WO2007068809A1

WO2007068809A1 - Redispersible powder of mineral particle dispersion stabilized with a polymer

Info

Publication number: WO2007068809A1
Application number: PCT/FR2006/002637
Authority: WO
Inventors: Jean-Marc Frances; Mikel Morvan; Amit Sehgal; Yoann Lalatonne
Original assignee: Rhodia Operations
Priority date: 2005-12-13
Filing date: 2006-12-04
Publication date: 2007-06-21

Abstract

The invention concerns a redispersible powder of mineral particle dispersion stabilized with a polymer, a method for preparing same and the applications and uses thereof. The mineral particle powder redispersible in water and/or in a solvent comprises: 1) mineral particles; and 2) a stabilizing polymer which is (2a) a phosphonate-terminated poly(oxyalkene) polymer, or (2b) a water-soluble or dispersible polymer obtained by polymerization of at least one linear or branched ethylenically unsaturated monocarboxylic or polycarboxylic, aliphatic, cyclic or aromatic acid, or anhydride, and a polyalkylene ester of an ethylenically unsaturated carboxylic acid. The invention is applicable to curable paints and coatings, more particularly silicone-based, for enhanced protection against UV radiation.

Description

POWDER THAT CAN BE REDISPERSEE OF DISPERSIONS OF MINERAL PARTICLES STABILIZED WITH A POLYMER

The invention relates to a redissoluble powder of polymer-stabilized mineral particle dispersions, process for their preparation and their applications and uses.

Critical emerging nanomaterials not only rely on chemical composition, but also on the size, shape and surface properties of mineral particles, particularly nanoparticles, in new applications with outstanding performance characteristics. Smaller than the wavelength of visible light, these nanoparticles have a wide range of applications including UV-absorbing clear coatings, scratch and dirt resistant surfaces, super-hard nano-composites, materials photonics and ultra-precise polishing additives, fuel cells, high-efficiency catalysts and automotive tires. In all this spectrum of uses, one must be able to dispose of the mineral particles, more particularly the nanoparticles, in all kinds of conditions of formulation and treatment.

The commercial viability of nanoparticle dispersions, particularly aqueous and / or solvent-based metal oxide nanoparticle sols, has so far been severely limited by their inherent instability to perturbations in the dispersion conditions. For aqueous systems, typical additives in formulations such as salts or surfactants, or pH variations, can result in aggregation and macroscopic precipitation of the nanoparticle suspension. For non-aqueous systems, variations in solvent or other additive molecules may result in destabilization of the dispersion. In order to translate the intrinsic properties to different applications and uses, there is a crucial need for technologies for stabilizing dispersions of mineral nanoparticles in aqueous and / or solvent-based media.

Current technologies address the problem of stabilization by surface modification of nanoparticles by coating them with all kinds of charged or neutral polyfunctional molecules, or ligands, which respectively form electrostatic or steric surface barriers, to prevent aggregation. The presence of this barrier is essential since it provides a minimal interparticle distance between the dense nuclei of the nanoparticles, providing colloidal stability. As a result, most of the inorganic oxide nanoparticles are synthesized, stored and marketed in relatively dilute solutions or suspensions in water and / or in a solvent.

These dispersions or suspensions in water and / or a solvent have allowed a great improvement of the colloidal stability, but there is still a need for concentrated dispersions to reduce the shipping cost and facilitate their addition to the final products. as coating compositions or paints. However, concentrating these suspensions reduces the distance between the particles, increasing the risk of particle aggregate formation and loss of stability.

One of the objectives of the present invention is to provide these mineral particles in the form of a powder product which can be redispersed easily, containing the smallest possible excess of solvent, water or dispersion medium, to reduce the cost of shipping and shipping.

Another objective is to provide these inorganic particles in a physical form having the greatest stability before use, either in the form of a powder or in the form of a dispersion.

Another object of the present invention is to provide these inorganic particles in a form that can be easily transferred from an aqueous medium to a form in a ready-to-use solvent for specific applications, and also in a form that could be formulated at any given concentration, dictated by this application.

