Interference pigment comprising a hollow plate-shaped capsule and synthesis process

Abstract

The present invention relates to interference pigments comprising a hollow capsule made from a metal oxide such as silica, and a layer of a material selected from zinc oxide, bismuth oxychloride and cerium dioxide. The invention further relates to a process for synthesizing these pigments, and to cosmetic compositions containing them.

Description

Description Title of the invention: Interference pigment comprising a hollow platelet capsule and method of synthesis Technical Field

[0001] The present invention relates to interference pigments comprising a substrate with a low refractive index, as well as their synthesis process. The invention has applications in numerous technical fields, including cosmetics. Prior art

[0002] Generally, white interference pigments with colored effects are obtained by depositing a layer of a material with a high refractive index on the surface of semi-transparent platelet particles made of mica, glass or alumina with a lower refractive index.

[0003] Titanium dioxide is the metal oxide with the highest refractive index, so it is very commonly used for the manufacture of interference pigments.

[0004] The need remains to have interference pigments of different composition that can generate physical colors. Presentation of Hnvention

[0005] The present invention addresses this need by providing an interference pigment comprising a solid platelet substrate and a high-index material. The platelet substrate is a metal oxide capsule, and the high-index material can be zinc oxide, bismuth oxychloride, or cerium dioxide.

[0006] The inventors have found, surprisingly, that the intensity of the colored reflection produced by the pigment of the invention is high enough to consider substituting titanium dioxide-based pigments.

[0007] The invention relates in particular to an interference pigment comprising a core of low refractive index and a layer of a material of higher refractive index whose thickness is chosen to generate silvery white or colored reflections by interference.

[0008] In a first embodiment, the pigment of the invention comprises a solid substrate and at least one first interference layer of a high-index material selected from zinc oxide, bismuth oxychloride, and cerium dioxide, said substrate being a hollow silica platelet capsule. In a second embodiment, the interference pigment of the invention comprises a solid substrate and at least one first interference layer of a high-index material selected from oxychloride. of bismuth and cerium dioxide, said substrate being a hollow platelet capsule of a metal oxide other than titanium dioxide.

[0009] In a third embodiment, the interference pigment of the invention comprises a solid substrate and at least one first interference layer of a high index material selected from zinc oxide, bismuth oxychloride and cerium dioxide, said substrate being a hollow platelet capsule comprising a core made of air coated with a metal oxide shell, which is preferably different from titanium dioxide.

[0010] The invention further proposes a method for synthesizing an interference pigment comprising a first step of coating an inorganic platelet support with a layer of silica, a second step of total or partial removal of the support to obtain the hollow silica capsule, and a third step of coating the hollow silica capsule with a layer of the high index material.

[0011] The pigment may include titanium dioxide, but it is preferred that it contain less than 0.1% by mass relative to the mass of the pigment.

[0012] The invention advantageously allows for the partial or total substitution of titanium dioxide used for the manufacture of interference pigments and thus makes it possible to offer cosmetic products with low levels of titanium dioxide. Brief Description of the Figures

[0013] Figure 1 represents the reflectance curves of an earlier art pigment comprising a mica plate coated with a layer of zinc sulfide, and of an earlier art pigment comprising a mica plate coated with a layer of zinc oxide.

[0014] Figure 2 represents the reflectance curves of a pigment of the invention comprising a hollow silica capsule coated with a layer of zinc oxide of Example 1 and of a prior art pigment comprising a hollow silica capsule coated with a layer of zinc sulfide prepared according to Example 2 of published application W02024 / 12150. Description of the implementation methods

[0015] A first object of the invention relates to an interference pigment comprising a solid substrate and at least one first interference layer of a high index material selected from zinc oxide, bismuth oxychloride and cerium dioxide, said substrate being a hollow platelet capsule of a metal oxide, which is for example silica.

[0016] The term "platelet" in the context of the invention refers to a capsule whose largest dimension (length) is much greater than its smallest dimension (thickness). Its form factor can be between 2 and 100.

[0017] The term "hollow metal oxide platelet capsule" refers to an object comprising a core that is at least partially hollow and encased in a metal oxide shell.

[0018] The core may consist of a fluid, or comprise both a fluid and at least one solid object. The fluid may be a liquid or a gas. If the core comprises both a fluid and a solid, it may be in the form of a porous solid.

[0019] In a first embodiment, the hollow core is made of air.

[0020] In a second embodiment, the hollow core comprises air and an inorganic material selected from magnesium hydroxide, calcium sulfate, mica, and borosilicate. The presence of air in the hollow core can be determined by any method known to those skilled in the art.

