KR20200090672A - Preparation method of super absorbent polymer - Google Patents

Abstract

A super absorbent polymer, according to the present invention, maintains excellent absorbing performance and exhibits excellent dryness, and thus may exhibit excellent performance when preferably used for sanitary products such as diapers.

Description

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

The present invention relates to a method for producing a super absorbent polymer having excellent dryness while maintaining excellent absorbent performance.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb about 500 to 1,000 times its own weight.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 paper diapers for children, soil repair materials for horticulture, civil engineering, construction index materials, nursery sheets, and freshness retention materials in the food distribution field, and It is widely used as a material for poultice.

In most cases, these superabsorbent polymers are widely used in the field of hygiene materials such as diapers and sanitary napkins. Within these hygiene materials, it is common that the superabsorbent polymer is contained in the pulp. However, in recent years, efforts have been made to provide hygiene materials such as diapers of a thinner thickness, and as a part thereof, the content of the pulp is reduced, or further, so-called pulpless diapers, which do not use pulp at all. Development is actively underway.

As such, in the case of a hygiene material in which the content of the pulp is reduced or the pulp is not used, a relatively high superabsorbent polymer is included in a high proportion, and these superabsorbent polymer particles are inevitably included in a multi-layer in the hygiene material. In order for the overall superabsorbent polymer particles contained in multiple layers to absorb liquids such as urine more efficiently, the superabsorbent polymer needs to exhibit a high absorption performance and absorption rate.

To this end, the conventional super absorbent polymer uses a method of lowering the degree of internal crosslinking and increasing the degree of surface crosslinking. However, the method has an aspect in which the absorption rate is increased, but after the superabsorbent polymer swells with the absorbed liquid, a liquid is present on the surface of the superabsorbent polymer, causing a decrease in wearing comfort and causing skin rash. do.

As described above, the degree to which no liquid is present on the surface after the superabsorbent polymer absorbs the liquid is referred to as dryness, and thus, the superabsorbent polymer has excellent dryness without impairing the absorbent performance and absorption rate of the superabsorbent polymer. Development of an absorbent resin is required.

The present invention is to provide a method for producing a superabsorbent polymer having excellent dryness while maintaining excellent absorbent performance.

In order to solve the above problems, the present invention provides the following super absorbent polymer:

A base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group; And

A superabsorbent polymer formed on the base resin powder, wherein the first crosslinked polymer comprises a surface crosslinked layer comprising a second crosslinked polymer further crosslinked via a surface crosslinking agent,

The water-soluble component according to EDANA method WSP 270.2 is 13% by weight or less,

The absorption rate measured according to the Vortex measurement method is 50 seconds or less,

6 hours dryness (dryness) of 1.5 g or less,

Super absorbent polymer.

In addition, the present invention provides the following super absorbent polymers:

A base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group; And

It is formed on the base resin powder, and the first crosslinked polymer comprises a second crosslinked polymer additionally crosslinked via a surface crosslinking agent comprising ethylene glycol diglycidyl ether and a surface crosslinking layer comprising an inorganic filler. As a super absorbent polymer,

The centrifugal water retention capacity (CRC) is 28 g/g or more,

6 hours dryness (dryness) of 1.5 g or less,

Super absorbent polymer.

As described above, the superabsorbent polymer according to the present invention is characterized by low water-soluble component, excellent absorption rate, and excellent dryness. The superabsorbent polymer as described above is possible by controlling the conditions of surface crosslinking of the superabsorbent polymer, as will be described later.

Hereinafter, the present invention will be described in detail.

Super absorbent polymer

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

[Formula 1]

R ₁ -COOM ¹

In Chemical Formula 1,

R ₁ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt.

Preferably, the monomer may be at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids. When acrylic acid or a salt thereof is used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent polymer with improved absorbency. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(metha) )Acrylamide-2-methyl propane sulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene Glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide, and the like can be used.

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

At this time, the neutralization degree of the monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 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 polymerization may be difficult to proceed smoothly. It may exhibit properties such as elastic rubber that are difficult to handle.

In the second crosslinked polymer, the surface of the base resin powder is further crosslinked through a surface crosslinking agent, and the surface crosslinking agent and the surface crosslinking method will be described later.

