Sustainable adsorbable polymers

Abstract

The present invention relates to an aqueous suspension of mineral pigment materials having high solids content, which contain dispersing agents and/or grinding agents based on renewable sources, and methods for preparing such a suspension and its use.

Claims

1. An aqueous suspension comprising a mineral pigment material, and at least one modified polysaccharide, as a dispersant, having a degree of carboxylation of hydroxyl groups in the range from 0.6 to 2.0 and an intrinsic viscosity in the range from 5 to 220 ml/g, wherein the carbon of the at least one modified polysaccharide shows a rate of nuclear transformation of .sup.14C to .sup.14N in the range from 400 to 890 transformations per hour and per gram carbon, wherein the at least one modified polysaccharide is present in an amount from 0.05 wt.-% to 5.0 wt.-%, based on the total weight of the solids in the suspension, wherein greater than or equal to 90% of the particles in the suspension are less than 2 m, wherein the Brookfield viscosity of the aqueous suspension is between 100 and 1500 mPa.Math.s at 20 C., wherein the solids content of the mineral pigment in the suspension is from 55 to 80 wt.-%, based on the total weight of the suspension, and wherein an acrylic acid based dispersant is not present in the suspension.

2. The suspension according to claim 1, wherein the mineral pigment material is a calcium carbonate containing material, calcium carbonate, calcium carbonate containing minerals, mixed carbonate based fillers, or any mixture thereof.

3. The suspension according to claim 1, wherein the mineral pigment is calcium carbonate selected from the group consisting of ground calcium carbonate, precipitated calcium carbonate, modified calcium carbonate, and any mixture thereof.

4. The suspension according to claim 1, wherein the mineral pigment material is in the form of particles having a weight median particle size d.sub.50 from 0.3 to 5 m.

5. The suspension according to claim 1, wherein the mineral pigment material is in the form of particles having a weight median particle size d.sub.50 from 0.4 to 3 m.

6. The suspension according to claim 1, wherein the at least one modified polysaccharide is a carboxymethyl derivate and/or a carboxymethyl hydroxypropyl derivate and/or a carboxymethyl hydroxyethyl derivate of a polysaccharide, an anionic starch, an anionic guar, or any mixture thereof.

7. The suspension according to claim 1, wherein the at least one modified polysaccharide is carboxymethyl cellulose.

8. The suspension according to claim 1, wherein the carbon of the at least one modified polysaccharide shows a rate of nuclear transformation of .sup.14C to .sup.14N in the range from 550 to 850 transformations per hour and per gram carbon.

9. The suspension according to claim 1, wherein the degree of carboxylation of hydroxyl groups of the at least one modified polysaccharide is in the range from 0.8 to 1.9.

10. The suspension according to claim 1, wherein the degree of carboxylation of hydroxyl groups of the at least one modified polysaccharide is in the range from 0.9 to 1.7.

11. The suspension according to claim 1, wherein the degree of carboxylation of hydroxyl groups of the at least one modified polysaccharide is in the range from 1.0 to 1.6.

12. The suspension according to claim 1, wherein the intrinsic viscosity of the at least one modified polysaccharide is in the range of 10 to 200 ml/g.

13. The suspension according to claim 1, wherein the carboxylic groups of the at least one modified polysaccharide are at least partly neutralized by one or more monovalent and/or one or more polyvalent cations.

14. The suspension according to claim 1, wherein the carboxylic groups of the at least one modified polysaccharide are at least partly neutralized by one or more cations selected from the group consisting of Li.sup.+, Na.sup.+, K.sup.+, Sr.sup.2+, Ca.sup.2+, Mg.sup.2+and any mixture thereof.

15. The suspension according to claim 1, wherein the at least one modified polysaccharide is present in an amount from 0.1 to 3 wt.-%, based on the total weight of the solids in the suspension.

16. The suspension according to claim 1, wherein the at least one modified polysaccharide is present in an amount from 0.2 to 2.0 wt.-%, based on the total weight of the solids in the suspension.

17. The suspension according to claim 1, wherein the at least one modified polysaccharide is present in an amount from 0.25 to 1.5 wt.-%, based on the total weight of the solids in the suspension.

