Process for producing water-absorbent polymer particles by polymerizing droplets of a monomer solution

Abstract

The present invention relates to a process for producing water-absorbent polymer particles by polymerizing droplets of a monomer solution in a surrounding heated gas phase in a reactor comprising a gas distributor (3), a reaction zone (5) and a fluidized bed (27), the gas leaving the reactor is treated in a condenser column (12) with an aqueous solution, the treated gas leaving the condenser column (12) is recycled at least partly to the fluidized bed (27), wherein the gas leaving the condenser column (12) comprises from 0.05 to 0.3 kg steam per kg dry gas and the steam content of the gas entering the gas distributor (3) is less than 80% of the steam content of the gas leaving the condenser column (12).

Claims

1. A process for producing water-absorbent polymer particles by polymerizing droplets of 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, in a surrounding heated gas phase in a reactor comprising a gas distributor (3), a reaction zone (5), and a fluidized bed (27), gas leaving the reactor is treated in a condenser column (12) with an aqueous solution, the treated gas leaving the condenser column (12) is recycled at least partly to the fluidized bed (27), wherein the treated gas leaving the condenser column (12) comprises from 0.05 to 0.3 kg steam per kg dry gas and a steam content of a drying gas entering the gas distributor (3) is less than 80% of the steam content of the treated gas leaving the condenser column (12).

2. A process according to claim 1, wherein the treated gas leaving the condenser column (12) comprises from 0.09 to 0.15 kg steam per kg dry gas.

3. A process according to claim 1, wherein the steam content of the drying gas entering the gas distributor (3) is less than 50% of the steam content of the treated gas leaving the condenser column (12).

4. A process according to claim 1, wherein the treated gas leaving the condenser column (12) is recycled at least partly to the gas distributor (3) and the treated gas leaving the condenser column (12) that is recycled at least partly to the gas distributor (3) is further treated in a gas drying unit (37).

5. A process according to claim 4, wherein the gas drying unit (37) comprises a gas cooler and a demister.

6. A process according claim 5, wherein the temperature of the gas leaving the gas drying unit (37) is less than 45 C.

7. A process according claim 6, wherein the temperature of the treated gas leaving the condenser column (12) is at least 45 C.

8. A process according to claim 1, wherein the gas velocity inside the reaction zone (5) is from 0.5 to 1.2 m/s.

9. A process according to claim 1, wherein temperature of the gas leaving the reaction zone (5) is from 110 to 120 C.

10. A process according to claim 1, wherein the residence time of the water-absorbent polymer particles in the fluidized (27) bed is from 120 to 240 minutes.

11. A process according to claim 1, wherein the gas velocity inside the fluidized bed (27) is from 0.5 to 1.5 m/s.

12. A process according to claim 1, wherein temperature of the water-absorbent polymer particles in the fluidized bed (27) is from 60 to 100 C.

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

14. A process according to claim 1, wherein the formed water-absorbent polymer particles have a centrifuge retention capacity of at least 15 g/g.

15. A process according to claim 1, wherein the gas is treated in the condenser column (12) with caustic.

16. A process according to claim 1, wherein the liquid effluent of the condenser column (12) is recycled for preparing the monomer solution.

Description

(1) Preferred embodiments are depicted in FIGS. 1 to 15.

(2) FIG. 1: Process scheme

(3) FIG. 2: Process scheme using dry air

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

(5) FIG. 4: Arrangement of the dropletizer units with 3 droplet plates

(6) FIG. 5: Arrangement of the dropletizer units with 9 droplet plates

(7) FIG. 6: Arrangement of the dropletizer units with 9 droplet plates

(8) FIG. 7: Dropletizer unit (longitudinal cut)

(9) FIG. 8: Dropletizer unit (cross sectional view)

(10) FIG. 9: Bottom of the internal fluidized bed (top view)

(11) FIG. 10: openings in the bottom of the internal fluidized bed

(12) FIG. 11: Rake stirrer for the intern fluidized bed (top view)

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

(14) FIG. 13: Process scheme (surface-postcrosslinking)

(15) FIG. 14: Process scheme (surface-postcrosslinking and coating)

