Super absorbent polymer and preparation method thereof

Abstract

The present invention relates to a superabsorbent resin and a method for manufacturing the same. According to the present invention, a superabsorbent resin with excellent water permeability can be obtained, which exhibits excellent absorption properties while reducing the content of water-soluble components so as not to cause skin damage.

Description

Technology Field

[0001] The present invention relates to a superabsorbent resin having excellent basic absorption performance as well as reduced water-soluble components, and a method for manufacturing the same. Background Technology

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

[0004] In most cases, these superabsorbent polymers are widely used in the field of hygiene products, such as diapers and sanitary pads. For these applications, they need to exhibit high absorption capacity for moisture and prevent absorbed water from escaping even under external pressure. Additionally, they must maintain their shape well even after swelling due to water absorption to demonstrate excellent permeability.

[0005] Meanwhile, during the manufacturing process of superabsorbent polymers, extractables, which are uncrosslinked polymers, are generated. While a high content of extractables has the advantage of enhancing the solution absorption characteristics of the superabsorbent polymer, it can also cause adverse effects, such as skin irritation, as the extractables easily leach out when the superabsorbent polymer comes into contact with a liquid. Furthermore, when the content of extractables is high, the leached extractables mostly remain on the surface of the superabsorbent polymer, making the polymer sticky and reducing its permeability, which is the ability to rapidly transfer a solution to another superabsorbent polymer.

[0006] Therefore, there is a need to develop excellent superabsorbent resins that maintain high absorption characteristics while reducing the content of water-soluble components. The problem to be solved

[0008] This specification aims to provide a method for manufacturing a superabsorbent resin that not only has excellent basic absorption performance but also has a reduced content of water-soluble components.

[0009] In addition, the present specification aims to provide a superabsorbent resin that not only has excellent basic absorption performance but also has a reduced content of water-soluble components. means of solving the problem

[0011] The present invention comprises the step of forming a hydrogel polymer by crosslinking a water-soluble ethylene-based unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal crosslinking agent and a polymerization initiator;

[0012] A step of drying, grinding, and classifying the above-mentioned hydrogel polymer to form a base resin powder; and

[0013] The method includes the step of surface-crosslinking the base resin powder in the presence of a surface-crosslinking liquid to form superabsorbent resin particles.

[0014] The above surface crosslinking agent comprises a polyvalent epoxy compound and a compound represented by the following chemical formula 1,

[0015] A method for manufacturing a superabsorbent resin is provided.

[0016] [Chemical Formula 1]

[0017]

[0018] In the above chemical formula 1,

[0019] n is an integer from 1 to 5.

[0021] In addition, the present invention comprises a base resin obtained by polymerizing and internally crosslinking a monomer composition comprising an acrylic acid-based monomer in which at least a portion of the acidic groups are neutralized, and

[0022] It includes a surface cross-linked layer formed on the surface of the above base resin, and

[0023] The above surface crosslinking layer comprises a polyvalent epoxy compound and crosslinking bonds derived from a compound represented by Chemical Formula 1,

[0024] Provides a superabsorbent resin.

[0026] Furthermore, the terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention.

[0027] A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0028] In this specification, terms such as “comprising,” “comprising,” or “having” are used to describe features, numbers, steps, components, or combinations thereof that are implemented, and do not exclude one or more other features, numbers, steps, components, combinations thereof, or the possibility of addition.

[0029] Additionally, in this specification, where each layer or element is referred to as being formed "on" or "above" each layer or element, it means that each layer or element is formed directly on each layer or element, or that another layer or element may be additionally formed between each layer, on an object, or on a substrate.

[0030] 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.

[0031] The terms "polymer" or "polymer" used in this specification refer to a state in which water-soluble ethylene-based unsaturated monomers are polymerized, and may encompass all ranges of moisture content or particle size. 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.

[0032] In addition, the term "superabsorbent resin particles" refers to a particulate material comprising a cross-linked polymer in which a water-soluble ethylene-based unsaturated monomer containing an acidic group and at least some of the acidic group is neutralized is polymerized and cross-linked by an internal cross-linking agent.

[0033] Additionally, the term "superabsorbent resin" is used to encompass, depending on the context, a cross-linked polymer formed by polymerizing a water-soluble ethylene-based unsaturated monomer containing acidic groups and at least some of said acidic groups neutralized, or a base resin in the form of a powder consisting of said cross-linked polymer and said superabsorbent resin particles, or said cross-linked polymer and said base resin that have been made into a state suitable for commercialization through additional processes, such as surface cross-linking, fine powder reassembly, drying, grinding, classification, etc. Accordingly, the term "superabsorbent resin composition" can be interpreted as a composition containing a superabsorbent resin, that is, containing a plurality of superabsorbent resin particles.

[0035] The present invention will be described in detail below.

