Preparation Method of Super Absorbent Polymer

Abstract

The present disclosure relates to a preparation method of a super absorbent polymer capable of preparing a super absorbent polymer exhibiting an improved absorption rate while reducing an amount of a blowing agent used. The preparation method of a super absorbent polymer includes: preparing a monomer mixture including a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups and an internal cross-linking agent; adjusting a dynamic pressure applied to the monomer mixture being transferred to 140 Pa or more by controlling a transfer rate while transferring the monomer mixture to a polymerization reactor; cross-linking and polymerizing the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent to form a surface cross-linked layer.

Claims

1. A preparation method of a super absorbent polymer, comprising: preparing a monomer mixture comprising a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups and an internal cross-linking agent; transferring the monomer mixture to a polymerization reactor; during the transferring the monomer mixture to the polymerization reactor, adjusting a dynamic pressure applied to the monomer mixture being transferred calculated by the following Equation 1 to 140 Pa or more by controlling a transfer rate; cross-linking and polymerizing the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent to form a surface cross-linked layer:
Dynamic pressure=1/2*p*V.sup.2   [Equation 1] in Equation 1, p denotes a density (g/cm.sup.3) of the monomer mixture being transferred, and V denotes a transfer rate (m/s) of the monomer mixture.

2. The preparation method of a super absorbent polymer of claim 1, wherein the monomer mixture is transferred along a transfer pipe having a diameter that varies from section to section, the monomer mixture has a maximum transfer rate in a minimum diameter section of the transfer pipe, and the dynamic pressure applied to the monomer mixture in the maximum transfer rate section is adjusted to 140 Pa or more.

3. The preparation method of a super absorbent polymer of claim 2, wherein the transfer pipe has a diameter of 0.002 to 0.01 m in the minimum diameter section, and has a diameter of 0.011 to 0.020 m in a maximum diameter section before the minimum diameter section.

4. The preparation method of a super absorbent polymer of claim 3, wherein the monomer mixture is transferred through the transfer pipe at a flow rate of 100 to 15000 kg/hr.

5. The preparation method of a super absorbent polymer of claim 2, wherein the monomer mixture is transferred in the minimum diameter section of the transfer pipe at a rate of 0.45 to 2.5 m/s, and is transferred in a maximum diameter section of the transfer pipe at a rate of 0.1 to 0.4 m/s.

6. The preparation method of a super absorbent polymer of claim 1, wherein the monomer mixture further comprises a blowing agent in an amount of 0.01 to 0.3 wt % based on a total mixture weight.

7. The preparation method of a super absorbent polymer of claim 1, wherein oxygen bubbles are generated in the monomer mixture during the dynamic pressure adjustment, and a foaming polymerization proceeds by the generated bubbles in the cross-linking polymerization.

8. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has T-20 of 170 seconds or less, wherein T-20 represents a time required for 1 g of the super absorbent polymer to absorb 20 g of an aqueous solution of sodium chloride and C12 to C14 alcohol ethoxylate under a pressure of 0.3 psi.

9. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has a centrifuge retention capacity (CRC) of saline (0.9 wt % aqueous solution of sodium chloride) for 30 min of 28 g/g or more.

10. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has an absorbency under pressure (AUP) at 0.7 psi of 23 to 27 g/g, measured according to EDANA method WSP 242.3-10.

11. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has a saline (0.685 wt % aqueous solution of sodium chloride) flow conductivity (SFC; .Math.10.sup.−7 cm.sup.3.Math.s/g) of 30(.Math.10.sup.−7 cm.sup.3.Math.s/g) or more.

12. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has a vortex time of 5 to 50 seconds by a vortex method.

13. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has a centrifuge retention capacity (CRC) of saline (0.9 wt % aqueous solution of sodium chloride) for 30 min of 40 g/g or less.

14. The preparation method of a super absorbent polymer of claim 1, wherein the super absorbent polymer has a saline (0.685 wt % aqueous solution of sodium chloride) flow conductivity (SFC; .Math.10.sup.−7 cm.sup.3.Math.s/g) of 70(.Math.10.sup.−7 cm.sup.3.Math.s/g) or less.

15. The preparation method of a super absorbent polymer of claim 1, wherein the dynamic pressure applied to the monomer mixture is adjusted to be within the range of 150 to 1000 Pa.

16. The preparation method of a super absorbent polymer of claim 12, wherein the vortex method comprises: adding an amount of the super absorbent polymer to a saline solution at a temperature of 23° C. to 24° C., stirring the super absorbent polymer in the saline solution using a magnetic bar at 600 rpm to produce a vortex, and measuring a time until the vortex disappears.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0112] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

EXAMPLE 1

[0113] A monomer aqueous solution having a degree of neutralization of acrylic acid of 70 mol % and a monomer concentration of 43 wt % was prepared, in which the monomer aqueous solution includes acrylic acid, sodium hydroxide, polyethyleneglycol diacrylate (Mw=523; 0.5 wt % based on acrylic acid) as an internal cross-linking agent, and 0.033 g of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide as a UV initiator.

