DE102005058631A1 - Continuous mixing of water-absorbent polymer with liquid, e.g. to make crosslinkable material for hygiene articles, involves using a rotating stirrer to give the particles an impetus against the product flow direction - Google Patents

Abstract

A method for continuously mixing water-absorbent polymer particles (I) with liquids or other particles with the particles (I) moving under their own weight in the direction of product flow (DPF), in which at least some of the mixed material receives an impetus against the DPF from the rotational motion of at least one mixing tool on a rotating shaft. An independent claim is included for a method for the production of water-absorbent polymer particles by mixing the particles with post-crosslinker(s) which may be in the form of a solution.

Description

The The present invention relates to a method for continuous Mixing water-absorbing polymer particles with liquids or other particles, wherein the polymer particles due to move their own weight in the direction of product flow and at least a part of the mix by the rotational movement of at least one a mixing tool attached to a rotating shaft received contrary to the product flow direction.

Water-absorbing Polymers are in particular polymers of (co) polymerized hydrophilic monomers, Graft (co) polymers of one or more hydrophilic monomers on a suitable graft, crosslinked cellulose or starch, crosslinked carboxymethyl cellulose, partially crosslinked polyalkylene oxide or in aqueous liquids swellable natural products, such as guar derivatives. Such Polymers are called aqueous solutions absorbent products for making diapers, tampons, sanitary napkins and other hygiene products, but also as water-retaining Funds used in agricultural horticulture.

The Preparation of water-absorbing polymers has been described many times see for example "Modern Superabsorbent Polymer Technology ", F.L. Buchholz and A.T. Graham, Wiley-VCH, 1998, pages 69 to 117.

Water-absorbing Polymers typically have a centrifuge retention capacity of 25 to 60 g / g, preferably of at least 30 g / g, preferably of at least 32 g / g, more preferably at least 34 g / g, especially preferably at least 35 g / g. The centrifuge retention capacity (CRC) is according to the recommended by the EDANA (European Disposables and Nonwovens Association) Test Method No. 441.2-02 "Centrifuge retention capacity ".

to Improve the application properties, such as permeability Water-absorbing polymers generally postcrosslinked. These Postcrosslinking can be carried out in aqueous Gel phase performed become. Preferably, however, ground and sieved polymer particles (Base polymer) on the surface coated with a postcrosslinker, dried and thermally postcrosslinked. Suitable crosslinkers are compounds which contain at least two Groups containing the carboxylate groups of the hydrophilic Polymers can form covalent bonds or at least two Carboxyl groups or other functional groups of at least two crosslink different polymer chains of the base polymer with each other can.

DE-A 35 23 617 discloses a process for post-crosslinking water-absorbing Polymer particles, wherein a polyol in one, preferably aqueous, solvent is dosed.

WHERE 04/037900 discloses a method for mixing water-absorbing Polymer particles with aqueous solutions, wherein due to a high kinetic energy of the polymer particles, the formation of agglomerates during mixing is avoided.

WHERE 05/080479 describes a process for the post-crosslinking of water-absorbing Polymer particles, with two separate solutions are dosed. According to the patent application For example, high speed mixers are used.

The Object of the present invention was to provide a improved method for mixing water-absorbing polymer particles with aqueous solutions.

Was solved the object by a method for continuously mixing water-absorbing polymer particles with liquids or other particles, wherein the polymer particles due to moving their own weight in the product flow direction, characterized that at least a part of the mix by the rotational movement at least one mixing tool attached to a rotating shaft receives a pulse against the product flow direction.

liquids are at 23 ° C liquid Substances or by increasing the temperature liquefied Solids. Suitable liquid Substances are, for example, liquid Postcrosslinkers or postcrosslinker solutions based on water-absorbing Polymer particles are applied.

Other particles are particulate solids derived from the water-absorbing polymer particles are separated. A suitable particulate solid is, for example, fumed silica.

The Product flow direction is the transport direction of the polymer particles through the mixer, i. the transport route through the mixer from the mixer entrance to the mixer output.

The Polymer particles move from top to bottom through the mixer. As a result, the polymer particles are due to their own weight accelerated by gravity in the product flow direction.

The Leading edge of the mixing tool in the direction of rotation is below its trailing edge, i. the mixing tool has a positive Anstellwinkel and transported the polymer particles against the product flow direction.

Therefore means a negative angle of attack that the mixing tool the Polymer particles transported in the product flow direction.

