EP2646512A1

EP2646512A1 - Use of alkaline carbonate salts to reduce the amount of acrylic polymer in a method for grinding calcium carbonate in water

Info

Publication number: EP2646512A1
Application number: EP11799476.4A
Authority: EP
Inventors: Christian Jacquemet; Olivier Guerret
Original assignee: Coatex SAS
Current assignee: Coatex SAS
Priority date: 2010-12-02
Filing date: 2011-11-03
Publication date: 2013-10-09
Also published as: CN103221489A; US20120142842A1; FR2968219B1; FR2968219A1; BR112013009289A2; WO2012073080A1; CN103221489B

Abstract

The invention relates to the use of alkaline carbonate salts in a method for producing an aqueous suspension of calcium carbonate by grinding. Said salts make it possible to reduce the amount of agents for assisting in grinding used, said agents being homopolymers or water-soluble acrylic acid copolymers. The latter contribute greatly to increasing the concentration of carbon dioxide in the atmosphere and are produced from fossil-fuel raw materials; limiting the amount thereof helps save the environment as well as our natural resources. Said alkaline carbonate salts are directly used by being mixed with the polyacrylate (i.e. prior to the grinding operation) and/or are added during grinding, at the same time as the polyacrylate.

Description

USE OF ALKALI SALTS OF CARBONATE FOR REDUCING ACRYLIC POLYMER DOSE IN A PROCESS FOR MILLING CALCIUM CARBONATE IN WATER

The present invention relates to a method of manufacturing an aqueous suspension of calcium carbonate by grinding in an aqueous medium by introducing alkali metal salts of carbonate in said aqueous suspension of calcium carbonate. These salts make it possible to reduce the amount of grinding aid agents used, which are homopolymers or copolymers of acrylic acid, for an equivalent level of performance in rheology and granulometry of the suspensions. These polyacrylates contribute significantly to enrich the atmosphere with carbon dioxide and are derived from raw materials from fossil fuels: by limiting their quantity, we preserve the environment as well as our natural resources.

These alkaline carbonate salts are introduced during grinding as a mixture with the polyacrylate and / or introduced during grinding in parallel with the polyacrylate. In the first case, the aqueous formulations resulting from the mixing of the salts and the polyacrylate constitute another object of the present invention, as well as their manufacturing process. Finally, the use of these alkaline salts is a final object of the present invention, as an additive to reduce the amount of acrylic grinding aid agent implemented.

The mineral industry is a big consumer of chemicals. These are used in the various stages of transformation / modification / treatment that the mineral materials undergo. Thus, in the case of calcium carbonate of natural or synthetic origin, many operations known as "grinding" (reduction of the particle size of the particles) are carried out in a dry state or in an aqueous medium, or "dispersion" (implementation of suspending the particles in a liquid).

These two operations are made easier by the implementation respectively of grinding aid agents, whose role is to facilitate the mechanical action of attrition and fragmentation of the particles, and dispersing agents whose function consists of to maintain the viscosity of the suspension within acceptable ranges as and when introduces mineral matter. The present invention relates to grinding processes which implement grinding aid agents.

The prior art is particularly rich about such additives. For many years, it has been known that the hydrosulfide homopolymers of acrylic acid are effective agents in aiding the dispersion or grinding of calcium carbonate in an aqueous medium. For reference, reference may be made to documents FR 2 539 137, FR 2 683 536, FR 2 683 537, FR 2 683 538, FR 2 683 539 and FR 2 802 830. For the same type of applications, it it is also advantageous to copolymerize acrylic acid with another carboxylic monomer, such as itaconic acid, methacrylic acid, or sulfonic acid such as acrylamido-2-methyl-2-propane sulfonic acid or maleic anhydride, and / or with another ethylenically unsaturated monomer but without carboxylic function, such as an acrylic ester: these variants are also described in the previous documents.

