TWI758242B - Method of preparing super absorbent polymer - Google Patents

Abstract

Provided is a method of preparing super absorbent polymer. The method comprising the steps of, preparing a base resin by adding at least one of compounds represented by Formula (1) below to the hydrogel crosslinked polymer; and drying the base resin.

<Formula(1)> X-(R)_n-Y

Description

Process for making superabsorbent polymers

This case claims the priority of Korean Patent Application No. 10-2015-0037502, which was filed on March 18, 2015, and all the rights and interests accumulated therefrom. The full disclosure of the case is hereby incorporated into the disclosure of this specification.

Field of Invention

The present invention relates to a process for preparing superabsorbent polymers.

Background of the Invention

Superabsorbent polymer (SAP) is a synthetic polymer material with the function of absorbing 500 times to 1000 times its own weight in water. AGM) etc. Since their practical application, these superabsorbent polymers have been widely used as materials in the following fields: soil water retention agents, water blocking agents for civil engineering and construction, sheets for sowing, and food distribution products, and hygiene products such as baby diapers.

As for the method of preparing the superabsorbent polymer, reversed-phase suspension polymerization or aqueous solution polymerization is known. For example, reversed-phase suspension polymerization is disclosed in JP-A-56-161408, JP-A-57-158209, and JP-A-57-198714. to As the aqueous solution polymerization, thermal polymerization in which polymerization is performed by heating an aqueous solution, photopolymerization in which polymerization is performed by irradiating an aqueous solution with ultraviolet light, and the like are known.

Summary of Invention

In the process of making superabsorbent polymers, water-soluble components are produced which are non-crosslinked polymers, and residual monomers. The content of water-soluble components and residual monomers varies depending on the content of the polymerization initiator, the polymerization temperature, the content of the internal cross-linking agent, the surface cross-linking conditions, and the like.

When the content of water-soluble components and residual monomers is high, the surface of the diaper becomes sticky, or its liquid permeability is reduced, which may cause skin diseases and produce bad odor.

An aspect of the present invention proposes a method for preparing a superabsorbent polymer by which processability can be improved by eliminating the surface crosslinking treatment, and a comparatively surface crosslinked superabsorbent polymer can be obtained that contains a small amount of water-soluble components of superabsorbent polymers.

However, the aspects of the invention are not limited to those set forth herein. The foregoing and other aspects of the present invention will become more apparent to those skilled in the art to which the present invention pertains by reference to the detailed description of the invention that follows.

According to an embodiment of the present invention, a method for preparing a superabsorbent polymer is provided. The method is a method for preparing a naked superabsorbent resin, and includes the following steps: preparing a hydrogel cross-linked polymer by polymerizing a monomer composition including a hydrophilic monomer, a cross-linking agent, and a polymerization initiator; adding at least one of the compounds represented by formula (1) to the hydrogel cross-linked polymer to prepare a base resin; drying the base resin; and pulverizing the dried base resin resin. The naked superabsorbent resin may have an extractable content (EC) of more than 0% to less than 15% and a residual monomer (RM) concentration of more than 0 ppm and less than 1000 ppm, preferably, may have a concentration of more than 0% to less than 15% Extractable contents (EC) of more than 0 ppm and residual monomer (RM) concentrations of less than 600 ppm.

In a specific embodiment, the method may further include: preparing a monomer composition, and the monomer composition may include a hydrophilic monomer, a crosslinking agent, a polymerization initiator, a neutralizing agent, and a solvent. For example, preparing the monomer composition may include: preparing a first composition including a neutralizer and a solvent; preparing a second composition including a hydrophilic monomer, a crosslinking agent, and a polymerization initiator; and mixing the the first composition and the second composition.

In a specific embodiment, preparing the hydrogel cross-linked polymer may include: polymerizing the monomer composition; and pulverizing the hydrogel cross-linked polymer.

In a specific embodiment, the polymerization initiator includes a photopolymerization initiator or a composite polymerization initiator, and for example, the composite polymerization initiator includes a photopolymerization initiator and a thermal polymerization initiator.

X-(R) _n -Y...(1)

In a specific embodiment, in formula (1), X can be an unsaturated hydrocarbon group or a derivative group thereof, for example, X can be a monovalent atomic group of at least one of the following: C _2-5 ( Methyl) vinyl (CH ₂ =CR _a -, R _a is a hydrogen atom, or a C _1-3 hydrocarbon group or its derivative group), C _3-5 (methyl) allyl (CH ₂ =CR _b -CH ₂ -, R _b is a hydrogen atom, or a C _1-2 hydrocarbon group or its derivative group), a C _1-5 acyl group (R _c C(=O)-, R _c is a hydrogen atom, or C _{1 -4} hydrocarbon group or its derivative group), C _3-5 (meth)acryloyl group (CH ₂ =CR _d -C(=O)-, R _d is hydrogen atom, or C _1-2 hydrocarbon group or its Derivative group), and C _3-5 (meth)acryloyloxy group (CH ₂ =CR _e -C(=O)-O-, _Re is a hydrogen atom, or a C _1-2 hydrocarbon group or its Derivative groups). In one embodiment, X can be a C _3-5 (meth)acryloyl group (CH ₂ =CR _d -C(=O)-, R _d is a hydrogen atom, or a C _1-2 hydrocarbon group or a derivative thereof group).

