KR101668856B1 - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for producing a superabsorbent resin excellent in solution permeability. Specifically, there is provided a method for producing a superabsorbent resin which minimizes a residual amount of a surface cross-linking agent or a residual amount of a degradation product derived therefrom during the production of a superabsorbent resin, thereby improving solution permeability and preventing property deterioration.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a superabsorbent resin,

The present invention relates to a method for producing a superabsorbent resin having excellent liquid-permeability characteristics.

Super Absorbent Polymer (SAP) is a synthetic polymer material capable of absorbing moisture of about 500 to 1,000 times its own weight. As a result, it is possible to develop a super absorbent polymer (SAM), an absorbent gel Material), and so on. Such a superabsorbent resin has started to be put into practical use as a sanitary article, and nowadays, in addition to sanitary articles such as diapers for children, there are currently used soil repair agents for horticultural use, index materials for civil engineering and construction, sheets for seedling growing, freshness- And it is widely used as a material for fomentation and the like.

Such a superabsorbent resin can be produced through polymerization, drying, pulverization, classification, and surface cross-linking processes.

At this time, it has been attempted to obtain a product having improved AUP by cross-linking the surface of the superabsorbent resin using a polyol or polyamine as a surface treatment method of a superabsorbent resin. However, as the residual amount of the surface cross-linking agent increases, there is a limit to the improvement of the SFC. In the case of the conventional method, the cross-linking agent remains after the surface cross-linking reaction proceeds, causing additional cross-linking reaction, thereby causing a problem of deteriorating the physical properties of the superabsorbent resin.

An object of the present invention is to provide a method for producing a superabsorbent resin having excellent solution permeability and excellent physical properties such as CRC and AUP.

The present invention relates to a process for preparing a monomer composition comprising: forming a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator;

Polymerizing the monomer composition in a polymerization reactor to produce a hydrogel polymer;

Drying the mixture of hydrogel polymers;

Pulverizing the dried polymer; And

Classifying the pulverized hydrogel polymer to prepare a base resin;

And surface treating the base resin,

In the surface-treating step, a surface cross-linking agent; And water, so that the residual amount of the surface cross-linking agent or the degradation product derived therefrom is 0.1 parts by weight or less based on 100 parts by weight of the base resin after the surface treatment,

Wherein the surface cross-linking agent is an alkylene carbonate having 3 to 4 carbon atoms.

In the present invention, it is more preferable that the residual amount of the surface cross-linking agent or the degradation product derived therefrom is 0.01 to 0.1 part by weight with respect to 100 parts by weight of the base resin after the surface treatment.

According to one embodiment of the present invention, the superabsorbent resin has a saline flow conductivity (SFC) of at least 50 to 130 units and a centrifuge retention capacity (CRC) for physiological saline measured according to the EDANA method WSP 241.2 is in the range of 17 to < 30 g / g.

In addition, the superabsorbent resin may have a pressure liquid permeability (PDAUP) of 20 or more to physiological saline measured according to the method of EDANA WSP 243.1, and a pressure solution permeability (PPUP) of 80% or more calculated by the following equation.

[Equation 4]

PPUP (%) = PDAUP / AUP x 100

In the above equation 4,

The PDAUP is pressurized liquid for physiological saline measured according to the method of EDANA WSP 243.1,

AUP is the amount of pressure absorbed by physiological saline solution measured according to the method of EDANA WAP 242.2.

The gel strength of the base resin may be 4500 to 5500 Pa.

The surface cross-linking agent may be used in an amount of 0.4 to 1 part by weight based on 100 parts by weight of the base resin.

The surface treating step may include surface cross-linking the mixture of hydrogel polymer at a temperature of 175 to 190 DEG C for 30 to 70 minutes.

The water-soluble ethylenic unsaturated monomer may be at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2- acryloylethanesulfonic acid, 2- methacryloylethanesulfonic acid, 2- (meth) Sulfonic acid, or an anionic monomer of 2- (meth) acrylamide-2-methylpropanesulfonic acid and its salt; (Meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate or polyethylene glycol Non-ionic hydrophilic-containing monomer of (meth) acrylate; And unsaturated monomers containing an amino group of (N, N) -dimethylaminoethyl (meth) acrylate or (N, N) -dimethylaminopropyl (meth) acrylamide and quaternary compounds thereof. have.

