SUPER ABSORBENT MIXTURES

Description

[0001] The present invention relates to superabsorbent mixtures M containing at least 70 wt.% superabsorbent A with a liquid absorption of 20 g / g (T20) of less than 300 s and / or a volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) with a τ value of less than 400 s and at least 5 wt.% superabsorbent B with a centrifuge retention capacity (CRC) of at least 30 g / g.

[0002] Superabsorbents are used in the manufacture of diapers, tampons, sanitary pads, and other hygiene products, as well as as water-retaining agents in agricultural horticulture. Superabsorbents are also known as water-absorbing polymers.

[0003] The production of superabsorbents is described in the monograph "Modern Superabsorbent Polymer Technology", FL Buchholz and AT Graham, Wiley-VCH, 1998, pages 71 to 103.

[0004] The object of the present invention was to provide improved superabsorbents, in particular superabsorbent mixtures with rapid liquid absorption and high centrifuge retention capacity.

[0005] The problem was solved by superabsorbent mixtures M containing at least 70 wt.% superabsorbent A with a liquid absorption of 20 g / g (T20) of less than 300 s and / or a volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) with a τ value of less than 400 s and at least 5 wt.% superabsorbent B with a centrifuge retention capacity (CRC) of at least 30 g / g.

[0006] The liquid absorption of 20 g / g (T20) of the superabsorbent A is preferably less than 240 s, particularly preferably less than 180 s, most preferably less than 120 s.

[0007] For volumetric liquid uptake under 0.3 psi (2.07 kPa) pressure (VAUL), the τ value is preferably less than 350 s, more preferably less than 250 s, most preferably less than 200 s.

[0008] The liquid absorption of 20 g / g (T20) and the volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) of superabsorbent A can be improved by increasing the amount of crosslinker in the monomer solution. However, it is also possible to extrude the polymer gel obtained during solution polymerization before drying, as described in WO 2014 / 118024 A1. Furthermore, it is possible to increase the amount of surface postcrosslinker.

[0009] The superabsorbent A has a mean sphericity (mSPHT) of preferably less than 0.72, more preferably less than 0.70, most preferably less than 0.68.

[0010] The superabsorbent A has a bulk density (ASG) of preferably less than 0.70 g / ml, particularly preferably less than 0.67 g / ml, most preferably less than 0.64 g / ml.

[0011] Superabsorbent A, for example, is produced by solution polymerization. The resulting polymer gel must be dried and comminuted. This results in an irregular shape of the polymer particles and a relatively low bulk density (BDD). Superabsorbent A can alternatively be produced by droplet polymerization or reverse suspension polymerization. Superabsorbent A is preferably surface post-crosslinked.

[0012] The centrifuge retention capacity (CRC) of the superabsorbent B is preferably at least 35 g / g, more preferably at least 40 g / g, most preferably at least 45 g / g.

[0013] The centrifuge retention capacity (CRC) of superabsorbent B can be improved by reducing the amount of crosslinker in the monomer solution. Furthermore, it is possible to reduce the amount of surface postcrosslinker or even omit surface postcrosslinking altogether.

[0014] The superabsorbent B has a mean sphericity (mSPHT) of preferably greater than 0.72, particularly preferably greater than 0.76, most preferably greater than 0.80.

[0015] The superabsorbent B has a bulk density (ASG) of preferably greater than 0.70 g / ml, particularly preferably greater than 0.75 g / ml, most preferably greater than 0.80 g / ml.

[0016] Superabsorbent B, for example, is produced by droplet polymerization. The resulting polymer particles have a largely spherical shape and a relatively high bulk density (ASG). Superabsorbent B can alternatively be produced by solution polymerization or reverse suspension polymerization. Superabsorbent B is preferably not surface postcrosslinked.

[0017] The superabsorbent A and / or the superabsorbent B has an average particle size of preferably 150 to 850 µm, particularly preferably 200 to 600 µm, most preferably 250 to 500 µm

[0018] The present invention is based on the finding that the liquid absorption of 20 g / g (T20) and the volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) in superabsorbent blends behave nonlinearly. Superabsorbent blends that predominantly contain a superabsorbent with a rapid liquid absorption of 20 g / g (T20) and / or a rapid volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) exhibit a liquid absorption of 20 g / g (T20) or volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) comparable to that of the pure superabsorbent. In contrast, the centrifuge retention capacity (CRC) behaves linearly in superabsorbent blends. The centrifuge retention capacity (CRC) of a superabsorbent blend can therefore be calculated using the centrifuge retention capacity (CRC) of the pure superabsorbents and their blending ratio.

[0019] If a superabsorbent A with a rapid liquid absorption of 20 g / g (T20) is mixed with a superabsorbent B with a high centrifuge retention capacity (CRC), a superabsorbent mixture is obtained with a liquid absorption of 20 g / g (T20) comparable to that of pure superabsorbent A and a centrifuge retention capacity (CRC) significantly higher than that of pure superabsorbent A.

[0020] If a superabsorbent A with a fast volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) is mixed with a superabsorbent B with a high centrifuge retention capacity (CRC), the result is a superabsorbent mixture with a volumetric liquid absorption under 0.3 psi (2.07 kPa) pressure (VAUL) comparable to that of pure superabsorbent A and a centrifuge retention capacity (CRC) significantly increased compared to pure superabsorbent A.

[0021] The production of superabsorbents is explained in more detail below: The superabsorbents can be produced by polymerizing a monomer solution or suspension containing a) at least one ethylenically unsaturated, acid group-bearing monomer, which may be at least partially neutralized, b) at least one crosslinker and c) at least one initiator, and are usually insoluble in water.

[0022] The monomers a) are preferably water-soluble, ie the solubility in water at 23°C is typically at least 1 g / 100 g water, preferably at least 5 g / 100 g water, particularly preferably at least 25 g / 100 g water, most particularly preferably at least 35 g / 100 g water.

[0023] Suitable monomers a) include, for example, ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, and itaconic acid. Particularly preferred monomers are acrylic acid and methacrylic acid. Acrylic acid is most preferred.

[0024] The proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, very particularly preferably at least 95 mol%.

[0025] The monomers a) usually contain polymerization inhibitors, preferably hydroquinone monomethyl ether (MEHQ), as a storage stabilizer.

[0026] The monomer solution preferably contains up to 250 ppm by weight, preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight, preferably at least 10 ppm by weight, more preferably at least 30 ppm by weight, in particular around 50 ppm by weight, of hydroquinone monomethyl ether (MEHQ), in each case based on the unneutralized monomer a). For example, an ethylenically unsaturated, acid-containing monomer with a corresponding content of hydroquinone monomethyl ether (MEHQ) can be used to prepare the monomer solution.

[0027] Suitable crosslinkers b) are compounds with at least two groups suitable for crosslinking. Such groups include, for example, ethylenically unsaturated groups that can be radically polymerized into the polymer chain and functional groups that can form covalent bonds with the acid groups of monomer a). Furthermore, polyvalent metal salts that can form coordinate bonds with at least two acid groups of monomer a) are also suitable as crosslinkers b). Other suitable crosslinkers b) are the "nano-clays" described in US 2017 / 0361305, the water glasses described in WO 00 / 31157 A1, and the aluminates described in WO 99 / 55767 A1.

