KR20200073044A - Super absorbent polymer and preparation method thereof - Google Patents

Abstract

As described herein, a super absorbent polymer according to the present invention has a high absorption rate even though the super absorbent polymer is manufactured without using a foaming agent, and thus can be used in sanitary materials such as diapers to exhibit excellent performance.

Description

SUPER ABSORBENT POLYMER AND PREPARATION METHOD THEREOF}

The present invention is to provide a superabsorbent polymer capable of increasing the absorption rate without using a blowing agent 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 resin 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, freshness preservatives in the food distribution field, and It is widely used as a material for poultice.

In most cases, these superabsorbent resins 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 to provide hygiene materials, such as diapers having a thinner thickness, have continued, and as a part thereof, the content of 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 such a multi-layer to absorb liquid such as urine more efficiently, it is necessary for the superabsorbent polymer to exhibit a high absorption performance and absorption rate.

In order to increase the absorption rate, a method of using a foaming agent in manufacturing a superabsorbent has been reported, but when a foaming agent is used, there is a problem in that the apparent density is lowered, and fine powder is generated in a pulverization step that is necessary in the manufacturing process of the superabsorbent polymer. There is a problem.

The present invention is to provide a superabsorbent polymer capable of increasing the absorption rate without using a blowing agent and a method for manufacturing the same.

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 an acidic group at least partially neutralized; 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,

In the first crosslinked polymer, a part of the acidic group is a potassium salt thereof,

Super absorbent polymer.

The superabsorbent polymer is generally prepared in the form of a base resin powder prepared through crosslinking polymerization of a water-soluble ethylenically unsaturated monomer, for example, acrylic acid, and a surface crosslinking layer formed by crosslinking the surface of the base resin powder. . In recent years, the absorption rate of the super absorbent polymer is important and considered, and attempts have been made to introduce pores inside the super absorbent polymer, particularly inside the base resin powder, in order to improve the absorption speed of the super absorbent polymer. When pores are formed in the base resin powder, moisture and the like can be absorbed into the space more quickly, so that the absorption rate can be improved.

To this end, conventionally, in the manufacture of the base resin powder, a blowing agent has been used. When a foaming agent is used, foaming may occur in a polymerization process such as acrylic acid, thereby forming pores in the base resin powder to be produced. However, when using a blowing agent, there is a problem that the apparent density is lowered, there is a problem that the fine powder is generated in the necessary grinding step in the manufacturing process of the super absorbent polymer.

Accordingly, the present invention is characterized in that instead of using a foaming agent, a potassium salt is used together when polymerizing the water-soluble ethylenically unsaturated monomer, or a potassium salt is used in a product produced after the polymerization. In the present specification, the term'part of the acidic group is a potassium salt thereof' means, for example, when the acidic group is -COOH, or -OH, -COO ^- K ⁺ , or -O ^- K ⁺ , respectively.

Through this, a part of the acidic group present in the base resin is present as its potassium salt. Since the potassium cation has a larger ionization tendency than sodium ions, more -COO ^- anions are produced in the base resin powder, and accordingly, the anion repulsive force between the crosslinked structures makes the crosslinked structure wider, thereby increasing the absorption rate. Can be improved.

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 super absorbent polymer with improved water absorption. 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. Accordingly, preferably, the first crosslinked polymer includes a crosslinked copolymer of acrylic acid, sodium salt of acrylic acid, and potassium salt of acrylic acid. The neutralization method will be described later.

Preferably, the crosslinked polymer includes a crosslinked copolymer of acrylic acid, a sodium salt of acrylic acid, a potassium salt of acrylic acid, and a monomer having a sulfuric acid functional group. As the monomer having the sulfuric acid functional group participates in the polymerization reaction, a sulfuric acid functional group can be introduced into the base resin powder, and the sulfuric acid functional group induces an anionic repulsive force between the crosslinked structures similarly to the -COO ^- anion, so that the crosslinked structure is wide The absorption rate can be further improved.

