RHEOLOGY MODIFIER FOR INORGANIC SUSPENSIONS

Abstract

The invention relates to a composition comprising () at least one water-soluble polymer based on (a) 5 to 40 wt % of at least one monomer of the formula (I) and (b) 5 to 95 wt % of at least one monomer (b) which comprises acid groups and is different from monomer (a), and () at least one associative thickener. Further disclosed is a mixture comprising an inorganic binder and also the composition of the invention. A further aspect of the present invention is the use of the composition of the invention as a rheological additive.

Claims

1. A composition comprising () at least one water-soluble polymer based on (a) 5 to 40 wt % of at least one monomer of the formula (I),
ZR.sup.1O(CH.sub.2CH.sub.2O).sub.k(CH.sub.2CH(R.sup.2)O).sub.l(CH.sub.2CH.sub.2O).sub.mR.sup.3 (I) where the units (CH.sub.2CH.sub.2O).sub.k, (CH.sub.2CH(R.sup.2)O).sub.l and (CH.sub.2CH.sub.2O).sub.m, where present, are arranged in block structure in the sequence shown in formula (I), and the radicals have the following definitions: Z: is an organic radical having at least one polymerizable structural group; k: is a number from 10 to 150; l: is a number from 1 to 25; m: is a number from 0 to 15; R.sup.1: is independently at each occurrence a single bond or a divalent linking group selected from the group consisting of (C.sub.nH.sub.2n), O(C.sub.nH.sub.2n) and C(O)O(C.sub.nH.sub.2n), where n, n and n are a natural number from 1 to 6; R.sup.2: is a hydrocarbyl radical having at least 2 carbon atoms, or an ether group of the general formula CH.sub.2OR.sup.2, where R.sup.2 is a hydrocarbyl radical having at least 2 carbon atoms and where R.sup.2 within the group (CH.sub.2CH(R.sup.2)O).sub.l may be identical or different; R.sup.3: is independently at each occurrence H or a hydrocarbyl radical having 1 to 24 carbon atoms, and also (b) 5 to 95 wt % of at least one polymerizable monomer (b), which is different from monomer (a) and comprises acid groups, and () at least one associative thickener, where the associative thickener () has an average molecular weight of 200,000 g/mol to 30,000,000 g/mol, as determined by the Mark-Houwink relationship (1),
M=([]/K).sup.1/(1) where K=0.0049, =0.8, is the intrinsic viscosity, and M is the average molecular weight, and the water-soluble polymer () has an average molecular weight of 5000 to 100,000 g/mol, as determined by gel permeation chromatography.

2. The composition according to claim 1, wherein the acid group of the monomer (b) comprises at least one acid group from the group consisting of carboxyl, phosphono, sulfino, sulfo, sulfamido, sulfoxy, sulfoalkyloxy, sulfinoalkyloxy, and phosphonooxy.

3. The composition according to claim 1, wherein the at least one water-soluble polymer (a) is a polycondensation product based on (a) at least one monomer of the formula (I), where Z is an aromatic or heteroaromatic, and (b) where the monomer (b) is phosphated or sulfonated and has an aromatic or heteroaromatic as the polymerizable group.

4. The composition according to claim 3, wherein Z in formula (I) is identical or different and is represented by a substituted or unsubstituted, aromatic or heteroaromatic compound having 5 to 10 carbon atoms in the aromatic system, and (b) is represented by the following general formula (II) ##STR00007## where D is identical or different and is represented by a substituted or unsubstituted, aromatic or heteroaromatic compound having 5 to 10 carbon atoms in the aromatic system, where E is identical or different and is represented by N, NH or O, where m=2 if E=N and m=1 if E=NH or O, where R.sup.4 and R.sup.5 independently of one another are identical or different and are represented by a branched or unbranched C.sub.1 to C.sub.10 alkyl radical, C.sub.5 to C.sub.8 cycloalkyl radical, aryl radical, heteroaryl radical or H, where b is identical or different and is represented by an integer from 0 to 300.