[0028] Crosslinkers b) are preferably compounds with at least two polymerizable groups that can be radically polymerized into the polymer network. Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallylammonium chloride, tetraallyloxyethane, as described in EP 0 530 438 A1, di- and triacrylates, as described in EP 0 547 847 A1, EP 0 559 476 A1, EP 0 632 068 A1, WO 93 / 21237 A1, WO 03 / 104299 A1, WO 03 / 104300 A1, WO 03 / 104301 A1 and DE 103 31 450 A1, mixed acrylates which, in addition to acrylate groups, contain further ethylenically unsaturated groups, as in DE 103 31 456 A1 and DE 103 55 401 A1, or crosslinker mixtures as described, for example, in DE 195 43 368 A1, DE 196 46 484 A1, WO 90 / 15830 A1 and WO 02 / 032962 A2.

[0029] Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, 15-fold ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate and triallylamine.

[0030] The amount of crosslinker b) is preferably 0.25 to 1.5 wt.%, particularly preferably 0.3 to 1.2 wt.%, very particularly preferably 0.4 to 0.8 wt.%, each calculated on the total amount of monomer a) used. With increasing crosslinker content, the centrifuge retention capacity (CRC) decreases, and the absorption under a pressure of 21.0 g / cm 2 < reaches a maximum.

[0031] As initiators c), all compounds that generate radicals under the polymerization conditions can be used, for example, thermal initiators, redox initiators, and photoinitiators. Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite, and hydrogen peroxide / sodium bisulfite. Mixtures of thermal initiators and redox initiators, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid, are preferably used. The disodium salt of 2-hydroxy-2-sulfonatoacetic acid or a mixture of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid, and sodium bisulfite is preferably used as the reducing component. Such mixtures are available as Brüggolite®< FF6 and Brüggolite®< FF7 (Brüggemann Chemicals; Heilbronn; Germany).However, pure 2-hydroxy-2-sulfonatoacetic acid or a salt thereof can also be used as a reducing component, especially if ascorbic acid is also used.

[0032] Chelating agents and 2-hydroxycarboxylic acids can be added to the monomer solution before or during polymerization, as described, for example, in WO 2017 / 170604 A1.

[0033] Typically, an aqueous monomer solution is used. The water content of the monomer solution is preferably from 40 to 75 wt.%, particularly preferably from 45 to 70 wt.%, most preferably from 50 to 65 wt.%. It is also possible to use monomer suspensions, i.e., monomer solutions with monomer a) that exceeds the solubility, for example, sodium acrylate. As the water content increases, the energy required for subsequent drying increases, and as the water content decreases, the heat of polymerization can only be dissipated insufficiently.

[0034] The acid groups of the resulting polymer gels are usually partially neutralized. Neutralization is carried out at the monomer stage. This is usually done by mixing in the neutralizing agent as an aqueous solution or, preferably, as a solid. The degree of neutralization is preferably from 25 to 85 mol%, more preferably from 30 to 80 mol%, most preferably from 40 to 75 mol%, and the usual neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates, or alkali metal bicarbonates, and mixtures thereof. Ammonium salts can also be used instead of alkali metal salts. Sodium and potassium are particularly preferred as alkali metals, but sodium hydroxide, sodium carbonate, or sodium bicarbonate, and mixtures thereof, are very particularly preferred.

[0035] Solution polymerization is explained below: Suitable reactors for solution polymerization include kneader reactors or belt reactors. In the kneader, the polymer gel formed during the polymerization of an aqueous monomer solution or suspension is continuously comminuted by, for example, counter-rotating stirrer shafts, as described in WO 2001 / 038402 A1. Belt polymerization is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928. Polymerization in a belt reactor produces a polymer gel that must be comminuted, for example, in an extruder or kneader.

[0036] To improve the drying properties, the crushed polymer gel obtained by means of a kneader can be additionally extruded.

[0037] The polymer gel is then dried, usually using a circulating air belt dryer, until the residual moisture content is preferably between 0.5 and 10 wt. %, more preferably between 1 and 6 wt. %, and most preferably between 1.5 and 4 wt. %, whereby the residual moisture content is determined according to the EDANA-recommended test method no. WSP 230.2-05 "Mass Loss Upon Heating." If the residual moisture content is too high, the dried polymer gel has a glass transition temperature T g that is too low and is difficult to process further. If the residual moisture content is too low, the dried polymer gel is too brittle, and undesirably large amounts of polymer particles with too small a particle size ("fines") are produced in the subsequent comminution steps. The solids content of the polymer gel before drying is preferably between 25 and 90 wt. %, more preferably between 35 and 70 wt. %, and most preferably between 40 and 60 wt. %.The dried polymer gel is then broken and optionally coarsely crushed.

[0038] The dried polymer gel is then usually ground and classified, whereby single- or multi-stage roller mills, preferably two- or three-stage roller mills, pin mills, hammer mills or vibrating mills can be used for grinding.

[0039] The average particle size of the polymer particles separated as the product fraction is preferably from 150 to 850 µm, more preferably from 250 to 600 µm, and most preferably from 300 to 500 µm. The average particle size of the product fraction can be determined using the EDANA-recommended test method No. WSP 220.2-05 "Particle Size Distribution," in which the mass fractions of the sieve fractions are plotted cumulatively and the average particle size is determined graphically. The average particle size is the mesh size value resulting for a cumulative 50 wt.%.

[0040] The proportion of polymer particles with a particle size of greater than 150 µm is preferably at least 90 wt.%, particularly preferably at least 95 wt.%, most preferably at least 98 wt.%.

[0041] Polymer particles with too small a particle size reduce gel bed permeability (GBP). Therefore, the proportion of too small polymer particles ("fines") should be low.

[0042] Therefore, polymer particles that are too small are usually separated and recycled back into the process, preferably before, during, or immediately after polymerization, i.e., before drying the polymer gel. The polymer particles that are too small can be moistened with water and / or aqueous surfactant before or during recycling.

[0043] It is also possible to separate out undersized polymer particles in later process steps, for example, after surface post-crosslinking or another coating step. In this case, the recycled undersized polymer particles are surface post-crosslinked or coated in another way, for example, with fumed silica.

[0044] If a kneader reactor is used for polymerization, the undersized polymer particles are preferably added during the last third of the polymerization process. However, it is also possible to incorporate the undersized polymer particles into the polymer gel in a kneader or extruder downstream of the polymerization reactor.

[0045] If the polymer particles are added too early, for example, already in the monomer solution, the centrifuge retention capacity (CRC) of the resulting polymer particles is reduced. However, this can be compensated, for example, by adjusting the amount of crosslinker b).

[0046] The proportion of polymer particles with a particle size of at most 850 µm is preferably at least 90 wt.%, particularly preferably at least 95 wt.%, most preferably at least 98 wt.%.

[0047] The proportion of polymer particles with a particle size of at most 600 µm is preferably at least 90 wt.%, particularly preferably at least 95 wt.%, most preferably at least 98 wt.%.

