KR20220077680A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for producing a super absorbent polymer, and more specifically, to a neutralizing solution containing a specific compound by adding a water-soluble ethylenically unsaturated monomer to neutralization, and then cross-linking and polymerizing it to quickly absorb when applied to sanitary materials such as diapers. It relates to a method for producing a superabsorbent polymer, which exhibits a speed and at the same time has improved absorption performance and rewet properties.

Description

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

The present invention exhibits excellent liquid permeability and fast absorption rate when applied to sanitary materials such as diapers by adding a water-soluble ethylenically unsaturated monomer to a neutralizing solution containing a specific compound to neutralize it, and then cross-linking it. rewet) to a method for producing a superabsorbent polymer having improved properties.

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 began to be put to practical use as a sanitary tool, and now, in addition to hygiene products such as paper diapers for children, a soil repair agent for gardening, a water-retaining material for civil engineering and construction, a sheet for seedlings, a freshness maintenance agent in the food distribution field, and It is widely used as a material for poultice, etc.

In most cases, these superabsorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins. For this purpose, it is necessary to exhibit high absorption capacity for moisture, etc., and excellent pressure in which the absorbed moisture does not escape even under external pressure. It is necessary to show lower absorption performance, etc.

In addition, when the superabsorbent polymer is included in sanitary materials such as diapers, it is necessary to spread urine and the like as wide as possible even in an environment pressurized by the user's weight. Through this, the absorption performance and absorption rate of the sanitary material can be further improved by using the super absorbent polymer particles included in the entire area of the sanitary material absorbent layer as a whole. In addition, due to this diffusion under pressure property, the rewet property of the diaper, which suppresses the reappearance of urine, etc., once absorbed into the superabsorbent polymer can be further improved, and at the same time, the leak suppression property of the diaper can be improved. be able to do

In the past, by changing the design itself of a sanitary material such as a diaper, it was attempted to improve the characteristic of widely spreading the urine. For example, a method of improving the diffusion characteristics of urine or the like has been attempted by introducing an Acquisition Distribution Layer (ADL) or the like into a sanitary material or utilizing an absorption channel.

However, the improvement of diffusion characteristics due to the design change of the sanitary material itself was not sufficient. Furthermore, in recent years, as the sanitary material is thinned and the content of superabsorbent polymer in the sanitary material is relatively increased, the improvement of diffusion properties by changing the design of the sanitary material itself has been limited, and the pressure of the superabsorbent polymer itself is limited. There is a growing need to improve the lower diffusion properties.

Due to these technical requirements, the pressure liquid permeability directly related to the diffusion property under pressure is further improved, and the development of a superabsorbent polymer that can further improve the rewet properties and leakage control properties of sanitary materials such as diapers. The need is increasing.

Accordingly, the present invention exhibits excellent liquid permeability and fast absorption rate when applied to hygiene materials such as diapers by adding a water-soluble ethylenically unsaturated monomer to a neutralizing solution containing a specific compound to neutralize it, and then cross-linking it. It relates to a method for producing a superabsorbent polymer having improved rewet properties.

The present invention in order to solve the above problems,

preparing a monomer mixture including a water-soluble ethylenically unsaturated monomer in which a part of the acidic group is neutralized by adding a water-soluble ethylenically unsaturated monomer having an acidic group to a neutralizing solution containing a neutralizing agent, calcium hydroxide and a carbonate-based compound;

forming a hydrogel polymer comprising a crosslinked polymer crosslinked by adding an internal crosslinking agent to the monomer mixture;

drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and

It provides a method for producing a superabsorbent polymer, comprising the step of crosslinking the surface of the base resin powder by heat-treating the base resin powder in the presence of a surface crosslinking agent.

According to the method for producing the superabsorbent polymer of the present invention, uniform and fine foamed cells can be formed by adding a specific compound to a neutralized solution of a monomer and then performing a polymerization step. Accordingly, the final prepared resin exhibits a fast absorption rate and excellent liquid permeability, and at the same time significantly improves rewet properties.

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.

Terms such as first, second, third, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from other components.

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.

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 size 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. have.

In addition, the term "superabsorbent polymer powder" 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 part 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.

In the method for producing a superabsorbent polymer according to an embodiment of the present invention, a water-soluble ethylenically unsaturated monomer having an acidic group is added to a neutralizing solution containing a neutralizing agent, calcium hydroxide, and a carbonate-based compound, and water-soluble ethylene in which a part of the acidic group is neutralized. preparing a monomer mixture including a systemically unsaturated monomer; forming a hydrogel polymer comprising a crosslinked polymer crosslinked by adding an internal crosslinking agent to the monomer mixture; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and crosslinking the surface of the base resin powder by heat-treating the base resin powder in the presence of a surface crosslinking agent.

In recent years, not only the basic absorption properties of superabsorbent polymers, but also the retention time of the dryness of the surface and the rewet characteristic that suppresses the re-exposure of absorbed urine in situations in which sanitary materials such as diapers are actually used. It has become an important metric for judging the quality of a product.

Accordingly, the present inventors have found that when a monomer mixture containing a neutralized monomer is cross-linked and polymerized using a neutralizing solution for a specific compound, uniform and fine foamed cells are formed in the polymerization step to improve the absorption rate, liquid permeability, absorbency under pressure, etc. In addition to excellent absorption performance, it remains dry even after swelling by water or saline and can effectively suppress the phenomenon of urine oozing absorbed into the superabsorbent polymer (i.e., improved re-wetting properties). Confirmation led to the present invention.

