Zinc sulfide interference pigments, synthesis methods and cosmetic compositions

Abstract

The present invention relates to interference pigments comprising layers of zinc sulfide-based materials. The pigments advantageously comprise a low refractive index core and at least one high refractive index layer comprising zinc sulfide. The present invention also proposes a method for synthesizing these pigments by heterogeneous precipitation of zinc sulfide onto a powdery support, which is achieved by adding a zinc salt solution to a reaction medium containing a dispersion of the powdery support and titrating a sodium sulfide solution at a certain pH. The present invention also relates to cosmetic compositions comprising these interference pigments but lacking titanium dioxide, which is typically introduced as a filler or by providing cosmetic ingredients containing titanium dioxide.

Description

[Technical Field]

[0001] The present invention relates to interference pigments comprising at least one zinc sulfide layer which may be free of titanium dioxide.

[0002] The present invention also relates to methods for synthesizing these pigments and to cosmetic compositions containing them, which themselves may contain no titanium dioxide or very small amounts. [Background technology]

[0003] Generally, white interference effect pigments are obtained by depositing a layer of a high refractive index material on the surface of translucent platelet-shaped particles of low refractive index mica, glass or alumina.

[0004] The most commonly used high index material is titanium dioxide, and there is still a need for alternative pigments that contain high refractive index materials to produce physical colors. Summary of the Invention

[0005] The present invention addresses this need and provides a zinc sulfide pigment, a compound that has the advantage of being suitable for a wide variety of industrial applications. The proposed pigment comprises a core coated with a thin layer of zinc sulfide.

[0006] In particular, the present invention provides interference pigments comprising a low refractive index core and at least one layer of a zinc sulfide compound of a thickness selected to produce a silvery-white or colored reflection by interference.

[0007] The present invention also proposes a method for the liquid deposition of submicron layers of zinc sulfide (ZnS) compounds onto micrometer substrates. The synthesis method advantageously follows a heterogeneous nucleation and homogeneous growth mechanism, resulting in the deposition of zinc sulfide layers whose chemical composition, crystallinity, crystallography, density, and thickness can be controlled. It is unexpected that a uniform zinc sulfide layer of controlled thickness, crystallinity, crystallography, and chemical composition can be successfully deposited on a powder substrate, such as mica, under mild chemical conditions and in a liquid process. This method allows for the production of zinc sulfide pigments using a process carried out in water at moderate temperatures and moderate pH.

[0008] The interference pigment of the present invention comprises a support and at least one layer of a material comprising high refractive index zinc sulfide.

[0009] According to a first variant, the pigment is a multilayer interference pigment lacking a layer containing titanium dioxide.

[0010] The pigment may contain titanium dioxide, but preferably contains less than 0.1% by weight based on the weight of the pigment.

[0011] The present invention advantageously makes it possible to partially or completely replace the titanium dioxide used in the manufacture of interference pigments and to provide cosmetic products with a low titanium dioxide content.

[0012] In a second variant of the invention, the pigment is a coherent single- or multi-layer pigment whose support comprises or consists of a gas such as air. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an elemental EDX map of a pigment according to the present invention. [Figure 2] 1 is a scanning electron microscope image of a pigment according to the present invention. [Figure 3] FIG. 1 is an X-ray diffraction diagram of a pigment according to the present invention. [Figure 4]1 is a transmission electron microscope image of a pigment according to the present invention including an outer protective layer of silica. [Figure 5] 1 shows a scanning electron microscopy characterization of the gypsum plate-like support used to prepare the hollow core of the pigment of the present invention. [Figure 6] 1 shows scanning electron microscopy characterization of gypsum platelets coated with a silica layer at two different magnifications. [Figure 7] 1 shows scanning electron microscopy characterization of gypsum platelets coated with a silica layer at two different magnifications. [Figure 8] Elemental characterization by EDX analysis of gypsum platelet powder coated with a silica layer. [Figure 9] 1 shows, at two different magnifications, the transmission electron microscopy characterization of a gypsum platelet coated with a layer of silica after dissolution. [Figure 10] 1 shows, at two different magnifications, the transmission electron microscopy characterization of a gypsum platelet coated with a layer of silica after dissolution. [Figure 11] 1 shows the characterization by scanning electron microscopy of a gypsum platelet coated with a layer of silica after dissolution at two different magnifications. [Figure 12] 1 shows the characterization by scanning electron microscopy of a gypsum platelet coated with a layer of silica after dissolution at two different magnifications. [Figure 13] Elemental characterization by EDX analysis of silica capsule powder after dissolution of gypsum. DETAILED DESCRIPTION OF THE INVENTION

[0014] A first object of the present invention relates to interference single- or multi-layer pigments comprising a core and at least one layer of a material comprising zinc sulfide.

[0015] The pigment of the present invention has a refractive index preferably in the range of 1.00 to 2.10 and may comprise a core coated with or bounded by at least one layer of a material comprising zinc sulfide.

[0016] The layer comprising zinc sulfide preferably has an average physical thickness in the range of 10 nm to 350 nm.

[0017] The average physical thickness of the layer of material comprising zinc sulfide can be, for example, in the range of 20 nm to 340 nm, 30 nm to 330 nm, 40 nm to 320 nm, 50 nm to 310 nm, 60 nm to 300 nm, 70 nm to 290 nm, 80 nm to 280 nm, 90 nm to 270 nm, 100 nm to 260 nm, or 110 nm to 250 nm. The physical thickness, also called optical thickness, can be measured by any method known to those skilled in the art.

[0018] The zinc sulfide may represent between 1% and 100% by weight of the pigment's weight, and the interference pigment of the present invention advantageously comprises between 1% and 70% by weight of zinc sulfide relative to the weight of the pigment, advantageously 15% to 65% by weight of the pigment, more advantageously 20% to 60% by weight, and even more preferably 25% to 55% by weight of the pigment.

[0019] In a particularly preferred embodiment, zinc sulfide accounts for 30% to 60% by mass, preferably 30% to 50% by mass, and more preferably 35% to 45% by mass of the mass of the pigment.

[0020] The pigment may be devoid of an interference layer containing titanium dioxide.

[0021] In a particularly advantageous embodiment of the invention, the entire composition of the interference pigment of the invention, including the core and the layer of material comprising zinc sulfide, is free of titanium dioxide, in the sense that it comprises less than 10% by weight, preferably less than 5% by weight, or even less than 1% by weight, relative to the weight of the interference pigment of the invention.

[0022] The interference pigments of the invention are advantageously powders consisting of particles each comprising a core coated with at least one layer of a material comprising zinc sulfide.

[0023] That size is advantageously the number-average size of the population of particles, equal to the D50 of the population of particles constituting the pigment, in the case of the present invention, the value of D50 being calculated from the particle size distribution obtained by conventional methods such as laser diffraction or image analysis obtained by scanning electron microscopy (SEM) or transmission electron microscopy (TEM).

