Super Absorbent Polymer Granules And Preparation Method Thereof

Abstract

The present disclosure relates to a preparation method of super absorbent polymer granules and super absorbent polymer granules prepared according to the same. More specifically, the preparation method of the present disclosure includes the steps of: forming a hydrogel polymer by carrying out a thermal polymerization or a photopolymerization of a monomer composition including a water-soluble ethylene-based unsaturated monomer and a polymerization initiator; drying and pulverizing the hydrogel polymer; classifying the pulverized polymer into a first fine powder having a particle size of 150 m or less, and a base resin having a particle size of 150 m or more and 850 m or less; surface-crosslinking the base resin; classifying the surface crosslinked base resin to separate a second fine powder having a particle size of 150 m or less; and forming fine powder granules by mixing the first fine powder, the second fine powder, and silica in a wet state.

Claims

1. Super absorbent polymer granules, which satisfy a relationship of y28.36x+0.5651, wherein x is the moisture content (%), and y is the content of the fine powder (%).

2. The super absorbent polymer granules of claim 1, wherein the formed fine powder granules have a gel strength of at least 8500 Pa.

3. The super absorbent polymer granules of claim 1, wherein the super absorbent polymer granules are prepared according to the preparation method comprising the steps of: forming a hydrogel polymer by carrying out a thermal polymerization or a photopolymerization of a monomer composition including a water-soluble ethylene-based unsaturated monomer and a polymerization initiator; drying and pulverizing the hydrogel polymer; classifying the pulverized polymer into a first fine powder having a particle size of 150 m or less, and a base resin having a particle size of 150 m or more and 850 m or less; surface-crosslinking the base resin; classifying the surface crosslinked base resin to separate a second fine powder having a particle size of 150 m or less; and forming fine powder granules by mixing the first fine powder, the second fine powder, and silica in a wet state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0098] FIG. 1 is a graph showing the relationship between the moisture content and the content of the fine powder of the fine powder granules prepared in Examples and Comparative Examples.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0099] Hereinafter, the preparation method of super absorbent polymer granules and the super absorbent polymer granules according to the exemplary embodiments of the present disclosure will be described in more detail.

Preparation Example

[0100] 100 g of acrylic acid, 0.5 g of polyethylene glycol diacrylate (Mw=523) as a crosslinking agent, 0.2 g of sodium persulfate as a thermal initiator, 0.008 g of phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide as a UV initiator, 40 g of NaOH, and 127 g of water were mixed to prepare a monomer aqueous solution composition having a monomer concentration of 45.8 wt %.

[0101] The monomer aqueous solution composition was introduced into a feeder of a polymerization reactor equipped with a continuous conveyer belt. And then, the composition was irradiated with ultraviolet rays (irradiation amount: 15 mW/cm.sup.2) by a UV irradiation apparatus while maintaining the polymerization atmosphere temperature at 80 C., and UV polymerization was carried out for 2 minutes to prepare a hydrogel polymer.

[0102] The hydrogel polymer was transferred to a meat chopper and then cut to 0.10.2 cm. At this time, the moisture content of the hydrogel polymer which was cut was 47 wt %.

[0103] Then, the hydrogel polymer was dried in a hot-air dryer at a temperature of 170 C. and an air flow rate of 0.8 m/sec for 30 minutes, and the dried hydrogel polymer was pulverized with a pin mill. Then, a polymer having a particle size (average particle diameter size) of 150 m or less and a polymer having a particle size of 150 m to 850 m were classified using a sieve. A base resin was prepared through this process. In order to reassemble the fine powder having a particle size of 150 m or less generated in the above process, it was separately classified and managed as a first fine powder.

[0104] Thereafter, the base resin and a surface-crosslinking solution (0.4 wt % of ethylene carbonate, 3.5 wt % of water) were uniformly mixed, and then the classified hydrogel polymer was introduced to a surface-crosslinking reactor. And, the surface-crosslinking reaction of the hydrogel polymer was carried out at a temperature of 180 C. or higher for 40 to 60 minutes.

[0105] After the surface-crosslinking treatment, a surface-treated super absorbent resin having an average particle size of 150 to 850 m was obtained by using a sieve with respect to the hydrogel polymer. In addition, the content of the fine powder of 150 m or less in each of the above super absorbent resins was less than 2%. In order to reassemble the fine powder having a particle size of 150 m or less generated in the above process, it was separately classified and managed as a second fine powder.

