KR20220034685A - Super absorbent polymer and preparation method thereof - Google Patents

Abstract

The present invention relates to a super absorbent polymer and a preparation method thereof, and more specifically, to a super absorbent polymer prepared to improve drying efficiency and uniformity of particle size distribution as suppressing aggregation between pulverized particles by comprising a carboxylic acid-based additive and a hydrophobic particle of a specific structure before drying the hydrogel polymer and a preparation method thereof.

Description

Superabsorbent polymer and manufacturing method thereof

The present invention relates to a super absorbent polymer and a method for preparing the same. More specifically, it relates to a superabsorbent polymer prepared to contain a carboxylic acid-based additive having a specific structure and hydrophobic particles to suppress aggregation between resin particles and improve drying efficiency and uniformity of particle size distribution.

Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb water 500 to 1,000 times its own weight. Material), etc., are named differently. The superabsorbent polymer as described above started to be put to practical use as a sanitary tool, and is now widely used as a soil repair agent for horticulture, water-retaining material for civil engineering and construction, a sheet for seedlings, a freshness maintenance agent in the food distribution field, and a material for poultice. .

Such superabsorbent polymers are mainly used in the field of sanitary materials such as diapers and sanitary napkins. In the sanitary material, the superabsorbent polymer is generally included in a state spread in the pulp. However, in recent years, efforts have been made to provide sanitary materials such as diapers having a thinner thickness, and as a part of that, the content of pulp is reduced or, further, so-called pulpless diapers such as diapers in which no pulp is used are used. Development is actively underway.

As such, in the case of a sanitary material in which the content of pulp is reduced or in which pulp is not used, the superabsorbent polymer is included in a relatively high ratio, so that the superabsorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire superabsorbent polymer particles included in the multi-layered structure to more efficiently absorb a large amount of liquid such as urine, the superabsorbent polymer needs to exhibit not only high absorption performance but also a fast absorption rate.

On the other hand, such a superabsorbent polymer is generally prepared by polymerizing a monomer to prepare a hydrogel polymer containing a large amount of moisture, and drying the hydrogel polymer and then pulverizing the hydrogel polymer into resin particles having a desired particle size. Representative examples of this include a method of shredding neutralized acrylic acid with a twin kneader while polymerizing an aqueous solution and drying with hot air, a method of polymerizing neutralized acrylic acid with an aqueous solution, then shredding the hydrogel with a shredder, drying with hot air or a drum type dryer, and drying the thin film with acrylic acid After aqueous solution polymerization, the hydrogel polymer is neutralized and shredded with a shredder, and the thin film is dried with hot air drying or a drum dryer. After polymerization, the high concentration aqueous acrylate solution is polymerized while removing the amount of heat generated during polymerization, followed by polymerization of the polymerized gel. The method of heating and drying, the method of superposing|polymerizing neutralized acrylic acid by the reverse-phase suspension polymerization method, and the method of heating and removing a solvent and water under reduced pressure as needed are mentioned.

Among these methods, in particular, in the case of hot air drying and drying using a drum type dryer, since the hydrogel polymer has adhesiveness, a phenomenon occurs that the hydrogel polymers pulverized during drying adhere to each other, so ventilation of hot air for drying occurs. This deteriorated, and the problem that drying efficiency fell arose arose.

Accordingly, in addition to the improvement of the water holding capacity (CRC), which is a physical property representing the basic water absorption and water holding power of the superabsorbent polymer, and the absorbency under pressure (AUP), which shows the property of retaining the liquid absorbed even under external pressure, aggregation of the hydrogel polymers The development of a technology capable of producing a super absorbent polymer with improved drying efficiency by preventing

Accordingly, the present invention relates to a superabsorbent polymer prepared to improve drying efficiency and uniformity of particle size distribution as aggregation between pulverized particles is suppressed by including a carboxylic acid-based additive and hydrophobic particles having a specific structure before drying of the hydrogel polymer, and preparation thereof it's about how

In order to solve the above problems, the present invention,

superabsorbent polymer particles comprising a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group and a crosslinked polymer of a crosslinking agent;

hydrophobic particles; and

a carboxylic acid-based additive,

The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by the following formula (1) and a salt thereof,

A superabsorbent polymer is provided:

[Formula 1]

In Formula 1,

A is alkyl having 5 to 21 carbon atoms,

EO means ethylene oxide (-CH ₂ CH ₂ O-),

m is an integer from 0 to 8,

B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,

Here, R ₁ is an alkyl having 1 to 5 carbon atoms,

B ₂ is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon atoms, or alkynylene having 2 to 5 carbon atoms,

n is an integer from 1 to 3,

C is a carboxyl group.

In addition, the present invention provides a method for preparing a super absorbent polymer comprising the steps of:

A first step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of a crosslinking agent and a polymerization initiator to form a hydrogel polymer;

a second step of pulverizing the hydrogel polymer after mixing it with a carboxylic acid-based additive;

a third step of mixing hydrophobic particles with the pulverized product prepared in the second step; and

A fourth step of drying the mixture prepared in the third step,

The carboxylic acid-based additive is at least one selected from the group consisting of the carboxylic acid represented by Formula 1 and salts thereof.

According to the superabsorbent polymer of the present invention, drying efficiency and uniformity of particle size distribution may be improved by simultaneously including the carboxylic acid-based particles and the hydrophobic particles, thereby exhibiting improved absorption performance. In addition, the super absorbent polymer may be pulverized in the presence of the carboxylic acid-based additive and pulverized to a desired particle size without re-agglomeration between pulverized particles, and dried in the presence of the hydrophobic particles to form a space between the pulverized particles in the drying process. Re-agglomeration is also prevented, so that the content of large powder included after the drying process can be significantly reduced.

1 shows an SEM image of the surface of the superabsorbent polymer particles prepared in Example 1. Referring to FIG.
2 shows an SEM image of the surface of the superabsorbent polymer particles prepared in Example 2.
3 shows an SEM image of the surface of the superabsorbent polymer particles prepared in Example 3.
4 shows an SEM image of the surface of the superabsorbent polymer particles prepared in Example 4.
5 shows an SEM image of the surface of the superabsorbent polymer particles prepared in Comparative Example 1. Referring to FIG.

The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises", "comprising" or "have" are intended to designate the presence of an embodied feature, step, element, or a combination thereof, but one or more other features or steps; It should be understood that the possibility of the presence or addition of components, or combinations thereof, is not precluded in advance.

Since the present invention may have various changes and may have various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Hereinafter, a super absorbent polymer and a method for manufacturing the same according to specific embodiments of the present invention will be described in more detail.

Before that, the terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. And, as used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite.

As used herein, the term “polymer” or “polymer” refers to a polymerized state of a water-soluble ethylenically unsaturated monomer, and may cover all water content ranges or particle diameter ranges. Among the above polymers, a polymer having a water content (moisture content) of about 40% by weight or more in a state before drying after polymerization 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. there is.

In addition, the term "super absorbent polymer particles" refers to a particulate material comprising an acidic group and a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer in which at least a portion of the acidic group is neutralized is polymerized and crosslinked by an internal crosslinking agent.

In addition, the term “super absorbent polymer” refers to a cross-linked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing an acidic group and neutralizing at least a portion of the acidic group, or powder composed of particles of a superabsorbent polymer obtained by pulverizing the cross-linked polymer, depending on the context. It means a base resin in the form of (powder), or the cross-linked polymer or the base resin is subjected to additional processes, such as surface cross-linking, fine powder reassembly, drying, pulverization, classification, etc., to a state suitable for commercialization. used to be all-inclusive. Accordingly, the term "super absorbent polymer" may be interpreted as including a plurality of super absorbent polymer particles.

In addition, the term "rough" refers to particles having a particle diameter greater than about 850 μm, and the term “fine powder” refers to particles having a particle diameter less than about 150 μm, and the European Disposables and Nonwovens Association (European Disposables and Nonwovens Association, It can be measured according to the EDANA) standard EDANA WSP 220.3 method.

During the manufacturing process of the superabsorbent polymer, in the pulverization step essential for producing particles of the superabsorbent polymer having a desired particle size, when the dried polymer is pulverized, a large amount of fine powder is generated, thereby reducing physical properties. . However, in the non-dried hydrogel polymer state, it is possible to coarsely pulverize to the extent of having a particle size of approximately 1 to 10 mm, but it was impossible to pulverize to have a particle size of less than 1 mm due to aggregation of the pulverized particles.

In addition, in the process of drying the coarsely pulverized hydrogel polymer, aggregation of the pulverized particles exhibiting adhesion occurs, and accordingly, hot air cannot sufficiently pass between the hydrogel polymers. As a result, some of the polymer is in an uneven dry state, making it difficult to pulverize the superabsorbent polymer particles to have a uniform particle size distribution in the subsequent pulverization process, and some of the polymer becomes overheated and finally the superabsorbent polymer particles are in a state of overheating. It caused a problem that the absorption performance was lowered.