[0036] According to one embodiment of the present invention, a method for manufacturing a superabsorbent resin is provided, comprising the steps of: forming a hydrogel polymer by crosslinking a water-soluble ethylene-based unsaturated monomer having at least some neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator; forming a base resin powder by drying, grinding, and classifying the hydrogel polymer; and forming superabsorbent resin particles by surface crosslinking the base resin powder in the presence of a surface crosslinking agent, wherein the surface crosslinking agent comprises a polyvalent epoxy compound and a compound represented by the following chemical formula 1.

[0037] [Chemical Formula 1]

[0038]

[0039] In the above chemical formula 1,

[0040] n is an integer from 1 to 5.

[0042] The inventors of the present invention have discovered that when a surface crosslinking liquid is used as a component of a polyvalent epoxy compound and a compound represented by Formula 1, the surface of the superabsorbent resin can have crosslinking bonds derived therefrom formed therefrom on the surface of the superabsorbent resin, thereby reducing the content of water-soluble components without lowering the water retention capacity of the superabsorbent resin, and thus completed the present invention.

[0044] Hereinafter, the method for manufacturing a superabsorbent resin of one embodiment will be described in more detail.

[0046] (polymerization)

[0047] First, as a step of forming a hydrogel polymer, the method comprises crosslinking a monomer mixture comprising a polymerization initiator, an internal crosslinking agent, and a water-soluble ethylene-based unsaturated monomer having at least some of neutralized acidic groups.

[0049] The monomer mixture, which is the raw material for the superabsorbent resin, may include a water-soluble ethylene-based unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized, more specifically, an acrylic acid-based monomer and a polymerization initiator.

[0051] (Monomer)

[0052] The above acrylic acid monomer is a compound represented by the following chemical formula 1:

[0053] [Chemical Formula 1]

[0054] R1-COOM1

[0055] In the above chemical formula 1,

[0056] R1 is an alkyl group having 2 to 5 carbon atoms containing unsaturated bonds, and

[0057] M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0059] The above acrylic acid-based monomer may specifically include one or more selected from the group consisting of, for example, acrylic acid, methacrylic acid, and their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts.

[0060] Here, the acrylic acid monomer may have an acidic group and at least a portion of the acidic group may be neutralized. Preferably, the monomer may be partially neutralized with a basic substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. In this case, the degree of neutralization of the acrylic acid monomer may be controlled to less than about 70 mol%, or about 40 to about 69 mol%, or about 50 to about 65 mol%.

[0061] If the degree of neutralization is excessively high, the neutralized monomer may precipitate, making it difficult for polymerization to proceed smoothly. Furthermore, the effect of additional neutralization after the initiation of surface crosslinking is substantially lost, so the degree of crosslinking of the surface crosslinked layer is not optimized, and the permeability of the superabsorbent resin may not be sufficient. 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 similar to elastic rubber, which is difficult to handle.

[0062] The concentration of the monomer may be about 20 to about 60 weight%, or about 30 to about 55 weight%, or about 40 to about 50 weight% with respect to the monomer mixture containing the raw material and solvent of the superabsorbent resin, and may be appropriately adjusted considering the polymerization time and reaction conditions, etc.

[0063] If the concentration of the above monomer becomes excessively low, the yield of the superabsorbent resin may decrease, leading to economic problems; conversely, if the concentration of the monomer becomes excessively high, process problems may arise, such as the precipitation of some of the monomer or a decrease in grinding efficiency during the grinding of the polymerized hydrogel polymer, and the physical properties of the superabsorbent resin may deteriorate.

[0065] (Polymer initiator)

[0066] The polymerization initiator used in the method for manufacturing a superabsorbent resin of the above embodiment is not particularly limited as long as it is one that is generally used in the manufacture of superabsorbent resins.

[0067] Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator based on UV irradiation, depending on the polymerization method. However, even in the photopolymerization method, a certain amount of heat may be generated by ultraviolet irradiation, and since a certain amount of heat may also be generated as the polymerization reaction, which is an exothermic reaction, proceeds, a thermal polymerization initiator may additionally be included.

[0068] The above photopolymerization initiator can be used without limitation on its composition as long as it is a compound capable of forming radicals by light such as ultraviolet light.

[0069] For example, one or more selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone may be used as the above photopolymerization initiator. Meanwhile, as a specific example of acyl phosphine, commercially available lucirin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide, may be used. A wider variety of photoinitiators is well described in Reinhold Schwalm's book 'UV Coatings: Basics, Recent Developments and New Applications (Elsevier 2007)' p. 115, and is not limited to the examples described above.

[0070] In addition, one or more initiators selected from the group consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid may be used as the thermal polymerization initiator. Specifically, examples of persulfate-based initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8), while examples of azo-based initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2, Examples include 2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride and 4,4-azobis-(4-cyanovaleric acid). A wider variety of thermal polymerization initiators are well described in Odian's book 'Principles of Polymerization' (Wiley, 1981), p. 203, and are not limited to the examples mentioned above.

