Super absorbent polymer

Abstract

The present invention relates to a super absorbent polymer which maintains excellent absorption performance and retains physical properties even after being physically damaged by an external force. The super absorbent polymer comprises: a base polymer powder including a first cross-linked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups; and a surface cross-linked layer formed on the base polymer powder and including a second cross-linked polymer in which the first cross-linked polymer is further cross-linked via an alkylene carbonate having 2 to 5 carbon atoms, wherein the super absorbent polymer satisfies predetermined physical properties.

Claims

1. A super absorbent polymer comprising: a base polymer powder including a first cross-linked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups; and a surface cross-linked layer formed on the base polymer powder and including a second cross-linked polymer in which the first cross-linked polymer is further cross-linked via the second cross-linked polymer, where the second cross-linked polymer comprises an alkylene carbonate having 2 to 5 carbon atoms, hydrophilic silica particles having a water-contact angle of 10 or less, and hydrophobic silica particles having a water-contact angle of more than 10, wherein the hydrophilic and hydrophobic silica particles are dispersed in the surface cross-linked polymer layer, wherein the super absorbent polymer has the following features: an EFFC represented by the following Formula 1 is 25 to 30 g/g, a saline flow conductivity (SFC) for a physiological saline solution (0.685 wt % sodium chloride aqueous solution) (.Math.10.sup.7 cm.sup.3.Math.s/g) is 100 to 130 (.Math.10.sup.7 cm.sup.3.Math.s/g), and a SFC(.Math.10.sup.7 cm.sup.3.Math.s/g) measured after crushing the super absorbent polymer powder by a crushing method using a paint shaker is 70 to 100(.Math.10.sup.7 cm.sup.3.Math.s/g),
EFFC=(CRC+AUP)/2[Formula 1] in Formula 1, CRC represents a centrifuge retention capacity for a physiological saline solution (0.9 wt % sodium chloride aqueous solution) of the super absorbent polymer for 30 minutes, and AUP represents an absorbency under pressure under 0.7 psi for a physiological saline solution (0.9 wt % sodium chloride aqueous solution) of the super absorbent polymer for 1 hour.

2. A super absorbent polymer comprising: a base polymer powder including a first cross-linked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups; a surface cross-linked layer formed on the base polymer powder and including a second cross-linked polymer in which the first cross-linked polymer is further cross-linked via the second cross-linked polymer, wherein the second cross-linked polymer comprises an alkylene carbonate having 2 to 5 carbon atom; and hydrophobic silica particles having a water-contact angle of more than 10, and hydrophilic silica particles having a water-contact angle of less than 10, wherein the hydrophilic and hydrophobic silica particles are dispersed in the surface cross-linked polymer layer, wherein the super absorbent polymer has the following features: an EFFC represented by the following Formula 1 is 25 to 30 g/g, and an EFFC measured after crushing the super absorbent polymer powder by a crushing method using a paint shaker is 25 to 30 g/g,
EFFC=(CRC+AUP)/2[Formula 1] in Formula 1, CRC represents a centrifuge retention capacity for a physiological saline solution (0.9 wt % sodium chloride aqueous solution) for 30 minutes, and AUP represents an absorbency under pressure under 0.7 psi for a physiological saline solution (0.9 wt % sodium chloride aqueous solution) for 1 hour.

3. The super absorbent polymer of claim 1, wherein CRC of the super absorbent polymer is 25 to 35 g/g.

4. The super absorbent polymer of claim 1, wherein AUP of the super absorbent polymer is 24 to 30 g/g.

5. The super absorbent polymer of claim 1, wherein an EFFC measured after crushing the super absorbent polymer powder by a crushing method using a paint shaker is 25 to 30 g/g.

6. The super absorbent polymer of claim 1, wherein the water-soluble ethylenically unsaturated monomer includes at least one selected from the group consisting of anionic monomers, non-ionic, hydrophilic group-containing monomers, and amino group-containing unsaturated monomers and their quaternary product.

7. The super absorbent polymer of claim 1, wherein the first cross-linked polymer includes a polymer in which the monomer is subjected to a crosslinking polymerization in the presence of at least one internal crosslinking agent selected form the group consisting of bis(meth)acrylamide having 8 to 12 carbon atoms, polyol of poly(meth)acrylate having 2 to 10 carbon atoms, and poly(meth)acrylate having 2 to 10 carbon atoms.

