Method for grinding mineral material

Abstract

The present invention relates to a method for producing mineral particles grinding a mineral material in the presence of a specific anionic polymer. The polymer used is obtained by means of polymerisation in the presence of sodium hypophosphite, disodium dipropionate trithiocarbonate and at least one radical-generating compound. The invention also relates to an aqueous composition comprising particles of ground mineral material and such a polymer, in particular a paper coating slip composition.

Claims

1. A method for preparing particles of at least one mineral matter, the method comprising: grinding the at least one mineral matter in water in the presence of at least one polymer with a molecular mass by weight M.sub.W (measured by SEC) of less than 8,000 g/mol and a polymolecularity index (PI) of less than 3, wherein the particles have a size of 50 μm or less, the at least one polymer is obtained by a radical polymerisation reaction in water or a solvent mixed with water, at a temperature higher than 50° C., of at least one anionic monomer selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid salt, and a methacrylic acid salt, in the presence of: sodium hypophosphite, 0.01 to 1.5% by weight of disodium 2,2′-(thiocarbonylbisthio)dipropanoate (DPTTC); and 0.1% to 5% by weight of at least one radical-generating compound selected from the group consisting of hydrogen peroxide, sodium persulphate, potassium persulphate, ammonium persulphate, wherein the viscosity of a suspension of the at least one mineral matter and the at least one polymer change less over an 8-day period than that of a suspension of the at least one mineral matter with a polymer that is otherwise the same as the at least one polymer but prepared in the absence of DPTTC and hypophosphite.

2. The method of claim 1, wherein: only one mineral matter or two or three mineral matters are subjected to the grinding or the at least one mineral matter is synthetic or of natural origin.

3. The method of claim 1, wherein the radical polymerisation reaction is carried out in a solvent mixed with water.

4. The method of claim 1, wherein the at least one polymer has: a weight-average molecular mass M.sub.W in a range of 1,000 g/mol to 7,500 g/mol or or a polymolecularity index (PI) of less than 2.8.

5. The method of claim 1, wherein the radical polymerisation reaction further comprises at least one monomer selected from the group consisting of: another different anionic monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and salts thereof, and mixtures thereof; a non-ionic monomer comprising at least one polymerisable olefinic unsaturation; and 2-acrylamido-2-methylpropanesulfonic acid, a salt of 2-acrylamido-2-methylpropanesulfonic acid, 2-(methacryloyloxy)ethanesulfonic acid, a salt of 2-(methacryloyloxy)ethanesulfonic acid, sodium methallyl sulfonate, styrene sulfonate and mixtures thereof.

6. The method of claim 1, wherein the radical polymerisation reaction comprises: 100% by weight of the at least one anionic monomer or from 70% to 99.5% by weight of the at least one anionic monomer and from 0.5% to 30% by weight of at least one monomer selected from the group consisting of: another different anionic monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, and salts thereof, and mixtures thereof; a non-ionic monomer comprising at least one polymerisable olefinic unsaturation; and 2-acrylamido-2-methylpropanesulfonic acid, a salt of 2-acrylamido-2-methylpropanesulfonic acid, 2-(methacryloyloxy)ethanesulfonic acid, a salt of 2-(methacryloyloxy)ethanesulfonic acid, sodium methallyl sulfonate, styrene sulfonate and mixtures thereof.

7. A method for preparing an aqueous suspension of particles of mineral matter, the method comprising implementing the grinding method of claim 1, to obtain particles of at least one mineral matter, and combining the particles with water to obtain an aqueous suspension with a solid content in mineral matter greater than 60% by weight.