[0072] Such a polymerization initiator may be added at a concentration of about 0.001 to 1 weight%, preferably about 0.1 to about 0.9 weight%, based on the total weight of the monomer mixture. If the concentration of the polymerization initiator is excessively low, the polymerization rate may be slowed 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 higher than the above range, the polymer chains forming the network may become shorter, which may lead to a higher content of water-soluble components and a lower pressurized absorption capacity, thereby degrading the physical properties of the resin, which is undesirable.

[0074] (Internal crosslinking agent)

[0075] According to one embodiment of the invention, the monomer mixture comprises an internal crosslinking agent as a raw material for a superabsorbent resin. This internal crosslinking agent is intended to crosslink the interior of a polymer in which acrylic acid-based monomers are polymerized, i.e., a base resin, and is distinguished from a surface crosslinking agent intended to crosslink the surface of the polymer.

[0077] The types of such internal crosslinking agents are not particularly limited, and any internal crosslinking agent that has been available for use in the manufacture of superabsorbent resins can be used. Specific examples of such internal crosslinking agents include poly(meth)acrylate compounds of polyols having 2 to 20 carbon atoms, polyglycidyl ether compounds of polyols having 2 to 20 carbon atoms, or allyl (meth)acrylate compounds having 2 to 20 carbon atoms.

[0078] More specific examples of these internal crosslinking agents include trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, Examples include propylene glycol diglycidyl ether or polypropylene glycol diglycidyl ether, and various other polyfunctional compounds can also be used as internal crosslinking agents.

[0080] Such internal crosslinking agents are included at a concentration of about 0.01 to about 1 weight%, or about 0.05 to about 0.8 weight%, or about 0.2 to about 0.7 weight% based on the total weight of the monomer mixture, thereby introducing a crosslinking structure into the hydrogel polymer and the base resin powder formed therefrom.

[0081] If the concentration of the internal crosslinking agent is excessively low, the absorption rate of the superabsorbent resin may be reduced and the gel strength may be weakened, which is undesirable. Conversely, if the concentration of the internal crosslinking agent is excessively high, the absorption capacity of the superabsorbent resin may be reduced, making it undesirable as an absorbent.

[0083] (Mixture of other additives and monomers)

[0084] In addition, the above monomer mixture may additionally include, in some cases, a foaming agent and a foam stabilizer, etc.

[0085] The above foaming agent forms pores within the hydrogel polymer by foaming within the monomer mixture during polymerization, thereby increasing the surface area of ​​the hydrogel polymer.

[0086] The above foaming agent may use carbonates, for example, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium bicarbonate, magnesium bicarbonate, or magnesium carbonate.

[0087] In addition, it is preferable to use the blowing agent at a concentration of 1,500 ppmw or less, or about 1,300 ppmw or less, relative to the weight of the water-soluble ethylene-based unsaturated monomer. If the amount of blowing agent used is too high, the number of pores becomes too large, which can cause the gel strength of the superabsorbent resin to decrease and the density to decrease, potentially leading to problems with distribution and storage. Furthermore, it is preferable to use the blowing agent at a concentration of 500 ppmw or more, or 1,000 ppmw or more, relative to the weight of the water-soluble ethylene-based unsaturated monomer.

[0089] Meanwhile, in the manufacturing method of the above-described embodiment, the monomer mixture may further include additives such as a thickener, a plasticizer, a preservative stabilizer, and an antioxidant as needed.

[0091] A monomer mixture comprising the above-described monomer mixture, a polymerization initiator, an internal crosslinking agent, and a water-soluble ethylene-based unsaturated monomer having at least some neutralized acidic groups, and optionally, other additives, can be prepared in the form of a monomer mixture solution dissolved in a solvent.

[0093] The solvent that can be used at this time may be used without limitation in composition as long as it can dissolve the components described above, and for example, one or more selected from 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, butyloractone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide may be used in combination.

[0095] The above solvent may be included in the remainder with respect to the total content of the monomer mixture so that each component is controlled to the concentration range described above.

[0097] (polymerization)

[0098] Meanwhile, the method of forming a hydrogel polymer by thermally polymerizing or photopolymerizing such a monomer mixture is also not limited in composition, as long as it is a commonly used polymerization method.

[0099] Specifically, polymerization methods can be broadly classified into thermal polymerization and photopolymerization depending on the polymerization energy source.

[0100] Typically, thermal polymerization can be carried out in a reactor equipped with a stirring shaft such as a kneader, and photopolymerization can be carried out in a reactor equipped with a movable conveyor belt; however, the polymerization method described above is merely an example, and the present invention is not necessarily limited to the polymerization method described above.

