Manufacturing method of superabsorbent resin

Abstract

The present invention provides a method for producing a superabsorbent polymer, the method including the steps of: supplying a composition including a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group, an internal crosslinking agent, and a polymerization initiator to a polymerization reactor, and polymerizing the composition to obtain a hydrous gel polymer; drying the hydrous gel polymer to obtain a dry body; hydrating the dry body to adsorb moisture into the dry body; and pulverizing the hydrated dry body to obtain a superabsorbent polymer.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0136874, filed on October 21, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing a superabsorbent polymer, and more particularly to a method for producing a superabsorbent polymer in which the amount of fine particles generated is reduced by a water addition treatment. [Background technology]

[0003] Super absorbent polymers (SAPs) are synthetic polymers capable of absorbing 500 to 1,000 times their own weight in water, and are given different names by different developers, such as SAM (Super Absorbency Material) or AGM (Absorbent Gel Material). These super absorbent polymers first began to be used in sanitary products and are now widely used as soil water retention agents in horticulture, water-stopping materials for civil engineering and construction, seedling sheets, freshness-maintaining agents and steaming materials in the food distribution industry, and are primarily used in sanitary products such as diapers and sanitary napkins.

[0004] Meanwhile, among the series of steps for producing a superabsorbent polymer, there has been a problem in that the amount of fine powder generated increases during the pulverization step due to surface destruction of the dried product. If such fine powder is generated during the pulverization process, the yield of the superabsorbent polymer that is made into the final product may decrease accordingly, and the fine powder may be inhaled into the respiratory tract of workers performing the pulverization step, causing health problems.

[0005] Therefore, there is a need for a method that can reduce the amount of fine powder generated when pulverization is performed in the pulverization step. Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a method for producing a superabsorbent resin that can reduce the amount of fine powder generated in the pulverization step in order to solve the problems mentioned in the background of the invention above. [Means for solving the problem]

[0007] According to one embodiment of the present invention for solving the above problems, there is provided a method for producing a superabsorbent polymer, the method comprising: supplying a composition including a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group, an internal crosslinking agent, and a polymerization initiator to a polymerization reactor and polymerizing the composition to obtain a hydrous gel polymer; drying the hydrous gel polymer to obtain a dried substance; hydrating the dried substance to adsorb moisture into the dried substance; and pulverizing the hydrated dried substance to obtain a superabsorbent polymer. [Effects of the Invention]

[0008] According to the method for producing a superabsorbent polymer of the present invention, a dried body can be hydrated after drying to adsorb moisture onto the dried body. The hydration treatment increases the moisture content on the surface of the dried body, thereby preventing the surface of the dried body from being damaged during pulverization. This reduces the amount of fine powder generated by the surface damage of the dried body during the pulverization step. Furthermore, this reduction in the amount of fine powder generated increases the yield of the superabsorbent polymer that is used as a final product. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart illustrating a method for producing a superabsorbent polymer according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0011] In order to facilitate understanding of the present invention, the present invention will now be described in more detail with reference to FIG.

[0012] A method for producing a superabsorbent polymer according to one embodiment of the present invention may include the steps of: supplying a composition containing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group, an internal crosslinking agent, and a polymerization initiator to a polymerization reactor and polymerizing the composition to obtain a hydrous gel polymer; drying the hydrous gel polymer to obtain a dried body a; hydrating the dried body a to adsorb moisture into the dried body a; and pulverizing the hydrated dried body b to obtain a superabsorbent polymer.

[0013] First, a method for producing a superabsorbent polymer according to one embodiment of the present invention can include feeding a composition containing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group, an internal crosslinking agent, and a polymerization initiator into a polymerization reactor and polymerizing the composition to obtain a hydrogel polymer. As described above, the composition can contain the water-soluble ethylenically unsaturated monomer, the internal crosslinking agent, and the polymerization initiator, and can further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, as needed.