Specifically, by using calcium hydroxide and a carbonate-based foaming agent in addition to the neutralizing agent in the neutralizing solution for neutralizing the water-soluble ethylenically unsaturated monomer having an acidic group, calcium hydroxide (Ca(OH) ₂ ) is converted into calcium carbonate (CaCO ₃ ), and the calcium carbonate It becomes possible to apply uniformly in the neutralizing liquid before this polymerization. Accordingly, the calcium carbonate used as the foaming nucleating agent in the polymerization step forms uniform and fine foamed cells in the polymer to increase the absorption rate, and at the same time, the calcium carbonate acts as a filler to provide liquid permeability and rewet properties. This can be effectively improved.

Hereinafter, the manufacturing method for each step will be described in detail.

The method for preparing a super absorbent polymer according to an embodiment of the present invention includes first preparing a neutralizing solution for neutralizing a portion of the acidic groups of a water-soluble ethylenically unsaturated monomer having an acidic group.

Specifically, a neutralizing solution including a neutralizing agent, calcium hydroxide, and a carbonate-based compound is prepared. Calcium hydroxide is converted into calcium carbonate (CaCO ₃ ) by the reaction in the neutralizing solution, and micro-foamed cells are formed in the polymer as a foaming nucleating agent in the polymerization step to be described later.

The calcium hydroxide forms calcium carbonate by reaction with the carbonate-based compound, which is a component of the foaming agent, and forms micro-foam cells in the polymer as a nucleating agent in the polymerization step. It makes it possible to effectively improve the rewet phenomenon at the same time.

The content of the calcium hydroxide is not particularly limited, but includes 500 ppmw to 3,000 ppmw, 750 ppmw to 2,500 ppmw, or 1,000 ppmw to 2,000 ppmw with respect to the water-soluble ethylenically unsaturated monomer. When included in the above range, it is preferable to achieve the above-described effect. On the other hand, when calcium hydroxide is included in less than 500 ppmw, it is difficult to achieve the desired effect in a small amount, and when it is included in excess of 3,000 ppmw, a problem that the absorbency under pressure is slightly lowered may occur.

The carbonate-based compound, as a foaming agent component, forms calcium carbonate by reaction with the above-described calcium hydroxide, thereby making it possible to form fine foamed cells in the polymer. Accordingly, it is possible to effectively improve the absorption rate, liquid permeability, and rewet characteristics of the superabsorbent polymer to be prepared at the same time.

The type of the carbonate-based compound is not particularly limited, but is sodium carbonate, sodium bicarbonate, or a combination thereof.

The content of the carbonate-based compound is not particularly limited, but includes 500 ppmw to 6,000 ppmw, 1,000 ppmw to 4,500 ppmw, or 1,500 ppmw to 3,000 ppmw with respect to the water-soluble ethylenically unsaturated monomer. When included in the above range, it is preferable to achieve the above-described effect. On the other hand, when the carbonate-based compound is included in less than 500 ppmw, it is difficult to achieve the desired effect in a trace amount, and when it is included in excess of 6,000 ppmw, the productivity is reduced due to an increase in the amount of fine powder generated due to excessive foaming, a decrease in the apparent specific gravity, etc. can occur

On the other hand, the calcium hydroxide and the carbonate-based compound are included in a weight ratio of 1:1 to 1:5 within the above-described content range, preferably 1:1 to 1:3 or 1:1 to 1:2 in a weight ratio of 1:2. Included. When used in a mixture in the above content range, it is possible to maximize the effect of improving the desired physical properties as a synergistic effect.

The neutralizing agent is a component used to neutralize some of the acidic groups of the water-soluble ethylenically unsaturated monomer having an acidic group, and a stronger basic compound than calcium hydroxide used together is used. If the neutralizing agent component is a compound stronger than calcium hydroxide, the type is not particularly limited, but, for example, sodium hydroxide, potassium hydroxide, or a mixture thereof is used.

The content of the neutralizing agent is not particularly limited, and the water-soluble ethylenically unsaturated monomer is used to neutralize 50 to 90 mol% of the acid group. The number of moles of the acidic group to be neutralized indicates the degree of neutralization of the monomer, and the degree of neutralization may be preferably 60 mol% to 80 mol% or 65 mol% to 75 mol%. If the degree of neutralization is too high, it may be difficult for the polymerization to proceed smoothly due to precipitation of neutralized monomers. Conversely, if the degree of neutralization is too low, not only the absorbency of the polymer is deteriorated, but it is also difficult to handle because it exhibits properties like elastic rubber.

Next, a water-soluble ethylenically unsaturated monomer having an acidic group is added to a neutralizing solution containing the above-described neutralizing agent, calcium hydroxide, and a carbonate-based compound to prepare a monomer mixture containing a water-soluble ethylenically unsaturated monomer in which a part of the acidic group is neutralized. includes steps.

