KR20210093741A - Preparation method of super absorbent polymer composition - Google Patents

Abstract

The present invention relates to a method for preparing a super absorbent polymer composition, and more specifically, to a method for preparing a super absorbent polymer composition, which adds an additive of a specific structure to a hydrogel polymer and pulverizes the additive for pulverization to a normal particle level without agglomeration between particles, can reduce manufacturing costs by performing drying and surface crosslinking processes at the same time, and can significantly reduce the amount of a fine powder generated during the process.

Description

Method for producing a superabsorbent polymer composition {PREPARATION METHOD OF SUPER ABSORBENT POLYMER COMPOSITION}

The present invention relates to a method for preparing a super absorbent polymer composition. More specifically, it relates to a method for manufacturing a superabsorbent polymer composition in which manufacturing costs are significantly reduced by simultaneously performing drying and surface crosslinking processes.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb water 500 to 1,000 times its own weight, and each developer uses either SAM (Super Absorbency Material) or AGM (Absorbent Gel). Material), etc., are named differently. The superabsorbent polymer as described above began to be put to practical use as a sanitary tool, and is now widely used as a soil repair agent for horticulture, a water-retaining material for civil engineering and construction, a sheet for seedlings, a freshness maintenance agent in the food distribution field, and a poultice. .

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

As such, in the case of a sanitary material in which the content of pulp is reduced or in which pulp is not used, the superabsorbent polymer is included in a relatively high ratio, so that the superabsorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire superabsorbent polymer particles included in the multi-layered structure to more efficiently absorb a large amount of liquid such as urine, the superabsorbent polymer needs to exhibit not only high absorption performance but also a fast absorption rate.

On the other hand, such a superabsorbent polymer is generally prepared by polymerizing a monomer to prepare a hydrogel polymer containing a large amount of moisture, and drying the hydrogel polymer and then pulverizing the hydrogel polymer into resin particles having a desired particle size. However, as described above, when the hydrogel polymer is dried and then pulverized, a large amount of fine powder is generated, thereby deteriorating the physical properties of the superabsorbent polymer finally manufactured.

In addition, in order to reuse the fine powder, it is common to mix the fine powder with water to agglomerate it to prepare a fine powder re-assembly, and then add the fine powder re-assembly prepared by a process such as drying/pulverization/classification. However, due to the water used at this time, energy consumption during the drying process may increase, and problems such as an increase in load on the device may occur, and thus productivity of the superabsorbent polymer may be reduced.

Accordingly, in order to fundamentally solve this problem, there is a continuous demand for the development of a technology capable of manufacturing a super absorbent polymer without generation of fine powder.

Accordingly, in the present invention, it is possible to grind to a normal particle level without agglomeration between particles by adding an additive of a specific structure to the hydrogel polymer and grinding, and it is possible to reduce the manufacturing cost by simultaneously performing the drying and surface crosslinking processes, and fine powder during the process The present invention relates to a method for producing a super absorbent polymer composition capable of significantly reducing the amount generated.

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

1) forming a hydrogel polymer by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator;

2) mixing the hydrogel polymer with a carboxylic acid-based additive and then pulverizing to prepare water-containing superabsorbent polymer particles and a pulverized product containing the additive; and

3) mixing a surface crosslinking agent with the pulverized product and drying the mixture to prepare a superabsorbent polymer composition including superabsorbent polymer particles having a surface crosslinking layer formed on at least a portion of the surface and the additive;

The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by the following formula (1) and a salt thereof, a method for preparing a superabsorbent polymer composition is provided:

[Formula 1]

In Formula 1,

A is alkyl having 5 to 21 carbon atoms,

B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,

B ₂ is -CH ₂ -, -CH ₂ CH ₂ -, -CH(R ₂ )-, -CH=CH-, or -C≡C-,

Here, R ₁ and R ₂ are each independently an alkyl having 1 to 4 carbon atoms,

n is an integer from 1 to 3,

C is a carboxyl group.

According to the method for preparing the superabsorbent polymer composition of the present invention, the hydrogel polymer is pulverized in the presence of the carboxylic acid-based additive to produce a superabsorbent polymer composition comprising superabsorbent polymer particles having a desired particle size without aggregation between the pulverized particles. manufacturing is possible. In addition, as the hydrogel polymer is pulverized to a normal particle level, the amount of fine powder generated during the preparation of the super absorbent polymer composition can be significantly reduced, and the drying process and the surface crosslinking process are simultaneously performed, thereby simplifying the manufacturing process and reducing the manufacturing cost. can be

1 is a flowchart of a conventional method for manufacturing a super absorbent polymer.
2 is a flowchart illustrating a method of manufacturing a super absorbent polymer composition according to an exemplary embodiment.

The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises", "comprises" or "have" are intended to designate the presence of an embodied feature, step, element, or a combination thereof, but one or more other features or steps; It should be understood that the possibility of the presence or addition of components, or combinations thereof, is not precluded in advance.

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

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

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

Before that, the terminology used herein is for the purpose of referring to particular embodiments only, and is not intended to limit the present invention. And, as used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite.

According to one embodiment of the invention,

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

2) mixing the hydrogel polymer with the following carboxylic acid-based additive and pulverizing to prepare water-containing superabsorbent polymer particles and a pulverized product containing the additive (step 2); and

3) mixing a surface crosslinking agent with the pulverized product and drying the mixture to prepare a superabsorbent polymer composition comprising superabsorbent polymer particles having a surface crosslinking layer formed on at least part of the surface and the additive (step 3),

The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by the following formula (1) and a salt thereof, a method for preparing a superabsorbent polymer composition is provided:

[Formula 1]

In Formula 1,

A is alkyl having 5 to 21 carbon atoms,

B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,

B ₂ is -CH ₂ -, -CH ₂ CH ₂ -, -CH(R ₂ )-, -CH=CH-, or -C≡C-,

Here, R ₁ and R ₂ are each independently an alkyl having 1 to 4 carbon atoms,

n is an integer from 1 to 3,

C is a carboxyl group.

As used herein, the term “polymer” or “polymer” refers to a polymerized state of a water-soluble ethylenically unsaturated monomer, and may cover all water content ranges or particle diameter ranges. Among the above polymers, a polymer having a water content (moisture content) of about 30% by weight or more in a state before drying after polymerization may be referred to as a hydrogel polymer, and particles obtained by pulverizing and drying the hydrogel polymer may be referred to as a crosslinked polymer. there is.

In addition, the term "superabsorbent polymer particles" refers to a particulate material comprising an acidic group and a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer in which at least a portion of the acidic group is neutralized is polymerized and crosslinked by an internal crosslinking agent.

In addition, the term “super absorbent polymer” refers to a cross-linked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing an acidic group and neutralizing at least a part of the acidic group, or powder consisting of superabsorbent polymer particles in which the cross-linked polymer is pulverized, depending on the context. It refers to a base resin in the form of (powder), or to the crosslinked polymer or the base resin through additional processes, such as drying, pulverization, classification, surface crosslinking, etc. used Accordingly, the term “super absorbent polymer composition” may be interpreted as including a composition including a super absorbent polymer, that is, a plurality of super absorbent polymer particles.

Also, the term “normal particles of superabsorbent polymer” refers to particles having a particle diameter of 150 μm to 850 μm among superabsorbent polymer particles.

In addition, the term “fine powder” refers to particles having a particle diameter of less than 150 μm among the superabsorbent polymer particles. The particle size of the resin particles may be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

In addition, the term "chopping" refers to shredding the hydrogel polymer into small pieces to increase drying efficiency, and is used separately from grinding to a normal particle level.

