阅读说明：本技术 超吸收性聚合物组合物的制备方法 (Method for preparing super absorbent polymer composition ) 是由 闵允栽 金琪哲 金起贤 朴晟秀 崔镇旭 金泰润 禹熙昶 于 2020-12-18 设计创作，主要内容包括：本公开内容涉及超吸收性聚合物组合物的制备方法。更具体地,其涉及这样的超吸收性聚合物组合物的制备方法,所述方法通过添加具有特定结构的添加剂能够将水凝胶聚合物粉碎至常规颗粒尺寸而没有颗粒之间的团聚,并且能够显著减少该过程期间产生的细粉的量。(The present disclosure relates to a method of preparing a superabsorbent polymer composition. More particularly, it relates to a method of preparing a superabsorbent polymer composition capable of pulverizing a hydrogel polymer to a conventional particle size without agglomeration between particles by adding an additive having a specific structure and capable of significantly reducing the amount of fine powder generated during the process.)

1. A method of making a superabsorbent polymer composition comprising

1) A step of forming a hydrogel polymer by crosslinking-polymerizing a water-soluble ethylenically unsaturated monomer having an at least partially neutralized acidic group in the presence of an internal crosslinking agent and a polymerization initiator;

2) a step of mixing the hydrogel polymer with a carboxylic acid-based additive, followed by pulverization to prepare a pulverized product comprising aqueous superabsorbent polymer particles and the additive; and

3) a step of preparing a superabsorbent polymer composition comprising superabsorbent polymer particles and the additive by drying the pulverized product,

wherein the carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by the following chemical formula 1 and salts thereof:

[ chemical formula 1]

In the chemical formula 1, the first and second,

a is an alkyl group having 5 to 21 carbon atoms,

B₁is-OCO-, -COO-or-COOCH (R)₁)COO-，

B₂is-CH₂-、-CH₂CH₂-、-CH(R₂) -, -CH-or-C.ident.C-,

wherein R is₁And R₂Each independently an alkyl group having 1 to 4 carbon atoms,

n is an integer of 1 to 3, and

c is carboxyl.

2. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the hydrogel polymer has a water content of 30 to 70 wt.%.

3. The method of preparing a superabsorbent polymer composition of claim 1,

wherein in the chemical formula 1, the metal oxide,

a is-C₆H₁₃、-C₁₁H₂₃、-C₁₂H₂₅、-C₁₇H₃₅or-C₁₈H₃₇。

4. The method of preparing a superabsorbent polymer composition of claim 1,

wherein in the chemical formula 1, the metal oxide,

B₁is composed of

Wherein is the bonding site to the adjacent atom.

5. The method of preparing a superabsorbent polymer composition of claim 1,

wherein in the chemical formula 1, the metal oxide,

B₂is composed of

Wherein is the bonding site to the adjacent atom.

6. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by chemical formula 1, alkali metal salts thereof, and alkaline earth metal salts thereof.

7. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the carboxylic acid-based additive is any one of compounds represented by the following chemical formulas 1-1 to 1-7:

8. the method of preparing a superabsorbent polymer composition of claim 1,

wherein the carboxylic acid-based additive is used in an amount of 0.01 to 10 parts by weight, based on 100 parts by weight of the hydrogel polymer.

9. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the carboxylic acid-based additive is mixed in the form of a solution dissolved in a solvent.

10. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the comminuting is performed by a meat grinder.

11. The method of preparing a superabsorbent polymer composition of claim 10,

wherein the meat grinder comprises a perforated plate, an

The breaker plate has a plurality of fine cut holes having a certain size.

12. The method of preparing a superabsorbent polymer composition of claim 11,

wherein the fine cut holes provided in the multi-well plate have a hole size of 0.2mm to 5 mm.

13. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the water content of the aqueous superabsorbent polymer particles is from 30 wt% to 70 wt%.

14. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the comminuted product comprises 89% by weight or more, based on the total weight, of aqueous superabsorbent polymer particles having a particle size of from 150 μm to 850 μm.

15. The method of preparing a superabsorbent polymer composition of claim 1,

at least some of the additive in the comminuted product is present on the surface of the aqueous superabsorbent polymer particles.

16. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the drying is performed in a mobile manner.

17. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the drying is performed at a temperature of 80 ℃ to 250 ℃ for 10 minutes to 3 hours.

18. The method of preparing a superabsorbent polymer composition of claim 1,

wherein the superabsorbent polymer composition is prepared to contain less than 10% by weight of fine powder having a particle size of less than 150 μm, based on the total weight.

19. The method of preparing a superabsorbent polymer composition of claim 1,

the method does not include an additional pulverization step after drying the pulverized product.

20. The method of preparing a superabsorbent polymer composition of claim 1,

further comprising the step of forming a surface cross-linked layer on at least a portion of the surface of the superabsorbent polymer particles in the presence of a surface cross-linking agent.

Technical Field

Cross Reference to Related Applications

The present application claims the benefits of korean patent application No. 10-2019-.

The present disclosure relates to a method of preparing a superabsorbent polymer composition. More particularly, it relates to a method of preparing a superabsorbent polymer composition in which the amount of fine powder generated is significantly reduced.

Background

Superabsorbent Polymer (SAP) is a synthetic polymeric material that is capable of absorbing 500 to 1000 times its own weight of moisture. Each manufacturer names them differently, such as SAM (Super Absorbent Material), AGM (Absorbent Gel Material), etc. Such super absorbent polymers are beginning to be put into practical use in sanitary products, and are now widely used not only in sanitary products but also in water-retentive soil products for gardening, water-stopping materials for civil engineering and construction, sheets for growing seedlings, freshness-retaining agents for the field of food circulation, materials for cataplasms, and the like.

These superabsorbent polymers have been widely used in the field of sanitary materials, such as diapers or sanitary napkins. In such sanitary materials, the superabsorbent polymer is generally contained in a state of being distributed in the slurry. However, in recent years, continuous efforts have been made to provide sanitary materials such as diapers having a thinner thickness. As part of such efforts, development of so-called pulp-free diapers and the like in which the content of pulp is reduced or no pulp is used at all is being actively advanced.

As described above, in the case of a sanitary material in which the content of pulp is reduced or pulp is not used, superabsorbent polymers are contained at a relatively high ratio, and these superabsorbent polymer particles are inevitably contained in multiple layers in the sanitary material. In order for all the superabsorbent polymer particles contained in the multiple layers to absorb a large amount of liquid such as urine more effectively, the superabsorbent polymer needs to exhibit substantially high absorption performance and a fast absorption rate.

Meanwhile, such superabsorbent polymers are generally prepared by a method including: a step of polymerizing the monomer to prepare a hydrogel polymer containing a large amount of moisture; and a step of drying the hydrogel polymer and then pulverizing the dried hydrogel polymer into polymer particles having a desired particle diameter. However, when the hydrogel polymer is dried and then pulverized as described above, a large amount of fine powder is generated, and thus there is a problem in that physical properties of the finally produced superabsorbent polymer are deteriorated.

Further, in order to reuse such fine powder, a fine powder reassembled body obtained by mixing the fine powder with water to agglomerate, and then drying/pulverizing/classifying is generally used. However, due to the water used at this time, problems such as an increase in energy consumption during the drying process and an increase in load on equipment may occur, and thus the productivity of preparing the superabsorbent polymer may be reduced.

Therefore, there is a continuing need to develop a technology capable of manufacturing superabsorbent polymers without generating fine powder to fundamentally solve the problem.

Disclosure of Invention

Technical problem

Accordingly, the present disclosure relates to a method of preparing a superabsorbent polymer composition capable of pulverizing a hydrogel polymer to a conventional particle size without agglomeration between particles by adding an additive having a specific structure, and capable of significantly reducing the amount of fine powder generated during the process.

Technical scheme

In order to solve the above problems, there is provided a method of preparing a superabsorbent polymer composition, the method comprising:

1) a step of forming a hydrogel polymer by crosslinking-polymerizing a water-soluble ethylenically unsaturated monomer having an at least partially neutralized acidic group in the presence of an internal crosslinking agent and a polymerization initiator;

2) a step of mixing the hydrogel polymer with the carboxylic acid-based additive, followed by pulverization to prepare a pulverized product comprising the aqueous superabsorbent polymer particles and the additive; and

3) a step of preparing a superabsorbent polymer composition comprising superabsorbent polymer particles and an additive by drying the pulverized product;

wherein the carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by the following chemical formula 1 and salts thereof:

[ chemical formula 1]

In the chemical formula 1, the first and second,

a is an alkyl group having 5 to 21 carbon atoms,

B₁is-OCO-, -COO-or-COOCH (R)₁)COO-，

B₂is-CH₂-、-CH₂CH₂-、-CH(R₂) -, -CH-or-C.ident.C-,

wherein R is₁And R₂Each independently an alkyl group having 1 to 4 carbon atoms,

n is an integer of 1 to 3, and

c is carboxyl.

Advantageous effects

The method of preparing the superabsorbent polymer composition of the present disclosure can prepare a superabsorbent polymer composition consisting of superabsorbent polymer particles having a desired particle size without agglomeration between the pulverized particles by pulverizing a hydrogel polymer in the presence of a carboxylic acid-based additive. In addition, since the hydrogel polymer is pulverized to a conventional particle size, the amount of fine powder generated during the manufacture of the superabsorbent polymer composition can be significantly reduced.

