KR20230057286A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a preparation method of a superabsorbent polymer. More specifically, the present invention relates to a preparation method of a superabsorbent polymer, which uses a combination of a specific reducing agent compound and sodium dodecyl sulfate in a polymerization step so as to achieve excellent drying efficiency, thereby improving the absorption properties of the polymer.

Description

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

The present invention relates to a method for preparing a superabsorbent polymer. More specifically, it relates to a method for preparing a superabsorbent polymer that realizes excellent drying efficiency by including a specific reducing agent compound in a polymerization step and thereby improves the absorbent properties of the resin.

Super Absorbent Polymer (SAP) is a synthetic high-molecular substance that has the ability to absorb moisture 500 to 1,000 times its own weight. Material), etc., are named by different names. The superabsorbent polymer as described above has begun to be put into practical use as a sanitary tool, and is currently widely used as a material for gardening soil remediation agents, civil engineering and construction waterstop materials, seedling sheets, freshness retainers in the field of food distribution, and steaming. .

These superabsorbent polymers are widely used in sanitary materials such as diapers and sanitary napkins. In the sanitary material, it is common that the superabsorbent polymer is included in a spread state in the pulp. However, in recent years, efforts have been made to provide sanitary materials such as diapers with a thinner thickness, and as part of this, the content of pulp is reduced or, furthermore, so-called pulpless diapers in which pulp is not used at all. Development is actively progressing.

As described above, in the case of a sanitary material in which the pulp content is reduced or pulp is not used, the super absorbent polymer is included in a relatively high ratio, so that the super absorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire superabsorbent polymer particles included in multiple layers to more efficiently absorb a large amount of liquid such as urine, the superabsorbent polymer basically needs to exhibit high absorption performance as well as a fast absorption rate.

Meanwhile, such a superabsorbent polymer is generally prepared by polymerizing monomers to prepare a water-containing gel polymer containing a large amount of moisture, drying the water-containing gel polymer, and then pulverizing the water-containing gel polymer into resin particles having a desired particle size. The water-containing gel polymer has a property of aggregating with each other, and when it is made of agglomerated fine particles, there is a problem in that drying does not occur well in a subsequent drying process. Specifically, due to the increase in cohesion of the water-containing gel polymer, the porosity in the drying layer significantly decreases during the drying process, and thus the differential pressure of the hot air increases, resulting in a problem in that only the outside of the drying layer is dried and the inside is not sufficiently dried. In this case, it affects the absorption properties of the superabsorbent polymer to be finally manufactured, and the water retention capacity, absorption rate, etc. are deteriorated, so the development of technology for increasing drying efficiency is continuously required.

Accordingly, the present invention provides a method for producing a superabsorbent polymer capable of producing a water-containing gel polymer using a specific additive in the polymerization step, thereby exhibiting excellent drying efficiency in the subsequent drying process and finally implementing excellent absorbent properties. .

In order to solve the above problems, the present invention,

forming a water-containing gel polymer by crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent, a polymerization initiator, sodium dodecyl sulfate, and a reducing agent; and

Preparing a base resin by drying the water-containing gel polymer;

The reducing agent is at least one selected from the group consisting of oxalic acid, sodium metabisulfite and sodium benzoate,

After classifying the base resin with a 4 mesh sieve according to ASTM E11, the undrying rate defined as the mass ratio of the base resin not sieved by the sieve is 5 wt% or less,

A method for preparing a superabsorbent polymer is provided.

According to the manufacturing method of the superabsorbent polymer of the present invention, a water-containing gel polymer is prepared by using a combination of a specific reducing agent and sodium dodecyl sulfate in the polymerization step, thereby forming micropores in the polymer by increasing the polymerization rate, followed by a drying step. exhibits excellent drying efficiency, and the non-drying rate of the base resin can be controlled within a desired range. Accordingly, it is an object of the present invention to provide a method for manufacturing a super absorbent polymer capable of finally implementing excellent absorbent properties.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, step, component, or combination thereof, but one or more other features or steps; It should be understood that the presence or addition of components, or combinations thereof, is not previously excluded.

The terms first, second, third, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

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

As used herein, the term “polymer” or “polymer” means a polymerized state of water-soluble ethylenically unsaturated monomers, and may cover all moisture content ranges or particle size ranges. Among the polymers, polymers in a state after polymerization and before drying and having a moisture content (moisture content) of about 40% by weight or more may be referred to as hydrogel polymers, and particles obtained by pulverizing and drying such hydrogel polymers may be referred to as crosslinked polymers. there is.