Conventional superabsorbent polymers are prepared by drying the hydrogel polymer and then pulverizing the hydrogel polymer to a desired particle size. In this case, the hydrogel polymer is generally chopped prior to the drying process to facilitate drying of the hydrogel polymer and to increase the efficiency of the grinding process. ) process is in progress. However, due to the adhesiveness of the hydrogel polymer in this chopping process, the hydrogel polymer cannot be pulverized to the level of micro-sized particles and becomes an agglomerated gel. When the hydrogel polymer in the form of agglomerated gel is left to dry, a plate-shaped dried body is formed, and in order to pulverize it to the level of micro-sized particles, a multi-stage pulverization process is required, so there is a problem that a lot of fine powder is generated in this process. come.

In addition, in the conventional case, since the surface crosslinking process is separately performed after chopping, drying, and pulverization, a lot of energy cost is generated during the process, which results in an increase in product production cost.

Specifically, FIG. 1 is a flowchart of a conventional method for manufacturing a super absorbent polymer. Referring to FIG. 1 , a conventional super absorbent polymer has been prepared including the following steps.

(Polymerization) forming a hydrogel polymer by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator;

(Chopping; chopping) chopping the hydrogel polymer;

(Drying) drying the chopped hydrogel polymer;

(Pulverization/Classification) classifying the dried polymer into normal particles and fine powder after pulverization; and

(Surface crosslinking) A step of surface crosslinking the classified normal particles in the presence of a surface crosslinking agent.

As described above, since the chopped hydrogel polymer has an agglomerated gel shape with a size of about 1 cm to 10 cm, the chopped hydrogel polymer exhibits a plate shape rather than a particle shape after drying. Accordingly, in the step of classifying the dried polymer after pulverizing, coarsely pulverizing and classifying the prepared particles so that they become normal particles, i.e., particles having a particle diameter of 150 μm to 850 μm, and then fine pulverizing again. has been carried out step by step. Since the amount of fine powder separated in the final classification step by this manufacturing method is about 10% to about 20% by weight relative to the total weight of the final manufactured superabsorbent polymer, the separated fine powder is mixed with an appropriate amount of water to re-assemble the fine powder It was reused as a method of inputting after chopping or before drying.

However, there have been problems such as causing an increase in device load and/or energy consumption when re-injecting the fine powder re-assembly mixed with water into the pulverization or drying process for reuse of the fine powder, and the fine powder remaining unclassified This caused deterioration of the physical properties of the superabsorbent polymer.

Therefore, the present inventors understood that the amount of fine powder generated in the conventional manufacturing method is greatly affected by the particle size input to the grinding process, and in the chopping process, the hydrogel polymer can be pulverized to a micro size without agglomeration between the hydrogel polymers. If there is, it was determined that the amount of fine powder generated during the manufacturing process could be reduced. Accordingly, as a result of experimenting with various kinds of additives that can lower the adhesiveness of the hydrogel polymer in the chopping process, when the hydrogel polymer is mixed with the above-described carboxylic acid-based additive and then pulverized, the The present invention was completed by confirming that the hydrogel polymer was able to be pulverized into micro-level particles due to the low adhesiveness of the hydrogel polymer. This is because the carboxylic acid-based additive mixed with the hydrogel polymer is adsorbed to the surface of the hydrogel polymer to prevent aggregation of the pulverized hydrogel polymers. In addition, since the drying process proceeds in the form of micro-sized particles, not only drying is facilitated, but also a separate grinding process is not required after the drying process, so that the content of generated fine powder can be significantly reduced.

Specifically, FIG. 2 is a flowchart illustrating a method for preparing a superabsorbent polymer composition according to an exemplary embodiment. Referring to FIG. 2 , unlike the prior art, after the hydrogel polymer is prepared, it is pulverized to a normal particle level, and then dried and surface cross-linking processes are performed to prepare a superabsorbent polymer composition.

In this case, the carboxylic acid-based additive has a hydrophobic functional group and a hydrophilic functional group at the same time. On the other hand, the water-soluble ethylenically unsaturated monomers are acid groups (-COOH) and / or neutralized acid groups (-COO ^-) contain the so, the function produced by the polymerization, the acid remaining without participating in polymerization the surface of the gel-based polymer A large amount of hydrophilic moieties due to (-COOH) and/or neutralized acidic groups (-COO ^{- ) are present.} Therefore, when the additive is mixed with the hydrogel polymer, the hydrophilic functional group of the additive is adsorbed to at least a part of the hydrophilic portion existing on the surface of the hydrogel polymer, and the surface of the polymer to which the additive is adsorbed is different from the additive. Hydrophobicity is exhibited by the hydrophobic functional group located at the terminal. Accordingly, aggregation between the resin particles can be suppressed.

More specifically, in the carboxylic acid-based additive, the hydrophobic functional group is an alkyl group having 5 to 21 carbon atoms (part A), the hydrophilic functional group is a C part, a carboxyl group (COOH), and in the case of a salt, a carboxylate group (COO ^- ), The hydrophobic functional group and the hydrophilic functional group are located at both ends of the additive, respectively. In particular, the carboxylic acid-based additive further includes a _{(B 1} -B ₂ ) portion in addition to the A and C portions at both ends, and _{the (B 1} -B ₂ ) portion is for the polymer surface, which may be insufficient with only the C portion. It plays a role in improving adsorption performance. Accordingly, the additive having the structure of Formula 1 has superior adsorption performance on the surface of the polymer exhibiting hydrophilicity, compared to the compound having an AC structure without a _{(B 1} -B _{2 ) moiety, thereby preventing aggregation of the superabsorbent polymer particles.} can be effectively suppressed.

Accordingly, the hydrogel polymer can be pulverized to a normal particle level without inter-particle agglomeration, and the amount of fine powder generated during the process can be significantly reduced as the drying process proceeds after the hydrogel polymer is pulverized to the normal particle level. In addition, the manufacturing method of the superabsorbent polymer composition according to an embodiment does not necessarily require a grinding process and a classification process after drying, and by performing the drying process and the surface crosslinking process together, the manufacturing cost can be greatly reduced, and the drying process and As the transfer process between the surface crosslinking processes is removed, physical damage to the particle surface can be reduced, thereby improving the physical properties of the superabsorbent polymer produced in the corresponding process.

Specifically, when the hydrogel polymer is pulverized in the presence of the carboxylic acid-based additive, part A, which is a hydrophobic functional group included in the additive, imparts hydrophobicity to the surface of the pulverized superabsorbent polymer particles to relieve friction between the particles, thereby reducing the friction between the particles. While increasing the apparent density of the water absorbent resin, the hydrophilic functional group C portion included in the additive is also bound to the super absorbent polymer particles to prevent the surface tension of the resin from being lowered. Accordingly, the superabsorbent polymer composition prepared according to the above-described manufacturing method may exhibit improved surface tension and apparent density compared to a composition not using such an additive.

Hereinafter, the method for preparing the superabsorbent polymer composition of one embodiment will be described in more detail for each step.

(Step 1)

The step is a step of cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer, wherein the water-soluble ethylenically unsaturated monomer, the internal crosslinking agent and polymerization It may consist of a step of preparing a monomer composition by mixing an initiator, and a step of thermally or photopolymerizing the monomer composition to form a hydrogel polymer.

The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the preparation of super absorbent polymers. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Chemical Formula 2:

[Formula 2]

R-COOM'

In Formula 2,

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

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

Preferably, the monomer may be at least one selected from the group consisting of (meth)acrylic acid and monovalent (alkali) metal salts, divalent metal salts, ammonium salts and organic amine salts of these acids.

