High solids precipitated calcium carbonate with copolymeric additive

Abstract

The present invention relates to a process for producing an aqueous suspension of precipitated calcium carbonate, an aqueous suspension of precipitated calcium carbonate and a precipitated calcium carbonate obtained by the process, a product comprising the aqueous suspension of precipitated calcium carbonate or the precipitated calcium carbonate as well as its use.

Claims

1. A process for producing an aqueous suspension of precipitated calcium carbonate comprising the steps of: i) providing a calcium oxide containing material; ii) providing at least one copolymer of the following formula (I): ##STR00016## wherein x, y and z are present in blocks, alternating or randomly; x is >0 and at least one of y or z is >0 and the sum of x+y+z is <150 and wherein a molar ratio of x to y and/or z in the at least one copolymer of step ii) [x:y and/or z] is from 10:1 to 1:2; R.sub.1 represents hydrogen or a sulfonic functional group; R.sub.2 represents a heteroatom, optionally substituted with an alkyl group, an alkenyl group, an heteroaryl group and/or a polyalkoxylated group; R.sub.3 and R.sub.4 are, independently from each other, a hydroxyl group, (O.sup.M.sup.+) with M.sup.+ being a monovalent, divalent or trivalent cation, an O-alkyl group comprising from 1 to 20 carbon atoms, an N-alkyl group comprising from 1 to 20 carbon atoms and/or a polyalkoxylated group; iii) preparing a milk of lime by mixing water, the calcium oxide containing material of step i), and the at least one copolymer of step ii) to obtain a milk of lime, wherein the calcium oxide containing material and the water are mixed in a weight ratio from 1:1 to 1:12; and iv) carbonating the milk of lime obtained in step iii) to form an aqueous suspension of precipitated calcium carbonate with a clustered scalenohedral crystal structure.

2. The process of claim 1, wherein y>0 and z>0.

3. The process of claim 1, wherein the calcium oxide containing material and the water are mixed in a weight ratio of from 1:2.5 to 1:5.

4. The process of claim 1, wherein step iii) comprises the steps of: a1) mixing the at least one copolymer of step ii) with water, and a2) adding the calcium oxide containing material of step i) to the mixture of step a1); or b1) mixing the calcium oxide containing material of step i), and the at least one copolymer of step ii), and b2) adding water to the mixture of step b1); or c) mixing the calcium oxide containing material of step i), the at least one copolymer of step ii) and water simultaneously.

5. The process of claim 1, wherein the process further comprises step v) of adding at least one slaking additive to process step iii).

6. The process of claim 1, wherein the milk of lime obtained in step iii) has a Brookfield viscosity from 1 to 1 000 mPa.Math.s at 25 C.; and/or the suspension of precipitated calcium carbonate obtained in step iv) has a Brookfield viscosity of less than or equal to 3 000 mPa.Math.s at 25 C.

7. The process of claim 6, wherein at least one of: the milk of lime obtained in step iii) has a Brookfield viscosity from 5 to 800 mPa.Math.s at 25 C.; and the suspension of precipitated calcium carbonate obtained in step iv) has a Brookfield viscosity of less than or equal to 2 500 mPa.Math.s at 25 C.

8. The process of claim 1, wherein the suspension of precipitated calcium carbonate obtained in step iv) has solids content of at least 15 wt.-%, based on the total weight of the suspension.

9. The process of claim 8, wherein the suspension of precipitated calcium carbonate obtained in step iv) has a solids content of no more than 70 wt.-%, based on the total weight of the suspension.

10. The process of claim 1, wherein the temperature of the water, which is used in mixing step iii), is adjusted to be in the range of from more than 0 C. to less than 100 C.; and/or the temperature of the milk of lime obtained in step iii), which is employed in step iv), is adjusted to be in the range from 20 C. to 65 C.

11. The process of claim 1, wherein the at least one copolymer of step ii) is a compound of the following formula (II): ##STR00017## wherein x and y are present in blocks, alternating or randomly; x and y are >0 and the sum of x+y is <150; R.sub.1 represents hydrogen or a sulfonic functional group; and R.sub.2 represents a heteroatom, optionally substituted with an alkyl group, an alkenyl group, an heteroaryl group and/or a polyalkoxylated group.

12. The process of claim 1, wherein the at least one copolymer of step ii) is a compound of the following formula (III): ##STR00018## wherein x and z are present in blocks, alternating or randomly; x and z are >0 and the sum of x+z is <150; R.sub.1 represents hydrogen or a sulfonic functional group; R.sub.3 is a hydroxyl group, (O.sup.M.sup.+) with M.sup.+ being a monovalent, divalent or trivalent cation, an O-alkyl group comprising from 1 to 20 carbon atoms, an N-alkyl group comprising from 1 to 20 carbon atoms and/or a polyalkoxylated group.

13. The process of claim 1, wherein the molar ratio of x to y and/or z in the at least one copolymer of step ii) [x:y and/or z] is from 5:1 to 1:2.