The liquids or other particles become common dosed from above into the mixer, preferably by means of suitable Nozzles sprayed on, especially preferably by means of at least one two-fluid nozzle, very particularly preferably by means of at least four two-fluid nozzles.

at Use of multiple nozzles can the sprayed on liquid and can the ones to be sprayed other particles are better distributed. Can also be advantageous several nozzles, for example, two, about a common supply line to be supplied.

By Use of mixers in which the mix falls freely can the agglomeration tendency when mixing water-absorbing polymer particles with watery liquids be minimized. The mixing result has so far been about one sufficiently high peripheral speed of the tips of the mixing tools reached. There were mixing tools with a negative angle of attack used and received the water-absorbing polymer particles by the rotation of the mixing tools a pulse in the product flow direction and transverse to the product flow direction.

Of the The present invention is based on the finding that by Reversal of the usual transport direction the mixing tools already at moderate peripheral speeds a residence time distribution is achieved for the previously much higher peripheral speeds were necessary.

suitable Mixing tools are, for example, knives or paddles.

The Number of mixing tools is preferably from 2 to 64, more preferably from 4 to 32, completely more preferably from 8 to 16. It is possible that each 2, 4 or 8 mixing tools are in a common plane.

The Mixing tools can protrude radially laterally from the shaft, i. the angle between the shaft axis and the connecting line from the attachment of the Mixing tool on the shaft and the tip of the mixing tool is about 90 °.

The Mixing tools can but also in pairs V-shaped protrude laterally from the shaft, with the arranged by the pair Blending tools included angles preferably from 30 to 120 °, especially preferably from 45 to 105 °, most preferably from 60 to 90 °.

It but it is also possible to use both arrangements of mixing tools in a mixer.

The Shaft is preferably mounted on one side or two sides.

The Peripheral speed of the mixing tools is typically from 3 to 20 m / s, preferably from 4 to 18 m / s, more preferably from 6 up to 15 m / s, most preferably from 8 to 12 m / s.

The Product flow direction is typically less than 45 °, preferably less than 30 °, more preferably less than 15 °, most preferably less as 5 °, across from inclined to the vertical. Preferably, the polymer particles fall vertically from top to bottom through the mixer, i. the product flow direction is vertical.

Of the Angle between product flow direction and shaft axis is preferably less than 10 °, especially preferably less than 5 °, most preferably less than 1 °. Preferably, product flow direction and shaft axis identical, i. the angle between both is 0 °.

Of the Incidence angle of the at least one mixing tool is typically from greater 0 to 30 °, preferably from 5 to 25 °, more preferably from 10 to 20 °, most preferably from 15 to 18 °.

Of the Mixer preferably has a cylindrical wall. The diameter of the cylinder is preferably from 90 to 500 mm, more preferably from 120 to 400 mm, completely more preferably from 150 to 350 mm.

The relationship of diameter of the orbit of the outer tip of the mixing tool to the largest possible Diameter of this orbit is preferably at least 0.6, more preferably at least 0.7, most preferably at least 0.8. The largest possible diameter the orbit is the theoretical diameter of the orbit, in which the tip of the mixing tool is closest to the shaft axis Just touch mixer wall would. In the case of a cylindrical mixer with centric shaft corresponds this largest possible diameter the orbit the inner diameter of the mixer.

The throughput of polymer particles per m ^{2 of} cross-sectional area of the mixer is preferably from 10 to 250 t / h, particularly preferably from 25 to 150 t / h, very particularly preferably from 50 to 100 t / h.

Preferably becomes the method according to the invention used for post-crosslinking water-absorbing polymer particles. For this purpose, preferably at least one postcrosslinker is used as the aqueous solution. The watery solution may be organic compounds such as isopropanol, propylene glycol or 1,3-propanediol, as co-solvent.

Farther the method according to the invention is suitable for mixing in other liquids, like water and watery Solutions, and other particles, such as fumed silica.

In a particularly preferred embodiment becomes a vertical cylindrical mixer with vertical shaft axis used. The mixing tools are stacked in two or three rows arranged, each row four pairs of V-shaped mixing tools having a positive angle of attack.

