148] The surface crosslinking mixture was supplied to a surface crosslinking reactor and a surface crosslinking reaction of the base polymer particles was performed at 130°C for 40 minutes. Thereafter, 0.05 parts by weight of fumed silica was mixed to obtain a superabsorbent polymer.

[0149] Example 2

[0150] A superabsorbent polymer was prepared in the same manner as in Example 1, except that 800 ppmw (with respect to 100 parts by weight of acrylic acid) of a chelating agent DTPA-5Na was used in the polymerization step 1 in Example 1.

[0151] Example 3

[0152] A superabsorbent polymer was prepared in the same manner as in Example 1, except that 1,000 ppmw (with respect to 100 parts by weight of acrylic acid) of EDTA was used instead of DTPA-5Na as a chelating agent in the polymerization step 1 in Example 1.

[0153] Example 4

[0154] A superabsorbent polymer was prepared in the same manner as in Example 1, except that 0.01 parts by weight (with respect to 100 parts by weight of base polymer particles) of a carboxyl-modified organosilicon compound was used in the surface crosslinking steps 3 and 4 in Example 1.

[0155] Example 5

[0156] A superabsorbent polymer was prepared in the same manner as in Example 1, except that 0.005 parts by weight (with respect to 100 parts by weight of base polymer particles) of a polyether-modified organosilicon compound was used instead of a carboxyl-modified organosilicon compound in the surface crosslinking steps 3 and 4 in Example 1.

[0157] Comparative Example 1

[0158] A superabsorbent polymer was prepared in the same manner as in Example 1, except that no modified organosilicon compound was used in the surface crosslinking steps 3 and 4 in Example 1.

[0159] Comparative Example 2

[0160] The superabsorbent polymer was prepared in the same manner as in Example 1, except that no chelating agent was used in the polymerization step 1 in Example 1, and no modified organosilicon compound was used in the surface crosslinking steps 3 and 4 in Example 1.

[0161] Comparative Example 3

[0162] The superabsorbent polymer was prepared in the same manner as in Example 1, except that no chelating agent was used in the polymerization step 1 in Example 1.

[0163] Comparative Example 4

[0164] The superabsorbent polymer was prepared in the same manner as in Example 1, except that no chelating agent was used in the polymerization step 1 in Example 1, and 0.03 parts by weight (relative to 100 parts by weight of base polymer particles) of DTPA-5Na was additionally used in the surface crosslinking steps 3 and 4 in Example 1.

[0165] Comparative Example 5

[0166] The superabsorbent polymer was prepared in the same manner as in Example 1, except that no chelating agent was used in the polymerization step 1 in Example 1, and 0.03 parts by weight (relative to 100 parts by weight of base polymer particles) of EDTMP-5Na was additionally used in the surface crosslinking steps 3 and 4 in Example 1.

[0167] Comparative Example 6

[0168] The superabsorbent polymer was prepared in the same manner as in Example 1, except that 0.005 parts by weight (relative to 100 parts by weight of base polymer particles) of an epoxy-modified organosilicon compound (KF 101, Shinetsu) was used instead of the carboxyl-modified organosilicon compound in the surface crosslinking steps 3 and 4 in Example 1.

[0169] Comparative Example 7

[0170] The superabsorbent polymer was prepared in the same manner as in Example 1, except that 0.005 parts by weight (relative to 100 parts by weight of base polymer particles) of an amino-modified organosilicon compound (KF 808, Shinetsu) was used instead of the carboxyl-modified organosilicon compound in the surface crosslinking steps 3 and 4 in Example 1.

[0171] [Experimental Example]

[0172] For the superabsorbent polymers containing base polymers prepared in the examples and comparative examples, physical properties were evaluated by the following methods, and the results are shown in Table 1.

[0173] Unless otherwise specified, all of the following physical properties were evaluated at room temperature (25 ± 1°C), and the physiological saline or saline means a 0.9 wt% sodium chloride (NaCl) aqueous solution, and the ascorbate saline means a 0.9 wt% sodium chloride (NaCl) and 0.005 wt% ascorbic acid aqueous solution.