14. The process of claim 1, wherein the at least one copolymer of step ii) has a molecular weight M.sub.w, in the range from 500 to 100,000 g/mol; and/or, provided in a water solution, has a Brookfield viscosity of less than or equal to 5000 mPa.Math.s at 25 C.

15. The process of claim 14, wherein the at least one copolymer of step ii) has a molecular weight M.sub.w, in the range from 1000 to 50,000 g/mol; and/or, provided in a water solution, has a Brookfield viscosity of less than or equal to 2000 mPa.Math.s at 25 C.

16. The process of claim 1, wherein the process further comprises, after step iv), a step viii) of contacting at least a part of the surface of the obtained precipitated calcium carbonate with at least one hydrophobising agent wherein the at least one hydrophobising agent is selected from the group consisting of an aliphatic carboxylic acid having a total amount of carbon atoms from C.sub.4 to C.sub.24 and/or reaction products thereof, a mono-substituted succinic anhydride consisting of succinic anhydride mono-substituted with a group selected from a linear, branched, aliphatic and cyclic group having a total amount of carbon atoms from at least C.sub.2 to C.sub.30 in the substituent and/or reaction products thereof, a 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, polyhydrogensiloxane and reaction products thereof, an inert silicone oil, an aliphatic aldehyde having from 6 to 14 carbon atoms and/or reaction products thereof, and mixtures thereof.

17. The process of claim 1, wherein the process further comprises step vi) of separating the precipitated calcium carbonate from the aqueous suspension obtained in step iv), and optionally step vii) of drying the separated precipitated calcium carbonate obtained in step vi).

18. Precipitated calcium carbonate with a clustered scalenohedral crystal structure obtained by a process according to claim 17.

19. A product comprising precipitated calcium carbonate with a clustered scalenohedral crystal structure according to claim 18, wherein the product is selected from the group consisting of: a paper product, an ink, a paint, a coating, a plastic, a polymer composition, an adhesive, a building product, a foodstuff, an agricultural product, a cosmetic product, and a pharmaceutical product.

Description

DESCRIPTION OF THE FIGURE

(1) FIG. 1 is a sketch of a continuous slaking process.

EXAMPLES

1. Measurement Methods

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

(3) Brookfield Viscosity

(4) The Brookfield viscosity of the aqueous suspensions was measured one hour after the production and after one minute of stirring at 25 C.1 C. at 100 rpm by the use of a Brookfield viscometer type RVT equipped with an appropriate disc spindle, for example spindle 2 to 5.

(5) pH Value

(6) The pH of a suspension or solution was 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 was first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20 C. (from Sigma-Aldrich Corp., USA). The reported pH values are the endpoint values detected by the instrument (the endpoint was when the measured signal differed by less than 0.1 mV from the average over the last 6 seconds).

(7) Particle Size Distribution

(8) The particle size distribution of the prepared PCC particles was measured using a Sedigraph 5120 or 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.

(9) Solids Content of an Aqueous Suspension

(10) 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.

(11) Specific Surface Area (SSA)

(12) The specific surface area was measured via the BET method according to ISO 9277 using nitrogen, 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 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.

(13) Specific Carbonation Time

(14) The monitoring of the conductivity, which slowly decreases during the carbonation reaction and rapidly decreases to a minimal level, thereby indicating the end of the reaction, was used to assess the time needed to perform the complete precipitation. The specific carbonation time (min/kg Ca(OH).sub.2) was determined by the following formula:

(15) $\mathrm{Specific}\mathrm{carbonation}\mathrm{time}=\frac{{10}^5.Math.T_f}{M.Math.{\mathrm{SC}}_{\mathrm{MoL}}}$
wherein: T.sub.f(min) is the time needed to complete the carbonation of the milk of lime, as determined by monitoring the conductivity, M (g) is the weight of the milk of lime introduced into the carbonation reactor, and SC.sub.MoL (%) is the weight solids content of the milk of lime.
Charge MeasurementMtek

(16) The charge measurement was carried out using a Mtek PCD 03 device equipped with a Mtek PCD titrator.

(17) About 1 g of the PCC suspension is weighed in the plastic measuring cell and is diluted with 20 mL of deionised water. Put the displacement piston on. While the piston oscillates in the cell, wait until the streaming current between the two electrodes stabilizes.

(18) The sign of the measured value shown on the display indicates whether the charge of the sample is positive (cationic) or negative (anionic). An oppositely charged polyelectrolyte of known charge density is added to the sample as a titrant (either sodium polyoxyethylene sulphate 0.001 N or pDADMAC 0.001 N). The titrant charges neutralize existing charges of the sample. Titration is discontinued as soon as the point of zero charge (0 mV) is reached.

