KR20200059023A - Preparation method of super absorbent polymer, and super absorbent polymer prepared therefrom - Google Patents

Abstract

The present invention relates to a method for preparing a high-absorbent resin and a high-absorbent resin prepared therefrom, which excellently maintains a basic absorption performance and also represents enhanced permeability. The method for preparing a high-absorbent resin comprises the steps of: forming a water-containing gel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer having an acid group, of which at least a portion is neutralized, in the presence of an internal cross-linking agent; adding an aqueous solution of a carbonate-based thermal cross-linking agent or an epoxy-based thermal cross-linking agent to the cross-linked and polymerized water-containing gel polymer; gel-grinding the water-containing gel polymer, to which the aqueous solution is added, to have a particle diameter of 10 mm or less; subjecting the water-containing gel polymer and the thermal cross-linking agent into an additional cross-linking reaction while drying the water-containing gel polymer at 100°C or higher; forming base resin powder by grinding and sorting the additionally cross-linked water-containing gel polymer; and forming a surface cross-linked layer by further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent.

Description

Manufacturing method of super absorbent polymer and super absorbent polymer {PREPARATION METHOD OF SUPER ABSORBENT POLYMER, AND SUPER ABSORBENT POLYMER PREPARED THEREFROM}

The present invention relates to a method for preparing a super absorbent polymer and a super absorbent polymer prepared therefrom, while maintaining excellent basic absorbent performance and exhibiting improved permeability.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb about 500 to 1,000 times its own weight, and SAM (Super Absorbency Material), AGM (Absorbent Gel) for each developer Material). The superabsorbent polymer as described above began to be put into practical use as a sanitary tool, and now, in addition to sanitary products such as children's paper diapers, soil repair agents for horticulture, civil engineering, construction index materials, nursery sheets, and freshness retention agents in the food distribution field, and It is widely used as a material for poultice.

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 absorbed moisture should not escape even under external pressure. In addition to this, it is necessary to show good permeability by absorbing water and maintaining its shape well even in a volume expanded (swelled) state.

However, in order for the superabsorbent polymer to exhibit such high permeability, it is basically necessary to maintain the shape even after the superabsorbent polymer particles absorb moisture and swell, thereby maintaining voids between the particles and the particles. This is because the pores between the particles serve as a flow path, so that the excellent permeability of the super absorbent polymer can be ensured. For this reason, in order to provide a superabsorbent polymer exhibiting improved permeability, etc., it is necessary for the superabsorbent polymer to exhibit a higher gel strength.

Meanwhile, FIG. 1 is a schematic diagram schematically showing a method of manufacturing a super absorbent polymer by a conventional technique and a form in which a crosslinked structure is formed in the process. Referring to FIG. 1, the superabsorbent polymer is generally prepared through a crosslinking polymerization step that proceeds in the presence of an internal crosslinking agent, a gel grinding, a drying and grinding step on a crosslinked polymerized hydrogel polymer, and a surface crosslinking step after that. Became.

In the method of manufacturing such a super absorbent polymer, in order to achieve high gel strength and thus excellent permeability, in order to increase the strength of the super absorbent polymer particle itself, the amount of internal crosslinking agent is increased to increase the degree of crosslinking inside the resin particle, A method of increasing the degree of surface crosslinking, such as increasing the amount of the surface crosslinking agent, has been generally applied.

However, when the internal crosslinking degree or the surface crosslinking degree is increased, it is a fact that the space inside the resin particles is reduced, thereby deteriorating the basic absorbency of the super absorbent polymer, for example, water retention capacity.

As a result, the development of a technique capable of producing a super absorbent polymer that exhibits improved permeability while maintaining excellent basic absorption performance has been continuously requested.

Accordingly, the present invention is to provide a method for preparing a super absorbent polymer and a super absorbent polymer prepared therefrom, while maintaining excellent basic absorption performance and exhibiting improved permeability.

The present invention comprises the steps of crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent to form a hydrogel polymer;

Adding an aqueous solution of a carbonate thermal crosslinking agent or an epoxy thermal crosslinking agent to the crosslinked polymerized hydrogel polymer;

Gel grinding the hydrogel polymer to which the aqueous solution is added to have a particle diameter of 10 mm or less;

Drying the hydrogel polymer at 100 ° C. or higher, and further crosslinking the hydrogel polymer and the thermal crosslinking agent;

Pulverizing and classifying the additional crosslinked hydrogel polymer to form a base resin powder; And

It provides a method for producing a super absorbent polymer comprising the step of forming a surface crosslinking layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent.

The present invention also provides a base resin powder comprising an internal crosslinking agent and a first crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized, via a carbonate-based thermal crosslinking agent or an epoxy-based thermal crosslinking agent; And

It is formed on the base resin powder, the first crosslinked polymer is a super absorbent polymer comprising a surface crosslinking layer comprising a second crosslinked polymer further crosslinked via a surface crosslinking agent,

Provides a superabsorbent polymer having a GBP under pressure of 25 to 60darcy, a GBP under 0.3psi pressure of 2.2 to 10darcy, and a centrifugal water retention capacity (CRC) of 28 to 35 g / g measured according to EDANA method WSP 241.3. .

