KR20220043689A - Super absorbent polymer and preparation method thereof - Google Patents

Abstract

The present invention relates to a superabsorbent resin and a method for preparing the same. According to the present invention, a superabsorbent resin, which has excellent absorption properties and a reduced content of water-soluble components, and thus has excellent liquid permeability without causing skin damage, can be obtained. The method for preparing the superabsorbent resin includes a step of forming a hydrated gel polymer; a step of forming base resin powder; and a step of forming superabsorbent resin particles.

Description

Superabsorbent polymer and manufacturing method thereof

The present invention relates to a superabsorbent polymer having excellent basic absorption performance and reduced water-soluble components, and a method for manufacturing the same.

Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb water 500 to 1,000 times its own weight. Material), etc., are named differently. The superabsorbent polymer as described above started to be put to practical use as a sanitary tool, and now, in addition to sanitary products such as paper diapers for children and sanitary napkins, a soil repair agent for horticulture, a water repellent material for civil engineering and construction, a sheet for seedlings, and a freshness maintenance agent in the food distribution field , and is widely used as a material for poultice.

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

On the other hand, in the manufacturing process of the superabsorbent polymer, water-soluble components (extractables), which are polymers that are not crosslinked, are generated. When it comes into contact with liquid, it is easily eluted, and it can also cause adverse effects, such as causing erosion on the contacted skin. In addition, when the content of water-soluble components is high, most of the eluted water-soluble components are present on the surface of the superabsorbent polymer, making the superabsorbent polymer sticky and liquid permeability, which is the ability to quickly transfer the solution to other superabsorbent polymers, is reduced. .

Accordingly, there is a need to develop an excellent superabsorbent polymer having a reduced content of water-soluble components while maintaining high absorption characteristics.

An object of the present specification is to provide a method for manufacturing a superabsorbent polymer having excellent basic absorption performance and reduced content of water-soluble components.

In addition, an object of the present specification is to provide a superabsorbent polymer having excellent basic absorption performance and reduced content of water-soluble components.

The present invention comprises the steps of cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer;

drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and

Forming superabsorbent polymer particles by surface-crosslinking the base resin powder in the presence of a surface crosslinking solution,

The surface crosslinking agent comprises a polyvalent epoxy compound and a compound represented by the following formula (1),

A method for preparing a super absorbent polymer is provided.

[Formula 1]

In Formula 1,

n is an integer from 1 to 5;

In addition, the present invention provides a base resin obtained by polymerizing and internally crosslinking a monomer composition including an acrylic acid-based monomer in which at least part of an acidic group is neutralized, and

A surface crosslinking layer formed on the surface of the base resin,

The surface crosslinking layer comprises a polyvalent epoxy compound and a crosslinking bond derived from a compound represented by Formula 1,

A super absorbent polymer is provided.

In addition, the terminology used herein is used only to describe exemplary embodiments, and is not intended to limit the present invention.

The singular expression includes the plural expression unless the context clearly dictates otherwise.

In this specification, terms such as "comprises", "comprises" or "have" are used to describe embodied features, numbers, steps, components, or combinations thereof, and include one or more other features, numbers, or steps. , components, combinations or additions thereof are not excluded.

Also in this specification, when it is said that each layer or element is formed "on" or "over" each layer or element, it means that each layer or element is formed directly on each layer or element, or other It means that a layer or element may additionally be formed between each layer, on the object, on the substrate.

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

As used herein, the term “polymer” or “polymer” refers to a polymerized state of a water-soluble ethylenically unsaturated monomer, and may cover all water content ranges or particle size ranges. Among the above polymers, a polymer having a water content (moisture content) of about 40% by weight or more in a state before drying after polymerization may be referred to as a hydrogel polymer, and particles in which the hydrogel polymer is pulverized and dried may be referred to as a crosslinked polymer. there is.

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

In addition, the term “super absorbent polymer” refers to a cross-linked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing an acidic group and neutralizing at least a portion of the acidic group, or powder composed of particles of a superabsorbent polymer obtained by pulverizing the cross-linked polymer, depending on the context. It means a base resin in the form of (powder), or the cross-linked polymer or the base resin is subjected to additional processes, such as surface cross-linking, fine powder reassembly, drying, pulverization, classification, etc., to a state suitable for commercialization. used to be all-inclusive. Accordingly, the term “super absorbent polymer composition” may be interpreted as including a composition including a super absorbent polymer, that is, a plurality of super absorbent polymer particles.

Hereinafter, the present invention will be described in detail.