[0014] Here, the water-soluble ethylenically unsaturated monomer may be (meth)acrylic acid or a salt thereof. For example, when acrylic acid in which at least a portion of acrylic acid is neutralized or an alkali metal salt thereof, such as a sodium salt, is used as the water-soluble ethylenically unsaturated monomer, a superabsorbent resin with improved water absorption properties can be obtained.

[0015] Other examples of the water-soluble ethylenically unsaturated monomer include anionic monomers such as maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and 2-(meth)acrylamido-2-methylpropanesulfonic acid, and salts thereof; nonionic hydrophilic monomers such as (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and polyethylene glycol (meth)acrylate; and amino group-containing unsaturated monomers such as (N,N)-dimethylaminoethyl (meth)acrylate and (N,N)-dimethylaminopropyl (meth)acrylamide, and quaternized products thereof. The salts of the anionic monomers may be metal salts, divalent metal salts, ammonium salts, or organic amine salts.

[0016] The water-soluble ethylenically unsaturated monomer may contain at least a partially neutralized acidic group. The water-soluble ethylenically unsaturated monomer may be prepared by neutralizing the acidic group of the water-soluble ethylenically unsaturated monomer with a neutralizing agent. Here, the neutralizing agent may be a basic substance capable of neutralizing the acidic group, such as sodium hydroxide (or caustic soda), potassium hydroxide, or ammonium hydroxide.

[0017] Meanwhile, the internal crosslinking agent may crosslink the unsaturated bonds of the water-soluble ethylenically unsaturated monomer to polymerize it.

[0018] The internal cross-linking agent may be a (meth)acrylate-based compound that undergoes a cross-linking reaction via a free-radical polymerization (FRP) reaction. Specifically, the internal cross-linking agent may be one or more compounds selected from the group consisting of ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate. More specifically, the internal cross-linking agent may be one or more of ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, and polyethylene glycol di(meth)acrylate.

[0019] Meanwhile, in the composition, the polymerization initiator can be a thermal polymerization initiator or a photopolymerization initiator using UV irradiation, depending on the polymerization method. However, even in the photopolymerization method, a certain amount of heat is generated by UV irradiation, and as the polymerization reaction, which is an exothermic reaction, progresses, a certain amount of heat is also generated, so a thermal polymerization initiator can also be included.

[0020] The photopolymerization initiator may be a compound capable of forming radicals when exposed to light such as ultraviolet light. The photopolymerization initiator may be at least one selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone. Specific examples of acyl phosphine include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate.

[0021] The thermal polymerization initiator may be one or more selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid. Specific examples of persulfate initiators include sodium persulfate (NaSO), potassium persulfate (KSO), and ammonium persulfate ((NH)SO).

[0022] Specifically, polymerization methods are broadly classified into thermal polymerization and photopolymerization depending on the polymerization energy source. Thermal polymerization can be carried out in a polymerization reactor having a stirring shaft such as a kneader, and photopolymerization can be carried out in a polymerization reactor equipped with a movable conveyor belt.

[0023] The hydrogel polymer of the present invention can be produced by a polymerization reaction in which a composition containing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator is supplied to a polymerization reactor. In the composition, the internal crosslinking agent can be present in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent can be present in an amount of 0.01 to 0.05 parts by weight, 0.1 to 0.2 parts by weight, or 5 to 3 parts by weight, 2 to 1 part by weight, or 0.5 to 1 part by weight per 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the internal crosslinking agent is too low, crosslinking may be insufficient, making it difficult to achieve adequate strength. If the content of the upper internal crosslinking agent is too high, the internal crosslink density may be high, making it difficult to achieve the desired water retention capacity.

[0024] The composition of the present invention may be prepared in the form of a solution dissolved in a solvent. Usable solvents include those capable of dissolving the raw materials described above. For example, the solvent may include water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or a mixture thereof.

[0025] Next, the hydrogel polymer formed by the polymerization reaction of the composition may be dried, pulverized, and classified. Here, a coarse pulverization step may be further performed to increase the efficiency of drying the hydrogel polymer. The pulverizer used in the coarse pulverization step may be any one selected from the group consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter.