Hereinafter, with reference to the accompanying drawings, a method of manufacturing a super absorbent polymer according to an embodiment of the present invention, and a super absorbent polymer produced therefrom will be described in detail. 2 is a schematic diagram schematically showing a method of manufacturing a super absorbent polymer according to an embodiment of the invention and a form in which a crosslinked structure is formed in the process.

According to one embodiment of the invention, in the presence of an internal crosslinking agent, crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized to form a hydrogel polymer;

Adding an aqueous solution of a carbonate thermal crosslinking agent or an epoxy thermal crosslinking agent to the crosslinked polymerized hydrogel polymer;

Gel grinding the hydrogel polymer to which the aqueous solution is added to have a particle diameter of 10 mm or less;

Drying the hydrogel polymer at 100 ° C. or higher, and further crosslinking the hydrogel polymer and the thermal crosslinking agent;

Pulverizing and classifying the additional crosslinked hydrogel polymer to form a base resin powder; And

A method for producing a super absorbent polymer comprising the step of forming a surface crosslinked layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent is provided.

As shown in Figure 2, in the manufacturing method of one embodiment, after preparing a hydrogel polymer through a conventional crosslinking polymerization process, while adding water for gel grinding, with a predetermined thermal crosslinking agent (100 ℃ or more A thermally reactive crosslinking agent) that can cause a crosslinking reaction at temperature is added. When the gel crushing and drying process is performed after the addition of the heat crosslinking agent, the heat crosslinking agent may cause the crosslinking reaction of the hydrogel polymer to form an additional crosslinking structure.

More specifically, the polymer in which the additional crosslinking structure is formed includes chains of the crosslinked polymer in which the unsaturated monomer is crosslinked and polymerized through an internal crosslinking agent, and the chains of these crosslinking polymers mediate the thermal crosslinking agent near the surface of the super absorbent polymer. It may include a cross-linked cross-linked structure that is further crosslinked.

This double-cross-linked cross-linked structure can achieve a more complex entangled cross-linked structure compared to a cross-linked structure formed of a single internal cross-linking agent, and in particular, may have a higher cross-linking density near the surface of the super absorbent polymer. As a result, the superabsorbent polymer finally produced by the method of one embodiment may exhibit a higher gel strength even if an internal crosslinking agent and / or a surface crosslinking agent having the same content are used. Due to this high gel strength, the superabsorbent polymer can exhibit improved permeability.

In addition, due to the double reticulated cross-linked structure (particularly, high cross-linking density near the superabsorbent polymer surface) that is uniquely formed by one embodiment, the permeability is not increased even if the amount of the internal cross-linking agent and / or the surface cross-linking agent is not significantly increased Since it can be improved, it is also possible to minimize the decrease in water absorption performance, for example, water retention capacity due to an increase in the amount of internal crosslinking and / or surface crosslinking.

As a result, according to one embodiment, a superabsorbent polymer that exhibits improved permeability and maintains excellent absorbent performance can be manufactured.

Hereinafter, a method of manufacturing an embodiment and a superabsorbent polymer obtained through the method will be described in more detail in each step.

First, in the manufacturing method of the above embodiment, the water-soluble ethylenically unsaturated monomer constituting the first crosslinked polymer may be any monomer commonly used in the production of super absorbent polymers. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by Formula 1 below:

[Formula 1]

R ₁ -COOM ¹

In Chemical Formula 1,

R ₁ is an alkyl group having 2 to 5 carbon atoms containing 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 (meth) acrylic acid, and monovalent (alkali) metal salts, divalent metal salts, ammonium salts and organic amine salts of these acids. When (meth) acrylic acid and / or a salt thereof are used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent polymer with improved absorbency. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid or 2- (metha) ) Acrylamide-2-methyl propane sulfonic acid, (meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene Glycol (meth) acrylate, polyethylene glycol (meth) acrylate, (N, N) -dimethylaminoethyl (meth) acrylate, (N, N) -dimethylaminopropyl (meth) acrylamide, and the like can be used.

Here, the water-soluble ethylenically unsaturated monomer has an acidic group, and at least a portion of the acidic group may be neutralized. Preferably, the monomer may be partially neutralized with an alkali material such as sodium hydroxide, potassium hydroxide or ammonium hydroxide.

At this time, the neutralization degree of the monomer may be 55 to 95 mol%, or 60 to 80 mol%, or 65 to 75 mol%. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, the neutralized monomer may precipitate and polymerization may be difficult to proceed smoothly. It can exhibit properties such as elastic rubber that are difficult to handle.

