WO2021054610A1 - Superabsorbent polymer preparation method - Google Patents

Abstract

The present invention relates to a superabsorbent polymer preparation method, which suitably controls the water content of a superabsorbent polymer by the addition of water, and the like, and thus damage during transport can be inhibited and deterioration of physical properties, such as the generation of macroparticles during the addition of water or the nonuniformity of water content, can be inhibited.

Description

Method for producing super absorbent polymer

Cross-reference with related application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0114791 filed on September 18, 2019 and Korean Patent Application No. 10-2020-0099393 filed on August 7, 2020. All contents disclosed in the literature are included as part of this specification.

The present invention is capable of suppressing crushing during transport by appropriately controlling the moisture content of the super absorbent polymer by means of water, etc., while suppressing deterioration of physical properties such as generation of large particles or non-uniform moisture content during the hydrolysis process. It relates to a method for producing a resin.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb moisture of 500 to 1,000 times its own weight, and each developer has a SAM (Super Absorbency Material), AGM (Absorbent Gel). Material) and so on. Since the above-described superabsorbent resin has begun to be put into practical use as a sanitary tool, nowadays, in addition to hygiene products such as paper diapers for children, soil repair agents for horticultural use, water resistant materials for civil engineering and construction, sheets for seedlings, freshness maintenance agents in the food distribution field, It is widely used as a material for poultice.

In most cases, such super absorbent polymers are widely used in the field of hygiene products such as diapers and sanitary napkins. For application to such sanitary materials, superabsorbent polymers typically have a form in which fine powders are gathered, and as these fine powders have a uniform particle diameter and a large surface area in the sanitary material, they rapidly absorb a large amount of moisture. Need to be indicated.

On the other hand, in the process of manufacturing the super absorbent polymer, there are many cases in which the super absorbent polymer is transferred in order to proceed with a subsequent process or apply to a packaging or sanitary material. However, as the super absorbent polymer has a form in which fine powders are collected, there are many cases where the super absorbent polymer powders physically collide and crush during the resin transfer process. Accordingly, various physical properties such as the overall absorption ability of the super absorbent polymer There is a problem that a decline occurs.

In order to solve this problem, after the final preparation of the super absorbent polymer, a hydrolysis process for controlling the moisture content by adding a small amount of water while cooling the super absorbent polymer has been performed. When the water content of the super absorbent polymer is partially increased by such a hydrolysis process, the overall crushing rate and deterioration of physical properties during transfer of the super absorbent polymer powder may be greatly reduced.

However, in the process of performing the hydrolysis process, when sufficient and uniform mixing of the superabsorbent polymer powders and water is not achieved, the resin powders agglomerate with each other, for example, large particles having a particle diameter larger than 850 μm ( There were many cases where a large amount of particles that did not pass through the standard body #20) occurred. The generation of such a large amount of large particles may lead to a decrease in properties of the overall superabsorbent polymer, and as a result, it is necessary to additionally remove the large particles by a classification process or the like, resulting in a decrease in the overall productivity of the super absorbent polymer.

Due to the above-described problem, the water content of the super absorbent polymer can be properly controlled by water, etc. to suppress crushing during transport, while also reducing problems such as generation of large particles during the hydrolysis process. The development of is continuously required.

Therefore, the present invention is capable of suppressing crushing during transport by appropriately controlling the moisture content of the super absorbent polymer by means of a water number, etc., while suppressing degradation of physical properties such as generation of large particles or non-uniform moisture content during the hydrolysis process. It is to provide a method for producing a water absorbent resin.

Accordingly, the present invention provides a super absorbent property comprising a base resin powder comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups, and a surface crosslinked layer formed on the surface of the base resin powder by further crosslinking the crosslinked polymer. Providing resin particles; And

It provides a method for producing a super absorbent polymer comprising the step of forming a hydrolyzed super absorbent polymer by mixing water and an additive including a carboxylic acid of an aliphatic hydrocarbon having 10 to 30 carbon atoms in the super absorbent polymer particles.

According to the method for producing a superabsorbent polymer of the present invention, as a specific additive is used in the hydrolysis step, the water content of the superabsorbent polymer may be appropriately controlled in the hydrolysis step or the like to suppress crushing or deterioration of physical properties during transport. Furthermore, by the use of the specific additive, it is possible to solve the problem that the physical properties of the super absorbent polymer are deteriorated due to phenomena such as generation of large particles or non-uniform moisture content during the hydrolysis process.

