Precipitated calcium carbonate particles and use thereof

Abstract

Use, as an opacifier, of precipitated calcium carbonate particles at least partially in the form of nano fibers or nanochain like agglomerates constituted by at least two interconnected primary particles.

Claims

1. An opacifier comprising precipitated calcium carbonate particles present in the form of nanofibers or nanochain like agglomerates, wherein the nanofibers or nanochain like agglomerates are at least partially combined in the form of microshell like aggregates and are constituted by at least two interconnected primary particles and visible at least on the inner part of the microshell.

2. The opacifier according to claim 1, wherein the opacifier is in a paint, paper mass filling, paper coating or plastic coating.

3. The opacifier according to claim 1, wherein the opacifier is in an aqueous paint.

4. The opacifier according to claim 1, wherein the opacifier improves the opacity of a paint, paper, paper coating or plastic coating.

5. The opacifier according to claim 1, wherein the precipitated calcium carbonate particles comprise a crystallization controller.

6. The opacifier according to claim 5, wherein the precipitated calcium carbonate particles comprise from 0.1 to 10 wt % of crystallization controller by weight of calcium carbonate.

7. The opacifier according to claim 5, wherein the crystallization controller has an average molecular weight from 500 to 15000 g/mol.

8. The opacifier according to claim 1, wherein the nanofibers or nanochain-like agglomerates have an average diameter from 10 to 100 nm and wherein the nanofibers or nanochain-like agglomerates have an average length from 20 to 2000 nm.

9. The opacifier according to claim 1, wherein the nanofibers or nanochain-like agglomerates result from the end-to-end juxtaposition of calcite crystals.

10. The opacifier according to claim 9, wherein the calcite crystals are in the shape of rhomboids.

11. The opacifier according to claim 1, wherein the nanofibers or nanochain-like agglomerates result from the end-to-end juxtaposition of 2 to 20 primary calcium carbonate primary particles.

12. The opacifier according to claim 11, wherein the nanofibers or nanochain-like agglomerates result from the end-to-end juxtaposition of 2 to 10 primary calcium carbonate primary particles.

13. The opacifier according to claim 1, wherein the microshell-like aggregates have an aggregate median size (D50) from 0.1 to 5 ?m.

14. The opacifier according to claim 1, wherein the microshell-like aggregates have an aggregate median size (D50) from 0.2 to 3 ?m.

Description

SHORT DESCRIPTION OF THE FIGURES

(1) FIG. 1: electron microscopy photograph (SEM) of nanochain like calcium carbonate particles prepared according to Example 6.

(2) FIG. 2: electron microscopy photograph (SEM) of microshell like aggregates resulting from nanofibres/nanochains agglomeration, prepared according to Example 6.

(3) FIG. 3: electron microscopy photograph (SEM) of rhomboid calcium carbonate prepared in conditions similar to Example 1 but in the absence of polyacrylate.

(4) The present invention is further illustrated below without limiting the scope thereto.

(5) Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it might render a term unclear, the present description shall take precedence.

EXAMPLES

Precipitated Calcium Carbonate (PCC) Particles Characterization Average Primary Particle Size (dp)

(6) dp was determined by permeability measured according to a method derived from BS 4359-2. The basis of this method is the measurement of the air permeability of a pellet, which is analogous to the Blaine or the Lea & Nurse method. The calculation of the dp derives from the Carman & Malherbe formula:

(7) $q?L=\frac{1.05{\mathrm{.Math.}}^2}{{\left(1-\mathrm{.Math.}\right)}^2}{\mathrm{ds}}^2+\frac{2.88{\mathrm{.Math.}}^3}{1-\mathrm{.Math.}}\mathrm{ds}$$\mathrm{with}$$\mathrm{.Math.}=1-\frac{W}{A?L?D}$

(8) It can be shown that the mean particle diameter ds which is determined according to the Carman & Malherbe formula is not absolutely independent from the porosity of the pellet. Consequently, a correction was brought considering the reference porosity ?=0.45 and the dp was calculated according to the formula:
dp=ds?e.sup.?3.2(??0.45)

(9) Definitions and unities are as follows: q=volumetric rate of air flow passed through the PCC pellet (cm.sup.3/g), ?=porosity, W=weight of PCC, L=thickness of the pellet, D=density of PCC (g/cm.sup.3), A=area of the cross section of the pellet (cm.sup.2), ds=mean particle diameter according to Carman & Malherbe (?m), and dp=mean particle diameter according to Solvay (?m).
Average Diameter and Average Length

(10) Average diameter and average length of the nanofibers or nanochain like agglomerates was estimated relying on scanning electron microscope (SEM) observations. The samples were prepared from a metallized powder and observed with a Hitachi S-4800 SEM. The samples were directly placed on a graphite tape, then metallized with platinum for 1 minute under a vacuum of 10.sup.?1 Pa with a beam intensity of 6 mA.

