KR20230097595A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for preparing a superabsorbent polymer. More specifically, in the step of forming the water-containing gel polymer, by using a foaming agent and a modified polyvinyl alcohol-based compound containing a sulfonyl group in combination, water-soluble components generated in the foaming process are reduced, resulting in the final production of the superabsorbent polymer. It relates to a method for manufacturing a superabsorbent polymer with improved absorption rate.

Description

Manufacturing method of super absorbent polymer {PREPARATION METHOD OF SUPER ABSORBENT POLYMER}

The present invention relates to a method for preparing a superabsorbent polymer. More specifically, in the step of forming a water-containing gel polymer, a modified polyvinyl alcohol-based compound containing a sulfonyl group is used in combination with a specific foaming agent to reduce water-soluble components generated in the foaming process, thereby finally producing the superabsorbent polymer. It relates to a method for producing a superabsorbent polymer with improved absorption rate.

Super Absorbent Polymer (SAP) is a synthetic high-molecular substance that has the ability to absorb moisture 500 to 1,000 times its own weight. Material), etc., are named by different names. The superabsorbent polymer as described above has begun to be put into practical use as a sanitary tool, and is currently widely used as a material for gardening soil remediation agents, civil engineering and construction waterstop materials, seedling sheets, freshness retainers in the field of food distribution, and steaming. .

These superabsorbent polymers are widely used in sanitary materials such as diapers and sanitary napkins. In the sanitary material, it is common that the superabsorbent polymer is included in a spread state in the pulp. However, in recent years, efforts have been made to provide sanitary materials such as diapers with a thinner thickness, and as part of this, the content of pulp is reduced or, furthermore, so-called pulpless diapers in which pulp is not used at all. Development is actively progressing.

As described above, in the case of a sanitary material in which the pulp content is reduced or pulp is not used, the super absorbent polymer is included in a relatively high ratio, so that the super absorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire superabsorbent polymer particles included in multiple layers to more efficiently absorb a large amount of liquid such as urine, the superabsorbent polymer basically needs to exhibit high absorption performance as well as a fast absorption rate.

Accordingly, a process using a foaming agent is known to improve the absorption properties of the superabsorbent polymer, and the absorption rate could be improved through bubbles generated by the foaming agent during the polymerization process.

However, there is a problem in that the water-soluble component also increases due to the use of a foaming agent, and since the water-soluble component has a property of being easily eluted when the superabsorbent polymer comes into contact with a liquid, most of the water-soluble component eluted when the content of the water-soluble component is high. It remains on the surface of the super-absorbent polymer and makes the super-absorbent polymer sticky, thereby reducing liquid permeability and absorption rate.

That is, research is required to improve the absorption rate compared to the amount of the foaming agent used to a desired degree.

Therefore, in the present invention, in the step of forming a water-containing gel polymer, a modified polyvinyl alcohol-based compound containing a sulfonyl group is used in combination with a foaming agent to reduce water-soluble components generated in the foaming process, and the superabsorbent polymer is finally prepared. It is to provide a method for producing a superabsorbent polymer with improved absorption rate.

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

forming a water-containing gel polymer having an acidic group by polymerizing a monomer mixture including an acrylic acid-based monomer having at least a partially neutralized acidic group, a foaming agent, and a polyvinyl alcohol-based compound including a sulfonyl group (step 1); and

Drying, pulverizing, and classifying the water-containing gel polymer to prepare base resin particles (step 2);

The foaming agent is at least one selected from the group consisting of carbonate-based foaming agents and encapsulated foaming agents,

A method for preparing a superabsorbent polymer is provided.

According to the manufacturing method of the superabsorbent polymer of the present invention, in the step of forming the water-containing gel polymer, a modified polyvinyl alcohol-based compound containing a sulfonyl group is used in combination with a foaming agent to reduce water-soluble components generated in the foaming process. , It is possible to manufacture a super absorbent polymer with improved absorption rate of the final super absorbent polymer.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, step, component, or combination thereof, but one or more other features or steps; It should be understood that the presence or addition of components, or combinations thereof, is not previously excluded.

The terms first, second, third, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

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

As used herein, the term "polymer" or "polymer" refers to a state in which acrylic acid-based monomers are polymerized, and may cover all moisture content ranges or particle size ranges. Among the polymers, polymers in a state after polymerization and before drying and having a moisture content (moisture content) of about 40% by weight or more may be referred to as hydrogel polymers, and particles obtained by pulverizing and drying such hydrogel polymers may be referred to as crosslinked polymers. there is.

Also, the term “superabsorbent polymer powder” refers to a particulate material including a crosslinked polymer in which an acrylic acid-based monomer containing an acidic group and at least a portion of the acidic group is neutralized is polymerized and crosslinked by an internal crosslinking agent.

