COATED PARTICLES OF OXIDES OF METALS AND OF PHOSPHORUS, AND THEIR PREPARATION BY FLAME SPRAY PYROLYSIS

The present invention relates to coated particles of oxides of metals and of phosphorus, to a process for the preparation of such coated particles by means of the flame spray pyrolysis technology, to the particles of oxides of metals and of phosphorus resulting from such a process, to the compositions comprising such particles and also to their uses.

Metal oxides are used in numerous applications (cosmetics, paints, stains, electronics, rubber, and the like), in particular for their dyeing properties.

Currently, the colours of formulations, for example cosmetic formulations, are generally obtained by the mixing of several coloured metal oxides.

In addition, metal oxides can also be used for their optical properties, in particular their light absorption and/or light scattering properties which make it possible to protect surfaces from UV radiation and/or to convert ambient light into electricity.

However, some oxides exhibit the disadvantage of being particularly unstable over time, which brings about a deterioration in their dyeing power, more particularly a deterioration in the intensity and/or in the chromaticity of the colour obtained They can also have a tendency to degrade in the presence of water originating from the composition comprising them or from atmospheric moisture. Such a degradation leads to a partial, indeed even complete, dissolution of the oxide in water and has the consequence of greatly reducing, indeed even removing, the desired properties of said oxide.

Thus, it may happen that the colours of the formulations change over time and result in colours which are not very intense, dull and/or undesired by the user. It might even be that the differences in stability of the different metal oxides which are mixed disrupt the homogeneity of the dyeing mixture and for example bring about migration of oxide to the surface or into the bottom of the formulation. This undesirable effect is referred to as “separation effect”.

It has been envisaged, in order to improve the stability of the metal oxides, to coat the metal oxides with silica, in particular by means of “sol-gel” processes, or also to graft fluorinated compounds to the metal oxides. However, these solutions are not entirely satisfactory. The metal oxides coated with silica by a sol-gel process generally exhibit poorer dyeing properties than a non-coated particle. As for the grafting technique, the use of fluorinated compounds can be harmful to the environment and dangerous to the user.

It is also known to use a flame spray pyrolysis technology or FSP method to prepare metal oxide particles.

Flame spray pyrolysis or FSP is a method well known today, which has essentially been developed for the synthesis of ultrafine powders of single or mixed oxides of various metals (e.g. SiCh, AI2O3, B2O3, Z1O2, GeCh, WO3, feOs, SnCh, MgO, ZnO), having controlled morphologies, and/or their deposition on various substrates, this being carried out starting from a wide variety of metal precursors, generally in the form of organic or inorganic, preferably inflammable, sprayable liquids; the liquids sprayed into the flame, on being consumed, in particular emit nanoparticles of metal oxides which are projected by the flame itself over these various substrates. The principle of this method has been restated, for example, in the recent (2011) publication by Johnson Matthey entitled “Flame Spray Pyrolysis: a Unique Facility for the Production of Nanopowders”, Platinum Metals Rev., 2011, 55 (2), 149- 151. Numerous alternative forms of FSP processes and reactors have also been described, by way of examples, in the patents or patent applications: US 5 958 361, US 2 268 337, WO 01/36332 or US 6 887 566, WO 2004/005184 or US 7 211 236, WO 2004/056927, WO 2005/103900, WO 2007/028267 or US 8 182 573, WO 2008/049954 or US 8 231 369, WO 2008/019905, US 2009/0123357, US 2009/0126604, US 2010/0055340, WO 2011/020204.

However, the particles prepared according to the known processes by flame spray pyrolysis are not always satisfactory in terms of stability.

In addition, the particles prepared by flame spray pyrolysis can still be improved, in particular in terms of intensity and of chromaticity of the colour provided.

There thus exists a real need to develop dyeing particles of metal oxides which exhibit good stability over time and good dyeing properties, in particular in terms of intensity and of chromaticity of the colour conferred; and also to develop a process which makes it possible to prepare such particles.

It is also desirable to develop a broad range of dyeing particles, making it possible to obtain a rich palette of colours. In addition, there exists a need to develop particles of metal oxides exhibiting good resistance to water and good optical properties, in particular in terms of absorption of and/or of scattering of light and more particularly ultraviolet radiation.

These aims are achieved with the present invention, a subject-matter of which is in particular a particle of oxides of metals and of phosphorus, in particular of the type of MP-M' oxide of core/shell structure, comprising:

(i) a core 1 constituted of at least one oxide of metal M and of phosphorus of formula (I):

M _a PbOc (I) in which:

M represents an element of the family of the metals, a and b, which are identical or different, represent an integer ranging from 1 to 10, c represents an integer ranging from 2 to 20, and

(ii) an upper coating layer 2, covering the surface of said core 1, constituted of at least one oxide of element M’ of formula (II):

M'dOe (II) in which:

M' is an element, other than M, chosen from the elements of columns 13 and

14 of the Periodic Table of the Elements, and the elements of the family of the lanthanides, d represents an integer ranging from 1 to 4, e represents an integer ranging from 1 to 4.

It has been found that the coated dyeing particles of oxides of metals and of phosphorus according to the invention only deteriorate very little over time, this being the case even when they are formulated in an in particular aqueous composition.

In particular, only very little in the way of “separation effects” have been observed with the particles according to the invention.

In addition, the particles according to the invention make it possible to obtain particularly intense and chromatic dyeings, for example for cosmetic or pharmaceutical usages.

Furthermore, it has been possible to prepare a large number of particles according to the invention, with a large number of different and atypical colours (for example fluorescent colours). The particles according to the invention have thus made it possible to obtain a rich palette of colours, which makes possible a greater number of dyeings and thus a dyeing closer to the wish of the user. This also makes it possible to reduce the number of metal oxides to be mixed in order to obtain the desired colour.

It has also been observed that the cosmetic make-up compositions comprising coated dyeing particles of oxides of metals and of phosphorus according to the invention exhibit a good power of masking (for example imperfections of the skin) and also make it possible to obtain dyeings which are particularly covering (for example for mascaras).

The particles according to the invention retain the properties intrinsic to the oxide of metal M used, such as good optical properties in terms of light absorption and/or light scattering. More particularly, they exhibit a high UV absorption and a low visible scattering or a high visible scattering, then making possible uses such as sun protection and/or modification of the visual appearance, while benefiting from good resistance in the presence of water.

