KR102541831B1 - Preparation method for super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for preparing a superabsorbent polymer. According to the manufacturing method of the super absorbent polymer of the present invention, a super absorbent polymer having an improved initial absorption rate can be provided.

Description

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

The present invention relates to a method for preparing a superabsorbent polymer. More specifically, it relates to a method for preparing a superabsorbent polymer having an improved initial absorption rate.

Super Absorbent Polymer (SAP) is a synthetic high-molecular substance that has the ability to absorb moisture 500 to 1,000 times its own weight. Material), etc., are named by different names. The superabsorbent polymer as described above has begun to be put into practical use as a sanitary tool, and now, in addition to sanitary products such as paper diapers and sanitary napkins for children, soil retaining agents for gardening, water retention materials for civil engineering and construction, sheets for raising seedlings, and freshness retainers in the food distribution field It is widely used as a material for steaming, steaming, etc.

In most cases, these superabsorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins. In addition, it is necessary to exhibit excellent permeability by maintaining its shape well even in a volume expansion (swelling) state by absorbing water.

However, it is known that it is difficult to improve both the water retention capacity (CRC), which is a physical property representing the basic absorption and water retention capacity of the superabsorbent polymer, and the absorbency under pressure (AUL), which represents a property of retaining moisture absorbed even under external pressure. . This is because when the overall crosslinking density of the superabsorbent polymer is controlled to be low, the water retention capacity may be relatively high, but the crosslinked structure becomes sparse and the gel strength is lowered, thereby reducing the absorbency under pressure. Conversely, when the absorbency under pressure is improved by controlling the crosslinking density to a high level, water is difficult to be absorbed between the dense crosslinked structures, and the basic water retention capacity may be deteriorated. For the above reasons, there is a limit to providing a superabsorbent polymer with improved water retention capacity and absorbency under pressure.

However, with the recent thinning of sanitary materials such as diapers and sanitary napkins, higher absorption performance is required for superabsorbent polymers. Among these, the simultaneous improvement of the water retention capacity and the pressure absorption capacity, which are opposite physical properties, and the improvement of the liquid permeability, etc. are emerging as important tasks.

In addition, after the surface of the super absorbent polymer applied to sanitary materials such as diapers or sanitary napkins absorbs liquid, the surface becomes damp to give an unpleasant feeling of use. To prevent this, the super absorbent polymer is required to exhibit a fast initial absorption rate. The faster the initial absorption rate, the more pleasant the use state can be maintained because the surface remains dry even after being swollen by the liquid.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide a method for preparing a super absorbent polymer having a fast initial absorption rate.

In order to achieve the above object, according to one aspect of the present invention,

forming a water-containing gel polymer by polymerizing a monomer composition including an acrylic acid-based monomer having an acidic group and at least partially neutralizing the acidic group, a foaming agent, a surfactant, an internal crosslinking agent, and a polymerization initiator;

mixing and pulverizing the water-containing gel polymer with a basic aqueous solution;

preparing a base resin by drying the pulverized polymer; and

performing a surface crosslinking reaction on the base resin;

It provides a method for producing a superabsorbent polymer comprising a.

According to the manufacturing method of the super absorbent polymer of the present invention, it is possible to provide a super absorbent polymer with improved initial absorption rate while exhibiting excellent water absorption properties.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, step, component, or combination thereof, but one or more other features or steps; It should be understood that the presence or addition of components, or combinations thereof, is not previously excluded.

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

Hereinafter, a method for preparing a superabsorbent polymer according to an embodiment of the present invention will be described in detail.

A method for producing a superabsorbent polymer according to an embodiment of the present invention,

forming a water-containing gel polymer by polymerizing a monomer composition including an acrylic acid-based monomer having an acidic group and at least partially neutralizing the acidic group, a foaming agent, a surfactant, an internal crosslinking agent, and a polymerization initiator; mixing and pulverizing the water-containing gel polymer with a basic aqueous solution; preparing a base resin by drying the pulverized polymer; and performing a surface crosslinking reaction on the base resin.

For reference, in the specification of the present invention, "polymer" or "polymer" means a state in which acrylic acid-based monomers are polymerized, and may cover all moisture content ranges or particle size ranges. Among the polymers, a polymer having a water content (moisture content) of about 40% by weight or more in a state after polymerization and before drying may be referred to as a hydrogel polymer.