[0174] (1) Centrifuge Retention Capacity (CRC)

[0175] From the superabsorbent polymers prepared in the examples and comparative examples, particles having a particle size of 150 μm to 850 μm were taken, and centrifuge retention capacity (CRC) by unloading absorption rate was measured according to European Disposables and Nonwovens Association (EDANA) Standard EDANA WSP 241.2.

[0176] In detail, each of the absorbent polymer samples W0 (g) (about 0.2 g) obtained by the examples and comparative examples was uniformly put into a bag made of a nonwoven fabric, and then sealed. Then, the bag was immersed in a physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was removed from the bag using a centrifuge at 250 G for 3 minutes, and then the weight W2 (g) of the bag was measured. Further, the same procedure was performed without using the polymer, and then the resulting weight W1 (g) was measured. By using each of the weights thus obtained, CRC (g / g) was calculated according to the following Equation 2.

[0177] [Equation 2]

[0178]

[0179] (2) Spontaneous Absorption Rate (seconds)

[0180] From the superabsorbent polymers prepared in the examples and comparative examples, particles having a particle size of 150 μm to 850 μm were taken, and 2 g of the superabsorbent polymer sample was added to 50 mL of physiological saline, and stirred at 600 rpm, and the time taken for the vortex to disappear was measured in seconds.

[0181] (3) Absorbency under Pressure (AUP)

[0182] The superabsorbent polymer particles prepared from the examples and comparative examples were taken particles having a size of 150 μm to 850 μm, and the absorbency under pressure (AUP) at a pressure of 0.7 psi was measured according to EDANA method WSP 242.3-10.

[0183] First, a 400 mesh stainless steel mesh was installed at the bottom of a plastic cylinder having an inner diameter of 60 mm. The superabsorbent polymer W0 (g) was uniformly spread on the steel mesh at room temperature and humidity of 50%, and a piston that can uniformly provide a load of 0.7 psi was placed thereon, wherein the outer diameter of the piston is slightly smaller than 60 mm, there is no gap between the inner wall of the cylinder and the piston, and the piston does not interfere with the up-and-down movement of the cylinder. At this time, the weight W3 (g) of the measuring device was measured.

[0184] After placing a glass filter having a diameter of 90 mm and a thickness of 5 mm in a petri dish having a diameter of 150 mm, a physiological saline solution consisting of 0.9 wt% sodium chloride was poured until the surface level of the physiological saline solution became flush with the upper surface of the glass filter. A filter paper having a diameter of 90 mm was placed thereon. The measuring device was installed on the filter paper so as to absorb the liquid under load for 1 hour. After 1 hour, the weight W4 (g) was measured after lifting the measuring device. The absorbency under pressure (g / g) was calculated according to Equation 3 below by using each weight thus obtained.

[0185] [Equation 3]

[0186]

[0187] (4) Liquid Permeability (seconds)

[0188] The superabsorbent polymer prepared from the examples and comparative examples was obtained using a #30-#50 sieve to size the polymer particles, and the liquid permeability was calculated according to Equation 1 below.

[0189] [Equation 1]

[0190] Liquid permeability (sec) = T1 - B

[0191] In Equation 1,

[0192] T1 denotes the time taken for the liquid level to drop from 40 ml to 20 ml when 0.2 g of a superabsorbent polymer sample is placed in a chromatographic column having a glass filter, a saline solution is applied to a saline solution volume of 50 ml and left for 30 minutes, then a piston having a weight of 0.3 psi is placed and left for 1 minute, and a lower valve is opened, and

[0193] B represents the time taken for the liquid level to drop from 40 ml to 20 ml when a piston having a weight of 0.3 psi is placed in a column filled with saline.

[0194] (5) Gel Strength (N)

[0195] Particles of the superabsorbent polymer prepared from the examples and comparative examples were taken in a size of 150 μm to 850 μm, and 2.5 g of a sample of the superabsorbent polymer was immersed in 50 g of an ascorbate aqueous solution and allowed to swell in an oven at 40°C for 24 hours. The gel strength of the swelled base polymer particles was measured using a tensile tester.

[0196] In detail, the swelled base polymer particles were measured using a digital force gauge FGP-2, which is a tensile tester. At the time of tip penetration, the peak value (N) of the force applied to the tip was measured three times according to the following conditions, and the arithmetic mean thereof was determined as the gel strength (unit: N).