The polymerization initiator may be any one selected from the group consisting of azo-based initiators, peroxide-based initiators, redox-based initiators, organic halide initiators, persulfate-based initiators, acetophenone, benzoin, benzophenone, Lt; / RTI >

The present invention reduces the residual amount of the surface crosslinking agent of the base resin or the degradation product derived therefrom in the surface cross-linking step, thereby improving the pressure absorption capacity (AUP), as well as improving the absorption capacity without load (CRC) Absorbent resin can be produced.

Hereinafter, a method for producing a superabsorbent resin according to a specific embodiment of the present invention will be described in detail.

According to one embodiment of the invention, there is provided a process for preparing a monomer composition comprising: forming a monomer composition comprising a water soluble ethylenically unsaturated monomer and a polymerization initiator; Polymerizing the monomer composition in a polymerization reactor to produce a hydrogel polymer; Drying the mixture of hydrogel polymers; Pulverizing the dried polymer; And classifying the pulverized hydrogel polymer to prepare a base resin; And surface treating the base resin, wherein in the surface treatment step, a surface cross-linking agent; And water, wherein the residual amount of the surface cross-linking agent or degradation product derived therefrom is not more than 0.1 part by weight with respect to 100 parts by weight of the base resin after the surface treatment step, wherein the surface cross- 3 to 4 alkylene carbonates.

The present invention provides a method for producing a superabsorbent resin comprising polymerization, drying, pulverization and surface cross-linking.

At this time, the base resin may be prepared by the polymerization process. The present invention is characterized in that the surface cross-linking agent specifically uses an alkylene carbonate to minimize the content of the surface cross-linking agent of the base resin after the surface cross-linking step to improve solution permeability .

According to a preferred embodiment of the present invention, a method for producing a superabsorbent resin according to the present invention comprises polymerizing a monomer composition in a polymerization reactor, pulverizing and classifying the monomer composition to prepare a base resin, passing the mixture through a surface treatment liquid, do. Thereafter, the surface cross-linking reaction is carried out in the surface cross-linking reactor, which can be classified and commercialized.

In the present invention, the surface treatment solution means a surface cross-linking solution and exhibits the following characteristics. The surface cross-linking solution of the present invention includes a solvent and a surface cross-linking agent. The solvent includes alcohols or glycol-based compounds having a specific boiling point with water.

At this time, in the surface treatment step, the cross-linking agent having excellent reactivity such as alkylene carbonate can be reacted with -COOH of the base resin to increase the cross-linking density of the surface. As a result, the residual amount of the surface cross-linking agent after the surface treatment reaction or the residual amount of the degradation product derived therefrom is lowered.

Therefore, the present invention can produce a superabsorbent resin of SFC 50 units or more. According to one embodiment of the present invention, the superabsorbent resin has a saline flow conductivity (SFC) of at least 50 units and a centrifugal separation capacity (CRC) of physiological saline measured according to EDANA method WSP 241.2 of 27 g / g. < / RTI > The superabsorbent resin has a saline flow conductivity (SFC) of at least 50 to 130 units and a centrifugal separation performance (CRC) of 17 to 30 g / g for physiological saline measured according to EDANA method WSP 241.2 May be more preferable.

Preferably, in the present invention, after the surface treatment step using the surface treatment solution, the residual amount of the surface cross-linking agent or degradation product derived therefrom is 0.1 parts by weight or less, 0.01 to 0.1 parts by weight, 0.03 to 0.09 parts by weight. At this time, the residual amount of the surface cross-linking agent or decomposition product derived therefrom may include the residual amount of the surface cross-linking agent on the surface of the super absorbent resin or the base resin after the surface cross-linking reaction or the residual amount of the degradation product derived therefrom. The residual amount of the surface crosslinking agent or decomposition product derived therefrom may be less than 1000 ppm, more preferably 300 to 800 ppm, on the surface of the base resin, based on the surface of the base resin. That is, the present invention uses the specific surface cross-linking agent to increase the cross-linking density because the surface cross-linking reactivity is higher than the conventional one, so that the addition reaction can be reduced by reducing the residual amount of the cross-linking agent or its decomposed product.