(11) Aggregate Median Size (D50 or Stoke's Diameter)

(12) D50 was measured on the basis of French standard ISO 13317-3, Particle size sedimentation analysis of a powder by variable height gravity in a liquid. Method by X-ray absorption measurement, in which the general method and the apparatus (Sedigraph) are described. Preparation of the sample influencing the results of the measurement, such preparation method is described below.

(13) Preparation of the samples: 2.7 g of precipitated calcium carbonate were introduced into 50 ml of Na-hexametaphosphate (2 g/L) and the solution was treated by magnetical stirring and ultrasound.

(14) For the measurements, a Sedigraph 5100? equipped with an automatic sampler Mastertech 51? from Micromeritics was used. The measurement was performed between 0.1 ?m (starting diameter) and 100 ?m (ending diameter).

(15) General Procedure for the Preparation of Aqueous Emulsion Paints

(16) The two following formulations were prepared.

(17) TABLE-US-00001 Formulation 1 Formulation 2 (wt %) (wt %) Demineralized water 28.2 31.1 TiO.sub.2 5.0 6.0 GCC* 38.0 36 to 44 PCC 15.0 6 to 14 Biocide 0.2 0.2 Defoamer 0.2 0.2 Binder 12.0 11.0 Dispersing agent: sodium 0.5 0.5 hexametaphosphate Wetting agent: ammonia polyacrylate 0.3 0.5 Rheological additive: cellulose 0.4 0.4 Ammonia 0.2 0.5 *Ground calcium carbonate

(18) Cellulose was added to the water with stirring. Ammonia was added and the mixture was stirred again and then allowed to swell for approximately 20 minutes with repeated stirring. The wetting agent, the dispersing agent and the defoamer were then added, followed by GCC, PCC and TiO.sub.2. The composition was transferred into a dissolver and was dispersed during approximately 5 minutes at 2500?500 Rpm, then the binder and the biocide were added and the mixture was further dispersed for approximately 2 minutes at 2000?500 Rpm. The paint was allowed to stand for one day at room temperature before testing.

(19) The resulting aqueous emulsion paints were characterized as follows, according to EN-13300 standards.

(20) Optical Properties

(21) Paint test cards were prepared using an automatic coater (Erichsen, Typ 509 MC) to coat contrast test cards (Leneta Form 09) with the paint samples to be tested, at a feed rate of 7.5 mm/s (layer of 200 ?m). Films were then left to dry before measurements.

(22) Optical properties were measured using a spectrophotometer (DataColor DC 600 and Datacolor QCX software), calibrated with a black standard (luminance factor 0.1%) and a white calibration standard (serial No. 12077) before each measuring cycle. This gave the following results: brightness (Y, DIN 53163), yellowness (DIN 6167) and opacity. Opacity corresponds to the contrast ratio which is the ratio Y.sub.black/Y.sub.white?100, where Y.sub.black and Y.sub.white are the brightness on respective black and white parts of the contrast test cards.

(23) Gloss was measured with a gloss measuring equipment such as micro-TRI-gloss from Byk-Gardner. Same cards were used as those used to measure the optical properties. The gloss was measured at an angle of 85? for at least three different positions on the sample surface. Gloss values are given in GU (Gloss Unit).

(24) Absrasivity

(25) Abrasivity was measured on the basis of standard ISO 11998. Wet abrasion was measured as the loss of layer thickness (?m) by scrubbing with a scrub cloth in defined cycles (200 cycles).

Example 1

Preparation of Precipitated Calcium Carbonate (PCC)

(26) A milk of lime with a concentration of 5% wt. Ca(OH).sub.2 and an initial temperature of 14.2? C. was enriched with 2 wt (percentage related to the final CaCO.sub.3 produced) of partially neutralized polyacrylic acid (molecular weight of 2500 g/mol, 70% of acid groups are neutralized with sodium ions, pH 5-6). The carbonation occurred under a 40% CO.sub.2 flow (diluted with air) at a flow rate of 12.5 m.sup.3/h. The final carbonation temperature was 15.5? C. The resulting precipitated calcium carbonate was filtered on a planar filter and was dried in an oven for 36 h at 95? C., before milling in an Alpine 160 Z at 10 000 rpm.

(27) The obtained product was constituted of nanochain like agglomerates, combined to form microshell like aggregates. Average primary particle size (dp) was 36 nm and average aggregate median size (D50) was 0.85 ?m in the PCC suspension after carbonation. Average diameter and average length as determined by image analysis of SEM pictures were respectively 41 nm and 180 nm. These values are based on the measurement of 20 nanofibers.

Example 2 and Comparative Example 1

(28) PCC prepared in Example 1 was tested into Formulation 1 and compared to a standard PCC grade, i.e. Socal? P3.

(29) The results are summarized in Table 1 below.

