Surface modified calcium carbonate containing minerals and its use

Abstract

The present invention is related to ball-shaped spherical surface modified spherical calcium carbonate comprising minerals, the process for preparing such ball-shaped spherical surface modified spherical calcium carbonate comprising minerals, and their use.

Claims

1. A process for producing ball-shaped spherical surface modified calcium carbonate comprising particles comprising the steps of: a) providing at least one aqueous calcium carbonate containing mineral slurry; b) providing at least one water-soluble acid; c) providing gaseous CO.sub.2 generated in situ and/or supplied externally; d) contacting the aqueous calcium carbonate containing mineral slurry of step a) with the acid of step b) and with the CO.sub.2 of step c) under stirring conditions to obtain ball-shaped spherical surface modified calcium carbonate comprising particles; and e) optionally dewatering the aqueous slurry, wherein at least one processing agent is added before, during or after the aqueous calcium carbonate containing mineral slurry of step a) is contacted with the acid of step b) and the CO.sub.2 of step c), and wherein the processing agent is selected from the group consisting of ferrous sulfate, ferric sulfate, ferrous chloride, aluminum sulfate, and their hydrated forms, and wherein the processing agent is added in an amount of up to 8 wt.- % based on the dry weight of the slurry.

2. The process according to claim 1, wherein the calcium carbonate containing mineral is selected from the group consisting of marble, chalk, limestone, calcite, dolomite, precipitated calcium carbonate (PCC), and any mixture thereof.

3. The process according to claim 1, wherein the calcium carbonate containing mineral in the slurry has a weight median particle diameter of 0.01 m to 10 m.

4. The process according to claim 1, wherein the calcium carbonate containing mineral in the slurry has a weight median particle diameter of 0.02 m to 2 m.

5. The process according to claim 1, wherein the calcium carbonate containing mineral in the slurry has a weight median particle diameter of 0.5 m to 1 m.

6. The process according to claim 1, wherein the slurry of step a) has a solids content of greater than 4 wt.- %, based on the weight of the slurry.

7. The process according to claim 1, wherein the slurry of step a) has a solids content of from 5 wt.- % to about 20 wt.- %, based on the weight of the slurry.

8. The process according to claim 1, wherein the slurry of step a) is stabilized by the addition of one or more dispersants.

9. The process according to claim 1, wherein the at least one water-soluble acid of step b) has a pK.sub.a from 0 to 6.

10. The process according to claim 1, wherein the at least one water-soluble acid of step b) has a pK.sub.a from 0 to 2.5.

11. The process according to claim 1, wherein the at least one water-soluble acid of step b) is phosphoric acid, citric acid, boric acid, or any mixture thereof.

12. The process according to claim 1, wherein the at least one water-soluble acid is dosed in a molar amount relative to the numbers of moles of the calcium carbonate containing mineral in the range from 0.01 mol/mol to about 1 mol/mol.

13. The process according to claim 1, wherein the at least one water-soluble acid is dosed in a molar amount relative to the numbers of moles of the calcium carbonate containing mineral in the range from 0.1 to 0.6 mol/mol.

14. The process according to claim 1, wherein the at least one water-soluble acid provided in step b) is added in one or more steps to the aqueous calcium carbonate containing mineral slurry.

15. The process according to claim 1, wherein the at least one water-soluble acid provided in step b) is added in one step to the aqueous calcium carbonate containing mineral slurry.

16. The process according to claim 1, wherein the addition of the at least one water-soluble acid of step b) and the contacting of the aqueous calcium carbonate containing mineral slurry of step a) with the acid of step b) and with the CO.sub.2 generated in situ and/or supplied externally of step d) take place in a stirred reactor under stirring conditions such as to develop a laminar flow.

17. The process according to claim 1, wherein the process takes place in an aqueous environment in a temperature range above and including 20 C.

18. The process according to claim 1, wherein the process takes place in an aqueous environment in a temperature range from 25 C. to 95 C.

