KR20200128970A - 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 super absorbent polymer and a super absorbent polymer. More particularly, the present invention relates to: a super absorbent polymer preparation method capable of preparing a more improved super absorbent polymer without excessive use of a surfactant and use of a foaming agent; and a super absorbent polymer prepared thereby.

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 producing a super absorbent polymer and a super absorbent polymer. More specifically, it relates to a method for producing a super absorbent polymer that enables the production of an improved super absorbent polymer without excessive use of a surfactant and a foaming agent, and a super absorbent polymer prepared therefrom.

Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb moisture of 500 to 1,000 times its own weight, and each developer has a Super Absorbency Material (SAM), AGM (Absorbent Gel). Material) and so on. Since the above superabsorbent resin has begun to be put into practical use as a sanitary tool, nowadays, in addition to hygiene products such as paper diapers for children, soil repair agents for horticulture, water resistant materials for civil engineering and construction, sheets for seedlings, freshness maintaining agents in the food distribution field, and It is widely used as a material for poultice.

In most cases, such super absorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins. In such sanitary materials, the super absorbent polymer is generally included in a state of being spread in pulp. However, in recent years, efforts to provide sanitary materials such as diapers with a thinner thickness are continuing, and as part of this, the content of pulp is reduced, and furthermore, so-called pulpless diapers are not used at all. Development is actively progressing.

In this way, the content of the pulp is reduced, or in the case of a sanitary material in which pulp is not used, a relatively high water-absorbent resin is included in a high proportion, and such super-absorbent resin particles are inevitably included in multiple layers in the sanitary material. In order for the entire superabsorbent polymer particles included in multiple layers to more efficiently absorb liquids such as urine, the superabsorbent polymer needs to basically exhibit high absorption performance and absorption rate.

Accordingly, in recent years, attempts to manufacture and provide a super absorbent polymer having an improved absorption rate have been continuously made.

The most common method for increasing the absorption rate is a method of increasing the surface area of the super absorbent polymer by forming a porous structure inside the super absorbent polymer.

As described above, in order to increase the surface area of the super absorbent polymer, conventionally, by using a carbonate-based foaming agent to perform crosslinking polymerization, a porous structure is formed in the base resin powder, or bubbles are formed in the monomer composition in the presence of a surfactant and/or a dispersant. After introducing, crosslinking polymerization was carried out to apply a method of forming the porous structure.

However, it is difficult to achieve an absorption rate above a certain level by any of the previously known methods, and therefore, there has been a continuous request for the development of a technology that enables additional absorption rate improvement.

Moreover, in order to obtain a super absorbent polymer having a further improved absorption rate by the conventional method, it is inevitably accompanied by the use of an excessive amount of a foaming agent and/or a surfactant. As a result, various physical properties of the super absorbent polymer, for example, The disadvantages such as lowering of surface tension, liquid permeability, or bulk density have emerged.

Accordingly, development of a technology capable of further improving the absorption rate of the super absorbent polymer while reducing the use of surfactants and/or foaming agents is continuously requested.

Accordingly, the present invention is to provide a method for producing a super absorbent polymer that enables the production of a super absorbent polymer exhibiting an improved absorption rate without excessive use of a surfactant and a foaming agent.

In addition, the present invention is to provide a super absorbent polymer that exhibits an improved absorption rate and excellent general physical properties manufactured by the above manufacturing method.

According to an embodiment of the present invention,

Preparing a monomer composition comprising a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator having at least partially neutralized acidic groups;

Generating air bubbles in the aqueous solution using a microbubble generator;

Introducing inorganic fine particles into the aqueous solution in which bubbles are generated, and generating fine bubbles using an ultrasonic device (ultrasonication);

Mixing the aqueous solution in which the microbubbles are generated and the monomer composition, followed by crosslinking polymerization to form a hydrogel polymer;

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

In the presence of a surface crosslinking agent, there is provided 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 addition, according to another embodiment of the present invention,

A base resin powder containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized; And a surface crosslinked layer formed on the base resin powder, wherein the crosslinked polymer is further crosslinked via a surface crosslinking agent,

The super absorbent polymer provides a super absorbent polymer having a vortex time of 5 to 35 seconds and a Gel-AUL of 19 to 24 g/g for 5 minutes at 0.3 psi.

As described above, according to the present invention, there can be provided a method for producing a super absorbent polymer that enables the production of a more improved super absorbent polymer without excessive use of a surfactant and a foaming agent.

The superabsorbent polymer prepared in this way may exhibit a more improved absorption rate, and the surfactant and/or foaming agent is not used, or the content thereof is reduced, thereby minimizing deterioration in physical properties, and excellent in addition to the absorption rate. Can maintain all physical properties.

The terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprises", "includes" or "have" are intended to designate the existence of a feature, step, component, or combination of the implemented features, one or more other features or steps, It is to be understood that the possibility of the presence or addition of components, or combinations thereof, is not excluded in advance.

The present invention will be described in detail below and exemplify specific embodiments, as various changes can be made and various forms can be obtained. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention will be described in detail below and exemplify specific embodiments, as various changes can be made and various forms can be obtained. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

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

According to one embodiment of the invention, at least a part of preparing a monomer composition comprising a water-soluble ethylenically unsaturated monomer having a neutralized acidic group, an internal crosslinking agent, and a polymerization initiator; Generating air bubbles in the aqueous solution using a microbubble generator; Introducing inorganic fine particles into the aqueous solution in which bubbles are generated, and generating fine bubbles using an ultrasonic device (ultrasonication); Mixing the aqueous solution in which the microbubbles are generated and the monomer composition, followed by crosslinking polymerization to form a hydrogel polymer; Drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; And in the presence of a surface cross-linking agent, there is provided a method for producing a super absorbent polymer comprising the step of forming a surface cross-linking layer by further cross-linking the surface of the base resin powder.

In the manufacturing method of one embodiment of the present invention, in order to generate nano-sized fine bubbles in the monomer composition, bubbles are generated by dividing into two steps, and the resulting bubbles are stabilized by introducing inorganic fine particles in the middle of the bubble generation step of the second step. Raise.

