A PROCESS FOR PRODUCING SURFACE-POSTCROSSLINKED WATER-ABSORBENT POLYMER PARTICLES BY POLYMERIZING DROPLETS OF A MONOMER SOLUTION

Abstract

The present invention relates to a process for producing surface-postcrosslinked water-absorbent polymer particles comprising polymerizing droplets of a monomer solution, wherein water-absorbent polymer particles having an average particle diameter from 150 to 400 , an amount of water-absorbent polymer particles having a particle size of less than 100 of less than 5% by weight and an amount of water-absorbent polymer particles having a particle size of more than 500 of less than 5% by weight are coated with at least one surface-postcrosslinker and thermal surface-postcrosslinked.

Claims

1. A process for producing surface-postcrosslinked water-absorbent polymer particles comprising polymerizing droplets of 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), e) optionally one or more water-soluble polymer, and f) water, in a surrounding heated gas phase or in a surrounding hydrophobic solvent, coating the water-absorbent polymer particles with at least one surface-postcrosslinker and thermal surface-postcrosslinking of the coated water-absorbent polymer particles, wherein the water-absorbent polymer particles are optionally classified prior to the coating, the water-absorbent polymer particles have an average particle diameter from 150 to 400 m prior to the coating and after the optional classification, the amount of water-absorbent polymer particles having a particle size of less than 100 m prior to the coating and after the optional classification is less than 5% by weight and the amount of water-absorbent polymer particles having a particle size of more than 500 m prior to the coating and after the optional classification is less than 5% by weight.

2. The process according to claim 1, wherein the water-absorbent polymer particles have an average particle diameter from 190 to 350 m prior to the coating and after the optional classification.

3. The process according to claim 1, wherein the amount of water-absorbent polymer particles having a particle size of less than 100 m prior to the coating and after the optional classification is less than 0.5% by weight.

4. The process according to claim 1, wherein the amount of water-absorbent polymer particles having a particle size of more than 500 m prior to the coating and after the optional classification is less than 0.5% by weight.

5. The process according to claim 1, wherein droplets of a monomer solution are polymerized in a surrounding heated gas phase, the droplets are generated by means of a plate having bores and the diameter of the bores is in the range from 50 to 170 m.

6. The process according to claim 5, wherein the diameter of the bores is in the range from 120 to 150 m.

7. The process according to claim 1, wherein a moisture content of the water-absorbent polymer prior to the coating and after the optional classification is in the range from 3 to 10% by weight.

8. The process according to claim 1, wherein temperature during the thermal surface-postcrosslinking is in the range from 140 to 160 C.

9. The process according to claim 1, wherein the at least one surface-postcrosslinker is selected from alkylene carbonates, 1,3 oxazolidin-2-ones, bis- and poly-1,3-oxazolidin-2-ones, bis- and poly-1,3-oxazolidines, 2 oxotetrahydro-1,3-oxazines, N-acyl-1,3 oxazolidin-2-ones, N-hydroxyethyl-1,3 oxazolidin-2-ones, cyclic ureas, bicyclic amide acetals, oxetanes, and morpholine-2,3-diones.

10. Water-absorbent polymer particles obtained according to claim 1.

11. Water-absorbent polymer particles having an average particle diameter from 150 to 400 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 5% by weight, a centrifuge retention capacity from 25 to 85 g/g, and an absorption under load of
AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC5.27 wherein AUL [g/g] is the absorption under load and CRC [g/g] is the centrifuge retention capacity.

12. Polymer particles according to claim 11, wherein the absorption under load is
AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC3.77 wherein AUL [g/g] is the absorption under load and CRC [g/g] is the centrifuge retention capacity.

13. Polymer particles according to claim 11, wherein the centrifuge retention capacity is from 45 to 65 g/g.

14. Water-absorbent polymer particles having an average particle diameter from 150 to 400 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 5% by weight, a centrifuge retention capacity from 20 to 60 g/g, and an absorption under load of
AUHL=0.00207CRC3+0.1755CRC24,485CRC+57,726 wherein AUHL [g/g] is the absorption under high load and CRC [g/g] is the centrifuge retention capacity.

15. Polymer particles according to claim 14, wherein the centrifuge retention capacity is from 30 to 50 g/g.

16. Polymer particles according to claim 10, wherein the average particle diameter is from 200 to 330 m.

17. Polymer particles according to claim 10, wherein the amount of water-absorbent polymer particles having a particle size of less than 100 m is less than 0.5% by weight.

18. Polymer particles according to claim 10, wherein the amount of water-absorbent polymer particles having a particle size of more than 500 m is less than 0.5% by weight.

19. Polymer particles according to claim 10, wherein the degree of polydispersity of the particle size is less than 0.3.

20. Polymer particles according to claim 10, wherein the roundness of the water-absorbent polymer particles is from 0.80 to 0.95.

21. Polymer particles according to claim 10, wherein water-absorbent polymer particles were thermal surface-postcrosslinked with at least one surface-postcrosslinker selected from alkylene carbonates, 1,3 oxazolidin-2-ones, bis- and poly-1,3-oxazolidin-2-ones, bis- and poly-1,3-oxazolidines, 2 oxotetrahydro-1,3-oxazines, N-acyl-1,3 oxazolidin-2-ones, N-hydroxyethyl-1,3 oxazolidin-2-ones, cyclic ureas, bicyclic amide acetals, oxetanes, and morpholine-2,3-diones.

22. A fluid-absorbent article, comprising water-absorbent polymer particles according to claim 10.

23. A fluid-absorbent article, comprising (A) an upper liquid-pervious layer, (B) a lower liquid-impervious layer, (C) a fluid-absorbent core between the layer (A) and the layer (B), comprising from 5 to 90% by weight fibrous material and from 10 to 95% by weight water-absorbent polymer particles, (D) an optional acquisition-distribution layer between (A) and (C), comprising from 80 to 100% by weight fibrous material and from 0 to 20% by weight water-absorbent polymer particles, (E) an optional tissue layer disposed immediately above and/or below (C) and (F) other optional components, wherein the water-absorbent polymer particles of (C) and (D) have an average particle diameter from 150 to 400 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 5% by weight, a centrifuge retention capacity from 25 to 85 g/g, and an absorption under load of
AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC5.27 wherein AUL [g/g] is the absorption under load and CRC [g/g] is the centrifuge retention capacity.

24. The fluid-absorbent article according to claim 23, wherein the fluid-absorbent article comprises in the fluid-absorbent core (C) less than 15% by weight fibrous material and/or adhesives.

Description

[0186] Preferred embodiments are depicted in FIGS. 1 to 15.

[0187] FIG. 1: Process scheme

[0188] FIG. 2: Process scheme using dry air

[0189] FIG. 3: Arrangement of the T_outlet measurement

[0190] FIG. 4: Arrangement of the dropletizer units with 3 droplet plates

[0191] FIG. 5: Arrangement of the dropletizer units with 9 droplet plates

[0192] FIG. 6: Arrangement of the dropletizer units with 9 droplet plates

[0193] FIG. 7: Dropletizer unit (longitudinal cut)

[0194] FIG. 8: Dropletizer unit (cross sectional view)

[0195] FIG. 9: Bottom of the internal fluidized bed (top view)

[0196] FIG. 10: openings in the bottom of the internal fluidized bed

[0197] FIG. 11: Rake stirrer for the intern fluidized bed (top view)

[0198] FIG. 12: Rake stirrer for the intern fluidized bed (cross sectional view)

[0199] FIG. 13: Process scheme (surface-postcrosslinking)

[0200] FIG. 14: Process scheme (surface-postcrosslinking and coating)

[0201] FIG. 15: Contact dryer for surface-postcrosslnking

[0202] The reference numerals have the following meanings: [0203] 1 Drying gas inlet pipe [0204] 2 Drying gas amount measurement [0205] 3 Gas distributor [0206] 4 Dropletizer unit(s) [0207] 4a Dropletizer unit [0208] 4b Dropletizer unit [0209] 4c Dropletizer unit [0210] 5 Reaction zone (cylindrical part of the spray dryer) [0211] 6 Cone [0212] 7 T_outlet measurement [0213] 8 Tower offgas pipe [0214] 9 Dust separation unit [0215] 10 Ventilator [0216] 11 Quench nozzles [0217] 12 Condenser column, counter current cooling [0218] 13 Heat exchanger [0219] 14 Pump [0220] 15 Pump [0221] 16 Water outlet [0222] 17 Ventilator [0223] 18 Offgas outlet [0224] 19 Nitrogen inlet [0225] 20 Heat exchanger [0226] 21 Ventilator [0227] 22 Heat exchanger [0228] 24 Water loading measurement [0229] 25 Conditioned internal fluidized bed gas [0230] 26 Internal fluidized bed product temperature measurement [0231] 27 Internal fluidized bed [0232] 28 Rotary valve [0233] 29 Sieve [0234] 30 End product [0235] 31 Static mixer [0236] 32 Static mixer [0237] 33 Initiator feed [0238] 34 Initiator feed [0239] 35 Monomer feed [0240] 36 Fine particle fraction outlet to rework [0241] 37 Gas drying unit [0242] 38 Monomer separator unit [0243] 39 Gas inlet pipe [0244] 40 Gas outlet pipe [0245] 41 Water outlet from the gas drying unit to condenser column [0246] 42 Waste water outlet [0247] 43 T_outlet measurement (average temperature out of 3 measurements around tower circumference) [0248] 45 Monomer premixed with initiator feed [0249] 46 Spray dryer tower wall [0250] 47 Dropletizer unit outer pipe [0251] 48 Dropletizer unit inner pipe [0252] 49 Dropletizer cassette [0253] 50 Teflon block [0254] 51 Valve [0255] 52 Monomer premixed with initiator feed inlet pipe connector [0256] 53 Droplet plate [0257] 54 Counter plate [0258] 55 Flow channels for temperature control water [0259] 56 Dead volume free flow channel for monomer solution [0260] 57 Dropletizer cassette stainless steel block [0261] 58 Bottom of the internal fluidized bed with four segments [0262] 59 Split openings of the segments [0263] 60 Rake stirrer [0264] 61 Prongs of the rake stirrer [0265] 62 Mixer [0266] 63 Optional coating feed [0267] 64 Postcrosslinker feed [0268] 65 Thermal dryer (surface-postcrosslinking) [0269] 66 Cooler [0270] 67 Optional coating/water feed [0271] 68 Coater [0272] 69 Coating/water feed [0273] 70 Base polymer feed [0274] 71 Discharge zone [0275] 72 Weir opening [0276] 73 Weir plate [0277] 74 Weir height 100% [0278] 75 Weir height 50% [0279] 76 Shaft [0280] 77 Discharge cone [0281] 78 Inclination angle [0282] 79 Temperature sensors (T.sub.1 to T.sub.6) [0283] 80 Paddle (shaft offset 90)

