KR20220067392A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for preparing a super absorbent resin, and more specifically, relates to a method for preparing a super absorbent resin having a high water holding capacity and fine powder cohesive strength without reduction of a pressure absorption capacity. The method for preparing a super absorbent resin includes a step of forming a first hydrous gel polymer; a step of pulverizing and drying the first hydrous gel polymer to be classified into fine powder and a first base resin; a step of preparing a reassembled member; a step of forming a second hydrous gel polymer; a step of the reassembled member with the hydrous gel polymer; a step of forming a second base resin; and a step of forming a surface crosslinking layer.

Description

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

The present invention relates to a method for producing a super absorbent polymer. More particularly, it relates to a method for producing a superabsorbent polymer having high water holding capacity and fine powder cohesive strength without deterioration of absorbency under pressure.

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.

As a method for preparing the superabsorbent polymer as described above, a method by reverse-phase suspension polymerization or a method by aqueous solution polymerization, etc. are known. Reversed-phase suspension polymerization is disclosed, for example, in Japanese Patent Application Laid-Open Nos. 56-161408, Japanese Patent Application Laid-Open No. 57-158209, and Japanese Patent Application Laid-Open No. 57-198714. As the method by aqueous solution polymerization, a thermal polymerization method in which the polymerization gel is broken and cooled in a kneader equipped with several axes, and a photopolymerization method in which a high-concentration aqueous solution is irradiated with ultraviolet rays or the like on a belt to perform polymerization and drying simultaneously etc. are known. During the polymerization reaction as described above, various internal crosslinking agents are introduced to form an internal network structure of the super absorbent polymer and to retain moisture even under pressure.

The hydrogel polymer obtained through the polymerization reaction as described above is generally marketed as a powdered product after being pulverized through a drying process.

At this time, fines having a particle size of less than about 150 μm may be generated during the steps of cutting, grinding and pulverizing the dried polymer. It is considered undesirable in hygiene articles, including baby diapers and adult incontinence appliances, because superabsorbent polymer particles prepared including the fine powder may exhibit reduced physical properties or migrated prior to use when applied to products.

Therefore, the final resin product is excluded from being included in the fine powder or undergoes a re-assembly process in which the fine particles are aggregated to a normal particle size. Rather, there is a problem in that the physical properties are deteriorated and the superabsorbent polymer including the same is also deteriorated in physical properties.

Accordingly, it is an object of the present invention to provide a method for manufacturing a high-quality superabsorbent polymer having high water holding capacity and fine cohesive strength without deterioration of absorbency under pressure while securing process economics by including the fine powder reassembly.

In order to achieve the above object, the present invention,

forming a first hydrogel polymer by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of an internal cross-linking agent;

classifying the first hydrogel polymer into fine powder having a particle diameter of less than 150 μm and a first base resin having a particle diameter of 150 μm to 850 μm by coarsely pulverizing, drying and pulverizing the first hydrogel polymer;

mixing the fine powder with water and re-assembling to prepare a fine powder re-assembly;

forming a second hydrogel polymer by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of an internal cross-linking agent;

coarsely pulverizing the fine powder re-assembly by mixing with the second hydrogel polymer;

drying and pulverizing a mixture of the coarsely pulverized second hydrogel polymer and the fine powder re-assembly to form a second base resin; and

Further crosslinking the surface of the second base resin in the presence of a surface crosslinking agent to form a surface crosslinking layer,

The internal crosslinking agent, a method for producing a super absorbent polymer, including a compound represented by the following formula (1) and polyethylene glycol diacrylate (PEGDA) is provided:

[Formula 1]

In Formula 1, R ¹ is a divalent organic group derived from an alkane having 1 to 10 carbon atoms, and R ² is hydrogen or a methyl group.

According to the manufacturing method according to an embodiment of the present invention, the advantage of using a thermally decomposable internal crosslinking agent in the manufacturing method of the superabsorbent polymer including the fine powder reassembly cycle process is maintained, and in particular, the decrease in absorbency under pressure is improved. Thus, it is possible to obtain a super absorbent polymer with high water holding capacity, absorbency under pressure and fine powder cohesive strength.

Accordingly, by using the above manufacturing method, the problems of the existing super absorbent polymer and the technical needs of the art are fundamentally solved, and the process economical including the fine powder reassembly can be secured, while exhibiting superior overall physical properties. Various hygiene products can be provided.

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.

In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

In addition, the terminology used herein is used only to describe exemplary embodiments, 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", "comprises" or "have" are used to describe embodied features, numbers, steps, components, or combinations thereof, and include one or more other features, numbers, or steps. , components, combinations or additions thereof are not excluded.

Also in this specification, when it is said that each layer or element is formed "on" or "over" each layer or element, it means that each layer or element is formed directly on each layer or element, or other It means that a layer or element may additionally be formed between each layer, on the object, on the substrate.

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

According to an embodiment of the present invention, a method comprising: cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of an internal cross-linking agent to form a first hydrogel polymer; classifying the first hydrogel polymer into fine powder having a particle diameter of less than 150 μm and a first base resin having a particle diameter of 150 μm to 850 μm by coarsely pulverizing, drying and pulverizing the first hydrogel polymer; mixing the fine powder with water and re-assembling to prepare a fine powder re-assembly; forming a second hydrogel polymer by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of an internal cross-linking agent; coarsely pulverizing the fine powder re-assembly by mixing with the second hydrogel polymer; drying and pulverizing a mixture of the coarsely pulverized second hydrogel polymer and the fine powder re-assembly to form a second base resin; and forming a surface cross-linking layer by further cross-linking the surface of the second base resin in the presence of a surface cross-linking agent, wherein the internal cross-linking agent comprises a compound represented by the following Chemical Formula 1 and polyethylene glycol diacrylate (PEGDA). A method for producing a super absorbent polymer is provided.