In addition, the term “superabsorbent polymer” refers to a crosslinked polymer obtained by polymerizing an acrylic acid-based monomer containing an acidic group and at least a portion of the acidic group neutralized, or a powder composed of superabsorbent polymer particles in which the crosslinked polymer is pulverized, depending on the context. ) form, or covers all of the crosslinked polymers or base resins in a state suitable for commercialization through additional processes such as surface crosslinking, fine powder reassembly, drying, pulverization, classification, etc. used to do

In addition, the term "crosslinked polymer" means crosslinked polymerization in the presence of the acrylic acid-based monomer and an internal crosslinking agent, and the "base resin particle" means a particulate (powder) material containing such a crosslinked polymer. .

A method for preparing a superabsorbent polymer according to an embodiment of the present invention is to polymerize a monomer mixture including an acrylic acid-based monomer having an acidic group, at least partially neutralized, a foaming agent, and a polyvinyl alcohol-based compound including a sulfonyl group, thereby polymerizing a superabsorbent polymer having an acidic group. Forming a hydrogel polymer (Step 1); and drying, pulverizing, and classifying the water-containing gel polymer to prepare base resin particles (step 2).

Conventionally, a process using a foaming agent is known to improve water absorption properties of superabsorbent polymers, and the absorption rate can be improved through bubbles generated by the foaming agent during the polymerization process. However, there is a problem in that the water-soluble component also increases due to the use of a foaming agent, and since the water-soluble component has a property of being easily eluted when the superabsorbent polymer comes into contact with a liquid, most of the water-soluble component eluted when the content of the water-soluble component is high. It remains on the surface of the super-absorbent polymer and makes the super-absorbent polymer sticky, thereby reducing liquid permeability and absorption rate.

Accordingly, the present inventors confirmed that water-soluble components generated in the foaming process can be effectively reduced by using a modified polyvinyl alcohol-based compound containing a sulfonyl group in combination with a specific foaming agent in the step of forming a water-containing gel polymer. completed the present invention.

The superabsorbent polymer prepared according to the present invention can realize excellent water absorption properties, and in particular, has excellent water absorption capacity and high water absorption rate.

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

(Polymerization step)

A method for preparing a superabsorbent polymer according to an embodiment of the present invention is to polymerize a monomer mixture including an acrylic acid-based monomer having an acidic group, at least partially neutralized, a foaming agent, and a polyvinyl alcohol-based compound including a sulfonyl group, thereby polymerizing a superabsorbent polymer having an acidic group. and forming a hydrogel polymer (Step 1).

The polymerization step is performed by photopolymerizing and/or thermally polymerizing a monomer composition including a specific kind of foaming agent and a polyvinyl alcohol-based compound including a sulfonyl group in the presence of an internal crosslinking agent and a polymerization initiator to form a water-containing gel polymer. It is a step.

In the above step, air bubbles generated by the foaming agent form pores in the water-containing gel polymer, increasing the surface area, thereby realizing excellent absorbent properties. In addition, in the above step, by using a polyvinyl alcohol-based compound containing a sulfonyl group in combination, a Semi-IPN (Interpenetrating Polymer Network) structure is formed, and at the same time, water-soluble components can be effectively reduced due to sulfonate ions.

First, a monomer mixture including an acrylic acid-based monomer having an acidic group at least partially neutralized, a foaming agent, and a polyvinyl alcohol-based compound including a sulfonyl group is prepared. The monomer mixture may include an internal crosslinking agent and a polymerization initiator for polymerization.

The foaming agent is a component that increases the surface area of the water-containing gel polymer by generating bubbles to form appropriate pores in the water-containing gel polymer, thereby improving the absorption properties of the resin. The foaming agent may use at least one selected from the group consisting of carbonate-based foaming agents and encapsulated foaming agents, and is preferably used in combination with a polyvinyl alcohol-based compound containing a sulfonyl group to effectively reduce water-soluble components. do.

As the carbonate-based foaming agent, for example, at least one selected from the group consisting of sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, or magnesium carbonate may be used. there is.

As the encapsulated foaming agent, for example, a foaming agent having a core-shell structure including a core containing hydrocarbon and a shell made of a thermoplastic resin formed on the core may be used.

The hydrocarbon is, for example, n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso - It may be at least one selected from the group consisting of heptane, cycloheptane, n-octane, iso-octane and cyclooctane.

As the thermoplastic resin, for example, a polymer formed from at least one monomer selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide, and vinylidene halide may be used. can Commercially available capsular foaming agents include, but are not limited to, F-36D (Asahi Kasei Corporation).

The foaming agent may be included in an amount of 1,000 ppmw to 10,000 ppmw based on the acrylic acid monomer, and preferably, the foaming agent is 1,000 ppmw or more, 1,500 ppmw or more, 2,000 ppmw or more, or 2,500 ppmw or more, and 10,000 ppmw or less, 7,000 ppmw or less, 5,000 ppmw or less may be included. When the content of the foaming agent is too low, the amount of bubbles generated is small, and the effect of improving the desired absorption properties is insignificant, and a problem of not absorbing the solution quickly may occur. The gel strength of the resin decreases and the density decreases, which may cause problems in distribution and storage, and in particular, problems may occur.

