Super absorbent polymer

Abstract

The present invention relates to superabsorbent polymer having excellent centrifuge retention capacity and permeability. The superabsorbent polymer simultaneously exhibits excellent centrifuge retention capacity and permeability, and thus, can fundamentally solve the problems of the existing superabsorbent polymer and technical requirement of the art, and can provide various hygienic goods exhibiting more excellent properties.

Claims

1. A superabsorbent polymer comprising a base resin powder comprising crosslinked polymer formed by the crosslinking polymerization, in an aqueous solution, of water soluble ethylenically unsaturated monomers having acid groups of which at least a part are neutralized, in the presence of an internal crosslinking agent comprising a compound represented by the following Chemical Formula 1, and inorganic material; and a surface crosslink layer on the base resin powder, formed by the additional crosslinking of the crosslinked polymer, wherein the inorganic material is montmorillonite, saponite, nontronite, laponite, beidelite, hectorite, sauconite, stevensite, vermiculite, volkonskoite, magadite, medmontite, kenyaite, kaolin mineral, serpentine mineral, mica mineral, chlorite mineral, sepolite, palygorskite, bauxite silica, alumina, titania or a mixture thereof, wherein the permeability calculated by the following Calculation Formula 1 is equal to or greater than 17 mL/1 minute: ##STR00004## in the Chemical Formula 1, R.sup.1 is a divalent organic group derived from C1-10 alkane, and R.sup.2 is hydrogen or a methyl group, wherein R.sup.1 in the Chemical Formula 1, is methane-1,1-diyl, propane-1,3-diyl, propane-1,2-diyl, propane-1,1-diyl, n-butane-1,4-diyl, n-butane-1,3-diyl, n-butane-1,2-diyl, n-butane-1,1-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, 2-methylpropane-1,1-diyl, 2-methylbutane-1,4-diyl, 2-methylbutane-2,4-diyl, 2-methylbutane-3,4-diyl, 2-metylbutane-4,4-diyl, 2-methylbutane-1,3-diyl, 2-methylbutane-1,2-diyl, 2-methylbutane-1,1-diyl or 2-methylbutane-2,3-diyl,
Perm=[20 mL/T.sub.1 (sec)]*60 sec[Calculation Formula 1] in the Calculation Formula 1, Perm is the permeability of superabsorbent polymer, and T.sub.1 is a time (seconds) taken for a saline solution of 20 mL to pass through swollen superabsorbent polymer under pressure of 0.3 psi, after putting 0.2 g of superabsorbent polymer in a cylinder, and pouring a saline solution (0.9 wt % sodium chloride aqueous solution) so that the superabsorbent polymer is completely submerged, thus swelling the superabsorbent polymer for 30 minutes.

2. The superabsorbent polymer according to claim 1, wherein centrifuge retention capacity(CRC) to a saline solution is 32 to 40 g/g, and absorbency under load(AUL) of 0.7 psi to a saline solution is 25 to 30 g/g.

3. The superabsorbent polymer according to claim 1, wherein R.sup.1 in the Chemical Formula 1, is methane-1,1-diyl, propane-1,3-diyl or propane-1,2-diyl.

4. The superabsorbent polymer according to claim 1, wherein the surface crosslink layer is formed using a surface crosslinking solution comprising, based on 100 parts by weight of the base rein powder, 0.10 to 1 parts by weight of a surface crosslinking agent, 5 to 15 parts by weight of water, and 5 to 15 parts by weight of methanol.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, the actions and the effects of the invention will be explained in detail through the specific examples. However, these examples are presented only as the illustrations of the invention, and the scope of the right of the invention is not limited thereby.

Example 1: Preparation of Superabsorbent Polymer

(2) Into a glass reactor, 100 g of acrylic acid, 0.6 g of 4-methylpentane-1,4-diyl diacrylate, 0.008 g of Irgacure TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), 0.18 g of laponite and 55 g of water were put. And, to the glass reactor, 123.5 g of 32 wt % caustic soda solution was slowly added dropwise and mixed.

(3) When adding the caustic soda solution dropwise, the temperature of the mixed solution increased by neutralization heat, thus waited until the mixed solution was cooled. When the temperature of the mixed solution was cooled to about 45 C., 0.2 g of sodium persulfate was added to the mixed solution to prepare a monomer mixture.

(4) On a conveyer belt with a width of 10 cm and a length of 2 m, rotating at the velocity of 50 cm/min, the monomer mixture was fed at 5002000 mL/min. And, simultaneously with the feeding of the monomer mixture, UV was irradiated at the intensity of 10 mW/cm.sup.2 to progress a polymerization reaction for 60 seconds.

(5) And, the polymer obtained through the polymerization reaction was passed through a hole with a diameter of 10 mm to prepare as crumb using a meat chopper. Subsequently, the crumb was uniformly dried by flowing hot air of 185 C. from the lower part to the upper part for 20 minutes using an oven capable of transferring air volume upward and downward, and flowing it again from the upper part to the lower part for 20 minutes. The dried crumb was ground with a grinder, and then, sieved to obtain base resin with a size of 150 to 850 m.

