WO2020101167A1 - Superabsorbent polymer and preparation method thereof - Google Patents

Abstract

The present invention relates to a superabsorbent polymer and a preparation method thereof. The preparation method of a superabsorbent polymer according to the present invention can provide a superabsorbent polymer having improved rewettability and liquid permeability.

Description

Super absorbent polymer and method for manufacturing the same

Cross-citation with relevant application (s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0139103 filed on November 13, 2018 and Korean Patent Application No. 10-2019-0113734 filed on September 16, 2019. All content disclosed in the literature is incorporated as part of this specification.

The present invention relates to a super absorbent polymer and a method for manufacturing the same. More particularly, it relates to a super absorbent polymer having improved rewet characteristics and liquid permeability, and a method for manufacturing the same.

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 and sanitary napkins, soil repair agents for horticulture, civil engineering, construction materials, nursery sheets, and freshness retention agents in the food distribution field , And 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 absorbency for moisture, etc., and the 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 the shape well even in a volume expanded (swelled) state.

However, it is known that the water retention capacity (CRC), which is a property that shows the basic water absorption and water retention capacity of the superabsorbent polymer, and the pressure absorption capacity (AUP), which exhibits the property of retaining moisture absorbed by external pressure, are difficult to improve together. . This is because, when the overall crosslinking density of the superabsorbent polymer is controlled to be low, the water retention capacity may be relatively high, but the crosslinking structure becomes coarse and the gel strength is lowered, so that the absorption capacity under pressure may be lowered. Conversely, when the absorption capacity under pressure is improved by controlling the crosslinking density to be high, water absorption between the dense crosslinked structures becomes difficult, and thus the basic water retention capacity may be reduced. For the above-mentioned reasons, there is a limit in providing a super absorbent polymer with improved water retention capacity and absorbency under pressure.

However, with the recent thinning of hygiene materials such as diapers and sanitary napkins, higher absorption performance is required for the super absorbent polymer. Among these, the accompanying improvement of water retention capacity and pressure absorption capacity, which are opposite properties, and improvement of liquid permeability, have emerged as important issues.

In addition, pressure may be applied to a hygiene material such as a diaper or a sanitary napkin according to a user's weight. In particular, after the superabsorbent polymer applied to sanitary materials such as diapers or sanitary napkins absorbs the liquid, when a pressure is applied by the user's weight, some liquid absorbed in the superabsorbent polymer is re-wet. And, leakage of urine may occur.

Accordingly, various attempts have been made to suppress this rewetting phenomenon. However, a specific method for effectively suppressing the re-wetting phenomenon has not been proposed.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide a super absorbent polymer and a manufacturing method thereof, in which re-wetting and urine leakage are suppressed.

In order to achieve the above object, according to an aspect of the present invention,

Preparing a base resin having an acidic group and having at least a portion of the acidic group neutralized and an internal crosslinking agent crosslinked and polymerized (step 1);

The base resin, the base resin, an inorganic filler, and an epoxy-based surface crosslinking agent are mixed, but the inorganic filler is first dry-mixed to the base resin, and then the epoxy-based surface crosslinking agent is dissolved in water to form a surface crosslinking solution. Mixing with (step 2); And

Including the step of performing the surface modification to the base resin by heating the mixture of step 2 (step 3),

The epoxy-based surface crosslinking agent comprises a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq. Provide a method.

In addition, according to another aspect of the present invention,

A base resin comprising a crosslinked polymer obtained by crosslinking and polymerizing an acrylic acid monomer in which at least a part of the acidic group is neutralized; And

It is formed on the particle surface of the base resin, and the crosslinked polymer includes a double surface modification layer that is additionally crosslinked through two epoxy-based surface crosslinking agents having different epoxy equivalents,

The surface modification layer includes an inorganic filler,

The two types of epoxy-based surface crosslinking agent include a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq, and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq. Provide resin.

According to the superabsorbent polymer of the present invention and a method for producing the superabsorbent polymer, it is possible to provide a superabsorbent polymer having excellent absorption properties while suppressing rewetting and urine leakage.

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

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

Method of manufacturing a super absorbent polymer according to an embodiment of the present invention,

Preparing a base resin having an acidic group and having at least a portion of the acidic group neutralized and an internal crosslinking agent crosslinked and polymerized (step 1);

Mixing an inorganic filler and an epoxy-based surface crosslinking agent in the base resin, but mixing the inorganic filler first in the base resin dryly, followed by dissolving an epoxy-based surface crosslinking agent in water and mixing in a surface crosslinking solution state ( Step 2); And

Including the step of performing the surface modification to the base resin by heating the mixture of step 2 (step 3),

The epoxy-based surface crosslinking agent includes a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq, and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq.

In the specification of the present invention, "base resin" or "base resin powder" is made of particles or powder by drying and pulverizing a polymer in which a water-soluble ethylenically unsaturated monomer is polymerized, or a surface modification described later or Refers to a polymer without performing a surface crosslinking step.

The hydrogel polymer obtained by the polymerization reaction of an acrylic acid monomer is marketed as a superabsorbent polymer that is a powdery product through processes such as drying, grinding, classification, and surface crosslinking.

In recent years, not only absorbent properties such as absorbency and liquid permeability in a super absorbent polymer, but also how much the dryness of the surface can be maintained in a situation where actual diapers are used has become an important measure of diaper characteristics.