On the other hand, in the superabsorbent polymer according to the present invention, the water-soluble component according to EDANA method WSP 270.2 is 13% by weight or less. The water-soluble component mainly occurs when a polymer chain forming a network during polymerization of a superabsorbent polymer is short, and the smaller the value, the better. Preferably, the water-soluble component according to EDANA method WSP 270.2 is 12 wt% or less, 11 wt% or less, or 10 wt% or less. In addition, the smaller the value, the better the lower limit of the water-soluble component is theoretically 0 wt%, but for example, 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, or 5 wt% or more.

In addition, in the superabsorbent polymer according to the present invention, the absorption rate measured according to the Vortex measurement method is 50 seconds or less. The absorption rate refers to a time when the vortex of the liquid disappears due to the rapid absorption when the superabsorbent resin is added to the physiological saline solution and stirred, and the rapid absorption rate of the superabsorbent resin may be defined. Preferably, the absorption rate measured according to the Vortex measurement method is 45 seconds or less, 40 seconds or less, or 35 seconds or less. In addition, the smaller the value, the better, and the lower limit of the absorption rate is theoretically 0 seconds, but for example, 10 seconds or more, 20 seconds or more, or 25 seconds or more. In addition, the measurement method of the said Vortex is more concrete in the following Examples.

In addition, the superabsorbent polymer according to the present invention has a dryness of 1.5 hours or less for 6 hours. The dryness of 6 hours refers to the amount of moisture present on the surface after 6 hours, after 2 g of the super absorbent polymer absorbs moisture and swells. The specific measuring method thereof is more concrete in the following examples. Preferably, the dryness for 6 hours is 1.4 g or less, 1.3 g or less, 1.2 g or less, 1.1 g or less, or 1.0 g or less. In addition, the smaller the value, the better, and the lower limit of the 6-hour drying degree is theoretically 0 g, but is 0.1 g or more, or 0.2 g or more, for example.

In addition, the superabsorbent polymer according to the present invention has a centrifugal water retention capacity (CRC) of 30 g or more for physiological saline (0.9 wt% sodium chloride aqueous solution) for 30 minutes or more. More preferably, the centrifugal water retention capacity is 28.5 g/g or more, or 29.0 g/g or more, and 35 g/g or less, 34 g/g or less, or 33 g/g or less. The method for measuring the centrifugal water retention capacity is more concrete in the following examples.

In addition, preferably, the superabsorbent polymer according to the present invention has a pressure absorption capacity (0.3 AUP) of 25 g/g or more under 0.3 psi for physiological saline (0.9 wt% sodium chloride aqueous solution). The method for measuring the pressure absorbing capacity is more concrete in the following examples. More preferably, the 0.3 AUP is 26 g/g or more, 27 g/g or more, or 28 g/g or more, 36 g/g or less, 35 g/g or less, 34 g/g or less, or 33 g /g or less.

Further, preferably, the superabsorbent polymer according to the present invention has a permeability of 10 seconds to 150 seconds. The method of measuring the liquid permeability is further specified in Examples below. Preferably, the liquid permeability is 20 seconds to 100 seconds.

Manufacturing method of super absorbent polymer

The present invention provides a method for producing a superabsorbent polymer, which includes the following steps:

Crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent to form a hydrogel polymer comprising a first crosslinked polymer;

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

In the presence of a surface crosslinking solution containing water and a surface crosslinking agent, the step of heat-treating the base resin powder to crosslink the surface to form superabsorbent polymer particles,

The water and the surface crosslinking agent, respectively, using 3.5 parts by weight or less, and 0.15 parts by weight or less compared to 100 parts by weight of the base resin powder,

Method for producing super absorbent polymer.

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

(Step 1)

Step 1 is a step of forming a hydrogel polymer, which is a step of crosslinking and polymerizing a monomer composition comprising an internal crosslinking agent and a water-soluble ethylenically unsaturated monomer having at least a neutralized acidic group.

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

Further, as the internal crosslinking agent, any compound can be used as long as it allows introduction of crosslinking during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di( Meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth) )Acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, penta Multifunctional crosslinking agents such as erythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, but are not limited thereto.

The internal crosslinking agent may be added at a concentration of about 0.001 to 1% by weight relative to the monomer composition. That is, when the concentration of the internal crosslinking agent is too low, the absorption rate of the resin is lowered and the gel strength may be weakened, which is not preferable. Conversely, when the concentration of the internal cross-linking agent is too high, the absorbency of the resin is lowered, which may make it undesirable as an absorber.