Moreover, the compositions comprising such particles have shown a good screening power, in particular with respect to long and short UV-A radiation.

In addition, as the coated particles of oxides of metals and of phosphorus according to the invention do not require a hydrophobic coating, it is possible to use them in a broad formulation spectrum (for example, in entirely aqueous formulations and/or surfactant-free formulations). When the formulations thus obtained end up in water (washbasin drainage, lake or sea), the risk of inappropriate deposition (on the edges of the washbasin, on the walls of the pipes or on rocks) is furthermore reduced.

Another subject-matter of the invention relates to a process for the preparation of such particles of oxides of metals M and of phosphorus which are coated with an oxide of element M’, in particular of the type of MP-M’ oxide of core/shell structure, comprising at least the following stages: a. preparing a composition (A) by adding one or more precursors of metal M and one or more precursors of phosphorus to a combustible solvent or to a mixture of combustible solvents; then b. forming a flame, in a flame spray pyrolysis device, by injecting the composition (A) and an oxygen-containing gas until aggregates of oxide of metal M and of phosphorus are obtained; then c. injecting a gaseous composition (B) comprising a gas (G3) and one or more precursors of element M' until an upper coating layer 2 constituted of oxide of element M’ is obtained, at the surface of said aggregates of oxides of metals M and of phosphorus; said element M' being other than M and said element M’ being chosen from the elements of columns 13 and 14 of the Periodic Table of the Elements, and the elements of the family of the lanthanides.

It has been found that the process according to the invention makes it possible to obtain particles of oxides of metals M and of phosphorus which are coated with a layer of inorganic material based on oxide of the element M’, which are particularly stable over time and exhibit good resistance to water.

Furthermore, unlike conventional coating processes, the process according to the invention has the advantage, despite the presence of an upper coating layer, of retaining good intrinsic performance qualities of the core. This is because, due to the specific nature of the upper coating layer, it is possible, for a given particle weight, to reduce the proportion of oxides of metals and of phosphorus, without, however, reducing and/or negatively affecting the properties of said oxides of metals and of phosphorus.

Thus, the process of the invention makes it possible to produce stable particles of oxides of metals and of phosphorus, while avoiding the inconveniences due to the increase in the amount of particles which would be conventionally necessary in order to maintain the good dyeing properties of the oxides of metals.

The invention also relates to a composition, preferably a cosmetic composition, comprising particles of oxides of metals and of phosphorus according to the invention, and also to the cosmetic and/or pharmaceutical use of at least one particle of oxides of metals and of phosphorus according to the invention.

More particularly, the invention also relates to the use of at least one particle of oxides of metals and of phosphorus according to the invention for the dyeing and/or making up of keratin materials.

Brief description of the figure

The appended drawing is diagrammatic. The drawing is not necessarily to scale; it is above all targeted at illustrating the principles of the invention. The figure 1 represents a cross-sectional view of a particle of oxide of metal M and of phosphorus of formula (I) coated with an oxide of element M’ of formula (II) according to one embodiment of the invention.

Other characteristics, aspects and advantages of the invention will become even more clearly apparent on reading the description and the example which follows.

In the present description, and unless otherwise indicated:

- the expression "at least one" is equivalent to the expression "one or more" and can be replaced therewith;

- the expression "of between" is equivalent to the expression "ranging from" and can be replaced therewith, and implies that the limits are included;

- the expression "keratin materials” denotes in particular the skin and human keratin fibres, such as the hair;

- the upper coating layer 2 is also referred to as "external layer", "casing", "coating” or “shell”;

- the term "alkyl” is understood to mean an "alkyl radical", that is to say a linear or branched Ci to Cio, particularly Ci to Cs, more particularly Ci to Ce and preferentially Ci to C4 hydrocarbon radical, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl or tert-butyl;

- the term "aryl" radical is understood to mean a monocyclic or fused or nonfused polycyclic carbon-based group comprising from 6 to 22 carbon atoms, at least one ring of which is aromatic; preferentially, the aryl radical is a phenyl, biphenyl, naphthyl, indenyl, anthracenyl or tetrahydronaphthyl, preferably a phenyl;

- the term "arylate" radical is understood to mean an aryl group which comprises one or more carboxylate -C(O)O" groups, such as naphthalate or naphthenate;

- the term "complexed metal” is understood to mean that the metal atom forms a "metal complex” or “coordination compound" in which the metal ion, corresponding to the central atom, i.e. M, is chemically bonded to one or more electron donors (ligands);

- the term "ligand" is understood to mean a coordinating organic chemical group or compound, i.e. which comprises at least one carbon atom and which is capable of coordination with the metal M, and which, once coordinated or complexed, results in metal compounds corresponding to principles of a coordination sphere with a predetermined number of electrons (internal complexes or chelates) - see Ullmann's Encyclopedia of Industrial Chemistry, ‘Metal-Complex Dyes ‘, 2005, pp. 1-42. More particularly, the ligand(s) are organic groups which comprise at least one group which is electron-donating via an inductive and/or mesomeric effect, more particularly carrying at least one amino, phosphino, hydroxyl or thiol electron-donating group, or the ligand is a persistent carbene, particularly of “Arduengo” type (imidazoleylidenes), or comprises at least one carbonyl group. Mention may more particularly be made, as ligand, of: i) those which contain at least one phosphorus -P< atom, i.e. phosphine, such as triphenylphosphines; ii) bidendate ligands of formula R-C(X)- CR'R"-C(X)-R"' with R and R'", which are identical or different, representing a linear or branched (Ci-C6)alkyl group and R' and R", which are identical or different, representing a hydrogen atom or a linear or branched (Ci-C6)alkyl group, preferentially R' and R" representing a hydrogen atom, X representing an oxygen or sulfur atom or an N(R) group with R representing a hydrogen atom or a linear or branched (Ci- Ce)alkyl group, such as acetylacetone or P-diketones; iii) (poly)hydroxycarboxylic acid ligands of formula [HO-C(O)] _n -A-C(O)-OH and their deprotonated forms with A representing a monovalent group when n has the value zero or a polyvalent group when n is greater than or equal to 1, which is saturated or unsaturated, cyclic or non-cyclic and aromatic or non-aromatic based on a hydrocarbon comprising from 1 to 20 carbon atoms which is optionally interrupted by one or more heteroatoms and/or is optionally substituted, in particular by one or more hydroxyl groups: preferably, A represents a monovalent (Ci-Ce)alkyl group or a polyvalent (Ci-Ce)alkylene group optionally substituted by one or more hydroxyl groups; and n representing an integer of between 0 and 10 inclusive; preferably, n is of between 0 and 5, such as among 0, 1 or 2; such as lactic, glycolic, tartaric, citric and maleic acids, and arylates, such as naphthalates; and iv) C2 to C10 polyol ligands comprising from 2 to 5 hydroxyl groups, in particular ethylene glycol or glycerol; more particularly still, the ligand(s) carry a carboxyl, carboxylate or amino group; particularly, the ligand is chosen from acetate, (Ci- Ce/alkoxylate, (di)(Ci-C6)alkylamino and arylate, such as naphthalate or naphthenate, groups;

