KR20200071658A - Super absorbent polymer and preparation method thereof - Google Patents

Abstract

The present invention relates to a super absorbent polymer and a method for producing the same. More particularly, the present invention relates to a super absorbent polymer that exhibits an improved initial absorption rate while maintaining excellent basic absorption performance such as centrifugal retention capacity, and to a production method capable of producing the super absorbent polymer.

Description

SUPER ABSORBENT POLYMER AND PREPARATION METHOD THEREOF}

The present invention relates to a super absorbent polymer and a method for manufacturing the same. More particularly, the present invention relates to a super absorbent polymer having excellent basic absorption ability and improved absorption speed, and a method for manufacturing the same.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb about 500 to 1,000 times its own weight, and has started to be put into practical use as a physiological tool. In addition to sanitary products such as gardening, it has been widely used as a material for soil repair agents for gardening, civil engineering, construction water supply materials, sheets for raising seedlings, freshness preservatives in the food distribution field, and poultices.

In most cases, these superabsorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins. For this purpose, it is necessary to exhibit high absorbency for moisture, etc., and absorbed moisture does not come out even under external pressure. It is necessary to exhibit excellent absorption properties. In addition, in recent years, an absorption rate for absorbing and storing a target solution such as moisture more rapidly is further required. Basically, absorption of the superabsorbent polymer to the aqueous solution occurs at the surface of the resin, so a method of increasing the surface area of the superabsorbent polymer can be considered to improve the absorption rate. Accordingly, the method for reducing the particle size of the super absorbent polymer or forming a porous structure has been considered as a method for increasing the absorption rate.

As an example, a method of manufacturing a superabsorbent polymer by adding a blowing agent to form a porous structure in a superabsorbent polymer has been proposed. However, the higher the content of the blowing agent, the absorption rate is improved to a certain level, but due to excessive foaming, the amount of fine powder generated in the super absorbent polymer increases, and there is a problem that the gel strength is lowered. In addition, the superabsorbent polymer tends to have reduced basic absorption characteristics as the particle size decreases. Thus, the known method has a limitation in improving the absorption rate while maintaining the basic absorption capacity.

The present invention is to solve the problems of the prior art as described above, while having excellent basic absorption performance such as water retention capacity (CRC) or pressure absorption capacity (AUL), and exhibits an improved initial absorption rate and a superabsorbent resin and a method for manufacturing the same It is intended to provide.

The present invention to achieve the above object,

Preparing a monomer composition by mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator;

Preparing a hydrogel polymer by thermal polymerization or photopolymerization of the monomer composition;

Drying and pulverizing the hydrogel polymer to form a base resin; And

It provides a method for producing a super absorbent polymer comprising the step of performing a surface modification on the base resin by mixing the base resin with one or more fibers of a fluff pulp and synthetic polymer fibers, and a surface crosslinking agent, and heating.

The fiber may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the base resin.

The length of the fiber may be 0.1 to 20 mm.

The width of the fiber may be 1 to 100 ㎛.

The surface crosslinking agent may be included in an amount of 0.01 to 3 parts by weight based on 100 parts by weight of the base resin.

The monomer composition may further include a blowing agent. At this time, the monomer composition is alkyl sulfate salt (alkyl sulfate salt), alkyl sulfonate salt (alkyl sulfonate salt), alkyl phosphate salt (alkyl phosphate salt), alkyl carbonate salt (alkyl carbonate salt), polyethylene glycol alkyl ester (polyethylene glycol alkyl esters, polypropylene glycol alkyl esters, glucoside alkyl esters, glycerol alkyl esters, block-copolymers of polyethylene glycol and polypropylene glycol of polyethylene glycol and polypropylene glycol) or a mixture of these, it may further include a foam stabilizer.

In addition, the present invention provides a super absorbent polymer produced by the above manufacturing method.

Specifically, the present invention provides a base resin powder comprising a crosslinked polymer in which at least a portion of a water-soluble ethylenically unsaturated monomer having a neutralized acidic group is crosslinked and polymerized; And

A superabsorbent polymer formed on the surface of the base resin powder, the crosslinked polymer comprising a surface crosslinking layer further crosslinked via a surface crosslinking agent,

The surface cross-linking layer provides a super absorbent polymer comprising at least one fiber among fluff pulp and synthetic polymer fibers.

The superabsorbent polymer may have a centrifugal water retention capacity (CRC) of 30 to 40 g/g measured according to EDANA method WSP 241.3.

The super absorbent polymer may have a pressure of 0.3 psi (AUL) of 20.0 to 37.0 g/g measured according to EDANA method WSP 241.3.

The superabsorbent polymer may have a vortex time of 65 seconds or less.

According to the superabsorbent polymer according to the present invention and a method for manufacturing the same, it is possible to provide a high quality superabsorbent polymer having excellent basic absorption performance such as conventional centrifugal water retention capacity and pressurized absorption capacity and exhibiting improved absorption speed.