In addition, in step 1, a polymerization initiator generally used in the preparation of a super absorbent polymer may be included. As a non-limiting example, as the polymerization initiator, a thermal polymerization initiator or a photo polymerization initiator may be used depending on the polymerization method, and a thermal polymerization initiator may be used. However, even by the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like and a certain amount of heat is generated according to the progress of the exothermic polymerization reaction, a thermal polymerization initiator may be additionally included.

As the thermal polymerization initiator, one or more compounds selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, as the persulfate-based initiator, sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), ammonium persulfate (Ammonium persulfate; (NH ₄ ) ₂ S ₂ O ₈ ) and the like. In addition, 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 (2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride), 4, For example, 4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)). More various thermal polymerization initiators are disclosed on page 203 of the Odian book "Principle of Polymerization (Wiley, 1981)", which can be referred to.

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

The polymerization initiator may be added in a concentration of about 0.001 to 1% by weight relative to the monomer composition. That is, when the concentration of the polymerization initiator is too low, the polymerization rate may be slow, and residual monomers in the final product may be extracted in large quantities, which is not preferable. Conversely, when the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network are shortened, and thus the content of the water-soluble component is increased and the pressure absorption capacity is lowered, so that the physical properties of the resin may be deteriorated, which is not preferable.

In addition, the monomer composition may further include additives such as blowing agents, surfactants, thickeners, plasticizers, storage stabilizers, and antioxidants, if necessary.

In addition, the foaming agent serves to increase the surface area by foaming during polymerization to form pores in the hydrogel polymer. The foaming agent may be a carbonate, for example, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium Carbonate (calcium bicarbonate), magnesium bicarbonate (magnesiumbicarbonate) or magnesium carbonate (magnesium carbonate) can be used.

In addition, it is preferable to use the blowing agent at 1500 ppmw or less based on the weight of the water-soluble ethylenically unsaturated monomer. When the amount of the foaming agent used exceeds 1500 ppmw, the pores become too large, the gel strength of the super absorbent polymer falls, and the density becomes small, which may cause problems in distribution and storage. In addition, the blowing agent is preferably used in the amount of 500 ppmw or more, or 1000 ppmw or more, based on the weight of the water-soluble ethylenically unsaturated monomer.

In addition, the surfactant induces uniform dispersion of the foaming agent to prevent the gel strength from being lowered or the density from lowering due to uniform foaming during foaming. It is preferable to use an anionic surfactant as the surfactant. Specifically, the surfactant includes SO ₃ ^- anion, and a compound represented by Formula 2 may be used.

[Formula 2]

R-SO ₃ Na

In Chemical Formula 2,

R is alkyl having 8 to 16 carbons.

In addition, the surfactant is preferably used at 300 ppmw or less based on the weight of the water-soluble ethylenically unsaturated monomer. When the amount of the surfactant used exceeds 300 ppmw, the content of the surfactant in the superabsorbent resin increases, which is not preferable. In addition, the surfactant is preferably used at least 100 ppmw, or 150 ppmw or more based on the weight of the water-soluble ethylenically unsaturated monomer.

In addition, such a monomer composition may be prepared in the form of a solution in which raw materials such as the above-described monomer, polymerization initiator, and internal crosslinking agent are dissolved in a solvent.

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

And, the formation of a hydrogel polymer through polymerization of the monomer composition may be performed by a conventional polymerization method, and the process is not particularly limited. As a non-limiting example, the polymerization method is largely divided into thermal polymerization and photo polymerization according to the type of polymerization energy source. When the thermal polymerization is performed, the polymerization method may be performed in a reactor having a stirring axis such as a kneader, and photo polymerization In the case of proceeding, it may proceed in a reactor equipped with a movable conveyor belt.

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

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

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

(Step 2)

The step 2 is a step of forming the base resin powder by drying, grinding, and classifying the hydrogel polymer prepared in step 1, wherein the base resin powder and the superabsorbent polymer obtained therefrom have a particle diameter of 150 to 850 μm. And provided. More specifically, at least 95% by weight or more of the base resin powder and the superabsorbent polymer obtained therefrom may have a particle diameter of 150 to 850 μm, and a fine powder having a particle diameter of less than 150 μm may be less than 3% by weight. As described above, as the particle size distribution of the base resin powder and the superabsorbent polymer is adjusted to a desired range, the final superabsorbent polymer can better express the above-described physical properties.