Accordingly, the present inventors have found that when the hydrogel polymer is pulverized in the presence of the carboxylic acid-based additive, pulverized particles can be pulverized to have a desired particle size without agglomeration, and when hydrophobic particles are additionally added before the drying process The present invention has been completed by confirming that a superabsorbent polymer with a uniform particle size distribution and a remarkably reduced amount of bulk after the drying process can be manufactured by preventing re-agglomeration during drying and increasing drying efficiency. In particular, the superabsorbent polymer has a relatively uniform particle size distribution of the produced superabsorbent particles (base resin) compared to the case in which the carboxylic acid-based additive and hydrophobic particles are not included. The efficiency is increased during processing, and when applied as a diaper absorbent, the physical properties such as absorption performance (CRC, AUP) and moisture blocking resistance are better and the physical properties appear reproducibly.

Specifically, the carboxylic acid-based additive has a hydrophobic functional group and a hydrophilic functional group at the same time. On the other hand, since the water-soluble ethylenically unsaturated monomer contains an acidic group (-COOH) and/or a neutralized acidic group (-COO- ⁾ , on the surface of the hydrogel polymer prepared by polymerization, an acidic group remaining without participating in polymerization A large amount of hydrophilic moieties due to (-COOH) and/or neutralized acidic groups (-COO- ⁾ are present. Therefore, when the carboxylic acid-based additive is mixed with the hydrogel polymer, the hydrophilic functional group of the carboxylic acid-based additive is adsorbed to at least a part of the hydrophilic portion present on the surface of the hydrogel polymer, and the carboxylic acid-based additive is The surface of the adsorbed polymer exhibits hydrophobicity due to a hydrophobic functional group located at the other end of the additive. Accordingly, aggregation between the resin particles can be suppressed.

More specifically, in the carboxylic acid-based additive, the hydrophobic functional group is an alkyl group having 5 to 21 carbon atoms (part A), the hydrophilic functional group is a carboxyl group (COOH) as part C, and in the case of a salt, a carboxylate group (COO ^- ), The hydrophobic functional group and the hydrophilic functional group are located at both ends of the additive, respectively. In particular, the carboxylic acid-based additive further includes a (B ₁ -B ₂ ) portion in addition to the A and C portions of both ends, and the (B ₁ -B ₂ ) portion is for the polymer surface, which may be insufficient only with the C portion. It plays a role in improving the adsorption performance. Accordingly, the additive having the structure of Formula 1 has superior adsorption performance on the surface of the polymer exhibiting hydrophilicity, compared to the compound having an AC structure without the (B ₁ -B ₂ ) moiety, thereby preventing aggregation of the superabsorbent polymer particles. can be effectively suppressed.

In addition, when the hydrogel polymer is pulverized in the presence of the carboxylic acid-based additive, part A, which is a hydrophobic functional group included in the additive, imparts hydrophobicity to the surface of the pulverized superabsorbent polymer particles to relieve friction between the particles, resulting in superabsorbent properties. While increasing the apparent density of the resin, the hydrophilic functional group C portion included in the additive is also bound to the superabsorbent polymer particles so that the surface tension of the resin is not reduced.

In addition, when the hydrophobic particles are dispersed in the pulverized hydrogel polymer and then dried, at least a portion of the hydrophobic particles are located on the surface of the hydrogel polymer, thereby preventing the phenomenon of re-aggregation between the polymer particles in the drying process. Thus, it is possible to manufacture a superabsorbent polymer having a uniform particle size distribution, a low rejection ratio, and improved absorption performance.

super absorbent resin

According to one embodiment, superabsorbent polymer particles comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer and a crosslinking agent, at least a part of which has a neutralized acidic group; hydrophobic particles; and a carboxylic acid-based additive, wherein the carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by the following Chemical Formula 1 and a salt thereof.

[Formula 1]

In Formula 1,

A is alkyl having 5 to 21 carbon atoms,

EO means ethylene oxide (-CH ₂ CH ₂ O-),

m is an integer from 0 to 8,

B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,

Here, R ₁ is an alkyl having 1 to 5 carbon atoms,

B ₂ is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon atoms, or alkynylene having 2 to 5 carbon atoms,

n is an integer from 1 to 3,

C is a carboxyl group.

Here, when n is 2 or more, two or more (B ₁ -B ₂ ) are the same as or different from each other.

Hereinafter, the super absorbent polymer of one embodiment will be described in more detail for each component.

The superabsorbent polymer according to an exemplary embodiment includes a plurality of superabsorbent polymer particles including a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acid groups. In this case, the cross-linked polymer is a three-dimensional network in which the water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized is cross-linked in the presence of a cross-linking agent, and main chains formed by polymerization of the monomers are cross-linked by the cross-linking agent. have a structure

In other words, the superabsorbent polymer according to an exemplary embodiment includes a plurality of superabsorbent polymer particles including a crosslinking polymer between a water-soluble ethylenically unsaturated monomer having at least partially neutralized acid groups and a crosslinking agent. As such, when the cross-linked polymer has a three-dimensional network structure in which main chains formed by polymerization of the monomers are cross-linked by the cross-linking agent, the superabsorbent polymer has a two-dimensional linear structure that is not further cross-linked by the cross-linking agent. The water holding capacity and absorbency under pressure, which are all physical properties of the , can be significantly improved.

The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the preparation of super absorbent polymers. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Chemical Formula 2:

[Formula 2]

R-COOM'

In Formula 2,

R is an alkyl group having 2 to 5 carbon atoms including an unsaturated bond,

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 these acids.

As such, when (meth)acrylic acid and/or its salt are used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a super absorbent polymer with improved water absorption. In addition, the monomer includes maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth) ) acrylamide-2-methyl propane sulfonic 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 can be used.

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

In addition, the degree of neutralization of the water-soluble ethylenically unsaturated monomer, which refers to the degree of neutralization by the neutralizing agent among the acidic groups included in the water-soluble ethylenically unsaturated monomer, is 50 to 90 mol%, or, 60 to 85 mol%, or 65 to 85 mole %, or 65 to 70 mole %. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, it may be difficult for the polymerization to proceed smoothly due to precipitation of neutralized monomers. It can exhibit properties like elastic rubber, which is difficult to handle.

In addition, the term 'crosslinking agent' used in this specification is a term used to distinguish it from an additional crosslinking agent for mainly crosslinking the surface of the superabsorbent polymer particles to be described later. serves to make The crosslinking in the above step proceeds without dividing the surface or the interior, but when the additional crosslinking process of the superabsorbent polymer particles to be described later proceeds, the surface of the particles of the superabsorbent polymer finally prepared mainly consists of a structure crosslinked by an additional crosslinking agent, , the interior is mainly composed of a structure crosslinked by the crosslinking agent. Accordingly, the additional cross-linking agent mainly serves to cross-link the surface of the superabsorbent polymer, so it can be seen that it serves as a surface cross-linking agent, and the cross-linking agent is distinguished from the second cross-linking agent and serves as an internal cross-linking agent.

As the crosslinking agent, any compound may be used as long as it enables the introduction of a crosslinking bond during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate. ) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate , hexanediol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerin tri ( Multifunctional crosslinking agents such as meth)acrylate, pentaerythol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, limited thereto it is not going to be Preferably, among them, polyethylene glycol di(meth)acrylate may be used.

The crosslinking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of such a crosslinking agent may be carried out by thermal polymerization, photopolymerization or hybrid polymerization in the presence of a polymerization initiator, optionally a thickener, plasticizer, storage stabilizer, antioxidant, etc. However, the specific details will be described later.

In addition, the superabsorbent polymer includes hydrophobic particles. In general, "hydrophobicity" is a concept distinct from hydrophilicity, and refers to a property that cannot be easily combined with water molecules. Specifically, when the contact angle to water is 70° or more, hydrophobicity can be seen. In addition, as used herein, the term "hydrophobic particle" refers to a water-insoluble particle that exhibits hydrophobicity and has a solubility in water of less than 1 mg/L at 20° C./1 atm, or does not dissolve in water. it means. When the hydrophobic particles are water-soluble particles, it is difficult to provide a gap between the particles while maintaining the particle shape when mixed with the pulverized hydrogel polymer particles containing water. Since aggregation between particles cannot be effectively prevented, it is not suitable for inclusion in the super absorbent polymer.

Accordingly, the hydrophobic particles have a contact angle with respect to water of 70° or more. More specifically, the hydrophobic particles have a contact angle with water of 80° or more, 90° or more, 94° or more, 100° or more, 105° or more, 117° or more, 120° or more, or 125° or more, and 175° or less. , or 128° or less.

The hydrophobic particles are included in the super absorbent polymer, and more specifically, the hydrophobic particles are mixed with the hydrogel polymer pulverized before the drying process in a dry manner, that is, as solid particles, to prevent re-agglomeration between the pulverized particles during drying. It is possible to increase drying efficiency while suppressing it.

In particular, the hydrophobic particles have a particle shape and are physically attached to the hydrogel to provide a gap (physical distance) between the particles and the particles to prevent fusion or agglomeration between the hydrophobic gels and improve moisture blocking. More specifically, the hydrophobic particles may be denatured during a high-temperature drying process in which the superabsorbent polymer contains a liquid material exhibiting hydrophobicity, so that the final prepared resin particles may be discolored, and agglomeration due to inability to maintain a physical gap between the hydrogel particles Since the prevention effect is not sufficient, a super absorbent polymer having a high rejection ratio may be manufactured, which is not preferable.