19. The process according to claim 1, wherein the process takes place in an aqueous environment in a temperature range from 30 C. to 80 C.

20. The process according to claim 1, wherein the process takes place in an aqueous environment in a temperature range from 50 C. to 75 C.

21. The process according to claim 1, wherein the processing agent is added in an amount of from 0.01 wt. % to 5 wt. % based on the dry weight of the slurry.

22. The process according to claim 1, wherein the processing agent is added in an amount of from 0.4 wt. % to 3 wt. % based on the dry weight of the slurry.

23. The process according to claim 1, wherein the processing agent is dosed in one or more steps to the aqueous calcium carbonate containing mineral slurry.

24. The process according to claim 1, wherein the processing agent is dosed in one step to the aqueous calcium carbonate containing mineral slurry.

25. The process according to claim 1, wherein the processing agent is aluminum sulfate or its hydrate.

26. The process according to claim 1, wherein the processing agent is aluminum sulfate hexadecahydrate.

27. The process according to claim 25, wherein the aluminum sulfate is added up to 5 wt. % based on the weight of the dry slurry.

28. The process according to claim 1, wherein the processing agent is added before, during or after step b).

Description

(1) FIG. 1: shows particle size distribution curves of surface modified calcium carbonate containing minerals according to the present invention

(2) FIG. 2a: shows an SEM picture of ball-shaped surface modified calcium carbonate containing mineral of E2, at 500 magnification.

(3) FIG. 2b: shows an SEM picture of ball-shaped surface modified calcium carbonate containing mineral of E2, at 2500 magnification.

(4) FIG. 3a: shows an SEM picture of ball-shaped surface modified calcium carbonate containing mineral of E6, at 500 magnification.

(5) FIG. 3b: shows an SEM picture of ball-shaped surface modified calcium carbonate containing mineral of E6, at 2 500 magnification.

USE OF THE INVENTION

(6) The inventive ball-shaped surface modified calcium carbonate containing mineral or a slurry comprising said inventive ball-shaped surface modified calcium carbonate containing mineral may be used in paper, tissue paper, digital photo paper, paints, coatings, adhesives, plastics, or in waste water treatment or waste water treating agents.

(7) In preferred embodiment, the inventive ball-shaped surface modified calcium carbonate containing mineral is used in paints or coatings as a matting agent. By matting agent, the applicant understands an agent being capable of scattering the incoming light away from the specular reflectance angle. This means diffracting the directed light that illuminates the substrate causing diffuse scatter.

(8) In particular the matting agent is present in amounts of 1 to 10 wt. %, preferably in amounts of 2 to 7 wt. %, more preferably in amount of 3 to 5 wt. %, based on the total weight of the paint or coating.

(9) The paints or coatings comprising the inventive ball-shaped surface modified calcium carbonate containing mineral as matting agents in the amounts mentioned above provide for a surface gloss at 85 in the range of below 10 gloss units (GU), preferably from 0.5 to 9.5, more preferably from 1 to 8, still more preferably from 2 to 6.5, of the dried film of the paint or coating, when measured according to DIN 67 530, which is very surprising due to the low content of the matting agent.

(10) A further advantage of the inventive ball-shaped surface modified calcium carbonate containing mineral present in amounts as described above is, that besides the matting effect of the dried film of the paint or coating, the surface of said dried paint or coating is smooth.

(11) Thus, the inventive ball-shaped surface modified calcium carbonate containing mineral of the present invention when used in paints and/or coatings, provide for matt appearance while at the same time providing a haptic smooth surface.

(12) The following examples are meant to illustrate the invention without restricting its scope:

(13) Measurement Methods

(14) The following measurement methods are used to evaluate the parameters given in the description, examples and claims.

(15) BET Specific Surface Area (SSA) of a Material

(16) The specific surface area is measured with nitrogen via the BET method according to ISO 9277 using a Gemini V sold by the company MICROMERITICS, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample is filtered within a Bchner funnel, rinsed with deionised water and dried overnight at 90 C. to 100 C. in an oven. Subsequently, the dry cake is ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130 C. until a constant weight is reached.