- the term “combustible” is understood to mean a liquid compound or a gas which, with oxygen and energy, is consumed in a heat-generating chemical reaction: combustion. In particular the liquid combustibles are chosen from protic solvents, in particular alcohols, such as methanol, ethanol, isopropanol or n-butanol; aprotic solvents, in particular chosen from esters, such as methyl esters and those resulting from acetate, such as 2-ethylhexyl acetate, acids, such as 2-ethylhexanoic acid (EHA), acyclic ethers, such as ethyl ether, methyl tert-butyl ether (MTBE), methyl tert-amyl ether (MTAE), methyl tert-hexyl ether (MTHE), ethyl tert-butyl ether (ETBE), ethyl tert-amyl ether (ETAE) or diisopropyl ether (DIPE), cyclic ethers, such as tetrahydrofuran (THF), aromatic hydrocarbons or arenes, such as xylene, non-aromatic hydrocarbons; and their mixtures. The combustibles can optionally be chosen from liquefied hydrocarbons, such as acetylene, methane, propane or butane; and their mixtures.

The coated particles of oxides of metals and of phosphorus

The particle of oxides of metals and of phosphorus, in particular of the type of MP-M' oxide of core/shell structure, comprises:

(i) a core 1 constituted of at least one oxide of metal M and of phosphorus of formula (I):

M _a PbOc (I) in which:

M represents an element of the family of the metals, a and b, which are identical or different, represent an integer ranging from 1 to 10, c represents an integer ranging from 2 to 20, and

(ii) an upper coating layer 2, covering the surface of said core 1, constituted of at least one oxide of element M’ of formula (II):

M'dOe (II) in which:

M' is an element, other than M, chosen from the elements of columns 13 and 14 of the Periodic Table of the Elements, and the elements of the family of the lanthanides, d represents an integer ranging from 1 to 4, e represents an integer ranging from 1 to 4.

Within the meaning of the invention, the term “metals” is understood to mean the elements of the Periodic Table of the Elements chosen from the transition metals and the lanthanides. In particular, the transition metals can be chosen from titanium, zirconium, vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel and copper. Preferably, the element M is chosen from the elements of columns 4 to 11 of the Periodic Table of the Elements and the elements of the family of the lanthanides.

More preferentially, the element M is chosen from titanium, zirconium, vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel, copper and cerium.

More preferentially still, the element M is chosen from vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel and copper.

Very particularly preferably, the element M is chosen from copper, iron and cobalt.

According to a specific embodiment of the invention, the element M is chosen from the elements of the family of the lanthanides, and preferably cerium.

According to another specific embodiment of the invention, the element M is chosen from the transition metals, in particular from the elements of columns 4 to 11 of the Periodic Table of the Elements; preferably from titanium, zirconium, vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel and copper; more preferentially from vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel and copper; and better still from copper, iron and cobalt.

Preferably, the integers a and b range, independently of each other, from 1 to 5.

Preferably, the integer c ranges from 4 to 10.

Preferably, the oxide(s) of metals M and of phosphorus of formula (I) is/are chosen from CuPCU, FePCU, CU2P2O7, CO3P2O7, CU3P3O8, CU4P4O9 and CU5P5O10.

According to the invention, the element M of a particle is different from the element M’ of this particle.

Preferably, the core is in the crystalline state.

The crystalline state of the core 1 and also its composition can be determined, for example, by a conventional X-ray diffraction method.

Advantageously, the core 1 of the particle according to the invention is constituted of one or more aggregates of crystalline primary particles of oxide of a metal M and of phosphorus. In other words, the core 1 is constituted of several microcrystals of oxide of metal M and of phosphorus. More particularly, the core 1 is constituted of a single oxide of metal M and of phosphorus of formula (I).

The coated particle of oxide of metal M and of phosphorus according to Figure 1 comprises a core 1 of average diameter D _m , constituted of an oxide of metal M and of phosphorus of formula (I).

The coated particle of oxide of metal M and of phosphorus according to Figure 1 also comprises an upper coating layer 2, constituted of an oxide of element M’ of formula (II), and completely covering the surface of the core 1 and of average thickness dm.

The number- average diameter D _m of the core 1 can, for example, be determined by transmission electron microscopy (abbreviated to TEM). Preferably, the number- average diameter D _m of the core 1 of the particle according to the invention is within the range extending from 3 to 5000 nm, more preferentially from 10 to 3000 nm, more preferentially still between 20 and 1000 nm.

The coated particle of oxides of metals M and of phosphorus according to the invention comprises an upper coating layer 2, covering the surface of the core 1, constituted of an oxide of element M’ of formula (II).

Advantageously, the upper coating layer 2 covers at least 90% of the surface of the core 1. More preferentially, the upper coating layer 2 covers the whole of the surface of the core 1.

The degree of coverage of the core by the upper coating layer can, for example, be determined by means of a visual analysis of TEM-BF or STEM-HAADF type, coupled to a STEM-EDX analysis.

Each of the analyses is carried out on a statistical number of particles, in particular on at least 20 particles. The particles are deposited on a metal grid made of a metal other than any metal forming part of the particles, whether in the core or in the upper coating layer. For example, the grid is made of copper (except in the case where it is desired to use copper in the manufacture of the particles).

Visual analysis of the TEM-BF and STEM-HAADF images makes it possible, based on the contrast, to deduce whether or not the coating completely surrounds the core of the particle. It is possible, by analysing each of the 20 (or more) images, to deduce therefrom a degree of coverage of the core and then, by taking the average, to determine an average degree of coverage. The STEM-EDX analysis makes it possible to check that the coating indeed contains predominantly or exclusively the oxide of element M’. For this, it is necessary to make pointings (on at least 20 particles), on the edges of the particles. These pointings then reveal the element M’.