In a specific embodiment, in formula (1), R is a divalent atomic group of at least one of the following: C _1-5 alkylene (-(CH ₂ ) _m -, m is 1 to Integer of 5), C _1-4 alkylene oxy (-(CH ₂ ) _m -O-, m is an integer from 1 to 4), C _2-6 alkylene (oxy) carbonyl (- (R _f ) _o -(C=O)-(R' _f ) _p -, o and p are each independently an integer from 0 to 2 and not simultaneously 0, and R _f and R' _f are each independently C _1-5 hydrocarbon group or its derivative group), and C _2-5 carbonyloxy group (-(R _g ) _r -(C=O)-O-, r is an integer from 0 to 2, and R _g is C _1-4 hydrocarbon group or its derivative group).

In one embodiment, n can be an integer from 2 to 20; and Y can be a hydrophilic group. The hydrophilic group may be any one of a hydroxyl group (-OH), a carboxyl group (-COOH), and an amine group (-NHR _h , -NH ₂ , or -NR _h2 , R _h is a C _1-5 hydrocarbon group). In one embodiment, the hydrophilic group may be a hydroxyl group.

In a specific embodiment, at least one of the compounds represented by formula (1) is at least one of the compounds represented by formula (2) below:

In a specific embodiment, in formula (2), R ₁ is any one of C _1-2 alkyl and C _1-2 alkoxy; R ₂ is C _1-5 alkylene (- (CH ₂ ) _m -, m is an integer from 1 to 5) and any one of C _1-5 alkyleneoxy groups (-(CH ₂ ) _m -O-, m is an integer from 1 to 5) ; Y is any one of a hydroxyl group (-OH), a carboxyl group (-COOH), and an amine group (-NHR _h , -NH ₂ , or -NR _h2 ).

In a specific embodiment, in formula (2), n may be an integer from 2 to 20.

In a specific embodiment, at least one of the compounds represented by formula (2) may be at least one of the compounds represented by formulas (3) to (14):

As described later, embodiments according to the present invention have the following effects.

According to the method for preparing the superabsorbent polymer of the present invention, since the surface crosslinking treatment can be eliminated, the processability can be improved.

Also, according to the method for preparing superabsorbent polymer of the present invention, superabsorbent polymer having centrifugal retention capacity (CRC) and absorbency under pressure (AUP) equal to surface cross-linking can be obtained, and superabsorbent polymer having surface cross-linking is compared The product contains a small amount of water-soluble components (EC) and residual monomers (RM).

The effects of the present invention are not limited to the foregoing, and other various Effect.

Steps P1-6, P11-13, P21, P22‧‧‧

The foregoing and other aspects and features of the present invention will become more apparent by describing in detail specific embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 is a schematic flow chart of a method for preparing a superabsorbent polymer according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The advantages and features of the present invention and the method for accomplishing these objects will be more readily understood by reference to the detailed description of the specific embodiments and the accompanying drawings which follow. However, the present invention may be implemented in many different embodiments and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are presented so that this disclosure will be thorough and complete, will fully convey the concept of the invention to those skilled in the art, and the invention will only be defined by the scope of the appended claims.

Although the terms "first, second, etc." are used to describe diverse constituent elements, such constituent element systems are not limited by these terms. These terms are only used to distinguish one constituent element from another. Accordingly, in the following description, the first constituent element may be the second constituent element.

In this specification, "surface-crosslinked superabsorbent polymer" is defined as a superabsorbent polymer having a core-shell structure in which a base resin is used as a core and a surface-crosslinked layer is formed on the surface of the core.

In this specification, "naked superabsorbent polymer" is defined as a superabsorbent polymer in which no surface cross-linked layer is formed on the surface of the base resin.

In the present specification, the "hydrogel cross-linked polymer" means any one of a sheet-like hydrogel cross-linked polymer and a particulate hydrogel cross-linked polymer.

In this specification, "C _AB " means that the number of carbon atoms is A to B. For example, "C _1-5 alkyl" is an alkyl group of 1 to 5 carbon atoms. In this specification, "C and/or D" is defined as C, D, or C and D. In this specification, "E to F" is defined as E or more to F or less.

In the present specification, an "unsaturated hydrocarbon group" is defined as a monovalent atom group, which is a residue obtained by removing one hydrogen atom from a hydrocarbon having an unsaturated bond. Examples of unsaturated hydrocarbon groups may include (methyl)vinyl and (meth)allyl.

In this specification, "alkyl" includes linear or branched alkyl groups, and examples thereof include n-butyl and tert-butyl. In this specification, "(methyl) vinyl group" is a monovalent atomic group having a double bond at its terminal, and is represented by CH ₂ =CR _a -. _Ra is _a hydrogen atom in vinyl and an alkyl group in methylvinyl. In this specification, "(meth)allyl" is a monovalent atomic group having a double bond at its terminal, and is represented by CH ₂ =CR _b -CH ₂ -. R _b is _a hydrogen atom in allyl, and an alkyl group in methallyl.