As a result, when crosslinking polymerization is carried out using the monomer composition formed by the method of one embodiment of the present invention, the formation of microbubbles is promoted and the generated microbubbles are stably maintained even when the use of a blowing agent or surfactant is omitted or the amount is reduced. As a result, it was confirmed that a base resin powder and a super absorbent polymer having a developed porous structure and excellent gel strength can be prepared.

Accordingly, according to the method of one embodiment, a super absorbent polymer having an improved absorption rate may be prepared as it has such a porous structure, and all absorbent properties of the super absorbent polymer, such as surface tension, liquid permeability, and gel strength. It was confirmed that the back can also be maintained excellently.

Hereinafter, a method of manufacturing a super absorbent polymer according to an embodiment, and a super absorbent polymer obtained through the method will be described in more detail.

First, in the manufacturing method of the embodiment, the water-soluble ethylenically unsaturated monomer may be any monomer conventionally used in the manufacture of a super absorbent polymer. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Formula 1:

[Formula 1]

R ₁ -COOM ¹

In 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.

In this way, when (meth)acrylic acid and/or a salt thereof is used as a water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a super absorbent polymer having improved water absorption. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth) )Acrylamide-2-methyl propane sulfonic acid, (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 may be used.

Here, the water-soluble ethylenically unsaturated monomer may have an acidic group, and at least a part of the acidic group may be neutralized. Preferably, the monomer partially neutralized with a basic substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or the like may be used.

At this time, the degree of neutralization 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 be precipitated and the polymerization may be difficult to proceed smoothly. On the contrary, if the degree of neutralization is too low, the absorbency of the polymer is greatly reduced. It may exhibit properties such as elastic rubber that are difficult to handle.

And, the monomer composition containing the monomer, for example, may be provided in a solution state, such as an aqueous solution, the monomer concentration in the monomer composition may be appropriately adjusted in consideration of the polymerization time and reaction conditions, for example For example, it may be 20 to 90% by weight, or 40 to 65% by weight.

This concentration range may be advantageous in order to control the pulverization efficiency during pulverization of the polymer, which will be described later, while eliminating the need to remove the unreacted monomer after polymerization by using the gel effect phenomenon occurring in the polymerization reaction of the high concentration aqueous solution. However, if the concentration of the monomer is too low, the yield of the super absorbent polymer may be lowered. On the contrary, if the concentration of the monomer is too high, a problem may occur in the process, such as a decrease in pulverization efficiency when a part of the monomer is precipitated or the polymerization hydrogel polymer is pulverized, and the physical properties of the super absorbent polymer may be deteriorated.

On the other hand, the above-described monomer may be mixed with an internal crosslinking agent and a polymerization initiator in a solvent to form a monomer composition.

As the internal crosslinking agent, any compound may be used as long as it allows the introduction of a crosslinking bond 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, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate )Acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, penta A polyfunctional crosslinking agent such as erythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, but is not limited thereto.

This internal crosslinking agent may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the internal crosslinking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened, which is not preferable. Conversely, when the concentration of the internal crosslinking agent is too high, the absorption power of the resin may be lowered, making it undesirable as an absorber.

As the polymerization initiator, any polymerization initiator generally used in the production of a super absorbent polymer may be used. In particular, even by the photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation, etc., and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, so that a photopolymerization initiator and/or a thermal polymerization initiator are used together. A super absorbent polymer having an excellent absorption rate and various physical properties can be prepared.

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

In addition, as the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyldimethyl ketal (Benzyl Dimethyl Ketal), acyl phosphine (acyl phosphine), and one or more compounds selected from the group consisting of alpha-aminoketone (α-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) may be used. . A wider variety of photopolymerization initiators are disclosed on page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)", which may be referred to.

This polymerization initiator may be added in an amount of 500 ppmw or less based on 100 parts by weight of the monomer. That is, if the concentration of the polymerization initiator is too low, the polymerization rate may be slowed, and a large amount of residual monomers in the final product may be extracted, 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 that the content of the water-soluble component increases and the absorption capacity under pressure may decrease, and thus the physical properties of the resin may be deteriorated.

According to an embodiment of the present invention, the monomer composition may further include a surfactant to further improve the absorption rate by developing a porous structure of the super absorbent polymer, and the surfactant may be an anionic surfactant or a nonionic surfactant. Surfactants can be used.

According to another embodiment of the present invention, the surfactant may be included in the monomer composition, or may be included in water or an aqueous solution for generating fine bubbles to be described later.

Examples of the anionic surfactant include sodium dodecyl sulfate, ammonium lauryl sulfate, sodium laureth sulfate, dioctyl sodium sulfosuccinate, perfluorooctane sulfonate, perfluorobutane sulfonate, alkyl-aryl ether And one or more selected from the group consisting of phosphate, alkyl ether phosphate, sodium myreth sulfate, and carboxylate salt.

Examples of the nonionic surfactant include fatty acid esters, sorbitan trioleate, polyethoxylated sorbitan monooleate (product name: TWEEN 80), sorbitan monooleate (product name: SPAN 80) and sugar ester (product name : S-570) is one or more selected from the group consisting of.

When the monomer composition further contains a surfactant, the total amount of surfactant including the anionic surfactant and the nonionic surfactant is at a concentration of 150 ppmw or less based on the total weight of the water-soluble ethylenically unsaturated monomer. Can be included. More specifically, 150 ppmw or less, or 120 ppmw or less, or 100 ppmw or less, or 70 ppmw or less, and 1 ppmw or more, or 5 ppmw or more, or 10 ppmw or more, or 20 ppmw or more, or 30 ppmw or more. I can. If the concentration of the surfactant is higher than 150 ppmw, other physical properties of the super absorbent polymer such as pressure absorption ability, gel strength, or surface tension may be deteriorated.If the concentration of the surfactant is too low, the addition of the surfactant Accordingly, the effect of improving the absorption rate may not be sufficient.