In the first step of the method of one embodiment, in the presence of an internal crosslinking agent or the like, a monomer composition comprising a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized as described above may be crosslinked and polymerized.

At this time, the water-soluble ethylenically unsaturated monomer is as described above. In addition, the concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition may be appropriately adjusted in consideration of polymerization time and reaction conditions, and may preferably be 20 to 90% by weight, or 40 to 65% by weight. This concentration range may be advantageous for controlling the grinding efficiency when pulverizing a polymer to be described later, while eliminating the need to remove unreacted monomers after polymerization by using the gel effect phenomenon that occurs in the polymerization reaction of a high concentration aqueous solution. However, if the concentration of the monomer is too low, the yield of the super absorbent polymer may be lowered. Conversely, if the concentration of the monomer is too high, a part of the monomer may be precipitated or there may be a process problem such as poor grinding efficiency when pulverizing the polymerized hydrogel polymer, and physical properties of the super absorbent polymer may be deteriorated.

In addition, as the internal crosslinking agent, any compound can be used as long as it allows introduction of crosslinking during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent is 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 Multifunctional crosslinking agents such as erythritol tetraacrylate, triarylamine, propylene glycol or glycerin may be used alone or in combination of two or more, but are not limited thereto.

The internal crosslinking agent may be added in an amount of 0.001 to 1 part by weight, or 0.005 to 0.5 part by weight based on 100 parts by weight of the unsaturated monomer. That is, if the content of the internal crosslinking agent is too low, the gel strength and / or permeability of the resin may not be sufficient. Conversely, if the content of the internal crosslinking agent is too high, the basic absorption performance of the resin, for example, water retention capacity may not be sufficient.

On the other hand, the monomer composition, for example, the aqueous monomer solution, in addition to the above-mentioned monomer and internal crosslinking agent, one or more additives selected from the group consisting of blowing agents, surfactants, polyvalent metal salts, photoinitiators, heat initiators and polyalkylene glycol-based polymers It may further include.

These additives further improve the permeability or liquid permeability of the super absorbent polymer (such as polymetallic salts or polyalkylene glycol-based polymers), further improve the absorption rate (such as foaming agents or surfactants), or crosslinking polymerization It can be used to improve the physical properties of the superabsorbent polymer by smoothing (such as a photoinitiator or a thermal initiator).

The above-described additive may be used in an amount of 2000 ppm or less, or 0 to 2000 ppm, or 10 to 1000 ppm, or 50 to 500 ppm, based on 100 parts by weight of the monomer, depending on each role. As a result, physical properties such as liquid permeability or absorption rate of the super absorbent polymer can be further improved.

Among the above-mentioned additives, polyethylene glycol or polypropylene glycol may be used as the polyalkylene glycol-based polymer.

Further, as the photo (polymerization) initiator and / or the thermal (polymerization) initiator, any polymerization initiator generally used in the production of super absorbent polymers can be used. In particular, even with the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like and a certain amount of heat is generated according to the progress of the exothermic polymerization reaction, the photo (polymerization) initiator and / or heat (polymerization) Initiators can be used together to produce superabsorbent polymers having better absorption rates and properties.

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, as the persulfate-based initiator, 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. In addition, 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- (carbamoyl azo) isobutyronitrile (2- (carbamoylazo) isobutylonitril), 2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride (2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride), 4, For example, 4-azobis- (4-cyanovaleric acid) (4,4-azobis- (4-cyanovaleric acid)). More various thermal polymerization initiators are disclosed on page 203 of the Odian book "Principle of Polymerization (Wiley, 1981)", which can be referred to.

Further, as the photo (polymerization) initiator, for example, benzoin ether (benzoin ether), dialkyl acetophenone (dialkyl acetophenone), hydroxyl alkyl ketone (hydroxyl alkylketone), phenyl glyoxylate (phenyl glyoxylate), One or more compounds selected from the group consisting of Benzyl Dimethyl Ketal, acyl phosphine and alpha-aminoketone may be used. Among them, as a specific example of acylphosphine, a commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) can be used. . More various photopolymerization initiators are disclosed on page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)", which can be referred to.

The initiator may be added in an amount of 500 ppmw or less with respect to 100 parts by weight of the monomer. That is, when the concentration of the polymerization initiator is too low, the polymerization rate may be slow, and residual monomers in the final product may be extracted in large quantities, which is not preferable. On the contrary, when the concentration of the polymerization initiator is higher than the above range, the polymer chain forming the network is shortened, so the content of the water-soluble component is increased and the pressure absorption capacity is lowered, which is not preferable.

On the other hand, in addition to each of the components described above, the monomer composition may further include a thickener, a plasticizer, a storage stabilizer, an antioxidant, etc., if necessary.

And, such a monomer composition may be prepared in the form of a solution in which a raw material such as the above-described monomer is dissolved in a solvent. At this time, as a usable solvent, any material that can dissolve the above-described raw materials can be used without limitation. For example, the solvent includes water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N, N-dimethylacetamide, or mixtures thereof can be used.