Consequently, according to the present invention, while being able to suppress crushing during transfer of the super absorbent polymer, the decrease in physical properties during the hydrolysis process or decrease in productivity due to the generation of large particles does not appear substantially, so that the super absorbent polymer exhibiting excellent physical properties is highly productive. By manufacturing and transferring, it can be preferably applied to the manufacture of various sanitary materials.

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 is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

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

Prior to that, the terminology used herein is for reference only to specific embodiments and is not intended to limit the invention. In addition, the singular forms used herein also include plural forms unless the phrases clearly represent the opposite meaning.

The term "polymer" or "polymer" used in the specification of the present invention means that a water-soluble ethylenically unsaturated monomer is polymerized, and may encompass all ranges of moisture content or particle size. 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, "super absorbent polymer" means the polymer or the base resin itself, depending on the context, or an additional process, such as surface crosslinking, fine powder reassembly, drying, grinding, classifying, for the polymer or the base resin, It is used to cover all products made suitable for commercialization through singers, etc.

According to an embodiment of the present invention, a base resin powder comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups, and a surface crosslinked layer formed on the surface of the base resin powder by further crosslinking the crosslinked polymer Providing a super absorbent polymer particle comprising; And

There is provided a method for producing a super absorbent polymer comprising the step of forming a hydrolyzed super absorbent polymer by mixing water and an additive including a carboxylic acid of an aliphatic hydrocarbon having 10 to 30 carbon atoms to the super absorbent polymer particles.

In the manufacturing method of one embodiment, after preparing a super absorbent polymer by proceeding to surface crosslinking, a small amount of an additive including a functional group of an aliphatic hydrocarbon having 10 or more carbon atoms and a carboxylic acid in the molecular structure, respectively, while performing a hydrolysis process on the super absorbent polymer. Will be added together. Such an additive has a hydrophobic functional group of a long-chain hydrocarbon in the molecule, and together with a hydrophilic functional group of a carboxylic acid at the terminal.

By adding these specific additives together in the hydrolysis process, it was confirmed that agglomeration between the resin particles in the process of the hydrolysis process can be greatly reduced. This seems to be because the hydrophobic functional group of the long-chain hydrocarbon can delay the contact of the resin particles and the water added in the hydrolysis process and moisture absorption. As a result, aggregation between super absorbent polymer particles, formation of large particles, and deterioration of physical properties during the hydrolysis process and the transfer process can be suppressed.

In addition, since the specific additive includes both the hydrophobic functional group and the hydrophilic functional group of carboxylic acid, the super absorbent polymer particles are evenly dispersed and distributed in the mixed water, so that crushing during transfer of the super absorbent polymer can be more effectively suppressed.

As a result, according to the manufacturing method of one embodiment, while the water content of the super absorbent polymer can be appropriately controlled in the hydrolysis process, etc., crushing or deterioration of physical properties during transfer of the super absorbent polymer can be suppressed, while large particles are generated during the hydrolysis process, or Problems in which physical properties of the super absorbent polymer are deteriorated due to phenomena such as non-uniform moisture content can also be solved.

On the other hand, in the case of using other additives different from the method of the embodiment, for example, a polycarboxylic acid copolymer previously known as an agglomeration inhibitor, or polyethylene glycol, which is a representative hydrophilic polymer, in the hydrolysis process, the hydrolysis process It was confirmed that agglomeration in the polymer was not properly suppressed, and a large amount of large particles exceeding 850 µm was generated or the moisture content became non-uniform, resulting in a decrease in overall physical properties or a decrease in productivity of the super absorbent polymer. This is predicted because a number of hydrophilic functional groups exist in the polymer.

As described above, according to the method of one embodiment, while being able to effectively suppress crushing during transfer of the superabsorbent polymer by the hydrolysis process, the decrease in physical properties during the hydrolysis process or decrease in productivity due to the generation of large particles substantially does not appear. By producing and transferring a super absorbent polymer having a high productivity, it can be preferably applied to the production of various sanitary materials.

