WO2019102114A1

WO2019102114A1 - Cerium oxide/silica particles

Info

Publication number: WO2019102114A1
Application number: PCT/FR2018/052884
Authority: WO
Inventors: Camille Jourde; Nour HAMDAN
Original assignee: Rhodia Operations
Priority date: 2017-11-24
Filing date: 2018-11-16
Publication date: 2019-05-31
Also published as: FR3074162A1

Abstract

The present invention relates to silica-coated cerium oxide particles and the use thereof in the field of cosmetics. The invention also relates to a cosmetic composition, in particular a photoprotective composition, comprising said particles.

Description

CERIUM OXIDE PARTICLES / SILICA

The present application claims the priority of the French patent application No. 1761164 filed on November 24, 2017 and the contents of which are incorporated in full by reference. In case of inconsistency between the text of the present application and the text of the French patent application which affects the clarity of a term or expression, reference will be made to this application only.

The present invention relates to cerium oxide particles coated with silica and their use in the field of cosmetics. The invention also relates to a cosmetic composition, especially a photoprotective composition, comprising said particles.

The technical problem

Keratinous substances, in particular the skin, are daily exposed to sunlight. It is known that prolonged exposure of keratin materials to sunlight is likely to induce skin disorders or even superficial damage. Radiation wavelengths between 280 nm and 400 nm allow tanning of the human epidermis and UVB rays harm the development of natural tanning.

UVA rays penetrate more deeply into the skin than UVB rays. UVA rays cause immediate and persistent browning of the skin. Daily exposure to UVA rays, even for short periods, under normal conditions can lead to degradation of collagen and elastin fibers which results in a change in the micro-relief of the skin, the appearance of wrinkles and irregular pigmentation (brown spots, heterogeneity of complexion).

Protection against UVA and UVB radiation is therefore necessary. An effective photoprotection product must protect both UVA and UVB radiation. There are already photoprotective cosmetic compositions filtering UVA and UVB.

Inorganic UV filters are already known. Titanium dioxide is the best known but it is likely to interact with some of the organic compounds of the photoprotective composition (photocatalytic action) as avobenzone. The cerium oxide functionalized with polyacrylic acid can be used as a UV filter, but it has a stability in a pH range <3.0, whereas the cosmetic compositions generally have a pH close to 7.0. In addition, the polyacrylic acid is capable of being gradually released into the cosmetic composition. Another disadvantage that can be observed with inorganic UV filters is that when the cosmetic composition is applied to the skin in the form of a film, it can generate on the latter a too marked coverage effect, a whitening effect and a dry touch that are cosmetically undesirable and generally unpopular with users. This effect is all the more marked as the concentration of inorganic filter in the composition is high.

The Applicant has developed a fully inorganic UV filter which exhibits stability in a pH range suitable for cosmetic compositions.

Brief description of the invention

The invention relates to cerium oxide particles totally or partially covered with silica, for which the SiO ₂ / CeO ₂ mass ratio is between 0.05 and 0.30, preferably between 0.05 and 0.25, having a mean diameter d ₅ o measured by a granulometer by centrifugation between 40 and 500 nm, rather between 100 and 500 nm, more particularly between 200 and 500 nm, more particularly between 300 and 500 nm, or between 400 and 500 nm, characterized in that these particles are formed of primary particles having a median diameter d _MET of between 25 and 150 nm, d _MET being obtained using a number distribution of the diameters of the primary particles, diameters determined from one or more transmission electron micrographs.

The invention also relates to the process for preparing said particles. These may be in the form of a dispersion in a liquid medium or in the form of a powder.

The invention also relates to a cosmetic composition, in particular a photoprotective composition, comprising these particles.

The invention also relates to the use of the particles of the invention or of the dispersion for the preparation of a cosmetic composition or to the use of the particles of the invention as a UV-filter, in particular in a cosmetic composition.

figures

Fig. 1 and FIG. 2 are TEM particle plates as prepared in Example 2. In FIG. 2, we can see that the primary particles are well individualized.

