Method for preparing superabsorbent polymers

Abstract

The present disclosure relates to a method for preparing a superabsorbent polymer. More specifically, it relates to a method for preparing a superabsorbent polymer, which can improve the drying efficiency, reduce the generation amount of recombinant fines, and simultaneously improve the absorption performance of the finally prepared superabsorbent polymer, especially the pressure absorption rate and permeability, by controlling the granulation strength of the extruded fine recombinant.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10 - 2020 - 0183356, filed with the Korean Intellectual Property Office on December 24, 2020, and 10 - 2021 - 0185042, filed with the Korean Intellectual Property Office on December 22, 2021, the entire disclosures of which are incorporated herein by reference.

[0003] The present disclosure relates to a method for preparing a superabsorbent polymer. More specifically, it relates to a method for preparing a superabsorbent polymer that can improve drying efficiency, reduce the generation amount of recombinant fines, and improve the absorption performance of the finally prepared superabsorbent polymer, especially the pressure - sensitive absorption rate and permeability, while controlling the granulation strength of the extruded fine recombinant. Background Art[[ID= / / 12]]

[0004] A superabsorbent polymer (SAP) is a class of synthetic polymer materials that can absorb 500 to 1000 times its own weight of water. Such superabsorbent polymers began to be practically applied to sanitary products, and they are now widely used not only in sanitary products such as baby diapers but also in water - retaining soil products for horticulture, water - stop materials for civil construction, sheets for raising seedlings, preservatives in the food circulation field, dressing materials, etc.

[0005] The absorption mechanism of the superabsorbent polymer depends on the following interactions: the penetration pressure caused by the difference in electric attraction force due to the charge of the polymer electrolyte, the affinity between water and the polymer electrolyte, the molecular swelling caused by the repulsion between polymer electrolyte ions, and the swelling inhibition caused by cross - linking. In other words, the water absorbency of the superabsorbent polymer depends on the affinity and molecular swelling, and the water absorption rate largely depends on the osmotic pressure of the absorbent polymer itself.

[0006] Meanwhile, particles with a particle size of 150 μm or less that are inevitably generated during the preparation of superabsorbent polymers are called fines, and it is known that in the preparation process of superabsorbent polymers, the amount of fines generated in the crushing or conveying process is about 20% to 30%. When the superabsorbent polymer contains such fines, they may cause a decrease in the main physical properties of the superabsorbent polymer, such as the pressure - sensitive absorption rate or water permeability. For this reason, in the preparation process of superabsorbent polymers, especially in the classification process, the fines are separated to produce a superabsorbent polymer having only the remaining polymer particles.

[0007] According to a known method, the fines separated during the preparation of superabsorbent polymers are recombined into large particles through a recombination process and then manufactured and used as superabsorbent polymers. As a representative method of the recombination method, there is a method of agglomerating by mixing the fines with water.

[0008] As the amount of water used in the fines recombination process increases, the granulation strength of the fines recombinant increases. However, when an excessive amount of water is used, the energy used in the drying process of the fines recombinant increases, resulting in high costs. In addition, if the moisture in the fines recombinant is not sufficiently removed during the drying process, problems such as an increase in the load on the device for manufacturing superabsorbent polymers may occur.

[0009] Conversely, when the amount of water used in the recombination process is small, the agglomeration strength decreases due to the low moisture content in the recombinant, so the recombination does not proceed properly, and the amount of the recombinant fines that are reduced to fines again increases. In addition, there is a problem that the physical properties (such as absorbency) of the superabsorbent polymer prepared by the recombination process are insufficient. Therefore, a method has been used to increase the granulation strength and reduce the amount of recombinant fines by performing an additional extrusion process on the fines recombinant with a low moisture content.

[0010] Therefore, there is a continuous need to develop a recombination process for fines that can solve the above problems. Summary of the Invention

[0011] Technical Problem

[0012] Therefore, in the present disclosure, there is provided a method for preparing a superabsorbent polymer, which can improve the drying efficiency of the recombinant, reduce the generation amount of recombinant fines, and at the same time improve the absorption performance of the finally prepared superabsorbent polymer, particularly the pressure absorption rate and permeability, by controlling the granulation strength of the extruded fines recombinant.

[0013] Technical Solution

[0014] According to an embodiment of the present disclosure, a method for preparing a superabsorbent polymer is provided, which includes: preparing a hydrogel polymer by polymerizing a monomer composition including a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups and a polymerization initiator; drying and pulverizing the hydrogel polymer, and classifying it into fine particles having a particle size of less than 150 μm and normal particles having a particle size of 150 to 850 μm; mixing the fine particles with water and a polycarboxylic acid copolymer, and then recombining to prepare a recombined fine particle; preparing an extruded recombined fine particle by extruding the recombined fine particle while adding water, and then drying, pulverizing and classifying; and mixing the extruded recombined fine particle with the normal particles, and then performing a surface crosslinking reaction by adding a surface crosslinking agent; wherein, when preparing the recombined fine particle, 30 to 30 parts by weight of water is used based on 100 parts by weight of the fine particles, and when preparing the extruded recombined fine particle, 15 to 30 parts by weight of water is used based on 100 parts by weight of the recombined fine particle.

[0015] Advantageous Effects

[0016] The method for preparing a superabsorbent polymer according to the present disclosure can improve the drying efficiency of the extruded recombined fine particle, reduce the generation amount of the recombined fine particle, and at the same time improve the absorption performance of the finally prepared superabsorbent polymer, especially the pressure absorption rate and permeability, by controlling the granulation strength of the extruded recombined fine particle prepared when preparing the superabsorbent polymer. Description of the Drawings

[0017] Figure 1 is a graph showing the change of the water content with time in the drying process of the extruded recombined fine particle in Example 1 and Comparative Example 2 in Experimental Example 1.

[0018] Figure 2 is a photograph of the extruded recombined fine particle prepared in Example 2 observed by a scanning electron microscope in Experimental Example 4.

[0019] Figure 3 is a photograph of the extruded recombined fine particle prepared in Comparative Example 3 observed by a scanning electron microscope in Experimental Example 4. Detailed Description

[0020] The terms used herein are only for explaining the specific embodiments and are not intended to limit the present invention. The singular forms are also intended to include the plural forms unless the context clearly indicates otherwise. In the present disclosure, the terms "comprising", "including" or "having" specify the presence of the described features, steps, components or combinations thereof, but do not exclude the presence or addition of one or more other features, steps, components or combinations thereof.

[0021] Since the present invention can be modified in various ways and has various forms, specific embodiments thereof are shown by way of example and will be described in detail. However, this is not intended to limit the present invention to the specific forms disclosed, and it should be understood that the present invention includes all modifications, equivalents, and substitutions within the spirit and scope of the present invention.

[0022] Hereinafter, a method for preparing a superabsorbent polymer will be described in more detail according to specific embodiments of the present invention.

[0023] In the present disclosure, fine particles having a particle size below a predetermined particle size (i.e., about less than 150 μm) are referred to as superabsorbent polymer fine powder, SAP fine powder, or fine powder (fine particles), and particles having a particle size of 150 μm to 850 μm are referred to as normal particles. The fine particles can be generated in the polymerization process, the drying process, or the pulverization process of the dried polymer. When the final product contains fine particles, it is difficult to handle, and the physical properties may deteriorate. For example, a gel plugging phenomenon may occur. Therefore, it is preferable to remove the fine particles from the final product or to make the fine particles into normal particles and reuse them. For example, a recombination process of aggregating the fine particles into particles having a normal particle size can be performed. Generally, in order to increase the aggregation strength in the recombination process, the fine particles are aggregated in a wet state. If the moisture content of the fine particles increases, the aggregation strength of the fine particles increases, but recombination lumps may be generated in the recombination process, which may cause problems during the operation of the process. If the moisture content decreases, the recombination process is easy, but the aggregation strength of the recombinant may be insufficient, which may cause the generation of recombinant fine particles after recombination. In addition, the physical properties of the fine particle recombinant obtained in this way, such as the centrifugal retention capacity (CRC) and the absorption under pressure (AUP), are lower than those of normal particles, which may cause a reduction in the quality of the superabsorbent polymer.

[0024] In addition, additives such as polyethylene glycol are usually added to reduce the generation of fine particles. However, when preparing a fine particle recombinant using such an additive, usually less water is added, which causes a problem of excessive increase in the granulation strength of the fine particle recombinant.

[0025] As a result of continuous experiments by the present inventors, the present invention has the following features: a polycarboxylic acid copolymer is added when preparing a fine particle recombinant, after preparing the fine particle recombinant, a process of preparing an extruded fine particle recombinant by extrusion is further performed on the fine particle recombinant, and the granulation strength of the prepared extruded fine particle recombinant is adjusted by controlling the amount of water input when preparing the fine particle recombinant and the extruded fine particle recombinant. Moreover, the present inventors have confirmed that during the subsequent drying process, the drying efficiency can be improved, the generation amount of recombinant fine particles can be reduced, and thus the absorption performance of the finally prepared superabsorbent polymer, particularly the absorption under pressure and the permeability, can be improved.

[0026] Accordingly, according to an embodiment of the present invention, a fine particle reconstitution process having various process advantages and a method for preparing a superabsorbent polymer using the reconstitution process can be provided, and thus a superabsorbent polymer exhibiting excellent physical properties can be manufactured.