The STEM-EDX analysis also makes it possible to check that the core indeed contains the metal M. For this, it is necessary to make pointings (on at least 20 particles), on the centres of the particles. These pointings then reveal the metal M and the element M’.

This method also makes it possible to confirm the presence of phosphorus in the core.

According to the invention, the element M’ is other than the element M and chosen from the elements of columns 13 and 14 of the Periodic Table of the Elements and the elements of the family of the lanthanides.

Preferably, the element M’ is chosen from aluminium and the elements of column 14 of the Periodic Table of the Elements.

More preferentially, the element M’ is chosen from silicon, tin and aluminium.

Very particularly preferably, the element M’ is silicon.

Preferably, the integer d is equal to 1 or 2. More preferentially, the integer d is equal to 1.

Preferably, the integer e is equal to 2 or 3. More preferentially, the integer e is equal to 2.

Preferably, the oxide of element M’ of formula (II) is chosen from SiOr, SnOr and AI2O3. More preferentially, the oxide of element M' of formula (II) is silicon dioxide SiCF.

More particularly, the upper coating layer 2, covering the surface of the core 1, is constituted of a single oxide of element M’ of formula (II).

According to a preferred embodiment of the invention, the particles comprise a core 1 constituted of oxide of metal M and of phosphorus of formula (I) chosen from CuPO ₄ , FePCE, CU2P2O7, CO3P2O7, CU3P3O8, CU4P4O9 and CU5P5O10 and an upper coating layer 2, covering the surface of the core 1, constituted of oxide of element M of formula (II) chosen from S1O2, SnCh and AI2O3.

According to a particularly preferred embodiment of the invention, the particles comprise a core 1 constituted of oxide of metal M and of phosphorus of formula (I) chosen from CuPCU, FePCU, G12P2O7, CO3P2O7, G13P3O8, G14P4O9 and CU5P5O10 and an upper coating layer 2, covering the surface of the core 1, constituted of silicon dioxide SiCh.

The number-average thickness d _m of the upper coating layer can also be determined by transmission electron microscopy.

Preferably, the number- average thickness d _m of the upper coating layer is within the range extending from 1 to 20 nm, more preferentially from 1 to 10 nm and more preferentially still from 2 to 7 nm.

Advantageously, the upper coating layer 2 is amorphous.

Advantageously, the upper coating layer 2 is transparent.

Advantageously, the particle of oxides of metals M and of phosphorus according to the invention comprises element M and element M’ according to a specific (M/M’) molar atomic ratio.

This ratio corresponds to the amount in moles of atoms of metals M present in the particle according to the invention, on the one hand, to the amount in moles of element M’ present in the particle according to the invention, on the other hand.

This ratio can be determined by spectrometry according to one of the following two methods. According to a first method, powder is spread out and an X- ray fluorimetry study is carried out with an X-ray spectrometer to deduce therefrom the metal ratio. According to another method, the particles of the invention are dissolved beforehand in an acid. Then an elemental analysis is carried out on the material obtained by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) to deduce therefrom the metal ratio.

Preferably, the (M/M’) molar atomic ratio of the particle according to the invention is strictly greater than 0.3; more preferentially greater than or equal to 1; more preferentially still greater than or equal to 3; better still within the range extending from 3 to 100; and even better still within the range extending from 3 to 10. The number- average diameter of the particle according to the invention can also be determined by transmission electron microscopy. Preferably, the numberaverage diameter of the particle according to the invention is within the range extending from 4 to 5000 nm; more preferentially from 10 to 3000 nm; more preferentially still from 20 to 1000 nm.

Preferably, the BET specific surface of the particle according to the invention is of between 1 m ² /g and 200 m ² /g, more preferentially between 30 and 100 m ² /g.

According to a specific embodiment of the invention, the coated particle of oxides of metals M and of phosphorus according to the invention can optionally further comprise an additional coating layer covering the upper coating layer 2 and comprising at least one hydrophobic organic compound.

The hydrophobic organic compound(s) included in the additional coating layer are more preferentially chosen from silicones, in particular silicones comprising at least one fatty chain; carbon-based derivatives comprising at least 6 carbon atoms, in particular fatty acid esters; and their mixtures.

The additional coating layer can be produced by a liquid route or by a solid route. By a liquid route, the hydroxyl functions are reacted with reactive functions of the compound which will form the coating (typically silanol functions of a silicone or the acid functions of a carbon-based fatty substance). By a solid route, the particles are brought into contact with a liquid or pasty compound comprising the hydrophobic substance.

Preferably, the coated particles of oxides of metals M and of phosphorus according to the invention are obtained by the preparation process of the invention as described below.

The process for the preparation of the coated particles of oxides of metals and of phosphorus

Another subject-matter of the invention relates to a process for the preparation of the particles of oxides of metals M and of phosphorus which are coated with an oxide of element M’, in particular of the type of MP-M’ oxide of core/shell structure, comprising at least one stage a. of preparation of a composition (A), then a stage b. of formation of the flame and a stage c. of injection of a gaseous composition (B). Stage a. of the process according to the invention consists of the preparation of a composition (A) by adding one or more precursors of metal M and one or more precursors of phosphorus to a combustible solvent or to a mixture of combustible solvents.

Preferably, the element M is chosen from the elements of columns 4 to 11 of the Periodic Table of the Elements and the elements of the family of the lanthanides.

More particularly, the element M is chosen from titanium, zirconium, vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel, copper and cerium.

More preferentially still, the element M is chosen from vanadium, chromium, molybdenum, manganese, iron, cobalt, nickel and copper.

Very particularly preferably, the element M is chosen from copper, iron and cobalt.

According to the invention, the element M is other than the element M’.

The precursors of the element M, the precursors of phosphorus and the combustible solvents which can be used according to the invention can be chosen from the precursors of the element M, the precursors of phosphorus and the combustible solvents conventionally used in flame spray pyrolysis.

Preferably, the precursors of the element M included in the composition (A) are chosen from: the nitrates of element M, for example copper nitrate or iron nitrate, the sulfates of element M, for example copper sulfate or iron sulfate, the compounds comprising one or more elements M complexed or not to one or more ligands containing at least one carbon atom, such as, for example, carbonates and citrates, and their mixtures.

