KR20200075196A - Preparation method for super absorbent polymer, and super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for producing a super absorbent polymer. More particularly, the present invention relates to a method for producing a super absorbent polymer, capable of implementing excellent absorption capacity in the produced super absorbent polymer by using a crosslinking agent having a specific composition during crosslinking polymerization, and to a super absorbent polymer.

Description

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

The present invention relates to a method for producing a super absorbent polymer, and more specifically, a method for producing a super absorbent polymer capable of realizing excellent absorbent performance in a prepared super absorbent polymer by using a crosslinking agent having a specific composition during crosslinking polymerization, and It relates to a super absorbent polymer.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb about 500 to 1,000 times its own weight.Sam (Super Absorbency Material), AGM (Absorbent Gel) for each developer Material). The superabsorbent resin as described above began to be put into practical use as a physiological tool, and now, in addition to sanitary products such as paper diapers and sanitary napkins for children, soil repair agents for horticulture, civil engineering, construction index materials, nursery sheets, and freshness retention agents in food distribution fields , And is widely used as a material for poultice.

In most cases, these superabsorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins. For this purpose, it is necessary to exhibit high absorbency for moisture, etc., and absorbed moisture should not escape even under external pressure. In addition to this, the absorption rate must be fast.

In particular, in recent years, demand for a complex core type diaper has increased, and a complex core type diaper must use a super absorbent polymer having excellent absorption rate and rewetting characteristics at the bottom of the diaper.

In order to provide a superabsorbent polymer having excellent absorption rate and rewetting characteristics, it is necessary to increase the surface area of the superabsorbent polymer. To this end, a technique using a carbonate blowing agent has been introduced, but it has not yet been developed a super absorbent polymer that exhibits sufficient initial absorption capacity.

The present specification provides a super absorbent polymer exhibiting excellent initial absorbing ability.

The present invention comprises the step of crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of a polymerization initiator and an internal crosslinking agent to form a hydrogel polymer; The internal crosslinking agent is a compound containing both an epoxy group and a (meth)acrylate group in the molecule; Provided is a method for producing a super absorbent polymer.

In addition, the present invention includes a base resin which is a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups; The crosslinking polymerization provides a superabsorbent polymer formed by a compound containing both an epoxy group and a (meth)acrylate group in the molecule.

In the present invention, terms such as first and second are used to describe various components, and the terms are used only for the purpose of distinguishing one component from other components.

In addition, the 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 indicates otherwise.

In the present specification, terms such as “include”, “have” or “have” are used to describe the implemented features, numbers, steps, elements, or combinations thereof, and one or more other features or numbers, steps , Components, combinations of these or the possibility of addition are not excluded.

Also, in this specification, when each layer or element is referred to as being formed “on” or “above” each layer or element, it means that each layer or element is directly formed on top of each layer or element, or is different. It means that a layer or element can be additionally formed between each layer, on an object or substrate.

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

Throughout this specification, physiological saline means physiological saline (0.9 wt% NaCl(s)).

Hereinafter, the present invention will be described in detail.

According to one aspect of the invention, in the presence of a polymerization initiator and an internal crosslinking agent, crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group to form a hydrogel polymer; The internal crosslinking agent is a compound containing both an epoxy group and a (meth)acrylate group in the molecule; A method for producing a super absorbent polymer is provided.

The inventors of the present invention use a compound having a specific chemical structure, in addition to an internal cross-linking agent, which has been conventionally used in polymerization and internal cross-linking processes, which is a process for producing super absorbent polymers, and, in addition, a foaming agent of a specific structure In the case of using, while discovering that the cross-linking density of the cross-linked polymer to be prepared can be appropriately adjusted, the surface area of the cross-linked polymer is effectively increased, thereby providing a base resin having excellent initial absorption ability, and a super absorbent polymer. The invention was completed.

The base resin and the superabsorbent polymer can be produced by the following method.

(polymerization)

First, as a step of forming a hydrogel polymer, it is a step of crosslinking and polymerizing a monomer mixture comprising 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 of the super absorbent polymer, has an acidic group and may include a water-soluble ethylenically unsaturated monomer in which at least a portion of the acidic group is neutralized, more specifically, an acrylic acid monomer and a polymerization initiator.

(Monomer)

The acrylic acid monomer is a compound represented by the following formula (2):

[Formula 2]

R1-COOM1

In Chemical Formula 2,

R1 is an alkyl group having 2 to 5 carbon atoms containing 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, for example, acrylic acid, methacrylic acid, and may include one or more selected from the group consisting of monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts.