[0114] Then, 0.3 wt % (based on monomer aqueous solution) of a blowing agent solution of 0.17 wt % of sodium hydrogen carbonate was mixed with the monomer aqueous solution, and the composition was first introduced through a single tube having a diameter (maximum diameter section) of 0.015 m at a flow rate of 110 kg/h. Secondarily, it was continuously transferred through a single tube (minimum diameter section) in which the diameter is changed to 0.008 m. Through this transfer, the monomer aqueous solution was introduced into a polymerization reactor equipped with a movable conveyor belt, and UV polymerization was performed for 2 minutes by irradiating ultraviolet rays (irradiation amount: 2 mW/cm.sup.2) through a UV irradiation device to prepare a hydrogel polymer.

[0115] At this time, the dynamic pressure of the monomer aqueous solution composition passing through the final secondary single tube was 152 pa.

[0116] After transferring the hydrogel polymer to a cutter, it was cut to a maximum length of 0.2 cm. At this time, the moisture content of the cut hydrogel polymer was 52 wt %.

[0117] Subsequently, the hydrogel polymer was dried for 30 minutes in a hot air dryer at a temperature of 190° C., and the dried hydrogel polymer was pulverized with a pin mill. Then, it was classified with a sieve to a polymer having a particle diameter of less than 150 μm and a polymer having a particle diameter of 150 μm to 850 μm.

[0118] Thereafter, the surface of the super absorbent polymer was treated by spraying an aqueous solution of surface cross-linking agent containing 1.5 parts by weight of ethylene carbonate based on 100 parts by weight of the prepared base resin powder. In addition, in the step of treating the surface, the classified base resin powder was supplied to a surface cross-linking reactor, and a surface cross-linking reaction was performed at a temperature of 190° C. or higher for 35 minutes.

[0119] After the surface treatment, the temperature of the super absorbent polymer was cooled to 90° C., and a surface treated super absorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve. The fine powder having a particle diameter of less than 150 μm was contained in the super absorbent polymer in less than 2 wt %.

EXAMPLE 2

[0120] It was carried out in the same manner as in Example 1, except that the transfer rate of the monomer aqueous solution was adjusted as shown in Table below by adjusting the flow rate of the monomer aqueous solution composition to 150 kg/h, and the dynamic pressure of the monomer aqueous solution passing through the secondary single tube (minimum diameter section) was 282 pa.

EXAMPLE 3

[0121] It was carried out in the same manner as in Example 1, except that the transfer rate of the monomer aqueous solution was adjusted as shown in Table 1 below by adjusting the flow rate of the monomer aqueous solution composition to 242 kg/h, and the dynamic pressure of the monomer aqueous solution passing through the secondary single tube (minimum diameter section) was 734 pa.

COMPARATIVE EXAMPLE 1

[0122] It was carried out in the same manner as in Example 1, except that the transfer rate of the monomer aqueous solution was adjusted as shown in Table below by adjusting the flow rate of the monomer aqueous solution composition to 90 kg/h, and the dynamic pressure of the monomer aqueous solution passing through the secondary single tube (minimum diameter section) was 101 pa.

COMPARATIVE EXAMPLE 2

[0123] It was carried out in the same manner as in Example 1, except that the flow rate of the monomer aqueous solution composition was adjusted to 242 kg/h, and the monomer aqueous solution was transferred without changing the diameter of the transfer pipe (single tube). At this time, the dynamic pressure of the monomer aqueous solution was 59 pa.

EXPERIMENTAL EXAMPLES

[0124] The properties of each super absorbent polymer prepared in Examples and Comparative Examples, and various factors in the manufacturing process were measured and evaluated in the following manner.

[0125] (1) Density of Monomer Aqueous Solution

[0126] The density of the monomer mixture immediately before being transferred through a transfer pipe was measured by a method using a hydrometer from Mettler Toledo. As a result of the measurement, it was confirmed that the monomer aqueous solution prepared in Examples and Comparative Examples had a density of 1.05 g/cm.sup.3.

[0127] (2) Transfer Rate of Monomer Aqueous Solution (m/s)

[0128] The transfer rate of the monomer aqueous solution was calculated from the following equation by obtaining a cross-sectional area from a diameter of the transfer pipe in the transfer section and measuring a flow rate of the monomer mixture in the same section:

Transfer rate(m/s)=flow rate(m.sup.3/hr)/cross-sectional area(m.sup.2)

[0129] (3) Dynamic Pressure (Pa)

[0130] The density and the transfer rate measured in (1) and (2) above were substituted into Equation 1 to calculate the dynamic pressure during transfer of the monomer aqueous solution.

[0131] (4) Particle Diameter Evaluation

[0132] The particle diameters of the base resin powder and the super absorbent polymer used in Examples and Comparative Examples were measured according to the EDANA (European Disposables and Nonwovens Association) WSP 220.3 method.

