Zinc sulfide interferometric pigment, synthetic method and cosmetic composition

Abstract

The invention relates to an interferometric pigment comprising a layer of zinc sulfide-based material. The pigment advantageously comprises a low refractive index core and at least one high refractive index layer comprising zinc sulfide. The invention also proposes a method for synthesizing these pigments by non-homogeneously precipitating zinc sulfide on a powdered support, by adding a zinc salt solution to a reaction medium containing a dispersion of the powdered support, titrating a sodium sulfide solution having a fixed pH at a moderate temperature to obtain a precipitate. The invention also relates to cosmetic compositions comprising these interference pigments free of titanium dioxide, titanium dioxide being typically introduced as a filler or by providing a cosmetic ingredient containing titanium dioxide.

Description

Technical Field

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

[0002] The invention also relates to a process for synthesizing these pigments, as well as to cosmetic compositions containing them, which compositions themselves can be free of titanium dioxide or contain very low amounts of titanium dioxide. Background Art

[0003] White interference effect pigments are usually obtained by depositing a layer of a high refractive index material on the surface of translucent flake particles of mica, glass or aluminum oxide with a lower refractive index.

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

[0005] The present invention addresses this need and provides zinc sulfide pigments, compounds having the advantage of being widely applicable in various industrial applications.The proposed pigment comprises an inner core covered with a thin layer of zinc sulfide.

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

[0007] The present invention also provides a method for liquid deposition of submicron-sized zinc sulfide (ZnS) compound layers on micron-sized supports. This synthesis method advantageously follows a heterogeneous nucleation and uniform growth mechanism, thereby depositing zinc sulfide layers with controllable chemical composition, crystallinity, crystallography, density, and thickness. The successful deposition of uniform zinc sulfide layers with controlled thickness, crystallinity, crystallography, and chemical composition, for example, on powdered supports such as mica, in a liquid process under mild chemical conditions is unexpected. This method allows the production of zinc sulfide pigments using a process conducted in water at moderate temperatures and pH.

[0008] The interference pigments of the present invention comprise 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 the pigment preferably contains less than 0.1% by mass of titanium dioxide relative to the mass of the pigment.

[0011] The present invention advantageously allows partial or complete replacement of titanium dioxide for the manufacture of interference pigments and allows the provision of cosmetic products having a low titanium dioxide content.

[0012] In a second variant of the invention, the pigment is an interference-type single-layer or multilayer pigment, the carrier of which comprises or consists of a gas such as air. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Elemental EDX diagram of the pigment according to the present invention.

[0014] Figure 2 is a scanning electron microscope image of a pigment according to the present invention.

[0015] Figure 3 is the X-ray diffraction pattern of the pigment according to the invention.

[0016] Figure 4 is a transmission electron microscope image of a pigment according to the present invention, said pigment comprising an outer protective layer of silica.

[0017] Figure 5 Characterization of the gypsum flake carrier used to prepare the hollow cores of the pigments of the present invention by scanning electron microscopy is shown.

[0018] Figure 6 and Figure 7 Shown are scanning electron microscopy characterizations of gypsum flakes covered with a silica layer at two different magnifications.

[0019] Figure 8 Elemental characterization of gypsum flake powder covered with a silica layer by EDX analysis.

[0020] Figure 9 and Figure 10 Shown are the characterizations of gypsum flakes covered with a silica layer after dissolution by transmission electron microscopy at two different magnifications.

[0021] Figure 11 and Figure 12 Shown are the characterizations of gypsum flakes covered with a silica layer after dissolution by scanning electron microscopy at two different magnifications.

[0022] Figure 13 Elemental characterization by EDX analysis of silica capsule powder after gypsum dissolution is shown. DETAILED DESCRIPTION

[0023] A first subject of the invention relates to an interference single- or multilayer pigment comprising a core and at least one layer of a material comprising zinc sulfide.

[0024] The pigments of the invention may comprise a core having a refractive index preferably in the range from 1.00 to 2.10, said core being covered with or delimited by at least one layer of a material comprising zinc sulfide.

[0025] The layer comprising zinc sulfide preferably has an average physical thickness in the range of 10 nm to 350 nm.

[0026] The average physical thickness of the layer of material comprising zinc sulfide can range from, for example, 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. Physical thickness (also referred to as optical thickness) can be measured by any method known to those skilled in the art.

[0027] Zinc sulfide may account for between 1% and 100% by mass of the pigment. The interference pigment of the present invention advantageously comprises from 1% to 70% by mass of zinc sulfide relative to the mass of the pigment, advantageously from 15% to 65% by mass of zinc sulfide relative to the mass of the pigment, more advantageously from 20% to 60% by mass of zinc sulfide relative to the mass of the pigment, and even more preferably from 25% to 55% by mass of zinc sulfide relative to the mass of the pigment.

[0028] In a particularly preferred embodiment, zinc sulfide represents 30% to 60% by mass, preferably 30% to 50% by mass, even better 35% to 45% by mass, based on the mass of the pigment.

[0029] The pigment may lack an interference layer comprising titanium dioxide.

[0030] In a particularly advantageous embodiment of the present invention, the overall composition of the interference pigment according to the invention (comprising the inner core and the layer of material comprising zinc sulfide) is free of titanium dioxide, meaning that it contains less than 10% by mass, preferably less than 5% by mass, or even less than 1% by mass of titanium dioxide relative to the mass of the interference pigment according to the invention.

[0031] The interference pigments of the invention are advantageously powders composed of particles each comprising a core covered with at least one layer of a material comprising zinc sulfide.

[0032] Its size is the number-average size of the population of particles and is advantageously equal to the D50 of the population of particles constituting the pigment. In the context of the present invention, the D50 value is calculated from the particle size distribution obtained by conventional methods such as laser diffraction or analysis of images obtained by scanning electron microscopy (SEM) or transmission electron microscopy (TEM).

[0033] Thus, the pigment may have a size (which may be defined as D50) ranging from 1 to 2000 microns, preferably from 10 to 500 microns, and the core may have a size ranging from 1 to 2000 microns, preferably from 10 to 500 microns.

