METHOD FOR THE MANUFACTURING OF A SUSPENSION COMPRISING A CALCIUM CARBONATE-COMPRISING MATERIAL

Abstract

The present invention relates to a process for the manufacturing of a calcium carbonate-comprising material, to a calcium carbonate-comprising material obtained by the process as well as the use of the calcium carbonate-comprising material for paper filler and paper coating applications, in plastics applications, in paints, in adhesives, in sealings, in concrete, in agriculture applications, in food applications, in cosmetic applications or in pharmaceutical applications.

Claims

1. Process for the manufacturing of a calcium carbonate-comprising material, the process comprising the steps of a) providing at least two aqueous suspensions comprising a calcium carbonate-comprising material, wherein i) the first aqueous suspension has a solid content from 1.0 to 82.0 wt.-%, based on the total weight of the aqueous suspension, and a content of particles having a particle size <2 μm in the range from 1.0 to 30.0 wt.-%; and ii) the second aqueous suspension has a solid content from 10.0 to 82.0 wt.-%, based on the total weight of the aqueous suspension, and a content of particles having a particle size <2 μm in the range from >30.0 to 100.0 wt.-%; b) mixing the at least two aqueous suspensions provided in step a) to obtain an aqueous suspension mixture; c) grinding the aqueous suspension mixture obtained in mixing step b), and/or at least one of the at least two aqueous suspensions provided in step a) before mixing step b), is carried out.

2. The process according to claim 1, characterized in that at least one dispersing agent is added to at least one of the at least two aqueous suspensions provided in step a) and/or to the aqueous suspension mixture obtained in mixing step b).

3. The process according to claim 2, characterized in that the at least one dispersing agent is selected from the group consisting of sodium, potassium, calcium, magnesium, lithium, strontium, primary amine, secondary amine, tertiary amine and/or ammonium salts, whereby the amine salts are linear or cyclic, of at least partly neutralized homopolymers or copolymers of (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid and derivatives of these acids, preferably esters or amides such as methylmethacrylate, methylacrylate, acrylamide, sodium hydrogen phosphate or polyphosphates such as alkalipolyphosphates, carboxymethylcellulose, steric dispersants, comb polymers and/or mixtures thereof, preferably sodium polyacrylate having a molecular weight M.sub.w of from 4 000 to 10 000 g/mol, preferably from 4 000 to 8 000 g/mol and most preferably of about 6 000 g/mol.

4. The process according to claim 1, characterized in that the BET specific surface area of i) the calcium carbonate-comprising material in the aqueous suspension mixture obtained in mixing step b) with the proviso that grinding step c) is carried out before mixing step b) or the calcium carbonate-comprising material in the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) has a BET specific surface area of between 0.1 and 30.0 m.sup.2/g, preferably between 1.0 and 20.0 m.sup.2/g, more preferably between 2.0 and 14.0 m.sup.2/g and most preferably between 8.0 and 10.0 m.sup.2/g, as measured using nitrogen and the BET method according to ISO 9277, and/or ii) the calcium carbonate-comprising material in the aqueous suspension mixture obtained in mixing step b) with the proviso that grinding step c) is carried out before mixing step b) or the calcium carbonate-comprising material in the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) has a BET specific surface area between 0.1 and 2.0 m.sup.2/g, preferably between 0.1 and 1.5 m.sup.2/g and more preferably between 0.2 and 1.0 m.sup.2/g lower than the BET specific surface area of a calcium carbonate-comprising material manufactured by a process using water instead of the second aqueous suspension.

5. The process according to claim 1, characterized in that the Brookfield viscosity of the aqueous suspension mixture obtained in mixing step b) with the proviso that grinding step c) is carried out before mixing step b) or the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) is between 50 and 5 000 mPa.Math.s, preferably between 75 and 1 500 mPa.Math.s and more preferably between 150 and 500 mPa.Math.s.

6. The process according to claim 1, characterized in that the calcium carbonate-comprising material in the aqueous suspension mixture obtained in mixing step b) with the proviso that grinding step c) is carried out before mixing step b) or the calcium carbonate-comprising material in the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) has a i) top cut particle size d.sub.98 of ≦50.0 μm, preferably ≦20.0 μm and most preferably ≦10.0 μm, and/or ii) weight median particle size d.sub.50 between 0.1 and 10.0 μm, preferably between 0.5 and 5.0 μm and most preferably between 1.0 and 2.0 μm.

