KR20210038081A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for producing a super absorbent polymer. More particularly, the present invention relates to a method for producing a super absorbent polymer, in which a binder of a specific component is used in a fine powder reassembly process to improve processability in the manufacturing process, and to realize excellent absorption-related physical properties in the manufactured super absorbent polymer.

Description

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

The present invention relates to a method for producing a super absorbent polymer.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has a function of absorbing moisture of 500 to 1,000 times its own weight, and it has begun to be put into practical use as a sanitary tool, and now is a paper diaper for children. In addition to hygiene products, etc., it is widely used as a material such as a soil repair agent for horticulture, a water-stop material for civil engineering and construction, a sheet for seedlings, a freshness maintenance agent in the food distribution field, and a poultice.

The absorption mechanism of this superabsorbent polymer is the interaction of penetration pressure due to the difference in electric attraction force expressed by the electric charge of the polymer electrolyte, the affinity between water and the polymer electrolyte, molecular expansion due to the repulsive force between the polymer electrolyte ions, and the inhibition of expansion due to crosslinking. Dominated by That is, the absorbency of the superabsorbent polymer depends on the affinity and molecular expansion described above, and the absorption rate is largely dependent on the permeation pressure of the absorbent polymer itself.

Meanwhile, particles having a particle diameter of 150 μm or less, which are inevitably generated during the manufacturing process of the super absorbent polymer, are called fines, and are finely divided at a rate of about 20 to 30% during the pulverization or transfer process during the manufacturing process of the super absorbent polymer. It is known to occur. When such fine powder is included in the super absorbent polymer, it may cause a decrease in absorbency under pressure or water permeability, which are major properties of the super absorbent polymer. For this reason, during the manufacturing process of the super absorbent polymer, especially in the classification process, such fine powder is separated to produce the super absorbent polymer only from the remaining polymer particles.

In addition, the separated fine powder is again manufactured into large particles through a reassembly process, and a method of manufacturing/using such reassembled particles back into a super absorbent polymer is known. In particular, as one of the representative methods of such a reassembly method, a method of preparing a fine powder reassembly and a super absorbent polymer by mixing the fine powder with water and agglomerating it is known.

However, in such a reassembly process, if the amount of water is increased, the amount of energy used during drying increases, and the process cost increases. Furthermore, if moisture is not properly removed by drying after reassembly, the super absorbent polymer Problems such as increasing the load of the device for manufacturing may occur.

On the contrary, when the amount of water used in the reassembly process is reduced, the cohesive strength of the assembly becomes insufficient, so that the reassembly is not properly performed and the amount of fun powder that is reduced back to fine powder increases significantly, and also due to the reassembly process. There is a disadvantage in that physical properties such as absorption capacity of the prepared super absorbent polymer are insufficient.

Accordingly, there is a continuing need to develop a fine powder reassembly process capable of solving the above-described problems.

The present specification provides a method of manufacturing a super absorbent polymer capable of solving the above-described problems by using a binder of a specific component when reassembling the fine powder inevitably obtained during the manufacturing process of the super absorbent polymer.

In the present specification, in the presence of a polymerization initiator and an internal crosslinking agent, crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized to form a hydrogel polymer; Drying, pulverizing, and classifying the hydrogel polymer into normal base resin particles having a particle diameter of more than 150 µm and 850 µm or less, and fine powder of a base resin having a particle size of 150 µm or less; Adding an aqueous binder solution to the fine powder of the base resin, mixing and drying to obtain a fine powder reassembly; And mixing the finely reassembled body with the normal base resin particles to obtain a finely reassembled base resin powder; The binder is a water-soluble polymer having a weight average molecular weight of more than 200,000 g/mol, providing a method for producing a super absorbent polymer.

According to an embodiment of the present invention, the step of mixing the fine powder reassembled with the base resin normal particles includes drying and pulverizing the fine powder reassembly to have a particle diameter of 150 µm or less, and a particle diameter of more than 150 µm and 850 µm. Classifying into normal reassembled particles of the following; And mixing the reassembled normal particles with the base resin normal particles.

In addition, the re-assembly fine powder generated at this time may be re-introduced to the step of manufacturing the fine re-assembly.

Then, thereafter, in the presence of a surface crosslinking liquid, the fine powder reassembled base resin powder may be surface crosslinked to form super absorbent polymer particles.

According to another embodiment of the present invention, the binder may be at least one selected from the group consisting of cellulose, polyvinylpyrrolidone, polyacrylic acid, polyacrylate, and derivatives thereof.

In addition, the binder may preferably be included in an amount of about 0.01 to about 10 parts by weight based on 100 parts by weight of the fine powder of the base resin.

In addition, the aqueous binder solution may preferably contain about 10 to about 200 parts by weight of water, based on 100 parts by weight of the fine powder of the base resin, in addition to the above-described binder component.

And at this time, the temperature of the aqueous binder solution may be preferably added to about 10 ℃ to about 90 ℃.

In addition, drying in the step of obtaining the fine powder reassembly may be preferably performed at about 100 to about 200°C.