8. An aqueous composition, comprising: particles of ground mineral matter obtained by or obtainable with the method of claim 1, and at least one polymer with a molecular mass by weight M.sub.W (measured by SEC) of less than 8,000 g/mol and a polymolecularity index (PI) of less than 3, obtained by a radical polymerisation reaction in water, at a temperature higher than 50° C., of at least one anionic monomer comprising at least one polymerisable olefinic unsaturation and a carboxylic acid group, in the presence of: sodium hypophosphite, disodium 2,2′-(thiocarbonylbisthio)dipropanoate (DPTTC); and at least one radical-generating compound selected from the group consisting of hydrogen peroxide; ammonium persulphate; an alcalin metal persulphate; hydrogen peroxide associated with an ion selected from the group consisting of Fe.sup.II, Fe.sup.III, Cu.sup.I, and Cu.sup.II; and mixtures thereof.

9. The aqueous composition of claim 8, further comprising an admixture selecting from the group consisting of dispersing agent, anti-foaming agent, biocide, colouring agent, lubricant agent, optical brightening agent, and bonding agent.

10. A method for preparing a paper coating colour, the method comprising: grinding at least one mineral matter in water in the presence of at least one polymer obtained by a radical polymerisation reaction in water or a solvent mixed with water, at a temperature greater than 50° C., of at least one anionic monomer selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid salt, and a methacrylic acid salt, in the presence of: sodium hypophosphite, 0.01 to 1.5% by weight of disodium 2,2′-(thiocarbonylbisthio)dipropanoate (DPTTC) and 0.1% to 5% by weight of at least one radical-generating compound selected from the group consisting of hydrogen peroxide, sodium persulphate, potassium persulphate, ammonium persulphate, wherein the viscosity of a suspension of the at least one mineral matter and the at least one polymer change less over an 8-day period than that of a suspension of the at least one mineral matter with a polymer that is otherwise the same as the at least one polymer but prepared in the absence of DPTTC and hypophosphite.

11. A grinding aid agent, comprising: at least one mineral matter, and at least one polymer obtained by a radical polymerisation reaction in water or a solvent mixed with water, at a temperature greater than 50° C., of at least one anionic monomer selected from the group consisting of acrylic acid, methacrylic acid, an acrylic acid salt, and a methacrylic acid salt, in the presence: sodium hypophosphite, 0.01 to 1.5% by weight of disodium 2,2′-(thiocarbonylbisthio)dipropanoate (DPTTC) and 0.1% to 5% by weight of at least one radical-generating compound selected from the group consisting of hydrogen peroxide, sodium persulphate, potassium persulphate, ammonium persulphate, wherein the viscosity of a suspension of the at least one mineral matter and the at least one polymer change less over an 8-day period than that of a suspension of the at least one mineral matter with a polymer that is otherwise the same as the at least one polymer but prepared in the absence of DPTTC and hypophosphite.

12. The grinding aid agent of claim 11, wherein the at least one polymer has a molecular mass by weight M.sub.W (measured by SEC) of less than 8,000 g/mol and a polymolecularity index (PI) of less than 3.

13. A paper product, obtained or obtainable from the aqueous composition of claim 8.

Description

EXAMPLES

(1) Molecular Mass by Size Exclusion Chromatography (SEC)

(2) The molecular weights and polymolecularity indices of the polymers obtained by a radical polymerisation reaction in water, at a temperature higher than 50° C., of at least one monomer comprising at least one polymerisable olefinic unsaturation and a carboxylic acid group, are measured by Size Exclusion Chromatography.

(3) A test portion of the polymer solution corresponding to 90 mg of dry matter is placed into a 10 mL flask. The mobile phase, supplemented with 0.04% dimethylformamide (DMF), is added to a total mass of 10 g. The composition of this mobile phase is as follows: NaHCO.sub.3: 0.05 mol/L, NaNO.sub.3: 0.1 mol/L, triethanolamine: 0.02 mol/L, NaN.sub.3 0.03% mass.

(4) The SEC chain is composed of a Waters 510 isocratic pump with a flow rate set to 0.8 mL/min, a Waters 717+ sample changer, an oven containing a Waters Ultrahydrogel Guard-type precolumn 6 cm long and 40 mm internal diameter, followed by a Waters Ultrahydrogel linear column 30 cm long and 7.8 mm internal diameter.