[0026] Meanwhile, referring to the flowchart of Figure 1, the method for producing a superabsorbent polymer of the present invention can include a step of drying a hydrogel polymer that has been coarsely pulverized as described above or that has not been subjected to the coarse pulverization step to obtain a dried product A. The drying method in the drying step can be specifically carried out by supplying hot air, irradiating with infrared rays, irradiating with ultrashort waves, or irradiating with ultraviolet rays, and the dried product A can be obtained by carrying out the drying step using any of the drying methods.

[0027] Here, the moisture content of the dried body (a) may be 2 to 9 wt %. More specifically, it may be 3 to 7 wt % or 4 to 6 wt %. Here, the moisture content of the dried body (a) may refer to the moisture content of the dried body (a) that has been subjected to a drying step but not a subsequent hydration treatment. If the moisture content of the dried body is less than 2 wt %, the dried body may be in an overdried state, and the content of fine powder in the dried body may increase excessively. If the moisture content of the dried body is more than 9 wt %, the dried body may be in an undried state, and if the dried body is subjected to a hydration treatment and introduced into the next pulverization step, pulverization may not proceed.

[0028] The method for producing a superabsorbent polymer according to one embodiment of the present invention may include a step of hydrating the dried material a to adsorb moisture to the dried material a. Specifically, the hydration treatment causes a certain amount of moisture to be adsorbed on the surface of the dried material a, thereby obtaining a hydrated dried material b.

[0029] The hydration treatment can be carried out under conditions of 15°C to 70°C, specifically under conditions of 20°C to 40°C. This allows an appropriate amount of moisture to be maintained on the surface of the dried body a, enabling smooth hydration treatment. Specifically, when the hydration treatment is carried out by spray hydration, the hydration treatment temperature can be the temperature of the droplets.

[0030] The hydration treatment is carried out under the above conditions, and a method for creating this atmosphere can be, for example, a method of directly spraying water. This hydration treatment allows moisture to be adsorbed onto the surface of dried body a. The moisture adsorbed onto the surface of the hydration-treated dried body b can be diffused and absorbed into the interior over time.

[0031] The amount of water adsorbed into the dried material (a) by the hydration treatment may be 1 wt % or more, 2 wt % or more, or 3 wt % or more, and 10 wt % or less, 7 wt % or less, or 5 wt % or less, based on 100 wt % of the dried material (a). The amount of water adsorption may refer to the amount of water adsorbed into the dried material (a) by the hydration treatment. When the amount of water adsorbed into the dried material (a) is within the above range, the moisture content of the hydration-treated dried material (b) can reach the desired level in the present invention. Here, the amount of water adsorption may be measured in accordance with the International Organization for Standardization (ISO) 171904-4:2001 method.

[0032] Meanwhile, the moisture content of the hydrated dried material (b) may be 5% by weight or more, 6% by weight or more, or 9% by weight or more, and 15% by weight or less, 13% by weight or less, or 11% by weight or less. Here, the moisture content of the hydrated dried material (b) may refer to the moisture content of the hydrated dried material (b) that has been subjected to the hydration treatment but not the subsequent pulverization step. When the moisture content of the hydrated dried material (b) is within the above range, the amount of fine powder generated in the pulverization step described below may be reduced to, for example, a level of less than 20%. Therefore, the moisture content of the hydrated dried material (b) may be controlled within the above range by adjusting the amount of moisture adsorbed by the dried material (a).

[0033] If the moisture content of the hydrated dried material (b) is less than 5 wt%, it may be difficult to reduce the generation of fine powder during pulverization, which is the objective of the present invention. If the moisture content of the hydrated dried material (b) is more than 15 wt%, the moisture content of the hydrated dried material (b) may be too high, making it impossible to pulverize the pulverization step. Here, the moisture content can be measured using a moisture meter (AND MX_50).