In addition, the fine powder reassembly is mixed with the base resin normal particles, based on 100 parts by weight of the base resin normal particles, about 10 to about 50 parts by weight, or about 20 to about 40 parts by weight, or about 30 It may be desirable to mix to about 40 parts by weight.

In the present invention, terms such as first and second are used to describe various components, and the terms are used only for the purpose of distinguishing one component from other components.

In addition, terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention.

Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present specification, terms such as "comprise", "include" or "have" are used to describe implemented features, numbers, steps, components, or combinations thereof, and one or more other features, numbers, and steps , Components, combinations thereof, or the possibility of addition are not excluded.

In addition, in the present specification, when each layer or element is referred to as being formed “on” or “on” each layer or element, it means that each layer or element is formed directly on each layer or element, or other It means that a layer or element may be additionally formed between each layer, on the object, or on the substrate.

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

Throughout this specification, the term physiological saline means physiological saline (0.9 wt% NaCl(s)).

Hereinafter, the present invention will be described in detail.

According to an aspect of the present invention, in the presence of a polymerization initiator and an internal crosslinking agent, crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized to form a hydrogel polymer; Drying, pulverizing, and classifying the hydrogel polymer into normal base resin particles having a particle diameter of more than 150 µm and 850 µm or less, and fine powder of a base resin having a particle size of 150 µm or less; Adding an aqueous binder solution to the fine powder of the base resin, mixing and drying to obtain a fine powder reassembly; And mixing the finely reassembled body with the normal base resin particles to obtain a finely reassembled base resin powder; The binder is a water-soluble polymer having a weight average molecular weight of more than 200,000 g/mol, and a method for producing a super absorbent polymer is provided.

The inventors of the present invention have found that when a binder aqueous solution of a specific component is used when reassembling fine powder, a fine powder reassembled body having excellent strength and uniform particle distribution can be obtained, and the present invention has been completed.

Hereinafter, a method of manufacturing a super absorbent polymer according to an embodiment will be described in more detail for each step.

For reference, in the present specification, "polymer" or "polymer" refers to a state in which a water-soluble ethylenically unsaturated monomer is polymerized, and may encompass all moisture content ranges, all particle diameter ranges, and all surface crosslinking states or processing states. . Among the above polymers, a polymer having a moisture content (moisture content) of about 40% by weight or more, which is in a state before drying after polymerization, may be referred to as a hydrogel polymer. In addition, among the polymers, a polymer having a particle diameter of 150 μm or less may be referred to as “fine powder”.

In addition, "super absorbent polymer" means the polymer itself depending on the context, or the polymer is in a state suitable for commercialization through an additional process, for example, surface crosslinking, fine powder reassembly, drying, pulverization, classification, etc. It is used to cover all things.

In the manufacturing method of one embodiment, first, a hydrous gel polymer is prepared.

The hydrogel polymer may be prepared by polymerizing a monomer mixture including a water-soluble ethylenically unsaturated monomer and a polymerization initiator.

As the water-soluble ethylenically unsaturated monomer, any monomer commonly used in the manufacture of a super absorbent polymer may be used without any other limitation. Here, any one or more monomers selected from the group consisting of anionic monomers and salts thereof, nonionic hydrophilic-containing monomers, amino group-containing unsaturated monomers, and quaternary products thereof may be used.

Specifically, (meth)acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-(meth)acryloylethane sulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth)acrylamide- Anionic monomers of 2-methyl propane sulfonic acid and salts thereof; (Meth)acrylamide, N-substituted (meth)acrylamide, 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 an amino group-containing unsaturated monomer of (N,N)-dimethylaminopropyl (meth)acrylamide and a quaternary product thereof. I can.

More preferably, acrylic acid or a salt thereof, for example, an alkali metal salt such as acrylic acid or a sodium salt thereof, may be used. By using such a monomer, it becomes possible to prepare a super absorbent polymer having superior physical properties. When the alkali metal salt of acrylic acid is used as a monomer, it can be used by neutralizing acrylic acid with a basic compound such as caustic soda (NaOH).

The concentration of the water-soluble ethylenically unsaturated monomer may be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, based on the monomer composition including the raw material and the solvent of the super absorbent polymer. It can be made into an appropriate concentration in consideration of time and reaction conditions. However, if the concentration of the monomer is too low, the yield of the super absorbent polymer may be low and economic problems may occur. If the concentration is too high, on the contrary, when the concentration is too high, a part of the monomer is precipitated or the pulverization efficiency is low when the polymerized hydrogel polymer is pulverized. In such process, problems may occur, and the physical properties of the super absorbent polymer may be deteriorated.

The polymerization initiator used in the polymerization in the method for preparing the super absorbent polymer of one embodiment is not particularly limited as long as it is generally used for preparing the super absorbent polymer.

Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation depending on the polymerization method. However, even in the photopolymerization method, a certain amount of heat is generated by irradiation such as UV irradiation, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, and thus a thermal polymerization initiator may be additionally included.