Further, the term "crosslinked polymer" means a crosslinked polymerized product in the presence of the water-soluble ethylenically unsaturated monomer and an internal crosslinking agent, and the "base resin" means a material containing such a crosslinked polymer.

In addition, the term “superabsorbent polymer” means a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing an acidic group and at least a portion of which is neutralized, or a base resin obtained by drying the crosslinked polymer, depending on the context. The crosslinked polymer or the base resin is used to cover all of those obtained by subjecting the crosslinked polymer or the base resin to a state suitable for commercialization through additional processes such as surface crosslinking, fine powder reassembly, drying, grinding, classification, and the like.

Also, the term “superabsorbent polymer powder” refers to a particulate material including a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer containing an acidic group and at least a part of the acidic group is neutralized is polymerized and crosslinked by an internal crosslinking agent.

A method for preparing a superabsorbent polymer according to an embodiment of the present invention is a water-soluble, ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal crosslinking agent, a polymerization initiator, sodium dodecyl sulfate, and a reducing agent, which is crosslinked and polymerized to obtain a hydrous gel. forming a polymer; and preparing a base resin by drying the hydrogel polymer.

Recently, with the thinning of sanitary materials such as diapers and sanitary napkins, higher absorption performance is required for superabsorbent polymers. method is being considered. However, in order to improve the centrifugal retention capacity (CRC) of the superabsorbent polymer even after surface crosslinking, it is necessary to further improve the centrifugal retention capacity (CRC) of the base resin. is being considered However, when the content of the internal crosslinking agent is reduced, the stickiness of the polymer increases, so that drying is not performed well in the subsequent drying process. Specifically, due to the increase in the cohesive force of the water-containing gel polymer, the porosity in the drying layer significantly decreased during the drying process, so that only the outside of the drying layer was dried and the inside was not sufficiently dried. In addition, a decrease in the porosity of the drying layer increases the differential pressure of the hot air in the drying layer, and in order to achieve a desired drying rate, the drying temperature is excessively increased or the drying time is taken for a long time, resulting in a significant decrease in process efficiency. Finally, there was a problem in implementing the desired absorbent properties.

Therefore, the inventors of the present invention can effectively form micropores inside the polymer by increasing the polymerization rate by using a specific reducing agent and sodium dodecyl sulfate in combination in the formation step of the hydrogel polymer, and in the drying layer in the subsequent drying process. The present invention was completed by finding that an appropriate void can be formed, and thus, the undrying rate of the base resin can be controlled within a desired range.

The superabsorbent polymer prepared according to the present invention can realize excellent water absorption properties, and in particular, has excellent drying rate and centrifugal water retention capacity (CRC).

Hereinafter, a method for manufacturing a superabsorbent polymer according to an embodiment of the present invention will be described in detail for each step.

(Polymerization step)

A method for preparing a superabsorbent polymer according to an embodiment of the present invention is a water-soluble, ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal crosslinking agent, a polymerization initiator, sodium dodecyl sulfate, and a reducing agent, which is crosslinked and polymerized to obtain a hydrous gel. Forming a polymer.

Specifically, it is a step of thermally or photopolymerizing a monomer composition including an internal crosslinking agent, a polymerization initiator, sodium dodecyl sulfate, a specific reducing agent, and a monomer mixture to form a water-containing gel polymer.

Here, the use of sodium dodecyl sulfate can further promote the formation of microbubbles when forming the water-containing gel polymer, and at the same time, by using a specific reducing agent in combination, the polymerization reaction is accelerated to effectively reduce the micropores formed inside the polymer at a fast polymerization rate. make it possible to capture Accordingly, it is possible to control the non-drying rate of the base resin within a desired range with excellent drying efficiency in the subsequent drying process.

As the reducing agent, one or more selected from the group consisting of oxalic acid, sodium metabisulfite, and sodium benzoate may be used.

The reducing agent may be included in an amount of 500 ppmw to 10,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer, and the aggregation of the hydrogel polymer may be controlled within an appropriate range by being included in the above range. Preferably, 500 ppmw or more, 800 ppmw or more, 900 ppmw or more or 1,000 ppmw or more, 10,000 ppmw or less, 8,000 ppmw or less, 7,000 ppmw or less, 5,000 ppmw or less, 800 ppmw to 8,000 ppmw, 900 ppmw to 7,000 ppmw, It may be included in 1,000 ppmw to 5,000 ppmw, and within the above range, the above-described effect may be further improved.