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 1:

[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 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. As such, when acrylic acid or a salt thereof is used as the water-soluble ethylenically unsaturated monomer, it is advantageous because a superabsorbent polymer with improved water absorption can be obtained. 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-( anionic monomers of meth)acrylamide-2-methyl propane sulfonic acid and salts thereof; (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol ( a nonionic hydrophilic-containing monomer of meth)acrylate; and (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide containing 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 water-soluble ethylenically unsaturated monomer has an acidic group, and at least a part of the acidic group is partially neutralized using the above-described neutralizing solution of the present invention. As described above, the neutralization degree satisfies 50 mol% to 90 mol%, preferably 60 mol% to 80 mol%, or 65 mol% to 75 mol%.

(cross-linking polymerization step)

In the method for producing a superabsorbent polymer according to an embodiment of the present invention, an internal crosslinking agent is added to the above-described monomer mixture to form a hydrogel polymer including the crosslinked polymer crosslinked. Specifically, it is a step of thermally polymerizing or photopolymerizing a monomer composition including a monomer mixture and a polymerization initiator in the presence of an internal crosslinking agent to form a hydrogel polymer.

In the polymerization step, calcium carbonate uniformly present in the monomer mixture acts as a foaming nucleating agent in the polymerization step to form uniform and fine foamed cells, thereby improving the absorption rate, and also, as the calcium carbonate acts as a filler, liquid permeability is improved, and the rewet property is significantly improved.

As used herein, the term "monomer mixture" means to include a water-soluble ethylenically unsaturated monomer in which a part of an acidic group is neutralized by adding a water-soluble ethylenically unsaturated monomer to a neutralizing solution, calcium carbonate, and the like, and "monomer composition" denotes a composition including the monomer mixture and components such as an internal crosslinking agent and polymerization initiator necessary for crosslinking polymerization.

The "crosslinked polymer" means crosslinked polymerization in the presence of the water-soluble ethylenically unsaturated monomer and an internal crosslinking agent, and the "base resin powder" means a material containing such a crosslinked polymer.

The crosslinked polymer included in the base resin powder may be a polymer in which the monomer is crosslinked and polymerized in the presence of an internal crosslinking agent.

As used herein, the term "internal crosslinking agent" is a term used to distinguish it from "surface crosslinking agent" for crosslinking the surface of the base resin, and serves to polymerize by crosslinking the unsaturated bonds of the above-mentioned water-soluble ethylenically unsaturated monomers. . The crosslinking in the above step proceeds without a surface or an internal division, but by the surface crosslinking process of the base resin to be described later, the surface of the particles of the superabsorbent polymer finally produced has a structure crosslinked by a surface crosslinking agent, and the inside is the inside A crosslinked structure is formed by the crosslinking agent.

Non-limiting examples of the internal crosslinking agent include N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di( Meth) acrylate, polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, hexanediol di (meth) ) acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, penta A polyfunctional crosslinking agent such as erythol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, but is not limited thereto. Preferably, among them, ethylene glycol diglycidyl ether or polyethylene glycol diacrylate may be used.

The internal crosslinking agent may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent is 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight, or 0.45 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. part by weight or less, 1 part by weight or less, or 0.7 part by weight or less. When the content of the upper internal crosslinking agent is too low, crosslinking does not occur sufficiently and it may be difficult to implement a strength above an appropriate level.

In addition, the monomer composition may include a polymerization initiator generally used in the preparation of the super absorbent polymer. As a non-limiting example, as the polymerization initiator, a thermal polymerization initiator or a photo polymerization initiator may be used depending on the polymerization method. However, even by the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation, etc., 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 α-aminoketone may be used. 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 compounds selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, the persulfate-based initiator is sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (Potassium persulfate; K ₂ S ₂ O ₈ ), ammonium persulfate (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(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), 4, 4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are disclosed on page 203 of Odian's book "Principle of Polymerization (Wiley, 1981)", which can be referred to.

The polymerization initiator may be added at a concentration of 0.001 to 1 part by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, when 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 excessively high, the polymer chain constituting the network is shortened, so that the content of water-soluble components is increased, and the physical properties of the resin may be lowered, such as lowered absorbency under pressure, which is not preferable.

In addition, the monomer composition may further include additives such as a surfactant, a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

The surfactant induces uniform dispersion of the foaming agent and prevents the gel strength from being lowered or the density from being lowered due to uniform foaming during foaming. It is preferable to use an anionic surfactant as the surfactant. Specifically, the surfactant may include a SO ₃ ⁻ anion, and a compound represented by the following Chemical Formula 2 may be used.

[Formula 2]

R-SO ₃ Na

In Formula 2,

R is alkyl having 8 to 16 carbon atoms.

In addition, the surfactant is preferably used in an amount of 300 ppmw or less based on the weight of the water-soluble ethylenically unsaturated 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 aforementioned water-soluble ethylenically unsaturated monomer, polymerization initiator, and internal crosslinking agent are dissolved in a solvent.

In this case, the usable solvent may be used without limitation in its composition as long as it can dissolve the above-mentioned raw materials. 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 a mixture thereof, and the like may be used.

Formation of the hydrogel polymer through cross-linking 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, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the type of polymerization energy source. In the case of thermal polymerization, the polymerization may be performed in a reactor having a stirring shaft such as a kneader, and photopolymerization In the case of proceeding, it may be carried out in a reactor equipped with a movable conveyor belt.

