SUPER ABSORBENT POLYMER AND METHOD FOR PRODUCING SAME

Abstract

A super absorbent polymer according to the present invention has fast absorption rate while having high permeability and suction power, and thus is preferably used for hygienic materials such as diapers and can exhibit excellent performance.

Claims

1. A super absorbent polymer comprising: a base polymer powder comprising 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 comprising a second cross-linked polymer in which the first cross-linked polymer is further cross-linked via a surface crosslinking agent, wherein the super absorbent polymer has: a permeability of 55 seconds or less, a suction power of 15 g/g or more, and an absorption rare (vortex) of 40 seconds or less.

2. The super absorbent polymer of claim 1, wherein the super absorbent polymer has a permeability of 50 seconds or less.

3. The super absorbent polymer of claim 1, wherein the super absorbent polymer has a suction power of 17 g/g or more.

4. The super absorbent polymer of claim 1, wherein the super absorbent polymer has an absorption rate (vortex) of 35 seconds or less.

5. The super absorbent polymer of claim 1, wherein the super absorbent polymer has a centrifuge retention capacity (CRC) of 30 g/g or more.

6. The super absorbent polymer of claim 1, wherein the super absorbent polymer has an absorbency under pressure (0.7 AUP) at 0.7 psi for 1 hours of 15 g/g or more.

7. A method for producing a super absorbent polymer, comprising the steps of: crosslinking a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of a foaming agent, a foam stabilizer, and an internal crosslinking agent to form a hydrogel polymer containing a first crosslinked polymer; drying, pulverizing and classifying the hydrogel polymer to form a base polymer power; and heat-treating and surface-crosslinking the base polymer powder in the presence of a surface crosslinking solution to form a super absorbent polymer particle, wherein the foam stabilizer comprises sugar ester, and polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO).

8. The method of claim 7, wherein the sucrose ester is sucrose stearate, or sucrose isobutylate.

9. The method of claim 7, wherein the sugar ester and the polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) are used in a weight ratio of 1:1 to 1:20.

10. The method of claim 7, wherein the surface crosslinking solution comprises at least one surface crosslinking agent selected from the group consisting of ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

11. The method of claim 7, wherein the heat treatment temperature is 175 to 200 C.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0084] Hereinafter, preferred examples are provided for better understanding of the invention. However, these Examples are given for illustrative purposes only and are not intended to limit the scope of the present invention thereto.

Example 1

[0085] (1) Preparation of Base Polymer

[0086] 100 parts by weight of acrylic acid, 83.3 parts by weight of 50% caustic soda (NaOH), 89.8 parts by weight of water, and the following components were mixed to prepare a monomer aqueous solution. [0087] Crosslinking agent: 0.27 parts by weight (2700 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw=400) and 0.054 parts by weight (540 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw=200) [0088] Polymerization initiator: 0.02 parts by weight (300 ppmw) of hydrogen peroxide (H.sub.2O.sub.2), 0.05 parts by weight (500 ppmw) of ascorbic acid, 0.2 parts by weight (2000 ppmw) of potassium persulfate (KPS) [0089] Foaming agent: 0.1 part by weight (1000 ppmw) of sodium bicarbonate (SBC) [0090] Surfactant: 0.032 parts by weight (320 ppmw) of sucrose stearate (S1670), and 0.16 parts by weight (1600 ppmw) of LPE (PEO-PPO-PEO, Mw: 2550)

[0091] The monomer aqueous solution was subjected to a thermal polymerization reaction to obtain a polymerized sheet. The polymerized sheer was taken out and cut into a size of 3 cm3 cm. Then, the cut sheet was subjected to a chopping process using a meat chopper to prepare crumbs. Then, the crumbs were dried in an oven capable of shifting airflow up and down. The crumbs were uniformly dried by flowing hot air at 180 C. from the bottom to the top for 15 minutes and from the top to the bottom for 15 minutes, so that the dried product had a water content of 2% or less. After drying, the crumbs were pulverized using a pulverizer and classified to prepare a base polymer having a particle diameter of 150 to 850 m.