[0027] Specifically, a method for preparing a superabsorbent polymer according to an embodiment of the present invention includes the following steps:

[0028] Preparing a hydrogel polymer by polymerizing a monomer composition containing a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups and a polymerization initiator (step 1);

[0029] Drying and pulverizing the hydrogel polymer, and classifying it into fine particles having a particle size of less than 150 μm and normal particles having a particle size of 150 to 850 μm (step 2);

[0030] Mixing the fine particles with water and a polycarboxylic acid copolymer, and then reconstituting to prepare a fine particle reconstitute (step 3);

[0031] Preparing an extruded fine particle reconstitute by extruding the fine particle reconstitute while adding water, and then drying, pulverizing, and classifying (step 4); and

[0032] Mixing the extruded fine particle reconstitute with normal particles, and then performing a surface crosslinking reaction by adding a surface crosslinking agent (step 5);

[0033] Wherein, when preparing the fine particle reconstitute, 30 to 30 parts by weight of water is used based on 100 parts by weight of the fine particles, and

[0034] When preparing the extruded fine particle reconstitute, 15 to 30 parts by weight of water is used based on 100 parts by weight of the fine particle reconstitute.

[0035] Each step will be described in more detail below.

[0036] The "polymer" in the present disclosure is in a state where a water-soluble ethylenically unsaturated monomer is polymerized, and may include all moisture content ranges, all particle size ranges, all surface crosslinking states or treatment states. Among polymers, a polymer having a moisture content of about 40% by weight or more in a state after polymerization and before drying can be referred to as a hydrogel polymer.

[0037] The term "superabsorbent polymer" refers to the polymer itself, or all polymers (depending on the situation) suitable for commercialization through additional processes such as surface crosslinking, fine particle reconstitution, drying, pulverizing, and classification.

[0038] In the preparation method according to an embodiment of the present disclosure, step 1 is a step of preparing a hydrogel polymer.

[0039] A hydrogel polymer can be specifically prepared by polymerizing a monomer composition containing a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups and a polymerization initiator.

[0040] The water-soluble ethylenically unsaturated monomer can be any monomer commonly used in the preparation of superabsorbent polymers. Specifically, the water-soluble ethylenically unsaturated monomer can have acidic groups, and some of the acidic groups can be neutralized by a neutralizing agent.

[0041] For example, as the water-soluble ethylenically unsaturated monomer, at least one monomer selected from the group consisting of anionic monomers and their salts, nonionic hydrophilic monomers, and amino-containing unsaturated monomers and their quaternary ammonium compounds can be used.

[0042] Specifically, as the water-soluble ethylenically unsaturated monomer, at least one selected from the group consisting of: anionic monomers such as (meth)acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth)acrylamide-2-methylpropanesulfonic acid and their salts; nonionic hydrophilic monomers such as (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, or polyethylene glycol (meth)acrylate; and amino-containing unsaturated monomers such as (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide and their quaternary ammonium compounds can be used.

[0043] More specifically, acrylic acid or its salt can be used, such as acrylic acid or its alkali metal salt, such as sodium salt. By using the monomer, a superabsorbent polymer having excellent physical properties can be prepared.

[0044] In addition, the water-soluble ethylenically unsaturated monomer can be used by neutralizing some of the acidic groups with a neutralizing agent. Thus, when a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups is used, the prepared polymer has a water retention property and absorbs the surrounding water to form a hydrogel polymer having a water content of 40% by weight or more.

[0045] At this time, a basic material capable of neutralizing the acidic groups in the water-soluble ethylenically unsaturated monomer, such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide, can be used as the neutralizing agent.

[0046] In addition, the amount of the neutralizing agent can be appropriately determined in consideration of the degree of neutralization of the water-soluble ethylenically unsaturated monomer or the degree of neutralization in the hydrogel polymer. For example, the degree of neutralization of the water-soluble ethylenically unsaturated monomer can be 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to 75 mol%, where the degree of neutralization refers to the degree to which the acidic groups contained in the water-soluble ethylenically unsaturated monomer are neutralized by the neutralizing agent. The range of the degree of neutralization can vary according to the final physical properties. An excessively high degree of neutralization causes precipitation of the neutralized monomer, and thus polymerization may not easily occur. In contrast, an excessively low degree of neutralization not only deteriorates the absorbency of the polymer but also imparts properties to the polymer that are difficult to handle, such as those of an elastic rubber.

[0047] In addition, based on the monomer composition of the raw material and solvent containing the superabsorbent polymer, the concentration of the water-soluble ethylenically unsaturated monomer can be about 20 to 60% by weight or about 40 to 50% by weight, and can be appropriately controlled in consideration of the polymerization time and reaction conditions. When the monomer concentration is too low, the yield of the superabsorbent polymer is low, and there may be problems in terms of economic efficiency. In contrast, when the concentration is too high, problems may occur in the process, that is, some monomers may be extracted, or the pulverization efficiency of the hydrogel polymer polymerized in the pulverization process may be reduced, and thus the physical properties of the superabsorbent polymer may deteriorate.

[0048] In the production method according to the present disclosure, the polymerization initiator is not particularly limited as long as it is commonly used for producing superabsorbent polymers.

[0049] Specifically, depending on the polymerization method, the polymerization initiator can be an initiator for thermal polymerization or an initiator for photopolymerization by UV radiation. However, even when the photopolymerization method is applied to it, a certain amount of heat is generated by UV radiation, and some heat is generated as the exothermic polymerization reaction proceeds. Therefore, the composition may additionally contain a thermal polymerization initiator.

[0050] Based on the total weight of the monomer composition, the amount of the polymerization initiator can be 0.001 to 2% by weight. When the concentration of the polymerization initiator is too low, the polymerization rate may slow down, and a large amount of residual monomer can be extracted from the final product. On the contrary, when the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network are shortened, so that the content of the extractable components increases, and the pressure absorbency decreases, thereby reducing the physical properties of the polymer.

[0051] More specifically, any compound that can form free radicals by light such as UV rays can be used as the photopolymerization initiator without limitation.

[0052] For example, the photoinitiator may be one or more compounds selected from the group consisting of benzoin ethers, dialkylacetophenones, hydroxyalkyl ketones, phenyl glyoxylates, benzyl dimethyl ketals, acylphosphines, and α-aminoketones. In addition, as a specific example of the acylphosphine, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, or commercially available lucirin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethylphosphine oxide, may be used. More various photoinitiators are fully disclosed in “UV Coatings: Basics, Recent Developments and New Application (Elsevier, 2007)” written by Reinhold Schwalm, page 115, and the present disclosure is not limited thereto.

[0053] When a photoinitiator is used, the concentration of the photoinitiator in the monomer composition may be about 0.01 to about 1.0% by weight. When the concentration of the photoinitiator is too low, the polymerization rate may become slow, while when the concentration is too high, the molecular weight of the superabsorbent polymer may become low, and the properties may be non-uniform.

[0054] In addition, as the thermal initiator, one or more initiators selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid may be used. Specifically, sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), etc. may be used as examples of the persulfate initiators; and 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethyl) isobutylamidine dihydrochloride, 2-(carbamoyl) isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), etc. may be used as examples of the azo initiators. More various thermal initiators are fully disclosed in “Principle of Polymerization (Wiley, 1981)” written by Odian, page 203, and the present disclosure is not limited thereto.

[0055] When a thermal initiator is used, the concentration of the thermal initiator contained in the monomer composition may be 0.001 to 0.5% by weight. When the concentration of the thermal initiator is too low, almost no additional thermal polymerization occurs, and the effect of adding the thermal initiator may not appear. When the concentration of the thermal initiator is too high, the molecular weight of the superabsorbent polymer may become low, and the properties may be non-uniform.

[0056] In the production method according to the present disclosure, the monomer composition may further contain an internal crosslinking agent as a raw material of the superabsorbent polymer.

[0057] In addition, the term "internal crosslinking agent" used herein is different from the surface crosslinking agent for crosslinking the surface of superabsorbent polymer particles, which will be described later, and the internal crosslinking agent polymerizes the unsaturated bonds of water-soluble ethylenically unsaturated monomers by crosslinking. The crosslinking in the above steps is carried out both on the surface and inside, but when the surface crosslinking process of the superabsorbent polymer particles, which will be described later, is carried out, the particle surface of the finally prepared superabsorbent polymer has a structure crosslinked by the surface crosslinking agent, and the particle interior has a structure crosslinked by the internal crosslinking agent.

[0058] The internal crosslinking agent can be a crosslinking agent having one or more ethylenically unsaturated groups in addition to a functional group capable of reacting with a water-soluble substituent of a water-soluble ethylenically unsaturated monomer; or a crosslinking agent having two or more substituents capable of reacting with a water-soluble substituent of the monomer and / or a water-soluble substituent formed by hydrolysis of the monomer.

[0059] As specific examples of the internal crosslinking agent, C8-C12 bisacrylamide, dimethylacrylamide, poly(meth)acrylates of C2-C10 polyols, poly(meth)allyl ethers of C2-C10 polyols, etc. can be used. More specifically, one or more reagents selected from the group consisting of N,N'-methylenebis(meth)acrylate, ethoxy(meth)acrylate, polyethoxy(meth)acrylate, polyethylene glycol diacrylate, polypropoxy(meth)acrylate, glycerol diacrylate, glycerol triacrylate, trimethylolpropane triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol, and propylene glycol can be used.