(30) TABLE-US-00002 TABLE 1 Ex. 2 Comp. Ex. 1 PCC PCC of Ex. 1 Socal P3 Optical data, wet Brightness (%) 85.8 86.4 Opacity (%) 97.19 96.61 Yellowness 1.4 1.4 Optical data, dry Brightness (%) 94.5 93.5 Opacity (%) 99.03 97.94 Yellowness 1.4 1.3 Gloss (GU) 6.5 6.0 Abrasivity Abrasivity (?m) 10 7

(31) It can be seen from Table 1 that an opacity increase of approximately 1% was obtained with the PCC of Example 1, while all the other properties remained compatible with a use in an application such as matte aqueous paints. Such an increase of 1% opacity is significant.

Examples 3-5 and Comparative Examples 2-4

(32) PCC prepared in Example 1 was tested into Formulations 2 comprising respectively 6, 10 and 14 wt % of PCC, and compared to a standard PCC grade, i.e. Socal? P3.

(33) The results are summarized in Table 2 below.

(34) TABLE-US-00003 TABLE 2 Comp. Comp. Comp. Ex. 3 Ex. 2 Ex. 4 Ex. 3 Ex. 5 Ex. 4 PCC PCC of Socal? PCC of Socal? PCC of Socal? Ex. 1 P3 Ex. 1 P3 Ex. 1 P3 PCC amount 6 6 10 10 14 14 (%) Optical data, dry Brightness 92.7 91.9 93.3 92.5 94.0 93.0 (%) Opacity (%) 98.2 97.2 98.8 97.7 98.9 97.9 Yellowness 2.0 2.1 1.7 1.9 1.6 1.8 Gloss (GU) 4.0 3.7 5.3 4.2 7.4 4.9 Abrasivity Abrasivity 8 17 8 15 9 12 (?m)

(35) It can be seen from Table 2 that, for the various PCC contents tested, the opacity obtained with the PCC according to the present invention was at least 1% higher than the opacity obtained with PCC of the prior art. All the other properties remained compatible with a use in an application such as matte aqueous paints.

Example 6

Preparation of Precipitated Calcium Carbonate (PCC)

(36) A milk of lime with a concentration of 14.6% wt. Ca(OH).sub.2 and an initial temperature of 12.7? C. was enriched with 0.5 wt % (percentage related to the final CaCO.sub.3 produced) of partially neutralized polyacrylic acid (molecular weight of 2500 g/mol). The carbonation occurred under a 40% CO.sub.2 flow (diluted with air) at a flow rate of 12.5 m.sup.3/h. The final carbonation temperature was 40.1? C. The resulting precipitated calcium carbonate was filtered on a planar filter and was dried in an oven for 36 h at 95? C.

(37) The obtained product was constituted of nanochain like agglomerates, combined to form microshell like aggregates. This is illustrated in FIGS. 1 and 2. Average primary particle size (dp) was 42 nm and the average aggregate median size (D50) was 1.32 ?m in the PCC suspension after carbonation, before milling in an Alpine 160 Z at 14 800 rpm. Average diameter and average length as determined by image analysis of SEM pictures were respectively 49 nm and 193 nm. These values are based on the measurement of 20 nanofibers.

Example 7 and Comparative Example 5

(38) PCC prepared in Example 6 was tested into Formulation 1 and compared to a standard PCC grade, i.e. Socal? P3.

(39) The results are summarized in Table 3 below.

(40) TABLE-US-00004 TABLE 3 Ex. 7 Comp. Ex. 5 PCC PCC of Ex. 6 Socal? P3 Optical data, wet Brightness (%) 86.6 86.4 Opacity (%) 96.5 96.6 Yellowness 1.5 1.4 Optical data, dry Brightness (%) 94.0 93.5 Opacity (%) 98.6 97.9 Yellowness 1.3 1.3 Gloss (GU) 6.0 6.0 Abrasivity Abrasivity (?m) 13 7

(41) It can be seen from Table 3 that an opacity increase was obtained with the PCC of Example 6, while all the other properties remained compatible with a use in an application such as matte aqueous paints.

Examples 8-10 and Comparative Examples 6-8

(42) PCC prepared in Example 6 was further tested into Formulations 2 comprising respectively 6, 10 and 14 wt % of PCC, and compared to a standard PCC grade, i.e. Socal? P3.

(43) The results are summarized in Table 4 below.

(44) TABLE-US-00005 TABLE 4 Comp. Comp. Comp. Ex. 8 Ex. 6 Ex. 9 Ex. 7 Ex. 10 Ex. 8 PCC PCC of Socal? PCC of Socal? PCC of Socal? Ex. 6 P3 Ex. 6 P3 Ex. 6 P3 PCC amount 6 6 10 10 14 14 (%) Optical data, dry Brightness 92.7 91.9 93.5 92.5 93.9 93.0 (%) Opacity (%) 98.3 97.2 98.5 97.7 98.9 97.9 Yellowness 2.1 2.1 1.9 1.9 1.8 1.8 Gloss (GU) 4.6 3.7 5.8 4.2 7.4 4.9 Abrasivity Abrasivity 12 17 13 15 12 12 (?m)

(45) It can be seen from Table 4 that, for the various PCC contents tested, the opacity obtained with the PCC according to the present invention was increased. All the other properties remained compatible with a use in an application such as matte aqueous paints.