Preferably, the monomer having a sulfuric acid functional group, sodium allyl sulfonate (Sodium allyl sulfonate, Sodium Vinyl Sulfonate), sodium 4-styrene sulfonate (Sodium Styrene Sulfonate), 3-sulfopropyl acrylate potassium Salt (3-sulfopropyl acrylate potassium salt; SPAK), 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS), sodium 4-vinylbenzenesulfonate (sodium 4-vinylbenzenesulfonate), or sodium allyloxy hydroxypropyl sulfonate.

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

On the other hand, the super absorbent polymer according to the present invention has an apparent density of 0.50 to 0.70 g/ml. The range of the apparent density corresponds to a superabsorbent polymer prepared using a conventional blowing agent, and in the present invention, it can have an apparent density of this range without the use of a blowing agent.

In addition, the superabsorbent polymer according to the present invention has an absorption rate (vortex) of 35 seconds or less. The absorption rate refers to a time when the vortex of the liquid disappears due to rapid absorption when the superabsorbent resin is added to the physiological saline solution and stirred, and the absorption rate of the superabsorbent polymer may be defined. The method for measuring the absorption rate is specified in the following Examples. Preferably, the absorption rate is 34 seconds or less, 33 seconds or less, 32 seconds or less, 31 seconds or less, 30 seconds or less, 29 seconds or less, 28 seconds or less, 27 seconds or less, 26 seconds or less, or 25 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, 15 seconds or more, or 20 seconds or more.

In addition, the superabsorbent polymer according to the present invention has a 1-minute absorbent capacity (capacity of water) of 130 g/g or more. The 1-minute absorbency is the total amount of tap water that can be absorbed for 1 minute when the super absorbent polymer is immersed in tap water, and the absorbent capacity of the super absorbent polymer can be defined. In this case, the tap water may be defined as tap water having a conductivity of 110±3 μS/cm. The method for measuring the 1-minute absorption capacity (capacity) is more concrete in the following Examples. Preferably, the 1-minute absorption capacity (capacity) is 135 g/g or more, 140 g/g or more, 145 g/g or more, 150 g/g or more, 155 g/g or more, or 160 g/g or more . In addition, the larger the value, the better, and there is no limit to the upper limit of the 1-minute absorption capacity, but is, for example, 200 g/g or less, 190 g/g or less, or 180 g/g or less.

Manufacturing method of super absorbent polymer

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

Cross-linking the monomer composition comprising a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer comprising a first crosslinked polymer (step 1) ;

Drying, grinding and classifying the hydrogel polymer to form a base resin powder (step 2); And

In the presence of a surface crosslinking liquid, the step of heat-treating the base resin powder to crosslink the surface to form superabsorbent polymer particles (step 3),

Adding a potassium salt to the reactant during the crosslinking polymerization of step 1, or adding a potassium salt to the product after the crosslinking polymerization of step 1,

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 comprising a first crosslinked polymer, in the presence of an internal crosslinking agent and a polymerization initiator, at least partially crosslinking a monomer composition comprising a water-soluble ethylenically unsaturated monomer having a neutralized acidic group. This is a step of polymerization.

The water-soluble ethylenically unsaturated monomer constituting the first crosslinked polymer is as described above.

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.

Preferably, the water-soluble ethylenically unsaturated monomer having an acidic group neutralized with sodium hydroxide, and at least partially neutralized, means acrylic acid and sodium acrylate salt.

Also preferably, sodium hydroxide and potassium hydroxide are neutralized, and the water-soluble ethylenically unsaturated monomer having an acidic group in which at least a portion is neutralized means acrylic acid, sodium acrylate salt, and potassium acrylate salt. In this case, sodium hydroxide and potassium hydroxide are preferably used in a molar ratio of 1-20:1, more preferably 10-20:1, and most preferably in a molar ratio of 10-15:1.

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 precipitate and polymerization may be difficult to proceed smoothly. It can exhibit properties such as elastic rubber that are difficult to handle.

In addition, the concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition may be appropriately adjusted in consideration of polymerization time and reaction conditions, and may preferably be 20 to 90% by weight, or 40 to 65% by weight. This concentration range may be advantageous for controlling the grinding efficiency when pulverizing a polymer, 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 a process problem such as a reduction in crushing efficiency upon pulverization of the polymerized hydrogel polymer may occur, and physical properties of the super absorbent polymer may be deteriorated.