In addition, the manufacturing method of the super absorbent polymer of the present invention is relatively simple because the process steps are high, it is possible to obtain a super absorbent polymer having a high absorption rate.

1 is a scanning electron microscope (SEM) photograph of the super absorbent polymer prepared in Example 1.

The terminology used herein is only used to describe exemplary embodiments, and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "include", "have" or "have" are intended to indicate that an implemented feature, step, component or combination thereof exists, 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 excluded in advance.

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

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

A method for preparing a super absorbent polymer according to an embodiment of the present invention includes preparing a monomer composition by mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator; Preparing a hydrogel polymer by thermal polymerization or photopolymerization of the monomer composition; Drying and pulverizing the hydrogel polymer to form a base resin; And mixing the base resin with at least one fiber among fluff pulp and synthetic polymer fibers, and a surface crosslinking agent, and heating the substrate resin to perform surface modification on the base resin.

In the present invention, one or more fibers of fluff pulp and synthetic polymer fibers are added to the surface crosslinking step of the base resin in order to realize an excellent absorption rate while maintaining the basic absorption performance of the super absorbent polymer. The superabsorbent polymer thus prepared contains fibers having excellent absorbent capacity in the surface crosslinking layer, and thus exhibits improved 1 minute tap water absorption and 1 minute saline absorption capacity compared to the existing superabsorbent resin. Thus, the superabsorbent polymer prepared according to the present invention can exhibit a more improved absorption rate while maintaining basic absorption properties such as water retention capacity and pressure absorption capacity.

In the specification of the present invention, "base resin" or "base resin powder" is made of a water-soluble ethylenically unsaturated monomer polymerized hydrogel polymer dried and pulverized in the form of particles or powders, which will be described later. Refers to a polymer without undergoing a modification or surface crosslinking step.

First, a monomer composition is prepared by mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator.

As the water-soluble ethylenically unsaturated monomer, any monomer commonly used in the production of superabsorbent polymers can be used without particular limitation. Any one or more monomers selected from the group consisting of anionic monomers and salts thereof, nonionic hydrophilic-containing monomers and amino group-containing unsaturated monomers and quaternaries thereof can be used.

Specifically, (meth)acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2- Anionic monomers of (meth)acrylamide-2-methyl propane sulfonic acid and salts thereof; (Meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol ( Nonionic hydrophilic monomers of meth)acrylate; And an amino group-containing unsaturated monomer of (N,N)-dimethylaminoethyl (meth) acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide, and quaternaries thereof. Can be.

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

The concentration of the water-soluble ethylenically unsaturated monomer may be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, with respect to the monomer composition containing the raw material and solvent of the superabsorbent polymer, and polymerization It may be an appropriate concentration in consideration of time and reaction conditions. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and economic problems may occur. Conversely, if the concentration is too high, a part of the monomer precipitates or the grinding efficiency of the polymerized hydrogel polymer is low. Such problems may occur in the process and physical properties of the super absorbent polymer may be deteriorated.

The polymerization initiator used in polymerization in the superabsorbent polymer production method of the present invention is not particularly limited as long as it is generally used for the production of superabsorbent polymers.

Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation depending on the polymerization method. However, even by the photopolymerization method, since a certain amount of heat is generated by irradiation with ultraviolet rays or the like and a certain amount of heat is generated as the polymerization reaction that is an exothermic reaction proceeds, a thermal polymerization initiator may be additionally included.

If the photopolymerization initiator is a compound capable of forming radicals by light such as ultraviolet rays, the composition may be used without limitation.

The photopolymerization initiator includes, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal. ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone). Meanwhile, as a specific example of acylphosphine, a commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) can be used. . For more photoinitiators, Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p. It is well specified in 115, and is not limited to the example described above.

The photopolymerization initiator may be included in a concentration of about 0.01 to about 1.0% by weight relative to the monomer composition. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slow, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the super absorbent polymer may be small and the properties may be uneven.

In addition, as the thermal polymerization initiator, one or more selected from the initiator 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 are 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 examples of the azo-based initiator are 2, 2-azobis-(2-amidinopropane) dihydrochloride (2, 2-azobis (2-amidinopropane) dihydrochloride), 2 , 2-azobis-(N, N-dimethylene)isobutyramidine dihydrochloride (2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoyl azo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2, 2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride), 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)). For more various thermal polymerization initiators, Odian's book'Principle of Polymerization (Wiley, 1981)', p. It is well specified in 203, and is not limited to the above-described example.

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

As the internal crosslinking agent, while having at least one functional group capable of reacting with the water-soluble substituent of the water-soluble ethylenically unsaturated monomer, a crosslinking agent having at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups capable of reacting with the water-soluble substituent of the monomer and/or the water-soluble substituent formed by hydrolysis of the monomer may be used.

