Method for preparing super absorbent polymer, and super absorbent polymer

Patent metadata

Field	Value
Publication number	US-10773237-B2
Application number	US-201715768343-A
Country	US
Kind code	B2
Filing date	Jan 3, 2017
Priority date	Mar 11, 2016
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

The present invention relates to a method for preparing a super absorbent polymer exhibiting improved liquid permeability, gel strength, absorption rate and the like while maintaining excellent absorption performance. The method for preparing the super absorbent polymer comprises the steps of: carrying out a crosslinking polymerization of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent to form a hydrogel polymer including a cross-linked polymer; drying, pulverizing, and classifying the hydrogel polymer to form a base polymer powder; and surface-crosslinking the base polymer powder by using a surface crosslinking liquid containing a surface crosslinking agent of an alkylene carbonate having 2 to 5 carbon atoms, in the presence of hydrophobic silica particles having a water-contact angle of more than 10° and 150° or less and hydrophilic silica particles having a water-contact angle of 10° or less.

First claim

The invention claimed is:

1. A super absorbent polymer comprising:
a base polymer powder including a first cross-linked polymer polymerized from a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups;
a surface cross-linked layer including a second cross-linked polymer formed on the base polymer powder, the second cross-linked polymer formed by further cross-linking the first cross-linked polymer using a surface crosslinking agent; and
a hydrophilic silica particle and having a water-contact angle of more than 1° and 10° or less, hydrophobic silica particles having a water-contact angle of more than 12° and 150° or less, and a polycarboxylic acid-based copolymer where the hydrophilic and hydrophobic particles, and the polycarboxylic acid-based copolymer are dispersed in the surface cross-linked layer,
wherein the super absorbent polymer has:
a EFFC represented by the following formula 1 of 24 to 28 g/g,
a saline flow conductivity (SFC) of 85 to 160 (·10 −7 cm 3 · s/g), the SFC measured using a physiological saline solution of 0.685 wt % sodium chloride aqueous solution, and
a gel strength (G′) of 9,000 to 15,000 Pa, wherein G′ is a horizontal gel strength of the super absorbent polymer measured using a rheometer, after absorbing and swelling the super absorbent polymer for 1 hour using a physiological saline solution of 0.9 wt % sodium chloride aqueous solution,
EFFC =( CRC+AUP )/2  [Formula 1]

in Formula 1,
the centrifuge retention capacity (CRC) of the superabsorbent polymer is measured for 30 minutes using a physiological saline solution of 0.9 wt % sodium chloride aqueous solution, and
the absorbency under pressure (AUP) of the superabsorbent polymer is measured under a load of 0.7 psi for 1 hour using a physiological saline solution of 0.9 wt % sodium chloride aqueous solution.

2. The super absorbent polymer of claim 1 , wherein the hydrophilic silica particles or the hydrophobic silica particles are dispersed in the surface cross-linked layer, or are embedded in the surface of the surface cross-linked layer.

3. The super absorbent polymer of claim 1 , wherein the hydrophilic silica particle have a water-contact angle of more than 1° and 3° or less, and
wherein the hydrophobic silica particles have a water-contact angle of 14° or more and 150° or less.

4. A method for preparing the superabsorbent polymer of claim 1 , the method comprising the steps of:
carrying out a crosslinking polymerization of the water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal crosslinking agent to form a hydrogel polymer including the cross-linked polymer;
drying, pulverizing, and classifying the hydrogel polymer to form the base polymer powder; and
surface-crosslinking the base polymer powder by using a surface crosslinking liquid containing a surface crosslinking agent of an alkylene carbonate having 2 to 5 carbon atoms, in the presence of the hydrophobic silica particles having a water-contact angle of more than 12° and 150° or less, and the hydrophilic silica particles having a water-contact angle of more than 1° and 10° or less.

5. The method for preparing a super absorbent polymer of claim 4 , wherein the surface crosslinking step comprises subjecting the base polymer powder to heat treatment in the presence of the hydrophobic silica particles, the hydrophilic silica particles, and the surface crosslinking liquid containing the surface crosslinking agent to carry out a surface crosslinking the surface.

6. The method for preparing a super absorbent polymer of claim 5 , wherein the hydrophobic silica particles have a water-contact angle of 50° to 150° and the surface crosslinking liquid further includes a dispersant.

7. The method for preparing a super absorbent polymer of claim 4 , wherein the hydrophobic silica particles and the hydrophilic silica particles are used in the content of 0.0001 to 0.3 parts by weight based on 100 parts by weight of the base polymer powder, respectively.

8. The method for preparing a super absorbent polymer of claim 4 , wherein the water-soluble ethylenically unsaturated monomer includes at least one selected from the group consisting of anionic monomers of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth)acrylamido-2-methylpropanesulfonic acid, and their salts; non-ionic, hydrophilic group-containing monomers of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, methoxypolyethylene glycol(meth)acrylate or polyethylene glycol (meth)acrylate; and amino group-containing unsaturated monomers of (N,N)-dimethylaminoethyl(meth)acrylate or (N,N)-dimethylaminopropyl(meth)acrylamide, and their quaternary product.

9. The method for preparing a super absorbent polymer of claim 4 , wherein the internal crosslinking agent includes at least one selected from the group consisting of bis(meth)acrylamide having 8 to 12 carbon atoms, poly(meth)acrylate of polyol having 2 to 10 carbon atoms and poly(meth)acrylate having 2 to 10 carbon atoms.

10. The method for preparing a super absorbent polymer of claim 4 , wherein the base polymer powder is pulverized and classified to have a particle size of 150 to 850 μm.

11. The method for preparing a super absorbent polymer of claim 4 , wherein the surface crosslinking step is carried out by subjecting to a heat treatment under the condition in which the temperature is raised from an initial temperature of 20° C. to 130° C. to a maximum temperature of 140° C. to 200° C. for 10 minutes to 40 minutes, and the maximum temperature is maintained for 5 minutes to 80 minutes.

Assignees

• Lg Chemical Ltd

Inventors

• Yoon Hyung Ki
• Nam Dae Woo
• Lee Hyemin
• Han Chang Sun
• Seo Sung Jong

Classifications

• C08L33/02

  Homopolymers or copolymers of acids; Metal or ammonium salts thereof · CPC title

• C08K7/26

  Silicon- containing compounds · CPC title

• C08J2300/14

  Water soluble or water swellable polymers, e.g. aqueous gels · CPC title

• C08J3/245 Primary

  Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking · CPC title

• C08F20/18

  with acrylic or methacrylic acids · CPC title