Manufacturing method of superabsorbent resin

Abstract

The present invention relates to a method for producing a superabsorbent resin, and more specifically, to a method for producing a superabsorbent resin that contains a cationic polymer as a surface cross-linking agent and can achieve excellent water absorption-related physical properties.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0163717, filed November 24, 2021, and Korean Patent Application No. 10-2022-0155321, filed November 18, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for producing a highly water-absorbent resin. [Background technology]

[0003] Super absorbent polymers (SAPs) are synthetic polymers capable of absorbing 500 to 1,000 times their own weight in water, and are given different names by different developers, such as SAM (Super Absorbency Material) or AGM (Absorbent Gel Material). These super absorbent polymers first came into practical use as sanitary products, and are now widely used in a variety of applications, including sanitary products such as baby diapers, soil water retention agents for gardening, waterproofing agents for civil engineering and construction, seedling sheets, freshness preservatives in the food distribution industry, and adhesive patches.

[0004] In most cases, such superabsorbent polymers are widely used in the field of sanitary materials, such as diapers and sanitary napkins. In such sanitary materials, the superabsorbent polymer is generally contained in a dispersed state in the pulp. However, in recent years, efforts have been made to provide thinner sanitary materials, such as diapers, and as part of these efforts, the pulp content has been reduced, or even going a step further, so-called pulpless diapers, which do not use pulp at all, have been actively developed.

[0005] Thus, in the case of sanitary materials with a reduced pulp content or no pulp used, the superabsorbent polymer is contained at a relatively high ratio, and such superabsorbent polymer particles are inevitably contained in multiple layers within the sanitary material. In order for the overall superabsorbent polymer particles contained in such multiple layers to more efficiently absorb liquids such as urine, the superabsorbent polymer must fundamentally exhibit high water absorption performance and water absorption speed. For this purpose, a method of crosslinking the surface of the superabsorbent polymer is used.

[0006] Surface cross-linking of superabsorbent polymers can improve the physical properties of the superabsorbent polymer by forming a surface cross-linked layer by bonding functional groups such as carboxyl groups present on the surface of the superabsorbent polymer. However, when a surface cross-linked layer is formed by such a method, although the physical strength can be increased, the water absorption rate of the superabsorbent polymer can be reduced. Therefore, a method for forming a surface cross-linked layer without impairing the inherent physical properties of the superabsorbent polymer is required. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a method for producing a superabsorbent resin that can solve the above-mentioned problems by using a polymeric substance of a specific component when forming a surface cross-linked layer of the superabsorbent resin. [Means for solving the problem]

[0008] The present invention provides a method for producing a superabsorbent resin, comprising: a step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of a polymerization initiator and an internal crosslinking agent to form a hydrogel polymer; a step of drying, pulverizing, and classifying the hydrogel polymer to form a base resin powder; and a surface crosslinking step of crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent and a cationic polymer to form a surface crosslinked layer; the cationic polymer containing a quaternary ammonium ion in its repeating unit.

[0009] The present invention also provides a superabsorbent resin comprising: a base resin powder containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group; and a surface crosslinked layer formed on the base resin powder by additional crosslinking of the crosslinked polymer via a surface crosslinking agent, wherein the surface crosslinked layer contains a cationic polymer containing a quaternary ammonium ion in the repeating unit.

[0010] In the present invention, terms such as first and second are used to describe various components, and the terms are used only to distinguish one component from another.

[0011] Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention.

[0012] The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0013] In this specification, the terms "comprises," "comprises," or "having" are intended to describe embodied features, numbers, steps, components, or combinations thereof, and do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additions thereof.

[0014] Furthermore, in this specification, when a layer or element is referred to as being formed "on" another layer or element, it means that the layer or element is formed directly on the other layer or element, or that other layers or elements can be additionally formed between the layers, on the object, or on the substrate.

[0015] Although the present invention can be embodied in various forms and with various modifications, specific embodiments are described in detail below by way of example, but it should be understood that the present invention is not limited to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0016] Throughout this specification, saline means saline (0.9 wt% NaCl(s)).

[0017] The present invention will be described in detail below.

[0018] According to one aspect of the present invention, there is provided a method for producing a superabsorbent resin, comprising: a step of crosslinking a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of a polymerization initiator and an internal crosslinking agent to form a hydrogel polymer; a step of drying, pulverizing, and classifying the hydrogel polymer to form a base resin powder; and a surface crosslinking step of crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent and a cationic polymer to form a surface crosslinked layer, wherein the cationic polymer contains a quaternary ammonium ion in the repeating unit.

[0019] The inventors of the present invention have found that when a cationic polymer is contained in addition to an existing, commonly used surface crosslinking agent during surface crosslinking, which is one step in the production of a superabsorbent resin, the physical and chemical properties of having a long polymer chain and a cation in the molecule contribute to the formation of a surface crosslinked layer of the existing surface crosslinking agent, and the water retention capacity and water absorption rate of the produced superabsorbent resin can be maintained while simultaneously improving the high-pressure water absorption capacity and liquid permeability, and have completed the present invention.

[0020] Hereinafter, each step of the method for producing a superabsorbent resin according to one embodiment will be described in more detail.

[0021] For reference, in this specification, "polymer" or "macromolecule" refers to a polymerized state of a water-soluble ethylenically unsaturated monomer, and can encompass all water content ranges, all particle size ranges, and all surface cross-linked or processed states. Among these polymers, polymers with a water content (moisture content) of about 40% by weight or more in the state after polymerization and before drying can be referred to as hydrogel polymers. Furthermore, among these polymers, polymers with a particle size of 150 μm or less can be referred to as "fine powder."

[0022] Furthermore, depending on the context, the term "superabsorbent polymer" may refer to the polymer itself, or may encompass all polymers that have been subjected to additional processes, such as surface crosslinking, regranulation into fine powder, drying, pulverization, classification, etc., to be made into a state suitable for commercialization.

[0023] (polymerization) First, in the step of forming a hydrogel polymer, a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group is cross-linked and polymerized in the presence of a polymerization initiator and an internal cross-linking agent to form a hydrogel polymer.