• a) mindestens ein ethylenisch ungesättigtes, säuregruppentragendes Monomer,
• b) mindestens einen Vernetzer,
• c) wahlweise ein oder mehrere mit a) copolymerisierbare ethylenisch und/oder allylisch ungesättigte Monomere und
• d) wahlweise ein oder mehrere wasserlösliche Polymere, auf die die Monomere a), b) und ggf. c) zumindest teilweise aufgepfropft werden können,

wobei das dabei erhaltene Polymer getrocknet und klassiert wird, hergestellt werden.The water-absorbing polymer particles which can be used in the process according to the invention can be obtained by polymerization of a monomer solution containing

• a) at least one ethylenically unsaturated, acid group-carrying monomer,
• b) at least one crosslinker,
• c) optionally one or more with a) copolymerizable ethylenically and / or allylic unsaturated monomers and
• d) optionally one or more water-soluble polymers to which the monomers a), b) and optionally c) can be at least partially grafted,

wherein the resulting polymer is dried and classified, are prepared.

suitable Monomers a) are, for example, ethylenically unsaturated carboxylic acids, such as Acrylic acid, methacrylic acid, maleic acid, fumaric acid and Itaconic acid. Particularly preferred monomers are acrylic acid and methacrylic acid. All especially preferred is acrylic acid.

Of the Proportion of acrylic acid and / or their salts to the total amount of monomers a) is preferably at least 50 mol%, more preferably at least 90 mol%, completely particularly preferably at least 95 mol%.

The Monomers a), in particular acrylic acid, preferably contain up to 0.025% by weight of a hydroquinone half ether. Preferred hydroquinone half ethers are hydroquinone monomethyl ether (MEHQ) and / or tocopherols.

wobei R¹ Wasserstoff oder Methyl, R² Wasserstoff oder Methyl, R³ Wasserstoff oder Methyl und R⁴ Wasserstoff oder ein Säurerest mit 1 bis 20 Kohlenstoffatomen bedeutet.Tocopherol is understood as meaning compounds of the following formula

wherein R ^{1 is} hydrogen or methyl, R ^{2 is} hydrogen or methyl, R ^{3 is} hydrogen or methyl and R ^{4 is} hydrogen or an acid radical having 1 to 20 carbon atoms.

Preferred radicals for R ⁴ are acetyl, ascorbyl, succinyl, nicotinyl and other physiologically acceptable carboxylic acids. The carboxylic acids may be mono-, di- or tricarboxylic acids.

Preference is given to alpha-tocopherol with R ¹ = R ² = R ³ = methyl, in particular racemic alpha-tocopherol. R ⁴ is particularly preferably hydrogen or acetyl. Especially preferred is RRR-alpha-tocopherol.

The monomer contains preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight, is preferred at least 10 ppm by weight, more preferably at least 30 ppm by weight, especially preferably by 50 ppm by weight, hydroquinone, in each case based on acrylic acid, wherein acrylic acid salts arithmetically as acrylic acid taken into account become. For example, for the preparation of the monomer solution acrylic acid used with a corresponding content of hydroquinone half-ether become.

The water-absorbing polymers are crosslinked, i. the polymerization is in the presence of compounds having at least two polymerizable Groups that radically polymerized into the polymer network can be carried out. Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, Diethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, Triallylamine, tetraallyloxyethane, as described in EP-A 0 530 438, Di- and triacrylates, as in EP-A 0 547 847, EP-A 0 559 476, EP-A 0 632 068, WO 93/21237, WO 03/104299, WO 03/104300, WO 03/104301 and DE-A 10331450, mixed acrylates, in addition to acrylate groups further ethylenically unsaturated Groups as described in DE-A 103 31 456 and DE-A 103 55 401, or crosslinker mixtures, as described, for example, in DE-A 195 43 368, DE-A 196 46 484, WO 90/15830 and WO 02/32962.

suitable Crosslinkers b) are in particular N, N'-methylenebisacrylamide and N, N'-methylenebismethacrylamide, esters unsaturated Mono- or polycarboxylic acids of polyols, such as diacrylate or triacrylate, for example butanediol or ethylene glycol diacrylate or methacrylate and trimethylolpropane triacrylate and allyl compounds, such as allyl (meth) acrylate, triallyl cyanurate, maleate, Polyallylester, tetraallyloxyethane, triallylamine, tetraallylethylenediamine, Allyl ester of phosphoric acid and vinylphosphonic acid derivatives, such as they are described, for example, in EP-A-0 343 427. Farther suitable crosslinkers b) are pentaerythritol di-, pentaerythritol tri- and pentaerythritol tetraallyl ether, polyethylene glycol diallyl ether, Ethylene glycol diallyl ether, glycerol di- and glycerol triallyl ether, Polyallyl ethers based on sorbitol, as well as ethoxylated variants from that. In the method according to the invention can be used di (meth) acrylates of polyethylene glycols, wherein the polyethylene glycol used has a molecular weight between 300 and 1000 has.