[0021] The metal oxide of the shell is preferably different from titanium dioxide. It can be chosen from transparent or semi-transparent materials resistant to acid and / or basic attack, such as, for example, SiO2, Al2O3, ZrO2. In one particular embodiment, the metal oxide is silicon dioxide, referred to as "silica" in this description. The refractive index of the hollow metal oxide platelet capsule preferably ranges from 1.00 to 1.90, and even more preferably from 1.00 to 1.55.

[0022] In a particular embodiment, the capsule comprises a hollow core and a metal oxide shell, which may be a silica shell, the silica shell having an average thickness ranging from 1 nm to 1000 nm. This thickness is advantageously uniform. The thickness may have a minimum value selected from the group consisting of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, and 90 nm. The maximum thickness may be selected from the group consisting of 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, and 900 nm. It may be measured by any method known to those skilled in the art. For example, the capsule includes a silica shell with an average thickness ranging from 1 nm to 100 nm.

[0023] The interference pigment can be "single-layer," i.e., comprising a single first interference layer of a high-index material chosen from zinc oxide, bismuth oxychloride, and cerium dioxide. "Single-layer" means a layer of homogeneous composition that can be applied in one or more manufacturing process steps, preferably in a single step.

[0024] The interference pigment can alternatively be "multilayer", that is to say, comprise at least two layers of different composition, including at least one layer of a high index material chosen from zinc oxide, bismuth oxychloride and cerium dioxide, and at least one interference layer of a lower refractive index material, referred to as "low index material" in the following description.

[0025] The pigment of the invention may comprise, regardless of the number of layers of different materials, one or more layers of the high index material selected from zinc oxide, bismuth oxychloride and cerium dioxide.

[0026] The pigment size and the capsule size can be defined as an average number size of a particle population, advantageously equal to the D50 of the particle population constituting the pigment. In the case of the present invention, the D50 value is calculated from particle size distributions obtained by conventional methods such as laser diffraction or image analysis obtained by scanning electron microscopy (SEM) or transmission electron microscopy (TEM).

[0027] The pigment dimension can also be defined as the largest dimension of a population of particles constituting the pigment.

[0028] The pigment can therefore have a size ranging from 1 micron to 1000 microns, preferably from 10 microns to 500 microns.

[0029] The high-index material layer preferably has an average physical thickness ranging from 10 nm to 350 nm. It can, for example, range from 20 nm to 340 nm, from 30 nm to 330 nm, from 40 nm to 320 nm, from 50 nm to 310 nm, from 60 nm to 300 nm, from 70 nm to 290 nm, from 80 nm to 280 nm, from 90 nm to 270 nm, from 100 nm to 260 nm, or from 110 nm to 250 nm. In an advantageous embodiment, the high-index material layer has an average physical thickness ranging from 10 microns to 160 microns, or even from 10 microns to 120 microns. Physical thickness, also called optical thickness, can be measured by any method known to a person skilled in the art.

[0030] The pigment may lack a layer containing titanium dioxide. It may also lack a layer made of titanium dioxide. In particular, it lacks an interference layer containing titanium dioxide.

[0031] In a particularly advantageous embodiment of the invention, the interference pigment of the invention is devoid of titanium dioxide in that it contains less than 10% by mass, preferably less than 5% by mass, and preferably less than 1% by mass, relative to the mass of the interference pigment.

[0032] The pigment of the invention is an interference pigment that can be colored or white. This pigment can also generate one or more reflections of different colors, the color of the reflection(s) being different from the color of the pigment itself. The reflections can thus be silvery-white or another color. In the cosmetics field, for example, we distinguish between white pearlescent pigments with silvery-white reflections, white pearlescent pigments with colored reflections, colored pearlescent pigments with silvery-white reflections, and colored pearlescent pigments with colored reflections. These reflections can result in pearlescent and / or iridescent effects during the transmission and reflection of light through them, caused by optical interference phenomena. The generated interference color results from the reinforcement or destruction of reflected light rays at certain wavelengths.A layer of high-index material deposited on the capsule or in contact with a material of lower refractive index can generate destructive and constructive waves, which in turn produce a color. Destructive interference of a given wavelength occurs if the reflections from the two surfaces—surrounding medium (air, gas, or liquid) / material and material / substrate—are completely out of phase. For example, minimum reflection occurs for light incident perpendicularly at a wavelength λ for the layer of high-index material, with refractive index N and thickness e, when N*e = (nλ)*X / 2, where n is an integer. When the material layer is illuminated by white light, all wavelengths except λ appear in the reflection. Enhancement of a given wavelength occurs if the reflections from the two surfaces of the high-index material layer are in phase with each other.Thus, for an incident light perpendicular to the free surface of the layer, this occurs when N*e=(2n-l)*À / 4.

[0033] The layer of high-index material is preferably an interference layer, but it is possible to consider the case where the hollow capsule is coated with a layer of high index whose thickness is less than the minimum thickness at which a color is generated, the color being provided in this case by interference layers of other materials.