8. The super absorbent polymer of claim 1, wherein it has a particle size of 150 to 850 m.

9. The super absorbent polymer of claim 2, wherein CRC of the super absorbent polymer is 25 to 35 g/g.

10. The super absorbent polymer of claim 2, wherein AUP of the super absorbent polymer is 24 to 30 g/g.

11. The super absorbent polymer of claim 2, wherein the first cross-linked polymer includes a polymer in which the monomer is subjected to a crosslinking polymerization in the presence of at least one internal crosslinking agent selected form the group consisting of bis(meth)acrylamide having 8 to 12 carbon atoms, polyol of poly(meth)acrylate having 2 to 10 carbon atoms and poly(meth)acrylate having 2 to 10 carbon atoms.

12. The super absorbent polymer of claim 6, wherein the anionic monomers is 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)acryloylpropanesulfonic acid or 2-(meth)acrylamido-2-methylpropanesulfonic acid, salts thereof, and mixtures thereof.

13. The super absorbent polymer of claim 6, wherein the non-ionic, hydrophilic group-containing monomers are selected from the group consisting of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, methoxypolyethylene glycol(meth)acrylate, polyethylene glycol (meth)acrylate, and mixtures thereof.

14. The super absorbent polymer of claim 6, wherein the amino group-containing unsaturated monomers are selected from the group consisting of (N,N)-dimethylaminoethyl(meth)acrylate, (N,N)-dimethylaminopropyl(meth)acrylamide, their quaternary products thereof, and mixtures thereof.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, the preferred Examples are provided for better understanding of the invention. However, these Examples are given for illustrative purposes only and not intended to limit the scope of the present invention.

(2) In Examples and Comparative Examples, the water-contact angles of hydrophobic silica particles and hydrophilic silica particles were measured as follows.

(3) First, a coating solution in which the hydrophobic silica particles were dispersed in a methylene chloride solvent in the concentration of 5% by weight was used. After spin-coating the coating solution on a wafer, water was dropped onto the coating layer, and the contact angle was measured. The contact angle thus measured is defined as a water-contact angle of the hydrophobic silica particles, and the measured values are shown in Table 1 below.

(4) Further, in the case of hydrophilic silica particles, the water-contact angle was measured in the same manner as in the case of the hydrophobic silica particles, except that a coating liquid dispersed in water at a concentration of 20% by weight was used.

(5) TABLE-US-00001 TABLE 1 Water contact angle Silica particles Product name () Hydrophobic silica particles Aerosil 200 14 Hydrophilic silica particles ST-O 3

(6) In the following Examples and Comparative Examples, the physical properties of each super absorbent polymer were measured and evaluated by the following methods.

(7) (1) Evaluation of Particle Size

(8) The particle sizes of the base polymer powders and the super absorbent polymers used in Examples and Comparative Examples were measured in accordance with EDANA (European Disposables and Nonwovens Association) recommended test method No. WSP 220.3.

(9) (2) CRC (Centrifuge Retention Capacity)

(10) For the absorbent polymer prepared in Examples and Comparative Examples, the centrifuge retention capacity (CRC) by absorption magnification under a non-loading condition was measured in accordance with EDANA (European Disposables and Nonwovens Association) recommended test method No. WSP 241.3.

(11) That is, after uniformly inserting W.sub.0(.sub.g) (about 0.2 g) of each polymer obtained in Examples and Comparative Examples in a nonwoven fabric-made bag and sealing the same, it was soaked in a physiological saline solution composed of 0.9 wt % sodium chloride aqueous solution at room temperature. After 30 minutes, water was removed from the bag by centrifugation at 250 G for 3 minutes, and the weight W.sub.2(g) of the bag was then measured. Further, the same procedure was carried out without using the polymer, and then the resultant weight W.sub.1(g) was measured.

(12) Using the respective weights thus obtained, the CRC(g/g) was determined according to the following Calculation Equation 1.
CRC(g/g)={[W.sub.2(g)W.sub.1(g)W.sub.0(g)]/W.sub.0(g)}[Calculation Equation 1]

(13) in Calculation Equation 1,

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

(15) W.sub.1(g) is a weight of the device not including the super absorbent polymer, measured after soaking the same in a physiological saline solution for 30 minutes and dehydrating the same by using a centrifuge at 250 G for 3 minutes, and

(16) W.sub.2(g) is a weight of the device including the super absorbent polymer, measured after soaking the same in a physiological saline solution at room temperature for 30 minutes, and then dehydrating the same by using a centrifuge at 250 G for 3 minutes.

(17) (3) Absorbency Under Pressure (AUP)

(18) For the absorbent polymer prepared in Examples and Comparative Examples, the absorbency under pressure was measured in accordance with EDANA (European Disposables and Nonwovens Association) recommended test method No. WSP 242.3.