[0060] Based on the monomer composition, the concentration of the internal crosslinking agent contained can be 0.01 to 0.5% by weight so that the polymerized polymer can be crosslinked. The polymer formed using the internal crosslinking agent has a three-dimensional network structure in which the main chain formed by the polymerization of water-soluble ethylenically unsaturated monomers is crosslinked by the internal crosslinking agent. When the polymer has a three-dimensional network structure, the water retention capacity and the pressure absorbency, which are general physical properties of the superabsorbent polymer, can be significantly improved compared to the case where it has a two-dimensional linear structure not further crosslinked by a crosslinking agent. However, when the content of the internal crosslinking agent exceeds 0.5% by weight, the internal crosslinking density increases, and thus it may be difficult to achieve the desired level of water retention capacity.

[0061] In the preparation method according to the present disclosure, if necessary, the monomer composition may further contain additives such as thickeners, plasticizers, storage stabilizers, and antioxidants.

[0062] Raw materials such as water-soluble ethylenically unsaturated monomers, photopolymerization initiators, thermal polymerization initiators, internal crosslinking agents, and additives can be prepared in the form of a monomer composition solution dissolved in a solvent.

[0063] At this time, any solvent capable of dissolving the components can be used without limitation. For example, one or more solvents 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, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, etc. can be used.

[0064] In addition to the above components, the monomer composition may contain a balance of solvent.

[0065] Meanwhile, the method for preparing the hydrogel polymer by thermal polymerization or photopolymerization of the monomer composition is not particularly limited as long as it is a common polymerization method for preparing superabsorbent polymers.

[0066] Specifically, according to the energy source of polymerization, the polymerization method is roughly divided into thermal polymerization and photopolymerization. In the case of thermal polymerization, it is usually carried out in a reactor equipped with a stirring shaft such as a kneader. In the case of photopolymerization, it can be carried out in a reactor equipped with a mobile conveyor belt. However, the polymerization method is only an example, and the present disclosure is not limited thereto.

[0067] For example, in a reactor equipped with a stirring shaft such as a kneader, the hydrogel polymer obtained by thermal polymerization by providing hot air or heating the reactor can be discharged to the reactor outlet in the form of a few centimeters to a few millimeters, depending on the shape of the stirring shaft provided in the reactor. Specifically, the size of the obtained hydrogel polymer can vary according to the concentration and injection rate of the monomer composition to be injected, and hydrogel polymers with a weight average particle size of 2 to 50 mm can generally be obtained.

[0068] In addition, when photopolymerization is carried out in a reactor equipped with a mobile conveyor belt as described above, a hydrogel polymer in the form of a sheet with a strip width can generally be obtained. At this time, the thickness of the polymer sheet can vary according to the concentration and injection rate of the monomer composition to be injected, and it is preferred to supply the monomer composition so that the polymer in the form of a sheet has a thickness of 0.5 to 5 cm. When the thickness of the polymer sheet formed by the supplied monomer composition is too thin, the production efficiency may be low. When the thickness of the polymer sheet exceeds 5 cm, due to the excessive thickness, the polymerization reaction may not occur uniformly throughout the thickness.

[0069] Through the above preparation process, a hydrogel polymer obtained by polymerization of a water-soluble ethylenically unsaturated monomer is prepared.

[0070] When the monomer composition further includes an internal crosslinking agent in the preparation of the hydrogel polymer, the prepared hydrogel polymer has a three-dimensional network structure, in which the main chain formed by the polymerization of the water-soluble ethylenically unsaturated monomer is crosslinked by the internal crosslinking agent.

[0071] Generally, the water content of the hydrogel polymer obtained by the above method can be 40 to 80% by weight. At this time, the "water content" of the hydrogel polymer in the present disclosure is the water content in the total weight of the hydrogel polymer, and means the value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer. Specifically, the water content is defined as the value calculated according to the following formula 1 by measuring the weight loss caused by the evaporation of the water in the polymer during the temperature increase process of drying the polymer by infrared heating. At this time, the drying conditions for measuring the water content are as follows: the temperature is raised to about 180 °C and maintained at about 180 °C, and the total drying time is 20 minutes, including a heating step of 5 minutes.

[0072] [Formula 1]

[0073] Water content (% by weight) = [(Ao - At) / Ao] X 100

[0074] In the above formula, At is the weight of the sample after drying, and Ao is the weight of the sample before drying. In addition, the sample is the hydrogel polymer targeted for measuring the water content.

[0075] In the preparation method according to the present disclosure, a coarse pulverization process can be selectively performed on the above-obtained hydrogel polymer.

[0076] Here, there is no specific limitation on the pulverizer used. In particular, it may include at least one selected from the group consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutting type pulverizer, a cutting mill, a disk mill, a shredder, a crusher, a chopper, and a disk cutter, but is not limited thereto.

[0077] In the coarse pulverization step, the hydrogel polymer can be pulverized into particles having a diameter of about 2 to 20 mm.

[0078] Due to its high water content, it is technically difficult to coarsely pulverize the hydrogel polymer into particles having a diameter of less than 2 mm, and there is a phenomenon that the pulverized particles agglomerate with each other. At the same time, when the polymer is coarsely pulverized into particles having a diameter of more than 20 mm, the efficiency enhancement effect in the subsequent drying step may not be obvious.

[0079] Subsequently, step 2 is a step of drying and pulverizing the hydrogel polymer prepared in step 1 and classifying it into fine particles having a particle size of less than 150 μm and normal particles having a particle size of 150 to 850 μm.

[0080] The drying process of the hydrogel polymer is carried out at 150 to 250 °C. When the drying temperature is lower than 150 °C, the drying time may become too long, and the properties of the finally prepared superabsorbent polymer may deteriorate. Moreover, when the drying temperature is higher than 250 °C, only the surface of the polymer is overdried, a large amount of fine particles may be generated in the subsequent grinding process, and the properties of the finally prepared superabsorbent polymer may deteriorate. More specifically, the drying process may preferably be carried out at 150 °C or higher or 160 °C or higher and 200 °C or lower or 180 °C or lower.

[0081] In addition, considering the process efficiency, the drying time can be about 20 to about 90 minutes.

[0082] The drying method is not particularly limited as long as it is commonly used for the drying process of hydrogel polymers. Specifically, the drying step can be carried out by methods such as hot air supply, infrared radiation, microwave radiation, UV ray radiation, etc.

[0083] The moisture content of the polymer after the drying step can be 0.1 to 10% by weight.

[0084] Subsequently, the dried polymer can be subjected to a pulverization process.

[0085] The pulverization process can be carried out according to a conventional method. Specifically, a needle mill, a hammer mill, a screw mill, a roll mill, a disk mill or a jog mill can be used, but the present disclosure is not limited thereto.

[0086] After the pulverization process, in order to control the properties of the superabsorbent polymer powder to be finally commercially available, the polymer powder obtained after pulverization is roughly classified according to the particle size.

[0087] Specifically, it is classified into normal particles with a particle size of 150 to 850 μm and fine particles with a particle size of less than 150 μm using an ASTM standard mesh.

[0088] Subsequently, step 3 is a step of mixing the fine particles with a particle size of less than 150 μm classified in step 2 with water and a polycarboxylic acid copolymer as an additive and then recombining them to prepare a fine particle recombinant.

[0089] When preparing the fine-grained recombinant, water can increase the agglomeration strength during the aggregation between the fine particles. Therefore, the granulation strength of the fine-grained recombinant can be controlled by adjusting the water input. Specifically, in the present disclosure, based on 100 parts by weight of the fine grains, the addition amount of water is 30 to 80 parts by weight. When the water input is less than 30 parts by weight, due to the fast absorption rate of the fine grains, it is difficult to uniformly disperse a small amount of water, so the uniformity of the fine-grained recombinant may deteriorate. In addition, the water content of the prepared fine-grained recombinant decreases, which may form hard lumps in the subsequent extrusion process, thus reducing the operation stability of the extrusion process. Furthermore, due to the low granulation strength of the fine-grained recombinant, the amount of the recombinant fine grains may increase, so the absorbency of the superabsorbent polymer to be finally prepared may decrease. At the same time, when the water input exceeds 80 parts by weight, the water content of the fine-grained recombinant increases excessively, so the amount of water evaporated in the drying process increases, increasing the load on the dryer. In addition, the drying is not properly carried out, so the subsequent pulverization process cannot be properly carried out. More specifically, based on 100 parts by weight of the fine grains, the addition amount of water can be 30 parts by weight or more, 35 parts by weight or more, 37 parts by weight or more, or 40 parts by weight or more, and 80 parts by weight or less, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less.

[0090] In addition, in the present disclosure, a polycarboxylic acid copolymer is added as an additive to increase the dispersibility during the formation of the fine-grained recombinant, thereby improving the stability of the continuous operation of the recombination process.

[0091] The polycarboxylic acid copolymer is used to improve the mixing stability and uniformity through the lubricating effect in the mixer. Generally, there is a trade-off relationship between the permeability in the physical properties of the superabsorbent polymer and the water retention capacity and the pressure absorption rate. When a polycarboxylic acid copolymer is added, a superabsorbent polymer with excellent permeability and excellent absorption characteristics (such as water retention capacity and pressure absorption rate) can be provided.

[0092] Specifically, the polycarboxylic acid copolymer may include at least one of the repeating units represented by the following Chemical Formula 1-a and the repeating units represented by the following Chemical

[0093] Formula 1-b:

[0094]

[0095]

[0096] In Chemical Formulas 1-a and 1-b,

[0097] R 1 、R 2 and R 3 are each independently hydrogen or a C1 to C6 alkyl group,

[0098] RO is an oxyalkylene group having 2 to 4 carbon atoms,

[0099] M 1 is hydrogen or a monovalent metal or non-metal ion,

[0100] X is -COO-, C1 to C5 alkoxy or C1 to C5 alkyldioxy,

[0101] m is an integer from 1 to 100,

[0102] n is an integer from 1 to 1000, and

[0103] p is an integer from 1 to 150. When p is 2 or more, two or more repeating -RO- groups may be the same or different from each other.