The superabsorbent polymer obtained by the manufacturing method according to an embodiment of the present invention exhibits excellent water absorption performance due to excellent physical properties such as water retention capacity, pressure absorption capacity, and liquid permeability, and remains dry even after being swollen with brine. It has been confirmed that the urine absorbed by the superabsorbent polymer can effectively prevent rewet and urine leakage from re-embedding.

In the method for producing a superabsorbent polymer of the present invention, first, a monomer composition that is a raw material of the superabsorbent polymer has an acidic group and a monomer composition comprising an acrylic acid-based monomer, an internal crosslinking agent, and a polymerization initiator in which at least a portion of the acidic group is neutralized. Polymerization to obtain a hydrogel polymer, dried, pulverized and classified to prepare a base resin (step 1).

This will be described in more detail below.

The monomer composition, which is a raw material of the super absorbent polymer, has an acidic group and includes an acrylic acid-based monomer and a polymerization initiator in which at least a portion of the acidic group is neutralized.

The acrylic acid monomer is a compound represented by Formula 1 below:

[Formula 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 acrylic acid-based monomer includes at least one selected from the group consisting of acrylic acid, methacrylic acid and their monovalent metal salt, divalent metal salt, ammonium salt and organic amine salt.

Here, the acrylic acid monomer may have an acidic group and at least a part 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 acrylic acid-based monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the neutralization degree can be adjusted according to the final physical properties. However, if the degree of neutralization is too high, the neutralized monomer may be precipitated and polymerization may be difficult to proceed smoothly. On the other hand, if the degree of neutralization is too low, it may exhibit properties such as elastic rubber that is not only poorly absorbed but also difficult to handle. have.

The concentration of the acrylic acid-based monomer may be from about 20 to about 60% by weight, preferably from about 40 to about 50% by weight relative to the monomer composition containing the raw material and solvent of the superabsorbent polymer, polymerization time and It may be an appropriate concentration in consideration of reaction conditions and the like. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and economic problems may occur. Conversely, if the concentration is too high, a part of the monomer precipitates or the grinding efficiency of the polymerized hydrogel polymer is low. Such problems may occur in the process and physical properties of the super absorbent polymer may be deteriorated.

The polymerization initiator used in polymerization in the superabsorbent polymer production method of the present invention is not particularly limited as long as it is generally used for the production of superabsorbent polymers.

Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation depending on the polymerization method. However, even by the photopolymerization method, since a certain amount of heat is generated by irradiation with ultraviolet rays or the like and a certain amount of heat is generated as the polymerization reaction that is an exothermic reaction proceeds, a thermal polymerization initiator may be additionally included.

If the photopolymerization initiator is a compound capable of forming radicals by light such as ultraviolet rays, the composition may be used without limitation.

The photopolymerization initiator includes, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal. Ketal), acyl phosphine and one or more selected from the group consisting of alpha-aminoketone. Meanwhile, 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. . For a wider variety of photoinitiators, it is well documented in Reinhold Schwalm's book 'UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)' p115, and is not limited to the examples described above.

The photopolymerization initiator may be included in a concentration of about 0.01 to about 1.0% by weight relative to the monomer composition. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slow, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the super absorbent polymer may be small and the properties may be uneven.

In addition, as the thermal polymerization initiator, one or more selected from the initiator group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator are 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 examples of the azo-based initiator are 2, 2-azobis- (2-amidinopropane) dihydrochloride (2, 2-azobis (2-amidinopropane) dihydrochloride), 2 , 2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride (2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride), 2- (carbamoyl azo) isobutyronitrile (2- (carbamoylazo) isobutylonitril), 2, 2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride (2,2-azobis [2- (2-imidazolin-2- yl) propane] dihydrochloride), 4,4-azobis- (4-cyanovaleric acid) (4,4-azobis- (4-cyanovaleric acid)). More various thermal polymerization initiators are well specified in the Odian book 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.

According to an embodiment of the present invention, the monomer composition includes an internal crosslinking agent as a raw material of a super absorbent polymer. As the internal crosslinking agent, while having at least one functional group capable of reacting with the acrylic acid monomer, a crosslinking agent having at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups capable of reacting with the substituents of the acrylic acid-based monomers and / or the substituents formed by hydrolysis of the monomers may be used.

The internal crosslinking agent is for crosslinking the interior of a polymer in which an acrylic acid monomer is polymerized, and is different from a surface crosslinking agent for crosslinking the surface of the polymer.

Specific examples of the internal crosslinking agent include N, N'-methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, (meth) acrylate, and propylene glycol di (meth) acrylic Rate, 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, pentaerythritol tetra One or more selected from the group consisting of acrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate can be used.

Such an internal crosslinking agent may be included in a concentration of about 0.01 to about 1.0% by weight relative to the monomer composition, thereby crosslinking the polymerized polymer.

In the production method of the present invention, the monomer composition of the super absorbent polymer may further include additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

Raw materials such as an acrylic acid-based monomer, a photopolymerization initiator, a thermal polymerization initiator, an internal crosslinking agent, and an additive having an acidic group and neutralizing at least a portion of the acidic group may be prepared in the form of a solution of a monomer composition dissolved in a solvent.

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

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

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

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the polymerization energy source, and in general, when performing thermal polymerization, it can be carried out in a reactor having a stirring axis such as a kneader, and when performing photopolymerization, it is movable Although it may be carried out in a reactor equipped with a conveyor belt, the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.