Especially advantageous crosslinkers b) are, however, di- and triacrylates of the 3 to 20-fold ethoxylated glycerol, the 3- to 20-fold ethoxylated Trimethylolpropane, 3 to 20 times ethoxylated trimethylolethane, in particular di- and triacrylates of the 2- to 6-fold ethoxylated Glycerol or trimethylolpropane, the 3-fold propoxylated glycerin or trimethylolpropane, as well as the 3-fold mixed ethoxylated or propoxylated glycerol or trimethylolpropane, 15-fold ethoxylated glycerol or trimethylolpropane, as well as the at least 40-times ethoxylated glycerol, trimethylolethane or trimethylolpropane.

All Particularly preferred crosslinkers b) are those with acrylic acid or methacrylic acid to di- or triacrylates esterified multi-ethoxylated and / or propoxylated glycerols as described, for example, in DE-A 103 19 462 are described. Particularly advantageous are di- and / or triacrylates of 3 to 10 times ethoxylated glycerol. Very particularly preferred are di- or triacrylates of 1 to 5 times ethoxylated and / or propoxylated Glycerol. Most preferred are the triacylates of 3 to 5 times ethoxylated and / or propoxylated glycerin. These are characterized by special low residual levels (typically below 10 ppm by weight) in the water-absorbent Polymer and the aqueous Extracts of the water-absorbing polymers produced therewith have an almost unchanged surface tension (typically at least 0.068 N / m) compared to water of the same Temperature up.

The Amount of crosslinker b) is preferably 0.001 to 10 mol%, particularly preferably 0.01 to 5 mol%, very particularly preferably 0.1 to 2 mol%, in each case based on the Monomer a).

With the monomers a) copolymerizable ethylenically unsaturated monomers c) are, for example, acrylamide, methacrylamide, crotonamide, Dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, Diethylaminopropyl acrylate, dimethylaminobutyl acrylate, dimethylaminoethyl methacrylate, Diethylami noethylmethacrylat, Dimethylaminoneopentylacrylat and Dimethylaminoneopentyl.

When water-soluble Polymers d) can Polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, polyglycols or Polyacyrlsäuren, preferably polyvinyl alcohol and starch.

The Preparation of a suitable polymer and other suitable hydrophilic ethylenically unsaturated Monomers a) are described in DE-A 199 41 423, EP-A 0 686 650, WO 01/45758 and WO 03/104300.

Suitable reactors are kneading reactors or belt reactors. In the kneader, the polymer gel formed in the polymerization of an aqueous monomer solution is comminuted continuously by, for example, counter-rotating stirring shafts, as described in WO 01/38402. The polymerization on the tape is described for example in DE-A 38 25 366 and US 6,241,928 described. Polymerization in a belt reactor produces a polymer gel which must be comminuted in a further process step, for example in a meat grinder, extruder or kneader.

Advantageous becomes the hydrogel after leaving the polymerization reactor even at higher Temperature, preferably at least 50 ° C, more preferably at least 70 ° C, whole more preferably at least 80 ° C, and preferably less than 100 ° C, stored, for example in insulated containers. By the storage, usually 2 to 12 hours, the monomer conversion is further increased.

The acid groups The hydrogels obtained are usually partially neutralized, preferably from 25 to 95 mol%, preferably to 50 to 80 mol%, particularly preferably to 60 to 75 mol%, wherein the usual Neutralizing agents can be used, preferably alkali metal hydroxides, Alkali metal oxides, alkali metal carbonates or alkali metal bicarbonates as well as their mixtures. Instead of alkali metal salts can also Ammonium salts are used. Sodium and potassium are called alkali metals particularly preferred, but most preferred are sodium hydroxide, Sodium carbonate or sodium bicarbonate and mixtures thereof.

The Neutralization is preferably carried out at the stage of the monomers. This usually happens by mixing the neutralizing agent as an aqueous solution, as Melt, or preferably as a solid. For example, can Sodium hydroxide with a water content well below 50% by weight present as a waxy mass with a melting point above 23 ° C. In this case, a dosage as piece goods or melt at elevated temperature possible.