Fig. 3 shows a volume distribution curve of particle diameters of Examples 1 and 2 obtained using a centrifugal sedimentation granulometer.

Fig. 4 illustrates the stability test of Example 3 (comparison between the starting cerium oxide particles and the particles of the invention of Example 2).

The prior art

WO 2005/095505 and FR 2867181 describe a colloidal dispersion comprising cerium oxide particles coated at least in part with silica having a mean size measured by DQEL of at most 85 nm. However, the particles are thinner and do not have a d _MET of at least 25 nm as the particles of the present application.

WO 2016/203062 discloses cerium oxide particles functionalized with polyacrylic acid and not with silica.

JP 2011/012031 discloses inorganic particles that can be coated with silica and functionalized with a polymer such as polyacrylic acid.

EP 0810181 describes a process for the preparation of cerium oxide and silica particles. The particles obtained by this method are different insofar as the process for obtaining cerium oxide is not controlled as in the present invention.

EP 0596442 discloses composite particles formed of a core of mica, talc or sericite coated with a layer based on cerium and silica. The particles of the invention do not comprise mica, talc or sericite. EP 1055642 describes particles of doped cerium oxide and silica. The particles of the present invention do not include doped cerium oxide.

US 2010/0003202 discloses inorganic particles coated with silica ([0032]). There is no mention of the average diameter of ₅ o measured by a centrifugal particle size between 40 and 500 nm.

None of these documents describes or suggests the particles according to the invention.

Detailed description of the invention

As regards the particles according to the invention, these are in the form of cerium oxide particles totally or partially covered with silica. These particles are characterized by a mean diameter of ₅ o measured by a granulometer by centrifugation between 40 and 500 nm, rather between 100 and 500 nm, more particularly between 200 and 500 nm, more particularly between 300 and 500 nm, or between 400 and 500 nm. d50 can also be between 150 and 500 nm.

The average diameter d ₅ o corresponds to the median diameter of a volume distribution of particle diameters obtained using a centrifugal sedimentation granulometer. It is therefore the value for which on the cumulative curve of the distribution, 50% of the particles have a diameter greater than d ₅ o and 50% of the particles have a diameter of less than d ₅ o This granulometer separates the particles into according to their size by centrifugal sedimentation in a liquid medium (water), the sedimentation being stabilized by a density gradient. The particles sediment by centrifugation in a transparent disk of optical quality and diffuse a light beam. The average diameter d ₅ o corresponds to the diameter which is measured on particles qualified as secondary because they are formed of particles of smaller sizes, qualified as primary particles.

Silica completely or partially covers the cerium oxide particles. For some of the particles, it is possible to observe by contrast difference on transmission electron microscopy (TEM) plates the presence of silica covering the particles. For some other particles, the TEM microscopy does not allow to observe the silica at certain areas of the surface of the cerium oxide particles either that there is no silica at this point (partial recovery) or that it is not possible to see silica at this zone (technical limitation of the MET). Reference may be made to the particles of FIG. 2.

The thickness of the silica layer determined on the TEM plates is generally at least 1 nm, or even at least 2 nm. This thickness may be between 1 and 10 nm, more particularly between 2 and 10 nm, more particularly between 2 and 7 nm, or even between 2 and 5 nm.

As can be seen in FIG. 2, the primary particles of cerium oxide may have a polygonal shape.

From one or more transmission electron microscopy _micrographs , it is possible to access the average diameter of the primary particles, as well as the standard deviation of the primary particle size distribution noted S _MET. - The method consists of measuring the diameter of at least 300 primary particles on one or more electron microscopy images. The enlargement of the microscope which is retained must make it possible to clearly distinguish the particles on a plate. The magnification can be for example between 50 000 and 500 000. The diameter of a primary particle which is retained is that of the circle allowing to circumscribe the entirety of the image of the primary particle as it is visible on a MET snapshot. Only primary particles with at least half of the perimeter are defined. ImageJ software can be used to do more simple processing; this open access software was originally developed by the NIH American Institute and is available at: http://rsb.info.nih.gov/ii/download.html