[0034] For the purposes of this invention, "interference layer" means a layer of a material whose optical thickness is capable of generating an optical color when deposited on a given support or on a layer of another material.

[0035] The high-index material layer may be in contact with the silica shell. Otherwise, one or more layers of other materials are interposed between the high-index material layer and the hollow silica platelet capsule.

[0036] The high-index material layer preferably comprises more than 50% by mass of the material from among zinc oxide, bismuth oxychloride and cerium dioxide. In In one embodiment, the high-index material is essentially composed of the material from among zinc oxide, bismuth oxychloride and cerium dioxide. "Essentially composed of" means a material comprising at least 90% by mass, preferably at least 99% by mass, of the high-index material.

[0037] The high-index material can be doped with at least one metal ion. Thus, the high-index material is essentially composed of a compound selected from zinc oxide, bismuth oxychloride, and cerium dioxide, and at least one metal ion selected from Fe 2+ Cu 2+ , Mn 2 ', Ag + , At 3+ , At + Eu 3 ', Al 3+ , This 3+ , Er 3 ', Ga 3 'and Mg 2+ The metal ion is advantageously present in such quantity that it forms a solid solution, i.e. a single crystalline phase, with zinc oxide, bismuth oxychloride and / or cerium dioxide.

[0038] The high-index material layer preferably has a refractive index ranging from 1.80 to 2.90, for example, 1.80 to 2.80, 2.40 to 2.70, or 2.45 to 2.65. In addition to the capsule and the high-index material, the pigment may include at least one material with a refractive index ranging from 1.80 to 2.90, such as, for example, a material selected from the group consisting of Fe₂O₃, FeTiO₃, Cr₂O₃, and / or Fe₃O₄. This material may be incorporated into the high-index material layer or be in the form of a separate layer. Thus, the high-index material layer may include, in addition to the high-index material, at least one material with a refractive index ranging from 1.80 to 2.90. According to one variant, the pigment comprises the first layer made of the high index material which is covered and in contact with a second layer made of a different material whose refractive index ranges from 1.80 to 2.90.

[0039] In a second particular embodiment of the invention, the interference pigment is multilayered and comprises at least one alternation of a first layer of the high index material, and a second layer, contiguous to the first, of a low index material, the difference in refractive index between said first layer and said contiguous second layer being greater than or equal to 0.3, and preferably ranging from 0.3 to 1.5, more preferably being on the order of 1.3.

[0040] In this description, "on the order of" or "close to" means a value that is equal to plus or minus 10% of the given numerical value, or a value that takes into account measurement uncertainties.

[0041] The refractive index of the layer of a low index material preferably ranges from 1.00 to 2.10, for example from 1.00 to 1.80 or from 1.00 to 1.60.

[0042] In the interference pigment of the invention, the layer of high-index material can be coated on one of its surfaces with a continuous or semi-continuous layer of metallic nanoparticles, for example gold, silver or copper nanoparticles, the nanoparticles having for example at least an average dimension less than or equal to 500 nm, preferably less than or equal to 100 nm.

[0043] The addition of metallic nanoparticles can generate a black background and a more or less pronounced color path for the nacre. These metallic nanoparticles can be noble metals such as gold or silver, or copper or chromium, which are preferably deposited semi-continuously. Depending on the precious metal content deposited on the final pigment layer, a black background can be created, allowing, in particular, iridescent white nacres to have a core color close to their reflective color, depending on the quantity of nanoparticles deposited. The iridescent white nacre thus becomes a colored nacre with colored reflections. Furthermore, the addition of nanoparticles with visible light absorption will modify the reflective and transmitted color of the nacre to a greater or lesser extent.

[0044] In a particular embodiment, the pigment of the invention is a multilayer interference pigment comprising a hollow metal oxide capsule covered by at least one stack comprising at least: - a first layer of the high-index material, - a second layer, adjacent to the first, of a material having a refractive index ranging from 1.00 to 1.80, and - a third layer of a high index material, contiguous to the second.

[0045] The first layer can be colorless, in the sense that it does not absorb wavelengths in the visible spectrum. The second layer can also be colorless.