As such, when (meth)acrylic acid and/or a salt thereof are used as the water-soluble ethylenically unsaturated monomer, it is advantageous because a superabsorbent polymer with improved water absorption can be obtained. In addition, the monomer includes maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth) ) acrylamide-2-methyl propane sulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene Glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide and the like can be used.

Here, the water-soluble ethylenically unsaturated monomer may have an acidic group, and at least a portion of the acidic group may be neutralized by a neutralizing agent. Specifically, in the mixing of the water-soluble ethylenically unsaturated monomer having the acidic group, the internal crosslinking agent, the polymerization initiator, and the neutralizing agent, at least a portion of the acidic groups of the water-soluble ethylenically unsaturated monomer may be neutralized. In this case, as the neutralizing agent, a basic material such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. that can neutralize an acidic group may be used.

In addition, the neutralization degree of the water-soluble ethylenically unsaturated monomer, which refers to the degree of neutralization by the neutralizing agent among the acidic groups included in the water-soluble ethylenically unsaturated monomer, is 50 to 90 mol%, or, 60 to 85 mol%, or 65 to 85 mole %, or 65 to 75 mole %. 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 is precipitated and it may be difficult for the polymerization to proceed smoothly. Conversely, if the degree of neutralization is too low, the absorption power of the polymer is greatly reduced as well as It can exhibit properties like elastic rubber, which is difficult to handle.

In addition, the term 'internal crosslinking agent' used in the present specification is a term used to distinguish it from a surface crosslinking agent for crosslinking the surface of the superabsorbent polymer particles to be described later, and is polymerized by crosslinking the unsaturated bonds of the above-described water-soluble ethylenically unsaturated monomers. serves to make The crosslinking in the above step proceeds without a surface or an internal division, but when the surface crosslinking process of the superabsorbent polymer particles described later proceeds, the surface of the particles of the superabsorbent polymer finally produced has a structure crosslinked by a surface crosslinking agent, The interior has a structure crosslinked by the internal crosslinking agent.

As the internal crosslinking agent, any compound may be used as long as it enables 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, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di( Meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylic Rate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri Multifunctional crosslinking agents such as (meth)acrylate, pentaerythol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, It is not limited. Preferably, among them, polyethylene glycol diacrylate may be used.

The crosslinking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of such an internal crosslinking agent may be carried out by thermal polymerization, photopolymerization or hybrid polymerization in the presence of a polymerization initiator, optionally a thickener, plasticizer, storage stabilizer, antioxidant, etc. There, the specific details will be described later.

In the monomer composition, the 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 is 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight, or 0.2 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or more, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. part by weight or less, 1 part by weight or less, or 0.5 part by weight or less. When the content of the upper internal crosslinking agent is too low, crosslinking does not occur sufficiently and it may be difficult to implement strength above an appropriate level. If the content of the upper internal crosslinking agent is too high, the internal crosslinking density increases and it may be difficult to implement the desired water holding capacity.

In addition, the polymerization initiator may be appropriately selected depending on the polymerization method. When using the thermal polymerization method, a thermal polymerization initiator is used, and when using the photopolymerization method, a photopolymerization initiator is used, and a hybrid polymerization method (thermal and light). both of the thermal polymerization initiator and the 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, so a thermal polymerization initiator may be additionally used.

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

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

In addition, as the thermal polymerization initiator, at least one selected from the group consisting of a persulfate-based initiator, an azo-based initiator, 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 (K ₂ S ₂ O ₈ ), ammonium persulfate (Ammonium persulfate; (NH ₄ ) ₂ S ₂ O ₈ ) and the like, and examples of the azo-based initiator 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-(carbamoylazo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride), and 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)). More various thermal polymerization initiators are well described in Odian's book 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.

The polymerization initiator may be used in an amount of 2 parts by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, when the concentration of the polymerization initiator is too low, the polymerization rate may be slowed and the residual monomer may be extracted in a large amount in the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is higher than the above range, the polymer chain constituting the network is shortened, so that the content of the water-soluble component is increased and the physical properties of the resin may be lowered, such as lowered absorbency under pressure, which is not preferable.

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

In addition, the monomer composition including the monomer may be in a solution state dissolved in a solvent such as water, and the solid content in the monomer composition in the solution state, that is, the concentration of the monomer, the internal crosslinking agent, and the polymerization initiator is determined by polymerization. It may be appropriately adjusted in consideration of time and reaction conditions. For example, the solids content in the monomer composition may be 10 to 80% by weight, or 15 to 60% by weight, or 30 to 50% by weight.

When the monomer composition has a solid content in the above range, it is not necessary to remove unreacted monomers after polymerization by using the gel effect phenomenon that occurs in the polymerization reaction of a high concentration aqueous solution, and the grinding efficiency of the polymer to be described later is improved. It may be advantageous to control.

The solvent that can be used at this time can be used without limitation in its composition as long as it can dissolve the above-mentioned 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 ethyl ether , toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide may be used in combination.

On the other hand, cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group may be carried out without limitation in structure, as long as the hydrogel polymer can be formed by thermal polymerization, photopolymerization, or hybrid polymerization.

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source. In general, when thermal polymerization is carried out, it may be carried out in a reactor having a stirring shaft such as a kneader. The polymerization may be carried out in a reactor equipped with a conveyor belt or in a flat-bottomed vessel, but the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.

For example, as described above, the hydrogel polymer obtained by thermal polymerization by supplying hot air or heating the reactor to a reactor such as a kneader having a stirring shaft is fed 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 hydrogel polymer obtained may vary depending on the concentration and injection rate of the injected monomer composition, and a hydrogel polymer having a weight average particle diameter of 2 to 50 mm can be obtained.

In addition, as described above, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or a flat-bottomed container, the form of the hydrogel polymer obtained may be a hydrogel polymer on a sheet having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration of the injected monomer composition, the injection rate, or the injection amount, but it is preferable to supply the monomer composition so that a polymer sheet having a thickness of about 0.5 to about 5 cm can be obtained. do. When the monomer composition is supplied so that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is not preferable. When the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction occurs evenly over the entire thickness due to the excessively thick thickness. it may not be

In this case, the hydrogel polymer obtained by this method may have a moisture content of 30 to 70 wt%. For example, the water content of the hydrogel polymer may be 30% by weight or more, 40% by weight or more, or 50% by weight or more, and 70% by weight or less, 65% by weight or less, or 60% by weight or less. If the water content of the hydrogel polymer is too low, it may not be effectively pulverized because it is difficult to secure an appropriate surface area in the subsequent pulverization step, and if the water content of the hydrogel polymer is too high, the pressure applied in the pulverization step afterward increases to a desired particle size. it can be difficult to do

Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer as the content of moisture occupied with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer in the crumb state through infrared heating. At this time, the drying condition is set to 40 minutes including 5 minutes of the temperature rise step in such a way that the temperature is raised from room temperature to about 180°C and then maintained at 180°C, and the moisture content is measured.

The hydrogel polymer formed through step 1 has a three-dimensional network structure in which main chains formed by polymerization of the water-soluble ethylenically unsaturated monomers are crosslinked by the internal crosslinking agent. As such, when the hydrogel polymer has a three-dimensional network structure, the water holding capacity and absorbency under pressure, which are general physical properties of the superabsorbent polymer, can be significantly improved compared to the case of a two-dimensional linear structure that is not further crosslinked by an internal crosslinking agent.