[0101] For example, a hydrogel polymer obtained by thermal polymerization in a reactor such as a kneader equipped with a stirring shaft as described above, by supplying hot air or heating the reactor, may be in the form of several centimeters to several millimeters depending on the shape of the stirring shaft equipped in the reactor. Specifically, the size of the hydrogel polymer obtained may vary depending on the concentration and injection speed of the monomer mixture injected, and typically, a hydrogel polymer with a weight average particle size of 2 to 50 mm or 3 to 30 mm can be obtained.

[0102] In addition, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the form of the hydrogel polymer typically obtained may be a sheet with the width of the belt. At this time, the thickness of the polymer sheet may vary depending on the concentration and injection speed of the injected monomer mixture, and it is preferable to supply the monomer mixture so that a hydrogel polymer in the form of a sheet with a thickness of typically 0.5 to 5 cm or 1 to 3 cm can be obtained.

[0103] If the monomer mixture is supplied to the extent that the thickness of the polymer on the sheet is excessively thin, the production efficiency is low and is undesirable. If the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction may not occur evenly across the entire thickness due to the excessive thickness.

[0104] The typical moisture content of the hydrogel polymer obtained by such a method may be about 40 to about 80 weight%, or about 50 to about 70 weight%. Meanwhile, throughout this specification, "moisture content" refers to the amount of water contained in the total weight of the hydrogel polymer, which is the value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer.

[0105] Specifically, it is 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 are set by raising the temperature from room temperature to about 180°C and maintaining it at about 180°C, and the total drying time is set to about 20 minutes, including the temperature raising step of about 5 minutes, to measure the moisture content.

[0107] (dry)

[0108] Next, a drying step is performed on the obtained hydrogel polymer.

[0109] At this time, if necessary, a coarse grinding step may be added before drying to increase the efficiency of the drying step.

[0110] At this time, the grinder used is not limited in its configuration, but specifically, it may include any one selected from the group of grinding machines consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter, but is not limited to the examples described above.

[0111] At this time, the grinding step can be performed so that the particle size of the hydrogel polymer is about 2 to about 10 mm, or about 3 to about 8 mm. The particle size of such hydrogel polymer can be defined as the longest straight distance among the straight distances connecting any point on the surface of the hydrogel polymer.

[0112] Grinding to a particle size of less than about 2 mm is not technically easy due to the high water content of the hydrogel polymer, and aggregation may occur between the ground particles. On the other hand, if the particle size is ground to more than about 10 mm, the effect of increasing the efficiency of the subsequent drying step is negligible.

[0113] Drying is performed on the hydrogel polymer immediately after polymerization, which is either ground as described above or has not undergone a grinding step.

[0114] At this time, the drying temperature of the above drying step may be about 150 to about 250 ℃. If the drying temperature is less than about 150 ℃, the drying time becomes excessively long and there is a risk that the physical properties of the finally formed superabsorbent resin will deteriorate. If the drying temperature exceeds about 250 ℃, only the surface of the polymer is dried excessively, which may result in fine powder being generated during the subsequent grinding process and there is a risk that the physical properties of the finally formed superabsorbent resin will deteriorate. Therefore, the above drying may be carried out at a temperature of about 150 to about 200 ℃, and more preferably at a temperature of about 160 to 180 ℃.

[0115] Meanwhile, regarding the drying time, considering process efficiency, etc., it may be carried out for about 20 to about 90 minutes or about 30 to about 70 minutes, but is not limited thereto.

[0116] The drying method of the above drying step can also be used without limitation in its composition, as long as it is a method commonly used for drying hydrogel polymers. Specifically, the drying step can be carried out using methods such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation.

[0117] The moisture content of the polymer after the drying step may be about 0.1 to about 10 weight%, or about 1 to about 8 weight%. If the moisture content after drying becomes excessively low, the water gel polymer may deteriorate during the drying process, which may lower the physical properties of the superabsorbent resin; conversely, if the moisture content becomes excessively high, the absorption performance may be reduced due to a large amount of moisture within the superabsorbent resin, or it may become difficult to proceed with subsequent processes.

[0118] Next, a step of grinding the dried polymer obtained through such a drying step is performed.

[0119] The polymer powder obtained after the grinding step may have a particle size of about 150 to about 850 μm. Specifically, the grinder used to grind to such a particle size may be a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog mill, but the invention is not limited to the examples described above.

[0120] In addition, to manage the physical properties of the superabsorbent resin powder that is finalized after such a grinding step, a separate process may be performed to classify the polymer powder obtained after grinding according to particle size, and the polymer powder may be classified into a certain weight ratio according to the particle size range.

[0122] (Surface bridge)

[0123] The above surface crosslinking step is a step of forming a superabsorbent resin with improved physical properties by inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a surface crosslinking liquid containing a surface crosslinking agent. Through this surface crosslinking, a surface crosslinking layer is formed on the surface of the pulverized and classified base resin powder.