In addition, "base resin" or "base resin powder" refers to a polymer obtained by drying and pulverizing the polymer into a powder form, before performing a surface crosslinking step to be described later.

The water-containing gel polymer obtained by polymerization of acrylic acid-based monomers is commercially available as a superabsorbent polymer in powder form after going through processes such as drying, pulverization, classification, and surface crosslinking.

Recently, in superabsorbent polymers, not only various absorption properties such as absorbency and liquid permeability, but also how much dryness of the surface can be maintained in actual use of diapers has become an important criterion for estimating diaper characteristics.

The superabsorbent polymer obtained by the manufacturing method according to one embodiment of the present invention exhibits excellent overall absorption performance in terms of physical properties such as water retention capacity, absorbency under pressure, liquid permeability, etc. It was confirmed that the state can be maintained, leading to the present invention.

In the method for preparing the super absorbent polymer of the present invention, the monomer composition, which is a raw material of the super absorbent polymer, includes an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, a foaming agent, a surfactant, an internal crosslinking agent, and a polymerization initiator. include

This will be described in more detail below.

First, the acrylic acid-based monomer is a compound represented by Formula 1 below:

[Formula 1]

R ¹ -COOM ¹

In Formula 1,

R ¹ is an alkyl group having 2 to 5 carbon atoms including an unsaturated bond;

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

Preferably, the acrylic acid-based monomer includes at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof.

Here, the acrylic acid-based monomer may have an acidic group and at least a portion of the acidic group may be neutralized. Preferably, those obtained by partially neutralizing the monomers with alkali substances such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide may be used. In this case, the degree of neutralization of the acrylic acid-based monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization may be adjusted according to final physical properties. However, if the degree of neutralization is too high, neutralized monomers may precipitate out, making it difficult for the polymerization to proceed smoothly. Conversely, if the degree of neutralization is too low, the absorbency of the polymer is greatly reduced, and it may exhibit properties such as elastic rubber that are difficult to handle. there is.

The concentration of the acrylic acid-based monomer may be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, based on the monomer composition including the raw material of the superabsorbent polymer and the solvent, and the polymerization time and The concentration may be appropriate in consideration of the reaction conditions and the like. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer is low and economic problems may arise. Conversely, if the concentration is too high, a part of the monomer is precipitated or the pulverization efficiency of the polymerized water-containing gel polymer is low. Process problems may occur, and physical properties of the superabsorbent polymer may be deteriorated.

The monomer composition of the present invention includes a blowing agent.

During polymerization by the foaming agent, foaming occurs and pores are formed in the water-containing gel polymer to increase the surface area.

A carbonate foaming agent may be used as the foaming agent, and examples of the carbonate foaming agent include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, and calcium bicarbonate. (calcium bicarbonate), calcium bicarbonate, magnesium bicarbonate or magnesium carbonate may be used.

In addition, the foaming agent may be added in an amount of about 0.01 to about 0.5 parts by weight, or about 0.01 to about 0.3 parts by weight, or about 0.01 to about 0.2 parts by weight based on 100 parts by weight of the acrylic acid monomer. If the amount of the foaming agent used is too large, the number of pores increases, and the gel strength of the superabsorbent polymer decreases and the density decreases, causing problems in distribution and storage. In addition, when too little is included, the role as a foaming agent may be insignificant.

The monomer composition of the present invention includes a surfactant.

The surfactant may play a role of inducing uniform distribution of components in the monomer composition during polymerization and uniformly distributing the bubbles throughout the polymer while maintaining the shape of the bubbles formed by the foaming agent.

As the surfactant, an anionic surfactant may be preferably used.

Examples of usable anionic surfactants include sodium dodecyl sulfate, sodium stearate, ammonium lauryl sulfate, sodium lauryl ether sulfate, sodium myreth sulfate, or alkyl ether sulfate-based compounds similar thereto. Anionic surfactants that can be used are not limited thereto, but sodium dodecyl sulfate or sodium stearate may be preferably used.

The surfactant may be added in an amount of about 0.001 to about 0.5 parts by weight or about 0.002 to about 0.05 parts by weight based on 100 parts by weight of the acrylic acid monomer. If the content of the surfactant is too low, it is difficult to achieve the effect of improving the absorption rate because the role as a cell stabilizer is insignificant.