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

In the method of manufacturing a super absorbent polymer according to an embodiment, first, super absorbent polymer particles are prepared. These super absorbent polymer particles are crosslinked, polymerized, and dried according to the manufacturing process and conditions of a general super absorbent polymer. It can be manufactured through processes such as pulverization, classification, and surface crosslinking. Hereinafter, an example of manufacturing super absorbent polymer particles will be described in detail.

First, a monomer composition is formed by mixing each component of a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator having an acidic group at least partially neutralized.

The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the preparation of a super absorbent polymer. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Formula 1:

[Formula 1]

R ₁ -COOM ¹

In Formula 1,

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

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

Suitably, 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, a super absorbent polymer having improved water absorption can be obtained, which is advantageous. 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-( Anionic monomers of meth)acrylamide-2-methyl propane sulfonic acid 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 an amino group-containing unsaturated monomer of (N,N)-dimethylaminopropyl (meth)acrylamide and a quaternary product thereof; Can be used.

Here, the water-soluble ethylenically unsaturated monomer may have an acidic group, and at least a part of the acidic group may be neutralized. Preferably, the monomer partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide or ammonium hydroxide may be used.

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%. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, the neutralized monomer precipitates and it may be difficult for the polymerization to proceed smoothly. On the contrary, if the degree of neutralization is too low, the absorbency of the polymer is greatly reduced. It may exhibit properties such as elastic rubber that are difficult to handle.

Meanwhile, the internal crosslinking agent is a term used to distinguish it from the surface crosslinking agent for further crosslinking the surface of the base resin to be described later, and serves to crosslink and polymerize the unsaturated bonds of the water-soluble ethylenically unsaturated monomers described above. The crosslinking in the above step proceeds without distinction between the surface or the interior, 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 interior is the internal crosslinking agent. It is made of a crosslinked structure by.

As the internal crosslinking agent, any compound may be used as long as it allows the introduction of a crosslinking bond during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, ( Poly)propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, (poly)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, Diglycidyl ether compounds of alkylene glycols such as glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate The multifunctional crosslinking agent may be used alone or in combination of two or more, but is not limited thereto.

This internal crosslinking agent may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent may be used in an amount of 0.01 parts by weight or more, 0.03 parts by weight or more, or 0.05 parts by weight or more, and 5 parts by weight or less and 3 parts by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. When the content of the internal crosslinking agent is too low, crosslinking does not occur sufficiently, and thus it may be difficult to implement strength above an appropriate level, and when the content of the internal crosslinking agent is too high, the internal crosslinking density is increased, and thus it may be difficult to implement the desired absorption performance.

In addition, the polymerization initiator may be appropriately selected according to the polymerization method, and when a thermal polymerization method is used, a thermal polymerization initiator is used, when a photopolymerization method is used, a photopolymerization initiator is used, and a hybrid polymerization method (heat and light In the case of using all of the methods), both a thermal polymerization initiator and a photopolymerization initiator can be used. However, even by the photopolymerization method, a certain amount of heat is generated by light irradiation such as ultraviolet 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 used.

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

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketone. Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group. 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)phenylphosphineate and the like. 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 0.0001 to 2.0% by weight based on the monomer composition. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slow, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the 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 persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (Potassium persulfate; K ₂ S ₂ O ₈ ), and 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 (2,2-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 2.0% by weight based on the monomer composition. 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 physical properties may become uneven. have.

The monomer composition may further include additives such as a thickener, a plasticizer, a storage stabilizer, an antioxidant, or a surfactant, if necessary.

In addition, the above-described water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator may be mixed together with a solvent. Therefore, the monomer composition prepared in the above step is in a form dissolved in the solvent, and the content of the solid content in the monomer composition may be 20 to 60% by weight.

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

Meanwhile, the mixing of the above-described components is not particularly limited, and may be performed through a method commonly used in the art, for example, stirring.

Next, crosslinking polymerization of the monomer composition is performed to form a hydrogel polymer.

The above step may be carried out without any particular limitation of the composition as long as the prepared monomer composition can be crosslinked and polymerized by a method of thermal polymerization, photopolymerization, or hybrid polymerization to form a hydrogel polymer.