(17) Solids Content of an Aqueous Slurry

(18) The slurry solids content (also known as dry weight) is determined using a Moisture Analyser HR73 commercially available from Mettler-Toledo with the following settings: temperature of 120 C., automatic switch off 3, standard drying, 5-20 g of slurry.

(19) Particle Size Distribution (Mass % Particles with a Diameter<x) and Weight Median Diameter (d50) of Non-Surface Reacted Calcium Carbonate Comprising Material (i.e. Calcium Carbonate Starting Material)

(20) Weight median grain diameter and grain diameter mass distribution of a particulate material such as calcium carbonate, are determined via the sedimentation method, i.e. an analysis of sedimentation behavior in a gravimetric field. The measurement is made with a Sedigraph TM 5120.

(21) The method and instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurements is carried out in an aqueous solution of 0.1 wt- % Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed mixer and ultrasound.

(22) Median Grain Diameter d.sub.50 and d.sub.98 of Ball-Shaped Surface Modified Calcium Carbonate Containing Mineral

(23) Median grain diameter, d.sub.50 and d.sub.98, of ball-shaped surface modified calcium carbonate containing mineral was determined using a Malvern Mastersizer 2000 Laser Diffraction System, with a defined RI of 1.57 and iRI of 0.005, Malvern Application Software 5.60. The measurement was performed on an aqueous dispersion. The samples were dispersed using a high-speed stirrer. In this respect, the d.sub.50 and d.sub.98 values define the diameters, at which 50 vol. % or 98 vol. % of the particles measured, have a diameter smaller than d.sub.50 or d.sub.98 value, respectively.

(24) Viscosity Measurements

(25) A. ICI Viscosity According to EN ISO 2884-1

(26) The ICI viscosity was measured according to EN ISO 2884-1 using a cone- and plate viscometer (Epprecht Instruments+Controls, Bassersdorf, Switzerland) at a shear rate of 10 000 l/s at a temperature of (230.2 C. The measured value after 15 s, which should be a constant value, depicts the measured viscosity of the sample.

(27) B. Viscosity with a Paar Physica M301 PP25 Rheometer

(28) This measurement was conducted with a Paar Physica M301 PP25 Rheometer, from the company Anton Paar GmbH, Austria, according to the following regime:

(29) Temp.: 23 C.

(30) Starting shear rate: 0.1 l/s

(31) End shear rate: 100 l/s, with a logarithmic gradient of 10 measurement points per decade, and each measurement point taken after 5 seconds.

(32) The measurement points are displayed in a decimal logarithmic manner, so that a linear plot with a negative slope results from this measurement. The x-axis of the graph represents the shear rate in a decimal logarithmic manner, and the y-axis depicts the measured viscosity in Pa.Math.s.

(33) Gloss of a Coated Surface

(34) The Gloss values are measured at the listed angles according to DIN 67 530 on painted surfaces prepared with a coater gap of 150 m and 300 m on contrast cards. The contrast cards used are Leneta contrast cards, form 3-B-H, size 711 (194289 mm), sold by the company Leneta, and distributed by Novamart, Stfa, Switzerland. The gloss is measured with a gloss measurement device from the company Byk Gardner, Geretsried, Germany. The gloss is obtained by measuring 5 different points on the card with the gloss measurement device, and the average value is calculated by the device and can be derived from the display of the device.

(35) Scrubbing Test

(36) For the scrubbing test, Laneta contrast cards, form 3-B-H, size 711 (194289 mm), sold by the company Leneta, and distributed by Novamart, Stfa, Switzerland, coated with a coater gap of 300 m, as mentioned above were submitted to a scrubbing test. The scrubbing was performed with a square felt-glider 22 mm22 mm fixed on the scrubbing device. The arm holding the felt-glider was loaded with a 500 g weight pressing the felt-glider onto the surface of the coated Leneta card. The scrubbing path length was 5 cm and 50 cycles (1 clyle=forth and back) where performed within 60 sec2 sec. The felt-glider was of the fix-o-moll type, provided by from Wilhelm Ritterath GmbH, Meckenheim, Germany. Gloss was measured according to DIN 67 530 at 60 and 85 before and after scrubbing.