(16) FIG. 15: Contact dryer for surface-postcrosslinking

(17) The reference numerals have the following meanings: 1 Drying gas inlet pipe 2 Drying gas amount measurement 3 Gas distributor 4 Dropletizer unit(s) 4a Dropletizer unit 4b Dropletizer unit 4c Dropletizer unit 5 Reaction zone (cylindrical part of the spray dryer) 6 Cone 7 T_outlet measurement 8 Tower offgas pipe 9 Dust separation unit 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 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 Gas drying unit 38 Monomer separator unit 39 Gas inlet pipe 40 Gas outlet pipe 41 Water outlet from the gas drying unit to condenser column 42 Waste water outlet 43 T_outlet measurement (average temperature out of 3 measurements around tower circumference) 45 Monomer premixed with initiator feed 46 Spray dryer tower wall 47 Dropletizer unit outer pipe 48 Dropletizer unit inner pipe 49 Dropletizer cassette 50 Teflon block 51 Valve 52 Monomer premixed with initiator feed inlet pipe connector 53 Droplet plate 54 Counter plate 55 Flow channels for temperature control water 56 Dead volume free flow channel for monomer solution 57 Dropletizer cassette stainless steel block 58 Bottom of the internal fluidized bed with four segments 59 Split openings of the segments 60 Rake stirrer 61 Prongs of the rake stirrer 62 Mixer 63 Optional coating feed 64 Postcrosslinker feed 65 Thermal dryer (surface-postcrosslinking) 66 Cooler 67 Optional coating/water feed 68 Coater 69 Coating/water feed 70 Base polymer feed 71 Discharge zone 72 Weir opening 73 Weir plate 74 Weir height 100% 75 Weir height 50% 76 Shaft 77 Discharge cone 78 Inclination angle 79 Temperature sensors (T.sub.1 to T.sub.6) 80 Paddle (shaft offset 90)

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

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

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

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

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

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

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

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

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

(27) The principle of a gas drying unit is described in the monograph Leitfaden fr Lftungs-und Klimaanlagen-Grundlagen der Thermodynamik Komponenten einer Vollklimaanlage Normen und Vorschriften, L. Keller, Oldenbourg Industrieverlag, 2009 (ISBN 978-3835631656).

(28) As gas drying unit can be used, for example, an air gas cooling system in combination with a gas mist eliminators or droplet separator (demister), for examples, droplet vane type separator for horizontal flow (e.g. type DH 5000 from Munters AB, Sweden) or vertical flow (e.g. type DV 270 from Munters AB, Sweden). Vane type demisters remove liquid droplets from continuous gas flows by inertial impaction. As the gas carrying entrained liquid droplets moves through the sinusoidal path of a vane, the higher density liquid droplets cannot follow and as a result, at every turn of the vane blades, these liquid droplets impinge on the vane surface. Most of the droplets adhere to the vane wall. When a droplet impinges on the vane blade at the same location, coalescence occurs. The coalesced droplets then drain down due to gravity.

(29) As air gas cooling system, any gas/gas or gas/liquid heat exchanger can be used. Preferred are sealed plate heat exchangers.

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

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

(32) 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.

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

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

(35) 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.

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

(37) 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.

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

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

(40) 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 (53) can have a greater thickness than the bore length when using an inlet bore channel. The droplet plate (53) is preferably long and narrow as disclosed in WO 2008/086976 A1. Multiple rows of bores per droplet plate can be used, preferably from 1 to 20 rows, more preferably from 2 to 5 rows.

(41) The dropletizer cassette (57) consists of a flow channel (56) having essential no stagnant volume for homogeneous distribution of the premixed monomer and initiator solutions and two droplet plates (53). The droplet plates (53) have an angled configuration with an angle of preferably from 1 to 90, more preferably from 3 to 45, most preferably from 5 to 20. Each droplet plate (53) is preferably made of a heat and/or chemically resistant material, such as stainless steel, polyether ether ketone, polycarbonate, polyarylsulfone, such as polysulfone, or polyphenylsulfone, or fluorous polymers, such as perfluoroalkoxyethylene, polytetrafluoroethylene, polyvinylidenfluorid, ethylene-chlorotrifluoroethylene copolymers, ethylene-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.

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

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

(44) 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.