[0124] Generally, since a surface crosslinking agent is applied to the surface of the base resin powder, the surface crosslinking reaction occurs on the surface of the base resin powder; this improves the crosslinking properties on the surface of the particles without substantially affecting the interior of the particles. Therefore, surface-crosslinked superabsorbent resin particles have a higher degree of crosslinking near the surface than in the interior, as the crosslinking polymer on the surface of the base resin powder undergoes additional crosslinking.

[0125] As a surface crosslinking agent according to the present invention, compounds capable of reacting with the functional groups of the base resin may be used, such as polyvalent epoxy compounds and compounds represented by the chemical formula 1.

[0126] Specifically, examples of polyvalent epoxy compounds may include one or more selected from the group consisting of ethyleneglycol diglycidyl ether, diethyleneglycol diglycidyl ether, triethyleneglycol diglycidyl ether, tetraethyleneglycol diglycidyl ether, glycerin polyglycidyl ether, and sorbitol polyglycidyl ether.

[0128] And, the compound represented by the above chemical formula 1 is a compound containing a dihydrazide functional group, and can form a crosslinked form represented by chemical formula 2 derived from the functional group of the base resin or the epoxy group of the polyvalent epoxy compound.

[0129] [Chemical Formula 2]

[0130]

[0132] In the final superabsorbent resin, the characteristic crosslinking form described above forms additional crosslinking bonds with the crosslinked polymer on the particle surface, thereby significantly reducing the content of uncrosslinked polymer chains, i.e., water-soluble components, without lowering the water retention capacity compared to existing superabsorbent resins.

[0134] In addition, in the compound of Formula 1 above, n is preferably an integer from 1 to 3.

[0135] More preferably, the compound of Formula 1 is adipic acid dihydrazide.

[0136] The surface crosslinking agent according to the present invention may further comprise a compound represented by Formula 1 on a weight basis more than the polyvalent epoxy compound. Specifically, for example, the weight ratio of the polyvalent epoxy compound to the compound represented by Formula 1 may be about 1:1 to 1:15, preferably about 1:1 to 1:10, more preferably about 1:2 to 1:8.

[0138] If the content of the polyvalent epoxy compound is excessively low compared to the compound represented by Chemical Formula 1, there may be a problem with the pressure absorption capacity of the superabsorbent resin decreasing, and if the content of the polyvalent epoxy compound is excessively high, there may be a problem with the water retention capacity of the superabsorbent resin decreasing.

[0139] If the content of the compound represented by Chemical Formula 1 is excessively low compared to the polyhydric epoxy compound, there may not be a significant effect on reducing the water-soluble component, and if the content of the compound represented by Chemical Formula 1 is excessively high, there may be a problem with the pressure absorption capacity of the superabsorbent resin decreasing.

[0141] The polyvalent epoxy compound may be included in an amount of about 0.01 to about 0.1 parts by weight, preferably about 0.03 to about 0.08 parts by weight, relative to 100 parts by weight of the base resin. If the content of the polyvalent epoxy compound is excessively low compared to the base resin, the surface crosslinking reaction may hardly occur, and if the content of the polyvalent epoxy compound is excessively high compared to the base resin, a decrease in water absorption capacity and physical properties may occur due to the progression of an excessive surface crosslinking reaction.

[0142] The compound represented by Chemical Formula 1 may be included in an amount of about 0.01 to about 1 part by weight, preferably about 0.1 to about 0.6 parts by weight, relative to 100 parts by weight of the base resin. If the content of the compound represented by Chemical Formula 1 is excessively low compared to the base resin, there may be a problem with insufficient reduction of water-soluble components, and if the content of the compound represented by Chemical Formula 1 is excessively high compared to the base resin, the amount of undissolved components not dissolved in the surface crosslinking solution increases, which may cause problems in preparing the surface crosslinking solution for proceeding the surface crosslinking reaction.

[0144] If the content of the surface crosslinking agent is excessively low, the surface crosslinking reaction hardly occurs, and if the content of the surface crosslinking agent is excessively high, a decrease in basic absorption properties such as water retention capacity may occur due to the progression of the excessive surface crosslinking reaction.

[0145] When adding the surface crosslinking agent, water may be additionally mixed together to form a surface crosslinking liquid. Adding water has the advantage of allowing the surface crosslinking agent to be evenly dispersed in the base resin. At this time, the amount of water added is preferably about 1 to about 10 parts by weight per 100 parts by weight of the base resin, for the purpose of inducing even dispersion of the surface crosslinking agent, preventing clumping of the base resin powder, and optimizing the surface penetration depth of the surface crosslinking agent.

[0147] Meanwhile, in addition to the surface crosslinking agent described above, one or more types selected from the group consisting of polyvalent metal salts, for example, aluminum salts, more specifically aluminum sulfates, potassium salts, ammonium salts, sodium salts, and hydrochloride salts may be further included.