The sodium dodecyl sulfate may be included in an amount of 500 ppmw to 10,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer, and when used together with a reducing agent in the above range, micropores can be effectively formed inside the hydrogel polymer. Preferably, 500 ppmw or more, 800 ppmw or more, 900 ppmw or more or 1,000 ppmw or more, 10,000 ppmw or less, 8,000 ppmw or less, 7,000 ppmw or less, 5,000 ppmw or less, 800 ppmw to 8,000 ppmw, 900 ppmw to 7,000 ppmw or It may be included in 1,000 ppmw to 5,000 ppmw, and within the above range, the above-described effect may be further improved.

The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the preparation 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 Formula 1,

R ₁ is an alkyl group having 2 to 5 carbon atoms including 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. As such, when acrylic acid or a salt thereof is used as a water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent polymer having improved water absorbency. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-( meth)acrylamide-2-methyl propane sulfonic acid anionic monomers and salts thereof; (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol ( nonionic hydrophilic containing monomers of meth)acrylate; and (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide, an amino group-containing unsaturated monomer and a quaternary product thereof; at least one selected from the group consisting of can be used

Here, the water-soluble ethylenically unsaturated monomer has an acidic group, and at least a part of the acidic group is partially neutralized using the neutralization liquid of the present invention described above.

In this case, the degree of neutralization of the monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%, as described above. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, neutralized monomers may be precipitated, making it difficult for the polymerization to proceed smoothly. It can exhibit properties like elastic rubber that are difficult to handle.

The term "internal cross-linking agent" used herein is a term used to differentiate from a "surface cross-linking agent" for cross-linking the surface of a base resin, and serves to polymerize by cross-linking the unsaturated bonds of the above-mentioned water-soluble ethylenically unsaturated monomers. . Crosslinking in this step proceeds regardless of surface or internal crosslinking, but by the surface crosslinking process of the base resin to be described later, the surface of the finally prepared superabsorbent polymer has a structure crosslinked by a surface crosslinking agent, and the inside is the internal crosslinking agent. It is composed of a cross-linked structure by a cross-linking agent.

The internal crosslinking agent may be a multifunctional component, for example, N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth) Acrylates, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate , Hexanedioldi(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri At least one selected from the group consisting of (meth)acrylate, pentaerythol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate may be used. Preferably, ethylene glycol diglycidyl ether may be used.

The internal crosslinking agent may be used in an amount of 50 ppmw to 1,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer. It is included in the above content range, and sufficient crosslinking can realize strength above an appropriate level, and sufficient water retention ability can be realized by introducing an appropriate crosslinking structure. Preferably, it is 100 ppmw or more, 200 ppmw or more, 300 ppmw or more or 600 ppmw or more, 1,000 ppmw or less or 800 ppmw or less, and included as 200 ppmw to 1,000 ppmw, 200 ppmw to 800 ppmw, or 600 ppmw to 800 ppmw can If the content of the internal cross-linking agent is too low, cross-linking does not occur sufficiently, making it difficult to realize an appropriate level of strength and significantly lowering the drying efficiency. this can be difficult

The polymerization initiator may be a radical polymerization initiator, initiates a polymerization reaction, and is used together with the above-described reducing agent component to easily form microbubbles inside the polymer by improving the speed of the polymerization reaction.

The polymerization initiator is, for example, 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) and 2, 2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride (2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride), 4,4- azo compounds of azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)); And persulfate-based compounds of sodium persulfate, potassium persulfate, and ammonium persulfate; at least one selected from the group consisting of may be used. Preferably, 2,2-azobis-(2-amidinopropane) dihydrochloride, sodium persulfate may be used.

The polymerization initiator may be included in an amount of 500 ppmw to 10,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer, and when used together with a reducing agent in the above range, the polymerization reaction may be accelerated to effectively form micropores inside the hydrogel polymer. Preferably, 500 ppmw or more, 750 ppmw or more, 800 ppmw or more or 1,000 ppmw or more, 10,000 ppmw or less, 8,000 ppmw or less, 7,000 ppmw or less, 5,000 ppmw or less or 1,000 ppmw or less, and 500 ppmw to 8,000 ppmw or 500 ppmw to 1,000 ppmw, 750 ppmw to 1,000 ppmw, 800 ppmw to 8,000 ppmw, 1,000 ppmw to 5,000 ppmw, or 1,500 ppmw to 4,500 ppmw, and within the range, the above-mentioned effects can be further improved.

In addition, as the polymerization initiator, a photopolymerization initiator or the like may be used in addition to the aforementioned radical initiator.

Examples of the photopolymerization initiator include, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyldimethyl ketal ( At least one compound selected from the group consisting of benzyl dimethyl ketal), acyl phosphine and alpha-aminoketone may be used. On the other hand, specific examples of acylphosphine include diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide, ethyl (2,4, 6-trimethylbenzoyl) phenylphosphinate etc. are mentioned. More various photoinitiators are well described in "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p115, a book by Reinhold Schwalm, and are not limited to the above examples.