The monomer composition of the present invention includes an internal crosslinking agent. The internal crosslinking agent includes a crosslinking agent having at least one functional group capable of reacting with the acrylic acid monomer and at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups capable of reacting with substituents of the acrylic acid-based monomers and/or substituents formed by hydrolysis of the monomers may be used.

Specific examples of the internal crosslinking agent include N, N'-methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, and propylene glycol di (meth) acrylate. )Acrylate, polypropylene glycol (meth)acrylate, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate Acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythyl At least one selected from the group consisting of stall tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate may be used.

The internal crosslinking agent may be included in a concentration of about 0.01 to about 0.5% by weight based on the monomer composition to crosslink the polymerized polymer.

The polymerization initiator used during polymerization in the method for preparing the super absorbent polymer of the present invention is not particularly limited as long as it is generally used in the preparation of the super absorbent polymer.

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

As the photopolymerization initiator, any compound capable of forming radicals by light such as ultraviolet light may be used without limitation in its configuration.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal. Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, as a specific example of acylphosphine, 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. . More various photoinitiators are well described in 'UV Coatings: Basics, Recent Developments and New Applications (Elsevier 2007)' p115, a book by Reinhold Schwalm, and are not limited to the above examples.

The photopolymerization initiator may be included in a concentration of about 0.01 to about 1.0% by weight based on the monomer composition. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slowed down, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may be non-uniform.

In addition, as the thermal polymerization initiator, at least one selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), and examples of the azo-based initiator include 2, 2-azobis (2-amidinopropane) dihydrochloride, 2 , 2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride (2,2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride), 2- (carbamoyl azo) isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2, 2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride), 4,4-azobis-(4-cyanovaleric acid), and the like. More various thermal polymerization initiators are well described in Odian's 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above examples.

In the manufacturing method of the present invention, the monomer composition of the superabsorbent polymer may further include additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

Raw materials such as an acrylic acid-based monomer having an acidic group and neutralizing at least a portion of the acidic group, a photopolymerization initiator, a thermal polymerization initiator, an internal crosslinking agent, and additives may be prepared in the form of a monomer composition solution dissolved in a solvent.

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

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

On the other hand, the method of forming a water-containing gel polymer by thermal polymerization or photopolymerization of such a monomer composition is also 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. In the case of normal thermal polymerization, it can be carried out in a reactor having an agitation shaft such as a kneader, and in the case of photopolymerization, a movable Although it may proceed in a reactor equipped with a conveyor belt, the above polymerization method is an example, and the present invention is not limited to the above polymerization method.

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

In addition, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt, the form of a water-containing gel polymer usually obtained may be a sheet-like water-containing gel polymer having the width of a belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection rate of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a polymer sheet having a thickness of about 0.5 to about 5 cm can be obtained. 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, the polymerization reaction does not occur evenly over the entire thickness due to the excessively thick thickness. may not be

At this time, the water-containing gel polymer obtained in this way may have a normal water content of about 40 to about 80% by weight. Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the dry polymer from the weight of the hydrogel polymer as the content of moisture with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to moisture evaporation in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying condition is a method of raising the temperature from room temperature to 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 raising step, and the moisture content is measured.

According to the manufacturing method of the present invention, polymerization is performed by the above-described method, and polymerization conditions are adjusted so that the water content of the water-containing gel polymer before coarse pulverization satisfies 40 to 50%, and process conditions are adjusted in the pulverization step described later, It is possible to manufacture a high-quality super-absorbent polymer with a fast initial absorption rate while exhibiting excellent overall absorbent properties.

Next, a step of pulverizing the obtained hydrogel polymer is performed. The pulverization may be performed by first mixing a basic aqueous solution with the water-containing gel polymer and then chopping the water-containing gel polymer mixed with the basic aqueous solution.

As described above, when a basic aqueous solution is mixed with a water-containing gel polymer, chopped, and then pulverized in a dry state, the surface of the water-containing gel polymer becomes ionic, thereby increasing the hydrophilicity of the water-containing gel polymer and increasing the initial absorption rate. there is. It was confirmed that the faster absorption rate was maintained even through the subsequent surface crosslinking process, and thus the superabsorbent polymer could exhibit optimized physical properties in terms of absorption rate.