[0104] Herein, the polycarboxylic acid copolymer may include at least one repeating unit having a different structure among the repeating units represented by Chemical Formula 1-a; at least one repeating unit having a different structure among the repeating units represented by Chemical Formula 1-b; or the repeating units represented by Chemical Formula 1-a and the repeating units represented by Chemical Formula 1-b.

[0105] More specifically, a copolymer containing repeating units derived from alkoxypolyalkylene glycol mono(meth)acrylate monomers (such as methoxypolyethylene glycol monomethacrylate (MPEGMAA), etc.) and repeating units derived from (meth)acrylic acid or its ester monomers (such as (meth)acrylic acid) can be more advantageously used as the polycarboxylic acid copolymer to achieve the above effects. More specifically, a copolymer containing repeating units derived from methoxypolyethylene glycol monomethacrylate and repeating units derived from (meth)acrylic acid, or a random copolymer containing repeating units derived from methoxypolyethylene glycol monomethacrylate and repeating units derived from (meth)acrylic acid can be more advantageously used.

[0106] In addition, the weight-average molecular weight of the polycarboxylic acid copolymer is preferably 500 to 1,000,000 g / mol so that the addition effect of the polycarboxylic acid copolymer can be fully exhibited. More specifically, the weight-average molecular weight can be 500 g / mol or more, 5,000 g / mol or more, 10,000 g / mol or more, 35,000 g / mol or more, or 40,000 g / mol or more, and 1,000,000 g / mol or less, 800,000 g / mol or less, 500,000 g / mol or less, 100,000 g / mol or less, or 60,000 g / mol or less. When the molecular weight of the polycarboxylic acid copolymer is less than 500 g / mol, the lubricating effect may be reduced, while when it exceeds 1,000,000 g / mol, the stability in water may be reduced.

[0107] Meanwhile, in the present disclosure, the weight-average molecular weight (Mw) of the polycarboxylic acid copolymer can be measured using gel permeation chromatography. Specifically, PL-GPC220 manufactured by Waters is used as the gel permeation chromatography (GPC) instrument, and a Polymer Laboratories PLgel MIX-B column (length 300 mm) is used. The evaluation temperature is 160 °C, and 1,2,4-trichlorobenzene is used as the solvent at a flow rate of 1 mL / min. Using PL-SP260 (manufactured by Agilent Technology) as the sample pretreatment system, a 10 mg polycarboxylic acid copolymer sample is dissolved in 1,2,4-trichlorobenzene containing 0.0125% of BHT at 160 °C for 10 hours for pretreatment, and a sample with a concentration of 10 mg / 10 mL is supplied in an amount of 200 μL. Mw is obtained using a calibration curve formed with polystyrene standards. Nine polystyrene standards with molecular weights of 2,000 g / mol, 10,000 g / mol, 30,000 g / mol, 70,000 g / mol, 200,000 g / mol, 700,000 g / mol, 2,000,000 g / mol, 4,000,000 g / mol, and 10,000,000 g / mol are used.

[0108] Based on 100 parts by weight of the fine particles, the amount of the polycarboxylic acid copolymer can be 0.01 to 5 parts by weight, more specifically 0.01 part by weight or more, 0.05 part by weight or more, or 0.1 part by weight or more, and 5 parts by weight or less, 1 part by weight or less, 0.9 part by weight or less, 0.8 part by weight or less, 0.5 part by weight or less, or 0.3 part by weight or less. When the content of the polycarboxylic acid copolymer is less than 0.01 part by weight, it is difficult to obtain the effect of improving the mixing stability and uniformity of the fine particle recombinant by the additive, while when the content of the polycarboxylic acid copolymer exceeds 5 parts by weight, the surface tension and decolorization performance of the final product may decrease.

[0109] In addition, the additive of the polycarboxylic acid copolymer can be mixed with water and the fine particles simultaneously, or can be mixed with water first and then with the fine particles.

[0110] Meanwhile, a mixing device or mixer capable of applying shear force can be used for the step of preparing the fine particle recombinant using water and the additive of the polycarboxylic acid copolymer. Specifically, using a mixing device or mixer, the fine particles, water, and the polycarboxylic acid copolymer are stirred and mixed at 300 to 2000 rpm, more specifically 300 rpm or more, 500 rpm or more, or 650 rpm or more, and 2000 rpm or less, 1,800 rpm or less, 1,500 rpm or less, or 1,000 rpm or less. When stirred at a speed within the above range, sufficient shear force is applied to achieve uniform mixing.

[0111] Subsequently, step 4 is a step of preparing an extruded fine-grained recombinant by extruding the fine-grained recombinant obtained in step 3 while adding water, and then pulverizing and classifying it.

[0112] The step of preparing the extruded fine-grained recombinant can be carried out according to a conventional preparation method of the extruded fine-grained recombinant, except that water is added in the extrusion process.

[0113] The extrusion process of the fine-grained recombinant can be carried out using a conventional extruder such as a meat grinder. In the preferred extruder of the present disclosure, a cutter such as an inverter cutter, a scraper, a blade, or a knife is installed at the rear end of the extruder, for example, at the orifice outlet, so that the fine-grained recombinant discharged in the form of a stem after extrusion can be subjected to a cutting process. For example, in the case of using an extruder with an inverter cutter installed at the orifice outlet at the rear end of an extruder such as SMC-22 (manufactured by SL Corporation), when the fine-grained recombinant is put into the extruder, it is conveyed by a screw provided in the extruder. Moreover, as it passes through the orifice, it is extruded and its strength increases. In the extrusion process, the fine-grained recombinant can be extruded in the form of a stem and then cut into granules by an inverter cutter while being discharged through the orifice outlet.

[0114] The extrusion force applied to the fine-grained recombinant in the extrusion process can be adjusted by controlling the orifice diameter at the extruder outlet and the extruder speed.

[0115] Specifically, the orifice diameter can be 10 mm or more, 12 mm or more, or 14 mm or more, and 20 mm or less or 16 mm or less. Additionally, the extruder speed can be 80 rpm or more and 150 rpm or less. This corresponds to 35 Hz or more and 60 Hz or less. When the orifice diameter and the extrusion speed are within the above ranges, sufficient pressure is applied to the fine-grained recombinant so that an extruded fine-grained recombinant with appropriate granulation strength can be formed. When the orifice diameter is less than 10 mm or the extruder speed exceeds 150 rpm, the pressure applied to the fine-grained recombinant may be too high, and it may be difficult to discharge the extruded fine-grained recombinant from the extruder. For example, in the case of using an extruder such as Fuji Paudal DG-L1 with a dome-shaped orifice diameter of 0.1 to 1 mm, when water is added in the manufacturing process of the extruded fine-grained recombinant, the extruded fine-grained recombinant is not discharged from the dome, so the instrument may stop. At the same time, when the orifice diameter exceeds 20 mm or the extruder speed is less than 80 rpm, sufficient pressure is not applied to the fine-grained recombinant, so that aggregation may not occur sufficiently.

[0116] Meanwhile, in the preparation method according to an embodiment of the present disclosure, water is added in the extrusion step to reduce the granulation strength of the extruded fine-grained recombinant to a certain level, and the granulation strength is optimized by controlling the water input amount. Specifically, in the extrusion step, based on 100 parts by weight of the fine-grained recombinant, 15 to 30 parts by weight of water is added. When the water input amount is less than 15 parts by weight, the input amount is small and the dispersibility of water in the fine-grained recombinant is reduced, so the effect of adjusting the strength is not obvious. When it exceeds 30 parts by weight, the granulation strength becomes too low, and there is a problem that the drying time becomes long due to an increase in the drying capacity. More specifically, the addition amount of water may be 15 parts by weight or more, 17 parts by weight or more, or 20 parts by weight or more, and 30 parts by weight or less or 25 parts by weight or less.

[0117] As described above, in the method for preparing a superabsorbent polymer according to an embodiment of the present disclosure, the water input amounts in the step of preparing the fine-grained recombinant and the step of preparing the extruded fine-grained recombinant are respectively controlled within the above ranges, so that the total input amount of water compared to the fine particles is less than that of the conventional method for preparing a superabsorbent polymer. Specifically, in the case of preparing a fine-grained recombinant according to the conventional method for preparing a superabsorbent polymer, the addition amount of water is usually equal to or greater than the total weight of the fine particles, that is, 100 parts by weight or more of water compared to 100 parts by weight of the fine particles. On the other hand, in the method for preparing a superabsorbent polymer according to the present disclosure, the total water input amount in the preparation of the fine-grained recombinant and the extruded fine-grained recombinant is less than the total weight of the fine particles. In other words, compared to 100 parts by weight of the fine particles, the total water input amount in the preparation of the fine-grained recombinant and the extruded fine-grained recombinant may be less than 100 parts by weight, 90 parts by weight or less, 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less, and greater than 0 parts by weight, 40 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, 55 parts by weight or more, or 60 parts by weight or more. Therefore, the amount of fine particles generated in the preparation of the superabsorbent polymer can be greatly reduced, and the physical properties of the superabsorbent polymer can be further improved, and the drying load can be reduced. If the total water input amount is greater than the total weight of the fine particles, the strength of the extruded fine-grained recombinant increases, but absorption properties such as AUP and permeability may decrease.