Here, the acrylic acid monomer may have an acidic group and at least a part of the acidic group may be neutralized. Preferably, the monomer may be partially neutralized with a basic substance such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide. In this case, the degree of neutralization of the acrylic acid monomer may be adjusted to less than about 85 mol%, or about 40 to about 80 mol%, or about 50 to about 70 mol%.

If the degree of neutralization is too high, the neutralized monomer may be precipitated and polymerization may be difficult to proceed smoothly. Furthermore, the effect of additional neutralization after the surface crosslinking is substantially eliminated, and the degree of crosslinking of the surface crosslinking layer is not optimized. , The liquid permeability of the super absorbent polymer may be insufficient. On the contrary, if the degree of neutralization is too low, the absorbency of the polymer is not only greatly reduced, but also exhibits properties such as an elastic rubber that is difficult to handle.

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 relative to the monomer mixture containing the raw material and solvent of the superabsorbent polymer. And may be appropriately adjusted in consideration of polymerization time and reaction conditions.

When the concentration of the monomer is too low, the yield of the superabsorbent polymer may be lowered, which may cause economic problems. Conversely, when the concentration of the monomer is too high, a part of the monomer is precipitated or crushed when the polymerized hydrogel polymer is crushed. This may cause process problems such as lowering, and may decrease the physical properties of the super absorbent polymer.

(Polymerization initiator)

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

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

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

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal. Dimethyl Ketal), acyl phosphine (acyl phosphine) and alpha-aminoketone (α-aminoketone) may be used. Meanwhile, as a specific example of acylphosphine, a commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) can be used. . For a wider variety of photoinitiators, it is well documented in Reinhold Schwalm's book'UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)' p115, and is not limited to the examples described above.

In addition, as the thermal polymerization initiator, one or more selected from the initiator group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator are sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), ammonium persulfate (A mmonium persulfate; (NH ₄ ) ₂ S ₂ O ₈ ), and examples of the azo-based initiator are 2, 2-azobis-(2-amidinopropane) dihydrochloride (2, 2-azobis (2-amidinopropane) dihydrochloride), 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoyl azo)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), 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 examples described above.

The polymerization initiator may be added at a concentration of about 0.001 to 1% by weight, preferably about 0.1 to about 0.9% by weight relative to the total weight of the monomer mixture. When the concentration of the polymerization initiator is too low, the polymerization rate may be slow, and residual monomers in the final product may be extracted in large quantities, 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 the content of the water-soluble component is increased and the pressure absorption capacity is lowered, so that the physical properties of the resin may be lowered, which is not preferable.

(Internal crosslinking agent)

According to one embodiment of the invention, the monomer mixture is a raw material of a super absorbent polymer, and includes an internal crosslinking agent having a special chemical structure.

Such an internal crosslinking agent is for crosslinking the inside of a polymer in which an acrylic acid monomer is polymerized, that is, a base resin, and is different from a surface crosslinking agent for crosslinking the surface of the polymer.

The internal crosslinking agent generally used in the preparation of superabsorbent polymers from before, specifically, a poly(meth)acrylate-based compound having a polyol having 2 to 20 carbon atoms, a polyglycidyl ether-based compound having a polyol having 2 to 20 carbon atoms, or And an allyl (meth)acrylate-based compound having 2 to 20 carbon atoms.

More specific examples of these internal crosslinking agents used in the past, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and 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, pentaerythritol tetraacrylate, And ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, or polypropylene glycol diglycidyl ether.

However, in the case of the present invention, a compound containing both an epoxy group and a (meth)acrylate group in a molecule other than the aforementioned internal crosslinking agent is used as the internal crosslinking agent.

These compounds, unlike the internal cross-linking agent used previously, have two different functional groups in the molecule, so that the cross-linking density of the cross-linked polymer to be prepared can be appropriately adjusted. In particular, when a specific blowing agent described later is used together, By optimizing the degree of foaming, the surface area of the crosslinked polymer can be effectively increased.

Such an internal crosslinking agent may be represented by, for example, Formula 1 below.

[Formula 1]

In Chemical Formula 1,

R1 is hydrogen or alkyl having 1 to 5 carbon atoms,

n is an integer of 1-5.

In Chemical Formula 1, R1 may be more preferably hydrogen or methyl, and n may be more preferably 1 to 3.