[Formula 1]

In Formula 1, R ¹ is a divalent organic group derived from an alkane having 1 to 10 carbon atoms, and R ² is hydrogen or a methyl group.

The compound represented by Formula 1 may be decomposed by heat as a thermally decomposable internal crosslinking agent. Accordingly, when a water-soluble ethylenically unsaturated monomer is crosslinked and polymerized in the presence of the compound of Formula 1, and then introduced into a high temperature subsequent process, at least a part of the crosslinked structure derived from the compound of Formula 1 in the crosslinked polymer is decomposed. Accordingly, the internal crosslink density in the crosslinked polymer is reduced. On the other hand, the cross-linked polymer surface is further cross-linked by the surface cross-linking agent to increase the external cross-linking density. Therefore, when cross-linking polymerization is carried out using the compound represented by Formula 1 and a subsequent process is performed, the internal cross-linked structure in the cross-linked polymer is decomposed, and the surface of the cross-linked polymer is further cross-linked to increase the cross-linking density from the inside to the outside of the resin. An increasing superabsorbent polymer can be obtained.

The superabsorbent polymer thus prepared may have a reduced internal crosslinking density than the base resin that does not include the compound of Formula 1 as an internal crosslinking agent. Accordingly, the superabsorbent polymer may exhibit relatively improved water holding capacity compared to the existing superabsorbent polymer. In addition, the superabsorbent polymer may have a thicker surface crosslinking layer than that of the existing superabsorbent polymer because the surface crosslinking proceeds after or while the internal crosslinking is decomposed. Accordingly, the superabsorbent polymer may exhibit excellent absorbency under pressure.

On the other hand, in various steps such as the polymerization process, the drying process, or the grinding step of the dried polymer in the general manufacturing process of the superabsorbent polymer, fines (fine powder) particles having a particle size of less than about 150 μm may be generated. However, when fine powder is included in the final product, it is difficult to handle and degrades physical properties such as gel blocking, so it is excluded from being included in the final resin product or undergoes a reassembly process to reuse it to become normal particles.

However, when the superabsorbent polymer is manufactured using only the thermally decomposable internal crosslinking agent represented by Formula 1 as the internal crosslinking agent, a significant portion of the crosslinked structure derived from the compound of Formula 1 at high temperature is is decomposed Accordingly, the crosslinking density is reduced, and in the case of fine powder having a small particle size, the degree of decrease in the internal crosslinking density is relatively larger. In particular, the fine powder derived from the base resin before performing the surface crosslinking process does not have a surface crosslinking layer, so the crosslinking density is greatly reduced, and accordingly, the absorbency under pressure is lowered. Therefore, the fine powder re-assembly reassembled using such fine powder and the super absorbent polymer produced by mixing the fine powder re-assembly body also have a reduced absorbency under pressure.

The present invention is to solve the above problems, and while maintaining the advantages of using a thermally decomposable internal crosslinking agent in a method for producing a superabsorbent polymer including a fine powder reassembly cycle process, the decrease in absorbency under pressure is improved. It is possible to provide a super absorbent polymer with better physical properties.

According to one embodiment of the present invention, when a mixture of a thermally decomposable internal crosslinking agent represented by Formula 1 and a non-pyrolytically degradable polyethylene glycol diacrylate (PEGDA) is used as an internal crosslinking agent, and when the fine powder reassembly is introduced in the manufacturing process By mixing with the hydrogel polymer, it is possible to prepare a superabsorbent polymer with little decrease in absorbency under pressure while maintaining high water holding capacity.

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

polymerization step

In the step of forming the hydrogel polymer, a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups is crosslinked and polymerized in the presence of an internal crosslinking agent to form a first hydrogel polymer.

The water-soluble ethylenically unsaturated monomer is, (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, sorbic acid, vinylphosphonic acid, vinylsulfonic acid, allylsulfonic acid, 2-(meth)acryloylethane anionic monomers of sulfonic acid, 2-(meth)acryloyloxyethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof; (meth)acrylamide, N-substituted (meth)acrylamide, 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 may include

As used herein, the term 'water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized' includes a monomer having an acidic group in the water-soluble ethylenically unsaturated monomer, and at least a portion of the acidic group of the monomer having an acidic group is neutralized. means

In particular, at least a portion of the water-soluble ethylenically unsaturated monomer may be composed of a monomer (salt of the anionic monomer) in which an acidic group contained in the anionic monomer is neutralized.

More specifically, as the water-soluble ethylenically unsaturated monomer, acrylic acid or a salt thereof may be used, and in the case of using acrylic acid, at least a portion thereof may be neutralized. Due to the use of such a monomer, it is possible to prepare a super absorbent polymer having better physical properties. For example, when an alkali metal salt of acrylic acid is used as the water-soluble ethylenically unsaturated monomer, it may be used by neutralizing the acrylic acid with a neutralizing agent such as caustic soda (NaOH). In this case, the degree of neutralization of the acrylic acid may be adjusted to about 50 to 95 mol% or about 60 to 85 mol%, and within this range, it is possible to provide a superabsorbent polymer having excellent water retention capacity without fear of precipitation during neutralization.

In the monomer mixture including the water-soluble ethylenically unsaturated monomer, the concentration of the water-soluble ethylenically unsaturated monomer is about 20 to about 60% by weight with respect to the total monomer mixture including each raw material, polymerization initiator and solvent to be described later, or It may be about 25 to about 50% by weight, and may be an appropriate concentration in consideration of polymerization time and reaction conditions. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be lowered and there may be problems in economic feasibility. Process problems may occur, and the physical properties of the superabsorbent polymer may be deteriorated.

According to one embodiment of the present invention, as the internal crosslinking agent, an internal crosslinking structure that can be decomposed by heat is introduced into the crosslinked polymer of a water-soluble ethylenically unsaturated monomer, and at the same time, in order to prevent excessive decrease in absorbency under pressure in the fine powder reassembly. The compound represented by the following formula (1) and polyethylene glycol diacrylate (PEGDA) are used together.

