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 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. Water-absorbing polymer particles having a centrifuge retention capacity of at least 41 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 20 g/g, a sum total of centrifuge retention capacity and absorption under a pressure of 21.0 g/cm.sup.2 of at least 71 g/g, a sum total of centrifuge retention capacity and absorption under a pressure of 49.2 g/cm.sup.2 of at least 61 g/g, and less than 20% by weight of extractables.

2. The water-absorbing polymer particles according to claim 1, having an absorption under a pressure of 21.0 g/cm.sup.2 of at least 34 g/g.

3. The water-absorbing polymer particles according to claim 1, having a sum total of centrifuge retention capacity and absorption under a pressure of 21.0 g/cm2 of at least 74 g/g.

4. The water-absorbing polymer particles according to claim 1, having less than 14% by weight of extractables.

5. The water-absorbing polymer particles according to claim 1, having a bulk density of at least 1.0 g/cm.sup.3.

6. The water-absorbing polymer particles according to claim 1, wherein a proportion of particles having a particle size of 300 to 600 μm is at least 30% by weight.

7. The water-absorbing polymer particles according to claim 1 having a mean sphericity of at least 0.84.

8. The water-absorbing polymer particles according to claim 1 prepared by a process comprising a) at least one ethylenically unsaturated monomer which bears an acid groups 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, wherein the monomer solution is suspended in a hydrophobic organic solvent during the polymerization to provide polymer particles, then thermally surface postcrosslinking the polymer particles using an organic surface postcrosslinker, wherein an amount of crosslinker b) is selected such that the 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 175° C.

9. A hygiene article comprising (A) an upper liquid-impermeable layer, (B) a lower liquid-permeable 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, (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 water-absorbing polymer particles of (C) and (D) are according to claim 1.

Description

EXAMPLES

Production of the Base Polymer

Example 1

(1) A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 896.00 g of cyclohexane and 6.00 g of ethyl cellulose, and heated to internal temperature 75° C. with stirring and introduction of nitrogen. The monomer solution, prepared from 150.00 g (2.082 mol) of acrylic acid, 129.00 g (1.613 mol) of 50% by weight aqueous sodium hydroxide solution, 136.80 g of water, 0.113 g (0.73 mmol) of N,N′-methylenebisacrylamide (MBA) and 0.500 g (1.85 mmol) of potassium persulfate, was then introduced into a feed vessel and purged with air. Immediately prior to the dropwise addition of the monomer solution over a period of 1 h, the solution was inertized by introduction of nitrogen. The stirrer speed was 300 rpm. Over the entire period over which the monomers were metered in, the reflux conditions were maintained. The end of feeding was followed by the 60-minute further reaction period. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

(2) 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 5% by weight.

(3) The properties of the resultant polymer particles are summarized in tables 2 and 3.

Examples 2 to 6

(4) The base polymer was produced analogously to example 1 with the amounts stated in table 1.

(5) The properties of the resultant polymer particles are summarized in tables 2 and 3.

Example 7

(6) The base polymer was produced analogously to example 4, with combination of 30 batches.

(7) The properties of the resultant polymer particles are summarized in tables 2 and 3.

Example 8

(8) A 2 L flange vessel equipped with impeller stirrer and reflux condenser was initially charged with 896.00 g of cyclohexane and 6.00 g of ethyl cellulose, and heated to internal temperature 75° C. with stirring and introduction of nitrogen. The monomer solution, prepared from 150.00 g (2.082 mol) of acrylic acid, 129.00 g (1.613 mol) of 50% by weight aqueous sodium hydroxide solution, 136.80 g of water, 0.113 g (0.73 mmol) of N,N′-methylenebisacrylamide (MBA), 0.250 g (0.925 mmol) of potassium persulfate and 2.250 g of an 11.1% aqueous solution of 2,2′-azobis(imino-1-pyrrolidino-2-ethylpropane) dihydrochloride (0.711 mmol), was then introduced into a feed vessel and purged with air. Immediately prior to the dropwise addition of the monomer solution over a period of 1 h, the solution was inertized by introduction of nitrogen. The stirrer speed was 300 rpm. Over the entire period over which the monomers were metered in, the reflux conditions were maintained. The end of feeding was followed by the 60-minute further reaction period. Subsequently, the reflux condenser was exchanged for a water separator and water was separated out.

(9) 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 5% by weight.

(10) The properties of the resultant polymer particles are summarized in tables 2 and 3.

Example 9

(11) The base polymer was produced analogously to example 1 using 0.075 g (0.194 mmol) of the triacrylate of 3-tuply ethoxylated glycerol (Gly-(EO-AA).sub.3) rather than 0.113 g (0.73 mmol) of N,N′-methylenebisacrylamide (MBA) as internal crosslinker.