More preferentially, said ligand(s) are chosen from acetate, (Ci- C6)alkoxylate, (C2-Cio)alkylcarboxylate, (di)(Ci-C6)alkylamino, and arylate, such as naphthalate or naphthenate, groups.

More preferentially, the precursors of metal M included in the composition (A) are chosen from the nitrates of elements M.

Preferably, the precursors of phosphorus included in the composition (A) are chosen from the phosphorus compounds of following formula (III):

PR1R2R3 (III) in which:

Ri, R2 and R3, which are identical or different, represent a hydrogen atom or an electron-donating (via an inductive and/or mesomeric effect) group.

Preferably, the electron-donating group is chosen from aromatic or nonaromatic, saturated or unsaturated, cyclic or acyclic, linear or branched, hydrocarbon groups of 1 to 20 carbon atoms; more preferentially from hydrocarbon groups of (Ci- Cs)alkyl, (C2-Cs)alkenyl, (C2-Cs)alkynyl and aryl, such as phenyl or benzyl, type; more preferentially still from hydrocarbon groups of (Ci-Cs)alkyl and (Cs-Ci2)aryl, in particular phenyl, type.

According to a preferred embodiment of the invention, the Ri, R2 and R3 radicals are identical.

Very particularly preferably, the precursor of phosphorus is tripheny Ipho sphine .

Preferably, the combustible solvent(s) are chosen from protic combustible solvents, aprotic combustible solvents, and their mixtures; more preferentially from alcohols, esters, acids, acyclic ethers, cyclic ethers, aromatic hydrocarbon or arenes, non-aromatic hydrocarbons, such as liquefied hydrocarbons, for example acetylene, methane, propane or butane, and their mixtures; and better still from 2-ethylhexyl acetate, 2-ethylhexanoic acid (EHA), ethyl ether, methyl tert-butyl ether (MTBE), methyl tert-amyl ether (MTAE), methyl tert-hexyl ether (MTHE), ethyl tert-butyl ether (ETBE), ethyl tert-amyl ether (ETAE), diisopropyl ether (DIPE), tetrahydrofuran (THF), xylene and their mixtures.

In particular, the combustible solvent(s) can be chosen from aprotic combustible solvents comprising at least three carbon atoms and their mixtures; and better still from xylene, toluene, tetrahydrofuran, 2-ethylhexyl acetate, 2-ethylhexanoic acid (EHA) and their mixtures.

Very particularly preferably, the composition (A) comprises a mixture of combustible solvents, preferably comprising at least two of the following combustible solvents: 2-ethylhexanoic acid (EHA), toluene, absolute ethanol and diethylene glycol monobutyl ether.

Better still, the composition (A) comprises a mixture of combustible solvents constituted of 2-ethylhexanoic acid (EHA), toluene, absolute ethanol and diethylene glycol monobutyl ether. Better still, the composition (A) comprises a mixture of combustible solvents constituted of at least 5% by volume of 2-ethylhexanoic acid (EHA), of at least 5% by volume of toluene, of at least 5% by volume of absolute ethanol and of at least 5% by volume of diethylene glycol monobutyl ether, with respect to the total volume of the mixture of combustible solvents.

Advantageously, the content of precursor of the element M in the composition (A) is of between 1% and 60% by weight, preferably between 15% and 30% by weight, with respect to the total weight of the composition (A).

Advantageously, the content of precursor of phosphorus in the composition (A) is between 1% and 60% by weight, preferably between 15% and 30% by weight, with respect to the total weight of the composition (A).

The preparation process according to the invention additionally comprises a stage b. of injection of the composition (A) and of an oxygen-containing gas (G) into a flame spray pyrolysis (FSP) device in order to form a flame.

Preferably, the flame formed during stage b. is at a temperature of greater than or equal to 2000°C, at at least one point of the flame.

Stage b. can optionally further comprise an additional injection of a “premix” mixture (P) comprising oxygen and one or more combustible gases, such as methane. This “premix” mixture (also referred to as “supporting flame oxygen”) makes possible the production of a support flame intended to ignite and maintain the flame resulting from the composition (A) and the oxygen-comprising gas (G) (i.e. “dispersion oxygen”). The mixture of the composition (A) with the gas (G), on the one hand, and the premix (P), on the other hand, are injected separately, that is to say that the mixture of the composition (A) with the oxygen-comprising gas (G) is injected by means of one tube and that the premix (P) is injected by means of another tube.

Preferably, during stage b., the composition (A), the oxygen-comprising gas and optionally the “premix” mixture (P), when it is present, are injected into a reaction tube (also referred to as “enclosing tube”). Preferably, this reaction tube is made of metal or of quartz. Advantageously, the reaction tube exhibits a height of greater than or equal to 30 cm, preferably of greater than or equal to 40 cm and more preferentially of greater than or equal to 50 cm. Preferentially, the length of said reaction tube is of between 30 cm and 300 cm, particularly between 40 cm and 200 cm and more particularly between 45 cm and 100 cm, such as 50 cm.

The ratio by weight of the weight of solvent(s) present in the composition (A), on the one hand, to the weight of oxy gen-containing gas, on the other hand, is defined as follows:

Firstly, the amount of oxygen-containing gas (also referred to as “oxidizer compound”) for the assembly formed by the composition (A), that is to say the combustible solvent(s), the precursor(s) of the element M and the precursor(s) of phosphorus, on the one hand, and the oxygen- containing gas, on the other hand, to be able to react together in a combustion reaction in a stoichiometric ratio (thus without an excess or deficit of oxidizer compound) is calculated.

Starting from this calculated amount of oxygen-containing gas (also referred to as “calculated oxidizer”), a new calculation is performed to deduce therefrom the amount of oxygen-containing gas to be injected (also referred to as “oxidizer to be injected”), according to the formula: Oxidizer to be injected = Calculated oxidizer/(p with (p a correction factor, preferably of between 0.2 and 2, more preferentially between 0.8 and 1.4, more preferentially still between 1 and 1.3, better still between 1.05 and 1.25 and even better still between 1.1 and 1.2.

This method is in particular defined by Turns, S. R. in An Introduction to Combustion: Concepts and Applications, 3rd ed.; McGraw-Hill: New York, 2012.