In this specification, "G derivative" is defined as a derivative in which some or all of the hydrogen atoms of the unsaturated hydrocarbon group or alkyl group of G are substituted with other atoms other than carbon atoms and hydrogen atoms, or by including Atomic group substitution of atoms other than carbon atoms and hydrogen atoms, such as oxygen (O), nitrogen (N), carbonyl (-(C=O)-), acyl (R _c C(=O)-), and (meth)acryloyl (CH ₂ =CR _d -C(=O)-).

In this specification, "alkoxy" is a monovalent atom group in which an alkyl group is bonded to an oxygen atom, and is a derivative of an alkyl group. Alkyl groups can be linear or branched. In the present specification, "acyl group" is a monovalent atomic group in which a carbonyl group is bonded to a hydrocarbon group or a derivative thereof, and is represented by R _c C(=O)-. In the acyl group, R _c is a hydrogen atom or a C _1-5 hydrocarbon group and derivatives thereof. In this specification, a "(meth)acryloyl group" is a monovalent atomic group in which a (meth)vinyl group is bonded to a carbonyl group, and is represented by CH ₂ =CR _d -C(=O)-. R _d in the acryl group may be a hydrogen atom, and in the methacryl group R _d may be an alkyl group or the like. In this specification, "(meth)acryloyloxy" is a monovalent atomic group in which the (meth)acryloyl group is bonded to an oxygen atom, and is represented by CH ₂ =CR _e -C(=O )-O- said. _Re in acryloxy group may be a hydrogen atom, and in methacryloyloxy group R _d may be an alkyl group or the like.

In this specification, the "alkylene group" is a divalent atom group consisting of a carbon atom and a hydrogen atom, and is represented by -(CH ₂ ) _m -. Examples of alkylene may include methylene ( _-CH2- ), ethylidene ( _{-CH2CH2- )} , and the like. In this specification, "alkyleneoxy" is a divalent atomic group in which the alkylene system is bonded to an oxygen atom, and is represented by -(CH ₂ ) _m -O-. Examples of alkyleneoxy may include methyleneoxy ( _-CH2O- , _-OCH2- ), ethyleneoxy _{( -CH2CH2O-} , _{-OCH2CH2- )} , and its class. In this specification, "alkylene(oxy)carbonyl" is a divalent atomic group in which the alkylene(oxy) is bonded to a carbonyl group, and is represented by -(R _f ) _o -(C=O) -(R' _f ) _p - means. Examples of alkylene(oxy)carbonyl groups may include methylenecarbonyl ( _-CH2- (C=O)-), methylenecarbonyloxy ( _-CH2- (C=O) _-CH2- ) , Methyleneoxycarbonyl (-CH ₂ -O-(C=O)-), Dimethyleneoxycarbonyl (-CH ₂ -O-(C=O)-OCH ₂ -, -OCH ₂ - (C=O) _-CH2 -O-), and species thereof. In this specification, "carbonyloxy" is a divalent atom group in which a carbonyl group is bonded to an oxygen atom, and is represented by -(R _g ) _r -(C=O)-O-. Examples of carbonyloxy may include carbonyloxy (-(C=O)-O-), methylenecarbonyloxy ( _-CH2- (C=O)-O-), and the like.

In this specification, the "amine group" is a residue obtained by removing one hydrogen atom from ammonia, and may be represented by -NHR _h , -NH ₂ , or -NR _h2 . R _h in the amine group may be an alkyl group or the like.

FIG. 1 is a schematic flow chart of a method for preparing a superabsorbent polymer according to an embodiment of the present invention.

1 , a method for preparing a superabsorbent polymer according to an embodiment of the present invention includes the following steps: (P1) preparing a monomer composition; (P2) preparing a hydrogel cross-linked polymer; (P3) using the following formula (1) At least one of the compounds represented is added to the hydrogel cross-linked polymer to prepare a base resin; (P4) The base resin is pulverized; (P5) The pulverized base resin is dried (hereinafter referred to as "" powdered product"); and (P6) powdered the dried base resin (hereinafter referred to as "dried product").

The step (P2) of preparing the hydrogel cross-linked polymer may further include the step (P21) of pulverizing the hydrogel cross-linked polymer, and the step (P21) of pulverizing the hydrogel cross-linked polymer may be used in the preparation of water The step (P2) of gel crosslinking the polymer is carried out before.

The step (P1) of preparing the monomer composition may include the following steps: (P11) preparing a first composition including a neutralizer and a solvent; (P12) preparing a hydrophilic monomer, a crosslinking agent, and a polymerization initiator and (P13) mixing the first composition and the second composition. The monomer composition may include Hydrophilic monomers, cross-linking agents, polymerization initiators, and neutralizing agents and solvents.

The hydrophilic monomer used is not limited as long as it is a monomer generally used for preparing superabsorbent polymers. The hydrophilic monomer is a monomer having a hydrophilic group, and examples of the hydrophilic group may include a hydroxyl group (-OH), a carboxyl group (-COOH), and an amine group (-NHR _h , -NH ₂ , or -NR _h2 , here, R _h may be C _1-5 alkyl or the like).