The photopolymerization initiator may be added in an amount of 10 ppmw to 30,000 ppmw, preferably 30 ppmw to 10,000 ppmw, or 50 ppmw to 5,000 ppmw, based on the weight of the water-soluble ethylenically unsaturated monomer.

In addition, additives such as a foaming agent, a thickener, a plasticizer, a storage stabilizer, and an antioxidant may be further included in the monomer composition, if necessary.

The foaming agent serves to increase the surface area by forming pores in the water-containing gel polymer by foaming during polymerization. Carbonate may be used as the foaming agent, for example, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium Calcium bicarbonate, magnesium bicarbonate or magnesium carbonate may be used. As a usable commercial blowing agent, F-36D, an encapsulated blowing agent, may be used, but is not limited thereto.

In addition, the foaming agent is preferably used in an amount of 1,500 ppmw or less based on the weight of the water-soluble ethylenically unsaturated monomer. If the amount of the foaming agent used exceeds 1,500 ppmw, the number of pores increases too much, and the gel strength of the superabsorbent polymer decreases and the density decreases, causing problems in distribution and storage. In addition, the foaming agent is preferably used in an amount of 500 ppmw or more, or 1,000 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 aforementioned reducing agent, internal crosslinking agent, water-soluble ethylenically unsaturated monomer, and polymerization initiator are dissolved in a solvent.

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

The step of forming the water-containing gel 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 photopolymerization according to the type of polymerization energy source. In the case of proceeding, it may proceed in a reactor equipped with a movable conveyor belt.

For example, a water-containing gel polymer may be obtained by introducing the monomer composition into a reactor such as a kneader equipped with an agitation shaft, supplying hot air thereto, or heating the reactor to perform thermal polymerization. At this time, depending on the shape of the stirring shaft provided in the reactor, the water-containing gel polymer discharged through the outlet of the reactor may be obtained as particles of several millimeters to several centimeters. Specifically, the obtained water-containing gel polymer may be obtained in various forms depending on the concentration and injection speed of the monomer composition to be injected, and a water-containing gel polymer having a (weight average) particle diameter of 2 to 50 mm may be obtained.

And, as another example, when photopolymerization of the monomer composition is performed in a reactor equipped with a movable conveyor belt, a sheet-type water-containing gel polymer may be obtained. At this time, the thickness of the sheet may vary depending on the concentration and injection speed of the monomer composition to be injected, but it is usually adjusted to a thickness of 0.5 to 10 cm in order to ensure the production rate while allowing the entire sheet to be polymerized evenly. desirable.

A typical moisture content of the water-containing gel polymer obtained in this way may be 40% to 80% by weight. Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the dry polymer from the weight of the hydrogel polymer as the content of moisture with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to moisture evaporation in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying conditions are such that the temperature is raised from room temperature to 180 ° C and then maintained at 180 ° C. The total drying time is set to 20 minutes including 5 minutes of the temperature raising step, and the moisture content is measured.

(drying step)

Next, a step of preparing a base resin by drying the water-containing gel polymer is included.

If necessary, a step of coarsely pulverizing the water-containing gel polymer may be further performed before drying to increase the efficiency of the drying step. The grinder used is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, and a cutting grinder It may include any one selected from the group of crushing devices consisting of a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter. However, it is not limited to the above examples.

The drying step is a step of preparing a base resin having a target particle size by removing moisture present in the water-containing gel polymer. By using a specific reducing agent in the polymerization step described above, micropores can be easily formed inside the polymer, and accordingly, appropriate pores are formed in the dried material, thereby improving the drying efficiency of the drying step.

At this time, the drying temperature of the drying step may be 150 ℃ to 250 ℃. As described above, by using a specific reducing agent in the polymerization step, excellent drying efficiency can be implemented even under relatively mild drying conditions, and accordingly, the green rate of the base resin can be controlled within a desired range.

On the other hand, when the drying temperature is less than 150 ° C, the drying time is excessively long and there is a concern that the physical properties of the finally formed superabsorbent polymer may deteriorate, and when the drying temperature exceeds 250 ° C, only the polymer surface is excessively dried, resulting Fine particles may be generated in the crushing process, and economic feasibility is reduced due to the increase in process cost. Preferably, the drying may be performed at a temperature of 150 °C to 200 °C, more preferably at a temperature of 150 °C to 185 °C. The drying may be performed in multiple stages by varying the temperature within the above temperature range.