(5) Detection is provided by means of a Waters 410 RI differential refractometer. The oven is heated to 60° C. and the refractometer is heated to 45° C.

(6) The SEC device is calibrated with a series of sodium polyacrylate standards provided by Polymer Standards Service with a peak molecular weight comprised between 1,000 g/mol and 1.Math.10.sup.6 g/mol and a polymolecularity index comprised between 1.4 and 1.7, as well as with a sodium polyacrylate with a molecular weight of 5,600 g/mol and a polymolecularity index equal to 2.4. The calibration curve is of linear type and takes into account the correction obtained by means of the flow rate marker: dimethylformamide (DMF).

(7) Acquisition and treatment of the chromatogram are carried out using the PSS WinGPC Scientific software v. 4.02. The chromatogram obtained is incorporated into the zone corresponding to molecular weights greater than 65 g/mol.

(8) Grinding Technique and Particle Size Distribution Measurement

(9) Using a peristaltic pump, suspensions of coarse grains of mineral matter prepared in the presence of a polymer according to the invention or to a comparative polymer are introduced into a 1.4 L Dyno Mill KDL grinder containing 2,850 g of ZirPro ER 120 S ceramic beads with a diameter of from 0.6 mm to 1.0 mm. The grinding conditions are adjusted so as to obtain a suspension of particles of mineral matter of the desired particle size distribution. The necessary amount of polymer introduced into the system is adjusted to achieve the desired particle size distribution. This suspension is then characterised using a particle size measurement, a Brookfield viscosity measurement followed by a stability test. This stability test consists in measuring the Brookfield viscosity of the ground suspension after a resting time of 8 days at a temperature of 25° C.±1° C. The particle size characteristics relative to the preparation of particles of mineral matter are determined using a SediGraph III 5120 apparatus (Micrometrics, USA). In a known manner, this method and this measuring instrument make it possible to measure the particle size distribution of the suspensions of mineral matter particles. They enable in particular to determine the percentage of the mass fraction of a population of mineral particles with an equivalent spherical diameter of less than 1 μm or 2 μm (esd<1 μm or esd<2 μm, both expressed in %). These measurements are carried out from a suspension of particles of diluted mineral matter at a concentration of approximately 33 g of dry matter per litre of solution of a sodium polyacrylate with a molecular weight of 4,000 g/mol and concentration equal to 1.6 g of dry sodium polyacrylate per litre of solution. This sample is dispersed and sonicated before measurement.

(10) Brookfield Viscosity Measurement

(11) Brookfield viscosities (mPa.Math.s) of suspensions of particles of mineral matter prepared according to the method of the invention are measured after the grinding operation (VB0) and after 8 days at rest (VB8) at 25° C.±1° C. and at a rotation speed of 100 rpm using a Brookfield DVIII viscometer equipped with a suitable module, for example 2 to 5.

Example 1: Preparation of Co-Neutralised Polymers According to the Invention

(12) Place a mixture (R) of water and sodium hypophosphite in a stirred reactor. Then, prepare mixture 1 (M1), mixture 2 (M2) and mixture 3 (M3) from water, acrylic acid (AA), hydrogen peroxide or sodium persulphate, sodium hypophosphite and DPTTC. The reactor is then heated so as to reach the polymerisation temperature (T in ° C.) and mixtures 1, 2 and 3 are simultaneously introduced into the reactor. Lastly, the reactor is cooled down and the polymer is neutralised by injecting the pre-prepared neutralisation mixture (MN). The amounts of reagents (in g), the reaction conditions and the characteristics of the prepared polymers (solid content SC, molecular mass M.sub.W and polymolecularity index PI) are shown in Tables 1, 2 and 3.