[0284] The drying gas is fed via a gas distributor (3) at the top of the spray dryer as shown in FIG. 1. The drying gas is partly recycled (drying gas loop) via a baghouse filter or cyclone unit (9) and a condenser column (12). The pressure inside the spray dryer is below ambient pressure.

[0285] The spray dryer outlet temperature is preferably measured at three points around the circumference at the end of the cylindrical part as shown in FIG. 3. The single measurements (43) are used to calculate the average cylindrical spray dryer outlet temperature.

[0286] In one preferred embodiment a monomer separator unit (38) is used for recycling of the monomers from the condenser column (12) into the monomer feed (35). This monomer separator unit is for example especially a combination of micro-, ultra-, nanofiltration and osmose membrane units, to separate the monomer from water and polymer particles. Suitable membrane separator systems are described, for example, in the monograph Membranen: Grundlagen, Verfahren und Industrielle Anwendungen, K. Ohlrogge and K. Ebert, Wiley-VCH, 2012 (ISBN: 978-3-527-66033-9).

[0287] The product accumulated in the internal fluidized bed (27). Conditioned internal fluidized bed gas is fed to the internal fluidized bed (27) via line (25). The relative humidity of the internal fluidized bed gas is preferably controlled by the temperature in the condensor column (12) and using the Mollier diagram.

[0288] The spray dryer offgas is filtered in a dust separation unit (9) and sent to a condenser column (12) for quenching/cooling. After dust separation (9) a recuperation heat exchanger system for preheating the gas after the condenser column (12) can be used. The dust separation unit (9) may be heat-traced on a temperature of preferably from 80 to 180 C., more preferably from 90 to 150 C., most preferably from 100 to 140 C.

[0289] Example for the dust separation unit are baghouse filter, membranes, cyclones, dust compactors and for examples described, for example, in the monographs Staubabscheiden, F. Liffler, Georg Thieme Verlag, Stuttgart, 1988 (ISBN 978-3137122012) and Staubabscheidung mit Schlauchfiltern und Taschenfiltern, F. Liffler, H. Dietrich and W. Flatt, Vieweg, Braunschweig, 1991 (ISBN 978-3540670629).

[0290] Most preferable are cyclones, for example, cyclones/centrifugal separators of the types ZSA/ZSB/ZSC from LTG Aktiengesellschaft and cyclone separators from Ventilatorenfabrik Oelde GmbH, Camfil Farr International and MikroPul GmbH.

[0291] Excess water is pumped out of the condenser column (12) by controlling the (constant) filling level in the condenser column (12). The water in the condenser column (12) is pumped counter-current to the gas via quench nozzles (11) and cooled by a heat exchanger (13) so that the temperature in the condenser column (12) is preferably from 40 to 71 C., more preferably from 46 to 69 C., most preferably from 49 to 65 C. and more even preferably from 51 to 60 C. The water in the condenser column (12) is set to an alkaline pH by dosing a neutralizing agent to wash out vapors of monomer a). Aqueous solution from the condenser column (12) can be sent back for preparation of the monomer solution.

[0292] The condenser column offgas may be split to the gas drying unit (37) and the conditioned internal fluidized bed gas (27).

[0293] The principle of a gas drying unit is described in the monograph Leitfaden for Loftungs-und KlimaanlagenGrundlagen der Thermodynamik Komponenten einer Vollklimaanlage Normen und Vorschriften, L. Keller, Oldenbourg Industrieverlag, 2009 (ISBN 978-3835631656). As gas drying unit can be used, for example, an air gas cooling system in combination with a gas mist eliminators or droplet separator (demister), for examples, droplet vane type separator for horizontal flow (e.g. type DH 5000 from Munters AB, Sweden) or vertical flow (e.g. type DV 270 from Munters AB, Sweden). Vane type demisters remove liquid droplets from continuous gas flows by inertial impaction. As the gas carrying entrained liquid droplets moves through the sinusoidal path of a vane, the higher density liquid droplets cannot follow and as a result, at every turn of the vane blades, these liquid droplets impinge on the vane surface. Most of the droplets adhere to the vane wall. When a droplet impinges on the vane blade at the same location, coalescence occurs. The coalesced droplets then drain down due to gravity.

[0294] As air gas cooling system, any gas/gas or gas/liquid heat exchanger can be used. Preferred are sealed plate heat exchangers.

[0295] In one embodiment dry air can be used as feed for the gas distributor (3). If air used as gas, then air can be transported via air inlet pipe (39) and can be dried in the gas drying unit (37), as described before. After the condenser column (12), the air, which not used for the internal fluidized bed is transported via the outlet pipe outside (40) of the plant as shown in FIG. 2.

[0296] The water, which is condensed in the gas drying unit (37) can be partially used as wash water for the condenser column (12) or disposed.

[0297] The gas temperatures are controlled via heat exchangers (20) and (22). The hot drying gas is fed to the cocurrent spray dryer via gas distributor (3). The gas distributor (3) consists preferably of a set of plates providing a pressure drop of preferably 1 to 100 mbar, more preferably 2 to 30 mbar, most preferably 4 to 20 mbar, depending on the drying gas amount. Turbulences and/or a centrifugal velocity can also be introduced into the drying gas if desired by using gas nozzles or baffle plates.

[0298] Conditioned internal fluidized bed gas is fed to the internal fluidized bed (27) via line (25). The steam content of the fluidized bed gas can be controlled by the temperature in the condenser column (12). The product holdup in the internal fluidized bed (27) can be controlled via rotational speed of the rotary valve (28).

[0299] The amount of gas in the internal fluidized bed (27) is selected so that the particles move free and turbulent in the internal fluidized bed (27). The product height in the internal fluidized bed (27) is with gas preferably at least 10%, more preferably at least 20%, more preferably at least 30%, even more preferably at least 40% higher than without gas.

[0300] The product is discharged from the internal fluidized bed (27) via rotary valve (28). The product holdup in the internal fluidized bed (27) can be controlled via rotational speed of the rotary valve (28). The sieve (29) is used for sieving off overs/lumps.

[0301] The monomer solution is preferably prepared by mixing first monomer a) with a neutralization agent and secondly with crosslinker b). The temperature during neutralization is controlled to preferably from 5 to 60 C., more preferably from 8 to 40 C., most preferably from 10 to 30 C., by using a heat exchanger and pumping in a loop. A filter unit is preferably used in the loop after the pump. The initiators are metered into the monomer solution upstream of the dropletizer by means of static mixers (31) and (32) via lines (33) and (34) as shown in FIG. 1 and FIG. 2. Preferably a peroxide solution having a temperature of preferably from 5 to 60 C., more preferably from 10 to 50 C., most preferably from 15 to 40 C., is added via line (33) and preferably an azo initiator solution having a temperature of preferably from 2 to 30 C., more preferably from 3 to 15 C., most preferably from 4 to 8 C., is added via line (34). Each initiator is preferably pumped in a loop and dosed via control valves to each dropletizer unit. A second filter unit is preferably used after the static mixer (32). The mean residence time of the monomer solution admixed with the full initiator package in the piping before dropletization is preferably less than 60 s, more preferably less than 30 s, most preferably less than 10 s.

[0302] For dosing the monomer solution into the top of the spray dryer preferably three dropletizer units are used as shown in FIG. 4. However, any number of dropletizers can be used that is required to optimize the throughput of the process and the quality of the product. Hence, in the present invention at least one dropletizer is employed, and as many dropletizers as geometrically allowed may be used.

[0303] A dropletizer unit consists of an outer pipe (47) having an opening for the dropletizer cassette (49) as shown in FIG. 7. The dropletizer cassette (49) is connected with an inner pipe (48). The inner pipe (48) having a PTFE block (50) at the end as sealing can be pushed in and out of the outer pipe (51) during operation of the process for maintenance purposes.

[0304] The temperature of the dropletizer cassette (57) is controlled to preferably 5 to 80 C., more preferably 10 to 70 C., most preferably 30 to 60 C., by water in flow channels (55) as shown in FIG. 8.