The photopolymerization initiator may be used without limitation of its configuration as long as it is a compound capable of forming a radical by light such as ultraviolet rays.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketone. dimethyl ketal), acyl phosphine, and alpha-aminoketone may be used. Meanwhile, as a specific example of acylphosphine, a commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) may be used. . More various photoinitiators are well specified in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p115, and are not limited to the above examples.

The photopolymerization initiator may be included in a concentration of about 0.01 to about 1.0% by weight based on the monomer mixture. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slow, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may become uneven.

In addition, as the thermal polymerization initiator, at least one selected from the group of initiators consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (Potassium persulfate; K ₂ S ₂ O ₈ ), ammonium persulfate (Ammonium persulfate; (NH ₄ )) ₂ S ₂ O ₈ ), etc., and examples of azo-based initiators include 2, 2-azobis-(2-amidinopropane) dihydrochloride (2, 2-azobis(2-amidinopropane) 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), 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are well specified in Odian's'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.

The thermal polymerization initiator may be included in a concentration of 0.001 to 0.5% by weight based on the monomer mixture. If the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs, so the effect of the addition of the thermal polymerization initiator may be insignificant.If the concentration of the thermal polymerization initiator is too high, the molecular weight of the super absorbent polymer may be small and the physical properties may become uneven. have.

According to an embodiment, the monomer mixture may further include an internal crosslinking agent as a raw material of the super absorbent polymer. As the internal crosslinking agent, a crosslinking agent having at least one functional group capable of reacting with the water-soluble substituent of the water-soluble ethylenically unsaturated monomer and having at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups capable of reacting with a water-soluble substituent of the monomer and/or a water-soluble substituent formed by hydrolysis of the monomer may be used.

Specific examples of the internal crosslinking agent include bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly(meth)acrylate of a polyol having 2 to 10 carbon atoms, or poly(meth)allyl ether of a polyol having 2 to 10 carbon atoms. And more specifically, N,N'-methylenebis(meth)acrylate, ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, propyleneoxy(meth)acrylate, glycerin diacrylate , Glycerin triacrylate, trimethylol triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol and propylene glycol may be used at least one selected from the group consisting of.

Such an internal crosslinking agent is included in a concentration of 0.01 to 0.5% by weight based on the monomer mixture, so that the polymerized polymer can be crosslinked.

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

Raw materials such as the above-described water-soluble ethylenically unsaturated monomer, photopolymerization initiator, thermal polymerization initiator, internal crosslinking agent, and additive may be prepared in the form of a monomer mixture solution dissolved in a solvent.

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

The solvent may be included in a residual amount excluding the above-described components with respect to the total content of the monomer mixture.

On the other hand, as long as the method of polymerizing such a monomer mixture to form a hydrogel polymer is also a commonly used polymerization method, there is no particular limitation on the configuration.

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source, and generally, when thermal polymerization is performed, it can be performed in a reactor having an agitation axis such as a kneader, and when photo polymerization is performed, Although it may be carried out in a reactor equipped with a movable conveyor belt, the polymerization method described above is an example and is not limited to the polymerization method described above.

For example, the hydrogel polymer obtained by thermal polymerization by supplying hot air or heating the reactor to a reactor such as a kneader equipped with a stirring shaft as described above, is passed to the reactor outlet according to the shape of the stirring shaft provided in the reactor. The discharged hydrogel polymer may be in the form of several centimeters to several millimeters. Specifically, the size of the resulting hydrogel polymer may vary depending on the concentration and injection speed of the monomer mixture to be injected, and a hydrogel polymer having a weight average particle diameter of 2 to 50 mm can be obtained.

In addition, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the form of the hydrogel polymer usually obtained may be a hydrogel polymer in the form of a sheet having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection speed of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a sheet-like polymer having a thickness of about 0.5 to about 5 cm can be obtained. In the case of supplying the monomer composition to the extent that the thickness of the polymer on the sheet is too thin, the production efficiency is not preferable, and when the thickness of the polymer on the sheet exceeds 5 cm, due to the excessively thick thickness, the polymerization reaction is evenly performed over the entire thickness. It may not happen.

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

According to one embodiment of the invention, a coarse pulverization process may be selectively further performed on the hydrogel polymer obtained above.

At this time, the grinder used in the coarse grinding process is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, and a rotary cutter mill), Cutter mill, Disc mill, Shred crusher, Crusher, Chopper, and Disc cutter. Any one may be included, but is not limited to the above-described example.

At this time, the coarse pulverization step may be pulverized so that the particle diameter of the hydrogel polymer is about 2 to 20 mm.

Coarse pulverization with a particle diameter of less than 2 mm is not technically easy due to the high moisture content of the hydrogel polymer, and the pulverized particles may aggregate with each other. On the other hand, when the particle diameter is coarsely pulverized to more than 20 mm, the effect of increasing the efficiency of the subsequent drying step may be insignificant.

Meanwhile, in the method for producing a super absorbent polymer according to an embodiment of the present invention, after preparing the hydrogel polymer, the hydrogel polymer may be dried and pulverized to be classified into fine powder and normal particles.