According to an embodiment of the present invention, when ethylene carbonate is used as a surface cross-linking agent, the residual amount of ethylene glycol, which is a decomposition product of ethylene carbonate, in the base resin remains at 20 wt% or less based on the amount of the ethylene carbonate.

The surface cross-linking agent may be one or more selected from the group consisting of ethylene carbonate and propylene carbonate.

The surface cross-linking agent may be used in an amount of 0.4 to 1 part by weight based on 100 parts by weight of the base resin. That is, when the amount of the surface cross-linking agent is reduced to a specific range, the SFC is increased, and the residual amount of the surface cross-linking agent or the degradation product derived therefrom is also lowered after the surface treatment. Particularly, in the present invention, the residual amount of the surface cross-linking agent or the degradation product derived therefrom can be lowered without using any other additive.

Further, if necessary, the present invention may further include a low boiling point alcohol solvent such as methanol or ethanol in the surface treatment solution. The content thereof may be 0.1 to 5 parts by weight based on 100 parts by weight of the base resin.

Preferably, the step of surface-treating comprises a step of surface cross-linking the mixture of hydrogel polymers at a temperature of 175 to 190 DEG C for 30 to 70 minutes.

Meanwhile, the superabsorbent resin according to one embodiment of the present invention may be processed by a method well known in the art, except for the surface crosslinking process.

For example, in the method of conducting thermal polymerization or UV polymerization of the monomer composition, the polymerization apparatus to be used is not particularly limited. For example, in the case of conducting thermal polymerization in general, it can be carried out in a reactor having a stirring axis such as a kneader, and can be carried out in a reactor having a conveyor belt capable of continuous movement when UV polymerization (light polymerization) However, the polymerization method described above is only an example, and the present invention is not limited to the polymerization method described above. Also, the conveyor belt may be used by circulating a belt made of rubber, cloth, wire netting, steel plate, plastic resin or the like to which some hydrophilicity is imparted.

For example, the hydrogel polymer obtained by supplying hot air or heating the reactor to a reactor such as a kneader having an agitating shaft as described above and thermally polymerizing the reactor may be supplied to the reactor outlet The discharged hydrogel polymer may be in the range of a few centimeters to a few millimeters. Specifically, the size of the resulting hydrogel polymer may vary depending on the concentration and the injection rate of the monomer composition to be injected, and a hydrogel polymer having a particle size of usually 2 to 50 mm can be obtained.

In addition, when photopolymerization proceeds in a reactor equipped with a movable conveyor belt as described above, the form of the hydrogel polymer that is usually obtained may be a hydrogel polymer on a sheet having a belt width. At this time, the thickness of the polymer sheet varies depending on the concentration and the injection rate of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a polymer in the form of a sheet having a thickness of usually 0.5 to 5 cm can be obtained. When the monomer composition is supplied to such an extent that the thickness of the polymer in 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, the polymerization reaction occurs evenly over the entire thickness due to the excessively thick thickness I can not.

Preferably, the present invention relates to a process for the preparation of a monomer composition comprising a monomer feeder having a separate feed transfer line and a polymerization initiator feed, a polymerization reactor connected to the monomer and a feed of the polymerization initiator, A superabsorbent resin can be produced through the device configuration. At this time, after the monomers and the cross-linking agent are mixed into the polymerization initiator supply unit, the conventional initiator system can be administered as needed.

In addition, the polymerization reactor may be equipped with a temperature control means for internal or external thermal polymerization, and it is preferable that the internal temperature is maintained at 60 to 100 ° C, preferably 90 ° C.

Also, in the present invention, the surface treatment solution used in the surface cross-linking may be supplied by spraying on the hydrogel polymer, but the method is not particularly limited.