[0092] (2) Preparation of Super Absorbent Polymer

[0093] To 100 parts by weight of the base polymer prepared, 4 parts by weight of water, 4 parts by weight of methanol, 0.3 parts by weight of ethyleneglycol diglycidyl ether, 0.06 parts by weight of silica (Aerosil 200), and 0.2 parts by weight of oxalic acid were added and mixed, and then surface crosslinking reaction was carried out at 180 C. for 40 minutes. The resultant product was pulverized and sieved to obtain a surface-treated super absorbent polymer having a particle diameter of 150 to 850 m.

Example 2

[0094] A super absorbent polymer was obtained in the same manner as in Example 1, except that the surface crosslinking temperature was set to 195 C. during preparation of the super absorbent polymer.

Comparative Example 1

[0095] A super absorbent polymer was obtained in the same manner as in Example 1, except that the surface crosslinking temperature was set to 140 C. during preparation of the super absorbent polymer.

Comparative Example 2

[0096] A super absorbent polymer was obtained in the same manner as in Example 1, except that the surface crosslinking temperature was set to 160 C. during preparation of the super absorbent polymer.

Comparative Example 3

[0097] A super absorbent polymer was obtained in the same manner as in Example 1, except that 0.032 part by weight (320 ppmw) of sucrose stearate (S1670) was used as a surfactant during preparation of the base polymer (LPE was not used), and the surface crosslinking temperature was set to 140 C. during preparation of the super absorbent polymer.

Experimental Example: Evaluation of Physical Properties of Super Absorbent Polymer

[0098] The physical properties of the super absorbent polymer prepared in Examples and Comparative Examples were evaluated by the following methods.

[0099] (1) Absorption Rate (Vortex)

[0100] 50 mL of a 0.9 wt % NaCl solution was put in a 100 mL beaker, and then 2 g of each super absorbent polymer prepared in Examples and Comparative Examples was added thereto while stirring at 600 rpm using a stirrer. Then, the vortex time was calculated by measuring the amount of time until a vortex of the liquid caused by the stirring disappeared and a smooth surface was formed, and the result was shown as the vortex removal time (absorption rate; vortex).

[0101] In addition, with respect to the respective base polymers produced in the preparation process of Examples and Comparative Examples, the absorption rate (BR Vortex) was measured in the same manner as described above.

[0102] (2) Suction Power (SP)

[0103] The suction power was measured with a measuring instrument as shown in FIG. 1. Specifically, on the right side of the measuring instrument, a glass tube with an inner diameter of 20 mm was filled with salt water (0.9% NaCl) up to a 0 mL scale. On the left side of the measuring instrument, a 100-micrometer glass filter was attached to the bottom of the cylindrical funnel with an inner diameter of 50 mm. 1.0 g of a super absorbent polymer was uniformly scattered on a glass filter under a condition of a temperature of 23 C. and a relative humidity of 50%. A cork of burette in the measuring instrument was opened simultaneously with scattering the super absorbent polymer, and the amount of salt water (g) absorbed by 1 g of the super absorbent polymer for 5 minutes was measured.

[0104] (3) Centrifuge Retention Capacity (CRC)

[0105] The centrifuge retention capacity (CRC) by water absorption capacity under a non-loading condition was measured for the super absorbent polymers of Examples and Comparative Examples in accordance with EDANA (European Disposables and Nonwovens Association) recommended test method No. WSP 241.3.

[0106] Specifically, W.sub.0 (g, about 0.2 g) of the super absorbent polymers of Examples and Comparative Examples were uniformly put in a nonwoven fabric-made bag, followed by sealing. Then, the bag was immersed in a physiological saline solution composed of 0.9 wt % aqueous sodium chloride 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 super absorbent polymer, and then the resultant weight W.sub.1(g) was measured.

[0107] Using the respective weights thus obtained, CRC (g/g) was calculated according to the following Mathematical Formula 1.

CRC(g/g)={[W.sub.2(g)W.sub.1(g)W.sub.0(g)]/W.sub.0(g)}[Mathematical Formula 1]

[0108] in Mathematical Formula 1,

[0109] W.sub.0(g) is an initial weight(g) of the super absorbent polymer, W.sub.1(g) is the weight of the device not including the super absorbent polymer, measured after immersing and absorbing the same into a physiological saline solution for 30 minutes and then dehydrating the same by using a centrifuge at 250 G for 3 minutes, and W.sub.2(g) is the weight of the device including the super absorbent polymer, measured after immersing and absorbing the super absorbent polymer into 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.

