METHOD FOR PRODUCING SUPER ABSORBER PARTICLES

Abstract

A process for agglomerating superabsorbent particles, wherein polymer particles having a particle size of 250 m or less are dispersed in a hydrophobic organic solvent, the dispersed polymer particles are mixed with an aqueous monomer solution, the amount of unneutralized monomer applied with the monomer solution being from 0.5% to 80% by weight, based on the dispersed polymer particles, and the monomer solution is polymerized.

Claims

1. A process for agglomerating superabsorbent particles by polymerizing a first aqueous monomer solution 1 comprising a) at least one ethylenically unsaturated monomer which bears an acid group and optionally at least partly neutralized, b) optionally one or more crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a), and e) optionally one or more water-soluble polymer, and optionally drying and/or comminuting the resulting polymer particles, which comprises removing polymer particles having a particle size of 250 m or less, dispersing the polymer particles removed in a hydrophobic organic solvent, mixing the dispersed polymer particles with a second aqueous monomer solution comprising a) at least one ethylenically unsaturated monomer which bears an acid group and optionally at least partly neutralized, b) optionally one or more crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a) and e) optionally one or more water-soluble polymer, where the first monomer solution and the second monomer solution may be the same or different, an amount of unneutralized monomer a) applied with the second monomer solution being from 0.5% to 80% by weight, based on the dispersed polymer particles, and polymerizing the second monomer solution.

2. The process according to claim 1, wherein polymer particles having a particle size of 150 m or less are removed.

3. The process according to claim 1, wherein the amount of unneutralized monomer a) applied with the second monomer solution is from 5% to 30% by weight, based on the dispersed polymer particles.

4. The process according to claim 1, wherein the second monomer solution comprises from 0.01 to 0.50 mmol of crosslinker b), based on unneutralized monomer a).

5. The process according to claim 1, wherein the second monomer solution comprises from 0.05 to 0.15 mmol of crosslinker b), based on unneutralized monomer a).

6. The process according to claim 1, wherein the first monomer solution is polymerized by dropletizing polymerization.

7. The process according to claim 6, wherein the polymer particles are removed from the offgas of the dropletizing polymerization by means of a filter or cyclone.

8. The process according to claim 1, wherein the first monomer solution is polymerized by suspension polymerization and the resulting polymer particles are dried.

9. The process according to claim 1, wherein the first monomer solution is polymerized by solution polymerization and the resulting polymer particles are dried and comminuted.

10. The process according to claim 8, wherein the polymer particles are removed by means of a sieve having a mesh size of 250 m or less.

11. The process according to claim 9, wherein the polymer particles are removed by means of a sieve having a mesh size of 150 m or less.

12. Superabsorbent particles obtained by a process of claim 1, having a centrifuge retention capacity of 35 to 80 g/g and a free swell rate of 0.6 to 1.6 g/g s.

13. Superabsorbent particles according to claim 12, having a centrifuge retention capacity of 36 to 70 g/g and a free swell rate of 0.7 to 1.4 g/g s.

14. Superabsorbent particles according to claim 13, having a centrifuge retention capacity of 37 to 60 g/g and a free swell rate of 0.8 to 1.2 g/g s.

15. A hygiene article comprising (A) an upper liquid-permeable layer, (B) a lower liquid-impermeable layer, (C) a liquid-absorbing storage layer between layer (A) and layer (B), comprising from 0% to 30% by weight of a fibrous material and from 70 to 100% by weight of superabsorbent particles, (D) optionally an acquisition and distribution layer between layer (A) and layer (C), comprising from 80% to 100% by weight of a fibrous material and from 0 to 20% by weight of water-absorbing polymer particles, (E) optionally a fabric layer directly above and/or beneath layer (C), and (F) further optional components, wherein the superabsorbent particles in (C) and the water-absorbing polymer particles of (D) are according to claim 12.

16. The process according to claim 8, wherein the polymer particles are removed by means of a sieve having a mesh size of 250 m or less.

17. The process according to claim 8, wherein the polymer particles are removed by means of a sieve having a mesh size of 150 m or less.