(Step 2)

In the above step, the hydrogel polymer is mixed with the carboxylic acid-based additive and then pulverized to prepare a pulverized product including the water-containing superabsorbent polymer particles and the additive, rather than chopping the hydrogel polymer, but a final product. To prepare water-containing superabsorbent polymer particles pulverized to a particle size of about 150 μm to about 850 μm that can be applied to, the carboxylic acid-based additive is used for this purpose.

In this case, the carboxylic acid-based additive is at least one selected from the group consisting of the carboxylic acid represented by Formula 1 and a metal salt thereof. Specifically, the carboxylic acid-based additive is a carboxylic acid represented by Formula 1, an alkali metal salt of the carboxylic acid represented by Formula 1, and an alkaline earth metal salt of a carboxylic acid represented by Formula 1 at least one selected from More specifically, the carboxylic acid-based additive is one of the carboxylic acid represented by the formula (1), an alkali metal salt of the carboxylic acid represented by the formula (1), and an alkaline earth metal salt of the carboxylic acid represented by the formula (1).

In Formula 1, A is a hydrophobic portion and may be a linear or branched alkyl group having 5 to 21 carbon atoms, but when A is an alkyl group having a linear structure, aggregation of pulverized particles is suppressed and dispersibility is improved in terms of more advantageous When A is an alkyl group having less than 5 carbon atoms, there is a problem that the aggregation control of the pulverized particles is not effectively achieved due to the short chain length, and when A is an alkyl group having more than 21 carbon atoms, the mobility of the additive is reduced and the hydrogel It may not be effectively mixed with the polymer, or there may be a problem in that the cost of the composition increases due to an increase in the cost of the additive.

Specifically, in Formula 1, A is a linear alkyl having 5 to 21 carbon atoms, that is, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decanyl, n-undecanyl , n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, n-octadecanyl, n-nonadecanyl, n- icosanil, or n-heticosanyl.

More specifically, A may be a linear alkyl having 6 to 18 carbon atoms. For example, A may be -C ₆ H ₁₃ , -C ₁₁ H ₂₃ , -C ₁₂ H ₂₅ , -C ₁₇ H ₃₅ , or -C ₁₈ H ₃₇ .

In addition, in Formula 1, the (B ₁ -B ₂ ) moiety serves to improve the adsorption performance to the polymer surface, which may be insufficient only with the C moiety, and when _{the carbon number of B 2} is 3 or more, the B ₁ moiety As the distance between the portion C and C increases, the adsorption performance for the hydrogel polymer may be deteriorated.

In this case, R ₁ and R ₂ are each independently, linear or branched alkyl having 1 to 4 carbon atoms, more specifically, R ₁ and R ₂ are each independently, methyl, ethyl, propyl, isopropyl , butyl, isobutyl, sec-butyl, or tert-butyl, but in terms of adsorption of the additive to the superabsorbent polymer particles, it is advantageous that the molecular structure of the additive is not bulky, so R ₁ and R ₂ may be all methyl.

Also, in Formula 1, n may be 1, 2, or 3. More specifically, n that indicates the number of (B ₁ -B ₂₎ is, (B ₁ -B ₂₎ a function part to a point and the acid-based additives for enhancing the adsorption capacity of the gel portion C Considering the molecular length for effectively adsorbing to the polymer, n is preferably 1.

,

, 또는

일 수 있고, 여기서, *는 이웃하는 원자와의 결합 사이트이다.Specifically, in Formula 1, B ₁ is

,

, or

may be, where * is a binding site with a neighboring atom.

, 또는

일 수 있다. For example, B ₁ is

, or

can be

,

,

,

,

, 또는

일 수 있고, 여기서, *는 이웃하는 원자와의 결합 사이트이다. 이때, C 부분과 함께 가교 중합체에 대한 첨가제의 흡착 성능을 향상시킨다는 측면에서 B₂가

,

, 또는

인 것이 바람직하다.In addition, in Formula 1, B ₂ is

,

,

,

,

, or

may be, where * is a binding site with a neighboring atom. At this time, in terms of improving the adsorption performance of the additive to the crosslinked polymer together with the C part, B ₂ is

,

, or

It is preferable to be

In addition, in Formula 1, part C is a hydrophilic part and is a carboxyl group (COOH), but when the carboxylic acid-based additive is a salt, it is a carboxylate group (COO ^- ).

In other words, the carboxylic acid-based additive may be a compound represented by the following Chemical Formula 1a:

[Formula 1a]

In Formula 1a,

M is H ⁺ , a monovalent cation of an alkali metal, or a divalent cation of an alkaline earth metal,

k is 1 if M is H ⁺ or a monovalent cation of an alkali metal, and 2 if M is a divalent cation of an alkaline earth metal,

Descriptions of A, B ₁ , B ₂ and n are the same as defined in Formula 1 above.

More specifically, when the carboxylic acid-based additive is an alkali metal salt of a carboxylic acid represented by Formula 1, the additive may be represented by Formula 1':

[Formula 1']

In Formula 1',

M ₁ is an alkali metal, for example sodium or potassium,

Descriptions of A, B ₁ , B ₂ and n are the same as defined in Formula 1 above.

In addition, when the carboxylic acid-based additive is an alkaline earth metal salt of a carboxylic acid represented by Formula 1, the additive may be represented by Formula 1”:

[Formula 1"]

In Formula 1", M ₂ is an alkaline earth metal, for example, calcium,

Descriptions of A, B ₁ , B ₂ and n are the same as defined in Formula 1 above.

For example, the carboxylic acid-based additive may be any one carboxylic acid selected from the group consisting of:

.

.

Alternatively, the carboxylic acid-based additive may be any one alkali metal salt selected from the group consisting of:

above,

M ₁ is each independently an alkali metal.

Alternatively, the carboxylic acid-based additive may be any one alkaline earth metal salt selected from the group consisting of:

above,

M ₂ is each independently an alkaline earth metal.

For example, the carboxylic acid-based additive may be any one of compounds represented by the following Chemical Formulas 1-1 to 1-7, but is not limited thereto:

.

.

Meanwhile, the carboxylic acid-based additive may be used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the hydrogel polymer. When the additive is used too little, it is not uniformly adsorbed on the surface of the hydrogel polymer, which may cause re-agglomeration of the particles after pulverization. can be For example, the carboxylic acid-based additive is 0.01 parts by weight or more, 0.015 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, relative to 100 parts by weight of the hydrogel polymer; Or 1 part by weight or less may be used.

A method of mixing these additives with the hydrogel polymer is not particularly limited as long as it is a method capable of uniformly mixing them with the hydrogel polymer, and may be appropriately adopted and used. Specifically, the additive may be mixed in a dry manner, dissolved in a solvent and then mixed in a solution state, or the additive may be melted and then mixed.

Among them, for example, the additive may be mixed in a solution state dissolved in a solvent. In this case, water may be used as the solvent in consideration of the ease of the drying process and the cost of the solvent recovery system. In addition, the solution is prepared by mixing the additive and the hydrogel polymer into a reaction tank, or by putting the hydrogel polymer in a mixer and spraying the solution, or by continuously supplying the hydrogel polymer and the solution to a continuously operated mixer and mixing them. etc. can be used.

After mixing the hydrogel polymer and the additive, the mixture may be pulverized to prepare a pulverized product in which the water-containing superabsorbent polymer particles and the additive are mixed. Specifically, the pulverizing step may be performed so that the pulverized water-containing superabsorbent polymer particles have a particle size of a normal particle size.

At this time, the pulverizer used for pulverization is a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, and a cutter mill. , a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter may include any one selected from the group consisting of a grinding device, but Examples are not limited.