In addition, as described above, the potassium salt is added to the monomer composition during the crosslinking polymerization of step 1, or the step so that the crosslinked polymer constituting the base resin powder contains a crosslinked copolymer of the potassium salt of the water-soluble ethylenically unsaturated monomer, or the step After the crosslinking polymerization of 1, potassium salt is added to the product. By the former, a part of the water-soluble ethylenically unsaturated monomer contained in the monomer composition may be changed to a potassium salt. In addition, by the latter, a part of the acidic group (COOH) of the prepared hydrogel polymer can be changed to potassium salt (COO ^- K ⁺ ). Preferably, the potassium salt is potassium carbonate (K ₂ CO ₃ ). Preferably, the potassium salt contains 1 to 30 parts by weight, more preferably 1 to 10 parts by weight, most preferably 3 to 100 parts by weight of the water-soluble ethylenically unsaturated monomer having an acidic group in which at least a portion is neutralized. To 7 parts by weight. In addition, the monomer composition does not contain a blowing agent.

In addition, as described above, the crosslinking polymer constituting the base resin powder may further include a monomer having a sulfuric acid functional group in the monomer composition during the crosslinking polymerization of step 1, so as to include a crosslinked copolymer of a monomer having a sulfuric acid functional group can do. Preferably, the monomer having a sulfuric acid functional group, sodium allyl sulfonate (Sodium allyl sulfonate, Sodium Vinyl Sulfonate), sodium 4-styrene sulfonate (Sodium Styrene Sulfonate), 3-sulfopropyl acrylate potassium Salt (3-sulfopropyl acrylate potassium salt; SPAK), 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS), sodium 4-vinylbenzenesulfonate (sodium 4-vinylbenzenesulfonate, or sodium allyloxy hydroxypropyl sulfonate, preferably, the monomer having a sulfuric acid functional group is 100% by weight of the water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized It contains 1 to 30 parts by weight based on parts, more preferably 1 to 10 parts by weight, and most preferably 3 to 7 parts by weight.

In addition, as the internal crosslinking agent, any compound can be used as long as it allows introduction of crosslinking during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di( Meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth) )Acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, penta Multifunctional crosslinking agents such as erythritol tetraacrylate, triarylamine, 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 crosslinking 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, Examples include 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. Preferably, ascorbic acid and potassium persulfate are used as the thermal polymerization initiator.

The photo polymerization initiator, for example, benzoin ether (benzoin ether), dialkyl acetophenone (dialkyl acetophenone), hydroxyl alkyl ketone (hydroxyl alkylketone), phenyl glyoxylate (phenyl glyoxylate), benzyl dimethyl ketal (benzyl 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 chain constituting the network is shortened, so 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 lowered, which is not preferable.

In addition, the monomer composition may further include additives such as surfactants, thickeners, plasticizers, storage stabilizers, and antioxidants, if necessary. On the other hand, as described above, the monomer composition does not contain a blowing agent.

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

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

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

At this time, the normal water content of the hydrogel polymer obtained in this way may be 40 to 80% by weight. Meanwhile, in the present specification, “water content” refers to a content of moisture occupied with respect to the total weight of the hydrogel polymer, which means the weight of the hydrogel polymer minus the dry polymer weight. Specifically, it is defined as a calculated value by measuring the weight loss due to evaporation of water in the polymer during the drying process by raising the temperature of the polymer through infrared heating. At this time, the drying condition is a method of raising the temperature from room temperature to about 180°C and then maintaining it at 180°C. The total drying time is set to 20 minutes including 5 minutes of the temperature rise step to measure the water content.

(Step 2)

The step 2 is a step of forming a 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 drying, pulverization and classification process.

First, in drying the hydrogel polymer, in order to increase the efficiency of the drying step, if necessary, the step of co-grinding before drying may be further performed. At this time, the pulverizer used is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, and 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 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 finally formed are deteriorated. 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. 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 the 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 water 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 pulverizing such a particle size is, specifically, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, or a disc. A mill or a jog mill may be used, but is not limited to the above-described example.