[0024] Thus, the pigment may have a dimension that can be defined as D50 in the range of 1 micron to 2000 microns, preferably in the range of 10 microns to 500 microns, while the core may have a dimension in the range of 1 micron to 2000 microns, preferably in the range of 10 microns to 500 microns.

[0025] The pigments of the present invention are interference pigments that can be colored or white. They can also generate one or more reflections of different colors, and the color of the reflections can be different from the color of the pigment itself. Thus, the reflections can be silvery-white or another color. In the cosmetic field, for example, white mother-of-pearl with silvery-white reflections, white mother-of-pearl with colored reflections, colored mother-of-pearl with silvery-white reflections, and colored mother-of-pearl with colored reflections are distinguished. These reflections can produce pearlescent and / or iridescent effects during the transmission and reflection of light through them, caused by the phenomenon of optical interference. The interference colors generated result from the enhancement or destruction of reflected light rays according to specific wavelengths. A layer of a material containing zinc sulfide deposited on a substrate with a lower refractive index can generate destructive and constructive waves that themselves generate color. Destructive interference of a given wavelength occurs when the reflections from the two surfaces, air / material and material / substrate, are completely out of phase. For example, minimum reflection occurs for light incident perpendicular to wavelength λ in a layer of material containing zinc sulfide with refractive index N and thickness e when N*e=(n-1)*λ / 2, where n is an integer. When the layer of material is illuminated with white light, all wavelengths except λ appear in the reflection. Enhancement of a given wavelength occurs when the reflections from the two surfaces of the layer of material containing zinc sulfide are in phase with each other. Thus, for light incident perpendicular to the free surface of the layer, this occurs when N*e=(2n-1)*λ / 4.

[0026] The layer of material comprising zinc sulfide is preferably an interference layer. For the purposes of the present invention, the term "interference layer" means a layer of material whose optical thickness is capable of producing an optical color when deposited on a given support or on a layer of another material.

[0027] The zinc sulfide-containing material preferably consists essentially of zinc sulfide. By "consisting essentially of zinc sulfide" we mean a material that contains more than 50% by weight of zinc sulfide relative to the weight of the material.

[0028] In one embodiment, the zinc sulfide-containing material consists essentially of zinc sulfide.

[0029] The term "consisting essentially of zinc sulfide" means a material which comprises at least 90% by weight of zinc sulfide, preferably at least 99% by weight of zinc sulfide, relative to the weight of said material.

[0030] A material containing zinc sulfide is a material that forms a solid solution of zinc sulfide, i.e., a single crystalline phase containing zinc sulfide. A person skilled in the art can characterize the crystalline phase number of a material, for example, by X-ray diffraction.

[0031] The material comprising zinc sulfide may be what is called "doped" zinc sulfide, i.e., a material consisting essentially of zinc sulfide and at least one chemical element, the chemical element preferably being in the form of a metal ion.

[0032] Thus, in another embodiment, the sulfide-containing material is a mixture of zinc sulfide and Fe 2+ , Cu 2+ , Mn 2+ , Ag + , Au 3+ ,EU 3+ , Al 3+ , Ce 3+ and In 3+ and at least one metal ion selected from the group consisting of:

[0033] "Consisting essentially of zinc sulfide and at least one metal ion" means a material comprising a mixture of zinc sulfide and metal ions in an amount of at least 90% by weight, preferably at least 99% by weight, relative to the weight of the material. In this embodiment, the chemical element, preferably the metal ion, is advantageously present in an amount such that it forms a solid solution with zinc sulfide, i.e. a single crystalline phase.

[0034] The layer of material containing zinc sulfide preferably has a refractive index in the range of 2.30 to 2.90, for example, 2.35 to 2.80, 2.40 to 2.70, 2.45 to 2.65, or 2.50 to 2.50. The refractive index of the layer of material containing zinc sulfide is preferably close to 2.40.

[0035] The pigment of the present invention may also include an outer protective layer. This outer protective layer is advantageously transparent and does not have a coloring function, and therefore is different from the interference layer containing zinc sulfide material. The outer protective layer may be obtained by surface treatment with a compound that performs the intended function. The protective layer may, for example, facilitate the formulation of the pigment in solvents or oils or provide protection from ultraviolet light.

[0036] The outer protective layer may be organic or mineral in nature, and may be hydrophilic or hydrophobic in nature, for example an inorganic layer such as silica or ceria, or a polymer such as PMMA, polystyrene or polyvinyl chloride.

[0037] The pigments of the present invention can advantageously be subjected to a hydrophobic treatment to facilitate the dispersion of said pigments in a fatty phase, for example an oily phase. Such treatment aims to apply a hydrophobic surface agent to all or part of the pigment surface. Such a surface agent can advantageously be selected from amino acids, metal soaps, esters, silicone or fluorinated compounds, acrylic compounds, or lipids, or a mixture of at least two of these compounds.

[0038] The amino acid surfactant may be, for example, an acylated amino acid derivative containing glycine, alanine, sarcosine, proline, hydroxyproline, aspartic acid, glutamic acid, or lysine, or a saturated or unsaturated fatty acid containing, for example, 1 to 22 carbon atoms, preferably 8 to 20 carbon atoms. Such an acylated amino acid surfactant may be, for example, stearoyl glutamic acid, lauroyl glutamic acid, lauroyl aspartic acid, myristoyl glutamic acid, stearoyl lysine, lauroyl lysine, myristoyl lysine, and palmitoyl proline, or a salt thereof, such as a sodium, potassium, calcium, magnesium, or aluminum salt. Particularly preferred salt forms are sodium myristoyl glutamate, disodium stearoyl glutamate, sodium lauroyl aspartate, dilauramidoglutamide lysine, sodium palmitoyl sarcosine, magnesium palmitoyl glutamate, and disodium cocoyl glutamate.

[0039] As surfactants of the metallic soap type, aluminum myristate and magnesium stearate may be advantageously mentioned.

[0040] As ester surfactants, mention may be made advantageously of isostearyl sebacate, dextrin and fatty acid esters such as dextrin stearate, dextrin isostearate, dextrin palmitate or polyglyceryl-2 tetraisostearate.

[0041] Advantageously, silicone surfactants that may be mentioned include methicone, hydrogen dimethicone, dimethicone, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, octadecyltriethoxysilane, and hexadecyltriethoxysilane.

[0042] As fluorinated surfactants, mention may be made advantageously of perfluorohexylethyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane or tridecafluorooctyltriethoxysilane.

[0043] Acrylic surfactants may include (co)polymers containing ethyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, oleyl (meth)acrylate or linoleyl (meth)acrylate groups.

[0044] Examples of lipid surfactants include phospholipids, lecithin, triglycerides, fats, oils, and waxes, and such agents are preferably of natural origin. The outer protective layer may also contain a UV-blocking material such as cerium-doped silica. The UV protective layer has the advantage of stabilizing the color and / or reflectance of the pigment over time, particularly throughout the use period of the formulation and manufactured product containing the pigment.