At least some of these hydrophobic particles may be present on the surface of the superabsorbent polymer particles. Here, “at least some of the hydrophobic particles are present on the surface of the superabsorbent polymer particles” means that at least some of the hydrophobic particles are adsorbed on the surface of the superabsorbent polymer particles. Specifically, the hydrophobic particles may be physically adsorbed to the surface of the superabsorbent polymer particles by van der Waals force. In addition, the presence of at least a portion of the hydrophobic particles on the surface of the superabsorbent polymer particles can be confirmed through the SEM image of the surface of the superabsorbent polymer particles prepared in Examples to be described later.

As the hydrophobic particles, any material that exhibits hydrophobicity and water insolubility may be used without limitation, but those that function as a reducing agent or a neutralizing agent for the superabsorbent polymer are excluded. More specifically, as the hydrophobic particles, organic-inorganic composite particles or inorganic particles exhibiting water insolubility may be used. For example, organic-inorganic composite particles such as hydrophobic silicone resin, or inorganic particles such as natural inorganic particles and synthetic inorganic particles exhibiting water insolubility excluding metal fine particles can be used. Specifically, as the hydrophobic particles, hydrophobic silicone resin; silicas such as hydrophobically surface-modified silica, finely divided silicic acid, hydrous silicic acid, diatomaceous earth and colloidal silica; hydrophobic clays such as kaolin, sericite, pyrophyllite, montmorillonite, bentonite and acid clay; carbonates such as precipitated (active, dry, heavy or hard) calcium carbonate, magnesium carbonate and the like; silicates such as finely divided magnesium silicate, talc, soap stone, steerite, calcium silicate, magnesium aluminosilicate, sodium aluminosilicate and the like; carbon blacks such as channel black, furnace black, thermal black and acetylene black; alumina such as aluminum oxide, aluminum hydroxide and alumina white; Barium sulfates (barium sulfates such as natural barium sulfate, precipitated barium sulfate and lithopone; zirconia (zirconium oxide); satin white; aluminum sulfate; anhydrite; hemihydrate gypsum; chalk; ash; chalk; white lead; mica powder; oxidized zinc; titanium oxide; magnesium oxide; activated calcium fluoride; zeolite; calcium sulfite; molybdenum disulfide; asbestos; glass fiber; rock fiber;

In this case, when using particles exhibiting hydrophilicity instead of the hydrophobic particles, for example, particles such as untreated dry/wet silica, phyllosilicate, hydrotalcite, sepiolite, etc., agglomeration between the pulverized polymer particles during the drying process of the hydrogel polymer This is not sufficiently prevented, so that 50% by weight or more of large powder having a particle diameter of more than 850 μm may be included based on the total weight of the superabsorbent polymer.

More specifically, the hydrophobic particles may be at least one selected from the group consisting of hydrophobic silicone resin particles, hydrophobic silica particles, and hydrophobic clay particles.

Specifically, the hydrophobic silicone resin may be polyorganosilsesquioxane. Here, polyorganosilsesquioxane refers to a silsesquioxane resin in which at least one of Si atoms included has an organic group, wherein the organic group may be an alkyl group or an aryl group that may exhibit hydrophobicity. In this case, the alkyl group refers to a linear or branched alkyl group having 1 to 10 carbon atoms, and the aryl group refers to an aryl group having 6 to 20 carbon atoms and showing aromaticity. That is, due to the organic groups included in the polyorganosilsesquioxane, a phenomenon in which the hydrogel polymer pulverized during the superabsorbent polymer manufacturing process is fused or aggregated again during drying can be effectively prevented.

More specifically, the polyorganosilsesquioxane may be polyalkylsilsesquioxane, that is, an alkylsilsesquioxane resin.

For example, the hydrophobic silicone resin particles may be polymethylsilsesquioxane, that is, methylsilsesquioxane resin particles. As the methylsilquesquioxane resin particles, commercially available Tospearl ^® 120, Tospearl ^® 130, Tospearl ^® 145, Tospearl ^® 150, Tospearl ^® 240, Tospearl ^® 2000B, or Tospearl ^® 3120 manufactured by Momentive can be used. can

In addition, the hydrophobic silicone resin particles may have an average particle size of about 0.1 μm to about 20 μm, and may be spherical particles. When the average particle diameter of the hydrophobic silicone resin particles is too small, the absorption capacity may decrease due to dense adsorption. This may be lowered. More specifically, the average particle diameter (㎛) of the hydrophobic silicone resin particles may be 0.1 or more, 0.5 or more, 1 or more, 1.5 or more, or 2 or more, or 20 or less, 15 or less, 12 or less, 10 or less, or 5 or less. there is.

At this time, the average particle diameter of the hydrophobic silicone resin particles was measured as a volume average diameter using a Coulter Counter Multisizer II, wherein the volume average diameter is the same as the weight and density of the spherical particles of each particle weight. The sum of the products of the diameters divided by the total particle weight.

In addition, the hydrophobic silica is fumed silica surface-modified by a surface treatment agent, and the surface treatment agent consists of dimethyldichlorosilane (DDS), polydimethylsiloxane (PDMS) and hexamethyldisilazane (HMDS). may be selected from the group. That is, the surface-modified fumed silica may exhibit hydrophobicity by introducing an organic group such as a methyl group to the silanol (-SiOH) group on the surface. can be prevented.

In addition, the specific surface area measured by the BET method of the hydrophobic silica may be 100 to 300 m ² /g, and the average particle diameter of the primary particles may be 5 nm to 50 nm. In this case, primary particles refer to particles in a state in which particles are not aggregated with each other, and are distinguished from aggregates/agglomerates.

In addition, the hydrophobic clay is selected from the group consisting of kaolin, sericite, pyrophyllite, montmorillonite, bentonite and acid clay (Acid Clay; Fuller's Earth) There may be more than one type. Here, clay means soft soil with an average particle diameter of 5 μm or less.

In particular, kaolin is a 1:1 type clay mineral made by combining tetrahedral silicate and octahedral alumina in a 1:1 ratio. It is represented by the formula Si ₂ Al ₂ O ₅ (OH) ₄ and is insoluble in water and exhibits water insolubility. In addition, the kaolin is naturally derived clay having a specific surface area of 10 to 30 m ² /g measured by the BET method, and is preferably included in the superabsorbent polymer in terms of being structurally hydrophobic and insoluble in water among various mineral types. Do.

In addition, the hydrophobic particles may be included in an amount of about 0.1 to about 10% by weight based on the total weight of the superabsorbent polymer. This may be approximately implemented by using the hydrophobic particles in an amount of about 0.1 to about 10 parts by weight based on 100 parts by weight of the hydrogel polymer.

In addition, the superabsorbent polymer includes the carboxylic acid-based additive. As described above, the carboxylic acid-based additive is mixed with the hydrogel polymer and added so that pulverization of the hydrogel polymer can be easily accomplished without agglomeration. In this case, the carboxylic acid-based additive may be at least one selected from the group consisting of the carboxylic acid represented by Chemical Formula 1 and a metal salt thereof. Specifically, the carboxylic acid-based additive is a carboxylic acid represented by Formula 1, an alkali metal salt of the carboxylic acid represented by Formula 1, and an alkaline earth metal salt of a carboxylic acid represented by Formula 1 at least one selected from More specifically, the carboxylic acid-based additive is one of the carboxylic acid represented by the formula (1), an alkali metal salt of the carboxylic acid represented by the formula (1), and an alkaline earth metal salt of the carboxylic acid represented by the formula (1).

In Formula 1, A is a hydrophobic portion and may be a linear or branched alkyl group having 5 to 21 carbon atoms, but when A is an alkyl group having a linear structure, in terms of inhibiting aggregation of pulverized particles and improving dispersibility more advantageous When A is an alkyl group having less than 5 carbon atoms, there is a problem that the aggregation control of the pulverized particles cannot be effectively achieved due to the short chain length, and when A is an alkyl group having more than 21 carbon atoms, the mobility of the carboxylic acid-based additive is reduced Therefore, it may not be effectively mixed with the hydrogel polymer, and there may be a problem in that the unit cost of the composition increases due to an increase in the cost of the additive.

Specifically, in Formula 1, A is a linear alkyl having 5 to 21 carbon atoms, that is, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl , n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, n-octadecanyl, n-nonadecanyl, n- icosanil, or n-heneicosanyl.

More specifically, it may be a linear alkyl having 6 to 18 carbon atoms. For example, A may be -C ₆ H ₁₃ , -C ₁₁ H ₂₃ , -C ₁₂ H ₂₅ , -C ₁₇ H ₃₅ , or -C ₁₈ H ₃₇ .

In addition, in Formula 1, the ethylene oxide (EO) linking group and (B ₁ -B ₂ ) moiety serves to improve the adsorption performance to the polymer surface, which may be insufficient only with the C moiety, and the carbon number of B ₂ is 5 In the case of exceeding the number, the distance between the B ₁ part and the C part increases, and the adsorption performance for the hydrogel polymer may be reduced. In addition, when m is 0, it is difficult to expect improvement in adsorption performance on the polymer surface, and when m is more than 8, hydrogen bonding between the water-containing gel polymer and/or superabsorbent polymer particles may be induced, resulting in aggregation of particles. This may not be suppressed.