And, 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 crushing 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 described later.

(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 a surface crosslinking agent, heat-treating the base resin powder to crosslink the surface to form superabsorbent polymer particles. It is a 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 Glycol, diethylene glycol, propylene glycol, triethylene glycol, tetra ethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol, trimethylolpropane, It may be one or more compounds selected from the group consisting of pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride.

At this time, the content of the surface crosslinking agent is preferably used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the base resin. When the content of the surface crosslinking agent exceeds 5 parts by weight, excessive surface crosslinking proceeds, and when the superabsorbent polymer absorbs water, a lot of moisture is present on the surface, resulting in a low drying degree.

In addition, the surface crosslinking solution is water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N, It may further include one or more solvents selected from the group consisting of N-dimethylacetamide. Preferably, water is included. The solvent may be used in 0.5 to 10 parts by weight relative to 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 You 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 method of mixing the surface crosslinking solution and the base resin in a reaction tank, a method of spraying a surface crosslinking solution to the base resin, the surface resin and the surface crosslinking to a continuously operated mixer A method of continuously supplying and mixing the liquid may be used.

And, the surface modification step may be performed under a temperature of 100 to 250 ℃. In addition, the surface modification may be performed for 1 minute to 120 minutes, preferably 1 minute to 100 minutes, and more preferably 10 minutes to 60 minutes. That is, in order to prevent the polymer particles from being damaged due to excessive reaction, while inducing a minimum amount of surface crosslinking reaction, the surface modification step may be performed under the above-described conditions.

As described above, the superabsorbent polymer according to the present invention has a high absorption rate even though it is produced without using a blowing agent, and can be used in hygiene materials such as diapers to exhibit excellent performance.

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

Example One

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 0.003 g of PEGDA400 (polyethylene glycol diacrylate 400), an internal crosslinking agent, 1.5 g of EX810 (ethylene glycol diglycidyl ether), diphenyl (2, photoinitiator) 4,6-trimethylbenzoyl)-phosphine oxide 0.048 g, heat initiator sodium persulfate (SPS) 0.6 g, surfactant sodium dodecyl sulfate 0.03 g, and 24.0% sodium hydroxide solution 902.4 g was added thereto, and 57.6 g of potassium carbonate (K ₂ CO ₃ , solid) was further added and mixed to prepare an aqueous water-soluble unsaturated monomer solution. It was poured into a stainless container.

When the temperature of the aqueous solution of the water-soluble unsaturated monomer became 50°C, UV polymerization was performed by irradiating ultraviolet light for 1 minute (irradiation amount: 10 mW/cm ² ), followed by aging at 80°C for 2 minutes to obtain a sheet-like hydrogel polymer.

(Step 2)

The hydrogel polymer (1,400 g) on the sheet obtained in step 1 was crushed to a size of 2 mm × 2 mm, and 200 g of water was added. 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. The particle size of the base resin was adjusted to 10 wt% #20-30 (850-600 μm), 70 wt% #30-50 (600-300 μm), and 20 wt% #50-100 (300-150 μm).

(Step 3)

EX810 (ethylene glycol diglycidyl ether) 0.03 parts by weight, water 6 parts by weight, Al-S (Al ₂ SO ₄ ·18H ₂ O) 0.1 parts by weight based on 100 parts by weight of the base resin prepared in step 2, inorganic Evenly mixed surface treatment solution containing 0.1 parts by weight of filler (Aerosil 200), 0.025 parts by weight of glycerol monostearate, and 0.025 parts by weight of polyethylene glycol (PEG, Mw: 6,000 g/mol), and then crosslinking one surface It was supplied to the reactor, and the surface crosslinking reaction of the base resin was performed at 140°C for 40 minutes. After the surface treatment was completed, a surface-treated superabsorbent polymer having an average particle size of 150 to 850 μm was obtained using a sieve.