For example, the hydrogel polymer may be obtained by introducing the monomer composition into a reactor such as a kneader equipped with a stirring shaft, and thermally polymerizing the monomer composition by supplying hot air or heating the reactor. At this time, depending on the shape of the stirring shaft provided in the reactor, the hydrogel polymer discharged to the reactor outlet may be obtained as particles of several millimeters to several centimeters. Specifically, the obtained hydrogel polymer can be obtained in various forms depending on the concentration and injection rate of the monomer composition to be injected. Usually, the hydrogel polymer having a (weight average) particle diameter of 2 to 50 mm can be obtained.

And, as another example, when photopolymerization of the monomer composition is performed in a reactor equipped with a movable conveyor belt, a sheet-form hydrogel polymer may be obtained. In this case, the thickness of the sheet may vary depending on the concentration of the injected monomer composition and the injection rate. In order to ensure the production rate while allowing the entire sheet to be uniformly polymerized, it is usually adjusted to a thickness of 0.5 to 10 cm. desirable.

Preferably, the crosslinking polymerization step of forming the hydrogel polymer may be performed at 40 °C to 80 °C, 40 °C to 60 °C, or 45 °C to 55 °C. When carried out within the above temperature range, foaming of the foaming nucleating agent contained in the monomer mixture is easy, and furthermore, it is suitable to form an appropriate cross-link to realize the desired absorption performance.

More preferably, photopolymerization may be performed by irradiating light on the polymerization belt of a continuous belt polymerization reactor having an ultraviolet irradiation device installed thereon in the above temperature range, and additionally, the thermal polymerization process may be further performed under conditions of no light source. .

A typical water content of the hydrogel polymer obtained in this way may be 40 wt% to 80 wt%. 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 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 180°C and then maintained at 180°C, and the moisture content is measured.

(Drying, pulverizing and classifying steps)

Next, drying, pulverizing and classifying the hydrogel polymer to form a base resin powder.

Specifically, a step of drying the obtained hydrogel polymer is performed. If necessary, in order to increase the efficiency of the drying step, a step of coarsely pulverizing the hydrogel polymer before drying may be further performed.

At this time, the crusher used is not limited in configuration, but specifically, a vertical pulverizer, a shredder type cutter, a turbo cutter, a turbo grinder, a rotary cutter mill), a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter selected from the group consisting of a grinding device. It may include any one, but is not limited to the above-described example.

In this case, in the coarse grinding step, the hydrogel polymer may have a particle diameter of 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 a phenomenon of agglomeration between the pulverized particles may occur. On the other hand, when the particle diameter is more than 10 mm, the effect of increasing the efficiency of the drying step performed later may be insignificant.

Drying is performed on the hydrogel polymer immediately after polymerization, either coarsely pulverized as described above, or without the coarse pulverization step.

Preferably, the drying step may be performed at 150 °C to 210 °C. Preferably, it is 170 °C to 200 °C, or 175 °C to 190 °C. If the drying temperature is less than 150 ℃, the drying time is excessively long and there is a risk that the physical properties of the superabsorbent polymer finally formed may decrease. Fine powder may be generated in the process, and there is a risk that the physical properties of the superabsorbent polymer finally formed may be deteriorated.

Meanwhile, the drying time may be performed for 20 to 90 minutes in consideration of process efficiency, but is not limited thereto.

If the drying method of the drying step is also commonly used in the drying process of the hydrogel polymer, 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. After the drying step, the moisture content of the polymer 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 powder obtained after the grinding step may have a particle diameter 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. A mill (jog mill) or the like may be used, but is not limited to the above-described example.

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

(Surface crosslinking step)

Next, the method for producing a superabsorbent polymer according to an embodiment of the present invention includes the step of surface crosslinking the base resin powder in the presence of surface crosslinking, thereby forming the superabsorbent polymer particles.

The surface crosslinking step induces a crosslinking reaction on the surface of the base resin powder in the presence of a surface crosslinking agent, and the unsaturated bonds of the water-soluble ethylenically unsaturated monomer remaining on the surface without crosslinking are crosslinked by the surface crosslinking agent. A superabsorbent polymer with increased crosslinking density is formed.

Specifically, in the presence of a surface cross-linking agent, a surface cross-linked layer may be formed through a heat treatment process, and the surface cross-linking density, that is, external cross-linking density, is increased during the heat treatment process, while the internal cross-linking density is not changed. The formed superabsorbent polymer has a structure having a higher crosslinking density on the outside than on the inside.

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

Meanwhile, as the surface crosslinking agent included in the surface crosslinking agent composition, any surface crosslinking agent that has been conventionally used in the manufacture of super absorbent polymers 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- 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 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 a cyclic urea compound; and the like. Preferably, the same as the above-described internal crosslinking agent may be used, 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 powder. 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, 0.3 parts by weight or less. By adjusting the content range of the surface crosslinking agent to the above-mentioned range, it is possible to prepare a superabsorbent polymer having excellent absorption performance and various physical properties such as liquid permeability.

The surface crosslinking composition may further include other additives commonly used in the art in terms of improving surface crosslinking efficiency.

For example, a polycarboxylic acid-based copolymer, a water-soluble polymer having a weight average molecular weight of 500 g/mol or more, a surfactant, and the like may be used. When the above component is included, the surface crosslinking efficiency can be improved, and due to the lubricating action, it can contribute to the improvement of the operability of the mixer during the surface crosslinking reaction.

As the water-soluble polymer having a weight average molecular weight of 500 g/mol or more, for example, polyethylene glycol having a corresponding weight average molecular weight may be used.