[0118] Subsequently, the extruded fine-grained recombinant is dried, pulverized, and classified into an extruded fine-grained recombinant (recombinant normal particles) and recombinant fine particles (hereinafter referred to as "recombinant fine particles").

[0119] The drying process is carried out using a conventional dryer. According to an embodiment of the present disclosure, it can be carried out using a forced circulation dryer.

[0120] In addition, in the drying process, the temperature and time can be appropriately determined in consideration of the moisture content in the extruded fine-grained recombinant. Specifically, the drying process can be carried out at a temperature of 120 to 220 °C for 30 to 120 minutes. When the temperature is less than 120 °C, the drying time may become longer, and when the temperature exceeds 220 °C, the physical properties may decrease due to the deterioration of the fine-grained recombinant. In addition, when the drying time is less than 30 minutes, it is difficult to dry sufficiently, and when the drying time exceeds 120 minutes, the moisture content in the extruded fine-grained recombinant is greatly reduced due to over-drying, so the generation rate of fine grains may increase in subsequent processes. More specifically, the drying process can be carried out at a temperature of 120 °C or higher, or 150 °C or higher and 220 °C or lower, or 200 °C or lower for 30 minutes or longer, or 50 minutes or longer and 120 minutes or shorter, 90 minutes or shorter, or 70 minutes or shorter.

[0121] In addition, the drying process can be carried out so that the moisture content in the dried extruded fine-grained recombinant is 5% by weight or less, or 4.5% by weight or less, and 1% by weight or more, or 1.5% by weight or more. When the drying process is carried out so that the moisture content in the dried extruded fine-grained recombinant is less than 1% by weight, there is a risk of deterioration of the physical properties of the fine-grained recombinant.

[0122] At the same time, the moisture content in the extruded fine-grained recombinant is defined as the value calculated according to Equation 1 by measuring the weight loss caused by the evaporation of moisture in the polymer during the temperature increase process of infrared heating and drying the polymer. At this time, the sample of Equation 1 is the extruded fine-grained recombinant, and the drying conditions are as follows: the temperature is raised to about 180 °C and maintained at 180 °C, and the total drying time is 20 minutes, including a heating step of 5 minutes.

[0123] After that, crushing and classification are carried out, and the crushing and classification can be carried out in the same manner as described above.

[0124] Crushing can be carried out so that the particle size of the dried extruded fine-grained recombinant is about 150 to about 850 μm. The crusher used to crush to this particle size is specifically a needle mill, a hammer mill, a screw mill, a roller mill, a disk mill, or a jog mill, but the present disclosure is not limited thereto.

[0125] After the crushing process, in order to control the properties of the superabsorbent polymer powder to be finally commercially available, the polymer powder obtained after crushing is roughly classified according to the particle size. Specifically, it is classified into recombinant fine grains with a particle size less than 150 μm and recombinant normal particles with a particle size of 150 to 850 μm.

[0126] The proportion of the extruded fine-grained recombinant obtained after drying, crushing, and classification that is broken into fine grains again after the crushing step is low, that is, the proportion of recombinant fine grains is low or the generated recombinant fine grains are few, and the granulation strength is high.

[0127] Specifically, based on the total weight of the extruded fine-grained recombinant, the production amount of recombinant fine grains with a particle size less than 150 μm after pulverization is about 20% by weight or less, 18% by weight or less, or 17% by weight or less. Although a lower production amount of recombinant fine grains can be evaluated as better, considering limitations in the process, etc., it can exceed 0% by weight, 1% by weight or more, or 10% by weight or more.

[0128] The extruded fine-grained recombinant prepared using a pulverization mechanism such as a hammer mill is pulverized, then classified, and then the content of recombinant fine grains with a particle size less than 150 μm is measured, thereby measuring the production amount of recombinant fine grains, and then calculating the percentage of the weight of the recombinant fine grains relative to the total weight of the extruded fine-grained recombinant.

[0129] In addition, the extruded fine-grained recombinant satisfies the following conditions a1) to a3):

[0130] a1) Moisture content: 1 to 5% by weight based on the total weight of the extruded fine-grained recombinant,

[0131] a2) Centrifugal retention capacity (CRC) measured according to EDANA WSP 241.3: 30 to 50 g / g, and

[0132] a3) Absorption rate (vortex) according to JIS K 7224: 30 to 50 seconds.

[0133] Specifically, the moisture content of the extruded fine-grained recombinant is 1 to 5% by weight, more specifically 5% by weight or less, or 4.5% by weight or less, and 1% by weight or more, or 1.5% by weight or more.

[0134] As described above, the moisture content in the extruded fine-grained recombinant is defined as the value calculated according to Equation 1 by measuring the weight loss caused by the evaporation of moisture in the polymer during the temperature rise of the polymer dried by infrared heating. At this time, the sample of Equation 1 is the extruded fine-grained recombinant, and the drying conditions are as follows: the temperature is raised to about 180 °C and maintained at about 180 °C, and the total drying time is 20 minutes, including a heating step of 5 minutes. The method and conditions for measuring the moisture content will be described in more detail in the following experimental examples.

[0135] In addition, the centrifugal retention capacity (CRC) of the extruded fine-grained recombinant measured according to EDANA WSP 241.3 is 30 to 50 g / g, and the absorption rate measured according to JIS K 7224 is 30 to 50 seconds. The methods and conditions for measuring the centrifugal retention capacity and the absorption rate will be described in more detail in the following experimental examples.

[0136] Subsequently, step 5 is a step of preparing a superabsorbent polymer by mixing the extruded fine-grained recombinant obtained in step 4 with normal particles and then performing a surface crosslinking reaction.

[0137] The extruded fine-grained recombinant obtained in step 4 can be used alone to prepare a superabsorbent polymer. However, in the preparation method according to an embodiment of the present disclosure, a superabsorbent polymer is prepared by mixing the extruded fine-grained recombinant with normal particles that are not recombinant fine grains and then performing a surface crosslinking reaction.

[0138] Specifically, after the classification process in step 4, the recombinant fine grains with a particle size of less than 150 μm are recycled to the fine-grained recombination process. Thereafter, the extruded recombinant fine grains, which are recombinant normal particles with a particle size of 150 to 850 μm, are mixed with the above-mentioned normal particles and then introduced into a surface crosslinking reactor, thereby performing a surface crosslinking process.

[0139] The mixing ratio of the extruded fine-grained recombinant and the normal particles can be appropriately adjusted according to the physical properties required for the final product. For example, the extruded fine-grained recombinant and the normal particles can be mixed at a weight ratio of 10:90 to 90:10, more specifically at a weight ratio of 10:90 to 50:50, 15:85 to 40:60, 20:80 to 30:70, or 20:80 to 25:75.

[0140] Surface crosslinking is a step of increasing the crosslinking density near the surface of the superabsorbent polymer particles relative to the crosslinking density inside the particles. Generally, a surface crosslinking agent is applied to the surface of the superabsorbent polymer particles. Therefore, a surface crosslinking reaction occurs on the surface of the superabsorbent polymer particles, which improves the crosslinking ability on the particle surface without significantly affecting the inside of the particles. Therefore, the degree of crosslinking on the surface of the surface-crosslinked superabsorbent polymer particles is higher than that inside.

[0141] Here, there is no limitation on the composition of the surface crosslinking agent as long as it is a compound capable of reacting with the functional groups of the polymer.

[0142] Specifically, in order to improve the properties of the superabsorbent polymer to be prepared, at least one selected from the group consisting of the following can be used as the surface crosslinking agent: polyol compounds; epoxy compounds; polyamine compounds; halogenated epoxy compounds; condensation products of halogenated epoxy compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; and alkylene carbonate compounds.

[0143] Specific examples of polyol compounds may include one or more selected from the group consisting of mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol and 1,2-cyclohexanedimethanol.

[0144] In addition, epoxy compounds may include ethylene glycol diglycidyl ether, glycidyl, etc. Polyamine compounds may include one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and polyamide polyamine.

[0145] In addition, halogenated epoxy compounds may include epichlorohydrin, epibromohydrin and α-methyl epichlorohydrin. At the same time, mono-, di- or polyoxazolidinone compounds may include, for example, 2-oxazolidinone, etc.

[0146] In addition, alkylene carbonate compounds may include ethylene carbonate, etc. These can be used alone or in combination with each other. At the same time, in order to improve the efficiency of the surface crosslinking process, one or more polyol compounds may preferably be included in these surface crosslinking agents. More preferably, polyol compounds having 2 to 10 carbon atoms can be used.

[0147] The amount of the surface crosslinking agent added can be appropriately selected according to the type of the surface crosslinking agent added or the reaction conditions. However, based on 100 parts by weight of the mixture of normal particles and extruded fine particle recombinants, the amount of the surface crosslinking agent is generally about 0.001 to about 5 parts by weight, specifically about 0.01 to about 3 parts by weight, and more specifically about 0.05 to about 2 parts by weight. When the amount of the surface crosslinking agent is too small, the surface crosslinking reaction is difficult to occur, and when the amount is higher than 5 parts by weight based on 100 parts by weight of the mixture, the absorption performance and physical properties may be reduced due to excessive surface crosslinking reaction.

[0148] The crosslinking reaction and the drying process can be carried out simultaneously by heating the polymer particles added with the surface crosslinking agent.

[0149] There is no specific limitation on the heating means for the surface crosslinking reaction. A heat medium can be provided to it or a heat source can be directly provided to it. At this time, the available heat medium can be a heated fluid, such as steam, hot air, hot oil, etc., but the present disclosure is not limited thereto. In addition, the temperature of the heat medium provided to it can be appropriately selected in consideration of the means of the heat medium, the heating rate and the target temperature of heating. At the same time, an electric heater or a gas heater can be used as the directly provided heat source, but the present disclosure is not limited thereto.