[0024] The monomer mixture, which is a raw material of the superabsorbent resin, may include a water-soluble ethylenically unsaturated monomer having an acidic group, at least a portion of which is neutralized, more specifically, an acrylic acid-based monomer, and a polymerization initiator.

[0025] (monomer) The acrylic acid monomer is a compound represented by the following Chemical Formula 1:

[0026] [Chemical formula 1] R 1 -COOM 1

[0027] In the above Chemical Formula 1, R 1 is an alkyl group having 2 to 5 carbon atoms and containing an unsaturated bond, M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0028] Specifically, the acrylic acid monomer may include at least one selected from the group consisting of acrylic acid, methacrylic acid, and their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts.

[0029] The acrylic acid monomer may have an acidic group, and at least a portion of the acidic group may be neutralized. Preferably, the monomer is partially neutralized with a basic substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide. In this case, the degree of neutralization of the acrylic acid monomer is adjusted to less than about 70 mol%, or about 40 to about 69 mol%, or about 50 to about 65 mol%.

[0030] If the degree of neutralization is too high, the neutralized monomer will precipitate, making it difficult to smoothly carry out polymerization, and even worse, the effect of additional neutralization after the initiation of surface crosslinking will be substantially lost, the degree of crosslinking in the surface crosslinked layer will not be optimized, and the liquid permeability of the superabsorbent resin may be insufficient. Conversely, if the degree of neutralization is too low, not only will the water absorption capacity of the polymer be significantly reduced, but it may also exhibit properties similar to elastic rubber, which are difficult to handle.

[0031] The concentration of the monomer may be about 20 to about 60% by weight, about 30 to about 55% by weight, or about 40 to about 50% by weight based on the monomer mixture containing the raw materials of the superabsorbent polymer and the solvent, and can be appropriately adjusted in consideration of the polymerization time, reaction conditions, etc.

[0032] If the concentration of the monomer is too low, the yield of the superabsorbent polymer will be low, resulting in economical problems. Conversely, if the concentration of the monomer is too high, process problems such as partial precipitation of the monomer or reduced pulverization efficiency during pulverization of the polymerized hydrogel polymer may occur, resulting in deterioration of the physical properties of the superabsorbent polymer.

[0033] (Polymerization initiator) The polymerization initiator used in the method for producing a superabsorbent resin according to the embodiment is not particularly limited as long as it is one that is generally used in the production of superabsorbent resins.

[0034] Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator using UV irradiation, depending on the polymerization method. However, even in the photopolymerization method, a certain amount of heat is generated by UV irradiation, and a certain amount of heat is generated as the polymerization reaction, which is an exothermic reaction, progresses, so a thermal polymerization initiator may also be included.

[0035] The photopolymerization initiator can be any compound capable of forming radicals by exposure to light such as ultraviolet light, and is not limited in its composition.

[0036] The photopolymerization initiator may be, 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. A specific example of an acyl phosphine is commercially available lucirin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide. A wide variety of photoinitiators are described in detail in "UV Coatings: Basics, Recent Developments and New Applications" by Reinhold Schwalm (Elsevier, 2007), p. 115, and are not limited to the above examples.

[0037] The thermal polymerization initiator may be one or more selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid. Specific examples of persulfate initiators include sodium persulfate (NaSO), potassium persulfate (KSO), and ammonium persulfate ((NHSO). Examples of azo initiators include 2,2-azobis(2-amidinopropane) dihydrochloride and 2,2-azobis(N,N-dimethylene)isobutyramidine dihydrochloride. dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), etc. A wide variety of thermal polymerization initiators are clearly described in Odian's "Principle of Polymerization" (Wiley, 1981), p. 203, and are not limited to the examples mentioned above.

[0038] The polymerization initiator is added at a concentration of about 0.001 to 1 wt %, preferably about 0.1 to about 0.9 wt %, based on the total weight of the monomer mixture. An excessively low concentration of the polymerization initiator is undesirable because it slows down the polymerization rate and can result in a large amount of residual monomer being extracted into the final product. Conversely, a concentration higher than the above range is undesirable because it can shorten the polymer chains forming the network, increase the content of water-soluble components, and reduce the water absorption capacity under pressure, thereby deteriorating the physical properties of the resin.

[0039] (internal crosslinking agent) According to one embodiment of the present invention, the monomer mixture includes an internal crosslinking agent as a raw material for the superabsorbent resin. The internal crosslinking agent crosslinks the inside of a polymer, i.e., a base resin, formed by polymerizing an acrylic acid-based monomer, and is distinguished from a surface crosslinking agent, which crosslinks the surface of the polymer.

[0040] The type of such internal cross-linking agent is not particularly limited, and any internal cross-linking agent that has been conventionally usable for producing superabsorbent resins can be used. Specific examples of such internal cross-linking 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, and allyl(meth)acrylate compounds having 2 to 20 carbon atoms.

[0041] 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, ether), polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and the like, and various other polyfunctional compounds can also be used as the internal crosslinking agent.

[0042] Such an internal crosslinking agent is contained in a concentration of about 0.01 to about 1 wt %, or about 0.05 to about 0.8 wt %, or about 0.2 to about 0.7 wt %, based on the total weight of the monomer mixture, and can introduce a crosslinked structure into the hydrogel polymer and the base resin powder formed therefrom.

[0043] If the concentration of the internal cross-linking agent is too low, the water absorption rate of the superabsorbent resin may decrease and the gel strength may be weakened, which is undesirable, whereas if the concentration of the internal cross-linking agent is too high, the water absorption capacity of the superabsorbent resin may decrease, which is undesirable as a water absorbent material.

[0044] (Other additives and monomer mixtures) The monomer mixture may further contain other additives such as a foaming agent and a foam stabilizer, if necessary.

[0045] The foaming agent serves to form pores in the hydrogel polymer by foaming in the monomer mixture during polymerization, thereby increasing the surface area of the hydrogel polymer.

