Blend of surface modified calcium carbonate comprising particles (MCC) and precipitated calcium carbonate comprising particles (PCC) and its uses

Abstract

The present invention relates to a process for producing an aqueous slurry comprising a blend of surface modified calcium carbonate comprising particles (MCC) and precipitated calcium carbonate comprising particles (PCC), an aqueous slurry comprising the blend, as well as the blend obtainable by drying the aqueous slurry and their uses in paper, paper coating, tissue paper, digital photo paper, paints, coatings, adhesives, plastics, waste water treating or waste water treating agents.

Claims

1. An aqueous slurry comprising a blend of a) surface modified calcium carbonate particles (MCC) and b) precipitated calcium carbonate particles (PCC), and having at least a 5 wt % solids content, wherein a) is different from b), and in a weight ratio [MCC/PCC] of from 95:5 to 65:35, wherein the modified calcium carbonate particles (MCC) have a particle size distribution d.sub.98/d.sub.50 of <3, wherein the precipitated calcium carbonate particles (PCC) have a particle size distribution d.sub.98/d.sub.50 of ≥3.2, wherein the blended particles in said blend have a median grain diameter d.sub.50 of from 5 μm to 100 μm, a BET specific surface area of from 20 m.sup.2/g to 150 m.sup.2/g, and a particle size distribution d.sub.98/d.sub.50 greater than or equal to 2.0; and wherein the precipitated calcium carbonate particles (PCC) consist of products following reaction of carbon dioxide and lime in an aqueous environment or precipitation of a calcium and carbonate ion source in water.

2. The aqueous slurry of claim 1, wherein the surface modified calcium carbonate particles (MCC) in the aqueous slurry are substantially spherical surface modified calcium carbonate particles (bMCC).

3. The aqueous slurry of claim 1, wherein the aqueous slurry includes at least one processing agent selected from ferrous sulfate, ferric sulfate, ferrous chloride, ferric chloride, aluminum sulfate, aluminum chloride, and/or their hydrated forms, silicates, water-soluble cationic polymers, water-soluble amphoteric polymers, water-soluble non-ionic polymers and combinations thereof.

4. The aqueous slurry of claim 1, wherein the precipitated calcium carbonate particles (PCC) in the aqueous slurry have a median grain diameter d.sub.50 from 0.1 to 100 μm.

5. The aqueous slurry of claim 1, wherein the aqueous slurry has a solids content of at least 15 wt. % based on the total weight of the aqueous slurry.

6. The aqueous slurry according to claim 1, wherein the amount of calcium carbonate in the precipitated calcium carbonate particles (PCC) is between 99.8 and 100 wt.-% based on the total dry weight of the precipitated calcium carbonate particles (PCC).

7. The aqueous slurry according to claim 1, wherein the precipitated calcium carbonate particles (PCC) are of scalenohedral mineralogical crystal form.

8. The aqueous slurry according to claim 1, wherein the amount of calcium carbonate in the precipitated calcium carbonate particles (PCC) is between 90 and 99.8 wt %, based on the total dry weight of the precipitated calcium carbonate comprising particles (PCC).

9. A blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC) in a weight ratio [MCC/PCC] of from 95:5 to 65:35 obtained by drying the aqueous slurry of claim 1.

10. Paper, tissue paper, digital photo paper, paints, coatings, adhesives, plastics, or a waste water treating agent comprising the blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC) of the aqueous slurry of claim 1, or a dried blend thereof.

11. A paint or a coating comprising 1 to 10 wt. % of the blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC) of the aqueous slurry of claim 1, or a dried blend thereof, based on a weight of wet paint or coating present.

12. A method for producing a paint or a coating exhibiting a matte surface when dry, said method comprising incorporating the blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC) of the aqueous slurry of claim 1, or a dried blend thereof, into said paint or coating when wet.

13. The method according to claim 12, wherein the blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC) is present in amounts of 1 to 10 wt.-%, based on a weight of wet paint.

