Superabsorbent polymer

Abstract

Disclosed herein are a superabsorbent polymer resin incorporated with a particles meeting the following properties i) to ii): i) a BET specific surface area of 300 to 1500 m.sup.2/g, ii) a porosity of 50% or more, and a method for preparing the same.

Claims

1. A superabsorbent polymer resin, meeting both the conditions represented by the following Mathematical Formulas 1 and 2:
RA1=D.sub.am(850 m+)/D.sub.bm(850 m+)0.2[Math Formula 1]
RA2=D.sub.am(600 m+)/D.sub.bm(600 m+)0.65[Math Formula 2] (wherein, D.sub.am(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater after milling and D.sub.bm(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater before milling).

2. The superabsorbent polymer resin of claim 1, further meeting the condition represented by the following Mathematical Formula 3:
RA3=[D.sub.bm(850 m+)/D.sub.bm(150850 m)]*1004.0[Math Formula 3] (wherein, D.sub.bm(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater before milling, and D.sub.bm(yz m) is a proportion of superabsorbent polymer resins having a particle size of from y m to z m before milling).

3. The superabsorbent polymer resin of claim 1, further meeting the condition represented by the following Mathematical Formula 4:
RA4=[D.sub.bm(850 m+)/D.sub.bm(300850 m)]*1004.5[Math Formula 4] (wherein, D.sub.bm(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater before milling, and D.sub.bm(yz m) is a proportion of superabsorbent polymer resins having a particle size of from y m to z m before milling).

4. The superabsorbent polymer resin of claim 1, wherein the superabsorbent polymer resin is incorporated with a particle meeting the following properties i) to ii): i) a BET specific surface area of 300 to 1500 m.sup.2/g, ii) a porosity of 50% or more.

5. A superabsorbent polymer resin, meeting both the conditions represented by the following Mathematical Formulas 2 and 3:
RA2=D.sub.am(600 m+)/D.sub.bm(600 m+)0.65[Math Formula 2]
RA3=[D.sub.bm(850 m+)/D.sub.bm(150850 m)]*1004.0[Math Formula 3] (wherein, D.sub.am(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater after milling, D.sub.bm(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater before milling, and D.sub.bm(yz m) is a proportion of superabsorbent polymer resins having a particle size of from y m to z m before milling).

6. The superabsorbent polymer resin of claim 5, further meeting the condition represented by the following Mathematical Formula 4:
RA4=[D.sub.bm(850 m+)/D.sub.bm(300850 m)]*1004.5[Math Formula 4] (wherein, D.sub.bm(x m+) is a proportion of superabsorbent polymer resins having a particle size of x m or greater before milling, and D.sub.bm(yz m) is a proportion of superabsorbent polymer resins having a particle size of from y m to z m before milling).

7. The superabsorbent polymer resin of claim 5, wherein the superabsorbent polymer resin is incorporated with a particles meeting the following properties i) to ii): i) a BET specific surface area of 300 to 1500 m.sup.2/g, ii) a porosity of 50% or more.

Description

EXAMPLES

Preparation Example 1

Preparation of Hydrogel Polymer

(1) A monomer mixture with a monomer content of 50% by weight was prepared by mixing 100 g of acrylic acid, 0.3 g of polyethylene glycol diacrylate as a crosslinking agent, 0.033 g of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide as an initiator, 38.9 g of caustic soda (NaOH), and 103.9 g of water.

(2) Subsequently, the monomer mixture was fed onto a continuously moving conveyer belt, and subjected to polymerization for 2 min under UV light (intensity: 2 mW/cm.sup.2) to obtain a hydrogel polymer.

Preparation Example 2

Preparation of Superabsorbent Polymer Resin

(3) The hydrogel polymer obtained in Preparation Example 1 was cut into a size of 55 mm, dried for 2 hrs at 170 C. in a hot air drier, milled using a pin mill, and screened with a sieve to give superabsorbent polymer resin particles with a size of 150 to 850 m.

(4) Subsequently, the superabsorbent polymer resinethylene was surface crosslinked with 3.5% glycol diglycidyl ether at 120 C. for 1 hr, milled, and screened with a sieve to give superabsorbent polymer resin particles with a size of 150 to 850 m.

Example

Preparation of Fine Particle-Incorporated Superabsorbent Polymer Resin

Example 1

(5) With 250 g of the superabsorbent polymer resin prepared in Preparation Example 2, 0.15 g of the porous superhydrophobic fine particle Silica Aerogel (AeroZel, JIOS) was blended at 1,000 RPM for 60 sec. Thereafter, 6.25 g of water was added to the mixture, followed by further mixing for 60 sec. Then, the resulting mixture was screened against a sieve to obtain superabsorbent polymer resin particles with a size of 150 to 850 m. The Aerogel had a particle size of 5 m, a BET specific surface area of 700 m.sup.2/g, a water contact angle of 144, and a porosity of 95%.