In this case, R ₁ and R ₂ are each independently, linear or branched alkyl having 1 to 4 carbon atoms, more specifically, R ₁ and R ₂ are each independently, methyl, ethyl, propyl, isopropyl , butyl, isobutyl, sec-butyl, or tert-butyl, but in terms of adsorption of the carboxylic acid-based additive to the superabsorbent polymer particles, it is advantageous that the molecular structure of the additive is not bulky, so R ₁ and R ₂ may all be methyl.

Also, in Formula 1, n may be 1, 2, or 3. More specifically, n, meaning the number of (B ₁ -B ₂ ), is that the (B ₁ -B ₂ ) part is for reinforcing the adsorption performance for the C part, and the carboxylic acid-based additive is a hydrogel Considering the molecular length for effectively adsorbing to the polymer, n is preferably 1.

,

, 또는

일 수 있고, 여기서, *는 이웃하는 원자와의 결합 사이트이다.Specifically, in Formula 1, B ₁ is

,

, or

may be, where * is a binding site with a neighboring atom.

, 또는

일 수 있다. For example, B ₁ is

, or

can be

,

,

,

,

,

, 또는

일 수 있고, 여기서, *는 이웃하는 원자와의 결합 사이트이다. 이때, C 부분과 함께 가교 중합체에 대한 첨가제의 흡착 성능을 향상시킨다는 측면에서 B₂가

,

,

, 또는

인 것이 바람직하다.In addition, in Formula 1, B ₂ is

,

,

,

,

,

, or

may be, where * is a binding site with a neighboring atom. At this time, in terms of improving the adsorption performance of the additive to the crosslinked polymer together with the C part, B ₂ is

,

,

, or

It is preferable to be

In addition, in Formula 1, part C is a hydrophilic part and is a carboxyl group (COOH), but when the carboxylic acid-based additive is a salt, it is a carboxylate group (COO ^- ).

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

[Formula 1a]

In Formula 1a,

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

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

A, EO, m, B ₁ , B ₂ and n are the same as defined in Formula 1 above.

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

[Formula 1']

In Formula 1',

M ₁ is an alkali metal, for example sodium or potassium,

A, EO, m, B ₁ , B ₂ and n are the same as defined in Formula 1 above.

In addition, when the carboxylic acid-based additive is an alkaline earth metal salt of a carboxylic acid represented by Formula 1, the additive may be represented by Formula 1”:

[Formula 1"]

In Formula 1", M ₂ is an alkaline earth metal, for example, calcium,

A, EO, m, B ₁ , B ₂ and n are the same as defined in Formula 1 above.

For example, in Formula 1, when m is 0, the carboxylic acid-based additive may be any one carboxylic acid selected from the group consisting of:

.

.

In addition, in Formula 1, when m is not 0, the carboxylic acid-based additive may be a carboxylic acid represented by Formula 1A-1 below:

[Formula 1A-1]

In Formula 1A-1,

m1 is 3, 4, 5, 6, 7, or 8.

Alternatively, in Formula 1, when m is 0, the carboxylic acid-based additive may be any one alkali metal salt selected from the group consisting of:

above,

M ₁ is each independently an alkali metal.

In addition, in Formula 1, when m is not 0, the carboxylic acid-based additive may be an alkali metal salt represented by Formula 1B-1 below:

[Formula 1B-1]

In Formula 1B-1,

m2 is 3, 4, 5, 6, 7, or 8;

M ₁ is an alkali metal.

Alternatively, in Formula 1, when m is 0, the carboxylic acid-based additive may be any one alkaline earth metal salt selected from the group consisting of:

above,

M ₂ is each independently an alkaline earth metal.

In addition, in Formula 1, when m is not 0, the carboxylic acid-based additive may be an alkali metal salt represented by Formula 1C-1 below:

[Formula 1C-1]

In Formula 1C-1,

m3 is 3, 4, 5, 6, 7, or 8;

M ₂ is an alkaline earth metal.

For example, the carboxylic acid-based additive may be any one of compounds represented by the following Chemical Formulas 1-1 to 1-9, but is not limited thereto:

.

In addition, the superabsorbent polymer may further include a compound formed by decomposing the ester bond of B ₁ while the carboxylic acid-based additive is pulverized and dried together with the hydrogel polymer in addition to the carboxylic acid-based additive.

Specifically, when the additive is a compound in which n is 1 and B ₁ is -OCO-, the superabsorbent polymer composition is an alcohol of A-(EO) _m -OH structure and a compound of HOOC-B ₂ -C structure. may include more.

In addition, when the additive is a compound in which n is 1 and B ₁ is -COO-, the superabsorbent polymer composition contains a carboxylic acid having a structure of A-(EO) _m -COOH and a compound having a structure of HO-B ₂ -C. may include more.

In addition, when the additive is a compound in which n is 1 and B ₁ is -COOCH(CH ₃ )COO-, the superabsorbent polymer composition includes a carboxylic acid having a structure of A-(EO) _m -COOH and HOCH(CH ₃ ) It may further include a compound of the structure COO-B ₂ -C.

As such, since the superabsorbent polymer composition further includes a compound formed by decomposition of an ester bond in an additive molecule, mobility of the additives is increased, and re-agglomeration after pulverization can be further prevented.

In this case, the carboxylic acid-based additive may be included in an amount of 0.01 to 10% by weight based on the total weight of the superabsorbent polymer. When the content of the carboxylic acid-based additive in the composition is too low, the agglomeration control effect by the carboxylic acid-based additive is small and the composition may include superabsorbent polymer particles that have not been pulverized to a desired particle size, and the content of the carboxylic acid-based additive When this is too high, the water holding capacity and absorbency under pressure, which are general physical properties of the superabsorbent polymer, may be deteriorated. This may be approximately implemented by using about 0.01 to about 10 parts by weight of the carboxylic acid-based additive based on 100 parts by weight of the hydrogel polymer. However, since the ester bond of B ₁ may be decomposed during pulverization and drying after the hydrogel polymer is formed, the amount of the added additive and the amount of the additive remaining in the final prepared superabsorbent polymer composition may not be the same.

The content of the additive in the superabsorbent polymer composition is determined by first adding 1 g of the superabsorbent polymer composition to 1 ml of distilled water, then sufficiently mixing for 1 hour until swelling, then filtering to extract only the solution portion, and then performing HPLC analysis. In this way, it can be measured by analyzing the additive content dissolved in the solution part.

For example, the carboxylic acid-based additive is 0.01 wt% or more, 0.02 wt% or more, 0.05 wt% or more, 0.1 wt% or more, 0.2 wt%, 0.31 wt% or more, or 0.4 wt% based on the total weight of the superabsorbent polymer. % or more, and may be included in 10 wt% or less, 8 wt% or less, 5 wt% or less, 3 wt% or less, 1 wt% or less, or 0.5 wt% or less.

Meanwhile, at least a portion of the carboxylic acid-based additive may be present on the surface of the superabsorbent polymer particles. Here, “at least a portion of the carboxylic acid-based additive is present on the surface of the superabsorbent polymer particles” means that at least a portion of the carboxylic acid-based additive is adsorbed or bonded to the surface of the superabsorbent polymer particle. do. Specifically, the carboxylic acid-based additive may be physically or chemically adsorbed on the surface of the superabsorbent polymer. More specifically, the hydrophilic functional group of the carboxylic acid-based additive may be physically adsorbed to the hydrophilic portion of the surface of the superabsorbent polymer by intermolecular force such as dipole-dipole interaction. As such, the hydrophilic portion of the carboxylic acid-based additive is physically adsorbed to the surface of the superabsorbent polymer particle to surround the surface, and the hydrophobic portion of the additive is not adsorbed to the surface of the resin particle, so that the resin particle is a kind of micelle. An additive may be coated in the form of a structure.

Therefore, when at least a portion of the carboxylic acid-based additive is present on the surface of the superabsorbent polymer particles, compared to the case where all of the carboxylic acid-based additive is present inside the superabsorbent polymer particles, specifically, the crosslinked polymer , aggregation between the pulverized particles during the manufacturing process of the superabsorbent polymer can be more effectively suppressed.

In addition, as at least a portion of the carboxylic acid-based additive is present on the surface of the superabsorbent polymer particles, the superabsorbent polymer including the carboxylic acid-based additive has a higher apparent density than a composition not including the additive. It can exhibit equivalent or greater surface tension.

On the other hand, when the superabsorbent polymer does not further include an additional cross-linking layer, which will be described later, the plurality of superabsorbent polymer particles, the carboxylic acid-based additive and the carboxylic acid-based additive are hydrolyzed during the manufacturing process of the superabsorbent polymer. Hydrophilic additives other than the hydrolyzate of the carboxylic acid-based additive may not be included.

Specifically, the superabsorbent polymer of one embodiment may not include a compound having a plurality of hydroxyl groups-containing glucose units in a molecule, such as microcrystalline cellulose. For example, when the superabsorbent polymer contains microcrystalline cellulose having an average particle diameter of 1 to 10 μm, such as AVICEL ^® PH-101 represented by the following formula 3 available from FMC, a plurality of hydroxyl groups Due to this, aggregation between the superabsorbent polymer particles cannot be suppressed, and the effect of the above-described additives may not be effectively expressed.