Specifically, when performing thermal polymerization, it may be performed in a reactor having a stirring shaft such as a kneader. In addition, when the thermal polymerization is performed, it may be performed at a temperature of about 80°C or more and less than about 110°C. The means for achieving the polymerization temperature in the above-described range is not particularly limited, and heating may be performed by supplying a heat medium to the reactor or directly supplying a heat source. 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 temperature of the heat medium supplied is not limited thereto. You can choose appropriately. On the other hand, the heat source directly supplied may include heating through electricity and heating through gas, but is not limited to the above-described example.

On the other hand, when the photopolymerization is performed, it may be performed in a reactor equipped with a movable conveyor belt, but the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.

For example, when thermal polymerization is performed by supplying a heat medium or heating the reactor to a reactor such as a kneader having a stirring shaft as described above, a hydrogel polymer discharged to the reactor outlet may be obtained. The hydrogel polymer thus obtained may be obtained in a size of several centimeters to several millimeters, depending on the shape of the stirring shaft provided in the reactor. Specifically, the size of the resulting hydrogel polymer may vary depending on the concentration and injection speed of the monomer composition to be injected.

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 on a sheet having a 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 10 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 10 cm, due to the excessively thick thickness, the polymerization reaction is evenly performed over the entire thickness. It may not happen.

The polymerization time of the monomer composition is not particularly limited, and may be adjusted to about 30 seconds to 60 minutes.

A typical moisture content of the hydrogel polymer obtained by this method may be about 30 to about 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 increasing the temperature from room temperature to about 180°C and then maintaining it at 180°C. The total drying time is set to 40 minutes including 5 minutes in the temperature raising step, and the moisture content is measured.

Next, the hydrogel polymer is dried, pulverized and classified to form a powdery base resin.

Meanwhile, in the step of forming the base resin, a process of coarsely pulverizing the hydrogel polymer before drying may be included in order to increase drying efficiency.

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

Through this coarse pulverization process, the particle diameter of the hydrogel polymer may be adjusted to about 0.1 to about 10 mm. Grinding so that the particle diameter is less than 0.1 mm is not technically easy due to the high moisture content of the hydrogel polymer, and a phenomenon of agglomeration between the pulverized particles may occur. On the other hand, when pulverizing so that the particle diameter exceeds 10 mm, the effect of increasing the efficiency of the subsequent drying step may be insignificant.

Drying is performed on the hydrogel polymer immediately after polymerization that has undergone the coarse pulverization process as described above or has not been subjected to the coarse pulverization process. In this case, the drying temperature may be about 60°C to about 250°C. At this time, when the drying temperature is less than about 70° C., the drying time is too long, and when the drying temperature exceeds about 250° C., only the polymer surface is dried excessively, and fine powder may be generated in a subsequent pulverization process. There is a concern that the physical properties of the super absorbent polymer may be deteriorated. Therefore, preferably, the drying may be performed at a temperature of about 100°C to about 240°C, more preferably about 110°C to about 220°C.

In addition, in the case of the drying time, it may be performed for about 20 minutes to about 12 hours in consideration of process efficiency and the like. For example, it may be dried for about 10 minutes to about 100 minutes, or about 20 minutes to about 60 minutes.

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.

Thereafter, the dried polymer obtained through the drying step is pulverized using a grinder.

Specifically, the pulverizer used to pulverize the powdered base resin to be made of particles having a particle diameter of about 150 µm to about 850 µm is specifically, a pin mill, a hammer mill, and a screw. Mill (screw mill), roll mill (roll mill), disk mill (disc mill), may be a jog mill (jog mill), etc., but is not limited to the above-described example.

In addition, in order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed. Preferably, a polymer having a particle diameter of 150 to 850 μm is classified, and only a polymer powder having such a particle diameter can be produced through a surface crosslinking reaction step. More specifically, the classified base resin powder has a particle diameter of 150 to 850 μm, and may include 50% by weight or more of particles having a particle diameter of 300 to 600 μm.

Meanwhile, after the base resin is formed through the above-described classification process, a step of forming a surface crosslinking layer by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent is performed.

The step is a step of forming a surface crosslinking layer using a surface crosslinking agent to increase the surface crosslinking density of the base resin, so that the unsaturated bonds of the water-soluble ethylenically unsaturated monomer remaining on the surface without crosslinking are crosslinked by the surface crosslinking agent. As a result, a super absorbent polymer having a high surface crosslinking density is formed. The surface crosslinking density, that is, the external crosslinking density, is increased by this heat treatment process, while the internal crosslinking density does not change, so that the superabsorbent polymer having a surface crosslinked layer formed thereon has a structure having a higher crosslinking density on the outside than on the inside.