The polymerization of the monomer composition is not particularly limited, and a method used in the production of a conventional superabsorbent resin can be used. For example, the polymerization of the monomer composition can be carried out by a redox polymerization method in which polymerization is carried out at a temperature of 30 to 100 ° C for 2 to 50 minutes or a thermal polymerization or a UV polymerization in which polymerization is carried out at a temperature of 40 to 90 ° C for 2 to 30 minutes have. Since the UV polymerization (photopolymerization) has little effect on the temperature, the UV polymerization can be performed by irradiating light with a wide temperature range at 25 to 99 ° C for 10 seconds to 5 minutes. The amount of ultraviolet light may be 0.1 to 30 mW / cm < ² > during UV irradiation. The light source and wavelength range used for UV irradiation can also be those well known in the art

The drying temperature and time of the polymer may be appropriately selected according to the water content of the hydrogel polymer, and preferably 20 to 40 minutes at 160 to 180 ° C. When the drying temperature is less than 160 ° C, the drying effect is insignificant, so that the drying time becomes too long and it is difficult to lower the water content by 30% or less. In addition, when the drying temperature exceeds 180 DEG C, only the surface of the hydrogel polymer is locally excessively dried, and a large amount of fine powder may be generated in the subsequent pulverization step.

The constitution of the apparatus in the drying step is not particularly limited, and drying can be performed by, for example, infrared irradiation, hot air, microwave irradiation, or ultraviolet irradiation. The drying temperature and time may be appropriately selected according to the water content of the polymer polymerized through thermal polymerization or thermal polymerization. Preferably, the drying temperature and time are preferably 20 to 120 minutes at a temperature of 80 to 200 ° C. When the drying temperature is lower than 80 ° C., the drying effect is insignificant and the drying time is excessively long. When the drying is performed at a temperature exceeding 200 ° C., there is a problem that the superabsorbent resin is thermally decomposed.

According to the present invention, in the step of drying and pulverizing the hydrous gel polymer, the dried hydrogel polymer may be pulverized to have a particle size of 150 to 850 탆.

The classifying step may include classifying the pulverized hydrogel polymer into particles having a particle size of less than 150 μm and particles having a particle size of 150 μm or more and 850 μm or less for 2 minutes can do. In the present invention, classification may be carried out at a rate of 2 minutes (minutes) or more per particle size in a classification stage as necessary.

At this time, the dried polymer may be subjected to additional pulverization, and in such a case, pulverization may be selected without limitation of the constitution as long as it is used for the pulverization of the resin. Preferably, any one of the grinding apparatuses selected from the group consisting of a pin mill, a hammer mill, a screw mill, and a roll mill may be selected and pulverized. At this time, the particle size of the final superabsorbent resin particles after the pulverization step is preferably 150 to 850 탆.

In the present invention, the water content of the functional gel polymer of the base resin for surface treatment is 30 to 60% by weight, and the water content of the hydrogel polymer obtained through the drying process may be 1 to 10% by weight. The water content of the hydrogel polymer means the amount of moisture occupied by the weight of the entire hydrogel polymer, minus the weight of the hydrogel polymer in dry state.

Further, in the present invention, after the surface of the hydrogel polymer is treated, the hydrogel polymer may be pulverized and classified into particles having a particle size of 150 to 850 탆.

The superabsorbent resin obtained in this way has a centrifugal retention capacity of 27 to 30 g / g for physiological saline solution measured according to EDANA method WSP 241.2 and a viscosity of less than 0.7 psi for physiological saline, measured according to EDANA method WAP 242.2 The pressure absorption capacity may be 22 to 25 g / g.

In addition, the superabsorbent resin may have a pressure liquid permeability (PDAUP) of 20 or more to physiological saline measured according to the method of EDANA WSP 243.1, and a pressure solution permeability (PPUP) of 80% or more calculated by the following equation.

[Equation 4]

PPUP (%) = PDAUP / AUP x 100

In the above equation 4,

The PDAUP is pressurized liquid for physiological saline measured according to the method of EDANA WSP 243.1,

AUP is the amount of pressure absorbed by physiological saline solution measured according to the method of EDANA WAP 242.2.

The gel strength of the superabsorbent resin may be 9500 to 13000 Pa, and the gel strength of the base resin to obtain the superabsorbent resin is preferably 4500 to 55000 Pa.

On the other hand, the constitution of each monomer for forming the monomer composition will be described.

In the present invention, the polymerization of the water-soluble ethylenically unsaturated monomer is preferably carried out in an aqueous solution.

