SYNTHESIS AND APPLICATION OF CaSO4-BASED HARDENING ACCELERATORS

Abstract

The invention concerns a method for producing pulverulent hardening accelerators by reactive spray drying, where an aqueous phase I comprising calcium ions, and an aqueous phase II comprising sulphate ions, the molar ratio of the calcium ions to the sulphate ions being from 1/5 to 5/1, are contacted at a spray nozzle, and the phases I and II contacted with one another at the spray nozzle are sprayed in a streaming environment of drying gas. Likewise concerned are the pulverulent hardening accelerators producible by the method of the invention, and their use for accelerating the hardening of bassanite and/or anhydrite with formation of gypsum.

Claims

1. A method for producing a pulverulent CaSO.sub.4-based hardening accelerator, the method comprising: a) contacting, at a spray nozzle, an aqueous phase I comprising liquid calcium ions and an aqueous phase H comprising liquid sulphate ions, the molar ratio of the calcium ions in phase I to the sulphate ions in phase II being from 1/5 to 5/1, and b) spraying phases I and II from said contacting with one another at the spray nozzle into a streaming environment of drying gas with an entry temperature in the range from 120 to 300 C. and an exit temperature in the range from 60 to 120 C., wherein the calcium ions react with the sulphate ions and, with removal of water by the carrier gas, the pulverulent hardening accelerator is obtained.

2. The method according to claim 1, wherein the spray nozzle is a multi-channel nozzle.

3. The method according to claim 2, wherein the multi-channel nozzle comprises at least two channels, the aqueous phase I comprising liquid calcium ions and the aqueous phase II comprising liquid sulphate ions are supplied separately into at least two of the channels, and phases I and II are contacted with one another at an outlet of the channels of the nozzle during said contacting.

4. The method according to claim 1, wherein phase I comprises an aqueous solution of a calcium salt, wherein phase II comprises an aqueous solution of a sulphate salt or of a sulphate ion-forming acid, and wherein the solubility of the calcium salt in the aqueous phase I is greater than 0.1 mol/l and the solubility of the sulphate salt or of the sulphate ion-forming acid in the aqueous phase II is greater than 0.1 mol/l, all solubilities being based on the temperature of 20 C. and atmospheric pressure.

5. The method according to claim 1, wherein a concentration of the calcium ions in phase I is from 0.1 mol/l to 3.5 mol/l, and a concentration of the sulphate ions in phase II is from 0.1 mol/l to 3.5 mol/l.

6. The method according to claim 4, wherein the calcium salt comprises at least one salt selected from the group consisting of calcium acetate, calcium formate, calcium chloride, calcium bromide, calcium iodide, calcium hydroxide, calcium sulphamidate, calcium lactate, calcium methanesulphonate, calcium propionate, calcium nitrate, and calcium carbonate.

7. The method according to claim 4, wherein the sulphate salt comprises at least one salt selected from the group consisting of an alkali metal sulphate, ammonium sulphate, aluminium sulphate, and magnesium sulphate, or the sulphate ion-forming acid comprises sulphuric acid.

8. The method according to claim 1, wherein the spraying of phases I and II produces droplets having an average drop size of 5 to 2000 m.

9. The method according to claim 1, wherein one or both of phases I and II comprises a polymer that comprises at least one acid group, or a salt of said polymer, said polymer or said salt of said polymer having an average molecular weight M.sub.w of 5000 g/mol to 100 000 g/mol.

10. The method according to claim 9, wherein each of said at least one acid group is an acid group selected from the group consisting of a carboxyl group, a phosphono group, a sulphino group, a sulpho group, a sulphamido group, a sulphoxy group, a sulphoalkyloxy group, a sulphinoalkyloxy group, and a phosphonooxy group.