(13) TABLE-US-00001 TABLE 1 Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 R water 282.8 282.8 198 198 198 277.2 277.2 282.8 NaH.sub.2PO.sub.2 .Math. H.sub.2O 2.61 2.47 15 13 9 12 12 2.72 M1 AA 439.8 439.8 208.6 208.6 208.6 205.6 205.6 439.8 DPTTC 20% 0 0 13.41 13.41 13.41 4.26 4.26 0 water 48.8 48.8 0 0 0 0 0 48.8 M2 H.sub.2O.sub.2 35% 0 0 7.1 7.1 7.1 3.5 4.5 0 Na persulphate 6.96 6.56 0 0 0 0 0 1.85 water 97.1 97.1 130 130 130 27.2 27.2 97.1 M3 NaH.sub.2PO.sub.2 .Math. H.sub.2O 23.45 22.21 0 0 0 0 0 24.44 DPTTC 20% 0.23 2.2 0 0 0 0 0 0.23 water 81.2 81.2 0 0 0 0 0 81.2 MN water 471.9 471.9 185 185 185 185 185 489.4 NaOH 50% 238.1 241.1 113.6 113.6 115.9 104.3 104.3 239.5 Ca(OH).sub.2 97% 116.1 117.2 55.31 55.31 56.44 62.08 62.08 117.9 T (° C.) 97 ± 1 97 ± 1 90 ± 2 90 ± 2 90 ± 2 90 ± 2 90 ± 2 97 ± 1 SC (%) 36 35.2 33.16 32.62 32.67 34.11 33.98 35.1 Mw (g/mol) 4,845 4,915 4,205 4,910 6,375 5,780 5,890 4,915 PI 2.2 2.2 2.2 2.3 2.5 2.4 2.3 2.1

(14) TABLE-US-00002 TABLE 2 Example 2-1 2-2 2-3 2-4 2-5 2-6 R Water 198 198 198 198 198 198 NaH.sub.2PO.sub.2 .Math. H.sub.2O 11 11.5 12 13 14 15 M1 AA 208.65 208.65 208.65 208.65 208.65 208.65 DPTTC 20% 13.41 13.41 13.41 13.41 13.41 13.41 Water 23.18 0 23.18 23.18 23.18 23.18 M2 H.sub.2O.sub.2 35% 7.1 7.1 7.1 7.1 7.1 7.1 Na persulphate 0 0 0 0 0 0 Water 130 130 130 130 130 130 M3 NaH.sub.2PO.sub.2 .Math. H.sub.2O 0 0 0 0 0 0 DPTTC 20% 0 0 0 0 0 0 Water 0 0 0 0 0 0 MN Water 170 170 170 170 170 170 NaOH 50% 160.66 159.85 160.66 159.03 159.85 159.85 Ca(OH).sub.2 97% 33.52 33.35 33.52 33.18 33.35 33.35 T (° C.) 90 ± 2 90 ± 2 90 ± 2 90 ± 2 90 ± 2 90 ± 2 SC (%) 31.69 32.5 31.69 31.68 31.38 31.5 Mw (g/mol) 6,165 5,465 5,640 5,225 5,145 4,590 PI 2.4 2.5 2.3 2.3 2.3 2.2

(15) TABLE-US-00003 TABLE 3 Example 3-1 3-2 3-3 3-4 R Water 198 198 198 198 NaH.sub.2PO.sub.2 .Math. H.sub.2O 14 13 12 15 M1 AA 208.65 208.65 208.65 231.83 DPTTC 20% 13.41 13.41 13.41 13.41 Water 23.18 23.18 23.18 23.18 M2 H.sub.2O.sub.2 35% 7.1 7.1 7.1 7.1 Na persulphate 0 0 0 0 Water 130 130 130 130 M3 NaH.sub.2PO.sub.2 .Math. H.sub.2O 0 0 0 0 DPTTC 20% 0 0 0 0 Water 0 0 0 0 MN Water 0 0 0 0 NaOH 50% 228 228 228 228 Ca(OH).sub.2 97% 0 0 0 0 T (° C.) 90 ± 2 90 ± 2 90 ± 2 90 ± 2 SC (%) 36.13 36.73 36.65 36.63 Mw (g/mol) 5,010 4,830 5,325 4,445 PI 2.2 2.2 2.3 2.2

Example 2: Preparation of Comparative Co-Neutralised Polymers

(16) In a similar manner to Example 1, comparative polymers were prepared. The amounts of reagents (in g), the reaction conditions and the characteristics of the prepared polymers are shown in Table 4.