Example 2

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 0.003 g of PEGDA400 as an internal crosslinking agent, 1.5 g of EX810, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide 0.048 g, a thermal initiator A water-soluble unsaturated monomer aqueous solution was prepared by mixing 0.6 g of sodium persulfate, 0.03 g of sodium dodecyl sulfate as a surfactant, and 972.2 g of a 24.0% sodium hydroxide solution. It was poured into a stainless container.

Thereafter, when the temperature of the aqueous monomer solution was 50°C, UV polymerization was performed by irradiating ultraviolet light for 1 minute (irradiation amount: 10 mW/cm ² ), followed by aging at 80°C for 2 minutes to obtain a sheet-like hydrogel polymer.

(Step 2)

The hydrogel polymer (1,400 g) on the sheet obtained in step 1 was pulverized to a size of 2 mm×2 mm, wherein 200 g of water and 57.6 g of potassium carbonate (K ₂ CO ₃ , solid) were added. 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. The particle size of the base resin was adjusted to 10 wt% #20-30 (850-600 μm), 70 wt% #30-50 (600-300 μm), and 20 wt% #50-100 (300-150 μm).

(Step 3)

A superabsorbent polymer was obtained in the same manner as in Step 3 of Example 1, except that the base resin prepared in Step 2 was used.

Example 3

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 0.003 g of PEGDA400 as internal crosslinking agent, 1.5 g of EX810, diphenyl (2,4,6-trimethylbenzoyl) as photoinitiator, 0.048 g of phosphine oxide, and thermal initiator Add 0.6 g of sodium persulfate, 0.03 g of sodium dodecyl sulfate as a surfactant, and 902.4 g of a 24.0% sodium hydroxide solution, to which 57.6 g of potassium carbonate (K ₂ CO ₃ , solid) and 23.4 of potassium hydroxide (KOH, solid) g was further added and mixed to prepare a water-soluble unsaturated monomer aqueous solution. It was poured into a stainless container.

(Steps 2 and 3)

A superabsorbent polymer was prepared in the same manner as in steps 2 and 3 of Example 1, except that the aqueous solution of the water-soluble unsaturated monomer prepared in step 1 was used.

Example 4

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 0.003 g of PEGDA400 as an internal crosslinking agent, 1.5 g of EX810, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide 0.048 g, a thermal initiator A water-soluble unsaturated monomer aqueous solution was prepared by mixing 0.6 g of sodium persulfate, 0.03 g of sodium dodecyl sulfate as a surfactant, 902.4 g of a 24.0% sodium hydroxide solution, and 23.4 g of potassium hydroxide (KOH, solid). It was poured into a stainless container.

Subsequently, when the temperature of the aqueous monomer solution became 50°C, UV polymerization was performed by irradiating ultraviolet light for 1 minute (irradiation amount: 10 mW/cm2), followed by aging at 80°C for 2 minutes to obtain a sheet-like hydrogel polymer.

(Steps 2 and 3)

A superabsorbent polymer was prepared in the same manner as in steps 2 and 3 of Example 2, except that the aqueous solution of the water-soluble unsaturated monomer prepared in step 1 was used.

Example 5

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 60 g of sodium allyl sulfonate (S-monomer), 0.003 g of PEGDA400 as an internal crosslinking agent, 1.5 g of EX810, diphenyl (2,4, photoinitiator) 6-trimethylbenzoyl)-phosphine oxide 0.048 g, thermal initiator sodium persulfate 0.6 g, surfactant sodium dodecyl sulfate 0.03 g, 24.0% sodium hydroxide solution 902.4 g, and potassium carbonate (K ₂ CO ₃₎ , Solid) 57.6 g was further added and mixed to prepare a water-soluble unsaturated monomer aqueous solution. It was poured into a stainless container.

When the temperature of the aqueous solution of the water-soluble unsaturated monomer became 50°C, UV polymerization was performed by irradiating ultraviolet light for 1 minute (irradiation amount: 10 mW/cm ² ), followed by aging at 80°C for 2 minutes to obtain a sheet-like hydrogel polymer.

(Steps 2 and 3)

A superabsorbent polymer was prepared in the same manner as in steps 2 and 3 of Example 1, except that the aqueous solution of the water-soluble unsaturated monomer prepared in step 1 was used.