The basic aqueous solution may include a basic material having a high ionization degree, such as potassium hydroxide (KOH), potassium carbonate (K ₂ CO ₃ ), or sodium hydroxide (NaOH).

The concentration of the basic material in the basic aqueous solution may be about 0.1 to about 10 M, or about 0.5 to about 8 M. If the concentration of the basic aqueous solution is too low, a problem in which a large amount of water must be injected to achieve the above-mentioned effect may occur, and if the concentration is too high, the sheet may become very sticky and the absorption rate may be reduced. From this point of view, it is preferable to use a concentration within the above range.

The basic aqueous solution may be mixed in an amount of about 5 to about 20 parts by weight, preferably about 5 to about 15 parts by weight, and more preferably about 10 to about 15 parts by weight, based on 100 parts by weight of the water-containing gel polymer. If the amount of the basic aqueous solution added is too small, there is little effect of improving the absorption rate, and if too much is added, the water-containing gel may become sticky. From this point of view, it is preferable to use it within the above range.

Next, a step of drying the pulverized polymer through the pulverization step described above is performed.

A drying temperature in the drying step may be about 150 to about 250 °C. When the drying temperature is less than 150 ° C, the drying time is too long and there is a risk of deterioration in the physical properties of the finally formed super absorbent polymer, and when the drying temperature exceeds 250 ° C, only the surface of the polymer is excessively dried, resulting in a subsequent pulverization process There is a concern that fine powder may be generated in the water, and physical properties of the finally formed superabsorbent polymer may be deteriorated. 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, the drying time may be about 20 to about 90 minutes in consideration of process efficiency, but is not limited thereto.

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

Next, a step of pulverizing the dried polymer obtained through such a drying step into a powder form is performed.

The polymer powder obtained after the grinding step may have a particle size of about 150 to about 850 μm. The grinder used for grinding 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 mill. A jog mill or the like may be used, but the present invention is not limited to the above example.

In addition, in order to manage the physical properties of the superabsorbent polymer powder to be finalized after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed, and the polymer powder is prepared at a certain weight ratio according to the particle size range. can be classified so that

Next, a surface crosslinking reaction is performed on the polymer obtained as described above, that is, the base resin, and a surface crosslinking reaction step is performed on the pulverized polymer.

In a general method for producing superabsorbent polymers, a surface crosslinking solution containing a surface crosslinking agent is mixed with a dried and pulverized polymer, that is, a base resin, and then heated by heating the mixture to perform a surface crosslinking reaction for the pulverized polymer. carry out

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

In general, since the surface crosslinking agent is applied to the surface of the superabsorbent polymer particle, a surface crosslinking reaction occurs on the surface of the superabsorbent polymer particle, which improves the crosslinkability on the surface of the particle without substantially affecting the inside of the particle. Therefore, the surface cross-linked superabsorbent polymer particles have a higher degree of cross-linking in the vicinity of the surface than in the inside.

The structure of the surface crosslinking agent is not limited as long as it is a compound capable of reacting with a functional group of a polymer.

Preferably, a polyhydric alcohol compound as the surface cross-linking agent in order to improve the properties of the resulting superabsorbent polymer; epoxy compounds; polyamine compounds; haloepoxy compounds; condensation products of haloepoxy compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; And at least one selected from the group consisting of alkylene carbonate compounds may be used.

Specifically, examples of polyhydric alcohol compounds include mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3 -pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and At least one selected from the group consisting of 1,2-cyclohexanedimethanol may be used.

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

In addition, epichlorohydrin, epibromohydrin, and ?-methylepichlorohydrin may be used as the haloepoxy compound. Meanwhile, as the mono-, di- or polyoxazolidinone compound, for example, 2-oxazolidinone or the like can be used.

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

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

If the content of the surface crosslinking agent is too small, surface crosslinking reaction hardly occurs, and when it exceeds 5 parts by weight with respect to 100 parts by weight of the polymer, excessive surface crosslinking reaction may cause deterioration in water absorption capacity and physical properties. .