The hydrophilic monomer may be a water-soluble unsaturated ethylene-based monomer. The water-soluble unsaturated ethylene-based monomer can be at least one of anionic monomers and their salts, non-ionic hydrophilic monomers, and amine group-containing unsaturated monomers and their fourth salts .

Examples of anionic monomers and salts thereof may include acrylic acid, methacrylic acid, anhydrous maleic acid, fumaric acid, crotonic acid, itaconic acid, 2-acryloethanesulfonic acid, 2- Methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and 2-(meth)acrylamido-2-methylpropanesulfonic acid.

Examples of nonionic hydrophilic monomers may include (meth)acrylamides, N-substituted (meth)acrylates, 2-hydroxyethyl (meth)acrylates, 2-hydroxypropyl (meth)acrylates base) acrylate, methoxy polyethylene glycol (meth)acrylate, and polyethylene glycol (meth)acrylate.

Examples of amine group-containing unsaturated monomers and their fourth salts may include (N,N)-dimethylaminoethyl (meth)acrylate and (N,N)-dimethylaminopropyl (meth)acrylamide.

Considering the polymerization time and reaction conditions (the feed rate of the monomer composition, and the irradiation time, irradiation range and irradiation intensity of heat and/or light, etc.), the monomer The concentration of the water-soluble unsaturated ethylene-based monomer in the body composition can be appropriately selected and used. In this embodiment, the concentration of the water-soluble unsaturated ethylene-based monomer may be in the range of 40wt% to 60wt%.

As for the crosslinking agent, a crosslinking agent having at least one functional group and at least one unsaturated ethylenic group which can react with the substituent of the monomer, or having two or more functional groups which can be substituted with the monomer can be used A crosslinking agent that reacts with radicals and/or substituents formed by the hydrolysis of monomers.

In this embodiment, examples of cross-linking agents may include _C8-12 diacrylamides, _C8-12 dimethacrylamides, _C2-12 polyol poly(meth)acrylic acid Esters, and poly(meth)allyl ethers of _C2-10 polyols.

Specific examples of crosslinking agents may include, but are not limited to, (poly)ethylene glycol (meth)acrylate, (poly)propylene glycol (meth)acrylate, trimethylolpropane tri(meth)acrylate , ethoxylated (3)-trimethylolpropane tri(meth)acrylate, ethoxylated (6)-trimethylolpropane tri(meth)acrylate, ethoxylated (9) - Trimethylolpropane tri(meth)acrylate, ethoxylated (15)-trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, glycerol acrylate methacrylic acid Esters, 2,2-II[(propenyloxy)methyl]butylacrylate (3EO), N,N'-Methylene II (meth)acrylate, Ethyleneoxy (methyl) Acrylates, Polyethyleneoxy (meth)acrylate, Propyleneoxy (meth)acrylate, Glycerin Diacrylate, Glycerin Triacrylate, Trimethylolpropane Triacrylate, Triallyl amine, triarylcyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol, propylene glycol, and mixtures of two or more thereof.

In this specific embodiment, the hydrophilic monomer is 100 parts by weight As a basis, the content of the crosslinking agent can be 0.01 to 0.5 parts by weight, but is not limited thereto.

The polymerization initiator may be at least one of a photopolymerization initiator, a thermal polymerization initiator, and an oxidation-reduction initiator. The polymerization initiator may be a composite polymerization initiator including two or more polymerization initiators. For example, the composite polymerization initiator may include a photopolymerization initiator and a thermal polymerization initiator. Also, for example, the composite polymerization initiator may include a thermal polymerization initiator and an oxidation-reduction initiator.

The photopolymerization initiator can initiate the polymerization of the monomer composition by irradiating ultraviolet rays, the thermal polymerization initiator can initiate the polymerization of the monomer composition by heating, and the oxidation-reduction initiator can initiate the polymerization of the monomer composition by oxidation-reduction reaction. And the polymerization of the starting monomer composition. When both a photopolymerization initiator and a thermal polymerization initiator are used, the polymerization of the monomer composition may be performed by the thermal polymerization initiator using heat generated during photopolymerization. When both the oxidation-reduction initiator and the thermal polymerization initiator are used, the polymerization of the monomer composition may be performed by the thermal polymerization initiator using heat generated during the oxidation-reduction reaction.

