Precipitated calcium carbonate, a method for its manufacture and uses thereof

Abstract

Dry precipitated calcium carbonate and a slurry of precipitated calcium carbonate (PCC) particles at least partially in the form elongated entities, especially of nanofibers or nanochain like agglomerates constituted by at least two interconnected primary particles, and preferably, with a content of scalenohedron particles, is provided having opacifying properties. The slurry may be produced on site of its use and, due to its high concentration of CaCO.sub.3, may be applied directly after its manufacture.

Claims

1. A precipitated calcium carbonate comprising scalenohedron particles and particles which are at least partially in the form of nanofibers or nanochain like agglomerates constituted by at least two interconnected primary particles, wherein at least a part of the scalenohedron particles and the nanofibers or nanochain like agglomerates form microshells.

2. The precipitated calcium carbonate according to claim 1 wherein the primary particle size of the nanofibers or nanochain like agglomerates is from 50 to 200 nm.

3. The precipitated calcium carbonate according to claim 1 wherein the average length of the scalenohedron particles is in a range of from 250 to 500 nm.

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

5. The precipitated calcium carbonate according to claim 3, wherein the crystallization controller has an average molecular weight from 500 to 15000 g/mol.

6. The precipitated calcium carbonate according to claim 1, wherein the nanofibers or nanochain like agglomerates have an average diameter from 50 to 200 nm, and wherein the nanofibers or nanochain like agglomerates have an average length from 80 to 1000 nm.

7. The precipitated calcium carbonate according to claim 1, wherein the nanofibers or nanochain like agglomerates are at least partially combined in the form of microshell like aggregates.

8. The precipitated calcium carbonate according to claim 1 wherein the precipitated calcium carbonate is in the form of an aqueous slurry.

9. The precipitated calcium carbonate in the form of an aqueous slurry according to claim 8 which comprises 19 to 60% by weight of the precipitated calcium carbonate.

10. The precipitated calcium carbonate of claim 8, obtained by a) reacting CaO with water to form Ca(OH).sub.2, a1) drying the Ca(OH).sub.2 of step a) to provide dry Ca(OH).sub.2; b) contacting the dry Ca(OH).sub.2 with water to form a slurry; and c) carbonating the slurry of Ca(OH).sub.2 from step b) with CO.sub.2.

11. A process for the manufacture of precipitated calcium carbonate which is suitable as opacifier, which process comprises a) reacting CaO with water to form dry Ca(OH).sub.2, b) contacting the dry Ca(OH).sub.2 of step a) with water to form a slurry; and c) carbonating the slurry of Ca(OH).sub.2 from step b) with CO.sub.2 to form scalenohedron particles.

12. The process of claim 11, wherein step a) comprises drying the Ca(OH).sub.2 to provide dry Ca(OH).sub.2.

13. A method for the manufacture of paint, plastics, paper, plastisol, sealant or ink wherein the precipitated calcium carbonate of claim 1 is applied in a production plant to provide precipitated calcium carbonate as filler.

14. The method of claim 13 wherein the precipitated calcium carbonate, in the form of a slurry, is applied in a production planter for the manufacture of paint, plastics, paper, or ink.

15. The method of claim 14 wherein the slurry is produced on site of the production plant.

16. The method of claim 13 comprising a step of drying the slurry to provide dry precipitated calcium carbonate which is then applied for the manufacture of plastisols, sealants or polymers.

17. The method of claim 13 wherein the paint, plastics, paper, plastisol, sealant or ink do not contain any TiO.sub.2 filler.

18. The method of claim 13 wherein the plastics are polyethylene plastics.

Description

EXAMPLES

Precipitated Calcium Carbonate (PCC) Particles Characterization Average Primary Particle Size (dp) (Measured on the Dried Slurry)

(1) dp is 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:

(2) $qL=\frac{1.05{\mathrm{.Math.}}^2}{{\left(1-\mathrm{.Math.}\right)}^2}{\mathrm{ds}}^2+\frac{2.88{\mathrm{.Math.}}^2}{1-\mathrm{.Math.}}\mathrm{ds}$$\mathrm{with}$$\mathrm{.Math.}=1-\frac{W}{ALD}$

(3) 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 is brought considering the reference porosity =0.45 and the dp was calculated according to the formula:

(4) Definitions dp=dse.sup.3.2(-0.45) and unities are as follows:

(5) q=volumetric rate of air flow passed through the PCC pellet (cm.sup.3/g),

(6) =porosity,

(7) W=weight of PCC,

(8) L=thickness of the pellet,

(9) D=density of PCC (g/cm.sup.3),

(10) A=area of the cross section of the pellet (cm.sup.2),

(11) ds=mean particle diameter according to Carman & Malherbe (m), and

(12) dp=mean particle diameter according to Solvay (m).

(13) Average Diameter and Average Length (is Measured on the Dried Slurry)

(14) Average diameter and average length of the scalenohedron particles, nanofibers or nanochain like agglomerates is estimated relying on scanning electron microscope (SEM) observations. The samples are prepared from a metallized powder and observed with a Hitachi S-4800 SEM. The samples are 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.

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

(16) D50 can be measured on the slurry or on dried particles. It is 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. Since the preparation of the sample influencing the results of the measurement, such preparation method is described below.

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

(18) 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).

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

(20) Optical Properties

(21) Paint test cards are prepared using an automatic coater (Erichsen, Type 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 are then left to dry before measurements.

(22) Optical properties are 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 provides 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.white100, where Y.sub.black and Y.sub.white are the brightness on respective black and white parts of the contrast test cards.

