METHOD FOR PRODUCING WATER-ABSORBING POLYMER PARTICLES BY SUSPENSION POLYMERIZATION

Abstract

A process for producing water-absorbing polymer particles by suspension polymerization and thermal surface postcrosslinking, wherein the agglomerated base polymer obtained by suspension polymerization has a centrifuge retention capacity of at least 37 g/g and the thermal surface postcrosslinking is conducted at 100 to 190° C.

Claims

1. A process for producing water-absorbing polymer particles by polymerizing a monomer solution comprising a) at least one ethylenically unsaturated monomer which bears an acid group and optionally is 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, the monomer solution suspended in a hydrophobic organic solvent during the polymerization being agglomerated during or after the polymerization in the hydrophobic organic solvent, and thermally surface postcrosslinking the resultant agglomerated polymer particles by means of an organic surface postcrosslinker, wherein the amount of crosslinker b) is selected such that the agglomerated polymer particles before the surface postcrosslinking have a centrifuge retention capacity of at least 37 g/g and the thermal surface postcrosslinking is conducted at 100 to 190° C.

2. The process according to claim 1, wherein agglomeration is effected in the hydrophobic organic solvent after the polymerization.

3. The process according to claim 1, wherein the polymerization is conducted in the presence of a chain transfer reagent.

4. The process according to claim 1, wherein the amount of crosslinker b) is selected such that the polymer particles before the surface postcrosslinking have a centrifuge retention capacity of at least 40 g/g.

5. The process according to claim 1, wherein the thermal surface postcrosslinking is conducted at 120 to 170° C.

6. The process according to claim 1, wherein the organic surface postcrosslinker is selected from the group consisting of alkylene carbonates, 2-oxazolidinones, bis- and poly-2-oxazolidinones, 2-oxotetrahydro-1,3-oxazines, N-acyl-2-oxazolidinones, cyclic ureas, bicyclic amido acetals, oxetanes, and morpholine-2,3-diones.

7. The process according to claim 1, wherein from 1 to 5% by weight of organic surface postcrosslinker is used, based on the resultant polymer particles.

8. The process according to claim 1, wherein at least one dispersing aid is used in the polymerization.

9. The process according to claim 1, wherein the resultant polymer particles are at least partly dewatered azeotropically after the polymerization.

10. The process according to claim 9, wherein the resultant polymer particles are filtered and dried after the azeotropic dewatering.

11. The process according to claim 1, wherein the thermal surface postcrosslinking is conducted in a mixer with moving mixing tools.

12. Water-absorbing polymer particles by a process of claim 1, having a centrifuge retention capacity of at least 37 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 of at least 30 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 of at least 14 g/g, a sum total of centrifuge retention capacity and absorption under a pressure of 21.0 g/cm.sup.2 of at least 69 g/g, a sum total of centrifuge retention capacity and absorption under a pressure of 49.2 g/cm.sup.2 of at least 54 g/g, and less than 20% by weight of extractables.

13. Water-absorbing polymer particles according to claim 12, having a centrifuge retention capacity of at least 41 g/g.

14. Water-absorbing polymer particles according to claim 12, having an absorption under a pressure of 21.0 g/cm.sup.2 of at least 34 g/g.

15. Water-absorbing polymer particles according to claim 12, having an absorption under a pressure of 49.2 g/cm.sup.2 of at least 20 g/g.

16. Water-absorbing polymer particles according to claim 12, having a sum total of centrifuge retention capacity and absorption under a pressure of 21.0 g/cm.sup.2 of at least 74 g/g.

17. Water-absorbing polymer particles according to claim 12, having a sum total of centrifuge retention capacity and absorption under a pressure of 49.2 g/cm.sup.2 of at least 59 g/g.

18. Water-absorbing polymer particles according to claim 12, having less than 14% by weight of extractables.

19. Water-absorbing polymer particles according to claim 12, having a bulk density of less than 1.0 g/cm.sup.3.

20. Water-absorbing polymer particles according to claim 12, wherein the proportion of particles having a particle size of 300 to 600 μm is at least 30% by weight.

21. 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 water-absorbing polymer particles according to, (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 according to, (E) optionally a fabric layer directly above and/or beneath layer (C) and (F) further optional components, wherein the water-absorbing polymer particles in (C) and (D) have a centrifuge retention capacity of at least 37 q/q, an absorption under a pressure of 21.0 g/cm.sup.2 of at least 30 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 of at least 14 g/g, a sum total of centrifuge retention capacity and absorption under a pressure of 21.0 g/cm.sup.2 of at least 69 g/g, a sum total of centrifuge retention capacity and absorption under a pressure of 49.2 g/cm.sup.2 of at least 54 g/g, and less than 20% by weight of extractables.