Specific examples of the internal crosslinking agent include bisacrylamide having 8 to 12 carbons, bismethacrylamide, poly(meth)acrylate of polyols having 2 to 10 carbons, or poly(meth)allyl ether of polyols having 2 to 10 carbons, etc. And more specifically, N,N'-methylenebis(meth)acrylate, ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, propyleneoxy(meth)acrylate, glycerin diacrylate , Glycerin triacrylate, trimethyrol triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol and propylene glycol.

Such an internal crosslinking agent may be included in a concentration of about 0.01 to about 0.5% by weight relative to the monomer composition, thereby crosslinking the polymerized polymer.

Meanwhile, in the manufacturing method of the present invention, the monomer composition may further include additives such as a foaming agent, a foaming stabilizer, a thickener, a plasticizer, a preservative stabilizer, and an antioxidant, if necessary.

The blowing agent may be used without limitation, inorganic blowing agents and encapsulating blowing agents commonly used in the art.

The inorganic blowing agent is calcium carbonate (CaCO ₃ ), sodium bicarbonate (NaHCO ₃ ), ammonium bicarbonate (NH ₄ HCO ₃ ), ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), ammonium nitrite (NH ₄ NO ₂ ), hydrogen borohydride One or more selected from sodium (NaBH ₄ ) and sodium carbonate (Na ₂ CO ₃ ) may be used, but is not limited thereto.

The encapsulated foaming agent exists in an encapsulated state during polymerization of the monomer composition, and then foams by heat applied during the drying process described below, thereby forming pores of appropriate size between the polymer structures of the super absorbent polymer, It is possible for the absorbent resin sheet to exhibit the structure of an open pore channel. Therefore, when the foaming agent encapsulated in the monomer composition is included, the absorption rate of the superabsorbent polymer can be further improved, which is preferable.

The encapsulated foaming agent may have a structure including a core including a hydrocarbon and a shell surrounding the core and formed of a thermoplastic resin. The encapsulated foaming agent has different expansion characteristics depending on the weight and diameter of the components constituting the core and the shell, and can be expanded to a desired size by controlling it, and can control the porosity of the superabsorbent polymer sheet.

Meanwhile, in order to determine whether pores of a desired size are formed, it is necessary to first grasp the expansion characteristics of the encapsulated blowing agent. However, the form in which the foaming agent encapsulated in the superabsorbent polymer is foamed may vary depending on the manufacturing conditions of the superabsorbent polymer, so it is difficult to define it as one form. Therefore, by first foaming the encapsulated foaming agent in the air, the expansion ratio and size can be checked to confirm whether it is suitable for forming desired pores.

Specifically, after applying the encapsulated blowing agent on a glass petri dish, heat of 150 °C in air was applied for 10 minutes to expand the encapsulated blowing agent. At this time, when the encapsulated foaming agent exhibits a maximum expansion ratio in the air of 3 to 15 times, 5 to 15 times, or 8.5 to 10 times, to form an appropriate open pore structure in the method of manufacturing the superabsorbent polymer sheet of the present invention It can be judged as suitable.

The encapsulated foaming agent may have an average diameter of 5 to 50 μm, or 5 to 30 μm, or 5 to 20 μm, or 7 to 17 μm. When the encapsulated foaming agent exhibits such an average diameter, it can be judged to be suitable for achieving an appropriate porosity.

In addition, when the encapsulated foaming agent exhibits a maximum expansion diameter of 20 to 190 μm, or 50 to 190 μm, or 70 to 190 μm, or 75 to 190 μm in air, the method of manufacturing the superabsorbent polymer sheet according to the present invention It can be judged to be suitable for forming a suitable open pore structure.

The maximum expansion ratio and maximum expansion diameter in the air of the encapsulated blowing agent will be described in more detail in the preparation examples described below.

The hydrocarbons constituting the core of the encapsulated blowing agent are n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n- It may be one or more selected from the group consisting of heptane, iso-heptane, cycloheptane, n-octane, iso-octane and cyclooctane. Among these, hydrocarbons having 3 to 5 carbon atoms (n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane) are suitable for forming pores of the size described above, and iso- Butane may be the most suitable.

In addition, the thermoplastic resin constituting the shell of the encapsulated foaming agent is formed from at least one monomer selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide, and vinylidene halide. It can be a polymer. Among them, a copolymer of (meth)acrylate and (meth)acrylonitrile may be most suitable for forming pores of the size described above.

The encapsulated blowing agent may contain 10 to 30% by weight of hydrocarbons based on the total encapsulated blowing agent weight. It may be most suitable to form an open pore structure within this range.

The encapsulated foaming agent may be prepared and used, or a commercialized foaming agent satisfying the above-described conditions may be used.