The water-soluble ethylenic unsaturated monomer can be used without limitation in the constitution as long as it is a monomer usually used in the production of a superabsorbent resin. At least one selected from the group consisting of anionic monomers and salts thereof, nonionic hydrophilic-containing monomers, and amino group-containing unsaturated monomers and quaternary amines thereof can be used.

Specifically, the water-soluble ethylenic unsaturated monomer is at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2- acryloylethanesulfonic acid, 2- methacryloylethanesulfonic acid, 2- Anionic monomers of 2- (meth) acrylamide-2-methylpropanesulfonic acid and its salts; (Meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol Non-ionic hydrophilic-containing monomer of (meth) acrylate; And at least one selected from the group consisting of unsaturated monomers containing an amino group of (N, N) -dimethylaminoethyl (meth) acrylate and (N, N) -dimethylaminopropyl (meth) . More preferably, the water-soluble ethylenically unsaturated monomer can use acrylic acid and a salt thereof, which is advantageous in that it has excellent physical properties.

The concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition may be appropriately selected in consideration of the polymerization time and the reaction conditions, and preferably 0.01 to 1.0% by weight. When the concentration of the water-soluble ethylenically unsaturated monomer is less than 0.01% by weight, the crosslinking concentration is low and high extractable contents values can be obtained. When the concentration is more than 1.0% by weight, desired properties can not be obtained due to high crosslinking concentration.

Wherein the thermal polymerization initiator is at least one selected from the group consisting of an azo-based initiator, a peroxide-based initiator, a redox-based initiator, an organic halide initiator, a persulfate-based initiator, acetophenone, benzoin, benzophenone, Or more can be used. The polymerization initiator may be used in an amount of 0.01 to 1.0% by weight based on the total monomer composition.

The monomer composition according to the present invention may further comprise a crosslinking agent.

The crosslinking agent may be selected from the group consisting of a water-soluble substituent of an ethylenically unsaturated monomer, a crosslinking agent having at least one ethylenic unsaturated group and at least one functional group capable of reacting with the water-soluble substituent of the ethylenically unsaturated monomer, or a mixture thereof; And a water-soluble substituent of the ethylenically unsaturated monomer, a cross-linking agent having at least two functional groups capable of reacting with a water-soluble substituent formed by hydrolysis of the vinyl monomer, and a mixture thereof. . Examples of the crosslinking agent having two or more ethylenic unsaturated groups include bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly (meth) acrylate of polyol having 2 to 10 carbon atoms, and poly (meth) acrylate having 2 to 10 carbon atoms (Meth) acrylate, ethyleneoxy (meth) acrylate, propyleneoxy (meth) acrylate, glycerin diacrylate, glycerin At least one selected from the group consisting of triacrylate, trimethylolpropane triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol and propylene glycol can be used.

The crosslinking agent used in the production of the hydrogel polymer may be used in an amount of 0.01 to 0.8% by weight based on the total monomer composition.

Best Mode for Carrying Out the Invention Hereinafter, the function and effect of the present invention will be described in more detail through specific examples of the present invention. It is to be understood, however, that these embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention.

Test Example : Property Evaluation of Superabsorbent Resin

(1) Absorption under pressure (AUP) measurement

For the superabsorbent resins of Examples and Comparative Examples, the pressure absorption amount was measured according to the method of EDANA method WAP 242.2.

The simple absorption capacity (AUP) is as follows.

That is, a 400 mesh wire mesh made of stainless steel was attached to the bottom of a plastic cylinder having an inner diameter of 60 mm. A piston capable of uniformly spraying 0.90 g of the water absorbent resin on the iron net and uniformly applying a load of 4.83 kPa (0.7 psi) under conditions of room temperature and humidity of 50% It has a small, cylindrical inner wall and no gap, so that the up and down movements are not disturbed. At this time, the weight Wa (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a Petro dish having a diameter of 150 mm and a physiological saline solution composed of 0.90% by weight sodium chloride was made to have the same level as the upper surface of the glass filter. And a filter paper having a diameter of 90 mm was placed thereon. The measuring device was placed on the filter paper and the liquid was absorbed under load for 1 hour. After one hour, the measuring device was lifted and its weight Wb (g) was measured.