It is also known that regulating the polymolecularity index of water-soluble polymers makes it possible to optimize certain of their performances. This is reported in the documents "Synthesis and Characterization of Poly (acrylic acid) Produced by RAFT Polymerization. Application as a Very Efficient Dispersant of CaCO3, Kaolin, and TiO2 "(Macromolecules, 36 (9), 3066-3077, 2003) and" Dispersion of calcite by poly (sodium acrylate) prepared by Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization "(Polymer (2005), 46 (19), 8565-8572). The control of this polymolecularity index is obtained in particular from so-called "living" polymerization techniques, as illustrated in the documents WO 02/070571 and WO 2005/095466. Patent FR 2 514 746 describes a method known as "Fractionation" for adjusting the polymolecularity index by selecting polymer chains having a given length, depending on the application chosen for the agent concerned.

It is also known that the choice of the molecular weight of the water-soluble acrylic polymer under consideration may, in certain particular processes for the production of calcium carbonate in an aqueous medium, improve the yield of said process: for example, EP 1 248 821 puts the emphasis on carboxylic polymers of high molecular weight, for dispersing a large amount of a calcium carbonate from a low concentration milling step in the absence of polymer.

Independently of these different axes of improvement of the application properties of a dispersing or grinding agent based on an acrylic acid (choice of a comonomer, a polymerization technique, regulation of the molecular weight), it is known that the Particular choice of certain neutralization agents leads to substantially improved application properties. Thus, the document EP 0 100 948 demonstrates the advantage of a neutralization by implementation of the combination between the sodium and calcium ions. A generation of subsequent patents (FR 2,683,538 and FR 2,683,539), for its part, focuses on the pair of magnesium / sodium ions. Finally, a last generation of patents (EP 1 347 834 and EP 1 347 835) which is based on a partial neutralization (all the carboxylic sites are not neutralized) is known from the joint action of a monovalent agent (preferentially sodium) and at least one divalent agent (preferentially calcium or magnesium).

Nevertheless, all of these solutions are based on the use of homopolymers and copolymers of acrylic acid, which are known to generate carbon dioxide, and which are derived from a raw material which is propylene, itself originating from oil, that is to say from a fossil energy. Minimizing their quantity in industrial processes such as calcium carbonate dispersion or grinding is now a major challenge for the chemical industry. This approach is part of the reduction of carbon dioxide as defined by the Kyoto Protocol, and the limitation of our processes to fossil fuels: more generally, it is part of the concepts of "green chemistry "and" sustainable development ". Continuing its research in this direction, the Applicant has developed a method of manufacturing an aqueous suspension of calcium carbonate by grinding in water with at least one horriopolymer and / or at least one water-soluble copolymer of acrylic acid. with introduction of at least one alkaline carbonate salt into said suspension. In a very advantageous way, we show that we succeed in reducing the amount of polyacrylate used, while maintaining or improving a number of properties related to the rheology and the particle size of the suspension (see the examples supporting the present Application). It is known that during the grinding operation, the concentration of calcium ions increases in the aqueous phase due to the fragmentation of the individual particles of calcium carbonate. However, it is well known that these calcium ions together with the polyacrylates complex ion-polymer species, more or less insoluble in the aqueous phase. Without wishing to be bound to any theory, the Applicant believes that the addition of alkaline carbonate salts in water modifies both the solubility of the polyacrylates in the aqueous phase and also the surface properties of the calcium carbonate particles: promotes the adsorption of acrylic polymers on the surface of mineral particles. The grinding mechanisms being favored by good adsorption of the polyacrylates on the surface of the mineral particles, the yield of the grinding process is thus improved.

In addition, the Applicant intends to point out that the alkali metal carbonate salts used according to the invention have no direct action on the grinding of calcium carbonate: they are not grinding aid agents within the meaning of the definition. given at the beginning of this Request. In addition, these salts do not alter the characteristics of the carbonate obtained after grinding compared to a ground carbonate with the same grinding aid agent but without the salt (it is however necessary to increase the dose of grinding agent to obtain the same granulometric and rheological characteristics for the final suspension). These characteristics essentially mean the usual optical properties of a calcium carbonate, such as its whiteness and opacity.