[0034] According to one embodiment of the present invention, the method for producing a superabsorbent polymer may include pulverizing the hydrated dried body (b) to obtain the superabsorbent polymer. The pulverization step may be performed once, but may also be performed multiple times. Conventional pulverization of a dry body without hydration results in the destruction of the surface of the dry body, resulting in the generation of excessive fine powder. Typically, the fine powder has a particle size (D50) of less than 150 μm, which may be unsuitable for commercialization as a superabsorbent polymer. Here, the particle size (D50) may refer to the particle size at the 50% point of the cumulative particle number distribution by particle size. Therefore, the greater the amount of fine powder generated during the pulverization step, the lower the yield of the superabsorbent polymer. However, in the present invention, hydration treatment prior to the pulverization step allows moisture to be adsorbed onto the surface of the dry body (a), thereby preventing the surface destruction of the hydrated dried body (b) due to the moisture. This reduces the amount of fine powder generated during pulverization, thereby increasing the yield of the superabsorbent polymer.

[0035] Meanwhile, the pulverizer used in the pulverization step may be, for example, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog mill.

[0036] According to one embodiment of the present invention, the step of pulverizing the hydrated dried body (b) to obtain a superabsorbent polymer can be performed immediately after the hydration of the dried body (a) or within 24 hours after the hydration. "Immediately after the hydration" can refer to the completion of the hydration or the minimum time required for the pulverization step after the hydration. Thus, the moisture content of the surface of the hydrated dried body (b) can be increased immediately after the hydration, thereby preventing surface damage during the pulverization step and achieving the desired results. Therefore, even if the moisture adsorption amount during the hydration is relatively low, e.g., 1% to 3% by weight, the moisture does not diffuse from the surface of the hydrated dried body (b) to the interior, and thus the amount of fine powder generated during pulverization can be reduced.

[0037] Meanwhile, after hydration, moisture present on the surface of the hydrated dried material (b) may diffuse into the interior over time. However, if the amount of moisture adsorbed by the dried material (a) during hydration is relatively high, for example, 4% to 10% by weight, the amount of moisture remaining on the surface of the hydrated dried material (b) may remain high even after stabilizing the hydrated dried material (b) for a predetermined period of time. Therefore, when a pulverization step is performed after the stabilization process, surface damage to the hydrated dried material (b) may be prevented, thereby reducing the amount of fine powder generated. Here, the stabilization may refer to, for example, aging the hydrated dried material (b) for a predetermined period of time in a humid atmosphere in a sealed container.

[0038] After the pulverization step, the resulting superabsorbent polymer may be classified into appropriate particle sizes to control the properties of the final product. The classification may be performed after each pulverization.

[0039] Here, the appropriate particle size (D50) may be a particle size of 150 μm to 850 μm, and particles having such a particle size can be classified as normal particles. On the other hand, as mentioned above, particles having a particle size of less than 150 μm can be classified as fine powder. This particle size can be measured in accordance with the EDANA WSP 220.3 method of the European Disposables and Nonwovens Association (EDANA).

[0040] Through such a series of grinding steps, normal particles, i.e., superabsorbent polymer, can be produced.

[0041] Next, if necessary, the method may further include a step of surface-crosslinking the produced superabsorbent polymer in the presence of a surface crosslinking agent to produce a superabsorbent polymer having a surface crosslinked layer formed on at least a portion of its surface. Here, the surface crosslinked layer may be produced from a surface crosslinking agent, which may include a polyvalent epoxy compound, and the polyvalent epoxy compound may be a glycidyl ether compound of a polyhydric alcohol.

[0042] Specifically, the surface cross-linking agent may include one or more polyfunctional epoxy compounds selected from the group consisting of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, tetraethylene glycol diglycidyl ether, glycerin polyglycidyl ether, and sorbitol polyglycidyl ether.