In addition, the content of the encapsulating foaming agent may be 0.001 to 10 parts by weight, preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 1 part by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the encapsulated foaming agent is too small, the open pore structure may not be properly formed, and if it is contained too much, the porosity may be too high and the strength of the super absorbent polymer may be weak, so the content range is preferable in this respect. Can be.

When using the foaming agent, in order to induce stable foaming, the monomer composition may further include a foaming stabilizer.

The foam stabilizer is an alkyl sulfate salt, an alkyl sulfonate salt, an alkyl phosphate salt, an alkyl carbonate salt, and a polyethylene glycol alkyl ester. ), polypropylene glycol alkyl ester, glucoside alkyl ester, glycerol alkyl ester, block-copolymers of polyethylene glycol and polypropylene glycol glycol and polypropylene glycol) or mixtures thereof. In this case, the alkyl group is not particularly limited, and may be a straight chain, branched chain or cyclic alkyl group having 1 to 30 carbon atoms. The foaming stabilizer may be included in a concentration of about 0.0001 to 0.1% by weight or about 0.001 to 0.1% by weight in 100% by weight of the monomer composition to improve the foaming efficiency of the foaming agent to form a crosslinked polymer having an appropriate pore structure.

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

The solvent that can be used at this time can be used without limitation of its composition as long as it can dissolve the above-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 can be used in combination.

The solvent may be included in the remaining amount excluding the above-mentioned components with respect to the total content of the monomer composition.

Next, the monomer composition is thermally polymerized or photopolymerized to form a hydrogel polymer, and then dried and pulverized to form a base resin.

The thermal polymerization or photopolymerization method of the monomer composition is not particularly limited as long as it is a commonly used polymerization method.

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the polymerization energy source, and in general, when performing thermal polymerization, it can be carried out in a reactor having a stirring axis such as a kneader, and when performing photopolymerization, it is movable Although it may be carried out in a reactor equipped with a conveyor belt, 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, a hydrogel polymer obtained by thermal polymerization by supplying hot air or heating a reactor to a reactor such as a kneader having a stirring shaft is used as a reactor outlet, depending on the type 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 speed of the monomer composition to be injected, and a hydrogel polymer having a weight average particle diameter of 2 to 50 mm can be usually obtained.

In addition, when the photopolymerization is performed in a reactor equipped with a movable conveyor belt as described above, the shape of the hydrogel polymer usually obtained may be a hydrogel polymer on a sheet having a belt width. At this time, the thickness of the polymer sheet varies depending on the concentration and the injection rate of the monomer composition to be injected, but it is usually preferable to supply the monomer composition so that a polymer on the sheet having a thickness of about 0.5 to about 5 cm can be obtained. When the monomer composition is supplied to such an extent that the thickness of the polymer on the sheet is too thin, production efficiency is low, which is undesirable. When the thickness of the polymer on the sheet exceeds 5 cm, due to the excessively thick thickness, the polymerization reaction does not occur evenly over the entire thickness. It may not.

At this time, the normal water content of the hydrogel polymer obtained in this way may be about 40 to about 80% by weight. On the other hand, in the present specification, "water 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 to the total weight of the hydrogel polymer. Specifically, it is defined as a calculated value by measuring the weight loss due to evaporation of water in the polymer during the drying process by raising the temperature of the polymer through infrared heating. At this time, the drying condition is a method of raising the temperature from room temperature to about 180°C and then maintaining it at 180°C. The total drying time is set to 20 minutes including 5 minutes of the temperature rise step to measure the water content.

Next, the hydrogel polymer is coarsely pulverized.

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

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

Coarse pulverization with a particle diameter of less than 2 mm is not technically easy due to the high water content of the hydrogel polymer, and there may also be a phenomenon in which the particles are aggregated with each other. On the other hand, when the particle size is roughly crushed to more than 20 mm, the effect of increasing the efficiency of the drying step to be performed later may be insignificant.

Next, the obtained hydrogel polymer is dried.

Drying is performed on the hydrogel polymer immediately after polymerization, which is coarsely pulverized as described above or has not been subjected to a co-pulverization step. At this time, the drying temperature of the drying step may be about 150 to about 250 ℃. When the drying temperature is less than 150°C, the drying time is too long and there is a fear that the physical properties of the superabsorbent resin to be formed are lowered. When the drying temperature exceeds 250°C, only the polymer surface is dried excessively, and a subsequent grinding process is performed. In the fine powder may be generated, there is a fear that the physical properties of the superabsorbent polymer to be formed finally decreases. Therefore, preferably, the drying may be performed at a temperature of about 150 to about 200°C, more preferably at a temperature of about 160 to about 180°C.

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

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

Next, the dried polymer obtained through such a drying step is pulverized.

The polymer powder obtained after the grinding step may have a particle size of about 150 to about 850 μm. The pulverizer used for pulverizing to such a particle size is specifically, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill or a jog. A mill may be used, but the present invention is not limited to the examples described above.

