Process for producing surface-postcrosslinked water-absorbent polymer particles

Abstract

The present invention relates to a process for producing surface-postcrosslinked water-absorbent polymer particles by coating of water-absorbent polymer particles having a content of residual monomers in the range from 0.03 to 15% by weight with at least one surface-postcrosslinker and thermal surface-postcrosslinking at temperatures in the range from 100 to 180? C.

Claims

1. A process for producing surface-postcrosslinked water-absorbent polymer particles, comprising forming water-absorbent polymer particles by polymerizing a monomer solution, comprising a) at least one ethylenically unsaturated monomer which bears an acid group and may be 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, coating the water-absorbent polymer particles with at least one surface-postcrosslinker, and thermal surface-postcrosslinking the coated water-absorbent polymer particles, wherein a content of residual monomers in the water-absorbent polymer particles prior to the coating with the surface-postcrosslinker is in the range from 0.1 to 15% by weight, and a temperature during the thermal surface-postcrosslinking is in the range from 100 to 180? C. wherein the surface-postcrosslinked water-absorbent polymer particles have a centrifuge retention capacity from 35 to 75 g/g.

2. The process according to claim 1, wherein the monomer solution comprises at least one crosslinker b).

3. The process according to claim 1, wherein the surface-postcrosslinker is selected from the group consisting of 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, cyclic ureas, bicyclic amide acetals, oxetanes, and morpholine-2,3-diones.

4. The process according to claim 1, wherein the content of residual monomers in the water-absorbent polymer particles prior to the coating with the surface-postcrosslinker is in the range from 0.1 to 10% by weight.

5. The process according to claim 1, wherein the ethylenically unsaturated monomer which bears acid groups is an ethylenically unsaturated carboxylic acid.

6. The process according to claim 1, wherein the ethylenically unsaturated monomer which bears an acid group is acrylic acid.

7. The process according to claim 1, wherein a moisture content of the water-absorbent polymer particles prior to the thermal surface-postcrosslinking is in the range from 3 to 10% by weight.

8. The process according to claim 1, wherein the content of residual monomers in the water-absorbent polymer particles prior to the coating with the surface-postcrosslinker is in the range from 0.25 to 2.5% by weight.

9. The process according to claim 1, wherein the surface-postcrosslinker is ethylene carbonate, 3-methyl-1,3-oxazolidin-2-one, 3-methyl-3-oxethanmethanol, 1,3-oxazolidin-2-one, 3-(2-hydroxyethyl)-1,3-oxazolidin-2-one, 1,3-dioxan-2-one, or a mixture thereof.

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

11. Surface-postcrosslinked water-absorbent polymer particles prepared according to claim 1.

12. Polymer particles according to claim 11, wherein the polymer particles have an absorption under high load from 15 to 50 g/g and a sum of centrifuge retention capacity and absorption under high load is from 60 to 120 g/g.

13. 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 prepared according to claim 1, (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 prepared according to claim 1, and (E) an optional tissue layer disposed immediately above and/or below (C).

14. The process according to claim 1, wherein the temperature during the thermal surface-postcrosslinking is in the range of 100 to 170? C.

15. The process according to claim 1, wherein the temperature during the thermal surface-postcrosslinking is in the range of 130 to 165? C.

16. The process according to claim 1, wherein the content of residual monomers in the water-absorbent polymer particles prior to the coating with the surface-postcrosslinker is in the range of 0.15 to 7.5% by weight.

17. The process according to claim 1, wherein the content of residual monomers in the water-absorbent polymer particles prior to the coating with the surface-postcrosslinker is in the range of 0.2 to 5% by weight.

Description

(1) Preferred embodiments are depicted in FIGS. 1 to 12.

(2) FIG. 1: Process scheme (without external fluidized bed)

(3) FIG. 2: Process scheme (with external fluidized bed)

(4) FIG. 3: Arrangement of the T_outlet measurement

(5) FIG. 4: Arrangement of the dropletizer units

(6) FIG. 5: Dropletizer unit (longitudinal cut)

(7) FIG. 6: Dropletizer unit (cross sectional view)

(8) FIG. 7: Bottom of the internal fluidized bed (top view)

(9) FIG. 8: openings in the bottom of the internal fluidized bed

(10) FIG. 9: Rake stirrer for the intern fluidized bed (top view)

(11) FIG. 10: Rake stirrer for the intern fluidized bed (cross sectional view)

(12) FIG. 11: Process scheme (surface-postcrosslinking)

(13) FIG. 12: Process scheme (surface-postcrosslinking and coating)

(14) FIG. 13: Contact dryer for surface-postcrosslnking

(15) The reference numerals have the following meanings: 1 Drying gas inlet pipe 2 Drying gas amount measurement 3 Gas distributor 4 Dropletizer units 5 Cocurrent spray dryer, cylindrical part 6 Cone 7 T_outlet measurement 8 Tower offgas pipe 9 Baghouse filter 10 Ventilator 11 Quench nozzles 12 Condenser column, counter current cooling 13 Heat exchanger 14 Pump 15 Pump 16 Water outlet 17 Ventilator 18 Offgas outlet 19 Nitrogen inlet 20 Heat exchanger 21 Ventilator 22 Heat exchanger 23 Steam injection via nozzles 24 Water loading measurement 25 Conditioned internal fluidized bed gas 26 Internal fluidized bed product temperature measurement 27 Internal fluidized bed 28 Rotary valve 29 Sieve 30 End product 31 Static mixer 32 Static mixer 33 Initiator feed 34 Initiator feed 35 Monomer feed 36 Fine particle fraction outlet to rework 37 External fluidized bed 38 Ventilator 39 External fluidized bed offgas outlet to baghouse filter 40 Rotary valve 41 Filtered air inlet 42 Ventilator 43 Heat exchanger 44 Steam injection via nozzle 45 Water loading measurement 46 Conditioned external fluidized bed gas 47 T_outlet measurement (average temperature out of 3 measurements around tower circumference) 48 Dropletizer unit 49 Monomer premixed with initiator feed 50 Spray dryer tower wall 51 Dropletizer unit outer pipe 52 Dropletizer unit inner pipe 53 Dropletizer cassette 54 Teflon block 55 Valve 56 Monomer premixed with initiator feed inlet pipe connector 57 Droplet plate 58 Counter plate 59 Flow channels for temperature control water 60 Dead volume free flow channel for monomer solution 61 Dropletizer cassette stainless steel block 62 Bottom of the internal fluidized bed with four segments 63 Split openings of the segments 64 Rake stirrer 65 Prongs of the rake stirrer 66 Mixer 67 Optional coating feed 68 Postcrosslinker feed 69 Thermal dryer (surface-postcrosslinking) 70 Cooler 71 Optional coating/water feed 72 Coater 73 Coating/water feed 74 Base polymer feed 75 Discharge zone 76 Weir opening 77 weir plate 78 Weir height 100% 79 Weir height 50% 80 Shaft 81 Discharge cone 82 Inclination angle ? 83 Temperature sensors (Ti to Ts) 84 Paddle (shaft offset 90?)

(16) 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 (9) and a condenser column (12). The pressure inside the spray dryer is below ambient pressure.

(17) 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 (47) are used to calculate the average cylindrical spray dryer outlet temperature.

(18) 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 adding steam via line (23).

(19) The spray dryer offgas is filtered in baghouse filter (9) and sent to a condenser column (12) for quenching/cooling. After the baghouse filter (9) a recuperation heat exchanger system for preheating the gas after the condenser column (12) can be used. The baghouse filter (9) may be trace-heated on a temperature of preferably from 80 to 180? C., more preferably from 90 to 150? C., most preferably from 100 to 140? C. Excess water is 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) is cooled by a heat exchanger (13) and pumped counter-current to the gas via quench nozzles (11) so that the temperature inside the condenser column (12) is preferably from 20 to 100? C., more preferably from 25 to 80? C., most preferably from 30 to 60? C. The water inside 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.

(20) The condenser column offgas is split to the drying gas inlet pipe (1) and the conditioned internal fluidized bed gas (25). 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.

(21) Conditioned internal fluidized bed gas is fed to the internal fluidized bed (27) via line (25). The relative humidity of the external fluidized bed gas is preferably controlled by adding steam via line (23). To prevent any condensation the steam is added together with the internal fluidized bed into the heat exchanger (22). The product holdup in the internal fluidized bed (27) can be controlled via rotational speed of the rotary valve (28).

(22) 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.

(23) The monomer solution is preferably prepared by mixing first monomer a) with a neutralization agent and optionally 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. 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 the droplet plates (57) is preferably less than 60 s, more preferably less than 30 s, most preferably less than 10 s.

(24) 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.

(25) A dropletizer unit consists of an outer pipe (51) having an opening for the dropletizer cassette (53) as shown in FIG. 5. The dropletizer cassette (53) is connected with an inner pipe (52). The inner pipe (53) having a PTFE block (54) at the end as sealing can be pushed in and out of the outer pipe (51) during operation of the process for maintenance purposes.

(26) The temperature of the dropletizer cassette (61) 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 (59) as shown in FIG. 6.

(27) The dropletizer cassette has preferably from 10 to 1500, more preferably from 50 to 1000, most preferably from 100 to 500, bores having a diameter of preferably from 50 to 500 ?m, more preferably from 100 to 300 ?m, most preferably from 150 to 250 ?m. The bores can be of circular, rectangular, triangular or any other shape. Circular bores are preferred. 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 (57) can have a greater thickness than the bore length when using an inlet bore channel. The droplet plate (57) 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.