18. The suspension according to claim 1, wherein the at least one modified polysaccharide is present in an amount from 0.5 to 1.25 wt.-%, based on the total weight of the solids in the suspension.

19. The suspension according to claim 1, wherein the Brookfield viscosity of the aqueous suspension is between 100 and 1000 mPa.Math.s at 20 C.

20. The suspension according to claim 1, wherein the Brookfield viscosity of the aqueous suspension is between 100 and 700 mPa.Math.s at 20 C.

21. The suspension according to claim 1, wherein the solids content of the suspension is from 60 to 79 wt.-%, based on the total weight of the suspension.

22. The suspension according to claim 1, wherein the solids content of the suspension is from 65 to 78 wt.-%, based on the total weight of the suspension.

23. The suspension according to claim 1, wherein the at least one modified polysaccharide is the only dispersant present in the suspension.

Description

EXAMPLES

(1) 1. Measurement Methods

(2) In the following, measurement methods implemented in the examples are described.

(3) Brookfield Viscosity

(4) The Brookfield viscosity of the pigment particles suspension was measured after one hour of production and after one minute of stirring at 20 C.2 C. at 100 rpm by the use of a Brookfield viscometer type RVT equipped with an appropriate spindle.

(5) Particle Size Distribution

(6) The particle size distribution of the pigment particles was measured using a Sedigraph 5100 from the company Micromeritics, USA. 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 was carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonics. For the measurement of dispersed samples, no further dispersing agents were added.

(7) Solids Content of an Aqueous Suspension

(8) The suspension solids content (also known as dry weight) was determined using a Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following settings: drying temperature of 160 C., automatic switch off if the mass does not change more than 1 mg over a period of 30 sec, standard drying of 5 to 20 g of suspension.

(9) Intrinsic Viscosity

(10) The intrinsic viscosity was determined by a Schott AVS 370 system. The samples were dissolved in a 0.2 M NaCl solution, and subsequently, the pH was adjusted to 10 with NaOH. Measurements were performed at 25 C. (+/0.1 C.) with a capillary type 0a and corrected using the Hagenbach correction. The intrinsic viscosity is automatically calculated with the software Dilution 370 (Software fr Verdnnungsreihen, Version 6.2.1, SI Analytics, Germany).

(11) Degree of Carboxylation

(12) The degree of carboxylation was determined by conductometric titration according to Katz et al. The determination of strong and weak acidic groups in sulfite pulps (Svensk Paperstidn., 1984, 6, pp. 48-53).

(13) Nuclear Carbon Transformation from .sup.14C to .sup.14N

(14) The rate of nuclear carbon transformation from .sup.14C to .sup.14N of the modified polysaccharide was measured, based on a stage of preparation consisting of a thermal decomposition at a high temperature (approximately 1000 C.) by combustion or calcination of the sample for analysis, followed by collection of the released carbon dioxide which is trapped at low temperature before its reduction, by catalytic hydrogenation, into elemental carbon atoms, the composition of which in .sup.13C/.sup.12C and .sup.15N/.sup.14N isotopes, and also .sup.14C isotopes, were measured by a mass spectrophotometer. The rate of nuclear carbon transformation from .sup.14C to .sup.14N is specified in transformation per hour and per gram carbon, which is expressed as decay/h/g.

(15) Necessary preparation and pre-treatment of the sample material for radiocarbon dating was carried out by the .sup.14C laboratory of the Department of Geography at the University of Zurich (GIUZ). The dating itself was done by AMS (accelerator mass spectroscopy) with the tandem accelerator of the Institute of Particle Physics of the Swiss Federal Institute of Technology Zurich (ETH).

(16) Wet Grinding

(17) Without any specific indications, wet grinding was done in tap water (15 dH) in a horizontal attritor mill (Dynomill, Type KDL-Pilot, Bachofen, Switzerland) having a volume of 1.4 liters in a recirculation mode, using zircon silicate beads of 0.6 to 1.2 mm diameter.