In order to manage the physical properties of the superabsorbent polymer powder finally produced after such a pulverization step, the polymer powder obtained after pulverization is generally classified according to particle size. Preferably, it may be subjected to a step of classifying particles having a particle diameter of less than about 150 μm, particles having a diameter of about 150 to about 850 μm, and particles having a particle diameter of greater than 850 μm.

Next, a surface crosslinking agent and fluff pulp and one or more fibers of synthetic polymer fibers are mixed with the base resin and heated to perform surface modification on the base resin.

The surface crosslinking step is a step of inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a surface crosslinking agent, thereby forming a superabsorbent polymer having improved physical properties. Through the surface crosslinking, a surface crosslinking layer (surface modification layer) is formed on the surface of the pulverized polymer particles.

In general, the surface crosslinking agent is applied to the surface of the superabsorbent polymer particles, so that the surface crosslinking reaction occurs on the surface of the superabsorbent polymer particles, which improves the crosslinkability on the surface of the particles without substantially affecting the inside of the particles. Therefore, the surface-crosslinked superabsorbent polymer particles have a higher degree of crosslinking near the surface than from the inside.

As the surface crosslinking agent, any surface crosslinking agent that has been used in the manufacture of super absorbent polymers can be used without any limitation. More specific examples thereof, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl- One or more polyols selected from the group consisting of 1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol ; At least one carbonate-based compound selected from the group consisting of ethylene carbonate and propylene carbonate; Epoxy compounds such as ethylene glycol diglycidyl ether; Oxazoline compounds such as oxazolidinone; Polyamine compounds; Oxazoline compounds; Mono-, di- or polyoxazolidinone compounds; Or cyclic urea compounds; And the like.

The surface crosslinking agent may be used in an amount of about 0.01 to 3 parts by weight based on 100 parts by weight of the base resin powder. By adjusting the content range of the surface crosslinking agent to the above-described range, it is possible to provide a super absorbent polymer exhibiting excellent water absorption properties.

In the present invention, in the surface crosslinking step of the base resin, one or more fibers of fluff pulp and synthetic polymer fibers are added to improve the initial absorption rate of the super absorbent polymer.

Usually, in hygiene materials such as diapers, fibers such as fluff pulp are used in a simple mixing manner with a superabsorbent resin having a surface crosslinking. In this case, the fluff pulp exists separately from the superabsorbent polymer, and the fluff pulp and the superabsorbent polymer act in such a way that each absorbs liquid, and the introduction of the pulp improves the absorbent properties of the superabsorbent polymer itself. It cannot be secured.

On the other hand, the superabsorbent polymer produced by the manufacturing method of the present invention includes fibers having excellent hygroscopicity in the surface crosslinking layer, and these fibers quickly absorb surrounding moisture through capillary action and transfer it to the internal superabsorbent polymer. Therefore, the initial absorption rate of the super absorbent polymer can be improved. In addition, fluff pulp and synthetic polymer fibers are not only easy to process and inexpensive, but also harmless to the human body, and according to the present invention, it is possible to manufacture a superabsorbent polymer that is human-friendly and has excellent absorbency according to the present invention. .

The fluff pulp is a cellulose fluff pulp, but may be wood fluff pulp such as softwood kraft paper, broadleaf kraft pulp, but is not limited thereto, and fluff pulp used for absorbent articles may be used without limitation.

The synthetic polymer fiber may be at least one selected from the group consisting of nylon, polypropylene, polyethylene, polyester, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyacrylate, and acetate. Such a synthetic polymer fiber is excellent in hygroscopicity, and it is easy to control the width or length of the fiber, so it is possible to easily control the physical properties of the super absorbent polymer.

The fiber may be preferably used having a length of 0.1 to 20 mm. In addition, the fiber may preferably have a width of 1 to 100 μm. If the length of the fiber is too short or the width is too narrow, the effect of improving the absorption rate and liquid permeability of the super absorbent polymer cannot be secured. Conversely, if the length of the fiber is too long or too wide, it may be difficult to uniformly distribute the fibers to the base resin in the surface crosslinking step.

In this aspect, the length of the fiber is preferably 0.3 mm or more, or 0.5 mm or more, and may be 10 mm or less, or 5 mm or less. As an example, while the individual fiber length satisfies 0.1 to 20 mm, the fiber having an average length of 0.5 to 5 mm may be preferably used. At this time, the average length of the fibers can be derived by randomly selecting 100 fibers, measuring the length of individual fibers, and calculating the average value thereof.

Further, the width of the fiber may be 5 μm or more, or 10 μm or more, and 80 μm or less, or 50 μm or less.

The content of the fiber may be 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, 2.5 parts by weight or less, or 1 part by weight or less based on 100 parts by weight of the base resin. If the fluff pulp is less than 0.01 part by weight based on 100 parts by weight of the base resin, it is impossible to secure an effect of improving the absorption rate of the superabsorbent polymer by including the fluff pulp, and if it exceeds 5 parts by weight, the fluff pulp in the superabsorbent resin The separation phenomenon may occur, and a problem that the apparent density of the super absorbent polymer is too low may occur.