Also, a first object of the invention consists in a process for manufacturing an aqueous suspension of calcium carbonate by grinding in water with at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid, with introducing at least one alkaline carbonate salt into said suspension.

In a first variant, this process is characterized in that said salt is introduced integrally in the form of a mixture in water with at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid and with possibly at least one another additive selected from a biocide and / or antifoam. Concretely, said mixing is carried out before the grinding operation of the calcium carbonate. It is this mixture which is then introduced into the corresponding mill.

In a second variant, this process is characterized in that said salt is introduced integrally and distinctly from the homopolymer and / or the water-soluble copolymer of acrylic acid, in the aqueous suspension of calcium carbonate, before and / or during and or after the introduction of said acrylic polymer. In this case, the polyacrylate and the alkali carbonate salt are introduced directly and distinctly into the aqueous suspension of calcium carbonate to be ground.

In a third variant, this process is characterized in that said salt is introduced:

partially in the form of a mixture in water with at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid, and with at least one other additive chosen from a biocide and / or an antifoam,

and partly by direct introduction into the aqueous suspension of calcium carbonate, optionally with a separate addition in said suspension of at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid.

This variant corresponds to a combination of the two previous ones.

In general, this process is also characterized in that the alkaline salt is chosen from sodium, potassium and lithium salts, and mixtures thereof, preferably from sodium, potassium and their mixtures (lithium constituting a relatively expensive compound ).

In general, this process is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid have a molecular weight of between 3,000 g / mol and 15,000 g / mol, preferably between 4,000 g / mol and 10,000 g / mol. This molecular weight is determined throughout the present Application by the method described in the part reserved for the examples.

This process is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are totally or partially neutralized, preferably completely neutralized by a neutralization agent chosen from hydroxides of sodium, potassium, oxides and hydroxides of calcium, magnesium, ammonia and mixtures thereof, preferentially with sodium hydroxide.

This process is also characterized in that the water-soluble copolymer of acrylic acid is a water-soluble copolymer of acrylic acid with another monomer chosen from methacrylic acid, crotonic acid, isocrotonic acid, cinnamic acid, maleic acid, itaconic acid and acrylamido-2-methyl acid. -2-propane sulfonic acid and mixtures thereof.

This process is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are obtained by radical polymerization processes in solution, in direct or inverse emulsion, in suspension or precipitation in appropriate solvents, in the presence of catalytic and transfer agents, or by controlled radical polymerization processes and preferably by controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization (ATRP), controlled radical polymerization by sulfur derivatives, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates.

This method is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are, before or after their neutralization, treated and separated into several phases, according to static or dynamic processes, with one or more polar solvents preferentially belonging to the group consisting of methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or mixtures thereof. A second object of the present invention is the use of at least one alkaline carbonate salt in a process for producing an aqueous suspension of calcium carbonate by grinding in water with at least one homopolymer and / or at least one less a water-soluble copolymer of acrylic acid, having the function of reducing the amount of acrylic polymer used. The term acrylic polymer refers to the homopolymer and / or copolymer mentioned above. The amount of the acrylic polymer refers to the amount of dry polymer engaged relative to the dry weight of calcium carbonate used. The reduction of this amount is carried out, with respect to the same amount of polymer used but without alkaline carbonate salts, without altering the viscosity and the particle size of the resulting suspension. A third subject of the present invention consists of an aqueous composition containing water, at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid and at least one alkaline carbonate salt.

This aqueous composition may also contain at least one other additive chosen from a biocide and / or an antifoam.

This aqueous composition is also characterized in that it contains:

from 5% to 50%, preferably from 30% to 50% by dry weight of a homopolymer and / or a water-soluble copolymer of acrylic acid, from 1% to 30% by dry weight of at least one alkaline carbonate salt,

from 0% to 1% by dry weight of at least one other additive chosen from a biocide, an antifoam and their mixtures

in relation to its total weight.

In general, this aqueous composition is also characterized in that the alkaline salt is chosen from sodium, potassium and lithium salts, and mixtures thereof, preferably from sodium, potassium and mixtures thereof.