11. The method according to claim 9, wherein the polymer comprises polyether groups.

12. The method according to claim 11, wherein each polyether group is represented by structural unit (I),
*U(C(O)).sub.kX-(AlkO).sub.nW(I) wherein * indicates the location of bonding to the polymer, U is a chemical bond or an alkylene group having 1 to 8 C atoms, X is oxygen or a group NR.sup.1, k is 0 or 1, n is an integer where the average value thereof, based on the polymer, is in the range from 3 to 300, Alk is an alkylene group that can be identical or different within the group (Alk-O).sub.n, W is a hydrogen atom, an alkyl radical, or an aryl radical, or W denotes the group YF, where Y is a linear or branched alkylene group having 2 to 8 C atoms and may carry a phenyl ring, F is a 5- to 10-membered nitrogen heterocycle which is bonded via nitrogen and which as ring members, besides the nitrogen atom and besides carbon atoms, may have 1, 2 or 3 additional heteroatoms, selected from the group consisting of oxygen, nitrogen and sulphur, it being possible for the nitrogen ring members to have a group R.sup.2, and it being possible for 1 or 2 carbon ring members to be present in the form of carbonyl group, R.sup.1 is hydrogen, C.sub.1-C.sub.4 alkyl or benzyl, and R.sup.2 is hydrogen, C.sub.1-C.sub.4 alkyl or benzyl.

13. The method according to claim 12, wherein the polymer is a polycondensation product comprising: (II) a structural unit comprising an aromatic or heteroaromatic group and a polyether group of the structural unit and (III) a phosphated structural unit comprising an aromatic or heteroaromatic group.

14. The method according to claim 13, wherein structural units (II) and (III) are obtained by copolymerization of monomers which are represented by general formulae (IIa) and (III), respectively:
A-U(C(O)).sub.kX-(AlkO).sub.nW(IIa) wherein each A is identical or different and represents a substituted or unsubstituted aromatic or heteroaromatic compound having 5 to 10 C atoms in the aromatic system, the further radicals possessing the definition stated above for structural unit (I), and ##STR00006## wherein each D is identical or different and represents a substituted or unsubstituted aromatic or heteroaromatic compound having 5 to 10 C atoms in the aromatic system, each E is identical or different and represents N, NH or O, m=2 if E=N, and m=1 if E=NH or O, each R.sup.3 and R.sup.4 is independently, a branched or unbranched C.sub.1 to C.sub.10 alkyl radical, C.sub.5 to C.sub.8cycloalkyl radical, aryl radical, heteroaryl radical or H, each b is identical or different and represents an integer from 0 to 300, and M represents H or one cation equivalent.

15. The method according to claim 13, wherein the polycondensation product further comprises a structural unit (IV) which is represented by formula (IV): ##STR00007## wherein each Y, independently, represents a group of (II), (III) or other constituents of the polycondensation product; and R.sup.5 and R.sup.6 are identical or different and represent H, CH.sub.3, COOH or a substituted or unsubstituted aromatic or heteroaromatic compound having 5 to 10 C atoms.

16. The method according to claim 12, wherein the polymer comprises at least one copolymer comprising monomer units from of a mixture of monomers comprising: (V) at least one ethylenically unsaturated monomer which comprises at least one radical selected from the group consisting of carboxylic acid, carboxylic salt, carboxylic ester, carboxylic amide, carboxylic anhydride and carboxylic imide, and (VI) at least one ethylenically unsaturated monomer having a polyether group of the structural unit (I).