[0150] After surface crosslinking, it can be classified into surface-crosslinked fine particles with a particle size of less than 150 μm and surface-crosslinked normal particles with a particle size of 150 to 850 μm. At this time, the surface-crosslinked fine particles with a particle size of less than 150 μm are reinjected into the process of fine particle recombination, and the surface-crosslinked normal particles can be used commercially.

[0151] The superabsorbent polymer prepared by the above process exhibits excellent absorption properties, especially the pressure absorption rate and permeability can be improved simultaneously. Specifically, the superabsorbent polymer satisfies the following conditions b1) to b4):

[0152] b1) Centrifugal retention capacity (CRC) measured according to EDANA WSP 241.3: 30 to 40 g / g;

[0153] b2) Pressure absorption rate (0.7AUP) of the superabsorbent polymer for a 0.9 wt% aqueous sodium chloride solution at 0.7 psi for 1 hour measured according to EDANA WSP 242.3: 17 to 25 g / g;

[0154] b3) Permeability: 20 to 400 seconds; and

[0155] b4) Absorption rate (vortex) according to JIS K 7224: 40 to 60 seconds.

[0156] Specifically, the 30-minute centrifugal retention capacity (CRC) of the superabsorbent polymer for brine (0.9 wt% aqueous sodium chloride solution) measured according to EDANA WSP 241.3 is 30 g / g or more. Since a higher value can be evaluated as better, there is no actual upper limit. However, the upper limit is, for example, 40 g / g or less.

[0157] In addition, the pressure absorption rate (0.7AUP) of the superabsorbent polymer for brine (0.9 wt% aqueous sodium chloride solution) at 0.7 psi for 1 hour measured according to Equation 2 is 17 to 25 g / g. The method and conditions for measuring the pressure absorption rate will be described in more detail in the following experimental examples.

[0158] [Equation 2]

[0159] 0.7AUP (g / g) = [W4 (g) - W3 (g)] / W0 (g)

[0160] In Equation 2, W0 (g) is the initial weight (g) of the superabsorbent polymer, W3 (g) is the sum of the weight of the superabsorbent polymer and the weight of the device providing a load to the polymer, and W4 (g) is the sum of the weight of the superabsorbent polymer after absorbing brine for 1 hour under a load (0.7 psi) and the weight of the device providing a load to the polymer.

[0161] In addition, the permeability of the superabsorbent polymer is from 20 to 400 seconds.

[0162] In the present disclosure, the permeability of the superabsorbent polymer can be measured by the method described in the literature (Buchholz, F. L. and Graham, A. T., "Modern Superabsorbent Polymer Technology," John Wiley & Sons (1998), page 161) using a 0.9% saline solution under a load of 0.3 psi. The method and conditions for measuring the permeability will be described in more detail in the experimental examples below.

[0163] In addition, the absorption rate (vortex) of the superabsorbent polymer measured according to JIS K 7224 is from 40 to 60 seconds. The method and conditions for measuring the absorption rate will be described in more detail in the experimental examples below.

[0164] Therefore, the superabsorbent polymer can be very preferably applied to various sanitary products such as adult diapers, and in particular can be effectively used in sanitary products with reduced pulp content. Sanitary products include disposable absorbent products, preferably diapers, and the diapers can be used for children or adults.

[0165] Hereinafter, the present invention will be described in more detail according to the following preferred embodiments. However, these embodiments are provided for illustrative purposes only, and the content of the present invention is not limited by the following embodiments. In addition, in the following examples and comparative examples, "%" and "parts" indicating content are by weight unless otherwise specified.

[0166] Preparation Example

[0167] 400 parts by weight of deionized water was poured into a 3 L four-necked flask reactor equipped with a stirrer, a thermometer, a nitrogen inlet, and a circulating condenser. While stirring, the inside of the reactor was purged with nitrogen and heated to 75 °C under a nitrogen atmosphere.

[0168] After adding 2 parts by weight of ammonium persulfate to the reactor and completely dissolving it, an aqueous monomer solution containing 600 parts by weight of methoxypolyethylene glycol monomethacrylate (average addition molar number of ethylene oxide (EO): about 50 mol), 99.6 parts by weight of methacrylic acid, and 190 parts by weight of water, 5 parts by weight of 3-mercaptopropionic acid and 60 parts by weight of water, and 150 parts by weight of an aqueous ammonium persulfate solution having a concentration of 3% by weight was continuously added at a uniform rate over 4 hours. After completion of the addition, 5 parts by weight of an aqueous ammonium persulfate solution having a concentration of 3% by weight was added again all at once. Thereafter, the internal temperature of the reactor was raised to 85 °C, and then the temperature was continuously maintained at 85 °C for 1 hour to complete the polymerization reaction.

[0169] When analyzed by gel permeation chromatography (GPC) under the following conditions, the prepared polycarboxylic acid copolymer exhibits a weight-average molecular weight of 40,000 g / mol.

[0170] <Analysis conditions>

[0171] GPC analyzer: PL-GPC220 manufactured by Waters

[0172] Column: PLgel MIX-B column (length 300 mm) manufactured by Polymer Laboratories

[0173] Measurement temperature: 160 °C

[0174] Solvent: 1,2,4-trichlorobenzene

[0175] Flow rate: 1 mL / min

[0176] Sample preparation: Using PL-SP260 (manufactured by Agilent Technology) as a sample pretreatment system, a 10 mg polycarboxylic acid copolymer sample was dissolved in 1,2,4-trichlorobenzene containing 0.0125% BHT at 160 °C for 10 hours for pretreatment, and a sample with a concentration of 10 mg / 10 mL was supplied in an amount of 200 μL.

[0177] Mw was obtained using a calibration curve formed with polystyrene standards (using 9 polystyrene standards with molecular weights of 2,000 g / mol, 10,000 g / mol, 30,000 g / mol, 70,000 g / mol, 200,000 g / mol, 700,000 g / mol, 2,000,000 g / mol, 4,000,000 g / mol, and 10,000,000 g / mol).

[0178] Example 1

[0179] 518 g of acrylic acid, 3.2 g of polyethylene glycol (400) diacrylate, and 0.04 g of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide were added and mixed in a 3 L glass container equipped with a stirrer, a nitrogen inlet, and a thermometer. 822.2 g of a 24.5% aqueous sodium hydroxide solution was added to the resulting mixed solution, and the mixture was stirred while continuously introducing nitrogen to prepare an aqueous solution of water-soluble unsaturated monomers as a monomer composition. The prepared aqueous solution of water-soluble unsaturated monomers was cooled to 40 °C.

[0180] Then, 500 g of the aqueous solution of water-soluble unsaturated monomers was placed in a stainless steel container with a width of 250 mm, a length of 250 mm, and a height of 30 mm, and irradiated with UV rays for 90 seconds (irradiation dose: 10 mV / cm2 )Perform UV polymerization to obtain a hydrogel polymer.

[0181] After coarsely crushing the obtained hydrogel polymer into a size of 2 mm × 2 mm, the obtained gel-type polymer is spread on a stainless steel wire mesh with a pore size of 600 μm to a thickness of about 30 mm and dried in a hot air furnace at 180 °C for 30 minutes. The dried polymer thus obtained is crushed using a crusher and classified with an ASTM standard mesh to obtain fine particles with a particle size of less than 150 μm and normal particles with a particle size of 150 μm to 850 μm.

[0182] 100 parts by weight of the fine particles, 40 parts by weight of water, and 0.1 part by weight of the polycarboxylic acid copolymer (PCE) prepared in the preparation example as an additive are added to a continuous mixer, and mixed for 1 minute while stirring at 650 rpm, and then reconstituted to prepare a fine particle reconstitute.

[0183] The fine particle reconstitute is placed in an extruder (SMC-22, manufactured by SL Corporation, pore diameter: 16 mm, extruder speed: 88 rpm) equipped with an inverter cutter at the orifice outlet at the rear end of the extruder, and extruded while adding 20 parts by weight of water to 100 parts by weight of the fine particle reconstitute. When the fine particle reconstitute is placed in the extruder, it is conveyed by a screw provided in the extruder and extruded while passing through the orifice, generating high strength. At this time, an extruded fine particle reconstitute in the form of a stem discharged from the extruder is obtained, placed in a forced circulation dryer, and then dried at a temperature of 180 °C for 1 hour. After crushing it with a hammer mill, it is classified with an ASTM standard mesh to obtain an extruded fine particle reconstitute with a particle size of 150 to 850 μm and reconstitute fine particles with a particle size of less than 150 μm.

[0184] The above-prepared normal particles and the extruded fine particle reconstitute are mixed at a weight ratio of 75:25 (normal particles: extruded fine particle reconstitute). A surface crosslinking solution prepared by mixing 0.2 part by weight of poly(ethylene glycol) diglycidyl ether, 5 parts by weight of methanol, and 4 parts by weight of water is added to 100 parts by weight of the obtained mixture and mixed, so as to carry out a surface crosslinking reaction at a temperature of 180 °C for 60 minutes to obtain a superabsorbent polymer.

[0185] Examples 2 to 4

[0186] A superabsorbent polymer is prepared in the same manner as in Example 1, except that the conditions are changed as shown in Table 1 below.

[0187] Comparative Example 1

[0188] It was prepared in the same manner as in Example 1, except that no additive was added in the step of preparing the fine-grained recombinant of Example 1.