The flame spray pyrolysis device which can be used in the preparation process according to the invention can comprise one or more chambers. Preferably, the flame spray pyrolysis device which can be used in the preparation process according to the invention comprises several chambers, more preferentially two chambers.

Preferably, said flame spray pyrolysis device is pressurized by an inert gas (G2) chosen, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide and ammonia; more preferentially from nitrogen, methane, hydrogen and argon; more preferentially still from nitrogen and argon, and better still by nitrogen.

According to a preferred embodiment of the invention, when the flame spray pyrolysis device comprises only a single chamber, the chamber of said flame spray pyrolysis device is pressurized by an inert gas (G2) chosen, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide and ammonia; preferably from nitrogen, methane, hydrogen and argon; more preferentially from nitrogen and argon, and better still by nitrogen.

According to another preferred embodiment of the invention, when the flame spray pyrolysis device comprises several chambers, the first chamber of said flame spray pyrolysis device is pressurized by an inert gas (G2) chosen, for example, from nitrogen, methane, argon, hydrogen, hydrogen sulfide and ammonia; preferably from nitrogen, methane, hydrogen and argon; more preferentially from nitrogen and argon, and better still by nitrogen.

Preferably, the flow rate of inert gas (G2) injected into the flame spray pyrolysis device ranges from 5 1/min to 701/min; more preferentially from 10 1/min to 50 1/min.

More preferentially, the flow rate of nitrogen (G2) injected into the flame spray pyrolysis device ranges from 5 1/min to 70 1/min; more preferentially from 10 1/min to 50 1/min.

According to a particularly preferred embodiment of the invention, the correction factor cp is between 0.2 and 2, more preferentially between 0.8 and 1.4, more preferentially still between 1 and 1.3, better still between 1.05 and 1.25 and even better still between 1.1 and 1.2; and the flow rate of inert gas (G2), more particularly nitrogen, injected into the flame spray pyrolysis device ranges from 5 1/min to 70 1/min; more preferentially from 10 1/min to 50 1/min.

The preparation process according to the invention additionally comprises a stage c. comprising the injection of a gaseous composition (B) comprising a gas (G3) and one or more precursors of element M' until an upper coating layer 2 constituted of oxide(s) of element M’ is obtained, at the surface of said aggregates of oxides of metals M and of phosphorus.

As indicated above, the element M’ is other than the element M and chosen from the elements of columns 13 and 14 of the Periodic Table of the Elements and the elements of the family of the lanthanides.

Preferably, the element M’ is chosen from aluminium and the elements of column 14 of the Periodic Table of the Elements.

More preferentially, the element M’ is chosen from silicon, tin and aluminium. Very particularly preferably, the element M is silicon.

Preferably, the precursor of element M’ comprises at least two M’ atoms and several M’-carbon covalent bonds. More preferentially, the precursor of element M’ comprises at least three M’ atoms and several M’-carbon covalent bonds.

More preferentially, the precursor of element M' is chosen from hexa(di)(Ci- C4)alkyldisiloxanes, such as hexadimethyldisiloxane, (di)(tri)(tetra)(Ci- C4)alkoxysilanes, such as tetraethoxysilane, bis[(di)(tri)alkoxysilyl](Ci-C4)alkanes, such as l,2-bis(triethoxysilyl)ethane or l,2-bis(trimethoxysilyl)ethane, (Ci- C4)alkoxy(di)(tri)(Ci-C4)alkylsilanes, such as methoxytrimethylsilane, hydrocarbon gases, such as acetylene, aluminium (di)(Ci-C6)alkoxylates, aluminium (di)(Ci- C6)alkylcarboxylates, such as aluminium diacetate hydroxide, (poly)(Ci-C6)alkoxylate stannates, (poly)(Ci-C6)alkylcarboxylate stannates, such as tetraacetate stannate, and their mixtures.

Better still, the precursor of element M’ is chosen from hexadimethyldisiloxane, tetraethoxy silane, l,2-bis(triethoxysilyl)ethane, 1,2- bis(trimethoxysilyl)ethane, methoxytrimethylsilane and their mixtures.

Preferably, the gas (G3) of the composition (B) is devoid of oxygen.

More preferentially, the gas (G3) of the composition (B) is chosen from nitrogen, methane, argon, hydrogen, hydrogen sulfide and ammonia, more preferentially from nitrogen, methane, hydrogen and argon.

More preferentially still, the gas (G3) of the composition (B) is chosen from nitrogen and argon.

The gas (G3) of the composition (B) acts as vehicle for the injection of the precursor(s) of element M' into the flame spray pyrolysis (FSP) device. The flow rate for injection of the precursor(s) of element M' into the device can then be controlled by the control of the flow rate of the gas (G3) of the composition (B).

Preferably, the content of precursor(s) of element M’ in the gaseous composition (B) injected during stage c. of the process according to the invention is between 1% and 60% by volume, more preferentially between 5% and 30% by volume, with respect to the total volume of the gaseous composition (B).

Preferably, the composition (B) is devoid of organic solvent. During the process according to the invention, an (M/M injected molar atomic ratio can be calculated. This ratio corresponds to the amount in moles of atoms of element M’ injected during stage b., on the one hand, to the the amount in moles of element M’ injected during stage c., on the other hand.

Preferably, the (M/M’)i _n jected molar atomic ratio is greater than or equal to 0.25; more preferentially within the range extending from 0.25 to 120; more preferentially still from 0.25 to 99; better still within the range extending from 1 to 80; and even better still within the range extending from 3 to 20.

Preferably, stage b. is carried out in a first chamber of the flame spray pyrolysis device and stage c. is carried out in a second chamber of said device in fluidic communication with the first chamber.

In particular, said second chamber might be contiguous with the first chamber and prolong said first chamber. In an alternative form, provision might be made for the two chambers to be connected by a pipe.

The invention also relates to the coated particles of oxides of metals M and of phosphorus which are obtained according to the preparation process according to the invention described above.

Another subject-matter of the invention relates to a composition, preferably a cosmetic composition, comprising at least one cosmetically acceptable carrier and one or more coated particles of oxides of metals M and of phosphorus as described above, and/or preferably obtained by the preparation process according to the invention.

The composition according to the invention is intended to be applied to keratin materials, preferably the skin and/or the hair, in order to dye and/or make up the keratin materials. An optional stage of drying the keratin materials can be carried out.