[0133] (5) Centrifuge Retention Capacity (CRC)

[0134] The centrifuge retention capacity (CRC) by absorption ratio under a non-loading condition was measured according to the EDANA (European Disposables and Nonwovens Association) WSP 241.3 method. After inserting W.sub.0 (g, about 0.2 g) of the super absorbent polymer (or base resin powder) uniformly in a nonwoven fabric envelope and sealing the same, it was soaked in saline (0.9 wt % aqueous solution of sodium chloride) at room temperature. After 30 min, 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 super absorbent 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 2, and the water retention capacity was confirmed.

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

[0135] (6) Absorbency Under Pressure (AUP)

[0136] The absorbency under pressure (AUP) of each super absorbent polymer prepared in Examples and Comparative Examples was measured according to the EDANA (European Disposables and Nonwovens Association) WSP 242.3-10 method.

[0137] First, a 400 mesh stainless steel screen was installed in a cylindrical bottom of a plastic having an inner diameter of 60 mm. W.sub.0 (g, 0.90 g) of the polymer prepared in each of Examples and Comparative Examples was uniformly scattered on the screen at a temperature of 23±2° C. and a relative humidity of 45%. Thereafter, a piston which can uniformly provide a load of 4.83 kPa (0.7 psi) was placed on the polymer. Herein, the outer diameter of the piston was slightly smaller than 60 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.

[0138] Subsequently, 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 saline (0.9 wt % sodium chloride) was poured in the dish. At this time, the saline was poured until the surface level of the saline became equal to the upper surface of the glass filter. After the measuring device was mounted on the glass filter, 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.

[0139] Then, AUP (g/g) was calculated by using the obtained weight values according to the following Equation 3.

AUP(g/g)=[W.sub.4(g)−W.sub.3(g)]/W.sub.0(g)   [Equation 3]

[0140] In Equation 3, W.sub.0 (g) is an initial weight (g) of the super absorbent polymer, W.sub.3(g) is a sum of a weight of the super absorbent polymer and a weight of the device providing a load to the polymer, and W.sub.4(g) is a sum of a weight of the super absorbent polymer and a weight of the device providing a load to the polymer, after making the super absorbent polymer absorb the saline for one hour under a load (0.7 psi).

[0141] (7) Saline Flow Conductivity (SFC)

[0142] The saline flow conductivity was measured and calculated according to the method disclosed in U.S. Pat. No. 5,562,646 at columns 54 to 59. It was measured in the same manner as the above US patent, except that the amount of the super absorbent polymer used in the measurement was changed to 1.5 g instead of 0.9 g.

[0143] (8) T-20

[0144] An aqueous solution in which 9 g of sodium chloride and 0.1 g of Lorodac (main component: C12 to C14 alcohol ethoxylate, CAS #68439-50-9) were dissolved in 1 L of distilled water was prepared, and the time required for 1 g of the super absorbent polymer to absorb 20 g of the aqueous solution under a pressure of 0.3 psi was calculated and measured. The specific measuring method of T-20 is disclosed in U.S. Patent Publication No. 2013-007940.

[0145] (9) Absorption Rate (Vortex Time)

[0146] The absorption rate (vortex time) of each super absorbent polymer of Examples and Comparative Examples was measured in seconds according to the method disclosed in International Patent Publication No. 1987-003208.

[0147] Specifically, the absorption rate (or vortex time) was calculated by adding 2 g of the super absorbent polymer to 50 mL of 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 until vortex disappeared in seconds.

[0148] The results of the above properties are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Exam- Exam- Exam- Comp. Comp. ple 1 ple 2 ple 3 Ex. 1 Ex. 2 Flow rate (kg/hr) 110 150 242 90 242 Pipe 1 Dia.(m) 0.015 0.015 0.015 0.015 0.015 (Dia. in maximum diameter) Transfer rate in 0.31 0.31 0.31 0.31 0.31 maximum diameter section (m/s) Pipe 2 Dia.(m) 0.008 0.008 0.008 0.008 0.015 (Dia. in minimum diameter section) Transfer rate in 0.5 0.68 1.10 0.41 0.31 minimum diameter section (m/s) Dynamic pressure (Pa) 152 282 734 101 59 CRC before surface 36.5 36.2 36.5 35.8 36.1 cross-linking (base resin powder; g/g) Properties after surface cross-linking CRC (g/g) 29.1 29 28.4 28.6 29.3 AUP (g/g) 25.1 25 25.3 25.1 24.9 SFC (1.5 g) 35 36 35 33 32 T20 (sec) 163 153 120 180 210 Vortex (sec) 45 43 40 58 70

[0149] Referring to Table 1, it was confirmed that the super absorbent polymers prepared in Examples 1 to 3 in which a dynamic pressure of 140 Pa or more was applied during the transfer of the monomer aqueous solution had an improved absorption rate, while exhibiting water retention capacity, absorbency under pressure, and liquid permeability equivalent to or higher than those of Comparative Examples.