7. The process according to claim 1, characterized in that the solid content i) of the first aqueous suspension is from 30.0 to 78.0 wt.-% and preferably from 50.0 to 76.0 wt.-%, based on the total weight of the aqueous suspension, and/or ii) of the second aqueous suspension is from 30.0 to 40.0 wt.-% and preferably from 34.0 to 43.0 wt.-%, based on the total weight of the aqueous suspension, and/or iii) of the aqueous suspension mixture obtained in mixing step b) with the proviso that grinding step c) is carried out before mixing step b) or the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) is from 20.0 to 80.0 wt.-% and preferably from 50.0 to 62.0 wt.-%, based on the total weight of the aqueous suspension.

8. The process according to claim 1, characterized in that at least one of the at least two aqueous suspensions provided in step a) is subjected to a concentration step, preferably mechanical dewatering by means of settling, or forced settling by a centrifuge.

9. The process according to claim 1, characterized in that the calcium carbonate-comprising material is selected from natural calcium carbonate, precipitated calcium carbonate, dolomite and mixtures thereof, preferably natural calcium carbonate such as marble, chalk and/or limestone.

10. The process according to claim 1, characterized in that the at least two aqueous suspensions provided in step a) comprise the first and the second aqueous suspension in an amount of more than 10.0 wt.-%, preferably more than 30.0 wt.-%, more preferably more than 60.0 wt.-% and most preferably more than 65.0 wt.-%.

11. The process according to claim 1, characterized in that the at least two aqueous suspensions provided in step a) consist of the first and the second aqueous suspension.

12. The process according to claim 1, characterized in that grinding step c) is carried out after mixing step b).

13. The process according to claim 1, characterized in that the process further comprises at least one step d) of concentrating the aqueous suspension mixture obtained in mixing step b) with the proviso that grinding step c) is carried out before mixing step b) or the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) to remove at least a portion of water by mechanical means and/or thermal means.

14. The process according to claim 1, characterized in that the process further comprises the steps of e) drying the aqueous suspension obtained in step b) with the proviso that grinding step c) is carried out before mixing step b) or the aqueous suspension mixture obtained in grinding step c) with the proviso that grinding step c) is carried out after mixing step b) or the aqueous suspension mixture obtained in concentrating step d) to remove at least a portion of water to obtain a partially dewatered calcium carbonate-comprising material or to obtain a dried calcium carbonate-comprising material; and optionally f) treating the dried calcium carbonate-comprising material obtained after step e) with at least one dispersing agent and re-diluting it to obtain an aqueous suspension comprising a dispersed calcium carbonate-comprising material, and/or g) treating the dried calcium carbonate-comprising material obtained after step e) with at least one saturated aliphatic linear or branched carboxylic acid and/or with at least one mono-substituted succinic anhydride and/or at least one mono-substituted succinic acid and/or salty reaction product(s) and/or with at least one phosphoric acid ester blend of one or more phosphoric acid mono-ester and/or reaction products thereof and one or more phosphoric acid di-ester and/or reaction products thereof to obtain a hydrophobized calcium carbonate-comprising material.

15. A calcium carbonate-comprising material obtained by a process according to claim 1.

16. A product comprising the calcium carbonate-comprising material according to claim 15 for paper filler and paper coating applications, in plastics applications, in paints, in adhesives, in sealants, in concrete, in agriculture applications, in food applications, in cosmetic applications, or in pharmaceutical applications.

Description

EXPERIMENTAL SECTION

1. Measurement Methods

[0146] In the following the measurement methods implemented in the examples are described.

[0147] Particle Size Distribution (Mass % Particles with a Diameter <X) and Weight Median Particle Size (d.sub.50) of a Particulate Material

[0148] Weight grain diameter and grain diameter mass distribution of a particulate material were determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravitational field. The measurement was made with a Sedigraph™ 5120 or a Sedigraph™ 5100 of Micromeritics Instrument Corporation.

[0149] The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples are dispersed using a high speed stirrer and supersonics.