Drawings

FIG. 1 is a flow chart illustrating a conventional method of preparing superabsorbent polymers.

FIG. 2 is a flow chart illustrating a method of making a superabsorbent polymer composition according to one embodiment.

Fig. 3 is a photograph showing evaluation of particle agglomeration characteristics of the hydrogel polymer prepared in example 3.

Fig. 4 is a photograph showing evaluation of particle agglomeration characteristics of the hydrogel polymer prepared in example 7.

Fig. 5 is a photograph showing evaluation of particle agglomeration characteristics of the hydrogel polymer prepared in comparative example 3.

Fig. 6 is a photograph showing evaluation of particle agglomeration characteristics of the hydrogel polymer prepared in comparative example 6.

Detailed Description

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "has," "having," or "having," when used in this specification, specify the presence of stated features, steps, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, components, or groups thereof.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example and will herein be described in detail. However, it is not intended to limit the invention to the particular forms disclosed, and it should be understood that the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example and will herein be described in detail. However, it is not intended to limit the invention to the particular forms disclosed, and it should be understood that the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Hereinafter, a method of preparing the superabsorbent polymer and the superabsorbent polymer will be described in more detail according to embodiments of the present invention.

Unless explicitly stated, the terms are used to refer to specific embodiments only, and are not intended to limit the disclosure. Unless the context dictates otherwise, singular expressions of the present disclosure may include plural expressions.

According to one embodiment of the present disclosure, there is provided a method of preparing a superabsorbent polymer composition, the method comprising:

1) a step of forming a hydrogel polymer by crosslinking-polymerizing a water-soluble ethylenically unsaturated monomer having an at least partially neutralized acidic group in the presence of an internal crosslinking agent and a polymerization initiator (step 1);

2) a step of mixing the hydrogel polymer with the carboxylic acid-based additive, followed by pulverization to prepare a pulverized product comprising the aqueous superabsorbent polymer particles and the additive (step 2); and

3) a step of preparing a superabsorbent polymer composition comprising superabsorbent polymer particles and an additive by drying the pulverized product (step 3),

wherein the carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by the following chemical formula 1 and salts thereof:

[ chemical formula 1]

In the chemical formula 1, the first and second,

a is an alkyl group having 5 to 21 carbon atoms,

B₁is-OCO-, -COO-or-COOCH (R)₁)COO-，

B₂is-CH₂-、-CH₂CH₂-、-CH(R₂) -, -CH-or-C.ident.C-,

wherein R is₁And R₂Each independently an alkyl group having 1 to 4 carbon atoms,

n is an integer of 1 to 3, and

c is carboxyl.

The term "polymer" in this disclosure is in a state in which the water-soluble ethylenically unsaturated monomer is polymerized, and may include all ranges of water content or all ranges of particle size. Among the polymers, a polymer having a water content of about 30% by weight or more after pulverization and before drying may be referred to as a hydrogel polymer, and particles in which the hydrogel polymer is pulverized and dried may be referred to as a crosslinked polymer.

Further, the term "superabsorbent polymer particles" refers to particulate materials comprising a crosslinked polymer in which water-soluble ethylenically unsaturated monomers having at least partially neutralized acidic groups are polymerized and crosslinked by an internal crosslinking agent.

Furthermore, the term "superabsorbent polymer" is used to include all of the following, depending on the context: a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized is polymerized or a base resin in the form of a powder composed of superabsorbent polymer particles in which the crosslinked polymer is pulverized, and a crosslinked polymer or a base resin which is further processed (e.g., dried, pulverized, classified, surface-crosslinked, etc.) in a state suitable for commercialization. Thus, the term "superabsorbent polymer" may be construed to include compositions comprising a superabsorbent polymer, i.e., a plurality of superabsorbent polymer particles.

Further, the term "conventional superabsorbent polymer particles" refers to particles having a particle size of 150 μm to 850 μm among the superabsorbent polymer particles.

Furthermore, the term "fines" refers to particles of superabsorbent polymer particles having a particle size of less than 150 μm. The particle size of these polymer particles can be measured according to EDANAWSP 220.3 of the European Disposables and Nonwovens Association (EDANA).

Further, the term "chopping" means that the hydrogel polymer is cut into small pieces to improve drying efficiency, and is used separately from being crushed into a conventional particle size.

Superabsorbent polymers are typically prepared by drying a hydrogel polymer and then comminuting it to the desired particle size. At this time, in order to facilitate the drying of the hydrogel polymer and to improve the efficiency of the crushing process, a process of chopping the hydrogel polymer is performed before the drying process. However, due to the viscosity of the hydrogel polymer during this chopping process, the hydrogel polymer cannot be crushed into micron-sized particles but becomes an agglomerated gel. When the agglomerated gel-like hydrogel polymer is dried in a fixed bed manner, a sheet-like dried body is formed, and a multistage pulverization process is required for pulverizing it into micrometer-sized particles. Therefore, there is a problem that many fine powders are generated in the process.

Specifically, FIG. 1 shows a flow diagram of a conventional method of preparing superabsorbent polymers. Referring to fig. 1, in the related art, a superabsorbent polymer has been prepared, including the following steps.

(polymerization) cross-linking polymerizing a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent and a polymerization initiator to form a hydrogel polymer;

(chopping) the hydrogel polymer;

(drying) drying the minced hydrogel polymer; and

(pulverization/classification) pulverizing the dried polymer, and then classifying the pulverized polymer into conventional particles and fine powder;

as noted above, the minced hydrogel polymer has an agglomerated gel shape with a size of about 1cm to 10 cm. This minced hydrogel polymer was laminated on a belt with a perforated plate at the bottom and dried by hot air supplied from the bottom or top. Since the polymer dried by the above drying method has a plate shape instead of a particle shape, the step of pulverization and subsequent classification is carried out as a step of coarse pulverization, subsequent classification and then fine pulverization, and subsequent classification again, so that the produced particles become conventional particles, i.e., particles having a particle diameter of 150 to 850 μm. Since the amount of the fine powder separated in the final classification step by the preparation method is up to about 10% to about 20% by weight based on the total weight of the finally prepared superabsorbent polymer, the separated fine powder is mixed with an appropriate amount of water for reassembly and added to the chopping step or added before the drying step.

However, when the fine powder reassembled body mixed with water is reinjected into a pulverizing or drying process for reuse of the fine powder, problems such as an increase in load on equipment and/or energy consumption arise. In addition, the physical properties of the superabsorbent polymer are deteriorated due to the fine powder that is not classified and remains.

Accordingly, the present inventors have recognized that the amount of fine powder generated in the conventional production method is largely affected by the particle size introduced into the pulverization process, and have determined that if the hydrogel polymer can be pulverized to a micrometer size without agglomeration between the hydrogel polymers in the chopping process, the amount of fine powder generated during the process can be reduced. Therefore, as a result of experiments with various types of additives that can reduce the viscosity of the hydrogel polymer during chopping, it was determined that when the hydrogel polymer is mixed with the carboxylic acid-based additive and then pulverized, the viscosity of the hydrogel polymer is reduced due to the carboxylic acid-based additive, and thus pulverization into particles at the micrometer level is possible. The present invention has been accomplished in view of the above. This is because the carboxylic acid-based additive mixed with the hydrogel polymer is adsorbed on the surface of the hydrogel polymer, thereby preventing agglomeration of the crushed hydrogel polymer. In addition, since the drying process is performed in the form of micron-sized particles, drying is facilitated, and a separate pulverizing process is not required after the drying process, so that the amount of fine powder generated can be significantly reduced.

Specifically, FIG. 2 shows a flow diagram of a method of making a superabsorbent polymer composition according to one embodiment. Referring to fig. 2, unlike the related art, a hydrogel polymer is prepared and pulverized to a conventional particle size, and then dried to prepare a superabsorbent polymer composition.

Herein, the carboxylic acid-based additive has both a hydrophobic functional group and a hydrophilic functional group. Meanwhile, since the water-soluble ethylenically unsaturated monomer contains an acid group (-COOH) and/or a neutralized acid group (-COO-), a large number of hydrophilic moieties are present on the surface of the hydrogel polymer prepared by polymerization because the acid group (-COOH) and/or the neutralized acid group (-COO-), which remain without participating in the polymerization. Therefore, when the additive is mixed with the hydrogel polymer, the hydrophilic functional group of the additive is adsorbed onto at least a part of the hydrophilic portion present on the surface of the hydrogel polymer, and the surface of the polymer on which the additive is adsorbed becomes hydrophobic due to the hydrophobic functional group located at the other end of the additive. Therefore, agglomeration between polymer particles can be suppressed.

More specifically, in the carboxylic acid-based additive, the hydrophobic functional group is an alkyl group having from 5 to 21 carbon atoms (moiety a), and the hydrophilic functional group is a moiety C, in particular a carboxyl group (COOH) or, in the case of a salt, a carboxylate group (-COO)^-). The hydrophobic functional group and the hydrophilic functional group are respectively positioned at both ends of the additive. In particular, the carboxylic acid-based additive comprises a part (B) in addition to a part A and a part C at both ends₁-B₂) And part (B)₁-B₂) The adsorption property to the polymer surface is improved, and the adsorption property to the polymer surface may be insufficient in the case of having only the portion C. Thus, and has an A-C structure without a moiety (B)₁-B₂) Has excellent adsorption property to the surface of the polymer exhibiting hydrophilicity, and thus effectively inhibits the agglomeration of the super absorbent polymer particles, compared to the compound of formula 1.