(37) Determination of Colour Values (Rx, Rv, Rz)

(38) The colour values Rx, Ry, Rz are determined over the white and black fields of the Leneta contrast card, and are measured with a spectraflas SF 450 X spectrophotomer of the company Datacolor, Montreuil, France.

(39) Contrast Ratio (Opacity) of a Coated Surface

(40) Contrast ratio values are determined according to ISO 2814 at a spreading rate of 7.5m.sup.2/l.

(41) The contrast ratio is calculated as described by the equation below:

(42) $\mathrm{Contrast}\mathrm{ratio}\left[\%\right]=\frac{{\mathrm{Ry}}_{\mathrm{black}}}{{\mathrm{Ry}}_{\mathrm{white}}}100\%$
with Ry.sub.black and Ry.sub.white being obtained by the measurement of the color values.

EXAMPLES

(43) The following illustrative examples of the invention involve contacting a calcium carbonate containing mineral, namely a ground natural marble according to the process of the present invention in a jacketed steel reactor equipped with a laminar mixing system in a batch size of 10 l. The solid content is adjusted to either 10 wt. % or 8 wt. % solids, as indicated in table 1.

(44) The addition of the at least one water-soluble acid of step b) and the contacting of said aqueous calcium carbonate containing mineral slurry of step a) with said acid of step b) and with said CO.sub.2 generated in situ and/or supplied externally of step d) take place in a stirred reactor under stirring conditions such as to develop an essentially laminar flow.

(45) The marble used in the process of the present invention and indicated as H90 in table 1., is a commercially available product from the applicant sold under the brand name Hydrocarb 90-ME 78%, which is a natural ground marble from Molde in Norway, having a top cut d.sub.98 of 5 m, and weight median particle size d.sub.50 of 0.7 m (size determined by Sedigraph), and provided in form of a slurry with solids content of 78 wt. % based on dry matter of the slurry and a viscosity of 400 mPas.

(46) The mixing speed is adjusted to either 140 or 300 rpm, and the temperature is adjusted to 70 C. Prior to the dosing of a 30 wt. % of phosphoric acid solution, which is added over a period of 10 or 30 min, the processing agent aluminum sulfate hexadecahydrate was added at once to the calcium carbonate containing mineral slurry in amounts of 0.5 wt. % or 0.6 wt. %.

(47) The reaction was mixed at the indicated mixing speeds and times according to table 1.

(48) TABLE-US-00001 TABLE 1 Tank Conditions H.sub.3PO.sub.4 30 wt. % Target Added Al.sub.2(SO.sub.4).sub.3*16H.sub.2O Batch Mixing Slurry Feed dosing over a Final Size Speed Solids Slurry Temp. of period conc. Addition (1) (rpm) wt. % Type C. wt. % of wt. % time E1 10.00 300 10.0 H90 70 30.0 10 min 0.5 b/a E2 10.00 300 8.0 H90 70 30.0 10 min 0.5 b/a E3 10.00 300 10.0 H90 70 30.0 10 min 0.6 b/a E4 10.00 140 10.0 H90 70 30.0 10 min 0.5 b/a E5 10.00 140 8.0 H90 70 30.0 10 min 0.5 b/a E6 10.00 140 10.0 H90 70 30.0 30 min 0.5 b/a E7 10.00 140 10.0 H90 70 30.0 10 min 0.6 b/a b/a means addition before acid

(49) The particle size distribution (PSD) of examples E1 to E7 were measured on a Malvern Mastersizer and the particle size distribution curves are shown in FIG. 1. Table 2 provides for the BET specific surface area SSA, the top cut d.sub.98 and the median grain diameter d.sub.50 for the examples E1 to E/.