(18) 2. Materials

(19) Mineral Pigment Materials

(20) Mineral Pigment Material A:

(21) Natural CaCO.sub.3 from Italy, Avenza, having a d.sub.90 value of 390 m, a d.sub.50 value of 165 m, and a d.sub.10 value of 20 m.

(22) Mineral Pigment Material B:

(23) Natural CaCO.sub.3 from Norway obtained by autogenously dry grinding in a ball mill 10 to 300 mm CaCO.sub.3 rocks to a fineness corresponding to a d.sub.50 value from 42 to 48 m (calcium carbonate powder, containing no grinding aid or dispersant).

(24) Mineral Pigment Material C:

(25) Natural CaCO.sub.3 from Austria, obtained trough dry grinding in a ball mill having a d.sub.50 value of 7.5 m, and a d.sub.98 value of 32 m.

(26) Modified Polysaccharides

(27) Carboxymethylcellulose 1 (CMC 1):

(28) CMC 1 is commercially available from ACROS Organics, Belgium. CMC 1 has an M.sub.w of 250000 g/mol, a carboxylation degree of 1.2, and an intrinsic viscosity of 774 ml/g. The rate of nuclear carbon transformation is 630 decay/h/g.

(29) Carboxymethylcellulose 2 (CMC 2):

(30) CMC 2 is commercially available from Sigma-Aldrich, Germany (product name C5678). CMC 2 has a carboxylation degree of 0.7 and an intrinsic viscosity of 147 ml/g. The rate of nuclear carbon transformation is 715 decay/h/g.

(31) Carboxymethylcellulose 3 (CMC 3):

(32) CMC 3 is commercially available from CP Kelco, Germany (Cekol 2000). CMC 3 has a carboxylation degree according to the specifications of 0.75 to 0.85.

(33) 3. Examples

(34) 3.1. Comparative Example

Example 1

(35) A slurry with a solid content of 45 wt.-% was prepared by mixing 2 wt.-%, based on the total weight of solids in the slurry, of the CMC 1 in form of a 9.9 wt.-% solution in water with the mineral pigment material A. Subsequently, the obtained mixture was wet ground with a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until a d.sub.98 value of 3 m was achieved.

(36) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 92 wt.-% smaller than 2 m, and 64 wt-% smaller than 1 m. During the grinding process, the Brookfield viscosity increased to such an extent so that no further grinding at the high solids content concentration was possible. The slurry was diluted with water to keep grinding running.

(37) The obtained pigment particle suspension had finally a solid content of 40.5 wt.-% and a Brookfield viscosity of 485 mPa.Math.s. The Brookfield viscosity at a concentration of 52 wt.-% was far above 1500 mPa.Math.s and very sticky.

(38) 3.2. Inventive Examples

Example 2

(39) Preparation of Carboxymethylcellulose (CMC)

(40) 214 g CMC 1 was dissolved in 2460 ml water and stirred for 12 h at room temperature. Subsequently, the solution was heated to 80 C., and 800 l of a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, were added dropwise. After 5 h, 60 l of said H.sub.2O.sub.2 solution were added dropwise. Thereafter, 2 times another 60 l of said H.sub.2O.sub.2 solution were added dropwise in 1.5 h intervals. Finally, the solution was stirred for another 1.5 h at 80 C.

(41) The obtained CMC had an intrinsic viscosity of 179 ml/g and a pH of 7.

(42) Preparation of the Aqueous Pigment Particle Suspension

(43) A slurry with a solid content of 60 wt.-% was prepared by mixing 2 wt.-%, based on the total weight of solids in the slurry, of the prepared CMC in form of a 9.9 wt.-% solution in water with the mineral pigment material A. Subsequently, the obtained mixture was wet ground with a 1.4-liter horizontal attritor mill by recirculation at 55 C. Furthermore, 300 ppm of Ca(OH).sub.2 were added during grinding. The grinding was carried out for 25 min until a d.sub.98 value of 3 m was achieved.

(44) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 91 wt.-% smaller than 2 m and 61 wt.-% smaller than 1 m. The obtained pigment particle suspension had a solid content of 60.8 wt.-%, a pH of 9.4, and a Brookfield viscosity of 922 mPa.Math.s.