[0048] Polymer particles with excessively large particle sizes reduce the swelling rate. Therefore, the proportion of oversized polymer particles should also be kept low. Oversized polymer particles are therefore usually separated and returned to the grinding process.

[0049] Droplet polymerization is explained below: In droplet polymerization, the monomer solution is metered into the reactor through at least one hole, forming droplets. Droplet polymerization is described, for example, in WO 2014 / 079694 A1 and WO 2015 / 110321 A1.

[0050] The holes can be located, for example, in a dropletizer plate. The number and size of the holes are selected according to the desired capacity and droplet size. The droplet diameter is typically 1.9 times the diameter of the hole. It is important that the liquid to be dropped does not pass through the hole too quickly and that the pressure loss across the hole is not too great. Otherwise, the liquid will not dropletize, but rather the liquid jet will be disrupted (sprayed) due to the high kinetic energy. The Reynolds number based on the throughput per hole and the hole diameter is preferably less than 2,000, preferably less than 1,600, more preferably less than 1,400, and most preferably less than 1,200.

[0051] The dropletizer plate preferably has at least 5, more preferably at least 25, most preferably at least 50, and preferably up to 750, more preferably up to 500, most preferably up to 250, holes. The diameter of the holes is selected according to the desired droplet size.

[0052] The diameter of the holes is preferably from 50 to 500 µm, more preferably from 70 to 300 µm, most preferably from 100 to 200 µm. The spacing of the holes is preferably 50 to 500 times, more preferably from 70 to 300 times, most preferably from 80 to 200 times the hole diameter. Spacing that is too small leads to the formation of agglomerates, while spacing that is too large reduces the yield.

[0053] The temperature of the monomer solution as it passes through the bores is preferably from 5 to 80°C, particularly preferably from 10 to 70°C, most preferably from 30 to 60°C.

[0054] A carrier gas flows through the reactor. The carrier gas can be passed through the reactor cocurrently or countercurrently to the freely falling drops of the monomer solution, preferably cocurrently, i.e., from bottom to top. Preferably, after each pass, at least some of the carrier gas, preferably at least 50%, particularly preferably at least 75%, is recycled to the reactor as recycle gas. Typically, a portion of the carrier gas is discharged after each pass, preferably up to 10%, particularly preferably up to 3%, and most particularly preferably up to 1%.

[0055] The oxygen content of the carrier gas is preferably from 0.5 to 15 vol.%, particularly preferably from 1 to 10 vol.%, most preferably from 2 to 7 vol.%.

[0056] The carrier gas preferably contains nitrogen in addition to oxygen. The nitrogen content of the carrier gas is preferably at least 80 vol.%, more preferably at least 90 vol.%, most preferably at least 95 vol. Gas mixtures can also be used. The carrier gas can also be loaded with water vapor and / or acrylic acid vapors.

[0057] The gas velocity is preferably adjusted so that the flow in the reactor is directed, for example there are no convection vortices opposite to the general flow direction, and is usually 0.1 to 2.5 m / s, preferably 0.3 to 1.5 m / s, preferably from 0.5 to 1.2 m / s, particularly preferably 0.6 to 1.0 m / s, very particularly preferably 0.7 to 0.9 m / s.

[0058] The carrier gas flowing through the reactor is advantageously preheated to the reaction temperature before entering the reactor.

[0059] Advantageously, the gas inlet temperature is controlled so that the gas outlet temperature, ie the temperature at which the carrier gas leaves the reactor, is usually from 90 to 150°C, preferably from 100 to 140°C, more preferably from 105 to 135°C, particularly preferably from 110 to 130°C, most preferably from 115 to 125°C.

[0060] The reaction can be carried out under overpressure or under vacuum, a vacuum of up to 100 mbar compared to ambient pressure is preferred.

[0061] The reaction offgas, i.e., the gas leaving the reactor, can be cooled, for example, in a heat exchanger. This condenses water and unreacted monomer a). The reaction offgas can then be at least partially reheated and recycled to the reactor as recycle gas. Part of the reaction offgas can be discharged and replaced with fresh carrier gas, whereby the water and unreacted monomer a) contained in the reaction offgas can be separated and recycled.

[0062] A heat network is particularly preferred, ie part of the waste heat from cooling the exhaust gas is used to heat the cycle gas.

[0063] The reactors can be traced. The trace heating is adjusted so that the wall temperature is at least 5°C above the reactor's internal temperature, reliably preventing condensation on the reactor walls.

[0064] The following describes reverse suspension polymerization: In reverse suspension polymerization, the monomer solution is suspended in a hydrophobic solvent during polymerization. Reverse suspension polymerization is described, for example, in WO 2008 / 068208 A1 and WO 2015 / 062883 A2.

[0065] All solvents known to the person skilled in the art for use in suspension polymerization can be used as hydrophobic solvents. Aliphatic hydrocarbons such as n-hexane, n-heptane, n-octane, n-nonane, n-decane, cyclohexane, or mixtures thereof are preferred. Hydrophobic solvents have a solubility in water of less than 5 g / 100 g at 23°C, preferably less than 1 g / 100 g, and particularly preferably less than 0.5 g / 100 g.

[0066] The hydrophobic solvent boils in the range of preferably 50 to 150°C, more preferably 60 to 120°C, most preferably 70 to 90°C.

[0067] The ratio between hydrophobic solvent and monomer solution is 0.5 to 3, preferably 0.7 to 2.5 and most preferably 0.8 to 2.2.

[0068] The average diameter of the monomer solution droplets in the suspension, if no agglomeration is carried out, is preferably at least 100 µm, particularly preferably from 100 to 1000 µm, particularly preferably from 150 to 850 µm, very particularly preferably from 300 to 600 µm, wherein the droplet diameter can be determined by light scattering and means the volume-averaged average diameter.

[0069] The diameter of the monomer solution droplets can be adjusted by the applied stirring energy and by suitable dispersing aids.

[0070] To disperse the aqueous monomer solution in the hydrophobic solvent or to disperse the resulting superabsorbent particles, dispersing agents are preferably added. These can be anionic, cationic, nonionic, or amphoteric surfactants, or natural, semi-synthetic, or synthetic polymers.

[0071] Examples of anionic surfactants include sodium polyoxyethylene dodecyl ether sulfate and sodium dodecyl ether sulfate. Examples of cationic surfactants include trimethylstearylammonium chloride. Examples of amphoteric surfactant include carboxymethyldimethylcetylammonium. Examples of nonionic surfactants include sucrose fatty acid esters, such as sucrose monostearate and sucrose dilaurate, sorbitan esters, such as sorbitan monostearate, and polyoxyalkylene compounds based on sorbitan esters, such as polyoxyethylene sorbitan monostearate.

[0072] The dispersing agent is typically dissolved or dispersed in the hydrophobic solvent. The dispersing agent is used in amounts between 0.01 and 10 wt.%, preferably between 0.2 and 5 wt.%, particularly preferably between 0.5 and 2 wt.%, based on the monomer solution. The diameter of the monomer solution droplets can be adjusted by the type and amount of the dispersing agent.