Accordingly, it is possible to crush the hydrogel polymer to a conventional particle size without agglomeration between particles, and to perform a drying process after crushing the hydrogel polymer to a conventional particle size, thereby significantly reducing the amount of fine powder generated during the process. In addition, the method of preparing the superabsorbent polymer composition according to one embodiment does not necessarily require a pulverization process and a classification process after drying, so that the manufacturing cost of the superabsorbent polymer can be greatly reduced.

Further, when the hydrogel polymer is pulverized in the presence of the carboxylic acid-based additive, the hydrophobic functional group part a included in the additive imparts hydrophobicity to the surface of the pulverized superabsorbent polymer particles, thereby reducing friction between the particles and increasing the bulk density of the superabsorbent polymer. In addition, the hydrophilic functional group part C included in the additive is also bonded to the superabsorbent polymer particles so that the surface tension of the polymer is not lowered. Thus, the superabsorbent polymer composition prepared by the above method may exhibit a higher bulk density and similar surface tension as compared to a composition without such additives.

Hereinafter, a method of preparing the superabsorbent polymer composition of one embodiment will be described in more detail with respect to each component.

(step 1)

The above steps form the hydrogel polymer by cross-linking polymerizing the water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of the internal cross-linking agent and the polymerization initiator, and may consist of: a step of preparing a monomer composition by mixing a water-soluble unsaturated monomer, an internal crosslinking agent and a polymerization initiator, and a step of forming a hydrogel polymer by thermally or photopolymerizing the monomer composition.

The water-soluble ethylenically unsaturated monomer can be any of the monomers commonly used in the preparation of superabsorbent polymers. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following chemical formula 2:

[ chemical formula 2]

R-COOM′

In the chemical formula 2, the first and second organic solvents,

r is a C2 to C5 hydrocarbon group having an unsaturated bond, and

m' is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt.

Preferably, the monomer may be at least one selected from the group consisting of: (meth) acrylic acid, and monovalent (alkali) metal salts, divalent metal salts, ammonium salts and organic amine salts of the acids.

When (meth) acrylic acid and/or a salt thereof is used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent polymer having improved absorption properties. In addition, the following may be used as monomers: maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, (meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, (N, N) -dimethylaminoethyl (meth) acrylate, (N, N) -dimethylaminopropyl (meth) acrylamide, and the like.

Herein, the water-soluble ethylenically unsaturated monomer may have an acidic group, and at least some of the acidic group may be neutralized by a neutralizing agent. Specifically, at least some of the acid groups of the water-soluble ethylenically unsaturated monomer may be neutralized in the step of mixing the water-soluble ethylenically unsaturated monomer having the acid groups, the internal crosslinking agent, the polymerization initiator, and the neutralizing agent. In this case, basic substances capable of neutralizing acidic groups, such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide, may be used as the neutralizing agent.

Further, the water-soluble ethylenically unsaturated monomer may have a neutralization degree of 50 to 90 mol%, 60 to 85 mol%, 65 to 85 mol%, or 65 to 75 mol%, wherein the neutralization degree refers to a degree to which an acidic group contained in the water-soluble ethylenically unsaturated monomer is neutralized by a neutralizing agent. The range of neutralization may vary depending on the final physical properties. Too high a degree of neutralization causes precipitation of the neutralized monomer, and thus polymerization may not easily occur. Conversely, too low a neutralization degree not only deteriorates the absorption rate of the polymer but also imparts a characteristic that the polymer is difficult to handle such as a characteristic of an elastic rubber.

Further, the term "internal crosslinking agent" used herein is different from a surface crosslinking agent for crosslinking the surface of the superabsorbent polymer particles, which will be described later, and the internal crosslinking agent polymerizes unsaturated bonds of the water-soluble ethylenically unsaturated monomer by crosslinking. The crosslinking in the above step is performed either on the surface or inside, but when a surface crosslinking process of the superabsorbent polymer particles, which will be described later, is performed, the surface of the particles of the finally prepared superabsorbent polymer has a structure crosslinked by a surface crosslinking agent, and the inside of the particles has a structure crosslinked by an internal crosslinking agent.

As the internal crosslinking agent, any compound may be used as long as it allows introduction of a crosslinking bond during polymerization of the water-soluble ethylenically unsaturated monomer. As non-limiting examples, the internal crosslinking agent may be a polyfunctional crosslinking agent, such as N, N' -methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, butane glycol di (meth) acrylate, butanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerol tri (meth) acrylate, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol di (meth) acrylate, butylene glycol di (meth) acrylate, propylene glycol tri (meth) acrylate, propylene glycol tetra (meth) acrylate, ethylene glycol tetra (meth) acrylate, propylene glycol tetra (meth) acrylate, ethylene glycol tetra (meth) acrylate, propylene glycol tetra (meth) acrylate, ethylene glycol tetra (meth) acrylate, propylene glycol, glycerin or ethylene carbonate, and these may be used alone or in a combination of two or more. However, the present disclosure is not limited thereto. Preferably, polyethylene glycol di (meth) acrylate may be used.

The crosslinking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of the internal crosslinking agent may be carried out by thermal polymerization, photopolymerization, or hybrid polymerization in the presence of a polymerization initiator with or without a thickener, a plasticizer, a storage stabilizer, an antioxidant, or the like, but specific details will be described later.

The internal crosslinking agent may be used in an amount of 0.01 to 5 parts by weight, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer in the monomer composition. For example, the internal crosslinking agent may be used in an amount of 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.7 parts by weight or less, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. When too little internal crosslinking agent is used, crosslinking does not sufficiently occur, and thus it may be difficult to achieve strength higher than an appropriate level, whereas when too much internal crosslinking agent is used, the internal crosslinking density increases, and thus it may be difficult to achieve a desired level of water holding capacity.

Further, the polymerization initiator may be appropriately selected depending on the polymerization method. In the case of thermal polymerization, a thermal polymerization initiator is used, and in the case of photopolymerization, a photopolymerization initiator is used. Further, in the case of a hybrid polymerization method (a method using both heat and light), all of the thermal polymerization initiator and the photopolymerization initiator may be used. However, even by the photopolymerization method, a certain amount of heat is generated by UV irradiation or the like, and some heat is generated as the polymerization reaction (exothermic reaction) proceeds. Accordingly, the composition may further comprise a thermal polymerization initiator.

Herein, any compound that can form radicals by light (e.g., UV rays) may be used without limitation as the photopolymerization initiator.

For example, the photopolymerization initiator may be one or more compounds selected from the group consisting of: benzoin ethers, dialkyl acetophenones, hydroxy alkyl ketones, phenyl glyoxylates, benzyl dimethyl ketals, acyl phosphines and alpha-amino ketones. Further, specific examples of acylphosphines include diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide, phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide, ethyl (2,4, 6-trimethylbenzoyl) phenylphosphinate, and the like. Further different photopolymerization initiators are well disclosed on page 115 of "UV Coatings: bases, Recent Developments and New Application (Elsevier, 2007)" written by Reinhold Schwalm, and the disclosure is not limited thereto.

Further, as the thermal polymerization initiator, one or more initiators selected from the group consisting of: persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid. Specifically, sodium persulfate (Na) may be used₂S₂O₈) Potassium persulfate (K)₂S₂O₈) Ammonium persulfate ((NH)₄)₂S₂O₈) And the like as examples of the persulfate-based initiator; and 2, 2-azobis (2-amidinopropane) dihydrochloride, 2-azobis-(N, N-dimethylene) isobutylamidine dihydrochloride, 2- (carbamoylazo) isobutyronitrile, 2-azobis- [2- (2-imidazolin-2-yl) propane]Dihydrochloride, 4-azobis- (4-cyanovaleric acid), and the like are examples of the azo-based initiator. More different thermal Polymerization initiators are well disclosed on page 203 of "principles of Polymerization (Wiley, 1981)" written by Odian, and the disclosure is not limited thereto.

The polymerization initiator may be used in an amount of 2 parts by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. When the concentration of the polymerization initiator is too low, the polymerization rate becomes slow, and a large amount of residual monomers may be extracted from the final product. In contrast, when the concentration of the polymerization initiator is higher than the above range, polymer chains forming the network are shortened, so that the content of extractable components is increased and the absorption rate under pressure is decreased, thereby decreasing the physical properties of the polymer.

If necessary, the monomer composition may further include additives such as a thickener, a plasticizer, a preservation stabilizer, an antioxidant, and the like.

Further, the monomer composition comprising the monomer may be, for example, in the form of a solution dissolved in a solvent (e.g., water). The solid content of the monomer composition in a solution state, that is, the concentrations of the monomer, the internal crosslinking agent and the polymerization initiator may be appropriately adjusted in consideration of the polymerization time and the reaction conditions. For example, the solid content of the monomer composition may be 10 to 80 wt.%, 15 to 60 wt.%, or 30 to 50 wt.%.