Alternatively, as a grinder, a pin mill, a hammer mill, a screw mill, a roll mill, a disk mill, or a jog mill may be used. , but is not limited to the above example.

Among them, the pulverization may be performed by a chopper, more specifically, a meat chopper. At this time, the meat chopper includes two or more perforated plates, and more specifically, the meat chopper includes a chopping module including two or more porous plates, and each of the two or more porous plates is to be passed through the hydrogel polymer. It may be provided with a plurality of small cut-outs having a certain size. In addition, the hole size of each of the small holes in the perforated plate may be 0.2 mm to 5 mm. In other words, it can be seen that the pulverization is performed by pushing the hydrogel polymer mixed with the additive to be pulverized while passing through the small holes of the perforated plate. At this time, an extruder may be used to extrude the hydrogel polymer, for example, a single or multiple screw type extruder may be used.

For example, the hydrogel polymer mixed with the carboxylic acid-based additive may be pulverized using a meat chopper including the first perforated plate and the second perforated plate. The hole size (meaning the diameter of the hole) of the small holes provided in each of the first perforated plate and the second perforated plate may be the same or different from each other, and in this case, for ease of pulverization, the second It is preferable that the hole size of the small cut hole provided in the stencil plate is smaller than the hole size of the small cut hole provided in the first perforated plate. For example, the hole size of the small hole provided in the first perforated plate may be about 1.5 mm to about 5 mm, and the hole size of the small hole provided in the second perforated plate may be about 0.2 mm to about 1.2 mm. there is.

As described above, after passing the hydrogel polymer mixed with the carboxylic acid additive through the first perforated plate having a plurality of small holes having a hole size of 1.5 mm to 5 mm, the hole size is 0.2 mm to 1.2 mm When the pulverization is performed by passing it through the second perforated plate having a plurality of fine cut holes of mm in diameter, the particle size distribution at the same level as that of the product is realized after drying, so that the process of pulverizing the dried body can be omitted. It has the advantage of fundamentally preventing the occurrence.

Here, the "water-containing superabsorbent polymer particles" included in the pulverized material are particles having a water content (moisture content) of about 30% by weight or more, and since the water-containing gel polymer is pulverized in the form of particles without a drying process, as with the water-containing gel polymer It may have a moisture content of 30 to 70% by weight.

In addition, the water-containing superabsorbent polymer particles may have a particle size of a normal particle level, that is, a particle diameter of 150 μm to 850 μm. Specifically, the pulverized product contains 90 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, or 95 wt% or more of the water-containing super absorbent polymer particles having a particle diameter of 150 μm to 850 μm relative to the total weight. can do. The particle size of the resin particles may be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method. Alternatively, the content of the water-containing superabsorbent polymer particles having a particle diameter of 150 μm to 850 μm in the pulverized product is the final manufactured product considering that no additional pulverization process is performed after drying and surface crosslinking processes when preparing the superabsorbent polymer composition. It can be seen that the content of the superabsorbent polymer particles having a particle diameter of 150 μm to 850 μm in the superabsorbent polymer composition is the same.

Meanwhile, at least some of the additives included in the pulverized material may be present on the surface of the water-containing superabsorbent polymer particles. Here, “at least a portion of the additives are present on the surface of the water-containing superabsorbent polymer particles” means that at least some of the additives are adsorbed or bonded to the surface of the water-containing superabsorbent polymer particles. Specifically, the additive may be physically or chemically adsorbed on the surface of the superabsorbent polymer. More specifically, the hydrophilic functional group of the additive may be physically adsorbed to the hydrophilic portion of the surface of the superabsorbent polymer by intermolecular forces such as dipole-dipole interaction. As described above, the hydrophilic portion of the additive is physically adsorbed to the surface of the superabsorbent polymer particle to surround the surface, and the hydrophobic portion of the additive is not adsorbed to the surface of the resin particle, so that the resin particle has a type of micelle structure. As an additive may be coated. This is because the carboxylic acid-based additive is not added during the polymerization process of the water-soluble ethylenically unsaturated monomer, but is added after the polymer is formed. Re-agglomeration between the superabsorbent polymer particles may be further suppressed.

(Step 3)

The step is a step of mixing the pulverized material with a surface crosslinking agent and drying the mixture to prepare a superabsorbent polymer composition including superabsorbent polymer particles having a surface crosslinking layer formed on at least a portion of the surface and the additive, wherein the pulverized material is subjected to surface This is a step of forming a surface crosslinking layer on the surface of the superabsorbent polymer particles while drying the moisture of the water-containing superabsorbent polymer particles in the presence of a crosslinking agent.

Specifically, the drying of the pulverized product may be performed so that the moisture content of each of the plurality of superabsorbent polymer particles included in the prepared superabsorbent polymer composition is about 10% by weight or less, specifically, about 0.01 to about 10% by weight. can

In addition, the crosslinked polymer included in the superabsorbent polymer particles may be further crosslinked through a surface crosslinking agent to form a surface crosslinking layer on at least a portion of the surface of the superabsorbent polymer particles. This is to increase the surface crosslinking density of the superabsorbent polymer particles. As described above, when the superabsorbent polymer particles further include a surface crosslinking layer, the superabsorbent polymer particles have a structure having a higher crosslinking density outside than inside.

As the surface cross-linking agent, any surface cross-linking agent that has been conventionally used in the production of superabsorbent polymers may be used without 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, propylene carbonate, and glycerol 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.

Specifically, one or more, or two or more, or three or more of the above-mentioned surface crosslinking agents may be used as the surface crosslinking agent. For example, propylene glycol and ethylene carbonate may be used together.

The surface crosslinking agent may be used in an amount of about 0.001 to about 5 parts by weight based on 100 parts by weight of the pulverized product. For example, the surface crosslinking agent is in an amount of 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.05 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, or 1 part by weight or less based on 100 parts by weight of the pulverized product. can be used as By adjusting the content range of the surface crosslinking agent to the above-mentioned range, a superabsorbent polymer having excellent absorbent properties can be prepared.

In addition, it may be carried out by adding an inorganic material to the surface crosslinking agent. That is, in the presence of the surface crosslinking agent and the inorganic material, the step of further crosslinking the surface of the water-containing superabsorbent polymer particles to form a surface crosslinking layer may be performed.

As the inorganic material, at least one inorganic material selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate may be used. The inorganic material may be used in powder form or liquid form, and in particular, may be used as alumina powder, silica-alumina powder, titania powder, or nano silica solution. In addition, the inorganic material may be used in an amount of about 0.001 to about 1 part by weight based on 100 parts by weight of the pulverized material.

In addition, about the method of mixing the said surface crosslinking agent with a pulverized product, there is no limitation in the structure. For example, a method of mixing the surface cross-linking agent and the pulverized product into a reaction tank, spraying the pulverized material with the surface cross-linking agent, continuously supplying the pulverized material and the surface cross-linking agent to a continuously operated mixer, and mixing can be used. .

When mixing the surface cross-linking agent with the pulverized product, water and/or methanol may be mixed and added. When water and methanol are added, there is an advantage that the surface crosslinking agent can be uniformly dispersed in the superabsorbent polymer composition. Alternatively, the surface crosslinking agent may be mixed in a solution state dissolved in water and/or methanol. In this case, the content of the added water and methanol may be appropriately adjusted to induce even dispersion of the surface crosslinking agent, prevent agglomeration of the superabsorbent polymer composition, and at the same time optimize the surface penetration depth of the crosslinking agent.

The drying and surface crosslinking process may be performed in a moving type. This moving type drying is divided into fixed-bed type drying and the presence/absence of flow of material during drying.