Examples of such compounds include oxira-2-ylmethyl acrylate, oxira-2-ylmethyl methacrylate, oxira-2-ylethyl acrylate, oxira-2-ylethyl methacrylate, and oxira And -2-ylpropyl acrylate, oxira-2-ylpropyl methacrylate, oxira-2-ylbutyl acrylate, and oxira-2-ylbutyl methacrylate, and the like. It may be used by mixing more, but the present invention is not necessarily limited thereto.

The internal crosslinking agent may be included at about 100 to about 1500 ppm, and preferably at about 500 to about 1000 ppm, based on the weight of the water-soluble ethylenically unsaturated monomer.

Separately, such an 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 relative to the total weight of the monomer mixture, hydrogel polymer and A crosslinked structure can be introduced into the base resin powder formed therefrom.

When the concentration of the internal crosslinking agent is too low, the absorption rate of the superabsorbent polymer is 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 absorbent power of the super absorbent polymer is lowered, which may make it undesirable as an absorber.

(blowing agent)

In addition, the monomer mixture, in addition to the internal crosslinking agent, may further include a blowing agent, and accordingly, the crosslinking polymerization may be performed in the presence of an encapsulating blowing agent.

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

Foaming agents that have been commonly used include carbonates, for example, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, and calcium bicarbonate bicarbonate), calcium bicarbonate, magnesium bicarbonate or magnesium carbonate has been used.

However, in the case of the present invention, a foaming agent having a specific structure, specifically, an encapsulating foaming agent is used, and by the interaction of the encapsulating foaming agent and the internal crosslinking agent described above, the crosslinking density and the degree of foaming of the crosslinked polymer can be appropriately adjusted. There will be.

The encapsulated blowing agent, for example, the average diameter measured before expansion is adjusted to 5 to 50 μm, 5 to 30 μm, 5 to 20 μm or 7 to 17 μm to prepare resin particles having large pores uniformly formed can do.

The encapsulated foaming agent may have a structure including a core including a hydrocarbon and a shell surrounding the core and formed of a thermoplastic resin. Since the encapsulated foaming agent can expand to a desired size, it can be used in the manufacture of a super absorbent polymer so that the super absorbent polymer contains resin particles having large pores described above in a predetermined content or more.

In order to manufacture a large amount of resin particles having pores of the above-described size, it is necessary to grasp the expansion characteristics of the encapsulated blowing agent. However, the form in which the foaming agent encapsulated in the superabsorbent polymer is foamed may vary depending on the manufacturing conditions of the superabsorbent polymer, so it is difficult to define it as one form. Therefore, by checking the expansion ratio and size by foaming the encapsulated blowing agent in the air, it can be confirmed that it is suitable for forming resin particles having large pores.

Specifically, the encapsulated blowing agent is expanded by applying heat to the glass petri dish for 10 minutes after applying the encapsulating blowing agent. At this time, if the encapsulated foaming agent exhibits a maximum expansion rate in air of 3 to 15 times, 5 to 15 times, or 8.5 to 10 times, it is suitable for mass-producing resin particles having pores of the size described above.

In addition, when the maximum expansion size in the air of the encapsulated foaming agent is 190 μm or less, a large number of resin particles having pores of the above-described size can be produced. Specifically, when the maximum expansion size in the air of the encapsulated blowing agent is 20 to 190 μm, 50 to 190 μm, 70 to 190 μm, or 75 to 190 μm, a large amount of resin particles having pores having the above-described size are generated. It is suitable for

The maximum expansion ratio and maximum expansion size in the air of the encapsulated blowing agent are described in detail in the preparation examples described below.

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

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

The encapsulated blowing agent may contain 10 to 30% by weight of hydrocarbons based on the total encapsulating blowing agent weight. Within this range, it is possible to manufacture a large amount of resin particles having pores of the size described above.

The encapsulated blowing agent may be included in an amount of about 1000 to about 5000 ppm, or about 2000 to about 4000 ppm, based on the weight of the water-soluble ethylenically unsaturated monomer.

In the above-mentioned content range, a base resin and a super absorbent polymer satisfying the above-described pore characteristics and various physical properties can be suitably obtained.

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

The monomer mixture containing the above-described monomer mixture, polymerization initiator, internal crosslinking agent, and water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized, 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 of its composition as long as it can dissolve the above-mentioned components, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, Propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol Ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N,N-dimethylacetamide can be used in combination.

The solvent may be included in a residual amount so that each component is controlled in the above-described concentration range with respect to the total content of the monomer mixture.

(polymerization)

On the other hand, the method for forming a hydrogel polymer by thermal polymerization or photopolymerization of such a monomer mixture is also not particularly limited, as long as it is a commonly used polymerization method.