(thioxanthone)為主的化 合物；醯基膦氧化物衍生物，諸如貳(2,4,6-三甲基苯甲醯基)-苯基膦氧化物及二苯基(2,4,6-三甲基苯甲醯基)-膦氧化物；偶氮化合物，諸如2-羥基-甲基-丙腈及2,2’-(偶氮-貳(2-甲基-N-(1,1’-貳(羥基甲基)-2-羥基乙基)丙醯胺)；及其混合物。此處，熱聚合起始劑並無特殊限制，但其實例包括以偶氮為主的起始劑、以過氧化物為主的起始劑、以氧化還原為主的起始劑、及以有機鹵化物為主的起始劑。其可單獨使用或呈其中二或多者之混合物使用。熱聚合起始劑之特定實例可包括，但非限制性，過硫酸鈉(Na₂S₂O₈)及過硫酸鉀(K₂S₂O₈)。 Examples of polymerization initiators may include, but are not limited to, acetophenone derivatives such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 4- (2-hydroxyethoxy)phenyl-(2-hydroxy)-2-propyl ketone, and 1-hydroxycyclohexyl phenyl ketone; benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether ethers, benzoin isopropyl ether, and benzoin isobutyl ether; benzophenone derivatives such as methyl o-benzyl benzoate, 4-phenylbenzophenone, 4-benzyl benzoate yl-4'-methyl-diphenyl sulfide, and (4-benzyl-benzyl)trimethylammonium chloride; with 9-oxosulfur

(thioxanthone)-based compounds; acylphosphine oxide derivatives such as bis(2,4,6-trimethylbenzyl)-phenylphosphine oxide and diphenyl(2,4,6- Trimethylbenzyl)-phosphine oxide; azo compounds such as 2-hydroxy-methyl-propionitrile and 2,2'-(azo-II(2-methyl-N-(1,1 '-2(hydroxymethyl)-2-hydroxyethyl)propionamide); and mixtures thereof. Here, the thermal polymerization initiator is not particularly limited, but examples thereof include azo-based initiators , peroxide-based initiator, redox-based initiator, and organic halide-based initiator. They can be used alone or in a mixture of two or more of them. Specific examples of polymerization initiators may include, but are not limited to, sodium persulfate (Na ₂ S ₂ O ₈ ) and potassium persulfate (K ₂ S ₂ O ₈ ).

The content of the polymerization initiator can be appropriately selected if the polymerization initiation effect can be exerted. For example, based on 100 parts by weight of the hydrophilic monomer, the photopolymerization initiator may be contained in the monomer composition in an amount of 0.005 to 0.5 parts by weight, and based on 100 parts by weight of the hydrophilic monomer, The thermal polymerization initiator may be contained in the monomer composition in an amount of 0.01 to 0.5 parts by weight.

Neutralizers are used to neutralize hydrophilic monomers. Typical examples thereof may include, but are not limited to, sodium hydroxide and sodium bicarbonate. The amount of the neutralizing agent is such that the degree of neutralization of the monomer composition falls within the range of 65 mol % to 75 mol %. However, the present invention is not limited thereto.

The solvent can be water, and water can be the polymerization medium.

The step (P2) of preparing the hydrogel cross-linked polymer may include the step (P21) of polymerizing the monomer composition, and the step (P22) of pulverizing the sheet-like hydrogel cross-linked polymer.

In the step (P21) of polymerizing the monomer composition, photopolymerization And/or thermal polymerization is carried out by applying light and/or heat to the monomer composition. For example, when the monomer composition is irradiated with ultraviolet light, the photopolymerization reaction is initiated by the photopolymerization initiator. Taking the monomer composition including both the photopolymerization initiator and the thermal polymerization initiator as an example, the thermal polymerization initiator can be used for the heat generated during the photopolymerization reaction to initiate the thermal polymerization reaction. The polymerization reaction can be performed using a belt-type polymerization reactor, and a sheet-like hydrogel cross-linked polymer can be obtained by the polymerization reaction.

In the step (P22) of pulverizing the flaky hydrogel cross-linked polymer, the flaky hydrogel cross-linked polymer is pulverized into a granular hydrogel cross-linked polymer having a particle size of 1 centimeter (cm) to 3 cm. linked polymer. The water content of the particulate hydrogel cross-linked polymer may be, for example, from about 40 weight percent (wt%) to about 60 wt%.

After the step (P2) of preparing a hydrogel cross-linked polymer, a step (P3) of preparing a base resin by adding at least one of the compounds represented by the following formula (1) to the hydrogel cross-linked polymer is carried out ).

At least one of the compounds represented by the following formula (1) can reduce the value of extractable content (EC) by reacting with a non-crosslinked linear polymer chain, and can reduce the residual value by reacting with unreacted monomers Numerical value of monomer (RM) concentration.

<Formula (1)> X-(R) _n -Y

In formula (1), X is an unsaturated hydrocarbon group or a derivative group thereof.

In formula (1), R is a divalent atomic group of at least one of the following: C _1-5 alkylene (-(CH ₂ ) _m -, m is an integer from 1 to 5), C _{1 -4} alkylene oxy (-(CH ₂ ) _m -O-, m is an integer from 1 to 4), C _2-6 alkyl (oxy) carbonyl (-(R _f ) _o -( C=O)-(R' _f ) _p -, o and p are each independently an integer from 0 to 2 and not simultaneously 0, and R _f and R' _f are each independently a C _1-5 hydrocarbon group or its Derivative group), and C _2-5 carbonyloxy group (-(R _g ) _r -(C=O)-O-, r is an integer from 0 to 2, and R _g is a C _1-4 hydrocarbon group or its Derivative groups).

In formula (1), n is an integer of 2 to 20, and Y is a hydrophilic group. Hydrophilic groups can form hydrogen bonds by reacting with unreacted monomers and with linear polymer chains.