The polyvinyl alcohol-based compound including the sulfonyl group forms a semi-IPN (Interpenetrating Polymer Network) structure, thereby forming a polymer chain with an appropriate length to effectively reduce the content of water-soluble components. At the same time, the content of the water-soluble component can be effectively controlled by the sulfonate anion (SO ₃ ^- ) generated by the terminal sulfonyl group, and at the same time, the absorption rate can be improved.

On the other hand, when using a polyvinyl alcohol-based compound containing a carboxyl group, there is a problem in that it is difficult to realize a sufficient water-soluble component reduction effect compared to a polyvinyl alcohol-based compound containing a sulfonate group.

The polyvinyl alcohol-based compound containing a sulfonyl group is a compound having a structure in which a sulfonate anion (SO ₃ ^- ) is substituted in the side chain of the polyvinyl alcohol-based compound, and is used in combination with the foaming agent of the present application described above, and is a water-soluble component. It is preferable because it can effectively reduce. A commercially available polyvinyl alcohol-based compound containing a sulfonyl group may include L-3266 (Nippon Gohsei), but is not limited thereto.

The polyvinyl alcohol-based compound including the sulfonyl group may be included in an amount of 1,000 ppmw to 30,000 ppmw based on the acrylic acid-based monomer, and preferably, the foaming agent is 1,000 ppmw or more, 3,000 ppmw or more, 5,000 ppmw or more, and 30,000 ppmw or more. It may be included in ppmw or less, 20,000 ppmw or less, or 15,000 ppmw or less. It is included in the above content range and used in combination with the above-described foaming agent to be suitable for realizing the desired effect of improving physical properties.

The acrylic acid-based monomer may be any monomer commonly used in the preparation of super absorbent polymers. As a non-limiting example, the acrylic acid-based monomer may be a compound represented by Formula 1 below:

[Formula 1]

R ₁ -COOM ¹

In Formula 1,

R ₁ is an alkyl group having 2 to 5 carbon atoms including an unsaturated bond;

M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

Preferably, the acrylic acid-based monomer may be at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids. In this way, the use of acrylic acid-based monomers is advantageous in that a superabsorbent polymer having improved water absorbency can be obtained. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-( meth)acrylamide-2-methyl propane sulfonic acid anionic monomers and salts thereof; (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol ( nonionic hydrophilic containing monomers of meth)acrylate; and (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide, an amino group-containing unsaturated monomer and a quaternary product thereof; at least one selected from the group consisting of can be used

Here, the acrylic acid-based monomer has an acidic group, and at least a part of the acidic group is partially neutralized using the neutralization solution of the present invention described above. At this time, as the neutralizing agent, a basic material such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide capable of neutralizing an acidic group may be used.

In this case, the degree of neutralization of the monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. there is. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, neutralized monomers may be precipitated, making it difficult for the polymerization to proceed smoothly. It can exhibit properties like elastic rubber that are difficult to handle.

The term "internal cross-linking agent" used herein is a term used to differentiate from a "surface cross-linking agent" for cross-linking the surface of the base resin, and serves to polymerize by cross-linking the unsaturated bonds of the above-mentioned acrylic acid-based monomers. Crosslinking in this step proceeds regardless of surface or internal crosslinking, but by the surface crosslinking process of the base resin to be described later, the surface of the finally prepared superabsorbent polymer has a structure crosslinked by a surface crosslinking agent, and the inside is the internal crosslinking agent. It is composed of a cross-linked structure by a cross-linking agent.

The internal crosslinking agent may be a multifunctional component, for example, N, N'-methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) ) Acrylate, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate, triethylene glycol di(meth)acrylate ) Acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythol tetraacrylate, triarylamine, Ethylene glycol diglycidyl ether, polyethylene glycol (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, polypropylene glycol di (meth) acrylate, propylene glycol, glycerin, and At least one selected from the group consisting of ethylene carbonate may be used. Preferably, ethylene glycol diglycidyl ether or polyethylene glycol di(meth)acrylate may be used.

The internal crosslinking agent may be used in an amount of 100 ppmw to 10,000 ppmw based on the weight of the acrylic acid-based monomer. It is included in the above content range, and sufficient crosslinking can realize strength above an appropriate level, and sufficient water retention ability can be realized by introducing an appropriate crosslinking structure. Preferably, 100 ppmw or more, 200 ppmw or more, 300 ppmw or more or 600 ppmw or more, 10,000 ppmw or less, 9,000 ppmw or less, 7,000 ppmw or 5,000 ppmw or less, 200 ppmw to 9,000 ppmw, 300 ppmw to 7,000 ppmw or 600 ppmw to 5,000 ppmw. The content refers to the mixed content of two or more internal crosslinking agents when used. When the content of the internal cross-linking agent is too low, cross-linking does not occur sufficiently, making it difficult to realize a strength higher than an appropriate level. When the content of the internal cross-linking agent is too high, the internal cross-linking density increases, making it difficult to realize a desired water retention capacity.