[0034] The pigments of the present invention are interference pigments, which can be colored or white. The pigments can also produce one or more reflected lights of different colors, one or more of which can be different from the color of the pigment itself. Thus, the reflected light can be silvery white or other colors. For example, in the cosmetic field, a distinction is made between white nacres with silvery white reflections, white nacres with colored reflections, colored nacres with silvery white reflections, and colored nacres with colored reflections. These reflected lights can produce pearlescent and / or iridescent effects during the transmission and reflection of light through them, which is caused by the phenomenon of optical interference. Interference colors are produced by the amplification or destruction of light reflected at certain wavelengths. A layer of zinc sulfide-containing material deposited on a support with a low refractive index can generate destructive and constructive waves that themselves produce color. Destructive interference occurs at a given wavelength if the reflections from the air / material and material / support surfaces are completely out of phase. For example, for a layer of zinc sulfide-containing material with a refractive index N and a thickness e, minimum reflection occurs for light incident perpendicular to the wavelength λ when N*e = (n-1)*λ / 2 (where n is an integer). When a layer of material is illuminated by white light, all wavelengths except λ appear in the reflected light. An enhancement of a given wavelength occurs if the reflections from the two surfaces of a layer of material containing zinc sulfide are in phase with each other. Thus, for incident light perpendicular to the free surface of the layer, this occurs when N*e = (2n-1)*λ / 4.

[0035] 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 of an optical thickness capable of producing an optical color when deposited on a given support or a layer of another material.

[0036] The material comprising zinc sulfide preferably consists essentially of zinc sulfide. "Consisting essentially of zinc sulfide" means that the material comprises more than 50% by mass of zinc sulfide relative to the mass of the material.

[0037] In one embodiment, the zinc sulfide-containing material consists essentially of zinc sulfide.

[0038] The term “essentially consisting of zinc sulfide” means that the material comprises at least 90% by mass of zinc sulfide, preferably at least 99% by mass of zinc sulfide, relative to the mass of the material.

[0039] The material comprising zinc sulfide is a solid solution of zinc sulfide, ie a material forming a single crystalline phase comprising zinc sulfide. A person skilled in the art is able to characterize the number of crystalline phases of a material, for example by X-ray diffraction.

[0040] The zinc sulfide-containing material may be what is known as "doped" zinc sulfide, ie a material consisting essentially of zinc sulfide and at least one chemical element, preferably in the form of a metal ion.

[0041] Thus, in another embodiment, the material comprising zinc sulfide is essentially composed of zinc sulfide and at least one selected from Fe 2+ 、Cu 2+ 、Mn 2+ 、Ag + 、Au 3+ 、Eu 3+ 、Al 3+ 、Ce 3+ and In 3+ Materials composed of metal ions.

[0042] "Essentially consisting of zinc sulfide and at least one metal ion" means that the material comprises at least 90% by mass, preferably at least 99% by mass, of a mixture of zinc sulfide and one or more metal ions, relative to the mass 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 (i.e., a single crystalline phase) with the zinc sulfide.

[0043] The layer of material comprising 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, 2.50 to 2.50. The refractive index of the layer of material comprising zinc sulfide is preferably close to 2.40.

[0044] The pigments of the present invention may include an outer protective layer. This outer protective layer is advantageously transparent and has no coloring function, thus distinguishing it from an interference layer comprising a zinc sulfide material. The outer protective layer may be obtained by surface treatment with a chemical compound that fulfills the relevant function. The protective layer may, for example, facilitate the formulation of the pigment in a solvent or oil, or provide protection against ultraviolet rays.

[0045] The outer protective layer can be organic or inorganic, and hydrophilic or hydrophobic. The layer is, for example, an inorganic layer (such as silicon dioxide or cerium dioxide) or a polymer layer (such as PMMA, polystyrene or polyvinyl chloride).

[0046] The pigments of the present invention may advantageously be subjected to an additional hydrophobic treatment to promote dispersion of the pigment in a fatty phase (e.g., an oil phase). The purpose of this treatment is to apply a hydrophobic surfactant to all or part of the surface of the pigment. This surfactant may advantageously be selected from amino acids, metal soaps, esters, organosilicon or fluorine compounds, acrylic compounds, or lipids, or a mixture of at least two of these compounds.

[0047] The amino acid surfactant can be, for example, glycine, alanine, sarcosine, proline, hydroxyproline, aspartic acid, glutamic acid or lysine, or a derivative, for example, comprises the acylated amino acid of the saturated or unsaturated fatty acid with 1 to 22 carbon atoms (preferably 8 to 20 carbon atoms). This acylated amino acid surfactant can 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 its salt (such as sodium salt, potassium salt, calcium salt, magnesium salt or aluminum salt). Particularly preferred salt form reagent is preferably sodium myristoyl glutamate, disodium stearoyl glutamate, sodium lauroyl aspartate, dilauroyl glutamine lysine, sodium palmitoyl sarcosinate, magnesium palmitoyl glutamate and disodium cocoyl glutamate.

[0048] As surfactants of the metal soap type, aluminum myristate and magnesium stearate may advantageously be mentioned.

[0049] As ester surfactants, mention may advantageously be made of isostearyl sebacate, dextrin and fatty acid esters such as dextrin stearate, dextrin isostearate, dextrin palmitate or polyglyceryl-2 tetraisostearate.

[0050] As silicone surfactants, there may advantageously be mentioned methylsiloxane, hydrogendimethylsiloxane, dimethylsiloxane, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, octadecyltriethoxysilane and hexadecyltriethoxysilane.

[0051] As fluorinated surfactants, mention may advantageously be made of perfluorohexylethyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane or tridecafluorooctyltriethoxysilane.

[0052] As acrylic surfactants, mention may be made of (co)polymers including 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.

[0053] Examples of lipid surfactants include phospholipids, lecithin, triglycerides, fats, oils, and waxes, which are advantageously 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 over the life of the formulated product or finished article containing the pigment.

[0054] The pigments of the invention may be monolaminar, ie they comprise a single layer covering an inner core, or multilaminar.

[0055] According to a first embodiment, the pigment is a monolayer pigment comprising a monolayer of a material comprising zinc sulfide. "Monolayer" means a layer of uniform composition that can be applied in one or more steps of the manufacturing process (preferably a single step). The pigment of the invention may also be multilayer, i.e. comprising at least two layers of different composition, including at least one layer of a material comprising zinc sulfide and one layer that does not comprise zinc sulfide. Preferably, the core does not comprise a plurality of layers of different materials and its composition is uniform.

[0056] The pigments of the present invention may comprise one or more layers of a material comprising zinc sulfide, independently of the number of layers of different materials that may cover the core.

[0057] The pigment may comprise, for example, two layers of a material containing zinc sulfide, a first layer consisting of zinc sulfide and a second layer consisting of doped zinc sulfide, the first and second layers being separated from each other by an intermediate layer having a low refractive index, comprising, for example, silicon dioxide, as described above.

[0058] 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, for example, a material selected from Fe2O3, FeTiO3, Cr2O3, and / or Fe3O4. This material may be part of the material composition of the zinc sulfide layer or in the form of a layer separate from the zinc layer. Thus, in addition to zinc sulfide, the layer containing zinc sulfide may also contain 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 composed of zinc sulfide, which is covered by and in contact with a second layer composed of a material different from zinc sulfide and having a refractive index in the range of 2.30 to 2.90.