For example, as described above, a reactor such as a kneader having a stirring shaft may be supplied with hot air or heated to heat-polymerize the reactor to obtain a hydrogel polymer, depending on the shape of the stirring shaft provided in the reactor, The hydrogel polymer discharged to the reactor outlet may be in the form of several centimeters to several millimeters. Specifically, the size of the hydrogel polymer obtained may vary 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 can be usually obtained.

In addition, when the photopolymerization is performed in a reactor equipped with a movable conveyor belt as described above, the shape of the hydrogel polymer usually obtained may be a hydrogel polymer on a sheet having a belt width. At this time, the thickness of the polymer sheet varies depending on the concentration and the injection rate of the monomer composition to be injected, but it is usually preferable to supply the monomer composition so that a polymer on the sheet having a thickness of about 0.5 to about 5 cm can be obtained. When the monomer composition is supplied to such an extent that the thickness of the polymer on the sheet is too thin, production efficiency is low, which is undesirable. When the thickness of the polymer on the sheet exceeds 5 cm, due to the excessively thick thickness, the polymerization reaction does not occur evenly over the entire thickness. It may not.

At this time, the normal water content of the hydrogel polymer obtained in this way may be about 40 to about 80% by weight. On the other hand, in the present specification, "water content" refers to a value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer as the content of moisture to the total weight of the hydrogel polymer. 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.

Next, a step of drying the obtained hydrogel polymer is performed.

At this time, if necessary, in order to increase the efficiency of the drying step, the step of coarsely pulverizing before drying may be further performed.

At this time, the used grinder is not limited in configuration, but specifically, a vertical cutter (Vertical pulverizer), a turbo cutter (Turbo cutter), a turbo grinder (Turbo grinder), a rotary cutting mill (Rotary cutter mill), cutting Cutter mill, disc mill, shred crusher, crusher, chopper, and disc cutter However, it is not limited to the above-described example.

At this time, the grinding step may be pulverized such that the particle diameter of the hydrogel polymer is about 2 to about 10 mm.

Grinding to a particle diameter of less than 2 mm is not technically easy due to the high water content of the hydrogel polymer, and there may also be a phenomenon in which agglomerated particles are aggregated with each other. On the other hand, when the particle diameter is pulverized to more than 10 mm, the effect of increasing the efficiency of the subsequent drying step is negligible.

Drying is performed on the hydrogel polymer immediately after polymerization, which is pulverized as described above or has not been subjected to a crushing step. At this time, the drying temperature of the drying step may be about 150 to about 250 ℃. When the drying temperature is less than 150 ° C, the drying time is too long and there is a fear that the physical properties of the superabsorbent resin to be formed are lowered. When the drying temperature exceeds 250 ° C, only the polymer surface is dried excessively, and a subsequent grinding process is performed. In the fine powder may be generated, there is a fear that the physical properties of the superabsorbent polymer to be formed finally decreases. Therefore, preferably, the drying may be performed at a temperature of about 150 to about 200 ° C, more preferably at a temperature of about 160 to about 180 ° C.

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

The drying method of the drying step may also be selected and used without limitation, as long as it is commonly used as a drying process for the hydrogel polymer. 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 the drying step may be about 0.1 to about 10% by weight.

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

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

And, in order to manage the physical properties of the superabsorbent polymer powder finally produced after such a pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle diameter may be performed, and the polymer powder may be subjected to a certain weight ratio according to the particle size range. You can classify as possible.

Next, an inorganic filler and an epoxy-based surface crosslinking agent are mixed with the base resin (step 2).

In a general superabsorbent polymer manufacturing method, a surface crosslinking reaction is performed on the pulverized polymer by mixing the dried and pulverized polymer, that is, a surface crosslinking solution containing a surface crosslinking agent in a base resin, and then heating the mixture by heating. Perform.

The surface crosslinking step is a step of inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a surface crosslinking agent, thereby forming a superabsorbent polymer having improved physical properties. Through the surface crosslinking, a surface crosslinking layer (surface modification layer) is formed on the surface of the pulverized polymer particles.

In general, the surface crosslinking agent is applied to the surface of the superabsorbent polymer particles, so that the surface crosslinking reaction occurs on the surface of the superabsorbent polymer particles, which improves the crosslinkability on the surface of the particles without substantially affecting the inside of the particles. Therefore, the surface-crosslinked superabsorbent polymer particles have a higher degree of crosslinking near the surface than from the inside.

Meanwhile, as the surface crosslinking agent, a compound capable of reacting with a functional group of the polymer is used, for example, a polyhydric alcohol compound, an epoxy compound, a polyamine compound, a haloepoxy compound, a condensation product of a haloepoxy compound, an oxazoline compound, a polyvalent metal salt, Or it is known that an alkylene carbonate compound or the like can be used.

Meanwhile, according to the manufacturing method of the present invention, an epoxy-based surface crosslinking agent is used, and two epoxy-based surface crosslinking agents having different epoxy equivalents are mixed and used. When two types of epoxy-based surface crosslinking agents are mixed in this way, a crosslinking layer is formed on the surface of the superabsorbent polymer as a double layer, and accordingly, the water repellent property of the superabsorbent polymer is not deteriorated, and the water passes through quickly. Liquidity can be further improved.

Specifically, in the manufacturing method of the present invention, as the epoxy surface crosslinking agent, a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq are used. do.