(17) TABLE-US-00004 TABLE 4 Example C1 C2 C3 C4 R Water 282.8 244.40 224.93 262.71 CuSO.sub.4 .Math. 5H.sub.2O 0 0.32 0.30 0.35 FeSO.sub.4 .Math. 7H.sub.2O 0 0.28 0.25 0.30 NaH.sub.2PO.sub.2 .Math. H.sub.2O 2.74 0 0 0 M1 AA 439.82 279.82 257.91 301.8 DPTTC 20% 0 0 0 0 Water 48.8 0 0 0 M2 H.sub.2O.sub.2 35% 0 35.33 32.57 38.11 Na persulphate 7.33 0 0 0 Water 97.1 9.34 8.62 10.07 M3 NaH.sub.2PO.sub.2 .Math. H.sub.2O 24.68 0 0 0 DPTTC 20% 0 3.47 3.55 3.74 Water 81.2 31.15 28.71 25.52 MN Water 357.37 127.99 226.73 27.86 NaOH 50% 248.91 144.99 80.35 323.53 Ca(OH).sub.2 97% 118.63 42.41 60.18 0 T (° C.) 97 ± 1 93 ± 1 93 ± 1 93 ± 1 SC (%) 35.3 38 35 41.2 Mw (g/mol) 4,710 5,700 5,700 5,700 PI 2.1 2.6 2.5 2.6

Example 3: Grinding of Calcium Carbonate with an Esd of Less than 1 μm Equal to 80% by Weight

(18) The polymers according to the invention and a comparative polymer are used as a grinding aid agent for natural calcium carbonate. The various polymers are used at the same doses and in the same operating conditions.

(19) Aqueous suspensions of natural calcium carbonate are prepared with a solid content by weight of 76%±1%. They are prepared in the presence of an amount of 1.07% by dry weight of an aqueous polymer solution, as a grinding aid agent, with regard to the solid content in calcium carbonate used in this grinding operation in order to obtain the desired particle size distribution. The polymer solutions have a concentration of 35%±1% in active matter and a pH of 8.5±0.5. The raw material used to prepare these aqueous suspensions is an aqueous suspension of coarse grain calcium carbonate with a solid content of 75%±1% by weight. Calcium carbonate is a coarse marble (marketed as Omyacarb 10 AV Omya) from the Carrare region in Italy. The grinding conditions were adjusted so as to obtain a suspension of mineral particles of which 80.0%±0.5% by weight of its population has an equivalent spherical diameter of less than 1 μm (esd<1 μm=80.0%±0.5%).

(20) The suspensions according to the invention and the comparative suspension are then analysed and characterised using Brookfield viscosity measurements after the grinding operation, then after 8 days at rest at 25° C. The results are shown in Table 5.

(21) TABLE-US-00005 TABLE 5 Suspension Polymer VB0 VB8 S1-1 1-1 291 650 S1-2 1-2 299 645 S1-3 1-3 232 750 SC1 C1 310 983

(22) The use of the grinding aids according to the invention makes it possible to prepare low-density suspensions of ground calcium carbonate. The viscosities of these suspensions change less significantly over time for an 8-day period than that of the suspension prepared in the presence of the comparative polymer. The suspensions prepared according to the invention therefore have lower viscosities than those of the comparative test suspension. They are more stable.

Example 4: Grinding of Calcium Carbonate with an Esd of Less than 1 μm Equal to 80% by Weight

(23) The polymers according to the invention and a comparative polymer are used as a grinding aid agent for natural calcium carbonate. The various polymers are used at the same doses and in the same operating conditions.