[0043] The surface cross-linking agent can be mixed with the superabsorbent polymer in a solution state, specifically, in a surface cross-linking solution state dissolved in a solvent. The surface cross-linking solution can contain water and methanol in addition to the surface cross-linking agent. Typically, the surface cross-linking solution is applied to the surface of the superabsorbent polymer. Thus, the surface cross-linking reaction occurs on the surface of the superabsorbent polymer, which improves the cross-linking property on the surface of the particles without substantially affecting the interior of the particles. Therefore, the surface-cross-linked superabsorbent polymer has a higher degree of cross-linking near the surface than in the interior. The surface cross-linking reaction and drying can be performed simultaneously by heating the superabsorbent polymer to which the surface cross-linking agent has been added.

[0044] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention, and the scope of the present invention is not limited thereto.

[0045] Example Example 1 A composition was prepared by mixing 100 g of acrylic acid, 0.16 g of polyethylene glycol diacrylate (PEGDA) as an internal crosslinking agent, 0.008 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator, 0.12 g of sodium persulfate as a thermal polymerization initiator, and 123.5 g of caustic soda (NaOH) solution as a neutralizer at room temperature to a solids content of 45.0 wt %.

[0046] Next, the composition was supplied at a rate of 500 to 2000 mL / min onto a conveyor belt having a width of 10 cm and a length of 2 m, which was moving at a speed of 10 cm / min. 2 The polymer was irradiated with ultraviolet light having an intensity of 1000 .mu.m for 60 seconds to carry out a polymerization reaction, thereby obtaining a hydrogel polymer.

[0047] Next, the hydrogel polymer was coarsely pulverized using a chopper. The pulverized hydrogel polymer was then dried in an air-flow oven with hot air at 185°C for 30 minutes, yielding 100 g of a dried polymer with a moisture content of 5% by weight.

[0048] The dried material was evenly spread on a 320mm x 200mm x 50mm SUS tray and 3.2g of water was sprayed onto it. As a result, the amount of water adsorbed onto the dried material was 3wt% based on 100wt% of the dried material, and the amount of water adsorption was measured according to the International Organization for Standardization (ISO) 17190-4:2001 method. The moisture content of the dried material hydrated by spraying water was 8wt%. Next, the hydrated dried material was placed in a sealed container and mixed by stirring. After that, a stabilization process was carried out in the sealed container for 24 hours.

[0049] After stabilization in this sealed container, the hydrated dried material was pulverized in a roll mill to obtain a pulverized product. The pulverized product was placed in a mesh set consisting of ASTM meshes #6, #10, #20, #25, #30, #40, #50, #70, #80, and #100, and the mesh set was attached to a sieve shaker. The sieve shaker was operated for 10 minutes at an amplitude of 1.5 mm to classify the pulverized product. This resulted in a superabsorbent resin with particle sizes of 150 μm to 850 μm.

[0050] Example 2 A superabsorbent polymer was produced in the same manner as in Example 1, except that 5.8 g of water (water adsorption amount 5 wt.% relative to 100 wt.% of the dried product) was sprayed onto the dried product to add water, so that the moisture content of the hydrated dried product became 10 wt.%.

[0051] Example 3 A superabsorbent polymer was produced in the same manner as in Example 1, except that 11 g of water (water adsorption amount 10 wt.% relative to 100 wt.% of the dried product) was sprayed onto the dried product to add water, so that the water content of the hydrated dried product became 15 wt.%.

[0052] Example 4 In Example 1, 1.1 g of water (water adsorption amount is 1 wt% relative to 100 wt% of the dried product) was sprayed onto the dried product to add water, resulting in a moisture content of 6 wt% of the hydrated dried product. A superabsorbent polymer was produced in the same manner as in Example 1, except that the stabilization process of the hydrated dried product was omitted and the product was pulverized immediately after the hydration treatment.

[0053] Example 5 In Example 1, 1.1 g of water (water adsorption amount is 1 wt% relative to 100 wt% of the dried product) was sprayed onto the dried product to add water, so that the moisture content of the hydrated dried product became 6 wt%, and the stabilization process of the hydrated dried product was carried out for 1 hour. A superabsorbent polymer was produced in the same manner as in Example 1.