On the other hand, the surface crosslinking reaction step includes a method of mixing the surface crosslinking agent and the pulverized polymer in a reaction tank, a method of spraying the surface crosslinking agent on the pulverized polymer, and continuously mixing the pulverized polymer and the surface crosslinking agent in a continuously operated mixer. It can be carried out by a conventional method such as supplying and mixing.

In addition, the surface crosslinking reaction step may be performed at a temperature of 100 to 250 °C. In addition, the surface crosslinking reaction may proceed for 1 minute to 120 minutes, preferably 1 minute to 100 minutes, and more preferably 10 minutes to 60 minutes. That is, the surface crosslinking reaction step may be performed under the above-described conditions in order to induce a minimum surface crosslinking reaction and prevent polymer particles from being damaged and deteriorating physical properties during excessive reaction.

The superabsorbent polymer prepared by the manufacturing method of the present invention may have a fast initial absorption rate without deteriorating physical properties such as water retention capacity and absorbency under load.

For example, the superabsorbent polymer prepared by the above manufacturing method has a water retention capacity (CRC) of about 27 g/g or more, or about 29 g/g or more, or about 30 g/g, measured according to EDANA method WSP 241.3 or greater, but may range from about 40 g/g or less, or about 38 g/g or less, or about 35 g/g or less.

In addition, the superabsorbent polymer prepared by the above manufacturing method may have a vortex time of 30 seconds or less, about 25 seconds or less, or about 22 seconds or less. The absorption rate is excellent as the value is small, and the lower limit of the absorption rate is 0 seconds in theory, but may be, for example, about 5 seconds or more, about 10 seconds or more, or about 12 seconds or more.

The absorption rate refers to the time (time, unit: seconds) at which the vortex of the liquid disappears due to rapid absorption when the superabsorbent polymer is added to physiological saline and stirred, and the shorter the time, the higher the superabsorbent polymer can be seen as having a fast initial absorption rate.

In addition, when 1 g of the super absorbent polymer is immersed in 2 L of tap water and swollen for 1 minute, the water absorption capacity for 1 minute, defined as the weight of water absorbed by the super absorbent polymer for 1 minute, is 100 g or more, or 110 g or more, or 120 g It can be more than 200g, or 190g or less, or 180g or less.

Tap water used in the evaluation of physical properties has an electrical conductivity of 170 to 180 μS/cm. Since the electrical conductivity of tap water has a great influence on the measured physical properties, it is necessary to measure the physical properties using tap water having the same electrical conductivity.

In addition, when 1 g of the super absorbent polymer is immersed in 150 ml of saline (0.9 wt% NaCl aqueous solution) and swollen for 1 minute, the 1-minute saline water absorption capacity defined as the weight of the saline absorbed by the super absorbent polymer for 1 minute is 25 g or more, or 30 g or more, or 35 g or more, and 100 g or less, or 90 g or less, or 80 g or less.

As described above, the superabsorbent polymer of the present invention has excellent absorbency and particularly has a fast initial absorption rate, so that high-quality sanitary materials can be provided.

The present invention is explained in more detail in the following examples. However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

<Example>-

Manufacture of superabsorbent polymer

Example 1

500 g of acrylic acid, 1.5 g of polyethylene glycol diacrylate (PEGDA, Mw = 523) as a crosslinking agent, and 0.04 g of diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide as a photoinitiator. was added to dissolve, and 640 g of 31.5% caustic soda (NaOH) and 170 g of water were mixed in another vessel and stirred. After 30 minutes, caustic soda (NaOH) and an aqueous solution of water were mixed by passing through an acrylic acid mixture vessel using a pump. When the temperature rises and goes down to about 45℃, this mixture is mixed with 0.4 g of sodium persulfate (SPS) as a thermal initiator, 0.9 g of sodium bicarbonate as a foaming agent, and sodium dodecyl sulfate as a surfactant. sulfate) was drained into a bottle containing 0.02 g. This aqueous solution was added to a stainless steel container having a width of 250 mm, a length of 250 mm, and a height of 30 mm, and ultraviolet rays were irradiated (irradiation amount: 10 mV/cm ² ) to perform UV polymerization for 60 seconds and heat was applied for 120 seconds to obtain a water-containing gel polymer. . After the obtained hydrogel polymer was pulverized to a size of 2 mm * 2 mm, the water content was measured and found to be 40.1%.