[0059] In a second particular embodiment of the invention, the interference pigment is multilayered and comprises at least one alternation of a first layer of a material comprising zinc sulfide and having a refractive index in the range of 2.30 to 2.90 and a second layer adjacent to the first layer 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 of about 1.3.

[0060] In this specification, "about" or "approximately" means a value equal to a given numerical value plus or minus 10%, or a value taking into account measurement uncertainty.

[0061] The layer of material having a refractive index in the range of 1.00 to 2.10 preferably has a refractive index in the range of 1.00 to 1.60.

[0062] In the interference pigments of the invention, the layer of material comprising zinc sulfide may be covered on one of its surfaces with a continuous or semi-continuous layer of metal nanoparticles (such as gold, silver or copper nanoparticles), said nanoparticles having, for example, at least one average size less than or equal to 500 nm, preferably less than or equal to 100 nm.

[0063] Adding metal nanoparticles can produce a black background and a more or less significant color path of the mother-of-pearl. The metal nanoparticles can be nanoparticles of a noble metal (such as gold or silver), or nanoparticles of copper or chromium, which are preferably deposited in a semi-continuous manner. Depending on the content of the noble metal deposited on the last layer of pigment (having a high refractive index (such as ZnS) or a low refractive index (such as silicon dioxide)), a black background can be produced, thereby making the core color of the white mother-of-pearl with reflected light close to its reflected light color, which depends on the amount of deposited nanoparticles. The white mother-of-pearl with reflected light becomes a colored mother-of-pearl with colored reflected light. In addition, adding nanoparticles with visible light absorption can more or less change the reflected light color and the light-transmitting color of the mother-of-pearl.

[0064] A silicon dioxide layer having a thickness ranging from 1 nanometer to 1 micrometer may be interposed between the core and the zinc sulfide layer and in contact with the core and the zinc sulfide layer. A post-treatment may also be performed to create pores within the silicon dioxide layer.

[0065] The multilayer interference pigments of the present invention may comprise a plurality of layers superposed, including at least one layer comprising zinc sulfide and 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 thickness of the different layers being selected to produce colored reflected light.

[0066] The pigments of the present invention can be synthesized by physically or chemically depositing zinc sulfide on a solid support.

[0067] In the case of physical deposition, a layer of material comprising zinc sulfide may be deposited on a solid support by atomic layer deposition methods.

[0068] In the case of chemical deposition, the pigment can be obtained by heterogeneously precipitating zinc sulfide onto a support from a zinc salt solution and a sodium sulfide solution. It can also be synthesized by bubbling H2S gas in the presence of a support or by thermally decomposing a sulfur precursor as an alternative to sodium sulfide. For example, a translucent powdered support such as mica is used, but any type of support, such as one of the solid substrates previously described in the context of the pigments of the present invention, is suitable.

[0069] Another method for synthesizing the pigment of the present invention uses a homogeneous precipitation method. This synthesis method involves slowly releasing one of the sulfur-containing reactants by increasing the temperature during the reaction process. The released reactant is evenly distributed throughout the entire volume of the solution, which allows for a low and uniform supersaturation to be maintained over time. This allows for a controlled formation of a zinc sulfide layer on a solid support. According to this method, a solid particle suspension, a zinc salt, and a room temperature inactive precipitant are mixed. Precipitants that can generate hydrogen sulfide by thermal decomposition are, for example, thioacetamide (with water as the reaction solvent) or thiourea (preferably heavy alcohols (such as polyols) as solvents).

[0070] In one embodiment, the heterogeneous precipitation of zinc sulfide can be carried out by titrating a sodium sulfide solution of fixed pH in a reaction medium comprising solid particles and a zinc salt solution in a dilution medium. The sodium sulfide solution is added continuously and the amount is adjusted by a titrator according to the pH fixed at the beginning. The purpose is to always be under low supersaturation conditions, so that the zinc sulfide germinates heterogeneously on the solid particles and forms a continuous and uniform zinc sulfide layer on the surface of the particles. 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 (called stable pH). The stable pH is selected to form a continuous, uniform, dense zinc sulfide layer of controllable thickness on the solid particles. Depending on the amount of zinc salt added, the thickness of the zinc sulfide layer increases until the optimal physical thickness condition for producing interference colors is reached.

[0071] The second subject matter of the present invention relates to a method for synthesizing a pigment (e.g., an interference pigment), the method comprising heterogeneously precipitating a material comprising zinc sulfide onto solid particles. The material comprising zinc sulfide may be zinc sulfide or a solid solution of zinc sulfide and a metal ion as described above.

[0072] The method may include:

[0073] - a first step of preparing an aqueous dispersion of solid particles, the pH of which is in the range of 2 to 8 and at a temperature close to the boiling point, and

[0074] - a second step of coating the solid particles, consisting in adding to said aqueous dispersion an aqueous solution of a zinc salt (such as zinc nitrate) and an aqueous solution of sodium sulphide, the pH of the reaction medium obtained being maintained between 2 and 7, so as to obtain a suspension of particles covered with a material comprising zinc sulphide.

[0075] The uniformity of the ZnS layer deposited on the particle surface can be controlled by different physicochemical parameters, such as temperature, salt solution concentration, and pH.

[0076] The concentration of the solid particle dispersion prepared in the first step ranges from 1 g / L to 20 g / L or from 5 g / L to 15 g / L, for example.

[0077] The second step is the step of coating the solid particles, which is preferably carried out while stirring the reaction medium. During the coating step, the temperature of the reaction medium may range from 20°C to 100°C, preferably from 60°C to 90°C.

[0078] The solid particles can 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, borosilicates, perlite, organic polymers (such as plastics), and metal oxides (such as zinc oxide or bismuth oxychloride). Their size can range from 1 micron to 2000 microns, preferably from 10 microns to 500 microns. This size is defined in the same manner as the substrate size described in the first subject matter of the present invention and can be measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The particles are preferably in the form of flakes, but may also be of any other shape.

[0079] The aqueous zinc salt solution is preferably diluted and acidified. Its concentration can range from 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 can range from 0.001 mL / min to 10 mL / min, or 0.1 mL / min to 1 mL / min. The zinc salt is preferably zinc nitrate.

[0080] The sodium sulfide aqueous solution is a dilute solution with a concentration between 0.5 M and 3 M. The pH of the reaction medium is preferably maintained between 2 and 7 by controlling the addition of the dilute sodium sulfide solution throughout the synthesis process.