X is a monovalent atomic group of at least one of the following: C _2-5 (methyl) vinyl (CH ₂ =CR _a -, R _a is a hydrogen atom, or a C _1-3 hydrocarbon group or a derivative thereof group), C _3-5 (methyl) allyl (CH ₂ =CR _b -CH ₂ -, R _b is a hydrogen atom, or C _1-2 hydrocarbon group or its derivative group), C _1-5 Acyl group (R _c C(=O)-, R _c is hydrogen atom, or C _1-4 hydrocarbon group or its derivative group), C _3-5 (meth)acryloyl group (CH ₂ =CR _d - C(=O)-, R _d is hydrogen atom, or C _1-2 hydrocarbon group or its derivative group), and C _3-5 (meth)acryloyloxy group (CH ₂ =CR _e -C ( =O)-O-, _Re is a hydrogen atom, or a C _1-2 hydrocarbon group or a derivative group thereof). In particular, X can be a C _3-5 (meth)acryloyl group (CH ₂ =CR _d -C(=O)-, R _d is a hydrogen atom, or a C _1-2 hydrocarbon group or a derivative group thereof).

Y can be any one of a hydroxyl group (-OH), a carboxyl group (-COOH), and an amine group (-NHR _h , -NH ₂ , or -NR _{h 2} , R _h is a C _1-5 hydrocarbon group). In particular, the hydrophilic group may be a hydroxyl group.

At least one of the compounds represented by formula (1) has improved reactivity with a hydrogel crosslinked polymer having hydrophilicity within the range of the number of carbon atoms of R and within the range of the value of n of R. Conversely, when the number of carbon atoms of R or the value of n increases, the water repellency increases, and thus crosslinks with the hydrogel having hydrophilicity The reactivity of the polymer may be reduced.

The content of at least one of the compounds represented by formula (1) may be in the range of 1 wt % to 10 wt % with respect to the total weight of the bare superabsorbent polymer. When the content of at least one of the compounds represented by the formula (1) falls within the aforementioned range, the value of the extractable content (EC) of the superabsorbent polymer of the present invention and the residual monomer (RM) concentration thereof The value can be reduced to a lower degree than that of conventional surface-crosslinked superabsorbent polymers, and its centrifugal retention capacity (CRC) can have a level equal to the CRC of conventional surface-crosslinked superabsorbent polymers.

At least one of the compounds represented by the formula (1) may be at least one of the compounds represented by the following formula (2).

In formula (2), R ₁ is any one of C _1-2 alkyl and C _1-2 alkoxy; R ₂ is C _1-5 alkylene (-(CH ₂ ) _m -, m is an integer from 1 to 5) and any of C _1-5 alkyleneoxy (-(CH ₂ ) _m -O-, m is an integer from 1 to 5); and Y is hydroxy (- OH), carboxyl group (-COOH), and amine group (-NHR _h , -NH ₂ , or -NR _h2 ). In formula (2), n is an integer of 2 to 20. Within the number of carbon atoms in R ₁ , the carbon-carbon double bond (C=C) in the (meth)acryloyl group can be chemically bonded to unreacted monomers and linear polymer chains without steric blocking.

At least one of the compounds represented by the formula (2) may be at least one of the compounds represented by the formulas (3) to (14).

In the step (P4) of pulverizing the base resin, the base resin is roughly pulverized into particles having a millimeter (mm) particle size. The step (P4) of pulverizing the base resin can be performed using a blade cutter, a chopping cutter, a kneading cutter, a vibration pulverizer, an impact pulverizer, or a friction pulverizer.

The drying step (P5) of the pulverized base resin may be performed at a temperature of about 150°C to about 200°C for about 20 minutes to 40 minutes. The drying step (P5) of the pulverized base resin can be performed using a hot air dryer, a fluid bed dryer, a flash dryer, an infrared dryer, or a dielectric heating dryer.

In the step (P6) of pulverizing the dried base resin, the dried product is finely pulverized into particles having a micrometer (μm) particle size. The step (P6) of pulverizing the dried base resin may include the step of classifying particles having an average particle size of 150 microns to 850 microns.

Methods of making superabsorbent polymers can provide naked superabsorbent polymers. The naked superabsorbent polymer may have a degree of Centrifugal Retention (CRC) and Absorbency Under Pressure (AUP) equal to that of the surface crosslinked superabsorbent polymer, and may have a level lower than that of the surface crosslinked superabsorbent polymer Extractable content (EC) and residual monomer (RM) concentrations at the level of .

Hereinafter, the present invention will be described in detail with reference to the following Examples and Experimental Examples.

<Preparation Example 1>

77.778 grams of 50% aqueous caustic soda (NaOH) solution and 88.84 grams of water were mixed to form a mixed solution. Then, 100 g of acrylic acid, 0.115 g of 2,2-2[(propenyloxy)methyl]butyl acrylate (3EO), 0.115 g of polyethylene glycol diacrylate (Mw=400) were added as cross-linking agents , and 0.033 g of diphenyl(2,4,6-trimethylbenzyl)-phosphine oxide was added to the mixed solution as a photopolymerization initiator, thereby preparing a monomer having a hydrophilic monomer concentration of 45 wt % composition.