[0046] Examples of interference pigments according to the invention include the following layer stacks, - the slash indicating the separation between two different layers, - parentheses denote a single layer comprising several materials, - the metallic oxide being preferably different from titanium dioxide, and preferably still being silica, - the term "high index material 1" designating ZnO, BiOCI or CeO2, and - the term "high index material 2" designates a high index material different from high index material 1: Hollow metal oxide capsule / High index material 1 Hollow metal oxide capsule / High index material 1 / Low index material / High index material 1 Hollow capsule of metallic oxide / High index material 1 / Low index material / High index material 1, the stacking of the three layers High index material 1 / Low index material / High index material 1 can be repeated several times successively Hollow capsule of metal oxide / High index material 1 doped with a metal ion Hollow capsule of metal oxide / High index material 1 / High index material 2 Hollow capsule of metal oxide / (High index material 1+High index material 2) Hollow capsule of metal oxide / High index material 1 / High index material 1 doped with a metal ion Hollow metal oxide capsule / High index material 1+High index material 1 doped with a metal ion) Hollow capsule of metal oxide / high index material 2 / High index material 1 Hollow capsule of metal oxide / high index material different from High index material / low index material / High index material. In these examples of interference pigments, the high-index material 2 preferably has a refractive index ranging from 2.10 to 2.90, and can be, for example, Fe2O3, FeTiO3, Cr2O3, Fe3O4. The low-index material preferably has a refractive index ranging from 1.00 to 1.60. The described stacks can be coated with a continuous or semi-continuous layer of metallic nanoparticles, for example, gold, copper, or silver nanoparticles. In these examples, a protective silica layer can be applied to the last layer of the stack.

[0047] The interference pigment of the invention may include an advantageously transparent outer layer without a coloring function. The outer layer may serve to protect the pigment from the external environment, for example from UV rays, or to facilitate the formulation of the pigment in compositions in which it is used.

[0048] The outer layer can be continuous or discontinuous on the surface of said pigment, of organic or mineral nature.

[0049] The pigment of the invention can thus advantageously undergo a hydrophobic treatment by applying a hydrophobic agent to all or part of the surface of the pigment in order to facilitate the dispersion of said pigment in a fatty phase, for example an oily phase.

[0050] Alternatively, the pigment of the invention can undergo a hydrophilic treatment by applying a hydrophilic agent to all or part of the surface of the pigment, in order to facilitate the dispersion of said pigment in an aqueous phase or consisting of a polar solvent such as an alcohol or an ester oil.

[0051] Such a surface agent can advantageously be chosen from natural or synthetic film-forming polymers, amino acids, metallic soaps, esters, silicone or fluorinated compounds, lipids, or a mixture of these compounds.

[0052] Examples of hydrophilic film-forming polymers include polyurethanes and their derivatives, acrylic polymers, native or modified polysaccharides, cellulose or one of its derivatives and mixtures thereof.

[0053] Examples of hydrophobic film-forming polymers include silicone polymers, vinylpyrrolidone and alkene copolymers, liposoluble vinyl ester copolymers, polyolefins, alkylcelluloses, crosslinked elastomers, dextrin and fatty acid esters, silicone or non-silicon resins, preferably rosinate and candelilla resin, and mixtures thereof.

[0054] The amino acid-type surfactant may be, for example, glycine, alanine, sarcosine, proline, hydroxyproline, aspartic acid, glutamic acid, or lysine, or a derivative such as, for example, an acylated amino acid comprising a fatty acid, saturated or unsaturated, having from 1 to 22 carbon atoms, preferably from 8 to 20 carbon atoms. Such an acylated amino acid-type 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 one of their salts, such as a sodium, potassium, calcium, magnesium, or aluminum salt.The agents particularly preferred in salt form are preferably sodium myristoyl glutamate, disodium stearoyl glutamate, sodium lauroyl aspartate, dilauramido-glutamide lysine, sodium palmitoyl sarcosine, magnesium palmitoyl glutamate and disodium cocoyl glutamate.

[0055] As metallic soap-type surfactants, aluminium myristate and magnesium stearate can be advantageously mentioned.

[0056] As an ester-type surfactant, advantageous examples include isostearyl sebacate, dextrin and fatty acid esters such as dextrin stearate, dextrin isostearate, dextrin palmitate, or polyglyceryl-2 tetraisostearate.

[0057] Examples of silicone-based surfactants include methicone, hydrogenodimethicone, dimethicone, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, isobutyltrimethoxysilane, and decyltrimethoxysilane. octyltrimethoxysilane, octyltriethoxysilane, octadecyltriethoxysilane and hexadecyltriethoxysilane.

[0058] As fluorinated surfactants, we can advantageously mention perfluorohexylethyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane or tridecafluorooctyltriethoxysilane.

[0059] Examples of lipid surfactants include phospholipids, lecithin, triglycerides, fats, oils, and waxes, such agents being advantageously of natural origin.

[0060] The outer layer may also include a UV-blocking material such as cerium-doped silica. A UV-protective layer has the advantage of stabilizing the color and / or reflections of the pigment over time, particularly throughout the service life of formulations and manufactured products containing the pigment. Pigment synthesis process

[0061] A second object of the invention relates to a method for synthesizing a pigment, in particular an interference pigment, comprising a hollow platelet capsule of silica and at least one first interference layer of a high-index material selected from zinc oxide, bismuth oxychloride, and cerium dioxide, said method comprising - a first step of coating an inorganic platelet support with a layer of silica, - a second step of total or partial removal of the inorganic platelet support to obtain the hollow silica platelet capsule, and - a third step of coating the hollow silica platelet capsule with a layer of the high index material.