[0081] The method of the present invention may include a third step, a washing and drying step, comprising centrifuging the suspension of zinc sulfide covered particles, redispersing the particles in ethanol, and then drying them at a temperature ranging from 20°C to 80°C for 12 to 24 hours.

[0082] The zinc sulfide-coated particles may need to be annealed 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 in which the zinc sulfide-coated particles obtained at the end of the third coating step or the fourth washing and drying step as described above are subjected to a heat treatment. The zinc sulfide-coated particles may be exposed to a temperature that reaches the thermal decomposition temperature of ZnS under air or argon. The synthesis method of the present invention may include a step in which the zinc sulfide-coated particles are coated with an organic or inorganic matrix to form a protective layer. This may be referred to interchangeably as coating or encapsulation.

[0083] When the coating step includes coating with silicon dioxide, the coating step can be carried out by a sol-gel method known to those skilled in the art. According to a variant of this method, the dried particles covered with zinc sulfide are dispersed in a citric acid solution to an alkaline pH. This solution is injected into a water-ethanol reaction medium (e.g., 25 / 75 v / v). A silicon dioxide precursor (e.g., tetraethyl orthosilicate (TEOS)) is then added to the mixture, and the solution is stirred at room temperature for 24 hours. The suspension is then centrifuged, washed with ethanol, and dried in an oven at 80°C for 24 hours.

[0084] Finally, the synthesis method of the present invention may include a step of completely or partially removing the core of the support composed of solid particles to obtain a solid porous core or a gaseous core. At the end of this second step, once the layer of zinc sulfide-containing material has been deposited on the solid particles, the core can be removed by chemical or physical methods. For example, calcium carbonate particles can be used, coated with zinc sulfide, and then dissolved with acid without destroying the structure of the layer of zinc sulfide-containing material.

[0085] The refractive index of the pigment core is preferably less than or equal to 2.20, preferably in the range of 1.00 to 2.10. It is composed of one or more materials, each of which has a refractive index less than or equal to 2.20, preferably in the range of 1.00 to 2.10. The refractive index can be measured by any method known to those skilled in the art.

[0086] The chemical nature of the pigment core can vary. The core can be a gas (such as air), or a porous or non-porous solid substrate, or it can contain both gas and solid. The solid substrate is, for example, a thin sheet substrate that serves as a support for depositing a thin layer of material. A core containing or consisting of a gas can be produced by chemical or thermal decomposition of the solid substrate.

[0087] When the core is a porous substrate, the core is a gas, or the core comprises both a gas and a 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 and then dissolving or thermally decomposing the solid support to obtain a gas core or a core comprising a gas.

[0088] In a first embodiment, the core of the pigment of the present invention is a solid substrate. This substrate can take various forms; for example, it can be in the form of flakes or beads. In the case of a flake-based substrate, the dimensions of the substrate are, for example, the average length of the flake population, where the length is the largest dimension of the flake. The substrate can also be defined by its thickness, which can represent the average thickness of the population.

[0089] The solid substrate can be transparent or translucent to obtain nacres, or opaque to obtain interference pigments with metallic effects.

[0090] In particular embodiments, transparent or translucent substrates are used.

[0091] The solid substrate can be advantageously 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 (such as plastics), and metal oxides (such as zinc oxide or bismuth oxychloride). The substrate may essentially consist of one or more of these materials, but the presence of impurities is not excluded.

[0092] The core of the interference pigment of the present invention is preferably free of zinc sulfide. However, it may contain zinc sulfide as an impurity, for example in an amount of less than 0.1% by mass, based on the mass of the core.

[0093] In this first embodiment, the pigments of the invention may be multilayer interference pigments comprising a transparent or translucent flake substrate covered with at least one stack comprising at least:

[0094] - a first layer of a material comprising zinc sulfide and having a refractive index in the range of 2.30 to 2.90,

[0095] - a second layer of material having a refractive index in the range of 1.00 to 2.10 adjacent to the first layer, and

[0096] a third layer adjacent to the second layer, of a material comprising zinc sulfide and having a refractive index ranging from 2.30 to 2.90, the difference in refractive index between the two adjacent layers being greater than or equal to 0.3, preferably ranging from 0.3 to 1.5, and the pigment not comprising a layer containing titanium dioxide.

[0097] The foil substrate is covered by at least one laminate, ie it may be covered with one or more laminates, each of which may comprise, in addition to the first, second and third layers, additional layers of other materials.

[0098] In a particular stack, the third layer contacts and covers the second layer, and the second layer contacts and covers the first layer.

[0099] The features described above in the context of the description of the pigments of the invention apply to the first variant embodiment.

[0100] The first layer may be colorless, ie, does not absorb wavelengths in the visible light range. The second layer may also be colorless.

[0101] In a second embodiment of the invention, the core of the pigment of the invention may contain or consist of a gas such as air, so that the pigment is in the form of particles, so-called "core-shell" particles, the core of which is hollow and the outer shell comprises at least one intervening layer of a material comprising zinc sulfide. As previously mentioned, this core may be obtained from a solid support which is partially or completely removed by physical or chemical methods after application of the outer shell consisting of the layer applied to the support.

[0102] According to this variant, the pigment of the invention is an interference-type single-layer or multilayer pigment comprising a platelet-shaped core covered with at least a first layer of a material comprising zinc sulfide and a support having a refractive index ranging from 1.00 to 2.10, characterized in that the support contains or consists of a gas such as air.

[0103] The first layer may have an average thickness ranging from 10 nm to 350 nm, and the value of the average thickness may be equal to one of the values ​​defined above.

[0104] The carrier 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" refers to an object that is hollow or porous inside and has a solid material layer outside. The material is preferably selected from transparent or translucent materials that are resistant to acid and / or alkali corrosion, such as SiO2, Al2O3, and ZrO2.

[0105] In a particular embodiment, the inner core is a silica capsule.The silica layer has, for example, a thickness in the range of 1 nm to 100 nm.

[0106] The capsules may have a larger size ranging from 1 micron to 1000 microns.

[0107] The first layer of material comprising zinc sulfide may cover the surface of the capsule, ie be in contact with the layer of solid material, and cover the entire surface thereof.

[0108] In another embodiment, the core consists 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 a layer of another material having a high refractive index.

[0109] The pigment of the second variant of the present invention may be a single-layer pigment comprising a single layer of a material containing zinc sulfide, or a multi-layer pigment comprising a first layer of a material containing 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 containing zinc sulfide. The difference between the refractive index of the first layer of the material containing zinc sulfide and the refractive index of the layer of the material having a refractive index in the range of 1.00 to 2.10 is preferably greater than or equal to 0.80.