[Formula 1]

In Formula 1,

R ¹ is a divalent organic group derived from an alkane having 1 to 10 carbon atoms, and R ² is hydrogen or a methyl group.

In Formula 1, R ¹ is a divalent organic group derived from an alkane having 1 to 10 carbon atoms as defined above, and R ² is hydrogen or a methyl group. In this case, the alkane may be a straight-chain, branched-chain or cyclic alkane, and the divalent organic group derived from the alkane is a divalent organic group in which two hydrogens are removed from one carbon or one each from different carbons. It may be a divalent organic group from which hydrogen has been removed. Specifically, R ¹ is methane-1,1-diyl, ethane-1,2-diyl, ethane-1,1-diyl, propane-1,3-diyl, propane-1,2-diyl, propane-1 ,1-diyl, n-butane-1,4-diyl, n-butane-1,3-diyl, n-butane-1,2-diyl, n-butane-1,1-diyl, 2-methylpropane- 1,3-diyl, 2-methylpropane-1,2-diyl, 2-methylpropane-1,1-diyl, 2-methylbutane-1,4-diyl, 2-methylbutane-2,4-diyl, 2-methylbutane-3,4-diyl, 2-methylbutane-4,4-diyl, 2-methylbutane-1,3-diyl, 2-methylbutane-1,2-diyl, 2-methylbutane-1 ,1-diyl or 2-methylbutane-2,3-diyl.

Among them, R ¹ in Formula 1 is methane-1,1-diyl, propane-1,3-diyl, propane-1,2-diyl, propane-1,1-diyl, n-butane-1,4-diyl , n-butane-1,3-diyl, n-butane-1,2-diyl, n-butane-1,1-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2 -diyl, 2-methylpropane-1,1-diyl, 2-methylbutane-1,4-diyl, 2-methylbutane-2,4-diyl, 2-methylbutane-3,4-diyl, 2-methyl Butane-4,4-diyl, 2-methylbutane-1,3-diyl, 2-methylbutane-1,2-diyl, 2-methylbutane-1,1-diyl or 2-methylbutane-2,3- It can be a dil

Specifically, R ¹ in Formula 1 may be methane-1,1-diyl, propane-1,3-diyl, or propane-1,2-diyl. More specifically, R ¹ in Formula 1 may be propane-1,3-diyl or propane-1,2-diyl.

The compound in which R ¹ of Formula 1 is the above-listed divalent organic group can provide an internal cross-linked structure that can easily control the resolution by thermal energy, and contains by-products or water-soluble components that change the general physical properties of the superabsorbent polymer after decomposition. may not be created.

Polyethylene glycol diacrylate (PEGDA) is an internal crosslinking agent known in the art to which the present invention belongs, and unlike the thermally decomposable internal crosslinking agent represented by Formula 1, it does not have thermal decomposition. Therefore, it is possible to prevent the internal crosslinking density from being excessively reduced at a high temperature such as a drying step, so that the absorbency under pressure can be maintained.

According to an embodiment of the present invention, the compound represented by Formula 1 and polyethylene glycol diacrylate (PEGDA) as an internal crosslinking agent may be included in a weight ratio of 2:1 to 10:1, or 2:1 to 5:1. can When the compound represented by Formula 1 and polyethylene glycol diacrylate (PEGDA) are included in the same weight ratio as described above, both physical properties of water holding capacity and absorbency under pressure can be achieved at an excellent level.

The compound represented by Formula 1 may be used in an amount of 0.01 to 1 parts by weight, or 0.01 to 0.5 parts by weight, or 0.1 to 0.5 parts by weight, or 0.2 to 0.5 parts by weight, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. In this case, the content of the water-soluble ethylenically unsaturated monomer is based on the weight of the water-soluble ethylenically unsaturated monomer before the acidic group of the monomer having an acidic group included in the water-soluble ethylenically unsaturated monomer is neutralized. For example, when the water-soluble ethylenically unsaturated monomer includes acrylic acid, the content of the internal crosslinking agent may be adjusted based on the weight of the monomer before neutralizing the acrylic acid.

When the amount of the compound represented by Formula 1 is too small, the performance as a thermally decomposable crosslinking agent cannot be exhibited.

Accordingly, when the compound represented by Chemical Formula 1 is used within the above-described range, it is possible to provide a super absorbent polymer having improved water holding capacity and absorbency under pressure at the same time.

The polyethylene glycol diacrylate (PEGDA) may be used in an amount of 0.01 to 0.2 parts by weight, or 0.05 to 0.2 parts by weight, or 0.1 to 0.2 parts by weight, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. In this case, the content of the water-soluble ethylenically unsaturated monomer is based on the weight of the water-soluble ethylenically unsaturated monomer before the acidic group of the monomer having an acidic group included in the water-soluble ethylenically unsaturated monomer is neutralized. For example, when the water-soluble ethylenically unsaturated monomer includes acrylic acid, the content of the internal crosslinking agent may be adjusted based on the weight of the monomer before neutralizing the acrylic acid. When the polyethylene glycol diacrylate (PEGDA) is used within the above-described range, it is possible to provide a superabsorbent polymer having improved water holding capacity and absorbent under pressure at the same time.

In addition, the monomer mixture may further include a polymerization initiator generally used in the preparation of the super absorbent polymer.

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

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

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

The photopolymerization initiator may be included in a concentration of about 0.0001 to about 2.0 wt% based on the monomer mixture. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slowed, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may be non-uniform.

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

The thermal polymerization initiator may be included in a concentration of about 0.001 to about 2.0 wt% based on the monomer mixture. If the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs and the effect of the addition of the thermal polymerization initiator may be insignificant. have.

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

Raw materials such as the above-described water-soluble ethylenically unsaturated monomer, internal crosslinking agent, polymerization initiator, and additive may be prepared in a dissolved form in a solvent.

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

The solvent may be included in the remaining amount excluding the above-mentioned components with respect to the total content of the monomer mixture.