These and other objectives, which will appear on reading the following, are achieved by means of a powder of mineral particles that can be redispersed in water and / or in a solvent and comprising:

(1) mineral particles; and

(2) an effective stabilizing amount of a polymer that is

(2a) a phosphonate-terminated poly (oxyalkene) polymer whose general structure corresponds to the formula Fl:

wherein R ₁ and R ₂ are independently H or C ₁ -C ₂₀ alkyl, C ₃ -C ₂ cycloalkyl, or C ₅ -C ₂ aralkyl; & ₃ is an alkyl group of C ₂ -C ₂₀ cycloalkyl, C ₄ -C ₂₀ aralkyl or C ₈ -C ₂₀ substituted or unsubstituted; R ₄ and R ₅ are independently H or C ₁ -C ₂ alkyl; Rg is H or alkyl C ₁ -C ₂₀ cycloalkyl, C ₃ -C ₂₀ aralkyl or C ₆ -C _20; m and n independently have values from 0 to 200; and the groups of which m and n are clues and to which they refer either blockwise or randomly or alternately along the chain between OR ₃ and R ₆ ; or (2b) a water-soluble or water-dispersible polymer obtained by polymerizing at least one monomer (I) corresponding to:

(I): a linear or branched, ethylenically unsaturated aliphatic, cyclic or aromatic monocarboxylic or polycarboxylic acid or anhydride; and a monomer (II) corresponding to:

(II): a polyoxyalkylene ester of an ethylenically unsaturated carboxylic acid; or obtained by polymerizing at least one linear or branched, ethylenically unsaturated aliphatic, cyclic or aromatic acid or anhydride, monocarboxylic or polycarboxylic acid.

In a particular embodiment, the polymer (2a) has the formula F 2:

in which

R _x and R ₂ are independently H or alkyl groups C ₁ -C ₂₀ cycloalkyl, C ₃ -C _{2O /} or aralkyl, C _e -C _20;

R ₃ is an alkyl group of C ₂ -C ₂₀ cycloalkyl, C ₄ -C ₂₀ aralkyl or C ₈ -C ₂ o substituted or unsubstituted;

R ₄ and R ₅ are independently H or C ₁ -C ₂ alkyl; m and n independently have values of 0-200, and the groups m and n are indexes and to which they refer are either randomly or blockwise or both along the polyoxyalkene chain. The phosphonate-terminated poly (oxyalkene) polymer used in the present invention, its method of preparation, and the solvent-based mineral particle dispersions already stabilized by a sufficient stabilizing amount of this polymer, have been described in the US Application No. Serial No. 11/099,011, filed April 5, 2005, and Serial Application Serial No. 60 / 667,176, filed Mar. 31, 2005, both of which are incorporated herein by reference.

According to a first variant of the invention, the water-soluble or water-dispersible polymer (2b) is obtained by polymerization of at least one monomer (A), said monomers corresponding to the following:

A): linear or branched, ethylenically unsaturated aliphatic, cyclic or aromatic acid, or anhydride, monocarboxylic or polycarboxylic acid.

The monomer (A) corresponds more particularly to the following formula:

(R ¹ ) (R ¹ ) -C = C (R ¹ ) -COOH (A) in which the radicals R ¹ , which are identical or different, represent a hydrogen atom or a C ₁ hydrocarbon radical; at C ₄ optionally having a -COOH group, or a -COOH group.

According to a preferred embodiment of the invention, the monomer of formula (A) is a monocarboxylic or polycarboxylic acid, a carboxylic anhydride corresponding to the following formula:

(R ¹¹ ) HC = C (R ¹² ) COOH in which: R ¹¹ represents a hydrogen atom, a -COOH group or a - (CH ₂₎ _n -COOH group in which _{n has} a value between 1 and 4, a C ₁ to C ₄ alkyl radical;

R ¹² represents a hydrogen atom, a group - (CH ₂ ) _m -COOH wherein ma is between 1 and 4, a C ₁ -C ₄ alkyl radical.