[0110] The pigment advantageously does not comprise a layer comprising titanium dioxide, which layer may be interferential or non-interferential.In a preferred embodiment, the pigment comprises titanium dioxide in an amount of less than 0.1% by mass, based on the mass of the pigment.

[0111] As described above, the material containing zinc sulfide may be a material consisting essentially of zinc sulfide, or a material consisting essentially of zinc sulfide and at least one selected from Fe 2+ 、Cu 2+ 、Mn 2+ 、Ag + 、Au 3+ 、Eu 3+ 、Al 3+ 、Ce 3+ and In 3+ The layer of material comprising zinc sulfide may be further covered on one surface thereof with a continuous or semi-continuous layer of metal nanoparticles (such as gold, silver or copper nanoparticles).

[0112] The pigments of the second variant form of the invention may comprise an outer protective layer, which may be of organic or inorganic nature, and of hydrophilic or hydrophobic nature. Examples of suitable outer protective layers have already been described above.

[0113] A method for synthesizing the interference pigments of the second variant of the invention comprises:

[0114] - a first step of preparing an aqueous dispersion of the core particles, the pH of the dispersion being in the range of 2 to 8 and the temperature being close to the boiling point, and

[0115] - a second step of coating the core particles, consisting in adding to said aqueous dispersion an aqueous solution of a zinc salt (such as zinc nitrate) and an aqueous solution of sodium sulphide, the pH of the reaction medium obtained being maintained between 2 and 7, so as to obtain a suspension of solid particles covered with a material comprising zinc sulphide.

[0116] The features already given above describing the second subject-matter of the invention can be applied to the method for synthesizing the pigment of the second variant form of the invention.

[0117] Pigments containing a gas in the core provide better color saturation and brightness than prior art pigments.

[0118] When the core is a capsule, in particular a silica capsule, the method of the present invention may include a step of synthesizing the capsule. The synthesis of the capsule may include a step of coating an organic or inorganic support with a layer of material to obtain a coated support, followed by a step of treating the coated support to remove all or part of the material constituting the support.

[0119] The step of treating the coated support may be carried out by placing it in an acidic aqueous solution or an alkaline aqueous solution.

[0120] The coated support may also or alternatively be heat treated by increasing the temperature.

[0121] In a first embodiment, an acid-insoluble metal oxide layer is deposited on the surface of an acid-soluble support, which is preferably in the form of flaky inorganic particles.

[0122] The support may be in the shape of a thin plate and made of an inorganic material, and may include, for example, a material selected from magnesium hydroxide, copper hydroxide, iron hydroxide, zinc oxide, calcium sulfate (such as gypsum), phyllosilicate (such as mica), and borosilicate.

[0123] The metal oxide is for example selected from SiO 2 , Al 2 O 3 , ZrO 2 and SnO 2 . The metal oxide can be deposited on the support by any method known to those skilled in the art.

[0124] The treatment of the coated support may comprise one or more steps of treatment in aqueous solution.

[0125] For example, the coated support can be placed in an acidic aqueous solution to completely or partially erode and / or dissolve the support without dissolving the metal oxide layer. The acidic aqueous solution is preferably an aqueous solution of an inorganic acid selected from hydrofluoric acid, phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid and mixtures thereof.

[0126] The coated support may be subjected to one or more consecutive steps of treatment in an acidic medium, washed to eliminate ions resulting from the dissolution of the inorganic support and then optionally treated in an alkaline medium.

[0127] Treatment in aqueous solution may be carried out at a temperature ranging from 20°C to 100°C, for a duration ranging from 1 hour to 24 hours.

[0128] In a second embodiment, the pigment comprises an inner core composed of a gas.

[0129] Such pigments can be produced, for example, by depositing a metal oxide layer or a zinc sulfide layer on micrometer-sized graphite flakes. The coated graphite flakes are then calcined to remove the graphite and obtain metal oxide capsules or zinc sulfide capsules, depending on the material deposited on the graphite particles.

[0130] Pigments comprising a gas core can also be obtained by depositing a zinc sulfide layer on a substrate (which can be chemically dissolved), according to the capsule synthesis method described above.

[0131] Examples of pigments of the present invention include stacks of the following layers, with slashes indicating the separation between two different layers and brackets indicating a single layer comprising multiple materials:

[0132] Core / ZnS

[0133] Core / ZnS / Low refractive index material / ZnS

[0134] The stacking of three layers of core / ZnS / low refractive index material / ZnS, ZnS / low refractive index / ZnS can be repeated many times.

[0135] Core / ZnS doped with metal ions

[0136] Core / SiO2 / ZnS

[0137] Core / SiO2 / ZnS / Low refractive index material / ZnS

[0138] Core / ZnS / High refractive index material different from ZnS

[0139] Core / (ZnS+high refractive index material different from ZnS)

[0140] Core / ZnS / ZnS doped with metal ions

[0141] Core / (ZnS+ZnS doped with metal ions)

[0142] Core / High refractive index material different from ZnS / ZnS

[0143] Core / high refractive index material different from ZnS / low refractive index material / ZnS.

[0144] In these examples, the refractive index of the high refractive index material other than ZnS ranges from 2.30 to 2.90 and can be, for example, Fe2O3, FeTiO3, Cr2O3, Fe3O4, while the refractive index of the low refractive index material preferably ranges from 1.00 to 1.60. The stack described can be covered with a continuous or semi-continuous layer of metal nanoparticles (e.g., gold, copper, or silver nanoparticles), but can also be covered with a non-interference protective layer. In these examples, a silicon dioxide protective layer can be applied to the last layer of the stack. The core can be a gas or a capsule with a metal oxide (e.g., SiO2) on the outside.

[0145] According to a particular embodiment, the pigment of the present invention is different from a pigment comprising zinc sulfide and a thin glass substrate having an average thickness of less than 1 μm. More specifically, the pigment of the present invention may be different from a pigment in which the glass substrate is made of ECR ​​glass having the following composition: SiO2 (63%-70%), Al2O3 (3%-6%), CaO (4%-7%), MgO (1%-4%), B2O3 (2%-5%), Na2O (9%-12%), K2O (0-3%), TiO2 (0.1%-4%), ZnO (1%-5%).

[0146] The pigment of the present invention is also preferably different from a pigment comprising a glass flake substrate, a zinc sulfide layer and a translucent metal layer, the glass comprising 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.

[0147] Finally, the pigments of the present invention may be different from reflective flake pigments provided with an inner support comprising zinc sulfide, said inner support having a thickness ranging from 50 nm to 1000 nm and comprising two main opposing surfaces and at least one side surface. In this reflective pigment, an outer metal layer having a thickness ranging from 10 nm to 150 nm partially covers the inner support, leaving the side surfaces of the inner support uncovered by the outer metal layer. This outer metal layer is, for example, selected from aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, tin, niobium, chromium and titanium.