[0073] It is advantageous to connect several stirred reactors in series for the polymerization. The subsequent reaction in additional stirred reactors can increase the monomer conversion and reduce backmixing. It is also advantageous if the first stirred reactor is not too large. As the size of the stirred reactor increases, the size distribution of the dispersed monomer solution droplets inevitably broadens. A smaller first reactor therefore enables the production of superabsorbent particles with a particularly narrow particle size distribution.

[0074] The reaction is preferably carried out under reduced pressure, for example, at a pressure of 800 mbar. The boiling point of the reaction mixture can be adjusted to the desired reaction temperature by adjusting the pressure.

[0075] If the polymerization is carried out under sufficient reflux, inerting is not necessary. In this case, the dissolved oxygen is removed from the polymerization reactor along with the evaporating solvent.

[0076] The superabsorbent particles can be azeotropically dewatered in the polymer dispersion, separated from the polymer dispersion, and the separated superabsorbent particles can be dried to remove the adhering residual hydrophobic solvent.

[0077] Surface post-crosslinking is described below: The polymer particles can be thermally surface-crosslinked to further improve their properties. Suitable surface post-crosslinkers are compounds containing groups that can form covalent bonds with at least two carboxylate groups of the polymer particles. Suitable compounds are, for example, polyfunctional amines, polyfunctional amidoamines, polyfunctional epoxides as described in EP 0 083 022 A2, EP 0 543 303 A1 and EP 0 937 736 A2, di- or polyfunctional alcohols as described in DE 33 14 019 A1, DE 35 23 617 A1 and EP 0 450 922 A2, β-hydroxyalkylamides as described in DE 102 04 938 A1 and US 6,239,230, or oxazolines as described in EP 0 999 938 A2.

[0078] Furthermore, DE 40 20 780 C1 contains cyclic carbonates, DE 198 07 502 A1 contains 2-oxazolidinone and its derivatives, such as 2-hydroxyethyl-2-oxazolidinone, DE 198 07 992 C1 contains bis- and poly-2-oxazolidinones, DE 198 54 573 A1 contains 2-oxotetrahydro-1,3-oxazine and its derivatives, DE 198 54 574 A1 contains N-acyl-2-oxazolidinones, DE 102 04 937 A1 contains cyclic ureas, EP 2 204 388 A1 contains oxetanes, DE 103 34 584 A1 contains bicyclic amidoacetals, EP 1 199 327 A2 contains Oxetanes and cyclic ureas and in WO 03 / 031482 A1 morpholine-2,3-dione and its derivatives are described as suitable surface post-crosslinkers.

[0079] Preferred surface post-crosslinkers are ethylene carbonate, ethylene glycol diglycidyl ether, reaction products of polyamides with epichlorohydrin and mixtures of propylene glycol and 1,4-butanediol.

[0080] Particularly preferred surface postcrosslinkers are 2-hydroxyethyl-2-oxazolidinone, 2-oxazolidinone and 1,3-propanediol.

[0081] Furthermore, surface post-crosslinkers can also be used which contain additional polymerizable ethylenically unsaturated groups, as described in DE 37 13 601 A1

[0082] The amount of surface postcrosslinker is preferably 0.001 to 3 wt.%, particularly preferably 0.02 to 1 wt.%, very particularly preferably 0.05 to 0.2 wt.%, in each case based on the polymer particles.

[0083] Surface postcrosslinking is typically performed by spraying a solution of the surface postcrosslinker onto the dried polymer particles. Following spraying, the polymer particles coated with the surface postcrosslinker are surface postcrosslinked and dried. The surface postcrosslinking reaction can occur either before or during drying.

[0084] The spraying of a solution of the surface post-crosslinker is preferably carried out in mixers with moving mixing tools, such as screw mixers, disc mixers and paddle mixers. Horizontal mixers, such as paddle mixers, are particularly preferred, and vertical mixers are most preferred. The distinction between horizontal mixers and vertical mixers is made by the bearing of the mixing shaft, i.e. horizontal mixers have a horizontally mounted mixing shaft and vertical mixers have a vertically mounted mixing shaft. Suitable mixers include, for example, Horizontale Pflugschar ®< mixers (Gebr. Lödige Maschinenbau GmbH; Paderborn; Germany), Vrieco-Nauta Continuous Mixer (Hosokawa Micron BV; Doetinchem; Netherlands), Processall Mixmill Mixer (Processall Incorporated; Cincinnati; USA) and Schugi Flexomix ®< (Hosokawa Micron BV; Doetinchem; Netherlands). However, it is also possible to spray the surface post-crosslinker solution in a fluidized bed.

[0085] Surface postcrosslinkers are typically used as an aqueous solution. The penetration depth of the surface postcrosslinker into the polymer particles can be adjusted by varying the non-aqueous solvent content or the total solvent quantity.

[0086] If water alone is used as the solvent, it is advantageous to add a surfactant. This improves wetting properties and reduces the tendency to clump. However, solvent mixtures are preferably used, for example, isopropanol / water, 1,3-propanediol / water, propylene glycol / water, 2-methyl-1,3-propanediol / water, ethylene glycol / water, diethylene glycol / water, triethylene glycol / water, tetraethylene glycol / water, or polyethylene glycol / water, with the mixing ratio preferably being between 20:80 and 40:60.

[0087] Surface post-crosslinking is preferably carried out in contact dryers, particularly preferably paddle dryers, and most preferably disc dryers. Suitable dryers include, for example, Hosokawa Bepex® Horizontal Paddle Dryers (Hosokawa Micron GmbH; Leingarten; Germany), Hosokawa Bepex® Disc Dryers (Hosokawa Micron GmbH; Leingarten; Germany), Holo-Flite® dryers (Metso Minerals Industries Inc.; Danville; USA), and Nara Paddle Dryers (NARA Machinery Europe; Frechen; Germany). Fluidized-bed dryers can also be used.

[0088] Surface post-crosslinking can occur in the mixer itself, by heating the jacket or blowing in warm air. A downstream dryer, such as a tray dryer, a rotary kiln, or a heatable screw, is also suitable. Mixing and thermal surface post-crosslinking are particularly advantageous in a fluidized-bed dryer.

[0089] Preferred reaction temperatures are in the range 100 to 250°C, preferably 120 to 220°C, particularly preferably 130 to 210°C, very particularly preferably 150 to 200°C. The preferred residence time at this temperature is preferably at least 10 minutes, particularly preferably at least 20 minutes, very particularly preferably at least 30 minutes, and usually at most 60 minutes.

[0090] In a preferred embodiment of the present invention, the polymer particles are cooled after surface postcrosslinking. Cooling is preferably carried out in contact coolers, particularly preferably paddle coolers, and most preferably disc coolers. Suitable coolers include, for example, Hosokawa Bepex® Horizontal Paddle Coolers (Hosokawa Micron GmbH; Leingarten; Germany), Hosokawa Bepex® Disc Coolers (Hosokawa Micron GmbH; Leingarten; Germany), Holo-Flite® coolers (Metso Minerals Industries Inc.; Danville; USA), and Nara Paddle Coolers (NARA Machinery Europe; Frechen; Germany). Fluidized-bed coolers can also be used.