Specifically, the polymerization method can be roughly divided into thermal polymerization and photo polymerization depending on the polymerization energy source.

Normally, when thermal polymerization is performed, it may be performed in a reactor having a stirring axis such as a kneader, and when photopolymerization is performed, it may be performed in a reactor 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, by supplying hot air to a reactor, such as a kneader having a stirring shaft, or by heating the reactor, the hydrogel polymer obtained by thermal polymerization, depending on the shape of the stirring shaft provided in the reactor , In the form of several centimeters to several millimeters. Specifically, the size of the hydrogel polymer obtained may vary depending on the concentration and the injection rate of the monomer mixture to be injected, and a hydrogel polymer having a weight average particle diameter of 2 to 50 mm or 3 to 30 mm is usually obtained. have.

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

When the monomer mixture is supplied to such an extent that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is undesirable. When the thickness of the polymer on the sheet exceeds 5 cm, due to the excessively thick thickness, the polymerization reaction does not occur evenly over the entire thickness. It may not.

The normal water content of the hydrogel polymer obtained in this way may be about 40 to about 80% by weight, or about 50 to about 70% by weight. Meanwhile, in the present specification, “water content” refers to a content of moisture occupied with respect to the total weight of the hydrogel polymer, which means the weight of the hydrogel polymer minus the dry polymer weight.

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

(dry)

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

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

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

At this time, the grinding step may be pulverized such that the particle diameter of the hydrogel polymer is 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 of a straight line connecting any point of the hydrogel polymer surface.

Grinding to a particle diameter of less than about 2 mm is not technically easy due to the high water content of the hydrogel polymer, and may also cause agglomeration between the crushed particles. On the other hand, when the particle diameter is pulverized to more than about 10 mm, the effect of increasing the efficiency of the subsequent drying step is negligible.

Drying is performed on the hydrogel polymer immediately after polymerization, which is pulverized as described above or has not been subjected to a crushing 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 is too long and there is a fear that the physical properties of the superabsorbent polymer finally formed are deteriorated. When the drying temperature exceeds about 250°C, only the polymer surface is excessively dried, so that fine powder may be generated in a subsequent pulverization process, and there is a fear that the physical properties of the superabsorbent polymer finally formed may be deteriorated. Therefore, 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.

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

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

The moisture content of the polymer after the drying step may be about 0.1 to about 10% by weight, or about 1 to about 8% by weight. If the water content after drying is too low, the water-containing gel polymer may deteriorate during the drying process, thereby deteriorating the physical properties of the superabsorbent polymer. On the contrary, when the water content is too high, the absorption performance may be deteriorated due to a large amount of moisture in the superabsorbent polymer, or subsequent processes. Progress can 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 pulverizer used to crush such a particle size is, in particular, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or 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 finally produced after such a pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle diameter may be performed, and the polymer powder may be subjected to a certain weight ratio according to the particle size range. You can classify as possible.

(Surface crosslinking)

And, the manufacturing method according to an embodiment of the present invention may further include a surface crosslinking step.

The surface crosslinking step is a step of forming a superabsorbent polymer having improved physical properties by inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a surface crosslinking solution containing a surface crosslinking agent. Through the surface crosslinking, a surface crosslinking layer is formed on the surface of the pulverized and classified base resin powder.

Generally, the surface crosslinking agent is applied to the surface of the base resin powder, so that the surface crosslinking reaction takes place 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 crosslinking degree in the vicinity of the surface than in the interior because the crosslinked polymer on the surface of the base resin powder is further crosslinked.

Meanwhile, as the surface crosslinking agent, a compound capable of reacting with a functional group of the base resin is used, and examples thereof include polyhydric alcohol compounds, polyhydric epoxy compounds, polyamine compounds, haloepoxy compounds, condensation products of haloepoxy compounds, and oxazoline compounds. Alternatively, an alkylene carbonate-based compound or the like can be used without particular limitation.

Specifically, examples of the polyhydric alcohol-based compound are di-, tri-, tetra- or polyethylene 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 1,2-cyclohexane One or more selected from the group consisting of dimethanol may be used.

In addition, ethylene glycol diglycidyl ether and glycidol may be used as the polyvalent epoxy-based compound, and ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, and pentaethylene hexa as polyamine compounds. One or more selected from the group consisting of min, polyethyleneimine and polyamide polyamine can be used.

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

In addition, alkylene carbonate or propylene carbonate may be used as the alkylene carbonate-based compound. These may be used alone or in combination with each other.