As the polycarboxylic acid-based copolymer, for example, a copolymer including a repeating unit represented by the following Chemical Formula 1-a and a repeating unit represented by the following Chemical Formula 1-a may be used:

[Formula 1-a]

[Formula 1-b]

In Formulas 1-a and 1-b,

R ¹ , R ² and R ³ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms,

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

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

X is -COO-, an alkyloxy group having 1 to 5 carbon atoms or an alkyldioxy group having 1 to 5 carbon atoms,

m is an integer from 1 to 100,

n is an integer from 1 to 1000,

p is an integer from 1 to 150, and when p is 2 or more, two or more repeated -RO- may be the same or different from each other.

As the polycarboxylic acid-based copolymer, an alkoxy polyalkylene glycol mono (meth) acrylic acid ester monomer (a typical example, methoxy polyethylene glycol monomethacrylate (MPEGMAA), etc.) and a (meth) acrylic acid ester monomer (a typical example, The use of random copolymers derived from hydrophilic monomers such as (meth)acrylic acid, etc.) may be more advantageous for the expression of the above-described effect. More preferably, the component (weight average molecular weight 40,000) prepared in Preparation Example 1 of Korean Patent Application Laid-Open No. 10-2015-0143167 may be used.

And, in order to better express the effect of adding the polycarboxylic acid-based copolymer, the polycarboxylic acid-based copolymer is measured according to a weight average molecular weight of 500 to 1,000,000 (gel permeation chromatography (GPC) method). ) is preferred.

The content of the additive may be appropriately adjusted according to reaction conditions, etc., and preferably may be adjusted to 0.001 to 5 parts by weight based on 100 parts by weight of the base resin powder. Included in the content range may be more advantageous for the expression of the above-described effect.

On the other hand, the surface crosslinking agent is added to the base resin powder in the form of a surface crosslinking agent composition containing the same, but there is no particular limitation on the composition of the method of adding the surface crosslinking agent composition. For example, a method of mixing the surface cross-linking agent composition and the base resin powder in a reactor, or spraying the surface cross-linking agent composition on the base resin powder, continuously supplying the base resin powder and the surface cross-linking agent composition to a continuously operated mixer and mixing method, 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 such, there is an advantage that the surface crosslinking agent and the like can be uniformly dispersed on the base resin powder. At this time, the content of water and hydrophilic organic solvent is added to 100 parts by weight of the base resin powder for the purpose of inducing even dissolution/dispersion of the surface crosslinking agent, preventing agglomeration of the base resin powder, and optimizing the surface penetration depth of the surface crosslinking agent. It can be applied by adjusting the addition ratio to the

The surface crosslinking step may be performed by heat treatment at a temperature of 160 °C to 220 °C, or 175 °C to 205 °C for 30 minutes or more. More specifically, in the surface crosslinking, the surface crosslinking reaction may be carried out by heat treatment for 30 to 80 minutes, or 40 to 70 minutes at the maximum reaction temperature using the above-described temperature as the maximum reaction temperature.

By satisfying the surface crosslinking process conditions (especially, the temperature rise condition and the reaction condition at the maximum reaction temperature), a superabsorbent polymer resin that adequately satisfies physical properties such as better pressurized liquid permeability can be manufactured.

A means for increasing the temperature for the surface 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 the present invention is not limited thereto. 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.

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

(super absorbent resin)

The superabsorbent polymer obtained according to the above-described manufacturing method exhibits a fast absorption rate due to the formation of uniform and fine foamed cells in the polymerization step, and at the same time has excellent liquid permeability and absorption performance and excellent rewet properties.

Meanwhile, the superabsorbent polymer according to an embodiment of the present invention may have a particle diameter of 150 to 850 μm. More specifically, at least 95% by weight of the base resin powder and the superabsorbent polymer including the same have a particle diameter of 150 to 850 μm, and may include 50% by weight or more of particles having a particle diameter of 300 to 600 μm, 150 The fines having a particle diameter of less than ㎛ may be less than 3% by weight.

Specifically, 1 g of the superabsorbent polymer is immersed in 25 g of brine to swell for 10 minutes, and then the swollen superabsorbent polymer is left on filter paper under a pressure of 0.7 psi for 2 minutes, and the filter paper is removed from the superabsorbent polymer. Pressurized brine rewet, defined as the weight of brine reclaimed from the furnace, is 1.3 g/g or less. Here, brine means 0.9 wt% sodium chloride (NaCl) aqueous solution. The lower the weight of the pressurized brine rewet, the better, so the lower limit of the pressurized brine rewet is 0 g in theory, for example, 0.5 g/g or more and 1.3 g/g or less, 0.5 g/g or more 1.2 g/ g or less, or 0.5 g/g or more and 1.1 g/g or less. The method for measuring the long-term re-wetting of the pressurized saline will be described in more detail in the Experimental Examples section to be described later.

The superabsorbent polymer has a vortex time of 30 seconds or less according to the vortex method. The absorption rate is excellent as the value is smaller, and the lower limit of the absorption rate is 0 seconds in theory, for example, 5 seconds or more and 30 seconds or less, or 10 seconds or more and 27 seconds or less. The absorption rate according to the vortex method refers to the time (time, unit: seconds) during which the liquid vortex disappears due to rapid absorption when the superabsorbent polymer is added to physiological saline and stirred. It can be seen that the superabsorbent polymer has a faster initial absorption rate. Here, physiological saline means 0.9 wt% sodium chloride (NaCl) aqueous solution. The method of measuring the absorption rate will be described in more detail in the experimental example section to be described later. Meanwhile, the absorption rate according to the vortex method may be measured by the same method for the base resin powder before surface crosslinking.