200 g of aqueous potassium hydroxide solution (0.5 M KOH) was added to 1400 g of pulverized water-containing gel polymer, chopped, and 1000 g of the resulting gel-type resin was spread on a stainless wire gauze with a hole size of 600 μm to a thickness of about 30 mm and heated in a hot air oven at 180 ° C. Dry for 30 minutes. The thus-obtained dry polymer was pulverized using a grinder, and classified using an ASTM standard mesh sieve to obtain a base resin having a particle size of 150 to 850 μm.

A surface crosslinking solution containing 1 part by weight of ethylene carbonate, 4 parts by weight of water, and 0.02 part by weight of silica is sprayed and mixed with 100 parts by weight of the base resin, and put into a container made of a stirrer and a double jacket, and surface crosslinking reaction at 185 ° C. for 60 minutes proceeded. Thereafter, the surface-treated powder was classified using an ASTM standard mesh sieve to obtain a superabsorbent polymer powder having a particle size of 150 to 850 μm.

Example 2

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium hydroxide (1.5 M KOH) was added when the hydrogel polymer was pulverized.

Example 3

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium hydroxide (2.5M KOH) was added when the hydrogel polymer was pulverized.

Example 4

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium hydroxide (5M KOH) was added when the hydrogel polymer was pulverized.

Example 5

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium hydroxide (7.5M KOH) was added when the hydrogel polymer was pulverized.

Example 6

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium carbonate (0.5M K ₂ CO ₃ ) was added when the hydrogel polymer was pulverized.

Example 7

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium carbonate (1.5M concentration K ₂ CO ₃ ) was added when the hydrogel polymer was pulverized.

Example 8

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium carbonate (2.5 M concentration K ₂ CO ₃ ) was added when the hydrogel polymer was pulverized.

Example 9

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium carbonate (5M K ₂ CO ₃ ) was added when the hydrogel polymer was pulverized.

Example 10

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that 200 g of an aqueous solution of potassium carbonate (7.5M K ₂ CO ₃ ) was added when the hydrogel polymer was pulverized.

Comparative Example 1

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that the basic aqueous solution was not added when the hydrogel polymer was pulverized.

<Experimental example>

The physical properties of the superabsorbent polymers prepared in Examples and Comparative Examples were evaluated in the following manner.

Unless otherwise indicated, all of the following physical property evaluations were conducted at room temperature (25° C.), and physiological saline or saline means a 0.9 wt% sodium chloride (NaCl) aqueous solution.

(1) Centrifuge Retention Capacity (CRC)

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

Specifically, the superabsorbent polymer W ₀ (g) (about 0.2 g) was uniformly put into a bag made of nonwoven fabric, sealed, and immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes, water was drained from the bag for 3 minutes under the condition of 250 G using a centrifuge, and the mass W ₂ (g) of the bag was measured. Moreover, after carrying out the same operation without using resin, the mass _W1 (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following equation.

[Equation 1]

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

(2) Absorption rate (Vortex time)

The absorption rate (vortex time) was measured in seconds according to the method described in International Publication No. 1987-003208.

Specifically, 2 g of superabsorbent polymer was added to 50 mL of physiological saline at 23 ° C to 24 ° C, and the magnetic bar (diameter 8 mm, length 30 mm) was stirred at 600 rpm, until the vortex disappeared. was calculated by measuring in seconds.

(3) Tap water absorption capacity for 1 minute

① 1g of superabsorbent polymer was put in a tea bag with a width of 15cm and a length of 30cm, and 2L of tap water was poured into the tea bag, followed by swelling for 1 minute.

② After swelling for 1 minute, lift the tea bag containing the super absorbent polymer out of the tap water, measure the weight of the tea bag and the super absorbent polymer together after 1 minute has elapsed, and then subtract the weight of the empty tea bag. It was set as 1 minute tap water absorption capacity.

At this time, when measured using Orion Star A222 (Company: Thermo Scientific), tap water having an electrical conductivity of 170 to 180 μS/cm was used.

(4) 1 minute salt water absorption capacity

① 1 g of superabsorbent polymer was placed in a 200 ml beaker, poured with 150 ml of saline, and then swollen for 1 minute.