The drying process is performed on the hydrogel polymer immediately after polymerization, which is coarsely pulverized or not subjected to a coarse pulverization step. In this case, the drying temperature in the drying step may be about 150 to about 250°C. When the drying temperature is less than 150°C, the drying time may be too long and the physical properties of the finally formed super absorbent polymer may be deteriorated. When the drying temperature exceeds 250°C, only the polymer surface is excessively dried, resulting in a subsequent pulverization process. Fine powder may be generated at, and there is a concern that the physical properties of the finally formed super absorbent polymer may be deteriorated. Therefore, preferably, the drying may be performed at a temperature of about 150° C. to about 200° C., more preferably at a temperature of about 160° C. to about 180° C.

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

As long as the drying method in the drying step is also commonly used as a drying process of the hydrous gel polymer, it may be selected and used without limitation of its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. The moisture content of the polymer after such a drying step may be about 0.1 to about 10% by weight.

Next, a pulverization process is performed on the dried polymer obtained through such a drying step.

The polymer powder obtained after the pulverization step may have a particle diameter of about 150 to about 850 μm. The pulverizer used to pulverize with 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 (jog mill) or the like may be used, but the invention is not limited to the above-described examples.

In order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the pulverization step, in general, the polymer powder obtained after pulverization is classified according to the particle size. Preferably, a step of classifying into particles having a particle diameter of 150 µm or less and particles having a particle diameter of more than 150 µm and 850 µm or less is performed.

Unless otherwise stated in the specification, "particle diameter or particle size" may be measured through a standard sieve analysis method or a laser diffraction method, preferably a standard sieve analysis method, and the "average particle diameter or weight average The "particle diameter" may mean a particle diameter (D50) that becomes 50% of a weight percentage in a particle size distribution curve obtained through a laser diffraction method.

In addition, in the present specification, fine particles having a particle size of a certain particle size or less, that is, about 150 μm or less, are referred to as base resin fine powder, super absorbent polymer fine powder, SAP fine powder or fine powder (fines, fine powder), and a particle diameter of 150 μm Particles that are more than 850 μm or less are referred to as normal particles.

The fine powder may be generated during the polymerization process, the drying process, or the pulverization step of the dried polymer. If the fine powder is included in the final product, it is difficult to handle and may deteriorate physical properties, such as a gel blocking phenomenon. Therefore, it is preferable to exclude the fine powder so that it is not included in the final resin product, or to reassemble the fine powder to become normal particles.

For example, the fine powder may be reassembled to a normal particle size. In the reassembly process, in general, in order to increase the cohesive strength, a reassembly process is performed in which fine particles are agglomerated in a wet state. At this time, the higher the moisture content of the fine powder, the higher the cohesive strength of the fine powder, but too large a reassembly mass may be formed during the reassembly process, which may cause problems during the process operation.If the moisture content is low, the reassembly process is easy, but the cohesive strength is low. After that, it is often crushed again into fine powder (re-fine differentiation). In addition, the fine powder reassembled thus obtained may have lower physical properties such as water holding capacity (CRC) and pressure absorption capacity (AUP) than normal particles, leading to a decrease in the quality of the super absorbent polymer.

However, as described above, in the manufacturing method according to the embodiment of the present invention, by mixing the fine powder with the binder aqueous solution of a specific component, it is possible to obtain a fine powder reassembly having a high cohesive strength and a uniform particle size distribution.

The binder is a water-soluble polymer having a weight average molecular weight greater than 200,000 g/mol, preferably a water-soluble polymer having a weight average molecular weight of about 200,000 to about 1,000,000 g/mol, more preferably a weight average molecular weight of 220,000 to 750,000 g/mol. , Cellulose, polyvinylpyrrolidone, polyacrylic acid, polyacrylate, and one or more selected from the group consisting of derivatives thereof may be used.

This binder component, when applied between finely divided particles, allows the particles to be held together without being scattered well, so that wet granules can be formed well. In addition, such water-soluble polymers are applied between the reassembled particles to form an intermolecular bond with the surface of each SAP particle, thereby forming a fine powder reassembled body having high cohesive strength.

However, if a water-soluble polymer with too small a weight average molecular weight value is used, the degree of reinforcement of the reassembled particles is weak due to a low viscosity, which may cause a problem of fine powder regeneration.If a water-soluble polymer with an excessively large weight average molecular weight value is used, It takes too long for the polymer to dissolve in water, which may cause a problem that is difficult to apply to an actual process, which is not preferable.

In the manufacturing step of the fine powder reassembly, the above-described binder component may be used in an amount of about 0.01 to about 10, preferably about 0.05 to about 5 parts by weight, or about 0.05 to about 3 parts by weight based on 100 parts by weight of the fine powder. It is possible to prepare a fine powder reassembly having excellent mechanical properties such as crushing strength while exhibiting excellent absorption properties within the above content range.

In addition, the added binder aqueous solution may be adjusted to about 10 to about 200 parts by weight, or about 50 to about 150 parts by weight based on 100 parts by weight of the fine powder.