When the monomer composition has a solid content within the above range, it may be advantageous for: the pulverization efficiency during pulverization of a polymer, which will be described later, is controlled while eliminating the need to remove unreacted monomers after polymerization by utilizing the gel effect phenomenon occurring in the polymerization reaction of a high-concentration aqueous solution.

At this time, any solvent that can dissolve the above components may be used without limitation. For example, the solvent may be a combination of at least one selected from the group consisting of: water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1, 4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N, N-dimethylacetamide.

Meanwhile, the crosslinking polymerization of the water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized may be performed without any particular limitation as long as the hydrogel polymer may be formed by thermal polymerization, photopolymerization, or hybrid polymerization.

Specifically, polymerization methods are roughly classified into thermal polymerization and photopolymerization according to the energy source of polymerization. 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 is generally carried out in a reactor equipped with a movable conveyor belt or in a container with a flat bottom. However, the above polymerization method is only an example, and the present disclosure is not limited thereto.

For example, the hydrogel polymer can be obtained by supplying hot air into a reactor having a stirring shaft, such as a kneader, or heating the reactor to perform thermal polymerization. The hydrogel polymer thus obtained may have a size of several centimeters to several millimeters, depending on the shape of the stirring shaft provided in the reactor. Specifically, the size of the obtained hydrogel polymer may vary depending on the concentration of the monomer composition injected thereto and the injection speed, and a hydrogel polymer having a weight-average particle diameter of 2mm to 50mm may be obtained.

Further, when the photopolymerization is carried out in a reactor equipped with a movable conveyor belt or in a vessel having a flat bottom as described above, the obtained hydrogel polymer may be generally a sheet-like hydrogel polymer having a width of a belt. In this case, the thickness of the polymer sheet may vary depending on the concentration of the injected monomer composition, the injection speed, or the injection amount, but in general, it is preferable to feed the monomer composition so that a sheet-like polymer having a thickness of about 0.5cm to about 5cm can be obtained. When the monomer mixture is fed so that the thickness of the sheet-like polymer becomes too thin, the production efficiency is low, which is not desirable. When the thickness of the sheet-like polymer is more than 5cm, the polymerization reaction cannot be uniformly performed over the entire thickness due to an excessively thick thickness.

At this time, the hydrogel polymer thus obtained may have a water content of 30 to 70% by weight. For example, the hydrogel polymer can have a water content of 35 wt.% or more, 40 wt.% or more, 45 wt.% or more, or 50 wt.% or more, and 70 wt.% or less, 65 wt.% or less, or 60 wt.% or less. When the water content of the hydrogel polymer is too low, it is difficult to ensure an appropriate surface area in the subsequent pulverization step, and thus pulverization may not be effective. When the water content of the hydrogel polymer is too high, the pressure to be received in the subsequent pulverization step increases, and thus pulverization may be difficult to proceed to a desired particle size.

Meanwhile, "water content" in the present specification is the content of moisture in the total weight of the hydrogel polymer, and it means a value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer. Specifically, the water content is defined as a value calculated by weight loss due to moisture evaporation of the polymer during the process of raising the temperature of the crumb polymer by infrared heating for drying. At this time, the drying conditions for measuring the moisture content were as follows: the temperature was raised to about 180 ℃ and maintained at 180 ℃ and the total drying time was 40 minutes (5 minutes including the heating step).

The hydrogel polymer formed through step 1 may have a three-dimensional network structure in which a main chain formed by polymerization of a water-soluble ethylenically unsaturated monomer is crosslinked by an internal crosslinking agent. When the hydrogel polymer has a three-dimensional network structure, the water retention capacity and the absorption rate under pressure, which are general physical properties of the superabsorbent polymer, can be significantly improved, as compared to the case of having a two-dimensional linear structure that is not further crosslinked by an internal crosslinking agent.

(step 2)

The above step is mixing the hydrogel polymer with the carboxylic acid-based additive, followed by pulverization to prepare a pulverized product comprising the aqueous superabsorbent polymer particles and the additive. In this step, the aqueous gel polymer is not chopped, but rather is pulverized to a particle size of about 150 μm to about 850 μm, thereby preparing aqueous superabsorbent polymer particles that can be applied to the final product, and a carboxylic acid-based additive is used therefor.

At this time, the carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by chemical formula 1 and metal salts thereof. Specifically, the carboxylic acid-based additive is at least one selected from the group consisting of: the carboxylic acid represented by chemical formula 1, the alkali metal salt of the carboxylic acid represented by chemical formula 1, and the alkaline earth metal salt of the carboxylic acid represented by chemical formula 1. More specifically, the carboxylic acid based additive is one of the following: the carboxylic acid represented by chemical formula 1, the alkali metal salt of the carboxylic acid represented by chemical formula 1, and the alkaline earth metal salt of the carboxylic acid represented by chemical formula 1.

In chemical formula 1, a is a hydrophobic moiety and may be a linear or branched alkyl group having 5 to 21 carbon atoms. However, the case where a is a linear alkyl group is more advantageous in terms of suppressing agglomeration of pulverized particles and improving dispersibility. When a is an alkyl group having less than 5 carbon atoms, there is a problem that the chain is short, so that the agglomeration of the pulverized particles cannot be effectively controlled. When a is an alkyl group having more than 21 carbon atoms, the fluidity of the additive may be reduced, so that the carboxylic acid-based additive may not be effectively mixed with the hydrogel polymer, and the cost of the composition may increase due to the increase in the cost of the additive.

Specifically, in chemical formula 1, a may be a linear alkyl group having 5 to 21 carbon atoms, such as n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl, or n-heneicosyl.

More specifically, a may be a linear alkyl group having 6 to 18 carbon atoms. For example, A may be-C₆H₁₃、-C₁₁H₂₃、-C₁₂H₂₅、-C₁₇H₃₅or-C₁₈H₃₇。

Further, a moiety of chemical formula 1 (B)₁-B₂) Improving the adsorption performance to the polymer surface, having only partial C adsorption performance may be insufficient. When B is present₂When the number of carbon atoms of (B) is 3 or more, the moiety B₁The distance from the portion C increases and the adsorption performance to the hydrogel polymer may deteriorate.

In this context, R₁And R₂May each independently be a linear or branched alkyl group having 1 to 4 carbon atoms. More specifically, R₁And R₂And may each independently be methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl. Since the additive can adsorb onto the superabsorbent polymer particles, it is advantageous that the molecular structure of the additive is not bulky, and therefore R₁And R₂Both may be methyl.

In addition, n of chemical formula 1 may be 1,2, or 3. More specifically, consider part (B)₁-B₂) Is a molecular length, n (which means (B) required for enhancing the adsorption property associated with the moiety C and for the carboxylic acid-based additive to be effectively adsorbed onto the hydrogel polymer₁-B₂) The number of (c) is preferably 1.

Specifically, in chemical formula 1, B₁Can be that Wherein is the bonding site to the adjacent atom.

For example, B₁Can be that

Further, in chemical formula 1, B₂Can be that

Wherein is the bonding site to the adjacent atom. At this time, in order to improve the adsorption property of the additive to the crosslinked polymer together with the part C, B₂Preferably, it is

Further, in chemical formula 1, the moiety C is a carboxyl group (COOH) as a hydrophilic moiety, and when the carboxylic acid-based additive is a salt, the hydrophilic moiety is a carboxylate group (COO)^-)。

In other words, the carboxylic acid-based additive may be a compound represented by the following chemical formula 1 a:

[ chemical formula 1a ]

In the chemical formula 1a, the first and second,

m is H⁺A monovalent cation of an alkali metal or a divalent cation of an alkaline earth metal,

if M is H⁺Or a monovalent cation of an alkali metal, then k is 1, if M is a divalent cation of an alkaline earth metal, then k is 2, and

A、B₁、B₂and n is described as defined in chemical formula 1.

More specifically, when the carboxylic acid-based additive is an alkali metal salt of a carboxylic acid represented by chemical formula 1, the additive may be represented by the following chemical formula 1':

[ chemical formula 1' ]

In the chemical formula 1', the reaction mixture is,

M₁is an alkali metal such as sodium or potassium, and

A、B₁、B₂and n is described as defined in chemical formula 1.

Further, when the carboxylic acid-based additive is an alkaline earth metal salt of a carboxylic acid represented by chemical formula 1, the additive may be represented by the following chemical formula 1 ″:

[ chemical formula 1 "]

In chemical formula 1', M₂Is an alkaline earth metal such as calcium, and

A、B₁、B₂and n is described as defined in chemical formula 1.

For example, the carboxylic acid-based additive may be any one of carboxylic acids selected from the group consisting of:

alternatively, the carboxylic acid-based additive may be any alkali metal salt selected from the group consisting of:

in the above-mentioned context, it is preferred that,

M₁each independently an alkali metal.

Alternatively, the carboxylic acid-based additive may be any one of the alkaline earth metal salts selected from:

in the above-mentioned context, it is preferred that,

M₂each independently an alkaline earth metal.

For example, the carboxylic acid-based additive may be any one of the compounds represented by the following chemical formulas 1-1 to 1-7, but is not limited thereto:

meanwhile, the carboxylic acid-based additive may be used in an amount of about 0.01 parts by weight to about 10 parts by weight, based on 100 parts by weight of the hydrogel polymer. When too little additive is used, the additive may not be uniformly adsorbed onto the surface of the hydrogel polymer, resulting in re-agglomeration of particles after pulverization, and when too much additive is used, the overall physical properties of the final superabsorbent polymer may be reduced. For example, the carboxylic acid-based additive may be used in an amount of 0.01 parts by weight or more, 0.015 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less, based on 100 parts by weight of the hydrogel polymer.