On the other hand, if the method for forming a hydrogel polymer by thermal polymerization, photopolymerization, or hybrid polymerization of such a monomer composition is also a commonly used polymerization method, there is no particular limitation on the configuration.

Specifically, the polymerization method can be largely divided into thermal polymerization and photopolymerization according to the polymerization energy source. In general, when thermal polymerization is carried out, it may be carried out in a reactor having a stirring shaft such as a kneader. In addition, in the case of thermal polymerization, the compound represented by Formula 1 may be conducted at a temperature of about 80° C. or higher and less than about 110° C. so that the compound is not decomposed by heat. A means for achieving the polymerization temperature in the above range is not particularly limited, and heating may be performed by supplying a heating medium to the reactor or directly supplying a heat source. As the type of heating medium that can be used, a fluid with increased temperature such as steam, hot air, or hot oil can be used, but it is not limited thereto. 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.

On the other hand, when the photopolymerization is carried out, it may be carried out in a reactor equipped with a movable conveyor belt, but the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.

For example, when thermal polymerization is performed by supplying a thermal medium to a reactor such as a kneader having a stirring shaft as described above or by heating the reactor, the hydrogel polymer discharged to the reactor outlet can be obtained. The hydrogel polymer thus obtained may have a size of several centimeters to several millimeters depending on the shape of the stirring shaft provided in the reactor. Specifically, the size of the resulting hydrogel polymer may vary depending on the concentration and injection rate of the injected monomer mixture.

In addition, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt, the form of the hydrogel polymer obtained may be a hydrogel polymer on a sheet having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration of the injected monomer mixture and the injection rate, but it is preferable to supply the monomer mixture so that a sheet-like polymer having a thickness of usually about 0.5 to about 10 cm can be obtained. When the monomer mixture is fed so that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is undesirable. it may not happen

The polymerization time of the monomer mixture is not particularly limited and may be adjusted to about 30 seconds to 60 minutes.

Typically, the water content of the first hydrogel polymer obtained in this way may be about 30 to about 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 a method of raising the temperature from room temperature to about 180° C. and then maintaining it at 180° C. The total drying time is set to 40 minutes including 5 minutes of the temperature rising step, and the moisture content is measured.

coarse grinding step

According to one embodiment of the invention, a coarse grinding process may be performed on the first hydrogel polymer obtained above.

At this time, the grinder used in the coarse grinding process is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill), a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter 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 first hydrogel polymer may have a particle diameter of about 2 to about 20 mm.

Coarse pulverization to a particle size of less than 2 mm is not technically easy due to the high water content of the first hydrogel polymer, and a phenomenon of aggregation between pulverized particles may occur. On the other hand, when the particle size is coarsely pulverized to more than 20 mm, the effect of increasing the efficiency of the drying step performed later may be insignificant.

Drying and grinding steps

In the method for producing a superabsorbent polymer according to an embodiment of the present invention, after the first hydrogel polymer is prepared, the first hydrogel polymer is dried and pulverized to obtain fine powder having a particle size of less than 150 μm, and 150 μm. It is classified with the first base resin having a normal particle diameter of from 850 μm.

The drying process is performed on the first hydrogel polymer after coarsely pulverizing or polymerization without a coarse pulverization step. In this case, the drying temperature of the drying step may be about 150 to about 250 ℃. When the drying temperature is less than 150°C, the drying time is excessively long and there is a risk that the physical properties of the superabsorbent polymer to be finally formed may decrease. In this case, a large amount of fine powder may be generated, and there is a possibility that the physical properties of the superabsorbent polymer finally formed may be deteriorated. Therefore, preferably, the drying may be carried out at a temperature of about 150 to about 200 °C, more preferably at a temperature of about 160 to about 180 °C.

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

If the drying method of the drying step is also commonly used as the drying process of the first 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 pulverization process is performed on the dried polymer obtained through such a drying step.

The polymer powder obtained after the grinding step may have a particle diameter of about 150 to about 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 the invention is not limited to the above-described examples.

In order to manage the physical properties of the super absorbent polymer powder to be finalized after the pulverization step, the polymer powder obtained after pulverization is generally classified according to particle size. Preferably, a step of classifying particles having a particle diameter of less than 150 μm and particles having a particle size of about 150 μm to about 850 μm or less is performed.

In the present specification, fine particles having a particle size of less than a certain particle size, that is, a particle size of less than about 150 μm, are referred to as super absorbent polymer fines, SAP fines or fines, and have a particle size of 150 μm to 850 μm or less. The particles are referred to as normal particles, or base resin. The fine powder may be generated during the polymerization process, the drying process, or the pulverization step of the dried polymer. When the fine powder is included in the final product, it is difficult to handle and degrades physical properties such as exhibiting a gel blocking phenomenon. It is preferable to exclude it so as not to be included or to reuse it so that it becomes a normal particle.

Differential reassembly step

A re-assembly process is performed to agglomerate the fine particles to a normal particle size. In general, in the reassembly process, in order to increase cohesive strength, a reassembly process is performed in which the fine particles are agglomerated in a wet state. At this time, the higher the moisture content of the fine powder, the higher the cohesive strength of the fine powder. After that, it is often crushed into fine powder again. In addition, the fine powder re-assembled body obtained in this way has lower physical properties such as water holding capacity (CRC) and absorbency under pressure (AUP) than normal particles, leading to a decrease in the quality of the superabsorbent polymer. In particular, when only a thermally decomposable crosslinking agent is used, an excessive decrease in internal crosslinking density results in a more severe decrease in physical properties compared to a case where a thermally decomposable crosslinking agent is used.

However, as already described above, in the manufacturing method of one embodiment of the present invention, a specific compound is mixed and used as an internal crosslinking agent, and when the fine powder reassembly is mixed with the hydrogel polymer when input in the manufacturing process, the deterioration of physical properties is small A fine powder re-assembly and superabsorbent resin can be obtained.