(45) 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)

(46) 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)

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

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

(49) 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.

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

(51) 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.

(52) Water-Absorbent Polymer Particles

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

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

(55) $\mathrm{Roundness}=\frac{4A}{U^2}$
where A is the cross-sectional area and U is the cross-sectional circumference of the polymer particles. The roundness is the volume-average roundness.

(56) The roundness can be determined, for example, with the PartAN image analysis system (Microtrac Europe GmbH; Meerbusch; Germany):

(57) 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.

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

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

(60) 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, cyclo-hexane, toluene.

(61) 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.

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

(63) 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.

(64) 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.

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

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

(67) The inventive water-absorbent polymer particles have a centrifuge retention capacity (CRC) of preferably from 35 to 100 g/g, more preferably from 40 to 80 g/g, most preferably from 45 to 60 g/g.

(68) The inventive water-absorbent polymer particles have a HC 60 value of preferably at least 80, more preferably of at least 85, most preferably of at least 90.

(69) The inventive water-absorbent polymer particles have an absorbency under a load of 21.0 g/cm.sup.2 (AUL) of preferably from 15 to 60 g/g, more preferably from 20 to 50 g/g, most preferably from 25 to 40 g/g.

(70) The level of extractable constituents of the inventive water-absorbent polymer particles is preferably from 0.1 to 30% by weight, more preferably from 0.5 to 25% by weight, most preferably from 1 to 20% by weight.

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

(72) Fluid-Absorbent Articles

(73) 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.

(74) 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.

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

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

(77) 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.

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

(79) Methods:

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

(81) Free Swell Rate (FSR)

(82) 1.00 g (=W1) of the dry water-absorbent polymer particles is weighed into a 25 ml glass beaker and is uniformly distributed on the base of the glass beaker. 20 ml of a 0.9% by weight sodium chloride solution are then dispensed into a second glass beaker, the content of this beaker is rapidly added to the first beaker and a stopwatch is started. As soon as the last drop of salt solution is absorbed, confirmed by the disappearance of the reflection on the liquid surface, the stopwatch is stopped. The exact amount of liquid poured from the second beaker and absorbed by the polymer in the first beaker is accurately determined by weighing back the second beaker (=W2). The time needed for the absorption, which was measured with the stopwatch, is denoted t. The disappearance of the last drop of liquid on the surface is defined as time t.

(83) The free swell rate (FSR) is calculated as follows:
FSR [g/gs]=W2/(W1t)

(84) 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.

(85) Vortex

(86) 50.01.0 ml of 0.9% NaCl solution are added into a 100 ml beaker. A cylindrical stirrer bar (306 mm) is added and the saline solution is stirred on a stir plate at 60 rpm. 2.0000.010 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.

(87) Residual Monomers

(88) The level of residual monomers in the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 410.2-05 Residual Monomers.

(89) Roundness

(90) The roundness is determined with the PartAn 3001 L Particle Analysator (Microtrac Europe GmbH; Meerbusch; Germany).

(91) Moisture Content

(92) The moisture content of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 430.2-05 Moisture Content.

(93) Centrifuge Retention Capacity (CRC)

(94) The centrifuge retention capacity of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 441.2-05 Centrifuge Retention Capacity, wherein for higher values of the centrifuge retention capacity larger tea bags have to be used.

(95) Absorbency Under No Load (AUNL)

(96) The absorbency under no load of the water-absorbent polymer particles is determined analogously to the EDANA recommended test method No. WSP 442.2-05 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.

(97) Absorbency Under Load (AUL)

(98) The absorbency under load of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 442.2-05 Absorption Under Pressure.

(99) Absorbency Under High Load (AUHL)

(100) The absorbency under high load of the water-absorbent polymer particles is determined analogously to the EDANA recommended test method No. WSP 442.2-05 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.

(101) Bulk Density

(102) The bulk density of the water-absorbent polymer particles is determined by the EDANA recommended test method No. WSP 460.2-05 Density.

(103) Extractables

(104) 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.