The composition according to the invention can be in various presentation forms. Thus, the composition according to the invention can be in the form of a powdered (pulverulent) composition or of a liquid composition, or in the form of a milk, of a cream, of a paste or of an aerosol composition.

The compositions according to the invention are in particular cosmetic compositions, i.e. the material(s) of the invention are in a cosmetically acceptable carrier. The term “ cosmetically acceptable carrier” is understood to mean a medium which is appropriate for application to keratin materials, in particular human keratin matenals, such as the skin, said cosmetically acceptable earner being generally constituted of water or of a mixture of water and of one or more organic solvents or of a mixture of organic solvents.

The composition according to the invention is advantageously an aqueous composition.

Preferably, the composition comprises water in a content in particular of between 5% and 95% inclusive, with respect to the total weight of the composition.

Within the meaning of the invention, the term “organic solvent” is understood to mean an organic substance capable of dissolving another substance without chemically modifying it.

Mention may be made, by way of organic solvent, for example, of lower C2- C<> alkanols, such as ethanol and isopropanol; polyols and polyol ethers, such as 2- butoxyethanol, propylene glycol, propylene glycol monomethyl ether and diethylene glycol monoethyl ether and monomethyl ether, and also aromatic alcohols, such as benzyl alcohol or phenoxyethanol, and their mixtures.

Preferably, the organic solvents are present in the composition according to the invention in a content of inclusively between 0.1% and 40% by weight approximately, with respect to the total weight of the composition, and more preferentially between 1% and 30% by weight approximately and more particularly still of inclusively between 5% and 25% by weight, with respect to the total weight of the composition.

The compositions of the invention can include a fatty phase and be in the form of direct or inverse emulsions.

The composition according to the invention can be prepared according to the techniques well known to a person skilled in the art, in the form of a simple or complex emulsion (oil-in-water, or abbreviated to O/W, water-in-oil or W/O, oil-in-water-in-oil or O/W/O, or water-in-oil-in-water or W/O/W), such as a cream, a milk or a cream gel.

According to a specific embodiment of the invention, the composition according to the invention can also be provided in the form of an anhydrous composition, such as, for example, in the form of an oil. The term "anhydrous composition" is understood to mean a composition containing less than 2% by weight of water, preferably less than 1% by weight of water and more preferentially still less than 0.5% by weight of water, with respect to the total weight of the composition, and indeed even a composition devoid of water. In compositions of this type, the water possibly present is not added during the preparation of the composition but corresponds to the residual water contributed by the mixed ingredients.

The coated particle(s) of oxides of metals M and of phosphorus according to the invention can also be in dry form (powder, flakes, plates), as a dispersion or as a liquid suspension or as an aerosol. The particle(s) according to the invention can be used as is or mixed with other ingredients.

Preferably, the compositions of the invention contain between 0.1% and 40% by weight of coated particles of oxides of metals M and of phosphorus according to the invention, more preferentially between 0.5% and 20% by weight, more preferentially still between 1% and 10% by weight and better still between 1.5% and 5% by weight, with respect to the total weight of the composition.

The compositions of the invention can be used in single application or in multiple application. When the compositions of the invention are intended for a multiple application, the content of coated particles of oxides of metals M and of phosphorus of the invention is generally lower than in the compositions intended for a single application.

Within the meaning of the present invention, the term "single application" is understood to mean just one application of the composition, it being possible for this application to be repeated several times per day, each application being separated from the next by one or more hours, or an application once each day, depending on the need.

Within the meaning of the present invention, the term “multiple application” is understood to mean an application of the composition repeated several times, in general from 2 to 5 times, each application being separated from the next by a few seconds to a few minutes. Each multiple application can be repeated several times per day, separated from the next by one or more hours, or each day, depending on the need.

Another subject-matter of the invention is the cosmetic and/or pharmaceutical use of at least one particle as described above.

More particularly, the invention also relates to the use of at least one particle as described above in the dyeing and/or making up of keratin materials, in particular of the skin and more particularly of the face. The invention also relates to the use of at least one particle as described above in protecting the skin against visible and/or ultraviolet radiation, for example by application(s) of at least one particle to the skin.

In other words, the invention also relates to a particle as described above for its use in protecting the skin against visible and/or ultraviolet radiation.

The following examples serve to illustrate the invention without, however, exhibiting a limiting nature.

Examples

Example 1:

1.1 In a first step, a composition (A) was prepared from copper nitrate (200 mM), triphenylphosphine (200 mM) and the mixture of combustible solvents: 30% by volume of 2-ethylhexanoic acid (EHA), 30% by volume of toluene, 20% by volume of absolute ethanol and 20% by volume of diethylene glycol monobutyl ether, with respect to the total volume of the mixture of combustible solvents.

Non-coated particles of oxide of copper and of phosphorus Pl were subsequently prepared using a conventional FSP preparation process Prep 1 with the preprepared composition (A) (outside the invention).

Then particles of oxide of copper and of phosphorus coated with silicon dioxide P2 were subsequently prepared using the preparation process Prep 2 according to the invention with the same composition (A) and a gaseous composition (B) comprising hexadimethyldisiloxane and nitrogen, in a proportion such that the Cu/Si _pa rticie molar atomic ratio = 0.48 (invention).

The parameters of the Prep 1 process are as follows:

- ratio (composition (A)/O2) = 3 ml/min of composition (A) and 2 1/min of gas (O2) + 3 l/min of methane. A cp = 0.82 is used to regulate the oxygen flow rate.

The parameters of the Prep 2 process are as follows:

- ratio (composition (A)/O2) = 3 ml/min of composition (A) and 2 1/min of gas (O2) + 3 1/min of methane. A cp = 0.82 is used to regulate the oxygen flow rate; - hexadimethyldisiloxane is injected into the second chamber of the FSP device by means of a 3 1/min nitrogen stream (composition (B)).

1.2 Once the particles had been prepared, it was observed that the particles of oxide of copper and of phosphorus obtained were crystalline.

Furthermore, the particles P2 obtained according to the process Prep 2 according to the invention are red in colour, are coated with an upper layer of silicon dioxide with a thickness of approximately 7 nm and exhibit a (Cu/Si) _pa rticie atomic ratio of 0.48.

The BET specific surface of the particles according to the process Prep 2 is 38 m ² /g.

The particles according to process Prep 2 have a number- average diameter equal to 25 nm.