The method of mixing the surface crosslinking agent and the fiber with the base resin is not particularly limited. As an example, a method of preparing a surface crosslinking solution by dispersing a surface crosslinking agent and fibers in a solvent, and adding it to the base resin and mixing it may be used. In another example, the base resin and the fiber may be mixed by dry first, and then a surface crosslinking solution containing a surface crosslinking agent may be added and mixed. As another example, a surface crosslinking solution containing a surface crosslinking agent may be added to the base resin to be mixed, and then the fibers may be added and mixed.

At this time, the solvent used for the surface crosslinking solution may be water, or a solvent such as methanol, ethanol, or propylene glycol may be mixed with water and used.

Meanwhile, in the surface crosslinking step, in addition to the surface crosslinking agent and fibers described above, a polyvalent metal salt, an inorganic filler, a thickener, etc. may be further included as necessary. These additives may be dry mixed with the base resin, or in the form added to the surface crosslinking solution.

The polyvalent metal salt may further include, for example, at least one selected from the group consisting of aluminum salts, more specifically aluminum sulfates, potassium salts, ammonium salts, sodium salts, and hydrochloride salts.

As the polyvalent metal salt is further used, the liquid permeability of the superabsorbent polymer produced by the method of one embodiment can be further improved. The polyvalent metal salt may be added to the surface crosslinking solution together with the surface crosslinking agent, and may be used in an amount of 0.01 to 4 parts by weight based on 100 parts by weight of the base resin.

The inorganic filler may include silica, aluminum oxide, or silicate. The inorganic filler may be included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the base resin powder. Such an inorganic filler can act as a lubricant to improve the application efficiency of the surface crosslinking solution on the surface of the super absorbent polymer, and further improve the liquid permeability of the prepared super absorbent polymer.

In the surface crosslinking step, a thickener may be further included. When the surface of the base resin powder is further crosslinked in the presence of a thickener in this way, deterioration in physical properties can be minimized even after grinding. Specifically, one or more selected from polysaccharides and hydroxy-containing polymers may be used as the thickener. As the polysaccharide, a gum-based thickener and a cellulose-based thickener may be used. Specific examples of the gum-based thickener include xanthan gum, arabic gum, karaya gum, tragacanth gum, ghatti gum, guar gum (guar gum), locust bean gum (locust bean gum) and silylium seed gum, and the like, and specific examples of the cellulose-based thickener include hydroxypropyl methyl cellulose, carboxymethyl cellulose, and methyl cellulose , Hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose and methylhydroxypropylcellulose You can. Meanwhile, specific examples of the hydroxy-containing polymer include polyethylene glycol and polyvinyl alcohol.

Next, by heating the mixture of the base resin, the surface crosslinking agent, and fluff pulp, the temperature is raised to perform surface modification on the base resin.

The surface crosslinking step may be performed by heating at a temperature of 185°C or higher, preferably 185 to about 230°C, for about 10 to about 90 minutes, preferably about 20 to about 70 minutes. If the crosslinking reaction temperature is less than 185 °C or the reaction time is too short, there may be a problem that the surface crosslinking agent does not sufficiently react with the base resin, and if it exceeds 230 °C or the reaction time is too long, the base resin decomposes to degrade the physical properties. Can occur.

The heating means for the surface modification reaction is not particularly limited. The heating medium may be supplied or a heat source may be directly supplied to heat. At this time, as the kind of heat medium that can be used, a heated fluid such as steam, hot air, and hot oil may be used, but the present invention is not limited to this, and the temperature of the heat medium supplied is the means of the heat medium, the rate of temperature increase, and the temperature increase. It can be appropriately selected in consideration of the target temperature. On the other hand, the heat source directly supplied may include a heating method through electricity or a gas, but the present invention is not limited to the above-described example.

By the surface crosslinking step as described above, a surface modification layer including fluff pulp may be formed on the surface of the base resin. The superabsorbent polymer thus prepared has a significantly improved initial absorption rate due to the fluff pulp of the surface modification layer, and exhibits excellent absorption performance.

Accordingly, according to another embodiment of the present invention, at least a base resin powder comprising a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having a neutralized acidic group is crosslinked; And a surface crosslinking layer formed on the surface of the base resin powder, wherein the crosslinking polymer is further crosslinked through a surface crosslinking agent, wherein the surface crosslinking layer is one of fluff pulp and synthetic polymer fibers. A superabsorbent polymer comprising the above fibers is provided.

The superabsorbent polymer may be prepared by the method for preparing the superabsorbent polymer of the present invention. The superabsorbent polymer of the present invention exhibits improved absorption rate while having excellent basic absorption properties, including fibers having excellent hygroscopicity in the surface crosslinking layer.