According to one embodiment of the present invention, cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and surface-crosslinking the base resin powder in the presence of a surface crosslinking solution to form superabsorbent polymer particles, wherein the surface crosslinking agent includes a polyvalent epoxy compound and a compound represented by Formula 1 below. A method of manufacturing is provided.

[Formula 1]

In Formula 1,

n is an integer from 1 to 5;

The inventors of the present invention, when a polyvalent epoxy compound and a compound represented by Formula 1 are included as a component of the surface crosslinking solution during surface crosslinking, which is a process of manufacturing the superabsorbent polymer, on the surface of the superabsorbent polymer from this It was discovered that the content of water-soluble components can be reduced without reducing the water holding capacity of the superabsorbent polymer, including the resulting cross-linking, and thus the present invention has been completed.

Hereinafter, a method of manufacturing the superabsorbent polymer according to an exemplary embodiment will be described in more detail.

(polymerization)

First, as a step of forming a hydrogel polymer, crosslinking polymerization of a monomer mixture including a polymerization initiator, an internal crosslinking agent, and a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group.

The monomer mixture, which is a raw material for the superabsorbent polymer, may include a water-soluble ethylenically unsaturated monomer having an acidic group and at least a portion of the acidic group neutralized, more specifically, an acrylic acid-based monomer and a polymerization initiator.

(monomer)

The acrylic acid-based monomer is a compound represented by the following formula (1):

[Formula 1]

R1-COOM1

In Formula 1,

R1 is an alkyl group having 2 to 5 carbon atoms including an unsaturated bond,

M1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

The acrylic acid-based monomer may include, for example, 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 is neutralized. Preferably, the monomer may be partially neutralized with a basic material such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, and the like. In this case, the degree of neutralization of the acrylic acid-based monomer may be adjusted to less than about 70 mol%, or from about 40 to about 69 mol%, or from about 50 to about 65 mol%.

If the degree of neutralization is too high, the neutralized monomer may be precipitated and it may be difficult for polymerization to proceed smoothly. Furthermore, the effect of additional neutralization after initiation of surface crosslinking is substantially lost, and the degree of crosslinking of the surface crosslinking layer cannot be optimized. , the liquid permeability of the superabsorbent polymer may not be sufficient. Conversely, if the degree of neutralization is too low, not only the absorbency of the polymer is greatly reduced, but also the properties such as elastic rubber that are difficult to handle may be exhibited.

The concentration of the monomer may be about 20 to about 60% by weight, or about 30 to about 55% by weight, or about 40 to about 50% by weight based on the monomer mixture including the raw material and solvent of the superabsorbent polymer. and may be appropriately adjusted in consideration of polymerization time and reaction conditions.

If the concentration of the monomer is too low, the yield of the superabsorbent polymer may be lowered, which may cause economic problems. Conversely, if the concentration of the monomer is too high, a part of the monomer is precipitated or when the polymerized hydrogel polymer is pulverized, the pulverization efficiency This may cause problems in the process, such as lowering, and the physical properties of the superabsorbent polymer may be deteriorated.

(Polymerization Initiator)

The polymerization initiator used in the method for preparing the superabsorbent polymer according to the embodiment is not particularly limited as long as it is generally used in the manufacture of the superabsorbent polymer.

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

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

The photopolymerization initiator is, for example, benzoin ether (benzoin ether), dialkyl acetophenone (dialkyl acetophenone), hydroxyl alkyl ketone (hydroxyl alkylketone), phenyl glyoxylate (phenyl glyoxylate), benzyl dimethyl ketal (Benzyl) Dimethyl Ketal), acyl phosphine (acyl phosphine) and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, as a specific example of the acylphosphine, commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) may be used. . A more diverse photoinitiator is well specified in Reinhold Schwalm's book 'UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)' p115, but is not limited to the above-described example.

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

The polymerization initiator may be added in a concentration of about 0.001 to 1 wt%, preferably about 0.1 to about 0.9 wt%, based on the total weight of the monomer mixture. If the concentration of the polymerization initiator is too low, the polymerization rate may be slowed and the residual monomer may be extracted in a large amount in the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is higher than the above range, the polymer chain constituting the network is shortened, so that the content of the water-soluble component increases, and the physical properties of the resin may be lowered, such as lowering the absorbency under pressure, which is not preferable.

(internal crosslinking agent)

According to one embodiment of the invention, the monomer mixture includes an internal crosslinking agent as a raw material for the super absorbent polymer. This internal crosslinking agent is for crosslinking the inside of the polymer in which the acrylic acid-based monomer is polymerized, that is, the base resin, and is distinguished from the surface crosslinking agent for crosslinking the surface of the polymer.