In the method of manufacturing a super absorbent polymer according to an embodiment of the present invention, a fine powder re-assembly is prepared using the fine powder classified in the above-described step.

More specifically, the steps of mixing fine powder having a particle diameter of less than about 150 μm with water and re-assembling it to prepare a fine powder re-assembly are performed. In this re-assembly process, the fine powder is mixed with water and re-assembled. In this case, water may be used in an amount of 100 parts by weight to 200 parts by weight based on 100 parts by weight of the fine powder. The manufacturing step of the fine powder re-assembly may be re-assembled by mixing the fine powder and water under stirring using a mixing device or mixer capable of adding a shear force.

According to another embodiment of the present invention, in the fine powder reassembly, the first base resin having a particle diameter of 150 µm to 850 µm is additionally cross-linked in the presence of a surface cross-linking agent to form a surface cross-linked layer. It can be prepared by further agglomerating the fine powder separated into particles having a particle diameter of less than 150 μm by reclassifying the obtained superabsorbent polymer. That is, the fine powder re-assembly is re-assembled by mixing fine powder without a surface cross-linking layer (this is referred to as "base resin fine powder") and water, or fine powder including a surface cross-linking layer (this is "product fine powder") ) and the fine powder of the base resin may be mixed with water and reassembled.

As a result of the reassembly process, the fine powder is aggregated to form a fine powder reassembly body. The fine powder re-assembly may have a particle diameter of greater than about 150 μm to about 50 mm, preferably from about 300 μm to about 30 mm. In addition, since the fine powder reassembly of the present invention has high water holding capacity and absorbency under pressure, excellent physical properties can be maintained even in subsequent drying, grinding, surface treatment, and the like steps.

Mixing step of pulverulent reassembly

The fine powder reassembled reassembled by the above process is cycled after the polymerization step of the hydrogel and before the coarse pulverization step, and is mixed with the second hydrogel polymer before the coarse pulverization.

The second hydrogel polymer is named to distinguishly refer to the first hydrogel polymer derived from fine powder and the polymer subsequently polymerized due to the time difference in the polymerization process in the continuous process.

Accordingly, according to one embodiment of the present invention, the second hydrogel polymer mixed with the fine powder re-assembly is prepared in the same process as the above-described first hydrogel polymer, i.e., a water-soluble ethylenically unsaturated monomer having at least partially neutralized acid groups inside It may be a polymer in a hydrogel state prepared by cross-linking polymerization in the presence of a cross-linking agent. In addition, the water-soluble ethylenically unsaturated monomer and the internal crosslinking agent having an acidic group at least partially neutralized may be the same as those used for crosslinking polymerization of the first hydrogel polymer.

On a commercial scale, the manufacturing process of the superabsorbent polymer is continuously performed, and as described above, the fine powder re-assembly is separately classified in the classification process after polymerization, coarse grinding, drying, grinding, and classification processes are performed during the continuous manufacturing process. It is obtained using the fine powder. Only the fine powder re-assembly thus obtained is separately dried, pulverized, and classified, mixed with the base resin of normal particles, and reused.

However, according to one embodiment of the present invention, the fine powder re-assembly is not mixed with the coarsely pulverized hydrogel polymer, but after polymerization and mixed with the hydrogel polymer before coarse grinding, and then coarsely pulverized together, followed by drying, pulverization, classification, A process such as surface crosslinking is performed. As such, by introducing the fine powder re-assembly during the coarse grinding process, the hydrogel polymer and the fine powder re-assembly are mixed evenly during the coarse grinding process, so that the cohesive strength of the hydrogel polymer and the fine powder re-assembly increases and a very uniform mixing effect can be obtained. have. On the other hand, when the dried base resin and the fine powder reassembly are mixed, a shaking process is required for uniform mixing, and when mixed during the surface crosslinking process, the cohesive strength of the base resin and the fine powder reassembly is inevitably low. In addition, in the case of mixing during the classification process, it is necessary to go through a drying process again afterwards, thereby complicating the process.

On the other hand, the hydrogel polymer to which the fine powder re-assembly is mixed may be a hydrogel polymer continuously manufactured in the same process as the process in which the fine powder reassembled into the fine powder re-assembly is generated, or a process different from the process in which the fine powder is generated. It may be a hydrogel polymer prepared in the process.

According to one embodiment of the present invention, the fine powder re-assembly may be mixed in an amount of 1 to 50 parts by weight based on 100 parts by weight of the second hydrogel polymer. More specifically, the fine powder reassembly is 1 part by weight or more, or 10 parts by weight or more, or 15 parts by weight or more, and 40 parts by weight or less, or 30 parts by weight or less, based on 100 parts by weight of the second hydrogel polymer; Or 25 parts by weight or less may be mixed.

If the mixing amount of the fine powder re-assembly is too small, process economics may deteriorate, and if the mixing amount is too large, the physical properties of the final superabsorbent polymer product may deteriorate.

The description of the step of coarsely pulverizing the fine powder reassembly after mixing the second hydrogel polymer with the second hydrogel polymer is the same as the description of the coarse pulverization process of the first hydrogel polymer.

Thereafter, the mixture of the coarsely pulverized second hydrogel polymer and the fine powder re-assembly is dried and pulverized to form a second base resin. The description of the drying and pulverizing step is also the same as that of the drying and pulverizing step of the first hydrogel polymer.

At this time, fine powder may be generated again by drying and pulverizing the mixture of the coarsely pulverized second hydrogel polymer and the fine powder re-assembly, and the fine powder generated in this way is reassembled in the same process as in the fine powder re-assembly process, and again after polymerization It can also be reused by mixing it with the hydrogel polymer before coarse grinding.

surface crosslinking

The second base resin, which is a normal particle having a particle diameter of about 150 μm to about 850 μm or less, is obtained by the above-described drying and pulverization steps.

