STABILIZED GYPSUM PARTICLES

Abstract

The present invention is directed to a construction chemical composition for the preparation of gypsum articles, said construction chemical composition comprising fine calcium sulfate and a dispersant being a polyarylether. Further the present invention is directed to a process for preparing said construction chemical composition as well as an article comprising said construction chemical composition.

Claims

1.-16. (canceled)

17. A construction chemical composition, comprising i) fine calcium sulfate particles having a D (0.63) particle size of less than 10.0 μm determined with laser diffraction according to Mie Theory, and ii) a dispersant being a polyarylether, wherein the weight ratio between the fine calcium sulfate particles and the dispersant is in the range of 0.1:99.9 to 99.9:0.1.

18. A construction chemical composition according to claim 17, wherein the fine calcium sulfate particles are present in the form of calcium sulfate hemihydrate, calcium sulfate dihydrate, anhydrous calcium sulfate or mixtures thereof.

19. A construction chemical composition according to claim 17, wherein the polyarylether is a polycondensation product comprising i) at least one aromatic or heteroaromatic structural unit comprising a polyether side chain, and ii) at least one phosphated aromatic or heteroaromatic structural unit.

20. A construction chemical composition according to claim 19, wherein the at least one aromatic or heteroaromatic structural unit comprising a polyether side chain is represented by formula (I) ##STR00010## wherein A are identical or different and are represented by a substituted or unsubstituted aromatic or heteroaromatic compound having 5 to 10 C atoms; B are identical or different and are represented by N, NH or O; n=2 if B=N and n=1 if B=NH or O; R.sup.1 and R.sup.2, independently of one another, are identical or different and are represented by a branched or straight-chain C1- to C10-alkyl radical, C5- to C8-cycloalkyl radical, aryl radical, heteroaryl radical or H; a are identical or different and are represented by an integer from 1 to 300; and X are identical or different and are represented by a branched or straight-chain C1- to C10-alkyl radical, C5- to C8-cycloalkyl radical, aryl radical, heteroaryl radical or H, and wherein the at least one phosphated aromatic or heteroaromatic structural unit is represented by formula (II) ##STR00011## wherein D are identical or different and are represented by a substituted or unsubstituted aromatic or heteroaromatic compound having 5 to 10 C atoms; E are identical or different and are represented by N, NH or O; m=2 if E=N and m=1 if E=NH or O; R.sup.3 and R.sup.4, independently of one another, are identical or different and are represented by a branched or straight-chain C1- to C10-alkyl radical, C5- to C8-cycloalkyl radical, aryl radical, heteroaryl radical or H; and b are identical or different and are represented by an integer from 0 to 300.

21. A process for the preparation of a construction chemical composition comprising fine calcium sulfate having a D (0.63) particle size of less than 10.0 um determined with laser diffraction according to Mie Theory and a dispersant being a polyarylether, said process comprising the steps of aa) providing a suspension comprising calcium sulfate particles having a D (0.63) particle size equal or above 10.0 um determined with laser diffraction according to Mie Theory, water and a dispersant being a polyarylether, and ab) wet-grinding of the slurry obtained in step aa), thereby obtaining the construction chemical composition, wherein the weight ratio between the fine calcium sulfate particles and the dispersant is in the range of 0.1:99.9 to 99.9:0.1.

22. A process according to claim 21, wherein the calcium sulfate particles are present in the form of calcium sulfate hemihydrate, calcium sulfate dihydrate, anhydrous calcium sulfate or mixtures thereof.

23. A process according to claim 21, wherein the suspension of step aa) comprises i) 0.07 to 70.0 wt.-% of gypsum, ii) 0.01 to 10.0 wt.-% of the dispersant being a polyarylether, and iii) the balance to 100 wt.-% being water, based on the overall weight of the suspension.

24. A process according to claim 21, wherein the wet-grinding according to step ab) is carried out in a ball mill, a rotary grinder or an agitator bead mill.

25. A process for the preparation of a construction chemical composition comprising fine calcium sulfate having a D (0.63) particle size of less than 10.0 μm determined with laser diffraction according to Mie Theory and a dispersant being a polyarylether, said process comprising the steps of ba) providing a liquid A comprising a calcium source, water and a dispersant being a polyarylether, bb) providing a liquid B comprising a sulfate source, water and optionally a dispersant being a polyarylether, and bc) precipitation of fine calcium sulfate by mixing liquid A and liquid B, thereby obtaining the construction chemical composition, wherein the weight ratio between the fine calcium sulfate particles and the dispersant is in the range of 0.1:99.9 to 99.9:0.1.