The content of the surface crosslinking agent to be added may be appropriately selected depending on the type or reaction conditions of the surface crosslinking agent to be added, but is usually about 0.001 to about 5 parts by weight, or about 0.01 to about 100 parts by weight of the base resin powder. About 0.5 part by weight, or about 0.01 to about 0.1 part by weight may be used.

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 excessively large, basic absorption characteristics such as water retention capacity may be deteriorated due to excessive surface crosslinking reaction.

When the surface crosslinking agent is added, water may be additionally mixed together and added in the form of a surface crosslinking solution. When adding water, there is an advantage that the surface crosslinking agent can be evenly dispersed in the base resin. At this time, the amount of water added induces the even dispersion of the surface crosslinking agent and prevents agglomeration of the base resin powder, and at the same time, optimizes the surface penetration depth of the surface crosslinking agent, with respect to 100 parts by weight of the base resin, about 1 to It is preferably added in a proportion of about 10 parts by weight.

On the other hand, the above-mentioned surface crosslinking solution, in addition to the surface crosslinking agent, further includes at least one selected from the group consisting of a polyvalent metal salt, for example, an aluminum salt, more specifically, a sulfate, potassium salt, ammonium salt, sodium salt, and hydrochloride salt of aluminum. can do.

In addition, the surface cross-linking solution is a surface by additionally adding one or more inorganic materials selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate. A crosslinking reaction can be performed. The inorganic material may be used in a powder form or a liquid form, and in particular, it 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% to about 2% by weight based on the total weight of the base resin powder.

Such a polyvalent metal salt can further improve the liquid permeability and the like of the superabsorbent polymer produced by the method of one 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, in the surface crosslinking process, the surface crosslinking structure of the superabsorbent polymer can be further optimized by adding polyvalent metal cations to the surface instead of the inorganic material or together with the inorganic material. This is expected because such metal cations can further reduce the crosslinking distance by forming a chelate with the carboxyl group (COOH) of the super absorbent polymer.

In addition, the method of adding the surface crosslinking agent and, if necessary, an inorganic substance and/or a polyvalent metal cation to the base resin powder is not limited. For example, a surface crosslinking agent and a base resin powder are mixed in a reaction tank, or a method of spraying a surface crosslinking agent or the like on a base resin powder, and a base resin powder and a surface crosslinking agent are continuously supplied to the mixer to be mixed and mixed. Method, etc. can be used.

When the surface crosslinking agent is added, water and methanol may be additionally mixed and added. When water and methanol are added, there is an advantage that the surface crosslinking agent can be evenly dispersed in the base resin powder. At this time, the content of water and methanol to be added can be appropriately adjusted to induce even dispersion of the surface crosslinking agent and to prevent the agglomeration of the base resin powder while optimizing the surface penetration depth of the surface crosslinking agent.

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 by heating.

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 140 to about 200° C. for about 20 minutes to about 60 minutes. In a more specific example, the surface crosslinking step adds a surface crosslinking agent or the like to a base resin powder having an initial temperature of about 20°C to about 80°C, and is about 140°C to about 30 minutes over about 10 minutes to about 30 minutes. The temperature may be increased to 200° C., or to a maximum temperature of about 175 to about 195° C., and the maximum temperature may be maintained for about 5 minutes to about 60 minutes to heat treatment.

Depending on the surface crosslinking conditions, basic absorption characteristics such as water retention capacity of the super absorbent polymer, and liquid permeability and/or pressure absorption capacity may be optimized together.

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

(Super absorbent polymer)

On the other hand, according to another aspect of the present invention, at least a part of the water-soluble ethylenically unsaturated monomer having a neutralized acidic group includes a base resin that is a crosslinked polymer; The crosslinking polymerization is provided by a superabsorbent polymer formed by a compound containing both an epoxy group and a (meth)acrylate group in the molecule.

The base resin may be a crosslinked polymer in which at least a part of the water-soluble ethylenically unsaturated monomer having a neutralized acidic group is crosslinked and polymerized in the presence of an encapsulated blowing agent, and the compound used for the internal crosslinking has been described above, and this superabsorbent The resin can be produced by the production method described above.

Further, the base resin may include a surface crosslinking layer formed of a surface crosslinking agent on its surface.

According to one embodiment of the invention, in the superabsorbent polymer, the base resin, CRC value for the saline solution of the base resin particles having a particle diameter of 300 to 420 μm is 35 g/g or more, or about 40 g/g or more May, and the upper limit has no significant meaning, but may be about 55 g/g or less, or about 50 g/g or less.