The drying step may be performed for 30 to 60 minutes, and when the time of the drying step is less than 30 minutes, the inside of the drying layer to be dried is not sufficiently dried to achieve the desired degree of undrying. It is difficult, and if it exceeds 60 minutes, drying efficiency may decrease and polymer degradation may occur in some particles. The time of the drying step is the sum of the execution times of each step when drying is performed in multiple steps.

The drying step may be preferably performed by hot air drying, and in this case, drying by hot air that satisfies the above-described temperature range is meant. In the drying step, the number of inputs of hot air is not particularly limited, and may be applied several times as long as the total drying time satisfies the aforementioned range.

The drying may be carried out in a fixed-bed type, in which hot air passes through the material from the bottom to the top while the material to be dried is suspended on the floor such as a perforated board through which air can flow. refers to the way in which Specifically, it is performed using a ventilated belt dryer equipped with a perforated plate. Specifically, the process is carried out by introducing the chopped mixture to be dried into a perforated board, and accordingly, the upward wind means blowing from the bottom to the top of the perforated board, and the downwind means blowing from the top to the bottom of the chopped mixture placed on the perforated board. it means.

The hot air drying is performed by introducing hot air at a linear velocity of 0.5 m/s to 3.0 m/s, 0.7 m/s to 2.5 m/s, and 0.85 m/s to 2.0 m/s. When the above speed range is satisfied, it is possible to uniformly dry the inside of the object to be dried, which is preferable. When the linear speed is less than 0.5 m/s, it is difficult for the hot air to reach the inside of the drying object, and when it exceeds 3.0 m/s, there is a possibility that the drying object is scattered inside the dryer.

The non-drying rate of the base resin prepared through the drying step is 3 wt% or less. The non-drying rate indicates the degree of drying of the crumb-type powder, which is relatively large in size and difficult to dry, among the base resins, and is one of the indicators of drying efficiency.

Specifically, the base resin is classified with a 4 mesh according to ASTM E11, which means the mass ratio of the base resin that is not filtered by the sieve, and the particles that are not filtered by performing the process of classifying the base resin with a 4 mesh sieve for more than 10 minutes This means that reagglomeration occurred due to internal moisture due to insufficient drying. In fact, by sifting through a 4 mesh sieve for more than 10 minutes, the moisture content of the particles not filtered by the sieve is more than 10%.

The green rate is excellent as the value is smaller, and the lower limit of the green rate is 0 wt%. Preferably, 0wt% or more, 0.001wt% or more, 0.001wt% or more, or 0.1wt% or more, or 3wt% or less, 1wt% or less, 0.7wt% or less, or 0.5wt% or less, or 0wt% to 3wt%, or 0wt%. % to 1 wt%, 0.01 wt% to 3 wt%, 0.01 wt% to 1 wt%, or 0.01 wt% to 0.7 wt%. The method for measuring the undrying rate of the base resin will be described in more detail in the experimental example section to be described later.

The base resin has a centrifugal retention capacity (CRC) of 60.0 g/g or more, preferably 62.0 g/g or more, 90.0 g/g or less, 87.0 g/g or less, measured according to EDENA method WSP 241.3, 60 g/g to 90 g/g or 62 g/g to 87 g/g. A specific method for measuring the centrifugal water retention capacity will be described in more detail in an experimental example to be described later.

(crushing and classifying step)

As described above, the base resin prepared as described above exhibits excellent drying efficiency, and it is possible to prepare a resin having a desired particle size only by sieving through a sieve. Accordingly, optionally, crushing and classifying the base resin may be further included.

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

In addition, in order to manage the physical properties of the superabsorbent polymer powder produced as a final product after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed. Preferably, polymers having particle diameters of 150 to 850 μm are classified, and only polymer powders having such particle diameters can be commercialized through a surface crosslinking reaction step. More specifically, the classified base resin may have a particle size of 150 to 850 μm, and may include particles having a particle size of 300 to 600 μm in an amount of 50% by weight or more.

(Surface cross-linking step)

Next, the manufacturing method of the superabsorbent polymer according to one embodiment of the present invention further includes crosslinking a part of the surface of the base resin by heat-treating the base resin in the presence of surface crosslinking.

The surface crosslinking step is to induce a crosslinking reaction on the surface of the base resin in the presence of a surface crosslinking agent, and unsaturated bonds of water-soluble ethylenically unsaturated monomers remaining on the surface without crosslinking are crosslinked by the surface crosslinking agent, A superabsorbent polymer with high surface crosslinking density is formed.

Specifically, a surface crosslinking layer may be formed by a heat treatment process due to the presence of a surface crosslinking agent, and the heat treatment process increases the surface crosslinking density, that is, the external crosslinking density, while the internal crosslinking density does not change, resulting in a surface crosslinking layer. The formed superabsorbent polymer has a structure in which the crosslinking density is higher on the outside than on the inside.