26. A process according to claim 25, wherein the precipitating according to step bc) is carried out in a continuous microreactor or a spray precipitation reactor.

27. A process according to claim 21, wherein the process further comprises a step ac) or bd) wherein the construction chemical composition obtained in step ab) or bc) is dried, thereby obtaining the construction chemical composition in powder form.

28. A process according to claim 21, wherein the polyarylether is a polycondensation product according to claim 19.

29. A method comprising utilizing the construction chemical composition according to claim 17 in a process for preparing a gypsum wallboard, said process comprising the steps of ca) providing a composition comprising gypsum, mixing water and optionally foam, cb) feeding the composition obtained in step ca) into a mixing device, thereby preparing a slurry, cc) applying the slurry obtained in step cb) to a first cardboard sheet, and cd) covering the slurry with a second cardboard sheet, wherein i) at least one of the mixing water and the foam contains the construction chemical composition, and/or ii) ii) the first cardboard sheet and/or the second cardboard sheet is coated with the construction chemical composition, and/or iii) the construction chemical composition is added to the slurry in the mixing device or through a feed valve at the outlet of the mixing device.

30. A method comprising utilizing a polyarylether as a dispersant in a wet-grinding or precipitation process for the preparation of fine calcium sulfate particles having a D (0.63) particle size of less than 10.0 um determined with laser diffraction according to Mie Theory.

31. Article, made by using the composition according to claim 17.

32. Article according to claim 31, wherein the article is selected from a gypsum wallboard, a non-woven gypsum board, a gypsum-based self-levelling underlayment, a joint filler, a plaster, a mold, or a floor screed.

Description

EXAMPLES

[0301] Used materials

[0302] The polyarylether (PAE) used in the inventive composition IE1 is comparative example 7 of WO 2015/091461 A1.

[0303] The polycarboxylate used in the comparative composition CE1 is the commercial product Me!flux PCE 239 L by BASF.

[0304] The polycarboxylate used in the comparative composition CE2 is the commercial product Me!flux PCE 1493 L by BASF

[0305] The poly-naphthalene sulfonate (PNS) used in different compositions is the commercial product Flube CA 40 by Bozzetto.

[0306] β-hemihydrate is the commercial product Gesso Alabastrino by Gessi Roccastrada having an average particle size of 40 μm.

[0307] Natural anhydrite is the commercial product Micro B by Casea having an average particle size of 35 μm.

[0308] Dihydrate is the commercial product CS-Dihydrat by Casea having an average particle size of 50 μm.

[0309] Plast Retard L is the commercial product by Sicit 2000.

[0310] Preparation of the slurries

Reference Example 1

[0311] As a reference, a blank gypsum slurry not containing any accelerator was produced using 300 g of β-hemihydrate. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.665 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate is sprinkled carefully into the water. Further, Plast Retard L in amounts as indicated in Table 1 is added to the mixing water. The slurry was stirred for 30 seconds at 285 rpm. Water-to-binder (w/g) ratio of 0.665 was adjusted to achieve a flow of 21.0 cm for reference example 1.

Comparative Examples CE1 and CE2

[0312] Preparation of the liquid accelerator

[0313] For the preparation of the liquid accelerator, a composition of 15 wt.-% dihydrate, 83 wt.-% water and 2.0 wt.-% PCE was subjected to wet-grinding on a Netzsch Labstar LS 01 using zirconium oxide balls in diameter of 0.4-0.6 mm and wetted area of 85%. Wet-grinding was carried out for a total of 240 min.

[0314] Application Test

[0315] Slurries were produced using 300 g of β-hemihydrate. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.665 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate is sprinkled carefully into the water. The Plast Retard L was added to the mixing water in amounts as indicated in Table 1. During mixing, the liquid accelerator was dosed by injection. The slurry was stirred for 30 seconds at 285 rpm.

Comparative Example CE3

[0316] Preparation of the Liquid Accelerator

[0317] For the preparation of the liquid accelerator, a composition of 15 wt.-% dihydrate and 83 wt.-% water was subjected to wet-grinding on a Netzsch Labstar LS 01 using zirconium oxide balls in diameter of 0.4-0.6 mm and wetted area of 85%. Wet-grinding was carried out for a total of 240 min.

[0318] Application Test

[0319] A slurry was produced using 300 g of β-hemihydrate. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.665 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate is sprinkled carefully into the water. The Plast Retard L was added to the mixing water in amounts as indicated in Table 1. During mixing, the liquid accelerator was dosed by injection. The slurry was stirred for 30 seconds at 285 rpm.