[0110] In addition, with respect to the respective base polymers produced in the preparation process of Examples and Comparative Examples, CRC (BR CRC) was measured in the same manner as described above.

[0111] (4) Absorbency Under Pressure (AUP)

[0112] The absorbency under pressure (AUP) of the super absorbent polymers of Examples and Comparative Examples was measured in accordance with EDANA (European Disposables and Nonwovens Association) recommended test method No. WSP 242.3.

[0113] Specifically, a 400 mesh stainless screen was installed at the bottom of a plastic cylinder having an inner diameter of 60 mm. W.sub.0(g, about 0.90 g) of the super absorbent polymers obtained in Examples and Comparative Examples were uniformly scattered on the stainless screen under a condition of a temperature of 232 C. and a relative humidity of 45%. Then, a piston capable of providing a load of 0.7 psi uniformly was designed so that the outer diameter was slightly smaller than 60 mm and thus it could move freely up and down without any gap with the inner wall of the cylinder. At this time, the weight W.sub.3(g) of the device was measured.

[0114] 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 a physiological saline solution composed of 0.90 wt % sodium hydroxide aqueous solution was poured until the surface level became equal to the upper surface of the glass filter. Then, a sheet of filter paper having a diameter of 120 mm was placed on the glass filter. The measuring device was placed on the filter paper, so that the liquid was absorbed under load for one hour. After one hour, the measuring device was lifted and the weight W.sub.4(g) was measured.

[0115] Using the respective weights thus obtained, AUP (g/g) was calculated according to the following [Mathematical Formula 2.

AUP(g/g)=[W.sub.4(g)W.sub.3(g)]/W.sub.0(g)[Mathematical Formula 2]

[0116] in Mathematical Formula 2,

[0117] W.sub.0(g) is an initial weight (g) of the super absorbent polymer, 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 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 (0.9 psi) for 1 hour.

[0118] (5) Permeability

[0119] In a state where a piston was introduced in a chromatography tube (F20 mm), the liquid surface was displayed as a 40 ml mark line and a 20 ml mark line. Then, water was inversely introduced in a chromatography tube so that bubbles are not generated between a glass filter and a cork at the bottom of the chromatography tube, filling the tube for approximately 10 ml, and the chromatography tube was washed 2 to 3 times with salt water and filled with 0.9% salt water up to 40 ml or greater. A piston was introduced in the chromatography tube, a valve at the bottom was opened, and then the time (B) taken for the liquid surface decreasing from a 40 ml mark line to a 20 ml mark line was recorded.

[0120] 10 mL of salt water was left in the chromatography tube, to which 0.20.0005 g of classified (30 # to 50 #) sample was added. Salt water was added thereto so that the salt water volume became 50 ml, and then the result was left for 30 minutes. After that, a piston with a weight (0.3 psi=106.26 g) was introduced in the chromatography tube, and the result was left for 1 minute. After opening a valve at the bottom of the chromatography tube, the time (T1) taken for the liquid surface decreasing from a 40 ml mark line to a 20 ml mark line was recorded (T1). Thereby, the permeability (time of T1-B) was measured.

[0121] The results of the above measurements are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Physical properties of Surface Physical properties of super Surfactant base polymer crosslinking absorbent polymer S1670 LPE CRC Vortex temperature Vortex SP CRC AUP Permeability (ppmw) (ppmw) (g/g) (sec) ( C.) (sec) (g) (g/g) (g/g) (sec) Ex. 1 160 1600 40.4 35 180 31 17 35 17 49 Ex. 2 160 1600 40.4 35 195 30 18 34 20 47 Comparative 160 1600 40.4 35 140 35 14 36 12 50 Ex. 1 Comparative 160 1600 40.4 35 160 34 17 36 16 52 Ex. 2 Comparative 320 38.6 43 140 35 13 33 15 65 Ex. 3

[0122] From the results of Table 1, it was confirmed that Examples according to the present invention had fast absorption rate while having high permeability and suction power. In contrast, even when the same base polymer was used as in Comparative Examples 1 and 2, the surface crosslinking temperature was low and thus physical properties of a level equivalent to Examples were not shown. In addition, it was confirmed that as in Comparative Example 3, the permeability and the suction power were very low due to the difference in the amount of the surfactant used.