[0305] The dropletizer cassette has preferably from 10 to 2000 bores, more preferably from 50 to 1500 bores, most preferably from 100 to 1000 bores. The diameter of the bores size area is 1900 to 22300 .sup.2, more preferably from 7800 to 20100 m.sup.2, most preferably from 11300 to 17700 m.sup.2. The bores can be of circular, rectangular, triangular or any other shape. Circular bores are preferred with a bore size from 50 to 170 m, more preferably from 100 to 160 m, most preferably from 120 to 150 m. The ratio of bore length to bore diameter is preferably from 0.5 to 10, more preferably from 0.8 to 5, most preferably from 1 to 3. The droplet plate (53) can have a greater thickness than the bore length when using an inlet bore channel. The droplet plate (53) is preferably long and narrow as disclosed in WO 2008/086976 A1. Multiple rows of bores per droplet plate can be used, preferably from 1 to 20 rows, more preferably from 2 to 5 rows.

[0306] The dropletizer cassette (57) consists of a flow channel (56) having essential no stagnant volume for homogeneous distribution of the premixed monomer and initiator solutions and two droplet plates (53). The droplet plates (53) have an angled configuration with an angle of preferably from 1 to 900, more preferably from 3 to 45, most preferably from 5 to 20. Each droplet plate (53) is preferably made of a heat and/or chemically resistant material, such as stainless steel, polyether ether ketone, polycarbonate, polyarylsulfone, such as polysulfone, or polyphenylsulfone, or fluorous polymers, such as perfluoroalkoxyethylene, polytetrafluoroethylene, polyvinylidenfluorid, ethylene-chlorotrifluoroethylene copolymers, ethylene-tetrafl uoroethylene copolymers and fluorinated polyethylene. Coated droplet plates as disclosed in WO 2007/031441 A1 can also be used. The choice of material for the droplet plate is not limited except that droplet formation must work and it is preferable to use materials which do not catalyze the start of polymerization on its surface.

[0307] The arrangement of dropletizer cassettes is preferably rotationally symmetric or evenly distributed in the spray dryer (for example see FIG. 3 to 5).

[0308] In a preferred embodiment the angle configuration of the droplet plate (53) is in the middle lower then outside, for example: 4a=3, 4b=5 and 4c=8 (FIG. 5).

[0309] The throughput of monomer including initiator solutions per dropletizer unit is preferably from 10 to 4000 kg/h, more preferably from 100 to 1000 kg/h, most preferably from 200 to 600 kg/h. The throughput per bore is preferably from 0.1 to 10 kg/h, more preferably from 0.5 to 5 kg/h, most preferably from 0.7 to 2 kg/h.

[0310] The start-up of the cocurrent spray dryer (5) can be done in the following sequence: [0311] starting the condenser column (12), [0312] starting the ventilators (10) and (17), [0313] starting the heat exchanger (20), [0314] heating up the drying gas loop up to 95 C., [0315] starting the nitrogen feed via the nitrogen inlet (19), [0316] waiting until the residual oxygen is below 4% by weight, [0317] heating up the drying gas loop, [0318] at a temperature of 105 C. starting the water feed (not shown) and [0319] at target temperature stopping the water feed and starting the monomer feed via dropletizer unit (4)

[0320] The shut-down of the cocurrent spray dryer (5) can be done in the following sequence: [0321] stopping the monomer feed and starting the water feed (not shown), [0322] shut-down of the heat exchanger (20), [0323] cooling the drying gas loop via heat exchanger (13), [0324] at a temperature of 105 C. stopping the water feed, [0325] at a temperature of 60 C. stopping the nitrogen feed via the nitrogen inlet (19) and [0326] feeding air into the drying gas loop (not shown)

[0327] To prevent damages the cocurrent spray dryer (5) must be heated up and cooled down very carefully. Any quick temperature change must be avoided.

[0328] The openings in the bottom of the internal fluidized bed may be arranged in a way that the water-absorbent polymer particles flow in a cycle as shown in FIG. 9. The bottom shown in FIG. 9 comprises of four segments (58). The openings (59) in the segments (58) are in the shape of slits that guides the passing gas stream into the direction of the next segment (58). FIG. 10 shows an enlarged view of the openings (59).

[0329] The opening may have the shape of holes or slits. The diameter of the holes is preferred from 0.1 to 10 mm, more preferred from 0.2 to 5 mm, most preferred from 0.5 to 2 mm. The slits have a length of preferred from 1 to 100 mm, more preferred from 2 to 20 mm, most preferred from 5 to 10 mm, and a width of preferred from 0.5 to 20 mm, more preferred from 1 to 10 mm, most preferred from 2 to 5 mm.

[0330] FIG. 11 and FIG. 12 show a rake stirrer (60) that may be used in the internal fluidized bed. The prongs (61) of the rake have a staggered arrangement. The speed of rake stirrer is preferably from 0.5 to 20 rpm, more preferably from 1 to 10 rpm most preferably from 2 to 5 rpm.

[0331] For start-up the internal fluidized bed may be filled with a layer of water-absorbent polymer particles, preferably 5 to 50 cm, more preferably from 10 to 40 cm, most preferably from 15 to 30 cm.

[0332] Water-Absorbent Polymer Particles

[0333] The present invention further provides water-absorbent polymer particles obtainable by the process according to the invention.

[0334] The present invention further provides water-absorbent polymer particles having an average particle diameter (d.sub.50) from 150 to 400 m, preferably from 170 to 379 m, more preferably from 190 to 370 m, most preferably from 200 to 330 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, most preferably less than 0.5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 15% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, most preferably less than 2% by weight, a centrifuge retention capacity (CRC) from 20 to 85 g/g, preferably from 25 to 80 g/g, more preferably from 30 to 75 g/g, most preferably from 40 to 70 g/g, and an absorption under load (AUL) of

AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC5.27(FIG. 16: y0(x))

preferred

AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC3.77(FIG. 16: y0(x))

more preferred

AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC3.27(FIG. 16: y2(x))

most preferred

AUL>0.000415CRC.sup.3+0.0145CRC.sup.2+1.1166CRC2.77(FIG. 16: y3(x))

wherein AUL [g/g] is the absorption under load and CRC [g/g] is the centrifuge retention capacity.

[0335] The present invention further provides water-absorbent polymer particles having an average particle diameter (d.sub.50) from 150 to 400 m, preferably from 170 to 379 m, more preferably from 190 to 350 m, most preferably from 200 to 330 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, most preferably less than 0.5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 15% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, most preferably less than 2% by weight, a centrifuge retention capacity (CRC) from 20 to 50 g/g, preferably from 25 to 48 g/g, more preferably from 30 to 46 g/g, most preferably from 30 to 45 g/g and an absorption under high load (AUHL) of

AUHL=0,00207CRC.sup.3+0,1755CRC.sup.24,485CRC+57,726(FIG. 27: y0(x))

wherein AUHL [g/g] is the absorption under high load and CRC [g/g] is the centrifuge retention capacity.

[0336] The present invention further provides water-absorbent polymer particles having an average particle diameter (d.sub.50) from 150 to 400 m, preferably from 170 to 379 m, more preferably from 190 to 350 m, most preferably from 200 to 330 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, most preferably less than 0.5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, most preferably less than 0.5% by weight, a centrifuge retention capacity (CRC) from 20 to 85 g/g, preferably from 25 to 80 g/g, more preferably from 25 to 75 g/g, most preferably from 30 to 70 g/g, and a degree of polydispersity of the particle size of

=(d.sub.84.13d.sub.15.87)/(2d.sub.50)

wherein a is less than 0.3, preferred a less than 0.28, more preferred a less than 0.25, most preferred a less than 0.20, and

[0337] wherein d.sub.15.87, d.sub.50 and d.sub.84.13 are the values of the mesh size which gives rise to a cumulative 15.87%, 50.00%, and 84.13% by weight.

[0338] Preferred are water-absorbent polymer particles having an average particle diameter (d.sub.50) from 170 to 379 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 2% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 2% by weight, and a centrifuge retention capacity (CRC) from 25 to 80 g/g.

[0339] More preferred are water-absorbent polymer particles having an average particle diameter (d.sub.50) from 190 to 350 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 1% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 1% by weight, and a centrifuge retention capacity (CRC) from 35 to 75 g/g.

[0340] Most preferred are water-absorbent polymer particles having an average particle diameter (d.sub.50) from 200 to 330 m, an amount of water-absorbent polymer particles having a particle size of less than 100 m of less than 0.5% by weight, an amount of water-absorbent polymer particles having a particle size of more than 500 m of less than 0.5% by weight, and a centrifuge retention capacity (CRC) from 38 to 72 g/g.

[0341] The inventive water-absorbent polymer particles have roundness from preferably from 0.80 to 0.95, more preferably from 0.82 to 0.93, even more preferably from 0.84 to 0.91, most preferably from 0.85 to 0.90.

[0342] Water-absorbent polymer particles with relatively low roundness are obtained by reverse suspension polymerization when the polymer beads are agglomerated during or after the polymerization.

[0343] Water-absorbent polymer particles with relatively low roundness are also obtained by customary solution polymerization (gel polymerization). During preparation such water-absorbent polymers are ground and classified after drying to obtain irregular polymer particles.

[0344] The inventive water-absorbent polymer particles have a bulk density preferably from 0.6 to 1 g/cm.sup.3, more preferably from 0.65 to 0.95 g/cm.sup.3, most preferably from 0.7 to 0.9 g/cm.sup.3.