It but it is also possible to carry out neutralization after polymerization at a hydrogel stage. Farther Is it possible up to 40 mol%, preferably 10 to 30 mol%, particularly preferably 15 to 25 mol%, the acid groups neutralize before polymerization by adding a part of the neutralizing agent already the monomer solution added and the desired Final degree of neutralization only after the polymerization at the stage the hydrogel is adjusted. Will the hydrogel be at least partially neutralized after the polymerization, the hydrogel is preferably crushed mechanically, for example by means of a meat grinder, wherein the neutralizing agent sprayed on, sprinkled or poured and then carefully can be mixed. For this, the gel mass obtained can still be pulled several times for homogenization.

The hydrogel is then preferably dried with a belt dryer until the residual moisture content is preferably below 15% by weight, in particular below 10% by weight, the water content being determined in accordance with the test method No. 430.2- recommended by EDANA (European Disposables and Nonwovens Association). 02 "Moisture content" is determined. Alternatively, a fluidized bed dryer or a heated ploughshare mixer can be used for drying. To obtain particularly white products, it is advantageous in the drying of this gel to ensure rapid removal of the evaporating water. For this purpose, the dryer temperature must be optimized, the air supply and removal must be controlled, and it is in any case to ensure adequate ventilation. The drying is naturally simpler and that Product whiter, if the solids content of the gel is as high as possible. The solids content of the gel before drying is therefore preferably between 30 and 80% by weight. Particularly advantageous is the ventilation of the dryer with nitrogen or other non-oxidizing inert gas. Optionally, however, it is also possible simply to lower only the partial pressure of the oxygen during the drying in order to prevent oxidative yellowing processes. As a rule, however, sufficient ventilation and removal of the water vapor also leads to an acceptable product. Advantageous in terms of color and product quality is usually the shortest possible drying time.

A Another important function of drying the gel is here Reduction of the residual monomer content in the superabsorbent taking place. That is, during drying, they decompose any remaining radicals of the initiators and lead to a Einpolymerisation of residual monomers remaining. In addition, the tear vaporizing amounts of water remaining free steam-volatile monomers, such as for example, acrylic acid with, and thus also reduce the residual monomer content in the superabsorbent.

The dried hydrogel is then ground and classified, with usually used for grinding or multi-stage roller mills, preferably two- or three-stage roller mills, pin mills, hammer mills or Mixer mills can be used.

Subsequently, the polymer obtained can be postcrosslinked. Suitable postcrosslinkers for this purpose are compounds which contain at least two groups which can form covalent bonds with the carboxylate groups of the polymers. Suitable compounds are, for example, alkoxysilyl compounds, polyaziridines, polyamines, polyamidoamines, di- or polyglycidyl compounds, as described in EP-A 0 083 022, EP-A 0 543 303 and EP-A 0 937 736, polyhydric alcohols, as in DE-C 33 14 019, DE-C 35 23 617 and EP-A 450 922 described, or β-hydroxyalkylamides, as in DE-A 102 04 938 and US 6,239,230 described. Also suitable are compounds having mixed functionality, such as glycidol, 3-ethyl-3-oxetanemethanol (trimethylolpropane oxetane), as described in EP-A 1 199 327, aminoethanol, diethanolamine, triethanolamine or compounds which form a further functionality after the first reaction, such as ethylene oxide, propylene oxide, isobutylene oxide, aziridine, azetidine or oxetane.

Of Further in DE-A 40 20 780 cyclic carbonates, in DE-A 198 07 502 2-Oxazolidone and its derivatives, such as N- (2-hydroxyethyl) -2-oxazolidone, in DE-A 198 07 992 bis- and poly-2-oxazolidinone, in DE-A 198 54 573 2-Oxotetrahydro-1,3-oxazine and its derivatives, in DE-A 198 54,574 N-acyl-2-oxazolidones, in DE-A 102 04 937 cyclic ureas, in DE-A 103 34 584 bicyclic amide acetals, in EP-A 1 199 327 oxetanes and cyclic ureas and in WO 03/031482 morpholine-2,3-dione and its derivatives are described as suitable postcrosslinkers e).

preferred Postcrosslinkers are oxazolidone and its derivatives, in particular N- (2-hydroxyethyl) -2-oxazolidone.

The Amount of postcrosslinker is preferably 0.001 to 5 wt .-%, particularly preferably 0.01 to 2.5 Wt .-%, most preferably 0.1 to 1 wt .-% in each case on the polymer.

The Post-crosslinking usually becomes so performed that a solution, preferably an aqueous one Solution, of the postcrosslinker on the hydrogel or the dry polymer particles sprayed becomes. Following the spraying is thermally dried, the postcrosslinking reaction both before as well as during the drying can take place.