[0148] The interference pigments of the present invention can be used in various manufactured products, such as foods, coatings, inks, dyes, plastics and cosmetics.

[0149] In a particular embodiment, the above-described interference pigments can be used in cosmetic products, such as beauty care or makeup.

[0150] Therefore, a third further subject matter of the present invention relates to a cosmetic composition, in particular a cosmetic care or make-up composition, comprising the above-mentioned pigments.

[0151] In a particularly advantageous embodiment, the cosmetic composition according to the invention comprises, in addition to the interference pigment, less than 3% by mass of titanium dioxide, in particular less than 1% by mass of titanium dioxide. The titanium dioxide may be present in the composition as a filler, a dye or a UV filter. Titanium dioxide may also be present in the composition via an ingredient containing titanium dioxide, such as a pigment.

[0152] The cosmetic compositions of the present invention are preferably free of titanium dioxide.

[0153] Makeup includes eyeshadow, nail polish, eyeliner, lipstick, eyebrow makeup products, liquid and cream foundations, pressed powders, and loose powders. Skincare includes, for example, white or tinted skin creams and lip balms.

[0154] These products may be liquid or solid, aqueous or anhydrous. For example, they may be in the form of hydrogels, water-in-oil or oil-in-water emulsions.

[0155] In addition to the interference pigments according to the invention, the cosmetic product may also contain at least one cosmetic ingredient known to those skilled in the art, in particular chosen from solvents, oils, pigments other than the pigments according to the invention, lakes, dyes, waxes, cosmetically active compounds, surfactants, UV filters, gelling agents and thickeners. A person skilled in the art will be able to select the cosmetic ingredient on the basis of his or her general knowledge.

[0156] In a particular embodiment, the cosmetic composition comprises an oily phase in which are dispersed interference pigments, said pigments comprising a hydrophobic outer protective layer.

[0157] A series of specific subject matters of the present invention are given below.

[0158] 1. An interference-type single-layer or multilayer pigment comprising an inner core having a refractive index ranging from 1.00 to 2.10, said inner core being covered with at least one layer of a material comprising zinc sulfide, said layer having an average physical thickness ranging from 10 nm to 350 nm.

[0159] 2. The interference pigment according to claim 1, characterized in that the average physical thickness ranges from 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.

[0160] 3. The interference pigment according to claim 1 or 2, characterized in that the pigment has a size ranging from 1 μm to 2000 μm.

[0161] 1bis. Interference-type single- or multilayer pigment comprising an inner core delimited by at least one layer of a material comprising zinc sulfide, said zinc sulfide representing between 1% and 100% by mass of the pigment.

[0162] 2bis. The interference pigment according to claim 1bis, characterized in that the zinc sulfide accounts for between 1% and 70% by mass, between 15% and 65% by mass, between 20% and 60% by mass, between 25% and 55% by mass, between 30% and 50% by mass, or between 35% and 45% by mass of the pigment.

[0163] 3bis. The interference pigment according to claim 1bis or 2bis, characterized in that the pigment has a size ranging from 1 μm to 2000 μm.

[0164] 1ter. Interference-type single- or multilayer pigment comprising a core delimited by at least one layer of a material comprising zinc sulfide, said pigment excluding an interference layer containing titanium dioxide.

[0165] 2ter. The interference pigment according to claim 1ter, wherein the pigment contains titanium dioxide in an amount of less than 0.1% by mass of the pigment.

[0166] 3ter. The interference pigment according to claim 1ter or 2ter, characterized in that the core contains less than 0.1% by mass of TiO2 relative to the mass of the core.

[0167] 4. The interference pigment according to any one of the preceding subjects, characterized in that the material comprising zinc sulfide is a material consisting essentially of zinc sulfide, or a material consisting essentially of zinc sulfide and at least one selected from Fe 2+ 、Cu 2+ 、Mn 2+ 、Ag + 、Au 3+ 、Eu 3+ 、Al 3+ 、Ce 3+ and In 3+ Materials composed of metal ions.

[0168] 5. Interference pigment according to any of the preceding subject matters, characterized in that the layer of material comprising zinc sulfide has a refractive index ranging from 2.30 to 2.90, preferably close to 2.40.

[0169] 6. Interference pigment according to any of the preceding subjects, characterized in that the core is a gas or a solid matrix.

[0170] 7. Interference pigment according to any of the preceding subjects, characterized in that the solid substrate is chosen 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.

[0171] 8. Interference pigment according to any of the preceding subject matters, characterized in that the pigment is a single-layer pigment comprising a single layer of a material comprising zinc sulfide.

[0172] 9. Interference pigment according to any of the preceding subject matters, characterized in that the pigment is multilayered and comprises at least one alternation of a first layer of a material comprising zinc sulfide and having a refractive index in the range of 2.30 to 2.90 and a second layer adjacent to the first layer of a material having a refractive index in the range of 1.00 to 2.10, the difference in refractive index between the first layer and the second adjacent layer being greater than or equal to 0.3, preferably ranging from 0.3 to 1.5, more preferably being about 1.3.

[0173] 10. Interference pigment according to any of the preceding subject matters, characterized in that the layer of material comprising zinc sulfide is covered on one of its surfaces with a continuous or semi-continuous layer of metal nanoparticles, such as gold, silver or copper nanoparticles.

[0174] 11. The pigment according to any of the preceding subjects, characterized in that it comprises an outer protective layer which can be organic or inorganic and hydrophilic or hydrophobic.

[0175] 12. A method for synthesizing pigments (e.g., interference pigments) comprising heterogeneously precipitating a material comprising zinc sulfide onto solid particles.

[0176] 13. A method for synthesizing pigments according to the preceding subject, comprising:

[0177] - a first step of preparing an aqueous dispersion of solid particles, the pH of which is in the range of 2 to 8 and at a temperature close to the boiling point, and

[0178] - a second step of coating the solid particles, consisting in adding to the aqueous dispersion an aqueous solution of a zinc salt (such as zinc nitrate) and an aqueous solution of sodium sulphide, the pH of the reaction medium obtained being maintained between 2 and 7, so as to obtain a suspension of solid particles covered with a material comprising zinc sulphide.

[0179] 14. A cosmetic composition comprising the interference pigment according to any one of subjects 1 to 11.

[0180] 15. The cosmetic composition according to the preceding subject matter, characterized in that it comprises an oily phase in which interference pigments are dispersed, said pigments comprising a hydrophobic outer protective layer.