(19) First, a 400 mesh stainless steel net was installed in the cylindrical bottom of a plastic having an internal diameter of 60 mm. W.sub.0(g, 0.90 g) of the absorbent polymers prepared in Examples 1-2 and Comparative Examples 1-3 were uniformly scattered on the steel net under conditions of temperature of 232 C. and relative humidity of 45%, and a piston which can further provide a load of 4.83 kPa (0.7 psi) uniformly was put thereon. The external diameter of the piston was slightly smaller than 60 mm, there was no gap between the cylindrical internal wall and the piston, and the jig-jog of the cylinder was not interrupted. At this time, the weight W.sub.3(g) of the device was measured.

(20) After putting a glass filter having a diameter of 125 mm and a thickness of 5 mm in a Petri dish having a diameter of 150 mm, a physiological saline solution composed of 0.90 wt % of sodium chloride was poured in the dish until the surface level became equal to the upper surface of the glass filter. A sheet of filter paper having a diameter of 120 mm was put thereon. The measuring device was put on the filter paper and the solution was absorbed under a load for 1 hour. After 1 hour, the weight W.sub.4(g) was measured after lifting the measuring device up.

(21) Using the respective mass fractions thus obtained, AUP(g/g) was calculated according to the following Calculation Equation 2, thereby confirming the absorbency under pressure.
AUP(g/g)=[W.sub.4(g)W.sub.3(g)]/W.sub.0(g)[Calculation Equation 2]

(22) in Calculation Equation 2,

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

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

(25) W.sub.4(g) is the total sum of a weight of the super absorbent polymer and a weight of the device capable of providing a load to the super absorbent polymer, after absorbing a physiological saline solution to the super absorbent polymer under a load (0.7 psi) for 1 hour.

(26) (4) Saline Flow Conductivity (SFC)

(27) The saline flow conductivity was measured in accordance with the method disclosed in paragraphs [0184] to [0189] of Column 16 of U.S. patent application publication no. 2009-0131255.

(28) (5) Physical Property Evaluation after Crushing

(29) After each super absorbent polymer was crushed by the crushing method using a paint shaker as follows, the particle size, CRC, AUP and SFC were evaluated by the above-mentioned method.

(30) First, two 500 ml glass containers were prepared. After taking the super absorbent polymer W.sub.0 (100 g) obtained in each of Examples and Comparative Examples, the initial particle size distribution of the polymer powder having a particle size of 150 to 850 m was measured. The weight W.sub.1 (50 g) of the polymer was measured in the same amount as the particle size distribution thus measured, and all was placed in the glass container. Thereafter, glass beads (particle diameter: 3 mm) W.sub.2 (10 g) were placed in the glass container. For the structural balance of the paint shaker, two samples could be fixed, so that the same experiment could be performed twice.

(31) The prepared polymer sample was fixed and then stirred in a paint shaker for 1 hour. The particle size of 150 to 850 m was measured once again for the stirred sample, and the particle size distribution changed based on the initial polymer W.sub.0 (100 g) was measured and calculated. After confirming the particle size distribution, all of the samples were collected, and the physical properties were re-measured in accordance with the above-described method.

Example 1

(32) 100 g of acrylic acid, 0.5 g of polyethylene glycol diacrylate (Mw=523) as a crosslinking agent, 83.3 g of 50% caustic soda (NaOH), and 89.8 g of water were mixed to prepare a monomer aqueous solution composition having a monomer concentration of 45% by weight.

(33) Subsequently, 810 g of the monomer aqueous solution was first mixed with 30.54 g of a 0.18% ascorbic acid solution and 33 g of a 1% sodium persulfate solution, and the mixture was fed through a feed section of a continuous polymerization reactor with a kneader, together with 30.45 g of a 0.15% hydrogen peroxide solution, so as to perform polymerization. At this time, temperature of the polymerization reactor was maintained at 80 C., and the maximum polymerization temperature was 110 C. and the polymerization time was 1 min and 15 s. Thereafter, kneading was continuously performed, and polymerization and kneading were performed for 20 min. Thereafter, the size of the polymer produced was distributed to less than 0.2 cm. At this time, the water content of the hydrogel polymer finally formed was 51% by weight.

(34) Subsequently, the resulting hydrogel polymer was dried in a hot-air dryer at a temperature of 180 C. for 30 minutes, and the dried hydrogel polymer was pulverized with a pin mill. Then, the polymer having a particle size of less than about 150 m and the polymer powder having a particle size of about 150 m to 850 m were classified using a sieve.

(35) A surface treatment liquid containing 0.02 wt % of hydrophobic silica particles (Aerosil 200), 0.02 wt % of hydrophilic silica particles (ST-O), 1 wt % of ethylene carbonate and 4 wt % of water as a solvent based on the weight of the classified base polymer powder was formed. This surface crosslinking liquid was sprayed onto the base polymer powder, stirred at room temperature, and mixed so that the surface treatment liquid was evenly distributed on the base polymer powder. Then, the base polymer powder was put in a surface crosslinking reactor and the surface crosslinking reaction was carried out.