(105) Saline Flow Conductivity

(106) The saline flow conductivity (SFC) of a swollen gel layer under a pressure of 0.3 psi (2070 Pa) is, as described in EP 0 640 330 A1, determined as the gel layer permeability of a swollen gel layer of water-absorbing polymer particles, the apparatus described on page 19 and in FIG. 8 in the cited patent application having been modified such that the glass frit (40) is not used, and the plunger (39) consists of the same polymer material as the cylinder (37) and now comprises 21 bores of equal size distributed homogeneously over the entire contact area. The procedure and evaluation of the measurement remain unchanged from EP 0 640 330 A1. The flow is detected automatically.

(107) The saline flow conductivity (SFC) is calculated as follows:
SFC [cm.sup.3s/g]=(Fg(t=0)L0)/(dAWP)
where Fg(t=0) is the flow of NaCl solution in g/s, which is obtained using linear regression analysis of the Fg(t) data of the flow determinations by extrapolation to t=0, 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 area of the gel layer in cm.sup.2, and WP is the hydrostatic pressure over the gel layer in dyn/cm.sup.2.
Gel Bed Permeability

(108) The gel bed permeability (GBP) of a swollen gel layer under a pressure of 0.3 psi (2070 Pa) is, as described in US 2005/0256757 (paragraphs [0061] and [0075]), determined as the gel bed permeability of a swollen gel layer of water-absorbing polymer particles.

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

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

(111) The measurement of the color value is in agreement with the tristimulus method according to DIN 5033-6.

(112) Accelerated Aging Test

(113) Measurement 1 (Initial color): A plastic dish with an inner diameter of 9 cm is overfilled with superabsorbent polymer particles. The surface is flattened at the height of the petri dish lip by means of a knife and the CIE color values and the HC 60 value are determined.

(114) Measurement 2 (after aging): A plastic dish with an inner diameter of 9 cm is overfilled with superabsorbent polymer particles. The surface is flattened at the height of the petri dish lip by means of a knife. The plastic dish (without a cover) is then placed in a humidity chamber at 60 C. and a relative humidity of 86%. The plastic dish is removed from the humidity chamber after 7, 14, and 21 days, cooled down to room temperature and the CIE color values are determined.

(115) The EDANA test methods are obtainable, for example, from the EDANA, Avenue Eugne Plasky 157, B-1030 Brussels, Belgium.

EXAMPLES

Example 1 to 3 (Comparative Examples)

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

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

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

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

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

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

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

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

(124) A dropletizer unit consisted of an outer pipe (47) having an opening for the dropletizer cassette (49) as shown in FIG. 5. The dropletizer cassette (49) was connected with an inner pipe (48). The inner pipe (48) having a PTFE block (50) at the end as sealing can be pushed in and out of the outer pipe (47) during operation of the process for maintenance purposes.

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

(126) 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 Brggolite FF7, 0.054% by weight of sodiumperoxodisulfate and water. The degree of neutralization was 71%. The feed per bore was 1.4 kg/h.

(127) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 1 to 3.

Example 4 to 6 (Inventive Examples)

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

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

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

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

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

(133) The gas leaving the condenser column (12) was split to the gas drying unit (37) and the conditioned internal fluidized bed gas (25). The gas drying unit (37) comprises a gas cooler and a demister. In the gas drying unit (37) the gas was cooled down to 40 C. and heated up prior to the drying gas inlet pipe (1). 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.

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

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

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

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

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

(139) 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 Brggolite FF7, 0.054% by weight of sodiumperoxodisulfate and water. The degree of neutralization was 71%. The feed per bore was 1.4 kg/h.

(140) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 1 to 3.

Example 7

(141) The example was performed analogous to example 6, except that 0.00075% by weight of Brggolite FF7 and 0.036% by weight Blancolen HP were used instead of 0.0029% by weight of Brggolite FF7.

(142) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 1 to 3.

Example 8

(143) The example was performed analogous to example 6, except that 0.011% by weight of 3-tuply ethoxylated glycerol triacrylate was used instead of 0.018% by weight of 3-tuply ethoxylated glycerol triacrylate.

(144) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 1 to 3.

Example 9

(145) The example was performed analogous to example 8, except that 0.00075% by weight of Brggolite FF7 and 0.036% by weight Blancolen HP were used instead of 0.0029% by weight of Brggolite FF7.

(146) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 1 to 3.