14. An aqueous slurry comprising a blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC) in a weight ratio [MCC/PCC] of from 95:5 to 65:35, having a solids content of at least 15 wt %, and obtained according to the following process: a) providing an aqueous slurry of surface modified calcium carbonate particles (MCC), wherein the surface modified calcium carbonate particles (MCC) have: i) a median grain diameter d.sub.50 of from 4 μm to 100 μm, and ii) a BET specific surface area of >15 m.sup.2/g, and iii) a particle size distribution d.sub.98/d.sub.50 of <3; b) providing an aqueous slurry of precipitated calcium carbonate particles (PCC), wherein the precipitated calcium carbonate particles (PCC) consist of products of precipitation following reaction of carbon dioxide and lime in an aqueous environment or precipitation of a calcium and carbonate ion source in water and have: i) a median grain diameter d.sub.50 from 0.1 to 100 μm, and ii) a BET specific surface area in the range from 1 to 100 m.sup.2/g, and iii) a particle size distribution d.sub.98/d.sub.50 of >3; c) contacting said aqueous slurry of surface modified calcium carbonate particles (MCC) of step a) with said aqueous slurry of precipitated calcium carbonate particles (PCC) of step b) to obtain an aqueous slurry comprising a blend of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC); and d) dewatering the aqueous slurry obtained in step c) thereby obtaining the aqueous slurry of at least 15 wt.-% solids content comprising blended particles of surface modified calcium carbonate particles (MCC) and precipitated calcium carbonate particles (PCC), wherein said blended particles have a median grain diameter d.sub.50 of from 5 μm to 100 μm, a BET specific surface area of from 20 m.sup.2/g to 150 m.sup.2/g, and a particle size distribution d.sub.98/d.sub.50 of ≥2.0.

Description

EXAMPLES

(1) Measurement Methods

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

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

(4) 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 Buchner 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.

(5) Solids Content of an Aqueous Slurry

(6) 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.

(7) 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)

(8) 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™ 5120.

(9) 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.

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

(11) 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.

(12) Viscosity Measurements

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

(14) 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 (23±0.2) ° C. The measured value after 15 s, which should be a constant value, depicts the measured viscosity of the sample.

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

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

(17) Temp.: 23° C.

(18) Starting shear rate: 0.1 l/s

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

(20) 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.

(21) Gloss of a Coated Surface

(22) The Gloss values are measured at the listed angles according to DIN 67 530 on painted surfaces prepared with a coater gap of 150 μm on contrast cards. The contrast cards used are Leneta contrast cards, form 3-B-H, size 7⅝×11⅜ (194×289 mm), sold by the company Leneta, and distributed by Novamart, Stäfa, 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.

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

(24) 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.

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

(26) Contrast ratio values are determined according to ISO 2814 at a spreading rate of 10±0.5 m.sup.2/l.

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

(28) $\mathrm{Contrast}\mathrm{ratio}\left[\%\right]=\frac{{\mathrm{Ry}}_{\mathrm{black}}}{{\mathrm{Ry}}_{\mathrm{white}}}⨯100\%$

(29) with Ry.sub.black and Ry.sub.white being obtained by the measurement of the color values.

Examples

(30) The following illustrative examples of the invention for the preparation of ball shaped MCC was prepared in a jacketed steel reactor equipped with a laminar mixing system in a batch size of 10 m.sup.3. The solid content is adjusted to 20 wt.-% solids, as indicated in table 1.

(31) The process comprises the steps of: a) providing at least one aqueous calcium carbonate containing mineral slurry; b) providing at least one water-soluble acid; c) optionally providing further gaseous CO.sub.2 via an external route; d) contacting 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 c) under stirring conditions. e) optionally dewatering the aqueous slurry.

(32) 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.

(33) 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 μm, and weight median particle size d.sub.50 of 0.7 μm (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.

(34) The mixing speed is adjusted to 48 rpm, and the temperature is adjusted to 70° C. Prior to the dosing of a 35 wt.-% of phosphoric acid solution, which is added over a period of 10 to 12 min., the processing agent aluminum sulfate hexadecahydrate was added at once to the calcium carbonate containing mineral slurry in amounts of about 0.3 wt.-%.