In the surface cross-linking step, a surface cross-linking agent composition containing an alcohol-based solvent and water may be used in addition to the surface cross-linking agent.

On the other hand, as the surface crosslinking agent included in the surface crosslinking agent composition, any crosslinking agent component previously used in the preparation of superabsorbent polymer may be used without any particular limitation. For example, the surface crosslinking agent is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2- 1 selected from the group consisting of methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol more than one polyol; At least one carbonate-based compound selected from the group consisting of ethylene carbonate and propylene carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; etc. may be included. Preferably, the same internal crosslinking agent as described above may be used, and for example, a diglycidyl ether-based compound of alkylene glycol such as ethylene glycol diglycidyl ether may be used.

Such a surface crosslinking agent may be used in an amount of 0.001 to 2 parts by weight based on 100 parts by weight of the base resin. Preferably, it is 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, and may be used in an amount of 0.5 parts by weight or less and 0.3 parts by weight or less. By adjusting the content range of the surface crosslinking agent within the above-described range, a superabsorbent polymer exhibiting various physical properties such as excellent absorption performance and liquid permeability can be prepared.

On the other hand, the surface cross-linking agent is added to the base resin in the form of a surface cross-linking agent composition containing the surface cross-linking agent composition. For example, a method of mixing a surface cross-linking agent composition and a base resin in a reaction tank, a method of spraying a surface cross-linking agent composition on a base resin, a method of continuously supplying and mixing a base resin and a surface cross-linking agent composition to a continuously operated mixer, etc. can be used.

In addition, the surface crosslinking agent composition may further include water and/or a hydrophilic organic solvent as a medium. As a result, there is an advantage in that the surface crosslinking agent and the like can be evenly dispersed on the base resin. At this time, the content of water and hydrophilic organic solvent is added to 100 parts by weight of the base resin for the purpose of inducing uniform dissolution / dispersion of the surface crosslinking agent, preventing aggregation of the base resin, and at the same time optimizing the surface penetration depth of the surface crosslinking agent It can be applied by adjusting the ratio.

The surface crosslinking step may be performed by heat treatment at a temperature of 110 °C to 200 °C or 110 °C to 150 °C for 30 minutes or more. More specifically, the surface crosslinking reaction may be performed by heat treatment for 30 to 80 minutes or 40 to 70 minutes at the maximum reaction temperature with the above-mentioned temperature as the maximum reaction temperature.

By satisfying these surface crosslinking process conditions (particularly, reaction conditions at elevated temperature and maximum reaction temperature), a superabsorbent polymer that appropriately satisfies physical properties such as better permeability under pressure can be produced.

The means for raising the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heat medium or directly supplying a heat source. At this time, as the type of heat medium that can be used, steam, hot air, and heated fluids such as hot oil may be used, but are not limited thereto, and the temperature of the heat medium supplied depends on the means of the heat medium, the heating rate, and the target temperature of the heating medium. can be selected appropriately. On the other hand, as a heat source that is directly supplied, heating through electricity and heating through gas may be mentioned, but it is not limited to the above-described example.

Meanwhile, in the method for preparing the superabsorbent polymer according to an embodiment of the present invention, aluminum salts such as aluminum sulfate salts and other various polyvalent metal salts may be further used to further improve liquid permeability and the like during surface crosslinking. Such a polyvalent metal salt may be included on the surface crosslinking layer of the finally prepared superabsorbent polymer.

(super absorbent polymer)

The superabsorbent polymer prepared according to the above-described embodiment may have a particle diameter of 150 to 850 μm. More specifically, at least 95% by weight of the super absorbent polymer has a particle size of 150 to 850 μm, and may include 50% by weight or more of particles having a particle size of 300 to 600 μm, and having a particle size of less than 150 μm Fines can be less than 3% by weight.

The superabsorbent polymer prepared according to the above-described embodiment realizes excellent absorbent properties, and in particular, has excellent centrifugal water retention capacity and absorbency under pressure.

Hereinafter, the action and effect of the invention will be described in more detail through specific examples of the invention. However, these embodiments are only presented as examples of the invention, and the scope of the invention is not determined thereby.