Example 10

(147) The example was performed analogous to example 6, except that acrylic acid having a dimer concentration of approx. 5000 ppm was used instead of fresh acrylic acid having a dimer concentration less than 500 ppm.

(148) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 1 to 3.

Examples 11 to 15

(149) 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 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 base polymer feed (70) and dried in a thermal dryer (65) (model NPD 5W-18, manufactured by GMF Gouda, Waddinxveen, the Netherlands) with a speed of the shaft (76) of 6 rpm. The thermal dryer (65) has two paddies with a shaft offset of 90 (80) and a fixed discharge zone (71) with two flexible weir plates (73). Each weir has a weir opening with a minimal weir height at 50% (75) and a maximal weir opening at 100% (74) as shown in FIG. 15.

(150) The inclination angle (78) between the floor plate and the thermal dryer was approx. 3. The weir height of the thermal dryer was 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 thermal dryer was in a range of 120 to 165 C. After drying, the surface-postcrosslinked polymer was transported over discharge cone (77) in a cooler (model NPD 5W18, manufactured by GMF Gouda, Waddinxveen, the Netherlands), to cool down the surface postcrosslinked 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 cut size of 710 m.

(151) Ethylene carbonate, water, Plantacare UP 818 (BASF SE, Ludwigshafen, Germany) and aqueous aluminum lactate (26% by weight) were premixed and used as surface-postcrosslinker solution as summarized in Tab. 5. As aluminum lactate, Lothragon Al 220 (manufactured by Dr. Paul Lohmann GmbH, Emmerthal, Germany) was used.

(152) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 4 to 6.

Examples 16 to 20

(153) 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 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 base polymer feed (70) and dried in a thermal dryer (65) (model NPD 5W-18, manufactured by GMF Gouda, Waddinxveen, the Netherlands) with a speed of the shaft (76) of 6 rpm. The thermal dryer (65) has two paddies with a shaft offset of 90 (80) and a fixed discharge zone (71) with two flexible weir plates (73). Each weir has a weir opening with a minimal weir height at 50% (75) and a maximal weir opening at 100% (74) as shown in FIG. 15.

(154) The inclination angle (78) between the floor plate and the thermal dryer was approx. 3. The weir height of the thermal dryer was 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 thermal dryer was in a range of 120 to 165 C. After drying, the surface-postcrosslinked polymer was transported over discharge cone (77) in a cooler (model NPD 5W18, manufactured by GMF Gouda, Waddinxveen, the Netherlands), to cool down the surface postcrosslinked 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 cut size of 710 m.

(155) Ethylene carbonate, water, Plantacare UP 818 (BASF SE, Ludwigshafen, Germany), aqueous aluminum lactate (26% by weight) and sodium bisulfite were premixed and used as surface-postcrosslinker solution as summarized in Tab. 5. As aluminum lactate, Lothragon Al 220 (manufactured by Dr. Paul Lohmann GmbH, Emmerthal, Germany) was used.

(156) 5.0 wt % of a 0.1% aqueous solution of Plantacare 818 UP (BASF SE, Ludwigshafen, Germany) having a temperature of approx. 60 C. was additionally added into the cooler using two nozzles in the first third of the cooler. The nozzles were placed below the product bed.

(157) The resulting water-absorbent polymer particles were analyzed. The trial conditions and results are summarized in Tab. 4 to 6.

(158) TABLE-US-00002 TABLE 1 Process conditions of the polymerization Steam Steam Content Content T T T T T CC GD gas inlet ogas utlet gas IFB IFB CC Overs/Lumbs Unit Example kg/kg kg/kg C. C. C. C. C. wt. % 1 0.0489 0.0489 167 115 103 78 40 2.4 2 0.0651 0.0651 167 115 103 78 45 4.5 3 0.0863 0.0863 167 115 103 78 50 7.9 4 0.0651 0.0489 167 115 103 78 45 1.9 5 0.0863 0.0489 167 115 103 78 50 2.2 6 0.1145 0.0489 167 115 103 78 55 2.4 7 0.1022 0.0489 167 115 103 78 53 2.2 8 0.1022 0.0489 167 115 103 78 53 2.2 9 0.1022 0.0489 167 115 103 78 53 2.1 10 0.1022 0.0489 167 115 103 78 53 2.3 Steam Content CC: steam content of the gas leaving the condenser column (12) Steam Content GD: steam content of the gas prior to the gas distributor (3) T gas inlet: temperature of the gas prior to the gas distributor (3) T gas outlet: temperature of the gas leaving the reaction zone (5) T IFB: temperature of the gas entering the internal fluidized bed (27) via line (25) T CC: temperature of the gas leaving the condenser column (12)