[0345] The inventive water-absorbent polymer particles have a HC 60 value of preferably at least 80, more preferably of at least 85, most preferably of at least 90.

[0346] The level of extractable constituents of the inventive water-absorbent polymer particles is preferably from 0.1 to 30% by weight, more preferably from 0.5 to 20% by weight, most preferably from 1 to 10% by weight.

[0347] The inventive water-absorbent polymer particles can be mixed with other water-absorbent polymer particles prepared by other processes, i.e. solution polymerization.

[0348] Fluid-Absorbent Articles

[0349] The present invention further provides fluid-absorbent articles. The fluid-absorbent articles comprise of [0350] (A) an upper liquid-pervious layer [0351] (B) a lower liquid-impervious layer [0352] (C) a fluid-absorbent core between (A) and (B) comprising from 5 to 90% by weight fibrous material and from 10 to 95% by weight water-absorbent polymer particles of the present invention; preferably from 20 to 80% by weight fibrous material and from 20 to 80% by weight water-absorbent polymer particles of the present invention; more preferably from 30 to 75% by weight fibrous material and from 25 to 70% by weight water-absorbent polymer particles of the present invention; most preferably from 40 to 70% by weight fibrous material and from 30 to 60% by weight water-absorbent polymer particles of the present invention; [0353] (D) an optional acquisition-distribution layer between (A) and (C), comprising from 80 to 100% by weight fibrous material and from 0 to 20% by weight water-absorbent polymer particles of the present invention; preferably from 85 to 99.9% by weight fibrous material and from 0.01 to 15% by weight water-absorbent polymer particles of the present invention; more preferably from 90 to 99.5% by weight fibrous material and from 0.5 to 10% by weight water-absorbent polymer particles of the present invention; most preferably from 95 to 99% by weight fibrous material and from 1 to 5% by weight water-absorbent polymer particles of the present invention; [0354] (E) an optional tissue layer disposed immediately above and/or below (C); and [0355] (F) other optional components.

[0356] Fluid-absorbent articles are understood to mean, for example, incontinence pads and incontinence briefs for adults or diapers for babies. Suitable fluid-absorbent articles including fluid-absorbent compositions comprising fibrous materials and optionally water-absorbent polymer particles to form fibrous webs or matrices for the substrates, layers, sheets and/or the fluid-absorbent core.

[0357] Suitable fluid-absorbent articles are composed of several layers whose individual elements must show preferably definite functional parameter such as dryness for the upper liquid-pervious layer, vapor permeability without wetting through for the lower liquid-impervious layer, a flexible, vapor permeable and thin fluid-absorbent core, showing fast absorption rates and being able to retain highest quantities of body fluids, and an acquisition-distribution layer between the upper layer and the core, acting as transport and distribution layer of the discharged body fluids. These individual elements are combined such that the resultant fluid-absorbent article meets overall criteria such as flexibility, water vapor breathability, dryness, wearing comfort and protection on the one side, and concerning liquid retention, rewet and prevention of wet through on the other side. The specific combination of these layers provides a fluid-absorbent article delivering both high protection levels as well as high comfort to the consumer.

[0358] The products as obtained by the present invention are also very suitable to be incorporated into low-fluff, low-fiber, fluff-less, or fiber-less hygiene article designs. Such designs and methods to make them are for example described in the following publications and literature cited therein and are expressly incorporated into the present invention: WO 2010/133529 A2, WO 2011/084981 A1, US 2011/0162989, US 2011/0270204, WO 2010/082373 A1, WO 2010/143635 A1, U.S. Pat. No. 6,972,011, WO 2012/048879 A1, WO 2012/052173 A1 und WO 2012/052172 A1.

[0359] The present invention further provides fluid-absorbent articles, comprising water-absorbent polymer particles of the present invention and less than 15% by weight fibrous material and/or adhesives in the absorbent core.

[0360] The water-absorbent polymer particles and the fluid-absorbent articles are tested by means of the test methods described below.

[0361] Methods:

[0362] The measurements should, unless stated otherwise, be carried out at an ambient temperature of 232 C. and a relative atmospheric humidity of 5010%. The water-absorbent polymers are mixed thoroughly before the measurement.

[0363] Residual Monomers

[0364] The level of residual monomers in the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 210.3 (11) Residual Monomers.

[0365] Particle Size Distribution

[0366] The particle size distribution of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 220.3 (11) Particle Size Distribution.

[0367] The average particle diameter (d.sub.50) here is the value of the mesh size which gives rise to a cumulative 50% by weight.

[0368] The degree of polydispersity of the particle size particle is calculated by

=(d.sub.84.13d.sub.15.87)/(2d.sub.50)

wherein d.sub.15.87 and d.sub.84.13 is the value of the mesh size which gives rise to a cumulative 15.87% respective 84.13% by weight.

[0369] Moisture Content

[0370] The moisture content of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 230.3 (11) Mass Loss Upon Heating.

[0371] Free Swell Capacity (FSC)

[0372] The free swell capacity of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 240.3 (11) Free Swell Capacity in Saline, Gravimetric Determination, wherein for higher values of the free swell capacity larger tea bags have to be used.

[0373] Centrifuge Retention Capacity (CRC)

[0374] The centrifuge retention capacity of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 241.3 (11) Fluid Retention Capacity in Saline, After Centrifugation, wherein for higher values of the centrifuge retention capacity larger tea bags have to be used.

[0375] Absorption Under Load (AUL)

[0376] The absorption under load of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 242.3 (11) Gravimetric Determination of Absorption Under Pressure.

[0377] Absorption Under High Load (AUHL)

[0378] The absortion under high load of the water-absorbent polymer particles is determined analogously to the EDANA recommended test method No. WSP 242.3 (11) Gravimetric Determination of Absorption Under Pressure, except using a weight of 49.2 g/cm.sup.2 instead of a weight of 21.0 g/cm.sup.2.

[0379] Bulk Density

[0380] The bulk density of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 250.3 (11) Gravimetric Determination of Density.

[0381] Extractables

[0382] The level of extractable constituents in the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 270.3 (11) Extractables.

[0383] Free Swell Rate (FSR)

[0384] 1.00 g (=W1) of the dry water-absorbent polymer particles is weighed into a 25 ml glass beaker and is uniformly distributed on the base of the glass beaker. 20 ml of a 0.9% by weight sodium chloride solution are then dispensed into a second glass beaker, the content of this beaker is rapidly added to the first beaker and a stopwatch is started. As soon as the last drop of salt solution is absorbed, confirmed by the disappearance of the reflection on the liquid surface, the stopwatch is stopped. The exact amount of liquid poured from the second beaker and absorbed by the polymer in the first beaker is accurately determined by weighing back the second beaker (=W2). The time needed for the absorption, which was measured with the stopwatch, is denoted t. The disappearance of the last drop of liquid on the surface is defined as time t.

[0385] The free swell rate (FSR) is calculated as follows:

FSR [g/gs]=W2/(W1t)

[0386] When the moisture content of the hydrogel-forming polymer is more than 3% by weight, however, the weight W1 must be corrected for this moisture content.

[0387] Roundness

[0388] The roundness is determined with the PartAn 3001 L Particle Analysator (Microtrac Europe GmbH; Meerbusch; Germany). The roundness is defined as

[00001]$\mathrm{Roundness}=\frac{4.Math..Math..Math.A}{U^2}$

where A is the cross-sectional area and U is the cross-sectional circumference of the polymer particles. The roundness is the volume-average roundness.

[0389] For the measurement, the product is introduced through a funnel and conveyed to the falling shaft with a metering channel. While the particles fall past a light wall, they are recorded selectively by a camera. The images recorded are evaluated by the software in accordance with the parameters selected.

[0390] Saline Flow Conductivity (SFC)

[0391] The saline flow conductivity of a swollen gel layer under a pressure of 0.3 psi (2070 Pa) is determined, as described in EP 2 535 698 A1, with a weight of 1.5 g of water-absorbing polymer particles as a urine permeability measurement (UPM) of a swollen gel layer. The flow is detected automatically.

[0392] The saline flow conductivity (SFC) is calculated as follows:

SFC[cm.sup.3s/g]=(Fg(t=0)L.sub.0)/(dAWP)

where Fg(t=0) is the flow of NaCl solution in g/s, which is obtained using linear regression analysis of the Fg(t) data of the flow determinations by extrapolation to t=0, L.sub.0 is the thickness of the gel layer in cm, d is the density of the NaCl solution in g/cm.sup.3, A is the area of the gel layer in cm.sup.2, and WP is the hydrostatic pressure over the gel layer in dynes/cm.sup.2.

[0393] Color Value (CIE Color Numbers [L, a, b])

[0394] Measurement of the color value is done by means of a colorimeter model LabScan XE S/N LX17309 (HunterLab; Reston; U.S.A.) according to the CIELAB procedure (Hunterlab, Volume 8, 1996, Issue 7, pages 1 to 4). Colors are described by the coordinates L, a, and b of a threedimensional system. L characterizes the brightness, whereby L=0 is black and L=100 is white. The values for a and b describe the position of the color on the color axis red/green resp. yellow/blue, whereby positive a values stand for red colors, negative a values for green colors, positive b values for yellow colors, and negative b values for blue colors.

[0395] The measurement of the color value is in agreement with the tristimulus method according to DIN 5033-6.