(28) The dropletizer cassette (61) consists of a flow channel (60) having essential no stagnant volume for homogeneous distribution of the premixed monomer and initiator solutions and two droplet plates (57). The droplet plates (57) have an angled configuration with an angle of preferably from 1 to 90?, more preferably from 3 to 45?, most preferably from 5 to 20?. Each droplet plate (57) 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-tetrafluoroethylene 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.

(29) The throughput of monomer including initiator solutions per dropletizer unit is preferably from 150 to 2500 kg/h, more preferably from 200 to 1000 kg/h, most preferably from 300 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.

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

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

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

(33) 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. 7. The bottom shown in FIG. 7 comprises of four segments (62). The openings (63) in the segments (62) are in the shape of slits that guides the passing gas stream into the direction of the next segment (62). FIG. 8 shows an enlarged view of the openings (63).

(34) 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.

(35) FIG. 9 and FIG. 10 show a rake stirrer (64) that may be used in the internal fluidized bed. The prongs (65) 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.

(36) 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.

(37) Water-Absorbent Polymer Particles

(38) The present invention provides water-absorbent polymer particles obtainable by the process according to the invention.

(39) The present invention further provides surface-postcrosslinked water-absorbent polymer particles having a centrifuge retention capacity from 35 to 75 g/g, an absorption under high load from 20 to 50 g/g, a level of extractable constituents of less than 10% by weight, and a porosity from 20 to 40%.

(40) It is particular advantageous that the surface-postcrosslinked water-absorbent polymer particles obtainable by the process according to the invention exhibit a very high centrifuge retention capacity (CRC) and a high absorption under high load (AUHL), and that the sum of these parameters (=CRC+AUHL) is at least 60 g/g, preferably at least 65 g/g, most preferably at least 70 g/g, and not more than 120 g/g, preferably less than 100 g/g, more preferably less than 90 g/g, and most preferably less than 80 g/g. The surface-postcrosslinked water-absorbent polymer particles obtainable by the process according to the invention further preferably exhibit an absorption under high load (AUHL) of at least 15 g/g, preferably at least 18 g/g, more preferably at least 21 g/g, most preferably at least 25 g/g, and not more than 50 g/g.

(41) As the centrifuge retention capacity (CRC) is the maximum water retention capacity of the surface-postcrosslinked water-absorbent polymer particles it is of interest to maximize this parameter. However the absorption under high load (AUHL) is important to allow the fiber-matrix in a hygiene article to open up pores during swelling to allow further liquid to pass easily through the article structure to enable rapid uptake of this liquid. Hence there is a need to maximize both parameters.

(42) The inventive water-absorbent polymer particles have a centrifuge retention capacity (CRC) from 35 to 75 g/g, preferably from 37 to 65 g/g, more preferably from 39 to 60 g/g, most preferably from 40 to 55 g/g.

(43) The inventive water-absorbent polymer particles have an absorbency under a load of 49.2 g/cm.sup.2 (AUHL) from 20 to 50 g/g, preferably from 22 to 45 g/g, more preferably from 24 to 40 g/g, most preferably from 25 to 35 g/g.

(44) The inventive water-absorbent polymer particles have a level of extractable constituents of less than 10% by weight, preferably less than 8% by weight, more preferably less than 6% by weight, most preferably less than 5% by weight.

(45) The inventive water-absorbent polymer particles have a porosity from 20 to 40%, preferably from 22 to 38%, more preferably from 24 to 36%, most preferably from 25 to 35%.

(46) Preferred water-absorbent polymer particles are polymer particles having a centrifuge retention capacity (CRC) from 37 to 65 g/g, an absorption under high load (AUHL) from 22 to 45 g/g, a level of extractable constituents of less than 8% by weight and a porosity from 22 to 45%.

(47) More preferred water-absorbent polymer particles are polymer particles having a centrifuge retention capacity (CRC) from 39 to 60 g/g, an absorption under high load (AUHL) from 24 to 40 g/g, a level of extractable constituents of less than 6% by weight and a porosity from 24 to 40%.

(48) Most preferred water-absorbent polymer particles are polymer particles having a centrifuge retention capacity (CRC) from 40 to 55 g/g, an absorption under high load (AUHL) from 25 to 35 g/g, a level of extractable constituents of less than 5% by weight and a porosity from 25 to 35%.

(49) The present invention further provides surface-postcrosslinked water-absorbent polymer particles having a total liquid uptake of
Y>?500?ln(X)+1880,
preferably Y>?495?ln(X)+1875,
more preferably Y>?490?n(X)+1870,
most preferably Y>?485?n(X)+1865,
wherein Y [g] is the total liquid uptake and X [g/g] is the centrifuge retention capacity (CRC), wherein the centrifuge retention capacity (CRC) is at least 25 g/g, preferably at least 30 g/g, more preferably at least 35 g/g, most preferably at least 40 g/g, and the liquid uptake is at least 30 g, preferably at least 35 g/g, more preferably at least 40 g/g, most preferably at least 45 g/g.

(50) The present invention further provides surface-postcrosslinked water-absorbent polymer particles having a change of characteristic swelling time of less than 0.6, preferably less than 0.5, more preferably less than 0.45, most preferably less than 0.4, and a centrifuge retention capacity (CRC) of at least 35 g/g, preferably at least 37 g/g, more preferably at least 38.5 g/g, most preferably at least 40 g/g, wherein the change of characteristic swelling time is
Z<(?.sub.0.5??.sub.0.1)/?.sub.0.5
wherein Z is the change of characteristic swelling time, ?.sub.0.1 is the characteristic swelling time under a pressure of 0.1 psi (6.9 g/cm.sup.2) and ?.sub.0.5 is the characteristic swelling time under a pressure of 0.5 psi (35.0 g/cm.sup.2).

(51) The inventive water-absorbent polymer particles have a mean sphericity from 0.80 to 0.95, preferably from 0.82 to 0.93, more preferably from 0.84 to 0.91, most preferably from 0.85 to 0.90. The sphericity (SPHT) is defined as

(52) $SPHT=\frac{4?A}{U_2},$
where A is the cross-sectional area and U is the cross-sectional circumference of the polymer particles. The mean sphericity is the volume-average sphericity.

(53) The mean sphericity can be determined, for example, with the Camsizer? image analysis system (Retsch Technology GmbH; Haan; Germany):

(54) 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.

(55) To characterize the roundness, the parameters designated as sphericity in the program are employed. The parameters reported are the mean volume-weighted sphericities, the volume of the particles being determined via the equivalent diameter xc.sub.min. To determine the equivalent diameter xc.sub.min, the longest chord diameter for a total of 32 different spatial directions is measured in each case. The equivalent diameter xc.sub.min is the shortest of these 32 chord diameters. To record the particles, the so-called CCD-zoom camera (CAM-Z) is used. To control the metering channel, a surface coverage fraction in the detection window of the camera (transmission) of 0.5% is predefined.

(56) Water-absorbent polymer particles with relatively low sphericity are obtained by reverse suspension polymerization when the polymer beads are agglomerated during or after the polymerization.

(57) The water-absorbent polymer particles prepared by customary solution polymerization (gel polymerization) are ground and classified after drying to obtain irregular polymer particles. The mean sphericity of these polymer particles is between approx. 0.72 and approx. 0.78.

(58) The inventive water-absorbent polymer particles have a content of hydrophobic solvent of preferably less than 0.005% by weight, more preferably less than 0.002% by weight and most preferably less than 0.001% by weight. The content of hydrophobic solvent can be determined by gas chromatography, for example by means of the headspace technique. A hydrophobic solvent within the scope of the present invention is either immiscible in water or only sparingly miscible. Typical examples of hydrophobic solvents are pentane, hexane, cyclohexane, toluene.

(59) Water-absorbent polymer particles which have been obtained by reverse suspension polymerization still comprise typically approx. 0.01% by weight of the hydrophobic solvent used as the reaction medium.

(60) The inventive water-absorbent polymer particles have a dispersant content of typically less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight and most preferably less than 0.05% by weight.

(61) Water-absorbent polymer particles which have been obtained by reverse suspension polymerization still comprise typically at least 1% by weight of the dispersant, i.e. ethylcellulose, used to stabilize the suspension.

(62) 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 0.9 g/cm.sup.3, most preferably from 0.68 to 0.8 g/cm.sup.3.

(63) The average particle diameter (APD) of the inventive water-absorbent particles is preferably from 200 to 550 ?m, more preferably from 250 to 500 ?m, most preferably from 350 to 450 ?m.

(64) The particle diameter distribution (PDD) of the inventive water-absorbent particles is preferably less than 0.7, more preferably less than 0.65, more preferably less than 0.6.

(65) The inventive water-absorbent polymer particles can be mixed with other water-absorbent polymer particles prepared by other processes, i.e. solution polymerization.

(66) Fluid-Absorbent Articles

(67) The present invention further provides fluid-absorbent articles. The fluid-absorbent articles comprise of (A) an upper liquid-pervious layer (B) a lower liquid-impervious layer (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; (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; (E) an optional tissue layer disposed immediately above and/or below (C); and (F) other optional components.

(68) 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.

(69) The acquisition-distribution layer acts as transport and distribution layer of the discharged body fluids and is typically optimized to affect efficient liquid distribution with the underlying fluid-absorbent core. Hence, for quick temporary liquid retention it provides the necessary void space while its area coverage of the underlying fluid-absorbent core must affect the necessary liquid distribution and is adopted to the ability of the fluid-absorbent core to quickly dewater the acquisition-distribution layer.

(70) For fluid-absorbent articles that possess a very good dewatering that has excellent wicking capability it is advantageous to use acquisition-distribution layers. For fluid-absorbent articles that possess a fluid-absorbent core comprising very permeable water-absorbent polymer particles a small and thin acquisition-distribution layer can be used.

(71) 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. 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.

