PROCESS FOR THE PREPARATION OF DISPERSING AGENTS IN A SOLID FORM AND THEIR USE IN MINERAL BINDING COMPOSITIONS

Abstract

A process for preparing powdered dispersants comprising at least 90% by weight of at least one copolymer CP of the polycarboxylate ether type. The powdered dispersants can be easily dispersed in water. The invention also relates to the use of such powdered dispersants in mineral binder compositions, in particular dry mortars, concrete or gypsum formulations.

Claims

1. A process for producing a dispersant in solid form, wherein the dispersant comprises at least 90% by weight in each case based on the total weight of dispersant, of at least one copolymer CP, wherein the copolymers CP comprise the following constituents: (i) repeat units A of general structure (I), ##STR00011## and (ii) repeat units B of general structure (II), ##STR00012## where each R.sup.u is independently hydrogen or a methyl group, each R.sup.v is independently hydrogen or COOM, where M is independently H, an alkali metal, or an alkaline earth metal, m=0, 1, 2 or 3, p=0 or 1, each R.sup.1 is independently —[YO].sub.n—R.sup.4, where Y is a C2 to C4 alkylene and R.sup.4 is H, C1 to C20 alkyl, cyclohexyl or alkylaryl, and n=2-350, and the repeat units A and B in the copolymer CP have a molar ratio A:B within a range from 10:90 to 90:10, wherein the process comprises the following steps: a) producing a mixture of at least one copolymer CP, at least one base, and water, wherein the molar ratio of base to copolymer CP is selected such that a degree of neutralization of at least 55%, results, b) optionally drying the neutralized aqueous preparation from step a), and c) optionally comminuting the material obtained in step b).

2. The process for producing a dispersant in solid form as claimed in claim 1, wherein the dispersant comprises at least 90% by weight in each case based on the total weight of dispersant, of a copolymer CP, wherein the copolymer CP comprises the following constituents: (i) repeat units A of general structure (I) ##STR00013## and (ii) repeat units B of general structure (II), ##STR00014## where Ru, Rv, m, p, and R1 and a molar ratio A:B are as defined in claim 1, wherein the process consists of the following steps: a) producing a mixture of a copolymer CP, at least one base, and water, wherein the molar ratio of base to copolymer CP is selected such that a degree of neutralization of at least 55% results, b) drying the neutralized aqueous preparation from step a), and c) comminuting the material obtained in step b).

3. The process as claimed in claim 1, wherein the one or more copolymers CP consist to an extent of at least 34 mol % of the repeat units A and B.

4. The process as claimed in claim 1, wherein the proportion of water in the mixture in step a) is 10-90% by weight, in each case based on the total weight of the mixture.

5. The process as claimed in claim 1, wherein the base is selected from the group of alkali metal and alkaline earth metal oxides, hydroxides, hydrogen carbonates and/or carbonates.

6. The process as claimed in claim 1, wherein the neutralized aqueous preparation is in step b) dried at a temperature of 20-180° C.

7. The process as claimed in claim 1, wherein the neutralized aqueous preparation is in step b) dried at standard pressure.

8. The process as claimed in claim 1, wherein the neutralized aqueous preparation is in step b) dried at a pressure of 900 mbar or lower, preferably at 500 mbar or lower.

9. The process as claimed in claim 1, wherein the solid dispersant is a powder.

10. The process as claimed in claim 1, wherein the solid dispersant has a particle size distribution with a D90 value of <300 μm, a D10 value of <60 μm, and a D50 value of between 70-130 μm.

11. The process as claimed in claim 1, wherein the solid dispersant comprises further substances selected from the group comprising biocides, antioxidants and/or anticaking agents.

12. A solid dispersant obtainable by a process as claimed in claim 1.

13. A method of using the solid dispersant as claimed in claim 12, comprising applying the solid dispersant to a mineral binder composition.

14. A mineral binder composition comprising a) 5-60% by weight, of one or more mineral binders selected from the group consisting of portland cement, aluminate cement, calcium sulfoaluminate cement, calcium sulfate dihydrate, α-calcium sulfate hemihydrate, β-calcium sulfate hemihydrate, anhydrite, lime, slag, fly ash, microsilica, metakaolin, tuff, trass, volcanic ash and burnt oil shale, b) 0.01-10% by weight, of at least one solid dispersant as claimed in claim 12, c) 30-90% by weight, of at least one aggregate selected from the group consisting of limestone, quartz flour, sand, gravel, and pigments.

15. A mineral binder composition comprising a) 30-99.9% by weight, of one or more mineral binders selected from the group consisting of calcium sulfate dihydrate, α-calcium sulfate hemihydrate, β-calcium sulfate hemihydrate, and anhydrite, b) 0.01-10% by weight, of at least one solid dispersant as claimed in claim 12, c) optionally 0.5-25% by weight, of one or more mineral binders selected from the group consisting of portland cement, aluminate cement, calcium sulfoaluminate cement, lime, slag, fly ash, microsilica, metakaolin, tuff, trass, volcanic ash and burnt oil shale, d) optionally aggregates selected from the group consisting of limestone, quartz flour, sand, gravel, and pigments.