Example 3

(45) A slurry with a solid content of 60 wt.-% was prepared by mixing 2 wt.-%, based on the total weight of solids in the slurry, of a CMC prepared according Example 2 in form of a 9.9 wt.-% solution in water with the mineral pigment material A. Subsequently, the obtained mixture was wet ground with a 1.4-liter horizontal attritor mill by recirculation, and 300 ppm of a aqueous 10% Ca(OH).sub.2 suspension and 500 ppm ammonium zirconium carbonate (Bacote 20, MEL Chemicals) were added during wet grinding. The grinding was carried out for 25 min at 40-50 C. until a d.sub.98 value of 3 m was achieved.

(46) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 91 wt.-% smaller than 2 m and 61 wt.-% smaller than 1 m. The obtained pigment particle suspension had a solid content of 61 wt.-%, a pH of 9.5, and a Brookfield viscosity of 940 mPa.Math.s.

Example 4

(47) Preparation of Carboxymethylcellulose (CMC)

(48) 90.8 g CMC 1 was dissolved in 1170 ml water and stirred for 12 h at room temperature. Subsequently, the solution was heated to 80 C., and 0.9 ml of a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, were added dropwise. After 5.5 h, 0.5 ml of said H.sub.2O.sub.2 solution were added dropwise. After 4 h, another 0.2 ml of said H.sub.2O.sub.2 solution were added dropwise. Thereafter, the solution was stirred for 2 h and another 0.4 ml of said H.sub.2O.sub.2 solution were added drop wise. Finally, the solution was stirred for another 4 h at 80 C.

(49) The obtained CMC had an intrinsic viscosity of 56 ml/g and a pH of 10, adjusted with aqueous 10% NaOH.

(50) Preparation of the Aqueous Pigment Particle Suspension

(51) A slurry with a solid content of 72.1 wt-% was prepared by mixing 0.69 wt.-% of the prepared CMC and 300 ppm of a aqueous 10% Ca(OH).sub.2 suspension with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until a d.sub.50 value of 0.8 m was achieved.

(52) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 90 wt.-% smaller than 2 m, 65 wt.-% smaller than 1 m, and 15 wt-% smaller than 0.2 m. The obtained pigment particle suspension had a solid content of 72.1 wt.-%, a pH of 9.6, and a Brookfield viscosity of 273 mPa.Math.s.

Example 5

(53) Preparation of Carboxymethylcellulose (CMC)

(54) 124 g CMC 1 was dissolved in 1299 ml water and stirred for 12 h at room temperature. Subsequently, the solution was heated to 80 C., and 2 ml of a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, were added dropwise over a period of 20 minutes. After 4.5 h, 1.2 ml of said H.sub.2O.sub.2 solution were added dropwise over a period of 20 minutes. After 2 h additional 0.8 ml of said H.sub.2O.sub.2 solution were added drop wise over a period of 20 minutes. Thereafter, the solution was stirred for 7 h at 80 C.

(55) The obtained CMC had an intrinsic viscosity of 23.7 ml/g and a pH of 10, adjusted with aqueous 10% NaOH.

(56) Preparation of Pigment Particles Suspension

(57) A slurry with a solid content of 73.8 wt-% was prepared by mixing 0.58 wt.-% of the prepared CMC with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until a d.sub.50 value of 0.8 m was achieved.

(58) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 90 wt.-% smaller than 2 m, 65 wt.-% smaller than 1 m, and 15 wt-% smaller than 0.2 m. The obtained pigment particle suspension had a solid content of 73.8 wt.-%, a pH of 8.4, and a Brookfield viscosity of 292 mPa.Math.s.

Example 6

(59) Preparation of Carboxymethylcellulose (CMC)

(60) 93 g CMC 1 was dissolved in 2255 ml water and stirred for 12 h at room temperature. Subsequently, the solution was heated to 80 C., and 0.34 ml of a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, were added dropwise over a period of 20 minutes. After 3 h, 27 l of said H.sub.2O.sub.2 solution were added. Finally, the solution was stirred for 2.5 h at 80 C.

(61) The obtained CMC had an intrinsic viscosity of 178 ml/g and a pH of 10, adjusted with aqueous 10% NaOH after cooling to room temperature.