As described above, as the particle size distribution of the second base resin is adjusted to a desirable range, the finally prepared super absorbent polymer may exhibit excellent absorbent properties. Therefore, in the classification step, a polymer having a particle diameter of about 150 to about 850 μm is classified, and only the base resin powder having such a particle diameter can be commercialized through a surface crosslinking reaction step.

Meanwhile, after forming the above-described second base resin, the surface of the second base resin may be further cross-linked in the presence of a surface cross-linking agent to form a surface cross-linking layer, thereby preparing a superabsorbent polymer.

As the surface crosslinking agent, any surface crosslinking agent that has been conventionally used in the manufacture of super absorbent polymers may be used without any particular limitation. More specific examples thereof include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl- 1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, at least one polyol selected from the group consisting of tripropylene glycol and glycerol ; 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.

Such a surface crosslinking agent may be used in an amount of about 0.01 to 3 parts by weight based on 100 parts by weight of the second base resin. By adjusting the content range of the surface crosslinking agent to the above-mentioned range, it is possible to provide a superabsorbent polymer having excellent absorbent properties.

And, in the surface crosslinking process, in addition to the surface crosslinking agent, at least one inorganic material selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate, etc. It can be added to carry out a surface crosslinking reaction. The inorganic material may be used in powder form or liquid form, and in particular, may be used as alumina powder, silica-alumina powder, titania powder, or nano silica solution. In addition, the inorganic material may be used in an amount of about 0.001 to about 2 parts by weight based on 100 parts by weight of the base resin powder.

In addition, in the surface crosslinking process, the surface crosslinking structure of the superabsorbent polymer may be further optimized by adding a polyvalent metal cation instead of or together with the inorganic material to perform surface crosslinking. This is expected because such a metal cation can further reduce the crosslinking distance by forming a chelate with the carboxyl group (COOH) of the superabsorbent polymer.

In addition, about the method of adding the said surface crosslinking agent to 2nd base resin, there is no limitation of the structure. For example, a method of mixing the surface crosslinking agent and the second base resin in a reaction tank, spraying the surface crosslinking agent on the second base resin, continuously supplying and mixing the second base resin and the surface crosslinking agent to a continuously operated mixer method and the like can be used.

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

The surface crosslinking reaction may be performed by heating the second base resin to which the surface crosslinking agent is added to a certain temperature or higher. In this surface crosslinking step, an internal crosslinking decomposition reaction may occur simultaneously with the surface crosslinking reaction. Accordingly, in the surface crosslinking step, at least a part of the crosslinked structure derived from the compound of Formula 1 in the second base resin may be thermally decomposed to lower the internal crosslinking density. And, due to the above reactions, a superabsorbent polymer having a crosslinking density gradient having an increased crosslinking density from the inside to the outside may be manufactured.

In particular, in order to prepare a superabsorbent polymer having both improved water holding capacity and absorbency under pressure, the surface crosslinking process condition may be performed at a temperature of about 110 to 200°C.

More specifically, the surface crosslinking process conditions may be a maximum reaction temperature of about 160 ° C. or higher, or about 180 to 200 ° C., a holding time at the maximum reaction temperature of about 20 minutes or more, or about 20 minutes or more and 2 hours or less. have. In addition, the temperature at the start of the initial reaction, for example, at a temperature of about 110 ° C. or higher, or about 160 to 170 ° C., the temperature increase time until the maximum reaction temperature is about 10 minutes or more, or about 10 minutes or more 1 It was confirmed that a superabsorbent polymer having excellent water holding capacity and absorbent under pressure can be prepared by satisfying the above-described surface crosslinking process conditions.

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.

The superabsorbent polymer obtained according to the above-described manufacturing method may exhibit very excellent properties improved in general physical properties such as water holding capacity and absorbency under pressure, and may exhibit excellent physical properties suitable for use in hygiene products such as diapers.

Specifically, the superabsorbent polymer obtained according to the above-described manufacturing method may have a centrifugation retention capacity (CRC) of 35 to 60 g/g for physiological saline, measured according to the EDANA method WSP 241.3.

More specifically, the superabsorbent polymer obtained according to the above-described manufacturing method has a centrifugal retention capacity (CRC) for physiological saline of 35 g/g or more, or 40 g/g or more, and 60 g/g or less, or 55 g/g or less, or 55 g/g or less.

In addition, the superabsorbent polymer obtained according to the above-described manufacturing method may have an absorbency under pressure (AUP) of 0.7 psi with respect to physiological saline measured according to EDANA method WSP 242.3 of 20 to 30 g/g.

More specifically, the superabsorbent polymer obtained according to the above-described manufacturing method may be 20 g/g or more, or 21 g/g or more, or 25 g/g or less, or 24 g/g or less.

For a more specific method of measuring CRC and AUP, reference may be made to the contents described in Test 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, this is presented as an example of the invention and the scope of the invention is not limited in any way by this.

<Example>

Preparation of super absorbent polymer

Example 1

In a glass reactor, 100 g of acrylic acid, 0.2 g of 4-methylpentane-1,4-diyl diacrylate as an internal crosslinking agent, and 0.1 g of polyethylene glycol diacrylate (PEGDA), Irgacure TPO (diphenyl (2,4,6- Trimethylbenzoyl)phosphine oxide) 0.008 g, and water 55 g were injected. Then, to the glass reactor, 123.5 g of a 45 wt% caustic soda solution was slowly added dropwise and mixed.

When the caustic soda solution was added dropwise, the temperature of the mixed solution was increased by the heat of neutralization, and the mixed solution was waited for cooling. When the temperature of the mixed solution was cooled to about 45° C., 0.2 g of sodium persulfate was added to the mixed solution to prepare a monomer mixture.

The monomer mixture was fed at a rate of 500 to 2000 mL/min on a conveyor belt in which a 10 cm wide and 2 m long belt rotated at a speed of 50 cm/min. And, at the same time as the supply of the monomer mixture, the polymerization reaction was carried out for 60 seconds by irradiating ultraviolet rays having an intensity of 10 mW/cm ² .