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

(36) TABLE-US-00001 TABLE 1 Tank Conditions H.sub.3PO.sub.4 35 wt. % Al.sub.2(SO.sub.4).sub.3*16H.sub.2O Batch Mixing Target Slurry Feed dosing Added over Final Size Speed Solids Slurry Temp. of a period conc. Addition (m.sup.3) (rpm) wt. % Type ° C. wt. % of wt. % time E1 10 48 20.0 H90 70 20.0 12 min 0.27 b/a E2 10 44 20.0 H90 70 20.0 11 min 0.27 b/a b/a means addition before acid

(37) The particle size distribution (PSD) of examples E1 and E2 of synthesized MCC were measured by using a Malvern Mastersizer and the particle size distribution and the BET specific surface area SSA, as well as the top cut d.sub.98 and the median grain diameter d.sub.50 for the examples E1 and E2 are shown in table 2.

(38) TABLE-US-00002 TABLE 2 E1(J) E2(S) SSA m.sup.2/g 48 42 d.sub.50* μm 9.6 23.7 d.sub.98* μm 26 67 d.sub.98/d.sub.50 2.71 2.82 *determinded by Malvern Mastersizer, (J) Jet dried, (S) Spray dried

(39) The slurry of example E2 obtained after the reaction was mixed and dried according to table 3, with a slurry of 54 wt-% of precipitated calcium carbonate commercially available (Omya AG), wherein the precipitated calcium carbonate is a scalenohedral shaped precipitated calcium carbonate (sPPC) having a top cut d.sub.98 of 7 μm, a weight median particle size diameter of d.sub.50 of 1.8 μm, and particle size of <2 μm of 60 wt %, determined by Sedigraph 5120, and a brightness Ry (C/2°, DIN 53163) of 97%. Further to this, the slurry E2 was first dried and then blended with the dry scalenohedral PCC as previously mentioned above in different ratios as shown in table 3.

(40) TABLE-US-00003 TABLE 3 Composition of Dry Blends and Wet Blend dried Dry blend Dry Blend Dry Blend Dry Blend Dry Blend Dry Blend Wet Blend dried* Sample R1 DB1 DB2 DB3 DB4 DB5 WBd1 E2 (MCC) 100 wt. % 90 wt-% 80 wt-% 70 wt-% 60 wt-% 50 wt-% 70 wt.-% sPCC 0 10 wt-% 20 wt-% 30 wt-% 40 wt-% 50 wt-% 30 wt.-% Ratio 100/0 90/10 80/20 70/30 60/40 50/50 70/30 MCC/sPCC State dry solid dry solid dry solid dry solid dry solid dry solid dry solid *the wet blend is a mixture of 6.21 parts of 20 wt.-% MCC and 1 part of 54 wt.-% of sPCC, which corresponds to slurry of a blend of MCC/sPCC at a ratio of 70/30 and a solids content of 24.7 wt.-%.

(41) The dry samples obtained of dry and wet blend dried of MCC and sPCC were tested in paints. For this, R1, DB1 to DB3 and WBd1 were mixed in formulations and compared with matting agents used in this area such as diatomaceous earths (R2-Celite 281). The dosage level of all matting agents was at 7 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 4 provides for the composition of the test paint.

(42) TABLE-US-00004 TABLE 4 Samples R1 DB1 DB2 DB3 DB4 DB5 WBd1 R2 Ratio (MCC/sPCC) 100/0 90/10 80/20 70/30 60/40 50/50 70/30 — Base Test Paint Water (deionised) kg 21.32 Calgon N neu kg 0.16 Bermocoll Prime 3500 kg 0.43 Sodium Hydroxide, 10% kg 0.21 BYK 038 kg 0.27 Texanol kg 0.27 Butyl Diglycol Acetate kg 0.27 Dowanol DPnB kg 0.53 Coapur 2025 kg 0.11 Byk 349 kg 0.21 Mergal 723 K kg 0.11 Water (deionised) kg 2.67 Ecodis P90 kg 0.30 Water (deionised) kg 8.00 Mowilith LDM 6119, 50% kg 15.99 Water kg 2.45 Omyacarb Extra-GU kg 39.70 Total kg 93.00 93.00 93.00 93.00 93.00 93.00 93.00 93.00 93.00 Matting agents Celite 281 kg 7.00 MCC kg 7.00 6.30 5.60 4.90 4.20 3.50 sPCC kg 0.70 1.40 2.10 2.80 3.50 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00

(43) 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 5 hereto below.