17. The method according to claim 16, wherein each ethylenically unsaturated monomer (V) is represented by one of general formulae (Va), (Vb) and (Vc): ##STR00008## wherein R.sup.7 and R.sup.8 independently of one another are hydrogen or an aliphatic hydrocarbon radical having 1 to 20 C atoms, B is H, COOM, COO(C.sub.qH.sub.2qO).sub.rR.sup.9 or CONH(C.sub.aH.sub.2qO).sub.rR.sup.9, M is H or one cation equivalent, R.sup.9 is hydrogen, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, or an optionally substituted aryl radical having 6 to 14 C atoms, q independently at each occurrence for each (C.sub.qH.sub.2O) unit is identical or different and is 2, 3 or 4 and r is 0 to 200, Z is O or NR.sup.3; R.sup.10 and R.sup.11 independently of one another being hydrogen or an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, or an optionally substituted aryl radical having 6 to 14 C atoms, R.sup.12 being identical or different and also represented by (C.sub.nH.sub.2n)SO.sub.3M 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.3M.sub.2 with n=0, 1, 2, 3 or 4, (C.sub.nH.sub.2n)OPO.sub.3M.sub.2 with n=0, 1, 2, 3 or 4, (C.sub.6H.sub.4)SO.sub.3M, (C.sub.6H.sub.4)PO.sub.3M.sub.2, (C.sub.6H.sub.4)OPO.sub.3M.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 being H, COOM, COO(C.sub.qH.sub.2qO).sub.rR.sup.9 or CONH(C.sub.qH.sub.2qO).sub.rR.sup.9, where M, R.sup.9, q and r possess definitions stated above, R.sup.14 being hydrogen, an aliphatic hydrocarbon radical having 1 to 10 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, or an optionally substituted aryl radical having 6 to 14 C atoms, and Q being identical or different and also represented by NH, NR.sup.15 or O; where R.sup.15 is an aliphatic hydrocarbon radical having 1 to 10 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, or an optionally substituted aryl radical having 6 to 14 C atoms.

18. The method according to claim 17, wherein the ethylenically unsaturated monomer (VI) is represented by the following general formula (VI): ##STR00009## in which all radicals have the definitions stated above.

19. A pulverulent hardening accelerator produced by the method according to claim 1, wherein the crystallite size of bassanite present in the hardening accelerator is from 1 to 45 nm, the crystallite size of the bassanite determined by X-ray diffraction with subsequent Rietveld analysis of the pulverulent hardening accelerator.

20-22. (canceled)

23. A method of hardening basanite or anhydrite, comprising: mixing bassanite or anhydrite and a pulverulent hardening accelerator according to claim 19, and hardening bassanite or anhydrite in the presence of the pulverulent hardening accelerator.

24. A method of forming a gypsum plasterboard panel, comprising: mixing a gypsum slurry that comprises bassanite, water, and a pulverulent hardening accelerator according to claim 19, depositing the gypsum slurry between at least two cardboard sheets to form a plasterboard panel, and hardening the gypsum slurry.

25. A method of forming a self-leveling screed, comprising: mixing bassanite or anhydrite and a pulverulent hardening accelerator according to claim 19 to form a self-leveling screed.

26. The method according to claim 25, further comprising: hardening the self-leveling screed.

Description

EXAMPLES

Production of the Inorganic Hardening Accelerators Via a Reactive Spraying Process

[0143] General Procedure 1 (without Addition of Polymer):

[0144] Prepared were an aqueous solution of CaCl.sub.2 and an aqueous solution of MgSO.sub.4 with defined concentration as described in Table 1a or 1b. These solutions are filtered through a 1 m Acrodisc glass fibre filter. Subsequently these solutions were introduced into a pressurizable glass bottle (from Schott), and a pressure of 1.5 bar was applied. The solutions were introduced with exact stoichiometry or at different flow rates as described in Table 1, via Bronkhorst mini Cori-Flow flow regulators with pre-positioned 30 m steel filter, into a B-290 spraying tower from Bchi. The flow regulators were connected by a Master-Slave circuit and are driven digitally by a computer. The spraying tower was equipped with a 0465555 three-fluid nozzle, a 004189 cylcone separator and a 044673 glass tower from Bchi. The inner channel was fed with the MgSO.sub.4 solution, and the outer channel with the CaCl.sub.2 solution. The drying gas used was nitrogen, with a flow rate of 65 m.sup.3/h. The entry temperature of the drying gas was varied as described in Table 1; the corresponding exit temperature of the drying gas was likewise measured and is listed in Table 1. The spray nozzle was cooled with process water. The flow rate of the atomizing gas (N.sub.2) was 819 Nl/h (STP).

[0145] General Procedure 2 (with Addition of Polymer):

[0146] Prepared were an aqueous solution of CaCl.sub.2 and an aqueous solution of MgSO.sub.4 additionally containing an amount as specified in Table 1a or 1b of the polymer Melflux 2650 L (BASF Construction Solutions GmbH) in phase II (MgSO.sub.4 solution).