[Formula 3]

In addition, the superabsorbent polymer of one embodiment includes polyethylene glycol, polypropylene glycol, poly(ethylene glycol)-poly(propylene glycol) copolymer, polyoxyethylene lauryl ether carboxylic acid, sodium polyoxyethylene lauryl ether carboxylate , may not contain hydrophilic additives such as lauryl sulfate, sodium lauryl sulfate, and the like. Since such additives do not have the (B ₁ -B ₂ ) moiety of Formula 1 in the molecule, they cannot be sufficiently adsorbed to the surface of the cross-linked polymer, so that aggregation between the super absorbent polymer particles is not effectively suppressed. Accordingly, when the superabsorbent polymer contains the hydrophilic additive as described above instead of the carboxylic acid-based additive, aggregation between particles is not suppressed after pulverization of the crosslinked polymer, so that the superabsorbent polymer contains a large amount of fine powder and has a low beam It will show the SAT and low apparent density.

Meanwhile, the superabsorbent polymer may further include, on at least a portion of the surface of the superabsorbent polymer particles, a crosslinking layer formed by further crosslinking the crosslinked polymer through an additional crosslinking agent. Here, the cross-linked layer is mainly formed on at least a portion on the surface of each of the super absorbent polymer particles, and has a structure in which the cross-linked polymer in the super absorbent polymer is cross-linked by an additional cross-linking agent. This is to increase the crosslinking density on the surface of the superabsorbent polymer particles. As described above, when the superabsorbent polymer particles further include a structure in which at least a portion of the superabsorbent polymer particles are crosslinked by the additional crosslinking agent, the outside rather than the inside has a structure with a high crosslinking density.

As the additional crosslinking agent, any additional crosslinking agent that has been conventionally used in the preparation of the superabsorbent polymer may be used without particular limitation. For example, the additional crosslinking agent is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2- One selected from the group consisting of methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol more than one polyol; 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; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or a cyclic urea compound; and the like.

Specifically, as the additional crosslinking agent, one or more, or two or more, or three or more of the aforementioned additional crosslinking agents may be used, for example, ethylene carbonate-propylene carbonate (ECPC), propylene glycol and/or glycerol carbonate. can be used.

In addition, the superabsorbent polymer has a water holding capacity (CRC) of 35 g/g or more, 36 g/g or more, 37.5 g/g or more, 38 g/g or more, 38.2 g/g measured according to the EDANA method WSP 241.3. or more, 39.1 g/g or more, 39.2 g/g or more, 39.3 g/g or more, and 45 g/g or less, 43 g/g or less, 42 g/g or less, or 40.8 g/g or less. there is.

In addition, the superabsorbent polymer has an absorbency under pressure (AUP) of 15 g/g or more, 18 g/g or more, 20.9 g/g or more, 21 g/g or more, at 0.7 psi measured according to EDANA method WSP 242.3, 21.1 g/g or more, 22.0 g/g or more, or 22.4 g/g or more, and may be 28 g/g or less, 26 g/g or less, 25 g/g or less, or 24.8 g/g or less.

Manufacturing method of super absorbent polymer

On the other hand, according to another embodiment, there is provided a method for producing a super absorbent polymer comprising the following steps:

A first step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of a crosslinking agent and a polymerization initiator to form a hydrogel polymer;

a second step of pulverizing the hydrogel polymer after mixing it with a carboxylic acid-based additive;

a third step of mixing hydrophobic particles with the pulverized product prepared in the second step; and

and a fourth step of drying the mixture prepared in the third step.

In this case, the carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by the following formula (1) and salts thereof.

Hereinafter, each step of the manufacturing method of the superabsorbent polymer according to an embodiment will be described in more detail.

In the method for producing a superabsorbent polymer according to an embodiment, first, in the presence of a crosslinking agent and a polymerization initiator, a first step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized to form a hydrogel polymer is performed. do.

The step may include preparing a monomer composition by mixing the water-soluble ethylenically unsaturated monomer, a crosslinking agent, and a polymerization initiator, and thermally or photopolymerizing the monomer composition to form a hydrogel polymer. In this case, the description of the water-soluble ethylenically unsaturated monomer and the crosslinking agent refer to the above bar.

In the monomer composition, the 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. For example, the crosslinking agent is 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 0.16 parts by weight or more, or 0.45 parts by weight or more, 5 parts by weight or less, 3 parts by weight or more, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer 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. If the content of the upper cross-linking agent is too low, cross-linking does not occur sufficiently, and it may be difficult to implement strength above an appropriate level.

In addition, the polymerization initiator may be appropriately selected depending on the polymerization method. When using the thermal polymerization method, a thermal polymerization initiator is used, and when using the photopolymerization method, a photopolymerization initiator is used, and a hybrid polymerization method (thermal and light). both of the thermal polymerization initiator and the photopolymerization initiator can be used. However, even by the photopolymerization method, a certain amount of heat is generated by light irradiation such as ultraviolet irradiation, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator may be additionally used.

The photopolymerization initiator may be used without limitation in its composition as long as it is a compound capable of forming radicals by light such as ultraviolet rays.

As the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal Ketal), acyl phosphine (acyl phosphine), and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, specific examples of acylphosphine include diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide, ethyl (2,4,6- trimethylbenzoyl)phenylphosphinate etc. are mentioned. A more diverse photoinitiator is well described in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p115, but is not limited to the above-described examples.

In addition, as the thermal polymerization initiator, one or more selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), ammonium persulfate (Ammonium persulfate; (NH ₄ ) ₂ S ₂ O ₈ ) and the like, and examples of the azo-based initiator include 2,2-azobis-(2-amidinopropane) dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2 ,2-Azobis-(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride), and 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)). More various thermal polymerization initiators are well described in Odian's book 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.

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. In one example, the polymerization initiator is 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 0.128 parts by weight or more, 0.2 parts by weight or more, and 1 part by weight or less, or 0.5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. It may be less than or equal to parts by weight. If the concentration of the polymerization initiator is too low, the polymerization rate may be slowed and the residual monomer may be extracted in a large amount in the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is higher than the above range, the polymer chain constituting the network is shortened, so that the content of the water-soluble component increases, and the physical properties of the resin may be lowered, such as lowering the absorbency under pressure, which is not preferable.

The monomer composition may further include additives such as a thickener, a plasticizer, a preservation stabilizer, and an antioxidant, if necessary.

In addition, the monomer composition including the monomer may be in a solution state dissolved in a solvent such as water, and the solid content in the solution state monomer composition, that is, the concentration of the monomer, the crosslinking agent and the polymerization initiator depends on the polymerization time. And it may be appropriately adjusted in consideration of the reaction conditions and the like. For example, the solids content in the monomer composition may be 10 to 80% by weight, or 15 to 60% by weight, or 30 to 50% by weight.

When the monomer composition has a solid content in the above range, it is not necessary to remove unreacted monomers after polymerization by using the gel effect phenomenon that occurs in the polymerization reaction of a high concentration aqueous solution, and the pulverization efficiency when pulverizing the polymer to be described later is improved. It can be advantageous to control.

The solvent that can be used at this time can be used without limitation in its composition as long as it can dissolve the above-mentioned components, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene Glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl At least one selected from ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N,N-dimethylacetamide may be used in combination.

On the other hand, cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group may proceed without limitation in structure, as long as the hydrogel polymer can be formed by thermal polymerization, photopolymerization, or hybrid polymerization.

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the polymerization energy source. In general, when thermal polymerization is carried out, it may be carried out in a reactor having a stirring shaft such as a kneader. Although the process may be carried out in a reactor equipped with a conveyor belt or in a flat-bottomed container, the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.

For example, as described above, the hydrogel polymer obtained by thermal polymerization by supplying hot air or heating the reactor to a reactor such as a kneader having a stirring shaft is fed to the reactor outlet according to the shape of the stirring shaft provided in the reactor. The discharged hydrogel polymer may be in the form of several centimeters to several millimeters. Specifically, the size of the hydrogel polymer obtained may vary depending on the concentration and injection rate of the monomer composition to be injected, and a hydrogel polymer having a weight average particle diameter of 2 to 50 mm can be obtained.

In addition, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt or a flat-bottomed container, the form of the hydrogel polymer obtained may be a hydrogel polymer on a sheet having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection rate or amount of the injected monomer composition, but it is preferable to supply the monomer composition so that a polymer sheet having a thickness of about 0.5 to about 5 cm can be obtained. Do. When the monomer composition is supplied so that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is undesirable. it may not happen

In this case, the hydrogel polymer obtained in this way may have a water content of 40 to 70 wt%. For example, the water content of the hydrogel polymer may be 40% by weight or more, 45% by weight or more, 50% by weight or more, or 55% by weight or more, and 70% by weight or less, 65% by weight or less, or 60% by weight or less. . When the water content of the hydrogel polymer is too low, it is difficult to secure an appropriate surface area in the subsequent pulverization step, and there is a risk that the drying efficiency decreases. Absorption capacity may be reduced, and there is a risk that a lot of energy and a long time are required in the drying step after pulverization.

Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer as the amount of moisture occupied with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer in the crumb state through infrared heating. At this time, the drying condition is set to 40 minutes including 5 minutes of the temperature rise step in such a way that the temperature is raised from room temperature to about 180°C and then maintained at 180°C, and the moisture content is measured.