1.33 g of potassium persulfate as a thermal polymerization initiator was dissolved in 8.67 g of water to obtain a solution, and 3.008 g of the solution mixed the monomer composition.

Then, the obtained monomer composition was placed in a polymerization reactor continuously moving on a conveyor belt at a temperature of 40° C., irradiated with ultraviolet rays (illumination dose: 9 Mw/cm ² ) by a UV irradiation device, and then UV-polymerized for 3 minutes, thereby preparing a sheet hydrogel-like cross-linked polymer.

The sheet-like hydrogel cross-linked polymer was transferred to a cutter, and then cut into a size of 2 cm to obtain a granular hydrogel cross-linked polymer. In these cases, the water content ratio of the obtained particulate hydrogel cross-linked polymer was 50 wt %.

<Preparation Example 2>

Granular hydrogel cross-linked polymer was prepared in the same manner as in Preparation 1, but using 0.033 g of diphenyl(2,4,6-trimethylbenzyl)-phosphine oxide and 2.256 g of aqueous The monomer composition of potassium persulfate solution was supplied to a polymerization reactor continuously moving on a conveyor belt at a temperature of 30°C, and then irradiated with ultraviolet rays for 2 minutes.

<Preparation Example 3>

Granular hydrogel cross-linked polymer was prepared in the same manner as in Preparation 1, but using 0.033 g of diphenyl(2,4,6-trimethylbenzyl)-phosphine oxide and 2.256 g of aqueous The monomer composition of potassium persulfate solution was supplied to a polymerization reactor continuously moving on a conveyor belt at a temperature of 20°C, and then irradiated with ultraviolet rays for 2 minutes.

<Example 1>

100 g of the granular hydrogel cross-linked polymer of Preparation Example 1 was uniformly mixed with 2 g of an ethoxylated (6) methacrylate compound (Bisomer PEM6LD), and then minced by a meat mincer. Subsequently, the pulverized granular hydrogel cross-linked polymer was dried at a temperature of 180° C. for 30 minutes by a hot air dryer, and the dried granular hydrogel cross-linked polymer was pulverized by a corner-column pulverizer. Thereafter, naked superabsorbent polymers having an average particle size of 150 microns to 850 microns were prepared by sieving.

<Example 2>

A naked superabsorbent polymer was prepared in the same manner as in Example 1, but with 100 grams of the granular hydrogel cross-linked polymer of Preparation Example 2 and 1 gram of ethoxylated (6) methacrylate compound (Bisomer PEM6LD) Mix evenly.

<Example 3>

A naked superabsorbent polymer was prepared in the same manner as in Example 1, but with 100 grams of the granular hydrogel cross-linked polymer of Preparation Example 2 and 2 grams of an ethoxylated (6) methacrylate compound (Bisomer PEM6LD) Mix evenly.

<Example 4>

The naked superabsorbent polymer was prepared in the same manner as in Example 1, but 100 grams of the granular hydrogel cross-linked polymer of Preparation Example 3 was mixed with 2 grams of ethoxylated (6) The methacrylate compound (Bissomo PEM6LD) was mixed uniformly.

<Comparative Example 1>

The granular hydrogel cross-linked polymer of Preparation Example 1 was minced by a meat mincer. Subsequently, the pulverized granular hydrogel cross-linked polymer was dried at a temperature of 180° C. for 30 minutes by a hot air dryer, and the dried granular hydrogel cross-linked polymer was pulverized by a corner-column pulverizer. Thereafter, a naked superabsorbent polymer having an average particle size of 150 microns to 850 microns is obtained by sieving. The naked superabsorbent polymer obtained in this way was sprayed with a 20% aqueous ethylene carbonate solution at a rate of 5 pph in a surface crosslinking mixer, and then dried again at a temperature of 180° C. for 30 minutes. The dried naked superabsorbent polymer was classified by standard sieving according to the ASTM standard, thereby producing a surface-crosslinked superabsorbent polymer having an average particle size of 150 microns to 850 microns.

<Comparative Example 2>

The surface-crosslinked superabsorbent polymer was prepared in the same manner as in Comparative Example 1, but using the particulate hydrogel cross-linked polymer of Preparation Example 2 instead of the particulate hydrogel cross-linked polymer of Preparation Example 1.

<Comparative Example 3>

The surface crosslinked superabsorbent polymer was prepared in the same manner as in Comparative Example 1, but using the particulate hydrogel crosslinked polymer of Preparation Example 3 instead of the particulate hydrogel crosslinked polymer of Preparation Example 1.

<Comparative Example 4>

77.778 grams of 50% aqueous caustic soda (NaOH) solution and 88.84 grams of water were mixed to form a mixed solution. Then, add 100 grams of acrylic acid, 0.115 grams of 2,2-II[(propenyloxy)methyl]butylacrylate (3EO), 0.115 grams of polyethylene glycol Alcohol diacrylate (Mw=400) as a cross-linking agent, 0.033 g of diphenyl(2,4,6-trimethylbenzyl)-phosphine oxide as a photopolymerization initiator, and 2 g of methyl ethoxylate A base acrylate compound (Bisomer PEM6LD) was added to the mixed solution as a comonomer, thereby preparing a monomer composition having a hydrophilic monomer concentration of 45 wt %.