The type of the internal crosslinking agent is not particularly limited, and any internal crosslinking agent may be used as it has been previously used in the preparation of the super absorbent polymer. Specific examples of the internal crosslinking agent include a poly(meth)acrylate-based compound of a polyol having 2 to 20 carbon atoms, a polyglycidyl ether-based compound of a polyol having 2 to 20 carbon atoms, or allyl (meth)acrylate having 2 to 20 carbon atoms. system compounds and the like.

More specific examples of these internal crosslinking agents include trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, triethylene glycol di (meth) Acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythol tetraacrylate, ethylene glycol diglycy dil ether (ethyleneglycol diglycidyl ether), polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether or polypropylene glycol diglycidyl ether, etc., and in addition to various polyfunctional compounds can be used as an internal crosslinking agent.

This internal crosslinking agent is included in a concentration of about 0.01 to about 1% by weight, or about 0.05 to about 0.8% by weight, or about 0.2 to about 0.7% by weight based on the total weight of the monomer mixture, and the hydrogel polymer and the hydrogel polymer formed therefrom A crosslinked structure may be introduced into the base resin powder.

When the concentration of the internal crosslinking agent is too low, the absorption rate of the superabsorbent polymer may be lowered and the gel strength may be weakened, which is not preferable. Conversely, when the concentration of the internal crosslinking agent is too high, the absorbency of the superabsorbent polymer may be lowered, which may make it undesirable as an absorber.

(Other additives and monomer mixtures)

In addition, the monomer mixture may further include, in some cases, a foaming agent and a bubble stabilizer.

The blowing agent forms pores in the hydrogel polymer by foaming in the monomer mixture during polymerization, and thus serves to increase the surface area of the hydrogel polymer.

The blowing agent may use a carbonate, for example sodium bicarbonate (sodium bicarbonate), sodium carbonate (sodium carbonate), potassium bicarbonate (potassium bicarbonate), potassium carbonate (potassium carbonate), calcium bicarbonate (calcium bicarbonate), calcium Carbonate (calcium bicarbonate), magnesium bicarbonate (magnesiumbicarbonate), or magnesium carbonate (magnesium carbonate) may be used.

In addition, the blowing agent is preferably used in an amount of 1500 ppmw or less, or about 1300 ppmw or less, based on the weight of the water-soluble ethylenically unsaturated monomer. If the amount of the foaming agent is too large, the pores become too large, the gel strength of the superabsorbent polymer decreases, and the density decreases, which may cause problems in distribution and storage. In addition, the blowing agent is preferably used in an amount of 500 ppmw or more, or 1000 ppmw or more, based on the weight of the water-soluble ethylenically unsaturated monomer.

On the other hand, in the manufacturing method of the above-described embodiment, the monomer mixture may further include additives such as a thickener, a plasticizer, a preservation stabilizer, and an antioxidant, if necessary.

The monomer mixture comprising the above-described monomer mixture, polymerization initiator, internal crosslinking agent, and a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups and, optionally, other additives, is in the form of a monomer mixture solution dissolved in a solvent can be prepared with

The solvent that can be used at this time can be used without limitation in its composition as long as it can dissolve the above-mentioned components, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, Propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol 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 the remaining amount so that each component is adjusted to the above-mentioned concentration range with respect to the total content of the monomer mixture.

(polymerization)

On the other hand, as long as the method for forming a hydrogel polymer by thermal polymerization or photopolymerization of such a monomer mixture is also a commonly used polymerization method, there is no particular limitation on the configuration.

Specifically, the polymerization method can be largely divided into thermal polymerization and photopolymerization according to the polymerization energy source.

In general, when thermal polymerization is carried out, it may be carried out in a reactor having a stirring shaft such as a kneader, and in the case of photo polymerization, it may be carried out in a reactor equipped with a movable conveyor belt, but the polymerization method described above is an example and the present invention is not necessarily limited to the polymerization method described above.

For example, as described above, the hydrogel polymer obtained by thermal polymerization by supplying hot air to a reactor such as a kneader having a stirring shaft or heating the reactor may be prepared according to the shape of the stirring shaft provided in the reactor. , may be in the form of several centimeters to several millimeters. Specifically, the size of the obtained hydrogel polymer may vary depending on the concentration and injection speed of the monomer mixture to be injected. Usually, a hydrogel polymer having a weight average particle diameter of 2 to 50 mm or 3 to 30 mm can be obtained. there is.