(62) Preparation of Pigment Particles Suspension

(63) A slurry with a solid content of 68.2 wt-% was prepared by mixing 0.93 wt.-% of the prepared CMC and 300 ppm Ca(OH).sub.2 with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until a d.sub.50 value of 0.8 m was achieved.

(64) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 90 wt.-% smaller than 2 m, 65 wt.-% smaller than 1 m, and 15 wt-% smaller than 0.2 m. The obtained pigment particle suspension had a solid content of 68.2 wt.-%, a pH of 9.5, and a Brookfield viscosity of 1016 mPa.Math.s.

Example 7

(65) Preparation of Carboxymethylcellulose (CMC)

(66) 3.4 kg CMC 1 was dissolved in 40 L water and stirred for 24 h at room temperature. Subsequently, the solution was heated to 80 C., and 150 ml of a a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, were added dropwise over a period of 2 h. After 22 h, additional 20 ml H.sub.2O.sub.2 solution were added over a period of 2 h. Finally, the solution was stirred for 8 h at 80 C.

(67) The obtained CMC had an intrinsic viscosity of 28 ml/g and a pH of 10, adjusted with aqueous 10% NaOH after cooling to room temperature. Subsequently, the CMC solution was spray dried.

(68) Preparation of Pigment Particles Suspension

(69) A slurry with a solid content of 76.1 wt-% was prepared by mixing 0.73 wt.-% of the prepared CMC and 0.03 wt.-% H.sub.3PO.sub.4 with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 50 C. until a d.sub.50 value of 0.8 m was achieved.

(70) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 90 wt.-% smaller than 2 m, 65 wt.-% smaller than 1 m, and 15 wt.-% smaller than 0.2 m. The obtained pigment particle suspension had a solid content of 76.0 wt.-%, a pH of 8.7, and a Brookfield viscosity of 482 mPa.Math.s.

Example 8

(71) Preparation of Carboxymethylcellulose (CMC)

(72) 159 g CMC 2 was dissolved in water to obtain a solution having a concentration of 10.9 wt.-%, based on the total amount of the solution. The pH was adjusted to 8.1 with aqueous 10% NaOH.

(73) Preparation of Pigment Particles Suspension

(74) A slurry with a solid content of 60 wt.-% was prepared by mixing 0.86 wt.-% of the prepared CMC with the mineral pigment material C. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C.

(75) The grinding process was carried out until the particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 90 wt.-% smaller than 2 m, 61 wt.-% smaller than 1 m, and 40 wt.-% smaller than 0.6 m. The obtained pigment particle suspension had a solid content of 61 wt.-%, a pH of 8.7, and a Brookfield viscosity of 478 mPa.Math.s.

Example 9

(76) A slurry with a solid content of 60.7 wt.-% was prepared by mixing 0.53 wt.-% of the prepared CMC with the mineral pigment material C. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. During grinding 100 ppm of Ca(OH).sub.2 were added in form of a 10 wt.-% aqueous Ca(OH).sub.2-suspension, based on the total weight of the suspension.

(77) The grinding process was carried out until the particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 89 wt.-% smaller than 2 m, 59 wt.-% smaller than 1 m, and 38 wt.-% smaller than 0.6 m. The obtained pigment particle suspension had a solid content of 62 wt.-% and a Brookfield viscosity of 478 mPa.Math.s.

Example 10

(78) Preparation of Carboxymethylcellulose (CMC)

(79) 159 g CMC 1 was dissolved in 1.95 l water and stirred for 12 h at room temperature. Subsequently, the solution was heated to 80 C., and 1 ml of a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, were added dropwise over a period of 20 minutes. After 5 h, 0.2 ml of said H.sub.2O.sub.2 solution were added dropwise over a period of 20 minutes. After 4 h additional 0.9 ml of said H.sub.2O.sub.2 solution were added drop wise over a period of 20 minutes. After additional 2 h additional 0.9 ml of said H.sub.2O.sub.2 solution were added drop wise over a period of 20 minutes. Finally, the solution was stirred for 2 h at 80 C.

