Method for Preparation of Super Absorbent Polymer

Abstract

According to the method for preparation of a super absorbent polymer according to of the present disclosure, fine particles present in the prepared super absorbent polymer are removed, thereby solving a dispersion problem of the fine particles and a problem of reduction in the physical properties of the super absorbent polymer.

Claims

1. A method for preparation of a super absorbent polymer, comprising: 1) forming a hydrogel polymer containing a first cross-linked polymer by cross-linking polymerization of a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent; 2) drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and 3) cross-linking a surface by heat-treating the base resin powder in the presence of a surface cross-linking solution to form super absorbent polymer particles; and 4) adding brine to the super absorbent polymer particles, wherein a conductivity of the brine is 15 to 55 mS/cm.

2. The method for preparation of a super absorbent polymer of claim 1, wherein the water-soluble ethylene-based unsaturated monomer is a compound represented by the following Chemical Formula 1,
R.sub.1—COOM.sub.1   [Chemical Formula 1] in Chemical Formula 1, R.sup.1 is a C2 to C5 alkyl group having an unsaturated bond, and M.sup.1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

3. The method for preparation 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, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, orethylene carbonate.

4. The method for preparation of a super absorbent polymer of claim 1, wherein the cross-linking is performed at 180 to 250° C.

5. The method for preparation of a super absorbent polymer of claim 1, wherein the conductivity of the brine is 20 to 55 mS/cm.

6. The method for preparation of a super absorbent polymer of claim 1, wherein the brine is an aqueous solution of Na.sub.2CO.sub.3, NaCl, or Mg(CH.sub.3COO).sub.2.

7. The method for preparation of a super absorbent polymer of claim 1, wherein an amount of the brine is 0.1 to 10 wt % based on the super absorbent polymer particles.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0076] Hereinafter, the function and effect of the present invention will be described in more detail through specific examples. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

EXAMPLE 1

[0077] As a manufacturing device for a super absorbent polymer, a continuous manufacturing device including a polymerization process, a hydrogel pulverizing process, a drying process, a pulverizing process, a classification process, a surface cross-linking process, a cooling process, a classification process, and a transport process connecting each process was used.

[0078] (Step 1)

[0079] A monomer solution was prepared by mixing 0.4 parts by weight of polyethylene glycol diacrylate (weight average molecular weight: ˜500 g/mol) as an internal cross-linking agent, 0.1 parts by weight of hexanediol diacrylate, and 0.01 parts by weight of IRGACURE 819 as a photoinitiator with 100 parts by weight of acrylic acid. Subsequently, while continuously supplying the monomer solution to a metering pump, 160 parts by weight of a 24 wt % sodium hydroxide aqueous solution was continuously line-mixed to prepare a monomer aqueous solution. At this time, after confirming that the temperature of the monomer aqueous solution had risen to about 72° C. or higher by the heat of neutralization, the solution was allowed to stand until the temperature was cooled to 40° C.

[0080] When cooled down to the temperature of 40° C., 6 parts by weight of solid sodium bicarbonate and 6 parts by weight of a 2 wt % aqueous sodium persulfate solution were added to the monomer aqueous solution.

[0081] The solution was poured into a Vat-type tray (tray, 15 cm wide×15 cm long) installed in a square polymerizer, wherein the polymerizer was provided with a light irradiation device on the top and preheated to 80° C., and then light irradiation was performed to initiate photopolymerization. It was confirmed that a gel was generated from the surface about 25 seconds after the light irradiation and a polymerization reaction occurred simultaneously with foaming after about 50 seconds, and the reaction was further performed for 3 minutes to obtain a sheet-shaped hydrogel polymer.

[0082] (Step 2)

[0083] The hydrogel polymer prepared in Step 1 was cut into a size of 3 cm×3 cm, and then pulverized (chopped) while pushing the hydrogel polymer into a porous plate having a plurality of holes using a screw-type extruder installed inside a cylindrical pulverizing machine.

[0084] Subsequently, the pulverized hydrogel polymer was dried in a dryer capable of changing wind direction up and down. The hydrogel polymer was uniformly dried by flowing hot air at 180° C. from the bottom to the top for 15 minutes, and then flowing from the top to the bottom for 15 minutes, so that the moisture content of the dried powder was less than about 2%.

[0085] The dried polymer was pulverized with a pulverizing machine, and then classified to obtain a base resin powder having a size of 150 to 850 um.

[0086] (Step 3)

[0087] 100 parts by weight of the base resin prepared in Step 2 was mixed with a cross-linking agent solution in which 3 parts by weight of water, 3 parts by weight of methanol, and 0.5 parts by weight of ethylene carbonate were mixed, followed by surface cross-linking reaction at 180° C. for 40 minutes.