5. The composition according to claim 4, wherein water-soluble polymer () is a polycondensation product which comprises a structural unit (III) which is represented by the following formula ##STR00008## where R.sup.6a and R.sup.6b independently of one another are identical or different and are represented by H, CH.sub.3, COOH or a substituted or unsubstituted, aromatic or heteroaromatic compound having 5 to 10 carbon atoms, and Y independently at each occurrence is identical or different and is represented by structural units which correspond to formula (I) and formula (II), or other constituents of the polycondensation product.

6. The composition according to claim 1, wherein the water-soluble polymer () is at least one copolymer based on (a) at least one monomer of the formula (I), where Z is an ethylenically unsaturated radical and (b) where the monomer (b) has at least one ethylenically unsaturated radical.

7. The composition according to claim 6, wherein the ethylenically unsaturated monomer (b) is represented by at least one of the following general formulae from the group consisting of (IV), (V) and (VI) ##STR00009## where R.sup.7 and R.sup.8 independently of one another are hydrogen or an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms B is H, COOM.sub.a, COO(C.sub.qH.sub.2qO).sub.rR.sup.9, or CONH(C.sub.qH.sub.2qO).sub.rR.sup.9 M is hydrogen, a mono- or divalent metal cation, ammonium ion or an organic amine radical a is or 1 R.sup.9 is hydrogen, an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms, a cycloaliphatic hydrocarbyl radical having 5 to 8 carbon atoms, or an optionally substituted aryl radical having 6 to 14 carbon atoms q independently at each occurrence for each (C.sub.qH.sub.2qO) unit identically or differently is 2, 3 or 4, and r is 0 to 200 Z is O, NR.sup.3, ##STR00010## where R.sup.10 and R.sup.11 independently of one another are hydrogen or an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms, a cycloaliphatic hydrocarbyl radical having 5 to 8 carbon atoms, or an optionally substituted aryl radical having 6 to 14 carbon atoms R.sup.12 is identical or different and is represented by (C.sub.nH.sub.2n)SO.sub.3H with n=0, 1, 2, 3 or 4, (C.sub.nH.sub.2n)OH with n=0, 1, 2, 3 or 4; (C.sub.nH.sub.2n)PO.sub.3H.sub.2 with n=0, 1, 2, 3 or 4, (C.sub.nH.sub.2n)OPO.sub.3H.sub.2 with n=0, 1, 2, 3 or 4, (C.sub.6H.sub.4)SO.sub.3H, (C.sub.6H.sub.4)PO.sub.3H.sub.2, (C.sub.6H.sub.4)OPO.sub.3H.sub.2 and (C.sub.nH.sub.2n)NR.sup.14.sub.b with n=0, 1, 2, 3 or 4 and b=2 or 3 R.sup.13 is H, COOM.sub.a, COO(C.sub.qH.sub.2qO).sub.rR.sup.9, or CONH(C.sub.qH.sub.2qO).sub.rR.sup.9, where M.sub.a, R.sup.9, q and r possess definitions stated above R.sup.14 is hydrogen, an aliphatic hydrocarbyl radical having 1 to 10 carbon atoms, a cycloaliphatic hydrocarbyl radical having 5 to 8 carbon atoms, or an optionally substituted aryl radical having 6 to 14 carbon atoms Q is identical or different and is represented by NH, NR.sup.13 or O; where R.sup.15 is an aliphatic hydrocarbyl radical having 1 to 10 carbon atoms, a cycloaliphatic hydrocarbyl radical having 5 to 8 carbon atoms, or an optionally substituted aryl radical having 6 to 14 carbon atoms.

8. The composition according to claim 6, wherein Z in formula (I) is represented by at least one radical of the formula (VII) ##STR00011## in which R.sup.7 and R.sup.8 have the definitions stated above.