If the content of water is too small, it is difficult to evenly disperse a small amount of water due to the rapid absorption rate of the fine powder, so there is a concern that the uniformity of the fine powder reassembly decreases. In addition, when the water content of the fine powder reassembled to be produced decreases, the amount of fun powder generated may increase, and the absorption capacity of the finally prepared super absorbent polymer may be lowered. Conversely, when the water content exceeds the above range, there is a concern that the stickiness of the fine powder reassembly increases, so that normal mixing cannot be achieved, and the amount of water to be evaporated during the drying process increases, thereby increasing the load on the dryer.

The temperature of the aqueous binder solution added to the manufacturing step of the fine powder reassembly is about 10 to about 90° C., 10° C. to about 50° C., so as not to place a load on the apparatus for manufacturing the fine powder re-assembly while improving the cohesive strength of the fine powder re-assembly, It may be adjusted to about 15°C to about 35°C, or about 20°C to about 30°C.

In the manufacturing step of the fine powder reassembly, using a mixing device or a mixer capable of applying a shearing force, the fine powder and the aqueous binder solution are mixed at a speed of about 10 to about 2000 rpm, about 100 to about 1000 rpm, or about 500 to about 800 rpm. It can be mixed by stirring with.

The drying temperature may be adjusted according to the content of water added in the manufacturing step of the fine powder reassembly. As an example, the drying process in the manufacturing step of the fine powder reassembly may be performed at about 100 to about 200°C to form a fine powder reassembly with improved cohesive strength through covalent bonding, and the moisture content of the fine powder reassembly may be reduced within an appropriate time. It can be adjusted to 1 to about 2% by weight.

The drying process may be performed using a conventional drying device, but according to an embodiment of the present invention, it may be performed using a hot air dryer, a paddle-type dryer, or a forced circulation dryer. In addition, there is no limitation on the configuration of the heating means for drying during the drying step. Specifically, a heat medium may be supplied or directly heated by means such as electricity, but the present invention is not limited to the above-described examples. Heat sources that can be specifically used include steam, electricity, ultraviolet rays, infrared rays, and the like, and a heated thermal fluid may be used.

Next, in the method for producing a super absorbent polymer according to an embodiment of the present invention, the fine powder reassembly prepared in the above step is pulverized as necessary, and the reassembly is finely divided (hereinafter referred to as'refine powder') and classified into normal particles of the reassembly. You can proceed with the steps.

The fine powder re-assembly obtained through the step of preparing the fine powder re-assembly has a high cohesive strength and is pulverized and then re-crushed into fine powder, that is, the ratio of the fine powder is low.

The pulverization of the fine powder reassembly may be performed so that the particle diameter of the fine powder reassembly is about 150 to about 850 µm. The pulverizer used to pulverize with 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 (jog mill) or the like may be used, but the present invention is not limited to the above-described examples.

In order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the pulverization step, in general, the polymer powder obtained after pulverization is classified according to the particle size. Preferably, it undergoes a step of classifying into fine powder having a particle diameter of 150 µm or less, and reassembled normal particles having a particle diameter of more than 150 µm and 850 µm or less.

In addition, in the method for producing a super absorbent polymer according to an embodiment of the present invention, a super absorbent polymer is prepared by selectively crosslinking the surface by mixing the fine powder reassembly prepared by the above-described method, in particular, the reassembled normal particles with the base resin normal particles. You may.

Specifically, after the classification, the fungus powder having a particle diameter of 150 μm or less is circulated through a fine powder reassembly process, and the reassembled normal particles having a particle diameter of more than 150 μm and 850 μm or less are mixed with the base resin normal particles described above.

At this time, the fine powder reassembly is mixed with the base resin normal particles, based on 100 parts by weight of the base resin normal particles, about 10 to about 50 parts by weight, or about 20 to about 40 parts by weight, or about It may be desirable to mix from 30 to about 40 parts by weight.

In addition, after the mixing process, the reassembled normal particles and normal particles may be additionally introduced into the surface crosslinking mixer to selectively perform the surface crosslinking process.

The surface crosslinking is a step of increasing the crosslinking density near the surface of the super absorbent polymer particle in relation to the crosslinking density inside the particle. In general, the surface crosslinking agent is applied to the surface of the super absorbent polymer particles. Therefore, this reaction takes place on the surface of the super absorbent polymer particles, which improves the crosslinkability on the surface of the particles without substantially affecting the inside of the particles. Therefore, the surface crosslinked superabsorbent polymer particles have a higher degree of crosslinking near the surface than at the inside.

At this time, the surface crosslinking agent is not limited in its configuration as long as it is a compound capable of reacting with a functional group of a polymer.

Preferably, in order to improve the properties of the resulting super absorbent polymer, a polyhydric alcohol compound as the surface crosslinking agent; Epoxy compounds; Polyamine compounds; Haloepoxy compounds; Condensation products of haloepoxy compounds; Oxazoline compounds; Mono-, di- or polyoxazolidinone compounds; Cyclic urea compounds; Polyvalent metal salts; And one or more selected from the group consisting of alkylene carbonate compounds may be used.