[0062] The inorganic platelet support may include at least one material selected from magnesium hydroxide, calcium sulfate (gypsum), mica, borosilicate and bismuth oxychloride.

[0063] Silica can be replaced by a metal oxide chosen from Al2O3 and ZrO2. The metal oxide can be deposited on the support by any method known to a person skilled in the art.

[0064] In the case where the metal oxide is silica, the coating of the platelet support can be carried out by a sol-gel process known to those skilled in the art.

[0065] The total or partial removal of the inorganic platelet support can be achieved by selective chemical or physical decomposition, so as not to alter the structure of the metal oxide layer of the substrate that was applied during the first step.

[0066] The treatment of the coated substrate may include one or more aqueous solution treatment steps. For example, the total or partial removal of the inorganic platelet substrate is achieved by dissolving said substrate in acid or base.

[0067] For example, the coated substrate can be placed in an acidic aqueous solution so as to attack and / or dissolve the substrate completely or partially, without dissolving the metal oxide layer. The acidic aqueous solution is preferably an aqueous solution of a mineral acid chosen from hydrofluoric acid, phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid, and mixtures thereof.

[0068] The coated support can successively undergo one or more stages of treatment in an acidic environment, washings to remove ions resulting from the dissolution of the inorganic support, possibly followed by treatment in a basic environment.

[0069] The aqueous solution treatment can be carried out at a temperature ranging from 20°C to 100°C, for a duration ranging from 1h to 24h.

[0070] The coated substrate can also, or alternatively, undergo heat treatment by raising the temperature.

[0071] The high index material can be deposited in thin films by any method known to a person skilled in the art by physical or chemical deposition, for example by atomic layer deposition.

[0072] The synthesis process of the invention may include a fourth step of encapsulating the capsules coated with high-index material with an organic or mineral matrix in order to form a protective layer,

[0073] The interference pigment of the invention can be incorporated into various manufactured products such as food products, paints, inks, dyes, plastics and cosmetics.

[0074] In a particular embodiment, the interference pigment described above can be used in cosmetic products, such as skincare or makeup cosmetic products.

[0075] A third other object of the invention therefore relates to a cosmetic composition, in particular a cosmetic composition for skincare or makeup, comprising a pigment as described above and at least one cosmetic ingredient.

[0076] The cosmetic ingredient is chosen from among solvents, oils, pigments other than the pigment of the invention, lacquers, colorants, waxes, cosmetically active compounds, surfactants, UV filters, gelling agents, and thickeners. A person skilled in the art may choose the cosmetic ingredients based on their general knowledge.

[0077] In an advantageous embodiment, the cosmetic ingredient does not include titanium dioxide. For example, the cosmetic composition of the invention comprises less than 3% by mass of titanium dioxide, in particular less than 1% by mass of titanium dioxide, the titanium dioxide being able to be added to the composition as a filler, colorant or UV filter. The cosmetic composition of the invention is preferably free of titanium dioxide, in the sense that it does not contain an ingredient comprising titanium dioxide.

[0078] Makeup products include eyeshadows, nail polishes, eyeliners, lipsticks, eyebrow products, liquid and compact foundations, pressed powders, and loose powders. Skincare products include, for example, white or tinted creams and lip balms.

[0079] These products can be liquid or solid, contain water or be anhydrous. They are, for example, in the form of aqueous gels, water-in-oil or oil-in-water emulsions.

[0080] In a particular embodiment, the cosmetic composition comprises an oily phase in which the interference pigment is dispersed, which includes an outer protective layer of a hydrophobic nature.

[0081] The invention is described in more detail by the following example. Unless otherwise stated, the temperature is between 20°C and 25°C, and the pressure is atmospheric pressure.