[0091] In the cooler, the polymer particles are cooled to preferably 40 to 90°C, particularly preferably 45 to 80°C, most preferably 50 to 70°C.

[0092] The polymer particles can be coated or remoistened to further improve their properties. Remoistening is preferably carried out at 40 to 120°C, particularly preferably at 50 to 110°C, and most preferably at 60 to 100°C. At temperatures that are too low, the polymer particles tend to clump together, and at higher temperatures, water evaporates noticeably. The amount of water used for remoistening is preferably from 1 to 10% by weight, particularly preferably from 2 to 8% by weight, and most preferably from 3 to 5% by weight. Remoistening increases the mechanical stability of the polymer particles and reduces their tendency to static charge.

[0093] Suitable coatings for improving the swelling rate and gel bed permeability (GBP) include, for example, inorganic inert substances such as water-insoluble metal salts, organic polymers, cationic polymers, and divalent or polyvalent metal cations. Suitable coatings for dust binding include, for example, polyols. Suitable coatings for counteracting the undesirable caking tendency of the polymer particles include, for example, fumed silica, such as Aerosil ®< 200, and surfactants, such as Span ®< 20. Suitable coatings for dust binding, reducing the caking tendency, and increasing mechanical stability include polymer dispersions, as described in EP 0 703 265 B1, and waxes, as described in US Pat. No. 5,840,321. Methods:

[0094] The standard test methods described below, designated "WSP," are described in "Standard Test Methods for the Nonwovens Industry," 2005 Edition, jointly published by the worldwide strategy partners EDANA (Avenue Eugène Plasky, 157, 1030 Brussels, Belgium, www.edana.org) and INDA (1100 Crescent Green, Suite 115, Cary, North Carolina 27518, USA, www.inda.org). This publication is available from both EDANA and INDA.

[0095] Unless otherwise specified, measurements should be performed at an ambient temperature of 23 ± 2 °C and a relative humidity of 50 ± 10%. The superabsorbent particles are thoroughly mixed before measurement. Fluid intake of 20 g / g (T20)

[0096] The liquid uptake of 20 g / g (T20) is determined according to the test method "K(t) Test Method (Dynamic Effective Permeability and Uptake Kinetics Measurement Test Method)" described in EP 2 535 027 A1 on pages 13 to 18. volumetric fluid absorption under 0.3 psi (2.07 kPa) pressure (VAUL)

[0097] During volumetric fluid absorption under 0.3 psi (2.07 kPa) pressure (VAUL), the τ value is determined according to the "Volumetric Absorbency Under Load (VAUL)" test method described in WO 2014 / 079694 A1 on pages 39 and 40. The τ value is referred to there as the "characteristic swelling time." Residual monomer

[0098] The residual monomer content is determined according to the EDANA recommended test method WSP No. 210.2 (05) "Residual Monomers". Moisture content

[0099] The moisture content is determined according to EDANA recommended test method No. WSP 230.2 (05) "Mass Loss Upon Heating". Free swell capacity

[0100] Free swell capacity (FSC) is determined according to EDANA recommended test method No. WSP 240.2 (05) "Free swell capacity in saline, gravimetric determination". Centrifuge retention capacity

[0101] The centrifuge retention capacity (CRC) is determined according to EDANA recommended test method No. WSP 241.2 (05) "Fluid Retention Capacity in Saline, After Centrifugation". Absorption under a pressure of 0.0 g / cm 2< (Absorption under No Load)

[0102] The absorption under a pressure of 0.0 g / cm 2 < (AUNL) is determined analogously to the EDANA recommended test method No. WSP 242.2 (05) "Absorption Under Pressure, Gravimetric Determination", whereby a pressure of 0.0 g / cm 2 < (0.0 psi) is set instead of a pressure of 21.0 g / cm 2 < (0.3 psi). Absorption under a pressure of 21.0 g / cm 2< (Absorption under Load)

[0103] The absorption under a pressure of 21.0 g / cm 2 (AUL) is determined according to EDANA recommended test method No. WSP 242.2 (05) "Absorption Under Pressure, Gravimetric Determination". Absorption under a pressure of 49.2 g / cm 2< (Absorption under High Load)

[0104] The absorption under a pressure of 49.2 g / cm 2 < (AUHL) is determined analogously to the EDANA recommended test method No. WSP 242.2 (05) "Absorption Under Pressure, Gravimetric Determination", whereby a pressure of 49.2 g / cm 2 < (0.7 psi) is set instead of a pressure of 21.0 g / cm 2 < (0.3 psi). Extractable

[0105] The extractable content of the superabsorbent particles is determined according to EDANA recommended test method No. WSP 270.2 (05) "Extractable". Saline Flow Conductivity

[0106] The liquid flow conductance (SFC) of a swollen gel layer under pressure load of 0.3 psi (2070 Pa) is determined as described in EP 0 640 330 A1 as the gel layer permeability of a swollen gel layer of superabsorbent particles, using the method described in the aforementioned patent application on page 19 and in Figure 8The apparatus described has been modified in that the glass frit (40) is no longer used, the plunger (39) is made of the same plastic material as the cylinder (37), and now contains 21 equally sized holes evenly distributed over the entire support surface. The procedure and evaluation of the measurement remain unchanged from EP 0 640 330 A1. The flow rate is recorded automatically.

[0107] The fluid transmission rate (SFC) is calculated as follows: SFC cm 3 s / g = Fg t = 0 × L 0 / d × A × WP , where Fg(t=0) is the flow rate of NaCl solution in g / s obtained from a linear regression analysis of the data Fg(t) of the flow determinations by extrapolation to t=0, L 0 is the thickness of the gel layer in cm, d is the density of the NaCl solution in g / cm 3< , A is the area of ​​the gel layer in cm 2< and WP is the hydrostatic pressure above the gel layer in dyn / cm 2< . Vortex test

[0108] 50.0 ml ± 1.0 ml of a 0.9 wt% aqueous sodium chloride solution is added to a 100 ml beaker containing a 30 mm x 6 mm magnetic stir bar. The sodium chloride solution is stirred at 600 rpm using a magnetic stirrer. 2.000 g ± 0.010 g of superabsorbent particles are then added as quickly as possible, and the time taken for the stirred cluster to disappear due to the absorption of the sodium chloride solution by the superabsorbent particles is measured. The entire contents of the beaker may still rotate as a uniform gel mass, but the surface of the gelled sodium chloride solution should no longer exhibit any individual turbulence. The required time is reported as a vortex. mean sphericity (mSPHT)

[0109] The mean sphericity (mSPHT) is determined using the PartAn ®< 3001 L particle analyzer (Microtrac Europe GmbH; Germany).

[0110] The sample to be analyzed is poured into a funnel. The computer-controlled measuring system starts the dosing device and ensures a continuous, concentration-controlled particle flow. The particles fall individually through the measuring shaft, creating high-contrast shadow images between the light source and the high-resolution camera. The light source is controlled by the camera and, thanks to very short exposure times, generates error-free image information for multiple analysis of each individual particle in real time.