The superabsorbent polymer has a water retention capacity (CRC) measured according to EDANA method WSP 241.3 of about 30 g/g or more, or about 32 g/g or more, and about 40 g/g or less, or about 35 g/g or less It can have a range.

In addition, the superabsorbent polymer, the pressure absorption capacity (AUL) of 0.3 psi measured in accordance with EDANA method WSP 242.3 is about 20 g/g or more, or about 25 g/g or more, or about 26 g/g or more, and about 37 g/g or less, or about 35 g/g or less, or about 30 g/g or less.

The superabsorbent polymer of the present invention has excellent basic absorption properties as described above, and at the same time has an improved absorption rate. Specifically, the superabsorbent polymer may have a vortex time of 65 seconds or less, 63 seconds or less, or 60 seconds or less. The method of measuring the absorption rate can be embodied by the examples described below.

Hereinafter, the present invention will be described in more detail based on examples. However, the following examples are only illustrative of the present invention, and the contents of the present invention are not limited by the following examples. In addition, "%" and "part" showing content in the following Examples and Comparative Examples are based on mass unless otherwise specified.

<Example>

Preparation of super absorbent polymer

Examples 1 to 10

(1) Preparation of base resin

100 g of acrylic acid, polyethylene glycol diacrylate (PEGDA, Mw=523) 3.0 g as crosslinking agent, Phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide 0.008 g as photoinitiator, sodium persulfate (SPS) as thermal initiator A monomer aqueous solution composition was prepared by mixing 0.08 g, 31.5% caustic soda (NaOH) 128 g, and water 63.5 g.

A photopolymerization reaction was performed on the monomer aqueous solution composition to obtain a polymerized sheet. The polymerized sheet was taken out and cut to a size of 3 cm X 3 cm, followed by chopping using a meat chopper (meat size 16 mm, speed 60 Hz) to prepare a crumb.

Then, the crumb was dried in an oven capable of transferring air volume up and down. The hot air at 185° C. was uniformly dried by flowing from bottom to top for 15 minutes and from top to bottom for 15 minutes, and after drying, the water content of the dried body was set to 2% or less. After drying, it was crushed with a grinder, and then divided into 10 minutes with Amplitude 1.5 mm (classification mesh combination: #20 / #30 / #50 / #100) and each classification (10% / 65% / 22% / 3 %) Was collected to obtain a base resin powder having a particle diameter of about 150 μm to 850 μm.

(2) Preparation of super absorbent polymer

To 100 parts by weight of the base resin prepared above, each fiber of Table 1 below was mixed by dry. Then, the surface crosslinking solution (6.2 parts by weight of water, 6.2 parts by weight of methanol, 0.03 parts by weight of ethylene glycol diglycidyl ether, 0.01 parts by weight of silica) was mixed evenly, and surface crosslinking was performed at 140°C for 30 minutes. The reaction proceeded. After the surface treatment was completed, a super absorbent polymer having an average particle diameter of 850 μm or less was obtained using a sieve.

Comparative Example 1

A superabsorbent polymer was prepared in the same manner as in Example 1, except that the fiber was not added in step (2).

Comparative Example 2

To 100 parts by weight of the superabsorbent polymer of Comparative Example 1, 0.5 parts by weight of fluff pulp used in Example 1 was added and mixed to prepare a superabsorbent polymer composite in which superabsorbent polymer and fluff pulp were simply mixed.

<Experimental Example>

The physical properties of the superabsorbent polymers of each of the Examples and Comparative Examples were measured by the following method, and the results are shown in Table 1.

(1) Centrifugal Retention Capacity (CRC)

The water retention capacity of each resin by the load-free absorption magnification was measured according to EDANA WSP 241.3.

Specifically, from the resins obtained through the examples and comparative examples, resins classified by a sieve of #40-50 were obtained. After the resin W0(g) (about 0.2g) was uniformly put in a nonwoven fabric bag and sealed, it was immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes, the bag was drained for 3 minutes under the condition of 250G using a centrifuge, and the mass W2 (g) of the envelope was measured. Moreover, the mass W1 (g) at that time was measured after performing the same operation without using a resin. CRC (g/g) was calculated according to the following equation using each obtained mass.

[Equation 1]

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

(2) Absorbency under Load (AUL)

The pressure absorption capacity of 0.3 psi of each resin was measured according to EDANA method WSP 242.3. In the measurement of the pressure absorption capacity, the resin classifier for the CRC measurement was used.