The method of mixing the additive with the hydrogel polymer is not particularly limited and may be appropriately selected as long as it is a method capable of uniformly mixing the additive with the hydrogel polymer. Specifically, the additives may be dry-blended, dissolved in a solvent and then mixed, or melted and then mixed.

For example, the additives may be mixed in the form of a solution dissolved in a solvent. At this time, any type of inorganic solvent or organic solvent may be used without limitation, but water is most preferably used for the solvent in view of the easiness of drying and the cost of the solvent recovery system. Further, a method of putting the additive in the form of a solution and the hydrogel polymer into a reaction tank to be mixed; a method of spraying the solution after placing the hydrogel polymer in a mixer; a method of continuously supplying the hydrogel polymer and the solution to a continuously operated mixer for mixing; and so on.

The comminuted product comprising aqueous superabsorbent polymer particles and additives can be prepared by mixing the hydrogel polymer with the additives followed by comminution. Specifically, the pulverization step may be performed such that the pulverized aqueous superabsorbent polymer particles have a conventional particle size.

Herein, the pulverizer for pulverization is not particularly limited. In particular, it may comprise at least one selected from: vertical mills, turbo cutters, turbo grinders, rotary shredders (rotary mills), shredders (chopper mills), disc mills, chip breakers, crushers, shredders (choppers), and disc cutters, although the disclosure is not so limited.

Alternatively, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog mill may also be used as the pulverizer, but the present disclosure is not limited thereto.

Wherein the comminution may be performed by a chopper, more particularly by a meat grinder. At this time, the meat grinder includes a perforated plate, and the perforated plate may have a plurality of fine-cut holes having a certain size. Further, the pore size (meaning the diameter of the pores) of the fine cut pores in the multiwell plate may be 0.2mm to 5 mm. In other words, it can be seen that the pulverization is performed by pushing the hydrogel polymer mixed with the additives so that the hydrogel polymer is pulverized while passing through the fine-cut holes of the perforated plate. At this time, an extruder may be used to push out the hydrogel polymer. For example, a single screw extruder or a multi-screw extruder may be used.

Further, the pulverization may be performed while passing through two or more porous plates. For this purpose, a meat grinder comprising a chopping module in which two or more perforated plates are connected in series may be used, or a meat grinder comprising two or more perforated plates may be connected in series and used.

For example, in the case of using a meat chopper having two or more perforated plates, the perforated plates may be arranged in series in the order of screw-knife-perforated plate, in which case the distance between the perforated plates and the knives is preferably 1mm or less to improve chopping efficiency.

More specifically, the hydrogel polymer mixed with the carboxylic acid-based additive may be pulverized using a meat chopper including a chopper module provided with a first perforated plate and a second perforated plate. The pore sizes of the slit pores provided in each of the first and second perforated plates may be the same as or different from each other. At this time, in order to facilitate the pulverization, it is preferable that the hole size of the fine cut holes provided in the second porous plate is smaller than the hole size of the fine cut holes provided in the first porous plate. For example, the pore size of the fine cut pores disposed in the first perforated plate may be about 1mm to about 5mm, and the pore size of the fine cut pores disposed in the second perforated plate may be about 0.2mm to about 1 mm.

When the hydrogel polymer mixed with the carboxylic acid-based additive is pulverized by passing it through a first porous plate having a plurality of fine-cut holes having a size of 1mm to 5mm and then passing it through a second porous plate having a plurality of fine-cut holes having a size of 0.2mm to 1.0mm, a particle size distribution similar to that of the product after drying is achieved, so that the process of pulverizing the dried body can be omitted, thereby fundamentally preventing the generation of fine powder.

As used herein, "aqueous superabsorbent polymer particles" included in the comminuted product are particles having a water content of about 30 weight percent or greater. Since they are particles in which the hydrogel polymer is pulverized into particles without being subjected to a drying process, their water content may be 30 to 70% by weight, like the hydrogel polymer.

Furthermore, the aqueous superabsorbent polymer particles may have the particle size of conventional particles, i.e. a particle size of 150 μm to 850 μm. Specifically, the comminuted product can comprise 89% by weight or more, 90% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, or 95% by weight or more, based on the total weight, of aqueous superabsorbent polymer particles having a particle size of from 150 μm to 850 μm. The particle size can be measured according to EDANA WSP 220.3 of the european disposables and nonwovens association (EDANA). Alternatively, the content of the aqueous superabsorbent polymer particles having a particle size of 150 μm to 850 μm in the pulverized product may be considered to be the same as the content of the superabsorbent polymer particles having a particle size of 150 μm to 850 μm in the finally prepared superabsorbent polymer composition, considering that no additional pulverization process is performed after the drying and surface-crosslinking process in the preparation of the superabsorbent polymer composition.

Meanwhile, at least some of the additives contained in the pulverized product may be present on the surface of the aqueous superabsorbent polymer particles. Herein, "at least some of the additives are present on the surface of the aqueous superabsorbent polymer particles" means that at least some of the additives are adsorbed or bonded on the surface of the aqueous superabsorbent polymer particles. Specifically, the additive may be physically or chemically adsorbed on the surface of the superabsorbent polymer. More specifically, the hydrophilic functional groups of the additive may be physically adsorbed on the hydrophilic portion of the surface of the superabsorbent polymer by intermolecular forces, such as dipole-dipole interactions. In this way, the hydrophilic part of the additive is physically adsorbed on the surface of the superabsorbent polymer particles to surround the surface, while the hydrophobic part of the additive is not adsorbed on the surface of the polymer particles, so that the polymer particles may be coated with the additive in the form of a micelle structure. This is because the carboxylic acid-based additive is not added during the polymerization process of the water-soluble ethylenically unsaturated monomer, but is added after the polymer is formed. Therefore, the re-agglomeration phenomenon between the aqueous superabsorbent polymer particles can be further suppressed, compared to the case where the additive is added during the polymerization process and is present inside the polymer.

(step 3)

The above steps are used to prepare a superabsorbent polymer composition comprising superabsorbent polymer particles and additives by drying the pulverized product. This step dries the comminuted product to dry the moisture of the aqueous superabsorbent polymer particles. Specifically, the drying of the pulverized product may be performed such that the water content of each of the plurality of superabsorbent polymer particles included in the prepared superabsorbent polymer composition is about 10% by weight or less, specifically, about 0.01% by weight to about 10% by weight.

The drying of the pulverized product may be performed in a mobile type manner. Mobile drying is classified into fixed bed drying according to whether the material flows during drying.

The mobile drying refers to a method of drying a material to be dried while mechanically stirring the material. At this time, the direction of the hot air passing through the material may be the same as or different from the circulation direction of the material. Alternatively, the material may be circulated inside the dryer and dried by passing a heat transfer fluid through a separate conduit outside the dryer.

On the other hand, fixed bed drying refers to a method in which a material to be dried is fixed on a bottom plate through which air can pass, such as a porous iron plate, and hot air is passed through the material from the bottom to the top to perform drying.

Therefore, it is preferable to dry the pulverized product in a moving type drying manner from the viewpoint of preventing agglomeration between the aqueous superabsorbent polymer particles in the pulverized product to be dried in the above step and completing the drying in a short time.

As a device capable of drying by such a moving type drying method, a horizontal mixer, a rotary kiln, a paddle dryer, a steam tube dryer, or a commonly used moving type dryer can be used.

Herein, the temperature in the dryer may be about 80 ℃ to about 250 ℃. When the temperature in the dryer is too low, the drying time may become excessively long, and when the drying temperature is too high, only the surface of the polymer is dried and the physical properties of the final superabsorbent polymer may be degraded. Thus, the drying process may preferably be carried out at a temperature in the dryer of about 100 ℃ to about 240 ℃, more preferably at a temperature of about 110 ℃ to about 220 ℃.

In addition, the drying time may be about 10 minutes to about 3 hours in consideration of process efficiency. For example, drying may be performed for about 10 minutes to about 100 minutes, or about 10 minutes to about 60 minutes.

The superabsorbent polymer composition prepared as described above may comprise 89 wt% or more, 90 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, or 95 wt% or more superabsorbent polymer particles having a particle size of 150 μm to 850 μm, i.e., conventional particles, based on the total weight.

Further, the superabsorbent polymer composition may include less than about 10 wt%, specifically less than about 5 wt%, more specifically less than about 3 wt%, based on total weight, of fine powders having a particle size of less than 150 μm. This is in contrast to having about 10% to about 20% by weight of fine powder when the hydrogel polymer is dried and then pulverized to prepare the superabsorbent polymer.

Therefore, an additional pulverization step after drying the pulverized product may not be included. In addition, since the superabsorbent polymer composition prepared contains a small amount of fine powder, a classification step may not be included. That is, the superabsorbent polymer composition which can be applied to the product without an additional pulverizing/classifying step can be prepared, but a fine pulverizing process or a classifying process can be additionally performed according to the purpose and necessity of the application of the product.