[0111] In a 3D process, each particle is analyzed multiple times, providing absolute results for length, width, thickness, area, and circumference. The size and shape are calculated based on the number of pixels covered by the particle. Bulk density

[0112] The bulk density (ASG) is determined according to EDANA recommended test method No. WSP 260.2 (05) "Density, Gravimetric Determination". average particle size

[0113] The mean particle size is determined using the EDANA-recommended test method No. WSP 220.2 (05) "Particle Size Distribution," in which the mass fractions of the sieve fractions are plotted cumulatively and the mean particle size is determined graphically. The mean particle size is the mesh size value resulting from a cumulative 50 wt.%. Examples Production example 1 - Superabsorbent B

[0114] A base polymer was prepared analogously to Example 1 of WO 2017 / 207330 A1. The degree of neutralization was 72.0 mol% and the solids content of the monomer solution was 43.0 wt%.

[0115] Triethoxylated glycerol triacrylate was used as the polyunsaturated crosslinker. The crosslinker was prepared according to Example 7 of WO 03 / 104299 A1. The crosslinker was used in an amount of 0.20 wt.%, based on acrylic acid before neutralization. The monomer solution also contained 0.75 wt.% polyethylene glycol 4000 (polyethylene glycol with an average molecular weight of 4000 g / mol), again based on acrylic acid before neutralization.

[0116] The polymerization initiators used were 0.16 wt% sodium peroxodisulfate, 0.0007 wt% hydrogen peroxide and 0.0028 wt% ascorbic acid, each based on acrylic acid before neutralization.

[0117] The prepared superabsorbent (base polymer) had a centrifuge retention capacity (CRC) of 44.8 g / g, an absorption under a pressure of 0.0 g / cm 2 (AUNL) of 48.2 g / g, an absorption under a pressure of 21.0 g / cm 2 (AUL) of 7.8 g / g, a swelling capacity (FSC) of 56.9 g / g, a moisture content of 3.2 wt% and a bulk density (ASG) of 0.67 g / ml.

[0118] The superabsorbent had the following particle size distribution: >710 µm 0.2 wt.% 600 - 710 µm 14.3% by weight 500 - 600 µm 19.0 wt.% 400 - 500 µm 28.8% by weight 300 - 400 µm 19.0 wt.% 200 - 300 µm 12.3 wt% 150 - 200 µm 5.2 wt.% 106 - 150 µm 1.2 wt.% <106 µm 0.0 wt.%

[0119] The superabsorbent had a mean particle size (d50) of 430 µm and a mean sphericity (mSPHT) of 0.60. Production example 2 - Superabsorbent B

[0120] 1200 g of the base polymer from Preparation Example 1 were placed in a Pflugschar ®< mixer with heating jacket type M5 (Gebr. Lödige Maschienbau GmbH, Paderborn, Germany) and coated at 23°C and a shaft speed of 200 revolutions per minute using a two-component spray nozzle with the following solution, in each case based on the base polymer: 0.04 wt% ethylene glycol diglycidyl ether 1.5 wt% propylene glycol 0.05 wt% aluminum sulfate 3.0 wt% water

[0121] The shaft speed was set to 60 revolutions per minute, and the product was heated to a temperature of 120°C. To maintain this temperature, the temperature of the heating fluid was reduced accordingly. After 30 minutes at 120°C, the product was cooled to ambient temperature.

[0122] The resulting polymer particles were then rehydrated in another mixer at 80°C. For this purpose, 7.0 wt.% of a 0.05 wt.% aqueous aluminum sulfate solution was sprayed onto the polymer using a nitrogen-operated two-component nozzle while stirring. While stirring, the polymer was cooled to 25°C within 20 minutes and sieved to a particle size of 150 to 710 µm.

[0123] The prepared superabsorbent had a centrifuge retention capacity (CRC) of 33.4 g / g, an absorption under a pressure of 0.0 g / cm 2 (AUNL) of 48.3 g / g, an absorption under a pressure of 21.0 g / cm 2 (AUL) of 31.7 g / g, an absorption under a pressure of 49.2 g / cm 2 (AUHL) of 23.9 g / g, a swelling capacity (FSC) of 54.4 g / g, a moisture content of 5.0 wt%, a liquid flow conductance (SFC) of 8 x 10 -7 cm 3 s / g, a vortex of 52 s, a residual monomer content of 310 ppm and a bulk density (ASG) of 0.67 g / ml.

[0124] The superabsorbent had the following particle size distribution: > 710 µm 0.50 wt.% 600 - 710 um 11.2% by weight 500 - 600 µm 20.9 wt% 425 - 500 µm 24.5% by weight 300 - 425 µm 23.6 wt% 150 - 300 µm 18.0% by weight 106 - 150 µm 0.4 wt.% <106 µm 0.0 wt.%

[0125] The superabsorbent had a mean particle size (d50) of 464 µm and a mean sphericity (mSPHT) of 0.60. Production example 3 - Superabsorbent A

[0126] A superabsorbent was prepared according to Example 14 of WO 2014 / 118024 A1. The prepared superabsorbent had a bulk density (ASG) of 0.60 g / ml, a centrifuge retention capacity (CRC) of 26.0 g / g, an absorption under pressure of 49.2 g / cm² (AUHL) of 23.9 g / g, and a liquid flow conductance (SFC) of 136 x 10 -7 cm³ s / g.

[0127] The superabsorbent had the following particle size distribution: >710 µm 8.7% by weight 600 - 710 µm 19.2 wt.% 500 - 600 µm 26.9 wt% 400 - 500 µm 21.9% by weight 300 - 400 µm 14.2 wt.% 150 - 300 µm 9.0 wt.% 106 - 150 um 0.1 wt.% <106 µm 0.0 wt.%

[0128] The superabsorbent had a mean particle size (d50) of 510 µm and a mean sphericity (mSPHT) of 0.66. Production Example 4 - Superabsorbent B

[0129] A superabsorbent was prepared analogously to Example 2 of WO 2016 / 134905 A1. The monomer solution used additionally contained 1.07 wt.% of the disodium salt of 1-hydroxyethylidene-1,1-diphosphonic acid.

[0130] The gas inlet temperature of the reaction zone (5) was 167°C, the gas outlet temperature of the reaction zone (5) was 107°C, the gas inlet temperature of the internal fluidized bed (27) was 100°C, the product temperature in the internal fluidized bed (27) was 78°C, the gas outlet temperature of the condensation column (12) was 57°C and the gas outlet temperature of the gas drying unit (37) was 47°C.

[0131] The prepared superabsorbent (base polymer) had a bulk density (ASG) of 0.681 g / ml, a centrifuge retention capacity (CRC) of 56.8 g / g, an absorption under a pressure of 21.0 g / cm 2 < (AUL) of 8.1 g / g, a residual monomer content of 8550 ppm, an extractable content of 9.7 wt% and a moisture content of 8.5 wt%.

[0132] The superabsorbent had the following particle size distribution: >1000 µm 0.3 wt.% 850 - 1000 µm 1.1 wt.% 600 - 850 µm 4.7 wt% 500 - 600 µm 13.9 wt% 400 - 500 µm 35.5 wt% 300 - 400 µm 34.3 wt% 250 - 300 µm 6.6 wt.% 200 - 250 µm 3.1 wt.% 106 - 200 µm 0.4 wt.% <106 µm 0.1 wt.%

[0133] The superabsorbent had a mean particle size (d50) of 397 µm and a mean sphericity (mSPHT) of 0.81.