In one embodiment, the first epoxy crosslinking agent may have an epoxy equivalent of 110 to 125 g / eq. The first epoxy crosslinking agent is used to obtain an effect of improving the overall absorption property through primary surface crosslinking of the base resin. If the epoxy equivalent of the first epoxy crosslinking agent is less than 100 g / eq, the above-described effect cannot be sufficiently secured.

The first epoxy crosslinking agent is preferably a bifunctional crosslinking agent. When a bifunctional epoxy crosslinking agent is used as the first epoxy crosslinking agent, flexibility of the crosslinking chain can be secured, thereby maximizing the absorption performance of the superabsorbent polymer.

In addition, the content of the first epoxy crosslinking agent may be 0.01 to 0.1 parts by weight, or 0.02 to 0.05 parts by weight based on 100 parts by weight of the base resin. If the content of the first epoxy crosslinking agent is less than 0.01 part by weight based on 100 parts by weight of the base resin, sufficient surface crosslinking may not proceed, and there may be a problem of reduced pressure absorption capacity and liquid permeability. There may be a problem that the wetting characteristics are deteriorated.

Examples of the first epoxy crosslinking agent include one or more selected from the group consisting of ethylene glycol diglycidyl ether and diethylene glycol diglycidyl ether.

The second epoxy crosslinking agent has a higher epoxy equivalent than that of the first epoxy crosslinking agent, and the penetration depth of the second epoxy crosslinking agent is different from that of the first epoxy crosslinking agent upon surface crosslinking of the base resin. Therefore, when surface crosslinking is performed using the first epoxy crosslinking agent and the second epoxy crosslinking agent at the same time, an effect of double crosslinking of the base resin surface is obtained.

In one embodiment, the epoxy equivalent of the second epoxy crosslinking agent is 135 g / eq or more, 150 g / eq or more, or 160 g / eq or more, and may be 195 g / eq or less, or 190 g / eq or less, but is not limited thereto. It does not work.

The content of the second epoxy crosslinking agent may be 0.001 to 0.1 parts by weight, or 0.005 to 0.05 parts by weight based on 100 parts by weight of the base resin. If the content of the second epoxy crosslinking agent is less than 0.001 part by weight based on 100 parts by weight of the base resin, a double surface crosslinking effect cannot be obtained, and if it exceeds 0.1 part by weight, the surface crosslinking strength is too strong, and there may be a problem of deterioration of rewetting properties. have.

Examples of the second epoxy crosslinking agent include glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether and sorbitol polyglycidyl. And one or more selected from the group consisting of sorbitol polyglycidyl ether. The polyglycerol polyglycidyl ether may preferably be triglycerol polyglycidyl ether having three repeating units.

The second epoxy crosslinking agent may preferably include 3 or more or 3 or 4 epoxy functional groups. When using a second epoxy crosslinking agent that satisfies the functional group number, it is possible to additionally improve only the crosslinking strength of the outermost surface of the superabsorbent particles, and accordingly, the liquid permeability and rewetting properties of the superabsorbent resin may be further improved.

When adding the epoxy-based surface crosslinking agent, water may be additionally mixed together and added in the form of a surface crosslinking solution. When adding water, there is an advantage that the surface crosslinking agent can be evenly dispersed in the polymer. At this time, the content of water to be added induces even dispersion of the surface crosslinking agent and prevents agglomeration of the polymer powder, and at the same time, for the purpose of optimizing the surface penetration depth of the surface crosslinking agent, about 1 to about 10 weight by weight of the polymer It is preferably added in a proportion of negative.

Meanwhile, in addition to the above-mentioned surface crosslinking agent, a multivalent metal salt, for example, an aluminum salt, more specifically, may further include at least one selected from the group consisting of sulfate, potassium salt, ammonium salt, sodium salt, and hydrochloride salt of aluminum.

As the polyvalent metal salt is further used, the liquid permeability of the superabsorbent polymer produced by the method of one embodiment can be further improved. The polyvalent metal salt may be added to the surface crosslinking solution together with the surface crosslinking agent, and may be used in an amount of 0.01 to 4 parts by weight based on 100 parts by weight of the base resin.

In addition, in the manufacturing method of the present invention, an inorganic filler is mixed with a base resin before raising the temperature to perform a surface modification reaction, thereby providing an anti-caking effect. In the present invention, the inorganic filler is mixed in a dry mixing method before mixing the surface crosslinking solution, in which case the base resin and the inorganic filler may be more uniformly mixed.

The inorganic filler may be mixed with either hydrophobic or hydrophilic, and for example, silica particles such as fumed silica and precipitated silica may be used, but the present invention is not limited thereto.

In addition, the inorganic filler may be added in a concentration of about 0.01 to about 0.5 parts by weight, or about 0.02 to about 0.2 parts by weight based on 100 parts by weight of the base resin or super absorbent polymer. When the amount of the inorganic filler exceeds 0.5 parts by weight, absorption characteristics such as pressure absorption capacity may be deteriorated, and when it is less than 0.01 parts by weight, there may be no effect of preventing aggregation, and thus it is preferable to use it in the range of parts by weight from this point of view. can do.

On the other hand, the pressure absorption capacity and permeability may be improved by the surface crosslinking reaction, but the rewetting characteristics need to be supplemented.

According to the manufacturing method of the present invention, it is possible to further improve the rewetting property by mixing the base resin with a hydrophobic material in the base resin prior to heating to perform a surface crosslinking reaction by mixing a surface crosslinking agent. In addition, the surface cross-linking efficiency is improved, so that the absorption rate and liquid permeability can be further improved compared to resins that do not use hydrophobic materials.