On the other hand, in the manufacturing method of the super absorbent polymer according to the present invention, the monomer composition is divided into two steps to generate nano-sized fine bubbles, and the stability of the generated bubbles is increased by introducing inorganic fine particles in the middle of the second step of generating bubbles. As a result, the absorption rate can be improved while supplementing the disadvantages of using the surfactant such as a decrease in surface tension by including only a small amount of 150 ppmw or less even if the surfactant is not included.

In addition, the monomer composition according to an embodiment of the present invention may not contain a foaming agent such as sodium bicarbonate, which was used to generate bubbles by a chemical method in a conventional method for producing a super absorbent polymer. In this way, the gel strength of the superabsorbent polymer can be maintained high when the foaming agent is not used.

Meanwhile, in addition to each of the above-described components, additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant may be further included in the monomer composition as needed.

In addition, 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, the usable solvent may be used without limitation of its configuration as long as it can dissolve the aforementioned raw materials. For example, as the solvent, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof, and the like may be used.

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

Next, bubbles are generated using a microbubble generator for the monomer composition or separate aqueous solution (or water) prepared as described above.

As a general method for improving the absorption rate of the super absorbent polymer, there is a method of increasing the surface area of the super absorbent polymer by forming a porous structure inside the super absorbent polymer.

In order to increase the surface area of the super absorbent polymer as described above, in the past, by using a carbonate-based foaming agent to perform crosslinking polymerization, a porous structure is formed in the base resin powder, or bubbles are formed in the monomer composition in the presence of a surfactant and/or a dispersant. After introduction, a method of forming a porous structure by crosslinking polymerization was applied.

However, even with this method, it is difficult to achieve an absorption rate above a certain level, and other physical properties of the super absorbent polymer, such as surface tension, liquid permeability, gel strength, etc., are difficult due to the use of an excessive amount of blowing agent and/or surfactant. There was a drawback of deteriorating.

Thus, in the manufacturing method of the present invention, the monomer composition is divided into two steps to generate nano-sized microbubbles, and inorganic fine particles are added in the middle of the two-step bubble generation step to increase the stability of the generated bubbles, Even without excessive use of and the use of a foaming agent, the absorption rate can be improved while maintaining the general physical properties of the super absorbent polymer.

In addition, in the method for producing a superabsorbent polymer according to the present invention, the bubble generation step is performed directly on the monomer composition, or a bubble solution in which fine bubbles are formed by performing a bubble generation step on the monomer composition or a separate aqueous solution or water Bubbles may be generated in the monomer composition by mixing.

More specifically, first, bubbles are generated using a microbubble generator for the monomer composition or a separate aqueous solution or water.

In the bubble generation step using the microbubble generator, the microbubble generator that can be used may use a commercialized device without limitation. Preferably, OB-750S, which is a microbubble generator manufactured by O2Bubble, may be used.

By such a microbubble generator, bubbles having a diameter of several microns to several hundreds microns are primarily generated inside the monomer composition or aqueous solution. However, when the surfactant is absent or only a small amount is present, the resulting bubbles do not have a long holding time, and thus it is difficult to form a sufficient porous structure.

According to an embodiment of the present invention, inorganic fine particles are added to the monomer composition or aqueous solution in which bubbles are generated, and fine bubbles are generated using an ultrasonic device (ultrasonication) for the monomer composition or aqueous solution into which the inorganic fine particles are added. .

As described above, inorganic fine particles are added to the monomer composition or aqueous solution in which micro-sized bubbles are generated, and bubbles are again generated using an ultrasonic device, so that the previously generated micro-sized bubbles are several nanometers to hundreds of nanometers in size. It is changed to microbubbles, and the microbubbles generated due to the inorganic fine particles adhering to these bubbles can be maintained in a stable form for a long time.

According to an embodiment of the present invention, the inorganic fine particles may include at least one selected from the group consisting of silica, clay, alumina, silica-alumina composite, and titania. The inorganic fine particles may be used in powder form or liquid form, and in particular, silica powder, alumina powder, silica-alumina powder, titania powder, or nano silica solution may be used.

In addition, the particle diameter of the inorganic fine particles may be tens to hundreds of nanometers in size, about 500 nm or less, or about 300 nm or less, and about 10 nm or more, or about 20 nm or more, or about 40 nm or more. When the particle diameter of the inorganic fine particles is too small, the generation of bubbles is small, and when the particle diameter of the inorganic fine particles is too large, the formation of bubbles may be rather suppressed.

In addition, the inorganic fine particles may be added in a concentration of about 0.05 parts by weight or more, or about 0.1 parts by weight or more, and about 1 part by weight or less and about 0.5 parts by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the amount of the inorganic fine particles is too small, the absorption rate may be slow, and if the amount of the inorganic fine particles is too large, the transmittance properties may be deteriorated. From this point of view, it may be preferable to use in the range of parts by weight.

As for the ultrasonic device, a commercially available device may be used without limitation, and a separate ultrasonic device may be used, or the same device may be used when the ultrasonic device is built into the microbubble generator previously used. Preferably, O2B-750S (with built-in ultrasonic wave generator) from O2Bubble is used.

By such an ultrasonic device, microbubbles having a size of several nanometers to several hundreds of nanometers may be generated inside the monomer composition or aqueous solution. In addition, since the inorganic fine particles previously introduced are attached to the periphery of the microbubbles, the generated microbubbles can be more stably maintained during the polymerization process to be described later, helping to form a porous structure of the super absorbent polymer, and also having a gel strength above a certain level. Can be maintained.

On the other hand, after forming microbubbles in the monomer composition or aqueous solution by the above-described method, the monomer composition is crosslinked and polymerized to form a hydrogel polymer.

According to an embodiment of the present invention, when fine bubbles are formed in a separate aqueous solution without directly generating bubbles in the monomer composition, the bubble solution, which is an aqueous solution in which the fine bubbles are generated, is mixed with the above-described monomer composition and then crosslinked. Polymerization to form a hydrogel polymer.