[0147] The comb polymer Melflux 2650 L is a commercially available polycarboxylate ether from BASF Construction Solutions GmbH. The polymer is based on the monomers maleic acid, acrylic acid and vinyloxybutyl-polyethylene glycol 5800; M.sub.w=36 000 g/mol, determined by GPC; the solids content is 33%.

[0148] These solutions are filtered through a 1 m Acrodisc glass fibre filter. Subsequently these solutions were introduced into a pressurizable glass bottle (from Schott), and a pressure of 1.5 bar was applied. The solutions were introduced with exact stoichiometry or at different flow rates as described in Table 1a and Table 1b, via Bronkhorst mini flow regulators with pre-positioned 30 m steel filter, into a B-290 spraying tower from Bchi. The flow regulators were connected by a Master-Slave circuit and are driven digitally by a computer. The spraying tower was equipped with a 0465555 three-fluid nozzle, a 004189 cylcone separator and a 044673 glass tower from Bchi. The inner channel was fed with the MgSO.sub.4 solution, and the outer channel with the CaCl.sub.2 solution. The drying gas used was nitrogen, with a flow rate of 65 m.sup.3/h. The entry temperature of the drying gas was varied as described in Tables 1a and 1b; the corresponding exit temperature of the drying gas was likewise measured and is listed in Table 1. The spray nozzle was cooled with process water. The flow rate of the atomizing gas was 819 Nl/h (STP).

[0149] Measurement of the Solids Content:

[0150] The solids content (SC) has been determined using an HR73 halogen moisture analyser from Mettler Toledo. Approximately 1 g of sample was weighed out onto aluminium weighing pans, 100 mm in diameter7 mm in height and placed in the instrument.

[0151] The sample was dried to constant weight (5 s) at 130 C.

Solids content(wt %)=final weight(t=measurement end point)/weight(t=0).Math.100%.

TABLE-US-00001 TABLE 1a Production of the hardening accelerators (equimolar) Pumping Melflux rate of 2650 (wt % phase I Solids Ex. based on Drying and phase Inlet Outlet content No.: Phase I Phase II CaSO.sub.4) gas II temperature temperature wt % 1 0.4M CaCl.sub.2 0.4M MgSO.sub.4 + 3.8% nitrogen 5 ml/min 210 C. 99-102 C. 84 Melflux 2650 L 2 2M CaCl.sub.2 2M nitrogen 6 ml/min 220 C. 90-93 C. 82 MgSO.sub.4 3 2M CaCl.sub.2 2M MgSO.sub.4 1.9% nitrogen 6 ml/min 220 C. 95-98 C. 82 Melflux 2650 L

TABLE-US-00002 TABLE 1b Production of the hardening accelerators with different molar ratios Melflux Phase I 2650 (wt % Phase II Ex. metering based on metering Inlet Outlet No.: Phase I rate Phase II CaSO.sub.4) rate Drying gas temperature temperature 4 0.4M CaCl.sub.2 5 ml/min 0.4M MgSO.sub.4 3.9% 2.5 ml/min nitrogen 205 C. 89-92 C. 5 0.4M CaCl.sub.2 2.5 ml/min 0.4M MgSO.sub.4 3.9% 5 ml/min nitrogen 195 C. 85-88 C. 6 0.4M CaCl.sub.2 5 ml/min 0.4M MgSO.sub.4 5 ml/min nitrogen 205 C. 86-89 C. 7 0.4M CaCl.sub.2 5 ml/min 0.4M MgSO.sub.4 2.5 ml/min nitrogen 195 C. 82-86 C. 8 0.4M CaCl.sub.2 2.5 ml/min 0.4M MgSO.sub.4 5 ml/min nitrogen 195 C. 81-85 C.

[0152] The physical properties of the hardening accelerator samples used are summarized in Table 2.