1.3 The colorimetric data of the particles Pl and P2 were measured in the CIELab system with a Data Color SF600X spectrophotometer (illuminant D65, angle 10° and specular component included). In this L* a* b* system, L* represents the lightness, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis. The higher the value of L*, the lighter or less intense the colour. Conversely, the lower the value of L*, the darker or more intense the colour. The higher the value of a*, the redder the shade, and the higher the value of b*, the yellower the shade.

The results are collated in the table below:

Table 1

It was observed that the red colour of the particles of oxide of copper and of phosphorus according to the process Prep 2 (invention) is much more intense than the pale green colour of the particles of oxide of copper and of phosphorus according to the process Prep 1 (outside the invention). It was also observed, after storage in the open air and at ambient temperature and ambient external light for 3 months, that the colour of the particles of oxide of copper and of phosphorus P2 according to the process Prep 2 (invention) did not vary over time, which is a significant performance quality for a red pigment.

This is because red pigments are usually produced by combination of an inorganic base (silica, titanium) with an organic dye (DC Red 7, for example). In point of fact, the weakness of the organic dye, in particular to external light, leads the colour to change over time and to lose its red chromaticity.

Example 2:

Particles of oxide of copper and of phosphorus coated with silicon dioxide P3 and P4 were subsequently prepared according to the same preparation process Prep 2 (invention) as in Example 1, with the sole difference that the proportions of the compositions are such that the Cu/Si _pa rtide molar atomic ratios are respectively 0.78 for the particles P3 and 1.75 for the particles P4.

The particles P3 obtained according to the process Prep 2 according to the invention are pink in colour, are coated with an upper layer of silicon dioxide with a thickness of approximately 5 nm and exhibit a (Cu/Si) _pa rticie atomic ratio of 0.78.

The particles P3 have a BET specific surface of 42 m ² /g and a number- average diameter equal to 22 nm.

The particles P4 obtained according to the process Prep 2 according to the invention are very pale pink in colour, are coated with an upper layer of silicon dioxide with a thickness of approximately 2.4 nm and exhibit a (Cu/Si) _pa rticie atomic ratio of 1.75.

The particles P4 have a BET specific surface of 42 m ² /g and a number- average diameter equal to 18 nm.

The colorimetric data of the particles P3 and P4 were also measured in the CIELab system.

The results are collated in the table below: Table 2

It was observed that the colour of the particles of oxide of copper and of phosphorus P3 and P4 according to the process Prep 2 (invention) retains an appropriate chromaticity while being lighter than that of the particles P2 according to the process Prep 2 (invention).

It was also observed, after storage in the open air and at ambient temperature and ambient external light for 3 months, that the colour of the particles of oxide of copper and of phosphorus P3 and P4 according to the process Prep 2 (invention) did not vary over time, which is a significant performance quality for a pink pigment.

This is because pink pigments are usually produced by combination of an inorganic base (silica, titanium) with an organic dye (DC Red 7, for example) to which doses of a white pigment (typically TiCh) are added. In point of fact, the weakness of the organic dye to external light, relative to the robustness of the inorganic compounds, leads the colour to change over time and to lose its pink chromaticity.

Example 3:

The goal is to obtain pigments with a colour close to that of a flesh tint. The aim is to be able to produce a make-up product with just one type of pigment, this being the case in order to avoid the problems which may occur when two or more pigments of different colours are combined. In particular, it is desired to approach as best as possible the colour target while reducing the risk of inaccuracy in the production of the make-up product and/or of a possible selective separation in the make-up product.

In this example, it was estimated, by graphical interpolation, that the Cu/Si _pa rticie molar atomic ratio of a particle of oxide of copper and of phosphorus coated with silicon dioxide had to be 1.05, in order to obtain a colour close to that of a flesh tint. Particles of oxide of copper and of phosphorus coated with silicon dioxide P5 were then prepared according to the same preparation process Prep 2 (invention) as in Example 1, with the sole difference that the proportions of the compositions are such that the Cu/Siparticie molar atomic ratio is 1.05.

The particles P5 obtained according to the process Prep 2 according to the invention have the desired flesh pink colour.

The particles P5 are coated with an upper layer of silicon dioxide with a thickness of approximately 3.8 nm and exhibit a (Cu/Si) _pa rticie atomic ratio of 1.05.

The particles P5 have a BET specific surface of 40 m ² /g and a number- average diameter equal to 23 nm.

The colorimetric data of the particles P5 were also measured in the CIELab system.

The results are collated in the table below:

Table 3

Example 4:

The cosmetic make-up compositions C2 to C5 were prepared by respectively mixing 10% by weight, with respect to the total weight of the composition, of particles of oxide of copper and of phosphorus coated with silicon dioxide P2 to P5 in a cosmetic base suitable for making up the face.

Each composition was subsequently applied, independently of one another, to a light skin of Caucasian type at a content of 1 mg/cm ² .

It was observed that:

- the composition C2 based on particles P2 modifies the natural colour of the skin towards pink - “rosy cheek effect”;

- the compositions C3 and C4 respectively based on particles P3 and P4 slightly lighten the natural colour of the skin; - the composition C5 based on particles P5 makes it possible to conceal the imperfections of the skin (dyschromia), without the result leaving it to be thought that the skin has been covered with a cosmetic composition.

Example 5:

An aqueous composition C6 (invention) based on 10% by weight, with respect to the total weight of the composition, of particles of oxide of copper and of phosphorus coated with silicon dioxide P3 was prepared.

An aqueous composition C7 (outside the invention) containing a mixture of silica and of iron oxide, in proportions such that the colour of the aqueous composition C7 is similar to that of the aqueous composition C6, was prepared.

Directly after the preparation, the compositions C6 and C7 were applied a first time, one beside the other, to a light skin of Caucasian type at a content of 1 mg/cm ² .

The colours observed on the skin for the compositions C6 and C7 are similar.

After a time of 5 minutes at rest after the preparation, the compositions C6 and C7 were applied a second time, one beside the other, to a light skin of Caucasian type at a content of 1 mg/cm ² .

The colour observed on the skin for the composition C6 (invention) is identical to the colour observed after the 1st application.

Conversely, the colour observed on the skin for the composition C7 (outside the invention) is whiter, in comparison with the colour observed after the 1st application.

It is thus apparent that the composition C6 according to the invention makes it possible to obtain a colour on the skin which is much more stable than that of the comparative composition C7 (outside the invention).