[0088] (Step 4)

[0089] After cooling the resulting product obtained in Step 3 to 90° C., 1 parts by weight of brine (Na.sub.2CO.sub.3 5% aqueous solution) based on 100 parts by weight of the resulting product was added using a dropper. Thereafter, while maintaining stirring, additional stirring/cooling was performed for 15 to 25 minutes to obtain surface cross-linked super absorbent polymer particles having a particle diameter of 150 to 850 um. The temperature of the finally obtained super absorbent polymer particles was 40° C.

EXAMPLE 2

[0090] A super absorbent polymer was prepared in the same manner as in Example 1, except that NaCl 2% aqueous solution was used instead of Na.sub.2CO.sub.3 5% aqueous solution in Step 4 of Example 1.

EXAMPLE 3

[0091] A super absorbent polymer was prepared in the same manner as in Example 1, except that Mg(CH.sub.3COO).sub.2 5% aqueous solution was used instead of Na.sub.2CO.sub.3 5% aqueous solution in Step 4 of Example 1.

Comparative Example 1

[0092] A super absorbent polymer was prepared in the same manner as in Example 1, except that Step 4 of Example 1 was omitted.

Comparative Example 2

[0093] A super absorbent polymer was prepared in the same manner as in Example 1, except that distilled water was used instead of Na.sub.2CO.sub.3 5% aqueous solution in Step 4 of Example 1.

Comparative Example 3

[0094] A super absorbent polymer was prepared in the same manner as in Example 1, except that NaCl 0.5% aqueous solution was used instead of Na.sub.2CO.sub.3 5% aqueous solution in Step 4 of Example 1.

Comparative Example 4

[0095] A super absorbent polymer was prepared in the same manner as in Example 1, except that Na.sub.2CO.sub.3 10% aqueous solution was used instead of Na.sub.2CO.sub.3 5% aqueous solution in Step 4 of Example 1.

Experimental Examples

[0096] Physical properties of the prepared super absorbent polymer were measured according to the following method.

[0097] (1) Dust View

[0098] 30 g of each of the super absorbent polymers prepared in Examples and Comparative Examples was prepared, and dust values were measured and analyzed using Dustview II (manufactured by Palas GmbH), which can measure the degree of dust of the super absorbent polymer with a laser. Since small particles and specific substances fall at a slower rate than coarse particles, dust number was calculated according to Equation 1 below.

[00001]$\begin{array}{cc}\mathrm{Dust}\mathrm{number}=\mathrm{Max}\mathrm{value}+30\sec .\mathrm{value}& \left[\mathrm{Equation}1\right]\end{array}$

[0099] (In Equation 1, Max value represents a maximum dust value, and 30 sec. value is a value measured 30 seconds after reaching the maximum dust value)

[0100] (2) Proportion of Coarse Particles Generated

[0101] The super absorbent polymer particles prepared in one of Examples and Comparative Examples were classified using a 710 um mesh (manufacturer: Retsch) for 10 minutes under the condition of Amp. 1.0 mm, and then a proportion (weight ratio) of the residue on the mesh was calculated.

[0102] (3) CRC (Centrifugal Retention Capacity)

[0103] The centrifuge retention capacity by absorption ratio under a non-loading condition of each polymer was measured in accordance with EDANA WSP 241.3.

[0104] Specifically, a polymer was obtained by classifying each of the polymers prepared in Examples and Comparative Examples through a sieve of #30-50. After inserting W.sub.0 (g, about 0.2 g) of the polymer uniformly in a nonwoven fabric envelope and sealing the same, it was soaked in physiological saline (0.9 wt %) at room temperature. After 30 minutes, 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 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 Equation.

[00002]$\begin{array}{cc}\mathrm{CRC}\left(g/g\right)=\left\{\left[W_2\left(g\right)-W_1\left(g\right)\right]/W_0\left(g\right)\right\}-1& \left[\mathrm{Equation}4\right]\end{array}$

[0105] (4) AAP (Absorption Against Pressure)

[0106] The absorption against pressure at 0.7 psi of each polymer was measured in accordance with EDANA WSP 242.3. In the measurement of the absorption against pressure, the classified polymer in the above CRC measurement was used.

[0107] Specifically, a 400 mesh stainless steel screen was installed in a cylindrical bottom of a plastic having an inner diameter of 25 mm. W.sub.0 (g, 0.16 g) of the super absorbent polymer was uniformly scattered on the screen at room temperature and a humidity of 50%. Thereafter, a piston which can uniformly provide a load of 0.7 psi was placed thereon. Herein, the outer diameter of the piston was slightly smaller than 25 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. Subsequently, a glass filter having a diameter of 90 mm and a thickness of 5 mm was placed in a petri dish having a diameter of 150 mm, and physiological saline (0.9 wt % sodium chloride) was poured in the dish. At this time, the physiological saline was poured until the surface level of the physiological saline became equal to the upper surface of the glass filter. One sheet of filter paper with a diameter of 90 mm was placed thereon. After the measuring device was placed on the filter paper, 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. Then, absorption against pressure (g/g) was calculated by using the obtained weight values according to the following Equation.