On the other hand, the more detailed description of the method of drying, grinding and classification is as follows.

First, in drying the hydrogel polymer, if necessary, in order to increase the efficiency of the drying step, the step of co-grinding before drying may be further performed. At this time, the grinder used 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 Includes any one selected from the group of crushers consisting of cutter mills, disc mills, shred crushers, crushers, choppers and disc cutters However, it is not limited to the above-described example.

At this time, the coarse crushing step may be pulverized so that the particle diameter of the hydrogel polymer is about 2 mm 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 of agglomeration between the crushed particles. On the other hand, when the particle diameter is crushed to more than 10 mm, the effect of increasing the efficiency of the subsequent drying step may be insignificant.

Drying is performed on the hydrogel polymer immediately after polymerization, which is coarsely pulverized as described above or has not been subjected to a co-pulverization step. At this time, the drying temperature of the drying step may be 50 to 250 ℃. When the drying temperature is less than 50°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 is finally formed. More preferably, the drying may be performed at a temperature of 150 to 200°C, and more preferably at a temperature of 160 to 190°C. Meanwhile, in the case of a drying time, process efficiency may be considered, and may be performed for 20 minutes to 15 hours, but is not limited thereto.

As long as it is commonly used as the drying process, it can be selected and used without limitation in its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. The moisture content of the polymer after the drying step may be 0.05 to 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 150 to 850 μm. The pulverizer used for crushing to such a particle size is specifically, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, or a disc. A mill or a jog mill may be used, but is not limited to the above-described example.

Then, in order to manage the physical properties of the superabsorbent polymer powder that is finally commercialized after such a crushing step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed. Preferably, a polymer having a particle diameter of 150 to 850 μm is classified, and only a polymer powder having such a particle diameter can be commercialized through a surface crosslinking reaction step to be described later.

In addition, it is preferable that the centrifugal water retention capacity (CRC) of the base resin powder prepared above is 32 to 37 g/g.

(Step 3)

The step 3 is a step of crosslinking the surface of the base resin prepared in step 2, in the presence of a surface crosslinking solution containing water and a surface crosslinking agent, heat-treating the base resin powder to crosslink the surface to obtain superabsorbent polymer particles. It is a forming step.

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

In this case, the surface crosslinking agent is preferably used in an amount of 0.15 parts by weight or less based on 100 parts by weight of the base resin. When the amount of the surface crosslinking agent exceeds 0.15 parts by weight, excessive surface crosslinking may occur, and various properties of the superabsorbent polymer, particularly, dryness may be deteriorated. Preferably, the surface crosslinking agent is used in an amount of 0.14 parts by weight or less, 0.13 parts by weight or less, 0.12 parts by weight or less, 0.11 parts by weight or less, or 0.10 parts by weight or less based on 100 parts by weight of the base resin. In addition, the surface crosslinking agent is preferably used in an amount of 0.01 parts by weight or more, 0.02 parts by weight or more, 0.03 parts by weight or more, 0.04 parts by weight or more, or 0.05 parts by weight or more based on 100 parts by weight of the base resin.

In addition, it is preferable to use the water at 3.5 parts by weight or less based on 100 parts by weight of the base resin. When the amount of water used exceeds 0.15 parts by weight, excessive surface crosslinking may occur, and various properties of the superabsorbent polymer, particularly, dryness may deteriorate. Preferably, the water is used in an amount of 3.4 parts by weight or less, 3.3 parts by weight or less, 3.2 parts by weight or less, 3.1 parts by weight or less, or 3.0 parts by weight or less based on 100 parts by weight of the base resin. In addition, it is preferable to use the water, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, or 0.5 parts by weight or more based on 100 parts by weight of the base resin.

In addition, the surface crosslinking solution may further include aluminum sulfate. The aluminum sulfate may be included in 0.02 to 0.3 parts by weight based on 100 parts by weight of the base resin powder.

In addition, the surface crosslinking solution may include an inorganic filler. The inorganic filler may include silica, aluminum oxide, or silicate. The inorganic filler may be included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the base resin powder.