(80) The obtained CMC had an intrinsic viscosity of 79 ml/g and a pH of 10, adjusted with aqueous 10% NaOH after cooling to room temperature. The final solids content of the CMC solution was 7.9 wt.-%.

(81) Preparation of Pigment Particles Suspension

(82) A slurry with a solid content of 51 wt.-% was prepared by mixing 0.3 wt.-% of the prepared CMC with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until 75 wt.-% of the particles were smaller than 1 m.

(83) The ground slurry was further thermally concentrated under steering at ambient pressure (temperature of heat exchanger oil: 140 C.) until a solids content of 67 wt.-%, based on the total weight of the slurry, was reached. During the concentration step additional 0.25 wt.-% of the prepared CMC were added.

(84) The obtained pigment particle suspension had a Brookfield viscosity of below 1000 mPa.Math.s.

Example 11

(85) Preparation of Carboxymethylcellulose (CMC)

(86) 6.0 kg CMC 1 was dissolved in 80 kg water and stirred at 80 C. After complete dissolution (about 4 h), a H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution, was added. 570 g of said H.sub.2O.sub.2 solution were added by means of a peristaltic pump. The solution was further stirred for 24 h at 80 C. After 24 h no hydrogen peroxide was detected anymore (tested with Titanium(IV) oxysulfate-sulfuric acid solution, No. 89532, commercially available from Sigma-Aldrich, Germany).

(87) The obtained CMC dispersant had an intrinsic viscosity of 21 ml/g and a pH of 10, adjusted with aqueous 10% NaOH after cooling to room temperature.

(88) Preparation of Pigment Particles Suspension

(89) A slurry with a solid content of 74 wt.-% was prepared by mixing 0.4 wt.-% of the prepared CMC with the mineral pigment material A using an Ystral mixer (Dispermix, Ystral GmbH, Germany). Subsequently, 0.15 wt.-% H.sub.3PO.sub.4 were added to the mixture in form of a 10% aqueous solution and the obtained mixture was wet ground in a 200-liter vertical attritor mill using zircon silicate beads of 0.6 to 1.0 mm diameter. Additional 0.1 wt.-% of the prepared CMC was added in the middle of the mill. The mill was operated with a flow of 230 l/h. The slurry temperature at the mill inlet was 39 C. and at the outlet 99 C.

(90) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 63.2 wt.-% smaller than 2 m, and 40.5 wt.-% smaller than 1 m. The obtained pigment particle suspension had a solid content of 75.8 wt.-%, a pH of 9.2, and a Brookfield viscosity of 935 mPa.Math.s.

Example 12

(91) Preparation of Carboxymethylcellulose (CMC)

(92) 0.533 kg of CMC 3 was dissolved in 1.6 kg water in a Ldige mixer under stirring at RT for 145 min before heating at 80 C. and addition by means of a peristaltic pump of 20 mL H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution over a timer period of one hour. The mixture was let stir 3 h until total consummation of H.sub.2O.sub.2 (color test based on Titanium (IV) oxysulfate-sulfuric acid, Sigma-Adlrich product number 89532). 3 mL of H.sub.2O.sub.2 were then added, and reaction was stir 2 h more at 80 C. The final solution had a solids content of 26 wt %.

(93) The obtained CMC dispersant had an intrinsic viscosity of 44 ml/g and a pH of 8.0, adjusted with aqueous 0.2M NaOH after cooling to room temperature.

(94) Preparation of Pigment Particles Suspension

(95) A slurry with a solid content of 70 wt-% was prepared by mixing 0.32 wt.-% of the prepared CMC with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until a d.sub.50 value of 1.52 m was achieved.

(96) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 61 wt.-% smaller than 2 m, 37 wt.-% smaller than 1 m, and 22 wt-% smaller than 0.5 m. The obtained pigment particle suspension had a solid content of 70.3 wt.-%, a pH of 8.8, and a Brookfield viscosity of 80 mPa.Math.s.