In addition, the superabsorbent polymer has a liquid permeability (unit: seconds) of 18 seconds or less as measured according to Equation 1 below. The lower the value, the better the liquid permeability, so the theoretical lower limit is 0 seconds, but for example, about 5 seconds or more and 18 seconds or less, or about 10 seconds or more and 17 seconds or less:

[Equation 1]

Permeability (sec) = T1 - B

In Equation 1 above,

For T1, put 0.2±0.0005 g of a classified (30# ~ 50#) sample of superabsorbent polymer in a chromatography tube, add brine to make the volume of brine 50 ml, and leave it for 30 minutes, and then increase the liquid level to 40 ml. The time taken to decrease to 20 ml, B is the time it takes for the liquid level to decrease from 40 ml to 20 ml in a chromatography tube filled with brine. Here, brine means 0.9 wt% sodium chloride (NaCl) aqueous solution. The method of measuring the liquid permeability will be described in more detail in the experimental example section to be described later.

In addition, the superabsorbent polymer has a centrifugation retention capacity (CRC) of 30 g/g or more, preferably 30 to 35 g/g, 31.0 to 32.0 g/g, 31.5 g/g, measured according to the EDENA method WSP 241.2. More than that. The method of measuring the centrifugation retention capacity will be described in more detail in the experimental example section to be described later. Meanwhile, the centrifugation retention capacity (CRC) measured according to the EDENA method WSP 241.2 may be measured by the same method for the base resin powder before surface crosslinking.

The absorbency under pressure (AUP) of 0.7 psi measured according to EDANA method WSP 242.3-10 is 20 g/g or more. Preferably it is 22.0 g/g or more, or 22 g/g to 29 g/g, 22.3 g/g to 28.5 g/g. A method of measuring the absorbency under pressure (AUP) of 0.7 psi will be described in more detail in the Experimental Examples section to be described later.

The superabsorbent polymer prepared according to the method for preparing the superabsorbent polymer according to the above-described exemplary embodiment exhibits excellent liquid permeability and a fast absorption rate while having excellent other physical properties, and thus, the rewet property is improved. Accordingly, excellent quality can be realized when applied to sanitary materials such as diapers and sanitary napkins.

Hereinafter, through specific examples of the invention, the operation and effect of the invention will be described in more detail. However, these embodiments are merely presented as an example of the invention, and the scope of the invention is not defined thereby.

[Example]

<Production of super absorbent polymer>

Example 1

A neutralization solution was prepared by mixing 38.9 g of sodium hydroxide (NaOH), 0.15 g of sodium bicarbonate, 0.15 g of calcium hydroxide, 103.9 g of water and 0.2 g of sodium persulfate.

After stirring the neutralization solution for 10 minutes, 100 g of acrylic acid monomer and 0.01 g of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide, which is a photopolymerization initiator, are added to the neutralization solution to partially neutralize the acrylic acid monomer. A mixture was prepared.

Next, 0.35 g of polyethylene glycol diacrylate, 0.05 g of 1,6-hexanediol diacrylate, and 0.02 g of trimethylolpropane triacrylate were added to the monomer mixture to prepare a monomer composition.

The monomer composition was flowed at a flow rate of 243 kg/hr on the polymerization belt of a continuous belt polymerization reactor having an ultraviolet irradiation device installed thereon. The reactor has an internal temperature of 45° C. and a light source having an intensity of 10 mW is irradiated with a mercury UV lamp light source. The light source was irradiated for 1.5 minutes, and the polymerization reaction was performed in the absence of a light source for an additional 2.5 minutes.

After the polymerization was completed, the gel-type polymerization sheet was first cut using a shredder type cutter and then coarsely crushed through a meat chopper. After drying through a hot air dryer at a temperature of 180 ° C. for 30 minutes, pulverized using a rotary mixer and classified into 150 μm to 850 μm to prepare a base resin powder.

Based on 100 parts by weight of the base resin powder, 4 parts by weight of water, 1 part by weight of ethylene carbonate, a polycarboxylic acid copolymer (a copolymer of methoxy polyethylene glycol monomethacrylate and methacrylic acid, a weight average molecular weight of 40,000) 0.1 The surface crosslinking solution containing parts by weight was continuously added to the high-speed mixing mixer (operating speed 80Kg/hr).

The resin uniformly mixed with the surface crosslinking solution was subjected to a surface treatment reaction at 185° C. for 1 hour in a paddle-type mixer to obtain a superabsorbent polymer.