This aqueous composition is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid have a molecular weight of between 3,000 g / mol and 15,000 g / mol, preferably between 4,000 g / mol and 10,000 g. / mol.

This aqueous composition is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are totally or partially neutralized, preferably completely neutralized, with a neutralization agent chosen from hydroxides of sodium, potassium, oxides and hydroxides. calcium, magnesium, ammonia and mixtures thereof, preferably with sodium hydroxide. This aqueous composition is also characterized in that the water-soluble copolymer of acrylic acid is a water-soluble copolymer of acrylic acid with another monomer chosen from methacrylic, crotonic, isocrotonic, cinnamic, maleic, itaconic and acrylamido-2- acids. 2-methylpropanesulfonic acid and mixtures thereof.

This aqueous composition is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are obtained by radical polymerization processes in solution, in direct or inverse emulsion, in suspension or precipitation in appropriate solvents, in the presence of catalytic systems and transfer agents, or by controlled radical polymerization processes and preferably by controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization (ATRP), radical polymerization controlled by sulfur derivatives, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates.

This aqueous composition is also characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are, before or after their neutralization, treated and separated into several phases, according to static or dynamic processes, by one or more polar solvents belonging to preferentially to the group consisting of methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or their mixtures.

A third and last object of the present invention consists in a process for manufacturing an aqueous composition, by introduction with stirring at a temperature of between 10 ° C. and 90 ° C., preferably between 30 ° C. and 60 ° C. at least one carbonate salt in the form of a powder in an aqueous solution of at least one homopolymer and / or a water-soluble copolymer of acrylic acid having an initial solids content of between 10% and 60%, preferably between % and 50%, and optionally by addition of at least one other additive selected from a biocide and / or an antifoam.

The examples which follow will make it possible to better apprehend the invention, without however limiting the scope thereof. EXAMPLES

Preamble Throughout the present application, the particle size characteristics relating to calcium carbonate are determined from a Sedigraph ™ 5100 device, sold by MICROMERITICS ™.

Molecular weights are determined by Steric Exclusion Chromatography, according to the following method.

A test portion of the polymer solution corresponding to 90 mg of dry matter is introduced into a 10 ml flask. Mobile phase, supplemented with 0.04% DMF, is added to a total mass of 10 g. The composition of this mobile phase is as follows: NaHCO 3: 0.05 mol / L, NaNO 3: 0.1 mol / L, triethanolamine: 0.02 mol / L, NaN 3 0.03% by weight.

The CES chain is composed of a Waters ™ 510 type isocratic pump, the flow rate of which is set to 0.8 mL / min, a Waters 717+ sample changer, an oven containing a precolumn type "Guard Column Ultrahydrogel Waters ™", followed by a linear column type "Ultrahydrogel Waters ™" 30 cm long and 7.8 mm inside diameter.

The detection is ensured by a Waters ™ 410 differential refractometer. The oven is heated to a temperature of 60 ° C, and the refractometer is heated to a temperature of 45 ° C.

The CES is calibrated with a series of sodium polyacrylate standards supplied by Polymer Standard Service with a peak molecular weight between 2000 and 1.10 ⁶ g / mol and a polymolecularity index between 1.4 and 1.7. as well as with a sodium polyacrylate with a molecular weight of 5,600 g / mol and a polymolecularity index of 2,4.

The calibration curve is of linear type and takes into account the correction obtained thanks to the flow rate marker (DMF). Acquisition and processing of the chromatogram is performed using the PSS WinGPC Scientific v 4.02 software. The chromatogram obtained is integrated in the zone corresponding to molecular weights greater than 65 g / mol. Example 1

This example illustrates the manufacture of different mixtures of polyacrylates with alkaline carbonate salts.