[0134] The base polymer was then surface-crosslinked analogously to Examples 11 to 15 of WO 2015 / 110321 A1. 2.0 wt.% ethylene carbonate, 5.0 wt.% water, and 0.4 wt.% aluminum sulfate were used, each based on the base polymer. The product temperature was 150°C and the weir height was 75%.

[0135] In the cooler after surface post-crosslinking, 4.7 wt% of a 0.1 wt% aqueous solution of sorbitan monolaurate was added.

[0136] The prepared superabsorbent had a bulk density (ASG) of 0.753 g / ml, a centrifuge retention capacity (CRC) of 46.8 g / g, an absorption under a pressure of 21.0 g / cm 2 < (AUL) of 33.0 g / g, an absorption under a pressure of 49.2 g / cm 2 < (AUHL) of 16.7 g / g, a liquid flow conductance (SFC) of 0 x 10 -7 < cm 3 < s / g, a vortex of 60 s, a moisture content of 4.4 wt%, a residual monomer content of 460 ppm and an extractable content of 5.0 wt%.

[0137] The surface-crosslinked superabsorbent had the following particle size distribution: >850 µm 0.0 wt.% 710 - 850 µm 0.6 wt.% 600 - 710 µm 4.5 wt.% 500 - 600 µm 10.9 wt% 400 - 500 µm 40.6 wt% 300 - 400 µm 34.0 wt.% 250 - 300 µm 6.1 wt.% 200 - 250 µm 2.6 wt.% 150 - 200 µm 0.5 wt.% <150 µm 0.2 wt.%

[0138] The superabsorbent had a mean particle size (d50) of 405 µm and a mean sphericity (mSPHT) of 0.80. Production Example 5 - Superabsorbent A

[0139] A superabsorbent was prepared analogously to Example 2 of WO 2016 / 134905 A1. The monomer solution used additionally contained 1.07 wt.% of the disodium salt of 1-hydroxyethylidene-1,1-diphosphonic acid. A dropper plate with 645 holes, a hole diameter of 100 µm, and a hole spacing of 8 mm was also used.

[0140] The gas inlet temperature of the reaction zone (5) was 167°C, the gas outlet temperature of the reaction zone (5) was 108°C, the gas inlet temperature of the internal fluidized bed (27) was 94°C, the product temperature in the internal fluidized bed (27) was 73°C, the gas outlet temperature of the condensation column (12) was 58°C and the gas outlet temperature of the gas drying unit (37) was 47°C.

[0141] The prepared superabsorbent (base polymer) had a bulk density (ASG) of 0.648 g / ml, a centrifuge retention capacity (CRC) of 54.7 g / g, an absorption under a pressure of 21.0 g / cm 2 < (AUL) of 8.8 g / g, a residual monomer content of 12600 ppm, an extractable content of 8.9 wt% and a moisture content of 9.0 wt%.

[0142] The superabsorbent had the following particle size distribution: >1000 µm 0.1 wt.% 850 - 1000 µm 0.1 wt.% 600 - 850 µm 0.6 wt.% 500 - 600 µm 2.6 wt.% 400 - 500 µm 13.1 wt% 300 - 400 µm 41.5% by weight 250 - 300 µm 22.0 wt.% 200 - 250 µm 15.0 wt.% 106 - 200 µm 4.9 wt% <106 µm 0.1 wt.%

[0143] The superabsorbent had a mean particle size (d50) of 284 µm and a mean sphericity (mSPHT) of 0.82.

[0144] The base polymer was then surface-crosslinked analogously to Examples 11 to 15 of WO 2015 / 110321 A1. 2.0 wt.% ethylene carbonate, 5.0 wt.% water, and 0.4 wt.% aluminum sulfate were used, each based on the base polymer. The product temperature was 175°C and the weir height was 75%.

[0145] In the cooler after surface post-crosslinking, 4.7 wt% of a 0.1 wt% aqueous solution of sorbitan monolaurate was added.

[0146] The prepared superabsorbent had a bulk density (ASG) of 0.733 g / ml, a centrifuge retention capacity (CRC) of 28.6 g / g, an absorption under a pressure of 21.0 g / cm 2 < (AUL) of 29.2 g / g, an absorption under a pressure of 49.2 g / cm 2 < (AUHL) of 23.8 g / g, a liquid flow conductance (SFC) of 32 × 10 -7 < cm 3 < s / g, a vortex of 43 s, a moisture content of 3.5 wt%, a residual monomer content of 790 ppm and an extractable content of 1.5 wt%.

[0147] The surface-crosslinked superabsorbent had the following particle size distribution: >850 µm 0.2 wt.% 710 - 850 µm 0.2 wt.% 600 - 710 µm 0.9 wt.% 500 - 600 µm 2.1 wt.% 400 - 500 µm 13.5 wt.% 300 - 400 µm 41.9% by weight 250 - 300 µm 24.2 wt.% 200 - 250 µm 11.8% by weight 150 - 200 µm 4.7 wt% <150 µm 0.5 wt.%

[0148] The superabsorbent had a mean particle size (d50) of 285 µm and a mean sphericity (mSPHT) of 0.80. Production Example 6 - Superabsorbent B

[0149] A superabsorbent of the type AQUA KEEP SA-60-SX-II (Sumitomo Seika Chemicals Co., Ltd.; Osaka, Japan) was used. AQUA KEEP SA-60-SX-II is a superabsorbent produced by reverse suspension polymerization.

[0150] The superabsorbent had a bulk density (ASG) of 0.66 g / ml, a centrifuge retention capacity (CRC) of 34.0 g / g, an absorption under a pressure of 0.0 g / cm 2 < (AUNL) of 54.8 g / g, an absorption under a pressure of 21.0 g / cm 2 < (AUL) of 32.8 g / g, an absorption under a pressure of 49.2 g / cm 2 < (AUHL) of 14.7 g / g, a liquid flow conductance (SFC) of 0 × 10 -7 < cm 3 < s / g, a vortex of 46 s and a moisture content of 11.1 wt%.

[0151] The superabsorbent had the following particle size distribution: >710 µm 6.5 wt.% 600 - 710 µm 9.6 wt.% 500 - 600 µm 16.1 wt.% 400 - 500 µm 24.7 wt% 300 - 400 µm 28.2 wt.% 150 - 300 µm 14.6 wt.% 106 - 150 µm 0.3 wt.% <106 µm 0.0 wt.%

[0152] The superabsorbent had a mean particle size (d50) of 429 µm and a mean sphericity (mSPHT) of 0.68.