[0150] BET Specific Surface Area of a Material

[0151] Throughout the present document, the specific surface area (in m.sup.2/g) of a particulate material was determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:1995). The total surface area (in m.sup.2) of the particulate material is then obtained by multiplication of the specific surface area and the mass (in g) of the particulate material. The method and the instrument are known to the skilled person and are commonly used to determine the specific surface of particulate materials.

[0152] Suspension pH Measurement

[0153] The pH of a suspension is measured at 25° C. using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab® Expert Pro pH electrode. A three point calibration (according to the segment method) of the instrument is first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20° C. (from Aldrich). The reported pH values are the endpoint values detected by the instrument (the endpoint is when the measured signal differs by less than 0.1 mV from the average over the last 6 seconds).

[0154] Brookfield Viscosity

[0155] For the purpose of the present invention, the term “viscosity” or “Brookfield viscosity” refers to Brookfield viscosity. The Brookfield viscosity is for this purpose measured by a Brookfield (Type RVT) viscometer at 25° C.±1° C. at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa.Math.s. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV-spindle set which is suitable for the viscosity range to be measured. For example, for a viscosity range between 200 and 800 mPa.Math.s the spindle number 3 may be used, for a viscosity range between 400 and 1600 mPa.Math.s the spindle number 4 may be used, and for a viscosity range between 800 and 3200 mPa.Math.s the spindle number 5 may be used.

[0156] Solids Content

[0157] The solids content (also known as “dry weight”) was determined using a Moisture Analyser HR73 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120° C., automatic switch off 3, standard drying, 5 to 20 g of product.

[0158] Pigment Whiteness

[0159] Pigment whiteness R457 was measured using an ELREPHO 3000 from the company Datacolor according to ISO 2469:1994 (DIN 53145-2:2000 and DIN 53146:2000).

[0160] Light Scattering Coefficient

[0161] The light scattering coefficient “S” was measured by preparing a paper coating colour using 10 parts (on dry basis) of Acronal™ S 360 D, BASF, a paper coating binder, and 90 parts (on dry basis) of the calcium carbonate suspension and coated on a plastic support (Synteape, Argo Wiggins) at a range of different coat weight using a laboratory coater Typ Model 624 from Ericksen, 58675 Hemer, Germany. All coating colours had, if not reported otherwise, a solid content of 45.0 wt.-%.

[0162] The light scattering coefficient S is measured according to the method described in US 2004/0250970, wherein the ability to scatter light is expressed by the Kubelka-Munk light scattering coefficient, determined by the method, well-known to experts, described in the publications of Kubelka and Munk (Zeitschrift für Technische Physik 12, 539 (1931)), and of Kubelka (J. Optical Soc. Am. 38 (5), 448 (1948) and J. Optical Soc. Am. 44 (4), 330 (1954)) and U.S. Pat. No. 5,558,850. The light scattering coefficient S is quoted as the value interpolated at 20 g/m.sup.2.

2. Examples

[0163] The following starting materials have been used for the examples:

TABLE-US-00001 TABLE 1 Starting materials. Compound Chemical description Dispersing agent 1 Polyacrylate dispersant 70 mol-% sodium-30 mol-% calcium neutralized, Mw 5500; aqueous solution at 38 wt.-%; pH 8 Dispersing agent 2 100 % sodium-neutralized polyacrylate, Mw = 3500 g/mol, pH = 8

[0164] Preparation of Aqueous Suspension 1 (AS1)

[0165] Norwegian marble (40-48 μm) was ground at a solid content of 25 wt.-% in a Dynomill Multilab from W. Bachofen AG (total volume of the grinding chamber=600 cm.sup.3, mill speed=2 500 rpm, flow=500 cm.sup.3/min, filled with 1070 g of melt fused grinding beads consisting of 68 wt.-% baddeleyite and 32 wt.-% amorphous silica, based on the total weight of grinding beads with a diameter in the range from 1.0 to 1.6 mm) until the d.sub.50 was 8 μm. The suspension was centrifuged to obtain a cake with 75% solid content and a supernatant with 2% solid content. The cake was dispersed with dispersing agent 1 or 2 in an amount as given in Table 2 below at a solid content of 75 wt.-%.