As the polymerization initiator, a thermal polymerization initiator or a photo polymerization initiator may be used depending on the polymerization method. However, even with the photopolymerization method, since a certain amount of heat is generated by irradiation of ultraviolet light and the like, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, a thermal polymerization initiator may be additionally included.

Here, as the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyldimethyl At least one compound selected from the group consisting of ketal (Benzyl Dimethyl Ketal), acyl phosphine and alpha-aminoketone (a-aminoketone) may be used. Among them, as a specific example of acylphosphine, commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) can be used. . More various photopolymerization initiators are disclosed on page 115 of "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)", a book by Reinhold Schwalm, and may be referred to.

And, as the thermal polymerization initiator, at least one compound selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ ) and the like. In addition, as an azo-based initiator, 2,2-azobis-(2-amidinopropane) dihydrochloride, 2,2-azobis-(N, N-dimethylene) isobutyramidine dihydrochloride (2,2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride), 2- (carbamoyl azo) isobutyronitrile (2- (carbamoylazo) isobutylonitril), 2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride (2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride), 4, 4-azobis-(4-cyanovaleric acid) and the like are exemplified. For more various thermal polymerization initiators, it is disclosed on page 203 of Odian's "Principle of Polymerization (Wiley, 1981)", which can be referred to.

The polymerization initiator may be used in an amount of 10 ppmw to 10,000 ppmw based on the weight of the acrylic acid-based monomer. It is included in the above content range, and sufficient crosslinking can realize strength above an appropriate level, and sufficient water retention ability can be realized by introducing an appropriate crosslinking structure. Preferably, 50 ppmw or more, 80 ppmw or more, 100 ppmw or more or 500 ppmw or more, 10,000 ppmw or less, 9,000 ppmw or less, 7,000 ppmw or 5,000 ppmw or less, 50 ppmw to 5,000 ppmw, 80 ppmw to 5,000 ppmw or 80 It may be included in ppmw to 3,000 ppmw. The above content refers to the mixed content when the photopolymerization initiator and the thermal polymerization initiator are mixed and used.

If the concentration of the polymerization initiator is too low, the polymerization rate may be slowed and a large amount of residual monomer may be extracted into the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is excessively high, the polymer chain constituting the network is shortened, which is undesirable because the physical properties of the resin may be deteriorated, such as an increase in the content of water-soluble components and a decrease in absorbency under pressure.

In addition, the monomer composition may include a thickener, a plasticizer, a storage stabilizer, and a surfactant as necessary. Additives such as antioxidants may be further included.

The surfactant induces uniform dispersion of the foaming agent to prevent lowering of gel strength or lowering of density due to uniform foaming during foaming. As the surfactant, it is preferable to use an anionic surfactant. Specifically, the surfactant includes SO ₃ ^- anion, and a compound represented by Formula 2 below may be used.

[Formula 2]

R—SO ₃ Na

In Formula 2,

R is an alkyl of 8 to 16 carbon atoms.

In addition, it is preferable to use the surfactant in an amount of 300 ppmw or less based on the weight of the acrylic acid-based monomer. When the amount of the surfactant exceeds 300 ppmw, the content of the surfactant in the superabsorbent polymer increases, which is not preferable. In addition, the surfactant is preferably used in an amount of 100 ppmw or more, or 150 ppmw or more, based on the weight of the water-soluble ethylenically unsaturated monomer.

In addition, the monomer composition may be prepared in the form of a solution in which raw materials such as the above-described monomer, foaming agent, and initiator are dissolved in a solvent.

At this time, as a usable solvent, any solvent capable of dissolving the above-described raw materials may be used without limitation in its configuration. For example, as the solvent, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof, and the like may be used.

The step of forming the water-containing gel polymer through polymerization of the monomer composition may be performed by a conventional polymerization method, and the process is not particularly limited. As a non-limiting example, solution polymerization may be carried out in a reactor equipped with a movable conveyor belt.

Specifically, when photopolymerization is performed on the monomer composition in a reactor equipped with a movable conveyor belt, a hydrogel polymer in the form of a sheet may be obtained. At this time, the thickness of the sheet may vary depending on the concentration and injection speed of the monomer composition to be injected, but it is usually adjusted to a thickness of 0.5 to 10 cm in order to ensure the production rate while allowing the entire sheet to be polymerized evenly. desirable.

A typical moisture content of the water-containing gel polymer obtained in this way may be 40% to 80% by weight. Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the dry polymer from the weight of the hydrogel polymer as the content of moisture 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 moisture evaporation in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying conditions are such that the temperature is raised from room temperature to 180 ° C and then maintained at 180 ° C. The total drying time is set to 20 minutes including 5 minutes of the temperature raising step, and the moisture content is measured.

(Drying, Grinding and Classifying Steps)

Next, forming a base resin by drying, pulverizing, and classifying the hydrogel polymer is included.

Specifically, a step of drying the obtained water-containing gel polymer is performed. If necessary, a step of coarsely pulverizing the water-containing gel polymer may be further performed before drying to increase the efficiency of the drying step.

At this time, the grinder used is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutting Includes any one selected from the group of crushing devices consisting of a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter However, it is not limited to the above example.