(44) TABLE-US-00005 TABLE 5 Material for Base Paint Producer Chemical Basis Function Water (deionised) In house H.sub.2O solvent Calgon N neu BK Giulini Chemie Sodium Wetting and dispersing polyphosphate agent Bermocoll Prime 3500 AkzoNobel Corp. Ethyl Hydroxethly Thickener cellulose Sodium Hydroxide, 10% Various NaOH solution pH regulator BYK 038 Byk Chemie Mineral Oil basis Defoamer Texanol Eastman Chemical CAS-Nr. 25265-77-4 Film forming aid Company Butyl Diglycol Various Diethylene Glycol Coalescing Agent Acetate Monobutyl Ether (Film forming aid) Acetate Dowanol DPnB Dow Dipropylenglycol-n- Coalescing Agent butylether (Film forming aid) Coapur 2025 Coatex Polyurethane basis Rheology modifier Byk 349 Byk Polyether modified Substrate wetting agent siloxane Mergal 723 K Troy Isothiazolinon (BIT) Preservative Ecodis P90 Coatex Ammonium salt of Wetting and dispersing polyacrylic acid agent Mowilith LDM 6119, Celanese Styrene-Acrylate Binder 50% dispersion Omyacarb Extra-GU Omya Calcium carbonate, extender marble

(45) The performance of the tested paints is summarized in table 6, wherein DB1, DB2, DB3, DB4 and DB5 refer to comparative paint examples being obtained from dry blends while R1 (being 100% MCC) and R2 (being Celite 281 of Imerys, a calcined diatomaceous earth) refer to reference paint examples. WBd1 refers to the paint example comprising the blend obtained by the process of the present invention.

(46) TABLE-US-00006 TABLE 6 Performance of Paint: Optical Properties at a draw down bar with 150 μm gap and 10 ± 0.5 m.sup.2/l 150 μm gap Samples R1 DB1 DB2 DB3 DB4 DB5 WBd1 R2 Ry over 88.2 88.2 88.2 88.1 88.1 88.1 87.8 88.1 white Ry over 82.1 82.0 81.8 81.8 81.8 81.6 81.8 79.4 black Yellowness 2.8 2.9 2.9 2.9 3.0 3.0 2.7 3.8 index Contrast 93.0 93.0 92.8 92.8 92.7 92.7 93.1 90.1 ratio Gloss 85° 2.5 3.0 3.6 4.6 5.7 7.3 3.5 3.6

(47) As can be seen from the results of table 6, the example according to the present invention (WBd1) shows a performance in matting effect superior to the dry blend of the same MCC/sPCC ratio DB3 or similar to matting agents of the prior art R2.

(48) The present invention therefore provides for alternative matting agents based on a wet blend of surface modified calcium carbonate and precipitated calcium carbonate, which, when dried and made into a paint provides on one side a better matting effect than a dry blend of the same ratio of surface modified calcium carbonate and precipitated calcium carbonate would provide, while at the same time the production and cost efficiency of the wet blend which subsequently is dried can be improved. Such improved production and cost efficiency is seen when a slurry of 20 wt.-% MCC is blended with a slurry of 54 wt.-% sPCC by 6.21 parts of MCC with 1 part sPCC obtaining a slurry with a MCC/sPCC ratio of 70/30 at solids content of 24.7 wt.-%, which is 4.7 higher than the 20 wt.-% of pure MCC. Thus for obtaining a dry blend of MCC/PCC at a ratio 70/30 with dry starting material more water needs to be eliminated than with wet blending and drying, therefore as a consequence leading improved production efficiency and lower production costs due to less water needed to be eliminated.

(49) The MCC/PCC blend of the present invention can be used in paper and paper coating, tissue paper, digital photo paper, paints, coatings, adhesives, plastics, or as a waste water treating agent.