[0082] Exempt 1; Pwment terférentü comyrenarst me cassate crease de siSîce et me coache mterféreetieUte d'oxyde de zinc, préparé à partir d gypse 1. Préparation de particules assiettetaires de gypse A first solution consisting of 41 g of anhydrous NaSO4 salt dissolved in 1900 mL of distilled water. The solution is placed on a magnetic hot plate, stirred at 600 rpm and heated to 55°C. A second solution is prepared by dissolving 42.4 g of CaCl₂·2H₂O in 100 mL of water containing 0.10 g of oxalic acid. This solution is stirred until homogeneous and poured all at once onto the first heated solution. Crystals form rapidly in solution. The solution is stirred for 20 minutes at 50°C. 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 platelets obtained were characterized by scanning electron microscopy. A heterogeneous distribution of gypsum particles in the form of more or less elongated platelets was observed. 2. Coating of gypsum platelet particles with silica A first step of citrate ion absorption onto gypsum platelets is carried out. 1 g of gypsum powder is mixed with 30 mL of a 0.2 M citric acid solution at pH~4. After 10 min of stirring, separation by centrifugation and washing with water is carried out to remove excess citrate not absorbed onto the gypsum. The pH is raised to a basic environment by adding ammonia to the pellet with a few drops of water in order to reach a higher pH at 9 and to generate electrostatic repulsions between the particles. A second step consists of preparing the reaction medium. A hydroalcoholic solution with a volume mixture of 24 / 76 (v / v) is prepared. Ammonia is added to the hydroalcoholic solution at a concentration of 0.37 M. The basic pellet containing the 1 g of gypsum substrate is added to the hydroalcoholic solution. A third step involves adding the hydrolyzable precursor to the reaction medium. TEOS (tetraethyl orthosilicate), a hydrolyzable precursor of silica, is added all at once to the reaction medium. The reaction medium is then sealed to prevent ammonia evaporation and stirred overnight. A TEOS concentration of 0.00075 M is recommended for gypsum particles with a particle size between 5 and 25 microns to obtain a silica layer 20 nm thick. This thickness can be adjusted depending on the amount of TEOS added. After this step, the powder is filtered and then oven-dried overnight at 75°C. 3. Preparation of hollow silica capsules In the first step, 6.6 g of encapsulated gypsum are introduced into a 5% nitric acid solution and heated under reflux for 3 hours. The solution is centrifuged (10,000 g - 5 min) and then washed with water and ethanol. The powder is oven-dried at 75°C and then gradually annealed in a furnace (3°C / min up to 400°C, held for 1 hour, then cooled down at 3°C / min). Characterizations by transmission electron microscopy and scanning electron microscopy (SEM) show that the platelets are more transparent after The gypsum dissolution step. The dissolution of the gypsum substrate is confirmed by EDX. The characteristic Calcium peak at 3.6 eV (KaCa), indicating the presence of gypsum, completely disappeared after dissolution. The Silicon peak at 1.739 eV (KaSi), however, is clearly present. These combined analyses demonstrate that hollow-core platelet particles were indeed obtained. 4. Coating of hollow silica capsules with ZnO In a first step, 1 g of hollow silica capsules are dispersed in 300 mL of water. Heterogeneous precipitation of the ZnS compound is carried out on the hollow capsules by simultaneously introducing a zinc nitrate solution and a sodium sulfide solution into the dispersion, which is maintained at pH 3.9 and a temperature of 75°C. The higher the volume of zinc nitrate added, the thicker the ZnS layer. The ZnS-coated hollow capsules are filtered, washed with water and ethanol, and then oven-dried at 80°C. In a second step, the dried ZnS-coated hollow capsules are gradually annealed in an oven (2°C / min up to 800°C, then decreasing by 2°C / min) to obtain platelet-like particles coated with ZnO.

[0083] Example 2; Interferometric material comprising a caslate crease of silica and an interferometric conche of cerium oxide (CeO2) prepared from 1. Preparation of hollow silica capsules The preparation of the hollow silica capsules is carried out by reproducing steps 1, 2 and 3 described in example 1 above. 2. Coating of hollow silica capsules with CeO2 100 g of hollow silica capsules, measuring 10–50 microns, were dispersed in 2 liters of deionized water. A 21 wt% Ce(NO3)3·6H2O solution was slowly added to the reactor. The pH of the suspension was set at 7.5 and maintained constant by the addition of a 20% aqueous sodium hydroxide solution. The temperature was maintained at 75°C. The layer thickness increased with the amount of salt added. A salt volume of 600 mL resulted in layer thicknesses of 60 nm, while a salt volume of 1300 mL yielded a layer thickness of 140 nm. At the end of the pigment preparation process, it is thus possible to generate different interference effects.

[0084] Exempt 3; Interference pigment comprising a hollow silica substrate and an interference coating of zinc oxide, prepared from BiO 1. Coating of BiOCI platelet particles with silica

[0085] A first step of absorption of citrate ions onto the BiOCI platelets is carried out.

[0086] 1g of BiOCI powder is mixed with 30 mL of a 0.2 M citric acid solution at pH-4. After 10 min of stirring, separation by centrifugation and washing with water is carried out to remove excess citrate not adsorbed on the BiOCI.

[0087] The pH is raised to a basic environment by adding ammonia to the pellet with a few drops of water in order to reach a higher pH at 9 and to generate electrostatic repulsions between the particles.