(36) In the surface crosslinking reactor, it was confirmed that the base polymer powder was gradually heated at an initial temperature near 120 C. After 20 minutes elapsed, operation was performed so as to reach the maximum reaction temperature of 190 C. After reaching the maximum reaction temperature, additional reaction was carried out for 40 minutes, and a sample of the finally produced super absorbent polymer was taken. After the surface crosslinking step, a surface cross-linked super absorbent polymer having a particle size of about 150 m to about 850 m was obtained using a sieve.

Example 2

(37) A base polymer powder was prepared in the same manner as in Example 1.

(38) Thereafter, based on the weight of the classified base polymer powder, 0.05 wt % of hydrophobic silica particles (Aerosil 200) was mixed by a method of directly charging in a high-speed mixer, and dry-treated to the base polymer powder. Then, a surface treatment liquid containing 0.02 wt % of hydrophobic silica particles (Aerosil 200), 1 wt % of ethylene carbonate and 4 wt % of water as a solvent based on the weight of the base polymer powder was formed. This surface crosslinking liquid was sprayed onto the base polymer powder, stirred at room temperature, and mixed so that the surface treatment liquid was evenly distributed on the base polymer powder. Then, the base polymer powder was put in a surface crosslinking reactor and the surface crosslinking reaction was carried out.

(39) In the surface crosslinking reactor, it was confirmed that the base polymer powder was gradually heated at an initial temperature near 120 C. After 20 minutes elapsed, operation was performed so as to reach the maximum reaction temperature of 190 C. After reaching the maximum reaction temperature, additional reaction was carried out for 40 minutes, and a sample of the finally produced super absorbent polymer was taken. After the surface crosslinking step, a surface cross-linked super absorbent polymer having a particle size of about 150 m to 850 m was obtained using a sieve.

Comparative Example 1

(40) A super absorbent polymer was prepared in the same manner as in Example 1, except that hydrophobic and hydrophilic silica particles were not included in the surface crosslinking liquid.

Comparative Example 2

(41) A super absorbent polymer was prepared in the same manner as in Example 1, except that hydrophobic silica particles were not included in the surface crosslinking liquid.

Comparative Example 3

(42) A super absorbent polymer was prepared in the same manner as in Example 1, except that that hydrophobic and hydrophilic silica particles were not included, and 0.05 wt % of the metal compound containing the polyvalent metal cation of aluminum was included.

(43) For the super absorbent polymers of Examples 1 to 2 and Comparative Examples 1 to 4, the measurement and evaluation of the particle size distribution, CRC, AUP, SFC, and respective physical properties before and after crushing were carried out, and the measured physical property values are shown in Table 2 below. Further, EFFC values of Formula 1 were calculated from the measured CRC and AUP before and after the crushing, and the results are shown together in the following Table 2 below.

(44) TABLE-US-00002 TABLE 2 Particle size distribution (m) Physical property More Less SFC than than CRC AUP EFFC (10.sup.7 850 600~850 300~600 150~300 150 (g/g) (g/g) (g/g) cm.sup.3 .Math. s/g Example 1 before 0.08 13.24 67.88 17.71 1.1 26.7 24.6 25.7 102 crushing after 0.02 9.5 64.5 22.67 3.31 27.0 24.7 25.9 74 crushing Example 2 before 1.67 16.03 65.36 15.47 1.47 27.0 24.2 25.6 103 crushing after 0.48 12.63 66.62 18.27 2.0 27.0 24.0 25.5 80 crushing Comparative before 7.1 17.76 63.06 11.2 0.88 26.1 24.1 25.1 95 Example 1 crushing after 1.41 12.04 67.96 16.78 1.81 25.1 22.7 23.9 69 crushing Comparative before 1.01 12.04 65.52 20.58 0.85 26.7 24.5 25.6 90 Example 2 crushing after 0.45 6.90 64.91 25.44 2.30 25.8 22.3 24.1 60 crushing Comparative before 0 20.56 67.1 11.56 0.78 24.5 22.7 23.6 95 Example 3 crushing after 0 9.77 65.2 22.13 2.9 22.5 21.5 22.0 65 crushing

(45) Referring to Table 2, it was confirmed that the super absorbent polymers of Examples exhibited excellent absorption performance such as EFFC, and excellent and liquid permeability, and further maintained excellent absorption performance and liquid permeability even after physical damage due to an external force.

(46) On the other hand, it was confirmed that the super absorbent polymers of Comparative Examples exhibited poor liquid permeability before and after the crushing or that the absorption performance after crushing was low.