In the method of one embodiment, in the step of forming the surface crosslinking layer, a surface crosslinking agent composition including a surface crosslinking agent, an alcohol-based solvent, and water may be used.

On the other hand, as the surface crosslinking agent included in the surface crosslinking agent composition, any surface crosslinking agent that has been conventionally used to manufacture a super absorbent 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- One 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 Or more polyols; 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 a cyclic urea compound; And the like. Preferably, the same thing as the above-described internal crosslinking agent may be used, for example, a diglycidyl ether 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. For example, the surface crosslinking agent may be used in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.02 parts by weight or more, and 0.5 parts by weight or less and 0.3 parts by weight or less based on 100 parts by weight of the base resin. By adjusting the content range of the surface crosslinking agent to the above-described range, it is possible to prepare a super absorbent polymer that exhibits excellent water absorption performance and various physical properties such as liquid permeability.

In addition, there is no limitation on the configuration of the method of mixing the surface crosslinking agent composition with the base resin. For example, a method of mixing a surface crosslinking agent composition and a base resin in a reaction tank, or spraying a surface crosslinking agent composition onto the base resin, a method of continuously supplying and mixing the base resin and the surface crosslinking agent composition to a continuously operated mixer, etc. Can be used.

The surface crosslinking process may be performed at a temperature of about 80°C to about 250°C. More specifically, the surface crosslinking process may be performed at a temperature of about 100°C to about 220°C, or about 120°C to about 200°C, for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. . When the above-described surface crosslinking process conditions are satisfied, the surface of the base resin is sufficiently crosslinked, so that the absorbency under pressure or liquid permeability may be increased.

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 temperature of the heat medium supplied is not limited thereto. It can be appropriately selected in consideration. On the other hand, the heat source directly supplied may include heating through electricity and heating through gas, but is not limited to the above-described example.

On the other hand, by proceeding to the surface crosslinking process through the process exemplarily described above, super absorbent polymer particles may be manufactured and provided. Such super absorbent polymer particles include, for example, a base resin powder comprising a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having at least a partly neutralized acidic group is polymerized through an internal crosslinking agent, and the crosslinked polymer is a surface crosslinking agent. It may have a form including a surface crosslinked layer formed on the surface of the base resin powder by being further crosslinked.

In addition, the super absorbent polymer particles may be in a form in which fine powders having a particle diameter of 150 to 850 μm are collected so that a large amount of moisture can be rapidly absorbed over a large surface area in the sanitary material. .

However, such super absorbent polymer particles may be crushed by physical collision in the process of being transferred to a subsequent packaging process or a subsequent sanitary material manufacturing process, etc., in order to suppress this, a predetermined additive and a predetermined additive to the super absorbent polymer particles and A hydrolysis process of forming a hydrolyzed superabsorbent resin is performed by mixing water.

In such a hydrolysis process, as already described above, a carboxylic acid of an aliphatic hydrocarbon having 10 to 30 carbon atoms is used as an additive, and these additives have both a hydrophobic functional group of a long-chain hydrocarbon and a hydrophilic functional group of a carboxylic acid in the molecule. And it is possible to effectively suppress the crushing and agglomeration of the super absorbent polymer during transport.

In a more specific example, the additive may be a compound in which a carboxylic acid is bonded to the terminal of an aliphatic saturated hydrocarbon such as a linear alkyl group having 12 to 20 carbon atoms, and in a more specific example, stearic acid, lauric acid ) And arachidic acid (Arachidic acid) may be one or more carboxylic acid compounds selected from the group consisting of.

By using such a compound as an additive during the hydrolysis process, it is possible to more effectively suppress the formation of large particles due to crushing and agglomeration during the hydrolysis process and transfer of the super absorbent polymer, and the resulting deterioration in physical properties of the super absorbent polymer.

In addition, the above-described additives are based on the weight of the super absorbent polymer particles so as to effectively suppress the formation of large particles due to the aggregation of the super absorbent polymer particles during the hydrolysis process, and not inhibit the uniform increase of the moisture content due to the hydrolysis process. It may be mixed in an amount of 5 to 20,000ppmw. In a more specific example, the additive may be mixed in an amount of 5 to 1000 ppmw, 10 to 500 ppmw, or 50 to 300 ppmw based on the weight of the super absorbent polymer particles.