(72) 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: EP 2 301 499 A1, EP 2 314 264 A1, EP 2 387 981 A1, EP 2 486 901 A1, EP 2 524 679 A1, EP 2 524 679 A1, EP 2 524 680 A1, EP 2 565 031 A1, U.S. Pat. No. 6,972,011, US 2011/0162989, US 2011/0270204, WO 2010/004894 A1, WO 2010/004895 A1, WO 2010/076857 A1, WO 2010/082373 A1, WO 2010/118409 A1, WO 2010/133529 A2, WO 2010/143635 A1, WO 2011/084981 A1, WO 2011/086841 A1, WO 2011/086842 A1, WO 2011/086843 A1, WO 2011/086844 A1, WO 2011/117997 A1, WO 2011/136087 A1, WO 2012/048879 A1, WO 2012/052173 A1 and WO 2012/052172 A1.

(73) 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.

(74) The water-absorbent polymer particles and the fluid-absorbent articles are tested by means of the test methods described below.

(75) Methods:

(76) The measurements should, unless stated otherwise, be carried out at an ambient temperature of 23?2? C. and a relative atmospheric humidity of 50?10%. The water-absorbent polymers are mixed thoroughly before the measurement.

(77) Vortex

(78) 50.0?1.0 ml of 0.9% NaCl solution are added into a 100 ml beaker. A cylindrical stirrer bar (30?6 mm) is added and the saline solution is stirred on a stir plate at 60 rpm. 2.000?0.010 g of water-absorbent polymer particles are added to the beaker as quickly as possible, starting a stop watch as addition begins. The stopwatch is stopped when the surface of the mixture becomes still that means the surface has no turbulence, and while the mixture may still turn, the entire surface of particles turns as a unit. The displayed time of the stopwatch is recorded as Vortex time.

(79) Residual Monomers

(80) 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.

(81) Particle Size Distribution

(82) The particle size distribution of the water-absorbent polymer particles is determined with the Camziser? image analysis system (Retsch Technology GmbH; Haan; Germany).

(83) For determination of the average particle diameter and the particle diameter distribution the proportions of the particle fractions by volume are plotted in cumulated form and the average particle diameter is determined graphically.

(84) The average particle diameter (APD) here is the value of the mesh size which gives rise to a cumulative 50% by weight.

(85) The particle diameter distribution (PDD) is calculated as follows:

(86) $PDD=\frac{x_2-x_1}{APD},$
wherein x.sub.1 is the value of the mesh size which gives rise to a cumulative 90% by weight and x.sub.2 is the value of the mesh size which gives rise to a cumulative 10% by weight.
Mean Sphericity

(87) The mean sphericity is determined with the Camziser? image analysis system (Retsch Technology GmbH; Haan; Germany) using the particle diameter fraction from 100 to 1,000 ?m.

(88) Moisture Content

(89) 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.

(90) Centrifuge Retention Capacity (CRC)

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

(92) Absorbency Under No Load (AUNL)

(93) The absorbency under no 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 0.0 g/cm.sup.2 instead of a weight of 21.0 g/cm.sup.2.

(94) Absorbency Under Load (AUL)

(95) The absorbency 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

(96) Absorbency Under High Load (AUHL)

(97) The absorbency 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.

(98) Porosity

(99) The porosity of the water-absorbent polymer particles is calculated as follows:

(100) $\mathrm{Porosity}=\frac{AUNL-CRC}{AUNL}$
Bulk Density/Flow Rate

(101) The bulk density (BD) and the flow rate (FR) of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 250.3 (11) Gravimetric Determination of flow rate, Gravimetric Determination of Density.

(102) Extractables

(103) The level of extractable constituents in the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 470.2-05 Extractables.

(104) Saline Flow Conductivity (SFC)

(105) The saline flow conductivity is, as described in EP 0 640 330 A1, determined as the gel layer permeability of a swollen gel layer of fluid-absorbent polymer particles, although the apparatus described on page 19 and in FIG. 8 in the aforementioned patent application was modified to the effect that the glass frit (40) is no longer used, the plunger (39) consists of the same polymer material as the cylinder (37) and now comprises 21 bores having a diameter of 9.65 mm each distributed uniformly over the entire contact surface. The procedure and the evaluation of the measurement remains unchanged from EP 0 640 330 A1. The flow rate is recorded automatically.

(106) The saline flow conductivity (SFC) is calculated as follows:
SFC[cm.sup.3s/g]=(Fg(t=0)?L0)/(d?A?WP),
where Fg(t=0) is the flow rate of NaCl solution in g/s, which is obtained by means of a linear regression analysis of the Fg(t) data of the flow determinations by extrapolation to t=0, L0 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 surface area of the gel layer in cm.sup.2 and WP is the hydrostatic pressure over the gel layer in dyn/cm.sup.2.
Free Swell Rate (FSR)

(107) 1.00 g (=W1) of the dry fluid-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.

(108) The free swell rate (FSR) is calculated as follows:
FSR[g/gs]=W2/(W1?t)

(109) 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.

(110) Volumetric Absorbency Under Load (VAUL)

(111) The volumetric absorbency 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.

(112) The set up is show in FIG. 14 and consists of 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. A PTFE cell (86) having adiameter of 75 mm, a height of 73 mm and an internal diameter of 52 mm A cylinder (87) made of metal or plastic having a diameter of 50 mm, a height of 71 mm and a mesh bottom) A metal reflector (88) having a diameter of 57 mm and a height of 45 mm Metal ring weights (89) having a diameter of 100 mm and weights calibrated to 278.0 g or 554.0 g

(113) 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:

(114) 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

(115) 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 + 0.70 large ring weight

(116) A sample of 2.0 g of water-absorbent polymer particles is placed in the PTFE cell (86). The cylinder (equipped with mesh bottom) and the metal reflector (88) on top of it are placed into the PTFE cell (86). In order to apply higher pressure, metal rings weights (89) can be placed on the cylinder.

(117) 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.

(118) 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.(1?e.sup.?t/?) as described by Modern Superabsorbent Polymer Technology (page 155, equation 4.13) wherein Q(t) is the swelling of the superabsorbent which is monitored during the experiment, Q.sub.max corresponds to the maximum swelling reached after 120 minutes (end of the experiment) and ? is the characteristic swelling time (? is the inverse rate constant k).

(119) 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.

(120) 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(1?e.sup.?t/?).

(121) Wicking Absorption

(122) The wicking absorption is used in order to measure the total liquid uptake of water-absorbent polymer particles under applied pressure. The set-up is show in FIG. 15.

(123) A 500 ml glass bottle (90) (scale division 100 mL, 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 bottle has an opening at the bottom end which can be connected to the Plexiglas plate through a flexible hose (91).

(124) A balance (92) connected to a computer is placed on Plexiglas block (area 20?26 cm.sup.2, height 6 cm). The glass bottle is then placed on the balance.

(125) A Plexiglas plate (93) (area: 11?11 cm.sup.2, height: 3.5 cm) is placed on a lifting platform. A porosity P1 glass frit of 7 cm in diameter and 0.45 cm high (94) has been liquid-tightly embedded in the Plexiglas plate, i.e. the fluid exits through the pores of the frit and not via the edge between Plexiglas plate and frit. A Plexiglas tube leads through the outer shell of Plexiglas plate into the center of the Plexiglas plate up to the frit to ensure fluid transportation. The fluid tube is then connected with the flexible hose (35 cm in length, 1.0 cm external diameter, 0.7 cm internal diameter) to the glass bottle (90).

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

(127) The fluid in the glass bottle (90) is made up to 500 mL before every run.

(128) In a Plexiglas cylinder (95) (7 cm in external diameter, 6 cm in internal diameter, 16 cm in height) 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 fill 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.

(129) The Plexiglas cylinder is placed on the (moist) frit and the electronic data recording started. A decrease in the weight of the balance 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.

(130) Rewet Under Load (RUL)

(131) The test determines the amount of fluid a fluid-absorbent article will release after being maintained at a pressure of 0.7 psi (49.2 g/cm.sup.2) for 10 min following multiple separate insults. The rewet under load is measured by the amount of fluid the fluid-absorbent article releases under pressure. The rewet under load is measured after each insult.

(132) The fluid-absorbent article is clamped nonwoven side upward onto the inspection table. The insult point is marked accordingly with regard to the type and gender of the diaper to be tested (i.e. in the centre of the core for girl, 2.5 cm towards the front for unisex and 5 cm towards the front for boy). A 3.64 kg circular weight (10 cm diameter) having a central opening (2.3 cm diameter) with perspex tube is placed with on the previously marked insult point.

(133) For the primary insult 100 g of aqueous saline solution (0.9% by weight) is poured into the perspex tube in one shot. Amount of time needed for the fluid to be fully absorbed into the fluid-absorbent article is recorded. After 10 minutes have elapsed, the load is removed and the stack of 10 filter papers (Whatman?) having 9 cm diameter and known dry weight (W1) is placed over the insult point on the fluid-absorbent article. On top of the filter paper, the 2.5 kg weight with 8 cm diameter is added. After 2 minutes have elapsed the weight is removed and filter paper reweighed giving the wet weight value (W2).

(134) The rewet under load is calculated as follows:
RUL[g]=W2?W1

(135) For the rewet under load of the secondary insult the procedure for the primary insult is repeated. 50 g of aqueous saline solution (0.9% by weight) and 20 filter papers are used.

(136) For the rewet under load of the tertiary and following insults the procedure for the primary insult is repeated. For each of the following insults 3.sup.rd, 4.sup.th and 5.sup.th 50 g of aqueous saline solution (0.9% by weight) and 30, 40 and 50 filter papers respectively are used.

(137) Rewet Value (RV)

(138) This test consists of multiple insults of aqueous saline solution (0.9% by weight). The rewet value is measured by the amount of fluid the fluid-absorbent article released under pressure. The rewet is measured after each insult.