After determining the diameters of the particles retained by the above method, said diameters are grouped into several size classes ranging for example from 0 to 500 nm, the width of each class being 1 nm (it being understood that for dispersions having a re-distribution, some of the classes may be empty). The number of particles in each class is the basic data to represent the (cumulative) number distribution. The mean diameter of _MET is the median diameter such that 50% of the particles (in number) taken into account on the MET plate (s) have a diameter smaller than this value. From this distribution, it is also possible to determine the standard deviation SMET which has the usual meaning used in mathematics and which can be defined as the square root of the variance:

n is the number of primary particles taken into account on the SEM image (s);

x, is the diameter of a particle i on the SEM image (s);

is the average arithmetic diameter of the n primary particles. In other words,

d _MET is between 25 and 150 nm. d _MET may be more particularly between 25 and 140 nm, more particularly between 60 and 120 nm.

The particles of the invention may have the following characteristics:

D ₅ o between 40 and 200 nm and d _MET of about 30 nm, for example between 25 and 40 nm; or

D ₅ o between 75 and 500 nm and d _MET of about 60 nm, for example between 60 and 120 nm.

The cerium oxide particles are totally or partially covered with silica. The weight average proportion by weight of silica with respect to cerium oxide is expressed by the SiO 2 / CeO 2 mass ratio, which may be between 0.05 and 0.30, more particularly between 0.05 and 0.20. The particles are all the more covered by the silica that this ratio is high. It is not necessary, however, that this ratio be very high to obtain stability in the pH range close to 7.0. This is all the more true as UV absorption is mainly due to cerium oxide. Thus, the ratio Si0 ₂ / Ce0 ₂ may more particularly be between 0.05 and 0.10, or even between 0.05 and 0.08. This average proportion can be determined by optical ICP determination (optical emission spectroscopy) of the levels of Si and Ce present in an attack solution of the particles. The etching solution can be obtained after dissolving the silica with a solution of HF and dissolving the cerium oxide by adding a concentrated nitric acid solution.

The primary particles are fine and have a homogeneous diameter distribution. This can be demonstrated by using the SMET standard deviation which is less than 30% of the average _MET diameter (SMET <30% xd _ME ). preferably less than 25%, more particularly less than 20%, of said diameter of _MET -

The diameter distribution of the particles of the invention may be narrow and has a dispersion index (s / m) of less than 0.70, preferably less than 0.50, more preferably less than 0.35. A narrow distribution is likely to lead to a better dispersibility and a better feel of the cosmetic composition, once it is applied to the keratin material. The dispersion index s / m of the distribution obtained by the centrifugal sedimentation granulometer is defined by:

s / m = (d ₈₄ - d 1 ₆ ) / 2 d ₅ o

for which :

d ₈₄ is the particle diameter for which 84% of the particles have a diameter of less than ₈₄ ;

- di ₆ is the particle diameter for which 16% of the particles have a diameter less than di ₆ -

The invention also relates to cerium oxide articules totally or partially covered with silica, for which the SiO ₂ / CeO ₂ mass ratio is between 0.05 and 0.30, preferably between 0.05 and 0.30. and 0.25, having a mean diameter d ₅ o measured by a centrifugal granulometer between 100 and 500 nm, more particularly between 200 and 500 nm, even more particularly between 300 and 500 nm, or even between 400 and 500 nm, characterized in that these particles are formed of primary particles having a median diameter d _MET of between 25 and 150 nm, d _MET being obtained using a number distribution of the diameters of the primary particles, diameters determined from a or several transmission electron micrographs, the particle size distribution having a dispersion index (s / m) of less than 0.70, preferably less than 0.50, more preferably less than 0.35.