(6) The measurement of the particle size of the Aerogel was conducted according to ISO 13320. A HELOS (Helium-Neon Laser Optical System) was used for the measurement of the particle size of the Aerogel, and a high-speed non-variable Laser Diffraction was used for analysis of the particle size of the Aerogel. The BET specific surface area and porosity were determined by using BET analyzer. The measurement of the water contact angle was conducted with a contact angle analyzer (KRUSS DSA100). Specifically, the double-sided tape was attached on a flat glass plate. Thereafter, the fine particles thereon was coated in the form of a monolayer. Thereafter, the ultra-pure water 5 l are placed in drop form over the monolayer, and then the angle value between the water drop and glass plate was measured by four times and the average value was calculated.

Example 2

(7) Superabsorbent polymer resin particles were obtained in the same manner as in Example 1, with the exception that water was use in an amount of 12.5 g.

Comparative Example 1

(8) Superabsorbent polymer resin particles were obtained in the same manner as in Example 1, with the exception that Reolosil DM-305 was used as porous superhydrophobic fine particles in an amount of 0.15 g. The REOLOSIL DM-305 had a particle size of 7 nm, a BET specific surface area of 230 m.sup.2/g, a water contact angle of 135, and a porosity of 20% or less.

Comparative Example 2

(9) Superabsorbent polymer resin particles were obtained in the same manner as in Example 1, with the exception that Aerosil R972 (Evonic) was used as porous superhydrophobic fine particles in an amount of 0.625 g. The Aerosil R972 had a particle size of 16 nm, a BET specific surface area of 110 m.sup.2/g, a water contact angle of 135, and a porosity of 20% or less.

Comparative Example 3

(10) Superabsorbent polymer resin particles were obtained in the same manner as in Example 1, with the exception that Aerosil R974 (Evonic) was used as porous superhydrophobic fine particles in an amount of 0.625 g. The Aerosil R974 had a particle size of 12 nm, a BET specific surface area of 170 m.sup.2/g, a water contact angle of 142, and a porosity of 20% or less.

Comparative Example 4

(11) Resin particles were obtained in the same manner as in Example 1, with the exception that neither fine particles nor water was used.

(12) Features of the preparation methods of Example 1 to 2 and Comparative Examples 1 to 4 are summarized in Table 1, below.

(13) TABLE-US-00001 TABLE 1 Type of Porous Amount of Porous Superabsorbent Superabsorbent Amount of Ex. # Fine Particle Fine Particle (g) Water (g) Ex. 1 Aerogel 0.15 6.25 Ex. 2 0.15 12.5 C. Ex. 1 REOLOSIL DM-30S 0.15 6.25 C. Ex. 2 Aerosil R972 0.625 6.25 C. Ex. 3 Aerosil R974 0.625 6.25 C. Ex. 4

Test Examples

Assay for Physical Property

(14) To evaluate physical properties of the superabsorbent polymer resins of Example 1 to 2 and Comparative Examples 1 to 4, the following tests were conducted.

(15) Prior to the following tests, the superabsorbent polymer resins prepared in Example 1 to 2 and Comparative Examples 1 to 4 were ball milled. Together with ceramic balls with a diameter of 2.5 cm, 20 g of superabsorbent polymer resins was placed in a ceramic bottle with an internal volume of 1 L, and milled by rotating at 300 RPM for 15 min. Subsequently, the resulting particles were classified by size according to the method of the following Test Example 4. In Test Examples 1 to 5, test data were obtained from the superabsorbent polymer resins before and after the ball milling.

Test Example 1

l Determination of Parameters of Superabsorbent Polymer Resin

(16) Superabsorbent polymer resins prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were measured for particle size. The measurement was conducted according to the EDANA-recommended method WSP 240.3. For this, the superabsorbent polymer resins were placed in an amount of 100 g on each of 850m, 600 m, 300 m, and 150 m pan meshes, and vibrated for 10 min at a frequency of 50 Hz with an amplitude of 1.44 mm. The amounts that remained on each of the sieves were weighed.

(17) From the measurements, the parameters RA1 to RA4 according to the following Mathematical Formulas 1 to 4 were calculated, and the results are given in Table 2, below.