(139) The fluid-absorbent article is clamped nonwoven side upward onto the inspection table. The insult point is marked accordingly with regard to the type and gender of the diaper to be tested (i.e. in the centre of the core for girl, 2.5 cm towards the front for unisex and 5 cm towards the front for boy). A separatory funnel is positioned above the fluid-absorbent article so that the spout is directly above the marked insult point.

(140) For the primary insult 100 g of aqueous saline solution (0.9% by weight) is poured into the fluid-absorbent article via the funnel in one shot. The liquid is allowed to be absorbed for 10 minutes, and after that time the stack of 10 filter papers (Whatman?) having 9 cm diameter and known dry weight (D1) is placed over the insult point on the fluid-absorbent article. On top of the filter paper, the 2.5 kg weight with 8 cm diameter is added. After 2 minutes have elapsed the weight is removed and filter paper reweighed giving the wet weight value (D2).

(141) The rewet value is calculated as follows:
RV[g]=D2?D1

(142) For the rewet of the secondary insult the procedure for the primary insult is repeated. 50 g of aqueous saline solution (0.9% by weight) and 20 filter papers are used.

(143) For the rewet of the tertiary and following insults the procedure for the primary insult is repeated. For each of the following insults 3.sup.rd, 4.sup.th and 5.sup.th 50 g of aqueous saline solution (0.9% by weight) and 30, 40 and 50 filter papers respectively are used.

(144) The EDANA test methods are obtainable, for example, from the EDANA, Avenue Eug?ne Plasky 157, B-1030 Brussels, Belgium.

EXAMPLES

(145) Preparation of the Base Polymer

Example 1

(146) The process was performed in a concurrent spray drying plant with an integrated fluidized bed (27) and an external fluidized bed (29) as shown in FIG. 1. The cylindrical part of the spray dryer (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. The external fluidized bed (EFB) had a length of 3.0 m, a width of 0.65 m and a weir height of 0.5 m.

(147) The drying gas was fed via a gas distributor (3) at the top of the spray dryer. The drying gas was partly recycled (drying gas loop) via a baghouse filter (9) and a condenser column (12). The drying gas was nitrogen that comprises from 1% to 4% by volume of residual oxygen: Before 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 cylindrical part of the spray dryer (5) was 0.8 m/s. The pressure inside the spray dryer was 4 mbar below ambient pressure.

(148) The spray dryer outlet temperature was measured at three points around the circumference at the end of the cyclindrical part as shown in FIG. 3. Three single measurements (47) were used to calculate the average cylindrical 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 117? C. by adjusting the gas inlet temperature via the heat exchanger (20).

(149) The product accumulated in the internal fluidized bed (27) until the weir height was reached. Conditioned internal fluidized bed gas having a temperature of 122? C. and a relative humidity of 4% 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 0.80 m/s. The residence time of the product was 120 min.

(150) The spray dryer offgas was filtered in baghouse filter (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 via quench nozzles (11) so that the temperature inside the condenser column (12) was 45? C. The water inside the condenser column (12) was set to an alkaline pH by dosing sodium hydroxide solution to wash out acrylic acid vapors.

(151) The condenser column offgas 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.

(152) The product was discharged from the internal fluidized bed (27) via rotary valve (28) into external fluidized bed (29). Conditioned external fluidized bed gas having a temperature of 60? C. was fed to the external fluidized bed (29) via line (40). The external fluidized bed gas was air. The gas velocity of the external fluidized bed gas in the external fluidized bed (29) was 0.8 m/s. The residence time of the product was 1 min.

(153) The product was discharged from the external fluidized bed (29) via rotary valve (32) into sieve (32). The sieve (33) was used for sieving off overs/lumps having a particle diameter of more than 800 ?m.

(154) 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 (41) and (42) via lines (43) and (44) as shown in FIG. 1. Sodium peroxodisulfate solution having a temperature of 20? C. was added via line (43) and [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride solution together with Br?ggolite FF7 having a temperature of 5? C. was added via line (44). 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 (42). For dosing the monomer solution into the top of the spray dryer three dropletizer units were used as shown in FIG. 4.

(155) A dropletizer unit consisted of an outer pipe (51) having an opening for the dropletizer cassette (53) as shown in FIG. 5. The dropletizer cassette (53) was connected with an inner pipe (52). The inner pipe (53) having a PTFE block (54) at the end as sealing can be pushed in and out of the outer pipe (51) during operation of the process for maintenance purposes.

(156) The temperature of the dropletizer cassette (61) was controlled to 8? C. by water in flow channels (59) as shown in FIG. 6. The dropletizer cassette (61) had 256 bores having a diameter of 170 ?m and a bore separation of 15 mm. The dropletizer cassette (61) consisted of a flow channel (60) having essential no stagnant volume for homogeneous distribution of the premixed monomer and initiator solutions and one droplet plate (57). The droplet plate (57) had an angled configuration with an angle of 3?. The droplet plate (57) was made of stainless steel and had a length of 630 mm, a width of 128 mm and a thickness of 1 mm.

(157) The feed to the spray dryer consisted of 10.45% by weight of acrylic acid, 33.40% by weight of sodium acrylate, 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate, 0.072% by weight of [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 0.0029% by weight of Br?ggolite FF7 (5% by weight in water), 0.054% by weight of sodiumperoxodisulfate solution (15% by weight in water) and water. The degree of neutralization was 71%. The feed per bore was 1.6 kg/h.

(158) The polymer particles (base polymer A1) exhibit the following features and absorption profile:

(159) CRC of 40.2 g/g

(160) AUNL of 51.8 g/g

(161) AUL of 22.4 g/g

(162) AUHL of 8.2 g/g

(163) Porosity of 22.3%

(164) Extractables of 4.3 wt. %

(165) Residual monomers of 12161 ppm

(166) Moisture content of 6.1 wt. %

(167) Vortex time of 67 s

(168) The resulting polymer particles had a bulk density of 68 g/100 ml and an average particle diameter of 407 ?m.

Example 2

(169) Example 1 was repeated, except that the resulting polymer particles having a content of the residual monomer of 12161 ppm were demonomerized in a plastic bottle in the lab oven at 90? C. for 60 minutes after spraying 15% by weight of water onto the polymer particles in a laboratory ploughshare mixer. Therefore the content of the residual monomer was decreased to 256 ppm and the moisture content was increased to 17.5% by weight.

(170) The polymer particles (base polymer B1) exhibit the following features and absorption profile:

(171) CRC of 33.1 g/g

(172) AUNL of 42.3 g/g

(173) AUL of 17.0 g/g

(174) AUHL of 8.1 g/g

(175) Porosity of 21.7%

(176) Extractables of 8.2 wt. %

(177) Residual monomers of 256 ppm

(178) Moisture content of 17.5 wt. %

(179) Vortex time of 54 s

Example 3

(180) Example 1 was repeated, except that the feed to the spray dryer consisted of 0.036% by weight of [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride and that the conditioned internal fluidized bed gas had a temperature of 122? C. and a relative humidity of 4% and that the residence time of the product in the internal fluidized bed was 120 min.

(181) The polymer particles (base polymer C1) exhibit the following features and absorption profile:

(182) CRC of 39.5 g/g

(183) AUNL of 51.4 g/g

(184) AUHL of 9.0 g/g

(185) Porosity of 23.2%

(186) Residual monomers of 1581 ppm

(187) Moisture content of 10.9 wt. %

(188) Surface-postcrosslinking of the base polymer

Example 4

(189) 1200 g of the water-absorbent polymer particles prepared in Example 1 (base polymer A1) having a content of residual monomers of 12161 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany). A surface-postcrosslinker solution was prepared by mixing 60 g of surface-postcrosslinker as described in Table 1 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 Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany) which was heated to 140? C. before. After mixing for further 80 minutes at 140? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 1.

(190) The resulting polymer particles that were surface-postcrosslinked with ethylene carbonate had a bulk density of 69.0 g/100 ml, an average particle diameter (APD) of 481 ?m, a particle diameter distribution (PDD) of 0.28, and a mean sphericity of 0.82.

(191) TABLE-US-00003 TABLE 1 Effect of the postcrosslinking agent Curing Time Residual Monomers Moisture CRC AUNL AUL AUHL Porosity Extractables Vortex Postcrosslinker [min] [ppm] [wt. %] [g/g] [g/g] [g/g] [g/g] [%] [wt. %] [s] EC 10 533 10.1 49.2 58.1 18.8 8.2 15.3 5.3 78 20 384 7.0 51.4 60.8 20.6 8.0 15.5 4.5 77 30 376 5.1 51.6 61.0 28.0 9.5 15.4 4.8 76 40 386 3.6 50.5 62.1 31.9 12.9 18.7 3.8 74 50 432 1.9 49.1 61.8 36.2 18.2 20.6 3.4 70 60 416 1.1 47.3 61.2 37.9 22.2 22.7 3.1 75 70 417 0.6 46.7 62.5 38.6 24.3 25.3 3.1 75 80 429 0.4 46.2 62.6 39.5 24.2 26.2 3.1 75 HEONON 10 1538 7.6 50.2 58.4 16.6 7.7 14.0 7.0 86 20 1377 5.3 51.3 59.7 16.3 7.8 14.1 6.8 85 30 1153 3.7 52.5 61.3 17.7 7.9 14.4 7.1 84 40 1061 2.8 51.5 61.4 19.8 8.0 16.1 6.6 86 50 1002 2.5 50.9 60.3 25.2 8.7 15.6 6.3 85 60 997 2.4 49.1 59.9 27.7 10.3 18.0 6.0 82 70 939 2.2 48.1 59.8 30.0 13.1 19.6 5.8 81 80 913 2.0 47.3 59.3 32.6 16.2 20.2 5.1 81 EGDGE 10 714 8.0 34.2 43.7 23.1 17.1 21.7 22.1 95 20 572 5.4 35.2 44.7 23.6 17.2 21.3 23.3 93 30 554 3.9 35.9 45.0 24.2 17.8 20.2 23.8 91 40 549 2.8 36.3 45.5 24.4 18.0 20.2 24.2 94 50 544 2.2 36.6 46.2 24.5 18.3 20.8 23.5 96 60 550 1.9 36.6 45.9 23.8 18.4 20.3 23.8 93 70 542 1.6 36.5 46.3 23.8 18.4 21.2 23.9 94 80 562 1.4 37.1 46.4 24.0 18.5 20.0 24.1 92 EC: Ethylene carbonate; HEONON: N-(2-hydroxy ethyl)-2-oxazolidinone; EGDGE: Ethylene glycol diglycidyl ether

Example 5

(192) 1200 g of the water-absorbent polymer particles as described in Table 2 having different contents of residual monomers were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany). A surface-postcrosslinker solution was prepared by mixing 30 g ethylene carbonate and 30 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 Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany) which was heated to 150? C. before. After mixing for further 80 minutes at 150? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 2.