As the additive is used in such a content range, aggregation between super absorbent polymer particles and generation of large particles during the hydrolysis process are more effectively suppressed, while the moisture content of the super absorbent polymer is uniform throughout the desired range due to the hydrolysis process and subsequent drying. Can be controlled.

Meanwhile, the water is 1 to 10 parts by weight of the super absorbent polymer particles so that water is uniformly mixed with the super absorbent polymer particles in the hydrolysis process so that the moisture content of the final super absorbent polymer can be uniformly controlled as a whole. It is appropriate to mix in an amount of 3 to 8 parts by weight, or 4 to 6 parts by weight.

The hydrolysis process of mixing the above-described additive and water may be performed while cooling the surface-crosslinked superabsorbent polymer particles under a temperature of, for example, 40 to 80°C or 45 to 75°C. As a result, while simplifying the overall process, it is possible to suppress deterioration of the physical properties of the super absorbent polymer.

After the hydrolyzing process is performed in the above-described method to form the hydrolyzed superabsorbent resin, the step of drying and classifying the hydrolyzing superabsorbent resin may be further performed. While drying the hydrolyzed superabsorbent resin in which water and additives are uniformly mixed in the hydrolysis process, a desired moisture content, for example, a moisture content of 1 to 2.5% by weight may be finally achieved. This moisture content range is an increase compared to the moisture content of about 0.5% by weight or less, or 0.3% by weight or less of the same superabsorbent polymer particles immediately after surface crosslinking, and due to the constant increase in the moisture content, physical crushing is effectively prevented during transport of the superabsorbent polymer. Can be suppressed.

Such a drying process can be performed under a drying apparatus and conditions equivalent to those performed in the manufacturing process of the super absorbent polymer particles, and a person skilled in the art can proceed with an appropriate drying time in consideration of the target moisture content.

On the other hand, after achieving the target moisture content through the drying, the super absorbent polymer may be further classified. In this additional classification process, large particles generated in the hydrolysis process, for example, particles having a particle diameter of more than 850 μm and particles having a particle size of less than 150 μm are removed, and the super absorbent polymer has a particle diameter of 150 to 850 μm. It can be manufactured to have.

However, in the method of one embodiment, as a specific additive is used in the hydrolysis process, generation of large particles by the hydrolysis may be greatly reduced. Therefore, the particles having a particle diameter of more than 850 μm removed in the classification process may be less than 5% by weight, or less than 3% by weight, or 0.1 to 3% by weight based on the total weight of the dried super absorbent polymer. have.

In contrast, when no additives are used in the hydrolysis process, or when an additive different from the method of one embodiment is used, a large amount of large particles are still generated during the hydrolysis process, so that particles having a particle diameter of more than 850 μm removed in the classification process are It may be about 20% by weight or more based on the total weight of the dried super absorbent polymer.

On the other hand, the superabsorbent polymer finally prepared by the method according to one embodiment through the above-described drying and classification process, when measured for the resin having a particle diameter of 150 to 850㎛, physiological saline solution (0.9% by weight sodium chloride) Aqueous solution) for 30 minutes centrifugation water retention capacity (CRC) is 30 to 45 g / g, it is possible to maintain excellent absorption performance. The water holding capacity may be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, and may be calculated according to the calculation formula A described in Test Examples to be described later.

The above-described dried and classified super absorbent polymer may be additionally transferred for application to a subsequent packaging or sanitary material manufacturing process. Such a super absorbent polymer does not substantially cause crushing or deterioration in physical properties due to appropriate control of the moisture content even during the transfer process. Furthermore, since the generation of large particles is also minimized in the hydrolysis process, it can be manufactured to have excellent physical properties and productivity as a whole.

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

<Example>

Example 1: Preparation of super absorbent polymer

Acrylic acid 100g, 32% caustic soda 123.5g, thermal polymerization initiator sodium persulfate 0.2g, photopolymerization initiator diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide 0.008g, internal crosslinking agent polyethylene glycol diacrylate 2.25 g and 59.0 g of water were mixed to prepare a monomer composition having a total solid content of 45% by weight. The monomer composition was supplied at a rate of 500 mL/min to 2000 mL/min on a rotary belt having a width of 10 cm and a length of 2 m and rotating at a speed of 50 cm/min. The supplied monomer composition was ^{irradiated with ultraviolet rays at an intensity of 10 mW/cm 2} to perform crosslinking polymerization for 60 seconds.