[0046] The foaming agent may be a carbonate, and examples thereof include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, and magnesium carbonate.

[0047] The blowing agent is preferably used in an amount of 1500 ppmw or less, or about 1300 ppmw or less, based on the weight of the water-soluble ethylenically unsaturated monomer. If the amount of blowing agent used is too large, the pores may become too large, reducing the gel strength of the superabsorbent resin and decreasing its density, which may cause problems in distribution and storage. The blowing agent is preferably used in an amount of 500 ppmw or more, or 1000 ppmw or more, based on the weight of the water-soluble ethylenically unsaturated monomer.

[0048] Meanwhile, in the above-described embodiment of the manufacturing method, the monomer mixture may further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

[0049] The monomer mixture containing the above-mentioned monomer mixture, a polymerization initiator, an internal crosslinking agent, a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group, and optionally other additives is prepared in the form of a monomer mixture solution dissolved in a solvent.

[0050] In this case, the solvent that can be used is not limited in composition as long as it can dissolve the above-mentioned components. For example, one or more solvents selected from the group consisting of water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide can be used in combination.

[0051] The solvent is contained in the remaining amount relative to the total content of the monomer mixture so that each component is adjusted to the above-mentioned concentration range.

[0052] (polymerization) On the other hand, the method for forming a hydrogel polymer by thermal polymerization or photopolymerization of such a monomer mixture is not particularly limited as long as it is a commonly used polymerization method.

[0053] Specifically, polymerization methods are roughly divided into thermal polymerization and photopolymerization depending on the polymerization energy source.

[0054] Generally, thermal polymerization is carried out in a reactor having a stirring shaft such as a kneader, and photopolymerization is carried out in a reactor equipped with a movable conveyor belt. However, the above-mentioned polymerization methods are merely examples, and the present invention is not necessarily limited to the above-mentioned polymerization methods.

[0055] For example, as described above, a hydrogel polymer obtained by thermal polymerization by supplying hot air to a reactor such as a kneader equipped with an agitator shaft or by heating the reactor may have a size of several centimeters to several millimeters depending on the shape of the agitator shaft equipped in the reactor. Specifically, the size of the obtained hydrogel polymer varies depending on the concentration of the injected monomer mixture, the injection rate, etc., but typically, a hydrogel polymer having a weight-average particle size of 2 to 50 mm or 3 to 30 mm is obtained.

[0056] When photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the resulting hydrogel polymer may generally be in the form of a sheet having the width of the belt. In this case, the thickness of the polymer sheet varies depending on the concentration and injection speed of the monomer mixture injected, and it is generally preferred to supply the monomer mixture so as to obtain a sheet-like hydrogel polymer having a thickness of 0.5 to 5 cm or 1 to 3 cm.

[0057] If the monomer mixture is supplied so that the thickness of the sheet polymer is too thin, the production efficiency will be low, which is undesirable. If the thickness of the sheet polymer exceeds 5 cm, the polymerization reaction may not occur uniformly throughout the entire thickness due to the excessively large thickness.

[0058] The water content of the hydrogel polymer obtained by such a method may usually be about 40 to about 80% by weight, or about 50 to about 70% by weight. Meanwhile, throughout this specification, the "water content" refers to the amount of water relative to the total weight of the hydrogel polymer, and refers to the value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer.

[0059] Specifically, it is defined as the value calculated by measuring the weight loss due to evaporation of water in the polymer during the drying process by increasing the temperature of the polymer using infrared heating. The drying conditions are to increase the temperature from room temperature to about 180°C and then maintain it at about 180°C, and the total drying time is set to about 20 minutes, including about 5 minutes for the temperature increase stage, and the moisture content is measured.

[0060] (Dry) Next, the resulting hydrogel polymer is dried.

[0061] At this time, if necessary, a coarse pulverization step may be performed before drying in order to increase the efficiency of the drying step.

[0062] In this case, the crusher used is not limited in configuration, but specifically may include any one selected from the group of crushing equipment 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 above examples.

[0063] In this case, the hydrogel polymer can be crushed to a particle size of about 2 to about 10 mm, or about 3 to about 8 mm in the crushing step. The particle size of the hydrogel polymer is defined as the longest distance among the straight line distances connecting any points on the surface of the hydrogel polymer.

[0064] Grinding to a particle size of less than about 2 mm is technically difficult due to the high water content of the hydrogel polymer, and the crushed particles may aggregate together. On the other hand, grinding to a particle size of more than about 10 mm only slightly increases the efficiency of the subsequent drying step.

[0065] The hydrogel polymer is either crushed as described above or immediately after polymerization without being subjected to a crushing step, and then dried.

[0066] The drying temperature in the drying step may be about 150 to about 250°C. If the drying temperature is less than about 150°C, the drying time will be too long, which may result in a deterioration in the physical properties of the resulting superabsorbent polymer. If the drying temperature is more than about 250°C, only the surface of the polymer may be excessively dried, which may result in the generation of fine powder in the subsequent pulverization process, which may result in a deterioration in the physical properties of the resulting superabsorbent polymer. Therefore, the drying is carried out at a temperature of about 150 to about 200°C, more preferably about 160 to 180°C.

[0067] On the other hand, the drying time is, but is not limited to, about 20 to about 90 minutes, or about 30 to about 70 minutes, taking into consideration process efficiency and the like.

[0068] The drying method in the drying step can be any method commonly used in the drying process of hydrogel polymers, without any limitations on its structure. Specifically, the drying step can be carried out by a method such as hot air supply, infrared radiation, ultrashort wave radiation, or ultraviolet radiation.

[0069] The water content of the polymer after such a drying step may be about 0.1 to about 10% by weight, or about 1 to about 8% by weight. If the water content after drying is too low, the hydrogel polymer will deteriorate during the drying process, resulting in a decrease in the physical properties of the superabsorbent polymer. Conversely, if the water content is too high, the large amount of water in the superabsorbent polymer will result in a decrease in water absorption performance or make it difficult to proceed with subsequent steps.