(6) To 100 g of the above prepared base resin powder, a mixed solution of 8 g of deionized water, 8 g of methanol, 0.2 g of ethylene carbonate, and 0.01 g of silica (product name: REOLOSIL DM30S, manufacturing company: Tokuyama Corporation) was added, and mixed for 1 minute, and then, surface crosslinking was conducted at 185 C. for 90 minutes.

(7) And, the obtained product was ground and sieved to obtain superabsorbent polymer with a particle diameter of 150 to 850 m.

Example 2: Preparation of Superabsorbent Polymer

(8) Superabsorbent polymer was prepared by the same method as Example 1, except that 0.6 g of 2-methylpentane-2,4-diyl diacrylate was used instead of 0.6 g of 4-methylpentane-1,4-diyl diacrylate in Example 1.

Example 3: Preparation of Superabsorbent Polymer

(9) Superabsorbent polymer was prepared by the same method as Example 1, except that 0.6 g of 2-methylpropane-1,2-diyl diacrylate was used instead of 0.6 g of 4-methylpentane-1,4-diyl diacrylate in Example 1.

Example 4: Preparation of Superabsorbent Polymer

(10) Superabsorbent polymer was prepared by the same method as Example 1, except that 0.6 g of 2-methylbutane-2,4-diyl diacrylate was used instead of 0.6 g of 4-methylpentane-1,4-diyl diacrylate in Example 1.

Comparative Example 1: Preparation of Superabsorbent Polymer

(11) Superabsorbent polymer was prepared by the same method as Example 1, except that laponite was not introduced.

Comparative Example 2: Preparation of Superabsorbent Polymer

(12) Superabsorbent polymer was prepared by the same method as Example 4, except that laponite was not introduced.

Experimental Example: Evaluation of the Properties of Superabsorbent Polymer

(13) The properties of the superabsorbent polymers prepared according to Examples and Comparative Examples were evaluated as follows, and shown in the following Table 1.

(14) (1) Permeability (Perm)

(15) For the superabsorbent polymers prepared according to Examples and Comparative Examples, permeabilities were measured according to the following Calculation Formula 1.
Perm=[20 mL/T.sub.1 (sec)]*60 sec[Calculation Formula 1]

(16) in the Calculation Formula 1,

(17) Perm is the permeability of superabsorbent polymer, and

(18) T.sub.1 is a time (seconds) taken for a saline solution of 20 mL to pass through swollen superabsorbent polymer under pressure of 0.3 psi, after putting 0.2 g of superabsorbent polymer in a cylinder, and pouring a saline solution (0.9 wt % sodium chloride aqueous solution) so that the superabsorbent polymer is completely submerged, thus swelling the superabsorbent polymer for 30 minutes.

(19) Specifically, a cylinder and a piston were prepared. As the cylinder, a cylinder having an inner diameter of 20 mm, and equipped with a glass filter and a stopcock at the bottom was used. As the piston, a piston wherein a screen that has an outer diameter slightly smaller than 20 mm, and thus, can freely move the cylinder upward and downward, is positioned at the bottom, a weight is positioned at the top, and the screen and weight are connected by a rod, was used. In the piston, a weight capable of adding a pressure of 0.3 psi due to the addition of the piston was installed.

(20) While the stopcock of the cylinder was locked, 0.2 g of superabsorbent polymer was put, and an excessive amount of a saline solution (0.9 wt % of a sodium chloride aqueous solution) was poured such that the superabsorbent polymer was completely submerged. And, the superabsorbent polymer was swollen for 30 minutes. Thereafter, on the swollen superabsorbent polymer, a piston was added to uniformly give a load of 0.3 psi.

(21) Subsequently, the stopcock of the cylinder was opened and a time for 20 mL of the saline solution to pass through the swollen superabsorbent polymer was measured (unit: second). Here, if the meniscus is marked when 40 mL of the saline solution is filled in the cylinder and the meniscus is marked when 20 mL of the saline solution is filled in the cylinder, the T.sub.1 of the Calculation Formula 1 can be easily measured by measuring a time taken to reach the level corresponding to 20 ml from the level corresponding to 40 mL.

(22) (2) Centrifuge Retention Capacity (CRC)

(23) The centrifuge retention capacity (CRC) of the superabsorbent polymer to a saline solution was measured according to EDANA method NWSP 241.0.R2.

(24) Specifically, among the superabsorbent polymer of which centrifuge retention capacity is to be measured, a sample with the particle diameter of 150 to 850 m, which passes through a US standard 20 mesh screen, and remains on a US standard 100 mesh screen, was prepared.

(25) And, W.sub.0 (g, about 0.2 g) of the sample having a particle diameter of 150 to 850 m were uniformly put in an envelope made of non-woven fabric, and the envelope was sealed. And, the envelope was soaked in a 0.9 wt % sodium chloride aqueous solution (saline solution) at room temperature. After 30 minutes, the envelope was drained at 250 G for 3 minutes using a centrifuge, and then, the mass W.sub.2 (g) of the envelope was measured. And, after the same operation using an empty envelope without a sample, the mass W.sub.1 (g) at that time was measured.