9. The composition according to claim 1, wherein the at least one associative thickener () comprises at least one water-soluble copolymer based on (c) 0.1 to 35 wt % of at least one monomer of the formula (VIII),
H.sub.2CC(R.sup.17)R.sup.1O(CH.sub.2CH.sub.2O).sub.k(CH.sub.2CH(R.sup.2)O).sub.l(CH.sub.2CH.sub.2O).sub.mR.sup.3 (VIII) where the units (CH.sub.2CH.sub.2O).sub.k, (CH.sub.2CH(R.sup.2)O).sub.l and (CH.sub.2CH.sub.2O).sub.m, where present, are arranged in block structure in the sequence shown in formula (VIII), and where R.sup.17: is H or methyl; and the remaining radicals have the definitions stated in formula (I), and (d) 10 to 99.9 wt % of at least one hydrophilic monomer (d) which is different from monomer (c).

10. The composition according to claim 1, wherein the radicals of the monomer of the formula (VIII) have the following definition: k: is a number from 23 to 26; l: is a number from 14 to 20; m: is a number from 2 to 5; R.sup.1: is a divalent linking group O(C.sub.nH.sub.2n), where n is 4, R.sup.2: is a hydrocarbyl radical having 2 carbon atoms; R.sup.3: is H, and R.sup.17: is H.

11. The composition according to claim 1, which comprises 5 to 95 wt % of the at least one water-soluble polymer (a) and 5 to 95 wt % of the at least one associative thickener ().

12. A mixture comprising an inorganic binder and 0.01 to 10 wt % of a composition according to claim 1, based on the dry mass of the mixture.

13. A process comprising mixing the composition according to claim 1 in a mixture comprising an inorganic binder and 0.01 to 10 wt % of the composition, based on the dry mass of the mixture, as a rheological additive.

Description

EXAMPLES

[0251] Preparation of Monomer M1:

[0252] A 2 l pressure autoclave with anchor stirrer was charged with 135.3 g (1.16 mol) of hydroxybutyl vinyl ether (HBVE) (stabilized with 100 ppm potassium hydroxide (KOH)) and the stirrer was engaged. 1.06 g of potassium methoxide (KOMe) solution (32% KOMe in methanol (MeOH), corresponding to 0.0048 mol of potassium) were run in and the stirred vessel was evacuated to a pressure of less than 10 mbar, heated to 80 C., and operated for 70 minutes at 80 C. under a pressure of less than 10 mbar. MeOH was removed by distillation.

[0253] In an alternative procedure, the potassium methoxide (KOMe) solution (32% KOMe in methanol (MeOH)) was run in and the stirred vessel was evacuated to a pressure of 10-20 mbar, heated to 65 C., and operated for 70 minutes at 65 C. under a pressure of 10-20 mbar. MeOH was removed by distillation.

[0254] The vessel was flushed three times with N.sub.2 (nitrogen). Thereafter the vessel was checked for pressure tightness, a superatmospheric pressure of 0.5 bar (1.5 bar absolute) was established, and heating took place to 120 C. The pressure was released to 1 bar absolute, and 1126 g (25.6 mol) of ethylene oxide (EO) were metered in up to a p.sub.max of 3.9 bar absolute and a T.sub.max of 150 C. Following addition of 300 g of EO, metering was interrupted (about 3 hours after the start) and, after a 30-minute pause, the vessel was let down to 1.3 bar absolute. Thereafter the remaining EO was metered in. The metering of EO, including let down, lasted for 10 hours in all.

[0255] Stirring was continued up to constant pressure at about 145-150 C. (1 h), followed by cooling to 100 C. and removal of low boilers under a pressure of less than 10 mbar for 1 hour. This gave a hydroxybutyl vinyl ether alkoxylate having 22 EO units.

[0256] A 2 l pressure autoclave with anchor stirrer was charged with 588.6 g (0.543 mol) of hydroxybutyl vinyl ether alkoxylate having 22 EO units, and the stirrer was switched on. Then 2.39 g of 50% strength NaOH solution (0.030 mol of NaOH, 1.19 g of NaOH) were added, reduced pressure of <10 mbar was applied, and the contents of the autoclave were heated to 100 C. and held for 80 minutes in order for the water to be distilled off.