Example 13

(97) Preparation of Carboxymethylcellulose (CMC)

(98) 0.376 kg of CMC 1 was dissolved in 1.6 kg water in a Ldige mixer under stirred at RT for 180 min. The mixture was heated at 80 C. before addition of 25 mL H.sub.2O.sub.2 solution having a concentration of 30 wt.-%, based on the total amount of the solution. Solution was stir 3 h at 80 C. until total consummation of H.sub.2O.sub.2 (color test based on Titanium (IV) oxysulfate-sulfuric acid, Sigma-Adlrich product number 89532). Stirring was stopped overnight.

(99) The obtained CMC dispersant had an intrinsic viscosity of 38.3 ml/g. At room temperature and under steering the pH was increased with a aqueous 10 wt % calcium hydroxide solution to pH 7.1 and subsequently to pH 8 with an aqueous 0.2 mol/L sodium hydroxide solution.

(100) Preparation of Pigment Particles Suspension

(101) A slurry with a solid content of 75 wt-% was prepared by mixing 0.95 wt.-% of the prepared CMC with the mineral pigment material B. Subsequently, the obtained mixture was wet ground in a 1.4-liter horizontal attritor mill by recirculation at 40-50 C. until 92 wt % of the particles were smaller than 2 m.

(102) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 92 wt.-% smaller than 2 m, 64.6 wt.-% smaller than 1 m, and 40.4 wt-% smaller than 0.5 m. The obtained pigment particle suspension had a solid content of 72.1 wt.-%, a pH of 9.2, and a Brookfield viscosity of 253 mPa.Math.s.

Example 14

(103) A slurry with a solid content of 74 wt.-% was prepared by mixing 0.8 wt.-% of the CMC prepared according to Example 11 with the mineral pigment material A using an Ystral mixer (Dispermix, Ystral GmbH, Germany). Subsequently, 0.15 wt.-% H.sub.3PO.sub.4 were added to the mixture in form of a 10% aqueous solution and the obtained mixture was wet ground in a 200-liter vertical attritor mill using zircon silicate beads of 0.6 to 1.0 mm diameter. Additional 0.2 wt.-% of the CMC prepared according to Example 11 was added in the middle of the mill. The mill was operated with a flow of 185 l/h. The slurry temperature at the mill inlet was 39 C. and at the outlet 96 C.

(104) The particle size distribution of the obtained pigment particles suspension, measured on a Sedigraph 5100, had a fraction of 90.1 wt.-% smaller than 2 m, and 60.3 wt.-% smaller than 1 m. The obtained pigment particle suspension had a solid content of 75.8 wt.-% after grinding. After further addition of 0.15 wt.-% of the CMC prepared according to Example 11, the slurry had a pH of 9.3, and a Brookfield viscosity of 1160 mPa.Math.s.

Example 15

(105) The inventive aqueous pigment particle suspensions of Examples 11 and 14 were tested in paper coating applications. The coating trials were performed at the pilot coater of BASF in Ludwigshafen, Germany using a blade coating set up (stiff blade). A coating weight of 11 to 12 g/m.sup.2 was applied on the employed paper.

(106) Coating Trial 1

(107) A coating color having a solid content of 65 wt.-% was prepared by mixing the pigment slurry of Example 11 with Styronal D628 binder (commercially available from BASF AG, Germany). The pigment to binder ratio was 100:10 (dry/dry). The pH of the coating color was adjusted to 8.9 and the viscosity was 120 mPa.Math.s.

(108) A wood free uncoated paper (Magno Star, 58 g/m.sup.2) was coated on both sides with 12 g/m.sup.2 on each side of the prepared coating color at a speed of 1500 m/min. During the coating trial no runability problems were observed and a coated paper of good quality was obtained.

(109) Coating Trial 2

(110) A coating color having a solid content of 65 wt.-% was prepared by mixing the pigment slurry of Example 14 with Styronal D628 binder (commercially available from BASF AG, Germany). The pigment to binder ratio was 100:9 (dry/dry). The pH of the coating color was adjusted to 8.9 and the viscosity was 110 mPa.Math.s.

(111) A wood free pre-coated paper (Magno Star, 80 g/m.sup.2) was coated on both sides with 12 g/m.sup.2 of the prepared coating color at a speed of 1500 m/min. During the coating trial no runability problems were observed and a coated paper of good quality was obtained.