Preparation method of super absorbent polymer

Abstract

The present disclosure relates to a preparation method of a super absorbent polymer capable of improving absorption performance of the super absorbent polymer by adding a simple additive later. The preparation method includes the steps of: forming a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; forming a surface cross-linked layer by further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent, adding a monovalent to trivalent metal cation on the surface cross-linked base resin powder at a temperature of 25° C. to 80° C., and maintaining and aging the resulting metal cation-added product at a temperature of 40° C. to 60° C. for 10 to 30 minutes.

Claims

1. A preparation method of a super absorbent polymer, comprising: forming a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; forming a surface cross-linked layer by further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent, adding a monovalent to trivalent metal cation on the surface cross-linked base resin powder at a temperature of 25° C. to 80° C., and maintaining and aging a resulting metal cation-added product at a temperature of 40° C. to 60° C. for 10 to 30 minutes, wherein an absorbency of the super absorbent polymer measured after the aging is increased by 0.2 to 3 g/g with respect to the absorbency measured immediately before the metal cation addition, wherein the absorbency is defined by Equation 1:
Absorbency=CRC+AUP  [Equation 1] in Equation 1, CRC is centrifuge retention capacity to saline for 30 min, and AUP is absorbency under pressure to the saline at 0.7 psi for 1 hour, wherein the saline is a 0.9 wt % aqueous solution of sodium chloride.

2. The preparation method of a super absorbent polymer of claim 1, wherein the water-soluble ethylene-based unsaturated monomer comprises at least one of: an anionic monomer selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, fumalic acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethane sulfonic acid, 2-(meth)acryloylpropane sulfonic acid, 2-(meth)acrylamide-2-methyl propane sulfonic acid, and a salt thereof; a nonionic hydrophilic monomer selected from the group consisting of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, methoxypolyethyleneglycol(meth)acrylate, and polyethyleneglycol(meth)acrylate; or an amino-containing unsaturated monomer of (N,N)-dimethylaminoethyl(meth)acrylate (N,N)-dimethylaminopropyl(meth)acrylamid, and a quaternary compound thereof.

3. The preparation method of a super absorbent polymer of claim 1, wherein the internal cross-linking agent comprises at least one of N,N′-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethyleneglycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, propyleneglycol di(meth)acrylate, polypropyleneglycol (meth)acrylate, butanediol di(meth)acrylate, butyleneglycol di(meth)acrylate, diethyleneglycol di(meth)acrylate, hexanediol di(meth)acrylate, triethyleneglycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, propylene glycol, or glycerin.

4. The preparation method of a super absorbent polymer of claim 1, wherein the classified base resin powder has a particle diameter of 150 to 850 μm.

5. The preparation method of a super absorbent polymer of claim 1, wherein the surface cross-linking agent comprises at least one of ethyleneglycol diglycidylether, polyethyleneglycol diglycidylether, glycerol polyglycidyl ether, propyleneglycol diglycidyl ether, polypropyleneglycol diglycidyl ether, ethylene carbonate, propylene carbonate, butylene carbonate, trimethylene carbonate, glycerol carbonate, ethyleneglycol, diethyleneglycol, propyleneglycol, triethylene glycol, tetraethylene glycol, propanediol, dipropyleneglycol, polypropyleneglycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol trimethylolpropane, pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, or iron chloride.

6. The preparation method of a super absorbent polymer of claim 1, wherein the metal cation comprises at least one of Na+, K+, Li+, Zn.sup.2+, mg.sup.2+, Ca.sup.2+, and Al.sup.3+.

7. The preparation method of a super absorbent polymer of claim 1, wherein the metal cation addition is performed by spraying an aqueous solution containing the metal cation onto the surface cross-linked base resin powder, or by dry-mixing a salt of the metal cation in solid state with the surface cross-linked base resin powder and adding water.

8. The preparation method of a super absorbent polymer of claim 7, wherein the aqueous solution containing the metal cation is an aqueous solution in which at least one metal cation-containing compound selected from the group consisting of oxides, hydroxides, acetates, carbonates, sulfates and halogen salts of the metal cation is dissolved in an aqueous medium.