[0148] Such polyvalent metal salts can further improve the permeability of the superabsorbent resin prepared by the method of one embodiment. Such polyvalent metal salts can be added to the surface crosslinking liquid together with the surface crosslinking agent, and can be used in an amount of about 0.01 to about 4 parts by weight per 100 parts by weight of the base resin powder.

[0149] In addition, the surface crosslinking liquid may perform a surface crosslinking reaction by further adding one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate. The inorganic material 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. Furthermore, the inorganic material may be used in an amount of about 0.05% to about 2% by weight relative to the total weight of the base resin powder.

[0150] In addition, regarding the method of adding the above-mentioned surface crosslinking agent, and optionally an inorganic material and / or a multivalent metal salt to the base resin powder, there are no limitations on the composition thereof. For example, methods such as placing the surface crosslinking agent and the base resin powder into a reaction vessel and mixing them, spraying the surface crosslinking agent onto the base resin powder, or continuously supplying the base resin powder and the surface crosslinking agent to a continuously operated mixer and mixing them may be used.

[0151] Meanwhile, a surface modification step is performed on the base resin powder by applying heat to the mixture of the base resin powder and the surface crosslinking liquid to raise the temperature.

[0152] The above surface crosslinking step can be carried out under well-known conditions depending on the type of surface crosslinking agent, for example, at a temperature of about 100 to about 200°C for about 20 minutes to about 60 minutes. In a more specific example, the above surface crosslinking step can be carried out by adding a surface crosslinking agent, etc. to a base resin powder having an initial temperature of about 20°C to about 80°C, raising the temperature to a maximum temperature of about 120°C to about 180°C or about 175 to about 195°C over about 10 minutes to about 40 minutes, and maintaining the maximum temperature for about 5 minutes to about 60 minutes.

[0153] Depending on the above surface crosslinking conditions, basic absorption characteristics such as water retention capacity of the superabsorbent resin, and liquid permeability and / or pressurized absorption capacity can be optimized together.

[0154] The means for raising the temperature for the surface crosslinking reaction is not particularly limited. Heating can be achieved by supplying a heat medium or by directly supplying a heat source. In this case, types of heat media that can be used include high-temperature fluids such as steam, hot air, and hot oil, but are not limited thereto. Furthermore, the temperature of the supplied heat medium can be appropriately selected considering the means of the heat medium, the rate of heating, and the target temperature. Meanwhile, heat sources supplied directly include heating via electricity and heating via gas, but the present invention is not limited to the examples described above.

[0156] By carrying out the surface crosslinking step described above, a superabsorbent resin can finally be manufactured according to the method of one embodiment. This superabsorbent resin includes a polyvalent epoxy compound and a compound represented by Chemical Formula 1, and can lower the content of water-soluble components through a characteristic crosslinking structure.

[0158] According to one embodiment of the invention, a method for manufacturing a superabsorbent resin is provided, wherein the centrifugal retention capacity (CRC) measured according to EDANA WSP 241.3 is about 30 g / g or more, preferably about 33 g / g or more.

[0159] In addition, according to one embodiment of the invention, a method for manufacturing a superabsorbent resin is provided in which the water-soluble component content measured according to the EDANA method WSP 270.2 is about 6% or less, preferably about 5.5% or less.

[0160] In addition, according to one embodiment of the invention, a method for manufacturing a superabsorbent resin having a pressurized absorption capacity of 26.5 g / g or more at 0.3 psi as measured according to the EDANA method WSP 242.3 is provided.

[0161] In addition, according to one embodiment of the invention, a method for manufacturing a superabsorbent resin having a Vortex absorption rate value of 26 sec or less for physiological saline is provided.

[0163] Meanwhile, according to another aspect of the present invention, a superabsorbent resin is provided comprising a base resin polymerized and internally crosslinked from a monomer composition comprising an acrylic acid-based monomer in which at least some of the acidic groups are neutralized, and a surface crosslinking layer formed on the surface of the base resin, wherein the surface crosslinking layer comprises a polyvalent epoxy compound and a crosslinking bond derived from a compound represented by Formula 1.

[0164] The above polyvalent epoxy compound and the cross-linking derived from the compound represented by Chemical Formula 1 may be included in the form represented by Chemical Formula 2, and such a superabsorbent resin may be manufactured by the manufacturing method described above.

[0165] A superabsorbent resin according to one embodiment of the invention has a centrifugal retention capacity (CRC) of about 30 g / g or more, preferably about 33 g / g or more, as measured according to EDANA WSP 241.3.

[0166] In addition, the superabsorbent resin according to one embodiment of the invention has a water-soluble component content of about 6% or less, preferably about 5.5% or less, as measured according to the EDANA method WSP 270.2.