[0257] The autoclave was flushed three times with N.sub.2. Thereafter the container was tested for pressure tightness, a superatmospheric pressure of 0.5 bar (1.5 bar absolute) was set, heating took place to 127 C., and thereafter the pressure was adjusted to 1.6 bar absolute. 59.7 g (1.358 mol) of EO were metered in at 127 C., the p.sub.max being 3.9 bar absolute. After a 30-minute pause, constant pressure was established, after which let down took place to 1.0 bar asbsolute. 625.5 g (8.688 mol) of BuO (butylene oxide) were metered in at 127 C., the p.sub.max being 3.1 bar absolute. Interim let down was needed in view of the increase in fill level. The BuO metering was halted, reaction was continued for an hour until the pressure was constant, and the vessel was let down to 1.0 bar absolute. Thereafter the metering of BuO was continued. P.sub.max was still 3.1 bar (first let down after 610 g of BuO, total BuO metering time 8 h including let down pause). After the end of the BuO metering, reaction was continued for 8 hours, followed by heating to 135 C. Thereafter 83.6 g (1.901 mol) of ED were metered in at 135 C., the p.sub.max being 3.1 bar absolute. After the end of the EO metering, reaction was continued for 4 hours. Cooling took place to 100 C.; residual oxide was drawn off until the pressure was below 10 mbar for at least 10 minutes. Then 0.5% of water was added at 120 C., and subsequent removal until the pressure was below 10 mbar for at least 10 minutes. The reduced pressure was eliminated with N2, followed by addition of 100 ppm of butylated hydroxytoluene (BHT). The product was discharged at 80 C. under N2.

[0258] This gave a hydroxybutyl vinyl ether alkoxylate having 24.5 EO units, 16 BuO units, and 3.5 EO units (monomer M1). Analysis (mass spectrum, GPC, .sup.1H NMR in CDCl.sub.3, .sup.1H NMR in MeOD) confirmed the structure.

Example 1

[0259] A glass reactor equipped with stirrer, pH electrode, thermometer, redox electrode was charged with 141.0 g of deionized water and 148.50 g of vinyloxybutylpolyethylene glycol 1100 (VOBPEG 1100) and 37.50 g of HBVE-24.5EO-16BuO-3.5EO (monomer M1) and this initial charge was cooled to a polymerization start temperature of 15 C. (initial charge).

[0260] In a separate feed vessel, 32.59 g of acrylic acid (99.5%) were mixed homogenously with 97.12 g of deionized water and 13.69 g of 50% KOH (solution A).

[0261] In parallel a 3% solution of a mixture of sodium sulfite, the disodium salt of 2-hydroxy-2-sulfinatoacetic acid, and the disodium salt of 2-hydroxy-2-sulfonatoacetic acid (Brggolit FF6 from Brggemann GmbH) in water was prepared (solution B). With stirring and cooling, first 47.1 g of solution A were added to the initial charge, after which 1.22 g of 3-mercaptopropionic acid (MPA) were added to the remainder of solution A. Then, in succession, 0.30 g of 3-mercaptopropionic acid and 0.047 g of iron(II) sulfate heptahydrate (FeSO.sub.4) were added to the initial charge solution. That solution was subsequently set to a starting pH of 5.7 using NaOH (50%). 0.3 ml of solution B was added to the initial charge.

[0262] With the addition of 2.87 g of hydrogen peroxide (30% solution in water) to the initial charge mixture, the reaction was initiated. At the same time, the addition of solution A and solution B to the stirred initial charge was commenced. Solution A was added over 45 minutes. Solution B was added in parallel at a constant metering rate of 18 ml/h until peroxide was no longer detectable in the solution. Thereafter the resulting polymer solution was adjusted to a pH of 6.5 using 50% sodium hydroxide solution.

[0263] The resulting copolymer was obtained in a solution having a solids content of 40.9 wt %. The weight-average molar mass of the copolymer is 33 200 g/mol, the polydispersity 2.10.

[0264] Examples 2 to 5 and also C1 and C2 were carried out in the same way as example 1, the quantities used being evident from tables 1 and 2.