Specifically, the moving type drying refers to a method of drying the drying body while mechanically stirring. At this time, the direction in which the hot air passes through the material may be the same as or different from the circulation direction of the material. Alternatively, the material may be circulated inside the dryer, and the heat medium fluid (fruit oil) may be passed through a separate pipe outside the dryer to dry the material.

On the other hand, fixed-bed type drying refers to a method in which a material to be dried is stopped on a floor such as a perforated iron plate through which air can pass, and hot air passes through the material from the bottom to dry.

Therefore, it is preferable to dry the pulverized material by a fluid drying method in terms of preventing aggregation between the water-containing superabsorbent polymer particles in the pulverized material to be dried in the above step, and drying can be completed within a short time.

As an apparatus capable of drying by such a fluid drying method, a horizontal-type mixer, a rotary kiln, a paddle dryer, a steam tube dryer, or a generally used A fluid dryer or the like may be used.

At this time, the temperature raising means for raising the temperature in a dryer is not specifically limited. It can be heated by supplying a heating medium or by directly supplying a heat source. At this time, as the type of heating medium that can be used, a fluid with increased temperature such as steam, hot air, or hot oil may be used, but it is not limited thereto, and the temperature of the supplied heating medium is determined by the means of the heating medium, the temperature increase rate and the temperature increase target temperature. Considering it, it can be appropriately selected. On the other hand, the directly supplied heat source may be a heating method through electricity or a heating method through a gas, but is not limited to the above-described example.

In addition, in order to simultaneously perform the drying and the surface crosslinking process, the drying may be performed at a temperature of 80° C. to 250° C. for 10 minutes to 3 hours.

Specifically, the temperature in the dryer may be 80 ℃ to 250 ℃. When the temperature in the dryer is too low, the drying time may be too long. When the drying temperature is too high, only the surface of the polymer is dried, and there is a risk that the physical properties of the superabsorbent polymer finally formed may be reduced. Therefore, preferably, the temperature in the dryer may be carried out at a temperature of about 100 °C to about 240 °C, more preferably at a temperature of about 150 °C to about 220 °C.

In addition, in the case of drying time, in consideration of process efficiency, etc., it may be dried for about 10 minutes to about 100 minutes, or about 30 minutes to about 80 minutes.

Meanwhile, at least some of the additives included in the superabsorbent polymer composition may be present on the surface of the superabsorbent polymer particles. Accordingly, the additive may be adsorbed or bound to at least a portion of the surface of the prepared superabsorbent polymer particles, and a surface cross-linking layer may be formed on the other portion.

In addition, in the superabsorbent polymer composition prepared by the above method, in addition to the superabsorbent polymer particles and the carboxylic acid-based additive, the _{ester bond of B 1} is decomposed and formed while the additive is pulverized and dried together with the hydrogel polymer. It may further include a compound.

Specifically, when the additive is a _{compound in which n is 1 and B 1} is -OCO-, the superabsorbent polymer composition may further include an alcohol having an A-OH structure and a compound having a _{HOOC-B 2 -C structure.} .

In addition, when the additive is a _{compound in which n is 1 and B 1} is -COO-, the superabsorbent polymer composition may further include a carboxylic acid having an A-COOH structure and a compound having a _{HO-B 2 -C structure.} .

In addition, when the additive is a _{compound in which n is 1 and B 1} is -COOCH(R ₁ )COO-, the superabsorbent polymer composition includes a carboxylic acid having an A-COOH structure and HOCH(R ₁ )COO-B ₂ - It may further include a compound of structure C.

As such, since the superabsorbent polymer composition further includes a compound formed by decomposition of an ester bond in an additive molecule, mobility of the additives is increased, and re-agglomeration after pulverization can be further prevented.

In addition, a compound having a plurality of hydroxyl groups-containing glucose units in a molecule, such as microcrystalline cellulose, may not be used during the manufacturing method process. For example, when the superabsorbent polymer composition includes microcrystalline cellulose having an average particle diameter of 1 to 10 μm, such as ^{AVICEL ®} PH-101 represented by the following formula 3 available from FMC, a plurality of hydroxy Due to the group, aggregation between the particles of the superabsorbent polymer finally prepared cannot be suppressed, and thus the effect of the above-described additives may not be effectively expressed.

[Formula 3]

As described above, since most of the inner portion of the superabsorbent polymer composition prepared according to the exemplary embodiment is normal particles and the fine powder content is low, an additional pulverizing step may not be included after drying the pulverized product. Accordingly, an additional classification step may not be included. That is, it is possible to manufacture a superabsorbent polymer composition applicable to a product without an additional pulverization/classification step, but fine pulverization may be additionally performed or a classification process may be additionally performed according to the use and necessity to which the product is applied.

On the other hand, the super absorbent polymer composition prepared by the above manufacturing method has a low fine powder content without a separate classification process, and has excellent water holding capacity (CRC) and absorbency under pressure (AUP) compared to the superabsorbent polymer composition prepared by the conventional method. It can be at or above the equivalent level. In addition, the superabsorbent polymer composition is characterized in that it exhibits an equivalent level of surface tension while having a high bulk density. This is because part A, which is a hydrophobic functional group included in the carboxylic acid-based additive, imparts hydrophobicity to the surface of the pulverized superabsorbent polymer particles to relieve friction between particles to increase the apparent density of the superabsorbent polymer, and is included in the additive. This is because the hydrophilic functional group C portion present is also bonded to the superabsorbent polymer particles so that the surface tension of the resin is not lowered.

Specifically, the superabsorbent polymer composition prepared as described above contains 90 wt% or more, 91 wt% or more, or 91.5 wt% or more of superabsorbent polymer particles having a particle diameter of 150 μm to 850 μm relative to the total weight, that is, normal particles. can do.

In addition, the superabsorbent polymer composition contains fine powder having a particle diameter of less than 150 μm relative to the total weight. Less than 10% by weight, specifically less than about 5% by weight, more specifically about 4% by weight, more specifically less than about 3% by weight. This is in contrast to having about 10 wt% to about 20 wt% of fine powder when the hydrogel polymer is dried and then pulverized to prepare a super absorbent polymer.

In addition, the superabsorbent polymer composition has a water holding capacity (CRC) of 25 g/g or more, 27 g/g or more, or 28 g/g or more and 45 g/g or less, measured according to the EDANA method WSP 241.3. can have

In addition, the superabsorbent polymer composition has an absorbency under pressure (AUP) of 18 g/g or more, 19 g/g or more, or 20 g/g or more at 0.7 psi measured according to WSP 242.3 of the EDANA method, and 26 g/g or less, 25 g/g or less, or 24 g/g or less.

In addition, the superabsorbent polymer composition may have an apparent density (bulk density) of 0.5 to 0.8 g/ml. At this time, the apparent density was measured by placing about 100 g of the superabsorbent polymer composition into a funnel-shaped bulk density measuring device, flowing it down into a 100 ml container, and then measuring the weight of the super absorbent polymer in the container. That is, the apparent density is calculated as (weight of superabsorbent polymer composition)/(volume of container, 100 ml). More specifically, the superabsorbent polymer composition may have an apparent density (bulk density) of 0.65 to 0.73 g/ml, or 0.68 to 0.72 g/ml.

In addition, the superabsorbent polymer composition may have a surface tension of 68 mN/m or more and less than 72 mN/m. In this case, the surface tension can be measured by adding 0.5 g of the superabsorbent polymer to 40 mL of 0.9% saline, stirring at 350 rpm for 3 minutes, and then measuring the brine containing the swollen superabsorbent polymer with a surface tension meter.