Tests n ° la to the

These tests involve the introduction of sodium carbonate in an aqueous solution of a homopolymer of acrylic acid completely neutralized with sodium hydroxide and with a molecular weight of 5500 g / mol. The sodium carbonate is introduced in powder form into a stirred reactor containing the polymer solution at 41% concentration and at a temperature of 50 ° C. The stirring and stirring phase is carried out until a clear and homogeneous mixture is obtained. After complete dissolution of the sodium carbonate, a sufficient quantity of water is introduced into the reactor to obtain a mixture whose solids content is 43%. The masses involved are given in Table 1.

Table 1

Tests n ° 2a and 2b

These tests involve the introduction of potassium carbonate into an aqueous solution of the same polyacrylic acid as for tests No. la. These tests are carried out in the same reactor as previously with which a disperser line. The polymer solution at a temperature of 20 ° C circulates in a loop and passes through a dispersion chamber consisting of a rotor / stator system where there are high shear effects. High vacuum is created inside the dispersion chamber. This vacuum sucks the potassium carbonate powder which is intimately mixed with the sodium polyacrylate solution. After complete incorporation of the powder, the in-line mixer is left in operation until complete dissolution of the potassium carbonate and obtaining a clear solution. A sufficient quantity of water is finally introduced into the reactor to obtain a mixture whose dry matter concentration is 43%. The masses involved are given in Table 2.

Table 2

Example 2

This example illustrates the use of different polyacrylate / alkali carbonate carbonate mixtures in a grinding process in an aqueous medium of calcium carbonate.

Thus, in practice, the operation of grinding the mineral substance to be refined consists in grinding the mineral substance with a grinding body in very fine particles in an aqueous medium containing the grinding aid agent. The actual grinding operation is carried out using a DYNO ^® - MILL type KDL - Pilot A equipment containing the grinding body of particle size advantageously between 0.20 and 4 millimeters. The grinding body is generally in the form of particles of materials as diverse as silicon oxide, aluminum oxide, zirconium oxide or mixtures thereof, as well as synthetic resins of high hardness, steels, or others. An example of a composition of such grinding bodies is given by the patent FR 2 303 681 which describes grinding elements formed from 30% to 70% by weight of zirconium oxide, 0.1% to 5% aluminum oxide and 5 to 20% of silicon oxide.

The grinding body is preferably used in an amount such that the ratio by weight between this grinding material and the mineral substance to be ground is at least 2/1, this ratio preferably being between the limits 3/1 and 5 / 1.

It begins by preparing an aqueous suspension of calcium carbonate to be milled by introducing with stirring water, the mixture containing the dispersant and an additive, and then calcium carbonate. After stirring for 20 minutes, this suspension is introduced into the grinding chamber containing the grinding body. This is set in motion by means of rotating blades. By successive passages the mineral suspension is then subjected to the mechanical action of crushing and attrition. The grinding chamber is equipped with a double cooling jacket in order to maintain the grinding temperature in a temperature range between 60 and 80 ° C as well as a pressure indicator.

The continuous milling operation is maintained until a pressure rise in the mill of 0.5 bar is observed. The crushed suspension is then removed and characterized.

For each of the tests carried out, the Brookfield ™ viscosity is determined at 100 rpm and at 25 ° C. at the outlet of the mill (μΙΟΟ in mPa.s): this datum makes it possible to quantify the fluidity of the suspension obtained.

The proportion by weight of particles whose diameter is less than 2 μιη (% <2 in%) is also determined with Sedigraph ™ 5100 from Micromeritics ™: the fineness of the grains of carbonate obtained after grinding is thus evaluated.

The corresponding results appear in Table 3.

In all the tests, the ppm designates mg of dry additive relative to the dry weight of calcium carbonate expressed in kg. Test n ° 1

This test illustrates the prior art and uses 2250 ppm of a water-soluble homopolymer of acrylic acid completely neutralized with sodium hydroxide and with a molecular weight of 5,500 g / mol.

Test n ° 2

This test illustrates the invention and uses 2500 ppm of the mixture manufactured according to test la of Example 1. Here 2250 ppm of a water-soluble homopolymer of acrylic acid completely neutralized with hydroxide is used. of sodium and molecular weight equal to 5,500 g / mol, and 250 ppm of sodium carbonate.