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

On the other hand, in order to perform the surface crosslinking, the surface crosslinking solution and the base resin are mixed in a reaction tank, a method of spraying a surface crosslinking solution on the base resin, and the surface resin and the surface crosslinking 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 proceeding at a relatively high temperature. At this time. The surface crosslinking reaction may be performed for 1 to 120 minutes, or 1 to 100 minutes, or 10 to 60 minutes. That is, while inducing a minimum amount of the surface crosslinking reaction, the polymer particles may be damaged during excessive reaction to prevent the physical properties from being deteriorated, and thus the conditions of the surface crosslinking reaction may be performed.

As described above, the superabsorbent polymer according to the present invention is excellent in dryness while maintaining excellent absorbent performance, and is preferably used for hygiene materials such as diapers, thereby exhibiting excellent performance.

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

Example 1

100 g of acrylic acid, 0.37 g of polyethylene glycol diacrylate (PEGDA, Mw=523) as a crosslinking agent, 0.15 g of sodium persulfate (SPS) as a thermal initiator, and phenylenebis (2,4,6-trimethyl) as a UV initiator Benzoyl) 0.008 g, caustic soda (NaOH) 40 g and 127 g of water were mixed to prepare a monomer aqueous solution composition having a monomer concentration of 45.8 wt%. After the monomer aqueous solution composition was introduced into the supply section of a polymerization reactor equipped with a conveyor belt that continuously moves, ultraviolet rays were irradiated with a UV irradiation device while maintaining the polymerization atmosphere temperature at 80°C (irradiation amount: 10 mW/cm ² ), UV polymerization was performed for 2 minutes to prepare a hydrogel polymer.

The hydrogel polymer was transferred to a meat chopper and cut into 0.05 cm to 1 cm. At this time, the water content of the cut hydrogel polymer was 47% by weight. Subsequently, the hydrogel polymer was dried in a hot air dryer at a temperature of 170° C. for 30 minutes, and the dried hydrogel polymer was pulverized with a pin mill grinder. Subsequently, a polymer having a particle size (average particle size) of 150 μm to 850 μm was classified using a sieve to prepare a base resin.

Subsequently, 100 parts by weight of the base resin prepared above, surface crosslinking solution (2.5 parts by weight of water, ethylene glycol diglycidyl ether (EX-810) 0.1 parts by weight, aluminum sulfate 18 hydrate; Al-S ) 0.1 parts by weight, and silica (Aerosil A200) 0.1 parts by weight) was evenly mixed, and then a surface crosslinking reaction was performed at 140°C for 30 minutes. After the surface treatment was completed, a superabsorbent polymer having an average particle size of 150 to 850 μm was obtained using a sieve. The superabsorbent polymer thus obtained had an average particle size of less than 150 μm in a content of less than 2%. On the other hand, CRC (#30-50) of the base resin prepared above was 35.5 g/g.

Examples 2-5 and Comparative Examples 1-4

A superabsorbent polymer was prepared in the same manner as in Example 1, except that the composition of PEGDA, SPS, and surface crosslinking solution was as shown in Table 1 below.

PEGDA
(ppmw) SPS
(ppmw) Surface crosslinking fluid composition (phr) water EX810 Al-S Aerosil Comparative Example 1 3700 4000 4.0 0.2 0.1 0.1 Comparative Example 2 4200 4000 4.0 0.2 0.1 0.1 Example 1 3700 1500 2.5 0.1 0.1 0.01 Example 2 3700 1500 2.0 0.07 0.1 0.05 Example 3 2900 1000 3.0 0.1 0 0.1 Example 4 1700 1500 2.0 0.1 0.1 0.1

Experimental Example: Evaluation of physical properties of super absorbent polymer

The physical properties of the superabsorbent polymer prepared in Examples and Comparative Examples were evaluated by the following method.

(1) Centrifuge Retention Capacity (CRC)

For the superabsorbent polymers of Examples and Comparative Examples according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, the centrifugal water retention capacity (CRC) by the unloaded absorption ratio was measured.

Specifically, the resin W ₀ (g, about 0.2 g) of Examples and Comparative Examples was uniformly placed in a non-woven fabric bag and sealed, and then immersed in physiological saline solution of 0.9 wt% sodium chloride aqueous solution at room temperature. After 30 minutes, the bag was centrifuged, and after draining for 3 minutes at 250G, the mass W ₂ (g) of the bag was measured. Moreover, the mass W ₁ (g) at that time was measured after performing the same operation without using a super absorbent polymer.