[0153] For the determination of the amount of bassanite and also of the crystallite size of bassanite, the pulverulent hardening accelerator, more particularly the bassanite present therein, was analysed by means of x-ray diffraction (XRD, Bruker D8 Discover) with subsequent Rietveld analysis (The Rietveld Method, edited by R. A. Young, 2002, International Union of Crystallography monographs on crystallography: 5, ISBN 0-19-855912-7). The measurement was carried out using CuK radiation in a 5-60 2 measurement range with a step width of 0.02 and a count time per step of 0.4 second. For the Rietveld evaluation, the Topas 4.2 software with fundamental parameter approach, from Bruker, was used. This determination of the crystallite size in the bassanite phase is based on the refining and adaptation of the diffraction pattern of the structure for bassanite (ICSD Database #79529). The parameter evaluated was the Lorentz crystallite size (Topas Parameter Cry Size L in nm), which results from the refining on the basis of adapted peak widths. It should be borne in mind here that the crystallite sizes cannot automatically be equated with the particle sizes.

TABLE-US-00003 TABLE 2 Crystallite size (from XRD measurements) and bassanite content Hardening Bassanite content accelerator Ex. Crystallite size of hardening No.: (nm) accelerator (wt %) 1 18.8 39.8 2 17.9 40.4 3 20.1 37.9 4 37.6 50.5 5 20.0 49.3 6 20.5 36.4 7 19.1 44.0 8 12.3 53.1

[0154] For comparison, for example, the crystallite size of a representative, bassanite-based binder (Schwarze Pumpe from Knauf), at 72.8 nm, is substantially larger than the hardening accelerators of the invention.

[0155] The crystallite size of bassanite-based binders ranges typically from 50 nm to about 200 nm, and is therefore substantially larger.

[0156] Calorimetric Determination of the Hardening Accelerator Performance

[0157] Since the bassanite binder has too high a reactivity to be analysed by heat flow calorimetry, the reaction is first of all retarded. For the measurement, 40 g of bassanite binder (Sigma-Aldrich>97%) are admixed with a mixture of 15 g of water and 25 g of a 0.056% strength solution of a calcium salt of an N-polyoxymethylene-amino acid (Retardan P retarder from Sika AG). The resulting composition is stirred for 60 seconds with an axial stirrer at 750 revolutions per minute. During a subsequent pause of 30 seconds, the respective accelerator is added, at a rate of 0.067 wt % of bassanite present in the accelerator (bassanite contents are disclosed in Table 2), based on the bassanite binder from Sigma-Aldrich, after which stirring is repeated for 30 seconds with an axial stirrer at 750 revolutions per minute. The heat flow is recorded with a TAM Air calorimeter (TA Instruments).

[0158] The FIG. 1 drawing shows, for example, a number of heat flow curves (reference and hardening accelerator samples 1 and 5). The reference (blank value) is the sample produced by the method specified above, from the bassanite binder and the above-stated retarder, without the addition of accelerator.

[0159] The performance of the accelerators is characterized by the acceleration factor a.sub.t, and is summarized in Table 3.

[0160] The acceleration factor a.sub.t is calculated from the shift in the time t of the maximum heat flow. In Example 1, the heat flow maximum is shifted from 307 min without accelerator (=t.sub.blank) to 100 min (Example 1=t.sub.sample), from which the acceleration factor a.sub.t is calculated as follows:

[00001]$a_t=\frac{t_{\mathrm{blank}}-t_{\mathrm{sample}}}{t_{\mathrm{blank}}}$

[0161] For Example 1 of Tables 2 and 3 (and shown in FIG. 1), therefore:

[00002]$a_t=\frac{307.Math..Math.\min -100.Math..Math.\min }{307.Math..Math.\min }=0.67=67.Math.\%$

TABLE-US-00004 TABLE 3 Relative acceleration of the hardening accelerators Relative acceleration a.sub.t Ex. No. (%) Reference.sup.1) 0 Comparative 1.sup.2) 51 Comparative 2.sup.2) 39 1 67 2 62 3 64 4 69 5 72 6 63 7 61 8 51 .sup.1)Bassanite from Sigma-Aldrich, with retarder, without accelerator .sup.2)Comparative Example 1 and Comparative Example 2 are standard accelerators based on ground calcium sulphate dihydrate.

[0162] The relative accelerators in Table 3 show that in all cases the hardening was accelerated effectively. Relative to the standard pulverulent accelerators, the results achievable were in most cases much better, or of similar quality.