Here, the 300 to 420 μm can be screened with a standard sieve of 40 mesh and 50 mesh.

The CRC according to EDANA WSP 241.3, that is, the water holding capacity, can be calculated by Equation 1 below.

[Equation 1]

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

In Equation 1,

W0 is the mass of the base resin before absorption, W2 is the base resin uniformly put in a non-woven bag, sealed, and then immersed in physiological saline at room temperature for 30 minutes, using a centrifugal separator under the condition of 250G. It is the mass of the bag, measured after removing moisture from the bag for 3 minutes, and W1 is the mass of the bag, measured after performing the same operation without using resin.

In addition, in the superabsorbent polymer, the base resin may have a particle size of 300 to 420 μm, a 1 minute absorbency value for tap water of 140 g/g or more, or about 150 g/g or more, and an upper limit thereof. Has no significant meaning, but may be about 250 g/g or less, or about 220 g/g or less, or about 210 g/g or less.

The tap water may mean that the electrical conductivity is about 170 to about 180 μS/cm, and the electrical conductivity may be measured using an electrical conductivity measuring device.

In addition, the 1-minute absorption capacity value for the tap water may be calculated by Equation 2 below.

[Equation 2]

1 minute tap water absorption capacity = {[W5(g)-W4(g)-W3(g)]/W3(g)}

In Equation 2,

W3(g) is the weight (g) of the super absorbent polymer used in the experiment,

W5(g) is the weight measured by immersing the superabsorbent polymer in the bag and immersing it in tap water for 1 minute, taking out the bag and hanging it for 1 minute to stand,

W4(g) is the weight measured after the superabsorbent resin is not used, only the envelope is immersed in tap water for 1 minute, the envelope is taken out, hung and left for 1 minute.

According to the method for producing a super absorbent polymer of the present invention, a super absorbent polymer capable of realizing excellent absorbent performance can be provided by using a crosslinking agent having a specific composition and an optionally encapsulated foaming agent. When such a superabsorbent polymer is used, it is possible to provide hygiene materials such as diapers and sanitary napkins that can absorb body fluids quickly and provide a soft texture.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, these examples are only presented as examples of the invention, and the scope of the invention is not thereby determined.

<Example>

Reference example

Preparation Example 1: Preparation of encapsulated blowing agent

An encapsulated blowing agent having a core-shell structure, the core is iso-butane, and the shell formed of a copolymer of acrylate and acrylonitrile was prepared. Iso-butane was included in an amount of 25% by weight based on the total encapsulated blowing agent weight.

The average diameter of the encapsulated blowing agent was 13 μm. The diameter of each encapsulated blowing agent was measured by an average Ferret diameter through an optical microscope. Then, the average value of the diameters of the encapsulated blowing agents was obtained and defined as the average diameter of the encapsulating blowing agents.

After applying 0.2 g of the encapsulated foaming agent on a glass petri dish, it was left for 10 minutes on a hot plate preheated to 150°C. The encapsulated blowing agent slowly expands by heat, and observed by an optical microscope to measure the maximum expansion ratio and the maximum expansion size in the air of the encapsulated blowing agent.

After the heat was applied to the encapsulated blowing agent, the diameter of the top 10% by weight was measured in the order of the particles expanded most, and the maximum expansion size was defined, and the heat for the average diameter (D0) measured before applying the heat to the encapsulating blowing agent was applied. Then, the ratio (DM/D0) of the average diameter (DM) of the top 10% by weight of the expanded particles was determined and defined as the maximum expansion ratio. Both the diameter and the average diameter were measured to be the same as the diameter and average diameter of the encapsulating foam.

The maximum expansion ratio in the air of the encapsulated blowing agent was about 9 times, and the maximum expansion size was about 80 to 150 μm.

Base resin production

Example 1

A monomer composition was prepared by mixing 515 g of acrylic acid, 635.9 g of 31.5% caustic soda (NaOH), 188.3 g of water, and the following components.

-Internal crosslinking agent: 0.41 g of glycidyl methacrylate (about 800 ppm), 0.01 g of PEGDA400 (about 15 ppm)

-Foaming agent: 1.7 g of capsule-type foaming agent of Preparation Example 1 (about 3300 ppm)

-Polymerization initiator: Irgacure-819 (photopolymerization initiator, i-819) 0.04 g (about 80 ppm), sodium persulfate 0.82 g (about 1600 ppm, thermal polymerization initiator)

-Surfactant: Sodium dodecyl sulfate 0.14 g (about 275 ppm)

The composition was introduced into a supply section of a polymerizer consisting of a conveyor belt continuously moving, and the polymerization reaction was performed by irradiating ultraviolet rays with a UV irradiation device for 90 seconds (irradiation amount: 10 mW/cm 2) to obtain a hydrogel polymer as a product. .