(26) Using the obtained weights, CRC (g/g) was calculated according to the following Calculation Formula 2.
CRC (g/g)={[W.sub.2(g)W.sub.1(g)]/W.sub.0(g)}1[Calculation Formula 2]

(27) In the Calculation Formula,

(28) W.sub.0 (g) is the initial weight of the sample having a particle diameter of 150 to 850 m(g),

(29) W.sub.1 (g) the weight of an empty envelope made of nonwoven fabric, measured after the empty envelope without a sample was soaked in a saline solution at room temperature for 30 minutes, and then, drained using a centrifuge at 250 G for 3 minutes, and

(30) W.sub.2 (g) is the weight of an envelope made of nonwoven fabric including the sample, measured after the envelope made of nonwoven fabric including the sample was soaked in a saline solution at room temperature for 30 minutes, and then, drained using a centrifuge at 250 G for 3 minutes.

(31) (3) Absorbency Under Load (AUL)

(32) The absorbency under load (AUL) of 0.7 psi of the superabsorbent polymer to a saline solution was measured according to EDANA method NWSP 242.0.R2.

(33) Specifically, a 400 mesh screen made of stainless was installed on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under the conditions of room temperature and relative humidity of 50%, W.sub.0 (g, 0.16 g) of superabsorbent polymer of which absorbency under load is to be measured were uniformly scattered on the screen. Subsequently, a piston that can uniformly give a load of 4.8 kPa (0.7 psi) was added on the superabsorbent polymer. Here, as the piston, a piston having an outer diameter slightly smaller than 25 mm was used such that there was no gap with the inner wall of the cylinder, and the movement upward and downward was not hindered. At this time, the weight W.sub.3 (g) of the apparatus was measured.

(34) Subsequently, on the inner side of a petri dish with a diameter of 150 mm, a glass filter with a diameter of 90 mm and a thickness of 5 mm was positioned, and a 0.90 wt % sodium chloride aqueous solution (saline solution) was poured on the petri dish. Here, the saline solution was poured until the water level of the saline solution became horizontal to the upper side of the glass filter. And, one filter paper with a diameter of 90 mm was put thereon.

(35) Subsequently, the above prepared apparatus was mounted on the filter paper so that the superabsorbent polymer in the apparatus was swollen by the saline solution under load. After 1 hour, the weight W.sub.4 (g) of the apparatus including swollen superabsorbent polymer was measured.

(36) Using the measured weights, absorbency under load was calculated according to the following Calculation Formula 3.
AUL (g/g)=[W.sub.4(g)W.sub.3(g)]/W.sub.0(g)[Calculation Formula 3]

(37) In the Formula 3,

(38) W.sub.0 (g) is the initial weight (g) of superabsorbent polymer,

(39) W.sub.3 (g) is the sum of the weight of superabsorbent polymer and the weight of the apparatus capable of giving load to the superabsorbent polymer, and

(40) W.sub.4 (g) is the sum of the weight of superabsorbent polymer and the weight of the apparatus capable of giving load to the superabsorbent polymer, after a saline solution is absorbed in the superabsorbent polymer under load (0.7 psi) for 1 hour.

(41) TABLE-US-00001 TABLE 1 Perm [mL] CRC [g/g] AUL (0.7 psi) [g/g] Example 1 17 34.0 25.7 Example 2 24 32.5 25.8 Example 3 25 32.2 25.3 Example 4 16 31.7 24.5 Comparative 15 33.1 25.2 Example 1 Comparative 13 31.4 24.2 Example 2

(42) Referring to Table 1, it is confirmed that the superabsorbent polymers of Examples 1 to 4 wherein superabsorbent polymer was prepared in the presence of a heat-degradable internal crosslinking agent and inorganic material, have permeability calculated by the above Calculation Formula 1 of 16 mL/1 minute or more, and have both excellent centrifuge retention capacity and absorbency under load.

(43) To the contrary, the superabsorbent polymers of Comparative Examples 1 and 2 wherein inorganic material was not used together with a heat-degradable internal crosslinking agent, exhibited low permeability calculated by the above Calculation Formula 1.

(44) Meanwhile, comparing Example 1 and Comparative Example 1 using the same heat-degradable internal crosslinking agent, it is confirmed that Example 1 has excellent centrifuge retention capacity and absorbency under load, as well as excellent permeability, compared to Comparative Example 1. Similarly, comparing Example 4 and Comparative Example 2 using the same heat-degradable internal crosslinking agent, it is also confirmed that Example 4 have excellent centrifuge retention capacity and absorbency under load, as well as excellent permeability, compared to Comparative Example 2.

(45) Meanwhile, comparing Examples 1 to 4, it is confirmed that among the compounds represented by the Chemical Formula 1, the compound wherein R.sup.1 is methane-1,1-diyl(Example 3); propane-1,3-diyl(Example 1); or propane-1,2-diyl(Example 2) can realize high permeability while exhibiting relatively high centrifuge retention capacity.