Next, the second step of mixing the hydrogel polymer with the above-mentioned carboxylic acid-based additive and pulverizing it to prepare a pulverized product including the water-containing superabsorbent polymer particles, which are pulverized hydrogel polymer particles, and the carboxylic acid-based additive carry out For details on the carboxylic acid-based additive, refer to the above bar.

In a conventional method for preparing a superabsorbent polymer, a superabsorbent polymer is prepared by coarsely pulverizing the hydrogel polymer, drying it, and then pulverizing it to a desired particle size in a dried state. In this case, a large amount of fine powder having a particle diameter of less than 150 μm may be generated by grinding in a dried state. Accordingly, there is a problem that a classification process of classifying the superabsorbent polymer particles according to the particle size is absolutely necessary.

However, as described above, when the pulverization is performed together with the additive having the structure of Formula 1 in the hydrogel polymer state, it is possible to prepare a group of particles having a desired particle size without aggregation between the pulverized particles. Accordingly, since the method of manufacturing the super absorbent polymer according to the exemplary embodiment does not require a grinding process and a classification process after drying, the manufacturing cost of the super absorbent polymer can be greatly reduced.

In the above step, the carboxylic acid-based additive may be used in an amount of about 0.01 to about 10 parts by weight based on 100 parts by weight of the hydrogel polymer. When too little of the carboxylic acid-based additive is used, it is not uniformly adsorbed on the surface of the hydrogel polymer, so that re-agglomeration of the particles may occur after pulverization. All physical properties of the resin may be deteriorated. More specifically, the carboxylic acid-based additive is 0.01 parts by weight or more, 0.02 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.4 parts by weight or more, relative to 100 parts by weight of the hydrogel polymer, It may be included in an amount of 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, 1 part by weight or less, or 0.5 parts by weight or less.

The method of mixing these additives with the hydrogel polymer is not particularly limited as long as they can be evenly mixed with the hydrogel polymer, but may be appropriately adopted and used.

For example, the carboxylic acid-based additive may be mixed in a solution state dissolved in a solvent, specifically, water. At this time, the solution is prepared by adding the carboxylic acid-based additive and the hydrogel polymer to a reaction tank and mixing them, or by putting the hydrogel polymer in a mixer and spraying the solution, or by continuously supplying the hydrogel polymer and the solution to a continuously operated mixer. A mixing method and the like can be used.

After mixing the hydrogel polymer and the additive, the mixture may be pulverized to prepare a pulverized product in which the water-containing superabsorbent polymer particles and the additive are mixed. Specifically, the pulverizing step may be performed so that the pulverized superabsorbent polymer particles have a particle diameter of 150 μm to 850 μm. Here, "water-containing superabsorbent polymer particles" are particles having a water content (moisture content) of about 40 wt% or more, and since the hydrogel polymer is pulverized into particles without a drying process, 40 to 70 wt% of the hydrogel polymer is It can have moisture content.

At this time, the pulverizer used for pulverization is a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, and a cutter mill. , a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter may include any one selected from the group consisting of a grinding device, but Examples are not limited.

Alternatively, as a grinder, a pin mill, a hammer mill, a screw mill, a roll mill, a disk mill, or a jog mill may be used. , but is not limited to the above example.

Meanwhile, at least some of the additives included in the pulverized material may be present on the surface of the water-containing superabsorbent polymer particles. As described above, “at least a portion of the carboxylic acid-based additive is present on the surface of the water-containing superabsorbent polymer particles” means that at least a portion of the carboxylic acid-based additive is adsorbed or means connected. 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. In comparison with the case where the water-containing superabsorbent polymer particles re-agglomerate with each other, it can be suppressed.

Next, a third step of mixing the hydrophobic particles with the pulverized product prepared in the second step is performed. At this time, the description of the hydrophobic particles refers to the above bar, and the method of mixing the hydrophobic particles in the pulverized material is not particularly limited as long as the hydrophobic particles can be evenly dispersed in the pulverized material, and may be appropriately adopted and used. .

For example, the hydrophobic particles may be mixed in a dry manner rather than in a mixed state in a solvent. Accordingly, the pulverized material and the hydrophobic particles may be mixed together by a method of putting them in a mixer and mixing them. The hydrophobic particles are not soluble in the solvent, or even if the hydrophobic particles are dissolved in the solvent, it is difficult to maintain the particle shape when mixed with the pulverized product in a liquid phase, so that it is not possible to exhibit the aggregation control effect between the pulverized hydrogel polymer particles. there is a problem.

In this case, the hydrophobic particles may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the hydrogel polymer. When the hydrophobic particles are used too little, the adsorption efficiency to the hydrogel superabsorbent polymer particles may be lowered, so that the drying efficiency may be lowered. More specifically, the hydrophobic particles are 0.1 parts by weight or more, 0.5 parts by weight or more, 0.8 parts by weight or more, or 1.0 parts by weight or more, and 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or more, relative to 100 parts by weight of the hydrogel polymer. It may be included in parts by weight or less, 3 parts by weight or less, or 2 parts by weight or less.

Next, a fourth step of manufacturing the super absorbent polymer by drying the mixture prepared in the third step is performed. In particular, after the drying step of the pulverized product, it is possible to manufacture a superabsorbent polymer including superabsorbent polymer particles having all desired physical properties without an additional pulverizing step.

The drying of the pulverized material may be performed so that the moisture content of each of the plurality of superabsorbent polymer particles included in the prepared superabsorbent polymer is about 10 wt% or less, specifically, about 0.1 to about 10 wt%.

At this time, the drying temperature may be about 60 ℃ to about 250 ℃. In this case, when the drying temperature is too low, the drying time may be too long. When the drying temperature is too high, only the surface of the polymer is dried, and there is a risk that the physical properties of the superabsorbent polymer to be finally formed may be reduced. Therefore, preferably, the drying may be carried out at a temperature of about 100 °C to about 240 °C, more preferably at a temperature of about 110 °C to about 220 °C.

In addition, the drying time may be carried out for about 20 minutes to about 12 hours in consideration of process efficiency and the like. For example, it may be dried for about 10 minutes to about 100 minutes, or about 20 minutes to about 60 minutes.

If the drying method of the drying step is also commonly used as a drying process, it may be selected and used without limitation in its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation.

The superabsorbent polymer prepared as described above, in addition to a plurality of superabsorbent polymer particles and additives, contains fine powder having a particle diameter of less than 150 μm relative to the total weight. It may include less than 10% by weight, more specifically less than about 5% by weight. This is in contrast to having about 10 wt% to about 20 wt% of fine powder when the hydrogel polymer is dried and then pulverized to prepare a super absorbent polymer.

The prepared superabsorbent polymer resin prepared as described above may contain less than 40 wt%, preferably less than 36 wt%, of bulk powder having a particle diameter of greater than 850 μm, based on the total weight. As can be seen in Examples and Comparative Examples to be described later, this is significantly lower than that in which the hydrophobic particles are not added, re-aggregation between the particles is suppressed by the hydrophobic particles, and it can be seen that an efficient drying process is achieved. . For example, the superabsorbent polymer contains 10 wt% or more, 17.4 wt% or more, 20 wt% or more, 20.1 wt% or more, 25 wt% or more, or 28.5 wt% of a powder having a particle diameter of greater than 850 μm, based on the total weight. or more, and may include less than 36% by weight, 35.5% by weight or less, 31.3% by weight or less, or 28.8% by weight or less. The content (removal rate) of such a dry matter can be calculated by the method of Equation 1:

[Equation 1]

Removal rate (%) = [(content of particles exceeding 850 μm that did not pass through 20 mesh)/(total content of particles)] * 100

Thereafter, if necessary, the method may further include forming an additional crosslinking layer on at least a portion of the surface of the superabsorbent polymer particles in the presence of an additional crosslinking agent. Through the above step, the crosslinked polymer included in the superabsorbent polymer particles may be further crosslinked through an additional crosslinking agent, thereby forming an additional crosslinking layer on at least a portion of the surface of the superabsorbent polymer particles.

The additional crosslinking agent may be used in an amount of about 0.001 to about 5 parts by weight based on 100 parts by weight of the superabsorbent polymer particles. For example, the additional crosslinking agent is 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. content can be used. By adjusting the content range of the additional crosslinking agent to the above-mentioned range, a superabsorbent polymer having excellent absorbent properties can be prepared.

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

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

In addition, there is no limitation on the composition of the method of mixing the additional crosslinking agent with the superabsorbent polymer. For example, a method of mixing an additional crosslinking agent and a superabsorbent polymer in a reaction tank, spraying an additional crosslinking agent to the superabsorbent polymer, or continuously supplying and mixing a superabsorbent polymer and an additional crosslinking agent to a continuously operated mixer, etc. can be used

When the additional crosslinking agent and the super absorbent polymer are mixed, water and methanol may be mixed and added. When water and methanol are added, there is an advantage that the additional crosslinking agent can be uniformly dispersed in the superabsorbent polymer. At this time, the content of the added water and methanol may be appropriately adjusted to induce even dispersion of the additional crosslinking agent, prevent agglomeration of the superabsorbent polymer, and at the same time optimize the surface penetration depth of the crosslinking agent.