In addition, as described above, when the photopolymerization is performed in a reactor equipped with a movable conveyor belt, the form of the hydrogel polymer obtained may be a sheet having the width of the belt. At this time, the thickness of the polymer sheet may vary depending on the concentration of the injected monomer mixture and the injection rate, and the monomer mixture is usually supplied so that a hydrogel polymer on a sheet having a thickness of 0.5 to 5 cm or 1 to 3 cm can be obtained. It is preferable to do

When the monomer mixture is supplied so that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is not preferable. When the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction occurs evenly over the entire thickness due to the excessive thickness it may not be

Typically, the water content of the hydrogel polymer obtained in this way may be from about 40 to about 80 wt%, or from about 50 to about 70 wt%. Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer as the amount of moisture occupied with respect to the total weight of the hydrogel polymer.

Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying condition is a method of raising the temperature from room temperature to about 180 ° C and maintaining it at about 180 ° C. The total drying time is set to about 20 minutes including about 5 minutes of the temperature rising step, and the moisture content is measured.

(dry)

Next, a step of drying the obtained hydrogel polymer is performed.

In this case, if necessary, a step of coarsely pulverizing before drying may be further performed in order to increase the efficiency of the drying step.

At this time, the grinder used is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, cutting Including any one selected from the group of crushing devices consisting of a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter However, it is not limited to the above-described example.

In this case, in the grinding step, the hydrogel polymer may have a particle diameter of about 2 to about 10 mm, or about 3 to about 8 mm. The particle diameter of the hydrogel polymer may be defined as the longest distance among straight-line distances connecting arbitrary points on the surface of the hydrogel polymer.

Grinding to a particle diameter of less than about 2 mm is not technically easy due to the high moisture content of the hydrogel polymer, and a phenomenon of agglomeration between the pulverized particles may occur. On the other hand, when the particle diameter exceeds about 10 mm, the effect of increasing the efficiency of the subsequent drying step is insignificant.

Drying is performed on the hydrogel polymer immediately after polymerization that has been pulverized as described above or has not undergone a 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 about 150° C., the drying time becomes excessively long, and there is a fear that the physical properties of the superabsorbent polymer finally formed may be deteriorated. When the drying temperature exceeds about 250° C., only the surface of the polymer is excessively dried, and fine powder may be generated in the subsequent pulverization process, and there is a risk that the physical properties of the finally formed superabsorbent polymer may be deteriorated. Accordingly, the drying may be performed at a temperature of about 150 to about 200 °C, more preferably at a temperature of about 160 to 180 °C.

Meanwhile, in the case of drying time, in consideration of process efficiency, etc., the drying time may be performed for about 20 to about 90 minutes, or about 30 to about 70 minutes, but is not limited thereto.

As long as the drying method of the drying step is also commonly used in the drying process of the hydrogel polymer, it may be used without limitation in its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation.

After the drying step, the moisture content of the polymer may be from about 0.1 to about 10% by weight, or from about 1 to about 8% by weight. If the moisture content after drying is too low, the hydrogel polymer deteriorates during the drying process and the physical properties of the superabsorbent polymer may be reduced. progress may be difficult.

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

The polymer powder obtained after the grinding step may have a particle diameter 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 A jog mill or the like may be used, but the invention is not limited to the above-described example.

And, 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 mixed in a certain weight ratio according to the particle size range. It can be classified as

(Surface crosslinking)

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 solution containing a surface crosslinking agent, thereby forming a superabsorbent polymer having more improved physical properties. Through this surface crosslinking, a surface crosslinking layer is formed on the surface of the pulverized and classified base resin powder.

In general, since the surface crosslinking agent is applied to the surface of the base resin powder, the surface crosslinking reaction occurs on the surface of the base resin powder, 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 inside because the crosslinked polymer on the surface of the base resin powder is further crosslinked.

The surface crosslinking agent according to the present invention is a compound capable of reacting with a functional group of the base resin, and a polyvalent epoxy-based compound and a compound represented by Formula 1 may be used.

Specifically, examples of the polyvalent epoxy compound include ethylene glycol diglycidyl ether (ethyleneglycol diglycidyl ether), diethyleneglycol diglycidyl ether (diethyleneglycol diglycidyl ether), triethyleneglycol diglycidyl ether (triethyleneglycol diglycidyl ether), tetra At least one selected from the group consisting of ethylene glycol diglycidyl ether, glycerin polyglycidyl ether, and sorbitol polyglycidyl ether may be used. .