Of the Postcrosslinker is advantageous according to the inventive method mixed with the polymer and then thermally dried.

The thermal drying is preferably carried out in contact dryers, more preferably paddle dryers, very particularly preferably disk dryers. Suitable dryers include for example Bepex ^® dryers and Nara ^® dryers. Moreover, fluidized bed dryers can also be used.

The Drying can be done by heating the jacket or blowing hot air respectively. Also suitable is a downstream dryer, such as For example, a rack dryer, a rotary kiln or a heated Slug. But it can also be, for example, an azeotropic distillation be used as a drying process.

Preferred drying temperatures are in the range 50 to 250 ° C, preferably at 50 to 200 ° C, and more preferably at 50 to 150 ° C. The preferred residence time at this temperature in the reaction mixer or dryer is less than 30 minutes, more preferably less than 10 minutes.

Examples

For example, the mixing behavior was in a Schugi Flexomix ^® Type 335 (Hosokawa Micron Group, Japan) simulated.

Of the Mixing process was calculated by discrete element method (DEM). The trajectories of each individual are located in the geometry Traced particles under the action of external forces simultaneously. The forces, the consideration in this case Gravity as well as contact forces are in contact between two particles or between particles and stationary (shell geometry) or moving walls (Mixing tools) occur. It is assumed here that exclusively Sliding friction occurs. For All particle contacts used a linear spring-damper model. A Interaction with a gas flow was not considered.

The simulated particles had a diameter of 5 mm and a solids density of 1640 kg / m ³ . The wall friction angle and the internal friction angle of the particles is 42 °. The spring constant is 400 N / m and the effective coefficient of restitution of the particles is set to 0.5. The mass flow of the particles is 8t / h. For each particle, the time between entry into the geometry and exit from the geometry is measured. A steady-state operating state occurred after 2 to 5 seconds, depending on the driving style. The residence time distribution was determined only after reaching the stationary operating state.

Example 1 (comparative example)

The Residence time distribution was for calculated a speed of 1,800 rpm. The mixing tools pointed a negative angle of attack of 18 °, i. the particles were received through the rotating mixing tools a pulse in the product flow direction.

Tab. 1: 1,800 rpm, negative angle of attack

Example 2 (Comparative Example)

It The procedure was as in Example 1. The speed was at 700 Upm lowered.

Tab. 2: 700 rpm, negative angle of attack

Example 3:

It The procedure was as in Example 2. The mixing tools showed a positive angle of attack of 18 °, i. the particles were received through the rotating mixing tools an impulse against the product flow direction.

Tab. 3: 700 rpm, positive angle of attack

Tab. 3: 700 rpm, positive angle of attack (continued)

Example 4:

It The procedure was as in Example 3. The speed was 575 Upm lowered.

Tab. 4: 575 rpm, positive angle of attack

Claims (12)

A method for continuously mixing water-absorbing polymer particles with liquids or other particles, wherein the polymer particles move in the product flow direction due to their own weight, characterized in that at least a portion of the mix receives an impulse against the product flow direction by the rotational movement of at least one mixing tool attached to a rotating shaft. Method according to claim 1, characterized in that at least two mixing tools used be, with the mixing tools at different heights along the shaft can be located. A method according to claim 1 or 2, characterized in that the shaft is one-sided or two-sided is stored. Method according to one the claims 1 to 3, characterized in that the outer tip of the mixing tool has a peripheral speed of 3 to 20 m / s. Method according to one the claims 1 to 4, characterized in that the product flow direction to less than 45 ° from the Vertical is inclined. Method according to one the claims 1 to 5, characterized in that the angle between the product flow direction and shaft axis is less than 10 °. Method according to one the claims 1 to 6, characterized in that the angle of attack of the mixing tool from greater 0 to 30 °. Method according to one the claims 1 to 7, characterized in that the mixer is a cylindrical Wall having a diameter of 90 to 500 mm. Method according to one the claims 1 to 8, characterized in that the ratio of diameter of the orbit the outer tip of the mixing tool to the largest possible Diameter of this orbit is at least 0.6. Method according to one of claims 1 to 9, characterized in that the throughput of polymer particles per m ² cross-sectional area of the mixer in the product flow direction of 10 to 250 t / h. Method according to one the claims 1 to 10, characterized in that the polymer particles have a Have diameter of less than 1 mm. Process for the preparation of water-absorbing polymer particles, characterized in that the polymer particles according to a Method of claims 1 to 11 with at least one postcrosslinker, optionally mixed as a solution become.