(159) TABLE-US-00003 TABLE 2 Properties of the water-absorbent polymer particles (base polymer) Bulk Density CRC AUNL AUL Residual Monomers Extractables Moisture Unit Example g/cm.sup.3 g/g g/g g/g ppm wt. % wt. % L a b 1 71.9 44.3 51.0 24.3 17900 3.8 2.9 92.8 2.4 1.4 2*) 70.3 47.8 54.4 18.7 11200 4.3 3.6 92.6 2.6 1.7 3**) 4 71.3 49.5 55.4 18.9 9800 3.9 3.7 93.1 1.7 1.9 5 71.9 51.5 57.7 18.3 6400 3.8 7.6 92.9 1.9 2.1 6 72.1 52.5 58.1 15.9 2900 3.8 8.9 92.7 2.1 2.3 7 71.8 53.1 56.9 13.9 4700 4.2 8.1 93.4 2.0 1.7 8 67.8 61.8 48.1 7.4 4900 8.6 8.2 93.3 1.8 2.0 9 68.1 66.8 48.9 7.6 5100 19.8 8.1 94.3 1.4 2.1 10 71.5 51.9 54.9 15.8 4800 6.5 8.0 92.8 2.5 2.0 *)significant polymer built-up in the cone (6) of the spray dryer and the top of the reaction zone (5) **)process stopped due to polymer built-up in the cone (6) of the spray dryer and the top of the reaction zone (5)

(160) TABLE-US-00004 TABLE 3 Particle size distribution of the water-absorbent polymer particles (base polymer) <150 150 200 250 300 350 400 500 600 700 850 1000 1400 Unit Example m m m m m m m m m m m m m Roundness 1 0.01 0.11 1.22 3.47 9.25 14.55 33.62 19.79 10.18 5.70 1.82 0.28 0.00 0.81 2*) 0.00 0.02 0.23 0.82 2.03 4.44 16.41 18.72 20.30 25.35 10.95 0.73 0.00 0.74 3**) 4 0.00 0.05 0.92 3.93 8.18 13.88 33.99 20.68 9.39 6.12 1.92 0.83 0.11 0.83 5 0.00 0.12 1.69 4.95 9.26 13.86 31.22 19.20 9.93 7.13 2.40 0.24 0.00 0.82 6 0.01 0.10 1.18 3.98 8.98 15.07 32.10 21.96 9.17 5.59 1.58 0.28 0.00 0.81 7 0.01 0.08 1.12 3.96 8.66 16.69 29.50 20.75 11.29 5.80 1.60 0.50 0.04 0.82 8 0.01 0.11 1.45 4.23 9.23 14.20 32.41 19.50 10.07 6.42 2.10 0.27 0.00 0.79 9 0.00 0.08 1.22 4.17 8.75 14.16 33.14 21.03 9.63 5.27 1.99 0.51 0.05 0.78 10 0.00 0.09 1.23 3.29 8.83 14.30 33.07 21.98 9.50 5.28 1.97 0.42 0.04 0.81 *)significant polymer built-up in the cone (6) of the spray dryer and the top of the reaction zone (5) **)process stopped due to polymer built-up in the cone (6) of the spray dryer and the top of the reaction zone (5)

(161) TABLE-US-00005 TABLE 4 Process conditions of the thermal dryer for the surface postcrosslinking (SXL) Product Temp. Steam Steam Set Pressure Pressure Heater Heater Heater Heater Heater Heater Through- Heater Value Wave Jacket T1 T2 T3 T4 T5 T6 put Weir Unit No. of Pos. of Example C. bar bar C. C. C. C. C. C. kg/h % Nozzles Nozzles 11 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 12 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 13 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 14 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 15 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 16 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 17 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 18 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 19 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270 20 140 6.4 6.4 84 81 111 123 130 140 470 80 3 90/180/270