[0166] Preparation of Aqueous Suspension 2 (AS2)

[0167] The supernatant from AS1 was placed in a settling jar and left for various days until the sediment had reached a solid content of 37%. The supernatant water was decanted and the sediment used as AS2.

[0168] Preparation and Grinding of the Mixture

[0169] AS1 was mixed with AS2, and or water. Additionally, the dispersant in an amount as given in Table 2 below was added. The mixture was vigorously stirred and pumped through the mill. One batch contained around 5 kg (dry) calcium carbonate. Subsequently, the obtained calcium carbonate containing suspension was ground at room temperature until the calcium carbonate containing material had the desired weight median particle size d.sub.50, i.e. for about 60 minutes. For grinding a Dynomill Multilab from W. Bachofen AG (total volume of the grinding chamber=600 cm.sup.3, mill speed=2 500 rpm, flow=500 cm.sup.3/min, filled with 1 070 g of melt fused grinding beads consisting of 68 wt.-% baddeleyite and 32 wt.-% amorphous silica, based on the total weight of grinding beads with a diameter in the range from 1.0 to 1.6 mm) was used. Physical data of the obtained products are given in Table 2 below. It is to be noted that the ΔSSA refers to the difference of BET specific surface area of the inventive example compared to the corresponding comparative example.

TABLE-US-00002 TABLE 2 E1 E2 E3 E4 CE1 CE2 CE3 CE4 AS1 AS2 AS1 AS2 AS1 AS2 AS1 AS2 AS1 H.sub.2O AS1 H.sub.2O AS1 H.sub.2O AS1 H.sub.2O sc [wt.-%] 75 37 75 37 75 37 75 37 75 — 75 — 75 — 75 — PSD <2 μm [wt.- 20 64 20 64 20 64 20 64 20 — 20 — 20 — 20 — %] <1 μm [wt.- 11 32 11 32 11 32 11 32 11 — 11 — 11 — 11 — %] Mixing ratio 70 30 70 30 70 30 70 30 100 — 100 — 100 — 100 — of AS1 and AS2 [dry/dry wt.-%] DA1 to AS1 600 600 600 600 600 600 600 600 [ppm] DA1 to 1 200 — 1 500 — 1 450 — 1 750 — Mixture [ppm] DA2 to — 1 150 — 1 500 — 1 400 — 1 700 Mixture [ppm] Sum DA 1 800 1 750 2 100 2 100 2 050 1 400 2 350 1 700 Time in the 45 45 56 56 60 60 75 75 mill [min] Mixture sc [wt.-%] 58.6 57.8 57.8 58.1 59.5 59.8 60.6 60.9 BV [mPas] 150 140 135 155 260 110 100 180 pH 9.5 9.6 9.5 9.6 9.4 9.8 9.6 9.8 PSD <2 μm [wt.- 79 78 86 87 79 78 84 87 %] <1 μm [wt.- 45 43 51 52 43 44 50 53 %] d.sub.50 [μm] 1.1 1.2 1.0 1.0 1.2 1.2 1.0 0.9 d.sub.98 [μm] 4 4 3 3 4 4 4 3 R457 [%] 95.6 95.4 95.7 95.6 96.0 96.3 95.7 96.3 Scat. [m.sup.2/kg] 129 127 135 143 135 131 134 134 SSA [m.sup.2/g] 8.3 8.0 9.4 9.2 8.6 8.6 9.8 10.1 ΔSSA [m.sup.2/g] −0.3 −0.6 −0.4 −0.8 — — — — AS = aqueous suspension, DA = Dispersing agent, sc = solid content, BV = Brookfield Viscosity, scat. = Scattering, SSA = specific surface area (BET).

[0170] The comparison of E1 with CE1, E2 with CE2, E3 with CE3 and E4 with CE4 in Table 2 shows that the inventive process allows to manufacture a calcium carbonate comprising material having a lower BET specific surface area. Thus, the inventive process for the manufacturing of a calcium carbonate-comprising material also results in a material allowing a lower consumption of dispersing agents in combination with improved optical properties as well as coating hold out. Furthermore, a grinding process according to the present invention is more time efficient and therefore also expected to be more energy efficient.