In addition, the monomer composition having the form of the above-described aqueous solution may be controlled such that the initial temperature has a temperature of 30 to 60 ° C, and light energy or thermal energy may be applied thereto to form crosslinking polymerization.

The formation of a hydrogel polymer through crosslinking polymerization of such a 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 photo polymerization according to the type of polymerization energy source. When the thermal polymerization is performed, the polymerization method may be performed in a reactor having a stirring axis such as a kneader, and photo polymerization In the case of proceeding, it may proceed in a reactor equipped with a movable conveyor belt.

For example, a hydrogel polymer can be obtained by introducing the monomer composition into a reactor, such as a kneader equipped with a stirring shaft, and supplying hot air to it or heating the reactor to thermally polymerize it. At this time, depending on the type of agitation 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 speed of the monomer composition to be injected, and a hydrogel polymer having a particle diameter of 2 to 50 mm (average weight) is usually obtained.

And, as another example, when the photopolymerization of the monomer composition in a reactor equipped with a movable conveyor belt is performed, a hydrogel polymer in the form of a sheet may be obtained. At this time, the thickness of the sheet may vary depending on the concentration and the injection rate of the monomer composition to be injected. In order to ensure the production speed and the like while allowing the entire sheet to be evenly polymerized, it is usually adjusted to a thickness of 0.5 to 5 cm. desirable.

At this time, the normal water content of the hydrogel polymer obtained in this way may be 40 to 80% by weight. Meanwhile, in the present specification, “water content” refers to a content of moisture occupied with respect to the total weight of the hydrogel polymer, which means the weight of the hydrogel polymer minus the dry polymer weight. Specifically, it is defined as a calculated value by measuring the weight loss due to evaporation of water in the polymer during the drying process 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 20 minutes including 5 minutes of the temperature rise step to measure the water content.

On the other hand, after preparing the hydrogel polymer by the above-described method, an aqueous solution of a carbonate thermal crosslinking agent or an epoxy thermal crosslinking agent may be added to the crosslinked polymerized hydrogel polymer. This thermal crosslinking agent is to further react with a hydrogel polymer in a subsequent high temperature drying process to form an additional crosslinking structure.

Specific examples of the thermal crosslinking agent include one or more selected from the group consisting of ethylene carbonate, propylene carbonate, glycerin carbonate, and glycidyl ether-based compounds, and in addition, crosslinking reaction with the hydrogel polymer at a temperature of 100 ° C. or higher. Any thermally reactive carbonate-based compound or epoxy-based compound that can be used can be used without particular limitation.

The thermal crosslinking agent may be added in an amount of 0.001 to 0.5 parts by weight, or 0.005 to 0.3 parts by weight, or 0.01 to 0.1 parts by weight based on 100 parts by weight of the unsaturated monomer used in the crosslinking polymerization step. That is, if the content of the thermal crosslinking agent is too low, the gel strength and / or permeability of the resin may not be sufficiently improved. Conversely, when the content of the thermal crosslinking agent is too high, the basic absorption performance of the resin, for example, water retention capacity may be deteriorated, so that the absorption performance of the super absorbent polymer may not be sufficient.

This thermal crosslinking agent may be added in the form of an aqueous solution together with water added for subsequent gel grinding.

Thereafter, the hydrogel polymer may be gel-pulverized to form a hydrogel polymer having a small average particle diameter. In the gel grinding step, the hydrogel polymer may be pulverized to have a particle diameter of 10 mm or less, or a particle diameter of 5 mm or less, or a particle diameter of 1.0 mm to 2.0 mm. In this case, the particle diameter of the hydrogel polymer may be defined as the longest distance among the straight lines connecting any two points on the surface in a single particle of the hydrogel polymer after gel grinding.

The pulverizer used for grinding the gel is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, and a rotary cutter mill , Cutter mill, Disc mill, Shred crusher, Crusher, Chopper and Disc cutter It may include, but is not limited to the above-described example.

Further, for the efficiency of gel grinding, gel grinding may be performed multiple times according to the size of the particle size. For example, the hydrogel polymer may be first pulverized to a particle size of 10 mm or less, and further pulverized to a smaller particle diameter.

Meanwhile, after the gel grinding, the hydrogel polymer may be dried at 100 ° C. or higher while further crosslinking the hydrogel polymer and the thermal crosslinking agent. The drying process may be performed at a temperature of 100 ° C. or higher, or 100 to 250 ° C., or 150 to 200 ° C. Through this, while drying the hydrogel polymer, the polymer chains included in the hydrogel polymer are used as the thermal crosslinking agent. Further crosslinking may form a double reticulated crosslinked structure as shown in the third figure of FIG. 2.