In addition, the compound represented by Formula 1 is a compound including a dihydrazide functional group, and may form a crosslinked form represented by Formula 2 derived from a functional group of the base resin or an epoxy group of a polyvalent epoxy compound.

[Formula 2]

In the final prepared superabsorbent polymer, the above characteristic crosslinked form forms additional crosslinks with the crosslinked polymer on the particle surface, so that the water holding capacity is not lowered compared to the existing superabsorbent polymer, and the non-crosslinked polymer chains, that is, the number of The content of solvent components can be greatly reduced.

In addition, in the compound of Formula 1, n is preferably an integer of 1 to 3.

More preferably, the compound of Formula 1 is adipic acid dihydrazide.

The surface crosslinking agent according to the present invention may further include a compound represented by Formula 1 rather than the polyvalent epoxy compound by weight. Specifically, for example, the weight ratio of the polyvalent epoxy compound: the compound represented by Formula 1 is about 1:1 to 1:15, preferably about 1:1 to 1:10, more preferably about 1:2 to It could be 1:8.

When the content of the polyvalent epoxy compound is too small compared to the compound represented by Formula 1, there may be a problem in that the absorbency under pressure of the superabsorbent polymer decreases. There may be a problem.

When the content of the compound represented by Formula 1 is too small compared to the polyvalent epoxy compound, there may be no significant effect in reducing water-soluble components, and when the content of the compound represented by Formula 1 is too high, the absorbency under pressure of the superabsorbent polymer decreases. There may be a problem.

The polyvalent epoxy compound may be included in an amount of about 0.01 to about 0.1 parts by weight, preferably about 0.03 to about 0.08 parts by weight, based on 100 parts by weight of the base resin. When the content of the polyvalent epoxy compound is too small compared to the base resin, the surface crosslinking reaction may hardly occur, and when the content of the polyvalent epoxy compound is too much compared to the base resin, excessive surface crosslinking reaction progresses, resulting in deterioration of absorption capacity and physical properties This can happen.

The compound represented by Formula 1 may be included in an amount of about 0.01 to about 1 part by weight, preferably about 0.1 to about 0.6 part by weight, based on 100 parts by weight of the base resin. When the content of the compound represented by Formula 1 is too small compared to the base resin, there may be a problem in that the effect of reducing water-soluble components is insufficient, and when the content of the compound represented by Formula 1 is too large compared to the base resin, the surface crosslinking solution There may be a problem in preparing a surface crosslinking solution for the surface crosslinking reaction due to an increase in the undissolved content not dissolved in the surface.

When the content of the surface crosslinking agent is too small, the surface crosslinking reaction hardly occurs, and when the content of the surface crosslinking agent is too large, the basic absorption properties such as water retention capacity may be deteriorated due to excessive surface crosslinking reaction proceeding.

When the surface crosslinking agent is added, water may be mixed with it and added in the form of a surface crosslinking solution. When water is added, there is an advantage that the surface crosslinking agent can be uniformly dispersed in the base resin. At this time, the content of the added water is about 1 to about 1 to 100 parts by weight of the base resin for the purpose of inducing even dispersion of the surface crosslinking agent and preventing agglomeration of the base resin powder and at the same time optimizing the surface penetration depth of the surface crosslinking agent. It is preferably added in a proportion of about 10 parts by weight.

On the other hand, in addition to the above-mentioned surface cross-linking agent, a polyvalent metal salt, for example, an aluminum salt, more specifically, at least one selected from the group consisting of sulfate, potassium, ammonium, sodium, and hydrochloride salts of aluminum may be further included.

Such a polyvalent metal salt may further improve the liquid permeability of the superabsorbent polymer prepared by the method of the embodiment. 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 about 0.01 to about 4 parts by weight based on 100 parts by weight of the base resin powder.

In addition, the surface crosslinking solution is obtained by adding one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate to the surface A crosslinking reaction may be carried out. The inorganic material may be used in powder form or liquid form, and in particular, may be used as alumina powder, silica-alumina powder, titania powder, or nano-silica solution. In addition, the inorganic material may be used in an amount of about 0.05 wt% to about 2 wt% based on the total weight of the base resin powder.

Moreover, about the method of adding the said surface crosslinking agent and an inorganic substance and/or a polyvalent metal salt to the base resin powder as needed, the structure is not limited. For example, a method of mixing a surface crosslinking agent and a base resin powder in a reaction tank, spraying a surface crosslinking agent on the base resin powder, or continuously supplying a base resin powder and a surface crosslinking agent to a continuously operated mixer and mixing method and the like can be used.