The hydrophobic material may be a material whose HLB is 0 or more, or 1 or more, or 2 or more as its lower limit, and 6 or less, or 5 or less, or 5.5 or less as its upper limit. In addition, the hydrophobic material is melted during the surface cross-linking reaction and must be located in the surface-modified layer of the base resin, so a material having a melting point below the surface cross-linking reaction temperature may be used.

Hydrophobic materials that can be used include, for example, glyceryl stearate, glycol stearate, magnesium stearate, glyceryl laurate, sorbitan stearate stearate), sorbitan trioleate, or PEG-4 dilaurate, and the like, and preferably glyceryl stearate or glyceryl laurate. The present invention is not limited to this.

The hydrophobic material is distributed in the surface modification layer of the surface of the base resin to prevent the swelling resin particles from agglomerating or agglomerating with each other according to the increased pressure in the process of absorbing the liquid and swelling the superabsorbent resin, and the hydrophobicity on the surface. By imparting, liquid permeation and diffusion can be made easier. Therefore, it can contribute to improving the re-wetting properties of the super absorbent polymer.

The hydrophobic material is at least about 0.001 part by weight, or at least about 0.005 part by weight, or at least about 0.01 part by weight, or less than about 0.5 part by weight, or about 0.3 part by weight or less, or about 0.1 part by weight relative to 100 parts by weight of the base resin It can mix so as to be the following. If the content of the hydrophobic material is too small, it may be insufficient to improve the rewetting properties, and if it is included too much, the base resin and the hydrophobic material may be detached from each other, so that there is no effect of improving rewetting or there may be a problem of acting as an impurity. In the range by weight may be preferred.

The method of mixing the hydrophobic material with the base resin is not particularly limited, but can be more uniformly coated on the superabsorbent polymer particles when mixed in a manner that is mixed with the base resin by dispersing it with the surface crosslinking agent in the surface crosslinking solution. desirable.

Next, a surface modification step is performed on the base resin by heating the mixture of the base resin and the epoxy-based surface crosslinking agent by heating (step 3).

The surface modification step may be performed by heating at a temperature of about 120 to about 190 ° C, preferably about 130 to about 180 ° C for about 10 to about 90 minutes, preferably about 20 to about 70 minutes. If the cross-linking reaction temperature is less than 120 ° C or the reaction time is too short, the surface cross-linking reaction does not occur properly, and thus the permeability may be lowered. If the temperature exceeds 190 ° C or the reaction time is too long, a problem that water retention capacity may be lowered may occur.

The heating means for the surface modification reaction is not particularly limited. The heating medium may be supplied or a heat source may be directly supplied to heat. At this time, as the kind of heat medium that can be used, a heated fluid such as steam, hot air, and hot oil may be used, but the present invention is not limited to this, and the temperature of the heat medium supplied is the means of the heat medium, the rate of temperature increase, and the temperature increase. It can be appropriately selected in consideration of the target temperature. On the other hand, the heat source directly supplied may include a heating method through electricity or a gas, but the present invention is not limited to the above-described example.

By the above surface modification step, a double surface crosslinking structure formed by reacting two different epoxy-based surface crosslinking agents with a functional group of the base resin is formed on the surface of the base resin, and the above-described surface crosslinking structure is used. A surface modification layer evenly distributed with a hydrophobic material and an inorganic filler may be formed.

Therefore, the superabsorbent polymer produced by the manufacturing method of the present invention can have improved rewetting and liquid permeability without deteriorating physical properties such as water retention capacity and pressure absorption capacity due to the dual surface modification layer.

Accordingly, according to another embodiment of the present invention, a base resin comprising a crosslinked polymer in which an acrylic acid monomer in which at least a portion of an acidic group is neutralized is crosslinked; And a double surface modification layer formed on the particle surface of the base resin, wherein the crosslinking polymer is additionally crosslinked through two epoxy-based surface crosslinking agents having different epoxy equivalents, and the surface modification layer is an inorganic filler. Including, the two epoxy-based surface crosslinking agent includes a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq, and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq. Phosphorus, superabsorbent resin is provided.

Detailed descriptions of the method and physical properties of the super absorbent polymer are as described above in the method of manufacturing the super absorbent polymer.

The superabsorbent polymer has a water retention capacity (CRC) of about 25 g / g or more, or about 29 g / g or more, or about 30 g / g or more, and about 40 g / g or less, measured according to EDANA method WSP 241.3. , Or about 38 g / g or less, or about 35 g / g or less.

In addition, the superabsorbent polymer, the pressure absorption capacity (AUP) of 0.3 psi measured in accordance with EDANA method WSP 242.3 is about 20 g / g or more, or about 23 g / g or more, or about 25 g / g or more, and about 37 g / g or less, or about 35 g / g or less, or about 32 g / g or less.

In addition, the superabsorbent polymer may have a vortex time of 40 seconds or less, or 35 seconds or less, or about 32 seconds or less. The smaller the absorption rate, the better the value, so the lower limit of the absorption rate is theoretically 0 seconds, but may be, for example, about 5 seconds or more, or about 10 seconds or more, or about 12 seconds or more.