[0167] In addition, the superabsorbent resin according to one embodiment of the invention has a pressurized absorption capacity of 0.3 psi measured according to the EDANA method WSP 242.3 of 26.5 g / g or more.

[0168] In addition, the superabsorbent resin according to one embodiment of the invention has a Vortex absorption rate value of 26 sec or less for physiological saline.

[0170] Therefore, the superabsorbent resin according to the present invention can secure excellent overall physical properties, while also resolving problems such as skin irritation, stickiness, and reduced usability caused by the leaching of water-soluble components when the superabsorbent resin comes into contact with a liquid. Effects of the invention

[0172] The superabsorbent resin produced according to the present invention not only has excellent basic absorption performance as described above, but also has a reduced content of water-soluble components, so it does not cause skin damage and has an excellent tactile feel. Specific details for implementing the invention

[0174] The operation and effects of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0176] <Example>

[0177] Example 1

[0178] 1-1: Preparation of Base Resin

[0179] A monomer composition was prepared by mixing 100 parts by weight of acrylic acid, 83.3 parts by weight of 50% caustic soda (NaOH), 89.8 parts by weight of water, and the following components.

[0180] - Internal crosslinking agent: 0.27 parts by weight (2700 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw=400) and 0.054 parts by weight (540 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw=200)

[0181] - Polymerization initiator: Cationic azo-based initiator (thermal polymerization initiator, V50) 0.1 parts by weight (1000 ppmw), hydrogen peroxide (H2O2) 0.02 parts by weight (300 ppmw), potassium persulfate (KPS) 0.2 parts by weight (2000 ppmw)

[0182] The above composition was fed into the feed section of a polymerization reactor consisting of a continuously moving conveyor belt, and the polymerization reaction was carried out by irradiating ultraviolet rays with a UV irradiation device for 2 minutes (irradiation dose: 2 mW / ㎠), and a hydrogel polymer was obtained as the product.

[0183] The above-mentioned hydrogel polymer was transferred to a cutter and cut into 0.2 cm pieces. 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 190 ℃ for 40 minutes, and the dried hydrogel polymer was ground using a pin mill grinder. Then, polymers with a particle size (average particle size) of 150 μm to 850 μm were classified using a sieve.

[0185] 1-2: Preparation of Superabsorbent Resin

[0186] Subsequently, a surface crosslinking solution (7.6 parts by weight of water, 7.6 parts by weight of methanol, 0.075 parts by weight of ethylene glycol diglycidyl ether (EGDGE), 0.536 parts by weight of adipic acid dihydrazide (ADH), 0.03 parts by weight of sodium metabisulfite, 0.1 parts by weight of aluminum sulfate 18 hydrate (Al-S), and 0.03 parts by weight of aluminum oxide (Alu 130)) was evenly mixed with 100 parts by weight of the base resin prepared above, and a surface crosslinking reaction was carried out at 140°C for 35 minutes. After the surface treatment was completed, a superabsorbent resin having an average particle size of 150 to 850 μm was obtained using a sieve.

[0187] Subsequently, 0.05 parts by weight of silica was dry-mixed into the superabsorbent resin prepared above.

[0189] Examples 2 to 4, Comparative Examples 1 and 2

[0190] In the above Example 1, a superabsorbent resin was prepared in the same manner as in Example 1, except that the compositions of EGDGE and ADH in the surface crosslinking liquid composition were adjusted as shown in Table 1 below.

[0192] Surface crosslinking agent content EGDGE (parts by weight) ADH (weight part) Example 1 0.075 0.536 Example 2 0.054 0.321 Example 3 0.032 0.107 Example 4 0.054 0.107 Comparative Example 1 0.032 - Comparative Example 2 - 0.107

[0193] <Experimental Example>

[0194] The characteristics of the superabsorbent resins prepared according to the examples and comparative examples in the following manner were evaluated and are shown in Table 1 below.

[0196] (1) Centrifuge Retention Capacity (CRC)

[0197] The water retention capacity of each resin based on the absorption ratio under no load was measured according to EDANA WSP 241.3.

[0198] Specifically, from the resins obtained through the examples and comparative examples, resins classified through a #30-50 sieve were obtained. This resin W0 (g) (about 0.2g) was uniformly placed into a nonwoven fabric bag, sealed, and then immersed in physiological saline solution (0.9 wt%) at room temperature. After 30 minutes, the water was drained from the bag for 3 minutes using a centrifuge under conditions of 250g, and the mass W2 (g) of the bag was measured. Additionally, the same operation was performed without using the resin, and the mass W1 (g) was measured. Using each obtained mass, the CRC (g / g) was calculated according to the following formula.

[0199] [Mathematical Formula 1]

[0200] CRC (g / g) = {[W2(g) - W1(g)] / W0(g)} - 1

[0202] (2) Water-use ingredients

[0203] The water-soluble components were measured according to the EDANA method WSP 270.2.