(193) The resulting polymer particles based on base polymer A1 had a bulk density of 68.0 g/100 ml, an average particle diameter (APD) of 397 ?m, a particle diameter distribution (PDD) of 0.38, and a mean sphericity of 0.87.

(194) The resulting polymer particles based on base polymer B1 had a bulk density of 64.7 g/100 ml, an average particle diameter (APD) of 553 ?m, a particle diameter distribution (PDD) of 0.25, and a mean sphericity of 0.74.

(195) The resulting polymer particles based on base polymer C1 had a bulk density of 69.8 g/100 ml, an average particle diameter (APD) of 377 ?m, a particle diameter distribution (PDD) of 0.42, and a mean sphericity of 0.86.

Example 6

(196) 1200 g of the water-absorbent polymer particles as described in Table 3 having different contents of residual monomers were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany). A surface-postcrosslinker solution was prepared by mixing 30 g ethylene carbonate 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 Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany) which was heated to 140? C. before. After mixing for further 80 minutes at 140? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 3.

(197) The resulting polymer particles based on base polymer A1 had a bulk density of 65.6 g/100 ml, an average particle diameter (APD) of 450 ?m, a particle diameter distribution (PDD) of 0.32, and a mean sphericity of 0.82.

(198) The resulting polymer particles based on base polymer B1 had a bulk density of 64.7 g/100 ml, an average particle diameter (APD) of 564 ?m, a particle diameter distribution (PDD) of 0.22, and a mean sphericity of 0.75.

(199) The resulting polymer particles based on base polymer C1 had a bulk density of 70.3 g/100 ml, an average particle diameter (APD) of 399 ?m, a particle diameter distribution (PDD) of 0.36, and a mean sphericity of 0.84.

(200) TABLE-US-00004 TABLE 2 Effect of the residual monomers Curing Time Residual Monomers Moisture CRC AUNL AUL AUHL Porosity Extractables Vortex Base Polymer [min] [ppm] [wt. %] [g/g] [g/g] [g/g] [g/g] [%] [wt. %] [s] Base Polymer A1 10 2187 5.2 57.5 61.4 11.0 7.6 6.4 8.4 20 1646 3.0 57.7 63.8 12.6 8.2 9.6 7.2 30 1273 1.5 53.5 65.4 33.5 11.6 18.2 5.3 40 1229 0.5 51.5 63.9 38.6 18.8 19.4 4.7 50 1225 0.5 49.7 63.5 40.6 24.5 21.7 5.0 60 1214 0.3 47.6 63.5 40.8 27.6 25.0 6.1 70 70 1243 0.3 48.1 62.7 40.3 30.2 23.3 6.2 69 80 1225 0.1 46.4 60.1 38.2 30.7 22.8 6.3 67 Base Polymer B1 10 133 13.7 35.8 20 133 8.4 36.9 30 136 3.3 35.5 89 40 157 1.9 33.2 7.5 93 50 160 1.3 30.9 43.0 27.7 18.9 28.1 92 60 166 0.9 28.8 40.9 27.3 20.3 29.6 95 70 172 0.7 26.7 38.2 26.6 21.2 30.1 94 80 178 0.7 25.9 36.9 26.4 21.2 29.8 3.7 94 Base Polymer C1 10 399 8.0 42.2 53.8 28.1 10.7 21.6 70 20 398 3.8 43.3 56.6 32.1 13.6 23.5 70 30 417 1.8 44.1 56.9 36.4 21.7 22.5 71 40 446 1.3 43.0 55.9 38.4 25.4 23.1 3.1 73 50 419 1.0 39.5 54.3 36.9 29.0 27.3 73 60 413 0.8 38.7 52.1 37.0 29.5 25.7 75 70 403 0.6 37.6 51.6 36.2 29.4 27.1 76 80 402 0.6 36.4 51.3 35.0 29.7 29.0 3.3 76

(201) TABLE-US-00005 TABLE 3 Effect of the residual monomers Curing Time Residual Monomers Moisture CRC AUNL AUL AUHL Porosity Extractables Vortex Base Polymer [min] [ppm] [wt. %] [g/g] [g/g] [g/g] [g/g] [%] [wt. %] [s] Base Polymer A1 10 506 7.7 51.7 59.3 17.4 7.8 12.8 5.9 20 417 4.9 53.0 61.2 22.1 8.0 13.4 5.5 30 312 2.7 51.6 61.9 29.8 10.8 16.6 4.8 40 328 2.0 52.2 62.3 35.5 14.6 16.2 4.1 50 359 1.1 50.1 62.1 37.3 19.0 19.3 4.3 60 370 0.8 49.5 62.9 38.4 22.6 21.3 4.3 70 385 0.7 47.1 61.9 39.0 25.4 23.9 4.2 73 80 340 0.5 45.3 60.3 37.9 27.5 24.9 4.0 72 Base Polymer B1 10 33.7 20 0.8 36.1 8.1 30 36.1 8.6 40 123 4.1 35.4 48.1 22.9 10.2 26.4 50 124 2.8 33.8 46.5 25.8 11.7 27.3 87 60 125 2.3 32.6 45.0 25.4 13.1 27.6 88 70 132 0.9 31.9 44.8 26.1 14.4 28.8 92 80 138 0.8 31.2 43.8 26.4 13.7 28.8 90 Base Polymer C1 10 373 9.6 41.1 52.9 28.8 13.1 22.0 70 20 356 5.6 42.6 55.1 31.5 14.4 23.0 71 30 362 3.0 42.0 55.6 34.1 19.6 24.0 72 40 378 1.3 42.2 55.8 34.8 23.2 24.0 4.2 73 50 381 1.1 41.4 55.2 34.7 24.9 25.0 73 60 389 0.7 40.2 55.4 35.2 26.0 27.0 72 70 396 0.6 40.9 53.9 34.4 26.8 24.0 70 80 395 0.4 40.6 53.5 35.2 26.6 24.0 4.2 72

Example 7

(202) The process was performed in a concurrent spray drying plant with an integrated fluidized bed (27) and an external fluidized bed (29) as shown in FIG. 1. The cylindrical part of the spray dryer (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.

(203) The drying gas was fed via a gas distributor (3) at the top of the spray dryer. The drying gas was partly recycled (drying gas loop) via a baghouse filter (9) and a condenser column (12). Instead of the baghouse filter (9) any other filter and/or cyclone can be used. The drying gas was nitrogen that comprises from 1% to 4% by volume of residual oxygen: Before 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 cylindrical part of the spray dryer (5) was 0.82 m/s. The pressure inside the spray dryer was 4 mbar below ambient pressure.

(204) The spray dryer outlet temperature was measured at three points around the circumference at the end of the cyclindrical part as shown in FIG. 3. Three single measurements (47) were used to calculate the average cylindrical 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 118? 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 was 0.058 kg steam per kg dry gas.

(205) The product accumulated in the internal fluidized bed (27) until the weir height was reached. Conditioned internal fluidized bed gas having a temperature of 104? C. and a steam content of 0.058 or 0.130 kg steam per kg dry gas 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 was 82? C.

(206) The spray dryer offgas was filtered in baghouse filter (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 via quench nozzles (11) so that the temperature inside the condenser column (12) was 45? C. The water inside the condenser column (12) was set to an alkaline pH by dosing sodium hydroxide solution to wash out acrylic acid vapors.

(207) The condenser column offgas 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.

(208) 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.

(209) 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 (41) and (42) via lines (43) and (44) as shown in FIG. 1. Sodium peroxodisulfate solution having a temperature of 20? C. was added via line (43) and [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride solution together with Br?ggolite FF7 having a temperature of 5? C. was added via line (44). 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 (42). For dosing the monomer solution into the top of the spray dryer three dropletizer units were used as shown in FIG. 4.

(210) A dropletizer unit consisted of an outer pipe (51) having an opening for the dropletizer cassette (53) as shown in FIG. 5. The dropletizer cassette (53) was connected with an inner pipe (52). The inner pipe (53) having a PTFE block (54) at the end as sealing can be pushed in and out of the outer pipe (51) during operation of the process for maintenance purposes.

(211) The temperature of the dropletizer cassette (61) was controlled to 8? C. by water in flow channels (59) as shown in FIG. 6. The dropletizer cassette (61) had 256 bores having a diameter of 170 ?m and a bore separation of 15 mm. The dropletizer cassette (61) consisted of a flow channel (60) having essential no stagnant volume for homogeneous distribution of the premixed monomer and initiator solutions and one droplet plate (57). The droplet plate (57) had an angled configuration with an angle of 3?. The droplet plate (57) was made of stainless steel and had a length of 630 mm, a width of 128 mm and a thickness of 1 mm.