[0396] Fixed Height Absorption (FHA)

[0397] The fixed height absorption is a method to determine the ability of a swollen gel layer to transport fluid by wicking. It is executed and evaluated as described on page 9 and 10 in EP 1 493 453 A1. The following adjustments need to be made: [0398] Glass frit: 500 ml glass frit P40, as defined by ISO 4793, nominal pore size 16 to 40 m, thickness 7 mm, e.g. Duran Schott pore size class 3. [0399] Wet strength tissue: maximum basis weight 24.6 g/cm.sup.2, size 8080 mm, minimum wet tensile strength 0.32 N/cm (CD direction), and 0.8 N/cm (MD direction), e.g. supplied by Fripa Papierfabrik Albert Friedrich KG, D-63883 Miltenberg.

[0400] The tissue is clamped with a metal ring on the bottom side of the sample holder.

FHA[g/g]=(m.sub.3m.sub.2)/(m.sub.2m.sub.1)

[0401] where m.sub.1 is the weight of the empty sample holder in g, m.sub.2 is the weight of the sample holder with dry water-absorbent polymer particles in g, and m.sub.3 is the weight of the sample holder with swollen water-absorbent polymer particles in g.

[0402] The fixed height absorption is only determined in the context of the present invention with a hydrostatic column pressure corresponding to fixed height absorption at 20 cm.

[0403] Volumetric Absorption Under Load (VAUL)

[0404] The volumetric absorption under a load is used in order to measure the swelling kinetics, i.e. the characteristic swelling time, of water-absorbent polymer particles under different applied pressures. The height of swelling is recorded as a function of time.

[0405] The set-up is shown in FIG. 17 and consists of [0406] An ultrasonic distance sensor (85) type BUS M18K0-XBFX-030-S04K (Balluff GmbH, Neuhausen a.d.F.; Germany) is placed above the cell. The sensor receives ultrasound reflected by the metal plate. The sensor is connected to an electronic recorder. [0407] A PTFE cell (86) having a diameter of 75 mm, a height of 73 mm and an internal diameter of 52 mm. [0408] A cylinder (87) made of metal or plastic having a diameter of 50 mm, a height of 71 mm and a mesh at the bottom. [0409] A metal reflector (88) having a diameter of 57 mm and a height of 45 mm. [0410] Metal ring weights (89) having a diameter of 100 mm and weights calibrated to 278.0 g or 554.0 g

[0411] It is possible to adjust the pressure applied to the sample by changing the combination of cylinder (86) and metal ring (88) weight as summarized in the following tables:

TABLE-US-00001 Available Equipment Weight psi Metal reflector 13.0 g 0.009 Plastic cylinder 28.0 g 0.020 Metal cylinder 126.0 g 0.091 Small ring weight 278.0 g 0.201 Large ring weight 554.0 g 0.401

TABLE-US-00002 Possible Combinations psi Metal reflector + plastic cylinder 0.03 Metal reflector + metal cylinder 0.10 Metal reflector + metal cylinder + small ring weight 0.30 Metal reflector + metal cylinder + large ring weight 0.50 Metal reflector + metal cylinder + small ring weight + large ring 0.70 weight

[0412] A sample of 2.0 g of water-absorbent polymer particles is placed in the PTFE cell (86). The cylinder (87) and the metal reflector (88) on top are placed into the PTFE cell (86). In order to apply higher pressure, metal rings weights (89) can be placed on the cylinder. 60.0 g of aqueous saline solution (0.9% by weight) are added into the PTFE cell (86) with a syringe and the recording is started. During the swelling, the water-absorbent polymer particles push the cylinder (87) up and the changes in the distance between the metal reflector (88) and the sensor (85) are recorded.

[0413] After 120 minutes, the experiment is stopped and the recorded data are transferred from the recorder to a PC using a USB stick. The characteristic swelling time is calculated according to the equation Q(t)=Q.sub.max.Math.(1e.sup.t/) as described by Modern Superabsorbent Polymer Technology (page 155, equation 4.13), wherein Q(t) is the swelling of the water-absorbent polymer particles which is monitored during the experiment, Q.sub.max corresponds to the maximum swelling reached after 120 minutes (end of the experiment) and t is the characteristic swelling time ( is the inverse rate constant k).

[0414] Using the add-in functionality Solver of Microsoft Excel software, a theoretical curve can be fitted to the measured data and the characteristic time for 0.03 psi is calculated.

[0415] The measurements are repeated for different pressures (0.1 psi, 0.3 psi, 0.5 psi and 0.7 psi) using combinations of cylinder and ring weights. The characteristic swelling times for the different pressures can be calculated using the equation Q(t)=Q.sub.max(1e.sup.t/).

[0416] Wicking Absorption

[0417] The wicking absorption is used in order to measure the total liquid uptake of water-absorbent polymer particles under applied pressure. The experimental set-up is shown in FIG. 18.

[0418] A 500 mL glass bottle (90) (100 ml scale, height 26.5 cm) equipped with an exit tube of Duran glass, is filled with 500 mL of aqueous saline solution (0.9% by weight). The glass bottle (90) has an opening at the bottom end that can be connected to the Plexiglas plate (93) through a flexible hose (91).

[0419] A balance (92) connected to a computer is placed on Plexiglas block (area 2026 cm.sup.2, height 6 cm). The glass bottle (90) is then placed on the balance.

[0420] A Plexiglas plate (93) (area 1111 cm.sup.2, height 3.5 cm) is placed on a lifting platform. A porosity P1 glass frit (94) of 7 cm in diameter and 0.45 cm high has been liquid-tightly embedded in the Plexiglas plate (93), i.e. the fluid exits through the pores of the glass frit (94) and not via the edge between Plexiglas plate (93) and glass frit (94). A Plexiglas tube leads through the outer shell of Plexiglas plate (93) into the center of the Plexiglas plate up to the glass frit (94) to ensure fluid transportation. The fluid tube is then connected with the flexible hose (length 35 cm, 1.0 cm external diameter, 0.7 cm internal diameter) to the glass bottle (90).

[0421] The lifting platform is the used to adjust the upper side of the glass frit (94) to the level of the bottom end of the glass bottle (90), so that an always atmospheric flux of fluid from the glass bottle (90) to the measuring apparatus is ensured during measurement. The upper side of the glass frit (94) is adjusted such that its surface is moist but there is no standing film of water on the glass frit (94).

[0422] The aqueous saline solution in the glass bottle (90) is made up to 500 mL before every run.

[0423] In a Plexiglas cylinder (95) (external diameter 7 cm, internal diameter 6 cm, height 16 cm) and equipped with a 400 mesh (36 m) at the bottom are placed 26 g of water-absorbent polymer particles. The surface of the water-absorbent polymer particles is smoothed. The filling level is about 1.5 cm. Then, a weight (96) of 0.3 psi (21.0 g/cm.sup.2) is placed on top of the water-absorbent polymer particles.

[0424] The Plexiglas cylinder (95) is placed on the glass frit (94) and the electronic data recording started. A decrease in the weight of the balance (92) is registered as a function of time. This then indicates how much aqueous saline solution has been absorbed by the swelling gel of water-absorbent polymer particles at a certain time. The data are automatically captured every 10 seconds. The measurement is carried out at 0.3 psi (21.0 g/cm.sup.2) for a period of 120 minutes per sample. The total liquid uptake is the total amount of aqueous saline solution absorbed by each 26 g sample.

[0425] The EDANA test methods are obtainable, for example, from the EDANA, Avenue Eugene Plasky 157, B-1030 Brussels, Belgium.

EXAMPLES

Example 1

[0426] The process was performed in a concurrent spray drying plant with an integrated fluidized bed (27) as shown in FIG. 1. The reaction zone (5) had a height of 22 m and a diameter of 3.4 m. The internal fluidized bed (IFB) had a diameter of 3 m and a weir height of 0.25 m.

[0427] The drying gas was feed via a gas distributor (3) at the top of the spray dryer. The drying gas was partly recycled (drying gas loop) via a cyclone as dust separation unit (9) and a condenser column (12). The drying gas was nitrogen that comprises from 1% to 4% by volume of residual oxygen. Prior to the start of polymerization the drying gas loop was filled with nitrogen until the residual oxygen was below 4% by volume. The gas velocity of the drying gas in the reaction zone (5) was 0.79 m/s. The pressure inside the spray dryer was 4 mbar below ambient pressure.

[0428] The temperature of the gas leaving the reaction zone (5) was measured at three points around the circumference at the end of the cylindrical part of the spray dryer as shown in FIG. 3. Three single measurements (43) were used to calculate the average temperature (spray dryer outlet temperature). The drying gas loop was heated up and the dosage of monomer solution is started up. From this time the spray dryer outlet temperature was controlled to 115 C. by adjusting the gas inlet temperature via the heat exchanger (20). The gas inlet temperature was 167 C. and the steam content of the drying gas is shown in Tab. 1.

[0429] The product accumulated in the internal fluidized bed (27) until the weir height was reached.

[0430] Conditioned internal fluidized bed gas having a temperature of 117 was fed to the internal fluidized bed (27) via line (25). The gas velocity of the internal fluidized bed gas in the internal fluidized bed (27) was 0.65 m/s. The residence time of the product was 150 min. The temperature of the water-absorbent polymer particles in the internal fluidized bed (27) was 78 C.

[0431] The spray dryer offgas was filtered in cyclone as dust separation unit (9) and sent to a condenser column (12) for quenching/cooling. Excess water was pumped out of the condenser column (12) by controlling the (constant) filling level inside the condenser column (12). The water inside the condenser column (12) was cooled by a heat exchanger (13) and pumped counter-current to the gas. The temperature and the steam content of the gas leaving the condenser column (12) are shown in Tab. 1. The water inside the condenser column (12) was set to an alkaline pH by dosing sodium hydroxide solution to wash out acrylic acid vapors.