After transferring the hydrogel polymer to a cutter, it was cut to 0.2 cm. At this time, the water content of the cut hydrogel polymer was 50% by weight. Subsequently, the hydrogel polymer was dried in a hot air dryer at 180° C. for 40 minutes, and the dried hydrogel polymer was pulverized with a pin mill grinder. Subsequently, a polymer having a particle size (average particle size) of 150 μm to 850 μm was classified using a sieve.

Example 2

A base resin was prepared in the same manner as in Example 1, except that the content of the internal crosslinking agent was changed to 0.20 g (about 400 ppm).

Example 3

As an internal crosslinking agent, base resin was prepared in the same manner as in Example 1 except that glycidyl acrylate was used instead of glycidyl methacrylate and 0.41 g (about 800 ppm) was added.

Example 4

As an internal crosslinking agent, base resin was prepared in the same manner as in Example 1, except that glycidyl acrylate was used instead of glycidyl methacrylate and 0.20 g (about 400 ppm) was added.

Comparative Example 1

As an internal crosslinking agent, Glyether(R) EJ-1030S instead of glycidyl methacrylate; Ethylene glycol diglycidyl ether; A base resin was prepared in the same manner as in Example 1, except that a JS product was used and 1300 ppm was added.

Comparative Example 2

As an internal crosslinking agent, Glyether(R) EJ300 instead of glycidyl methacrylate; Ethylene glycol diglycidyl ether; A base resin was prepared in the same manner as in Example 1, except that a product of JS Eye was used and 1070 ppm was added.

Test Example: Evaluation of base resin

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

Here, the base resin, using a standard mesh of 40 mesh, and 50 mesh, was selected to have a particle diameter of about 300 to about 420 ㎛.

(1) Centrifuge Retention Capacity (CRC)

The centrifugal water retention capacity (CRC) of the base resin against physiological saline was measured according to the method of EDANA method NWSP 241.0.R2, and base resins of examples and comparative examples classified with a sieve of 40 mesh and 50 mesh were used.

Specifically, the base resin W ₀ (g, about 0.2 g) was uniformly put in a non-woven bag and sealed. Then, the bag was immersed in 0.9 wt% aqueous sodium chloride solution (physiological saline) at room temperature. After 30 minutes, the envelope was dehydrated at 250 G for 3 minutes using a centrifuge, and then the weight W ₂ (g) of the envelope was measured. On the other hand, after performing the same operation using an empty bag without resin, the weight W ₁ (g) at that time was measured.

Using each weight thus obtained, the centrifugal water retention capacity was confirmed by the following equation (1).

[Equation 1]

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

In Equation 1,

W ₀ (g) is the initial weight of the resin (g),

W ₁ (g) is the weight of the non-woven fabric empty bag measured after immersing the non-woven fabric empty bag without base resin in physiological saline at room temperature for 30 minutes, and then dehydrating at 250 G for 3 minutes using a centrifuge. ,

W ₂ (g) was absorbed by immersing and absorbing the nonwoven fabric bag containing the base resin in physiological saline at room temperature for 30 minutes, and then dehydrating at 250 G for 3 minutes using a centrifuge, and measuring the nonwoven fabric including the base resin. It is the weight of my envelope.

(2) 1 minute water absorption capacity

As the tap water, one having an electrical conductivity of about 180 μS/cm was used.

The electrical conductivity was measured using an electrical conductivity measuring device of Orion Star A222 (manufactured by Thermo Scientific).

For the measurement, base resins of Examples and Comparative Examples classified by 40mesh and 50mesh sieve were used.

1.0 g (W3) of the base resin was placed in a nonwoven bag (15 cm Х 15 cm) and immersed in 1000 mL of water at 24° C. for 1 minute.

After 1 minute, the bag was taken out from distilled water, hung and left to stand for another minute, drained, and the mass (W5) of the nonwoven bag was measured.

In addition, the mass W4 (g) of the nonwoven fabric bag was measured after performing the same operation on the nonwoven fabric bag without using a super absorbent polymer.

Using each mass thus obtained, water absorption capacity (g/g) for 1 minute was calculated according to Equation 2 below.