Then, the pressure absorption ability was calculated from Wa and Wb according to the following equation.

[Equation 1]

AUP (g / g) = [Wb (g) - Wa (g)] / W (g)

In the above equation 1,

W (g) is the weight (g) of the water absorbent resin,

Wa (g) is the sum of the weight of the water absorbent resin and the weight of the apparatus capable of applying a load to the water absorbent resin,

Wb (g) is the sum of the weight of the water absorbed resin absorbed by water (physiological saline solution) supplied to the water absorbent resin for 1 hour under a load of 0.7 psi and the weight of the apparatus capable of applying a load to the water absorbent resin to be.

(2) CRC (Centrifuge Retention Capacity)

According to the EDANA method WSP 241.2, the water absorbency of the superabsorbent resins of the above Examples and Comparative Examples was measured by the zero-load absorption capacity.

That is, the resin W (g) (about 0.1 g) obtained in Examples and Comparative Examples was uniformly put in an envelope made of a nonwoven fabric and sealed, and then immersed in 0.9% by mass physiological saline solution at room temperature. After 30 minutes, the envelope was subjected to centrifugal separation at 250G for 3 minutes, and the weight W2 (g) of the envelope was measured. After the same operation was performed without using a resin, the mass W1 (g) at that time was measured. Using the obtained masses, CRC (g / g) was calculated according to the following equation.

[Equation 2]

CRC (g / g) = {(W2 (g) - W1 (g)) / W (g)

In the above equation 2,

W (g) is the weight (g) of the water absorbent resin,

W1 (g) is the weight of the device measured after immersing the nonwoven fabric bag in which the water absorbent resin is not impregnated into 0.9 wt% of physiological saline at room temperature for 30 minutes, dehydrating it at 250G for 3 minutes using a centrifugal separator,

W2 (g) is the weight of the apparatus measured by impregnating a nonwoven fabric bag with a water absorbent resin in 0.9% by weight of physiological saline at room temperature for 30 minutes and then dewatering for 3 minutes at 250 G using a centrifuge .

(3) saline flow conductivity (SFC)

The solution permeability was measured according to the method described in [0184] to [0189] of column 16 of U.S. Published Patent Application No. 2009-0131255.

(4) Gravimetric Determination of Permeability Dependent Absorption Under Pressure (PDAUP)

The properties of the products of the examples and comparative examples were analyzed for pressure-permeability (PDAUP) according to the method of EDANA WSP 243.1 of the European Disposables and Nonwovens Associa- tion (EDANA) standard. At this time, the pressure absorption ability was measured using an apparatus as shown in Fig.

First, a 400 mesh wire mesh made of stainless steel was attached to the bottom of a plastic cylinder having an inner diameter of 60 mm. The water absorbent resin W (g, 5.0 g) of Examples 1 and 2 and Comparative Examples 1 and 2 was uniformly sprayed on a iron mesh under conditions of room temperature and humidity of 50%, and a load of 4.83 kPa (0.7 psi) The outer diameter of the piston is slightly smaller than 60 mm, so that there is no gap between the inner wall of the cylinder and the up and down movements are not disturbed. At this time, the weight W ₃ (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a Petro dish having a diameter of 150 mm and a physiological saline solution composed of 0.9% by weight sodium chloride was made to have the same level as the upper surface of the glass filter. And a filter paper having a diameter of 90 mm was placed thereon. The measuring device was placed on the filter paper and the liquid was absorbed under load for 1 hour. After one hour, the measuring device was lifted and its weight W ₄ (g) was measured.

Using each mass thus obtained, PDAUP (g / g) was calculated according to the following equation (3) to confirm pressurized liquid permeability.

[Equation 3]

PDAUP (g / g) = [ W 4 (g) - W 3 (g)] / W (g)

In the above equation 3,

W (g) is the weight (g) of the water absorbent resin,

W ₃ (g) is the sum of the weight of the water absorbent resin and the weight of the apparatus capable of applying a load to the water absorbent resin,

W ₄ (g) represents the weight of the water absorbed resin absorbed after the water (physiological saline solution) is supplied to the water absorbent resin for 1 hour under a load of 0.7 psi and the weight of the apparatus capable of applying a load to the water absorbent resin Total.