9. The preparation method of a super absorbent polymer of claim 7, wherein the salt of the metal cation is at least one salt compound selected from the group consisting of oxides, hydroxides, acetates, carbonates, sulfates and halogen salts of the metal cation.

10. The preparation method of a super absorbent polymer of claim 8, wherein the metal cation-containing compound or the salt of the metal cation is added in an amount of 0.1 to 3 parts by weight based on 100 parts by weight of the surface cross-linked base resin powder.

11. The preparation method of a super absorbent polymer of claim 1, wherein an ionic functional group of —COO— deprotonated by the metal cation is formed on a surface of the super absorbent polymer.

12. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has a moisture content of 0.8 to 1.5 wt % after the aging.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

Example 1

(2) After adding 500 g of acrylic acid, 3 g of polyethyleneglycol diacrylate and 0.04 g of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide to a 3 L glass container equipped with a stirrer, a nitrogen injector, and a thermometer to dissolve, 896.4 g of 24.5 wt % sodium hydroxide solution was added thereto to prepare a water-soluble unsaturated monomer aqueous solution while continuously introducing nitrogen. The water-soluble unsaturated monomer aqueous solution was cooled to 45° C. 500 g of this aqueous solution was added to a stainless steel container having a width of 250 mm, a length of 250 mm, and a height of 30 mm. Then, UV polymerization was performed for 60 seconds by irradiating ultraviolet rays (irradiation amount: 10 mV/cm.sup.2) to prepare a hydrogel polymer. After pulverizing the obtained hydrogel polymer to a size of 2 mm*2 mm, the moisture content was measured to be 40.1%.

(3) The obtained gel-type resin was spread on a stainless wire gauze having a pore size of 600 μm to a thickness of about 30 mm and dried in a 180° C. hot air oven for 30 minutes. The dried polymer thus obtained was pulverized using a pulverizer, and classified using an ASTM standard mesh to obtain a base resin powder having a particle diameter of 150 to 850 μm.

(4) 1 parts by weight of ethylene carbonate, 4 parts by weight of water, and 0.02 parts by weight of silica were sprayed onto 100 parts by weight of the base resin powder for mixing, and placed in a container equipped with a stirrer and a double jacket to perform a surface cross-linking reaction at 185° C. for 60 minutes. Thereafter, the surface-treated powder was classified using an ASTM standard mesh to obtain a super absorbent polymer powder having a particle diameter of 150 to 850 μm.

(5) After the surface cross-linking was performed by the above-described method, 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface cross-linked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 25° C.

(6) Thereafter, a super absorbent polymer of Example 1 was prepared by aging/maintaining at a temperature of 50° C. for 15 minutes.

Example 2

(7) Up to the surface cross-linking, the same method as in Example 1 was applied.

(8) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 25° C.

(9) Thereafter, a super absorbent polymer of Example 2 was prepared by aging/maintaining at a temperature of 50° C. for 25 minutes.

Example 3

(10) Up to the surface cross-linking, the same method as in Example 1 was applied.

(11) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 40° C.

(12) Thereafter, a super absorbent polymer of Example 3 was prepared by aging/maintaining at a temperature of 50° C. for 15 minutes.

Example 4

(13) Up to the surface cross-linking, the same method as in Example 1 was applied.

(14) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 40° C.

(15) Thereafter, a super absorbent polymer of Example 4 was prepared by aging/maintaining at a temperature of 50° C. for 25 minutes.

Example 5

(16) Up to the surface cross-linking, the same method as in Example 1 was applied.

(17) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 70° C.

(18) Thereafter, a super absorbent polymer of Example 5 was prepared by aging/maintaining at a temperature of 50° C. for 15 minutes.

Comparative Example 1

(19) Up to the surface cross-linking, the same method as in Example 1 was applied.

(20) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 140° C.

(21) Thereafter, a super absorbent polymer of Comparative Example 1 was prepared by aging/maintaining at a temperature of 50° C. for 15 minutes.

Comparative Example 2

(22) Up to the surface cross-linking, the same method as in Example 1 was applied.

(23) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 140° C.

(24) Thereafter, a super absorbent polymer of Comparative Example 2 was prepared by aging/maintaining at a temperature of 50° C. for 25 minutes.