(12) The properties of the resultant polymer particles are summarized in tables 2 and 3.

Example 10

(13) The base polymer was produced analogously to example 9, except using 118.00 g (1.475 mol) of 50% by weight aqueous sodium hydroxide solution rather than 129.00 g (1.613 mol) of 50% by weight aqueous sodium hydroxide solution.

(14) The properties of the resultant polymer particles are summarized in tables 2 and 3.

(15) TABLE-US-00001 TABLE 1 Amounts of crosslinker b) used Ex. Crosslinker b) g mmol ppm boaa mmol % boaa 1 MBA 0.1125 0.730 750 35 2 MBA 0.0750 0.486 500 23 3 MBA 0.0563 0.365 375 18 4 MBA 0.0375 0.243 250 12 5 MBA 0.0188 0.122 125 6 6 MBA 0.0000 0.000 0 0 8 MBA 0.0375 0.243 250 12 9 Gly-(EO-AA).sub.3 0.0750 0.194 500 9 10 Gly-(EO-AA).sub.3 0.0750 0.194 500 9 boaa: based on (unneutralized) acrylic acid MBA: methylenebisacrylamide Gly-(EO-AA).sub.3 triacrylate of 3-tuply ethoxylated glycerol

(16) TABLE-US-00002 TABLE 2 Properties of the water-absorbing polymer particles (base polymer) CRC AUNL AUL AUHL Bulk density Moisture content Extractables Residual monomers Residual cyclohexane Ex. g/g g/g g/g g/g g/100 ml % % ppm ppm 1 33.6 41.5 24.5 16.5 94 3.6 8 12 380 2 31.1 37.0 22.1 13.6 98 10.1 7 0 200 3 39.9 46.4 22.2 9.8 102 2.7 16 26 260 4 43.6 47.4 15.6 9.2 102 2.8 13 24 220 5 50.8 53.4 10.2 7.6 102 3.7 20 15 200 6 61.7 53.4 7.6 6.4 102 2.8 31 23 170 7 41.6 45.6 20.3 8.5 99 2.8 13 14 210 8 49.6 48.4 8.7 7.4 101 3.4 17 39 200 9 45.3 50.8 15.5 7.2 100 1.9 14 21 210 10 45.2 49.9 12.6 7.2 101 3.0 16 24 190

(17) TABLE-US-00003 TABLE 3 Sieve analysis (base polymer) Sieve analysis in % by weight <100 100-200 200-300 300-400 400-500 500-600 600-710 710-800 800-900 900-1000 >1000 Ex. μm μm μm μm μm μm μm μm μm μm μm 1 1 7 28 37 16 4 3 1 1 0 2 2 1 9 26 37 19 5 2 0 0 0 0 3 1 7 27 36 18 5 3 1 1 1 1 4 1 6 24 37 19 5 4 2 1 1 0 5 0 5 21 33 19 7 6 3 2 1 2 6 1 10 33 39 13 2 1 0 0 0 0 7 0 3 17 31 23 10 8 3 2 1 2 8 0 3 13 24 19 9 11 6 6 4 5 9 0 8 32 37 15 4 2 1 0 0 0 10 0 4 20 29 17 8 10 6 4 1 1

Thermal Surface Postcrosslinking

Examples 1-1 and 1-2

(18) 20 g of base polymer from example 1 were introduced into a Waring® 32BL80 (8011) blender. Subsequently, the Waring® blender 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 4, were introduced into a pipette and metered into the blender within 2 sec. After 3 sec, the Waring® blender 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 75 min. 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.

(19) The properties of the polymer particles are summarized in table 5.

Examples 2-1 and 2-2

(20) The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 2. The heat treatment time was 60 or 75 min. The conditions are summarized in table 4.

(21) The properties of the polymer particles are summarized in table 5.

Examples 3-1 and 3-2

(22) The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 3. The heat treatment time was 75 or 90 min. The conditions are summarized in table 4.

(23) The properties of the polymer particles are summarized in table 5.

Examples 4-1 and 4-2

(24) The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 4. The heat treatment time was 60 or 75 min. The conditions are summarized in table 4.

(25) The properties of the polymer particles are summarized in table 5.

Example 4-3

(26) The thermal surface postcrosslinking was effected analogously to example 1-1, except using the base polymer from example 4 and additionally using aluminum trilactate. The heat treatment time was 90 min. The conditions are summarized in table 4.

(27) The properties of the polymer particles are summarized in table 5.

Examples 4-4 and 4-5

(28) The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 4 and using N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (Primid 6 XL 552) as surface postcrosslinker. The heat treatment time was 60 or 75 min. The conditions are summarized in table 4.

(29) The properties of the polymer particles are summarized in table 5.