[0054] Example 6 In Example 1, 3.2 g of water (water adsorption amount is 3 wt% relative to 100 wt% of the dried product) was sprayed onto the dried product having a moisture content of 2 wt%, so that the moisture content of the hydrated dried product became 5 wt%. A superabsorbent polymer was produced in the same manner as in Example 1, except that the stabilization process of the hydrated dried product was omitted and the product was pulverized immediately after the hydration treatment.

[0055] Example 7 A superabsorbent polymer was produced in the same manner as in Example 1, except that 18 g of water (water adsorption amount 15 wt.% relative to 100 wt.% of the dried product) was sprayed onto the dried product to add water, and the water content of the hydrated dried product became 20 wt.%.

[0056] Example 8 A superabsorbent polymer was produced in the same manner as in Example 1, except that 26 g of water (water adsorption amount 20 wt.% relative to 100 wt.% of the dried product) was sprayed onto the dried product to add water, and the water content of the hydrated dried product became 25 wt.%.

[0057] Comparative Example Comparative Example 1 A superabsorbent resin was produced in the same manner as in Example 1, except that the dried product was not hydrated but was immediately pulverized.

[0058] Comparative Example 2 A highly water-absorbent resin was produced in the same manner as in Example 1, except that the dried product having a moisture content of 2% by weight was crushed immediately without adding moisture.

[0059] Comparative Example 3 A highly water-absorbent resin was produced in the same manner as in Example 1, except that the dried product with a moisture content of 10% by weight was not subjected to a moisture treatment but was immediately pulverized.

[0060] Experimental example The superabsorbent resins produced in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

[0061] 1) Moisture content The moisture content may refer to the moisture content of the hydrated dried body after hydration and before pulverization in the case where hydration was performed (Examples), and may refer to the moisture content of the dried body after drying and before pulverization in the case where hydration was not performed (Comparative Examples). Specifically, the moisture content was measured from the change in weight caused by heating the hydrated dried body or dried body with a halogen lamp (400W) in a moisture meter (AND MX_50) to evaporate the moisture. Specifically, the moisture content was measured according to the following procedure.

[0062] (i) Set the measurement conditions of the moisture meter (heating temperature: 180°C, heating time: 40 minutes). (ii) With no sample present on the sample pan, adjust the weight to zero (0). (iii) A 5 g sample (error: 0.02%) of the hydrated dried body or dried body is taken and uniformly loaded onto the sample pan. (iv) After the measurement is completed, check the moisture content.

[0063] 2) Amount of fine powder generated The amount of fine powder generated may refer to the amount of fine powder having a particle size of less than 150 μm contained in the pulverized product obtained by the pulverization step. Specifically, the amount of fine powder generated was measured by the following method.

[0064] First, 100 g of the pulverized material obtained in the Examples and Comparative Examples was sampled as a sample and placed on a mesh set consisting of ASTM meshes #6, #10, #20, #25, #30, #40, #50, #70, and #100. The mesh set was attached to a sieve shaker and operated for 10 minutes at an amplitude of 1.5 mm to classify the pulverized material according to particle size for each mesh. The mesh ratio corresponding to each mesh was then calculated using the following mathematical formula 1.

[0065]

number

[0066] Next, the mesh ratio of the pulverized material corresponding to below #100 (particle size less than 150 μm) was added up to measure the amount of fine powder generated.

[0067] 3) Particle size The particle size was measured by measuring the particle size of the pulverized material, and was calculated according to the following mathematical formula 2, in the same manner as in the method for measuring the "amount of fine powder generated" described above, by classifying the pulverized material (100 g) using a mesh set.

[0068]

number

[0069] Here, the meshes (#40 to #100) are the meshes #40 to #100 included in the mesh set, and the mesh ratio is the mesh ratio according to the above-mentioned mathematical formula 1. That is, the particle size is the result of calculating the arithmetic mean of the average particle size based on the mesh ratio of meshes #40 to #100.