Description

EXAMPLES

[0140] Production of the base polymer:

[0141] Example 1

[0142] A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 340.00 g of heptane and 0.92 g of sucrose stearate (Ryoto® Sugar Ester S-370, Mitsubishi Chemical Europe GmbH, Dusseldorf, Germany), and heated to 70° C. until the sucrose stearate had dissolved fully.

[0143] A monomer solution (first metered addition), prepared from 73.40 g (1.019 mol) of acrylic acid, 61.20 g (0.765 mol) of 50% by weight aqueous sodium hydroxide solution, 109.5 g of water and 0.11 g (0.407 mmol) of potassium peroxodisulfate, was then introduced into a feed vessel and purged with air. Immediately prior to the dropwise addition of the monomer solution, at a stirrer speed of 300 rpm, the solution was inertized by means of introduction of nitrogen and an oil bath temperature of 55° C. was established.

[0144] After feeding had ended, the mixture was stirred at 70° C. for a further hour, then the reaction solution was cooled to about 25° C. and an ice-cooled monomer solution (second metered addition), prepared from 95.90 g (1.331 mol) of acrylic acid, 79.30 g (0.991 mol) of 50% by weight aqueous sodium hydroxide solution, 143.10 g of water and 0.14 g (0.518 mmol) of potassium peroxodisulfate, was introduced into a feed vessel and purged with air. Immediately prior to the dropwise addition of the monomer solution, at a stirrer speed of 300 rpm, the solution was inertized by means of introduction of nitrogen. The monomer solution was added dropwise within 15 minutes.

[0145] After the feeding had ended, an oil bath temperature of 70° C. was established. 120 minutes after commencement of heating, the reflux condenser was exchanged for a water separator and water was separated out.

[0146] The suspension present was cooled to 60° C. and the resultant polymer particles were filtered off with suction using a Büchner 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.

[0147] The properties of the resulting polymer particles are summarized in table 2.

[0148] Examples 2 and 3

[0149] The base polymer was produced analogously to example 1 with the amounts stated in table 1. The properties of the resulting polymer particles are summarized in table 2.

[0150] Example 4

[0151] The base polymer was produced analogously to example 1 with the amounts stated in table 1, and the first monomer solution (first metered addition) additionally comprised 3.0 g of 2-propanol (isopropanol).

[0152] The properties of the resulting polymer particles are summarized in table 2.

[0153] Example 5

[0154] A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 896.00 g of cyclohexane, 2.00 g of Span® 20 (sorbitan monolaurate), 3.20 g of Tixogel® VZ (organophilic bentonite) and 20.0 g of a 0.015% aqueous ascorbic acid solution, and heated to internal temperature 75° C. while stirring and with introduction of nitrogen.

[0155] A monomer solution, prepared from 150.00 g (2.082 mol) of acrylic acid, 125.10 g (1.613 mol) of 50% by weight aqueous sodium hydroxide solution, 138 g of water, 0.0375 g (0.243 mmol) of N,N′-methylenebisacrylamide (MBA) and 0.5 g (1.850 mmol) of potassium peroxodisulfate, was then introduced into a feed vessel and purged with air. Immediately prior to the dropwise addition of the monomer solution, at a stirrer speed of 300 rpm, the solution was inertized by means of introduction of nitrogen. Over the entire period over which the monomers were metered in, the reflux conditions were maintained. The monomer solution was added dropwise within 60 minutes.

[0156] The end of feeding was followed by a further reaction time of 60 minutes. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

[0157] The suspension present was cooled to 60° C. and the resultant polymer particles were filtered off with suction using a Büchner 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.

[0158] The properties of the resulting polymer particles are summarized in table 2.

[0159] Example 6

[0160] A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 896.00 g of cyclohexane, 2.00 g of Span® 20 (sorbitan monolaurate), 3.20 g of Tixogel® VZ (organophilic bentonite) and 20.0 g of a 0.015% aqueous ascorbic acid solution, and heated to internal temperature 75° C. while stirring and with introduction of nitrogen.

[0161] A monomer solution, prepared from 150.00 g (2.082 mol) of acrylic acid, 118.0 g (1.475 mol) of 50% by weight aqueous sodium hydroxide solution, 136.8 g of water, 0.075 g (0.194 mmol) of the triacrylate of 3-tuply ethoxylated glycerol (Gly-(EO-AA).sub.3) and 0.5 g (1.850 mmol) of potassium peroxodisulfate, was then introduced into a feed vessel and purged with air. Immediately prior to the dropwise addition of the monomer solution, at a stirrer speed of 300 rpm, the solution was inertized by means of introduction of nitrogen. Over the entire period over which the monomers were metered in, the reflux conditions were maintained. The monomer solution was added dropwise within 60 minutes.