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

A means for increasing the temperature for the additional crosslinking reaction is not particularly limited. It can be heated by supplying a heating medium or by directly supplying a heat source. At this time, as the type of heating medium that can be used, a fluid having an elevated temperature such as steam, hot air, or hot oil may be used, but it is not limited thereto, and the temperature of the supplied heating medium depends on the means of the heating medium, the temperature increase rate and the temperature increase target temperature. Considering it, it can be appropriately selected. On the other hand, the directly supplied heat source may be a heating method through electricity or a heating method through a gas, but is not limited to the above-described example.

Hereinafter, preferred embodiments are presented to help the understanding of the invention. However, the following examples are only for illustrating the invention, and do not limit the invention thereto.

Example - Preparation of super absorbent polymer

Example 1

(Step 1) In a 3L glass container equipped with a stirrer and a thermometer, 100 g (1.388 mol) of acrylic acid, 0.16 g of a crosslinking agent polyethylene glycol diacrylate (Mn = 508), a photopolymerization initiator diphenyl (2, 4,6-trimethylbenzoyl) ) 0.008 g of phosphine oxide, 0.12 g of sodium persulfate, a thermal polymerization initiator, and 123.5 g of a 32% caustic soda solution were mixed at room temperature to prepare a monomer composition (neutralization degree of acrylic acid: 70 mol%, solid content: 45% by weight) ).

Thereafter, the monomer composition was supplied at a rate of 500 to 2000 mL/min on a conveyor belt in which a belt having a width of 10 cm and a length of 2 m was rotated at a speed of 50 cm/min. And, at the same time as the supply of the monomer composition, the polymerization reaction was carried out for 60 seconds by irradiating ultraviolet rays having an intensity of 10 mW/cm ² to obtain a hydrogel polymer having a water content of 55 wt%.

(Second step) Next, sodium stearoyl-2-lactylate (Almax-6900, Ilshin Wells Co., Ltd.) represented by Formula 1-6 below is added to the hydrogel polymer obtained through the polymerization reaction. prepared) in the form of an aqueous solution (sodium stearoyl-2-lactylate 3% by weight) in hot water so as to be 0.4 parts by weight based on 100 parts by weight of the hydrogel polymer, and then pulverized using a meat chopper After that, it was cut through a perforated plate having a hole size of 1 mm. At this time, the moisture content of the water-containing superabsorbent polymer particles included in the final pulverized pulverized material was 50% by weight.

After (3rd step), hydrophobic particles methylsilsesquioxane (Tospearl ^® 120, average particle diameter 2 μm, contact angle to water 117°, manufactured by Momentive) was added to the pulverized product in 1.0 parts by weight based on 100 parts by weight of the hydrogel polymer After the input, the mixture was mixed using a shaker for 5 minutes.

(Step 4) Thereafter, the mixture was dried at 220° C. for 50 minutes using a rotary dryer (1.2 revolutions/minute, capacity 5L) to prepare a superabsorbent polymer having a moisture content of less than 5% by weight.

[Formula 1-6]

Example 2

In Example 1, instead of methylsilsesquioxane (Tospearl ^® 120) as the hydrophobic particles, methylsilsesquioxane (Tospearl ^® 2000B, average particle diameter 4-8 μm, manufactured by Momentive) was added, except that Example A super absorbent polymer was prepared using the same method as in 1.

Example 3

In Example 1, instead of methylsilsesquioxane (Tospearl ^® 120) as the hydrophobic particles, hydrophobic fumed silica surface-modified with polydimethylsiloxane (PDMS) (AEROSIL ^® R 202, contact angle to water 128°, manufactured by Evonik) was used. A super absorbent polymer was prepared in the same manner as in Example 1, except that it was added.

Example 4

In Example 1, instead of methylsilsesquioxane (Tospearl ^® 120) as the hydrophobic particles, hydrophobic fumed silica surface-modified with dimethyldichlorosilane (DDS) (AEROSIL ^® R 974, contact angle to water 105°, manufactured by Evonik) was used. A super absorbent polymer was prepared in the same manner as in Example 1, except that it was added.

Example 5

The same method as in Example 1 was followed, except that in Example 1, kaolin obtained from Sigma-Aldrich (contact angle to water 94°) was added instead of methylsilsesquioxane (Tospearl ^® 120) as the hydrophobic particles in Example 1 was used to prepare a super absorbent polymer.

Example 6

Except that in Example 1, sodium lauroyl lactylate represented by the following formula 1-7 (Sodium Lauroyl Lactylate, manufactured by Ilshin Wells) was used instead of sodium stearoyl-2-lactylate as a carboxylic acid-based additive, A super absorbent polymer was prepared using the same method as in Example 1.

[Formula 1-7]

Comparative Example 1

A super absorbent polymer was prepared in the same manner as in Example 1, except that hydrophobic particles were not used in Example 1.

Comparative Example 2

In Example 1, the same method as in Example 1 was used, except that polydimethylsiloxane (KF-96-1,000 cs, manufactured by Shin-Etsu) was added instead of hydrophobic particles methylsilsesquioxane (Tospearl ^® 120). Thus, a super absorbent polymer was prepared.

Comparative Example 3

Example 1, except that in Example 1, fumed silica without surface treatment (AEROSIL ^® 300, contact angle to water 35°, manufactured by Evonik) was added instead of hydrophobic particles methylsilsesquioxane (Tospearl ^® 120) A superabsorbent polymer was prepared using the same method as described above.

Comparative Example 4

Example 1, except that in Example 1, wet silica (Sipernat ^® 22S, contact angle to water 31°, manufactured by Evonik) was added instead of hydrophobic particles methylsilsesquioxane (Tospearl ^® 120). A superabsorbent polymer was prepared using the same method as described above.

Comparative Example 5

Using the same method as in Example 1, except that in Example 1, phyllosilicate (Optigel, contact angle to water 32°, manufactured by BYK-Chem) was added instead of the hydrophobic particles methylsilsesquioxane (Tospearl ^® 120) A super absorbent polymer was prepared.

Comparative Example 6

In Example 1, the same method as in Example 1 was used, except that Hydrotalcite (contact angle to water, 42°, manufactured by Kisuma Chemicals) was used instead of hydrophobic particles methylsilsesquioxane (Tospearl ^® 120). A resin was prepared.

Comparative Example 7

In Example 1, the same method as in Example 1 was used, except that Sepiolite (contact angle to water 66°) obtained from Sigma-Aldrich was added instead of hydrophobic particles methylsilsesquioxane (Tospearl ^® 120). A super absorbent polymer was prepared.

Comparative Example 8

Superabsorbent property was used in the same manner as in Example 1, except that magnesium stearate (manufactured by Sigma-Aldrich) was added instead of sodium stearoyl-2-lactylate as a carboxylic acid-based additive in Example 1 A resin was prepared.

Test Example 1 - Surface image analysis of superabsorbent polymer

For surface analysis of the superabsorbent polymers prepared in Examples 1, 2, 3, 4 and Comparative Example 1, SEM analysis was performed on each surface, and the images are shown in FIGS. 5 is shown.

Through this, in the superabsorbent polymers prepared in Examples 1 to 4, unlike the superabsorbent polymer prepared in Comparative Example 1 in which hydrophobic particles were not added, the hydrophobic particles were physically well adsorbed to the surface of the superabsorbent polymer. It can be confirmed that there is This is considered to be because the carboxylic acid-based additive is not only fine particles compared to the hydrophobic particles, but is added in a dissolved state in water, a solvent, during the manufacturing process, and does not remain in the form of particles on the surface of the final superabsorbent polymer.

Test Example 2- Carboxylic acid-based additive content analysis

For the superabsorbent polymers prepared in Example 1 and Comparative Example 1, using high-performance liquid chromatography (HPLC), the content of additives contained in the superabsorbent polymer was measured in the following manner, respectively. was measured, and the results are shown in Table 1 below.

① 1 ml of distilled water was added to 1.0±0.0001 g of the final superabsorbent polymer composition, and then sufficiently swollen for 1 hour.

② 6 mL of solvent (MeOH:Methylene chloride = 2:1 v/v) was added to the swollen superabsorbent polymer composition, and then filtered after 4 hours to extract only the solution portion, which was used as a sample solution.

③ The content of the residual substance was obtained by passing the sample solution through high-performance liquid chromatography (HPLC), and the content of the additive dissolved in the sample solution was quantified.

At this time, the measurement conditions of high performance liquid chromatography (HPLC) are as follows:

- column: Acquity BEH C ₁₈ (2.1 mm ID × 50 mm L, particle size: 1.7㎛)

- Mobile phase A: ACN (Acetonitrile (0.1% trifluoroacetic acid))

- Mobile phase B: D.I Water (0.1% trifluoroacetic acid)

- column temp.: 40℃

- Flaw rate: 0.4 mL/min

Additive type Additive content ¹⁾
(weight%) Example 1 1-6 0.3178 Comparative Example 1 - 0

1) Weight % based on the total weight of the super absorbent polymer

Referring to Table 1, unlike the superabsorbent polymer composition prepared in Comparative Example 1, the superabsorbent polymer prepared in Example 1 contains sodium stearoyl-2-lactylate represented by Chemical Formula 1-6. It can be confirmed that there is

Test Example 3 Evaluation of physical properties of super absorbent polymer

For the superabsorbent polymers prepared in Examples and Comparative Examples, the removal rate, centrifugation retention capacity (CRC) and absorbency under pressure (AUP) were respectively measured in the following manner, and the results are shown in Table 2 below.