Example 6

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 60 g of sodium allyl sulfonate (S-monomer), 0.003 g of PEGDA400 as an internal crosslinking agent, 1.5 g of EX810, diphenyl (2,4, photoinitiator) A water-soluble unsaturated monomer aqueous solution was prepared by mixing 0.048 g of 6-trimethylbenzoyl)-phosphine oxide, 0.6 g of sodium persulfate as a thermal initiator, 0.03 g of sodium dodecyl sulfate as a surfactant, and 974.7 g of a 24.0% sodium hydroxide solution. It was poured into a stainless container.

Thereafter, when the temperature of the aqueous monomer solution was 50°C, UV polymerization was performed by irradiating ultraviolet light for 1 minute (irradiation amount: 10 mW/cm ² ), followed by aging at 80°C for 2 minutes to obtain a sheet-like hydrogel polymer.

(Steps 2 and 3)

A superabsorbent polymer was prepared in the same manner as in steps 2 and 3 of Example 2, except that the aqueous solution of the water-soluble unsaturated monomer prepared in step 1 was used.

Comparative example One

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 600 g of acrylic acid, 0.003 g of PEGDA400 as an internal crosslinking agent, 1.5 g of EX810, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide 0.048 g, a thermal initiator A water-soluble unsaturated monomer aqueous solution was prepared by mixing 0.6 g of sodium persulfate, 0.03 g of sodium dodecyl sulfate as a surfactant, and 974.7 g of a 24.0% sodium hydroxide solution. It was poured into a stainless container.

When the temperature of the aqueous solution of the water-soluble unsaturated monomer became 50°C, UV polymerization was performed by irradiating ultraviolet light for 1 minute (irradiation amount: 10 mW/cm ² ), followed by aging at 80°C for 2 minutes to obtain a sheet-like hydrogel polymer.

(Steps 2 and 3)

A superabsorbent polymer was prepared in the same manner as in steps 2 and 3 of Example 1, except that the aqueous solution of the water-soluble unsaturated monomer prepared in step 1 was used.

Comparative example 2

Prepared in the same manner as in Comparative Example 1, using a 24.0% sodium hydroxide solution 1111.11 g to prepare a super absorbent polymer.

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) Absorption rate (Vortex)

In a 100 mL beaker, 50 mL of a 0.9% by weight aqueous sodium chloride solution was added, and then, while stirring at 600 rpm using a stirrer, 2 g of the superabsorbent polymer prepared in the above Examples and Comparative Examples were respectively added. 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).

(2) 1 minute absorption capacity (capacity)

1.0 g (W ₁ ) of the superabsorbent polymer of Examples and Comparative Examples was placed in a nonwoven bag (15 cm × 15 cm) and immersed in 500 mL of 24°C tap water (conductivity 110±3 μS/cm) for 1 minute. After 1 minute, the envelope was removed from the tap water and hung for 1 minute. Then, the mass (W ₃ ) of the envelope was measured. In addition, after performing the same operation without using a super absorbent polymer, the mass W ₂ (g) at that time was measured. Using each mass thus obtained, 1 minute absorption capacity was calculated according to Equation 1 below.

[Equation 1]

1 minute absorption capacity (frequency) = {[W ₃ (g)-W ₂ (g)-W ₁ (g)]/W ₁ (g)}

In Equation 1,

W ₁ (g) is the initial weight (g) of the super absorbent polymer, and W ₂ (g) is the weight of the device measured after being absorbed by immersing in tap water for 1 minute without using the super absorbent polymer and measuring W ₃ (g) is a device weight measured by immersing and absorbing water for 1 minute, and then including a super absorbent polymer.

The measured results are shown in Table 1 below.