[0189] However, lumps were formed in the mixer for preparing the fine-grained recombinant, so continuous operation was impossible. Therefore, it was impossible to carry out the subsequent steps of preparing the extruded fine-grained recombinant and the superabsorbent polymer (see Experimental Example 3 below).

[0190] Comparative Examples 2 to 13

[0191] The superabsorbent polymer was prepared in the same manner as in Example 1, except that the conditions were changed as shown in Table 1 below.

[0192] Table 1

[0193]

[0194] In Table 1, a) is based on 100 parts by weight of the fine grains, and b) is based on 100 parts by weight of the fine-grained recombinant.

[0195] In addition, PCE is the polycarboxylic acid copolymer prepared in the preparation example (weight average molecular weight: 40,000 g / mol), and PEG6000 is polyethylene glycol (number average molecular weight: 6000 g / mol).

[0196] Experimental Example 1

[0197] In the preparation of the extruded fine-grained recombinant, the drying characteristics were evaluated comparatively according to whether water was added in the extrusion step.

[0198] Specifically, the extruded fine-grained recombinants of Example 1 and Comparative Example 2 were heated to 180 °C and dried. Then, the change in the moisture content of the extruded fine-grained recombinant with time was calculated according to the following formula 1. The results are shown in Table 2 below and Figure 1 as follows.

[0199] [Formula 1]

[0200] Moisture content (weight %) = [(Ao - At) / Ao] X 100

[0201] In the above formula, At is the weight of the sample after drying, that is, the weight of the extruded fine-grained recombinant after drying, and Ao is the weight of the sample before drying, the weight of the extruded fine-grained recombinant before drying.

[0202] Table 2

[0203]

[0204] As a result of the experiment, compared with Comparative Example 2, the example in which water was added in the extrusion step had a higher initial moisture content but a faster drying rate.

[0205] Experimental Example 2

[0206] In order to evaluate the changes and processability of the extruded fine-grained recombinant depending on whether water was added during the preparation of the extruded fine-grained recombinant and the water input amount, the extruded fine-grained recombinants of Examples 1 and 2 and Comparative Examples 2 and 8 and the extruder after manufacturing were observed.

[0207] As a result, when no water was added (Comparative Example 2) or the water input amount was too small (Comparative Example 8) in the extrusion step of preparing the extruded fine-grained recombinant, the strongly extruded recombinant was discharged in the form of a stem. Therefore, an increase in the drying time and the load during the drying process can be expected.

[0208] Experimental Example 3

[0209] In order to evaluate the influence of the water input amount and whether an additive was added during the preparation process of the fine-grained recombinant on the manufacture of the superabsorbent polymer, the mixer used for preparing the fine-grained recombinant was observed in the manufacture of the superabsorbent polymers of Example 1 and Comparative Examples 1 and 10.

[0210] As a result, when preparing the fine-grained recombinant in Example 1, no agglomerates were formed in the mixer and stable continuous operation was possible.

[0211] On the other hand, in Comparative Example 1 where no polycarboxylic acid copolymer was added, agglomerates were formed in the mixer, making continuous operation impossible, and thus the subsequent process of manufacturing the superabsorbent polymer could not be carried out. In addition, in Comparative Example 10 where the water input amount during the manufacture of the fine-grained recombinant was further increased compared to Comparative Example 1, continuous operation was possible, but a large number of agglomerates were formed in the mixer.

[0212] Experimental Example 4

[0213] The physical properties of the extruded fine-grained recombinants prepared in the examples and comparative examples were evaluated in the following manner, and the shape was observed. The results are shown in Table 3, Figure 2 and 3 as follows.

[0214] (1) Moisture content (wt%)

[0215] The moisture content is the content of water in the total weight of the extruded fine-grained recombinant and can be calculated according to the following formula 1.

[0216] Specifically, the moisture content is calculated by measuring the weight loss caused by the evaporation of moisture in the recombinant during the temperature increase process of the infrared-heated extruded fine-grained recombinant. At this time, the drying conditions are as follows: the temperature is raised to about 180 °C and maintained at about 180 °C, and the total drying time is 20 minutes, including a heating step of 5 minutes. The weights of the extruded fine-grained recombinant before and after drying are measured respectively and calculated according to the following formula 1.

[0217] [Formula 1]

[0218] Moisture content (wt%) = [(Ao - At) / Ao] X 100

[0219] In the above formula, At is the weight of the extruded fine-grained recombinant after drying, and Ao is the weight of the extruded fine-grained recombinant before drying.

[0220] (2) CRC (Centrifugal Retention Capacity)

[0221] The centrifugal retention capacity of the extruded fine-grained recombinant prepared in the examples and comparative examples is measured based on EDANA WSP 241.3.

[0222] Place 0.2 g of the extruded fine-grained recombinant sample in a tea bag and precipitate it in 0.9% saline for 30 minutes. After dehydrating with a centrifugal force of 250 G (gravity) for 3 minutes, measure the amount of saline absorbed, W2 (g). In addition, after performing the same operation without the extruded fine-grained recombinant, measure the weight W1 (g) at this time.

[0223] Then, calculate CRC (g / g) using the obtained weight values according to the following formula 3.

[0224] [Formula 3]

[0225] CRC (g / g) = {[W2 (g) - W1 (g)] / W0 (g)} - 1

[0226] In formula 3,

[0227] W0 (g) is the initial weight of the sample (g),

[0228] W1 (g) is the weight of the device measured after dehydrating for 3 minutes at 250 G using a centrifuge without using the sample,

[0229] W2 (g) is the weight of the device containing the sample after immersing the sample in 0.9 wt% physiological saline at room temperature for 30 minutes for absorption and then dehydrating for 3 minutes at 250 G using a centrifuge.

[0230] (3) Absorption Rate (Vortex)

[0231] It is measured according to JIS K 7224.

[0232] Specifically, 2 g of the extruded fine-grained recombinant prepared in one of the examples and comparative examples was added to 50 mL of brine at 25°C, and a magnetic stir bar (8 mm in diameter and 30 mm in length) was stirred at 600 rpm, and the time until vortex disappearance was measured in seconds to calculate the absorption rate (vortex time).

[0233] (4) Yield of recombinant fine grains (wt%)

[0234] After the extruded fine-grained recombinant prepared in one of the examples and comparative examples was pulverized using a hammer mill and then classified, the content of recombinant fine grains with a particle size less than 150 μm was measured. Then, the percentage of the recombinant fine grains relative to the total weight of the extruded fine-grained recombinant was calculated and recorded as the yield of recombinant fine grains.

[0235] (5) Shape of the extruded fine-grained recombinant

[0236] The shapes of the extruded fine-grained recombinants prepared in Example 2 and Comparative Example 3 were observed using a scanning electron microscope (SEM). The results are shown in Figure 2 and 3 respectively.

[0237] Table 3

[0238]

[0239] In Table 3, "ND" indicates not detected.

[0240] Referring to the experimental results, as water was added in the extrusion process, the recombination strength became weaker and the yield of recombinant fine grains increased. Compared with the comparative examples prepared under the same conditions except that no water was added in the extrusion process, the extruded fine-grained recombinants of Examples 1 to 3 with the extrusion strength controlled in this way showed a low moisture content. Therefore, the processing time in the subsequent drying process of the extruded fine-grained recombinant can be shortened, and problems in the pulverization and transfer processes due to the low moisture content can be prevented.

[0241] Meanwhile, in Comparative Example 1, agglomerates were formed in the mixer during the process of forming the fine-grained recombinant, and continuous operation was impossible, so the extruded fine-grained recombinant and the superabsorbent polymer could not be manufactured.

[0242] In addition, as shown in Figure 2 and 3As shown, surface pores were observed when the extruded fine-grained recombinant of Example 2, in which water was added at a controlled content during the preparation of the extruded fine-grained recombinant, had an appropriate level of recombinant strength. However, in Comparative Example 3 where no water was added during the preparation of the extruded fine-grained recombinant, almost no surface pores were observed. This result is due to the fact that when no water was added, the recombinant strength in Comparative Example 3 increased significantly.

[0243] Experimental Example 5

[0244] The physical properties of the superabsorbent polymers prepared in the examples and comparative examples were evaluated in the following manner, and the results are shown in Table 4.

[0245] (1) CRC (Centrifugal Retention Capacity)

[0246] In the same manner as the method for measuring the centrifugal retention capacity of the extruded fine-grained recombinant, the centrifugal retention capacity of the superabsorbent polymers prepared in the examples and comparative examples was measured based on EDANA WSP 241.3.

[0247] Specifically, 0.2 g of the superabsorbent polymer was placed in a tea bag and precipitated in 0.9% saline for 30 minutes. After dehydrating for 3 minutes with a centrifugal force of 250 G (gravity), the amount of saline absorbed, W2 (g), was measured. In addition, after performing the same operation without using the extruded fine-grained recombinant, the weight W1 (g) at this time was measured.

[0248] Then, CRC (g / g) was calculated using the obtained weight values according to Equation 2.

[0249] (2) Pressurized Absorbency Rate (0.7 AUP)

[0250] The pressurized absorbency rate (AUP) of the superabsorbent polymers in the examples and comparative examples was measured according to EDANA (European Disposables and Nonwovens Association) WSP 242.3.