[0070] Next, the dried polymer obtained through this drying step is subjected to a pulverization step.

[0071] The polymer powder obtained after the pulverization step may have a particle size of about 150 to about 850 μm. Specific examples of the pulverizer used to pulverize to such a particle size include a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, and a jog mill, but the invention is not limited to the above examples.

[0072] After the pulverization step, in order to control the physical properties of the superabsorbent resin powder to be manufactured as a final product, a separate process of classifying the polymer powder obtained after pulverization according to particle size may be performed, and the polymer powder may be classified to have a certain weight ratio according to particle size range.

[0073] (Surface crosslinking) The surface cross-linking step is a step of inducing a cross-linking reaction on the surface of the pulverized polymer in the presence of a surface cross-linking liquid containing a surface cross-linking agent to form a superabsorbent resin with improved physical properties. This surface cross-linking results in the formation of a surface cross-linked layer on the surface of the pulverized and classified base resin powder.

[0074] Generally, the surface cross-linking agent is applied to the surface of the base resin powder, so that the surface cross-linking reaction occurs on the surface of the base resin powder, which improves the cross-linking property on the surface of the particle without substantially affecting the interior of the particle. Therefore, the surface-cross-linked superabsorbent resin particles have a higher degree of cross-linking near the surface than inside, as the cross-linked polymer on the surface of the base resin powder is additionally cross-linked.

[0075] Meanwhile, as the surface cross-linking agent, a compound capable of reacting with a functional group of the base resin is used, and examples thereof include polyhydric alcohol-based compounds, polyhydric epoxy-based compounds, haloepoxy compounds, and alkylene carbonate-based compounds, and the like, and any of these may be used without any particular limitation.

[0076] Specifically, examples of polyhydric alcohol compounds that can be used include one or more selected from the group consisting of di-, tri-, tetra- or polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedimethanol.

[0077] Furthermore, as the polyfunctional epoxy compound, one or more compounds selected from the group consisting of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, tetraethylene glycol diglycidyl ether, glycerin polyglycidyl ether, and sorbitol polyglycidyl ether can be used.

[0078] The haloepoxy compound may be epichlorohydrin, epibromohydrin, or α-methylepichlorohydrin, while the mono-, di-, or polyoxazolidinone compound may be, for example, 2-oxazolidinone.

[0079] The alkylene carbonate compound may be ethylene carbonate or propylene carbonate, which may be used alone or in combination.

[0080] The method for producing a superabsorbent resin of the present invention further includes a cationic polymer in addition to the general surface cross-linking agent described above. The cationic polymer refers to a substance having a cation in the main chain or side chain of the molecule. When the cationic polymer is added together with the surface cross-linking agent to promote the surface cross-linking reaction, the interaction between the ions present in the polymer and the existing surface cross-linking agent allows the resin to maintain water retention capacity even at a high cross-linking density while maintaining high pressure water absorption capacity. In addition, the surface of the base resin can be uniformly treated to improve liquid permeability.

[0081] Meanwhile, the cationic polymer may have one or more cations selected from the group consisting of ammonium, imidazolium, pyridinium, phosphonium, and sulfonium. Preferably, the cationic polymer contains a cation in the repeating unit, more preferably an ammonium ion group in the repeating unit. The ammonium ions can be classified into primary to quaternary ammonium ions depending on the number of hydrogen atoms in the ammonium ion substituted with organic groups. For example, the cationic polymer may contain a quaternary ammonium ion in the repeating unit, but the present invention is not necessarily limited thereto.

[0082] According to one embodiment of the present invention, the cationic polymer may include a repeating unit derived from an ethylenically unsaturated monomer to which an ammonium ion is linked. For example, the ethylenically unsaturated monomer may be (meth)acrylic acid, (meth)acrylate, (meth)acrylamide, vinyl acetate, ethylene, propylene, butadiene, or styrene. The ammonium ion may be directly bonded to the repeating unit derived from the ethylenically unsaturated monomer, or may be bonded to the repeating unit via a C 1-10 It can be attached by an alkylene.

[0083] According to one embodiment of the present invention, the cationic polymer may include a cyclic ammonium ion in a repeating unit. The cyclic ammonium ion refers to a structure in which at least two organic groups substituted with ammonium ions are bonded to each other to form a ring. The cyclic ammonium ion may be in a form in which a monomer of the cationic polymer is converted into a ring during polymerization, or the monomer of the cationic polymer may include the cyclic ammonium ion.

[0084] Specifically, the cationic polymer includes at least one selected from the group consisting of poly(diallyldimethylammonium chloride), poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate), poly(2-(dimethylamino)ethyl methacrylate methyl chloride quaternary salt), and poly(acrylamide-dimethylaminoethyl acrylate quaternary salt). Meanwhile, the poly(diallyldimethylammonium chloride) is a compound containing a repeating unit represented by the following chemical formula 1, and the poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) is a compound containing a repeating unit represented by the following chemical formula 2.

[0085] [ka]

[0086] Preferably, the cationic polymer has a weight-average molecular weight of 50,000 g / mol to 700,000 g / mol, more preferably 80,000 g / mol to 600,000 g / mol, or 100,000 g / mol to 500,000 g / mol. When the weight-average molecular weight of the cationic polymer satisfies the above range, it is suitable for coating a base resin through interaction with an existing surface crosslinking agent, and various water absorption properties can be improved.

[0087] Preferably, the cationic polymer is contained in an amount of 0.01 to 0.9 parts by weight per 100 parts by weight of the base resin. More preferably, the amount is 0.3 to 0.8 parts by weight, or 0.05 to 0.5 parts by weight per 100 parts by weight of the base resin. When the cationic polymer is contained in the above range, it is suitable for surface treatment of the base resin, and can simultaneously improve high-pressure water absorption capacity and liquid permeability.