(18) TABLE-US-00002 TABLE 2 Condition Condition for both for both RA1 RA2 RA3 RA4 RA1 & RA2 RA2 & RA3 Ex. 1 1.50 0.873 0.40 0.45 Met Met Ex. 2 0.21 0.675 3.95 4.05 Met Met C. Ex. 1 0.05 0.422 102.84 103.68 Unmet Unmet C. Ex. 2 0.17 0.73 4.41 4.72 Unmet Unmet C. Ex. 3 0.13 0.624 5.55 5.92 Unmet Unmet C. Ex. 4 3.0 0.583 0.10 0.12 Unmet Unmet [Math Formula 1] RA1 = D.sub.am(850 m+)/D.sub.bm(850 m+) 0.2 [Math Formula 2] RA2 = D.sub.am(600 m+)/D.sub.bm(600 m+) 0.65 [Math Formula 3] RA3 = [D.sub.bm(850 m+)/D.sub.bm(150~850 m)]*100 4.0 [Math Formula 4] RA4 = [D.sub.bm(850 m+)/D.sub.bm(300~850 m)]*100 4.5

Test Example 2

Particle Size of Superabsorbent Polymer Resin

(19) Each of the superabsorbent polymer resins prepared in Example 1 to 2 and Comparative Examples 1 to 4 was measured for particle size. The measurement of particle size was carried out according the EDANA-recommended method WSP 240.3. 100 Grams of the superabsorbent polymer resin sample was placed on a collection pan with a mesh of 850 m, 600 m, 300 m, or 150 m. After vibration at an amplitude of 1.44 mm at a frequency of 50 Hz for 10 min, the amount of the particles retained on each sieve was measured to calculate the content as a percentage.

(20) Particle sizes measured before and after ball milling are summarized in Table 3, below.

(21) TABLE-US-00003 TABLE 3 Particle Size Distribution (%) Ball <150 150~300 300~600 600~850 >850 Milling m m m m m Ex. 1 Before 0.5 10.3 49.4 37.4 0.4 After 1.0 11.0 55.0 31.5 0.6 Ex. 2 Before 0.0 2.4 44.3 48.3 3.8 After 0.4 7.8 56.6 33.6 0.8 C. Ex. 1 Before 0.0 0.4 13.7 34.5 50.7 After 0.9 8.8 53.6 33.8 2.5 C. Ex. 2 Before 0.6 6.3 46.4 42.5 4.2 After 1.3 7.9 56.7 33.3 0.7 C. Ex. 3 Before 1.1 5.9 45.7 42.1 3.2 After 1.4 11.4 57.7 28.2 0.7 C. Ex. 4 Before 0.8 15.8 52.7 30.6 0.1 After 4.9 17.4 59.8 16.8 0.3

Test Example 3

Centrifugal Retention Capacity (CRC)

(22) Each of the superabsorbent polymer resins prepared in Example 1 to 2 and Comparative Examples 1 to 4 was measured for centrifugal retention capacity (CRC). The measurement of CRC was carried out according the EDANA-recommended method WSP 241.3. A tea bag containing 0.2 g of a superabsorbent polymer resin sample with a particle size of 300 to 600 m was immersed in a 0.9% saline solution for 30 min. Following centrifugation at 250 G (gravity) for 3 min, the amount of the saline solution absorbed was measured.

Test Example 4

Absorption Under Pressure (AUP)

(23) Each of the superabsorbent polymer resins prepared in Example 1 to 2 and Comparative Examples 1 to 4 was measured for absorption under pressure (AUP). The measurement of AUP was carried out according the EDANA-recommended method WSP 241.3. 0.9 Grams of a superabsorbent polymer resin sample with a particle size of 300 to 600 m was introduced into a cylinder designated by the EDANA-recommended method, and pressed under a pressure of 0.7 psi using a piston and a poise. Then, the amount of the saline solution absorbed for 60 min was measured.

Test Example 5

Saline Flow Conductivity (SFC)

(24) Each of the superabsorbent polymer resins prepared in Example 1 to 2 and Comparative Examples 1 to 4 was measured for saline flow conductivity (SFC). Reference was made to the SFC test method disclosed in EP 0640330 A1 with regard to the measurement of SFC. After the height (L0) of the SFC measurement device was measured, 0.9 g of a superabsorbent polymer resin sample with a particle size of 300 to 600 m was introduced into a cylinder, and pressed under a pressure of 0.3. Subsequently, the sample was allowed to absorb previously prepared, artificial urine for 60 min. The height (L) of the SFC measurement device in the absorbed state was measured, and the amount of saline passing through the gel was recorded with time while the saline of 0.118 M was maintained at a height of 5 cm. Finally, SFC was calculated according to the following Equation 1.
SFC [cm.sup.3.Math.s/g]=(Fg(t=0)L0)/(dAWP)[Equation 1]

(25) Results of CRC, AUP, and SFC, measured in Test Examples 3 to 5, are summarized in Table 4, below.