The absorption rate refers to a time (time, unit: second) in which a vortex of a liquid disappears due to rapid absorption when a superabsorbent resin is added to a physiological saline solution and stirred. The shorter the time, the higher the superabsorbent resin is Can be seen to have a fast initial absorption rate.

In addition, the superabsorbent polymer may have a permeability (unit: second) measured according to Equation 1 below about 35 seconds or less, or about 30 seconds or less. The lower the value of the liquid permeability, the better the theoretical lower limit is 0 seconds, but may be, for example, about 5 seconds or more, or about 10 seconds or more, or about 12 seconds or more.

[Equation 1]

In the above formula 1,

T1 is 0.2 ± 0.0005 g of a superabsorbent polymer sample (300 to 600 μm) classified in a chromatography tube, brine is added to make the volume of the brine 50 ml, and after standing for 30 minutes, the liquid level is 40 ml to 20 The time it takes to reduce to ml, and B is the time it takes for the liquid level to decrease from 40 ml to 20 ml in a saline-filled chromatography tube.

In addition, the superabsorbent polymer may exhibit excellent resorption characteristics while exhibiting excellent absorption characteristics.

More specifically, after 4 g of the superabsorbent polymer is immersed in 200 g of tap water for swelling for 2 hours, the swollen superabsorbent polymer is left on a filter paper for 1 minute under a pressure of 0.75 psi, and then the superabsorbent polymer is absorbed. The re-wetting properties (long-term re-wetting of pressurized tap water), defined as the weight of water that has re-emerged back to the filter paper from may be 1.0 g or less, or 0.9 g or less, or 0.8 g or less. The smaller the weight of the water is, the better the theoretical lower limit is 0 g, but may be, for example, 0.1 g or more, or 0.2 g or more, or 0.3 g or more.

The tap water used in the evaluation of the rewet properties has an electrical conductivity of 140 to 150 μS / cm. Since the electrical conductivity of tap water greatly affects the measurement properties, it is necessary to measure properties such as rewetting using tap water having an equal level of electrical conductivity.

As described above, the superabsorbent polymer of the present invention has an excellent absorbing ability, and even when a large amount of urine is absorbed, rewetting and urine leakage can be suppressed.

The present invention will be described in more detail in the following examples. However, the following examples are only illustrative of the present invention, and the detailed description of the present invention is not limited by the following examples.

<Example>

Preparation of super absorbent polymer

Example 1

(1) Preparation of base resin

In a 3L glass container equipped with a stirrer, nitrogen injector, and thermometer, 518 g of acrylic acid, 3.2 g of polyethyleneglycol (400) diacrylate, and diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide 0.04 After dissolving by adding g, 822.2 g of a 24.5% sodium hydroxide solution was added to prepare a water-soluble unsaturated monomer aqueous solution while continuously introducing nitrogen. The water-soluble unsaturated monomer aqueous solution was cooled to 40 ° C. 500 g of this aqueous solution was added to a container made of stainless steel having a width of 250 mm, a height of 250 mm, and a height of 30 mm, and ultraviolet ray was irradiated (irradiation amount: 10 mV / cm ² ) to perform UV polymerization for 90 seconds to obtain a hydrogel polymer. . After the obtained hydrogel polymer was pulverized to a size of 2 mm * 2 mm, the obtained gel-like resin was spread on a stainless wire gauze having a pore size of 600 μm to a thickness of about 30 mm and dried in a 180 ° C. hot air oven for 30 minutes. The dried polymer thus obtained was pulverized using a grinder, classified by a standard mesh body of ASTM standard, to obtain a base resin having a particle size of 150 to 850 μm.

(2) Preparation of super absorbent polymer

After dry mixing of 0.1 parts by weight of silica with 100 parts by weight of the base resin, 0.02 parts by weight of ethylene glycol diglycidyl ether (epoxy equivalent 113-125 g / eq), glycerol polyglycidyl ether (epoxy equivalent 135-155 g / eq, trifunctional) The surface crosslinking solution containing 0.01 parts by weight, 6.2 parts by weight of water, 0.2 parts by weight of aluminum sulfate, and 0.03 parts by weight of glyceryl stearate (HLB 3.8) is sprayed and mixed, and placed in a container consisting of a stirrer and a double jacket at 140 ° C, 35 The surface crosslinking reaction proceeded for a minute. Subsequently, the surface-treated powder was classified as a standard mesh of ASTM standards to obtain a super absorbent polymer powder having a particle size of 150 to 850 μm.

Example 2

The superabsorbent polymer powder was obtained in the same manner as in Example 1, except that in step (2), glycerol polyglycidyl ether was used in an amount of 0.005 parts by weight based on 100 parts by weight of the base resin.

Example 3

The superabsorbent polymer powder was obtained in the same manner as in Example 1, except that in step (2), glycerol polyglycidyl ether was used in an amount of 0.03 parts by weight based on 100 parts by weight of the base resin.

Example 4

The superabsorbent polymer powder was obtained in the same manner as in Example 1, except that in step (2), glycerol polyglycidyl ether was used in 0.05 parts by weight based on 100 parts by weight of the base resin.

Example 5

In the same manner as in Example 1, except that in step (2), instead of glycerol polyglycidyl ether, polyglycerol polyglycidyl ether (epoxy equivalent 168 g / eq) was used as 0.01 part by weight based on 100 parts by weight of the base resin. A superabsorbent polymer powder was obtained.