[0070] [Table 1]

[0071] Referring to Table 1, in the examples in which the dried body was subjected to a hydration treatment by adsorbing moisture and then a pulverization step was performed, it was confirmed that the amount of fine powder generated due to surface destruction during the pulverization step was reduced because moisture was adsorbed onto the surface of the dried body by the hydration treatment. In addition, it was confirmed that the amount of fine powder generated was lower in Examples 1 to 5 in which a dried body with the same moisture content was subjected to a hydration treatment than in Comparative Example 1 in which a dried body with the same moisture content was not subjected to a hydration treatment step.

[0072] However, in Examples 7 and 8, the dried material absorbed a large amount of water during the hydration treatment, resulting in a moisture content that was beyond the range of the hydration-treated dried material that is intended to be obtained in the present invention, and it was confirmed that pulverization was impossible in the pulverization step.

[0073] On the other hand, Comparative Example 1 is a superabsorbent resin obtained by pulverizing a dried body with a moisture content of 5% by weight that was not subjected to a moisture treatment step, and it was confirmed that the amount of fine powder generated was significantly increased compared to Examples 1 to 5. In Examples 1 to 5, a dried body with the same moisture content as Comparative Example 1 was pulverized after being subjected to a moisture treatment, but in Comparative Example 1, no moisture treatment was performed, and it was confirmed that the surface of the dried body was destroyed by the pulverization step, resulting in an increase in the amount of fine powder generated.

[0074] In addition, Comparative Example 2 is a superabsorbent resin obtained by pulverizing a dried body with a moisture content of 2% by weight that was not subjected to a moisture treatment step, and it was confirmed that the amount of fine powder generated was increased compared to Example 6, in which a dried body with the same moisture content was subjected to moisture treatment. As described above, it was confirmed that the amount of fine powder generated can be improved depending on whether or not the moisture treatment step is performed for a dried body with the same moisture content.

[0075] On the other hand, in Comparative Example 3, a hydration treatment step was not performed and a dried body with a moisture content of 10 wt% was pulverized, but it was confirmed that pulverization was impossible. As described above, when the moisture content of the dried body is high, the hydrogel polymer may be in an undried state in the drying step, and when it is introduced into the pulverization step in this undried state, pulverization may be impossible as in Comparative Example 3.

Claims

1. A method for producing a hydrous gel polymer by supplying a composition containing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acid group, an internal crosslinking agent, and a polymerization initiator to a polymerization reactor and carrying out a polymerization reaction therein; drying the hydrogel polymer to obtain a dry body; hydrating the dried body to adsorb moisture into the dried body; and pulverizing the hydrated dried product to obtain a superabsorbent polymer. the amount of water adsorbed by the dried body by the hydration treatment is 1% by weight to 10% by weight relative to 100% by weight of the dried body; The hydration treatment is carried out by spraying water onto the dried body, The method for producing a superabsorbent resin, wherein the moisture content of the hydrated dried product is 5% by weight to 15% by weight.

2. Before drying the hydrogel polymer, The method for producing a highly water-absorbent resin according to claim 1, further comprising the step of coarsely pulverizing the hydrogel polymer.

3. The step of pulverizing the hydrated dried product to obtain a superabsorbent polymer includes:

3. The method for producing a highly water-absorbent polymer according to claim 1, wherein the method is carried out immediately after the hydration treatment of the dried body or within 24 hours after the hydration treatment.

4. The method for producing a highly water-absorbent resin according to claim 1, wherein the hydration treatment is carried out under conditions of 15°C to 70°C.

5. After the step of pulverizing the hydrated dried body to obtain a superabsorbent resin, surface cross-linking is performed in the presence of a surface cross-linking agent; The method for producing a highly water-absorbent resin according to claim 1, further comprising the step of forming a surface cross-linked layer on at least a portion of the surface.

6. 2. The method for producing a highly absorbent resin according to claim 1, wherein the internal crosslinking agent is one or more of ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, and polyethylene glycol di(meth)acrylate.

7. The method for producing a highly water-absorbent resin according to claim 1, wherein the water-soluble ethylenically unsaturated monomer is (meth)acrylic acid or a salt thereof.

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