Specifically, examples of the polyhydric alcohol compound include mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, dipropylene glycol, polypropylene glycol, 2,3,4-trimethyl-1,3-pentanediol , Glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanedi One or more selected from the group consisting of methanol may be used.

In addition, ethylene glycol diglycidyl ether and glycidol may be used as the epoxy compound, and as polyamine compounds, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine , Polyethyleneimine and polyamide polyamine may be used at least one selected from the group consisting of.

And as the haloepoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin may be used. Meanwhile, as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone may be used.

In addition, ethylene carbonate or the like may be used as the alkylene carbonate compound. These may be used alone or in combination with each other. On the other hand, in order to increase the efficiency of the surface crosslinking process, it is preferable to use one or more polyhydric alcohol compounds among these surface crosslinking agents, and more preferably, polyhydric alcohol compounds having 2 to 10 carbon atoms may be used.

The content of the surface crosslinking agent to be added may be appropriately selected depending on the type of the surface crosslinking agent to be added or reaction conditions, but is usually about 0.001 to about 5 parts by weight, preferably about 0.01 to about 100 parts by weight of the polymer. 3 parts by weight, more preferably about 0.05 to about 2 parts by weight may be used.

When the content of the surface crosslinking agent is too small, the surface crosslinking reaction hardly occurs, and when the content of the surface crosslinking agent is too large, the absorption capacity and physical properties may be deteriorated due to the progress of the excessive surface crosslinking reaction.

By heating the polymer particles to which the surface crosslinking agent has been added, the surface crosslinking reaction and drying may be performed simultaneously.

The means for increasing the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heat medium or by directly supplying a heat source. At this time, as the type of the heat medium that can be used, a heated fluid such as steam, hot air, or hot oil may be used, but the present invention is not limited thereto, and the temperature of the supplied heat medium is the means of the heat medium, the rate of temperature increase, and the temperature increase. It can be appropriately selected in consideration of the target temperature. Meanwhile, as a heat source directly supplied, heating through electricity and heating through gas may be mentioned, but the present invention is not limited to the above-described examples.

In addition, after the surface crosslinking, the surface crosslinking fine powder having a particle diameter of 150 μm or less, and the surface crosslinking normal particles having a particle diameter of more than 150 μm and 850 μm or less are classified, and the surface crosslinking fine powder having a particle diameter of 150 μm or less is a fine powder. Reintroduced as a process for assembly, and normal surface crosslinked particles can be commercialized and used.

The super absorbent polymer prepared by the above-described manufacturing method is manufactured from fine powder, but when surface-modified inorganic material having a reactive functional group is added when reassembling the fine powder, it has excellent mechanical properties such as crushing strength and can exhibit a uniform particle size distribution. have.

According to an embodiment of the present invention, the fine powder inevitably obtained in the manufacturing process of the super absorbent polymer is effectively reassembled to provide excellent absorption properties, excellent mechanical properties such as crush strength, and a super absorbent polymer having a uniform particle distribution. A manufacturing method can be provided.

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

Preparation of base resin-Examples and Comparative Examples

A monomer composition was prepared by mixing 100 parts by weight of acrylic acid, 123.5 parts by weight of 31.5% caustic soda (NaOH), 65.5 parts by weight of water, and the following components.

-Internal crosslinking agent: polyethylene glycol diacrylate (PEGDA; Mw = 400) 0.001 parts by weight (10 ppmw) and ethylene glycol diglycidyl ether 0.30 parts by weight (3000 ppmw)

-Polymerization initiator: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (photoinitiator) 0.008 parts by weight (80 ppmw) and sodium persulfate (thermal initiator) 0.125 parts by weight (1250 ppmw)

-Additional additive: 0.1 parts by weight of microcapsules (1000ppmw)

The composition was introduced into the supply section of a polymerization reactor consisting of a conveyor belt that continuously moves, and ultraviolet rays were irradiated with a UV irradiation device for 1.5 minutes (about 2 mW/cm ² ) to proceed with the polymerization reaction, and a water-containing gel polymer was obtained as a product. .

The hydrogel polymer was cut through a cutter. Subsequently, the hydrogel polymer was dried for 40 minutes in a hot air dryer at 190°C, and the dried hydrogel polymer was pulverized with a grinder. Subsequently, a polymer having a particle size (average particle size) of 150 µm to 850 µm was classified using a sieve to obtain fine powder of the base resin and normal particles of the base resin.

The CRC value of the obtained base resin was about 33.1 g/g.

Fine powder reassembly-Comparative Example 1

With respect to 100 parts by weight of the fine powder of the base resin obtained above, 100 parts by weight of water at 25° C. was mixed, and mixed for 15 seconds at 650 rpm using a high shear mixer.

The fine powder reassembly recovered from the inside of the mixer was dried for 1 hour in a hot air dryer at a temperature of 170° C., pulverized with a hammer mill, and then classified to prepare normal fine powder reassembled particles having a particle diameter of more than 150 µm and 850 µm or less.