[Example]

<Manufacture of superabsorbent polymer>

Example 1

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 500 g of acrylic acid, 600 ppmw of ethylene glycol diglycidyl ether as an internal crosslinking agent (relative to 100 parts by weight of acrylic acid), 5,000 ppmw of oxalic acid compared to acrylic acid as a reducing agent, and diphenyl as a photopolymerization initiator (2,4 After adding and dissolving 80 ppmw of ,6-trimethylbenzoyl)-phosphine oxide (relative to 100 parts by weight of acrylic acid), 627 g of a 31.5% caustic soda solution was added to prepare a water-soluble unsaturated monomer aqueous solution (degree of neutralization: 70 mol%; solid content) content: 44.9% by weight). When the temperature of the aqueous solution of the water-soluble unsaturated monomer reaches 40° C. after rising due to heat of neutralization, 750 ppmw of 2,2-azobis-(2-amidinopropane) dihydrochloride as a radical polymerization initiator (relative to 100 parts by weight of acrylic acid) and a foaming agent After putting F36D in a container containing 1,000 ppmw (relative to 100 parts by weight of acrylic acid) and 1,000 ppmw sodium dodecyl sulfate (compared to 100 parts by weight of acrylic acid), UV polymerization was performed by irradiating ultraviolet rays (irradiation amount: 10mV/cm ² ) for 1 minute. A hydrogel polymer sheet was obtained.

The obtained hydrogel polymer sheet was passed through a chopper having a hole size of 16 mm to prepare crumbs.

Next, the crumbs were dried in an oven capable of shifting air volume upwards and downwards. The drying was performed in multiple stages, and specifically, 150°C for 13 minutes, 170°C for 5 minutes, 175°C for 5 minutes, 180°C for 5 minutes, and 160°C for 5 minutes using an air flow oven. Through the above drying process, a superabsorbent polymer including a base resin was prepared.

Examples 2 to 5 and Comparative Examples 1 to 7

A superabsorbent polymer was prepared in the same manner as in Example 1, except that the components and contents in Table 1 were used in the polymerization step.

division polymerization step dried sweet crab crushing step internal cross-linking agent
(type/content ^* ) reducing agent
(type/content ^* ) radical polymerization initiator
(type/content*) SDS
(content*) (Temperature ℃/
timemin) (type/content ^* ) Example 1 A-1/600 B-1/5,000 C-1/750 1,000 150/13-170/5-
175/5-180
/5-160/5 - Example 2 A-1/600 B-2/1,000 C-1/750 1,000 same - Example 3 A-1/600 B-3/1,000 C-1/750 1,000 same - Example 4 A-1/200 B-1/5,000 C-1/750 1,000 same - Example 5 A-1/800 B-1/5,000 C-1/750 1,000 same - Example 6 A-1/600 B-3/1,000 C-1/750 800 same - Example 7 A-1/600 B-3/1,000 C-1/750 3,000 same - Example 8 A-1/600 B-3/1,000 C-1/750 5,000 same - Comparative Example 1 A-1/600 - C-1/750 1,000 150/5-150/8-170
/5-175/5-180
/5-160/5 - Comparative Example 2 A-1/600 - C-1/750 1,000 same B-1/5,000 Comparative Example 3 A-1/600 - C-1/750 1,000 same B-2/1,000 Comparative Example 4 A-1/600 - C-1/750 1,000 same B-3/1,000 Comparative Example 5 A-1/600 - C-1/750 1,000 same B-3/5,000 Comparative Example 6 A-1/200 - C-1/750 1,000 same B-3/1,000 Comparative Example 7 A-1/600 B-1/5,000 C-1/750 - same - Internal cross-linking agent (*ppmw by weight of water-soluble ethylenically unsaturated monomers)
A-1: ethylene glycol diglycidyl ether
Reducing agent (*ppmw by weight of water-soluble ethylenically unsaturated monomers)
B-1: oxalic acid
B-2: sodium metabisulfite
B-3: sodium benzoate
Radical polymerization initiator (*ppmw by weight of water-soluble ethylenically unsaturated monomers)
C-1: 2,2-azobis-(2-amidinopropane) dihydrochloride
Sodium dodecyl sulfate (SDS) (*ppmw by weight of water-soluble ethylenically unsaturated monomer)

<Experimental example>

The physical properties of the superabsorbent polymers including the base resins prepared in Examples and Comparative Examples were evaluated in the following manner, and the results are shown in Table 2.

(1) Centrifuge Retention Capacity (CRC)

With respect to the base resin prepared in the above Examples and Comparative Examples, by taking those having a particle size of 150 to 850 μm, according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.2 by absorption capacity under no load Centrifuge retention capacity (CRC) was measured.

Specifically, from the base resins obtained through Examples and Comparative Examples, resins classified through a #30-50 sieve were obtained. This resin W0 (g) (about 0.2 g) was uniformly put into a bag made of nonwoven fabric, sealed, and immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes, water was drained from the bag for 3 minutes under the condition of 250 G using a centrifugal separator, and the mass W2 (g) of the bag was measured. Moreover, after carrying out the same operation without using resin, the mass W1 (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to Equation 1 below.