At this time, the coarsely pulverizing step may be pulverized so that the particle size of the water-containing gel polymer is 2 to 10 mm. Grinding to a particle diameter of less than 2 mm is not technically easy due to the high water content of the hydrogel polymer, and also may cause agglomeration of the pulverized particles. On the other hand, when the particle diameter is greater than 10 mm, the effect of increasing the efficiency of the subsequent drying step may be insignificant.

Drying is performed on the water-containing gel polymer immediately after polymerization that has been coarsely pulverized or has not undergone the coarse pulverization step. At this time, the drying temperature of the drying step may be 150 to 250 ℃. When the drying temperature is less than 150 ° C, the drying time is too long and there is a concern that the physical properties of the finally formed superabsorbent polymer may deteriorate, and when the drying temperature exceeds 250 ° C, only the polymer surface is excessively dried, resulting in a subsequent pulverization process There is a concern that fine powder may be generated in the water, and physical properties of the finally formed superabsorbent polymer may be deteriorated. Therefore, preferably, the drying may be performed at a temperature of 150 to 200 °C, more preferably at a temperature of 170 to 195 °C.

Meanwhile, in the case of the drying time, in consideration of process efficiency, etc., it may be carried out for 20 to 90 minutes, but is not limited thereto.

As long as the drying method of the drying step is also commonly used as a drying process for hydrogel polymers, the composition may be selected and used without limitation. Specifically, the drying step may be performed by a method such as hot air supply, infrared ray irradiation, microwave irradiation, or ultraviolet ray irradiation. The water content of the polymer after the drying step may be about 0.1 to about 10% by weight.

Next, a step of pulverizing the dried polymer obtained through such a drying step is performed.

The polymer base resin obtained after the grinding step may have a particle size of 150 to 850 μm. The grinder used for grinding to such a particle size is specifically, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog mill. A jog mill or the like may be used, but is not limited to the above example.

In addition, in order to manage the physical properties of the superabsorbent polymer particles to be finalized after the pulverization step, a separate process of classifying the base resin particles obtained after pulverization according to the particle size may be performed. Preferably, polymers having a particle size of 150 to 850 μm are classified, and only polymer particles having such a particle size can be commercialized through a surface crosslinking reaction step. More specifically, the classified base resin particles may have a particle size of 150 to 850 μm and include 50% by weight or more of particles having a particle size of 300 to 600 μm.

The base resin particles prepared according to the above-described embodiment implement excellent water absorption properties.

The base resin particles have a centrifugal retention capacity (CRC) of 30 g/g to 48 g/g, measured according to EDENA method WSP 241.2. Preferably, the centrifuge retention capacity may be 35 g/g or more, 40 g/g or more, 45 g/g or more, or 47 g/g or less, or 46.5 g/g or less. The method for measuring the centrifugation water retention capacity will be described in more detail in Experimental Examples to be described later.

The base resin particles contain 8 wt% to 9 wt% of water-soluble components measured according to the EDANA method WSP 270.2. Preferably, it is 8.0 wt% to 8.9 wt% or 8.0 wt% to 8.7 wt%. A method for measuring the water-soluble component will be described in more detail in Experimental Examples to be described later.

The base resin particles have a tap water absorption capacity of 140 g/g or more for 1 minute, measured by the weight of tap water absorbed by the base resin particles when 1 g of the base resin is added to 1000 ml of tap water and allowed to stand for 1 minute. Preferably, it is 140 g/g to 160 g/g, 142 g/g to 158 g/g. The method for measuring the tap water absorption capacity for 1 minute will be described in more detail in an experimental example to be described later.

The base resin particles have a vortex time of less than 35 seconds at 24.0° C. according to the vortex method. Preferably, it is less than 33 seconds and less than 31 seconds. In addition, the absorption rate is excellent as the value is small, and the lower limit of the absorption rate is 0 seconds in theory, but may be, for example, 5 seconds or more, 8 seconds or more, or 10 seconds or more. In this case, a method for measuring the absorption rate of the superabsorbent polymer will be described in more detail in Experimental Examples to be described later.

(Surface cross-linking step)

Next, the manufacturing method of the superabsorbent polymer according to one embodiment of the present invention further includes crosslinking a part of the surface of the base resin by heat-treating the base resin particles in the presence of surface crosslinking.

The surface cross-linking step is to induce a cross-linking reaction on the surface of the base resin particles in the presence of a surface cross-linking agent, and unsaturated bonds of acrylic acid-based monomers remaining on the surface are cross-linked by the surface cross-linking agent, thereby increasing the surface cross-linking density. A superabsorbent polymer with high is formed.

Specifically, a surface crosslinking layer may be formed by a heat treatment process due to the presence of a surface crosslinking agent, and the heat treatment process increases the surface crosslinking density, that is, the external crosslinking density, while the internal crosslinking density does not change, resulting in a surface crosslinking layer. The formed superabsorbent polymer has a structure in which the crosslinking density is higher on the outside than on the inside.