[0251] Specifically, a 400-mesh stainless steel mesh was installed at the bottom of a plastic cylinder with an inner diameter of 60 mm. At a temperature of 23 ± 2 °C and a relative humidity of 45%, the polymer prepared in one of the examples and comparative examples with a weight of W0 (g, 0.90 g) was evenly spread on the mesh. After that, a piston capable of uniformly providing a 0.7 psi load was placed on the polymer. Here, the outer diameter of the piston was slightly smaller than 60 mm, there was no gap with the inner wall of the barrel, and the jig-jog of the barrel fixture was not interrupted. At this time, the weight W3 (g) of the measuring device was measured.

[0252] Subsequently, a glass filter with a diameter of 125 mm and a thickness of 5 mm was placed in a covered Petri dish with a diameter of 150 mm, and brine (0.9 wt% sodium chloride) was poured into the Petri dish. At this time, brine was poured until the surface level of the brine became equal to the upper surface of the glass filter. A filter paper with a diameter of 120 mm was placed thereon. After installing the measuring device on the filter paper, the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted, and the weight W4 (g) was measured.

[0253] Then, according to the following formula 2, the obtained weight value was used to calculate 0.7 AUP (g / g).

[0254] [Formula 2]

[0255] 0.7 AUP (g / g) = [W4 (g) - W3 (g)] / W0 (g)

[0256] In Formula 2

[0257] W0 (g) is the initial weight (g) of the superabsorbent polymer, W3 (g) is the sum of the weight of the superabsorbent polymer and the weight of the device providing a load to the polymer, and W4 (g) is the sum of the weight of the superabsorbent polymer after absorbing brine for 1 hour under a load (0.7 psi) and the weight of the device providing a load to the polymer.

[0258] (3) Permeability

[0259] Permeability was measured by the method described in the literature (Buchholz, F.L. and Graham, A.T., "Modern Superabsorbent Polymer Technology," John Wiley & Sons (1998), page 161) using a 0.9% brine solution under a load of 0.3 psi.

[0260] Specifically, 0.2 g of superabsorbent polymer particles with a particle size of 300 to 600 μm (hereinafter referred to as samples) were collected from the superabsorbent polymers prepared in the examples and comparative examples and placed in a barrel At this time, one end of the barrel included a stopcock valve, and the upper limit line and the lower limit line were marked. The upper limit line of the barrel was marked at the position where 40 mL of brine solution was filled, and the lower limit line of the barrel was marked at the position where 20 mL of brine solution was filled.

[0261] 50 g of a 0.9% brine (NaCl) solution was added to the barrel with the stopcock valve locked. Additional brine solution was added if necessary so that the level of the brine solution reached the upper limit line of the barrel.

[0262] Apply a load of 0.3 psi to the barrel containing the absorbent brine superabsorbent polymer and let it stand for 1 minute. Then, open the stopcock valve at the bottom of the barrel to measure the time it takes for the 0.9% brine solution to flow from the upper marked line to the lower marked line on the barrel. All measurements are carried out at a temperature of 24 ± 1 °C and a relative humidity of 50 ± 10%.

[0263] Measure the time it takes for each sample (T S ) and when no superabsorbent polymer is added (T0) to flow from the upper line to the lower line, and calculate the permeability according to Equation 4 below.

[0264] [Equation 4]

[0265] Permeability (sec) = T S - T0

[0266] In Equation 4, Ts (unit: seconds) represents the time it takes for a 0.9% brine (NaCl) solution to permeate the superabsorbent polymer containing absorbent brine after swelling 0.2 g of the superabsorbent polymer with the 0.9% brine solution for 30 minutes, under a pressure of 0.3 psi. T0 (unit: seconds) represents the time it takes for the 0.9% brine solution to permeate without the superabsorbent polymer containing absorbent brine, under a pressure of 0.3 psi.

[0267] (4) Absorption rate (vortex)

[0268] Measure the absorption rate (vortex time) according to JIS K 7224. Specifically, calculate the absorption rate (vortex time) by adding 2 g of the superabsorbent polymer to 50 mL of brine at 25 °C, stirring with a magnetic stir bar (diameter 8 mm, length 30 mm) at 600 rpm, and measuring the time until the vortex disappears, in seconds.

[0269] Table 4

[0270]

[0271] In Table 4, "ND" indicates not detected.

[0272] Referring to the experimental results, in Examples 1 to 4 where the extrusion strength was controlled by adding water during the extrusion process of preparing the extruded fine-grained recombinant, as the drying efficiency of the extruded fine-grained recombinant increased, the finally prepared superabsorbent polymer exhibited excellent absorption properties, particularly excellent pressure absorption rate and permeability.

[0273] On the other hand, in the case of the superabsorbent polymer prepared according to Comparative Example 9, the absorption performance is comparable to that of the examples, but the content of the recombinant fine particles generated during the preparation of the extruded fine particle recombinant is significantly higher than that of the examples (see Table 3). In view of this, it can be seen that Examples 1 to 4 prepared by the preparation method according to the present disclosure have better processability.

Claims

1. A method for preparing a superabsorbent polymer, the method comprising: Preparing a hydrogel polymer by polymerizing a monomer composition comprising a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups and a polymerization initiator; Drying and pulverizing the hydrogel polymer, and classifying it into fine particles having a particle size of less than 150 μm and normal particles having a particle size of 150 to 850 μm; Mixing the fine particles with water and a polycarboxylic acid copolymer, and then recombining them to prepare a recombined fine particle; Preparing an extruded recombined fine particle by extruding the recombined fine particle while adding water, and then drying, pulverizing, and classifying; and Mixing the extruded recombined fine particle with the normal particle, and then performing a surface crosslinking reaction by adding a surface crosslinking agent; Wherein, when preparing the recombined fine particle, 30 to 80 parts by weight of water is used based on 100 parts by weight of the fine particles, Wherein, based on 100 parts by weight of the fine particles, the addition amount of the polycarboxylic acid copolymer is 0.01 part by weight to 5 parts by weight, and When preparing the extruded recombined fine particle, 15 to 30 parts by weight of water is used based on 100 parts by weight of the recombined fine particle, Wherein, the polycarboxylic acid copolymer is a copolymer comprising a repeating unit represented by the following Chemical Formula 1-a and a repeating unit represented by the following Chemical Formula 1-b, and the weight average molecular weight of the polycarboxylic acid copolymer is 10,000 g / mol to 1,000,000 g / mol: [Chemical Formula 1-a] [Chemical Formula 1-b] Wherein, in Chemical Formulas 1-a and 1-b, R 1 、R 2 and R 3 are each independently hydrogen or C1 to C6 alkyl, RO is C2 to C4 oxyalkylene, M 1 is hydrogen or a monovalent metal or non-metal ion, X is -COO-, C1 to C5 alkyleneoxy, or C1 to C5 alkylenedioxy, m is an integer of 1 to 100, n is an integer of 1 to 1000, and p is an integer of 1 to 150, and when p is 2 or more, two or more repeating -RO- are the same or different from each other.

2. The method for preparing a superabsorbent polymer according to claim 1, Among them, The total amount of water used when preparing the recombined fine particle and the extruded recombined fine particle is less than the total weight of the fine particles used when preparing the recombined fine particle.

3. The method for preparing a superabsorbent polymer according to claim 1, Among them, The polycarboxylic acid copolymer is a copolymer comprising a repeating unit derived from methoxypolyethylene glycol monomethacrylate and a repeating unit derived from (meth)acrylic acid.

4. The method for preparing a superabsorbent polymer according to claim 1, Among them, Based on 100 parts by weight of the fine particles, the addition amount of the polycarboxylic acid copolymer is 0.05 part by weight to 5 parts by weight.

5. The method for preparing a superabsorbent polymer according to claim 1, Among them, The mixing of the fine particles with water and the polycarboxylic acid copolymer is performed at a mixing speed of 300 rpm to 2000 rpm.

6. The method for preparing a superabsorbent polymer according to claim 1, Among them, The extrusion is performed at a speed of 80 rpm to 150 rpm using an extruder provided with an outlet having a pore diameter of 10 mm to 20 mm.

7. The method for preparing a superabsorbent polymer according to claim 1, Among them, When preparing the extruded fine-grained recombinant, the drying is carried out at a temperature of 120 °C to 220 °C for 30 minutes to 120 minutes.

8. The method for preparing a superabsorbent polymer according to claim 1, Among them, When preparing the extruded fine-grained recombinant, based on the total weight of the extruded fine-grained recombinant, the amount of recombinant fine grains having a particle size of less than 150 μm is 20% by weight or less.

9. The method for preparing a superabsorbent polymer according to claim 1, Among them, The extruded fine-grained recombinant satisfies the following conditions a1) to a3): a1) Moisture content: 1% by weight to 5% by weight based on the extruded fine-grained recombinant, a2) Centrifugal retention capacity measured according to EDANA WSP 241.3: 30 g / g to 50 g / g, and a3) Absorption rate according to JIS K 7224: 30 seconds to 50 seconds.

10. The method for preparing a superabsorbent polymer according to claim 1, Among them, The extruded fine-grained recombinant and the normal particles are mixed at a weight ratio of 10:90 to 90:

10.

11. The method for preparing a superabsorbent polymer according to claim 1, Among them, The superabsorbent polymer satisfies the following conditions b1) to b4): b1) Centrifugal retention capacity measured according to EDANA WSP 241.3: 30 g / g to 40 g / g; b2) Pressurized absorption rate of the superabsorbent polymer for a 0.9 wt% aqueous sodium chloride solution at 0.7 psi for 1 hour measured according to EDANA WSP 242.3: 17 g / g to 25 g / g; b3) Permeability: 20 seconds to 400 seconds; and b4) Absorption rate according to JIS K 7224: 40 seconds to 60 seconds.

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