(212) The feed to the spray dryer consisted of 10.45% by weight of acrylic acid, 33.40% by weight of sodium acrylate, 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate, 0.036% by weight of [2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 0.0029% by weight of Br?ggolite FF7, 0.054% by weight of sodium peroxodisulfate and water. The degree of neutralization was 71%. The feed per bore was 1.4 kg/h.

(213) The resulting water-absorbent polymer particles were analyzed. The results are summarized in Table 4.

(214) TABLE-US-00006 TABLE 4 Base polymers, used for the surface-postcrosslinking reactions Steam Bulk Residual Content Density CRC Monomers Extractables Moisture FSR Example [kg/kg] [g/cm.sup.3] [g/g] [ppm] [wt. %] [wt. %] [g/gs] 7a 0.058 0.74 47.2 9300 4.5 5.7 0.20 7b 0.130 0.71 49.1 4000 5.4 7.5 0.07

Examples 8 to 26

(215) In a Schugi Flexomix? (model Flexomix-160, manufactured by Hosokawa Micron B.V., Doetinchem, the Netherlands) with a speed of 2000 rpm, the base polymer 7a or 7b was coated with a surface-postcrosslinker solution by using 2 or 3 round spray nozzle systems (model Gravity-Fed Spray Set-ups, External Mix Typ SU4, Fluid Cap 60100 and Air Cap SS-120, manufactured by Spraying Systems Co, Wheaton, Ill., USA) and then filled via inlet (74) and dried in a NARA heater (model NPD 5W-18, manufactured by GMF Gouda, Waddinxveen, the Netherlands) with a speed of the shaft (80) of 6 rpm. The NARA heater has two paddles with a shaft offset of 90? (84) and a fixed discharge zone (75) with two flexible weir plates (77). Each weir has a weir opening with a minimal weir height at 50% (79) and a maximal weir opening at 100% (78) as shown in FIG. 13.

(216) The inclination angle ? (82) between the floor plate and the NARA paddle dryer is approx. 3?. The weir height of the NARA heater is between 50 to 100% corresponding to a residence time of approx. 40 to 150 min, by a product density of approx. 700 to 750 kg/m. The product temperature in the NARA heater is in a range of 120 to 165? C. After drying, the surface-postcrosslinked base polymer was transported over discharge cone (81) in the NARA cooler (GMF Gouda, Waddinxveen, the Netherlands), to cool down the surface postcrosslinked base polymer to approx. 60? C. with a speed of 11 rpm and a weir height of 145 mm. After cooling, the material was sieved with a minimum cut size of 150 ?m and a maximum size cut of 710 ?m.

(217) Ethylene carbonate, water, Plantacare? UP 818 (BASF SE, Ludwigshafen, Germany) and aqueous aluminum lactate (26% by weight) was premixed and spray coated as summarized in Tab 6. Aqueous aluminum sulfate (26% by weight) was separate spray coated (position of the nozzle=180?). As aluminum lactate, Lothragon? AI 220 (manufactured by Dr. Paul Lohmann GmbH, Emmerthal, Germany) was used.

(218) The metered amounts and conditions of the coating into the Schugi Flexomix?, the conditions, the formulation and values of the drying and cooling step are summarized in Table 5 to 6:

(219) All physical properties of the resulting polymers are summarized in Table 7 and 8:

(220) TABLE-US-00007 TABLE 5 Process parameters of the thermal treatment in the heater Product Steam Steam Temp. Pres- Pres- Set sure sure Heater Heater Heater Heater Heater Heater Through- Heater Value valve Jacket T1 T2 T3 T4 T5 T6 put Weir No. of Pos. of Example ? C. bar bar ? C. ? C. ? C. ? C. ? C. ? C. kg/h % Nozzles Nozzles Polymer particles without aluminum salt 8 140 4.6 4.3 84 81 111 123 130 140 400 56 2 90/270? 9 150 6.2 6.2 90 86 115 129 137 150 400 56 2 90/270? 10 150 7.4 7.4 79 81 110 121 133 159 500 67 3 90/180/270? Polymer particles with aluminum lactate 11 120 2.5 2.3 69 72 103 111 114 120 500 57 3 90/180/270? 12 130 2.3 3.5 75 84 110 117 121 130 500 57 3 90/180/270? 13 140 6.7 6.6 82 93 118 127 135 150 500 67 3 90/180/270? 14 150 5.5 5.0 84 107 117 131 138 150 400 56 2 90/270? 15 150 5.2 6.2 71 100 118 132 140 150 400 56 2 90/270? 16 150 5.9 5.9 91 109 120 131 140 150 500 68 3 90/180/270? 17 150 6.1 6.1 83 110 120 131 139 150 500 68 3 90/180/270? 18 160 6.5 6.5 89 114 123 138 151 160 400 82 3 90/270? 19 170 8.1 8.1 91 113 129 151 163 170 400 82 2 90/270? Polymer particles with aluminum sulfate 20 150 5.6 5.5 66 99 119 137 145 150 500 87 3 90/180/270? 21 150 5.0 5.0 95 96 121 135 144 150 400 75 3 90/180/270? 22 150 5.6 5.6 74 104 117 127 136 150 500 87 3 90/180/270? 23 155 6.1 6.0 79 100 119 130 142 155 500 87 3 90/180/270? 24 160 6.6 6.6 109 115 124 143 154 160 400 75 3 90/180/270? 25 160 6.5 6.5 96 105 125 144 154 160 400 75 3 90/180/270? 26 165 7.8 7.8 79 109 122 138 152 165 500 87 3 90/180/270?

(221) TABLE-US-00008 TABLE 6 Surface-postcrosslinker formulation of the thermal treatment in the heater Ex- Plantacare Al-lactate Al-sulfate am- Base EC Water 818 UP (dry) (dry) ple polymer bop % bop % bop ppm bop % bop % Polymer particles without aluminum salt 8 7b 2.5 5.0 50 9 7b 2.5 5.0 50 10 7b 2.5 5.0 25 Polymer particles with aluminum lactate 11 7b 2.5 5.0 25 0.5 12 7b 2.5 5.0 25 0.5 13 7b 1.5 5.0 50 0.5 14 7a 2.5 5.0 0.5 15 7a 2.5 5.0 50 0.5 16 7a 2.5 5.0 25 0.5 17 7b 2.5 5.0 25 0.5 18 7b 2.5 5.0 25 0.5 19 7a 2.5 5.0 25 0.5 Polymer particles with aluminum sulfate 20 7b 2.5 5.0 25 0.50 21 7a 2.5 5.0 25 0.36 22 7b 2.5 5.0 25 0.75 23 7b 2.5 5.0 25 0.50 24 7b 2.5 5.0 50 0.36 25 7a 2.5 5.0 25 0.36 26 7b 2.5 5.0 25 0.50 Ethylene carbonate; bop: based on polymer

(222) TABLE-US-00009 TABLE 7 Physical properties of the polymer particles after surface-postcrosslinking Ex- SFC Mois- Residual Extract- Bulk Fines Overs am- CRC AUNL AUL AUHL 10.sup.?7 cm.sup.3 .Math. GBP Vortex FSR ture Monomers ables Density FR <150 ?m >710 ?m ple g/g g/g g/g g/g s/g Da S g/g .Math. s % ppm % g/100 ml g/s % % Polymer particles without aluminum salt 8 47 61 37 21 0 1 73 0.29 1.7 373 5 78 15 0.0 2.0 9 42 55 36 26 3 2 69 0.27 1.2 557 6 74 15 0.0 2.4 10 37 48 33 26 6 5 91 0.22 1.2 170 3 80 14 0.1 0.5 Polymer particles with aluminum lactate 11 41 54 33 21 1 5 60 0.39 5.1 282 4 77 14 0.2 0.9 12 39 53 34 25 1 6 65 0.31 2.6 367 4 79 14 0.5 1.1 13 36 51 33 25 6 9 74 0.19 1.0 351 4 77 14 0.1 0.6 14 46 60 37 20 0 1 73 0.30 1.2 510 6 75 13 0.3 0.5 15 45 60 36 22 9 1 65 0.32 1.1 515 8 73 13 1.0 2.5 16 42 55 36 26 3 2 69 0.27 1.2 557 6 72 12 0.3 0.2 17 39 54 35 27 8 5 68 0.32 1.2 510 5 77 14 0.3 1.0 18 28 41 28 24 125 32 86 0.22 0.8 565 3 75 14 0.4 0.9 19 25 36 26 23 153 31 111 0.20 0.6 629 5 74 13 1.0 2.0 Polymer particles with aluminum sulfate 20 32 49 29 22 41 36 70 0.30 1.2 421 4 79 14 0.4 0.5 21 37 53 33 25 23 17 74 0.31 1.1 373 6 78 13 1.0 2.6 22 28 43 25 20 93 78 75 0.25 1.2 296 3 80 15 0.3 0.7 23 28 43 27 22 106 59 89 0.22 0.9 375 3 81 14 0.1 0.0 24 32 48 30 24 65 35 80 0.29 0.6 594 5 75 13 0.3 1.0 25 35 52 32 23 24 25 66 0.30 0.7 684 7 75 13 1.1 2.0 26 24 36 24 20 275 100 100 0.21 0.6 360 3 80 15 0.2 0.1

(223) TABLE-US-00010 TABLE 8 Physical properties of the polymer particles after surface-postcrosslinking Total Ex- ? ? ? ? ? liquid am- CRC 0.03 psi 0.1 psi 0.3 psi 0.5 psi 0.7 psi uptake ple g/g s s s s s g Polymer particles with aluminum salt 8 47.1 464 525 659 832 924 61.5 9 41.7 418 501 546 678 716 108.9 10 36.5 324 387 437 571 568 149.5 Polymer particles with aluminum lactate 11 40.8 490 611 493 439 383 73.5 12 38.7 463 563 538 489 465 86.2 13 136.0 14 46.4 467 551 598 599 596 54.7 15 46.3 466 551 535 535 497 62.9 16 42.6 93.3 17 26.9 261.1 18 27.6 235 281 407 393 391 261.0 19 25.3 324.6 Polymer particles with aluminum sulfate 20 31.7 134.0 21 37.7 105.8 22 27.5 171.3 23 28.2 272 323 382 436 494 167.8 24 32.4 295 358 418 404 363 158.3 25 35.0 309 376 401 389 385 125.8 26 23.6 210 258 278 358 338 218.3

Example 27

(224) 1200 g of the water-absorbent polymer particles prepared in Example 7b (base polymer) having a content of residual monomers of 4000 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 12 g of 3-methyl-2-oxazolidinone as described in Table 1 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 Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany) which was heated to 150? C. before. After mixing for further 80 minutes at 150? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 10.