In the surface cross-linking step, a surface cross-linking agent composition containing an alcohol-based solvent and water may be used in addition to the surface cross-linking agent.

On the other hand, as the surface crosslinking agent included in the surface crosslinking agent composition, any crosslinking agent component previously used in the preparation of superabsorbent polymer may be used without any particular limitation. For example, the surface crosslinking agent is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2- 1 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 and propylene carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; etc. may be included. Preferably, the same internal crosslinking agent as described above may be used, and for example, a diglycidyl ether-based compound of alkylene glycol such as ethylene glycol diglycidyl ether may be used.

The surface crosslinking agent may be used in an amount of 0.001 to 2 parts by weight based on 100 parts by weight of the base resin particles. Preferably, it is 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, and may be used in an amount of 0.5 parts by weight or less and 0.3 parts by weight or less. By adjusting the content range of the surface crosslinking agent within the above-described range, a superabsorbent polymer exhibiting various physical properties such as excellent absorption performance and liquid permeability can be prepared.

Meanwhile, the surface cross-linking agent is added to the base resin particles in the form of a surface cross-linking agent composition containing the surface cross-linking agent composition. For example, the surface cross-linking agent composition and the base resin particles are mixed in a reaction tank, or the surface cross-linking agent composition is sprayed on the base resin particles, and the base resin particles and the surface cross-linking agent composition are continuously supplied to a continuously operated mixer and mixed. How to do it, etc. can be used.

In addition, the surface crosslinking agent composition may further include water and/or a hydrophilic organic solvent as a medium. As a result, there is an advantage in that the surface crosslinking agent and the like can be evenly dispersed on the base resin. At this time, the content of water and hydrophilic organic solvent is based on 100 parts by weight of the base resin particles for the purpose of inducing uniform dissolution / dispersion of the surface crosslinking agent, preventing aggregation of the base resin, and at the same time optimizing the surface penetration depth of the surface crosslinking agent. It can be applied by adjusting the addition ratio.

The surface crosslinking step may be performed by heat treatment at a temperature of 110 °C to 200 °C or 110 °C to 150 °C for 30 minutes or more. More specifically, the surface crosslinking reaction may be performed by heat treatment for 30 to 80 minutes or 40 to 70 minutes at the maximum reaction temperature with the above-mentioned temperature as the maximum reaction temperature.

By satisfying these surface crosslinking process conditions (particularly, reaction conditions at elevated temperature and maximum reaction temperature), a superabsorbent polymer that appropriately satisfies physical properties such as better permeability under pressure can be produced.

The means for raising the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heat medium or directly supplying a heat source. At this time, as the type of heat medium that can be used, steam, hot air, and heated fluids such as hot oil may be used, but are not limited thereto, and the temperature of the heat medium supplied depends on the means of the heat medium, the heating rate, and the target temperature of the heating medium. can be selected appropriately. On the other hand, as a heat source that is directly supplied, heating through electricity and heating through gas may be mentioned, but it is not limited to the above-described example.

Meanwhile, in the method for preparing the superabsorbent polymer according to an embodiment of the present invention, aluminum salts such as aluminum sulfate salts and other various polyvalent metal salts may be further used to further improve liquid permeability and the like during surface crosslinking. Such a polyvalent metal salt may be included on the surface crosslinking layer of the finally prepared superabsorbent polymer.

(super absorbent polymer)

The superabsorbent polymer prepared according to the above-described embodiment may have a particle diameter of 150 to 850 μm. More specifically, at least 95% by weight of the superabsorbent polymer has a particle size of 150 to 850 μm, and may include 50% by weight or more of particles having a particle size of 300 to 600 μm, having a particle size of less than 150 μm Fines can be less than 3% by weight.

The superabsorbent polymer prepared according to one embodiment described above implements excellent absorbent properties, and in particular, exhibits excellent absorbent rate and effective absorbent capacity.

The superabsorbent polymer has a centrifugal retention capacity (CRC) of 25 g/g to 40 g/g, measured according to EDENA method WSP 241.2. Preferably, the centrifuge retention capacity may be 28 g/g or more, 30 g/g or more, 32 g/g or more, or 38 g/g or less, or 36 g/g or less. The method for measuring the centrifugation water retention capacity will be described in more detail in Experimental Examples to be described later.

The superabsorbent polymer has a vortex time of less than 35 seconds, preferably less than 32 seconds or less than 30 seconds at 24.0 ° C according to the vortex method at 24.0 ° C. In addition, the absorption rate is excellent as the value is small, and the lower limit of the absorption rate is 0 seconds in theory, but may be, for example, 5 seconds or more, or 10 seconds or more. In this case, a method for measuring the absorption rate of the superabsorbent polymer will be described in more detail in Experimental Examples to be described later.

Hereinafter, the action and effect of the invention will be described in more detail through specific examples of the invention. However, these embodiments are only presented as examples of the invention, and the scope of the invention is not determined thereby.