Description

EXAMPLES

Example 1—Preparation of Solid Dispersants

[0103] A copolymer CP having a backbone of acrylic acid and methacrylic acid (molar ratio 1:1, Mn of the backbone: 6000 g/mol) and methoxy-terminated polyethylene glycol side chains (Mn of the side chain: 5000 g/mol) with a molar ratio of acid to side chain of 12:1 was heated to 90° C. To the resulting melt of the copolymer CP was added a slurry of Ca(OH).sub.2 in water.

[0104] For the preparation of examples 1-4, the respective amount of Ca(OH).sub.2 shown in Table 1 was slurried in the specified amount of water and added to the copolymer CP.

[0105] The resulting mixtures were stirred at 20° C. for 2 min on a high-speed stirrer, then dried in an oven at 60° C. to a residual moisture content of <5% and then ground. This afforded inventive pulverulent dispersants (examples 1-4) having the degrees of neutralization and residual moisture contents shown in Table 1.

[0106] Reference 1, which is noninventive, was prepared as described above. However, Ca(OH).sub.2 was added directly, without slurrying in water, to a melt of the copolymer CP. Cooling and grinding of the melt afforded reference 1.

TABLE-US-00001 TABLE 1 Preparation of polymer powders 1-4 Ca(OH).sub.2 HO H.sub.2O [mg/g [mg/g [% by Degree of Residual Example polymer] polymer] wt.]* neutralization moisture Reference 80 0 0 110 n.d. 1 1 80 120 10 110 3.8 2 80 462 30 110 3.3 3 69 119 10 95 n.d. 4 40 116 10 55 n.d. *based on the total mass of the mixture n.d.: not determined

Example 2— Determination of Melting Points/Softening Points

[0107] Melting points/softening points were measured using an M-560 melting point apparatus from Büchi AG (measurement range: 50-400° C., heating rate: 20° C./min, apparatus calibrated against 4-nitrotoluene, diphenylacetic acid, caffeine, and potassium nitrate).

[0108] The inventive polymer powders 1˜4 did not melt, but softened followed by decomposition. Table 2 below shows the results of the measurement.

[0109] The noninventive reference 2 corresponds to reference 1, with the difference that no Ca(OH).sub.2 was added to reference 2.

TABLE-US-00002 TABLE 2 Melting/softening points and decomposition points of the polymer powders Melting point/softening Decomposition point Example point [° C.] [° C.] Reference 60 n.d. 1 Reference 60 n.d. 2 1 261 311 2 n.d. n.d. 3 225 282 4 176 279 n.d.: not determined

[0110] It is found that higher melting points are attained with increasing degree of neutralization. Reference 1 demonstrates clearly that it is not possible to increase the melting point by neutralizing directly in the melt. The unneutralized reference 2 shows a low melting point.

Example 3— Testing of the Polymer Powders in Gypsum Mixtures

[0111] 0.4 g of one of the inventive polymer powders 1-4 or the noninventive reference sample 2 was in each case dissolved in 106 g of water. To this was added 200 g of calcium sulfate β-hemihydrate and 0.2 g of calcium sulfate dihydrate and the resulting slurry was allowed to stand for 15 seconds. The mixture was then stirred intensively by hand for 30 seconds.

[0112] A mini-cone 50 mm in diameter and 51 mm in height was then filled with the resulting slurry and this was allowed to stand for 75 seconds. The slump (ABM) in millimeters was then determined. This was done by lifting the mini-cone and measuring the diameter of the gypsum cake that formed, once no more flow was observed. The time interval between completing the mixing process and lifting the mini-cone was 2 minutes. The diameter in mm is referred to as the slump.

[0113] The initial setting time and the final setting time were determined by the knife-cut method in accordance with DIN EN 13279-2:2014-03 and the thumb pressure method. The initial setting time (VB) has been reached when, after a knife cut through the gypsum cake, the cut edges no longer flow together. The final setting time (VE) has been attained when water no longer issues from the gypsum cake when pressing down with a finger with pressure of approx. 5 kg. Alternatively, the initial setting time and final setting time can also be determined using the Vicat needle apparatus in accordance with DIN EN 13279-2:2014-03.

[0114] Table 3 below gives an overview of the results. The noninventive example reference 3 is a gypsum mixture without addition of polymer powder. Reference 3 was prepared as described above from 200 g of calcium sulfate β-hemihydrate, 0.2 g of calcium sulfate dihydrate, and 106 g of water, without addition of a polymer powder.

TABLE-US-00003 TABLE 3 Results for the gypsum mixtures Example Slump [mm] VB [min] VE [min] Reference 140 3.00 8.00 3 Reference 184 4.00 10.00 2 1 188 3.66 9.75 2 188 3.58 9.92 3 175 3.50 9.33 4 167 3.42 9.25

[0115] It is found that dispersants of the invention bring about an improvement in slump with increasing degree of neutralization. At a degree of neutralization of 110% (examples 1 and 2), the plasticizing effect corresponds approximately to that of the non-neutralized reference 2.

[0116] It is additionally found that, at low degrees of neutralization, there is initially a less pronounced retarding effect than when adding a non-neutralized polymer powder, but that this increases again with increasing degree of neutralization.