Example 6

The same method as in Example 1, except that in step (2), sorbitol polyglycidyl ether (epoxy equivalent 160-190 g / eq) was used as 0.01 part by weight based on 100 parts by weight of the base resin instead of glycerol polyglycidyl ether. As a result, a super absorbent polymer powder was obtained.

Comparative Example 1

(1) Preparation of base resin

In a 3 L glass container equipped with a stirrer, nitrogen injector, and thermometer, 518 g of acrylic acid, 3.2 g of polyethyleneglycol (400) diacrylate, and diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide After dissolving by adding 0.04 g, 822.2 g of a 24.5% sodium hydroxide solution was added to prepare a water-soluble unsaturated monomer aqueous solution while continuously adding nitrogen. The water-soluble unsaturated monomer aqueous solution was cooled to 40 ° C. 500 g of this aqueous solution was added to a container made of stainless steel having a width of 250 mm, a height of 250 mm, and a height of 30 mm, and ultraviolet ray was irradiated (irradiation amount: 10 mV / cm ² ) to perform UV polymerization for 90 seconds to obtain a hydrogel polymer. . After the obtained hydrogel polymer was pulverized to a size of 2 mm * 2 mm, the obtained gel-like resin was spread on a stainless wire gauze having a pore size of 600 μm to a thickness of about 30 mm and dried in a 180 ° C. hot air oven for 30 minutes. The dried polymer thus obtained was pulverized using a grinder, classified by a standard mesh body of ASTM standard, to obtain a base resin having a particle size of 150 to 850 μm.

(2) Preparation of super absorbent polymer

After mixing 0.1 parts by weight of silica with 100 parts by weight of the base resin, 0.02 parts by weight of ethylene glycol diglycidyl ether (epoxy equivalent 113-125 g / eq), 6.2 parts by weight of water, 0.2 parts by weight of aluminum sulfate, glycerol The surface crosslinking solution containing 0.03 parts by weight of reel stearate (HLB 3.8) was sprayed and mixed, and then placed in a container made of a stirrer and a double jacket, the surface crosslinking reaction was performed at 140 ° C for 35 minutes. Subsequently, the surface-treated powder was classified as a standard mesh of ASTM standards to obtain a super absorbent polymer powder having a particle size of 150 to 850 μm.

Comparative Example 2

The superabsorbent polymer powder was obtained in the same manner as in Comparative Example 1, except that in step (2), ethylene glycol diglycidyl ether was used in an amount of 0.03 parts by weight based on 100 parts by weight of the base resin.

Comparative Example 3

In step (2), superabsorbent polymer powder was obtained in the same manner as in Comparative Example 1, except that 0.05 parts by weight of ethylene glycol diglycidyl ether was used in 100 parts by weight of the base resin.

<Experimental Example>

For the superabsorbent polymer prepared in Examples and Comparative Examples, physical properties were evaluated in the following manner.

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

In addition, the tap water used in the evaluation of the re-wet properties was used when measured using Orion Star A222 (Company: Thermo Scientific) with electrical conductivity of 140 to 150 μS / cm.

(1) Centrifuge Retention Capacity (CRC)

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

Specifically, the super absorbent polymer W ₀ (g) (about 0.2 g) was uniformly put in a nonwoven fabric bag, sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the bag was drained for 3 minutes under the condition of 250 G 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]

(2) Absorption speed (Vortex time)

The vortex time was measured in seconds according to the method described in International Publication No. 1987-003208.

Specifically, 2 g of superabsorbent polymer was added to 50 mL of physiological saline at 23 ° C., and a magnetic bar (8 mm in diameter and 30 mm in length) was stirred at 600 rpm to time the time until vortex disappeared. It was calculated by measuring in units.

(3) Absorption Under Pressure (AUP)

The pressure absorption capacity of 0.3 psi of each resin was measured according to EDANA method WSP 242.3.

Specifically, a 400 mesh wire mesh made of stainless steel was mounted on a cylindrical bottom of a plastic having an inner diameter of 60 mm. A piston capable of uniformly spreading super absorbent polymer W ₀ (g) (0.90 g) on a wire mesh under conditions of normal temperature and humidity of 50%, and a piston capable of uniformly applying a load of 0.3 psi thereon is slightly smaller than an outer diameter of 60 mm. It is small and has 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 inside a 150 mm diameter petri dish, and the physiological saline composed of 0.9% by weight 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]

(4) Permeability

The line was marked on the liquid level of 20 ml and 40 ml of the liquid amount in a state where a piston was put in a chromatography tube (F20 mm). Thereafter, water was added in reverse to fill up about 10 ml and washed 2-3 times with brine to prevent bubbles from forming between the glass filter and the bottom of the chromatography tube, and 0.9% brine was added up to 40 ml or more. The piston was placed in the chromatography tube and the lower valve was opened to record the time (B) at which the liquid level decreased from 40 ml to 20 ml mark.

10 ml of brine was left in the chromatography tube, 0.2 ± 0.0005 g of a superabsorbent polymer sample classified (300 to 600 μm) was added, and brine was added to a volume of 50 ml, and then allowed to stand for 30 minutes. Thereafter, an additional piston (0.3 psi = 106.26 g) was placed in the chromatography tube, left for 1 minute, and the time (T1) at which the liquid level decreased from 40 ml to 20 ml mark was recorded by opening the lower valve of the chromatography tube, The time (unit: second) of T1-B was calculated.

(5) Pressurized tap water long-term rewetting (2 hrs)

① Sprinkle evenly with 4 g of superabsorbent resin on a 13 cm diameter petri dish, pour 200 g of tap water and swell for 2 hours.