Surface crosslinking step

Thereafter, a step of forming a surface cross-linked layer on at least a part of the surface of the superabsorbent polymer particles in the presence of a surface cross-linking agent may be further included, as necessary. Through the above steps, the crosslinked polymer contained in the superabsorbent polymer particles may be further crosslinked with a surface crosslinking agent, so that a surface crosslinked layer may be formed on at least a portion of the surface of the superabsorbent polymer particles.

As the surface cross-linking agent, any surface cross-linking agent generally used for preparing superabsorbent polymers may be used without any particular limitation. Examples of the surface crosslinking agent may include: selected from ethylene glycol and propylene glycolAt least one polyol selected from the group consisting of alcohol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol, 1, 2-hexanediol, 1, 3-hexanediol, 2-methyl-1, 3-propanediol, 2, 5-hexanediol, 2-methyl-1, 3-pentanediol, 2-methyl-2, 4-pentanediol, tripropylene glycol, and glycerol; at least one carbonate-based compound selected from the group consisting of ethylene carbonate, propylene carbonate, and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether;azoline compounds, e.g.An oxazolidinone; a polyamine compound;an oxazoline compound; sheetOxazolidinone, diOxazolidinones or polypeptidesAn oxazolidinone compound; a cyclic urea compound; and so on.

Specifically, as the surface cross-linking agent, one or more, two or more, or three or more of the aforementioned surface cross-linking agents may be used. For example, ethylene carbonate-propylene carbonate (ECPC), propylene glycol and/or glycerol carbonate may be used.

Such a surface cross-linking agent may be used in an amount of about 0.001 parts by weight to about 5 parts by weight, based on 100 parts by weight of the superabsorbent polymer particles. For example, the surface cross-linking agent may be used in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.05 parts by weight or more, and 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less, based on 100 parts by weight of the superabsorbent polymer particles. By adjusting the content of the surface cross-linking agent within the above range, a superabsorbent polymer having excellent absorption characteristics can be prepared.

Further, the step of forming the surface cross-linked layer may be performed by adding an inorganic material in addition to the surface cross-linking agent. That is, the step of forming a surface cross-linked layer by further cross-linking the surface of the superabsorbent polymer particles may be performed in the presence of a surface cross-linking agent and an inorganic material.

As the inorganic material, at least one inorganic material selected from silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate may be used. The inorganic material may be used in a powdery form or in a liquid form, and in particular, alumina powder, silica-alumina powder, titania powder, or a nano-silica solution may be used. In addition, the inorganic material may be used in an amount of about 0.001 parts by weight to about 1 part by weight, based on 100 parts by weight of the superabsorbent polymer particles.

Further, the method of mixing the surface cross-linking agent with the superabsorbent polymer composition is not particularly limited. For example, a method of adding the surface cross-linking agent and the superabsorbent polymer composition in a reactor for mixing; a method of spraying a surface cross-linking agent onto a superabsorbent polymer composition; or a method of mixing the superabsorbent polymer composition and the surface cross-linking agent while continuously supplying them to a continuously operating mixer.

When the surface cross-linking agent is mixed with the superabsorbent polymer composition, water and methanol may be further mixed therewith. When water and methanol are added thereto, there is an advantage in that the surface cross-linking agent can be uniformly dispersed in the superabsorbent polymer composition. At this time, the amounts of water and methanol to be added may be appropriately controlled for the purpose of inducing uniform dispersion of the surface cross-linking agent, preventing agglomeration of the superabsorbent polymer composition, and optimizing the surface penetration depth of the surface cross-linking agent.

The surface crosslinking process may be performed at a temperature of about 80 ℃ to about 250 ℃. More specifically, the surface crosslinking process may be performed at a temperature of about 100 ℃ to about 220 ℃, or about 120 ℃ to about 200 ℃ for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. When the above surface crosslinking conditions are satisfied, the surface of the superabsorbent polymer particles is sufficiently crosslinked to increase the absorption rate under pressure.

The means for surface crosslinking is not particularly limited. It may be provided with a thermal medium or a heat source directly. At this time, a usable heat medium may be a heated fluid such as steam, hot air, hot oil, etc., but the present invention is not limited thereto. Further, the temperature of the heat medium supplied thereto may be appropriately selected in consideration of the manner of the heat medium, the heating speed, and the target temperature of heating. Meanwhile, an electric heater or a gas heater may be used as a heat source directly provided, but the present invention is not limited thereto.

Further, the superabsorbent polymer composition prepared by the above method may further comprise, in addition to the superabsorbent polymer particles and the carboxylic acid-based additive, a method of crushing the additive with the hydrogel polymer followed by drying B₁The ester bond of (a) is decomposed to form a compound.

In particular, when the additive is one in which n is 1 and B₁When the compound is an-OCO-, the superabsorbent polymer composition may further comprise an alcohol having an A-OH structure and a compound having a HOOC-B structure₂-a compound of structure C.

Furthermore, when the additive is one in which n is 1 and B₁When the compound is-COO-, the superabsorbent polymer composition may further comprise a carboxylic acid having an A-COOH structure and a compound having HO-B₂-a compound of structure C.

Furthermore, when the additive is one in which n is 1 and B₁is-COOCH (R)₁) COO-Compound the superabsorbent polymer composition may also contain a carboxylic acid having an A-COOH structure and a compound having a HOCH (R)₁)COO-B₂-a compound of structure C.

Since the superabsorbent polymer composition further includes a compound formed by decomposing ester bonds in the molecules of the additive, the fluidity of the additive is increased, and a phenomenon of re-agglomeration after pulverization can be further prevented.

Further, a compound having a glucose unit containing a plurality of hydroxyl groups in the molecule, such as microcrystalline cellulose, may not be used in the above production method. For example, when the superabsorbent polymer composition includes microcrystalline cellulose having an average particle size of 1 μm to 10 μm (e.g., available from FMC and represented by the following chemical formula 3)PH-101), agglomeration between superabsorbent polymer particles finally prepared may not be inhibited due to a plurality of hydroxyl groups, and thus the effects of the above additives may not be effectively exhibited.

[ chemical formula 3]

Meanwhile, the superabsorbent polymer composition prepared by the above method has a low fine powder content without a separate classification process, and may have a similar or higher water retention capacity (CRC) and Absorption Under Pressure (AUP), which are general physical properties, as compared to superabsorbent polymer compositions prepared by conventional methods. In addition, superabsorbent polymer compositions are characterized by having a high bulk density along with an equivalent level of surface tension. This is because the hydrophobic functional group (part a) included in the carboxylic acid-based additive imparts hydrophobicity to the surface of the pulverized superabsorbent polymer particles, thereby reducing friction between the particles and increasing the bulk density of the superabsorbent polymer. In addition, the hydrophilic functional group (part C) contained in the additive is also bonded to the superabsorbent polymer particles so that the surface tension of the polymer is not reduced.

Specifically, the superabsorbent polymer composition may comprise 90 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, or 95 wt% or more of superabsorbent polymer particles having a particle size of from 150 μm to 850 μm, i.e., conventional particles, based on the total weight.

Further, the superabsorbent polymer composition may comprise less than about 10 wt%, specifically less than about 5 wt%, more specifically less than about 3 wt%, more specifically less than about 1 wt%, of fine powders having a particle size of less than 150 μm, based on total weight.

Further, the superabsorbent polymer composition can have a Centrifuge Retention Capacity (CRC) of 28g/g or greater, 30g/g or greater, or 38g/g or greater, and 45g/g or less, as measured according to EDANA method WSP 241.3.

Further, the superabsorbent polymer composition can have an Absorbency Under Pressure (AUP) of 20g/g or greater, 23g/g or greater, or 24g/g or greater, and 28g/g or less, 27g/g or less, or 26g/g or less at 0.7psi as measured according to EDANA method WSP 242.3.

Further, the superabsorbent polymer composition may have a bulk density of from 0.5g/ml to 0.8 g/ml. At this time, in order to measure the bulk density, about 100g of the superabsorbent polymer composition was placed in a funnel-type bulk density measuring device, flowed down into a 100ml container, and the weight of the superabsorbent polymer contained in the container was measured. That is, bulk density is calculated as (weight of superabsorbent polymer composition)/(container volume, 100 ml). More specifically, the superabsorbent polymer composition may have a bulk density of from 0.69g/ml to 0.73g/ml, or from 0.70g/ml to 0.72 g/ml.

Further, the surface tension of the superabsorbent polymer composition may be 68mN/m or more and less than 72 mN/m. At this time, the surface tension of the saline containing swollen superabsorbent polymer may be measured using a surface tensiometer after adding 0.5g of superabsorbent polymer to 40mL of 0.9% saline, followed by stirring at 350rpm for 3 minutes.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the present invention is not intended to be limited by these examples.

EXAMPLE-preparation of superabsorbent Polymer composition

Examples 1 to 1

(step 1)

100g (1.388mol) of acrylic acid, 0.16g of polyethylene glycol diacrylate (Mn ═ 508) as an internal crosslinking agent, 0.008g of diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide as a photopolymerization initiator, 0.12g of sodium persulfate as a thermal polymerization initiator, and 123.5g of a 32% caustic soda solution were mixed at room temperature in a 3L glass vessel equipped with a stirrer and a thermometer to prepare a monomer composition (neutralization degree of acrylic acid: 70 mol%; solid content: 45 wt%).