When the drying temperature is excessively low, the drying time becomes too long, an additional crosslinked structure is not properly formed, and there is a fear that physical properties such as permeability of the finally formed superabsorbent polymer are deteriorated. Conversely, if the drying temperature is excessively high, only the polymer surface is excessively dried, and fine powder may be generated. Accordingly, there is a fear that the physical properties of the superabsorbent polymer finally formed may be deteriorated. Meanwhile, the drying time may be performed for 20 minutes to 15 hours in consideration of process efficiency and the like, but is not limited thereto.

As long as it is commonly used as the drying process, it can be selected and used without limitation in its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. The water content of the polymer after the drying step may be 0.05 to 10% by weight.

Next, a step of (un) grinding the dried polymer obtained through such a drying step is performed.

The polymer powder obtained after the grinding step may have a particle size of 150 to 850 μm. The pulverizer used for pulverizing such a particle size is, specifically, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, or a disc. A mill or a jog mill may be used, but is not limited to the above-described example.

Then, in order to manage the physical properties of the superabsorbent polymer to be finalized, a step of selectively classifying particles having a particle diameter of 150 to 850 μm from the polymer particles obtained through the grinding step may be further performed. This classifying step may be performed using a standard sieve, according to the classifying method of a general superabsorbent polymer.

On the other hand, after proceeding to the above-described classification, as a step of crosslinking the surface of the base resin powder, in the presence of a surface crosslinking solution containing a surface crosslinking agent, the base resin powder is heat-treated to perform surface crosslinking, resulting in super absorbency. Resin can be produced.

Here, the type of the surface crosslinking agent contained in the surface crosslinking solution is not particularly limited. As a non-limiting example, the surface crosslinking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene Carbonate, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol trimethylol Propane, pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and one or more compounds selected from the group consisting of iron chloride.

At this time, the content of the surface crosslinking agent may be appropriately adjusted according to the type or reaction conditions thereof, and preferably 0.001 to 5 parts by weight based on 100 parts by weight of the base resin powder. When the content of the surface cross-linking agent is too low, the surface cross-linking degree is lowered, and physical properties of a super absorbent polymer such as permeability or pressure absorbing ability may be deteriorated. Conversely, if the surface crosslinking agent is used in an excessively large amount, the basic absorption properties of the super absorbent polymer may be lowered due to excessive surface crosslinking reaction, which is not preferable.

In addition, the surface crosslinking solution is 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 and N, It may further include one or more solvents selected from the group consisting of N-dimethylacetamide. The solvent may be included in 0.5 to 10 parts by weight based on 100 parts by weight of the base resin.

In addition, the surface crosslinking solution may further include a thickener. When the surface of the base resin powder is further crosslinked in the presence of a thickener in this way, deterioration in physical properties can be minimized even after grinding. Specifically, one or more selected from polysaccharides and hydroxy-containing polymers may be used as the thickener. As the polysaccharide, a gum-based thickener and a cellulose-based thickener may be used. Specific examples of the gum-based thickener include xanthan gum, arabic gum, karaya gum, tragacanth gum, ghatti gum, guar gum (guar gum), locust bean gum (locust bean gum) and silylium seed gum, and the like, and specific examples of the cellulose-based thickener include hydroxypropyl methyl cellulose, carboxymethyl cellulose, and methyl cellulose. , Hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose and methylhydroxypropylcellulose Can be. Meanwhile, specific examples of the hydroxy-containing polymer include polyethylene glycol and polyvinyl alcohol.

On the other hand, in order to perform the surface crosslinking, the surface crosslinking solution and the base resin powder are mixed in a reaction tank, a method of spraying a surface crosslinking solution on the base resin, the base resin and the surface in a continuously operated mixer. A method in which a crosslinking solution is continuously supplied and mixed may be used.

In addition, the surface crosslinking may be performed under a temperature of 100 to 250 ° C., or may be continuously performed after the drying and pulverizing steps proceeding at a relatively high temperature. At this time. The surface crosslinking reaction may be performed for 1 to 120 minutes, or 1 to 100 minutes, or 10 to 60 minutes. That is, while inducing a minimum amount of the surface crosslinking reaction, the polymer particles may be damaged during excessive reaction to prevent the physical properties from being deteriorated, and thus the conditions of the surface crosslinking reaction may be performed.

The superabsorbent polymer prepared by the method of one embodiment described above may include a double reticulated crosslinked structure inside the base resin powder due to the introduction of a thermal crosslinking agent that is added after crosslinking polymerization and reacts in a drying step.

More specifically, the superabsorbent polymer comprises an internal crosslinking agent and a first crosslinked polymer crosslinked with a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized through a carbonate-based thermal crosslinking agent or an epoxy-based thermal crosslinking agent. Base resin powder; And it is formed on the base resin powder, the first crosslinked polymer may have a structure including a surface crosslinking layer including a second crosslinked polymer further crosslinked through a surface crosslinking agent. In particular, in the structure of such a superabsorbent polymer, the first crosslinked polymer contains chains of a crosslinked polymer in which the unsaturated monomer is crosslinked and polymerized via an internal crosslinking agent, and the chains of such crosslinked polymer are in the vicinity of the surface of the superabsorbent polymer. It may include a double cross-linked cross-linked structure that is further cross-linked through the thermal cross-linking agent.