TABLE-US-00001 TABLE 1 Quantities used for the initial charge for synthesis of the inventive water-soluble polymers. Initial charge HBVE- HBVE- HBVE- 24.5EO- 24.5EO- 24.5EO- VOBPEG VOBPEG 500 16BuO- 22BuO- 10PO-3.5EO H.sub.2O deionized Example 1100 [g] [g] 3.5EO [g] 3.5EO [g] [g] [g] 1 148.50 37.50 141.0 2 74.25 21.99 73.0 3 67.50 37.50 95.0 4 74.25 33.75 37.50 130.0 5 152.63 28.13 137.0 C1 148.50 28.92 134.0 C2 165.00 125.0 C = Comparative example

TABLE-US-00002 TABLE 2 Quantities used for synthesis of the inventive water-soluble polymers. Initial Solution A fraction of MPA KOH monomer (to (50%) solution A solution FeSO.sub.4 H.sub.2O.sub.2 Example AA [g] H.sub.2O [g] [g] [ml] A) [g] [g] [g] MPA [g] 1 32.59 97.12 13.69 47.1 1.22 0.047 2.87 0.30 2 16.29 48.56 6.84 23.6 0.61 0.023 1.44 0.15 3 32.59 97.12 13.69 47.1 1.68 0.028 1.72 0.78 4 32.59 97.12 13.69 47.1 1.68 0.028 1.72 0.78 5 32.59 97.12 13.69 47.1 1.22 0.047 2.87 0.30 C1 32.59 97.12 13.69 47.1 1.22 0.047 2.87 0.30 C2 32.59 97.12 13.69 41.7 1.22 0.047 2.87 0.30 [g] = grams; [ml] = milliliters; AA = 99.5% acrylic acid; MPA = 3-mercaptopropionic acid; H.sub.2O.sub.2 = 30%

TABLE-US-00003 TABLE 3 Overview of analytical data. Example Mw g/mol* PD* Solids wt % 1 33 200 2.10 40.9 2 41 100 1.98 39.6 3 15 500 1.66 29.9 4 18 300 1.57 28.6 5 40 500 2.17 40.4 C1 34 700 1.83 41.7 C2 26 600 1.66 40.7 *Mw (average molecular weight) and PD (polydispersity) determined by gel permeation chromatography (GPC): Column combinations: Shodex OHpak SB 804HQ from Showa, Japan (polyhydroxymethacrylate gel, particle size 10 m, pore size 2000 , plate number >16 000, column diameter and length 8 mm 300 mm) and Shodex OHpak 802.5HQ from Showa, Japan (polyhydroxymethacrylate gel, particle size 6 m, pore size 200 , plate number >16 000, column diameter and length 8 mm 300 mm); eluent: 0.05M ammonium formate/methanol (80/20 vol %), pH 6.5; flow rate: 0.5 ml/min; column temperature: 50 C.; detection: RI; calibration: PEG/PEO standards in the 10e6-10e2 g/mol range.

[0265] Synthesis of the Associative Thickener:

[0266] A plastic pail with magnetic stirrer, pH meter, and thermometer was charged with 53.8 g of a 50% aqueous solution of acrylamido-2-methylpropanesulfonic acid, Na salt, after which, in succession, 148 g of distilled water, 0.4 g of a commercial silicone-based defoamer (Dow Corning Antifoam Emulsion RD), 6.1 g of HBVE-24.5EO-16BuO-3.5EO (monomer M1), 185.5 g of acrylamide (50% solution in water), 1.2 g of a 5% aqueous solution of diethylenetriaminepentaacetic acid, pentasodium salt, and 0.5 g of sodium hypophosphite (10% solution in water) were added.

[0267] Following adjustment to a pH of 6.5 using 20% sodium hydroxide solution, and following addition of the remaining water to achieve the target monomer concentration of 31% (total amount of water minus the amount of water already added, minus the required amount of acid), the monomer solution was set to the starting temperature of 4 C. The solution was transferred to a Thermos flask, the temperature sensor for temperature recording was mounted, flushing with nitrogen was carried out for 45 minutes, and polymerization was initiated using 4 g of a 4% methanolic solution of the azo initiator 2,2-azobis(2-methylpropionitrile), 0.4 g of a 1% tert-butyl hydroperoxide solution, and 0.4 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 80-90 C. within about 25 minutes. A solid polymer gel was obtained.