Then, the hydrogel polymer obtained through the polymerization reaction was passed through a hole having a diameter of 16 mm using a meat chopper to prepare a crumb. Then, using an oven capable of transferring the air volume up and down, hot air at 190° C. was flowed from the bottom to the top for 20 minutes, and then flowed from the top to the bottom for 20 minutes to dry the powder uniformly. . The dried powder was pulverized with a pulverizer and classified into a standard mesh sieve of ASTM standard to classify the first base resin having a size of 150 to 850 μm and fine powder less than 150 μm.

160 g of the fine powder and 160 g of water were mixed at 1000 rpm using a high-speed rotary stirrer to prepare a fine powder re-assembly having a particle size of 150 μm to 1500 μm.

320 g of the fine powder reassembly and 1,280 g of the hydrogel polymer were added together with a meat chopper, and passed through a hole having a diameter of 16 mm to prepare a crumb. Then, using an oven capable of transferring the air volume up and down, hot air at 190° C. was flowed from the bottom to the top for 20 minutes, and then flowed from the top to the bottom for 20 minutes to dry the powder uniformly. . The dried powder was pulverized with a pulverizer and classified into a standard mesh sieve of ASTM standard to classify the second base resin having a size of 150 to 850 μm and fine powder less than 150 μm.

A solution of 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate was added to 100 g of the second base resin prepared above, mixed for 1 minute, and then surface cross-linked at 198° C. for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (A) having a particle size of 150 to 850 µm.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (A') having a particle size of 150 to 850 µm.

Example 2

In Example 1, the superabsorbent polymer resin was used in the same manner as in Example 1, except that 0.3 g of 4-methylpentane-1,4-diyl diacrylate and 0.1 g of polyethylene glycol diacrylate (PEGDA) were used as internal crosslinking agents. (B) was prepared.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (B') having a particle size of 150 to 850 µm.

Example 3

In Example 1, in the same manner as in Example 1, except that 0.4 g of 4-methylpentane-1,4-diyl diacrylate and 0.1 g of polyethylene glycol diacrylate (PEGDA) were used as the internal crosslinking agent, the superabsorbent properties were performed in the same manner as in Example 1. Resin (C) was prepared.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (C') having a particle size of 150 to 850 µm.

Example 4

In Example 1, in the same manner as in Example 1, except that 0.4 g of 4-methylpentane-1,4-diyl diacrylate and 0.15 g of polyethylene glycol diacrylate (PEGDA) were used as internal crosslinking agents, the superabsorbent properties were performed in the same manner as in Example 1. Resin (D) was prepared.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (D') having a particle size of 150 to 850 µm.

Comparative Example 1

In a glass reactor, 100 g of acrylic acid, 0.2 g of 4-methylpentane-1,4-diyl diacrylate as an internal crosslinking agent, and 0.1 g of polyethylene glycol diacrylate (PEGDA), Irgacure TPO (diphenyl (2,4,6- Trimethylbenzoyl)phosphine oxide) 0.008 g, laponite 0.18 g and water 55 g were injected. Then, to the glass reactor, 123.5 g of a 45 wt% caustic soda solution was slowly added dropwise and mixed.

Thereafter, the superabsorbent polymer (E) was prepared in the same manner as in Example 1.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (E') having a particle size of 150 to 850 µm.

Comparative Example 2

In Example 1, a superabsorbent polymer (F) was prepared in the same manner as in Example 1, except that 0.3 g of polyethylene glycol diacrylate (PEGDA) alone was used as an internal crosslinking agent.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (F') having a particle size of 150 to 850 µm.

Comparative Example 3

In Example 1, a superabsorbent polymer (G) was prepared in the same manner as in Example 1, except that 0.2 g of only 4-methylpentane-1,4-diyl diacrylate was used as an internal crosslinking agent.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (G') having a particle size of 150 to 850 µm.

Comparative Example 4

In Example 1, a super absorbent polymer (H) was prepared in the same manner as in Example 1, except that 0.4 g of only 4-methylpentane-1,4-diyl diacrylate was used as an internal crosslinking agent.

Separately, for comparison of absorbency under pressure, a solution obtained by mixing 3.0 g of ultrapure water, 3.5 g of methanol, and 0.15 g of ethylene carbonate in 100 g of the first base resin without performing the process of preparing and mixing the fine powder reassembly was administered and mixed for 1 minute. The surface crosslinking reaction was carried out at 198°C for 60 minutes.

Then, the obtained product was pulverized and classified to obtain a super absorbent polymer (H') having a particle size of 150 to 850 µm.

<Experimental example>

Evaluation of physical properties of super absorbent polymers

The properties of the superabsorbent polymers prepared according to Examples and Comparative Examples were evaluated in the following manner, and are shown in Table 1 below.

(1) Centrifuge Retention Capacity (CRC)

The water holding capacity by the no-load absorption magnification of each resin was measured according to EDANA WSP 241.3.

Specifically, the superabsorbent polymer 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 mass W ₂ (g) of the envelope was measured using a centrifuge under the condition of 250 G. 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 1]

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

(2) Absorbtion Under Pressure (AUP)

The absorbency under pressure of 0.7 psi of each resin was measured according to the EDANA method WSP 242.3.

Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 60 mm. Under the conditions of room temperature and humidity of 50%, the super absorbent polymer W ₀ (g) (0.90 g) is uniformly sprayed on the wire mesh, and the piston that can apply a load of 0.7 psi more uniformly thereon is slightly more than 60 mm in outer diameter. It is small and there is no gap with the inner wall of the cylinder, and the vertical movement is not disturbed. At this time, the weight W ₃ (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed on the inside of 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 equation.