Examples 2 to 7 and Comparative Examples 1 to 5

A super absorbent polymer was prepared in the same manner as in Example 1, except that the components and contents of Table 1 were used and the drying temperature of the hydrogel polymer was adjusted as follows.

division
(unit ppmw)* Neutralizing liquid composition other ingredients Drying temperature (℃) carbonate-based compounds calcium hydroxide Example 1 A1/1500 1500 - 180 Example 2 A1/3000 1500 - 183 Example 3 A1/6000 1500 - 185 Example 4 A1/1500 1000 - 179 Example 5 A1/3000 3000 - 188 Example 6 A2/1500 1000 - 179 Example 7 A2/3000 3000 - 186 Comparative Example 1 - - 175 Comparative Example 2 A1/1500 - - 178 Comparative Example 3 - - A3/1500 176 Comparative Example 4 A1/1500 - A4/1500 178 Comparative Example 5 A1/1500 - - 181 * Based on water-soluble ethylenically unsaturated monomer
A1: Sodium Bicarbonate
A2: sodium carbonate
A3: Calcium carbonate (added to the monomer composition)
A4: Calcium hydroxide (added to the surface crosslinking step)

<Experimental example>

The superabsorbent polymer compositions prepared in Examples and Comparative Examples were evaluated for physical properties in the following manner, and the results are shown in Table 2.

Unless otherwise indicated, all of the following physical property evaluations were performed at room temperature (23±1° C.) and relative humidity (50±10%), and physiological saline or saline means 0.9 wt% sodium chloride (NaCl) aqueous solution.

(1) Centrifuge Retention Capacity (CRC)

By taking a superabsorbent polymer (or base resin) having a particle diameter of 150 to 850 μm, centrifugal water retention capacity ( CRC) was measured.

Specifically, from the resins obtained through Examples and Comparative Examples, a resin classified through a sieve of #30-50 was obtained. This resin W ₀ (g) (about 0.2 g) was uniformly put in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt %) at room temperature. After 30 minutes, the bag was drained of water for 3 minutes under the conditions of 250G using a centrifuge, 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. Using each obtained mass, CRC (g/g) was calculated according to the following formula.

[Equation 2]

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

(2) Absorbency under Pressure (AUP: Absorbency under Pressure)

The absorbency under pressure of 0.7 psi of the superabsorbent polymer was measured according to the EDANA method WSP 242.3-10. When measuring the absorbency under pressure, the resin obtained after the surface crosslinking was used without classification.

Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylindrical cylinder having an inner diameter of 60 mm. Under the condition of room temperature and humidity of 50%, the water absorbent resin W ₀ (g) (0.90 g) is uniformly spread on the wire mesh, and the piston that can further apply a load of 0.7 psi on it is slightly smaller than the outer diameter of 60 mm There is no gap between 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 150 mm diameter Petro dish, and physiological saline composed of 0.9 wt% sodium chloride was placed 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.

Using each obtained mass, absorbency under pressure (g/g) was calculated according to the following formula, and it is shown in Table 1.

[Equation 3]

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

(3) Permeability

The permeability measurement method was measured according to the method described in Patent No. US9656242 B2. In the measurement of liquid permeability, the resin obtained after surface crosslinking was used without classification.

The liquid permeability measuring device is a chromatography tube with an inner diameter of 20 mm and a glass filter installed at the bottom. Lines were marked on the liquid levels of 20 ml and 40 ml in a state in which a piston was placed in the chromatography tube. Thereafter, water was added in reverse to prevent bubbles from forming between the glass filter and the cock at the bottom of the chromatography tube to fill about 10 ml, washed 2-3 times with brine, and filled with 0.9% brine to 40 ml or more. Put the piston into the chromatography tube, open the lower valve, and record the time (B) for the liquid level to decrease from 40ml to 20ml.

Leaving 10 ml of brine in the chromatography tube, 0.2±0.0005 g of each resin sample was added, brine was added to make the volume of brine 50 ml, and then left for 30 minutes. After that, put an additional piston (0.3 psi = 106.26 g) in the chromatography tube, leave it for 1 minute, open the lower valve of the chromatography tube, and record the time (T1) for the liquid level to decrease from 40 ml to 20 ml, the formula Table 1 shows the liquid permeability values calculated for the time (unit: seconds) of T1 - B of 1.

[Equation 1]

Permeability (sec) = T1 - B

(4) Absorption rate (Vortex time)

The absorption rate (vortex time) was measured in seconds according to the method described in International Publication No. 1987-003208. In the measurement of the absorption rate, the resin obtained after the surface crosslinking was used without classification.

Specifically, 2 g of each resin is added to 50 mL of physiological saline at 23°C, and the magnetic bar (diameter 8 mm, length 30 mm) is stirred at 600 rpm to determine the time until the vortex disappears in seconds. It was calculated by measuring.

(5) Pressurized brine rewet

In the measurement of pressurized brine rewet, the resin obtained after surface crosslinking was used without classification.

A plastic cylinder of the same size used for measuring Absorbency under Pressure (AUP) of WSP 242.3-10 of the EDANA method was used.

1.0 g (weight W ₀ (g)) of the superabsorbent polymer was evenly sprinkled on the cylinder, and 25 g of brine was poured thereto, followed by swelling. After swelling the superabsorbent polymer for 10 minutes, on 20 sheets of filter paper with a diameter of 11 cm (manufacturer whatman, catalog No. 1004-110, pore size 20-25 μm, diameter 11 cm) (weight W ₅ (g)) The swollen AUP measuring cylinder was placed and pressurized at 0.7 psi for 2 minutes. After pressurizing for 2 minutes, the filter paper (weight W ₆ (g)) in which the brine was absorbed was measured.

Using each obtained weight, pressurized brine rewet (g/g) was calculated according to the following formula, and it is shown in Table 1.