Addition amount of sodium salt and/or potassium salt ¹⁾ Addition amount of additional monomer ^{1 )} Chopping
Amount of K ₂ CO ₃ in step ¹⁾ Vortex
(sec) 1 minute absorption capacity (capacity)
(g/g) Example 1 NaOH 65 mol%
K ₂ CO ₃ 5 mol% - - 26 155 Example 2 NaOH 70 mol% - 5 mol% 22 178 Example 3 NaOH 65 mol%
KOH 5 mol%
K ₂ CO ₃ 5 mol% - - 22 163 Example 4 NaOH 65 mol%
KOH 5 mol% - 5 mol% 25 165 Example 5 NaOH 65 mol%
K ₂ CO ₃ 5 mol% S-monomer 10 mol% - 22 177 Example 6 NaOH 70 mol% S-monomer 10 mol% 5 mol% 27 162 Comparative Example 1 NaOH 70 mol% - - 35 110 Comparative Example 2 NaOH 80 mol% - - 33 120 1) Shown as the number of moles of acrylic acid used for polymerization

Claims (15)

A base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized; 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,
In the first crosslinked polymer, a part of the acidic group is a potassium salt thereof,
Super absorbent polymer.
According to claim 1,
The first crosslinked polymer comprises a crosslinked copolymer of acrylic acid, a sodium salt of acrylic acid, and a potassium salt of acrylic acid,
Super absorbent polymer.
According to claim 1,
The crosslinked polymer includes a crosslinked copolymer of acrylic acid, a sodium salt of acrylic acid, a potassium salt of acrylic acid, and a monomer having a sulfuric acid functional group,
Super absorbent polymer.
According to claim 3,
The monomer having a sulfuric acid functional group, sodium allyl sulfonate (Sodium Vinyl Sulfonate), sodium 4-styrene sulfonate (Sodium Styrene Sulfonate), 3-sulfopropyl acrylate potassium salt (3- sulfopropyl acrylate potassium salt (SPAK), 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS), sodium 4-vinylbenzenesulfonate , Or sodium allyloxy hydroxypropyl sulfonate,
Super absorbent polymer.
According to claim 1,
The absorption rate of the superabsorbent polymer measured according to the Vortex measurement method is 35 seconds or less,
Super absorbent polymer.
According to claim 1,
The super absorbent polymer has a water absorption capacity (water content) of 130 g/g or more,
Super absorbent polymer.
Cross-linking the monomer composition comprising a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer comprising a first crosslinked polymer (step 1). ;
Drying, grinding and classifying the hydrogel polymer to form a base resin powder (step 2); And
In the presence of a surface crosslinking liquid, the step of heat-treating the base resin powder to crosslink the surface to form superabsorbent polymer particles (step 3),
When adding the potassium salt to the monomer composition during the crosslinking polymerization of step 1, or adding a potassium salt to the product after the crosslinking polymerization of step 1,
Method for producing super absorbent polymer according to claim 1.
The method of claim 7,
The potassium salt is contained in 1 to 30 parts by weight compared to 100 parts by weight of the water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized,
Manufacturing method.
The method of claim 7,
The potassium salt is potassium carbonate (K ₂ CO ₃ ),
Manufacturing method.
The method of claim 7,
A part of the water-soluble ethylenically unsaturated monomer having an acidic group is neutralized with sodium hydroxide,
Manufacturing method.
The method of claim 7,
A part of the water-soluble ethylenically unsaturated monomer having an acidic group is neutralized with sodium hydroxide and potassium hydroxide,
Manufacturing method.
The method of claim 11,
The sodium hydroxide and potassium hydroxide are used in a molar ratio of 1-20:1,
Manufacturing method.
The method of claim 7,
The monomer composition further comprises a monomer having a sulfuric acid functional group,
Manufacturing method.
The method of claim 13,
The monomer having a sulfuric acid functional group is contained in 1 to 30 parts by weight compared to 100 parts by weight of the water-soluble ethylenically unsaturated monomer having an acidic group in which at least a portion is neutralized,
Manufacturing method.
The method of claim 14,
The monomer having a sulfuric acid functional group, sodium allyl sulfonate (Sodium Vinyl Sulfonate), sodium 4-styrene sulfonate (Sodium Styrene Sulfonate), 3-sulfopropyl acrylate potassium salt (3- sulfopropyl acrylate potassium salt (SPAK), 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS), sodium 4-vinylbenzenesulfonate , Or sodium allyloxy hydroxypropyl sulfonate,
Manufacturing method.