Comparative Example 3

(25) Up to the surface cross-linking, the same method as in Example 1 was applied.

(26) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 100° C.

(27) Thereafter, a super absorbent polymer of Comparative Example 3 was prepared by aging/maintaining at a temperature of 50° C. for 15 minutes.

Comparative Example 4

(28) Up to the surface cross-linking, the same method as in Example 1 was applied.

(29) 1.5 parts by weight of an aqueous solution in which 5 wt % sodium hydroxide was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 40° C.

(30) Thereafter, a super absorbent polymer of Comparative Example 4 was prepared by aging/maintaining at a temperature of 60° C. for 45 minutes.

Example 6

(31) Up to the surface cross-linking, the same method as in Example 1 was applied.

(32) 1.5 parts by weight of an aqueous solution in which 15 wt % sodium carbonate was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 25° C.

(33) Thereafter, a super absorbent polymer of Example 6 was prepared by aging/maintaining at a temperature of 40° C. for 30 minutes.

Example 7

(34) Up to the surface cross-linking, the same method as in Example 1 was applied.

(35) 1.5 parts by weight of an aqueous solution in which 15 wt % sodium carbonate was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 80° C.

(36) Thereafter, a super absorbent polymer of Example 7 was prepared by aging/maintaining at a temperature of 40° C. for 30 minutes.

Example 8

(37) Up to the surface cross-linking, the same method as in Example 1 was applied.

(38) 1.5 parts by weight of an aqueous solution in which 20 wt % zinc acetate was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 40° C.

(39) Thereafter, a super absorbent polymer of Example 8 was prepared by aging/maintaining at a temperature of 40° C. for 30 minutes.

Example 9

(40) Up to the surface cross-linking, the same method as in Example 1 was applied.

(41) 1.5 parts by weight of an aqueous solution in which 15 wt % magnesium acetate was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 40° C.

(42) Thereafter, a super absorbent polymer of Example 9 was prepared by aging/maintaining at a temperature of 40° C. for 30 minutes.

Example 10

(43) Up to the surface cross-linking, the same method as in Example 1 was applied.

(44) 1.5 parts by weight of an aqueous solution in which 10 wt % potassium carbonate was dissolved was added to 100 parts by weight of the surface-crosslinked resin powder by spraying. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 40° C.

(45) Thereafter, a super absorbent polymer of Example 10 was prepared by aging/maintaining at a temperature of 40° C. for 30 minutes.

Example 11

(46) Up to the surface cross-linking, the same method as in Example 1 was applied.

(47) 100 parts by weight of the surface cross-linked base resin powder was dry-mixed with 1.5 parts by weight of calcium carbonate powder, and 1.5 parts by weight of water was further mixed. Upon this addition, a temperature of the surface of the surface cross-linked base resin powder was adjusted to 25° C.

(48) Thereafter, a super absorbent polymer of Example 11 was prepared by aging/maintaining at a temperature of 40° C. for 30 minutes.

Experimental Examples

(49) The physical properties of each super absorbent polymer prepared in Examples and Comparative Examples were measured and evaluated in the following manner.

(50) (1) Moisture Content

(51) The super absorbent polymer was heated at 140° C. for 10 minutes. The weight of the super absorbent polymer was measured before and after heating, respectively, and the moisture content was calculated according to the following formula: “Moisture content (wt %)=(weight of super absorbent polymer before heating−weight of super absorbent polymer after heating)/weight of super absorbent polymer before heating*100”

(52) (2) Centrifuge Retention Capacity (CRC)

(53) The centrifuge retention capacity (CRC) by absorption ratio under a non-loading condition was measured according to the EDANA (European Disposables and Nonwovens Association) WSP 241.3 method. After inserting W.sub.0 (g, about 0.2 g) of the super absorbent polymer uniformly in a nonwoven fabric envelope and sealing the same, it was soaked in saline (0.9 wt % aqueous solution of sodium chloride) at room temperature. After 30 min, the envelope was centrifuged at 250 G for 3 minutes to drain, and the weight W.sub.2 (g) of the envelope was measured. Further, after carrying out the same operation without using the super absorbent polymer, the weight W.sub.1 (g) of the envelope was measured. Then, CRC (g/g) was calculated by using the obtained weight values according to the following Formula 1, and the water retention capacity was confirmed.
CRC(g/g)={[W.sub.2(g)−W.sub.1(g)−W.sub.0(g)]/W.sub.0(g)}  [Formula 1]

(54) (3) Absorbency Under Pressure (AUP)

(55) The absorbency under pressure (AUP) of each super absorbent polymer prepared in Examples and Comparative Examples was measured according to the EDANA (European Disposables and Nonwovens Association) WSP 242.3 method.