[0162] The end of feeding was followed by a further reaction time of 60 minutes. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

[0163] The suspension present was cooled to 60° C. and the resultant polymer particles were filtered off with suction using a Büchner 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.

[0164] The properties of the resulting polymer particles are summarized in table 2.

TABLE-US-00001 TABLE 1 Amounts of crosslinker b) used Step/ ppm mmol % Ex. feed Crosslinker b) g mmol boaa boaa 1 1 MBA 0 0 0 0 2 MBA 0 0 0 0 2 1 MBA 0.009 0.06 125 6 2 MBA 0.012 0.08 125 6 3 1 MBA 0.018 0.12 250 12 2 MBA 0.023 0.15 250 12 4 1 MBA*) 0.018 0.12 250 12 2 MBA*) 0.023 0.15 250 12 5 — MBA**) 0.0375 0.24 250 12 6 — Gly-(EO-AA).sub.3**) 0.075 0.19 500 9 *)isopropanol as additional chain transfer reagent **)one-stage metering boaa: based on (unneutralized) acrylic acid MBA: methylenebisacrylamide Gly-(EO-AA).sub.3 triacrylate of 3-tuply ethoxylated glycerol

TABLE-US-00002 TABLE 2 Properties of the water-absorbing polymer particles (base polymer) Bulk Moisture Extract- CRC AUNL AUL AUHL density content ables Ex. g/g g/g g/g g/g g/100 ml % % 1 55.0 44.3 7.2 6.6 89 2.2 34 2 46.1 54.1 7.3 6.7 78 4.5 21 3 42.8 52.0 7.4 6.5 79 4.4 21 4 48.4 54.1 7.8 7.2 83 4.0 20 5 40.7 39.9 7.5 6.6 70 3.5 26 6 64.0 9.7 6.9 6.1 91 2.0 29

[0165] Thermal surface postcrosslinking:

[0166] Examples 1-1 and 1-2

[0167] 20 g of base polymer from example 1 were introduced into a mixer of the Waring® 32BL80 (8011) blender type. Subsequently, the mixer was switched on at level 1. Immediately thereafter, 1.5 g of an aqueous solution consisting of 0.5 g of ethylene carbonate and 1.0 g of water, according to table 3, were introduced into a pipette and metered into the mixer within 2 seconds. After 3 seconds, the mixer was switched off and the resultant polymer particles were distributed homogeneously in a glass dish having a diameter of 20 cm. For thermal surface postcrosslinking, the glass dish filled with the polymer particles was heated in an air circulation drying cabinet at 160° C. for 60 or 120 minutes. The polymer particles were transferred to a cold glass dish. Finally, the coarser particles were removed with a sieve having a mesh size of 850 μm.

[0168] The properties of the polymer particles are summarized in table 4.

[0169] Examples 2-1 and 2-2

[0170] The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 2. The temperature in the air circulation drying cabinet was 160° C. The heat treatment time was 60 or 120 minutes. The conditions are summarized in table 3.

[0171] The properties of the polymer particles are summarized in table 4.

[0172] Examples 3-1 and 3-2

[0173] The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 3. The temperature in the air circulation drying cabinet was 160° C. The heat treatment time was 60 or 120 minutes. The conditions are summarized in table 3.

[0174] The properties of the polymer particles are summarized in table 4.

[0175] Examples 3-3 and 3-4

[0176] The thermal surface postcrosslinking was effected analogously to example 1-1, except using the base polymer from example 3 and using N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (Primid® XL 552) as surface postcrosslinker. The temperature in the air circulation drying cabinet was 160° C. The heat treatment time was 60 minutes. The conditions are summarized in table 3.

[0177] The properties of the polymer particles are summarized in table 4.

[0178] Examples 3-5 and 3-6

[0179] The thermal surface postcrosslinking was effected analogously to example 1-1, except using the base polymer from example 3. The temperature in the air circulation drying cabinet was 90° C. or 200° C. The heat treatment time was 60 minutes. The conditions are summarized in table 3.

[0180] The properties of the polymer particles are summarized in table 4.

[0181] Examples 4-1 and 4-2

[0182] The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 4. The temperature in the air circulation drying cabinet was 160° C. The heat treatment time was 60 or 120 minutes. The conditions are summarized in table 3.

[0183] The properties of the polymer particles are summarized in table 4.

[0184] Examples 5-1 and 5-2

[0185] The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 5. The temperature in the air circulation drying cabinet was 160° C. The heat treatment time was 60 or 120 minutes. The conditions are summarized in table 3.

[0186] The properties of the polymer particles are summarized in table 4.