[0088] On the other hand, the content of the surface cross-linking agent can be more appropriately selected depending on the type of surface cross-linking agent added and the reaction conditions, but typically, about 0.001 to about 5 parts by weight, or about 0.005 to about 2 parts by weight, or about 0.01 to about 1 part by weight, or about 0.02 to about 0.5 parts by weight can be used relative to about 100 parts by weight of the base resin powder. If the content of the surface cross-linking agent is too low, the surface cross-linking reaction hardly occurs, and if the content of the surface cross-linking agent is too high, the surface cross-linking reaction may proceed excessively, resulting in a decrease in basic water absorption properties such as water retention capacity.

[0089] When adding the surface cross-linking agent, water may be additionally mixed and added in the form of a surface cross-linking liquid. When water is added, it has the advantage that the surface cross-linking agent can be uniformly dispersed in the base resin. At this time, the content of the added water is preferably about 1 part by weight to about 10 parts by weight per 100 parts by weight of the base resin in order to induce uniform dispersion of the surface cross-linking agent, prevent clumping of the base resin powder, and optimize the surface penetration depth of the surface cross-linking agent.

[0090] Meanwhile, the surface cross-linking reaction can be carried out by adding at least one inorganic substance selected from the group consisting of silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate to the surface cross-linking liquid. The inorganic substance can be used in powder or liquid form, and particularly can be used in the form of alumina powder, silica-alumina powder, titania powder, or nanosilica solution. The inorganic substance can be used in an amount of about 0.05 to about 2 parts by weight per 100 parts by weight of the base resin.

[0091] Furthermore, in the surface cross-linking step, the surface cross-linking structure of the superabsorbent resin can be further optimized by adding polyvalent metal cations instead of or together with the inorganic substance to promote surface cross-linking. This is presumably because such metal cations form chelates with the carboxyl groups (COOH) of the superabsorbent resin, thereby further reducing the cross-linking distance.

[0092] Furthermore, there is no limitation on the constitution of a method for adding the inorganic substance and / or polyvalent metal cation to the base resin powder, if necessary. For example, a method in which a surface crosslinking agent containing an inorganic substance and / or polyvalent metal cation, a base resin powder, etc. are placed in a reaction tank and mixed, a method in which a surface crosslinking agent containing an inorganic substance and / or polyvalent metal cation, etc. is sprayed onto the base resin powder, a method in which a base resin powder, a surface crosslinking agent containing an inorganic substance and / or polyvalent metal cation, etc. are continuously supplied to a continuously operated mixer and mixed, etc. can be used.

[0093] When adding the surface cross-linking agent, water and methanol may be added together. When water and methanol are added, the surface cross-linking agent can be uniformly dispersed in the base resin powder. The amount of water and methanol added can be appropriately adjusted to induce uniform dispersion of the surface cross-linking agent and prevent clumping of the base resin powder, while optimizing the surface penetration depth of the surface cross-linking agent.

[0094] Meanwhile, the mixture of the base resin powder and the surface cross-linking liquid is heated to increase the temperature, thereby performing a surface modification step on the base resin powder.

[0095] The surface cross-linking step can be carried out under well-known conditions depending on the type of surface cross-linking agent, for example, at a temperature of about 140°C to about 200°C for about 20 minutes to about 60 minutes. In a more specific example, the surface cross-linking step is carried out by adding a surface cross-linking agent to a base resin powder having an initial temperature of about 20°C to about 80°C, raising the temperature to about 140°C to about 200°C or to a maximum temperature of about 175°C to about 195°C over about 10 minutes to about 30 minutes, and maintaining the maximum temperature for about 5 minutes to about 60 minutes.

[0096] By adjusting the surface cross-linking conditions, it is possible to optimize both the basic water absorption properties such as water retention capacity of the superabsorbent resin, and the liquid permeability and / or water absorption capacity under pressure.

[0097] The temperature raising means for the surface crosslinking reaction is not particularly limited. Heating can be performed by supplying a heat medium or directly supplying a heat source. At this time, the type of heat medium that can be used may be a high-temperature fluid such as steam, hot air, or hot oil, but is not limited thereto. The temperature of the heat medium to be supplied can be appropriately selected in consideration of the heat medium means, the temperature raising rate, and the target temperature. Meanwhile, the heat source that is directly supplied may be an electric heating method or a gas heating method, but the present invention is not limited to the above-mentioned examples.

[0098] (Super absorbent resin) Meanwhile, the manufacturing method may further include a step of classifying the base resin made of the crosslinked polymer having the surface crosslinked layer formed thereon.

[0099] The physical properties of the superabsorbent resin powder to be manufactured as a final product can be controlled by classifying the base resin made of a crosslinked polymer having the surface crosslinked layer according to particle size. It is appropriate that the superabsorbent resin obtained from such processes as pulverization and classification be manufactured and provided so as to have a particle size of about 150 to 850 μm. More specifically, about 90% by weight, preferably 95% by weight or more, of the base resin having the surface crosslinked layer formed thereon has a particle size of about 150 to 850 μm, with less than about 3% by weight of fine powder having a particle size of less than about 150 μm.

[0100] In this way, by adjusting the particle size distribution of the superabsorbent polymer to a preferred range, the final superabsorbent polymer can exhibit excellent water absorption properties. Therefore, in the classification step, polymers with particle sizes of about 150 to about 850 μm can be classified and used as products.

[0101] Meanwhile, the present invention provides a superabsorbent resin comprising: a base resin powder containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group; and a surface crosslinked layer formed on the base resin powder by additional crosslinking of the crosslinked polymer via a surface crosslinking agent, wherein the surface crosslinked layer comprises a cationic polymer containing a quaternary ammonium ion in the repeating unit.

[0102] As described above, the superabsorbent resin prepared by the method of the present invention includes a surface cross-linked layer in which a cationic polymer is added in the surface cross-linking step and the cationic polymer is distributed within the surface cross-linked structure on the surface of the base resin. The surface cross-linking agent including the cationic polymer that forms the surface cross-linked layer has been described above.