Meanwhile, a surface modification step is performed on the base resin powder by heating the mixture of the base resin powder and the surface crosslinking solution to increase the temperature.

The surface crosslinking step may be performed under well-known conditions depending on the type of the surface crosslinking agent, for example, at a temperature of about 100 to about 200° C. for about 20 minutes to about 60 minutes. In a more specific example, in the surface crosslinking step, a surface crosslinking agent is added to the base resin powder having an initial temperature of about 20 °C to about 80 °C, and from about 120 °C to about 120 °C over about 10 minutes to about 40 minutes Heat treatment may be carried out by raising the temperature to a maximum temperature of 180 °C, or about 175 to about 195 °C, and maintaining the maximum temperature for about 5 minutes to about 60 minutes.

According to the surface crosslinking conditions, basic absorption characteristics such as water holding capacity of the superabsorbent polymer and liquid permeability and/or absorbency under pressure may be optimized together.

A means for increasing the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heating medium or by supplying a heat source directly. At this time, as the type of heat medium that can be used, a high-temperature fluid such as steam, hot air, or hot oil may be used, but the present invention is not limited thereto. It can be appropriately selected in consideration of the target temperature. On the other hand, the directly supplied heat source may be a heating method through electricity or a heating method through a gas, but the present invention is not limited to the above-described example.

When the above-described surface crosslinking step is performed, a super absorbent polymer may be finally prepared according to the method of an embodiment. The superabsorbent polymer may lower the content of water-soluble components through a characteristic cross-linking structure, including the polyvalent epoxy compound and the compound represented by Formula 1 above.

According to one embodiment of the present invention, there is provided a method for producing a superabsorbent polymer having a centrifugal separation retention capacity (CRC) of about 30 g/g or more, preferably about 33 g/g or more, measured according to EDANA WSP 241.3.

In addition, according to one embodiment of the present invention, there is provided a method for preparing a super absorbent polymer having a water-soluble component content of about 6% or less, preferably about 5.5% or less, measured according to WSP 270.2 of the EDANA method.

In addition, according to an embodiment of the present invention, there is provided a method for preparing a super absorbent polymer having a absorbency under pressure of 0.3 psi measured according to WSP 242.3 of the EDANA method of 26.5 g/g or more.

In addition, according to one embodiment of the present invention, there is provided a method for preparing a super absorbent polymer having a Vortex absorption rate value for physiological saline of 26 sec or less.

On the other hand, according to another aspect of the present invention, a base resin obtained by polymerizing and internally crosslinking a monomer composition containing an acrylic acid-based monomer in which at least a portion of the acidic group is neutralized, and a surface crosslinking layer formed on the surface of the base resin, , wherein the surface crosslinking layer includes a polyvalent epoxy compound and a crosslinking linkage derived from a compound represented by Formula 1, and a superabsorbent polymer is provided.

The polyvalent epoxy compound and the cross-linkage derived from the compound represented by Formula 1 may be included in the form represented by Formula 2, and the superabsorbent polymer may be prepared by the above-described manufacturing method.

The superabsorbent polymer according to an embodiment of the present invention has a centrifugal separation capacity (CRC) measured according to EDANA WSP 241.3 of about 30 g/g or more, preferably about 33 g/g or more.

In addition, in the superabsorbent polymer according to an embodiment of the present invention, the content of water-soluble components measured according to the EDANA method WSP 270.2 is about 6% or less, preferably about 5.5% or less.

In addition, the superabsorbent polymer according to an embodiment of the present invention has an absorbency under pressure of 0.3 psi measured according to WSP 242.3 of the EDANA method of 26.5 g/g or more.

In addition, in the superabsorbent polymer according to an embodiment of the present invention, the vortex absorption rate value for physiological saline is 26 sec or less.

Therefore, the superabsorbent polymer according to the present invention can solve problems such as skin irritation, stickiness, and decreased feeling of use caused by the dissolution of water-soluble components when the superabsorbent polymer is in contact with a liquid while ensuring excellent physical properties.

The superabsorbent polymer prepared according to the present invention has excellent basic absorption performance as described above, and has excellent tactile feel without causing skin damage due to a reduced content of water-soluble components.

Hereinafter, through specific examples of the invention, the operation and effect of the invention will be described in more detail. However, these embodiments are merely presented as an example of the invention, and the scope of the invention is not defined thereby.

<Example>

Example 1

1-1: Preparation of base resin

A monomer composition was prepared by mixing 100 parts by weight of acrylic acid, 83.3 parts by weight of 50% caustic soda (NaOH), 89.8 parts by weight of water, and the following components.