Formation of the 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. However, in order to perform polymerization while stably maintaining microbubbles in the monomer composition formed by the above-described method, that is, to form a polymer having a more developed porous structure, the crosslinking polymerization is more preferably performed by aqueous solution polymerization. Do.

In addition, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the type of polymerization energy source.In the case of performing the thermal polymerization, the polymerization method can be performed in a reactor having a stirring axis such as a kneader, and photopolymerization is performed. In some cases, it may be carried out in a reactor equipped with a movable conveyor belt.

For example, the monomer composition may be added to a reactor such as a kneader equipped with a stirring shaft, and hot air is supplied thereto, or the reactor is heated to perform thermal polymerization to obtain a hydrogel polymer. At this time, the hydrogel polymer discharged to the reactor outlet according to the shape of the stirring shaft provided in the reactor may be obtained as particles of several millimeters to several centimeters. Specifically, the resulting hydrogel polymer may 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 (weight average) particle diameter of 2 to 50 mm may be obtained.

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

At this time, the moisture content of the hydrogel polymer obtained by this method may be 40 to 80% by weight. On the other hand, throughout the present specification, "water content" refers to a value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer as the content of moisture occupied by the total weight of the hydrogel polymer. Specifically, it is defined as a calculated value 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 increasing 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 increase step, and the moisture content is measured.

On the other hand, after preparing the hydrogel polymer by the above-described method, drying and pulverizing the hydrogel polymer may be performed. Before such drying, first, the step of preparing a hydrogel polymer having a small average particle diameter by coarsely pulverizing the hydrogel polymer may be performed first.

In this coarse pulverization step, the hydrogel polymer may be pulverized to 1.0 mm to 2.0 mm.

The grinder used for coarse grinding 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.

On the other hand, after the selective coarse pulverization, the hydrogel polymer may be dried. This drying temperature may be 50 to 250 ℃. If the drying temperature is less than 50°C, the drying time may be too long and the physical properties of the finally formed super absorbent polymer may be deteriorated.If the drying temperature exceeds 250°C, only the polymer surface may be excessively dried, resulting in fine powder. In addition, there is a concern that physical properties of the finally formed super absorbent polymer may be deteriorated. More preferably, the drying may be performed at a temperature of 150 to 200°C, more preferably 160 to 190°C. Meanwhile, the drying time may be performed for 20 minutes to 15 hours in consideration of process efficiency, etc., but is not limited thereto.

As long as it is commonly used in the drying process, it may be selected and used without limitation of 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 moisture content of the polymer after such a drying step may be 0.05 to 10% by weight.

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

The polymer powder obtained after the pulverization step may have a particle diameter of 150 to 850 μm. The pulverizer used to pulverize with such a particle size is specifically, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, and a disk. Mill (disc mill) or jog mill (jog mill) may be used, but is not limited to the above-described example.

And, in order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed.

This classification step may be performed by a method of separating, for example, normal particles having a particle diameter of 150 to 850 μm and fine or large particles outside the particle diameter range.

This classification step can be carried out using a standard sieve according to a general method for classifying a super absorbent polymer.

A base resin powder having such a particle diameter, that is, a particle diameter of 150 to 850 μm, may be commercialized through a surface crosslinking reaction step to be described later.

On the other hand, after proceeding to the above classification, as a step of crosslinking the surface of the base resin powder, in the presence of a surface crosslinking liquid containing a surface crosslinking agent, heat treatment of the base resin powder to perform surface crosslinking Resin can be produced.

Here, the kind of the surface crosslinking agent contained in the surface crosslinking liquid 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, propanediol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol trimethylol It may be one or more compounds selected from the group consisting of propane, pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride.

At this time, the content of the surface cross-linking agent may be appropriately adjusted according to the type or reaction conditions thereof, and preferably may be adjusted to 0.001 to 5 parts by weight based on 100 parts by weight of the base resin powder. If the content of the surface crosslinking agent is too low, the surface crosslinking may not be properly introduced, and the physical properties of the final super absorbent polymer may be deteriorated. On the contrary, if the surface crosslinking agent is used in an excessively large amount, the water absorbing power of the super absorbent polymer may be rather lowered due to an excessive surface crosslinking reaction, which is not preferable.

In addition, the surface crosslinking liquid 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 an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin.

In addition, the surface crosslinking liquid may further include a thickener. If the surface of the base resin powder is further crosslinked in the presence of a thickener in this way, degradation of 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, and psyllium seed gum, etc., and specific examples of the cellulose-based thickener include hydroxypropylmethylcellulose, carboxymethylcellulose, methylcellulose , Hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose and methylhydroxypropylcellulose, etc. I can. On the other hand, specific examples of the hydroxy-containing polymer include polyethylene glycol and polyvinyl alcohol.

On the other hand, in order to perform the surface crosslinking, a method of mixing the surface crosslinking solution and the base resin in a reaction tank, spraying a surface crosslinking solution onto the base resin, and surface crosslinking with the base resin in a continuously operated mixer. A method of continuously supplying and mixing the liquid may be used.

In addition, the surface crosslinking may be performed under a temperature of 100 to 250°C, and may be continuously performed after the drying and pulverizing steps performed 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, in order to induce a surface crosslinking reaction of a minimum limit and to prevent physical properties from deteriorating due to damage to the polymer particles during excessive reaction, the above-described surface crosslinking reaction may be performed.

In addition, in order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the surface crosslinking step, a separate process of classifying the super absorbent polymer powder according to the particle diameter using a sieve may be performed. By this classification process, the superabsorbent polymer having a particle diameter of 150 to 850 µm may be 90% by weight or more, or 92% by weight or more, or 95% by weight or more.

In addition, particles having a particle diameter of 300 μm or less may be included in an amount of 20% by weight or less, or 15% by weight or less.

As the superabsorbent polymer prepared as described above has a highly developed porous structure, it can exhibit an improved absorption rate, and also maintain excellent properties including gel strength and various physical properties.