[0432] The gas leaving the condenser column (12) was split to the drying gas inlet pipe (1) and the conditioned internal fluidized bed gas (25). The gas temperatures were controlled via heat exchangers (20) and (22). The hot drying gas was fed to the concurrent spray dryer via gas distributor (3). The gas distributor (3) consists of a set of plates providing a pressure drop of 2 to 4 mbar depending on the drying gas amount.

[0433] The product was discharged from the internal fluidized bed (27) via rotary valve (28) into sieve (29). The sieve (29) was used for sieving off overs/lumps having a particle diameter of more than 800 m. The weight amounts of overs/lumps are summarized in Tab. 1.

[0434] The monomer solution was prepared by mixing first acrylic acid with 3-tuply ethoxylated glycerol triacrylate (internal crosslinker) and secondly with 37.3% by weight sodium acrylate solution. The temperature of the resulting monomer solution was controlled to 10 C. by using a heat exchanger and pumping in a loop. A filter unit having a mesh size of 250 m was used in the loop after the pump. The initiators were metered into the monomer solution upstream of the dropletizer by means of static mixers (31) and (32) via lines (33) and (34) as shown in FIG. 1. Sodium peroxodisulfate solution having a temperature of 20 C. was added via line (33) and [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride solution together with Brggolite FF7 having a temperature of 5 C. was added via line (34). Each initiator was pumped in a loop and dosed via control valves to each dropletizer unit. A second filter unit having a mesh size of 140 m was used after the static mixer (32). For dosing the monomer solution into the top of the spray dryer three dropletizer units were used as shown in FIG. 4.

[0435] A dropletizer unit consisted of an outer pipe (47) having an opening for the dropletizer cassette (49) as shown in FIG. 5. The dropletizer cassette (49) was connected with an inner pipe (48).

[0436] The inner pipe (48) having a PTFE block (50) at the end as sealing can be pushed in and out of the outer pipe (47) during operation of the process for maintenance purposes.

[0437] The temperature of the dropletizer cassette (49) was controlled to 8 C. by water in flow channels (55) as shown in FIG. 8. The dropletizer cassette (49) had 256 bores having a diameter of 170 m and a bore spacing of 15 mm. The dropletizer cassette (49) consisted of a flow channel (56) having essential no stagnant volume for homogeneous distribution of the premixed monomer and initiator solutions and one droplet plate (53). The droplet plate (53) had an angled configuration with an angle of 3. The droplet plate (53) was made of stainless steel and had a length of 630 mm, a width of 128 mm and a thickness of 1 mm.

[0438] The feed to the spray dryer consisted of 9.56% by weight of acrylic acid, 33.73% by weight of sodium acrylate, 0.018% by weight of 3-tuply ethoxylated glycerol Triacrylate (purity approx. 85% by weight), 0.071% by weight of [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 0.0028% by weight of Brggolite FF7 (Brggemann Chemicals; Heilbronn; Germany), 0.071% by weight of sodiumperoxodisulfate and water. The degree of neutralization was 73%. The feed per bore was 1.4 kg/h.

[0439] The resulting water-absorbent polymer particles were analyzed. The conditions and results are summarized in Tab. 1 to 3.

Example 2

[0440] The example was performed analogous to example 1, except that 0.014% by weight 3-tuply ethoxylated glycerol triacrylate was used instead of 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate Example 3 The example was performed analogous to example 1, except that 0.011% by weight 3-tuply ethoxylated glycerol triacrylate was used instead of 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate Example 4 The example was performed analogous to example 1, except that 0.007% by weight 3-tuply ethoxylated glycerol triacrylate was used instead of 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate Example 5 The example was performed analogous to example 1, except that no 3-tuply ethoxylated glycerol triacrylate was used.

Example 6

[0441] The example was performed analogous to example 1, except that 0.012% by weight 3-tuply ethoxylated glycerol triacrylate was used instead of 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate.

Example 7

[0442] The example was performed analogous to example 6, except that the feed to the spray dryer comprised further 0.053% by weight of Blancolen HP (Brggemann Chemicals; Heilbronn; Germany).

TABLE-US-00003 TABLE 1 Process conditions of the polymerization for examples 1 to 7 Steam Steam Content Content T T T T T T CC GD gas inlet gas outlet gas IFB IFB CC GDU kg/kg kg/kg C. C. C. C. C. C. 0.1100 0.0651 167 115 105 78 54 45 Steam Content CC: steam content of the gas leaving the condenser column (12) Steam Content GD: steam content of the gas prior to the gas distributor (3) T gas inlet: temperature of the gas prior to the gas distributor (3) T gas outlet: temperature of the gas leaving the reaction zone (5) T gas IFB temperature of the gas entering the internal fluidized bed (27) via line (25) T IFB: temperature of the water-absorbent polymer particles in the fluidized bed (27) T CC: temperature of the gas leaving the condenser column (12) T GDU: temperature of the gas leaving the gas drying unit (37)

TABLE-US-00004 TABLE 2 Properties of the water-absorbent polymer particles (base polymer) Bulk Density CRC AUL Residual Monomers Extractables Moisture Example g/cm.sup.3 g/g g/g ppm wt. % wt. % L a b 1 73.9 49.6 10.4 5220 4.6 7.9 93.18 2.48 1.56 2 74.4 51.9 9.7 4715 3.8 8.4 93.1 2.3 1.7 3 72.2 57.0 8.3 4940 6.7 8.6 93.3 2.3 1.6 4 73.5 64.8 7.5 4862 9.4 8.8 92.8 2.2 1.9 5 74.7 38.0 5.7 4123 3.8 8.3 93.5 2.2 2.2 6 69.8 48.1 8.6 5922 9.6 8.7 92.5 2.3 1.8 7 70.6 57.9 8.3 5541 9.8 8.1 92.8 1.9 3.5

TABLE-US-00005 TABLE 3 Particles Size Distribution (PSD) of the water-absorbent polymer particles (base polymer), measured by sieve fraction analysis 0-100 m 100-200 m 200-250 m 250-300 m 300-400 m 400-500 m 500-600 m 600-850 m 850-1000 m >1000 m Example wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % 1 0.1 2.2 6.2 12.6 44.4 26.7 5.7 1.9 0.2 0.0 2 0.1 2.1 6.5 12.9 43.6 28.7 4.6 1.4 0.1 0.0 3 0.1 1.7 5.8 12.2 43.8 26.1 6.4 3.7 0.2 0.0 4 0.0 0.7 3.0 8.6 41.1 32.5 9.1 4.6 0.2 0.0 5 0.2 2.2 5.8 11.4 45.1 27.9 5.7 1.7 0.1 0.0 6 0.1 1.4 7.1 10.6 35.2 31.6 8.6 4.8 0.4 0.2 7 0.3 2.4 5.8 9.3 38.9 27.8 8.0 6.6 0.8 0.3

Example 8

[0443] 1200 g of the water-absorbent polymer particles prepared in example 1 (base polymer) were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebrder Ldige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 24 g of ethylene carbonate, 2.4 g aluminum lactate and 60 g of deionized water, into a beaker, as described in Tab. 4. At a mixer speed of 200 rpm, the aqueous solution was sprayed onto the polymer particles within one minute by means of a spray nozzle. The mixing was continued for additional 5 minutes. The product was removed and transferred into another ploughshare mixer (model MR5, manufactured by Gebrder Ldige Maschinenbau GmbH; Paderborn; Germany) which was heated to 160 C. before. After mixing for further minutes at 150 or 160 C. with sample taking every 10 minutes, the product was removed from the mixer. The trial conditions and the results are summarized in Tab. 5 and 6.

Examples 9 to 14

[0444] The example was performed analogous to example 8, except that polymer particles prepared in examples 2 to 7 were used and the temperature of the thermal surface-postcrosslinking was 150 or 160 C., as described in Tab. 4.

Examples 13 a and b

[0445] The example was performed analogous to example 13, except that the polymer particles prepared in example 6 were sieved using a 400 m sieve prior to the thermal surface-postcrosslinking. Both fractions were separately thermal surface-postcrosslinked.

Examples 14 a and b

[0446] The example was performed analogous to example 14, except that the polymer particles prepared in example 7 were sieved using a 400 m sieve prior to the thermal surface-postcrosslinking. Both fractions were separately thermal surface-postcrosslinked.

Examples 14 c to f

[0447] The example was performed analogous to example 14, except that the polymer particles prepared in example 7 were sieved using 200, 300, 400, 500, and 850 m sieves prior to the thermal surface-postcrosslinking. The sieve fractions 200 to 300, 300 to 400, 400 to 500, and 500 to 850 m were separately thermal surface-postcrosslinked.