[0045] The pigments of the present invention may be single layered, in the sense of comprising a single layer coating a core, or may be multilayered.

[0046] According to a first embodiment, the pigment is a monolayer pigment comprising a single layer of a material containing zinc sulfide. "Monolayer" refers to a layer of uniform composition that can be applied in one or more manufacturing process steps, preferably in a single step. Alternatively, the pigment of the present invention may be multilayered, i.e., comprise at least two layers of different compositions, including at least one layer of a material containing zinc sulfide and one layer free of zinc sulfide. Preferably, the core does not comprise several layers of different materials, and its composition is uniform.

[0047] The pigments of the present invention may comprise one or more layers of material comprising zinc sulfide, regardless of the number of layers of different materials that may coat the core.

[0048] The pigment may, for example, comprise two layers of a material containing zinc sulfide: a first layer of the above-mentioned zinc sulfide and a second layer of doped zinc sulfide, separated from each other by an intermediate layer of low refractive index, for example comprising silica.

[0049] In addition to the material containing zinc sulfide, the pigment may also contain at least one material having a refractive index in the range of 2.30 to 2.90, such as a material selected from the group consisting of Fe2O3, FeTiO3, Cr2O3 and / or Fe3O4. This material may be part of the composition of the material of the zinc sulfide layer or may be in the form of a layer separate from the zinc layer. Thus, the layer containing zinc sulfide may also contain, in addition to zinc sulfide, at least one material having a refractive index in the range of 2.30 to 2.90. According to a variant, the pigment comprises a first layer of zinc sulfide coated on and in contact with a second layer of a material different from zinc sulfide, the second layer having a refractive index in the range of 2.30 to 2.90.

[0050] In a second particular embodiment of the present invention, the interference pigment is multilayered and comprises at least one alternation of a first layer of a material comprising zinc sulfide having a refractive index in the range of 2.30 to 2.90 and a second layer adjacent to the first of a material having a refractive index in the range of 1.00 to 2.10, the difference in refractive index between said first layer and said second adjacent layer being greater than or equal to 0.3, preferably in the range of 0.3 to 1.5, more preferably around 1.3.

[0051] As used herein, "on the order of" or "close to" means a value equal to plus or minus 10% of a given numerical value, or a value taking into account measurement uncertainty.

[0052] The refractive index of the layer of material ranges from 1.00 to 2.10, preferably from 1.00 to 1.60.

[0053] In the interference pigments of the present invention, the layer of material comprising zinc sulfide may be coated on one of its surfaces with a continuous or semi-continuous layer of metal nanoparticles, such as gold, silver or copper nanoparticles, the nanoparticles having at least one average dimension of, for example, 500 nm or less, preferably 100 nm or less.

[0054] The addition of metal nanoparticles can produce a black background and more or less significant color channels in the mother-of-pearl. The metal nanoparticles can be nanoparticles of precious metals, such as gold or silver, or copper or chromium, preferably deposited semi-continuously. Depending on the amount of precious metal deposited in the final layer of a pigment with a high refractive index, such as ZnS, or a low refractive index, such as silica, a black background can be produced, which allows particularly reflective white mother-of-pearl to have a core color close to their reflective color depending on the amount of nanoparticles deposited. Reflective white mother-of-pearl becomes colored mother-of-pearl with a colored reflection. Furthermore, the addition of nanoparticles with absorption in visible light can more or less change the reflective and transmitted color of the mother-of-pearl.

[0055] A layer of silicon dioxide, ranging in thickness from 1 nm to 1 micron, can be inserted between the core and the zinc sulfide layer, and can be in contact with both. It can also be post-treated to create porosity within the silica layer.

[0056] The multilayer interference pigment of the present invention can comprise a stack of several layers, including at least one layer comprising zinc sulfide having a refractive index in the range of 2.30 to 2.90, at least one layer of a material having a refractive index in the range of 1.00 to 2.10, and at least one layer of a material not comprising zinc sulfide and having a refractive index in the range of 2.30 to 2.90, the order and thicknesses of the different layers being selected to produce a colored reflection.

[0057] The pigments of the present invention can be synthesized by physical or chemical deposition of zinc sulfide onto a solid support.

[0058] In the case of physical deposition, a layer of material comprising zinc sulfide can be deposited on a solid support by atomic layer deposition.

[0059] In the case of chemical deposition, the pigment can be obtained by heterogeneously precipitating zinc sulfide on a support from a zinc salt solution and a sodium sulfide solution. Alternatively, it can be synthesized by bubbling gaseous HS in the presence of the support, or by thermal decomposition of a sulfur precursor as an alternative to sodium sulfide. For example, a translucent powder support such as mica is used, but any type of support is suitable, such as one of the solid substrates previously described in the context of the description of the pigment of the present invention.

[0060] Another method for synthesizing the pigment of the present invention uses the homogeneous precipitation method. This synthesis method involves slowly releasing one of the sulfur-containing reactants by increasing the temperature during the reaction. The released reactant is uniformly distributed throughout the solution volume, which allows a low, uniform supersaturation to be maintained over time. This allows for the controlled production of a zinc sulfide layer on a solid support. In this method, a suspension of solid particles is mixed with a zinc salt and a precipitating agent that is inert at room temperature. The precipitating agent produces hydrogen sulfide by thermal decomposition, such as thioacetamide, using water as the reaction solvent, or thiourea, preferentially using heavy alcohols such as polyols as the solvent.

[0061] In one embodiment, heterogeneous precipitation of zinc sulfide can be carried out by titrating a sodium sulfide solution at a fixed pH in a reaction medium containing solid particles and a zinc salt solution in a dilution medium. The sodium sulfide solution is added continuously, its amount being adjusted by a titrator according to a pH fixed at the start. The goal is to always maintain a low supersaturation condition that allows for the heterogeneous generation of zinc sulfide on the solid particles and the formation of a continuous, uniform layer of zinc sulfide on their surfaces. The titrator containing the sodium sulfide solution is used to compensate for the decrease in pH during the addition of the zinc salt solution by maintaining a predetermined fixed pH, referred to as the fixed pH. The fixed pH is selected to form a continuous, uniform, and compact layer of zinc sulfide of controlled thickness on the solid particles. Depending on the amount of zinc salt added, the thickness of the zinc sulfide layer increases until it reaches the optimal physical thickness condition for producing interference colors.

[0062] A second object of the present invention relates to a method for synthesizing pigments, such as interference pigments, consisting of the heterogeneous precipitation of a zinc sulfide-containing material onto solid particles. The zinc sulfide-containing material may be zinc sulfide, as described above, or a solid solution of zinc sulfide with a metal ion.