[0103] According to one embodiment of the present invention, the cationic polymer may include a repeating unit derived from an ethylenically unsaturated monomer to which an ammonium ion is linked. For example, the ethylenically unsaturated monomer may be (meth)acrylic acid, (meth)acrylate, (meth)acrylamide, vinyl acetate, ethylene, propylene, butadiene, or styrene. The ammonium ion may be directly bonded to the repeating unit derived from the ethylenically unsaturated monomer, or may be bonded to the repeating unit via a C 1-10 It can be attached by an alkylene.

[0104] According to one embodiment of the present invention, the cationic polymer may include a cyclic ammonium ion in a repeating unit. The cyclic ammonium ion refers to a structure in which at least two organic groups substituted with ammonium ions are bonded to each other to form a ring. The cyclic ammonium ion may be in a form in which a monomer of the cationic polymer is converted into a ring during polymerization, or the monomer of the cationic polymer may include the cyclic ammonium ion.

[0105] Preferably, the cationic polymer may include any one or more selected from the group consisting of poly(diallyldimethylammonium chloride), poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate), poly(2-(dimethylamino)ethyl methacrylate methyl chloride quaternary salt), and poly(acrylamide-dimethylaminoethyl acrylate quaternary salt).

[0106] Preferably, the surface cross-linking agent is a compound capable of reacting with a functional group of the base resin, and examples thereof include polyhydric alcohol compounds, polyhydric epoxy compounds, haloepoxy compounds, and alkylene carbonate compounds, and the like, all of which can be used without any particular limitation.

[0107] Specific examples of polyhydric alcohol compounds, polyhydric epoxy compounds, haloepoxy compounds, or alkylene carbonate compounds are as described above, and examples thereof include di-, tri-, tetra-, or polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, ethylene glycol diglyceride, 1,2-cyclohexanedimethanol, 1,3-cyclohexanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanediol, 1,4-butanediol, 1,5-butanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanediol, 1,4-butanediol, 1,3-cyclohexanediol, 1,5-but ... glycidyl ether, diethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, tetraethylene glycol diglycidyl ether, glycerin polyglycidyl ether, sorbitol polyglycidyl ether, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polyamidepolyamine, epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, 2-oxazolidinone, ethylene carbonate, and propylene carbonate.

[0108] Based on this, the superabsorbent resin of the present invention can improve its water absorption capacity under pressure while maintaining its water retention capacity due to the surface cross-linked layer formed on such a base resin, and can achieve excellent high-pressure water absorption capacity and liquid permeability even at a high cross-linking density.

[0109] The term "Centrifugal Retention Capacity (CRC)" used in the present invention refers to the amount of solution that can be absorbed under no load. The CRC can be measured using EDANA WSP241.3, and the specific measurement method is described in detail in the following Examples. Preferably, the CRC of the superabsorbent polymer is 25 g / g to 40 g / g, or 30 g / g to 35 g / g.

[0110] The term "AUP (Absorbency Under Pressure)" used in the present invention is also referred to as water absorption capacity under pressure, and refers to the amount of solution that can be absorbed under a certain pressure (0.7 psi). The AUP can be measured by EDANA method WSP242.3, and a specific measurement method is described in detail in the following examples. Preferably, the AUP of the superabsorbent polymer is 10 g / g to 30 g / g. More preferably, the AUP of the superabsorbent polymer is 13 g / g to 25 g / g.

[0111] The term "EFFC" used in the present invention is also referred to as effective water absorption capacity, and the effective water absorption capacity (EFFC) can be calculated by substituting the water retention capacity (CRC) and the water absorption capacity under pressure (AUP) of 0.7 psi into the following formula 3:

[0112] [Formula 3] Effective water absorption capacity = {Water retention capacity (CRC) + Water absorption capacity under pressure (AUP) at 0.7 psi} / 2

[0113] Preferably, the EFFC of the superabsorbent resin is 22 g / g to 30 g / g, more preferably 23 g / g to 28 g / g, or 25 g / g to 28 g / g.

[0114] The term "vortex" used in the present invention is also referred to as the water absorption rate, and refers to the rate at which a solution is absorbed into a superabsorbent polymer. Specific methods for measuring the vortex are described in detail in the following examples. Preferably, the vortex of the superabsorbent polymer is 40 seconds or less. More preferably, the vortex of the superabsorbent polymer is 35 seconds or less, 30 seconds or less, or 25 seconds or less. Meanwhile, the smaller the vortex value, the better, with the theoretical lower limit being 0 seconds. However, for example, the vortex of the superabsorbent polymer is 10 seconds or more, 15 seconds or more, or 20 seconds or more.

[0115] The term "permeability" used in the present invention refers to the ability of a superabsorbent polymer to rapidly transfer a solution absorbed in the polymer to another superabsorbent polymer, in other words, the mobility of a solution within the superabsorbent polymer. A specific method for measuring permeability is described in detail in the following examples. Preferably, the permeability of the superabsorbent polymer is 18 seconds or less. More preferably, the permeability of the superabsorbent polymer is 17 seconds or less, 16 seconds or less, or 15 seconds or less. The smaller the permeability, the better. The theoretical lower limit is 0 seconds. However, for example, the permeability of the superabsorbent polymer is 3 seconds or more, 5 seconds or more, or 10 seconds or more.

[0116] Furthermore, the superabsorbent resin of the present invention satisfies at least one, preferably two or more of the above-described physical property ranges of water retention capacity (CRC), absorbency under pressure (AUP), effective absorbency (EFFC), water absorption rate (vortex), and liquid permeability, and more preferably satisfies all of the physical property ranges simultaneously. [Effects of the Invention]

[0117] According to the above-described method for producing a superabsorbent resin of the present invention, a cationic polymer can be added during surface crosslinking to produce a superabsorbent resin that has excellent water absorption properties even at a high crosslink density. DETAILED DESCRIPTION OF THE INVENTION

[0118] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, but these examples are presented only as examples of the present invention and do not define the scope of the invention.

[0119] <Production of base resin> Manufacturing example An aqueous monomer solution composition was prepared by mixing 100 g of acrylic acid, 3.0 g of polyethylene glycol diacrylate (PEGDA, MW=523) as a crosslinker, 0.008 g of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide as a photoinitiator, 0.08 g of sodium persulfate (SPS) as a thermal initiator, 128 g of 31.5% caustic soda (NaOH), and 63.5 g of water.