TABLE-US-00006 TABLE 4 Process conditions of the surface-postcrosslinking (SXL) Al- Lactate EC Water (dry) Temper- Base Sieve (SXL) (SXL) (SXL) ature Exam- polymer Cut wt. % wt. % wt. % (SXL) ple Example m bop bop bop C. 8*) 1 0-850 2.0 5.0 0.2 160 9*) 2 0-850 2.0 5.0 0.2 160 10*) 3 0-850 2.0 5.0 0.2 160 11*) 4 0-850 2.0 5.0 0.2 160 12*) 5 0-850 2.0 5.0 0.2 160 13*) 6 0-850 2.0 5.0 0.2 150 13a 6 0-400 2.0 5.0 0.2 150 13b*) 6 400-850 2.0 5.0 0.2 150 14*) 7 0-850 2.0 5.0 0.2 150 14a 7 0-400 2.0 5.0 0.2 150 14b*) 7 400-850 2.0 5.0 0.2 150 14c 7 200-300 2.0 5.0 0.2 150 14d 7 300-400 2.0 5.0 0.2 150 14e*) 7 400-500 2.0 5.0 0.2 150 14f*) 7 500-850 2.0 5.0 0.2 150 EC: Ethylene carbonate bop: based on polymer *)comparative

TABLE-US-00007 TABLE 5 Properties of the water-absorbent polymer particles after surface-postcrosslinking (SXL) Sieve Cut Time CRC AUL Example Base Polymer m min g/g g/g 8*) Example 1 0-850 30 38.7 35.7 40 35.2 33.2 50 33.3 32.5 60 31.9 31.2 70 30.2 30.5 80 29.9 29.6 9*) Example 2 0-850 30 39.9 36.1 40 36.1 34.4 50 34.5 33.0 60 32.3 31.7 70 31.3 31.5 80 30.7 30.5 10*) Example 3 0-850 30 43.3 36.2 40 40.5 35.8 50 38.2 35.1 60 36.8 34.4 70 35.2 33.8 80 34.6 33.5 11*) Example 4 0-850 30 45.7 36.4 40 42.8 36.5 50 40.9 36.6 60 38.8 35.8 70 37.8 35.3 80 36.8 34.7 12*) Example 5 0-850 30 61.3 21.7 40 53.3 33.1 50 48.0 35.7 60 45.1 36.3 70 43.0 36.3 80 40.9 36.0 90 35.1 33.3 100 34.4 32.9 13*) Example 6 0-850 30 50.0 34.6 40 48.9 35.5 50 47.0 35.7 60 46.1 36.4 70 44.2 36.3 13a 0-400 30 57.2 34.5 40 55.4 36.5 50 53.7 37.7 60 51.8 38.6 70 50.8 38.7 13b*) 400-850 30 43.7 34.4 40 42.3 34.5 50 41.1 34.4 60 40.5 34.3 70 39.9 34.1 14*) Example 7 0-850 20 48.0 33.6 30 44.4 34.7 40 42.5 35.0 50 41.4 34.9 60 40.6 34.7 14a 0-400 20 57.0 28.5 30 53.6 32.3 40 50.6 34.5 50 49.0 35.3 60 47.0 36.0 14b*) 400-850 20 65.5 21.3 30 61.5 30.0 40 57.8 33.7 50 55.2 36.1 60 54.0 36.9 14c 200-300 60 50.8 39.2 14d 300-400 60 48.2 38.4 14e*) 400-500 60 45.1 35.6 14f*) 500-850 60 44.6 33.1 *)comparative

TABLE-US-00008 TABLE 6 Particles Size Distribution (PSD) and average particle size (d.sub.50) of the water-absorbent polymer particles, measured by sieve fraction analysis. 0-50 50-100 100-150 150-200 200-300 300-400 400-500 500-600 600-850 >850 m m m m m m m m m m D.sub.15.87 d.sub.50 d.sub.84.13 Example wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % m m m 8*) 0.00 0.00 0.02 0.56 10.56 42.87 31.00 8.18 6.80 0.01 318 384 481 0.21 9*) 0.01 0.00 0.10 0.44 10.05 42.08 32.10 7.99 7.22 0.03 320 387 481 0.21 10*) 0.00 0.01 0.20 1.71 17.54 46.02 24.84 5.47 4.18 0.03 268 361 455 0.26 11*) 0.02 0.04 0.11 0.66 12.60 47.35 28.46 6.50 4.27 0.02 311 373 466 0.21 12*) 0.00 0.02 0.15 1.11 15.54 48.26 26.28 5.37 3.24 0.02 286 365 455 0.23 13*) 0.02 0.02 0.06 0.44 10.42 45.14 31.07 7.64 5.20 0.01 319 382 475 0.20 13a 0.03 0.04 0.11 0.79 18.57 78.22 2.21 0.03 0.00 0.00 276 340 380 0.15 13b*) 0.00 0.00 0.00 0.01 0.04 4.53 66.16 17.39 11.85 0.02 437 461 524 0.09 14*) 0.01 0.02 0.16 0.79 14.07 44.69 30.91 6.10 3.24 0.01 298 374 465 0.22 14a 0.02 0.03 0.27 1.32 23.55 71.25 3.45 0.11 0.00 0.00 253 336 380 0.19 14b*) 0.00 0.00 0.00 0.00 0.07 4.01 72.69 15.15 8.04 0.04 439 459 509 0.08 14c 0.00 0.00 0.02 6.10 85.45 8.41 0.02 0.00 0.00 0.00 216 245 284 0.14 14d 0.00 0.00 0.02 0.30 5.93 87.90 5.61 0.21 0.03 0.00 334 350 384 0.07 14e*) 0.00 0.00 0.00 0.03 0.67 8.02 84.89 5.54 0.83 0.02 428 448 484 0.06 14f*) 0.00 0.00 0.01 0.21 0.45 0.89 3.14 60.64 32.50 2.16 525 549 604 0.07 *)comparative

Example 15

[0448] 1200 g of the water-absorbent polymer particles prepared in example 1 (base polymer) were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebrder Ldige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 30 g of ethylene carbonate, 3.0 g aluminum lactate and 60 g of deionized water, into a beaker. At a mixer speed of 200 rpm, the aqueous solution was sprayed onto the polymer particles within one minute by means of a spray nozzle. The mixing was continued for additional 5 minutes. The product was removed and transferred into another ploughshare mixer (model MR5, manufactured by Gebrder Ldige Maschinenbau GmbH; Paderborn; Germany) which was heated to 160 C. before. After mixing for 55 minutes at 160 C. the product was removed from the mixer. The trial conditions and the results are summarized in Tab. 7 and 8 and FIG. 19 to 25.

Examples 15 a to g

[0449] The example was performed analogous to example 15, except that the polymer particles prepared in example 7 were sieved using 100, 200, 300, 400, 500, 600, 710, 850 and 1000 m sieves prior to the thermal surface-postcrosslinking. The sieve fractions 100 to 200, 200 to 300, 300 to 400, 400 to 500, 500 to 600, 600 to 710, and 710 to 850 m were separately thermal surface-postcrosslinked. The trial conditions and the results are summarized in Tab. 7 and 8 and FIG. 19 to 25.

Example 16 (Comparative Example)

[0450] By continuously mixing water, 50% by weight sodium hydroxide solution and acrylic acid, a 42.7% by weight acrylic acid/sodium acrylate solution was prepared such that the degree of neutralization was 69.0 mol %. After the components had been mixed, the monomer solution was cooled continuously to a temperature of 30 C. by means of a heat exchanger and degassed with nitrogen.

[0451] The polyethylenically unsaturated crosslinker used was 3-tuply ethoxylated glyceryl triacrylate (purity approx. 85% by weight). The amount used, based on the acrylic acid (boaa) used, was 0.35% by weight. To initiate the free-radical polymerization, the following components were used: 0.0008% by weight boaa of hydrogen peroxide, metered in as a 2.5% by weight aqueous solution, 0.13% by weight boaa of sodium peroxodisulfate, metered in as a 15% by weight aqueous solution, and 0.0023% by weight boaa of ascorbic acid, metered in as a 0.5% by weight aqueous solution. The throughput of the monomer solution was 800 kg/h.

[0452] The individual components were metered continuously into a continuous kneader reactor (model ORP 250 Contikneter, List AG, Arisdorf, Switzerland). In the first third of the reactor, 26.3 kg/h of removed undersize with a particle size of less than 150 m were additionally added.

[0453] The reaction solution had a feed temperature of 30 C. The residence time of the reaction mixture in the reactor was approx. 15 minutes.

[0454] Some of the polymer gel thus obtained was extruded with an SLRE 75 R extruder (Sela Maschinen GmbH; Harbke; Germany). The temperature of the polymer gel in the course of extrusion was 95 C. The perforated plate had 12 holes having a hole diameter of 8 mm. The thickness of the perforated plate was 16 mm. The ratio of internal length to internal diameter of the extruder (L/D) was 4. The specific mechanical energy (SME) of the extrusion was 26 kWh/t. The extruded polymer gel was distributed on metal sheets and dried at 175 C. in an air circulation drying cabinet for 90 minutes. The loading of the metal sheets with polymer gel was 0.81 g/cm.sup.2.

[0455] The dried polymer gel was ground by means of a one-stage roll mill (three milling runs, 1st milling run with gap width 1000 m, 2nd milling run with gap width 600 m and 3rd milling run with gap width 400 m). The ground dried polymer gel was classified and a synthetic particle size distribution (PSD) with the following composition was mixed: [0456] 600 to 710 m: 10.6% by weight [0457] 500 to 600 m: 27.9% by weight [0458] 300 to 500 m: 42.7% by weight [0459] 200 to 300 m: 13.8% by weight [0460] 150 to 200 m: 5.0% by weight

[0461] 1.2 kg of this polymer (base polymer) were coated in a plowshare mixer with heating jacket (model Pflugschar M5, Gebr. Ldige Maschinenbau GmbH, Paderborn, Germany) at 23 C. and a shaft speed of 200 revolutions per minute by means of a two-substance spray nozzle with 54.6 g of a mixture of 0.07% by weight of N-hydroxyethyl-2-oxazolidinone, 0.07% by weight of 1,3-propanediol, 0.7% by weight of propylene glycol, 2.27% by weight of a 22% by weight aqueous aluminum lactate solution, 0.448% by weight of a 0.9% by weight aqueous sorbitan monolaurate solution and 0.992% by weight of isopropanol, the percentages by weight each being based on base polymer.