Specifically, a 400 mesh wire mesh made of stainless steel was mounted on a cylindrical bottom of a plastic having an inner diameter of 25 mm. A piston capable of uniformly spreading the absorbent resin W3(g) (0.16 g) on a wire mesh under conditions of normal temperature and humidity of 50%, and giving a load of 0.3 psi evenly thereon, the piston is slightly smaller than the outer diameter of 25 mm and a cylinder. There was no gap with the inner wall of the and the vertical movement was not disturbed. At this time, the weight W4(g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside the petri dish of 150 mm in diameter, and the physiological saline composed of 0.9 wt% sodium chloride was brought to the same level as the top surface of the glass filter. A sheet of filter paper having a diameter of 90 mm was placed thereon. The measuring device was mounted on a filter paper, and the liquid was absorbed for 1 hour under a load. After 1 hour, the measuring device was lifted, and the weight W5 (g) was measured.

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

[Equation 2]

AUP(g/g) = [W5(g)-W4(g)]/W3(g)

(3) Absorption rate (vortex)

The absorption rate of each resin was measured in seconds according to the method described in International Patent Publication No. 1987-003208.

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

fiber Properties of super absorbent polymer Kinds width
(㎛) Average length*
(mm) content
(Parts by weight) CRC
(g/g) 0.3 psi AUL (g/g) vortex
(sec) Example 1 Fluff pulp 30-50 One 0.05 33.0 28.0 63 Example 2 Fluff pulp 30-50 One 0.1 33.0 28.0 61 Example 3 Fluff pulp 30-50 One 0.3 33.0 28.0 57 Example 4 Fluff pulp 30-50 One 0.5 33.0 27.0 55 Example 5 Fluff pulp 30-50 One 1.0 33.0 26.0 51 Example 6 Fluff pulp 30-50 One 3.0 33.0 24.0 48 Example 7 Fluff pulp 10-15 0.5 0.5 33.0 27.0 57 Example 8 PP 20-25 0.5 0.5 33.0 27.0 53 Example 9 PVA 10-15 One 0.5 33.0 25.0 55 Example 10 Nylon 10-15 0.5 0.5 33.0 26.0 54 Comparative Example 1 - 0 34.0 28.0 70 Comparative Example 2 (The pulp mixture of Example 1 was added to the superabsorbent polymer after the surface crosslinking) 0.5 32.0 26.1 76

*The average length of fibers is calculated by randomly selecting 100 fibers.

Referring to Table 1, the superabsorbent polymer prepared according to the present invention is superior in basic physical properties such as CRC and AUL, but the pulp fiber is simple in Comparative Example 1 that does not contain fibers and the superabsorbent resin previously prepared as described above. It can be seen that it shows a significantly improved absorption rate compared to the mixed comparative example 2.

Claims (12)

Preparing a monomer composition by mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator;
Preparing a hydrogel polymer by thermal polymerization or photopolymerization of the monomer composition;
Drying and pulverizing the hydrogel polymer to form a base resin; And
A method for producing a super absorbent polymer comprising mixing the base resin with at least one fiber among fluff pulp and synthetic polymer fibers, and a surface crosslinking agent, and heating the base resin to perform surface modification on the base resin.
According to claim 1,
The fiber is contained in 0.01 to 5 parts by weight based on 100 parts by weight of the base resin, a method for producing a super absorbent polymer.
According to claim 1,
The length of the fiber is 0.1 to 20 mm Method of manufacturing super absorbent polymer.
According to claim 1,
Method of manufacturing a super absorbent polymer having a width of 1 to 100 μm.
According to claim 1,
The surface crosslinking agent is contained in 0.01 to 3 parts by weight based on 100 parts by weight of the base resin, a method for producing a super absorbent polymer.
According to claim 1,
The monomer composition further comprises a blowing agent, a method for producing a super absorbent polymer.
The method of claim 6,
The monomer composition is an alkyl sulfate salt, alkyl sulfonate salt, alkyl phosphate salt, alkyl carbonate salt, polyethylene glycol alkyl ester ), polypropylene glycol alkyl ester, glucoside alkyl ester, glycerol alkyl ester, block-copolymers of polyethylene glycol and polypropylene glycol glycol and polypropylene glycol) or a mixture of these, further comprising a foam stabilizer, a method for producing a super absorbent polymer.
A super absorbent polymer produced by the method of any one of claims 1 to 7.
A base resin powder comprising a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups is crosslinked and polymerized; And
As a super absorbent polymer formed on the surface of the base resin powder, the crosslinked polymer further comprises a surface crosslinking layer which is further crosslinked through a surface crosslinking agent,
The surface cross-linking layer comprises a fluff pulp and one or more fibers of synthetic polymer fibers, super absorbent polymer.
The method of claim 9,
A superabsorbent polymer having a centrifugal water retention capacity (CRC) of 30 to 40 g/g measured according to EDANA method WSP 241.3.
The method of claim 9,
A super absorbent polymer having a 0.3 psi pressure absorbing capacity (AUL) of 20.0 to 37.0 g/g measured according to EDANA method WSP 241.3.
The method of claim 9,
A super absorbent polymer having a vortex time of 65 seconds or less.

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