Using each mass thus obtained, CRC (g/g) was calculated according to Equation 1 below.

[Equation 1]

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

In Equation 1,

W ₀ (g) is the initial weight (g) of the superabsorbent polymer, and W ₁ (g) does not use the superabsorbent polymer, and is absorbed by immersion in physiological saline for 30 minutes, followed by centrifugation to 250 G. The weight of the device measured after dehydration for 3 minutes, W ₂ (g) is absorbed by immersing the superabsorbent resin in physiological saline at room temperature for 30 minutes, and then dehydrating at 250G for 3 minutes using a centrifuge, followed by superabsorption It is the weight of the device measured including resin.

In addition, CRC (BR CRC) was measured in the same manner as described above for the base resins prepared in Examples and Comparative Examples.

(2) Extractable contents (16 hr E/C)

Water-soluble component measurements were measured in the same manner as described in the European Disposables and Nonwovens Association standard EDANA method WSP 270.2.

Specifically, 1.0 g of the superabsorbent polymer was added to a NaCl solution of 0.9 wt% in 200 g, soaked for 16 hours while stirring at 500 rpm, and the aqueous solution was filtered through filter paper. The filtered solution is first titrated to pH 10.0 with a 0.1 N caustic soda solution, and then back-titrated with a pH of 2.7 with a 0.1 N hydrogen chloride solution to calculate and measure a polymer material that is not crosslinked from the amount required for neutralization as a water-soluble component. Did.

(3) Dryness

2 g of the superabsorbent polymer was placed in a 500 mL beaker, and 200 mL of distilled water at 22 to 24°C was added. After the superabsorbent polymer swelled, it was taken out and placed at room temperature for 6 hours. Subsequently, after stacking 5 sheets of filter paper of 5 cm in diameter, the filter paper was placed on the superabsorbent polymer, pressed to 0.2 psi for 1 minute, and then the weight of the distilled water absorbed by the filter paper (dryness, g) was measured. Did.

(4) Vortex

After adding 50 mL of a 0.9 wt% NaCl solution to a 100 mL beaker, 2 g of the superabsorbent polymer prepared in Examples and Comparative Examples was added while stirring at 600 rpm using a stirrer. Then, the time until the vortex of the liquid generated by stirring disappeared and a smooth surface was formed was measured, and the result was expressed as the vortex removal time.

After adding 50 mL of 0.9 wt% NaCl solution to a 100 mL beaker, insert a 30 mm magnetic bar (polygon type with a length of 30 mm and a thickness of 8 mm) and stirring at 600 rpm using a magnetic stirrer. 2.0 g of superabsorbent polymers prepared in Examples and Comparative Examples were added, respectively. Then, the time until the vortex of the liquid generated by stirring disappeared and a smooth surface was formed was measured, and the result was expressed as the vortex removal time (absorption rate; vortex).

(5) Absorbing under Pressure (AUP)

Absorbency under pressure (AUP) of superabsorbent polymers of Examples and Comparative Examples was measured according to the method of the European Disposables and Nonwovens Association standard EDANA 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. The resin W ₀ (g, 0.90 g) obtained in Examples and Comparative Examples was uniformly spread on a wire mesh under a temperature of 23±2° C. and a relative humidity of 45%, and a load of 0.3 psi was further uniformly applied thereon. The possible piston was slightly smaller than the outer diameter of 60 mm, had no gaps with the inner wall of the cylinder, and prevented the vertical movement from being disturbed. At this time, the weight W ₃ (g) of the device was measured.

A 150 mm diameter petri dish was placed inside a 125 mm diameter glass filter with a thickness of 5 mm, and the physiological saline composed of 0.90% by weight sodium chloride was brought to the same level as the top surface of the glass filter. A filter paper having a diameter of 120 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.

AUP (g/g) was calculated according to Equation 2 below using each mass thus obtained.

[Equation 2]

AUP(g/g) = [W ₄ (g)-W ₃ (g)]/ W ₀ (g)

In Equation 2,

W ₀ (g) is the initial weight of the superabsorbent polymer (g), W ₃ (g) is the sum of the weight of the superabsorbent polymer and the weight of the device capable of applying a load to the superabsorbent polymer, W ₄ (g ) Is the sum of the weight of the superabsorbent polymer and the weight of the device capable of applying a load to the superabsorbent polymer after absorbing physiological saline in the superabsorbent polymer for 1 hour under a load (0.9 psi).