(50) TABLE-US-00002 TABLE 2 E1 E1 E3 E4 E5 E6 E7 SSA m.sup.2/g 53.9 62.5 56.7 62.2 56.9 57.8 59.6 d.sub.50* m 19.7 27.9 18.9 34.5 30.4 15.3 22.8 d.sub.98* m 41.6 46.6 38.3 57.8 50.7 27.3 39.3 d.sub.98/d.sub.50 2.1 1.7 2.1 1.7 1.7 1.8 1.7 *determined by Malvern Mastersizer

(51) The examples E2, E6, and E7 of surface modified calcium carbonates were tested in paints. For this, E2, E6 and E7 were mixed in formulations and compared with matting agents used in this area such as diatomaceous earths (C1, C3) or aluminum silicate (C2). The dosage level of all matting agents was at 3 wt. %. Said formulations further comprise common additives such as defoamers, dispersing agents, sodium hydroxide, fungicides, bactericides, titanium dioxide (rutile), talcum, fillers, pigments, thickeners, plasticizer, viscosity modifiers, water, and others known to the skilled person. Table 3 provides for the composition of the test paint.

(52) TABLE-US-00003 TABLE 3 Base test paint C1 C2 C3 P2 P6 P7 Water g 331 331 331 331 331 331 Calgon N neu g 1 1 1 1 1 1 Bermocoll EHM 200 g 3 3 3 3 3 3 Sodium hydroxide, 10% g 2 2 2 2 2 2 BYK 038 g 3 3 3 3 3 3 ECODIS P 50 g 3 3 3 3 3 3 Mergal 723K g 2 2 2 2 2 2 Tiona 595 g 60 60 60 60 60 60 Finntalc M20SL - AW g 80 80 80 80 80 80 Omyacarb EXTRA - CL g 150 150 150 150 150 150 Omyacarb 2 - GU g 220 220 220 220 220 220 Mowilith LDM 6119, 50% g 115 115 115 115 115 115 Matting agents Celite 281 g 30 (Diatomaceous Earth) OpTiMat 2550 g 30 (Aluminum Silicate) Celatom MW 27 g 30 (Diatomaceous Earth) E2 g 30 E6 g 30 E7 30 COAPUR 4435* g 10 10 10 10 10 10 (Polyurethan thickener) Total g 1 010 1 010 1 010 1 010 1 010 1 010 *the 1% of COAPUR 4435 was added after the paint production to raise the viscosity to an applicable level.

(53) The fillers and pigments were replaced on a volume basis, i.e. at identical Pigment Volume Concentration (PVC). The paints were tested for dry opacity (ISO 2814), whiteness Ry (DIN 53145) and sheen (DIN67530) (gloss at 85). The components and functions of the materials for the base test paint are commercially available products known to the skilled person and listed in table 4 hereto below.

(54) TABLE-US-00004 TABLE 4 Material for base paint. Producer Chemical basis Function Base test paint Water In house, deionized H.sub.2O Solvent Calgon N new BK Giulini Chemie Sodium polyphosphate Wetting and dispersing agent Bermocoll EHM 200 AkzoNobel Corp. Ethyl Hydroxyethyl cellulose Thickener Sodium hydroxide, 10% Various NaOH solution pH regulator BYK 038 Byk Chemie Mineral oil basis Defoamer ECODIS P 50 Coatex SA Sodium salt of acrylic polymer Wetting and dispersing agent Mergal 723K Troy Chemie GmbH Benzisothiazolone basis, without Preservative formaldehyde Tiona 595 Millenium Inorganic Chemials Titanium dioxide, rutile (Al, org. White pigment coated) Finntalc M20SL - AW Mondo Minerals Magnesium Silicate Extender Omyacarb EXTRA - CL Omya Clariana SA Calcium carbonate, marble Extender Omyacarb 2 - GU Omya Calcium carboanate, marble Extender Mowilith LDM 6119, 50% Clariant non-plasticized aqueous polymer Binder (copolymer) dispersion based on styrene and an acrylic acid ester Matting agents Celite 281 (Diatomaceous Earth) Celite France Diatomaceous Earth (silica) Matting agent OpTiMat 2550 Imerys Aluminum silicate Matting agent Celatom MW 27 EP Minerals Diatomaceous Earth Matting agent E2 Omya Surface modified marble Matting agent E6 Omya Surface modified marble Matting agent Paint thickener Various Producers Polyurethane Thickener