Test n ° 3

This test illustrates the invention and uses 2500 ppm of the mixture manufactured according to test 1a of Example 1. Thus, 2125 ppm of a water-soluble homopolymer of acrylic acid completely neutralized with hydroxide is used. of sodium and molecular weight equal to 5,500 g / mol, and 375 ppm of sodium carbonate.

Test n ° 4

This test illustrates the invention and uses 2500 ppm of the mixture manufactured according to test 2a of Example 1. Here, 2250 ppm of a water-soluble homopolymer of acrylic acid completely neutralized with hydroxide is used. of sodium and molecular weight equal to 5,500 g / mol, and 250 ppm of potassium carbonate.

Test n ° 5

This test illustrates the invention and uses 2500 ppm of a mixture of a water-soluble homopolymer of acrylic acid completely neutralized with sodium hydroxide and with a molecular weight of 5 500 g / mol (2125 ppm), and potassium carbonate (375 ppm). This mixture was prepared according to the procedure of Example 1. Test No. 6

This test illustrates a field outside the invention and implements a mixture between the acrylic polymer (2250 ppm) of test No. 1 and sodium silicate (250 ppm). This The mixture was prepared in the same manner as the mixture used in Test No. 2.

Test n ° 7

This test illustrates a field outside the invention and implements a mixture between the acrylic polymer (2250 ppm) of test No. 1 and sodium gluconate (250 ppm). This mixture was prepared in the same manner as the mixture used in Test No. 2. Test No. 8

This test illustrates a field outside the invention and implements a mixture between the acrylic polymer (2250 ppm) of test No. 1 and urea (250 ppm). This mixture was prepared in the same way as the mixture used in Test No. 2. Test No. 9

This test illustrates a field outside the invention and implements a mixture between the acrylic polymer (2250 ppm) of test No. 1 and glucose (250 ppm). This mixture was prepared in the same way as the mixture used in Test No. 2. Test No. 10

This test illustrates a field outside the invention and uses a mixture between the acrylic polymer (2250 ppm) of test No. 1 and glycerol (250 ppm). This mixture was prepared in the same manner as the mixture used in Test No. 2. Test No. 1 1

This test illustrates a field outside the invention and uses a mixture between the acrylic polymer (2250 ppm) of test No. 1 and of sodium acetate (250 ppm). This mixture was prepared in the same way as the mixture used in test No. 2.

Test n ° 12

This test illustrates a field outside the invention and implements a mixture between the acrylic polymer (2125 ppm) of test No. 1 and sodium silicate (375 ppm). This The mixture was prepared in the same manner as the mixture used in Test No. 3.

Test n ° 13

This test illustrates a field outside the invention and implements a mixture between the acrylic polymer (2125 ppm) of test No. 1 and glucose (375 ppm). This mixture was prepared in the same manner as the mixture used in test No. 3.

Table 3

Table 3 (continued)

Table 3 (end) ΑΑ / ΓΝ / ΗΙ: prior art / invention / outside the invention

ABr (ppm): acrylic grinding aid agent (quantity in ppm)

Add (ppm): additive possibly used with the grinding aid agent (quantity in ppm)

By comparing test No. 1 according to the prior art with tests No. 2 and 4 according to the invention (same dose of acrylic polymer), it is shown all the advantages of using sodium or potassium carbonate: the proportion of particles whose diameter is less than 2 μηι is increased, while substantially decreasing the viscosity at the outlet of the mill. There is therefore a more fluid aqueous suspension with finer particles.

None of the tests outside the invention n ° 6 to 1 1 which implements the same quantity of additives as for the tests n ° 2 and 4 (namely 250 ppm) makes it possible to obtain a degree of finesse comparable: one obtains at better 60.2% by weight of particles with a diameter less than 2 μηι, this percentage being systematically at least equal to 62% in the case of tests No. 2 and 4.