[0063] This method is a first step of preparing an aqueous dispersion of solid particles having a pH in the range of 2 to 8 and a temperature close to the boiling point, wherein the dispersion has a pH in the range of 2 to 8 and a temperature close to the boiling point; a second step of coating the solid particles, comprising the addition to said aqueous dispersion of an aqueous solution of a zinc salt, such as zinc nitrate, and of sodium sulfide, the pH of the resulting reaction medium being maintained between 2 and 7 to obtain a suspension of particles coated with a material comprising zinc sulfide; may include:

[0064] The uniformity of the zinc sulfide layer deposited on the surface of the particles can be controlled by different physicochemical parameters such as temperature, concentration and pH of the salt solution.

[0065] The concentration of the solid particle dispersion prepared in the first step is, for example, 1 g / L to 20 g / L or 5 g / L to 15 g / L.

[0066] The second step is a coating step of solid particles, which is preferably carried out while stirring the reaction medium. The temperature of the reaction medium during the coating step can be in the range of 20°C to 100°C, preferably 60°C to 90°C.

[0067] The solid particles may be selected from natural mica, synthetic mica, alkaline earth carbonates such as calcium carbonate, alkaline earth sulfates such as barium sulfate, natural pearls such as guanine or hypoxanthine, alumina, aluminum, silica, borosilicate, perlite, organic polymers (e.g., plastics), and metal oxides such as zinc oxide or bismuth oxychloride. Their size may range from 1 micron to 2000 microns, preferably 10 microns to 500 microns. The size is defined in the same way as the size of the substrate described above in the context of the first object of the present invention and can be measured by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). The particles are preferably plate-like, but may also have any other shape.

[0068] The aqueous zinc salt solution is preferably diluted to acidify it. Its concentration may be in the range of 0.001 M to 10 M or 0.01 M to 0.1 M, and its addition rate to the aqueous dispersion of solid particles may be in the range of 0.001 mL / min to 10 mL / min or 0.1 mL / min to 1 mL / min. Zinc nitrate is preferred as the zinc salt.

[0069] The aqueous sodium sulfide solution is a dilute solution that can have a concentration of 0.5 M to 3 M. The pH of the reaction medium is preferably maintained at 2 to 7 throughout the synthesis by controlled addition of dilute sodium sulfide solution.

[0070] The method of the present invention may include a third step which is a washing and drying step which consists of centrifuging the suspension of zinc sulfide coated particles, redispersing the particles in ethanol, and then drying at a temperature in the range of 20°C to 80°C for 12 to 24 hours.

[0071] Annealing the zinc sulfide-coated particles may be necessary to densify the zinc sulfide layer and enhance the color of the interference pigment. Therefore, the method of the present invention may include a step of subjecting the zinc sulfide-coated particles obtained at the end of the third coating step or the fourth washing and drying step to heat treatment. The zinc sulfide-coated particles may be placed under air or argon at a temperature that can reach the thermal decomposition temperature of ZnS. The synthesis method of the present invention may also include a step of coating the zinc sulfide-coated particles with an organic or mineral matrix to form a protective layer. This is interchangeably referred to as coating or encapsulation.

[0072] If this encapsulation step consists of coating with silica, it can be carried out by the sol-gel method known to those skilled in the art. According to a variant of this method, dried zinc sulfide-coated particles are dispersed in a citric acid solution at a basic pH. This solution is poured into a water-ethanol reaction medium (e.g., 25 / 75 v / v). A silica precursor, such as tetraethyl orthosilicate (abbreviated as TEOS), is then added to the mixture, and the solution is left stirring at room temperature for 24 hours. The suspension is then centrifuged, washed with ethanol, and then dried in an oven at 80°C for 24 hours.

[0073] Finally, the synthesis method of the present invention can include a step of completely or partially removing the core of the support consisting of solid particles to obtain a solid porous core or gas core. Once a layer of material containing zinc sulfide is deposited on the solid particles at the end of the second step, core removal can be carried out by chemical or physical means. For example, it is possible to use calcium carbonate particles, coat them with zinc sulfide, and then dissolve the calcium carbonate with acid without damaging the structure of the layer of material containing zinc sulfide.

[0074] The pigment core preferably has a refractive index of 2.20 or less, preferably in the range of 1.00 to 2.10, and is composed of one or more materials each having a refractive index of 2.20 or less, preferably in the range of 1.00 to 2.10, and the refractive index may be measured by any method known to those skilled in the art.

[0075] The chemical nature of the pigment core can vary. The core can be a gas, such as air, a solid substrate, which can be porous or non-porous, or it can contain both gas and solid. A solid substrate is, for example, a plate-like substrate used as a support for depositing thin layers of material. Cores containing or consisting of gas can be produced by chemical or thermal decomposition of a solid substrate.

[0076] When the core is a porous substrate, when the core is gaseous, or when the core comprises both gas and solid, the interference pigment of the present invention can be obtained by depositing a layer of a material comprising zinc sulfide on a solid support, which is subjected to a dissolution or pyrolysis treatment to obtain the gaseous core or the gas-containing core.

[0077] In a first embodiment, the core of the pigment of the present invention is a solid substrate. This substrate may have different forms, for example, in the form of plates or beads. If the substrate is a plate-based substrate, the dimensions of the substrate are, for example, the average length of a group of plates, the length being the largest dimension of the plates. The substrate can also be defined by its thickness, which can represent the average thickness of the group.

[0078] The solid substrate can be transparent or translucent, yielding mother of pearl, or opaque, yielding interference pigments with metallic effects.

[0079] In certain embodiments, a transparent or translucent substrate is used.

[0080] The solid substrate may advantageously be chosen from natural mica, synthetic mica, alkaline earth carbonates such as calcium carbonate, alkaline earth sulfates such as barium sulfate, natural pearls such as guanine or hypoxanthine, alumina, aluminum, silica, borosilicates, perlite, organic polymers (such as plastics), and metal oxides such as zinc oxide or bismuth oxychloride. The substrate may consist essentially of one or more of these materials, without excluding the possible presence of impurities.

[0081] The core of the interference pigment of the present invention is preferably free of zinc sulfide, although it may nevertheless contain zinc sulfide as an impurity, for example in an amount of less than 0.1% by weight of the weight of the core.

[0082] In this first embodiment, the pigment of the present invention comprises at least: a first layer of a material comprising zinc sulfide having a refractive index in the range of -2.30 to 2.90; a second layer adjacent to the first of a material having a refractive index in the range of −1.00 to 2.10; a third layer adjacent to the second and made of a material containing zinc sulfide having a refractive index in the range of 2.30 to 2.90, the difference in refractive index between the two adjacent layers being greater than or equal to 0.3, preferably in the range of 0.3 to 1.5, and the third layer being devoid of a layer whose pigment contains titanium dioxide; The pigment may also be a multilayer interference pigment comprising a transparent or translucent platelet-like substrate coated with at least one stack comprising:

[0083] The plate-like substrate is coated with at least one stack in the sense that it can be coated with one or more stacks, and each stack can include additional layers of other materials in addition to the first, second and third layers.

[0084] In a particular stack, the third layer contacts and covers the second layer, and the second layer contacts and covers the first layer.