[0462] After the spray application, the product temperature was increased to 185 C. and the reaction mixture was held at this temperature and a shaft speed of 50 revolutions per minute for 35 minutes. The resulting product was cooled to ambient temperature and classified again with a 850 m sieve. The trial conditions and the results are summarized in Tab. 7 and 8 and FIG. 19 to 25.

Example 16 a to g (Comparative Examples)

[0463] The example was performed analogous to example 16, except that the polymer particles prepared in example 7 were sieved using 100, 200, 300, 400, 500, 600, 710, 850 and 1000 m sieves prior to the thermal surface-postcrosslinking. The sieve fractions 100 to 200, 200 to 300, 300 to 400, 400 to 500, 500 to 600, 600 to 710, and 710 to 850 were separately thermal surface-postcrosslinked. The trial conditions and the results are summarized in Tab. 7 and 8 and FIG. 19 to 25.

TABLE-US-00009 TABLE 7 Properties of the water-absorbent polymer particles after surface-postcrosslinking (SXL) Sieve Average Wicking Fraction Sieve Width FSC CRC AUHL SFC CRC + AUHL FHA 0.3 psi uptake m m g/g g/g g/g 10.sup.7cm.sup.3s/g g/g g/g s g Example 15a 100-200 150 40.8 24.8 23.1 51 47.9 23.5 144 Example 15b 200-300 250 48.1 29.7 26.0 48 55.7 26.0 232 266 Example 15c 300-400 350 50.8 31.9 26.2 55 58.1 26.5 321 298 Example 15d*) 400-500 450 48.8 31.0 25.6 64 56.6 25.5 404 267 Example 15e*) 500-600 550 47.3 29.7 24.3 69 54.0 24.1 478 227 Example 15f*) 600-710 655 48.2 29.2 23.8 64 53.0 23.3 563 Example 15g*) 710-850 780 48.3 29.2 23.6 50 52.8 23.1 633 Example 15*) 0-850 47.1 30.3 24.6 62 54.9 25.4 290 Example 16a 100-200 150 35.9 20.3 21.0 116 41.3 20.9 46 Example 16b 200-300 250 42.6 22.9 22.5 102 45.4 21.9 81 284 Example 16c 300-400 350 46.8 25.2 23.3 88 48.5 21.6 136 242 Example 16d*) 400-500 450 50.0 27.4 23.9 74 51.2 19.8 206 223 Example 16e*) 500-610 550 51.5 28.3 24.0 77 52.3 19.4 279 203 Example 16f*) 610-710 655 51.6 29.4 23.9 68 53.3 17.8 360 186 Example 16g*) 710-850 780 50.9 29.7 23.6 65 53.3 14.0 478 Example 16 0-850 46.1 26.6 23.8 92 50.4 20.8 227 *)comparative

TABLE-US-00010 TABLE 8 Particles Size Distribution (PSD) and average particle size (d.sub.50) of the water-absorbent polymer particles, measured by sieve fraction analysis. 0-100 100-200 200-300 300-400 400-500 500-600 600-710 710-850 850-1000 m m m m m m m m m d.sub.50 d.sub.84.13 wt % wt % wt % wt % wt % wt % wt % wt % wt % D.sub.15.87 m m Example 15*) 0.31 5.31 21.35 54.32 13.34 3.42 1.54 0.40 0.01 284 344 410 0.18 Example 16*) 0.02 2.92 15.51 19.24 30.10 26.60 5.40 0.21 0.00 249 442 553 0.34 *)comparative

Example 17

[0464] 1200 g of the water-absorbent polymer particles prepared in example 1 (base polymer) were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebrder Ldige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 30 g of ethylene carbonate, 3.0 g aluminum lactate and 60 g of deionized water, into a beaker, as described in Table 4. At a mixer speed of 200 rpm, the aqueous solution was sprayed onto the polymer particles within one minute by means of a spray nozzle. The mixing was continued for additional 5 minutes. The product was removed and transferred into another ploughshare mixer (model MR5, manufactured by Gebrder Ldige Maschinenbau GmbH; Paderborn; Germany) which was heated to 160 C. before. After mixing for further minutes at 160 C. with sample taking every 10 minutes, the product was removed from the mixer. The trial conditions and the results are summarized in Tab. 9 and 11 and FIG. 26.

Example 17 a

[0465] The example was performed analogous to example 17, except that the polymer particles prepared in example 1 were sieved using a 400 m sieve prior to the thermal surface-postcrosslinking. The sieve fraction 0 to 400 m was separately thermal surface-postcrosslinked. The trial conditions and the results are summarized in Tab. 9 and 11 and FIG. 26.

Example 18

[0466] The example was performed analogous to example 17, except that water-absorbent polymer particles prepared in example 6 (base polymer) were used as base polymer. The trial conditions and the results are summarized in Tab. 10 and 11 and FIG. 26.

Example 18a

[0467] The example was performed analogous to example 18, except that the polymer particles prepared in example 6 were sieved using a 400 m sieve prior to the thermal surface-postcrosslinking. The sieve fraction 0 to 400 m was separately thermal surface-postcrosslinked. The trial conditions and the results are summarized in Tab. 10 and 11 and FIG. 26.

TABLE-US-00011 TABLE 9 Properties of the water-absorbent polymer particles after surface-postcrosslinking (SXL) Time FSC CRC AUL AUHL (CRC + AUHL) SFC FHA FSR min g/g g/g g/g g/g g/g 10.sup.7cm.sup.3 s/g g/g g/g Example 17a 20 70.0 52.1 34.0 14.1 66.2 30 62.5 43.7 37.1 25.7 69.4 40 59.3 40.5 36.5 27.3 67.8 50 56.4 37.2 35.2 27.6 64.8 7 60 54.5 35.5 34.2 27.7 63.2 11 70 52.0 33.9 33.3 27.1 61.0 18 80 51.5 33.0 32.8 26.8 59.8 23 90 50.9 32.3 32.2 26.8 59.1 33 100 49.3 31.3 31.6 26.3 57.6 34 27.0 0.27 Example 17*) 20 62.9 44.1 35.1 23.1 67.2 30 56.2 37.3 33.4 27.1 64.4 40 52.8 34.0 32.1 26.9 60.9 50 49.9 32.4 31.1 26.3 58.6 31 60 48.7 31.0 30.2 25.7 56.7 40 70 47.5 30.2 29.7 25.2 55.4 52 25.4 0.2 80 46.9 29.3 29.1 24.9 54.3 62 90 45.1 28.8 28.4 24.5 53.2 73 100 45.0 27.8 28.2 24.1 51.9 88 *)comparative

TABLE-US-00012 TABLE 10 Properties of the water-absorbent polymer particles after surface-postcrosslinking (SXL) Time FSC CRC AUL AUHL (CRC + AUHL) SFC FHA FSR min g/g g/g g/g g/g g/g 10.sup.7cm.sup.3 s/g g/g g/g Example 18a 20 72.9 54.8 33.7 9.2 64.0 30 63.6 43.6 37.3 25.0 68.6 40 58.9 38.9 36.0 27.7 66.6 5 50 55.7 36.5 34.6 27.7 64.2 10 60 53.0 34.2 33.5 27.5 61.7 18 70 51.9 33.1 32.8 26.9 60.0 23 80 50.6 32.0 31.8 26.8 58.8 34 90 48.7 30.5 31.2 26.5 57.0 43 100 48.3 30.3 30.6 25.9 56.2 47 26.5 0.26 Example 18*) 20 63.3 44.1 35.2 23.9 68.0 30 55.9 37.0 33.5 26.9 63.9 40 52.9 34.2 32.2 26.4 60.7 50 50.8 32.3 31.1 26.1 58.4 60 49.1 30.7 30.4 25.4 56.2 39 70 47.1 29.9 29.2 24.8 54.7 48 24.7 0.2 80 45.8 28.7 29.0 24.5 53.2 67 90 45.6 28.2 28.5 24.4 52.7 100 44.8 27.4 28.1 24.0 51.4 *)comparative

TABLE-US-00013 TABLE 11 Particles Size Distribution (PSD) and average particle size (d.sub.50) of the water-absorbent polymer particles, measured by sieve fraction analysis. 0-50 50-100 100-150 150-200 200-300 300-400 400-500 500-600 600-850 >850 m m m m m m m m m m d.sub.15.87 d.sub.50 d.sub.84.13 Unit Exp. wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % m m m 17*) 0.01 0.02 0.08 0.47 11.42 46.17 30.07 6.68 5.07 0.01 315 377 472 0.25 17a 0.03 0.04 0.12 0.76 18.46 78.22 2.35 0.02 0.00 0.00 276 339 358 0.06 18*) 0.01 0.02 0.13 0.72 13.07 46.45 31.87 5.08 2.64 0.01 305 374 465 0.24 18a 0.02 0.03 0.24 1.24 23.34 71.01 4.04 0.08 0.00 0.00 254 335 361 0.08 *)comparative