1.33 g of potassium persulfate as a thermal polymerization initiator was dissolved in 8.67 g of water to obtain a solution, and 3.008 g of the solution mixed the monomer composition.

Then, the obtained monomer composition was placed in a polymerization reactor continuously moving on a conveyor belt at a temperature of 40° C., irradiated with ultraviolet rays (illumination dose: 9 Mw/cm ² ) by a UV irradiation device, and then UV-polymerized for 3 minutes, thereby preparing a sheet hydrogel-like cross-linked polymer.

The sheet-like hydrogel cross-linked polymer was transferred to a cutter, and then cut into a size of 2 cm to obtain a granular hydrogel cross-linked polymer. In these cases, the water content ratio of the obtained particulate hydrogel cross-linked polymer was 50 wt%.

Subsequently, the granular hydrogel cross-linked polymer was dried by a hot air dryer at a temperature of 180° C. for 30 minutes, and the dried granular hydrogel cross-linked polymer was pulverized by a corner-column pulverizer. Thereafter, a naked superabsorbent polymer having an average particle size of 150 microns to 850 microns is obtained by sieving.

<Experimental example 1>

The unreacted monomer concentrations of the particulate hydrogel cross-linked polymers prepared in Preparation Examples 1 to 3 were measured, and the results thereof are shown in Table 1 below.

<Experimental example 2>

Centrifugal retention capacity (CRC), extractable content (EC), pressurized absorbency of the naked superabsorbent polymers obtained in Examples 1 to 4 and the surface-crosslinked superabsorbent polymers obtained in Comparative Examples 1 to 3 (AUP) and residual monomer (RM) were measured separately, the results of which are summarized in Table 2 below. Centrifugal retention capacity (CRC) is measured based on the European Disposables and Nonwovens Association (EDANA) WSP 241.2.R3 standard. Extractable content (EC) is measured based on the EDANA WSP 270.2.R3 standard. Absorbency under pressure (AUP) is measured based on the EDANA WSP 242.2.R3 standard. Residual monomer (RM) concentrations are measured based on the EDANA WSP 210.2.R3 standard.

With reference to Table 2, the extractable content (EC) and residual monomer (RM) concentrations of each of the naked superabsorbent polymers obtained in the examples can be determined The values are lower than those of each of the surface-crosslinked superabsorbent polymers obtained in the comparative examples.

Again, it was possible to determine the centrifugation retention capacity (CRC) and addition of each of the naked superabsorbent polymers obtained in Examples 2 to 4, using a hydrogel cross-linked polymer containing many unreacted monomers. The absorbency under pressure (AUP) is approximately equal to the value of the surface-crosslinked superabsorbent polymers obtained in Comparative Examples 1 to 3, even though these bare superabsorbent polymers are not surface-crosslinked.

At the same time, it can be confirmed that each of the naked superabsorbent polymers obtained in the examples has excellent centrifugation retention capacity (CRC) and low residual monomers compared to the surface-crosslinked superabsorbent polymer obtained in Comparative Example 4. Body (RM) concentration.

Summarizing the detailed description, those skilled in the art will appreciate that many changes and modifications may be made to the preferred embodiment without materially departing from the principles of the present invention. Accordingly, the disclosed preferred embodiments of the present invention are used in a general descriptive sense only and not for purposes of limitation.

Steps P1-6, P11-13, P21, P22‧‧‧

Claims (6)

A method for preparing a naked superabsorbent polymer, comprising the steps of: preparing a hydrogel cross-linked polymer by polymerizing a monomer composition comprising a hydrophilic monomer, a cross-linking agent, and a polymerization initiator; by combining the following formula ( 3) at least one of the compounds represented by (14) is added to the hydrogel cross-linked polymer to prepare a base resin; drying the base resin; and pulverizing the dried base resin;

The method of claim 1, further comprising: preparing the monomer composition, wherein the preparing the monomer composition comprises: preparing a first composition including a neutralizer and a solvent; preparing a first composition including the hydrophilic monomer, the a crosslinking agent, and a second composition of the polymerization initiator; and mixing the first composition and the second composition. The method of claim 1, wherein the polymerization initiator includes a photopolymerization initiator or a composite polymerization initiator, and the composite polymerization initiator includes the photopolymerization initiator and a thermal polymerization initiator. As in the method of claim 1, Wherein the preparing the hydrogel cross-linked polymer comprises: polymerizing the monomer composition; and pulverizing the hydrogel cross-linked polymer. The method of claim 1, wherein the naked superabsorbent resin has an extractable content (EC) greater than 0% and less than 15% and a residual monomer (RM) concentration greater than 0 ppm and less than 1000 ppm. The method of claim 5, wherein the naked superabsorbent resin has an extractable content (EC) greater than 0% and less than 15% and a residual monomer (RM) concentration greater than 0 ppm and less than 600 ppm.

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