Preferably, R ¹¹ represents a hydrogen atom, a -COOH or (CH ₂ ) -COOH group, a methyl radical or an ethyl radical, and R ¹² represents a hydrogen atom, a -CH ₂ COOH group or a methyl radical.

According to a more specific embodiment, the monomer of formula (A) is chosen from acrylic, methacrylic, citraconic, maleic, fumaric, itaconic or crotonic acids or anhydrides.

A part of the monomer (A), for example up to 50 mol%, can be replaced by the following monomers: neutral hydrophilic monomers such as acrylamide and its derivatives (N-methylacrylamide, N-isopropylacrylamide), methacrylamide, polyethylene glycol methacrylate and polyethylene glycol acrylate; anionic hydrophilic monomers: 2-sodium acrylamido-2-methylpropanesulphonate (SAMPS), sodium styrenesulphonate and sodium vinylsulphonate.

It is also possible to use small amounts, for example not more than 5 mol%, of acidic monomers, or of their salts, such as: vinylsulfonic acid, 2-propene-1-sulphonic acid, methallylsulphonic acid, sulfopropyl (meth) acrylate, styrene sulfonic acid or

1 acid acrylamido _r vinylbenzoic acid, fumaric acid, itaconic acid, citraconic acid, maleic acid, their salts or their anhydrides,

Vinylphosphonic acid.

According to a second variant, the polymer (2b) is obtained by polymerization of at least one monomer (A) and at least one monomer (B).

As regards the monomer (B), it more particularly corresponds to the following formula:

(R ¹ ) (R ¹ ) -C = C (R ³ ) -C (O) -O- [CH ₂ CH (R ⁴ ) O] _m - [CH (R ⁵ ) -CH ₂ O] _n -R ⁶ in which formula: the radicals R ^1, which are identical or different, are as defined above, R ³ is a hydrogen atom or a methyl radical,

R ⁴ and R ⁵ , which are identical or different, represent a hydrogen atom or an alkyl radical containing from 1 to 4 carbon atoms,

R ^β is a hydrogen atom or an alkyl, aryl, alkylaryl or arylalkyl radical containing from 1 to 30, preferably from 1 to 8, carbon atoms, for example a value between 2 and 100, preferably between 6 and 100, for example a value between 0 and 50.

Among the monomers of this type which may be used include those described in patents EP 705 854, US 4 138 381 or US 4 384 096.

The polymer (2b) obtained by reaction of the monomers (A) and (B) is preferably obtained by radical polymerization.

The copolymer (2b) thus obtained has a "comb" structure with, for example, a polyacrylate main chain and polyoxyalkylene segments grafted onto said main chain.

The comb polymers of the second embodiment of the invention are well known to those skilled in the art. They can be obtained by various processes, such as, for example, by copolymerization of an anionic monomer with a monomer or non-macromonomer. ionic, or by polymerization of an anionic type monomer, followed by grafting of nonionic chains.

The polymer (2b) used in the present invention, and the aqueous dispersions of mineral particles already stabilized by the latter, have been described in the provisional US application Serial No. 60 / 642,458, filed January 7, 2005, the content of which is incorporated herein by reference.

The liquid medium (1) used for the redispersion of the powder of the present invention may be water, a solvent, a mixture of miscible solvents or a mixture of water and a miscible solvent.

A mixture of organic solvents can be used.

A polar organic solvent is preferably used.