[0085] The features mentioned above in the context of the description of the pigments of the invention apply to the first variant embodiment.

[0086] The first layer may be colorless, meaning that it does not absorb wavelengths in the visible range, and the second layer may also be colorless.

[0087] In a second embodiment of the present invention, the core of the pigment of the present invention can comprise or consist of a gas, such as air, so that the pigment is in the form of a particle called a "core-shell" particle, the core of which is hollow and the shell of which comprises at least one interference layer of a material comprising zinc sulfide. As explained above, such a core can be obtained from a solid support that has been partially or totally removed by physical or chemical means after application of a shell consisting of layers applied to the support.

[0088] According to this variant, the pigment of the invention is an interference single-layer or multi-layer pigment comprising a platelet-shaped core coated with at least a first layer of a material comprising zinc sulfide, the support having a refractive index in the range of 1.00 to 2.10, characterized in that the support comprises or consists of a gas such as air.

[0089] The first layer may have an average thickness ranging from 10 nm to 350 nm, and the average thickness value may be equal to any of the values ​​defined above.

[0090] The support advantageously has a refractive index in the range of 1.00 to 1.40. It may be in the form of a capsule of a solid material other than zinc sulfide. The term "capsule" means an object whose interior is hollow or porous and whose exterior is a layer of solid material. The material is preferably selected from transparent or translucent materials that are resistant to attack by acids and / or bases, such as, for example, SiO2, Al2O3, ZrO2.

[0091] In a particular embodiment, the core is a silica capsule. The thickness of the silica layer is, for example, in the range of 1 nm to 100 nm.

[0092] The capsules can have larger dimensions ranging from 1 micron to 1000 microns.

[0093] The first layer of material comprising zinc sulfide covers the surface of the capsule, in the sense that it is in contact with the layer of solid material, and may coat the entire surface.

[0094] In another embodiment, the core is composed of a gas and the pigment comprises a gas core, which may be bounded by a first layer of a material comprising zinc sulfide or by a layer of another material having a high refractive index.

[0095] The pigment of the second variant of the invention may be a single-layer pigment comprising a single layer of a material comprising zinc sulfide, or a multi-layer pigment comprising a first layer of a material comprising zinc sulfide, at least one layer of a material having a refractive index in the range of 1.00 to 2.10, and at least one second layer of a material comprising zinc sulfide. The difference in refractive index between the first layer of material comprising zinc sulfide and the layer of material having a refractive index in the range of 1.00 to 2.10 is preferably 0.80 or more.

[0096] Advantageously, the pigment is devoid of a layer containing titanium dioxide, which layer may or may not be coherent. In a preferred embodiment, the pigment comprises titanium dioxide in an amount of less than 0.1% by weight of the pigment.

[0097] As mentioned above, the zinc sulfide-containing material may be a material consisting essentially of zinc sulfide or a material consisting essentially of zinc sulfide and Fe. 2+ , Cu 2+ , Mn 2+ , Ag + , Au 3+ ,EU 3+ , Al 3+ , Ce 3+ and In 3+ and at least one metal ion selected from the group consisting of: The layer of material comprising zinc sulfide may be further coated on one of its surfaces with a continuous or semi-continuous layer of metal nanoparticles, such as gold, silver or copper nanoparticles.

[0098] The pigments of the second variant of the invention may also comprise an outer protective layer which may be of organic or mineral nature and of hydrophilic or hydrophobic nature. Examples of suitable outer protective layers have been mentioned above.

[0099] The method for synthesizing the interference pigment of the second variant of the invention comprises: a first step of preparing an aqueous dispersion of core particles having a pH in the range of 2 to 8 and a temperature close to the boiling point, wherein the dispersion has a pH in the range of 2 to 8 and a temperature close to the boiling point; a second step of coating the core particles, comprising the addition to said aqueous dispersion of an aqueous solution of a zinc salt, such as zinc nitrate, and of sodium sulfide, the pH of the resulting reaction medium being maintained between 2 and 7 to obtain a suspension of solid particles coated with a material comprising zinc sulfide; Includes.

[0100] The characteristics given above to explain the second object of the invention can be applied to the process for synthesizing the pigment of the second variant of the invention.

[0101] Pigments with gas in the core provide better color saturation and brightness compared to prior art pigments.

[0102] When the core is a capsule, in particular a silica capsule, the method of the present invention may comprise a step of synthesizing the capsule, which may comprise a step of coating an organic or inorganic support with a layer of material to obtain a coated support, the coating step being followed by a step of treating the coated support with the aim of removing all or part of the material that constitutes the support.

[0103] Treating the coated substrate can be accomplished by placing it in the presence of an aqueous acid or base solution.

[0104] The coated substrate may also, or alternatively, be subjected to a heat treatment by increasing the temperature.

[0105] In a first embodiment, a layer of an acid-insoluble metal oxide, preferably in the form of plate-like inorganic particles, is deposited on the surface of an acid-soluble support.

[0106] The support may be in plate-like form and may be made of an inorganic material, for example, a material selected from magnesium hydroxide, copper hydroxide, iron hydroxide, zinc oxide, calcium sulfate (such as gypsum), phyllosilicates (such as mica), and borosilicates.

[0107] The metal oxide is selected from, for example, SiO2, Al2O3, ZrO2 and SnO2. The metal oxide can be deposited on the support by any method known to those skilled in the art.

[0108] Treatment of the coated substrate may involve one or more treatment steps in aqueous solution.

[0109] For example, the coated support may be placed in an aqueous acidic solution to completely or partially attack and / or dissolve the support without dissolving the metal oxide layer. The aqueous acidic solution is preferably an aqueous solution of a mineral acid selected from hydrofluoric acid, phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid, and mixtures thereof.

[0110] The coated support may be subjected successively to one or more steps of treatment in an acidic medium, washing to remove ions resulting from the dissolution of the inorganic support, optionally followed by treatment in a basic medium.

[0111] Treatment in aqueous solution can be carried out at a temperature ranging from 20° C. to 100° C. for a period ranging from 1 hour to 24 hours.

[0112] In a second embodiment, the pigment comprises a core consisting of a gas.

[0113] Such pigments can be produced, for example, by depositing a layer of metal oxide or zinc sulfide on micron-sized graphite platelets, then calcining the coated graphite platelets to remove the graphite and yield metal oxide or zinc sulfide capsules, depending on the material deposited on the graphite particles.

[0114] Pigments containing a gas core can also be obtained by depositing a layer of zinc sulfide on a substrate that can be chemically solubilized, following the capsule synthesis method described above.