[Equation 4]

Rewet(g/g) = [W ₆ (g) - W ₅ (g)]/W ₀ (g)

division base resin
(before surface crosslinking) super absorbent resin CRC
(g/g) Votex time
(sec) CRC
(g/g) 0.7psi
AUP
(g/g) Votex time
(sec) Rewet
(g/g) Permeability
(g) Example 1 37 28 31.5 22.6 26 1.1 17 Example 2 37 24 31.5 22.6 23 1.1 17 Example 3 37 22 31.5 22.4 20 0.9 17 Example 4 37 30 31.5 23.7 28 1.1 18 Example 5 37 19 31.5 22.2 17 0.8 14 Example 6 37 31 31.5 24.0 29 1.1 18 Example 7 37 21 31.5 22.4 19 0.9 13 Comparative Example 1 37 41 31.5 22.7 39 1.5 27 Comparative Example 2 37 34 31.5 22.8 32 1.5 28 Comparative Example 3 37 39 31.5 21.4 36 1.4 18 Comparative Example 4 37 34 31.5 19.6 32 1.8 18 Comparative Example 5 39 34 32.7 21.3 31 1.6 31

Referring to the data contents of Table 2, the super absorbent polymer of Examples prepared according to the present invention shows a fast absorption rate by adding a carbonate-based compound and calcium hydroxide to a neutralizing solution, and then performing a polymerization process of the monomer, and at the same time has excellent stability. In terms of liquid and absorption performance, it was confirmed that the rewet property was excellent.

In the case of Comparative Examples in which some components of the carbonate-based compound and calcium hydroxide were not used in the neutralizing solution, it was confirmed that the absorption rate was slow compared to the Example and the rewet property was lowered.

In addition, as in Comparative Example 3, when calcium carbonate was directly used in the polymerization step, it was difficult to form uniform foamed cells, and thus, it was confirmed that the desired degree of absorption rate and rewet characteristics could not be realized.

In addition, in the case of Comparative Example 4 in which the component of calcium hydroxide was included in the surface crosslinking step, it was difficult to form the desired foamed cells, and accordingly, it was confirmed that the overall physical properties of these resins were significantly lowered compared to the Example.

Claims (12)

preparing a monomer mixture including a water-soluble ethylenically unsaturated monomer in which a part of the acidic group is neutralized by adding a water-soluble ethylenically unsaturated monomer having an acidic group to a neutralizing solution containing a neutralizing agent, calcium hydroxide, and a carbonate-based compound;
forming a hydrogel polymer including a crosslinked polymer crosslinked by adding an internal crosslinking agent to the monomer mixture;
drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and
In the presence of a surface crosslinking agent, heat-treating the base resin powder to crosslink the surface of the base resin powder, a method for producing a superabsorbent polymer.
According to claim 1,
The carbonate-based compound is sodium carbonate, sodium bicarbonate or a combination thereof,
A method for producing a super absorbent polymer.
According to claim 1,
The neutralizing agent is sodium hydroxide, potassium hydroxide, or a combination thereof,
A method for producing a super absorbent polymer.
According to claim 1,
The calcium hydroxide is included in an amount of 500 ppmw to 3,000 ppmw with respect to the water-soluble ethylenically unsaturated monomer,
A method for producing a super absorbent polymer.
According to claim 1,
The carbonate-based compound is included in an amount of 500 ppmw to 6,000 ppmw with respect to the water-soluble ethylenically unsaturated monomer,
A method for producing a super absorbent polymer.
The method of claim 1,
The calcium hydroxide and carbonate-based compound is included in a weight ratio of 1:1 to 1:5,
A method for producing a super absorbent polymer.
The method of claim 1,
The water-soluble ethylenically unsaturated monomer is 50 mol% to 90 mol% of the acid group is neutralized,
A method for producing a super absorbent polymer.
According to claim 1,
The crosslinking polymerization step of forming the hydrogel polymer is carried out at 40 °C to 80 °C,
A method for producing a super absorbent polymer.
According to claim 1,
The drying step of the hydrogel polymer is carried out at 150 ° C. to 210 ° C.,
A method for producing a super absorbent polymer.
According to claim 1,
After 1 g of the superabsorbent polymer was immersed in 25 g of brine to swell for 10 minutes, the swollen superabsorbent polymer was left on a filter paper under a pressure of 0.7 psi for 2 minutes, and cut again from the superabsorbent polymer into the filter paper. a pressurized brine rewet of 1.3 g/g or less, defined as the weight of the exiting brine;
A method for producing a super absorbent polymer.
According to claim 1,
The superabsorbent polymer has an absorption rate of 30 seconds or less according to the vortex method,
A method for producing a super absorbent polymer.
The method of claim 1,
The superabsorbent polymer has a liquid permeability of 18 seconds or less measured according to Equation 1 below,
Method for preparing super absorbent polymer:
[Equation 1]
Permeability (sec) = T1 - B
In Equation 1 above,
For T1, put 0.2±0.0005 g of the classified (30# ~ 50#) superabsorbent polymer sample in the chromatography tube, add brine to make the brine volume 50 ml, and leave it for 30 minutes, and then increase the liquid level to 40 ml. It is the time it takes to reduce to 20 ml,
B is the time it takes for the liquid level to decrease from 40 ml to 20 ml in a chromatography tube filled with brine.