Examples 5-1 and 5-2

(30) The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 2. The heat treatment time was 75 or 90 min. The conditions are summarized in table 4.

(31) The properties of the polymer particles are summarized in table 5.

Examples 6-1 and 6-2

(32) The thermal surface postcrosslinking was effected analogously to example 1-1 and 1-2, except using the base polymer from example 6. The heat treatment time was 60 or 75 min. The conditions are summarized in table 4.

(33) The properties of the polymer particles are summarized in table 5.

Examples 7-1 to 7-2

(34) 1.5 kg of water-absorbing polymer particles from example 7 were introduced at 23° C. into a Pflugschar® M5R paddle drier (Gebr. Lödige Maschinenbau GmbH, Paderborn, Germany), and a speed of 200 rpm was set on the Pflugschar® paddle drier. A solution consisting of 37.5 g of ethylene carbonate and 75.0 g of water was sprayed onto the product from above by means of a Büchi two-phase nozzle with 1 bar nitrogen within about 2 min, and then stirring of the product mixture continued for about 5 min.

(35) Subsequently, the product was transferred to a further Pflugschar® paddle drier. The Pflugschar® paddle drier had been preheated to a wall temperature of 190° C. Subsequently, the Pflugschar® paddle drier was set to a speed of 200 rpm. The temperature fell significantly as a result of the introduction of the product. The stirrer was started. On attainment of a product temperature of 143° C., the thermostat for the oil heating was turned down from 250° C. to 190° C. During the experiment, the heating was regulated such that a constant product temperature of 160° C. was established after about 20 min. The cooled product was sieved down to smaller than 850 μm on an AS400 sieve shaker (Retsch GmbH, Haan, Germany).

(36) The properties of the polymer particles are summarized in tables 6 and 7.

Examples 7-3 and 7-4

(37) The thermal surface postcrosslinking was effected analogously to example 7-1 and 7-2, except at lower temperature.

(38) The Pflugschar® paddle drier had been preheated to a wall temperature of 110° C. The temperature fell significantly as a result of the introduction of the product. On attainment of a product temperature of 83° C., the thermostat for the oil heating was turned down from 250° C. to 110° C. During the experiment, the heating was regulated such that a constant product temperature of 90° C. was established after about 20 min.

(39) The properties of the polymer particles are summarized in table 6.

Examples 7-5 and 7-6

(40) The thermal surface postcrosslinking was effected analogously to example 7-1 and 7-2, except at higher temperature.

(41) The Pflugschar® paddle drier had been preheated to a wall temperature of 220° C. The temperature fell significantly as a result of the introduction of the product. On attainment of a product temperature of 183° C., the thermostat for the oil heating was turned down from 250° C. to 230° C. During the experiment, the heating was regulated such that a constant product temperature of 200° C. was established after about 20 min.

(42) The properties of the polymer particles are summarized in table 6.

Examples 8-1, 8-2, 9-1 and 10-1

(43) The thermal surface postcrosslinking was effected analogously to example 1-1, except using the base polymer from example 8, 9 or 10. The conditions are summarized in table 4.

(44) TABLE-US-00004 TABLE 4 Thermal surface postcrosslinking in Waring ® blender-conditions Ethylene Temperature Time carbonate Water Al lactate Primid ® XL 552 Ex. Crosslinker b) ° C. min % by wt. bop % by wt. bop % by wt. bop % by wt. bop 1 750 ppm MBA — — — — — — 1-1*) 160 60 2.5 5 — — 1-2*) 160 75 2.5 5 — — 2 500 ppm MBA — — — — — — 2-1*) 160 60 2.5 5 — — 2-2*) 160 75 2.5 5 — — 3 375 ppm MBA — — — — — — 3-1 160 75 2.5 5 — — 3-2 160 90 2.5 5 — — 4 250 ppm MBA — — — — — — 4-1 160 60 2.5 5 — — 4-2 160 75 2.5 5 — — 4-3 160 75 2.5 5 0.5 — 4-4 160 75 — 5 — 0.25 4-5 160 90 — 5 — 0.25 5 125 ppm MBA — — — — — — 5-1 160 75 2.5 5 — — 5-2 160 90 2.5 5 — — 6  0 ppm MBA — — — — — — 6-1 160 60 2.5 5 — — 6-2 160 75 2.5 5 — — 8 250 ppm MBA — — — — — — 8-1 160 60 2.5 5 — — 8-2 160 75 2.5 5 — — 9 500 ppm Gly-(EO-AA).sub.3 — — — — — — 9-1 160 60 2.5 5 — — 10  500 ppm Gly-(EO-AA).sub.3 — — — — — — 10-1  160 60 2.5 5 — — *)comparative example