(56) First, a 400 mesh stainless steel screen was installed in a cylindrical bottom of a plastic having an inner diameter of 60 mm. W.sub.0 (g, 0.90 g) of the polymer prepared in each of Examples 1 to 6 and Comparative Examples 1 to 4 was uniformly scattered on the screen at a temperature of 23±2 t and a relative humidity of 45%. Thereafter, a piston which can uniformly provide a load of 4.83 kPa (0.7 psi) was placed on the polymer. Herein, the outer diameter of the piston was slightly smaller than 60 mm, there was no gap with the inner wall of the cylinder, and jig-jog of the cylinder was not interrupted. At this time, the weight W.sub.3 (g) of the device was measured.

(57) Subsequently, a glass filter having a diameter of 125 mm and a thickness of 5 mm was placed in a petri dish having a diameter of 150 mm, and saline (0.9 wt % sodium chloride) was poured in the dish. At this time, the saline was poured until the surface level of the saline became equal to the upper surface of the glass filter. After the measuring device was mounted on the glass filter, the liquid was absorbed for 1 hour under a load. After 1 hour, the measuring device was lifted, and the weight W.sub.4 (g) was measured.

(58) Then, AUP (g/g) was calculated by using the obtained weight values according to the following Formula 2.
AUP(g/g)=[W.sub.4(g)−W.sub.3(g)]/W.sub.0(g)  [Formula 2]

(59) In Formula 2,

(60) W.sub.0 (g) is an initial weight (g) of the super absorbent polymer,

(61) W.sub.3 (g) is a sum of a weight of the super absorbent polymer and a weight of the device providing a load to the polymer, and

(62) W.sub.4 (g) is a sum of a weight of the super absorbent polymer and a weight of the device providing a load to the polymer, after making the super absorbent polymer absorb the saline for one hour under a load (0.7 psi).

(63) (4) Difference in Absorbency

(64) The above-described centrifuge retention capacity and absorbency under pressure were first measured between the surface cross-linking and adding the metal cation, and then measured again after the aging step. Then, the absorbency was calculated by Equation 1 below from the centrifuge retention capacity and absorbency under pressure measured first and second, respectively, and a difference between the second measured absorbency and the first measured absorbency was obtained:
Absorbency=CRC+AUP  [Equation 1]

(65) in Equation 1,

(66) CRC is centrifuge retention capacity to saline (0.9 wt % aqueous solution of sodium chloride) for 30 min, and

(67) AUP is absorbency under pressure to saline (0.9 wt % aqueous solution of sodium chloride) at 0.7 psi for 1 hour.

(68) The physical properties of Examples 1 to 11 and Comparative Examples 1 to 4 measured according to the above methods are summarized in Table 1 below.

(69) TABLE-US-00001 TABLE 1 Moisture content Difference in (wt %) absorbency (g/g) Example 1 1.11 0.7 Example 2 0.98 0.4 Example 3 1.09 1.0 Example 4 0 1.0 Example 5 0.85 0.4 Comparative 0.62 −0.2 Example 1 Comparative 0 0 Example 2 Comparative 0.65 −0.2 Example 3 Comparative 0.46 −0.2 Example 4 Example 6 1.05 0.3 Example 7 1.13 2.1 Example 8 1.21 0.4 Example 9 1.32 0.5  Example 10 1.09 0.5  Example 11 0.98 0.6

(70) Referring to Table 1, the improvement in absorbency after the metal cation addition step and the aging step was clearly confirmed in Examples 1 to 11. On the other hand, there was no improvement in absorbency, or rather, there was a decrease in absorbency in Comparative Examples 1 to 4 despite the addition of the metal cation, since the temperature at the time of addition was too high or the aging conditions were out of the preferred range.