- Internal crosslinking agent: 0.27 parts by weight (2700 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw = 400) and 0.054 parts by weight (540 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw = 200)

-Polymerization initiator: cationic azo initiator (thermal polymerization initiator, V50) 0.1 parts by weight (1000 ppmw), hydrogen peroxide (H ₂ 0 ₂ ) 0.02 parts by weight (300 ppmw), potassium persulfate (KPS) 0.2 parts by weight (2000 ppmw)

The composition was introduced into the supply part of the polymerization reactor consisting of a conveyor belt moving continuously, and the polymerization reaction was carried out by irradiating ultraviolet rays for 2 minutes with a UV irradiation device (irradiation amount: 2 mW/cm 2 ), and a hydrogel polymer was obtained as a product .

After transferring the hydrogel polymer to a cutter, it was cut into 0.2 cm. At this time, the water content of the cut hydrogel polymer was 50% by weight. Then, the hydrogel polymer was dried in a hot air dryer at 190° C. for 40 minutes, and the dried hydrogel polymer was pulverized with a pin mill grinder. Then, the polymer having a particle size (average particle size) of 150 μm to 850 μm was classified using a sieve.

1-2: Preparation of super absorbent polymer

Then, to 100 parts by weight of the prepared base resin, a surface crosslinking solution (7.6 parts by weight of water, 7.6 parts by weight of methanol, 0.075 parts by weight of ethylene glycol diglycidyl ether (EGDGE), adipic acid dihydrazide (ADH)) 0.536 parts by weight, 0.03 parts by weight of sodium metabisulfite, 0.1 parts by weight of aluminum sulfate 18 hydrate (Al-S), and 0.03 parts by weight of aluminum oxide (Alu 130)) were mixed evenly , the surface crosslinking reaction was carried out at 140 °C for 35 minutes. After the surface treatment was completed, a superabsorbent polymer having an average particle size of 150 to 850 μm was obtained using a sieve.

Thereafter, 0.05 parts by weight of silica was dry mixed with the superabsorbent polymer prepared above.

Examples 2 to 4, Comparative Examples 1 and 2

In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that the composition of EGDGE and ADH in the surface crosslinking solution was adjusted as shown in Table 1 below.

Surface crosslinking agent content EGDGE (parts by weight) ADH (parts by weight) Example 1 0.075 0.536 Example 2 0.054 0.321 Example 3 0.032 0.107 Example 4 0.054 0.107 Comparative Example 1 0.032 - Comparative Example 2 - 0.107

<Experimental example>

The properties of the superabsorbent polymers prepared according to Examples and Comparative Examples were evaluated in the following manner, and are shown in Table 1 below.

(1) Centrifuge Retention Capacity (CRC)

The water holding capacity by the no-load absorption magnification of each resin was measured according to EDANA WSP 241.3.

Specifically, from the resins obtained through Examples and Comparative Examples, a resin classified through a sieve of #30-50 was obtained. This resin W0 (g) (about 0.2 g) was uniformly put in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt %) at room temperature. After 30 minutes, the bag was drained of water for 3 minutes under the conditions of 250G using a centrifuge, and the mass W2 (g) of the bag was measured. Moreover, after performing 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) = {[W2(g) - W1(g)]/W0(g)} - 1

(2) water-soluble ingredients

Water-soluble components were measured according to the method of EDANA method WSP 270.2.

(3) Absorption under pressure 0.3 psi

The absorbency under pressure of 0.3 psi of each resin was measured according to the EDANA method WSP 242.3.

First, in the measurement of the combined absorption capacity, the fraction of the resin in the CRC measurement was used.

Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm. Under the conditions of room temperature and humidity of 50%, the water absorbent resin W0(g) (0.16g) is uniformly spread on the wire mesh, and the piston that can apply a load of 0.3 psi more uniformly thereon is slightly smaller than the outer diameter of 25 mm and is cylindrical There is no gap between the inner wall and the vertical movement of the device. At this time, the weight W3 (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed on the inside of a 150 mm diameter petro dish, and physiological saline composed of 0.9 wt% sodium chloride was placed at the same level as the upper surface of the glass filter. One filter paper having a diameter of 90 mm was loaded thereon. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted and the weight W4 (g) was measured.