For example, the superabsorbent polymer prepared as described above has a vortex time of 35 seconds or less, or 30 seconds or less, or 26 seconds or less, or 22 seconds or less, or 20 seconds or less, while 5 It may be more than a second, or more than 8 seconds, or more than 10 seconds.

In addition, the super absorbent polymer prepared as described above has a 5 minute Gel-AUL at 0.3 psi of 19 g/g or more, or 20 g/g or more or 21 g/g or more, and 24 g/g or less, or It may be less than or equal to 23 g/g.

In addition, the superabsorbent polymer prepared as described above may have a surface tension of 68 mN/m or more, or 69 mN/m or more or 70 mN/m or more, and 72 mN/m or less, or 71 mN/m or less. .

In addition, the super absorbent polymer prepared as described above has a water holding capacity (CRC) of 25 g/g or more, or 28 g/g or more, or 29 g/g or more, as measured according to EDANA method WSP 241.3, and 35 g /g or less, or 34g/g or less, or 33g/g or less.

Thus, according to another embodiment of the present invention, at least a part of the base resin powder comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having a neutralized acidic group; And a surface crosslinked layer formed on the base resin powder, wherein the crosslinked polymer is further crosslinked through a surface crosslinking agent, wherein the superabsorbent resin has a vortex time by a vortex method. It is 5 to 35 seconds, and provides a super absorbent polymer having a 5 minute Gel-AUL of 19 to 24 g/g at 0.3 psi.

The superabsorbent polymer according to another embodiment of the present invention may exhibit a very improved absorption rate defined as a vortex absorption rate of 35 seconds or less, which was not previously achieved, and furthermore, non-use of a foaming agent and/or a surfactant Or, as it is manufactured in a reduced amount, it is possible to maintain excellent surface tension and gel strength.

In the superabsorbent polymer, the absorption rate can be measured by measuring the time (time, unit: second) at which the vortex of the liquid disappears due to rapid absorption when the superabsorbent polymer is added to physiological saline and stirred. It can be, and it can be measured with reference to the method described in more detail in the following examples.

The absorption rate of the super absorbent polymer may be 35 seconds or less, or 30 seconds or less, or 26 seconds or less, or 22 seconds or less, or 20 seconds or less, and 5 seconds or more, or 8 seconds or more, or 10 seconds or more.

In addition, the super absorbent polymer may have a high absorption capacity of 19 to 24 g/g for 5 minutes of Gel-AUL at 0.3 psi. More specifically, the 5-minute Gel-AUL at 0.3 psi of the super absorbent polymer of the present invention is 19 g/g or more, or 20 g/g or more or 21 g/g or more, while 24 g/g or less, or 23 g/ It may be less than or equal to g. The 5 minutes Gel-AUL at 0.3 psi can be measured according to the method described in Examples to be described later. The 0.3 psi 5-minute gel-AUL means the ability to absorb a large amount of water continuously within a short time under 0.3 psi pressure.

In addition, according to an embodiment of the present invention, the super absorbent polymer may have a surface tension of 68 to 72 mN/m. As described above, the superabsorbent polymer of the present invention does not use a foaming agent and/or a surfactant, or has a high surface tension by using only a very small amount even if it is used, and thus leakage can be significantly reduced. More specifically, the surface tension of the superabsorbent polymer of the present invention may be 68 mN/m or more, or 69 mN/m or more, or 70 mN/m or more, and 72 mN/m or less, or 71 mN/m or less. The surface tension may be measured according to the method described in Examples to be described later.

In addition, according to an embodiment of the present invention, the super absorbent polymer has a water holding capacity (CRC) of 25 g/g or more, or 28 g/g or more, or 29 g/g or more, measured according to the EDANA method WSP 241.3. Meanwhile, it may have a range of 35 g/g or less, or 34 g/g or less, or 33 g/g or less. This water holding capacity may reflect the excellent absorption capacity of the super absorbent polymer.

In addition, the super absorbent polymer of the other embodiment may have a pressure absorption capacity (AUL) of 0.9 psi measured according to the EDANA method WSP 242.3 of 16 to 23 g/g, or 18 to 21 g/g. As this range is satisfied, the super absorbent polymer may exhibit excellent water absorption and moisture retention properties even under pressure.

In addition, according to an embodiment of the present invention, the super absorbent polymer may have a particle diameter of 150 to 850 μm in a superabsorbent polymer having a particle diameter of 90% by weight or more, 92% by weight or more, or 95% by weight or more based on the total weight.

In addition, the super absorbent polymer may have a gel bed transmittance (GBP) of 25 to 50 darcy, or 30 to 48 darcy, or 35 to 45 darcy. It can show liquidity.

In addition, the super absorbent polymer may have a bulk density of 0.50 to 0.65 g/ml, or 0.55 to 0.62 g/ml, or 0.56 to 0.61 g/ml.

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

<Example>

Preparation of super absorbent polymer

Example 1

A solution in which 8.6 g of IRGACURE 819 initiator diluted to 0.5% by weight in acrylic acid (80 ppmw based on the monomer) and 12.3 g of polyethylene glycol diacrylate (PEGDA, Mw = 400) diluted in 20% by weight in acrylic acid are mixed (solution A ) Was prepared.

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

In addition, 832 g of a 25% by weight caustic soda solution (solution C) was gradually added dropwise to the glass reactor and mixed. After confirming that the temperature of the mixed solution was increased to about 72°C or higher by the neutralization heat, the mixed solution was waited for cooling. In the thus obtained mixed solution, the degree of neutralization of acrylic acid was about 70 mol%.

Separately, water was added to a microbubbler (O2 Bubble Co., OB-750S) circulating at a flow rate of 500 kg/h per hour to prepare a D solution in which bubbles were generated. Silica was added thereto, and an F solution was prepared by placing it in an ultrasonic device (O2 Bubble Co., OB-750S). Then, when the temperature of the neutralized mixed solution was cooled to about 45° C., the solution F prepared in advance was injected into the mixed solution and mixed. At this time, the silica was 0.05 parts by weight based on 100 parts by weight of the mixed solution.