[Examples and Comparative Examples]

Example 1

In a 3L glass container equipped with a stirrer and a thermometer, 484 g of acrylic acid, 10 ppmw of PEGDA400 (compared to acrylic acid monomer) as an internal crosslinking agent, 1,000 ppmw of Ethylene Glycol Diglycidyl Ether (EJ1030) (compared to acrylic acid monomer), and 80 ppmw of Irgacure-819 (compared to monomeric acid) as a polymerization initiator contrast), 3,000 ppmw (compared to acrylic acid monomer) of F-36D (Asahi Kasei Corporation), a capsular foaming agent, and 5,000 ppmw (compared to 100 parts by weight of acrylic acid) of L-3266 (Nippon Gohsei) as a modified PVA containing a sulfonyl group. After adding and dissolving, 643 g of a 31.5% NaOH solution was added to prepare a water-soluble unsaturated monomer aqueous solution (degree of neutralization: 70 mol%; solid content: 45.8 wt%).

When the temperature of the water-soluble unsaturated monomer aqueous solution rises to 40 ° C. due to the heat of neutralization, the mixed solution is placed in a container containing 1,500 ppmw of sodium persulfate (SPS), a thermal polymerization initiator (compared to acrylic acid monomer), and then irradiated with ultraviolet rays for 1 minute ( Irradiation amount: 10 mV/cm ² ), UV polymerization was performed, and heat was applied in an oven at 80° C. for 120 seconds to age to obtain a water-containing gel polymer sheet.

The obtained hydrogel polymer sheet was passed through a chopper having a hole size of 16 mm to prepare crumbs.

Next, the crumbs were dried in an oven capable of shifting air volume upwards and downwards. The crumb was dried in an oven capable of transferring air volume up and down. Hot air at 185 ° C. was flowed from the bottom to the top for 15 minutes and from the top to the bottom for 15 minutes to uniformly dry, and after drying, the water content of the dried product was set to 2% by weight or less.

The thus-obtained dry polymer was pulverized using a grinder and classified using a standard ASTM sieve to obtain base resin particles having a particle size of 150 μm to 850 μm.

Examples 2 and 3 and Comparative Examples 1 to 5

In the preparation of the base resin particles of Example 1, the base resin particles were prepared in the same manner as in Example 1, except for using the ingredients and contents in Table 1 below.

division PVA compound blowing agent ingredient content
(ppmw) ingredient content
(ppmw) Example 1 L-3266 5,000 F-36D 3,000 Example 2 L-3266 10,000 F-36D 3,000 Example 3 L-3266 20,000 F-36D 3,000 Comparative Example 1 - - - - Comparative Example 2 - - F-36D 3,000 Comparative Example 3 T-330 5,000 F-36D 3,000 Comparative Example 4 T-330 10,000 F-36D 3,000 Comparative Example 5 T-330 20,000 F-36D 3,000 L3266: PVA with sulfonyl group (Nippon Gohsei)
T330: Carboxyl group-containing PVA (Nippon Gohsei)
F-36D: Encapsulated blowing agent (Asahi Kasei Corporation)

<Experimental example>

With respect to the base resin prepared in the above Examples and Comparative Examples, physical properties were evaluated in the following manner, and the results are shown in Table 2.

Experimental Example: Evaluation of Physical Properties of Base Resin (Before Surface Crosslinking)

(1) Centrifuge Retention Capacity (CRC)

Among the base resins prepared in the above Examples and Comparative Examples, those having a particle size of 150 to 850 μm were taken and centrifuged according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.2 by absorption magnification under no load Water retention capacity (CRC) was measured.

Specifically, resins were obtained by sifting the base resins obtained in Examples and Comparative Examples through a #30-50 sieve. This resin W'0(g) (about 0.2 g) was uniformly placed in a bag made of nonwoven fabric and sealed, and then immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes, water was drained from the bag for 3 minutes under the condition of 250 G using a centrifugal separator, and the mass W'2 (g) of the bag was measured. Moreover, after carrying out the same operation without using resin, the mass W'1(g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to Equation 1 below.

[Equation 1]

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

(2) Water-soluble components (EC, %)

For the base resins of Examples and Comparative Examples, water-soluble components (EC) were measured according to the method of EDANA method WSP 270.2.

Specifically, the base resin film was cut to a weight of 1.0 g, put in 200 g of 0.9 wt % NaCl solution, and soaked for 16 hours while stirring at 500 rpm, and then the aqueous solution was filtered with filter paper. The filtered solution was first titrated to pH 10.0 with 0.1 N caustic soda solution, and then back titrated to pH 2.7 with 0.1 N hydrogen chloride solution. measured.

(3) Absorption rate (Vortex time)

Absorption rates (vortex time) of the base resins of Examples and Comparative Examples were measured in the following manner.

① First, 50 mL of 0.9% saline was added to a 100 mL beaker with a flat bottom using a 100 mL Mass Cylinder.

② Next, after placing the beaker in the center of the magnetic stirrer, a magnetic bar (diameter 8 mm, length 30 mm) was placed in the beaker.

③ Then, the stirrer was operated so that the magnetic bar was stirred at 600 rpm, and the lowest part of the vortex generated by the stirring was brought into contact with the top of the magnetic bar.