(23) Gloss is measured with a gloss measuring equipment such as micro-TRI-gloss from Byk-Gardner. Same cards are used as those used to measure the optical properties. The gloss is 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) General Procedure to Produce Paint Formulations: Test to Substitute 40% TiO.sub.2

(25) The following formulations are prepared: Formulation 1: reference without PCC from the invention. Formulation 2: Substitution of 40% TiO.sub.2 using a dry PCC prepared from a 19 wt. % PCC slurry prepared according to the present invention. Formulation 3: Substitution of 40% TiO.sub.2 using a 19 wt. % PCC slurry prepared according to the present invention. Formulation 4: Substitution of 40% TiO.sub.2 using a dry PCC prepared from a 30 wt. % PCC slurry prepared according to the present invention. Formulation 5: Substitution of 40% TiO.sub.2 using a 30 wt. % PCC slurry prepared according to the present invention.

(26) TABLE-US-00001 Formu- Formu- Formu- Formu- Formu- lation 1 lation 2 lation lation lation (wt %) (wt %) 3 (wt %) 4 (wt %) 5 (wt %) Demineralized 289 289 76 289 169 water PCC slurry from 0 0 263 0 170 the invention Dry PCC from 0 50 0 50 0 the invention Rheological 0.3 0.3 0.3 0.3 0.3 additive (cellulose) Ammonia 0.1 0.1 0.1 0.1 0.1 Dispersing 0.8 0.8 0.8 0.8 0.8 agent Defoamer 0.2 0.2 0.2 0.2 0.2 TiO2 12.5 7.5 7.5 7.5 7.5 Socal P2 (PCC) 5.0 5.0 5.0 5.0 5.0 *GCC 41.0 41.0 41.0 41.0 41.0 Biocide 0.2 0.2 0.2 0.2 0.2 Binder 11.0 11.0 11.0 11.0 11.0 *GCC is ground calcium carbonate

(27) Cellulose is added to the water with stirring. Ammonia is 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 are then added, followed by GCC, PCC and TiO.sub.2. The composition is transferred into a dissolver and is dispersed during approximately 5 minutes at 2500500 Rpm, then the binder and the biocide are added and the mixture is further dispersed for approximately 2 minutes at 2000500 Rpm. The paint is allowed to stand for one day at room temperature before testing.

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

Example 1

Preparation of a Dry PCC from a Milk of Lime Presenting a Concentration of 15 wt. %

(29) CaO is reacted with water such that dry Ca(OH).sub.2 is obtained. The reaction is controlled such that 1 molar equivalent of water is reacted per one molar equivalent of CaO and the water content of the dry Ca(OH).sub.2 is less than 2%. The dry Ca(OH).sub.2 is contacted with water to provide a milk of lime. CO.sub.2 is bubbled into a milk of lime presenting a solid concentration of 15 wt. % in the presence of a crystallization controller consisting of a mixture of polyacrylic acid and sodium polyacrylate. The resulting PCC slurry presents a concentration of 19 wt. % and is then filtered, dried and milled to obtain a dry PCC (Formulation 2). The PCC contains nanochain like agglomerates, combined to form microshell like aggregates.

Example 2

Preparation of a PCC Slurry from a Milk of Lime Presenting a Concentration of 15 wt. %

(30) CO.sub.2 is bubbled into a milk of lime presenting a solid concentration of 15 wt. % in the presence of a crystallization controller consisting of a mixture of polyacrylic acid and sodium polyacrylate. The resulting PCC slurry presents a concentration of 19 wt. % (Formulation 3). The analysis of the PCC particles recovered from the slurry shows a morphology of nanochain like agglomerates, combined to form microshell like aggregates.

Example 3

Tests in Paints of the PCC Prepared in the Example 1 and 2

(31) TABLE-US-00002 Formulation 1 Formulation 2 Formulation 3 Optical data dry, Datacolor 600 Brightness/Y (%) 92.2 92.7 92.6 Opacity 200 m (%) 98.67 98.45 98.61 Yellowness DIN 6167 2.6 2.3 2.3 Gloss 85 3.9 5.1 4.9

(32) The obtained results show that it is possible to substitute up to 40% of TiO.sub.2 while keeping an opacity close to the reference one. Opacity of the slurry is similar to the slurry one.

Example 4

Preparation of a Dry PCC from a Milk of Lime Presenting a Concentration of 26 wt. %

(33) CO.sub.2 is bubbled into a milk of lime presenting a solid concentration of 26 wt. % in the presence of a crystallization controller consisting of a mixture of polyacrylic acid and sodium polyacrylate. The resulting PCC slurry presents a concentration of 30 wt. % and is then filtered, dried and milled to obtain a dry PCC (Formulation 4). The analysis of the PCC particles recovered from the slurry shows a morphology of nanochain like agglomerates, combined to form microshell like aggregates.

Example 5

Preparation of a PCC Slurry from a Milk of Lime Presenting a Concentration of 26 wt. %

(34) CO.sub.2 is bubbled into a milk of lime presenting a solid concentration of 26 wt. % in the presence of a crystallization controller consisting of a mixture of polyacrylic acid and sodium polyacrylate. The resulting PCC slurry presents a concentration of 30 wt. % (Formulation 6). The analysis of the PCC particles recovered from the slurry shows a morphology of nanochain like agglomerates, combined to form microshell like aggregates.

Example 6

Tests in Paints of the PCC Prepared in the Example 4 and 5

(35) TABLE-US-00003 Formulation 1 Formulation 4 Formulation 6 Optical data dry, Datacolor 600 Brightness/Y (%) 92.2 92.5 91.2 Opacity 200 m (%) 98.67 98.46 98.41 Yellowness DIN 6167 2.6 2.3 2.5 Gloss 85 3.9 5.1 4.6

(36) The obtained results show that it is possible to substitute up to 40% of TiO.sub.2 while keeping an opacity close to the reference one. Opacity of the slurry is similar to the slurry one.