Comparative Example CE4

[0320] Preparation of the Dry Accelerator

[0321] For comparative purposes, a dry accelerator was prepared by subjecting dihydrate having a particle size of 5 μm in amounts as indicated in Table 1 was subjected by dry grinding of dihydrate with 5% of alkylbenzene sulfonic acid, amine salt in a ball mill for a total of 4 min.

[0322] Application Test

[0323] A slurry was produced using 250 g of β-hemihydrate and 0.05 g (0.02% bws) dry accelerator. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.685 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate including the dry accelerator is sprinkled carefully into the water. The Plast Retard L was added to the mixing water in amounts as indicated in Table 1. The slurry was stirred tor 30 seconds at 285 rpm. Water-to-binder (w/g) ratio of 0.665 was adjusted to achieve a flow of 21.0 cm for comparative example CE4.

Inventive examples IE1, IE2 and IE3

[0324] Preparation of the Liquid Accelerator

[0325] For the preparation of the liquid accelerator, a composition of dihydrate, water and PAE in amounts as indicated in Table 1 was subjected to wet-grinding on a Netzsch Labstar LS 01 using zirconium oxide balls in diameter of 0.4-0.6 mm and wetted area of 85%. Wet-grinding was carried out for a total of 240 min.

[0326] Application Test

[0327] The inventive slurries were produced using 300 g of β-hemihydrate. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.665 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate is sprinkled carefully into the water. The Plast Retard L was added to the mixing water in amounts as indicated in Table 1. During mixing, the respective liquid accelerator was dosed by injection. The slurry was stirred for 30 seconds at 285 rpm.

Inventive Example IE4

[0328] Preparation of the Liquid Accelerator

[0329] For the preparation of the liquid accelerator, a composition of hemihydrate, water and PAE in amounts as indicated in Table 1 was subjected to wet-grinding on a Netzsch Labstar LS 01 using zirconium oxide balls in diameter of 0.4-0.6 mm and wetted area of 85%. Wet-grinding was carried out for a total of 240 min.

[0330] Application Test

[0331] A slurry was produced using 250 g of β-hemihydrate. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.685 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate is sprinkled carefully into the water. The Plast Retard L was added to the mixing water in amounts as indicated in Table 1. During mixing, the liquid accelerator was dosed by injection. The slurry was stirred for 30 seconds at 285 rpm.

Inventive Example IE5

[0332] Preparation of the Liquid Accelerator

[0333] For the preparation of the liquid accelerator, a composition of natural anhydrite, water and PAE in amounts as indicated in Table 1 was subjected to wet-grinding on a Netzsch Labstar LS 01 using zirconium oxide balls in diameter of 0.4-0.6 mm and wetted area of 85%. Wet-grinding was carried out for a total of 240 min.

[0334] Application Test

[0335] A slurry was produced using 250 g of natural anhydrite. The quantity of water needed corresponding to a water-to-binder (w/g) ratio of 0.685 and determined on the basis of the untreated gypsum slurry is charged into a mixing vessel (mixer according to DIN EN 196-1) and then the β-hemihydrate is sprinkled carefully into the water. The Plast Retard L was added to the mixing water in amounts as indicated in Table 1. During mixing, the liquid accelerator was dosed by injection. The slurry was stirred for 30 seconds at 285 rpm.

[0336] The compositions of the liquid accelerators are summarized in Table 1. Table 2 contains the composition and properties of application examples containing the liquid accelerators.

[0337] Particle Size

[0338] The particle size was determined with laser diffraction (Mastersizer 2000 from Malvern Instruments) according to Mie Theory for small particles (Particle RI=1.531, Dispersant RI=1,.330; Absorption=0.1; Obscuration between 10 and 20%).

[0339] The results are summarized in Table 2.

[0340] Slump Test

[0341] Flow was determined after a time of 60 seconds. After adding powder components to liquid the stucco had to soak for 15 seconds. Then the slurry was mixed for 30 seconds with a Hobart mixer. After a total time of 45 seconds an ASTM ring was filled with the stucco slurry up to the top edge and lifted after 60 seconds. At the end the patty diameter was measured with a caliper rule on two perpendicular axes.

[0342] Hardening Time

[0343] Initial setting was determined with the so-called knife-cut method (analogous to DIN EN 13279-2).

[0344] 2). The results are summarized in Table 2.