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

Then, the cut sheet was manufactured into a crumb by using a meat chopper and through a chopping process. The average particle size of the prepared crumb was 1.5 mm.

Then, the powder (crump) was dried in an oven in which the air volume can be adjusted up and down. In order that the moisture content of the dried powder is less than about 2% by weight, hot air at 180° C. is flowed from the bottom to the top for 15 minutes, and then flows from the top to the bottom for 15 minutes to remove the crumb. Dry uniformly. The dried powder was pulverized with a grinder and then classified to obtain a base resin having a size of 150 to 850 μm.

Thereafter, to 100 g of the prepared base resin, 4.5 g of water, 1 g of ethylene carbonate, 0.05 g of Aerosil 200 (Aerosil 200, Evonik), 0.25 g of a 20% by weight aqueous silica (Snowtex, ST-O) solution were added. After the mixed crosslinking agent solution was mixed, a surface crosslinking reaction was performed at 190°C for 30 minutes. Then, the obtained product was pulverized and a surface crosslinked superabsorbent polymer having a particle diameter of 150 to 850 µm was obtained using a sieve. A super absorbent polymer was prepared by further mixing 0.1 g of Aerosil 200 to the obtained super absorbent polymer in a dry manner.

Example 2

From Example 1 to the preparation of the neutralizing solution, it was the same as in Example 1.

Separately, an aqueous solution containing sodium dodecylsulfate diluted in water was added to a microbubbler (O2 Bubble Co., OB-750S) circulating at a flow rate of 500 kg/h per hour to generate bubbles. Was prepared. At this time, the content of sodium dodecyl sulfate in the D solution was 10 ppmw based on the total weight of the acrylic acid. Silica was added thereto and placed in an ultrasonic device (O2 Bubble Co., OB-750S) to prepare a F solution. Then, when the temperature of the neutralized mixed solution was cooled to about 45° C., the solution F prepared in advance was injected into the mixed solution and mixed. At this time, the silica was 0.05 parts by weight based on 100 parts by weight of the acrylic acid.

Subsequent processes were carried out in the same manner as in Example 1 to prepare a super absorbent polymer.

Example 3

In Example 2, a superabsorbent polymer was prepared in the same manner as in Example 2, except that the content of sodium dodecyl sulfate in the D solution was 50 ppmw based on the total weight of acrylic acid.

Example 4

In Example 2, a superabsorbent polymer was prepared in the same manner as in Example 2, except that the content of sodium dodecyl sulfate in the D solution was 100 ppmw based on the total weight of the acrylic acid.

Comparative Example 1

A solution in which 8.6 g of IRGACURE 819 initiator diluted to 0.5% by weight in acrylic acid (80 ppmw based on the monomer) and 12.3 g of polyethylene glycol diacrylate (PEGDA, Mw = 400) diluted in 20% by weight in acrylic acid are mixed (solution A ) Was prepared.

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

In addition, 832 g of a 25% by weight caustic soda solution (solution C) was gradually added dropwise to the glass reactor and mixed. After confirming that the temperature of the mixed solution was increased to about 72°C or higher by the neutralization heat, the mixed solution was waited for cooling. In the thus obtained mixed solution, the degree of neutralization of acrylic acid was about 70 mol%.

Meanwhile, sodium dodecylsulfate was diluted in water to prepare a D solution. At this time, the content of sodium dodecyl sulfate in the D solution was 200 ppmw based on the total weight of the acrylic acid. In addition, 30 g of an E solution obtained by diluting sodium bicarbonate to 4% by weight in water was prepared. Then, when the temperature of the neutralized mixed solution was cooled to about 45° C., previously prepared D and E solutions were injected and mixed into the neutralized mixed solution.

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

Then, the cut sheet was manufactured into a crumb by using a meat chopper and through a chopping process. The average particle size of the prepared crumb was 1.5 mm.

Then, the powder (crump) was dried in an oven in which the air volume can be adjusted up and down. In order that the moisture content of the dried powder is less than about 2% by weight, hot air at 180° C. is flowed from the bottom to the top for 15 minutes, and then flows from the top to the bottom for 15 minutes. Dry uniformly. The dried powder was pulverized with a grinder and then classified to obtain a base resin having a size of 150 to 850 μm.

Thereafter, to 100 g of the prepared base resin, 4.5 g of water, 1 g of ethylene carbonate, 0.05 g of Aerosil 200 (Aerosil 200, Evonik), 0.25 g of a 20% by weight aqueous silica (Snowtex, ST-O) solution were added. After the mixed crosslinking agent solution was mixed, a surface crosslinking reaction was performed at 190°C for 30 minutes. Then, the obtained product was pulverized and a surface crosslinked superabsorbent polymer having a particle diameter of 150 to 850 µm was obtained using a sieve. A super absorbent polymer was prepared by further mixing 0.1 g of Aerosil 200 to the obtained super absorbent polymer in a dry manner.

Comparative Example 2

From Comparative Example 1 to the preparation of the neutralizing solution, it was the same as in Comparative Example 1.

Separately, an aqueous solution containing sodium dodecylsulfate diluted in water was added to a microbubbler (O2 Bubble Co., OB-750S) circulating at a flow rate of 500 kg/h per hour to create a bubble D solution. Was prepared. At this time, the content of sodium dodecyl sulfate in the D solution was 200 ppmw based on the total weight of the acrylic acid. Then, when the temperature of the neutralized mixed solution was cooled to about 45° C., the D solution prepared in advance was injected into the mixed solution and mixed.

Subsequent processes were carried out in the same manner as in Comparative Example 1 to prepare a super absorbent polymer.

Comparative Example 3

In Comparative Example 2, a super absorbent polymer was prepared in the same manner as in Comparative Example 2, except that 0.05 parts by weight of silica was added to 100 parts by weight of acrylic acid to the D solution.

Comparative Example 4

From Comparative Example 1 to the preparation of the neutralizing solution, it was the same as in Comparative Example 1.