(5) The permeability potential under pressure

The pressurized solution permeability (PPUP) was measured according to the following equation (4). The method can be interpreted as a high proportion indicating the high permeability of the gel formed during the test.

[Equation 4]

PPUP (%) = PDAUP / AUP x 100

In the above equation 4,

The PDAUP is pressurized liquid for physiological saline measured according to the method of EDANA WSP 243.1,

AUP is the amount of pressure absorbed by physiological saline solution measured according to the method of EDANA WAP 242.2.

Example  One

100 g of acrylic acid, 0.6 g of polyethylene glycol diacrylate as a cross-linking agent, 40.6 g of 50% caustic soda (NaOH) and 140 g of water were mixed to prepare a monomer composition.

Thereafter, the monomer composition was fed through a continuous kneader polymerization reactor and 2 g of a 10% hydrogen peroxide solution and 1 g of 10% ascorbic acid aqueous solution were added as a polymerization initiator to the monomer mixture.

The polymerization initiator was mixed, polymerization was started after 1 minute, and polymerization was continued for 15 minutes. At this time, the internal temperature of the reactor was 99 ° C. The polymerized hydrogel polymer was transferred to a cutter and then cut to 0.2 cm. At this time, the water content of the cut functional gel polymer was 50% by weight.

Thereafter, the polymer discharged from the cutter was dried for 1 hour in a hot-air drier at 180 ° C. Subsequently, the resultant was pulverized with a pin mill, and then classified into a polymer having a particle size of less than 150 μm and a polymer having a particle size of 150 μm to 850 μm using a sieve.

To 100 g of the base resin, a solution prepared by mixing 3.5 parts by weight of methanol, 2.8 parts by weight of distilled water, and 0.4 part by weight of ethylene carbonate was thoroughly mixed with 100 g of base resin and crosslinked in a convection oven at 180 ° C for 50 minutes. When the surface cross-linking reaction was completed, the resin was cooled to room temperature and a superabsorbent resin was prepared in a conventional manner. That is, after completion of the surface treatment, a surface-treated superabsorbent resin (Gel Strength 4700 Pa) having an average particle size of 150 to 850 탆 was obtained for the hydrogel polymer by using a sieve.

The thus prepared superabsorbent resin was 29.8 g / g of CRC, 26.1 g / g of AUP, 61 units of SFC, PDAUP 22.3 and 85.4% of PPUP. After completion of the surface cross-linking reaction, the residual amount of ethylene glycol as a decomposition product of ethylene carbonate was measured to be 0.08 parts by weight on the surface of the base resin.

Example  2

A solution prepared by mixing 2.8 parts by weight of distilled water and 1.0 part by weight of ethylene carbonate with 100 g of the base resin prepared in the same manner as in Example 1 was thoroughly mixed with 100 g of a base resin (Gel Strength 4700 Pa) Crosslinking reaction was carried out at a temperature of 45 minutes. When the surface cross-linking reaction was completed, the resin was cooled to room temperature and a superabsorbent resin was prepared in a conventional manner. That is, after completion of the surface treatment, a surface-treated superabsorbent resin having an average particle size of 150 to 850 탆 was obtained for the hydrogel polymer by using a sieve.

The thus prepared superabsorbent resin had a CRC of 30.5 g / g, an AUP of 25.1 g / g, an SFC of 55 units, a PDAUP of 21.8 and a PPUP of 86.9%. After completion of the surface cross-linking reaction, the residual amount of ethylene carbonate was measured at the surface of the base resin at 800 ppm.

Comparative Example  One

100 g of the base resin (CRC 36.4 g / g) was added to 100 g of the base resin prepared in the same manner as in Example 1, in which 3.5 parts by weight of methanol, 2.8 parts by weight of distilled water and 0.14 parts by weight of 1,3- Followed by crosslinking reaction in a convection oven at a temperature of 190 캜 for 40 minutes. When the surface cross-linking reaction was completed, the resin was cooled to room temperature and a superabsorbent resin was prepared in a conventional manner. That is, after completion of the surface treatment, a surface-treated superabsorbent resin having an average particle size of 150 to 850 탆 was obtained for the hydrogel polymer by using a sieve.