(6) Permeability

A line was marked on the liquid level of 20 mL and 40 mL of the liquid with the piston inserted in the chromatography tube (F20 mm). Subsequently, to prevent bubbles from forming between the glass filter at the bottom of the chromatography tube and the cock, water was added in reverse to fill about 10 mL, washed 2-3 times with brine, and 0.9% brine to 40 mL or more. Insert the piston into the chromatography tube and open the lower valve to record the time (B) at which the liquid level decreases from 40 mL to the 20 mL mark.

10 mL of brine was left in the chromatographic tube, 0.2±0.0005 g of sample (30# ~ 50#) was added, brine was added, and the volume of the brine became 50 mL, and then allowed to stand for 30 minutes. After that, add an additional piston (0.3 psi = 106.26 g) into the chromatography tube and leave it for 1 minute, open the lower valve of the chromatography tube, record the time (T1) at which the liquid level decreases from 40 mL to the 20 mL mark (T1). Liquidity (time of T1-B) was measured.

The measured results are shown in Table 2 below.

BR CRC
(g/g) CRC
(g/g) 16hr E/C
(wt%) Dryness
(g) 0.3 psi AUP
(g/g) Liquidity
(sec) Comparative Example 1 35.1 30.1 19.1 2.5 29.7 38 Comparative Example 2 32.8 28.1 16.8 1.7 30.8 18 Example 1 35.5 30.5 12.5 0.9 28.1 23 Example 2 34.3 30.3 11.3 0.7 28.5 45 Example 3 34.3 29.1 9.5 0.6 30.3 31 Example 4 34.5 30.5 7.8 0.3 29.1 21

As shown in Table 2, it was confirmed that the superabsorbent polymer of the Examples according to the present invention maintains the physical properties equal to or higher than the superabsorbent polymer of the comparative examples, while the water-soluble components are low and the dryness is excellent.

Claims (11)

Crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent to form a hydrogel polymer comprising a first crosslinked polymer;
Drying, grinding and classifying the hydrogel polymer to form a base resin powder; And
Surface crosslinking by heat-treating the base resin powder in the presence of a surface crosslinking liquid comprising 3.5 parts by weight or less of water, 0.15 parts by weight or less of a surface crosslinking agent, and 0.01 to 0.5 parts by weight of an inorganic filler relative to 100 parts by weight of the base resin powder And comprising the step of forming a super absorbent polymer particles,
The surface crosslinking agent is polyethylene glycol diacrylate, ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, or polypropylene glycol diglycidyl ether,
Method for producing super absorbent polymer.
According to claim 1,
The inorganic filler is silica,
Method for producing super absorbent polymer.
According to claim 1,
The inorganic filler is contained in the surface crosslinking solution in an amount of 0.01 to 0.1 parts by weight relative to 100 parts by weight of the base resin powder,
Method for producing super absorbent polymer.
According to claim 1,
The surface crosslinking solution, which further comprises aluminum sulfate,
Method for producing super absorbent polymer.
According to claim 1,
The base resin powder has a centrifugal water retention capacity (CRC) of 32 to 37 g/g,
Method for producing super absorbent polymer.
According to claim 1,
6 hours dryness (dryness) of the super absorbent polymer is 1.0 g or less,
Method for producing super absorbent polymer.
According to claim 1,
The absorption rate of the superabsorbent polymer measured according to the Vortex measurement method is 50 seconds or less,
Method for producing super absorbent polymer.
According to claim 1,
The water-soluble component according to EDANA method WSP 270.2 of the super absorbent polymer is 13% by weight or less,
Method for producing super absorbent polymer.
According to claim 1,
The superabsorbent polymer has a centrifugal water retention capacity (CRC) of 28 g/g or more,
Method for producing super absorbent polymer.
According to claim 1,
Pressurized absorption capacity (0.3 AUP) of the superabsorbent polymer for 1 hour under 0.3 psi in physiological saline (0.9% by weight aqueous sodium chloride solution) is 25 g/g or more,
Method for producing super absorbent polymer.
According to claim 1,
The liquid permeability of the super absorbent polymer is 10 seconds to 150 seconds,
Method for producing super absorbent polymer.