(19) Titrant consumption in mL forms the basis for further calculations. The specific charge quantity q [Val/g of slurry] is calculated according to the following formula:
q=(Vc)/m
V: consumed titrant volume [l]
c: titrant charge concentration [Val/l]
m: mass of the weighed slurry [g]
q: specific charge quantity [Val/g of slurry]
Zeta Potential

(20) For measuring the Zeta potential, a few drops of the PCC suspensions are dispersed in a sufficient quantity of serum obtained by mechanical filtration of the said suspension in order to obtain a colloidal suspension which is slightly cloudy.

(21) This suspension is introduced into the measuring cell of the Zetasizer Nano-ZS from Malvern, which directly displays the value of the Zeta potential of the PCC suspension in mV.

2. Polymers and Slaking Additives

(22) NaCi: Sodium citrate, commercially available from Sigma-Aldrich, Switzerland.

(23) P1: Copolymer of the following formula (III)

(24) ##STR00014## wherein x and z are present alternating; x and z are independently from each other each an integer in the range from 1 to 149 and the sum of x+z is an integer in the range from 2 to 150; R.sub.1 represents hydrogen; R.sub.3 is (O.sup.M.sup.+) with M.sup.+ being sodium; and M.sup.+ being sodium, and the molar ratio of x to z is about 1:1 (M.sub.w=5 000 g/mol; solids content of 30 wt.-%)

(25) P2: polyacrylic acid with the following formula,

(26) ##STR00015## wherein R.sub.1 is H, X is Na, and m=45; the M.sub.w being 4 270 g/mol, and the polydispersity index being 2.3. The molecular weight M.sub.w and the polydispersity index are determined according to the corresponding method described in EP 14 166 751.9.

3. Examples

Example 1

(27) A milk of lime was prepared by mixing under mechanical stirring water with dry sodium citrate (NaCi) as slaking additive (if present) and copolymer P1 (if present) (according to the invention) or polymer P2 (comparison) at an initial temperature between 40 and 41 C. (the amounts of slaking additives and copolymer or polymer are indicated in Table 1 below). Subsequently, calcium oxide (quicklime raw material from Golling, Austria) was added. The obtained mixture was stirred for 25 min and then sieved through a 200 m screen.

(28) The obtained milk of lime was transferred into a stainless steel reactor, wherein the milk of lime was cooled down to 50 C. Then the milk of lime was carbonated by introducing an air/CO.sub.2 mixture (26 vol-% CO.sub.2 at a rate of 23 L/min). During the carbonation step, the reaction mixture was stirred with a speed of 1 400 rpm. The kinetic of the reaction was monitored by online pH and conductivity measurements.

(29) TABLE-US-00001 TABLE 1 Characteristics of produced milks of lime of Example 1 (comp: comparative example; IN: inventive example). Slaking Solids Polymer additive content amount amount of milk Polymer [wt.-%/wt. Slaking [wt.-%/wt. of lime Sample additive CaO] additive CaO] [wt.-%] 1 (comp) No NaCi 0.1 25.2 2 (comp) No NaCi 0.1 16.2 3 (IN) P1 0.15 NaCi 0.1 26.9 4 (IN) P1 0.15 27.1 5 (comp) P2 0.15 NaCi 0.1 29.5

(30) The characteristics of the prepared milks of lime and aqueous PCC suspensions are described in Table 2 below.

(31) TABLE-US-00002 TABLE 2 Characteristics of the obtained aqueous PCC suspensions of Example 1 Viscosity Solids of the content Viscosity Mutek milk of Carbonation of the of the charge lime time PCC PCC Zeta (Val/g (mPa .Math. s) (min/kg (wt.- (mPa .Math. s) SSA d.sub.50 potential of Sample 100 rpm Ca(OH).sub.2) %) 100 rpm [m.sup.2/g] [m] (mV) slurry) 1 Viscosity of milk of lime is too high Not measured (comp) 2 23 44 20.5 20 4.7 1.6 +5.5 +0.1 (comp) 3 (IN) 150 46 35.0 199 4.2 1.5 18.1 0.5 4 (IN) 101 51 34.2 1730 4.5 1.7 +3.1 +3.4 5 329 47 37.6 940 5.0 1.3 35.2 0.9 (comp) (comp: comparative example).

(32) The results compiled in Table 2 show that the use of a slaking additive alone leads to a milk of lime (calcium hydroxide suspension) having a high Brookfield viscosity (sample 1), and it is not possible to increase the solids content of the milk of lime without an increase in the viscosity of the suspension (comparison of sample 1 and sample 2).

(33) By contrast, inventive sample 3 confirms that the viscosity of the obtained milk of lime and PCC suspension is totally compatible with the intended use of the PCC so obtained that is to say suspensions of PCC having a Brookfield viscosity of less than or equal to 1 500 mPa.Math.s at 25 C. Additionally, the kinetic of carbonation and the crystallographic structure of the prepared PCC (results not shown) is similar to the one obtained with a process involving the use of an anionic polymer (P2: polyacrylic acid where 100 mole-% of the carboxylic groups have been neutralized by sodium ions, the M.sub.w being 4270 g/mol, and the polydispersity index being 2.3; sample being outside of the invention).