Hereinafter, preferred embodiments are presented to help the understanding of the invention. However, the following examples are only for illustrating the invention, and do not limit the invention thereto.

Example - Preparation of super absorbent polymer composition

Example 1

(Step 1)

In a 3L glass container equipped with a stirrer and a thermometer, 100 g (1.388 mol) of acrylic acid, 0.26 g of internal crosslinking agent polyethylene glycol diacrylate (Mn = 508), and photopolymerization initiator diphenyl (2, 4,6-trimethylbenzoyl) phosphine oxide 0.008 g, 0.2 g of sodium persulfate, a thermal polymerization initiator, and 123.5 g of a 32% caustic soda solution were mixed at room temperature to prepare a monomer composition (neutralization degree of acrylic acid: 70 mol%, solid content: 45 wt%).

Thereafter, the monomer composition was supplied at a rate of 500 to 2000 mL/min on a conveyor belt in which a belt having a width of 10 cm and a length of 2 m was rotated at a speed of 50 cm/min. Then, at the same time as the supply of the monomer composition, the polymerization reaction was carried out for 60 seconds by irradiating ultraviolet rays having an intensity of ^{10 mW/cm 2 to obtain a hydrogel polymer having a water content of 55 wt%.}

(Step 2)

Next, sodium stearoyl-2-lactylate (Almax-6900, manufactured by Ilshin Wells, Ltd., melting point: 48) represented by the following Chemical Formula 1-6 in the hydrogel polymer obtained through the polymerization reaction -51° C.) was mixed in an aqueous solution in high temperature water so as to be 0.3 parts by weight relative to 100 parts by weight of the hydrogel polymer, and then pulverized to particles having a particle diameter of 150 μm to 850 μm using a meat chopper. did. At this time, the used meat chopper includes a minced module including a plurality of perforated plates, and each porous plate has a plurality of fine cut holes, so that the hydrogel polymer is discharged in a minced state through the plurality of fine cut holes. Specifically, the prepared hydrogel polymer was first passed through a perforated plate having a hole size of 2 mm, and then passed through a perforated plate having a hole size of 0.5 mm secondarily through the prepared hydrogel polymer, Grind to normal particle level. At this time, the water content of the water-containing super absorbent polymer particles included in the pulverized product was 55 wt%.

[Formula 1-6]

(Step 3)

Thereafter, a mixed solution for surface crosslinking in which 4.5 g of ultrapure water, 0.1 g of a surface crosslinking agent propylene glycol, and 0.4 g of ethylene carbonate were mixed was administered to 200 g of the pulverized product and mixed for 1 minute. Next, the mixture was put into a paddle dryer capable of drying in a fluid manner, and then kneaded at an internal temperature of 185° C. for 60 minutes, followed by drying and surface crosslinking. After completion of the reaction, a superabsorbent polymer composition was obtained without an additional pulverization process.

Example 2

A superabsorbent polymer composition was prepared in the same manner as in Example 1, except that 0.15 g of the internal crosslinking agent polyethylene glycol diacrylate was used in Example 1.

Example 3

A superabsorbent polymer composition was prepared in the same manner as in Example 2, except that 0.5 g of ethylene carbonate was used in the mixed solution for surface crosslinking in Example 2.

Example 4

In Example 2, sodium C _14-18 -2-lactylate instead of sodium stearoyl-2-lactylate (Sodium C _14-18 -2-Lactylate, Almax-6600, manufactured by Ilshin Wells, melting point: 44-46 ℃), except that a superabsorbent polymer composition was prepared in the same manner as in Example 2.

Example 5

Superabsorbent absorption was performed in the same manner as in Example 2, except that monolauryl maleate represented by the following formula 1-1 was used instead of sodium stearoyl-2-lactylate in Example 2 A resin composition was prepared. In this case, monolauryl maleate represented by the following Chemical Formula 1-1 was prepared by mixing maleic acid anhydride and 1-dodecanol in a molar ratio of 1:1 and reacting at 60° C. for 3 hours.

[Formula 1-1]

Comparative Example 1

(Polymerization) Using the same method as in Example 1, a hydrogel polymer having a water content of 55 wt% was obtained.

(Chopping) Next, the water-containing gel polymer obtained through the polymerization reaction was mixed with the same amount of water as in Example 1, and then using a meat chopper having a perforated plate having a hole size of 16 mm. cut.

After (drying) , a mixed solution for surface crosslinking in which 4.5 g of ultrapure water, 0.1 g of propylene glycol, and 0.4 g of ethylene carbonate were mixed with 200 g of the cut hydrogel polymer was administered and mixed for 1 minute. Next, after putting the mixture into a paddle dryer, drying and surface crosslinking reaction were attempted, but kneading could not proceed due to aggregation between the hydrogel polymers.

Comparative Example 2

In Example 1, the same method as in Example 1, except that polyethylene glycol (Mw=2000, manufactured by Miwon Specialty Chemical Co.) was used instead of sodium stearoyl-2-lactylate represented by Formula 1-6. was used to prepare a superabsorbent polymer composition, but excessive pressure was generated inside the chopper, so that the polymer could not be discharged through the perforated plate and the machine was stopped.

Comparative Example 3

Example 1, except that sodium polyoxyethylene (3) lauryl ether carboxylate (LCA-30D, manufactured by Sanyo chemical) was used instead of sodium stearoyl-2-lactylate represented by Formula 1-6 in Example 1 A superabsorbent polymer composition was prepared using the same method as described above.

Comparative Example 4

(Polymerization) Using the same method as in Example 1, a hydrogel polymer having a water content of 55 wt% was obtained.

(Chopping) Next, after mixing the same amount of water as in Example 1 with the hydrogel polymer obtained through the polymerization reaction, a meat chopper having a perforated plate having a number of small holes having a hole size of 16 mm (meat chopper) chopper) was used to pulverize.

(Drying) After that, the chopped hydrogel polymer was dried by standing in an oven at 200° C. for 30 minutes.

(Pulverization/Classification) The dried polymer is coarsely pulverized to a particle size of about 2 mm with a cutting grinder (PULVERISETTE 19, manufactured by Fritsch), and then classified, and among the classified particles, larger than 850 μm is removed by a roll mill (66 F Gran-U-Lizer (manufactured by MPE) was finely pulverized, and it was classified into normal particles and fine particles.

(Surface crosslinking) Then , a mixed solution for surface crosslinking in which 4.5 g of ultrapure water, 0.1 g of propylene glycol, and 0.4 g of ethylene carbonate are mixed with 200 g of the classified normal particles is administered, mixed for 1 minute, and then convection was performed at 198°C for 60 minutes. The surface crosslinking reaction was performed using an oven. Thereafter, they were classified to prepare a superabsorbent polymer composition containing superabsorbent polymer particles having a size of 150 to 850 μm.

Test Example 1

For the superabsorbent polymer compositions prepared in Examples and Comparative Examples, centrifugation retention capacity (CRC) and absorbency under pressure (AUP) were respectively measured in the following manner, and the results are shown in Table 1 below.

(1) Centrifuge Retention Capacity (CRC)

The water holding capacity of each resin composition according to the no-load absorption magnification was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3.

Specifically, in the resin compositions obtained through Examples and Comparative Examples, a resin composition classified through a sieve of #30-50 was obtained. This resin composition W ₀ (g) (about 0.2 g) was uniformly put in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt %) at room temperature. After 30 minutes, the bag was drained of water for 3 minutes under the conditions of 250G using a centrifugal separator, and the mass W ₂ (g) of the bag was measured. Further, after the same operation without using the resin then the weight W ₁ (g) was measured.