Due to the reticulated cross-linking structure derived from such a thermal crosslinking agent, in particular, high crosslinking density near the surface of the resin, the superabsorbent polymer may exhibit higher gel strength and improved permeability, along with excellent absorption performance, for example, It can maintain excellent water retention capacity.

The improved gel strength and permeability of these superabsorbent resins can be defined by gel bed permeability (GBP) measured under no pressure and / or under a pressure of 0.3 psi. The superabsorbent polymer prepared by the method of the above embodiment may exhibit excellent permeability of GBP under pressure of 25 to 60darcy, or 26 to 58darcy, and GBP under pressure of 0.3psi to 2.2 to 10darcy, or 2.3 to 8 darcy. have. Such GBP can be measured by using the apparatus shown in FIGS. 1 to 3 of Patent Application No. 2014-7018005 according to the method described in the specification of the document.

In addition, the superabsorbent polymer has a centrifugal water retention capacity (CRC) measured according to EDANA method WSP 241.3 of 28 to 35 g / g, or 28 to 33 g / g, and 0.9 psi measured according to EDANA method WSP 242.3. The pressure absorbing capacity (AUL) may be 18 to 23 g / g, or 19 to 22 g / g. As such, the superabsorbent polymer can maintain excellent absorption performance, that is, excellent water retention capacity and pressure absorption capacity, while exhibiting improved transmittance as described above.

As described above, according to the present invention, it is possible to manufacture a super absorbent polymer that exhibits improved permeability while maintaining excellent absorbent performance.

1 is a schematic view schematically showing a method of manufacturing a super absorbent polymer by a conventional technique and a form in which a crosslinked structure is formed in the process.
2 is a schematic diagram schematically showing a method of manufacturing a super absorbent polymer according to an embodiment of the present invention and a form in which a crosslinked structure is formed in the process.

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

Comparative example  One

(Step 1)

8.6 g of IRGACURE 819 initiator diluted to 0.5% by weight in acrylic acid (80 ppmw for monomer) and 10.75 g of polyethylene glycol diacrylate (PEGDA, Mw = 400) diluted to 20% by weight in acrylic acid (total included in the monomer composition A solution (A solution) in which PEGDA (0.4 parts by weight of PEGDA) was mixed with respect to 100 parts by weight of the monomer was prepared.

540 g of acrylic acid and the A solution were injected into a 2 L glass reactor surrounded by a jacket in which a heat medium previously cooled to 25 ° C. was circulated.

Then, 832 g of a 25% by weight caustic soda solution (C solution) was slowly added dropwise to the glass reactor and mixed. After confirming that the temperature of the mixed solution rose to about 72 ° C or more due to the heat of neutralization, the mixed solution was waited for cooling. The neutralization degree of acrylic acid in the mixed solution thus obtained was about 70 mol%.

On the other hand, as a surfactant, a solution (D) containing sodium dodecylsulfate (HLB: about 40) and SPAN-80 (HLB: 4.6) diluted in water was prepared. In addition, 30 g of a sodium persulfate solution (E solution) diluted to 4% by weight in water was prepared. And 13.4 g of sodium hydrogen carbonate solution (F) diluted to 4% by weight in water was prepared. Subsequently, when the temperature of the mixed solution was cooled to about 45 ° C., the prepared D, E, and F solutions were injected into the mixed solution and mixed. At this time, the content of sodium dodecyl sulfate in the D solution was 110 ppmw compared to acrylic acid, and SPAN-80 was 50 ppmw, so that the total amount of surfactant was 160 ppmw.

(Step 2)

Subsequently, the mixed solution prepared above was poured into a Vat-shaped tray (15 cm x 15 cm horizontal) installed in a square polymerizer equipped with a light irradiation device on the top and preheated to 80 ° C inside. Thereafter, the mixed solution was irradiated with light. It was confirmed that a gel was formed from the surface about 20 seconds after the light irradiation time, and that polymerization reaction occurred simultaneously with foaming after about 30 seconds from the light irradiation time. Subsequently, the polymerization reaction was performed for an additional 2 minutes, and the polymerized sheet was taken out and cut to a size of 3 cm x 3 cm.

(Step 3)

Then, using the meat chopper (meat chopper) and through the chopping process (chopping), the cut sheet was manufactured into a crump. The average particle size of the produced crump was 1.5 mm.

(Step 4)

Subsequently, the crump was dried in an oven capable of controlling air volume up and down. The hot air at 180 ° C. was flowed from the bottom to the top for 15 minutes, and again from the top to the bottom for 15 minutes so that the water content of the dried powder was about 2% by weight or less. It was dried uniformly. The dried powder was pulverized by a grinder and then classified to obtain a base resin having a size of 150 to 850um.