[0181] The present invention is described in more detail by the following examples. Unless otherwise stated, the temperature is between 20°C and 25°C and the pressure is atmospheric pressure.

[0182] Example 1: Synthesis of a pigment comprising a zinc sulfide layer

[0183] The equipment used includes a titrator, a peristaltic pump, and a thermally regulated reactor with a stirring system.

[0184] 1-Preparation of a dispersion of flake particles in a reactor

[0185] An acidic aqueous dispersion of mica particles (trademark PDM-2OL from Topy Industries, Inc.) at a concentration of approximately 10 g / L was heated to a temperature near boiling point while stirring.

[0186] 2-Preparation of Zn 2+ saline solution

[0187] The concentration of 0.03M acidified Zn 2+ The salt solution was placed in a peristaltic pump and injected into the reactor at a flow rate of 0.5 mL / min.

[0188] 3- Titration solution and titrator conditions

[0189] Prepare a 1 M Na2S solution as a sulfiding agent for synthesizing the ZnS layer. Set the static acidic pH on the titrator to greater than 3.

[0190] 4-Coating by nucleation and growth of zinc sulfide

[0191] Throughout the synthesis, the salt solution was added to the reactor with moderate stirring and the temperature near boiling. Throughout the synthesis, the statically stable pH, controlled by the previously selected titrator, was maintained by controlled addition of dilute sodium sulfide solution. In this case, 100 mL of salt water was added.

[0192] 5-Washing

[0193] After the reaction was complete, the ZnS-coated mica particles were centrifuged and redispersed in ethanol, followed by drying in an oven at 80°C for 12 hours.

[0194] 6-Observation

[0195] After the synthesis is complete, a continuous and uniform layer of zinc sulfide nanoparticles is observed on the mica particles. The coverage and thickness of the ZnS layer are controlled by the volume of zinc salt introduced into the reaction medium. In this example, adding 100 mL of solution results in a white powder that produces a yellow / orange reflected light.

[0196] Microstructural analysis by transmission electron microscopy and scanning electron microscopy revealed that the ZnS layer had a deposition thickness ( Figure 1 )(about 75nm) and its surface uniformity ( Figure 2 ). X-ray diffraction analysis shows the crystallinity and crystallographic properties of ZnS ( Figure 3 ).

[0197] Example 2: Interference Pigments Comprising a Hollow Core

[0198] 1. Preparation of gypsum flake particles

[0199] The first solution consisted of 41 g of anhydrous NaSO4 salt dissolved in 1900 mL of distilled water. The solution was placed on a magnetic hot plate, stirred at 600 rpm and heated to 55°C.

[0200] By adding 42.4 g of CaCl 2. Prepare a second solution by dissolving 2H2O in 100 mL of water containing 0.10 g of oxalic acid. Stir this solution until homogeneous and then pour it all at once into the heated first solution. Crystals will quickly form in the solution.

[0201] The solution was stirred at 50°C for 20 minutes. The solution was filtered. The filtrate was clear. The resulting solid was washed three times with water. All three washes were clean. The solid was dried in an oven at 75°C.

[0202] The obtained flakes were characterized by scanning electron microscopy (see Figure 5 ). Gypsum particles were observed to be unevenly distributed in the form of more or less elongated flakes.

[0203] 2. Coating gypsum flake particles with silica

[0204] The first step performed was the adsorption of citrate ions on the gypsum board.

[0205] 1 g of gypsum powder was mixed with 30 mL of 0.2 M citric acid solution (pH = 4) and stirred for 10 minutes, followed by centrifugation and washing with water to remove excess citrate not adsorbed on the gypsum.

[0206] The pH is raised in an alkaline medium to above pH 9 by adding ammonia and a few drops of water to the pellets, and electrostatic repulsion is generated between the particles.

[0207] The second step involves the preparation of a reaction medium: a hydroalcoholic solution with a volume mixing ratio of 24 / 76 (v / v) is prepared, and ammonia at a concentration of 0.37 M is added to the hydroalcoholic solution.

[0208] Basic pellets containing 1 g of gypsum base were added to the hydroalcoholic solution.

[0209] The third step is to add the hydrolyzable precursor to the reaction medium. The hydrolyzable silica precursor TEOS (tetraethyl orthosilicate) is added to the reaction medium all at once. The reaction medium is sealed to prevent ammonia evaporation and stirred overnight.

[0210] For gypsum particles with a particle size of 5-25 microns, a TEOS concentration of 0.00075 M is recommended to obtain a silicon dioxide layer with a thickness of 20 nm. This thickness can be adjusted according to the amount of TEOS added.

[0211] After this step, the powder was filtered and then dried in an oven at 75°C overnight.

[0212] Characterization of coated gypsum see Figure 6 and Figure 7 .

[0213] The powder was dried in an oven at 75°C.

[0214] In order to verify the presence of silica (characterized by the presence of silicon), EDX analysis was also performed ( Figure 8 ).

[0215] The surface microstructure differs from the smooth appearance previously achieved on the gypsum board, and a rough surface can be inferred. EDX analysis confirmed the presence of silicon.

[0216] 3. Deposition of zinc sulfide layer

[0217] According to the protocol of Example 1, the obtained silicon capsules were covered with a zinc sulfide layer.

[0218] Example 3: Interference Pigments Comprising a Hollow Core

[0219] In a first step, 6.6 g of silica-coated gypsum were introduced into a 5% nitric acid solution, and the whole was then heated under reflux for 3 hours.

[0220] The solution was centrifuged (10000 g - 5 minutes) and then washed with water and ethanol.

[0221] The powder was dried in an oven at 75 °C and then gradually annealed in the oven (heating to 400 °C at 3 °C / min, holding for 1 hour, and then cooling at 3 °C / min). Figure 9 and Figure 10) and scanning electron microscopy ( Figure 11 and Figure 12 ) were characterized.

[0222] Electron microscopy characterization revealed that more electrons passed through the particles during the acquisition of the SEM images, making the flakes more transparent than before dissolution. Dissolution of the gypsum matrix was confirmed by EDX. Figure 8 The calcium characteristic peak (KαCa) at 3.6eV proves the existence of gypsum. Figure 13 The peak of silicon (KαSi) at 1.739 eV also appeared. These combined analyses clearly indicate that thin flake particles with a hollow core were obtained.

[0223] Example 4: Synthesis of interference pigments including an outer protective layer

[0224] After the synthesis of the nacres described in Example 1, the recovered dry powder is subjected to various chemical treatments in order to be coated with silica.

[0225] The first step carried out was the adsorption of citrate ions on the nacre.