[0197] Tip size: tip diameter 10 ± 0.1 mm

[0198] Beaker size: 50 ± 0.1 mm

[0199] Penetration speed: 500 ± 0.5 mm / minute

[0200] [Table 1]

[0201]

[0202] As shown in the results of Table 1, it was determined that the superabsorbent polymer according to the examples of the present application can have improved under-pressure absorbency, liquid permeability, and gel strength simultaneously by including a specific chelating compound inside the base polymer and including a modified silicone compound in the surface crosslinked layer of the base polymer, which are required for improving the rewet characteristics.

[0203] In the case of the comparative examples in which one or more of the two components of the present application were not included or were not introduced into different steps, it was difficult to improve the under-pressure absorbency, liquid permeability, and gel strength simultaneously.

Claims

1. A superabsorbent polymer, comprising: A base polymer particle comprising a crosslinked polymer in which a water-soluble olefinic unsaturated monomer having at least partially neutralized acidic groups is crosslinked in the presence of an aminocarboxylic acid-based metal chelating agent; and A surface crosslinking layer is formed by further crosslinking the crosslinked polymer on a portion of the surface of the base polymer particles via a surface crosslinking agent. At least one of the interior or surface of the said surface crosslinking layer contains a modified organosilicon compound. The modified organosilicon compound has a polysiloxane backbone, and At least one of the side chains or ends of the polysiloxane contains one or more carboxylic acid groups or polyether groups.

2. The superabsorbent polymer according to claim 1, wherein the aminocarboxylic acid-based metal chelating agent comprises one or more of the following: ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylenediaminetriacetic acid, triethylenetetraaminehexaacetic acid, trans-1,2-diaminocyclohexanetetraacetic acid, and their metal salts.

3. The superabsorbent polymer according to claim 1, wherein the aminocarboxylic acid-based metal chelating agent is included in an amount from 50 ppmw to 5,000 ppmw relative to the water-soluble olefinic unsaturated monomer.

4. The superabsorbent polymer according to claim 1, wherein the modified organosilicon compound is included in an amount of 0.001 parts by weight to 0.1 parts by weight relative to the base polymer particles.

5. The superabsorbent polymer according to claim 1, wherein the absorption rate (AUP) at a centrifugal pressure of 0.7 psi according to EDANA method WSP 242.3-10 is 13.0 g / g or greater.

6. The superabsorbent polymer according to claim 1, wherein the liquid permeability determined according to Equation 1 is 180 seconds or less: [Equation 1] Liquid permeability (seconds) = T1 - B In equation 1, T1 represents the time it takes for the liquid level to drop from 40 ml to 20 ml when a 0.2 ± 0.0005 g superabsorbent polymer sample is placed in a chromatographic column with a glass filter, brine is added to a volume of 50 ml and allowed to stand for 30 minutes, then a stopcock with a weight of 0.3 psi is placed and allowed to stand for 1 minute, and the lower valve is opened. B represents the time it takes for the liquid level to drop from 40 ml to 20 ml when the piston (0.3 psi) with a weight of 0.3 psi is placed in the chromatographic column containing brine.

7. The superabsorbent polymer according to claim 1, wherein the gel strength measured by immersing 2.5 g of the superabsorbent polymer sample in 50 g of ascorbate water, allowing it to swell in an oven at 40°C for 24 hours, and then measuring the swollen superabsorbent polymer using a tensile-compression testing machine, is 0.70 N or greater.

8. A method for preparing the superabsorbent polymer according to claim 1, the method comprising the following steps: A hydrogel polymer is formed by crosslinking a water-soluble olefinic unsaturated monomer having at least partially neutralized acidic groups in the presence of an aminocarboxylic acid-based metal chelating agent (step 1). Basic polymer particles are formed by drying, pulverizing and size sorting the hydrogel polymer (step 2). A surface crosslinking mixture is prepared by mixing the base polymer particles with a surface crosslinking composition (step 3). as well as A surface cross-linking layer is formed on a portion of the surface of the base polymer particles by heat treatment of the surface cross-linking mixture (step 4). A modified organosilicon compound is added to at least one of steps 3 and 4, or after step 4. The modified organosilicon compound has a polysiloxane backbone, and At least one of the side chains or ends of the polysiloxane contains one or more carboxylic acid groups or polyether groups.

Images