Thereafter, the monomer composition was supplied at 500 mL/min to 2000 mL/min onto a conveyor belt in which a belt having a width of 10cm and a length of 2m was rotated at a speed of 50 cm/min. Further, while supplying the monomer composition, the irradiation intensity was 10mW/cm²To perform a polymerization reaction for 60 seconds, thereby obtaining a hydrogel polymer having a water content of 55% by weight.

(step 2)

Subsequently, sodium stearoyl-2-lactylate (Almax-6900, manufactured by IIshinwells) represented by the following chemical formulae 1 to 6 was added to the hydrogel polymer obtained by the above polymerization reaction in the form of an aqueous solution in hot water so that the content was 0.019 parts by weight based on 100 parts by weight of the hydrogel polymer. Then, the mixture was pulverized into particles having a particle size of 150 to 850 μm using a meat grinder. At this time, as the meat chopper, a meat chopper including a first perforated plate having a plurality of fine-cut holes having a hole size of 2mm and a second perforated plate having a plurality of fine-cut holes having a hole size of 0.5mm was used. Specifically, the hydrogel polymer mixed with sodium stearoyl-2-lactylate is first passed through a first perforated plate, and then subsequently passed through a second perforated plate to be pulverized to a conventional particle size. Herein, the water content of the aqueous superabsorbent polymer particles contained in the pulverized product was 55% by weight.

[ chemical formulas 1 to 6]

(step 3)

Thereafter, the pulverized product was introduced into a horizontal mixer using a heat transfer fluid having a temperature of 200 ℃, and then dried in a mobile type for 30 minutes while being stirred at 100 rpm. At this time, the internal temperature of the horizontal mixer was maintained at about 190 ℃. After completion of drying, a superabsorbent polymer composition was obtained and classified to measure the content of conventional particles and fine powder in the composition, and the results are shown in table 1.

Examples 1 to 2

A superabsorbent polymer composition was prepared in the same manner as in example 1-1, except that a meat chopper provided with a first perforated plate having a plurality of fine cut holes with a size of 1mm and a second perforated plate having a plurality of fine cut holes with a size of 1mm was used in step 2. Then, classification was performed to measure the contents of conventional particles and fine powder in the composition, and the results are shown in table 2.

Examples 1 to 3

A superabsorbent polymer composition was prepared in the same manner as in example 1-1, except that a meat chopper provided with a perforated plate having a plurality of fine-cut holes having a hole size of 1mm was used in step 2. Then, classification was performed to measure the contents of conventional particles and fine powder in the composition, and the results are shown in table 2.

Comparative example 1-1

(polymerization) A hydrogel polymer having a water content of 55% by weight was obtained in the same manner as in example 1.

(chopping) subsequently, the hydrogel polymer obtained by the polymerization reaction was mixed with the same amount of water as in example 1, and chopped using a meat chopper having a perforated plate with a plurality of fine-cut holes having a hole size of 16 mm.

(drying) thereafter, the minced hydrogel polymer was dried in a fixed bed manner in an oven at 200 ℃ for 30 minutes.

(coarse pulverization) the dried polymer was coarse pulverized to a particle size of about 2mm using a chopper (PULVERISETTE 19, manufactured by Fritsch), and then classified to measure the contents of conventional particles and fine powder in the composition, and the results are shown in table 1.

(fine pulverization) thereafter, of the classified particles, particles larger than 850 μm were pulverized using a roll mill (66F Gran-U-sizer, manufactured by MPE), and then classified to measure the contents of conventional particles and fine powder in the composition, and the results are shown in table 1.

Comparative examples 1 to 2

The hydrogel polymer having a water content of 55% by weight obtained in the same manner as in example 1 and the same amount of water as in example 1 were mixed, and crushing was attempted using a meat chopper having a perforated plate having a hole size of 4 mm. However, due to excessive pressure generated inside the chopper, the polymer was not discharged through the perforated plate, and the apparatus was stopped.

Comparative examples 1 to 3

A superabsorbent polymer composition was prepared in the same manner as in example 1-1 except that polyethylene glycol (Mw ═ 2000, manufactured by Sigma Aldrich) was used instead of sodium stearoyl-2-lactylate represented by chemical formula 1-6. Then, classification was performed to measure the contents of conventional particles and fine powder in the composition, and the results are shown in table 2.

Test example 1

The superabsorbent polymer compositions prepared in example 1-1 and comparative example 1-1 were classified using #20 to # 100 mesh, and the results are shown in table 1 as the weight of various particle sizes based on the total weight of the compositions.

[ Table 1]

[ Table 2]

As shown in tables 1 and 2, it can be seen that the example in which the carboxylic acid-based additive is added during pulverizing the hydrogel polymer to prepare the superabsorbent polymer composition has a higher conventional particle content and the amount of fine powder generated is significantly reduced, compared to the comparative example in which the additive is not used. Further, considering that no additional pulverization process is performed after the drying process in the preparation of the superabsorbent polymer composition, it can be considered that the content of the conventional particles finally measured in the examples is the same as the content of the conventional particles in the pulverized product prepared in (step 2). Thus, it was determined that preparing a superabsorbent polymer composition according to the examples can provide a composition containing superabsorbent polymer particles having a desired particle size without an additional pulverizing or classifying process after drying, thereby improving productivity.

Example 2

(step 1)

100g (1.388mol) of acrylic acid, 0.16g of polyethylene glycol diacrylate (Mn ═ 508) as an internal crosslinking agent, 0.008g of diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide as a photopolymerization initiator, 0.12g of sodium persulfate as a thermal polymerization initiator, and 123.5g of a 32% caustic soda solution were mixed at room temperature in a 3L glass vessel equipped with a stirrer and a thermometer to prepare a monomer composition (neutralization degree of acrylic acid: 70 mol%; solid content: 45 wt%).

Thereafter, the monomer composition was supplied at 500 mL/min to 2000 mL/min onto a conveyor belt in which a belt having a width of 10cm and a length of 2m was rotated at a speed of 50 cm/min. Further, while supplying the monomer composition, the irradiation intensity was 10mW/cm²To perform a polymerization reaction for 60 seconds, thereby obtaining a hydrogel polymer having a water content of 55% by weight.

(step 2)

Subsequently, monolauryl maleate represented by the following chemical formula 1-1 was added to the hydrogel polymer obtained by the above polymerization reaction in the form of an aqueous solution in hot water so that the content was 1 part by weight based on 100 parts by weight of the hydrogel polymer. Then, the mixture was pulverized into particles having a particle size of 150 to 850 μm using a meat grinder. Herein, monolauryl maleate represented by the following chemical formula 1-1 was prepared by mixing maleic anhydride and 1-dodecanol in a molar ratio of 1:1, followed by reaction at 60 ℃ for 3 hours. The water content of the aqueous superabsorbent polymer particles contained in the final comminuted product was 55% by weight.

[ chemical formula 1-1]

(step 3)

Thereafter, the pulverized product was dried by flowing hot air of 185 ℃ from the bottom to the top for 20 minutes and then from the top to the bottom for 20 minutes using a convection oven capable of changing the wind direction up and down.

(surface crosslinking)

Thereafter, a mixed solution for surface crosslinking containing 4.8g of water, 0.1g of propylene glycol, 0.8g of ethylene carbonate, 0.8g of propylene carbonate, and 0.87g of 23% aluminum sulfate aqueous solution was added to 100g of the dried product, followed by mixing for 2 minutes, and after drying for 60 minutes at 185 ℃, a final superabsorbent polymer composition was prepared.

Example 3

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monohexyl maleate represented by the following chemical formula 1-2 was used instead of monolauryl maleate represented by the following chemical formula 1-1. Herein, monohexyl maleate represented by the following chemical formula 1-2 is prepared by mixing maleic anhydride and 1-hexanol at a molar ratio of 1:1, followed by reaction at 60 ℃ for 3 hours.

[ chemical formulas 1-2]

Example 4

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monohexyl succinate represented by the following chemical formula 1-3 was used instead of monolauryl maleate represented by chemical formula 1-1. Herein, the monohexyl succinate represented by the following chemical formulae 1 to 3 was prepared by mixing succinic anhydride and 1-hexanol in a molar ratio of 1:1, followed by reaction at 60 ℃ for 3 hours.

[ chemical formulas 1-3]

Example 5

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monostearyl maleate represented by the following chemical formulas 1 to 4 was used instead of monolauryl maleate represented by chemical formulas 1 to 1. Herein, monohexyl maleate represented by the following chemical formulae 1 to 4 is prepared by mixing maleic anhydride and stearyl alcohol at a molar ratio of 1:1, followed by reaction at 80 ℃ for 3 hours.

[ chemical formulas 1 to 4]

Example 6

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monolauryl succinate represented by the following chemical formula 1-5 was used instead of monolauryl maleate represented by chemical formula 1-1. Herein, monolauryl succinate represented by the following chemical formulas 1 to 5 was prepared by mixing succinic anhydride with 1-dodecanol in a molar ratio of 1:1, followed by reaction at 110 ℃ for 3 hours.

[ chemical formulas 1 to 5]

Example 7

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that sodium stearoyl-2-lactylate (Almax-6900, manufactured by IIshinwells) represented by the following chemical formulae 1 to 6 was used in place of monolauryl maleate represented by chemical formulae 1 to 1.