(Step 5)

Then, to the prepared base resin 100 g, water 4.5 g, ethylene carbonate 1 g, Aerosil 200 (Aerosil 200, Evonik Co.) 0.05 g, 20% by weight of water dispersion silica (Snowtex, ST-O) solution 0.25g The mixed crosslinking agent solution was mixed and then subjected to a surface crosslinking reaction at 190 ° C for 30 minutes. Then, the obtained product was crushed and a surface-crosslinked superabsorbent polymer having a particle diameter of 150 to 850 um was obtained using a sieve. 0.1 g of Aerosil 200 was further dry-mixed with the obtained superabsorbent polymer to prepare a superabsorbent polymer.

Example  One

First, steps 1 and 2 were performed in the same manner as in Comparative Example 1.

Thereafter, to the polymer sheet 1500g, 260.005 g of an aqueous heat crosslinking agent in which 0.005 g of ethylene carbonate as a thermal crosslinking agent (0.001 part by weight of ethylene carbonate relative to 100 parts by weight of the total monomer of the monomer composition formed in step 1) and 260 g of water were mixed.

Subsequently, steps 3 to 5 were performed in the same manner as in Comparative Example 1 to prepare the superabsorbent polymer of Example 1. However, it was confirmed that in the drying process of step 4 in the manufacturing process, the thermal crosslinking agent and the polymer sheet caused a crosslinking reaction.

Example  2

First, steps 1 and 2 were performed in the same manner as in Comparative Example 1.

Thereafter, to the polymer sheet 1500g, 260.05 g of an aqueous heat crosslinking agent was mixed with 0.05 g of ethylene carbonate as a heat crosslinking agent (0.01 part by weight of ethylene carbonate relative to 100 parts by weight of the total monomer of the monomer composition formed in step 1) and 260 g of water. .

Subsequently, steps 3 to 5 were performed in the same manner as in Comparative Example 1 to prepare superabsorbent polymers of Example 2. However, it was confirmed that in the drying process of step 4 in the manufacturing process, the thermal crosslinking agent and the polymer sheet caused a crosslinking reaction.

Example  3

First, steps 1 and 2 were performed in the same manner as in Comparative Example 1.

Subsequently, to the polymer sheet 1500g, 260.5 g of an aqueous heat cross-linking agent in which 0.5 g of ethylene carbonate as a thermal crosslinking agent (0.1 parts by weight of ethylene carbonate relative to 100 parts by weight of the total monomer of the monomer composition formed in step 1) and 260 g of water were mixed. .

Subsequently, steps 3 to 5 were performed in the same manner as in Comparative Example 1 to prepare the superabsorbent polymer of Example 1. However, it was confirmed that in the drying process of step 4 in the manufacturing process, the thermal crosslinking agent and the polymer sheet caused a crosslinking reaction.

Comparative example  2

In step 1 of Comparative Example 1, except for further mixing ethylene carbonate 0.05g (100 parts by weight of ethylene carbonate relative to 100 parts by weight of the total monomer of the monomer composition), the same method as in Comparative Example 1, An absorbent resin was prepared.

Experimental Example : Evaluation of physical properties of super absorbent polymer

The physical properties of the superabsorbent polymer prepared in Examples and Comparative Examples were evaluated by the following methods, and the results are shown in Table 1.

(1) Centrifugation Water retention capacity ( CRC : Centrifuge Retention Capacity)

The water retention capacity of each resin by the load-free absorption magnification was measured according to EDANA WSP 241.3.

Specifically, from the resins obtained through Examples and Comparative Examples, resins classified by a sieve of # 30-50 were obtained. After the resin W ₀ (g) (about 0.2 g) was uniformly put in a nonwoven fabric bag and sealed, it was immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the bag was drained for 3 minutes under the condition of 250G using a centrifuge, and the mass W ₂ (g) of the envelope was measured. Moreover, the mass W ₁ (g) at that time was measured after performing the same operation without using a resin. CRC (g / g) was calculated according to the following equation using each obtained mass.

[Equation 1]

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

(2) Pressurization Absorption capacity  ( AUL : Absorbency under Load)

The pressure absorption capacity of 0.9 psi of each resin was measured according to EDANA method WSP 242.3.

First, when measuring the absorbent absorption capacity, a resin classifier for the CRC measurement was used.

Specifically, a 400 mesh wire mesh made of stainless steel was mounted on a cylindrical bottom of a plastic having an inner diameter of 25 mm. A piston capable of uniformly spreading the absorbent resin W ₀ (g) (0.16 g) on a wire mesh under conditions of normal temperature and humidity of 50%, and giving a uniform load of 0.9 psi thereon is slightly smaller than the outer diameter of 25 mm. There was no gap with the inner wall of the cylinder, and the vertical movement was 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 the petri dish of 150 mm in diameter, and the physiological saline composed of 0.9 wt% sodium chloride was brought to the same level as the top surface of the glass filter. A sheet of filter paper having a diameter of 90 mm was placed thereon. The measuring device was mounted on a filter paper, and the liquid was absorbed for 1 hour under a load. After 1 hour, the measuring device was lifted, and the weight W ₄ (g) was measured.