② Put super absorbent resin swollen for 2 hours on 20 sheets of filter paper (manufacturer: whatman, catalog No. 1004-110, pore size 20-25 μm, diameter 11 cm) and put 11 cm in diameter, 5 kg weight (0.75 psi) Pressurized with for 1 minute.

③ After pressing for 1 minute, the amount of tap water on the filter paper (unit: g) was measured.

Table 1 shows the physical properties of the examples and comparative examples.

Referring to Table 1, it can be seen that Examples 1 to 6 of the present invention all exhibit excellent rewetting properties and liquid permeability. On the other hand, it can be seen that Comparative Examples 1 to 2 using only the first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq have poor liquid-permeability and re-wetting properties than in Examples. That is, when comparing the case where the same amount of epoxy-based surface crosslinking agent was used, it was confirmed that the case of the example exhibited superior liquid permeability and rewetting properties compared to the comparative example.

Claims (14)

1. Preparing a base resin having an acidic group and having at least a portion of the acidic group neutralized and an internal crosslinking agent crosslinked and polymerized (step 1);

   Mixing an inorganic filler and an epoxy-based surface crosslinking agent in the base resin, but mixing the inorganic filler first in the base resin dryly, followed by dissolving an epoxy-based surface crosslinking agent in water and mixing in a surface crosslinking solution state ( Step 2); And

   Including the step of performing the surface modification to the base resin by heating the mixture of step 2 (step 3),

   The epoxy-based surface crosslinking agent comprises a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq. Way.
2. According to claim 1,

   The first epoxy cross-linking agent is contained in 0.01 to 0.1 parts by weight based on 100 parts by weight of the base resin, the second epoxy cross-linking agent is contained in 0.001 to 0.1 parts by weight based on 100 parts by weight of the base resin, a method for producing a super absorbent polymer.
3. According to claim 1,

   The first epoxy cross-linking agent is at least one member selected from the group consisting of ethylene glycol diglycidyl ether and diethylene glycol diglycidyl ether.
4. According to claim 1,

   The second epoxy crosslinking agent is glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether and sorbitol polyglycidyl ether ( sorbitol polyglycidyl ether) is selected from the group consisting of at least one, superabsorbent polymer production method.
5. According to claim 1,

   In step 2, the HLB further comprises a hydrophobic material having 0 to 6, the method for producing a super absorbent polymer.
6. The method of claim 5,

   The hydrophobic material is glyceryl stearate, glycol stearate, magnesium stearate, glyceryl laurate, sorbitan stearate, sorbitan stearate Method for producing a super absorbent polymer comprising at least one member selected from the group consisting of sorbitan trioleate, and PEG-4 dilaurate.
7. The method of claim 5,

   The hydrophobic material is mixed with 0.001 to 0.5 parts by weight based on 100 parts by weight of the base resin, a method for producing a super absorbent polymer.
8. According to claim 1,

   The step 3 is carried out at a temperature of 120 to 190 ℃, super absorbent polymer production method.
9. According to claim 1,

   Step 1 above,

   Polymerizing a monomer composition comprising an acrylic acid-based monomer having an acidic group and at least a part of which is neutralized, an internal crosslinking agent, and a polymerization initiator to form a hydrogel polymer;

   Drying the hydrogel polymer;

   Crushing the dried polymer; And

   Method of producing a super absorbent polymer comprising the step of classifying the pulverized polymer.
10. A base resin comprising a crosslinked polymer obtained by crosslinking and polymerizing an acrylic acid monomer in which at least a part of the acidic group is neutralized; And

    It is formed on the particle surface of the base resin, and the crosslinked polymer includes a double surface modification layer that is additionally crosslinked through two epoxy-based surface crosslinking agents having different epoxy equivalents,

    The surface modification layer includes an inorganic filler,

    The two types of epoxy-based surface crosslinking agent include a first epoxy crosslinking agent having an epoxy equivalent of 100 g / eq or more and less than 130 g / eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 to 200 g / eq. Suzy.
11. The method of claim 10,

    The super absorbent polymer has a super absorbent polymer having a vortex time of 40 seconds or less.
12. The method of claim 10,

    The superabsorbent polymer has a superabsorbent polymer having a permeability (unit: second) of 35 seconds or less measured according to the following Equation 1:

    [Equation 1]

    

    In the above formula 1,

    T1 is 0.2 ± 0.0005 g of a super absorbent polymer sample (300 to 600 μm) classified in a chromatography tube, brine is added to make the volume of the brine 50 ml, and after standing for 30 minutes, the liquid level is 40 ml to 20 The time it takes to reduce to ml, and B is the time it takes for the liquid level to decrease from 40 ml to 20 ml in a saline-filled chromatography tube.
13. The method of claim 10,

    The superabsorbent polymer is a superabsorbent polymer having a centrifugal water retention capacity (CRC) of 25 g / g or more.
14. The method of claim 10,

    The superabsorbent polymer, after immersing the superabsorbent polymer 4 g in 200 g of tap water for 2 hours, and then swelling the swollen superabsorbent polymer on a filter paper for 1 minute under a pressure of 0.75 psi, A superabsorbent polymer having a rewetting characteristic (pressurized tap water long-term rewetting) of 1.0 g or less, defined by the weight of water that has re-extruded from the absorbent resin into the filter paper.