After the crosslinking polymerization reaction, the hydrogel polymer was coarsely pulverized with a meat chopper, and dried at 190° C. for 40 minutes using an air-flow oven.

To 100 g of the base resin thus prepared, a surface crosslinking agent composition, which is a mixed solution of 3 g of ultrapure water, 3.5 g of methanol, 0.25 g of 1,3-propanediol, and 0.16 g of oxalic acid, was added, and mixed for 2 minutes. This was heat-treated at 185° C. for 50 minutes to perform surface crosslinking, and then classified to take particles having a particle diameter of 150 to 850 μm to prepare super absorbent polymer particles.

Subsequently, while rotating 200 g of the super absorbent polymer particles in a crucible at 60° C., a mixed solution of 10 g of ultrapure water and 0.0250 g of lauric acid was administered and mixed for 2 minutes. The resultant was further dried for 25 minutes and then classified to obtain a final product.

Example 2: Preparation of super absorbent polymer

A final product of a super absorbent polymer was obtained in the same manner as in Example 1, except that 0.0250 g of stearic acid was used instead of 0.0250 g of lauric acid.

Example 3: Preparation of super absorbent polymer

A final product of a super absorbent polymer was obtained in the same manner as in Example 1, except that 0.0250 g of arachidic acid was used instead of 0.0250 g of lauric acid.

Comparative Example 1: Preparation of super absorbent polymer

First, super absorbent polymer particles were prepared in the same manner as in Example 1. However, the step of administering and mixing the mixed solution of ultrapure water and lauric acid, which was additionally performed in Example 1, and the subsequent drying and classification step, was not performed, and the superabsorbent polymer particles themselves were added to the final of the superabsorbent polymer of Comparative Example 1. It was made into a product.

Comparative Example 2: Preparation of super absorbent polymer

First, super absorbent polymer particles were prepared in the same manner as in Example 1.

Subsequently, while rotating 200 g of the super absorbent polymer particles in a crucible at 60° C., 10 g of ultrapure water not mixed with lauric acid was administered and mixed for 2 minutes. The resultant was further dried for 25 minutes and then classified to obtain a final product.

Comparative Example 3: Preparation of super absorbent polymer High water absorption in the same manner as in Example 1, except that 0.0250 g of the polycarboxylic acid copolymer disclosed in Preparation Example 1 of Korean Patent Publication No. 2015-0143167 was used instead of 0.0250 g of lauric acid. The final product of the resin was obtained.

Comparative Example 4: Preparation of super absorbent polymer

A final product of a super absorbent polymer was obtained in the same manner as in Example 1, except that 0.25 g of polyethylene glycol having Mw 600 was used instead of 0.0250 g of lauric acid.

Test example

For the super absorbent polymer prepared in the above Examples and Comparative Examples, various physical properties were measured in the following manner, and the results are shown in Table 1 below.

(1) Centrifuge retention capacity (CRC)

First, take a super absorbent resin with a particle diameter of 150 to 850 μm (between the standard sieves of #20 to 100), and absorb the power under no load according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3. The water holding capacity (CRC) by centrifugation was measured.

Specifically, the superabsorbent polymer (or base resin powder; hereinafter the same) W ₀ (g, about 0.2 g) is uniformly placed in a nonwoven bag and sealed, and the physiology of 0.9% by weight sodium chloride aqueous solution at room temperature. It was immersed in saline. After 30 minutes, the bag was centrifuged and dried at 250 _{G for 3 minutes, and the mass W 2} (g) of the bag was measured. In addition, after performing the same operation without using a super absorbent polymer, the mass W ₁ (g) at that time was measured. Using each of the masses thus obtained, CRC (g/g) was calculated according to the following calculation formula A to confirm the water holding capacity.