(26) TABLE-US-00004 TABLE 4 Ball CRC AUP SFC Ex. # milling (g/g) (g/g) (10.sup.7 cm.sup.3 .Math. s/g) Ex. 1 Before 33.2 22.1 8.2 After 34.0 20.0 4.5 Ex. 2 Before 33.2 21.5 7.1 After 33.1 18.9 5.5 C. Ex. 1 Before 33.5 19.6 5.8 After 33.7 18.2 4.8 C. Ex. 2 Before 34.5 16.6 7.7 After 34.4 15.3 5.8 C. Ex. 3 Before 34.0 15.3 9.0 After 34.1 15.1 8.4 C. Ex. 4 Before 35.1 23.7 6.4 After 36.4 19.4 2.4

(27) With an increase in surface hydrophobicity, as is understood from the data, the superhydrophobic fine particle-incorporated superabsorbent polymer resin was less apt to agglomerate and became better in processability.

(28) In the surface crosslinking process of the superabsorbent polymer resin, the surface crosslinking agent is generally dissolved in water such that it is evenly distributed over and penetrates into the resin upon mixing. The water used increases the surface viscosity of the superabsorbent polymer resin, thus causing agglomeration.

(29) In addition, the agglomerated superabsorbent polymer resin is disintegrated by a strong force, which, in turn, damages the superabsorbent polymer resin.

(30) In detail, as shown in Table 4, the superabsorbent polymer resins that were modified to be hydrophobic in Examples 1 and 2 exhibited particle size distributions similar to that of the superabsorbent polymer resin of Comparative Example 4 even though water was used in an amount of 2.5% and 5.0% by weight, respectively.

(31) This is attributed to the fact that the superhydrophobic fine particles interrupt water-induced agglomeration. In addition, the absorbed water was well-retained by the porous superhydrophobic fine particles on the surface of the superabsorbent polymer resin, so that the resin underwent fewer changes in physical property and particle size even upon, for example, ball milling, compared to the superabsorbent polymer resin prepared in Comparative Example 4.

(32) It is also understood from the data of Table 3 that there is a difference in physical property according to hydrophobicity among the superabsorbent polymer resins prepared in Examples 1 and Comparative Examples 1 to 3.

(33) Compared to the polymer resin of Comparative Example 1 with fine particles of relatively weak hydrophobicity introduced thereto, the superabsorbent polymer resin of Example 1 in which fine particles of relatively strong hydrophobicity are employed was less prone to increasing in particle size. For superabsorbent polymer resins of Comparative Examples 2 and 3 in which different types of hydrophobic fine particles were used, a greater amount of fine particles was required for controlling an increase in particle size in the presence of an equal amount of water.

(34) Further, the superabsorbent polymer resins of Comparative Examples 1 to 3 decreased in centrifugal retention capacity and absorption under pressure with an increase in agglomeration and fine particle amount, respectively.

(35) With an increase in surface hydrophobicity, as is understood from data of Test Examples 1 to 5, the superabsorbent polymer resins of Examples 1 and 2, which meet the conditions for both the parameters RA1 and RA2 or the parameters RA2 and RA3, are less apt to agglomerate and are thus better in processability.

(36) Further, as shown in Table 3, the superabsorbent polymer resins of Examples 1 and 2, which meet the conditions for both the parameters RA1 and RA2 or the parameters RA2 and RA3, exhibited particle size distributions similar to that of the superabsorbent polymer resins of Comparative Example 4 even though water was used in an amount of 2.5% and 5.0% by weight, respectively.

(37) It is also understood from the data of Table 4 that there is a difference in physical property according to the hydrophobicity of the hyperhydrophobic fine particles between the superabsorbent polymer resin of Example 1, which meets the conditions for both the parameters RA1 and RA2 or the parameters RA2 and RA3, and the superabsorbent polymer resins of Comparative Examples 1 to 3, which do not meet the conditions.

(38) The superabsorbent polymer resins of Example 1, which met the conditions for both the parameters RA1 and RA2 or the parameters RA2 and RA3, were less prone to increasing in particle size, compared to the polymer resins of Comparative Example 1, which did not meet the conditions. For superabsorbent polymer resins of Comparative Examples 2 and 3, which did not meet the conditions for both the parameters RA1 and RA2 or the parameters RA2 and RA3, a greater amount of fine particles was required for controlling an increase in particle size in the presence of an equal amount of water.

(39) Further, the superabsorbent polymer resins of Comparative Examples 1 to 3 decreased in centrifugal retention capacity and absorption under pressure with an increase in agglomeration and fine particle amount, respectively, compared to those of Example 1, which met the conditions for both the parameters RA1 and RA2 or the parameters RA2 and RA3.

(40) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.