[Equation 2]

1 minute tap water absorption capacity = {[W5(g)-W4(g)-W3(g)]/W3(g)}

In Equation 2,

W3(g) is the weight (g) of the super absorbent polymer used in the experiment,

W5(g) is the weight measured by immersing the superabsorbent polymer in the bag and immersing it in tap water for 1 minute, taking out the bag and hanging it for 1 minute to stand,

W4(g) is the weight measured after the superabsorbent resin is not used, only the envelope is immersed in tap water for 1 minute, the envelope is taken out, hung and left for 1 minute.

Table 1 summarizes the conditions for preparing the base resin and the properties measured from the prepared base resin.

CRC
(g/g) 1 minute water absorption capacity
(g/g) Example 1 41.7 206 Example 2 48.5 162 Example 3 42.7 201 Example 4 47.6 158 Comparative Example 1 43.2 153 Comparative Example 2 39.5 133

Referring to Table 1, it can be seen that the base resin of the example has superior or lower water absorption capacity for 1 minute while having a CRC value equal to or higher than that of the comparative example.

The 1-minute tap water absorbing capacity is a property for evaluating the initial absorbing capacity of the absorbent resin, and the base resin according to an example of the present invention shows a very excellent 1-minute tap water absorbing capacity value compared to the comparative example.

Therefore, when the base resin prepared according to the above example is used for the production of a super absorbent polymer, it is considered that excellent water retention and initial water absorption can be realized simultaneously.

Claims (16)

Crosslinking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of a polymerization initiator and an internal crosslinking agent to form a hydrogel polymer;
The internal crosslinking agent is a compound containing both an epoxy group and a (meth)acrylate group in the molecule;
Method for producing super absorbent polymer.
According to claim 1,
Drying, grinding and classifying the hydrogel polymer to form a base resin powder; And
In the presence of the surface crosslinking solution, further comprising the step of heat-treating the base resin powder to crosslink the surface to form superabsorbent polymer particles,
Method for producing super absorbent polymer.
According to claim 1,
The internal crosslinking agent is a compound represented by the following formula (1), a method for producing a super absorbent polymer:
[Formula 1]

In Chemical Formula 1,
R1 is hydrogen or alkyl having 1 to 5 carbon atoms,
n is an integer of 1-5.
According to claim 1,
The internal crosslinking agent, based on the weight of the water-soluble ethylenically unsaturated monomer, is contained in 100 to 1500 ppm, a method for producing a super absorbent polymer.
According to claim 1,
The crosslinking polymerization is carried out in the presence of an encapsulated blowing agent, a method for producing a super absorbent polymer
The method of claim 5,
The encapsulated foaming agent has an average diameter of 5 to 50 μm, a method for producing a super absorbent polymer.
The method of claim 5,
The encapsulated foaming agent has an expansion ratio of 3 to 15 times in air, and a method for producing a super absorbent polymer.
The method of claim 5,
The encapsulated blowing agent,
A core comprising a hydrocarbon; And
It is formed of a thermoplastic resin, and has a structure including a shell surrounding the core;
A method for producing a super absorbent polymer having a maximum expansion size in air of 20 to 190 μm.
The method of claim 8,
The hydrocarbon is n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso-heptane, cycloheptane , n-octane, iso-octane, and cyclooctane.
The method of claim 8,
The thermoplastic resin is a polymer formed from one or more monomers selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide, and vinylidene halide, and a method for producing super absorbent polymer .
The method of claim 5,
The encapsulated foaming agent, based on the weight of the water-soluble ethylenically unsaturated monomer, is contained in 1000 to 5000 ppm, a method for producing a super absorbent polymer.
A base resin which is a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a part of neutralized acidic groups;
The crosslinking polymerization is formed by a compound containing both an epoxy group and a (meth)acrylate group in the molecule,
Super absorbent polymer.
The method of claim 12,
The base resin is a superabsorbent polymer in which a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized is a crosslinked polymer crosslinked and polymerized in the presence of an encapsulated blowing agent.
The method of claim 12,
The base resin is a superabsorbent polymer having a CRC value of 35 g/g or more for physiological saline of particles having a particle diameter of 300 to 420 μm.
The method of claim 12,
The base resin is a superabsorbent polymer having a particle diameter of 300 to 420 μm, a value of 1 minute absorption capacity for tap water of 140 g/g or more.
The method of claim 12,
The base resin is a super absorbent polymer comprising a surface crosslinking layer formed by a surface crosslinking agent.