[Equation 1]

CRC (g/g) = {[W2(g) - W1(g)]/W0(g)} - 1

(2) Evaluation of undrying rate

For the base resins prepared in the above Examples and Comparative Examples, the undrying rate according to Equation 2 was evaluated, and the results are shown in Table 2.

Specifically, with respect to the initial weight A′1 (g) of the base resin sample (A1), the base resin sample (A1) was classified for 10 minutes through a 4 mesh sieve according to ASTM E11, and the sample not sieved by the sieve ( A2) was obtained, and the ratio of the weight A′2(g) of the sample not sieved by the sieve was measured.

[Equation 2]

Undrying rate (wt%) = {[A'1(g) - A'2(g)]/A'1(g)} * 100

division base resin Undrying rate (wt%) CRC (g/g) Example 1 0 67.6 Example 2 0 85.3 Example 3 0 69.6 Example 4 1.0 70.1 Example 5 0 62.5 Example 6 0 76.7 Example 7 0 72.5 Example 8 0 81.0 Comparative Example 1 4.0 59.0 Comparative Example 2 3.8 58.3 Comparative Example 3 3.4 57.7 Comparative Example 4 3.5 58.8 Comparative Example 5 3.4 57.8 Comparative Example 6 6.5 64.0 Comparative Example 7 4.1 59.9

As can be seen from the data in Table 2, the examples according to the manufacturing method of the present invention confirmed that excellent drying efficiency and CRC properties can be implemented at the same time by using a specific reducing agent compound and sodium dodecyl sulfate in combination in the polymerization step. .

In the case of Comparative Example 1 in which the reducing agent of the present application was not used, internal bubbles of the polymer were not sufficiently formed, and it was confirmed that the undrying rate increased due to the re-agglomeration of the particles in the drying process.

In the case of Comparative Examples 2 to 6, which included the same reducing agent compound as the present application but used in the grinding step rather than the polymerization step, it was confirmed that the green rate increased significantly and the CRC value of the base resin was slightly lowered compared to the examples.

In addition, in the case of Comparative Example 7 not containing SDS, it was confirmed that it was difficult to form bubbles inside the polymer, and the green rate value increased, and the CRC value also decreased compared to Examples.

Claims (10)

forming a water-containing gel polymer by crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent, a polymerization initiator, sodium dodecyl sulfate, and a reducing agent; and
Preparing a base resin by drying the water-containing gel polymer;
The reducing agent is at least one selected from the group consisting of oxalic acid, sodium metabisulfite and sodium benzoate,
After classifying the base resin with a 4 mesh sieve according to ASTM E11, the undrying rate defined as the mass ratio of the base resin not sieved by the sieve is 3 wt% or less,
A method for producing a superabsorbent polymer.
According to claim 1,
The undrying rate of the base resin is 1 wt% or less,
A method for producing a superabsorbent polymer.
According to claim 1,
The centrifugal retention capacity (CRC) according to the EDENA method WSP 241.3 of the base resin is 60.0 g / g or more,
A method for producing a superabsorbent polymer.
According to claim 1,
The reducing agent is included in 500 ppmw to 10,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer,
A method for producing a superabsorbent polymer.
According to claim 1,
The sodium dodecyl sulfate is included in 500 ppmw to 10,000 ppmw based on the weight of the ethylenically unsaturated monomer,
A method for producing a superabsorbent polymer.
According to claim 1,
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, pentaerythol tetraacrylic acid at least one member selected from the group consisting of lactate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate,
A method for producing a superabsorbent polymer.
According to claim 1,
The internal crosslinking agent is included in an amount of 50 ppmw to 1,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer.
A method for producing a superabsorbent polymer.
According to claim 1,
The polymerization initiator,
2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidin dihydrochloride Hydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutylonitril (2-(carbamoylazo)isobutylonitril) and 2,2-azobis[2-( 2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride), 4,4-azobis-(4-cyano azo compounds of valeric acid) (4,4-azobis-(4-cyanovaleric acid)); and
Selected from the group consisting of persulfate compounds of sodium persulfate, potassium persulfate and ammonium persulfate,
A method for producing a superabsorbent polymer.
According to claim 1,
The polymerization initiator is included in 500 ppmw to 10,000 ppmw based on the weight of the water-soluble ethylenically unsaturated monomer,
A method for producing a superabsorbent polymer.
According to claim 1,
Further comprising crosslinking a part of the surface of the base resin by heat-treating the base resin in the presence of a surface crosslinking agent,
A method for producing a superabsorbent polymer.