[0153] Superabsorbent A and superabsorbent B were mixed in different ratios, and the resulting superabsorbent blends M were analyzed. The results are summarized in Tables 1 to 6: Table 1: Mixtures of superabsorbent A (Example 3) and superabsorbent B (Example 1) Example Superabsorbent Superabsorbent CRC T20 VAUL B A g / g s s 1*) 100% 0% 44,4 > 1200 2567 2*) 80% 20% 40,0 > 1200 1330 3*) 60% 40% 35,8 > 1200 386 4*) 40% 60% 33,0 393 243 5 20% 80% 28,5 210 179 6*) 0% 100% 26,0 165 180 *) Comparison example

[0154] The results of Table 1 are shown in the Figures 1 and 2 shown. Table 2: Mixtures of superabsorbent A (Example 5) and superabsorbent B (Example 4) Example Superabsorbent Superabsorbent CRC T20 VAUL B A g / g s s 7*) 100% 0% 46,8 > 1200 887 8*) 80% 20% 44,3 749 762 9*) 60% 40% 39,6 396 689 10*) 40% 60% 36,5 300 470 11 20% 80% 31,6 220 365 12*) 0% 100% 28,6 182 254 *) Comparison example

[0155] The results of Table 2 are shown in the Figures 3 and 4 shown. Table 3: Mixtures of superabsorbent A (Example 3) and superabsorbent B (Example 4) Example Superabsorbent Superabsorbent CRC T20 VAUL B A g / g s s 13*) 100% 0% 46,8 > 1200 887 14*) 80% 20% 41,8 563 614 15*) 60% 40% 37,6 317 422 16*) 40% 60% 32,8 228 303 17 20% 80% 28,5 187 206 18*) 0% 100% 26,0 165 180 *) Comparison example

[0156] The results of Table 3 are shown in the Figures 5 and 6 shown. Table 4: Mixtures of superabsorbent A (Example 5) and superabsorbent B (Example 1) Example Superabsorbent Superabsorbent CRC T20 VAUL B A g / g s s 19*) 100% 0% 44,4 > 1200 2567 20*) 80% 20% 41,0 > 1200 1309 21*) 60% 40% 38,4 > 1200 561 22*) 40% 60% 34,0 546 378 23 20% 80% 30,7 323 300 24*) 0% 100% 28,6 182 254 *) Comparison example

[0157] The results of Table 4 are shown in the Figures 7 and 8 shown. Table 5: Mixtures of superabsorbent A (Example 3) and superabsorbent B (Example 6) Example Superabsorbent Superabsorbent CRC T20 VAUL B A g / g s s 25*) 100% 0% 34,0 > 1200 1398 26*) 80% 20% 32,1 753 520 27*) 60% 40% 29,9 222 177 28*) 40% 60% 28,0 167 145 29 20% 80% 26,9 155 161 30*) 0% 100% 26,0 165 180 *) Comparison example

[0158] The results of Table 5 are shown in the Figures 9 and 10 shown. Table 6: Mixtures of superabsorbent A (Example 3) and superabsorbent B (Example 2) Example Superabsorbent Superabsorbent CRC T20 VAUL B A g / g s s 31*) 100% 0% 33,4 285 362 32*) 80% 20% 32,6 271 323 33*) 60% 40% 29,3 217 287 34*) 40% 60% 27,6 182 192 35 20% 80% 26,1 143 163 36*) 0% 100% 26,0 165 180 *) Comparison example

[0159] The results of Table 6 are shown in the Figures 11 and 12 shown.

Claims

1. A superabsorbent mixture M comprising at least 70% by weight of superabsorbent A having a liquid absorption of 20 g / g (T20) of less than 300 s and / or a volumetric liquid absorption under a pressure of 0.3 psi (2.07 kPa) (VAUL) with a t value of less than 400 s, and at least 5% by weight of superabsorbent B having a centrifuge retention capacity (CRC) of at least 30 g / g, where liquid absorption of 20 g / g (T20) is determined by the "K(t) Test Method (Dynamic Effective Permeability and Uptake Kinetics Measurement Test Method)" described in EP 2 535 027 A1 on pages 13 to 18, the t value for volumetric liquid absorption under a pressure of 0.3 psi (2.07 kPa) (VAUL) is determined by the "Volumetric Absorbency Under Load (VAUL)" test method described in WO 2014 / 079694 A1 on pages 39 and 40, wherein the t value is described as "characteristic swelling time", and the centrifuge retention capacity (CRC) is determined by EDANA recommended test method No. WSP 241.2 (05) "Fluid Retention Capacity in Saline, After Centrifugation".

2. The superabsorbent mixture M according to claim 1, wherein superabsorbent A has a liquid absorption of 20 g / g (T20) of less than 240 s and / or a volumetric liquid absorption under a pressure of 0.3 psi (2.07 kPa) (VAUL) with a t value of less than 350 s.

3. The superabsorbent mixture M according to claim 1 or 2, wherein superabsorbent A has a liquid absorption of 20 g / g (T20) of less than 180 s and / or a volumetric liquid absorption under a pressure of 0.3 psi (2.07 kPa) (VAUL) with a t value of less than 250 s.

4. The superabsorbent mixture M according to any of claims 1 to 3, wherein superabsorbent A has a liquid absorption of 20 g / g (T20) of less than 120 s and / or a volumetric liquid absorption under a pressure of 0.3 psi (2.07 kPa) (VAUL) with a t value of less than 200 s.

5. The superabsorbent mixture M according to any of claims 1 to 4, wherein superabsorbent B has a centrifuge retention capacity (CRC) of at least 35 g / g.

6. The superabsorbent mixture M according to any of claims 1 to 5, wherein superabsorbent B has a centrifuge retention capacity (CRC) of at least 40 g / g.

7. The superabsorbent mixture M according to any of claims 1 to 6, wherein superabsorbent B has a centrifuge retention capacity (CRC) of at least 45 g / g.

8. The superabsorbent mixture M according to any of claims 1 to 7, wherein superabsorbent A has a mean sphericity (mSPHT) of less than 0.72, where the mean sphericity (mSPHT) is determined with the PartAn® 3001 L particle analyzer (Microtrac Europe GmbH; Germany).

9. The superabsorbent mixture M according to any of claims 1 to 8, wherein superabsorbent B has a mean sphericity (mSPHT) of greater than 0.72.

10. The superabsorbent mixture M according to any of claims 1 to 9, wherein superabsorbent A has a bulk density (ASG) of less than 0.70 g / ml, where the bulk density (ASG) is determined by EDANA recommended test method No. WSP 260.2 (05) "Density, Gravimetric Determination".

11. The superabsorbent mixture M according to any of claims 1 to 10, wherein superabsorbent B has a bulk density (ASG) of greater than 0.70 g / ml.

12. The superabsorbent mixture M according to any of claims 1 to 11, wherein superabsorbent A has been surface postcrosslinked.

13. The superabsorbent mixture M according to any of claims 1 to 12, wherein superabsorbent B has not been surface postcrosslinked.

14. The superabsorbent mixture M according to any of claims 1 to 13, wherein superabsorbent A and / or superabsorbent B have / has an average particle size of 250 to 500 µm, where the average particle size is determined by EDANA recommended test method No. WSP 220.2 (05) "Particle Size Distribution", by plotting the proportions by mass of the screen fractions in cumulated form and determining the average particle size from the graph, where the average particle size is the value of the mesh size which arises for a cumulative 50% by weight.

15. A hygiene article comprising a superabsorbent mixture M according to any of claims 1 to 14.