④ After confirming that the temperature of the brine in the beaker has reached 24.0 ° C, 2 ± 0.01 g of the superabsorbent polymer composition sample is injected, the stop watch is operated at the same time, and the time until the vortex disappears and the liquid surface becomes perfectly level It was measured in seconds, and this was taken as the absorption rate.

(4) Tap water absorption capacity for 1 minute

1.0 g (W'3) of the base resin of Examples and Comparative Examples was placed in a nonwoven fabric bag (18 cm × 28 cm) and immersed in 1000 mL of tap water at 24 ° C. for 1 minute. After 1 minute, the bag was taken out of the distilled water and left hanging for 1 minute. Then, the mass (W'5) of the bag was measured. In addition, after performing the same operation without using the superabsorbent polymer, the mass (W'4) at that time was measured. Using each mass obtained in this way, the tap water absorption capacity (g/g) for 1 minute was calculated according to Equation 2 below.

[Equation 2]

Tap water absorption capacity for 1 minute = {[W'5(g) - W'4(g) - W'3(g)]/W'3(g)}

division base resin CRC (g/g) Ingredients for water use
(%) Vortex
(sec) 1 minute tap water absorption capacity
(g/g) Example 1 46.5 8.2 31 142 Example 2 46.1 8.1 30 150 Example 3 45.4 8.0 29 158 Comparative Example 1 50.1 7.5 60 80 Comparative Example 2 46.5 9.5 35 130 Comparative Example 3 46.2 9.3 35 132 Comparative Example 4 45.3 9.2 32 135 Comparative Example 5 45.0 9.1 33 136

As can be seen from the data in Table 2, the examples according to the manufacturing method of the present invention use a specific foaming agent in combination with a modified polyvinyl alcohol-based compound containing a sulfonyl group in the formation step of the water-containing gel polymer, thereby performing the foaming process. By reducing the water-soluble components generated from the water-soluble components, it is possible to implement excellent absorbent properties, and in particular, it was confirmed that the absorption rate of the finally prepared superabsorbent polymer was remarkably improved.

In the case of Comparative Examples 3 to 5, in the case of using a modified polyvinyl alcohol-based compound containing a carboxyl group, the CRC of the base resin shows a degree similar to that of Examples, but the content of water-soluble components is higher than that of Examples, and the absorption rate , It was confirmed that the tap water absorption capacity for 1 minute was lowered compared to the examples.

Claims (10)

forming a water-containing gel polymer having an acidic group by polymerizing a monomer mixture including an acrylic acid-based monomer having at least a partially neutralized acidic group, a foaming agent, and a polyvinyl alcohol-based compound including a sulfonyl group (step 1); and
Drying, pulverizing, and classifying the water-containing gel polymer to prepare base resin particles (step 2);
The foaming agent is at least one selected from the group consisting of carbonate-based foaming agents and encapsulated foaming agents,
A method for producing a superabsorbent polymer.
According to claim 1,
The carbonate-based foaming agent is at least one selected from the group consisting of sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate or magnesium carbonate,
A method for producing a superabsorbent polymer.
According to claim 1,
The encapsulated foaming agent has a core-shell structure including a core containing hydrocarbon and a shell made of a thermoplastic resin formed on the core,
The hydrocarbon is n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso-heptane, cycloheptane , at least one selected from the group consisting of n-octane, iso-octane and cyclooctane,
The thermoplastic resin is a polymer formed from at least one monomer selected from the group consisting of (meth) acrylate, (meth) acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide, and vinylidene halide,
A method for producing a superabsorbent polymer.
According to claim 1,
The foaming agent is included in 1,000 to 10,000 ppmw based on the weight of the acrylic acid-based monomer,
A method for producing a superabsorbent polymer.
According to claim 1,
The polyvinyl alcohol-based compound containing the sulfonyl group is included in 1,000 to 30,000 ppmw based on the weight of the acrylic acid-based monomer,
A method for producing a superabsorbent polymer.
According to claim 1,
The base resin particles have a centrifugal retention capacity (CRC) of 30 g / g to 48 g / g, measured according to the EDENA method WSP 241.2,
A method for producing a superabsorbent polymer.
According to claim 1,
In the base resin particles, the water-soluble component measured according to the EDANA method WSP 270.2 is 8 wt% to 9 wt%,
A method for producing a superabsorbent polymer.
According to claim 1,
When 1 g of the base resin particles is added to 1000 ml of tap water and left for 1 minute, the 1-minute tap water absorption capacity measured by the weight of tap water absorbed by the base resin is 140 g / g or more,
A method for producing a superabsorbent polymer.
According to claim 1,
The base resin particles have a vortex time of less than 35 seconds at 24.0 ° C according to the vortex method,
A method for producing a superabsorbent polymer.
According to claim 1,
Further comprising crosslinking a part of the surface of the base resin by heat-treating the base resin particles in the presence of a surface crosslinking agent,
A method for producing a superabsorbent polymer.