[0120] The aqueous monomer solution composition was photopolymerized to obtain a polymerized sheet. The polymerized sheet was taken out and cut into 3cm x 3cm pieces, then chopped using a meat chopper to produce crumbs. The crumbs were dried in an oven capable of rotating airflow from top to bottom. Hot air at 185°C was blown from bottom to top for 15 minutes and then from top to bottom for 15 minutes to uniformly dry the crumbs, ensuring that the moisture content of the dried product was less than 2%.

[0121] After drying, the mixture was crushed in a crusher and then classified for 10 minutes at an amplitude of 1.5 mm (classification mesh combination: #20, #30, #50, #100). Each classified powder (10%, 65%, 22%, 3%) was collected to obtain a base resin powder with a particle size of approximately 150 μm to 850 μm.

[0122] <Production of superabsorbent resin> Comparative Example 1 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (5 parts by weight of water, 3 parts by weight of methanol, 0.06 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1)), and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Thereafter, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0123] Example 1 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (5 parts by weight of water, 3 parts by weight of methanol, 0.06 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.1 parts by weight of poly(diallyldimethylammonium chloride) (manufacturer: SINOFLOC, Mw: 150,000 g / mol)), and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0124] Example 2 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (5 parts by weight of water, 3 parts by weight of methanol, 0.06 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.1 parts by weight of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0125] Comparative Example 2 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (7 parts by weight of water, 3 parts by weight of methanol, 0.025 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1)), and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Thereafter, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0126] Example 3 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (7 parts by weight of water, 3 parts by weight of methanol, 0.025 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.05 parts by weight of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0127] Example 4 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (7 parts by weight of water, 3 parts by weight of methanol, 0.025 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.1 part by weight of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 part by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0128] Example 5 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (7 parts by weight of water, 3 parts by weight of methanol, 0.025 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.2 parts by weight of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0129] Example 6 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking solution (7 parts by weight of water, 3 parts by weight of methanol, 0.035 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.2 parts by weight of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0130] Example 7 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (7 parts by weight of water, 3 parts by weight of methanol, 0.035 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.3 parts by weight of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0131] Comparative Example 3 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking liquid (5 parts by weight of water, 3 parts by weight of methanol, 0.06 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1), and 0.1 parts by weight of polyethyleneimine (manufacturer: Polysciences, Inc., Mw: 100,000 g / mol)), and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Then, silica (Aerosil 200, 0.1 parts by weight) was added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0132] Comparative Example 4 100 parts by weight of the base resin powder prepared in the above Preparation Example was uniformly mixed with a surface cross-linking solution (7 parts by weight of water, 3 parts by weight of methanol, and 0.035 parts by weight of ethylene glycol diglycidyl ether (EJ1030s, n=1)) and the surface cross-linking reaction was carried out at 140°C for 30 minutes. Poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate) (manufacturer: Senka, Mw: 400,000 g / mol, 0.3 parts by weight) and silica (Aerosil 200, 0.1 parts by weight) were then added and mixed. After the surface treatment was completed, a superabsorbent resin with an average particle size of 850 μm or less was prepared using a sieve.

[0133] Experimental Example The superabsorbent resins obtained in the above Examples and Comparative Examples were measured for various physical properties by the following methods.

[0134] Unless otherwise stated, the evaluation of the physical properties of the superabsorbent resin was carried out on resin having particle sizes of 150 μm to 850 μm classified using an ASTM standard sieve.

[0135] (1) CRC The water retention capacity of each resin was measured by the water absorption capacity under no load using EDANA WSP241.3.

[0136] Specifically, W0 (g) (approximately 0.2 g) of superabsorbent resin was evenly placed in a nonwoven fabric envelope, sealed, and then immersed in physiological saline (0.9 wt%) at room temperature (23°C to 25°C). After 30 minutes, the envelope was centrifuged at 250 G for 3 minutes to remove water, and the mass of the envelope, W2 (g), was measured. The same procedure was repeated without using the superabsorbent resin, and the mass, W1 (g), at that time was measured. The CRC (g / g) was calculated using the obtained masses according to the following formula 1.

[0137] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0138] (2) 0.7 AUP The water absorption capacity of the superabsorbent polymer at a pressure of 0.7 psi was measured by EDANA method WSP242.3.

[0139] First, when measuring the water absorption capacity under pressure, the resin-classified powder used in the CRC measurement was used.

[0140] Specifically, a 400-mesh stainless steel wire mesh was attached to the bottom of a plastic cylinder with an inner diameter of 25 mm. At room temperature (23°C to 25°C) and 50% humidity, 0.16 g of superabsorbent resin W0 (g) was evenly spread on the wire mesh. A piston capable of applying a uniform load of 0.7 psi to the mesh was placed slightly smaller than the outer diameter of 25 mm, with no gap between it and the inner wall of the cylinder, allowing for unhindered up-and-down movement. The weight of the device, W3 (g), was then measured.

[0141] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a 150 mm diameter petroleum dish, and physiological saline solution containing 0.9 wt% sodium chloride was poured onto the glass filter so that it was flush with the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was then placed on top of the filter. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for one hour. After one hour, the measuring device was lifted and its weight W4 (g) was measured.

[0142] Using the obtained masses, the water absorption capacity under pressure (g / g) was calculated according to the following formula 2.

[0143] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0144] (3)EFFC The water retention capacity (CRC) measured in (1) above and the water absorption capacity under pressure (AUP) at 0.7 psi measured in (2) above were substituted into the following formula 3 to calculate the effective water absorption capacity (EFFC).

[0145] [Formula 3] Effective water absorption capacity = {Water retention capacity (CRC) + Water absorption capacity under pressure (AUP) at 0.7 psi} / 2

[0146] (4) Vortex The water absorption rate was measured according to the Japanese standard method (JIS K7224).