[Equation 2]

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

(3) Decrease in absorbency under pressure (%)

The decrease in absorbency under pressure (%) was measured by measuring the absorbency under pressure of 0.7 psi according to (2) for each superabsorbent polymer (A' to H') obtained without mixing the fine powder re-assembly, and mixing the fine powder re-assembly. For each of the obtained superabsorbent polymers (A to H), the absorbency under pressure of 0.7 psi was separately measured according to (2), and the degree of decrease in the absorbency under pressure was calculated according to the following formula.

[Equation 3]

Decrease in absorbency under pressure (%) = [{1- (absorbency under pressure of 0.7 psi with pulverized reassembled) / (absorbed under pressure of 0.7 psi without pulverized reassembled)}*100]

division Amount of thermal decomposition crosslinking agent
(parts by weight) PEGDA
usage
(parts by weight) Use of inorganic substances during polymerization CRC
(g/g) 0.7psi AUP (g/g) Pressure
absorbency
decrease(%) Example 1 0.2 0.1 X 43.7 22.3 11 Example 2 0.3 0.1 X 42.1 23.0 10 Example 3 0.4 0.1 X 40.1 23.7 10 Example 4 0.4 0.15 X 37.6 24.1 9 Comparative Example 1 0.2 0.1 O 41.4 21.3 16 Comparative Example 2 0 0.2 X 36.4 22.3 15 Comparative Example 3 0.2 0 X 41 14.9 25 Comparative Example 4 0.4 0 X 37.3 16.6 25

Referring to Table 1, in the case of Comparative Examples 3 and 4 using only the thermally decomposable internal crosslinking agent, it can be seen that the absorbency under pressure is rapidly reduced during the fine powder reassembly process. This is considered to be because the internal cross-linked structure easily collapsed due to the decomposition of the thermally decomposable internal cross-linking agent in the high-temperature process of the drying and surface cross-linking steps, and thus the minimum cross-linking density required to express absorbency under pressure was not maintained. In addition, in Comparative Example 2 using only a general PEGDA crosslinking agent without a thermally decomposable crosslinking agent, there was almost no decomposition of the internal crosslinked structure, and only the absorbency under pressure was reduced without an effect of increasing water holding capacity.

On the other hand, in the case of Examples 1 to 4, polymerization is carried out by mixing a certain amount of PEGDA without thermal decomposition property, and by using the fine powder re-assembly derived therefrom, the internal crosslinking density is maintained to show the effect of increasing water holding capacity and at the same time absorbency under pressure The degree of deterioration was small.

On the other hand, in the case of Comparative Example 1, in which polymerization was carried out by further including laponite during polymerization, the final superabsorbent polymer exhibited lower physical properties. This is presumed to be because, when inorganic fine particles such as laponite exist in the fine powder re-assembly, the cross-linked structure is weakened and the internal cross-linked structure is more likely to collapse in a high-temperature process.

Claims (9)

forming a first hydrogel polymer by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of an internal cross-linking agent;
classifying the first hydrogel polymer into fine powder having a particle diameter of less than 150 μm and a first base resin having a particle diameter of 150 μm to 850 μm by coarsely pulverizing, drying and pulverizing the first hydrogel polymer;
mixing the fine powder with water and re-assembling to prepare a fine powder re-assembly;
forming a second hydrogel polymer by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal crosslinking agent;
coarsely pulverizing the fine powder re-assembly by mixing with the second hydrogel polymer;
drying and pulverizing a mixture of the coarsely pulverized second hydrogel polymer and the fine powder re-assembly to form a second base resin; and
Further crosslinking the surface of the second base resin in the presence of a surface crosslinking agent to form a surface crosslinking layer,
The internal crosslinking agent, comprising a compound represented by the following formula (1) and polyethylene glycol diacrylate (PEGDA),
Method for preparing super absorbent polymer:
[Formula 1]

In Formula 1,
R ¹ is a divalent organic group derived from an alkane having 1 to 10 carbon atoms, and R ² is hydrogen or a methyl group.
The method of claim 1,
In Formula 1, R ¹ is methane-1,1-diyl, propane-1,3-diyl, propane-1,2-diyl, propane-1,1-diyl, n-butane-1,4-diyl, n -Butane-1,3-diyl, n-butane-1,2-diyl, n-butane-1,1-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl , 2-methylpropane-1,1-diyl, 2-methylbutane-1,4-diyl, 2-methylbutane-2,4-diyl, 2-methylbutane-3,4-diyl, 2-methylbutane- which is 4,4-diyl, 2-methylbutane-1,3-diyl, 2-methylbutane-1,2-diyl, 2-methylbutane-1,1-diyl or 2-methylbutane-2,3-diyl A method for producing a superabsorbent polymer, comprising the compound.
The method of claim 1,
The method for producing a superabsorbent polymer, wherein the compound represented by Formula 1 is included in an amount of 0.01 to 1 part by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer.
The method of claim 1,
The PEGDA is included in an amount of 0.01 to 0.2 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer.
The method of claim 1,
The method for producing a superabsorbent polymer, wherein the internal crosslinking agent includes the compound represented by Formula 1 and polyethylene glycol diacrylate (PEGDA) in a weight ratio of 2:1 to 5:1.
The method of claim 1,
The method for producing a superabsorbent polymer, wherein the fine powder re-assembly has a particle diameter of more than 150 μm and 50 mm.
The method of claim 1,
The method for producing a super absorbent polymer, wherein the fine powder re-assembly is mixed in an amount of 1 to 50 parts by weight based on 100 parts by weight of the second hydrogel polymer.
The method of claim 1,
The method for producing a superabsorbent polymer, wherein the superabsorbent polymer has a centrifugation retention capacity (CRC) of 35 to 60 g/g for physiological saline measured according to WSP 241.3 of the EDANA method.
The method of claim 1,
The method for producing a superabsorbent polymer, wherein the superabsorbent polymer has an absorbency under pressure (AUP) of 20 to 30 g/g of 0.7 psi with respect to physiological saline, measured according to the EDANA method WSP 242.3.