[0115] Examples of pigments of the present invention include the following stack of layers, where the diagonal lines indicate the separation between two different layers and the brackets indicate a single layer containing several materials: Core / ZnS Core / ZnS / Low index material / ZnS The triple stack of core / ZnS / low index material / ZnS, ZnS / low index / ZnS layers can be repeated several times in succession Metal ion doped core / ZnS Core / SiO2 / ZnS Core / SiO2 / ZnS / Low index material / ZnS Core / ZnS / ZnS different high index material Core / (ZnS + high index material different from ZnS) Core / ZnS / metal ion doped ZnS Core / (ZnS + ZnS doped with metal ions) Core: High index material different from ZnS: ZnS Core / High index material different from ZnS / Low index material / ZnS

[0116] In these examples, the high-index material other than ZnS has a refractive index in the range of 2.30 to 2.90, and may be, for example, Fe2O3, FeTiO3, Cr2O3, or Fe3O4, while the low-index material preferably has a refractive index in the range of 1.00 to 1.60. The described stacks may be coated with a continuous or semi-continuous layer of metal nanoparticles, such as gold, copper, or silver nanoparticles, or may be coated with a non-interfering protective layer. In these examples, a silica protective layer can be applied to the last layer of the stack. The core may be a gas or a capsule whose outer portion is a metal oxide, such as SiO2.

[0117] According to a particular embodiment, the pigment of the present invention is different from pigments comprising zinc sulfide and a plate-shaped glass substrate having an average thickness of less than 1 μm. More specifically, the pigment of the present invention may be different from pigments in which the glass substrate is made of ECR ​​glass with the composition: SiO (63-70%), AlO (3-6%), CaO (4-7%), MgO (1-4%), BO (2-5%), NaO (9-12%), KO (0-3%), TiO (0.1-4%), ZnO (1-5%).

[0118] The pigment of the present invention is also preferably different from pigments comprising a glass plate-like substrate, a zinc sulfide layer, and a translucent metal layer, in which the glass comprises 65 to 75% by mass of silicon oxide; 2 to 9% by mass of aluminum oxide; 0.0 to 5% by mass of calcium oxide; 5 to 12% by mass of sodium oxide; 8 to 15% by mass of boron oxide; 0.1 to 5% by mass of titanium oxide; and 0.0 to 5% by mass of zirconium oxide.

[0119] Finally, the pigments of the present invention may differ from plate-shaped reflective pigments having an internal support comprising zinc sulfide, having a thickness in the range of 50 nm to 1000 nm, two main opposing surfaces, and at least one outer surface. In this reflective pigment, the internal support is partially covered by an outer metal layer having a thickness in the range of 10 nm to 150 nm, so that the outer surface of the internal support is not covered by the outer metal layer. This outer metal layer is selected from, for example, aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, tin, niobium, chromium, and titanium.

[0120] The interference pigments of the present invention can be incorporated into a variety of manufactured products, such as foods, paints, inks, dyes, plastics, and cosmetics.

[0121] In certain embodiments, the interference pigments described above can be used in cosmetic products, such as cosmetic care or makeup products.

[0122] A third and further object of the present invention therefore relates to a cosmetic composition, in particular a cosmetic care or make-up composition, comprising a pigment as defined above.

[0123] In a particularly advantageous embodiment, the cosmetic composition of the present invention contains, in addition to the interference pigment, less than 3% by weight of titanium dioxide, in particular less than 1% by weight of titanium dioxide.Titanium dioxide can be provided in the composition as a filler, dye or UV filter.Titanium dioxide can also be provided in the composition by a titanium dioxide-containing ingredient, such as a pigment.

[0124] The cosmetic composition of the present invention is preferably free of titanium dioxide.

[0125] Make-up products include eye shadows, nail polishes, eyeliners, lipsticks, eyebrow makeup products, liquid and compact foundations, compact powders, and loose powders. Skin care products include, for example, white or colored skin care creams and lip balms.

[0126] These products may be liquid or solid, may contain water or may be anhydrous, and may be in the form of, for example, aqueous gels, water-in-oil or oil-in-water emulsions.

[0127] In addition to the interference pigment of the present invention, the cosmetic product may contain at least one cosmetic ingredient known to those skilled in the art, in particular selected from solvents, oils, pigments different from the pigment of the present invention, lakes, dyes, waxes, cosmetic active compounds, surfactants, UV filters, gelling agents and thickeners, who will be able to select the cosmetic ingredient based on their general knowledge.

[0128] In certain embodiments, the cosmetic composition comprises an oily phase in which is dispersed an interference pigment comprising a hydrophobic outer protective layer.

[0129] A list of specific objects of the present invention is set forth below. 1. An interference single- or multi-layer pigment comprising a core having a refractive index in the range of 1.00 to 2.10, coated with at least one layer of a material comprising zinc sulfide, said layer having an average physical thickness in the range of 10 nm to 350 nm. 2. The interference pigment according to Object 1, characterized in that the average physical thickness is in the range of 20 nm to 340 nm, 30 nm to 330 nm, 40 nm to 320 nm, 50 nm to 310 nm, 60 nm to 300 nm, 70 nm to 290 nm, 80 nm to 280 nm, 90 nm to 270 nm, 100 nm to 260 nm, or 110 nm to 250 nm. 3. An interference pigment according to object 1 or 2, characterized in that the pigment has a size in the range of 1 micron to 2000 microns. 1bis. Interference single-layer or multi-layer pigments comprising a core bounded by at least one layer of material comprising zinc sulfide, the zinc sulfide comprising 1% to 100% by weight of the pigment's mass. 2bis. An interference pigment according to object 1bis, characterized in that zinc sulfide accounts for 1% by weight to 70% by weight, 15% by weight to 65% by weight, 20% by weight to 60% by weight, 25% by weight to 55% by weight, 30% by weight to 50% by weight, or 35% by weight to 45% by weight of the pigment. 3bis. Interference pigments according to object 1bis or 2bis, characterized in that the pigments have dimensions in the range of 1 micron to 2000 microns. 1ter. An interference single-layer or multi-layer pigment comprising a core bounded by at least one layer of material comprising zinc sulfide, the pigment lacking an interference layer containing titanium dioxide. 2. An interference pigment according to claim 1, characterized in that the pigment contains titanium dioxide in an amount of less than 0.1% by weight of the pigment. 3. An interference pigment according to object 1 or 2, characterized in that the core contains less than 0.1% by weight of TiO2 relative to the weight of the core. 4. The material containing zinc sulfide is a material consisting essentially of zinc sulfide, or a material consisting essentially of zinc sulfide and Fe 2+ , Cu 2+ , Mn 2+ , Ag + , Au 3+ ,EU 3+ , Al 3+ , Ce 3+ and In 3+ and at least one metal ion selected from the group consisting of: 5. An interference pigment according to any one of the preceding objects, characterized in that the layer of material comprising zinc sulfide has a refractive index in the range of 2.30 to 2.90, preferably close to 2.40. 6. An interference pigment according to any one of the preceding objects, characterized in that the core is a gas or solid substrate. 7. An interference pigment according to any one of the preceding objects, characterized in that the solid substrate is selected from natural mica, synthetic mica, alkaline earth carbonates, alkaline earth sulfates, natural pearls such as guanine or hypoxanthine, alumina, aluminum, silica, borosilicates, perlite, organic polymers, and metal oxides. 8. An interference pigment according to any one of the preceding objects, characterized in that the pigment is a single layer pigment comprising a single layer of material comprising zinc sulfide. 9. An interference pigment according to any one of the preceding objects, wherein the pigment is multilayered and comprises at least one alternation of a first layer of a material comprising zinc sulfide having a refractive index in the range of 2.30 to 2.90 and a second layer adjacent to the first of a material having a refractive index in the range of 1.00 to 2.10, the difference in refractive index between said first layer and said second adjacent layer being 0.3 or more, preferably in the range of 0.3 to 1.5, more preferably around 1.3. 10. An interference pigment according to any one of the preceding objects, characterized in that the layer of material comprising zinc sulfide is coated on one of its surfaces with a continuous or semi-continuous layer of metal nanoparticles, such as gold, silver or copper nanoparticles. 11. An interference pigment according to any one of the preceding objects, characterized in that the pigment comprises an outer protective layer, which may be organic or mineral and may be hydrophilic or hydrophobic. 12. A method for synthesizing pigments, such as interference pigments, consisting of the heterogeneous precipitation of a material containing zinc sulfide onto solid particles. 13.- A first step of preparing an aqueous dispersion of solid particles having a pH in the range of 2 to 8 and a temperature close to the boiling point, wherein the dispersion has a pH in the range of 2 to 8 and a temperature close to the boiling point; a second step of coating the solid particles, comprising adding to said aqueous dispersion an aqueous solution of a zinc salt, such as zinc nitrate, and an aqueous solution of sodium sulfide, the pH of the resulting reaction medium being maintained between 2 and 7 to obtain a suspension of solid particles coated with a material comprising zinc sulfide. A method for synthesizing a pigment according to the preceding object. 14. A cosmetic composition comprising an interference pigment according to any one of Objects 1 to 11. 15. A cosmetic composition according to the preceding object, characterized in that it comprises an oily phase in which an interference pigment comprising a hydrophobic outer protective layer is dispersed.