[0268] After having cooled to about 50 C., the block of gel was comminuted using a mincer, and the gel granules obtained were dried in a fluidized-bed dryer at 55 C. for two hours. This gave hard, white granules which were converted to a powder state using a centrifugal mill.

[0269] Average molecular weight of the associative thickener: 7 000 000 g/mol.

[0270] The average molecular weight of the associative thickener was determined, as already described, by way of the Mark-Houwink relationship (1). For the present polymer/solvent pairing, the parameters K and are unknown. The parameters used were therefore those for pure polyacrylamide in water (according to J. Klein, K-D. Conrad, Makromol. Chem. 1980, 18, 227), i.e., K=0.0049 and =0.8.

[0271] For determining the intrinsic viscosity [] a 0.5% solution of the copolymer in water was prepared. This solution was diluted with a buffer (116.66 g of NaCl+32.26 g of Na.sub.2HPO.sub.4*12H.sub.2O+1.795 g of Na.sub.2HPO.sub.4*H.sub.2O in 2 liters of demineralized water) to give a c=0.01% polymer solution. This solution was analyzed with an Ubbelohde viscometer (at 20 C.; Ubbelohde capillary type 1). The intrinsic viscosity was determined from the transit time of the 0.01% polymer solution, the reference used being the solvent without polymer.

[0272] The transit time (t(polymer)) of the polymer solution was determined in comparison to the pure solvent (t.sub.sv) as reference (t=t(polymer)t.sub.sv). The intrinsic viscosity [] can be calculated from this according to Solomon-Ciuta:

[]={square root over (2(v.sub.relative1)2lnv.sub.relative))}/c

[0273] where v.sub.relative=cv.sub.reduced+1

[0274] and v.sub.reduced=t/(ct.sub.sv)

[0275] Performance Tests

[0276] The self-leveling calcium sulfate screed was composed of 39.55 wt % of anhydrite and 60.0 wt % of standard sand (DIN EN 196-1). As an initiator, 0.45 wt % of potassium sulfate was added. The water content was 14.0 wt %, based on the amount of anhydrite, standard sand, and potassium sulfate, corresponding to a water-to-binder ratio of 0.35. To plasticize the self-leveling calcium sulfate screed, a water-soluble polymer according to table 3 was added. The amount of the water-soluble polymer was selected relative to the anhydrite content in such a way that the self-leveling calcium sulfate screed, without the addition of an associative thickener, 5 minutes after addition of water, achieved a Hagermann cone slump flow of 3255 mm.

[0277] The self-leveling calcium sulfate screeds were produced in a method based on DIN EN 196-1:2005 in a mortar mixer with a capacity of approximately 5 liters. For mixing up, water, water-soluble polymer, associative thickener, an initiator, and anhydrite were placed into the mixing vessel. Immediately thereafter the mixing operation was commenced, with the fluidizer at low speed (140 revolutions per minute (rpm)). After 30 seconds, the standard sand was added at a uniform rate within 30 seconds to the mixture. Thereafter the mixer was switched to a higher speed (285 rpm) and mixing was continued for 30 seconds more. After that the mixer was stopped for 90 seconds. During the first 30 seconds, the self-leveling calcium sulfate screed, which stuck to the wall and to the lower part of the bowl, was removed with a rubber scraper and put into the middle of the bowl. After the wait, the self-leveling calcium sulfate screed was mixed for a further 60 seconds at the higher mixing speed. The total mixing time was 4 minutes.