The thus prepared superabsorbent resin had a CRC of 30.0 g / g, an AUP of 26.1 g / g, an SFC of 35 units, a PDAUP of 19.1 and a PPUP of 73.2%. After completion of the surface cross-linking reaction, the residual amount of 1,3-propanediol was measured to be 1200 ppm on the surface of the base resin.

Comparative Example  2

100 g of the base resin (CRC 36.4 g / g) was mixed with 100 g of the base resin prepared in the same manner as in Example 1, in which 3.5 parts by weight of methanol, 2.8 parts by weight of distilled water and 0.7 parts by weight of 1,3- Followed by crosslinking reaction in a convection oven at a temperature of 190 캜 for 70 minutes. When the surface cross-linking reaction was completed, the resin was cooled to room temperature and a superabsorbent resin was prepared in a conventional manner. That is, after completion of the surface treatment, a surface-treated superabsorbent resin having an average particle size of 150 to 850 탆 was obtained for the hydrogel polymer by using a sieve.

The thus prepared superabsorbent resin was 30.8 g / g of CRC, 26.1 g / g of AUP, 30 units of SFC, PDAUP 18.6 and 71.3% of PPUP. After completion of the surface cross-linking reaction, the residual amount of 1,3-propanediol was measured at 2800 ppm on the surface of the base resin.

From the above results, the examples of the present invention exhibited excellent liquid-permeability characteristics as compared with the comparative examples, and the physical properties of the superabsorbent resin were improved.

Claims (9)

Forming a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator;
Polymerizing the monomer composition in a polymerization reactor to produce a hydrogel polymer;
Drying the mixture of hydrogel polymers;
Pulverizing the dried polymer; And
Classifying the pulverized hydrogel polymer to prepare a base resin;
And surface treating the base resin,
In the surface-treating step, a surface cross-linking agent; And water, the surface-treating step is carried out through surface cross-linking reaction of the mixture of hydrogel polymer at 180 to 195 degrees and 50 to 70 minutes, Or the residual amount of the degradation product derived therefrom is 0.1 parts by weight or less,
Wherein the surface cross-linking agent is an alkylene carbonate having 3 to 4 carbon atoms and is used in an amount of 0.4 to 1 part by weight based on 100 parts by weight of the base resin,
The gel strength of the base resin is 4500 to 5500 Pa,
Wherein the saline flow conductivity (SFC) is at least 50 to 61 units, and the centrifugal separation performance (CRC) against physiological saline measured according to EDANA method WSP 241.2 is 27 to 30 g / g.
The method according to claim 1,
Wherein the residual amount of the surface cross-linking agent or the degradation product derived therefrom is 0.01 to 0.1 parts by weight based on 100 parts by weight of the base resin after the step of surface-treating.
delete The method according to claim 1,
(PDAUP) of 20 to 22.3 g / g for physiological saline measured according to the method of EDANA WSP 243.1, and a pressure-water permeability (PPUP) of 80% to 86.9% calculated by the following equation Gt;
[Equation 4]
PPUP (%) = PDAUP / AUP x 100
(In the above equation 4,
The PDAUP is pressurized liquid for physiological saline measured according to the method of EDANA WSP 243.1,
AUP is the amount of pressure absorption for physiological saline measured according to the method of EDANA WAP 242.2)
delete delete delete The water-soluble ethylenically unsaturated monomer according to claim 1, wherein the water-
(Meth) acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2- methacryloylethanesulfonic acid, 2- ) Anionic monomers of acrylamido-2-methylpropanesulfonic acid and its salts; (Meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate or polyethylene glycol Non-ionic hydrophilic-containing monomer of (meth) acrylate; And at least one selected from the group consisting of an unsaturated monomer containing an amino group of (N, N) -dimethylaminoethyl (meth) acrylate or (N, N) -dimethylaminopropyl (meth) By weight.
The method according to claim 1, wherein the polymerization initiator
A thermal polymerization initiator selected from the group consisting of an azo-based initiator, a peroxide-based initiator, a redox-based initiator, an organic halide initiator and a persulfate-
A photopolymerization initiator selected from the group consisting of acetophenone, benzoin, benzophenone, benzyl compounds and derivatives thereof.