Specific examples which may be mentioned are: optionally hydroxylated nitrogen compounds, such as: ethylene diamine, NMP (N-methylpyrrolidone), pyridine, MEA (monoethanolamine), diethanolamine, triethanolamine, t-butyldiethanolamine, 1-isopropanolamine, 2-amino-1-propanolamine, 3-amino-1-propanolamine, isobutanolamine, 2-amino-2-ethoxyethanol, DGA [diglycolamine or 2- (2-amino) - ethoxy) ethanol], the compounds of alcohol and / or ether and / or ester type such as: ethanol, propanol, butanol, ethyl acetate, propyl acetate, butyl acetate , ethylene glycol, propylene glycol, TEG [triethylene glycol], glyme, diglyme, PGMEA [propylene glycol monomethyl ether acetate or 2- (1-methoxy) propyl acetate], PGME [propylene glycol monomethyl ether] , ethyl lactate, - S -

anisole, methyl adipate, cyclopentanol, hydrocarbon compounds such as toluene, xylene, ketone compounds such as acetone, dimethyl ketone, methyl ethyl ketone, 2-pentanone, cyclopentanone cyclohexanone, mesityl oxide, dimethylsulfoxide.

The inorganic particles may be amphoteric, anionic or cationic. Preferably, the particles are cationic. The mineral is preferably a metal and more preferably a metal oxide. In this regard, virtually any "metal" capable of forming a metal oxide can be used to form the metal oxide particles. Suitable metal elements include, among others, niobium, indium, titanium, zinc, zirconium, aluminum, tin, cerium, hafnium, tantalum, tungsten and bismuth. What is also suitable for the place of the metal in the oxide is the semi-metallic compound that is silicon.

The metal oxides can be made of a single metal, or can be a combination of metals, such as cerium, aluminum, zirconium, phosphorus, gallium, germanium, barium, strontium, yttrium , antimony and cesium. Preferred metal oxide particles include zirconium oxide, aluminum oxide and cerium oxide. The metal oxide particles can be prepared using any known method, such as

"sol-gel" means the direct hydrolysis of metal alkoxides by the addition of water, the forced hydrolysis of relatively inexpensive metal salts, or the non-hydrolytic reactions of metal alkoxides with metal halide salts. The present invention also relates to a process for preparing the redispersible powder of the invention from aqueous or solvent-based dispersions of inorganic particles.

The term "aqueous or solvent-based dispersions of mineral particles" refers to all systems formed of solid inorganic fine particles, more particularly metal oxide particles having colloidal sizes, suspended in an aqueous phase or solvent-based which may be different or identical to the liquid medium used to redisperse the powder of the present invention. The term particle used in this specification covers discrete particles or aggregates of particles. These particles may furthermore comprise residual amounts of bound or absorbed ions such as nitrate, acetate or ammonium ions. Colloidal sizes refer to particle sizes between 1 nm and 5000 nm. It should be noted that in the dispersion defined above, the metal oxide may be in a colloidal form or at the same time in the form of ions and colloids.

According to the present invention, the polymer (2) is present with the mineral particles in "effective amount". By "effective amount" is meant an amount sufficient to achieve a significant increase in the stability of the redispersed particles in a desired liquid medium. The molar ratio between the number of moles of phosphonate equivalent of the phosphonate polymer

(2a) or the molar ratio between the total number of moles of acid of the polymer (2b) and the total number of moles of metal oxides of the dispersion is between 0.001 and 10.0, preferably between 0.1 and 1.5.

The present invention also relates to a process for preparing the powders that can be redispersed at from the aqueous or solvent-based dispersions of mineral particles already stabilized by a sufficient stabilizing amount of polymer (2a) or (2b).

The water and / or the solvent of these dispersions of mineral particles is then removed and the product obtained is pulverized and / or ground to give a powder. The steps of removing the water and / or the solvent and

for obtaining a powder can be separated or combined. It is thus possible to use a freezing process, followed by a sublimation or freeze-drying step, simple drying or spray-drying (spray drying). Spray drying is the preferred method because it makes it possible to directly obtain the powder of the desired particle size, without necessarily going through a grinding step.

According to one embodiment of the process of the invention, the powder of mineral particles which can be redispersed by spray-drying the aqueous or solvent-based dispersions of mineral particles already stabilized by a sufficient stabilizing amount of polymer (2a) or (2b).