[Calculation A]

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

(2) particle size distribution

In order to measure the particle size distribution, a super absorbent polymer was classified using a standard mesh of ASTM standard. More specifically, standard mesh bodies having eye sizes of 850 µm, 600 µm, 300 µm, and 150 µm, respectively, were sequentially stacked, and then 100 g of a super absorbent polymer was put on the top and set in a sieve shaker (AS200). Classification was performed for 10 minutes at Amplitude 1.0mm/g. The superabsorbent polymer remaining between each standard mesh was taken out, weighed, and calculated as a percentage, to calculate the particle size distribution of the superabsorbent polymer.

(3) moisture content

In the process of drying the superabsorbent polymer while heating infrared rays, the weight loss due to evaporation of moisture in the superabsorbent polymer was measured and measured as a calculated value. At this time, the drying conditions were set to a total drying time of 10 minutes in a manner that the temperature was raised from room temperature to about 140°C and then maintained at 140°C. The moisture content was calculated from the measurement result of the above weight reduction.

Properties		Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Example 1	Example 2	Example 3
	CRC(#20~100; g/g)	33.4	31.8	32.0	31.5	31.9	32.0	32,8
	Moisture content (#20~100; wt%)	0.3	2.2	1.98	1.89	1.71	1.60	1.79
Particle size distribution	More than #20 (more than 850㎛)	0.4	39.3	21.2	20.0	0.8	0.7	0.4
	#20~30(600~850㎛)	17.2	30.0	31.2	30.6	20.9	21.3	19.8
	#30~50(300~600㎛)	65.1	29.2	37.7	39.7	65.0	65.0	65.1
	#50~100(300~150㎛)	16.2	1.5	9.4	9.4	12.8	12.6	14.5
	Less than #100 (less than 150㎛)	1.1	0	0.5	0.3	0.5	0.4	0.2

Referring to Table 1, in Comparative Example 1 in which the hydrolysis process was not performed, it is predicted that physical crushing will occur during the subsequent transfer process because the moisture content is low. In addition, Comparative Examples 2 to 4 are predicted to be controlled to an appropriate moisture content by the hydrolysis process to suppress crushing during transport, but due to the non-use of additives or the use of other additives such as polycarboxylic acid or polyethylene glycol during the hydrolysis process, large particles are It was confirmed that a number of occurrences occurred, resulting in a decrease in physical properties and a decrease in productivity of the super absorbent polymer.

In contrast, Examples 1 to 3 were found to be able to suppress crushing during transport by appropriate control of the moisture content, while the amount of large particles generated in the hydrolysis process was also significantly reduced.

Claims (10)

1. Provides super absorbent polymer particles comprising a base resin powder comprising a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups, and a surface crosslinked layer formed on the surface of the base resin powder by further crosslinking the crosslinked polymer The step of doing; And

   A method for producing a super absorbent polymer comprising the step of forming a hydrolyzed super absorbent polymer by mixing water and an additive including a carboxylic acid of an aliphatic hydrocarbon having 10 to 30 carbon atoms to the super absorbent polymer particles.
2. The method of claim 1, wherein the additive comprises a compound in which a carboxylic acid is bonded to an end of a linear alkyl group having 12 to 20 carbon atoms.
3. The method of claim 1, wherein the additive comprises at least one carboxylic acid compound selected from the group consisting of stearic acid, lauric acid, and arachidic acid.
4. The method of claim 1, wherein the additive is mixed in an amount of 5 to 20,000 ppmw based on the weight of the super absorbent polymer particles.
5. The method of claim 1, wherein the water is mixed in an amount of 1 to 10 parts by weight based on 100 parts by weight of the super absorbent polymer particles.
6. The method of claim 1, wherein the step of mixing the additive and water is performed under a temperature of 40 to 80°C.
7. The method of claim 1, further comprising drying and classifying the hydrolyzed superabsorbent resin after the step of mixing the additive and water,

   The dried and classified super absorbent polymer has a particle diameter of 150 to 850 μm and a water content of 1 to 2.5% by weight.
8. The method of claim 7, wherein the particles having a particle diameter of more than 850 μm removed during the classification process are less than 5% by weight based on the total weight of the dried super absorbent polymer.
9. The method of claim 7, wherein the dried and classified superabsorbent polymer has a centrifugal water retention capacity (CRC) of 30 to 45 g/g for physiological saline (0.9 wt% sodium chloride aqueous solution) for 30 minutes. Manufacturing method.
10. The method of claim 7, further comprising transferring the dried and classified super absorbent polymer.