Fine powder reassembly-Examples and Comparative Examples

With respect to 100 parts by weight of the fine powder of the base resin obtained above, 100 parts by weight of water at 25° C. and the binder components listed in Table 1 were mixed, and mixed for about 15 seconds at about 650 rpm using a high shear mixer.

The fine powder reassembly recovered from the inside of the mixer was dried for 1 hour in a hot air dryer at a temperature of 170° C., pulverized with a hammer mill, and then classified to prepare normal fine powder reassembled particles having a particle diameter of more than 150 µm and 850 µm or less.

Composition of reassembly solution
(Water, binder (Mw), unit: parts by weight) Comparative Example 1 Water 100 Comparative Example 2 Water 100, NaOH 1.0 Comparative Example 3 Water 100, Polyethylene glycol (Mw: ~6k) 0.5 Comparative Example 4 Water 100, Polyethylene glycol (Mw: ~6k) 1.0 Example 1 Water 100, Polyvinyl Pyrrolidone (Mw: ~360k)0.1 Example 2 Water 100, Polyvinyl Pyrrolidone (Mw: ~360k) 0.5 Example 3 Water 100, Polyvinyl Pyrrolidone (Mw: ~360k)1.0 Example 4 Water 100, Sodium Carboxymethyl Cellulose (Mw: ~700k) 0.1 Example 5 Water 100, Sodium Carboxymethyl Cellulose (Mw: ~700k) 0.5 Example 6 Water 100, Hydroxypropyl Cellulose (Mw: ~370k) 0.1 Example 7 Water 100, Hydroxypropyl Cellulose (Mw: ~370k) 1.0 Example 8 Water 100, Polyacrylic acid (Mw: ~250k) 0.1 Example 9 Water 100, Polyacrylic acid (Mw: ~250k) 0.5 Example 10 Water 100, Polyacrylic acid (Mw: ~250k) 0.5

Mixing with base resin and surface crosslinking-Examples and Comparative Examples

With respect to 100 parts by weight of the base resin normal particles, about 33 parts by weight of the finely reassembled normal particles were mixed to obtain a finely reassembled base resin powder.

Water 5 parts by weight, Glyether(R) EJ-1030S (ethylene glycol diglycidyl ether; manufactured by JSI) 0.03 parts by weight, aluminum sulfate 0.2 parts by weight, S-570 (sucrose stearic acid ester; Mitsubishi Chemical Co., Ltd.) Product) 0.03 parts by weight were mixed to prepare a surface crosslinking solution.

Here, the surface crosslinking solution was additionally added, mixed well, and maintained at about 140° C. for about 35 minutes, and the surface crosslinking reaction was performed.

Thereafter, 0.1 parts by weight of a dry inorganic filler (Aerosil 200, manufactured by Evonik) was added and mixed well.

After pulverization, a surface-treated super absorbent polymer having a particle diameter of 150 to 850 µm was obtained using a sieve.

With respect to the surface-treated superabsorbent polymer obtained above, physical properties were evaluated by the following method.

CRC value measurement

The water holding capacity of each resin was measured according to EDANA WSP 241.3 by the absorption rate under no load.

Specifically, from the base resin, the surface-treated super absorbent polymer obtained through each of the Examples and Comparative Examples, a resin classified through a sieve of #30-50 was obtained. This resin W0(g) (about 0.2g) was evenly put in a nonwoven bag and sealed, and then immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes elapsed, water was removed from the bag for 3 minutes under the condition of 250 G using a centrifuge, and the mass W2 (g) of the bag was measured. Moreover, after performing the same operation without using a resin, the mass W1 (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following equation.

[Equation 1]

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

0.3 AUP value measurement

The absorbency under pressure of 0.3 psi of each resin was measured according to the EDANA method WSP 242.3.

First, in the measurement of the combined absorption capacity, the resin classified in the CRC measurement was used in the same manner.

Specifically, a 400 mesh stainless steel mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm. The piston that can uniformly spray the water absorbent resin W0(g) (0.16 g) on the wire mesh under the conditions of room temperature and humidity of 50%, and apply an additional load of 0.7 psi (or 0.3, 0.9 psi) evenly thereon. It is slightly smaller than the outer diameter of 25 mm, and there is no gap with the inner wall of the cylinder, and the vertical movement is not disturbed. At this time, the weight W3 (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed on the inside of a 150 mm diameter PET dish, and a physiological saline solution composed of 0.9 wt% sodium chloride was at the same level as the upper surface of the glass filter. One sheet of filter paper with a diameter of 90 mm was mounted on it. The measuring device was placed on the filter paper, and the liquid was absorbed for 1 hour under load. After 1 hour, the measuring device was lifted and the weight W4 (g) was measured.

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

[Equation 2]

AUP(g/g) = [W4(g)-W3(g)]/W0(g)

Water absorption capacity for 1 minute

As the tap water, tap water within a temperature range of about 24 °C (error range of 0.2 °C) and conductivity range of about 110 µs/cm (error range of 5 µs/cm) was used, and each resin was classified as a resin in the CRC measurement. Was used in the same way.