The particle size of the powder is generally less than 5000 nm, preferably less than 100 nm (nanometers). Spray drying may be carried out in the usual manner in any known apparatus such as, for example, an aerosol or spray atomization tower produced by a nozzle or a turbine with a stream of hot gas. The inlet temperature of the hot gas (generally air) at the top of the column is preferably between 40 ° C. and 90 ° C. and the exit temperature is preferably between 25 ° C. and 45 ° C. vs. These parameters depend on the glass transition temperature of the polymer (2), and the degree of drying desired .

An anti-setting agent may be further added to the apparatus separately from the dispersion to enhance the storage stability and flowability of the redispersible powder. It is also preferable to add the anti-setting agent in the spray column at the same time as the aqueous or solvent-based dispersions of mineral particles to obtain a preferable deposit of the anti-setting agent. on the particles of the dispersion.

Preferred anti-blocking agents are aluminum silicates, calcium or magnesium carbonates, or mixtures thereof, silicas, hydrated alumina, bentonite, talc, or mixtures of dolomite and talc, or calcite and talc, kaolin, barium sulfate, titanium oxide or calcium sulfoaluminate (satin white).

The polymer (2a) is soluble both in water and in many organic solvents, which makes it possible to prepare the redispersible powder from dispersions and / or aqueous solutions, and then to redisperse the powder in a solvent. . This property is of great interest for solvent-based coatings and paints such as silicone coatings. The drying step and the ability of the particle-polymer complex to dissolve in more than one solvent provides an easy method for effecting complexation in the usual aqueous media, and for transferring the hybrid complex to an organic solvent. Now, the process of the invention now makes it easy to redisperse and add large amounts of mineral particles to coating formulations and to obtain key value-added properties such as UV absorption. In this respect, the present invention also relates to solvent-based paints or coatings, more particularly to silicone-type coatings, more particularly to silicone-type hard layers based on silicone resins containing a powder addition that can be redispersed in a non-aqueous solvent. Silicone hard layers find applications for imparting scratch resistance or antifouling properties to plastic substrates, such as polycarbonate sheets which have a high impact strength but poor resistance properties. stripe.

The present invention relates to a silicon resin coating comprising: an organosilicon resin, a silica filler, a redispersible powder, as defined above, and redispersed in a non-aqueous solvent, where appropriate, a curing catalyst if desired, a cationic polymerization initiator, and optionally a formulation solvent.

The inorganic particles of the powder are, for example, lanthanide oxides, such as cerium oxides, to provide UV resistance to the cured silicone coating and possibly to the coated support, for example a polycarbonate support.

In general, the particle size of the redispersed particles is at most 5000 nm, preferably at most 200 nm.

The amount of lanthanide oxide in the silicone composition (based on the solids content) is between 0.1% and 20%, preferably between 0.5 and 10%. - -

A cationic initiator is, for example, disclosed in US 6,468,902 and a thermal initiator in US 6,473,883.

The following examples illustrate the invention better.

Example 1

Preparation of stabilized aqueous colloidal dispersions of cerium oxide nanoparticles with poly (oxyalkene) phosphonates (polymer (2a))

The colloidal dispersions of cerium oxide nanoparticles are prepared by the process described in US Pat. No. 5,344,588. The colloidal dispersion of bare cerium oxide nanoparticles, as synthesized (ie without any coating organic or inorganic on the surface of the particle), is available at a pH of 1.5. The dispersion precipitates however when the pH increases to pH 3 by addition of base (in the form of ammonium hydroxide, NH ₄ OH). The nanoparticles of cerium oxide are complexed with the two molecules whose structure is indicated below:

The above molecules correspond to the general structure of formula (Fl) and have a unique geometry consisting of a phosphonate chain end of ionic complexation and a neutral tail, which comprise respectively 10 and 4 monomers oxide d 'ethylene.

The cerium oxide dispersion is simply mixed at a pH of 1.5 with Phos-PEO-1 or Phos-PEO-2 in - -

a mass ratio X = [CeO ₂ ] / [Polymer] = 2 to give a clear stable dispersion.