[0187] Examples 6-1 and 6-2

[0188] The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 6. The temperature in the air circulation drying cabinet was 160° C. The heat treatment time was 60 or 120 minutes. The conditions are summarized in table 3.

[0189] The properties of the polymer particles are summarized in table 4.

[0190] Example 7

[0191] Example 1 from U.S. Pat. No. 8,003,210 was reworked.

[0192] The properties of the polymer particles are summarized in table 4.

TABLE-US-00003 TABLE 3 Thermal surface postcrosslinking in Waring ® blender - conditions Ethylene Ethylene carbonate Primid ® XL 552 Temperature Time carbonate mmol per 20 Water Primid ® XL 552 mmol per 20 Ex. Crosslinker b) ° C. min % by wt. bop g of polymer % by wt. bop % by wt. bop g of polymer 1  0 ppm MBA — — — — — — — 1-1 160 60 2.5 5.68 5 — — 1-2 160 120  2.5 5.68 5 — — 2 125 ppm MBA — — — — — — — 2-1 160 60 2.5 5.68 5 — — 2-2 160 120  2.5 5.68 5 — — 3 250 ppm MBA — — — — — — — 3-1 160 60 2.5 5.68 5 — — 3-2 160 120  2.5 5.68 5 — — 3-3 160 60 — — 5 4.55 2.84 3-4 160 60 — — 5 9.05 5.68 3-5  90 60 2.5 5.68 5 3-6 200 60 2.5 5.68 5 — — 4 250 ppm MBA*) — — — — — — — 4-1 160 60 2.5 5.68 5 — — 4-2 160 120  2.5 5.68 5 — — 5 250 ppm MBA**) — — — — — — — 5-1 160 60 2.5 5.68 5 — — 5-2 160 120  2.5 5.68 5 — — 6 500 ppm — — — — — — 6-1 Gly-(EO-AA).sub.3**) 160 60 2.5 5.68 5 — — 6-2 160 120  2.5 5.68 5 — — bop: based on (base) polymer *)isopropanol as additional chain transfer reagent **)one-stage agglomeration

TABLE-US-00004 TABLE 4 Thermal surface postcrosslinking in Waring ® blender - properties of the polymer particles CRC AUNL AUL AUHL Moisture content Extractables Vortex FSR CRC + AUL CRC + AUHL Ex. g/g g/g g/g g/g % by wt. % by wt. s g/g s g/g g/g 1 55.0 44.3 7.2 6.6 2.2 34 200 0.06 62.2 61.6 1-1 46.0 59.0 26.0 9.3 1.2 5 194 0.08 72.0 55.3 1-2 43.8 55.5 34.0 19.7 1.1 13 192 0.12 77.8 63.5 2 46.1 54.1 7.32 6.7 4.5 21 96 0.27 53.4 52.79 2-1 37.5 63.8 32.9 10.7 0.6 6 100 0.19 70.4 48.2 2-2 37.5 60.4 38.7 24.3 0.8 4 95 0.15 76.2 61.8 3 42.8 52.0 7.4 6.5 4.4 21 70 0.28 50.2 49.3 3-1 38.8 61.1 36.4 17.8 1.2 17 85 0.12 75.2 56.6 3-2 34.0 61.9 32.9 18.1 1.1 8 91 0.15 66.9 52.1 3-3 30.4 50.0 22.5 15.1 0.8 18 50 0.34 52.9 45.5 3-4 29.1 42.6 22.4 14.9 1.2 21 75 0.30 51.5 43.9  .sup.  3-5*) 41.9 52.6 7.6 7.1 2.9 22 71 0.26 49.5 49.0  .sup.  3-6*) 29.0 49.2 26.2 14.2 1.3 21 76 0.33 55.2 43.2 4 48.4 54.1 7.8 7.2 4.0 20 130 0.13 56.2 55.6 4-1 45.0 62.3 37.5 14.4 1.7 3 120 0.07 82.5 59.4 4-2 42.8 60.2 39.3 26.2 1.2 3 127 0.10 82.1 69.0 5 40.7 39.3 7.5 6.6 3.5 26 60 0.09 48.2 47.3 5-1 40.1 53.7 18.8 7.2 2.4 16.1 50 0.14 58.9 47.3 5-2 37.8 55.3 33.0 16.3 0.9 11.2 49 0.18 70.8 54.1 6 64.0 9.7 6.9 6.1 2 29 92 0.18 70.9 70.1 6-1 45.2 53.0 26.9 12.1 1.1 18.3 90 0.13 72.1 57.3 6-2 40.5 56.6 30.3 16.3 0.9 12.0 90 0.11 70.8 56.8  .sup.  7*) 44.3 63.9 12.1 7.1 4.0 22 62 0.33 56.4 51.4 *)comparative example