Finally, if we compare the tests of the invention No. 3 and 5 which implement 2125 ppm of dispersant for 375 ppm of alkali carbonate salt, with the tests outside the invention No. 12 and 13 which implement the same doses grinding aid agents and an additive outside the invention which is sodium silicate and glucose (additives chosen on the basis of the performances obtained at 250 ppm in tests Nos. 6 and 9), the superiority performance obtained in the context of the invention.

Example 3

In this example, starting from 3 aqueous suspensions obtained in Example 2 (according to tests No. 1, 2 and 4) whose fineness is sought to improve by continuing the grinding in the presence of a homopolymer of acrylic acid, half of which The carboxylic acid is neutralized with sodium hydroxide and the other half with calcium hydroxide and with a molecular weight of 5,500 g / mol. The corresponding tests are denoted 1 bis, 2 bis and 4 bis.

The grinding is continued until a suspension of calcium carbonate is obtained, 80% by weight of the particles of which have a diameter of less than 1 μιη.

Brookfield ™ viscosity, at 100 rpm and at 25 ° C., is then measured at the outlet of the mill (μΙΟΟ in mPa.s), as is the demand for acrylic grinding aid agent implemented during this process. second milling step (ABr in ppm).

The corresponding results appear in Table 4.

Table 4

Not only is it possible according to the invention to reduce the demand by dispersing during this second grinding stage, but more fluid aqueous suspensions are obtained. This demonstrates the value of using alkaline carbonate salts in combination with acrylic polymers.

Example 4

This example illustrates the separate introduction of acrylic polymer and salts in an aqueous grinding process of calcium carbonate.

We begin here by making an aqueous suspension of calcium carbonate by successive introduction, in water, of an additive which is a sodium carbonate (Invention) or sodium sulfate (outside the invention) or sodium chloride (outside the invention), or a salt of a grinding agent which is a homopolymer of partially neutralized acrylic acid (90 mol% of its sites carboxylic acids are neutralized with sodium hydroxide) of molecular weight equal to 5,500 g / mol, followed by calcium carbonate to be milled.

The grinding was then carried out according to the same protocol as that described in Example 2, with the difference that the grinding is continued until a suspension having a dry weight content of calcium carbonate equal to 75% of its weight is obtained. total. Test n ° 14

This test illustrates the prior art and implements 2250 ppm of the aforementioned acrylic polymer. Test n ° 15

This test illustrates the invention and uses 2250 ppm of the abovementioned acrylic polymer, and 250 ppm of sodium carbonate.

Test n ° 16

This test illustrates a field outside the invention and uses 2250 ppm of the abovementioned acrylic polymer, and 250 ppm of sodium sulfate.

Test n ° 17

This test illustrates a field outside the invention and uses 2250 ppm of the abovementioned acrylic polymer and 250 ppm of sodium chloride.

The characteristics of the tests and suspensions obtained are shown in Table 5.

Table 5 The sodium carbonate used according to test No. 15 makes it possible to increase the fineness of the crushed calcium carbonate by using the same dose of dispersant as according to test No. 14 describing the prior art; this is impossible with the other salts used according to tests No. 16 and 17.

Claims

1 - Process for manufacturing an aqueous suspension of calcium carbonate by grinding in water with at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid, with introduction of at least one alkaline carbonate salt in said suspension.

2 - Process according to claim 1, characterized in that said salt is introduced integrally in the form of a mixture in water with at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid and with possibly at least another additive selected from a biocide and / or antifoam.

3 - Process according to claim 1, characterized in that said salt is introduced integrally and distinctly from the homopolymer and / or water-soluble copolymer of acrylic acid, in the aqueous suspension of calcium carbonate, before and / or during and or after the introduction of said acrylic polymer.

4 - Process according to claim 1, characterized in that said salt is introduced:

5 - Process according to one of claims 1 to 4, characterized in that the alkaline salt is selected from sodium, potassium and lithium salts, and mixtures thereof, preferably from the sodium, potassium and mixtures thereof.