[0130] The invention will be explained in more detail by the following examples, in which, unless otherwise stated, the temperature is between 20°C and 25°C and the pressure is atmospheric.

[0131] Example 1: Synthesis of a pigment containing a layer of zinc sulfide The equipment used includes a titrator connected to a stirring system, a peristaltic pump and a thermoregulated reactor. 1- Preparation of a dispersion of platelet-shaped particles in a reactor An acidic aqueous dispersion of mica particles (Topy Industries, trade name PDM-2OL) with a concentration of approximately 10 g / L is heated to near boiling temperature while stirring. 2-Zn 2+ Preparation of salt solutions Acidified Zn at 0.03M concentration 2+ The salt solution is placed in a peristaltic pump and pumped into the reactor at a flow rate of 0.5 mL / min. 3-Conditions of titrant solution and titrator. Prepare a 1M NaS solution to serve as the sulfur reagent for synthesizing the ZnS layer. The static acid pH set in the titrator is greater than 3. 4-Zinc sulfide nucleation and growth coating During the addition of the salt solution to the reactor, moderate stirring and near-boiling temperatures were applied throughout the synthesis. A static, steady pH, controlled by the previously selected titrator, was maintained throughout the synthesis by the controlled addition of dilute sodium sulfide solution. In this case, 100 mL of salt solution was used. 5- Washing Once the reaction was complete, the zinc sulfide-coated mica particles were centrifuged and redispersed in ethanol, then dried in an oven at 80°C for 12 hours. 6- Observation A continuous, uniform layer of zinc sulfide nanoparticles is then observed on the mica particles at the end of the synthesis. The coverage and thickness of the ZnS layer are controlled depending on the volume of zinc salt introduced into the reaction medium. In this example, adding 100 mL of solution yields a white powder with yellow / orange reflections. Microstructural analysis by transmission electron microscopy and scanning electron microscopy made it possible to visualize the deposited thickness of the ZnS layer, which was about 75 nm (FIG. 1), and its surface uniformity (FIG. 2). X-ray diffraction analysis was able to demonstrate the crystalline and crystallographic properties of ZnS (Fig. 3).

[0132] Example 2: Interference pigments containing hollow cores 1. Preparation of Gypsum Plate-like Particles The first solution consisted of 41 g of anhydrous NaSO4 dissolved in 1900 mL of distilled water. The solution was placed on a magnetic heating plate, stirred at 600 rpm, and heated to 55°C. The second solution was diluted with 42.4 g of CaCl 2. Prepare 2H2O by dissolving 0.10 g of oxalic acid in 100 mL of water. Stir this solution until homogeneous and pour it all at once into the first heated solution. Crystals will form rapidly in the solution. The solution is stirred at 50°C for 20 minutes. The solution is filtered. The filtrate is clear. The solid formed is washed three times with water. All three washes are clear. The solid is dried in an oven at 75°C. The obtained platelets were characterized by scanning electron microscopy (see Figure 5). A non-uniform distribution of gypsum particles in the somewhat elongated platelets is observed. 2. Coating of gypsum platelet particles with silica The first step is absorption of citrate ions on the plaster plate. 1 g of gypsum powder is mixed with 30 mL of 0.2 M citric acid solution at pH = 4. After stirring for 10 minutes, the mixture is separated by centrifugation and washed with water to remove excess citrate not adsorbed on the gypsum. The pH is raised in the base medium by adding ammonia with a few drops of water to the pellets so that the pH is higher than 9, creating electrostatic repulsion between the particles. The second step involves preparing the reaction medium: a water-alcohol solution with a volume ratio of 24 / 76 (v / v) is prepared; ammonia is added to the water-alcohol solution at a concentration of 0.37 M. A base pellet containing 1 g of gypsum substrate is added to the water-alcohol solution. The third step is to add the hydrolyzable precursor to the reaction medium. TEOS (tetraethyl orthosilicate), a hydrolyzable precursor of silica, is added to the reaction medium all at once. The reaction medium is sealed to prevent the ammonia from evaporating and is left stirring overnight. A TEOS concentration of 0.00075M is recommended for gypsum particles between 5 and 25 microns in size to obtain a 20 nm thick silica layer. This thickness can be adjusted depending on the amount of TEOS added. At the end of this process, the powder is filtered and then dried in an oven at 75°C overnight. Characterization of the encapsulated gypsum is shown in Figures 6 and 7. The powder is dried in an oven at 75°C. Characterization by EDX analysis was also carried out to verify the presence of silica, which is characterized by the presence of silicon (Figure 8). The surface microstructure differs from the smooth appearance previously achieved with gypsum board, suggesting a surface roughness. EDX analysis confirms the presence of silicon. 3. Deposition of a layer of zinc sulfide The silica capsules obtained are coated with a layer of zinc sulfide according to the protocol of Example 1.