(1) Rejection rate evaluation

In order to measure the content of large dust, which are particles having a particle size greater than 850 μm, contained in the super absorbent polymer prepared in Examples and Comparative Examples, the super absorbent polymer was passed through 20 mesh to measure the content, and the method of Equation 1 below The rejection rate was calculated with

[Equation 1]

Removal rate (%) = [(content of particles exceeding 850 μm that did not pass through 20 mesh)/(total content of particles)] * 100

(2) Centrifuge Retention Capacity (CRC)

The water holding capacity of each resin composition according to the absorption magnification under no load was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3.

Specifically, in the resin compositions obtained through Examples and Comparative Examples, a resin composition classified through a sieve of #30-50 was obtained. This resin composition W ₀ (g) (about 0.2 g) was uniformly placed in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt %) at room temperature. After 30 minutes, water was drained from the bag for 3 minutes under the conditions of 250G using a centrifugal separator, and the mass W ₂ (g) of the bag was measured. Moreover, after performing the same operation without using resin, the mass W1 (g) _at that time was measured.

CRC (g/g) was calculated according to Equation 2 below using each obtained mass.

[Equation 2]

CRC (g/g) = {[W ₂ (g) - W ₁ (g)]/W ₀ (g)} - 1

(3) Absorbency under Pressure (AUP: Absorbency under Pressure)

The absorbency under pressure of 0.7 psi of the superabsorbent polymers of Examples and Comparative Examples was measured according to WSP 242.3 of the EDANA method.

First, when measuring the absorbency under pressure, the resin fraction at the time of the CRC measurement was used.

Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm. Under conditions of room temperature and humidity of 50%, the water absorbent resin composition W ₀ (g) (0.16 g) is uniformly sprayed on the wire mesh, and the piston that can further apply a load of 0.7 psi thereon is slightly more than 25 mm in outer diameter. It is small, there is no gap with the inner wall of the cylinder, and the vertical movement is not disturbed. At this time, the weight W ₃ (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a petro dish having a diameter of 150 mm, and physiological saline composed of 0.9 wt% sodium chloride was made to be at the same level as the upper surface of the glass filter. One filter paper having a diameter of 90 mm was loaded thereon. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted and the weight W ₄ (g) was measured.

Absorption under pressure (g/g) was calculated according to the following Equation 3 using each obtained mass.

[Equation 3]

AUP(g/g) = [W ₄ (g) - W ₃ (g)]/W ₀ (g)

carboxylic acid
additive hydrophobic particles rejection rate
(%) Super absorbent polymer properties CRC
(g/g) AUP
(g/g) Example 1 chemical formula
1-6 Tospearl ^® 120 20.1 38.2 21.1 Example 2 chemical formula
1-6 Tospearl ^® 2000B 28.5 39.1 21.1 Example 3 chemical formula
1-6 AEROSIL ^® R 202 31.3 39.3 22.4 Example 4 chemical formula
1-6 AEROSIL ^® R 974 35.5 39.2 22.0 Example 5 chemical formula
1-6 kaoline 28.8 40.8 24.8 Example 6 chemical formula
1-7 Tospearl ^® 120 17.4 37.5 20.9 Comparative Example 1 chemical formula
1-6 - 42.8 37.6 21.1 Comparative Example 2 chemical formula
1-6 KF-96-1,000 cs 60.2 20.4 10.4 Comparative Example 3 chemical formula
1-6 AEROSIL ^® 300 68.6 28.5 16.7 Comparative Example 4 chemical formula
1-6 Sipernat ^® 22S 70.1 29.0 15.2 Comparative Example 5 chemical formula
1-6 phyllosilicate 56.7 32.5 22.4 Comparative Example 6 chemical formula
1-6 hydrotalcite 54.5 33.7 18.5 Comparative Example 7 chemical formula
1-6 sepiolite 81.6 35.2 18.4 Comparative Example 8 Magnesium stearate Tospearl ^® 120 80.8 36.9 17.5

Referring to Table 2, the superabsorbent polymers of Examples 1 to 6 prepared by adding the hydrophobic particles before the drying process during the preparation of the superabsorbent polymer had the superabsorbent properties of Comparative Example 1 prepared without adding the hydrophobic particles. It can be seen that, compared to the resin, it exhibits a significantly lower rejection ratio, as well as an equal or higher absorption capacity and improved water retention capacity.

On the other hand, in the case of the superabsorbent polymers of Comparative Example 2 using a liquid material instead of the hydrophobic particles of Example and Comparative Examples 3 to 8 using non-hydrophobic particles, a higher retention rate and lower absorption than the superabsorbent polymer of Comparative Example 1 It is confirmed that the performance is shown.

Accordingly, it can be seen that when the hydrophobic particles are used to prepare the superabsorbent polymer, it is possible to prepare a superabsorbent polymer with improved absorption performance while suppressing aggregation between the pulverized hydrogel polymer particles to have a uniform particle size distribution.

Claims (17)

superabsorbent polymer particles comprising a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group and a crosslinked polymer of a crosslinking agent;
hydrophobic particles; and
a carboxylic acid-based additive,
The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by the following formula (1) and a salt thereof,
Super absorbent polymer:
[Formula 1]

In Formula 1,
A is alkyl having 5 to 21 carbon atoms,
EO means ethylene oxide (-CH ₂ CH ₂ O-),
m is an integer from 0 to 8,
B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,
Here, R ₁ is an alkyl having 1 to 5 carbon atoms,
B ₂ is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon atoms, or alkynylene having 2 to 5 carbon atoms,
n is an integer from 1 to 3,
C is a carboxyl group.
According to claim 1,
At least a portion of the hydrophobic particles are present on the surface of the superabsorbent polymer particles,
Super absorbent resin.
According to claim 1,
The hydrophobic particles are at least one selected from the group consisting of hydrophobic silicone resin particles, hydrophobic silica particles and hydrophobic clay particles,
Super absorbent resin.
4. The method of claim 3,
The hydrophobic silicone resin is polyorganosilsesquioxane,
Super absorbent resin.
4. The method of claim 3,
The hydrophobic silica is fumed silica surface-modified by a surface treatment agent selected from the group consisting of dimethyldichlorosilane (DDS), polydimethylsiloxane (PDMS) and hexamethyldisilazane (HMDS),
Super absorbent resin.
4. The method of claim 3,
The hydrophobic clay is at least one selected from the group consisting of kaolin, sericite, pyrophyllite, montmorillonite, bentonite and acid clay,
Super absorbent resin.
According to claim 1,
In Formula 1,
A is -C ₆ H ₁₃ , -C ₁₁ H ₂₃ , -C ₁₂ H ₂₅ , -C ₁₇ H ₃₅ , or -C ₁₈ H ₃₇ ;
Super absorbent resin.
According to claim 1,
In Formula 1,
B ₁ is

, or

ego,
where * is a binding site with a neighboring atom,
Super absorbent resin.
According to claim 1,
In Formula 1,
B ₂ is

,

,

, or

ego,
where * is a binding site with a neighboring atom,
Super absorbent resin.
According to claim 1,
The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by Formula 1, an alkali metal salt thereof, and an alkaline earth metal salt thereof,
Super absorbent polymer:
According to claim 1,
The carboxylic acid-based additive is any one of the compounds represented by the following formulas 1-1 to 1-9,
Super absorbent polymer:

.
A first step of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of a crosslinking agent and a polymerization initiator to form a hydrogel polymer;
a second step of pulverizing the hydrogel polymer after mixing it with a carboxylic acid-based additive;
a third step of mixing hydrophobic particles with the pulverized product prepared in the second step; and
A fourth step of drying the mixture prepared in the third step,
The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by the following formula (1) and a salt thereof,
Method for preparing super absorbent polymer:
[Formula 1]

In Formula 1,
A is alkyl having 5 to 21 carbon atoms,
EO means ethylene oxide (-CH ₂ CH ₂ O-),
m is an integer from 0 to 8,
B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,
Here, R ₁ is an alkyl having 1 to 5 carbon atoms,
B ₂ is alkylene having 1 to 5 carbon atoms, alkenylene having 2 to 5 carbon atoms, or alkynylene having 2 to 5 carbon atoms,
n is an integer from 1 to 3,
C is a carboxyl group.
13. The method of claim 12,
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 water-soluble ethylenically unsaturated monomer,
A method for producing a super absorbent polymer.
13. The method of claim 12,
The carboxylic acid-based additive is mixed in a solution state dissolved in a solvent,
A method for producing a super absorbent polymer.
13. The method of claim 12,
The hydrophobic particles are used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the hydrogel polymer,
A method for producing a super absorbent polymer.
13. The method of claim 12,
The hydrophobic particles are mixed in a dry manner,
A method for producing a super absorbent polymer.
13. The method of claim 12,
The prepared superabsorbent polymer contains less than 40% by weight of bulk powder having a particle diameter of more than 850 μm based on the total weight,
A method for producing a super absorbent polymer.

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