Description

EXAMPLE 1

[0132] A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 500.00 g of heptane, 0.92 g of sucrose stearate (Ryoto Sugar Ester S-370, Mitsubishi Chemical Europe GmbH, Dusseldorf, Germany) and 60.00 g of superabsorbent particles, and heated to 70 C. while stirring under nitrogen until the sucrose stearate had dissolved fully. The superabsorbent particles were produced according to Example 1 of WO 2014/079694 A1 and separated out of stream (8) in FIG. 1.

[0133] A monomer solution 2 prepared from 50.00 g (0.694 mol) of acrylic acid, 41.63 g (0.520 mol) of 50% by weight aqueous sodium hydroxide solution, 46.71 g of water, 0.0125 g (0.081 mmol) of N,N-methylenebisacrylamide (MBA) and 0.167 g (0.618 mmol) of potassium peroxodisulfate was introduced into a feed vessel and purged with air. Monomer solution 2 was added dropwise at a stirrer speed of 400 rpm within 30 minutes. Monomer solution 2 was inertized with nitrogen immediately prior to the dropwise addition.

[0134] After feeding had ended, the mixture was stirred at 70 C. for a further 60 minutes. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

[0135] The suspension present was cooled to 60 C. and the resultant polymer particles were filtered off with suction using a Bchner funnel with a paper filter. The further drying was effected at 45 C. in an air circulation drying cabinet and optionally in a vacuum drying cabinet at 800 mbar down to a residual moisture content of less than 15% by weight.

[0136] The properties of the resultant polymer particles are summarized in tables 1 and 2.

EXAMPLE 2

[0137] The procedure was as in example 1, except that a monomer solution 2 prepared from 12.50 g (0.173 mol) of acrylic acid, 10.41 g (0.130 mol) of 50% by weight aqueous sodium hydroxide solution, 18.62 g of water, 0.0031 g (0.020 mmol) of N,N-methylenebisacrylamide (MBA) and 0.019 g (0.069 mmol) of potassium peroxodisulfate was used.

[0138] The properties of the resultant polymer particles are summarized in tables 1 and 2.

EXAMPLE 3

[0139] The procedure was as in example 1, except that a monomer solution 2 prepared from 12.50 g (0.173 mol) of acrylic acid, 10.41 g (0.130 mol) of 50% by weight aqueous sodium hydroxide solution, 18.62 g of water, 0.0063 g (0.041 mmol) of N,N-methylenebisacrylamide (MBA) and 0.019 g (0.069 mmol) of potassium peroxodisulfate was used.

[0140] The properties of the resultant polymer particles are summarized in tables 1 and 2.

EXAMPLE 4

[0141] The procedure was as in example 1, except that a monomer solution 2 prepared from 12.50 g (0.173 mol) of acrylic acid, 10.41 g (0.130 mol) of 50% by weight aqueous sodium hydroxide solution, 18.62 g of water, 0.0125 g (0.081 mmol) of N,N-methylenebisacrylamide (MBA) and 0.019 g (0.069 mmol) of potassium peroxodisulfate was used.

[0142] The properties of the resultant polymer particles are summarized in tables 1 and 2.

TABLE-US-00001 TABLE 1 Properties of the agglomerated superabsorbents AA MBA CRC FSR Moisture content Example % by wt. bop mmol boa g/g g/gs % by wt. 1*) 83 0.46 24.7 0.76 4.1 2 21 0.12 38.0 0.81 5.1 3 21 0.24 36.4 0.76 4.8 4 21 0.46 33.8 0.76 4.7 AA acrylic acid bop based on superabsorbent particles (polymer) MBA N,N-methylenebisacrylamide boa based on (unneutralized) acrylic acid *)comparative example

TABLE-US-00002 TABLE 2 Sieve analysis (% by weight) 100- 300- 400- 500- 600- 700- 800- 900- 200 300 400 500 600 700 800 900 1000 >1000 Ex. <100 m m m m m m m m m m m 1*) 1 2 5 8 9 6 10 7 7 5 40 2 2 13 27 24 12 4 4 2 2 2 8 3 1 8 20 22 14 6 7 3 3 2 12 4 2 8 20 24 16 7 8 3 2 2 8 *)comparative example