Separately, an aqueous solution containing sodium dodecylsulfate diluted in water was added to a microbubbler (O2 Bubble Co., OB-750S) circulating at a flow rate of 500 kg/h per hour to create a bubble D solution. Was prepared. At this time, the content of sodium dodecyl sulfate in the D solution was 200 ppmw based on the total weight of the acrylic acid. This D solution was put into an ultrasonic device (O2 Bubble Co., OB-750S) to prepare a F solution. Then, when the temperature of the mixed solution was cooled to about 45° C., the F solution prepared in advance was injected into the mixed solution and mixed.

Subsequent processes were carried out in the same manner as in Comparative Example 1 to prepare a super absorbent polymer.

<Experimental Example>

Evaluation of physical properties of super absorbent polymer

The physical properties of the super absorbent polymer prepared in the above Examples and Comparative Examples were evaluated by the following method, and the results are shown in Table 1.

(1) Bulk density:

About 100 g of the super absorbent polymer was placed in a funnel-type bulk density measuring device, flowed down into a 100 ml container, and the weight of the super absorbent polymer entered into the container was measured. The bulk density was calculated as (super absorbent polymer weight)/(container volume, 100 ml). (Unit: g/ml).

(2) absorption rate (Vortex time)

The absorption rate of the superabsorbent polymers of Examples and Comparative Examples was measured in seconds according to the method described in International Patent Publication No. 1987-003208.

Specifically, for the absorption rate (or vortex time), 2 g of superabsorbent resin was added to 50 mL of physiological saline at 23°C to 24°C, and a magnetic bar (diameter 8 mm, length 31.8 mm) was stirred at 600 rpm to vortex ( vortex) was calculated by measuring the time until disappearance in seconds.

(3) Centrifuge Retention Capacity (CRC)

The water holding capacity of each resin was measured according to EDANA WSP 241.3.

Specifically, from the resin obtained through the Examples and Comparative Examples, respectively, to obtain a resin classified through a sieve #30-50. This resin W ₀ (g) (about 0.2 g) was evenly put in a nonwoven bag and sealed, and then immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes elapsed, water was removed from the bag for 3 minutes under the condition of 250 G using a centrifuge, and the mass W ₂ (g) of the bag was measured. Moreover, after performing the same operation without using a resin, the mass W ₁ (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following equation.

[Equation 1]

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

(4) Absorbency under load (AUL)

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

First, in the measurement of the absorbency under pressure, the resin fraction in the CRC measurement was used.

Specifically, a 400 mesh stainless steel mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm. The piston that can uniformly spray the water absorbent resin W ₀ (g) (0.16 g) on the wire mesh under the conditions of room temperature and humidity of 50% and uniformly apply a load of 0.9 psi on it is slightly smaller than the outer diameter of 25 mm. 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 PET dish, and a physiological saline solution composed of 0.9 wt% sodium chloride was at the same level as the upper surface of the glass filter. One sheet of filter paper with a diameter of 90 mm was mounted on it. The measuring device was placed on a filter paper, and the liquid was absorbed for 1 hour under load. After 1 hour, the measuring device was lifted and the weight W ₄ (g) was measured.

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

[Equation 2]

AUL(g/g) = [W ₄ (g)-W ₃ (g)]/W ₀ (g)

(5) 0.3 psi 5min Gel-AUL (Absorbency under Load)

Among the super absorbent polymers to be measured, the super absorbent polymers that pass through the US standard 30 mesh screen and remain on the US standard 50 mesh screen are selected. For super absorbent polymers having a particle diameter of 300 µm to 600 µm, Gel-AUL is used. Measured.

Specifically, a 400 mesh stainless steel mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm. The piston that can uniformly spray the water absorbent resin W ₀ (g) (0.16 g) on the wire mesh under the conditions of room temperature and humidity of 50%, and uniformly apply a load of 0.3 psi on it is slightly smaller than the outer diameter of 25 mm. 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.

Subsequently, the physiological saline solution was absorbed under 0.3 psi pressure for 5 minutes, and then vacuum desorbed for 30 seconds under 5 psi under vacuum to remove the physiological saline solution existing between the gel and the gel, and the weight of the measuring device including the physiological saline solution containing the gel intact. W ₄ (g) was measured.

Using each mass thus obtained, a 5-minute gel-AUL (g/g) of 0.3 psi was calculated according to Equation 2 below.

[Equation 2]

0.3 psi for 5 minutes gel-AUL(g/g) = [W ₄ (g)-W ₃ (g)]/ W ₀ (g)

In Equation 2,

W ₀ (g) is the initial weight (0.16 g) of the super absorbent polymer,

W ₃ (g) is the sum of the initial weight of the super absorbent polymer and the weight of the device capable of applying a 0.3 psi load to the super absorbent polymer (g),

W ₄ (g) absorbs physiological saline for 5 minutes under a pressure of 0.3 psi, and vacuum desorption under 5 psi for 30 seconds under vacuum, and then a weight of the super absorbent polymer and a 0.3 psi load can be applied to the super absorbent polymer. It is the sum of the weights of the devices in grams.

(6) Surface tension (S/T)

The surface tension of the liquid was measured using a Fisher tensiometer. The measurement method is as follows. About 150g of 0.9 wt% brine is put in a 250ml beaker, and a 2inch deep vortex is made while stirring with a magnetic stirrer.

Then, 1.0±0.01 g of a sample is accurately weighed and added to the stirring solution. When the stirring time elapses for 3 minutes, stop stirring, remove the stirring rod with clean tweezers, and leave for at least 15 minutes so that the gel of the sample sinks to the bottom. After leaving for 15 minutes, put the tip of the pipette just under the surface of the emulsion and draw out enough solution.

Transfer the emulsion to a clean sample cup. After placing the sample cup containing the emulsion on the sample table, set the dial to zero.

Fix a clean platinum-iridium ring (P-I ring) to a tension gauge with a scale. Raise the sample table by turning the bottom handle clockwise until it is submerged under the surface of the P-I Ring fluid.