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

[Equation 1]

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

(2) Absorbency under Pressure (AUP)

The absorbency under pressure of 0.7 psi of the superabsorbent polymer compositions of Examples and Comparative Examples was measured according to WSP 242.3 of the EDANA method.

First, when measuring the absorbency under pressure, the resin at the time of the CRC measurement

A glass filter was placed, and physiological saline composed of 0.9 wt% sodium chloride was placed at the same level as the upper surface of the glass filter. One filter paper having a diameter of 90 mm was loaded thereon. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted and the weight W ₄ (g) was measured.

The absorbency under pressure (g/g) was calculated according to the following Equation 2 using each of the obtained masses.

[Equation 2]

AUP(g/g) = [W ₄ (g) - W ₃ (g)]/W ₀ (g)

additive normal particle
content
(weight%) differential generation
(weight%) SAP properties CRC
(g/g) AUP
(g/g) S/T
(mN/m) BD (g/ml) Example 1 Sodium Stearoyl-2-lactylate 91.1 2.9 28.3 20.2 72.3 0.69 Example 2 Sodium Stearoyl-2-lactylate 92.2 2.2 36.1 21.3 71.8 0.69 Example 3 Sodium Stearoyl-2-lactylate 92.0 2.3 34.9 23.8 71.7 0.69 Example 4 Sodium C _14-18 -2-lactylate 91.9 2.4 35.9 21.6 72.1 0.69 Example 5 monolauryl maleate 91.9 2.3 36.0 21.5 71.6 0.69 Comparative Example 1 - measurement
impossible measurement
impossible measurement
impossible measurement
impossible measurement
impossible measurement
impossible Comparative Example 2 polyethylene glycol measurement
impossible measurement
impossible measurement
impossible measurement
impossible measurement
impossible measurement
impossible Comparative Example 3 Sodium polyoxyethylene (3) lauryl ether carboxylate 92.1 3.0 26.1 20.4 61.5 0.68 Comparative Example 4 - 90.1 9.2 35.8 22.9 71.9 0.67

As shown in Table 1, in the case of the example in which the superabsorbent polymer composition was prepared by adding the carboxylic acid-based additive during pulverization of the hydrogel polymer, Comparative Example 1 not using such an additive and Comparative Example 2 using polyethylene glycol Alternatively, it can be seen that it is possible to simultaneously perform the drying and surface crosslinking processes of the pulverized product after the hydrogel polymerization and pulverization.

In particular, in the preparation of the superabsorbent polymer composition in Examples, the final measured normal particle content in the example is the same as the normal particle content in the pulverized product prepared in (Step 2) because an additional grinding process is not performed after the drying and surface crosslinking processes. As can be seen, it is confirmed that the hydrogel polymer can be pulverized to the level of normal particles, unlike the method for preparing the superabsorbent polymer composition of Comparative Examples 1 and 2 above.

In addition, the superabsorbent polymer composition prepared according to the above Example was equivalent to that of the superabsorbent polymer composition of Comparative Example 3 prepared by adding sodium polyoxyethylene (3) lauryl ether carboxylate before pulverizing the hydrogel polymer. It can be confirmed that the surface tension is large and the bulk density is high while having the above water holding capacity and absorbency under pressure.

In addition, the superabsorbent polymer composition prepared according to the above example was prepared according to the conventional process as described in FIG. 1, specifically, after chopping without the use of additives, dried, pulverized and classified, and then separately subjected to a surface crosslinking process. Compared to the superabsorbent polymer composition of Comparative Example 4, the amount of fine powder generated was significantly reduced.

Therefore, when the carboxylic acid-based additive is added during pulverization of the hydrogel polymer in the production of the superabsorbent polymer and the drying and surface crosslinking processes are simultaneously performed, pulverization to the normal particle level is possible without an additional pulverization process, while the amount of fine powder is reduced and improved It can be seen that the surface tension and apparent density values can be used to prepare the superabsorbent polymer.

Claims (20)

1) forming a hydrogel polymer by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator;
2) mixing the hydrogel polymer with a carboxylic acid-based additive and then pulverizing to prepare water-containing superabsorbent polymer particles and a pulverized product containing the additive; and
3) mixing a surface crosslinking agent with the pulverized product and drying the mixture to prepare a superabsorbent polymer composition including superabsorbent polymer particles having a surface crosslinking layer formed on at least a portion of the surface and the additive;
The carboxylic acid-based additive is at least one selected from the group consisting of carboxylic acids represented by the following formula (1) and salts thereof,
Method for preparing the superabsorbent polymer composition:
[Formula 1]

In Formula 1,
A is alkyl having 5 to 21 carbon atoms,
B ₁ is -OCO-, -COO-, or -COOCH(R ₁ )COO-,
B ₂ is -CH ₂ -, -CH ₂ CH ₂ -, -CH(R ₂ )-, -CH=CH-, or -C≡C-,
Here, R ₁ and R ₂ are each independently an alkyl having 1 to 4 carbon atoms,
n is an integer from 1 to 3,
C is a carboxyl group.
According to claim 1,
The hydrogel polymer has a moisture content of 30 wt% to 70 wt%,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
In Formula 1,
A is -C ₆ H ₁₃ , -C ₁₁ H ₂₃ , -C ₁₂ H ₂₅ , -C ₁₇ H ₃₅ , or -C ₁₈ H ₃₇ ;
A method for preparing a superabsorbent polymer composition.
According to claim 1,
In Formula 1,
B ₁ is

, or

ego,
where * is a binding site with a neighboring atom,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
In Formula 1,
B ₂ is

,

, or

ego,
where * is a binding site with a neighboring atom,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The carboxylic acid-based additive is at least one selected from the group consisting of a carboxylic acid represented by Formula 1, an alkali metal salt thereof, and an alkaline earth metal salt thereof,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The carboxylic acid-based additive is any one of the compounds represented by the following formulas 1-1 to 1-7,
Method for preparing the superabsorbent polymer composition:

.
According to claim 1,
The carboxylic acid-based additive is used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the hydrogel polymer,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The carboxylic acid-based additive is mixed in a solution state dissolved in a solvent,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The grinding is performed by a meat chopper,
A method for preparing a superabsorbent polymer composition.
11. The method of claim 10,
The meat chopper includes two or more perforated plates,
Each of the two or more perforated plates is provided with a plurality of small holes having a certain size,
A method for preparing a superabsorbent polymer composition.
12. The method of claim 11,
The meat chopper includes a first perforated plate and a second perforated plate,
The hole size of the small hole provided in the first perforated plate is 1.5 mm to 5 mm,
The hole size of the small hole provided in the second perforated plate is 0.2 mm to 1.2 mm,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The water-containing super absorbent polymer particles have a moisture content of 30 wt% to 70 wt%,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The pulverized product comprises 90% by weight or more of water-containing superabsorbent polymer particles having a particle diameter of 150 μm to 850 μm relative to the total weight,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
At least some of the additives in the pulverized material are present on the surface of the water-containing superabsorbent polymer particles,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The surface crosslinking agent is used in an amount of 0.001 to 5 parts by weight based on 100 parts by weight of the pulverized product,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The drying is carried out in a moving type,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The drying is carried out at a temperature of 80 ° C to 250 ° C for 10 minutes to 3 hours,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
The prepared superabsorbent polymer composition comprises less than 10% by weight of fine powder having a particle diameter of less than 150 μm relative to the total weight,
A method for preparing a superabsorbent polymer composition.
According to claim 1,
After drying the pulverized product, it does not include an additional pulverizing step,
A method for preparing a superabsorbent polymer composition.

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