[0205] (3) Pressurized absorption capacity 0.3 psi

[0206] The 0.3 psi pressurized absorption capacity of each resin was measured according to the EDANA method WSP 242.3.

[0207] First, when measuring the combined absorption capacity, the resin classifier from the above CRC measurement was used.

[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) (0.16 g) was uniformly spread over the wire mesh, and a piston capable of uniformly applying a load of 0.3 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.

[0210] Using each obtained mass, the pressurized absorption capacity (g / g) was calculated according to the following formula.

[0211] [Mathematical Formula 2]

[0212] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0214] (4) Vortex absorption rate

[0215] The absorption rate (vortex time) of the superabsorbent resins of the examples and comparative examples was measured according to the Japanese standard method (JIS K 7224). More specifically, 2g of superabsorbent resin was added to 50 mL of physiological saline solution at 25°C, and a magnetic bar (diameter 8 mm, length 31.8 mm) was stirred at 600 rpm, and the time until the vortex disappeared was measured in seconds and calculated.

[0217] Water retention capacity (g / g) Water-soluble components (%) Pressurized absorption capacity (g / g) Absorption rate (sec) Example 1 33.3 4.3 28.5 26 Example 2 33.9 5.2 27.5 25 Example 3 34.5 5.5 26.9 25 Example 4 33.4 5.5 28.9 25 Comparative Example 1 33.2 5.8 27.8 25 Comparative Example 2 38.9 9.1 8.6 26

[0218] Referring to Table 1 above, it can be seen that the superabsorbent resin of the example has a water retention capacity, pressurized absorption capacity, and absorption rate that are equivalent to or superior to those of the comparative example, and that the content of water-soluble components is relatively low.

Claims

Claim 1 A method for manufacturing a superabsorbent resin comprising: a step of forming a hydrogel polymer by crosslinking a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent and a polymerization initiator; a step of forming a base resin powder by drying, grinding, and classifying the hydrogel polymer; and a step of forming superabsorbent resin particles by surface crosslinking the base resin powder in the presence of a surface crosslinking liquid comprising a surface crosslinking agent, wherein the surface crosslinking agent comprises a polyvalent epoxy compound and adipic acid dihydrazide, and comprises a structure represented by the following Chemical Formula 2 derived from the polyvalent epoxy compound and adipic acid dihydrazide: [Chemical Formula 2] (However, R is -(CH2)4-) Claim 2 A method for manufacturing a superabsorbent resin according to claim 1, wherein the surface crosslinking agent comprises one or more polyvalent epoxy compounds selected from the group consisting of ethyleneglycol diglycidyl ether, diethyleneglycol diglycidyl ether, triethyleneglycol diglycidyl ether, tetraethyleneglycol diglycidyl ether, glycerin polyglycidyl ether, and sorbitol polyglycidyl ether. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 A method for manufacturing a superabsorbent resin according to claim 1, wherein the superabsorbent resin has a centrifugal retention capacity (CRC) of 30 g / g or more as measured according to the EDANA method 441.2-02. Claim 10 A method for manufacturing a superabsorbent resin according to claim 1, wherein the superabsorbent resin has a water-soluble component content of 6% by weight or less as measured according to EDANA method 270.

2. Claim 11 A method for manufacturing a superabsorbent resin according to claim 1, wherein the superabsorbent resin has a pressurized absorption capacity of 26.5 g / g or more at 0.3 psi as measured according to the EDANA method WSP 242.

3. Claim 12 A method for manufacturing a superabsorbent resin according to claim 1, wherein the superabsorbent resin has a Vortex absorption rate value of 26 sec or less for physiological saline. Claim 13 A superabsorbent resin comprising a base resin polymerized and internally crosslinked from a monomer composition comprising an acrylic acid-based monomer in which at least some of the acidic groups are neutralized, and a surface crosslinking layer formed on the surface of the base resin, wherein the surface crosslinking layer comprises crosslinking bonds represented by the following Chemical Formula 2 derived from a polyvalent epoxy compound and adipic acid dihydrazide: [Chemical Formula 2] (However, R is -(CH2)4-) Claim 14 delete Claim 15 In paragraph 13, a superabsorbent resin having a centrifugal retention capacity (CRC) of 30 g / g or more as measured in accordance with EDANA method 441.2-02. Claim 16 In paragraph 13, a superabsorbent resin having a water-soluble component content of 6% by weight or less as measured in accordance with 270.2 of the EDANA Act. Claim 17 In paragraph 13, a superabsorbent resin having a pressurized absorption capacity of 26.5 g / g or more at 0.3 psi as measured according to the EDANA method WSP 242.

3. Claim 18 In Clause 13, a superabsorbent resin having a Vortex absorption rate value of 26 sec or less for physiological saline.

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