(225) The resulting polymer particles that were surface-postcrosslinked with 3-methyl-1,3-oxazolidin-2-one had a bulk density of 70.4 g/100 ml and a flow rate of 11.5 g/s.

Example 28

(226) 1200 g of the water-absorbent polymer particles prepared in Example 7b (base polymer) having a content of residual monomers of 4000 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH; Paderborn; Germany). A surface-postcrosslinker solution was prepared by mixing 6 g of 3-Methyl-3-oxethanmethanol as described in Table 9 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 Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany) which was heated to 150? C. before. After mixing for further 80 minutes at 150? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 10.

(227) The resulting polymer particles that were surface-postcrosslinked with 3-methyl-3-oxethanmethanol had a bulk density of 72.2/100 ml and a flow rate of 12.0 g/s.

Example 29

(228) 1200 g of the water-absorbent polymer particles prepared in Example 7b (base polymer) having a content of residual monomers of 4000 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 6 g of 2-oxazolidinone as described in Table 9 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 Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany) which was heated to 150? C. before. After mixing for further 80 minutes at 150? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 10.

(229) The resulting polymer particles that were surface-postcrosslinked with 1,3-oxazolidin-2-one had a bulk density of 69.7 g/100 ml and a flow rate of 10.8 g/s.

Example 30

(230) 1200 g of the water-absorbent polymer particles prepared in Example 7b (base polymer) having a content of residual monomers of 4000 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 6 g of Solution of 3-(2-hydroxyethyl)-2-oxazolidinon and 6 g propandiol as described in Table 9 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 Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany) which was heated to 165? C. before. After mixing for further 80 minutes at 165? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 10.

(231) The resulting polymer particles that were surface-postcrosslinked with of 3-(2-hydroxyethyl)-1,3-oxazolidin-2-one and 6 g propandiol had a bulk density of 67.4 g/100 ml and a flow rate of 10.1 g/s.

Example 31

(232) 1200 g of the water-absorbent polymer particles prepared in Example 7b (base polymer) having a content of residual monomers of 4000 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 3 g of N,N,N,N-Tetrakis(2-hydroxyethyl)adipamide (Primid? XL 552, manufactured by Ems Chemie AG; Domat; Switzerland) as described in Table 9 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 Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany) which was heated to 160? C. before. After mixing for further 80 minutes at 160? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 10.

(233) The resulting polymer particles that were surface-postcrosslinked with N,N,N,N-Tetrakis(2-hydroxyethyl)adipamide had a bulk density of 65.8 g/100 ml and a flow rate of 10.2 g/s.

Example 32

(234) 1200 g of the water-absorbent polymer particles prepared in Example 7b (base polymer) having a content of residual monomers of 4000 ppm were put into a laboratory ploughshare mixer (model MR5, manufactured by Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany). A surface-postcrosslinker solution was prepared by mixing 24 g of 1.3-Dioxan-2-on as described in Table 9 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 Gebr?der L?dige Maschinenbau GmbH, Paderborn, Germany) which was heated to 160? C. before. After mixing for further 80 minutes at 160? C. with sample taking every 10 minutes, the product was removed from the mixer and sifted from 150 to 850 ?m. The samples were analyzed. The results are summarized in Table 10.

(235) The resulting polymer particles that were surface-postcrosslinked with 1.3-Dioxan-2-on had a bulk density of 68.4 g/100 ml and a flow rate of 10.5 g/s.

(236) TABLE-US-00011 TABLE 9 Formulation of the polymer particles after surface-postcrosslinking by using different surface-postcrosslinkers Surface- postcrosslinker Water Temperature Time Example Surface-postcrosslinker - Typ bop % bop % ? C. min Base polymer 27 3-Methyl-2-oxazolidinone 1.00 5.0 150 80 7b 28 3-Methyl-3-oxethanmethanol 0.50 5.0 150 80 7b 29 2-oxazolidinone 0.50 5.0 150 80 7b 30 50 wt % solution of 3-(2-hydroxyethyl)-2- 0.50 5.0 165 80 7b oxazolidinone in 1,3-propandiol 31 N,N,N,N-Tetrakis(2-hydroxyethyl)adipamide 0.25 5.0 160 80 7b 32 1.3-Dioxan-2-on 2.0 5.0 160 80 7b Bop: based on polymer

(237) TABLE-US-00012 TABLE 10 Physical properties of the polymer particles after surface-postcrosslinking by using different surface-postcrosslinkers SFC Total Ex- 10?7 liquid am- CRC AUNL AUL AUHL cm.sup.3 .Math. GBP Vortex uptake ple g/g g/g g/g g/g s/g Da s g 27 41.9 56.4 36.1 24.8 0 2 83 114.8 28 41.3 55.0 33.9 22.8 0 0 61.5 92.5 29 39.3 53.1 33.0 22.1 9 13 54.5 102.2 30 30.9 43.1 29.2 23.6 0 2 83 208.5 31 34.3 46.3 30.5 24.1 6 8 104 91.9 32 39.2 53.6 36.6 30.1 12 25 87 110.5

Comparative Examples

(238) AQUA KEEP? SA60SII, AQUA KEEP? SA55XSII, AQUA KEEP? SA60SXII are water-absorbent polymer particles from SUMITOMO SEIKA CHEMICALS CO., LTD, produced by a suspension polymerization process.

(239) ASAP? 535, Hysorb? B7075, Hysorb? T9700, Hysorb? B7055, Hysorb? T8760, Hysorb? M7055N, Hysorb? B7015, Hysorb? M7015N, Hysorb? M7015 and Hysorb? 7400 are water-absorbent polymer particles from BASF SE, produced by a kneader polymerization process.

(240) CE1 and CE2 correspond to water-absorbent polymer particles that are prepared in accordance to Example 7 and Example 26 of WO 2012/045705 A1.

(241) CE3 corresponds to water-absorbent polymer particles that are prepared in accordance to Example 25 of WO 2013/007819 A1.

(242) FIG. 16 is a diagram that shows that the water-absorbent polymer particles according to the present invention have an improved total quid uptake compared to conventional water-absorbent polymer particles having the same centrifuge retention capacity (CRC).

(243) TABLE-US-00013 TABLE 11 Physical Properties of Comparison Example Total Com- SFC Extract- ? ? ? ? ? liquid parison CRC AUNL AUL AUHL 10.sup.?7 cm.sup.3 .Math. GBP Vortex ables FSR 0.03 psi 0.1 psi 0.3 psi 0.5 psi 0.7 psi uptake Example g/g g/g g/g g/g s/g Da s % g/g .Math. s s s s s s g Comparison Polymer Particles - Suspension Polymerization AQUA 34.4 56 27 14 0 2 38 3.1 108 134 1033 1667 1534 32.9 KEEP? SA60SII AQUA 28.9 22 7 6 42 4.4 0.50 82 98 190 549 892 KEEP? SA55XSII AQUA 33.2 15 0 2 38 4.2 0.37 74 138 1215 2103 2154 KEEP? SA60SXII Comparison Polymer Particles - Kneader Polymerization CE1 25.9 37.0 27.1 22.7 67 34 142 12.9 0.20 195.1 CE2 26.9 42.0 27.4 22.2 138 90 103 11.9 0.16 295 357 425 437 143.0 CE3 27.6 34.9 26.7 22.8 98 15 120 12.7 0.38 275 218 271 248 214.2 Hysorb? 28.8 40.9 29.4 24.3 45 7 92 8.2 0.25 319 389 467 442 372 155.6 B7075 ASAP? 30.1 45.6 29.7 23.5 50 18 13.0 0.18 317 395 425 456 432 161.0 535 Hysorb? 30.5 46.9 26.5 19.4 33 55 11.5 0.26 376 406 400 374 372 115.1 T9700 Hysorb? 29.4 43.3 29.8 22.3 9 4 93 10.0 0.19 291 363 353 462 106.4 B7055 Hysorb? 30.9 49.2 28.8 19.3 18 33 69 13.7 0.26 300 333 367 483 451 93.1 T8760 Hysorb? 32.0 40.9 29.1 24.5 9 4 97 12.2 0.23 429 469 538 566 702 70.6 M7055N Hysorb? 33.5 45.2 30.3 22.2 4 1 84 9.5 0.21 343 391 365 409 509 75.5 B7015 Hysorb? 34.0 46.3 30.2 22.0 3 2 81 11.9 0.23 260 379 427 434 1184 57.0 M7015N Hysorb? 34.0 47.2 29.5 21.7 2 7 59 12.5 0.29 227 229 356 500 74.9 M7015 Hysorb? 34.8 50.0 28.8 13.2 0 3 35 16.7 0.33 238 276 374 738 841 26.0 7400