(162) TABLE-US-00006 TABLE 5 Process conditions of the surface postcrosslinking (SXL) 0.1% aqueous Plantacare Sodium solution 818 UP Al-Lactate bisulfite Plantacare EC Water (dry) (dry) (dry) 818 UP Base (SXL) (SXL) (SXL) (SXL) (SXL) (Cooler) Example polymer wt. % bop wt. % bop ppm bop wt. % bop wt. % bop wt. % bop 11 1 2.5 5.0 25 0.2 12 2 2.5 5.0 25 0.2 13 4 2.5 5.0 25 0.2 14 5 2.5 5.0 25 0.2 15 6 2.5 5.0 25 0.2 16 6 2.5 5.0 25 0.2 0.05 5.0 17 7 2.5 5.0 25 0.2 0.05 5.0 18 8 2.5 5.0 25 0.2 0.05 5.0 19 9 2.5 5.0 25 0.2 0.05 5.0 20 10 2.5 5.0 25 0.2 0.05 5.0 EC: Ethylene carbonate bop: based on polymer

(163) TABLE-US-00007 TABLE 6 Properties of the water-absorbent polymer particles (after surface postcrosslinking) Residual Bulk Fines Overs CRC AUNL AUL AUHL SFC GBP Vortex FSR Moisture Monomers Extractables Density <150 m >850 m Unit Exp. g/g g/g g/g g/g 10.sup.7cm.sup.3 .Math. s/g Da s g/g .Math. s wt. % ppm wt. % g/100 ml wt. % wt. % 11 38.9 48.6 35.6 23.5 3 6 75 0.22 1.8 640 2.8 75.1 0.5 0.3 12 39.9 49.9 37.2 24.9 2 3 69 0.27 1.8 600 3.5 74.0 0.4 3.9 13 39.5 49.3 36.1 24.5 2 4 73 0.24 1.9 580 3.5 74.8 0.3 0.4 14 40.5 50.9 38.1 25.2 2 6 71 0.28 2.2 510 3.3 73.8 0.3 0.4 15 41.9 52.0 38.3 25.6 1 4 68 0.30 2.3 460 4.0 75.1 0.2 0.2 16 41.9 52.6 37.3 25.0 2 5 59 0.33 5.1 310 3.9 75.6 0.1 2.4 17 41.5 52.1 37.1 24.9 2 6 57 0.31 5.2 320 4.1 75.4 0.2 2.5 18 49.9 59.3 31.3 15.2 0 1 49 0.34 5.6 290 5.8 69.9 0.1 3.1 19 50.5 60.3 30.9 15.3 0 2 50 0.34 5.5 300 6.2 70.1 0.1 3.2 20 41.3 50.9 37.3 25.0 2 6 58 0.30 5.2 280 4.6 76.2 0.2 2.4

(164) TABLE-US-00008 TABLE 7 Effect of Blancolen HP in the monomer solution (Accelerated Aging Test) After 0 days After 7 days After 14 days After 21 days Unit Example L a b L a b L a b L a b Examples without Blancolen HP in the monomer solution 6 92.7 2.1 2.3 82.1 0.4 11.2 79.2 0.7 13.9 76.0 1.5 16.6 16 92.6 1.1 8.2 77.4 2.3 10.5 71.8 3.9 12.9 67.0 5.2 14.9 8 93.3 1.8 2.0 82.3 0.6 11.4 79.9 1.0 13.8 76.2 1.7 16.7 18 93.8 1.4 7.7 77.2 2.5 10.6 71.6 3.6 12.4 67.3 5.4 15.3 Examples with 2000 ppm Blancolen HP in the monomer solution 7 93.4 2.0 1.7 85.0 1.3 9.5 83.1 1.5 10.7 82.3 1.6 11.9 17 93.1 1.5 8.2 85.6 0.9 8.8 84.7 0.8 9.4 84.2 0.8 10.5 9 94.3 1.4 2.1 85.0 1.3 9.5 83.4 1.8 10.3 82.7 1.7 11.6 19 92.4 1.0 8.5 85.7 1.1 8.6 85.1 1.0 9.3 84.1 0.9 10.4