[00003]$\begin{array}{cc}\mathrm{AAP}\left(g/g\right)=\left[W_4\left(g\right)-W_3\left(g\right)\right]/W_0\left(g\right)& \left[\mathrm{Equation}2\right]\end{array}$

[0108] (5) Permeability (Perm)

[0109] Permeability of the super absorbent polymer prepared in one of Examples and Comparative Examples was measured according to the following Equation 3.

[00004]$\begin{array}{cc}\mathrm{Perm}=\left[20\mathrm{mL}\text{/}{T}_1\left(\sec \right)\right]*60\sec & \left[\mathrm{Equation}3\right]\end{array}$

[0110] in Equation 3,

[0111] Perm is a permeability of the super absorbent polymer, and

[0112] T.sub.1 is the time (in seconds) taken for 20 mL of physiological saline to pass through the swollen super absorbent polymer under a pressure of 0.3 psi, after adding 0.2 g of the super absorbent polymer in a cylinder and then pouring physiological saline (0.9 wt % sodium chloride aqueous solution) thereto so that the super absorbent polymer is completely immersed to be swollen for 30 minutes.

[0113] Specifically, a cylinder and a piston were prepared. As the cylinder, a cylinder having an inner diameter of 20 mm equipped with a glass filter and a stopcock at the bottom was used. A piston including a screen having an outer diameter slightly smaller than 20 mm and capable of freely moving the cylinder up and down at the bottom, a weight at the top, and a rod connecting the screen and the weight was used. The piston was equipped with a weight capable of applying a pressure of 0.3 psi by the addition of the piston.

[0114] With the stopcock of the cylinder closed, 0.2 g of the super absorbent polymer was added, and an excess of physiological saline (0.9 wt % sodium chloride aqueous solution) was poured so that the super absorbent polymer was completely immersed. Then, the super absorbent polymer was swollen for 30 minutes. Thereafter, a piston was added to uniformly apply a load of 0.3 psi on the swollen super absorbent polymer.

[0115] Subsequently, the time taken for 20 mL of physiological saline to pass through the swollen super absorbent polymer was measured in seconds by opening the stopcock of the cylinder. At this time, the meniscus when the cylinder was filled with 40 mL of physiological saline, and the meniscus when the cylinder was filled with 20 mL of physiological saline were marked. Then, the time taken to reach the level corresponding to 20 ml from the level corresponding to 40 mL was measured to easily measure the T1 of the above Equation 3.

[0116] (6) Vortex (Absorption Rate by Vortex Method)

[0117] The absorption rate of the super absorbent polymer prepared in one of Examples and Comparative Examples was measured in seconds according to the method disclosed in International Patent Publication No. 1987-003208.

[0118] Specifically, the absorption rate was calculated by adding 2 g of the super absorbent polymer to 50 mL of physiological saline at 23° C. to 24° C., stirring a magnetic bar (8 mm in diameter and 31.8 mm in length) at 600 rpm, and measuring the time taken until vortex disappeared in seconds.

[0119] The measurement results are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Comp. Comp. Comp. Comp. Unit Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Materials used Na.sub.2CO.sub.3 NaCl Mg(CH.sub.3COO).sub.2 — H.sub.2O NaCl Na.sub.2CO.sub.3 5% 2% 5% 0.5% 10% Conductivity mS/cm 50.5 30.5 20.5 — 0 10.0 83.6 Amount treated wt % based 1.0 1.0 1.0 — 1.0 1.0 1.0 on SAP Moisture content wt % 0.95 0.89 0.90 0.25 0.92 0.91 0.92 Dust view — 0.4 0.5 0.6 1.5 0.5 0.5 0.4 Proportion of % 1.0 1.3 1.7 0 3.5 2.6 1.2 coarse particles generated CRC g/g 28.1 28.2 28.0 28.2 27.4 27.7 27.3 AAP g/g 24.7 24.5 24.6 24.6 24.6 24.4 24.1 CRC + AAP g/g 52.8 52.7 52.6 52.8 52.0 52.1 51.4 Permeability mL 41 40 39 38 40 37 42 Vortex sec 44 42 41 43 45 44 42

[0120] As shown in Table 1, it was confirmed that Examples 1 to 3 treated with brine having a conductivity according to the present disclosure had lower dust view compared to Comparative Example 1 without the treatment with brine, while maintaining inherent physical properties of the super absorbent polymer. This is due to the fact that fine particles were removed without affecting the inherent physical properties of the super absorbent polymer by performing the treatment with brine.

[0121] On the other hand, when the conductivity of the brine was small as in Comparative Examples 2 and 3, the dust view could be improved, but the generation of coarse particles increased, so that CRC properties were particularly deteriorated.

[0122] In addition, when the conductivity of the brine was high as in Comparative Example 4, it can be seen that CRC properties were deteriorated even though the proportion of coarse particles generated was similar to that of Examples according to the present disclosure. This is due to the fact that the brine having high conductivity damaged the degree of cross-linking of the super absorbent polymer, resulting in deterioration of CRC properties.