Example 33

(244) A fluid-absorbent articlethe baby diaper of size Lconsisting 53% by weight of surface-postcrosslinked polymer of Example 12, was manufactured in a standard diaper production process:

(245) The fluid-absorbent article comprises (A) an upper liquid-pervious layer comprising a spunbond nonwoven (three piece coverstock) having a basis weight of 12 gsm (B) a lower liquid-impervious layer comprising a composite of breathable polyethylene film and spunbond nonwoven; (C) an absorbent core between (A) and (B) comprising 1) lower fluff layer of hydrophilic fibrous matrix of wood pulp fibers (cellulose fibers) acting as a dusting layer; 2) a homogenous mixture of wood pulp fibers (cellulose fibers) and surface-postcrosslinked polymer. The fluid-absorbent core holds 53% by weight distributed surface-postcrosslinked polymer, the quantity of surface-postcrosslinked polymer within the fluid-absorbent core is 14.5 g. Dimensions of the fluid-absorbent core: length: 42 cm; front width: 12.8 cm; crotch width: 8.4 cm; rear width: 11.8 cm. The density of the fluid-absorbent core is for the font overall average 0.23 g/cm.sup.3, for the insult zone 0.29 g/cm.sup.3, for the back overall average 0.19 g/cm.sup.3. The average thickness of fluid-absorbent core is 0.36 cm. The fluid-absorbent core is wrapped with a spunbondmeltblownspunbond (SMS) nonwoven material having a basis weight of 10 gsm. The basis weight of fluid-absorbent core is for the font overall average 990 g/cm.sup.3, for the insult zone 1130 g/cm.sup.3, for the back overall average 585 g/cm.sup.3. (D) an air through bonded acquisition-distribution layer between (A) and (C) having a basis weight of 60 g/m.sup.2; the acquisition-distribution layer is rectangular shaped and smaller than the fluid-absorbent core having a size of about 212 cm.sup.2.

(246) Dimension of the fluid-absorbent article: length: 51 cm; front width: 31.8 cm; crotch width: 22.4 cm; rear width: 31.8 cm. The fluid-absorbent article has average weight of 38.1 g.

(247) The fluid-absorbent article further comprises: a. flat rubber elastics; elastics from spandex type fibers: 2 leg elastics and 1 cuff elastic b. leg cuffs from synthetic fibers, nonwoven material showing the layer combination SMS and having a basis weight of between 13 to 15 g/m.sup.2 and a height of 3.0 cm c. mechanical closure system with landing zone of dimension 16.9 cm?3.4 cm and flexiband closure tapes of 3.1 cm?5.4 cm; attached to hook fastening tape of 1.9 cm?2.7 cm

(248) The rewet under load and rewet value of the fluid-absorbent article were determined. The results are summarized in Table 12 and 13.

Example 34

(249) A fluid-absorbent articlethe baby diaper of size Lconsisting 49% by weight of surface-postcrosslinked polymer of Example 12 was manufactured in a standard diaper production process:

(250) The fluid-absorbent article comprises the same components (A), (B) and (D) as in Example 33.

(251) The absorbent core (C) between (A) and (B) comprises 1) lower fluff layer of hydrophilic fibrous matrix of wood pulp fibers (cellulose fibers) acting as a dusting layer; 2) a homogenous mixture of wood pulp fibers (cellulose fibers) and surface-postcrosslinked polymer. The fluid-absorbent core holds 49% by weight distributed surface-postcrosslinked polymer, the quantity of surface-postcrosslinked polymer within the fluid-absorbent core is 12.5 g. Dimensions of the fluid-absorbent core are the same as in Example 32. The density of the fluid-absorbent core is for the font overall average 0.26 g/cm.sup.3, for the insult zone 0.27 g/cm.sup.3, for the back overall average 0.19 g/cm.sup.3. The average thickness of fluid-absorbent core is 0.31 cm. The fluid-absorbent core is wrapped with a spunbondmeltblownspunbond (SMS) nonwoven material having a basis weight of 10 gsm. The basis weight of fluid-absorbent core is for the font overall average 971 g/cm.sup.3, for the insult zone 979 g/cm.sup.3, for the back overall average 515 g/cm.sup.3.

(252) Dimensions of the fluid-absorbent article are the same as in Example 33. The fluid-absorbent article has average weight of 35.7 g.

(253) The fluid-absorbent article further comprises: a. flat rubber elastics as in Example 33 b. leg cuffs, as in Example 33 c. mechanical closure system, as in Example 33

(254) The rewet under load and rewet value of the fluid-absorbent article were determined. The results are summarized in Table 12 and 13.

Example 35

(255) A fluid-absorbent articlethe baby diaper of size Lconsisting 47.5% by weight of surface-postcrosslinked polymer of Example 12 was manufactured in a standard diaper production process:

(256) The fluid-absorbent article comprises the same components (A), (B) and (D) as in Example 33.

(257) The absorbent core (C) between (A) and (B) comprises 1) lower fluff layer of hydrophilic fibrous matrix of wood pulp fibers (cellulose fibers) acting as a dusting layer; 2) a homogenous mixture of wood pulp fibers (cellulose fibers) and surface-postcrosslinked base polymer. The fluid-absorbent core holds 47.7% by weight distributed surface-postcrosslinked polymer, the quantity of surface-postcrosslinked polymer within the fluid-absorbent core is 11.5 g. Dimensions of the fluid-absorbent core are the same as in Example 32. The density of the fluid-absorbent core is for the font overall average 0.24 g/cm.sup.3, for the insult zone 0.26 g/cm.sup.3, for the back overall average 0.18 g/cm.sup.3. The average thickness of fluid-absorbent core is 0.32 cm. The fluid-absorbent core is wrapped with a spunbondmeltblownspunbond (SMS) nonwoven material having a basis weight of 10 gsm. The basis weight of fluid-absorbent core is for the font overall average 928 g/cm.sup.3, for the insult zone 967 g/cm.sup.3, for the back overall average 495 g/cm.sup.3.

(258) Dimensions of the fluid-absorbent article are the same as in Example 33. The fluid-absorbent article has average weight of 34.8 g.

(259) The fluid-absorbent article further comprises: a. flat rubber elastics as in Example 33 b. leg cuffs, as in Example 33 c. mechanical closure system, as in Example 33

(260) The rewet under load and rewet value of the fluid-absorbent article were determined. The results are summarized in Table 12 and 13.

Comparative Example

(261) A fluid-absorbent articlethe baby diaper of size Lconsisting 52% by weight of surface-postcrosslinked polymer HySorb?B7075 (BASF SE, Ludwigshafen, Germany) was manufactured in a standard diaper production process:

(262) The fluid-absorbent article comprises the same components (A), (B) and (D) as in Example 33.

(263) The absorbent core (C) between (A) and (B) comprises 1) lower fluff layer of hydrophilic fibrous matrix of wood pulp fibers (cellulose fibers) acting as a dusting layer; 2) a homogenous mixture of wood pulp fibers (cellulose fibers) and surface-postcrosslinked base polymer (HySorb?B7075). The fluid-absorbent core holds 52% by weight distributed surface-postcrosslinked polymer, the quantity of surface-postcrosslinked polymer within the fluid-absorbent core is 14.5 g. Dimensions of the fluid-absorbent core are the same as in Example 32. The density of the fluid-absorbent core is for the font overall average 0.24 g/cm.sup.3, for the insult zone 0.25 g/cm.sup.3, for the back overall average 0.19 g/cm.sup.3. The average thickness of fluid-absorbent core is 0.34 cm. The fluid-absorbent core is wrapped with a spunbondmeltblownspunbond (SMS) nonwoven material having a basis weight of 10 gsm. The basis weight of fluid-absorbent core is for the font overall average 1013 g/cm.sup.3, for the insult zone 971 g/cm.sup.3, for the back overall average 548 g/cm.sup.3.

(264) Dimensions of the fluid-absorbent article are the same as in Example 33. The fluid-absorbent article has average weight of 38 g.

(265) The fluid-absorbent article further comprises: a. flat rubber elastics as in Example 33 b. leg cuffs, as in Example 33 c. mechanical closure system, as in Example 33

(266) The rewet under load and rewet value of the fluid-absorbent article were determined. The results are summarized in Table 12 and 13.

(267) TABLE-US-00014 TABLE 12 Rewet Under Load Rewet Under Load Example 1st insult 2nd insult 3rd insult 4th insult 5th insult 33 0.10 g 0.12 g 0.10 g 0.09 g 0.16 g 34 0.10 g 0.08 g 0.07 g 0.10 g 0.27 g 35 0.10 g 0.06 g 0.07 g 0.14 g 0.30 g Comparative 0.08 g 0.08 g 0.08 g 0.29 g 0.52 g Example

(268) TABLE-US-00015 TABLE 13 Rewet value Rewet value Example 1st insult 2nd insult 3rd insult 4th insult 5th insult 33 0.14 g 0.10 g 0.09 g 0.10 g 0.75 g 34 0.15 g 0.11 g 0.11 g 0.40 g 1.61 g 35 0.14 g 0.10 g 0.09 g 0.87 g 3.84 g Comparative 0.12 g 0.22 g 0.11 g 0.82 g 4.30 g Example

(269) The examples demonstrate that the fluid-absorbent article comprising spherical shaped surface-postcrosslinked polymer particles shows better rewet performance, even when the loading of spherical shaped surface-postcrosslinked polymer particles in the absorbent core is reduced up to 20%, in comparison to the fluid-absorbent article containing irregular shaped surface-postcrosslinked polymer particles.