[0278] Immediately after the end of the mixing operation, the slump flow was determined on all samples using the Hgermann cone, with no compaction energy being supplied, in accordance with the SVB guidelines of the Deutscher Ausschuss fr Stahlbeton [German Reinforced Concrete Committee] (see: Deutscher Ausschuss fr Stahlbetonbau (ed.): DAfStb Guidelines for Self-compacting Concrete (SVB guidelines), Berlin, 2003). The Hgermann cone (d top=70 mm, d bottom=100 mm, h=60 mm) was placed centrally on a dry glass plate having a diameter of 400 mm and was filled with the self-leveling calcium sulfate screed up to the level intended. Immediately after leveling had taken place, or 5 minutes after the first contact between anhydrite and water, the Hgermann cone was taken off, held over the slumping self-leveling calcium sulfate screed for 30 seconds to allow for dripping, and then removed. As soon as the slump flow came to a standstill, the diameter was determined, using a caliper gauge, at two axes lying at right angles to one another, and the average was calculated. The slump flow was tested in order, as described above, for all samples to be adjusted to the same fluid consistency by varying the amount of water-soluble polymer.

[0279] Additionally, a determination was made of the yield point using a rotational rheometer from

[0280] Schleibinger, model Viskomat NT, with a vane cell, at low shear rates, as occur during flow of self-leveling calcium sulfate screed. The purpose of determining the yield point was to provide information on possible flocculation of the anhydrite particles. For this purpose, after mixing, in parallel with the test of the slump flow, the self-leveling calcium sulfate screed was introduced into the measuring vessel, which was inserted into the rotational rheometer. Immediately thereafter the measuring head of the rheometer was lowered, the internal rigid sensor of the vane cell was immersed into the sample within the measuring vessel, and rheological measurement was commenced at an age of 5 minutes. In order to undo the resting structure, the sample was subjected to preliminary shearing at a shear rate of 50 s.sup.1 for 30 seconds. This was followed by determination of the yield point under rate control in steps of 25, 10, 5, 2.5, and 1.0 s.sup.1 for 10 seconds in each case. The dynamic yield point was evaluated using the known Bingham model =.sub.n+.Math.{dot over ()}.

[0281] In order to characterize the effect of the combination of water-soluble polymer and associative thickener on the robustness of the self-leveling calcium sulfate screed with respect to sedimentation and bleeding (settling of water on the surface), 200 ml of the self-leveling calcium sulfate screed, after having been mixed up, were introduced into a glass cylinder with a diameter of 35 mm (see: A. Perrot et al./Cement and Concrete Research 42 (2012) pp. 937-944). After rest times of 30, 60, and 120 minutes, the height of the water film (bleed water) on the surface of the self-leveling calcium sulfate screed was measured. The higher the film of water on the surface of the mortar, the lower the stabilizing effect of the associative thickener used. The results are summarized in table 4.

TABLE-US-00004 TABLE 4 Results of the performance trials Amount of water- Amount of soluble associative polymer thickener Water- added added Slump soluble [% based on [% based on flow Yield Height of water film in [mm] after polymer anhydrite] anhydrite] [cm] point [Pa] 0 min 30 min 60 min 120 min 1 0.22 0 33.0 11.0 0.00 0.00 0.25 0.29 0.22 0.02 30.2 46.1 0.00 0.00 0.00 0.00 2 0.25 0 32.5 9.44 0.00 0.10 0.15 0.37 0.25 0.02 24.6 53.0 0.00 0.00 0.00 0.00 3 0.32 0 32.0 12.3 0.00 0.00 0.15 0.26 0.32 0.02 21.0 109.4 0.00 0.00 0.00 0.01 4 0.27 0 32.3 12.4 0.00 0.00 0.15 0.26 0.27 0.02 23.8 52.6 0.00 0.00 0.00 0.03 5 0.18 0 32.5 11.5 0.00 0.03 0.07 0.20 0.18 0.02 22.4 63.2 0.00 0.00 0.00 0.00 C1 0.15 0 32.0 11.5 0.00 0.00 0.08 0.24 0.15 0.02 24.9 31.4 0.00 0.00 0.07 0.11 C2 0.12 0 32.8 10.9 0.00 0.00 0.12 0.39 0.12 0.02 30.0 22.7 0.00 0.00 0.04 0.12

[0282] It can be seen that the combination of inventive water-soluble polymer and the associative thickener exhibits advantages relative to the prior art.