(45) TABLE-US-00005 TABLE 5 Thermal surface postcrosslinking in Waring ® blender- properties of the polymer particles CRC AUNL AUL AUHL Moisture content Extractables Vortex FSR Bulk density CRC + AUL CRC + AUHL Ex. g/g g/g g/g g/g % by wt. % by wt. s g/g s g/100 ml g/g g/g 1 33.6 41.5 24.5 16.5 3.6 8 94 58.1 50.1 1-1*) 35.0 45.4 31.5 24.3 1.7 3 101 0.09 96 66.5 59.3 1-2*) 33.7 46.7 32.9 25.0 1.5 3 112 0.10 97 66.6 58.7 2 31.1 37.0 22.1 13.6 10.1 7 98 53.2 44.7 2-1*) 35.8 47.0 32.2 25.0 1.3 4 117 0.09 101 68.0 60.8 2-2*) 35.1 45.5 32.4 24.9 1.1 4 125 0.09 102 67.5 60.0 3 39.9 46.4 22.2 9.8 2.7 16 102 62.1 49.7 3-1 43.8 52.6 32.6 19.4 1.3 9 126 0.14 101 76.4 63.2 3-2 42.9 52.8 31.1 19.1 1.2 6 189 0.09 102 74.0 62.0 4 45.3 49.4 18.9 7.3 3.1 13 102 64.2 52.6 4-1 45.3 47.0 29.0 13.2 1.2 5 107 0.11 100 74.3 58.5 4-2 45.2 45.5 30.2 19.0 1.1 4 112 0.09 102 75.4 64.2 4-3 38.8 50.1 30.8 16.0 1.5 10.8 152 0.17 99 69.6 54.7 4-4 41.1 41.5 23.5 10.0 1.2 15.0 179 0.13 100 64.5 51.1 4-5 41.8 45.2 24.3 13.3 1.2 16.6 178 0.11 101 66.1 55.1 5 50.8 53.4 10.2 7.2 3.7 20 102 61.0 58.0 5-1 47.3 57.1 28.2 10.2 1.5 8 131 0.10 99 75.5 57.5 5-2 49.4 58.0 25.3 12.4 1.3 6 125 0.08 102 74.7 61.8 6 61.7 53.4 7.6 6.4 2.8 31 102 69.3 68.1 6-1 59.3 64.9 18.3 8.3 1.4 10 102 0.13 102 77.6 67.6 6-2 54.8 65.7 18.1 9.5 1.3 11 91 0.14 103 76.5 64.3 8 49.6 48.4 8.7 7.4 3.4 17 166 — 101 58.3 57.0 8-1 44.3 52.1 32.6 20.7 1.2 9 105 0.14 98 76.9 61.0 8-2 44.1 51.5 34.7 23.9 0.9 5 110 0.13 97 78.8 68.0 9 45.3 50.8 15.5 7.2 1.9 14 170 — 100 60.8 52.5 9-1 50.2 63.0 33.8 14.0 0.4 5 112 0.13 103 84.0 64.2 10  45.2 49.9 12.6 7.2 3.0 16 — — 101 54.8 52.4 10-1  39.3 54.4 31.4 20.8 1.0 14 255 0.08 103 70.7 60.1 *)comparative example

(46) TABLE-US-00006 TABLE 6 Thermal surface postcrosslinking in a Pflugschar ® paddle drier-influence of temperature Moisture Extract- Bulk CRC + CRC + Temperature Time CRC AUNL AUL AUHL content ables Vortex FSR density AUL AUHL Ex. ° C. min g/g g/g g/g g/g % by wt. % by wt. s g/g s g/100 ml g/g g/g 7 — 41.6 45.6 20.3 8.5 2.8 8.8 155 0.1 99 59.1 50.1 7-1 160 40 37.8 52.9 35.8 23.1 1.3 3.3 149 0.1 102 72.2 60.9 7-2 160 60 36.0 49.7 33.4 24.1 1.1 8.7 143 0.1 101 53.5 60.1 7-3*) 90 40 38.7 43.7 19.5 7.5 4.8 10.1 165 0.1 94 58.2 46.2 7-4*) 90 60 39.2 44.2 19.1 7.4 4.3 10.3 172 0.1 93 58.3 46.6 7-5*) 200 40 33.8 38.1 30.0 21.0 1.1 11.1 145 0.1 99 63.8 54.8 7-6*) 200 60 31.9 36.6 29.6 18.8 0.5 13.9 181 0.1 99 61.5 50.7 *)comparative example

(47) TABLE-US-00007 TABLE 7 Thermal surface postcrosslinking in a Pflugschar ® paddle drier - Analysis with a PartAn ® 3001 L particle analyzer Ex. Mean sphericity (mSPHT) Mean particle diameter (D.sub.50) 7 0.89 381 μm 7-1 0.90 379 μm 7-2 0.90 374 μm