Example 2

Preparation of a silicone-type hard coat formulation

The silicone-type hard layer is a silica nanoparticle formulation (D _h = 15 nm), with hydrolyzed and condensed trimethoxymethylsilane which corresponds to a MQ resin, stabilized with acetic acid (pH 5-6), and then diluted. with a mixture of 2-butanol and diacetone (43/10 solvent composition ratio). This formulation is sprayed or immersed on a polycarbonate sheet, the solvent is evaporated at 120-130 ^° C. and then cooled in air. The thermal cure chemistry involves hydrolysis of the alkoxy groups of the silanol resin followed by condensation of the silanol leading to a vitreous silicone network.

The hard coat formulation has the following composition, shown in Table 1:

Table 1

SiO ₂ 0, 07896

Trimethoxymethylsilane 0.2491

Acetic acid 0, 0235

H ₂ O 0.11844

2-Butanol 0.43

Diacetone alcohol 0.1

Example 3 Preparation of a powder that can be redispersed

The stabilized dispersion of cerium oxide nanoparticles obtained in Example 1 is then concentrated and washed with demineralized H ₂ O to remove the excess salt, until a final aqueous dispersion of 719 is obtained. 5 g / L, density = 1.61 g / cm ³ , pH 5.9. This concentrated dispersion is then lyophilized to give a CeO ₂ -polymer (2a) powder that can be redispersed. This powder is redissolved spontaneously in water to give stable dispersions of nanoparticles at pH ~ 6.

This powder is also dissolved spontaneously in chloroform, in about 1 hour, with stirring, in a mixture of 2-butanol and diacetone, and very slowly in pure 2-butanol.

Two dispersions of Ce0 ₂ ~ Phos-Peo-2 redispersed in a mixture of 2-butanol and diacetone are prepared with 2% and 5% by weight of CeO ₂ .

In the attached drawing:

FIG. 1A represents four transparent glass slides with or without coating S1 to S4 on a white background.

Figure 1B shows photos of the four samples under UV exposure.

Example 4

UV absorbance of silicone-type hard layers The two dispersions of CeO ₂ -Phos-Peo-2 (2% and 5% by weight of CeO ₂ ) redispersed in mixtures of 2-butanol and diacetone, prepared in Example 3 , are mixed with a silicone-type hard layer prepared in Example 2, in a ratio of 1: 1, to give stable clear dispersions called H 2 and

H3.

Four samples of glass slips S1, S2, S3 and S4 are coated with: S1: no coating;

52: the silicone type hardcoat composition of Example 2 as such;

53: the silicone composition H2, and S4: the silicone composition H3.

The solvent is evaporated and the films heat-cured to give clear coatings. Under a UV lamp, the films of S3 and S4 clearly have a high UV absorbance.

Figure 1A shows four clear glass slides with or without coating S1 to S4 on a white background.

Figure 1B shows photos of the four samples under UV exposure. Figure 1 shows that S1 and S2 have no visible absorbance difference. On the other hand, S3 and S4 have a high UV absorbance (dark coloration).

Example 5

The hard coat silicone composition is prepared by condensing a colloidal silica in aqueous phase with methyltrimethoxysilane in the presence of acetic acid as a catalyst. The quantity of methanol produced represents 8% by weight and the percentage by mass of the solids content is 15%.

The final composition of the hard layer H1 (in mass) is as follows:

Methyltrimethoxysilane 10%

Colloidal silica 5.52% Diacetone alcohol 10.3%

Butanol-2 43%

Monopropylene glycol 6.7%

Methanol 18.9%

H ₂ O 5.8%

Six sheets of polycarbonate (10 cm × 5 cm) were prepared as follows: PO, P1, P2, P3, P4 and P5: All the sheets except PO were coated with silicone coating H1, H2, H3, H4 and H5 different, with a spiral applicator: Pl with Hl,

P2, where H2 is H1, with 1.4% by weight of added cerium oxide, with the dispersion of redispersed Ce0 ₂ -polyphosphate in a mixture of 2-butanol and diacetone having 2% by weight of CeO ₂ ,