[0088] A second step consists of preparing the reaction medium. A hydroalcoholic solution with a volume mixture of 24 / 76 (v / v) is prepared. Ammonia is added to the hydroalcoholic solution at a concentration of 0.37 M.

[0089] The basic pellet containing the 1 g of BiOCI substrate is added to the hydroalcoholic solution.

[0090] A third step involves adding the hydrolyzable precursor to the reaction medium. TEOS (tetraethyl orthosilicate), a hydrolyzable precursor of silica, is added all at once to the reaction medium. The reaction medium is then sealed to prevent ammonia evaporation and stirred overnight.

[0091] A TEOS concentration of 0.00075 M is recommended for BiOCI particles with a particle size between 6 and 15 microns to obtain a silica layer 20 nm thick. This thickness can be adjusted depending on the amount of TEOS added.

[0092] At the end of this step the powder is filtered and then dried in an oven overnight at 75°C. 2. Preparation of hollow silica capsules from silica-coated BIOCI platelet particles

[0093] In the first step, 21g of encapsulated BiOCI are introduced into a 5% hydrochloric acid solution and heated under reflux for 3 hours. The solution is filtered and then washed with ethanol. The powder is air-dried and then gradually annealed in an oven (2°C / min up to 1000°C, held for 1 hour, then cooled down at 2°C / min). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) characterizations show that the platelets are more transparent after the BiOCI dissolution step. The dissolution of the BiOCI substrate is confirmed by EDX. The characteristic bismuth peak at 2.4 eV, which indicates the presence of BiOCI, completely disappeared after dissolution. The silicon peak at 1.739 eV (KaSi), however, is clearly present. Coupled analyses clearly show that hollow-core platelet particles were indeed obtained. 3. Coating of hollow silica capsules with ZnO This step is identical to step 4 of coating the hollow silica capsules with zinc oxide which is described in Example 1.

[0094] Exempt 4; Cosmetic formulas containing yq pigment interferences according to T rangeion Cosmetic formulas for makeup, particularly intended for application on the skin and / or lips, are being prepared. These formulas include an interference pigment according to the invention. Table 1 - Liquid Lipstick INGREDIENTS % BY MASS MINERAL OIL 5 PASTY FAT BODY 10 RED IRON OXIDES 2 ZINC OXIDE 2 ORGANIC LACQUERS 2 INTERFERENCE PIGMENT OF THE INVENTION 2 SILICA 6 MICA 4 Ester oils q.s. 100 Table 2 - Anhydrous lip balm INGREDIENTS % BY MASS SILICA 5 POLYETHYLENE WAX 5.5 CANDELILLA WAX 3 SHEA BUTTER 1.5 IRON OXIDES 5 ORGANIC PIGMENTS (LACQUERS) 2 INTERFERENCE PIGMENT OF THE INVENTION 5 POLYDECENE HYDROGEN QSP 100 Table 3 - Lip Balm INGREDIENTS % BY MASS NYLON 8 SILICA 9 POLYETHYLENE 17 GLYCERIN 14 INTERFERENCE PIGMENT OF THE INVENTION 1 ISONONYL ISONONANOATE QSP 100 Table 4 - Compact Powder Foundation INGREDIENTS % BY MASS MICA 50 SILICA 10 NYLON 8 MAGNESIUM STEARATE 2 SORBIC ACID 0.1 IRON OXIDES 10 INTERFERENCE PIGMENT OF THE INVENTION 5 Glycols, 2-Isononyl Isononanoate, q.s. 100, Preservatives, q.s. Table 5 - Emulsion Foundation INGREDIENTS % BY MASS OILS ESTERS 6.5 MINERAL OIL 3.5 CAPRYLIC / CAPRIC TRIGLYCERIDES 2.2 BEESWAX 0.8 METHYL POLYMETHACRYLATE 1.1 INVENTIONAL INTERFERENCE PIGMENT 3 IRON OXIDES (black, red and yellow) 10 SILICA 2 WATER QSP 100 Table 6 - Anhydrous Eyeshadow INGREDIENTS % BY MASS SILICA 15 SYNTHETIC FLUORPHLOGOPITE 10 IRON OXIDES 8 INTERFERENCE PIGMENT OF THE INVENTION 15 OILS AND WAXES QSP 100 Table 7 - Serum INGREDIENTS % BY MASS GLYCOL 3 GELDING POLYMER 3 MINERAL OIL 2 POLYETHYLENE GLYCOL 1.5 INVENTIONAL INTERFERENCE PIGMENT 4 PRESERVATIVES QS PERFUME CONCENTRATE 0.3 WATER QSP 100 Table 8 - Loose Scented Powder INGREDIENTS % BY MASS MICA 33.5 SILICA (AND) LAUROYL LYSINE 10 INVENTIONAL INTERFERENCE PIGMENT 20.5 CALCIUM ALUMINUM BOROSILICATE 16.5 CORN STARCH (AND) AQUA 11 CAPRYLYL GLYCOL 1 PENTYLENE GLYCOL 1 PRESERVATIVES AND FRAGRANCES QS Table 9 - Fluid Care Cream INGREDIENTS % BY MASS INVENTIONAL INTERFERENCE PIGMENT 0.5 POLYURETHANE-35 4 OILS 12 PASTY 2 FAT ALCOHOL 1.3 STEARETH-21 1 STEARETH-2 0.5 UREE 10 AQUEOUS PHASE GELDING AGENT 0.5 PHENOXYETHANOL 0.35 ACRYLATES / C10-C30 ALKYL ACRYLATE 0.3 CROSSPOLYMER XANTHAN GUM 0.1 Hyaluronic acid 0.2, polyglycerol 17 GLYCEROL 3.9 Glycols 3.6, preservatives and perfumes qs, water qsp 100