6 - Process according to one of claims 1 to 5, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid have a molecular weight of between 3,000 g / mol and 15,000 g / mol, preferably between 4,000 g mol and 10,000 g / mol. 7 - Method according to one of claims 1 to 6, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are totally or partially neutralized, preferably completely neutralized, with a neutralizing agent selected from sodium hydroxides, potassium, oxides and hydroxides of calcium, magnesium, ammonia and mixtures thereof, preferably with sodium hydroxide.

8 - Method according to one of claims 1 to 7, characterized in that the water-soluble copolymer of acrylic acid is a water-soluble copolymer of acrylic acid with another monomer selected from methacrylic acid, crotonic, isocrotonic, cinnamic, maleic, itaconic, acrylamido-2-methyl-2-propanesulfonic acid and mixtures thereof.

9 - Process according to one of claims 1 to 8, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are obtained by radical polymerization methods in solution, in direct or inverse emulsion, in suspension or precipitation in suitable solvents, in the presence of catalytic systems and transfer agents, or by controlled radical polymerization processes and preferentially by controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization ( ATRP), the controlled radical polymerization with sulfur derivatives, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates.

10 - Process according to one of claims 1 to 9, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are, before or after their neutralization, treated and separated into several phases, according to static or dynamic processes, by one or more polar solvents preferentially belonging to the group consisting of methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or their mixtures.

11 - Use of at least one alkaline carbonate salt in a process for manufacturing an aqueous suspension of calcium carbonate by grinding in water with at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid , having the function of reducing the quantity of acrylic polymer used. 12 - an aqueous composition containing water, at least one homopolymer and / or at least one water-soluble copolymer of acrylic acid, at least one alkaline carbonate salt and optionally at least one other additive selected from a biocide and / or a antifoam. 13 - Aqueous composition according to claim 12, characterized in that it contains:

from 5% to 50%, preferably from 30% to 50% by dry weight of a homopolymer and / or a water-soluble copolymer of acrylic acid,

from 1% to 30% by dry weight of at least one alkaline carbonate salt,

in relation to its total weight.

14 - An aqueous composition according to one of claims 12 or 13, characterized in that the alkaline salt is selected from sodium, potassium and lithium, and mixtures thereof, preferably from the sodium, potassium and mixtures thereof.

15 - Aqueous composition according to one of claims 12 to 14, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid have a molecular weight of between 3,000 g / mol and 15,000 g / mol, preferably between 4,000 g / mol and 10,000 g / mol.

16 - Aqueous composition according to one of claims 12 to 15, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are totally or partially neutralized, preferably completely neutralized, with a neutralization agent chosen from sodium hydroxides, potassium, oxides and hydroxides of calcium, magnesium, ammonia and mixtures thereof, preferably with sodium hydroxide.

17 - aqueous composition according to one of claims 12 to 16, characterized in that the water-soluble copolymer of acrylic acid is a water-soluble copolymer of acrylic acid with another monomer selected from methacrylic acid, crotonic, isocrotonic, cinnamic, maleic itaconic, acrylamido-2-methyl-2-propane sulfonic acid and mixtures thereof. 18 - aqueous composition according to one of claims 12 to 17, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are obtained by radical polymerization processes in solution, in direct or inverse emulsion, in suspension or precipitation in suitable solvents, in the presence of catalytic systems and transfer agents, or by controlled radical polymerization processes and preferably by the controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization (ATRP), the controlled radical polymerization with sulfur derivatives, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates.

19 - aqueous composition according to one of claims 12 to 18, characterized in that the homopolymer and the water-soluble copolymer of acrylic acid are, before or after their neutralization, treated and separated into several phases, according to static or dynamic processes, by one or more polar solvents preferentially belonging to the group consisting of methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or their mixtures.

20 - Process for manufacturing an aqueous composition according to one of claims 12 to 19, by introduction with stirring at a temperature between 10 ° C and 90 ° C, preferably between 30 ° C and 60 ° C at least one carbonate salt in the form of a powder in an aqueous solution of at least one homopolymer and / or a water-soluble copolymer of acrylic acid having an initial solids content of between 10% and 60%, preferably between 25% and 50% %, and optionally by addition of at least one other additive selected from a biocide and / or an antifoam.