An 18 cm * 28 cm tea bag made of polyethylene and polypropylene composite fiber was prepared, and the tea bag was well spread inside a 2L PP beaker without a fold.

1±0.0005 g of the water absorbent resin was accurately weighed, taking care not to stick the resin to the flask wall, and spreading it evenly on the bottom of the tea bag.

Tap water was poured into a tea bag in a 2L beaker within about 1 second, and the water absorbent resin inside was swollen for about 1 minute, and then the tea bag containing the swollen water absorbent resin was quickly lifted.

After maintaining the lifted tea bag in a static state as much as possible, waiting for no more water to drip from the tea bag, and confirming that the water did not drip for more than 5 minutes, the weight was measured.

The water absorption capacity for 1 minute was calculated by subtracting the original weight of the tea bag and 1 g of the water absorbent resin from the measured weight.

Vortex value measurement

It was measured in seconds according to the method described in International Patent Publication No. 1987-003208, and when measuring the Vortex value, the resin classification component in the CRC measurement was used in the same manner.

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

The measured values are summarized in Table 2 below.

BR CRC
(g/g) Product CRC
(g/g) 0.3AUP 1 minute water supply
Absorption capacity Vortex Comparative Example 1 33.1 30.6 25.3 91 38 Comparative Example 2 33.1 30.3 26.1 95 38 Comparative Example 3 33.1 30.2 24.7 102 36 Comparative Example 4 33.1 30.5 24.5 103 36 Example 1 33.1 30.2 25.7 113 35 Example 2 33.1 30.3 25.9 115 33 Example 3 33.1 30.2 25.9 120 32 Example 4 33.1 31.0 25.2 122 32 Example 5 33.1 30.7 25.0 123 31 Example 6 33.1 31.1 25.3 122 33 Example 7 33.1 30.5 25.8 127 31 Example 8 33.1 30.7 25.8 118 35 Example 9 33.1 31.0 25.2 116 34 Example 10 33.1 30.8 25.5 125 32

Referring to Table 1, it can be seen that the superabsorbent polymer according to an embodiment of the present invention generally has excellent absorption properties.

In particular, the super absorbent polymer according to the embodiment of the present invention is improved by about 15 to 30% compared to the comparative example, despite the use of the same base resin as the comparative example and undergoing fine powder reassembly and surface crosslinking in a similar process. It can be clearly confirmed that the water absorption capacity for 1 minute is provided, and nevertheless, it can be confirmed that the vortex time is reduced by about 10 to 30% compared to the comparative example.

Accordingly, the method for producing a super absorbent polymer of the present invention can significantly improve fairness and economics by recycling fine powders in the manufacturing process, while having excellent water absorption capacity for one minute and a fast absorption rate in the super absorbent polymer prepared. All properties related to absorption can be implemented.

Claims (10)

Crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of a polymerization initiator and an internal crosslinking agent to form a hydrogel polymer;
Drying, pulverizing, and classifying the hydrogel polymer into normal base resin particles having a particle diameter of more than 150 µm and 850 µm or less, and fine powder of a base resin having a particle size of 150 µm or less;
Adding an aqueous binder solution to the fine powder of the base resin, mixing and drying to obtain a fine powder reassemble; And
Mixing the finely reassembled body with the normal base resin particles to obtain a finely reassembled base resin powder;
The binder is a water-soluble polymer having a weight average molecular weight greater than 200,000 g/mol,
Method for producing a super absorbent polymer.
The method of claim 1,
The step of mixing the fine powder reassembly with the base resin normal particles,
Drying and pulverizing the fine reassembled to classify reassembled fine particles having a particle diameter of 150 µm or less, and reassembled normal particles having a particle diameter of more than 150 µm and 850 µm or less; And
A method for producing a super absorbent polymer comprising the step of mixing the reassembled normal particles with the base resin normal particles.
The method of claim 2,
The re-assembly fine powder is re-introduced to the step of preparing the fine powder re-assembly, a method for producing a super absorbent polymer.
The method of claim 1,
In the presence of a surface crosslinking liquid, the method of producing a super absorbent polymer comprising the step of surface crosslinking the fine powder reassembled base resin powder to form super absorbent polymer particles.
The method of claim 1,
The binder is at least one selected from the group consisting of cellulose, polyvinylpyrrolidone, polyacrylic acid, polyacrylate, and derivatives thereof.
The method of claim 1,
The binder is contained in an amount of 0.01 to 10 parts by weight, based on 100 parts by weight of the fine powder of the base resin.
The method of claim 1,
The aqueous binder solution contains 10 to 200 parts by weight of water based on 100 parts by weight of the fine powder of the base resin.
The method of claim 1,
The temperature of the aqueous binder solution is 10 ℃ to 90 ℃, the method for producing a super absorbent polymer.
The method of claim 1,
Drying in the step of obtaining the fine powder reassembly is performed at 100 to 200° C., a method for producing a super absorbent polymer.
The method of claim 1,
The fine powder reassembly is mixed with the base resin normal particles in an amount of 10 to 50 parts by weight of the fine powder reassembly based on 100 parts by weight of the base resin normal particles.