(55) The performance of the tested paints is summarized in table 5, wherein C1, C2, and C3 refer to comparative paint examples and P2, P6, and P7 refer to the paint examples comprising the surface modified calcium carbonate containing minerals obtained by the process of the present invention.

(56) TABLE-US-00005 TABLE 5 Performance of paints C1 C2 C3 P2 P6 P7 Temperature C. 23 23 23 23 23 23 ICI Viscosity 180 170 160 200 200 200 Paar Physica Viscosity Viscosity, = 1 s.sup.1 Pas 16 800 19 000 18 700 22 500 24 100 24 600 Viscosity, = 5 s.sup.1 Pas 6 450 7 130 7 010 8 940 9 680 9 240 Viscosity, = 10 s.sup.1 Pas 4 380 4 790 4 700 6 150 6 640 6 190 Viscosity, = 40 s.sup.1 Pas 2 080 2 270 2 160 2 860 3 60 2 710 Optical properties 150 micrometer, 300 micrometers and 7.5 m.sup.2/l 150 micrometer Ry % 90.4 89.8 90.2 90.9 91.0 91.1 Ry over black % 87.9 87.4 88.0 89.1 89.1 89.4 Yellowness Index 2.5 2.6 2.5 2.0 2.0 2.1 Contrast Ratio % 97.2 97.4 97.5 98.0 98.0 98.2 Gloss 85 4.9 2.9 3.9 3.6 5.6 3.6 300 micrometer Ry % 90.9 90.2 90.8 91.6 91.7 91.8 Ry over black % 90.3 89.7 90.3 91.2 91.3 91.3 Yellowness Index 2.7 2.8 2.7 2.3 2.3 2.4 Contrast Ratio % 99.3 99.4 99.4 99.5 99.5 99.5 Gloss 85 5.0 3.3 4.5 4.4 6.2 4.1 Opacity at 7.5 m.sup.2/l Contrast ratio % 98.1 98.1 98.1 98.8 98.8 98.9 Polishing CROWN 300 Gloss 60 unscrub 2.7 2.6 2.6 2.7 2.7 2.7 Gloss 60 scrub 5.7 5.9 5.6 6.6 6.5 6.5 Gloss 85 unscrub 5.4 3.1 4.6 4.2 6.2 4.2 Gloss 85 scrub 29.5 18.7 27.1 31.7 36.3 29.5

(57) As can be seen from the results of table 4, the examples of the present invention show a performance in matting effect similar to matting agents of the prior art. Such matting effects have up to now not been observed for paints comprising the surface modified calcium carbonate containing minerals having a median grain diameter from about 10 m to about 50 m, and having a BET specific surface area from about 30 m.sup.2/g to about 90 m.sup.2/g of the present invention. The paint properties were measured for dry opacity at 150 m and 300 m film thickness, and the contrast ratio was determined at 7.5 m.sup.2/l. P2, P6, and P7 provide for a gloss at 85 of 4.1, 6.2, and 4.1 at a coating thickness of 300 m. This is also in expectation of the matting effect to decrease with decreasing particle size.

(58) Therefore, the present invention provides for alternative matting agents based on calcium carbonate containing mineral, providing a matting effect when used in paints and/or coatings, while at the same time providing a haptic smooth surface. Further to this, the present invention provides for a process for obtaining such surface modified calcium carbonate containing minerals, wherein said surface modified calcium carbonate containing minerals can be used in paper and paper coating, tissue paper, digital photo paper, paints, coatings, adhesives, plastics, or in waste water treating agents.