[0133] Example 3: Interference pigments containing hollow cores In a first step, 6.6 g of silica-encapsulated gypsum are introduced into a 5% nitric acid solution and the whole is heated under reflux for 3 hours. The solution is centrifuged (10000 g-5 min) and then washed with water and ethanol. The powder was dried in an oven at 75°C and then gradually annealed in the oven (3°C / min to 400°C, 1 hour, then 3°C / min decrease). The samples were characterized by transmission electron microscopy (Figures 9 and 10) and scanning electron microscopy (Figures 11 and 12). Characterization by electron microscopy shows that more electrons pass through the particles during SEM image acquisition, resulting in more transparent platelets than before dissolution. Dissolution of the gypsum substrate is confirmed by EDX. The characteristic calcium peak (KαCa) at 3.6 eV, which justifies the presence of gypsum in Figure 8, completely disappears after dissolution in Figure 13. The silicon peak (KαSi) at 1.739 eV is then present. These bond analyses clearly demonstrate that platelet-shaped particles with a hollow core have been obtained.

[0134] Example 4: Synthesis of interference pigments with outer protective layers After the synthesis of mother of pearl as described in Example 1, the recovered dry powder is subjected to various chemical treatments to be encapsulated by silica. The first step is absorption of citrate ions onto the mother of pearl. -ZnS mother-of-pearl powder encapsulated on mica (base mica particle size 5-25 microns) is mixed with 30 mL of 0.2 M citric acid solution at pH = 4. After 10 minutes of stirring, the mixture is centrifuged and washed with water to remove excess citrate not adsorbed onto the mother-of-pearl. The pH is raised in the base medium by adding ammonia with a few drops of water to the pellets so that the pH is above -9, creating electrostatic repulsion between the particles. The second step consists in preparing the reaction medium = - Prepare a water-alcoholic solution with a volume mixture of 24 / 76 (v / v). Add ammonia to the water-alcoholic solution at a concentration of 0.37 M. - Add a base pellet containing 1 g of mother of pearl substrate to the aqueous alcohol solution. The third step consists in adding a hydrolyzable precursor to the reaction medium= TEOS (tetraethyl orthosilicate), a hydrolyzable precursor of silica, is added to the reaction medium all at once. The reaction medium is sealed to prevent the ammonia from evaporating and is left stirring overnight. In this example, a TEOS concentration of 0.00075 M is recommended to obtain a 20 nm thick silica layer, which can be visualized in the transmission electron microscope image shown in Figure 4. This thickness can be adjusted depending on the amount of TEOS added. At the end of this, the powder is filtered and then dried in an oven overnight to obtain the Mica / ZnS / SiO2 mother-of-pearl powder.

[0135] Example 5: Cosmetic formulation containing pigments Cosmetic formulations for makeup are prepared, in particular intended for application to the skin and / or lips, which formulations comprise interference pigments according to the invention.

[0136] Table 1

[0137] Table 2

[0138] Table 3

[0139] Table 4

[0140] Table 5

[0141] Table 6

[0142] Table 7

[0143] Table 8

[0144] Table 9

Claims

1. 1. A single- or multi-layer interference pigment comprising a platelet-shaped core coated with at least one first layer of a material comprising zinc sulfide, characterized in that the support has a refractive index in the range of 1.00 to 2.10, and the core comprises or consists of a gas, for example air.

2. 2. The interference pigment according to claim 1, wherein the average thickness of the first layer is in the range of 10 nm to 350 nm.

3. 2. The interference pigment of claim 1, wherein the core has a refractive index in the range of 1.00 to 1.

40.

4. The core is SiO ２ , Al ２ O ３ , ZrO ２ 2. The interference pigment according to claim 1, characterized in that it is a capsule of a solid material other than zinc sulfide selected from:

5. 5. The interference pigment of claim 4, wherein the core is a silica capsule.

6. 6. An interference pigment according to claim 5, characterized in that the capsules have a larger dimension in the range of 1 to 1000 microns and the silica layer has a thickness in the range of 1 to 100 nm.

7. 7. An interference pigment according to claim 5 or 6, characterized in that the first layer of material comprising zinc sulfide coats the silica layer.

8. 4. The interference pigment according to claim 1, wherein the core is composed of a gas, and the pigment comprises a gas core bounded by the first layer of material comprising zinc sulfide.

9. 10. An interference pigment according to any one of the preceding claims, characterized in that the pigment is a single layer pigment comprising a single layer of material comprising zinc sulfide.

10. 9. The interference pigment according to claim 1, wherein the pigment is a multi-layer pigment and comprises the first layer of a material comprising zinc sulfide, at least one layer of a material having a refractive index in the range of 1.00 to 2.10, and at least one second layer of a material comprising zinc sulfide.

11. 10. An interference pigment according to any one of the preceding claims, characterized in that the difference between the refractive index of the first layer of material comprising zinc sulfide and the refractive index of the layer of material having a refractive index in the range of 1.00 to 2.10 is 0.80 or more.

12. 10. An interference pigment according to any one of the preceding claims, characterized in that the pigment is devoid of a layer containing titanium dioxide.

13. 10. An interference pigment according to any one of the preceding claims, characterized in that the pigment comprises titanium dioxide in an amount of less than 0.1% by weight of the pigment.

14. The material containing zinc sulfide is a material consisting essentially of zinc sulfide, or a material consisting essentially of zinc sulfide and Fe ２＋ , Cu ２＋ , Mn ２＋ , Ag ＋ , Au ３＋ , Eu ３＋ , Al ３＋ , Ce ３＋ and In ３＋ 10. An interference pigment according to claim 9, characterized in that it is a material consisting essentially of at least one metal ion selected from the group consisting of:

15. 10. An interference pigment according to any one of the preceding claims, characterized in that the layer of material comprising zinc sulfide is coated on one of its surfaces with a continuous or semi-continuous layer of metal nanoparticles, such as gold, silver or copper nanoparticles.

16. 10. A pigment according to any one of the preceding claims, characterized in that it comprises an outer protective layer which may be of organic or mineral nature and of hydrophilic or hydrophobic nature.

17. a first step of preparing an aqueous dispersion of core particles having a pH between 2 and 8 and a temperature close to the boiling point; a second step of coating said core particles, comprising adding to said aqueous dispersion an aqueous solution of a zinc salt, such as zinc nitrate, and an aqueous solution of sodium sulfide, the pH of the resulting reaction medium being maintained between 2 and 7 to obtain a suspension of solid particles coated with said zinc sulfide-containing material, A method for synthesizing an interference pigment according to any one of the preceding claims.

18. 18. The method for synthesizing an interference pigment according to claim 5, characterized in that the silica capsules are obtained by dissolving an organic or inorganic plate-like support coated with a silica layer in an acid, and the treatment is intended to remove part or all of the material constituting the support.

19. 10. A method for synthesizing a pigment according to any one of the preceding claims, characterized in that the inorganic support comprises a material selected from magnesium hydroxide, calcium sulfate, mica and borosilicates.

20. A cosmetic composition comprising an interference pigment according to any one of claims 1 to 16.

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