[0095] interference according to prior art The optical effects generated by pigments of the invention and pigments of the prior art were compared. The silica capsule used to manufacture the pigments of the invention was identical to the silica capsule used for the pigment of the prior art. 1. Measurements L*a*b* The results of the measurements which were carried out on the pigment of Example 1 and on the pigment of the earlier art prepared according to Example 2 of published application WO2024 / 121505 are presented in the following table. Table 10 - Measurements of L*a*b* Pigment | L* a* b* Previous Art | 97.13 0.23 2.60 Invention Example 1 | 99.13 -2.00 5.20

[0096] For identical thicknesses of high-index material, ZnO nacre is whiter than ZnS nacre. The nacre of the invention is also greener and yellower. 2. Reflectance Measurements Optical simulations were performed on: - a pigment of the invention comprising a hollow silica capsule coated with a layer of zinc oxide of Example 1, - a pigment of the prior art comprising a hollow silica capsule coated with a layer of zinc sulfide prepared according to Example 2 of published application WO2024 / 121505, - a pigment from the earlier art comprising a mica platelet coated with a layer of zinc sulfide, and - a pigment from the earlier art comprising a mica plate coated with a layer of zinc oxide. The reflectance curves obtained for each of the four pigments are shown in Figure 1 and Figure 2.

Claims

DEMANDS

1. Interference pigment comprising a solid substrate and at least one first interference layer of a high index material selected from zinc oxide, bismuth oxychloride and cerium dioxide, said substrate being a hollow platelet capsule of silica.

2. Interference pigment according to claim 1, characterized in that the hollow silica capsule comprises a hollow core and a silica shell having an average thickness ranging from 1 nm to 1000 nm.

3. Interferential pigment according to claim 1, characterized in that the hollow silica capsule comprises a core at least partially hollow and a non-interferential silica shell having an average thickness ranging from 1 nm to 1000 nm.

4. Interference pigment according to any one of claims 1 to 3, characterized in that it is a white mother-of-pearl with silvery-white reflections, a white mother-of-pearl with colored reflections, a colored mother-of-pearl with silvery-white reflections or a colored mother-of-pearl with colored reflections,

5. Interference pigment according to any one of the preceding claims, characterized in that the layer of the high index material has an average physical thickness ranging from 10 nm to 160 nm, for example from 50 nm to 100 nm.

6. Interference pigment according to any one of the preceding claims, characterized in that the hollow core comprises air and an inorganic material selected from magnesium hydroxide, calcium sulfate, mica and borosilicate.

7. Interference pigment according to any one of the preceding claims, characterized in that the hollow silica platelet capsule has a refractive index ranging from 1.00 to 1.

55.

8. Interference pigment according to any one of the preceding claims, characterized in that the pigment is devoid of titanium dioxide.

9. A method for synthesizing an interference pigment comprising a hollow platelet capsule of silica and at least one first interference layer of a high-index material selected from zinc oxide, bismuth oxychloride and cerium dioxide, said method comprising: - a first step of coating an inorganic platelet support with a layer of silica, - a second step of total or partial removal of the inorganic platelet support to obtain the hollow silica platelet capsule, and - a third step of coating the hollow silica platelet capsule with a layer of the high index material.

10. A method for synthesizing an interference pigment according to the preceding claim, characterized in that the total or partial removal of the inorganic platelet support is achieved by acid or basic dissolution of said support.

11. A method for synthesizing an interference pigment according to the preceding claim, characterized in that the inorganic platelet support comprises a material selected from magnesium hydroxide, calcium sulfate, mica, borosilicate and bismuth oxychloride.

12. Cosmetic composition comprising an interference pigment according to any one of claims 1 to 7 and at least one cosmetic ingredient, said composition comprising less than 3% by mass of titanium dioxide.

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