Examples

[0106] 1800 g of the first fine powder and 200 g of the second fine powder separated in the above Preparation Example were placed in a 40 L planetary mixer (PM-040, DNTEK Co., Ltd.), and the silica shown in the following Table 1 was measured and introduced thereto. Aerosil 200 was a fumed silica of Evonik Degussa, DM-30S was a silica of Tokuyama Corporation, and SnowTex O was a colloidal silica of Nissan Chemical. Then, after closing the lid of the mixer, pressed the start button of the mixer, set the impeller rpm to 60, and set the rpm to 0 again after 60 seconds. Then, water heated to 80 C. was added to the mixer. After 60 seconds from the addition, pressed the stop button to end the mixing. Then, the fine powder granules were taken out from the mixer, placed in a tray that the bottom and side surfaces are made of stainless steel mesh, and then dried in a convection oven at 180 C. for 3 hours. Thereafter, 250 g of the dried granules were put into a hood mixer (HMF-3260S) manufactured by Hanil Electric Co., Ltd., and pulverized twice for 15 seconds with a crushing strength of weak. Then, 500 g of the fine powder granules were classified on a sieve having a scale of 25, 30, 50, 80 and 100 mesh using a classifying apparatus (AS200, Retsch). After weighing the weights of the classified fine powder granules for each mesh, the wt % of the fine powder granules for each mesh relative to the total weight of the fine powder granules was calculated.

TABLE-US-00001 TABLE 1 Amount of input.sup.1 Silica (phr) Example 1-1 Aerosil 200 0.038 Example 1-2 Aerosil 200 0.076 Example 1-3 Aerosil 200 0.076 Example 2-1 SnowTex O 0.038 Example 2-2 SnowTex O 0.076 Example 2-3 SnowTex O 0.076 Example 3-1 DM-30S 0.038 Example 3-2 DM-30S 0.076 Example 3-3 DM-30S 0.076 Comparative Example 1 Comparative Example 2 Comparative Example 3 * Amount of input.sup.1(phr): an amount to be added to 100 parts by weight of the first fine powder and the second fine powder

Experimental Examples

[0107] (1) Fines.sup.2(%) under #100: It refers to the wt % of the particles (fine powder) that have passed through 100 mesh after classifying the fine powder granules.

[0108] (2) CRC (Centrifugal Retention Capacity).sup.3: CRC was measured in accordance with EDANA method WSP 241.2 using 0.1 g of the particles between mesh #30-50 among the pulverized and classified granules.

[0109] Specifically, W(g) (about 0.1 g) of resin obtained from the Examples and Comparative Examples were uniformly placed into a non-woven bag, sealed, and then immersed in a saline solution (0.9 wt %) at room temperature for 30 minutes. After 30 minutes, residual water was drained by centrifugal device under the condition of 250 G for 3 minutes, and the weight W.sub.2(g) of the bag was measured. In addition, the same manipulation was performed without super absorbent polymer, and the weight W.sub.1(g) of the bag was measured. CRC (g/g) was calculated using the weights measured above by following equation.

CRC (g/g)={(W.sub.2 (g)W.sub.1 (g))/W (g)}1[Equation 1]

[0110] (3) The gel strength (Pa): The fine powder granules were measured after sieving through a 3050 Mesh (300-600 m) sieve, and were swollen sufficiently in 50 g of 0.9% NaCl solution for 1 hour. Thereafter, a swollen gel was spread on a Buchner funnel covered with a filter paper (Whatman, 1004-110 Model, pore size of 20-25 m), and the remaining fluid was removed by vacuum for 3 minutes. The gel was kept in an airtight container until the test is ready.

[0111] Then, before the gel was placed between the rheometer and a parallel plate, it was sucked into the filter paper so that there was no residual water between the particles during testing.

[0112] 2 g of the swollen gel was measured using a rheometer. Herein, the test conditions of the rheometer were: Plate Gap Size 2 mm; Strain amplitude 1%; Oscillation frequency 10 radian/sec; ambient temperature 22 C.; plate 25 mm, TA InstrumentsAR Series. It was measured for 5 minutes and then taken as an average value.

[0113] (4) The moisture content (%).sup.4: It refers to the moisture content (M/C) of the granules, and was obtained by measuring the reduced % of the weight at 140 C. for 10 minutes using MX-50 manufactured by AND Co.

TABLE-US-00002 TABLE 2 Gel Moisture CRC.sup.3 Strength content.sup.4 Fines.sup.2 (g/g) (Pa) (%) (%) Example 1-1 26.1 8748 1.03 24.9 Example 1-2 25.7 9046 0.96 24.4 Example 1-3 25.6 9745 0.84 12.8 Example 2-1 26.0 9824 0.77 29.7 Example 2-2 26.1 9638 0.72 28.7 Example 2-3 26.1 10265 0.82 14.3 Example 3-1 25.5 9275 1.06 19.7 Example 3-2 25.8 9046 0.96 18.2 Example 3-3 25.6 10171 1.01 18.7 Comparative Example 1 26.9 8251 0.76 36.8 Comparative Example 2 26.4 9437 0.86 29.9 Comparative Example 3 25.6 10232 1.35 18.6

[0114] Referring to the Tables 1 and 2, it is confirmed that the super absorbent polymer granules prepared according to the preparation method of the Examples satisfy a relationship of y28.36x+0.5651, wherein x is the moisture content, and y is the content of the fine powder, and have a high gel strength more than 8500 Pa.

[0115] In contrast, the super absorbent polymer granules of the Comparative Examples prepared without using silica exhibit the higher fine powder content at the moisture content similar to that of the Examples, and thus cannot satisfy the relationship of y28.36x+0.5651, and have a lower gel strength compared with the Examples.