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

[Equation 2]

AUP(g/g) = [W4(g) - W3(g)]/W0(g)

(4) Vortex absorption rate

The absorption rate (vortex time) of the superabsorbent polymers of Examples and Comparative Examples was measured according to a Japanese standard method (JIS K 7224). More specifically, 2 g of superabsorbent resin is added to 50 mL of physiological saline at 25°C, and the magnetic bar (diameter 8 mm, length 31.8 mm) is stirred at 600 rpm to determine the time until the vortex disappears. It was calculated by measuring in units.

maintenance capacity
(g/g) water-soluble ingredients
(%) Absorption under pressure
(g/g) Absorption rate (sec) Example 1 33.3 4.3 28.5 26 Example 2 33.9 5.2 27.5 25 Example 3 34.5 5.5 26.9 25 Example 4 33.4 5.5 28.9 25 Comparative Example 1 33.2 5.8 27.8 25 Comparative Example 2 38.9 9.1 8.6 26

Referring to Table 1, it can be seen that the superabsorbent polymer of Examples had the same or superior water holding capacity, absorbency under pressure, and absorption rate as those of Comparative Examples, and had a relatively low content of water-soluble components.

Claims (18)

forming a hydrogel polymer by crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent and a polymerization initiator;
drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and
Forming superabsorbent polymer particles by surface-crosslinking the base resin powder in the presence of a surface crosslinking solution,
The surface crosslinking agent comprises a polyvalent epoxy compound and a compound represented by the following formula (1),
Method for preparing super absorbent polymer:
[Formula 1]

In Formula 1,
n is an integer from 1 to 5;
According to claim 1,
The surface crosslinking agent is ethylene glycol diglycidyl ether (ethyleneglycol diglycidyl ether), diethylene glycol diglycidyl ether (diethyleneglycol diglycidyl ether), triethylene glycol diglycidyl ether (triethyleneglycol diglycidyl ether), tetraethylene glycol diglycol Containing one or more polyvalent epoxy compounds selected from the group consisting of tetraethyleneglycol diglycidyl ether, glycerin polyglycidyl ether, and sorbitol polyglycidyl ether,
A method for producing a super absorbent polymer.
According to claim 1,
Containing a structure represented by the following formula (2) derived from the polyvalent epoxy compound and the compound represented by formula (1),
A method for producing a super absorbent polymer.
[Formula 2]

According to claim 1,
In Formula 1,
n is an integer from 1 to 3,
A method for producing a super absorbent polymer.
According to claim 1,
The compound represented by Formula 1 is adipic acid dihydrazide,
A method for producing a super absorbent polymer.
According to claim 1,
The polyvalent epoxy compound: the weight ratio of the compound represented by Formula 1 is 1:1 to 1:15,
A method for producing a super absorbent polymer.
According to claim 1,
The polyvalent epoxy compound is included in an amount of 0.01 parts by weight to 0.1 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 compound represented by Formula 1 is included in an amount of 0.01 part by weight to 1 part 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 superabsorbent polymer has a centrifugal separation retention capacity (CRC) of 30 g/g or more, measured according to EDANA method 441.2-02,
A method for producing a super absorbent polymer.
According to claim 1,
The superabsorbent polymer has a water-soluble component content of 6 wt% or less measured according to EDANA method 270.2,
A method for producing a super absorbent polymer.
According to claim 1,
The superabsorbent polymer has an absorbency under pressure of 0.3 psi measured according to EDANA WSP 242.3 of 26.5 g/g or more,
A method for producing a super absorbent polymer.
According to claim 1,
The superabsorbent polymer has a Vortex absorption rate value for physiological saline of 26 sec or less,
A method for producing a super absorbent polymer.
A base resin obtained by polymerizing and internally crosslinking a monomer composition comprising an acrylic acid-based monomer in which at least a portion of an acidic group is neutralized, and
A surface cross-linking layer formed on the surface of the base resin,
The surface crosslinking layer comprises a polyvalent epoxy compound and a crosslinking linkage derived from a compound represented by Formula 1,
Super absorbent resin.
14. The method of claim 13,
The polyvalent epoxy compound and the cross-linkage derived from the compound represented by Formula 1 include a compound represented by the following Formula 2,
Super absorbent resin.
[Formula 2]

14. The method of claim 13,
A centrifugal separation capacity (CRC) of 30 g/g or more, measured in accordance with EDANA Law 441.2-02;
Super absorbent resin.
14. The method of claim 13,
The content of water-soluble components measured in accordance with EDANA Law 270.2 is 6% by weight or less,
Super absorbent resin.
14. The method of claim 13,
an absorbency under pressure of 0.3 psi of at least 26.5 g/g, as measured in accordance with EDANA Method WSP 242.3;
Super absorbent resin.
14. The method of claim 13,
Vortex absorption rate value for physiological saline of 26 sec or less,
Super absorbent resin.