[0147] Specifically, 2 g of superabsorbent resin was placed in 50 mL of saline at 25°C, and a magnetic bar (diameter 8 mm, length 31.8 mm) was used to stir at 600 rpm. The time until the vortex disappeared was measured in seconds and calculated.

[0148] (5) Permeability The liquid permeability was measured using the following equation 4.

[0149] [Formula 4] Perm=[20mL / T1(sec)]×60 seconds

[0150] In the formula 4, Perm is the liquid permeability of superabsorbent resin. T1 is the time (seconds) required for 20 mL of saline to pass through the swollen superabsorbent polymer under a pressure of 0.3 psi after 0.2 g of superabsorbent polymer was placed in a cylinder and physiological saline (0.9 wt % sodium chloride aqueous solution) was poured in so that the polymer was completely immersed in the solution. The superabsorbent polymer was allowed to swell for 30 minutes. The measurement was carried out at room temperature (23°C to 25°C).

[0151] Specifically, a cylinder and a piston were prepared. The cylinder had an inner diameter of 20 mm and was equipped with a glass filter and a stopcock at its bottom. The piston had an outer diameter slightly smaller than 20 mm and was equipped with a screen at its bottom that could move freely up and down inside the cylinder, and a weight at its top, with the screen and weight connected by a rod. The piston was equipped with a weight that could apply a pressure of 0.3 psi when the piston was pressed.

[0152] With the stopcock of the cylinder closed, 0.2 g of superabsorbent polymer was placed in the cylinder, and excess saline (0.9 wt % sodium chloride solution) was poured in so that the superabsorbent polymer was completely immersed. The superabsorbent polymer was then allowed to swell for 30 minutes. Thereafter, a piston was added so that a load of 0.3 psi was uniformly applied to the swollen superabsorbent polymer.

[0153] Next, the stopcock of the cylinder was opened, and the time required for 20 mL of saline to pass through the swollen superabsorbent polymer was measured in seconds. At this time, by marking the meniscus when the cylinder was filled with 40 mL of saline and the meniscus when the cylinder was filled with 20 mL of saline, T1 in Equation 4 above could be calculated by measuring the time required for the level to reach the level corresponding to 40 mL to the level corresponding to 20 mL.

[0154] The results are shown in Tables 1 and 2.

[0155] [Table 1]

[0156] *PDADMAC: Poly(diallyldimethylammonium chloride) (Manufacturer: SINOFLOC, Mw: 150,000 g / mol) *PMETAMS: Poly(2-(methacryloyloxy)ethyltrimethylammonium methylsulfate) (Manufacturer: Senka, Mw: 400,000 g / mol)

[0157] [Table 2]

[0158] As shown in Table 1, the superabsorbent resins of the Examples prepared according to the present invention further contain a cationic polymer as a component of the surface cross-linking solution during surface cross-linking, and are therefore superior in water absorption properties compared to the Comparative Examples.

[0159] Furthermore, as shown in Table 2, even when the superabsorbent resin was prepared with a composition in which the content of the surface crosslinking agent was reduced to lower the crosslinking density, the superabsorbent resins of the Examples prepared according to the present invention were found to have excellent high-pressure water absorption capacity and liquid permeability while maintaining the same level of other physical properties as the Comparative Examples.

Claims

1. a step of cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acid group in the presence of a polymerization initiator and an internal cross-linking agent to form a hydrogel polymer; drying, grinding, and classifying the hydrogel polymer to form a base resin powder; and a surface cross-linking step of cross-linking the surface of the base resin powder in the presence of a surface cross-linking agent and a cationic polymer to form a surface cross-linked layer; the cationic polymer contains a quaternary ammonium ion in a repeat unit; The cationic polymer includes at least one selected from the group consisting of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate), poly(2-(dimethylamino)ethyl methacrylate methyl chloride quaternary salt), and poly(acrylamide-dimethylaminoethyl acrylate quaternary salt); A method for producing superabsorbent resin.

2. The cationic polymer has a weight average molecular weight of 50,000 g / mol to 700,000 g / mol. A method for producing the highly water-absorbent resin according to claim 1.

3. The cationic polymer is contained in an amount of 0.01 to 0.9 parts by weight per 100 parts by weight of the base resin. A method for producing the highly water-absorbent resin according to claim 1.

4. The surface cross-linking agent includes a polyhydric alcohol-based compound, a polyhydric epoxy-based compound, a haloepoxy compound, or an alkylene carbonate-based compound. A method for producing the highly water-absorbent resin according to claim 1.

5. The surface cross-linking agent is used in an amount of 0.001 to 5 parts by weight per 100 parts by weight of the base resin. A method for producing the highly water-absorbent resin according to claim 1.

6. a base resin powder comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group; and a surface cross-linked layer formed on the base resin powder by additional cross-linking of the cross-linked polymer via a surface cross-linking agent; the surface cross-linked layer contains a cationic polymer containing a quaternary ammonium ion in a repeating unit within a surface cross-linked structure, The cationic polymer includes at least one selected from the group consisting of poly(2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate), poly(2-(dimethylamino)ethyl methacrylate methyl chloride quaternary salt), and poly(acrylamide-dimethylaminoethyl acrylate quaternary salt); Super absorbent resin.

7. The surface cross-linking agent includes a polyhydric alcohol-based compound, a polyhydric epoxy-based compound, a haloepoxy compound, or an alkylene carbonate-based compound. The highly water-absorbent polymer according to claim 6.

8. The liquid permeability of the superabsorbent resin is 18 seconds or less. The highly water-absorbent polymer according to claim 6.

9. The centrifugal retention capacity (CRC) of the superabsorbent resin measured by EDANA method WSP241.3 is 25 g / g to 40 g / g. The highly water-absorbent polymer according to claim 6.

10. The superabsorbent resin has a water absorption capacity (AUP) at 0.7 psi measured by EDANA method WSP242.3 of 10 g / g to 30 g / g. The highly water-absorbent polymer according to claim 6.

11. The vortex of the superabsorbent resin is 40 seconds or less. The highly water-absorbent polymer according to claim 6.

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