[ chemical formulas 1 to 6]

Example 8

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that sodium lauroyl-2-lactate (manufactured by IIshinwells) represented by the following chemical formula 1-7 was used instead of monolauryl maleate represented by chemical formula 1-1.

[ chemical formulas 1 to 7]

Example 9

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that 0.1 parts by weight of monolauryl maleate represented by chemical formula 1-1 was used based on 100 parts by weight of the hydrogel polymer.

Comparative example 3

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monolauryl maleate represented by chemical formula 1-1 was not used.

Comparative example 4

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that dodecanoic acid represented by the following chemical formula X-1 (manufactured by Sigma Aldrich) was used instead of monolauryl maleate represented by chemical formula 1-1.

[ chemical formula X-1]

Comparative example 5

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that stearic acid (manufactured by Sigma Aldrich) represented by the following chemical formula X-2 was used instead of monolauryl maleate represented by chemical formula 1-1.

[ chemical formula X-2]

Comparative example 6

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that a nonionic surfactant compound represented by the following chemical formula X-3 (A) was usedL35, manufactured by BASF) was used instead of monolauryl maleate represented by chemical formula 1-1.

[ chemical formula X-3]

HO-(EO)₁₁-(PO)₁₆-(EO)₁₁-H

In the chemical formula X-3, the compound,

EO is ethylene oxide and PO is propylene oxide.

Comparative example 7

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monobutyl maleate represented by the following chemical formula X-4 was used instead of monolauryl maleate represented by chemical formula 1-1. Herein, monobutyl maleate, represented by formula X-4 below, is prepared by mixing maleic anhydride and 1-butanol at a molar ratio of 1:1, followed by reaction at 60 ℃ for 3 hours.

[ chemical formula X-4]

Comparative example 8

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that behenyl maleate represented by the following chemical formula X-5 was used instead of monolauryl maleate represented by chemical formula 1-1. Herein, the monobehenyl maleate represented by the following chemical formula X-5 was prepared by mixing maleic anhydride and 1-docosanol at a molar ratio of 1:1, followed by reaction at 80 ℃ for 3 hours.

[ chemical formula X-5]

Comparative example 9

A superabsorbent polymer composition was prepared in the same manner as in example 2, except that monolauryl glutarate represented by the following chemical formula X-6 was used instead of monolauryl maleate represented by chemical formula 1-1. Herein, monolauryl glutarate represented by the following chemical formula X-6 was prepared by mixing glutaric anhydride and 1-dodecanol in a molar ratio of 1:1, followed by reaction at 80 ℃ for 3 hours.

[ chemical formula X-6]

Comparative example 10

A superabsorbent polymer composition was prepared in the same manner as in example 1, except that sodium polyoxyethylene (3) lauryl ether carboxylate (LCA-30D, manufactured by Sanyo chemical) represented by the following chemical formula X-7 was used instead of monolauryl maleate represented by chemical formula 1-1.

[ chemical formula X-7]

Comparative example 11

A superabsorbent polymer composition was prepared in the same manner as in example 1, except that sodium lauryl sulfate represented by the following chemical formula X-8 was used instead of monolauryl maleate represented by chemical formula 1-1.

[ chemical formula X-8]

Experimental example 2

For the superabsorbent polymer compositions prepared in examples and comparative examples, particle agglomeration characteristics, Centrifuge Retention Capacity (CRC), Absorbency Under Pressure (AUP), surface tension, bulk density, and the amount of generated fine powder were measured in the following manner, and the results are shown in table 4 below. Further, photographs of the agglomeration evaluation results of the superabsorbent polymer compositions prepared in example 3, example 7, comparative example 3, and comparative example 6 are shown in fig. 3, fig. 4, fig. 5, and fig. 6, respectively.

(1) Evaluation of particle agglomeration characteristics

After 20g of the hydrogel polymer prepared in one of examples and comparative examples was taken out, it was cut into 6 equal parts using scissors so as to include at least one edge of 2cm or more. Next, according to the type and content used in one of the examples and comparative examples, the carboxylic acid-based additive or the comparative compound corresponding thereto was mixed in the form of an aqueous solution.

② the mixture was pulverized at 7200rpm for 15 seconds using a homomixer.

(iii) visual evaluation of the pulverized product according to the evaluation criteria in table 3 below.

[ Table 3]

Evaluation of	Standard of merit
		X	6 or more particles of 2cm or larger, or not pulverized
△	1 to 5 particles of 2cm or more
		○	There were no 2cm or larger particles, but notIs uniformly crushed
◎	Has no particles of 2cm or larger, and is uniformly pulverized

(2) Centrifuge Retention Capacity (CRC)

The centrifuge retention capacity of the absorption ratio under no load condition of each polymer composition was measured according to EDANA (european disposables and nonwovens association) WSP 241.3 method.

Specifically, polymer compositions were obtained by classifying each of the polymer compositions prepared in examples and comparative examples through a sieve of #30 to # 50. In the process of mixing W₀(g, about 0.2g) after the polymer composition was uniformly placed in a nonwoven fabric enclosure and sealed, it was immersed in saline (0.9 wt%) at room temperature. After 30 minutes, the encapsulates were centrifuged at 250G for 3 minutes to drain and the weight W of the encapsulates was measured₂(g) In that respect Further, after the same operation was performed without using the resin, the weight W of the envelope was measured₁(g)。

Then, CRC (g/g) was calculated according to the following formula 2 by using the obtained weight value.

[ formula 2]

CRC(g/g)＝{[W₂(g)-W₁(g)]/W₀(g)}-1

(3) Yield on suction under pressure (AUP)

The superabsorbent polymer compositions prepared in the examples and comparative examples were measured for absorption at 0.7psi pressure according to the EDANA WSP 242.3 method.

First, in the measurement of the absorption rate under pressure, the fractionated polymer in the above CRC measurement was used.

Specifically, a 400 mesh stainless steel screen was installed in the bottom of a plastic cylinder with an inner diameter of 25 mm. W is brought to room temperature and 50% humidity₀(g, 0.16g) the superabsorbent polymer composition was uniformly dispersed on the screen. Thereafter, the composition can be uniformly placed thereonA piston providing a load of 0.7 psi. In this context, the outer diameter of the piston is slightly less than 25mm, there is no clearance with the inner wall of the barrel, and up-and-down movement of the barrel is not hindered. At this time, the weight W of the apparatus is measured₃(g)。

Subsequently, a glass filter having a diameter of 90mm and a thickness of 5mm was placed in a culture dish having a diameter of 150mm, and saline (0.90 wt% sodium chloride) was poured into the dish. At this time, brine was poured until the surface level of the brine became comparable to the upper surface of the glass filter. On which a piece of filter paper with a diameter of 90mm is placed. After placing the measuring device on the filter paper, the liquid was allowed to be absorbed under load for 1 hour. After 1 hour, the measuring device is raised and the weight W is measured₄(g)。

Then, the absorption under pressure (g/g) was calculated according to the following formula 3 by using the obtained weight value.

[ formula 3]

AUP(g/f)＝＝[W_,(g)-W₃(g)l/W₀(g)

(4) Surface tension (S/T)

To measure the surface tension of the superabsorbent polymer compositions prepared in the examples and comparative examples, 0.5g of each superabsorbent polymer composition was added to 40mL of 0.9% saline and stirred at 350rpm for 3 minutes. After the stirring was stopped, a brine containing swollen superabsorbent polymer was obtained. Using the saline water as a sample, the surface tension of each superabsorbent polymer composition was measured using a surface tension meter (product name: Force Tensiometer-K100, manufactured by KRUSS).

(5) Bulk Density (BD)

100g of the superabsorbent polymer composition prepared in one of the examples and comparative examples was flowed through the orifice of a standard flowability measuring device and placed in a container having a volume of 100 ml. Thereafter, the superabsorbent polymer composition was cut to be horizontal, and the volume of the superabsorbent polymer composition was adjusted to 100 ml. Then, the weight of the superabsorbent polymer composition alone, except the container, was measured. The weight of the superabsorbent polymer composition alone is then divided by 100ml (which is the volume of the superabsorbent polymer composition) to obtain a bulk density corresponding to the weight of the superabsorbent polymer composition per unit volume.

(6) Amount of fines produced

The amount of the fine powder generated in the superabsorbent polymer composition prepared in one of the examples and comparative examples was calculated as the weight-to-total weight ratio of the polymer having a particle size of less than 150 μm after passing the prepared superabsorbent polymer composition once through a coarse crusher (2800rpm, 0.4mm open, 1mm lower mesh condition).

[ Table 4]

As shown in table 4, it can be seen that the example in which the carboxylic acid-based additive is added during the pulverization of the hydrogel polymer to prepare the superabsorbent polymer composition inhibits the agglomeration between particles after the pulverization, as compared to the comparative example in which no additive or another additive is used. Thus, a composition comprising superabsorbent polymer particles having a desired particle size can be prepared without an additional comminution process following drying, thus reducing the amount of fine powder produced.

Further, it can be seen that the superabsorbent polymer compositions prepared according to the examples had high bulk density without a decrease in surface tension, while having water retention capacity and absorption under pressure equal to or higher than those of the superabsorbent polymer compositions prepared according to the comparative examples.