P3, where P3 is H3, with 2.1% by weight of added cerium oxide, with the dispersion of rediscolated Ce0 ₂ -polyphosphate in a mixture of 2-butanol and diacetone having 2% by weight of CeO ₂ ,

P4, where P4 is H4, with 3.8% by weight of added cerium oxide, with the dispersion of redispersed Ce0 ₂ -polyphosphate in a mixture of 2-butanol and diacetone having 2% by weight of CeO ₂ ,

P5, where P5 is H5, with 5.1% by weight of added cerium oxide, with the dispersion of redispersed Ce0 ₂ -polyphosphate in a mixture of 2-butanol and diacetone having 2% by weight of CeO ₂ .

The leaves are fixed in a Suntest CPS (Atlas) ^® climate oven.

The cycle is 100 minutes under UV, then 18 minutes in the dark for 4,000 hours. The radiation energy for accelerated aging is 468 W / cm ² . The evolution of the chromatic difference is calculated as a function of time.

The results are grouped in the following table 2: Table 2

where Delta, for panels PO to P5, represents the degree of yellowness in standard LAB (L, a, b) colorimetric co-ordinates, by

Delta = [(Lt _{n + I} -L _tn ) ² + (has _t n ₊ ia _t n) ² + (b _{tπ +} ib _tn ) ² ] ^M

The table shows that the cerium oxide added to the silicone-type hard layer prevents the polycarbonate from yellowing and blackening, both phenomena being related to aging.

No phase separation occurs during the mixing of the redispersed cerium and the silicone hard layer.

Claims

A powder of mineral particles that can be redispersed in water and / or a solvent and comprising:

(1) mineral particles; and

(2) an effective stabilizing amount of a polymer that is

wherein R ₁ and R ₂ are independently H or C ₁ -C ₂ alkyl, C ₃ -C ₂₀ cycloalkyl, or C ₅ -C ₂ aralkyl; R ₃ is alkyl C ₂ -C ₂ o cycloalkyl, C ₄ -C ₂₀ aralkyl or C ₈ -C ₂₀ substituted or unsubstituted; R ₄ and R ₅ are independently H or alkyl groups C _x -C _2; R ₆ is H or an alkyl group -C ₂₀ cycloalkyl, C ₃ -C ₂ O, or aralkyl, C ₆ -C _20; m and n independently have values from 0 to 200; and the groups of which m and n are indices and to which they refer are either randomly or blockwise or alternately along the chain between the OR ₃ and R _{6 groups} ; or

(2b) a polymer soluble in water or dispersible in water obtained by polymerization of at least one monomer (I) corresponding to:

II): a polyoxyalkylene ester of an ethylenically unsaturated carboxylic acid; or obtained by polymerization of at least one acid, or anhydride, monocarboxylic or polycarboxylic acid, phaetic, cyclic or aromatic, linear or branched, ethylenically unsaturated.

2. The powder according to claim 1, wherein the polymer (2a) has the formula F 2:

in which

R 1 and R ₂ are independently H or C 1 -C ₂₀ alkyl, C ₃ -C ₂ cycloalkyl, or C ₆ -C ₂₀ aralkyl;

R ₃ is alkyl C ₂ -C ₂ o cycloalkyl, -C ₄ -C _2O, or aralkyl Cg to C ₂ o, substituted or unsubstituted;

R ₄ and R ₅ are independently H or C ₁ -C ₂ alkyl; m and n independently have values of 0-200, and the groups m and n are indexes and to which they refer are either randomly or blockwise or both along the polyoxyalkene chain.

3. Powder according to claim 1 or 2, wherein the solvent is water, a solvent, a mixture of miscible solvents or a mixture of water and a miscible solvent.

The powder of claim 3, wherein the solvent is a polar organic solvent.