[0226] - ZnS nacre powder coated on mica (basic mica particle size 5-25 microns) was mixed with 30 mL of 0.2 M citric acid solution at pH = 4. After stirring for 10 minutes, it was centrifuged and washed with water to remove excess citrate not adsorbed on the nacre.

[0227] - The pH is raised in an alkaline medium to above pH 9 by adding ammonia and a few drops of water to the pellets, creating electrostatic repulsion between the particles.

[0228] The second step involves the preparation of the reaction medium.

[0229] - Prepare a hydroalcoholic solution with a volume mixing ratio of 24 / 76 (v / v). Add ammonia to a concentration of 0.37 M to the hydroalcoholic solution.

[0230] - Basic pellets containing 1 g of nacre substrate are added to the hydroalcoholic solution.

[0231] The third step involves adding a hydrolyzable precursor to the reaction medium.

[0232] - The hydrolyzable silica precursor TEOS (tetraethyl orthosilicate) was added to the reaction medium in one portion. The reaction medium was sealed to prevent evaporation of ammonia and kept stirring overnight.

[0233] - In this embodiment, the TEOS concentration is recommended to be 0.00075M to obtain a silicon dioxide layer with a thickness of 20nm, which can be Figure 4As shown in the transmission electron microscopy image, the thickness can be adjusted according to the amount of TEOS added.

[0234] -Finally, the powder was filtered and then dried in an oven overnight to obtain mica / ZnS / SiO2 mother-of-pearl powder.

[0235] Example 5: Cosmetic formulation containing pigments

[0236] Cosmetic formulations for makeup, in particular intended for application to the skin and / or lips, are prepared. These formulations comprise the interference pigments according to the invention.

[0237] Table 1 - Liquid Lipstick

[0238] Element quality% mineral oil 5 Creamy fat 10 Red iron oxide 2 zinc oxide 2 Organic varnish 2 Interference pigments of the present invention 2 Silicon dioxide 6 Mica 4 Ester oil 100 margin

[0239] Table 2 - Anhydrous Lip Balm

[0240] Element quality% Silicon dioxide 5 Polyethylene wax 5.5 Candelilla wax 3 Shea butter 1.5 Iron oxides 5 Organic pigments (varnishes) 2 Interference pigments of the present invention 3 Polydecene Hydrogen 100 margin

[0241] Table 3 - Lip Balm

[0242]

[0243]

[0244] Table 4 - Pressed Powder

[0245] Element quality% Mica 50 Silicon dioxide 10 nylon 8 magnesium stearate 2 Sorbic acid 0.1 Iron oxides 10 Interference pigments of the present invention 5 Ethylene glycol 2 Isononyl Isononanoate 100 margin preservative QS

[0246] Table 5 - Emulsion Foundation

[0247] Element quality% Ester oil 6.5 mineral oil 3.5 Caprylic / capric triglyceride 2.2 beeswax 0.8 Methyl polymethacrylate 1.1 Interference pigments of the present invention 3 Iron oxides (black, red and yellow) 10 Silicon dioxide 2 water 100 margin

[0248] Table 6- Waterless Eyeshadow

[0249]

[0250]

[0251] Table 7- Essence

[0252] Element quality% Ethylene glycol 3 Gel polymer 3 mineral oil 2 polyethylene glycol 1.5 Interference pigments of the present invention 4 preservative QS concentrated spices 0.3 water 100 margin

[0253] Table 8 - Scented Loose Powder

[0254] Element quality% Mica 33.5 Silica (and) Lauroyl Lysine 10 Interference pigments of the present invention 20.5 Calcium aluminum borosilicate 16.5 Corn starch (and) water 11 Caprylyl Glycol 1 Pentylene glycol 1 Preservatives and fragrances QS

[0255] Table 9 - Liquid Care Cream

[0256]

[0257]

Claims

1. A single-layer or multilayer interference pigment comprising a platelet-shaped core and a support, said core being covered with at least one first layer of a material comprising zinc sulfide, said support having a refractive index ranging from 1.00 to 2.10, characterized in that The core contains or consists of a gas, such as air.

2. The interference pigment according to claim 1, characterized in that The first layer has an average thickness ranging from 10 nm to 350 nm.

3. The interference pigment according to claim 1, characterized in that The inner core has a refractive index ranging from 1.00 to 1.

40.

4. The interference pigment according to claim 1, characterized in that The inner core is a capsule of a solid material other than zinc sulfide, and the solid material is selected from SiO2, Al2O3, and ZrO2.

5. The interference pigment according to claim 4, characterized in that The inner core is a silicon dioxide capsule.

6. The interference pigment according to claim 5, characterized in that The capsules have a larger size ranging from 1 micron to 1000 microns, and the silicon dioxide layer has a thickness ranging from 1 nm to 100 nm.

7. The interference pigment according to any one of claims 5 or 6, characterized in that A first layer of material comprising zinc sulfide overlies the silicon dioxide layer.

8. The interference pigment according to any one of claims 1 to 3, characterized in that The core is composed of a gas, and the pigment includes a gas core bounded by a first layer of material comprising zinc sulfide.

9. 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 a material comprising zinc sulfide.

10. The interference pigment according to any one of claims 1 to 8, characterized in that The pigment is a multilayer pigment and comprises 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.

11. Interference pigment according to the preceding claim, characterized in that The difference between the refractive index of the first layer of the material including zinc sulfide and the refractive index of the layer of the material having a refractive index in the range of 1.00 to 2.10 is greater than or equal to 0.

80.

12. Interference pigment according to any one of the preceding claims, characterized in that The pigment does not include a layer containing titanium dioxide.

13. Interference pigment according to any one of the preceding claims, characterized in that The pigment contains titanium dioxide in an amount of less than 0.1% by mass based on the mass of the pigment.

14. Interference pigment according to any one of the preceding claims, characterized in that The material containing zinc sulfide is a material consisting essentially of zinc sulfide, or a material consisting essentially of zinc sulfide and at least one selected from Fe 2+ 、Cu 2+ 、Mn 2+ 、Ag + 、Au 3+ 、Eu 3+ 、Al 3+ 、Ce 3+ and In 3+ Materials composed of metal ions.

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

16. The pigment according to any one of the preceding claims, characterized in that The pigment includes an outer protective layer, which is organic or inorganic, and hydrophilic or hydrophobic.

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

18. The method for synthesizing the interference pigment according to claim 5 according to claim 17, characterized in that Silica capsules are obtained by acid dissolution of an organic or inorganic flaky support covered with a silica layer, the purpose of the treatment being to remove part or all of the material constituting the support.

19. Process for synthesizing pigments according to the preceding claim, characterized in that The inorganic support comprises a material selected from the group consisting of magnesium hydroxide, calcium sulfate, mica, and borosilicate.

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

Images