After soaking the P-I Ring for about 35 seconds, loosen the rotation pin and let it hang freely. Turn the floor handle until the reference arm is parallel to the line on the mirror. Slowly lift the P-I Ring at a constant rate.

Record the number on the front dial when it leaves the surface of the P-I Ring fluid. This is the surface tension expressed in dyne/cm2. Calculate the actual surface tension value by correcting the measured surface tension value.

Actual surface tension = P x F 20

P = measured surface tension (scale read from dial)

F = adjusted equation

R = radius of the ring

r = radius of ring rod

C = circumference of the ring

(7) Gel bed transmittance (GBP)

The free-swelling gel bed permeability (GBP) of the superabsorbent polymers of Examples and Comparative Examples with respect to physiological saline was determined by using the apparatus shown in FIGS. 1 to 3 of 2014-7018005, and the specification of the 2014-7018005 It was measured according to the method described in.

Bulk density
(g/ml) Vortex (sec) Surface tension
(mN/m) CRC
(g/g) 0.3 psi 5min Gel AUL
(g/g) GBP
(darcy) 0.9 AUL (g/g) Example 1 0.63 35 71 30 19.8 50 19.5 Example 2 0.61 25 70.8 30.2 21.8 47 18.3 Example 3 0.57 20 71 30.4 21.5 40 17.8 Example 4 0.57 18 70.5 30.1 22.2 33 17.0 Comparative Example 1 0.62 45 65 30.1 16.5 47 19.0 Comparative Example 2 0.60 40 64 30.4 17 36 18.0 Comparative Example 3 0.60 42 65 30.2 19 39 18.5 Comparative Example 4 0.57 37 67 30 19.5 30 17.4

Referring to Table 1, it was confirmed that Examples 1 to 4 had an improved absorption rate when exhibiting excellent gel strength and surface tension compared to Comparative Examples 1 to 4.

On the other hand, Comparative Example 1, in which bubbles were generated without a mechanical foaming process, was shown to have a gel AUL and absorption rate for 5 minutes that were much lower than those of the Examples even though a large amount of foaming agent and surfactant were used. Comparative Examples 2 to 3, in which the microbubble generation step by ultrasonic waves was not performed, had an absorption rate as low as 40 seconds or more, and when the second-step bubble generation step was performed without adding inorganic fine particles, Comparative Example 4 is Comparative Example 2 or The absorption rate was slightly faster than that of 3, but the absorption rate was not improved to the level of the Example. In addition, in Comparative Examples 1 to 4, the surface tension was lowered to less than 68 mN/m by using a large amount of surfactant, whereby the possibility of urine leakage was expected to be high when applied to a diaper.

Claims (19)

Preparing a monomer composition comprising a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator having at least partially neutralized acidic groups;
Generating air bubbles in the aqueous solution using a microbubble generator;
Introducing inorganic fine particles into the aqueous solution in which bubbles are generated, and generating fine bubbles using an ultrasonic device (ultrasonication);
Mixing the aqueous solution in which the microbubbles are generated and the monomer composition, followed by crosslinking polymerization to form a hydrogel polymer;
Drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; And
In the presence of a surface crosslinking agent, the 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.
The method of claim 1,
The inorganic fine particles are silica (silica), clay (clay), alumina, silica-alumina composite, and a method of producing a super absorbent polymer comprising at least one selected from the group consisting of titania.
The method of claim 1,
The inorganic fine particles are added in an amount of 0.05 to 1 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer.
The method of claim 1,
The monomer composition or aqueous solution further comprises a surfactant, a method for producing a super absorbent polymer.
The method of claim 4,
The surfactant comprises an anionic surfactant or a nonionic surfactant, a method for producing a super absorbent polymer.
The method of claim 4,
The surfactant is contained in a concentration of 150 ppmw or less based on the total weight of the water-soluble ethylenically unsaturated monomer, a method for producing a super absorbent polymer.
The method of claim 1,
The monomer composition does not contain a foaming agent, a method for producing a super absorbent polymer.
The method of claim 1,
The water-soluble ethylenically unsaturated monomer is a compound represented by the following formula (1), a method for producing a super absorbent polymer:
[Formula 1]
R ₁ -COOM ¹
In 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.
The method of claim 1,
The super absorbent polymer has a vortex time of 5 to 35 seconds according to the vortex method.
The method of claim 1,
The super absorbent polymer has a 5 minute Gel-AUL at 0.3 psi of 19 to 24 g/g, a method for producing a super absorbent polymer.
The method of claim 1,
The super absorbent polymer has a surface tension of 68 to 72 mN/m, a method for producing a super absorbent polymer.
The method of claim 1,
The super absorbent polymer has a water holding capacity (CRC) of 25 to 35 g/g measured according to EDANA method WSP 241.3, a method for producing a super absorbent polymer.
A base resin powder containing a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized; And a surface crosslinked layer formed on the base resin powder, wherein the crosslinked polymer is further crosslinked via a surface crosslinking agent,
The super absorbent polymer has a vortex time of 5 to 35 seconds and a 5 minute Gel-AUL at 0.3 psi of 19 to 24 g/g.
The method of claim 13,
A superabsorbent polymer having a surface tension of 68 to 72 mN/m.
The method of claim 13,
The water holding capacity (CRC) measured according to the EDANA method WSP 241.3 is 25 to 35 g / g, super absorbent polymer.
The method of claim 13,
A super absorbent polymer having a particle diameter of 150 to 850 μm is included in an amount of 90% by weight or more based on the total weight, and particles having a particle diameter of 300 μm or less are included in an amount of 20% by weight or less.
The method of claim 13,
The super absorbent polymer is a super absorbent polymer having a gel bed transmittance (GBP) of 25 to 50 darcy.
The method of claim 13,
The super absorbent polymer has a bulk density of 0.50 to 0.65 g/ml.
The method of claim 13,
The super absorbent polymer has a pressure absorption capacity (AUL) of 0.9 psi measured according to the EDANA method WSP 242.3 from 16 to 23 g/g.