(24) Aqueous suspensions of natural calcium carbonate are thus prepared with a solid content by weight of 76%±1%. They are prepared in the presence of an effective amount (EA, expressed in % dry/dry) by dry weight of an aqueous polymer solution in relation to 100 g of dry calcium carbonate used as a grinding aid agent in order to obtain the desired particle size distribution. The polymer solutions have a concentration of 35%±1% in active matter and a pH of 8.5±0.5. The raw material used to prepare these aqueous suspensions is an aqueous suspension of coarse grain calcium carbonate with a solid content of 75%±1% by weight. Calcium carbonate is a coarse calcite (marketed as BL 200 Omya) from the Orgon region in France. The grinding conditions were adjusted so as to obtain a suspension of mineral particles of which 80.0%±0.5% by weight of its population has an equivalent spherical diameter of less than 1 μm (esd<1 μm=80.0%±0.5%).

(25) The calcium carbonate suspensions are then analysed and characterised using Brookfield viscosity measurements after the grinding operation, then after 8 days at rest at 25° C. The effective amount (EA) of dry polymer for obtaining the desired particle size distribution is also measured. The results are shown in Table 6.

(26) TABLE-US-00006 TABLE 6 Suspension Polymer EA VB0 VB8 S2-1 2-1 0.93 679 1,356 S2-2 2-2 0.99 508 1,406 S2-3 2-3 0.96 670 1,352 S2-4 2-4 0.95 547 1,226 S2-5 2-5 0.95 580 1,326 SC2 C2 1.05 1,019 1,786

(27) The use of the polymers according to the invention makes it possible to reduce the effective amount of the grinding aid agent. Again, the use of the grinding aid agents according to the invention makes it possible to prepare low-viscosity suspensions of ground calcium carbonate. The viscosities of these suspensions change less significantly over time for an 8-day period than that of the suspension prepared in the presence of the comparative polymer. The suspensions prepared according to the invention therefore have lower viscosities than those of the comparative test suspension. They are more stable.

Example 5: Grinding of Calcium Carbonate with an Esd of Less than 2 μm Equal to 60% by Weight

(28) The polymers according to the invention and a comparative polymer are used as a grinding aid agent for natural calcium carbonate. The various polymers are used at the same doses and in the same operating conditions.

(29) Aqueous suspensions of natural calcium carbonate are thus prepared with a solid content by weight of 74%±1%. They are prepared in the presence of an amount of 0.26% by dry weight of an aqueous polymer solution, as a grinding aid agent, with regard to the solid content in calcium carbonate used in this grinding operation in order to obtain the desired particle size distribution. The polymer solutions have a concentration of 35%±1% in active matter and a pH of 8.5±0.5. The raw material used to prepare these aqueous suspensions is an aqueous suspension of coarse grain calcium carbonate with a solid content of 75%±1% by weight. Calcium carbonate is a coarse marble (marketed as Omyacarb 10 AV Omya) from the Carrare region in Italy. The grinding conditions are adjusted so as to obtain a suspension of mineral particles of which 60.0%±0.5% by weight of its population has an equivalent spherical diameter of less than 2 μm (esd<2 μm=60.0%±0.5%).

(30) The calcium carbonate suspensions are then analysed and characterised using Brookfield viscosity measurements after the grinding operation, then after 8 days at rest at 25° C. The results are shown in Table 7.

(31) TABLE-US-00007 TABLE 7 Suspension Polymer VB0 VB8 S3-1 3-1 98 276 S3-2 3-2 105 304 SC3 C3 123 450

(32) Again, the use of the grinding aid agents according to the invention makes it possible to prepare low-viscosity suspensions of ground calcium carbonate. The viscosities of these suspensions change less significantly over time for an 8-day period than that of the suspension prepared in the presence of the comparative polymer. The suspensions prepared according to the invention therefore have lower viscosities than those of the comparative test suspension. They are more stable.