② The swollen superabsorbent polymer was placed on a 100 mesh round sieve with an inner diameter of 8 cm and saline was drained for 1 minute. This discharged brine was collected in another beaker.

③ From 150 ml of saline, the weight of the saline discharged from the superabsorbent polymer for 1 minute in ② was subtracted to calculate the saline absorption capacity for 1 minute.

The physical property values of the Examples and Comparative Examples are listed in Table 1 below.

base resin Super absorbent polymer (after surface crosslinking) CRC
(g/g) 1 minute tap water
absorption capacity
(g) Vortex time
(sec) CRC
(g/g) 1 min
tap water
absorption capacity
(g) 1 min
brine
absorption capacity
(g) Vortex time
(sec) Example 1 36.4 142 27 27.1 138 31 22 Example 2 35.8 152 26 27.9 140 34 21 Example 3 35.1 174 26 28.5 162 52 18 Example 4 35.3 168 24 30.2 151 46 19 Example 5 36.5 160 25 31.0 141 40 19 Example 6 36.8 138 24 31.2 130 31 21 Example 7 37.0 145 26 30.8 134 35 23 Example 8 37.2 160 26 30.7 158 44 22 Example 9 37.7 148 27 30.8 131 34 24 Example 10 37.7 139 26 31.0 126 31 25 Comparative Example 1 36.1 92 47 32.1 88 22 38

Referring to Table 1, it was confirmed that the examples of the present invention showed fast absorption rates both when measured by the vortex method and when measuring the absorption capacity of tap water/salt water for 1 minute.

On the other hand, it can be seen that the comparative example has both the initial absorption rate evaluated by the 1-minute tap water absorption capacity and the 1-minute salt water absorption capacity and the absorption rate by the vortex method are worse than those of the Example.

Claims (11)

forming a water-containing gel polymer by polymerizing a monomer composition including an acrylic acid-based monomer having an acidic group and at least partially neutralizing the acidic group, a foaming agent, a surfactant, an internal crosslinking agent, and a polymerization initiator;
mixing and pulverizing the water-containing gel polymer with a basic aqueous solution;
preparing a base resin by drying the pulverized polymer; and
and performing a surface crosslinking reaction on the base resin, wherein the basic aqueous solution is added in an amount of 10 to 15 parts by weight based on 100 parts by weight of the water-containing gel polymer.
According to claim 1,
The foaming agent is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium bicarbonate, magnesium A method for producing a superabsorbent polymer comprising at least one selected from the group consisting of carbonate (magnesiumbicarbonate) and magnesium carbonate (magnesium carbonate).
According to claim 1,
The foaming agent is 0.01 to 0.5 parts by weight based on 100 parts by weight of the acrylic acid monomer. Included, a method for producing a superabsorbent polymer.
According to claim 1,
The surfactant is sodium dodecyl sulfate, sodium stearate, ammonium lauryl sulfate, sodium lauryl ether sulfate, and sodium myreth sulfate ( A method for producing a superabsorbent polymer comprising at least one selected from the group consisting of sodium myreth sulfate).
According to claim 1,
The surfactant is included in 0.001 to 0.5 parts by weight based on 100 parts by weight of the acrylic acid-based monomer, a method for producing a super absorbent polymer.
According to claim 1,
The basic aqueous solution includes at least one basic material selected from the group consisting of potassium hydroxide (KOH), potassium carbonate (K ₂ CO ₃ ), and sodium hydroxide (NaOH).
According to claim 1,
The concentration of the basic material in the basic aqueous solution is 0.1 to 10 M, a method for producing a super absorbent polymer.
delete According to claim 1,
The super absorbent polymer has a water absorption capacity of 100 g or more per minute, defined as the weight of water absorbed by the super absorbent polymer for 1 minute when 1 g of the super absorbent polymer is immersed in 2 L of tap water and swollen for 1 minute. A method for producing resin.
According to claim 1,
The super-absorbent polymer is 1-minute saline absorption capacity defined as the weight of saline absorbed by the super-absorbent polymer for 1 minute when 1 g of the super-absorbent polymer is immersed in 150 ml of saline (0.9 wt% NaCl aqueous solution) and swollen for 1 minute. A method for producing a superabsorbent polymer having a weight of 25 g or more.
According to claim 1,
The super absorbent polymer has a vortex time of 30 seconds or less.