[0345] As can be gathered from Table 2, the hardening times of the inventive compositions containing

[0346] PAE as dispersant for liquid accelerator are significantly lower than the hardening time of the reference example containing no dispersant for liquid accelerator. Compared to examples CE1 and CE2 containing PCE as dispersant, the hardening times of examples IE1 and IE2 containing the same amount of PAE are also lower. The effect of the inventive dispersant is also shown for hemihydrate (IE4) and natural anhydrite (IE5) as gypsum components. Example CE4 shows that the hardening time and, therefore, the particle size of fine calcium sulfate obtained from the inventive wet-grinding process is superior to that of fine calcium sulfate obtained by a dry grinding method.

TABLE-US-00001 TABLE 1 Composition of the comparative and inventive construction chemical compositions Ref1 IE1 CE1 CE2 IE2 IE3 CE3 IE4 IE5 Dihydrate [wt.-%] — 15 15 15 35 15 15 Hemihydrate 25 Natural Anhydrite 25 Solids content [wt.-%] — 17 17 17 37 15.1 15 25.5 25.5 Water content [wt.-%] 83 83 83 63 84.9 85 74.5 74.5 PAE [wt.-%] — 2.0 — — 2.0 0.1 — 0.5 0.5 PCE [wt.-%] — 2.0 2.0 —

TABLE-US-00002 TABLE 2 Composition and properties of the application examples containing the comparative and inventive construction chemical compositions Ref1 IE1 CE1 CE2 IE2 IE3 CE3 IE4 IE5 CE4 Hemihydrate (Binder) [g] 300 300 300 300 300 300 300 250 250 250 H.sub.2O/Hemihydrate [—] 0.665 0.665 0.665 0.665 0.665 0.665 0.665 0.685 0.685 0.685 Dry Powder Ball Mill [% bws] 0.02 Accelerator Liquid Accelerator (active [% bws] 0.00 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.00 matter) Plast Retard L (1% Ig) [g] 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.5 1.5 1.5 Particle size, D(0.63) [μm] — 0.75 0.60 0.97 0.69 0.55 2.48 0.82 1.62 69.55 Stiffening time [min:s] 18:20 2:10 2:50 2:40 2:00 3:15 6:05 2:20 2:25 3:50

[0347] Mechanical Properties

[0348] For determining the flexural strength and compressive strength of gypsum articles prepared from the above described slurries, test specimens were prepared as follows:

[0349] The weight and density of said test specimens prepared at seed dosages of 0.02% and 0.01% are summarized in Tables 3 and 4.

[0350] Test specimens (4×4×16 cm.sup.3 prism) were prepared according to DIN 196-1 for investigation on strength development. Before testing flexural and compressive strength all samples were dried until mass consistency in the following way. After setting of the gypsum slurry all test specimens were stored at 20° C./65% relative humidity for one day. Afterwards all samples were stripped of the molds and then dried at 40° C. until mass consistency. Dry density was calculated by weighing and by volume (256 cm.sup.3). Tables 3 and 4 contain the result of different measurements of the flexural strength and compressive strength and the average values thereof.

TABLE-US-00003 TABLE 3 Mechanical properties (seed dosage: 0.02%) Ref1 IE1 CE1 CE2 Prism weight [g] 605.74 586.62 585.29 587.44 Density [kg/dm.sup.3] 1.183 1.146 1.143 1.147 Flexural strength [N/mm.sup.2] 5.280 7.105 7.240 7.040 Compressive strength [N/mm.sup.2] 20.70 24.70 21.40 22.10 (1) Compressive strength [N/mm.sup.2] 19.60 23.50 22.28 22.20 (average)

TABLE-US-00004 TABLE 4 Mechanical properties (seed dosage: 0.01%) IE1 CE1 CE2 IE3 CE3 Prism weight [g] 585.52 584.40 584.16 584.98 591.01 Density [kg/dm.sup.3] 1.144 1.141 1.141 1.143 1.154 Flexural strength [N/mm.sup.2] 7.460 6.910 6.545 6.410 6.040 Compressive strength [N/mm.sup.2] 23.70 21.78 21.43 17.20 15.85

[0351] According to Table 3, the flexural strength and compressive strength of the compositions prepared in the presence of a dispersant are improved compared to the blank reference. The compressive strength of the resulting gypsum article containing PAE are improved compared to the compositions containing PCE. Thus, the application of PAE instead of PCE according to the inventive wet-grinding process has a beneficial effect on the compressive strength of the resulting gypsum article.