,

The powder according to claim 4, wherein the solvent is ethanol, propanol, butanol, ethylene glycol, propylene glycol, triethylene glycol, glyme, diglyme, ethyl acetate, propyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether or 2- (1-yl) acetate. methoxy) propyl, propylene glycol monomethyl ether, ethyl lactate, anisole, methyl adipate or cyclopentanol.

6. The powder according to any one of claims 1 to 5, wherein the mineral particles are cationic.

The powder according to any one of claims 1 to 6, wherein the mineral particles are metal oxide particles.

The powder of claim 7, wherein the metal is aluminum, zirconium, phosphorus, gallium, cerium, germanium, barium, strontium, yttrium, antimony, cesium, or a combination of these.

9. The powder of claim 7, wherein the molar ratio between the number of moles of phosphonate equivalent of the polymer (2a) and the total number of moles of metal oxides of the dispersion is between 0.001 and 10.0.

10. The powder according to any one of claims 1 to 9, wherein the polymer (2b) soluble in water or dispersible in water is obtained by polymerization of at least one monomer (A), said monomers corresponding to the following: (A): linear or branched, ethylenically unsaturated aliphatic, cyclic or aromatic acid, or anhydride, monocarboxylic or polycarboxylic acid.

The powder of claim 10, wherein the monomer of formula (A) is a monocarboxylic or polycarboxylic acid, a carboxylic anhydride having the following formula:

(R ¹¹ ) HC = C (R ¹² ) COOH formula in which:

R ¹¹ represents a hydrogen atom, a -COOH group or a - (CH ₂ ) _n -COOH group in which _{n has} a value between 1 and 4, a C ₁ -C ₄ alkyl radical; R ¹² represents a hydrogen atom, a group - (CH ₂₎ _m -C00H wherein m has a value between 1 and 4, alkyl radical C _x -C ₄ alkyl, where appropriate, R ¹¹ represents a hydrogen atom, hydrogen, -COOH or (CH ₂ ) -COOH, methyl or ethyl, and R ¹² represents hydrogen, -CH ₂ COOH or methyl.

12. The powder according to claim 10, wherein the monomer of formula (A) is selected from acrylic, methacrylic, citraconic, maleic, fumaric, itaconic or crotonic acids or anhydrides.

13. The powder according to claim 1, wherein the polymer (2b) is obtained by polymerization of: at least one monomer of formula (I):

(R ¹ ) (R ¹ ) -C = C (R ¹ ) -COOH (I) in which: the radicals R ¹ , which are identical or different, represent a hydrogen atom, a hydrocarbon radical C ₁ to C ₄ optionally comprising a -COOH group, a -COOH group; and, optionally, at least one monomer of formula (II):

(R ¹ ) (R ¹ ) -C = C (R ³ ) -C (O) -O- [CH ₂ CH (R ⁴ ) O] _1n - [CH (R ⁵ ) -CH ₂ O] _n -R ⁶ wherein: the R ¹ radicals, which are identical or different, are as defined above,

R ³ is a hydrogen atom or a methyl radical,

R ^ε is a hydrogen atom or an alkyl, aryl, alkylaryl or arylalkyl radical containing from 1 to 30, preferably from 1 to 8, carbon atoms, n is between 2 and 100, preferably between 6 and 100, and m is between 0 and 50.

A powder according to any one of the preceding claims wherein the molar ratio of the number of moles of acid of the water-soluble or water-dispersible polymer to the total number of moles of cerium of the dispersion is between 0.001 and 5.0.

15. A paint or varnish composition comprising a redispersible powder as defined in any one of claims 1 to 14.

A process for preparing a redispersible powder as defined in any one of claims 1 to 14, comprising the steps of: a) spray drying the aqueous or solvent-based dispersions of mineral particles whose size is less than 500 μm, preferably less than 100 μm.

17. The method as defined in claim 16, wherein step a) is performed in an atomization tower associating a spray produced by means of a nozzle or a turbine with a stream of hot gas.

The method of claim 16 or 17, further comprising adding an anti-setting agent and / or a redispersion agent.