Using each mass obtained, pressure absorption capacity (g / g) was calculated according to the following equation.

[Equation 2]

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

(3) Under pressure  & 0.3 psi Under pressure  Gel Bed  Transmittance ( GBP )

Examples and Comparative Examples of the superabsorbent resin in the unpressurized gel bed permeability (GBP) for physiological saline, using the apparatus shown in FIGS. 1 to 3 of patent application 2014-7018005, the specification of the patent application 2014-7018005 It measured according to the method described in.

The gel bed permeability (GBP) under pressure was also measured under pressure of 0.3 psi using the same apparatus and method.

Table 1 shows the results measured as described above.

Unpressurized GBP
(darcy) Pressurized GBP
(darcy) (# 30-50)
CRC (g / g) (# 30-50)
0.9 AUL (g / g) Example 1 27 2.3 30.4 20.7 Example 2 45 3.5 29.9 21.3 Example 3 56 6.2 28.1 22.0 Comparative Example 1 24 2.0 30.5 20.5 Comparative Example 2 25 2.1 30.1 20.2

Referring to Table 1, it was confirmed that the superabsorbent polymer of the Examples exhibits improved water permeability and pressure retention while maintaining the same or higher level of water retention and pressurization.

Claims (12)

Crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent to form a hydrogel polymer;
Adding an aqueous solution of a carbonate thermal crosslinking agent or an epoxy thermal crosslinking agent to the crosslinked polymerized hydrogel polymer;
Gel grinding the hydrogel polymer to which the aqueous solution is added to have a particle diameter of 10 mm or less;
Drying the hydrogel polymer at 100 ° C. or higher, and further crosslinking the hydrogel polymer and the thermal crosslinking agent;
Pulverizing and classifying the additional crosslinked hydrogel polymer to form a base resin powder; And
A method for producing a super absorbent polymer comprising the step of forming a surface crosslinking layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent.
The method of claim 1, wherein the monomer comprises a (meth) acrylic acid partially neutralized with (meth) acrylic acid and an alkali metal salt thereof, and has a neutralization degree of 55 to 95 mol%.
The method of claim 1, wherein the thermal crosslinking agent comprises one or more selected from the group consisting of ethylene carbonate, propylene carbonate, glycerin carbonate and glycidyl ether-based compounds.
The method of claim 1, wherein the thermal crosslinking agent is used in an amount of 0.001 to 0.5 parts by weight based on 100 parts by weight of the unsaturated monomer.
The method of claim 1, wherein the internal crosslinking agent is 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, Method for producing a super absorbent polymer comprising at least one member selected from the group consisting of pentaerythritol tetraacrylate, triarylamine, propylene glycol, and glycerin.
The method of claim 1, wherein the internal crosslinking agent is used in an amount of 0.001 to 1 part by weight based on 100 parts by weight of the unsaturated monomer.
The method of claim 1, wherein the drying step is performed at a temperature of 100 to 250 ° C.
A base resin powder comprising an internal crosslinking agent and a first crosslinking polymer crosslinked with a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized through a carbonate-based thermal crosslinking agent or an epoxy-based thermal crosslinking agent; And
It is formed on the base resin powder, the first crosslinked polymer is a super absorbent polymer comprising a surface crosslinking layer comprising a second crosslinked polymer further crosslinked via a surface crosslinking agent,
Gel bed permeability (GBP) under no pressure is 25 to 60 darcy, gel bed permeability (GBP) under 0.3 psi pressure is 2.2 to 10 darcy, and centrifugal water retention capacity (CRC) measured according to EDANA method WSP 241.3 is 28 to 35 Super absorbent polymer, g / g.
9. The network of claim 8, wherein the first crosslinked polymer comprises chains of a crosslinked polymer in which the unsaturated monomer is crosslinked polymerized via an internal crosslinker, and the chains of these crosslinked polymers are further crosslinked via the thermal crosslinker. Super absorbent polymer comprising a crosslinked structure.
The super absorbent polymer according to claim 8, wherein the thermal crosslinking agent comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, glycerin carbonate and glycidyl ether-based compounds.
The method according to claim 8, wherein the internal crosslinking agent is 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, Super absorbent polymer comprising at least one member selected from the group consisting of pentaerythritol tetraacrylate, triarylamine, propylene glycol, and glycerin.
The superabsorbent polymer according to claim 8, wherein the absorbency under pressure (AUL) of 0.9 psi measured in accordance with EDANA method WSP 242.3 is 18 to 23 g / g.

Images