The particles of the invention can be used in the form of powder or in the form of a dispersion in a liquid medium. The liquid medium may be water or a mixture of water and a liquid organic compound, miscible with water, selected from alcohols, ketones, ethers, carboxylic acids, polyols, hydroxyketones. The liquid organic compound and the proportion thereof in the liquid medium are preferably such that agglomeration of the particles is not observed. The proportion of the particles of the invention in the dispersion can vary over a wide range, for example between 0.5% and 60.0% by weight relative to the overall dispersion. This proportion can be between 0.5% and 40.0%.

As regards the process for preparing the particles of the invention, it consists in introducing an aqueous solution of an alkali metal silicate into a dispersion of cerium oxide particles in the water in such a way as to to precipitate the silica on the particles of cerium oxide.

The alkali silicate may be sodium silicate. The target Si0 ₂ / CeO ₂ ratio is adjusted by adjusting the amount of cerium oxide in the dispersion and the total amount of silicate.

The reaction involving the silicate is conducted under stirring. The temperature is greater than or equal to 60 ° C, or even 80 ° C. The temperature is less than or equal to 120 ° C., or even 110 ° C. It is generally between 80 ° C and 110 ° C.

The reaction must be at a pH at a fixed value that is greater than or equal to 7.0. The set value is generally between 8.0 and 9.0. The dispersion of cerium oxide used initially, especially when it is prepared according to the teaching of WO 2008/043703, may have an initial pH around 5. It is then necessary to adjust this pH to a value close to that fixed by the addition of a base, such as for example sodium hydroxide. When the silicate is added, the pH varies and it should be kept substantially constant at the set value, that is to say at a pH varying from ± 0.5 pH units around the set value, by adding base and / or acid to the reaction mixture.

As much as possible, silica precipitation should be avoided outside the cerium oxide particles. To do this, it is preferable to carry out the precipitation in a medium that has a low ionic strength. Thus, to adjust the pH between 8.0 and 9.0, the minimum of base and / or acid needed should be added.

In addition, it is preferable to introduce the silicate solution with a controlled rate. An empirical rule that can be used is to introduce the silicate solution at a speed S (expressed as a mass of silica per hour relative to the mass of cerium oxide) given by the following formula:

S = (A / 200) 2 ⁿ

in which :

N is equal to (T-90) / 10;

• T is the temperature of the reaction mixture in ° C;

• A represents the specific surface area of the cerium oxide expressed in m ² / g and measured by the BET method (adsorption N ₂ ).

If the introduction at a given speed S leads to excessive precipitation of the silica outside the particles, it is then necessary to introduce the silicate solution at a lower speed. It is also possible to use a more dilute silicate solution so that the rate of introduction of the silicate is decreased. Examples 1 and 2 illustrate the means of obtaining good silica precipitation for two distant Si0 ₂ / CeO ₂ ratios.

At the end of the introduction of the silicate solution, it is possible to let the reaction mixture mature. The reaction mixture is then left at a temperature greater than or equal to 60 ° C., or even 80 ° C. It is generally between 80 ° C and 100 ° C. This curing temperature may be close to or identical to that used for the silicate introduction step. The duration and the ripening temperature depend on the proportion of silica. The duration is generally between 10 minutes and 10 hours, this upper limit is not critical for obtaining the particles according to the invention.

The reaction mixture is allowed to cool, which makes it possible to obtain a dispersion of the particles according to the invention. The particles can be washed by adding water to the dispersion thus obtained, then a portion of the liquid is withdrawn. This washing operation can take place several times. The washing operation may also consist of filtering or centrifuging the dispersion obtained and adding water to wash the particles. The advantage of the washing is to eliminate compounds that could affect the stability of the dispersion or the tolerance of the cosmetic composition. Another advantage of the washing is to reduce the ionic strength of the dispersion, which contributes to reducing the rate of aggregated particles (thus to decrease d ₅ o).

To reduce the aggregate particle rate and decrease by ₅ o, it is also possible to subject the particles deagglomeration. The disagglomeration step can be carried out before or after the washing step. She can be carried out for example using a wet jet mill (in English: "wet jet mill"). It may be for example a device of Sugino brand. Deagglomeration also reduces s / iti.

To obtain the particles of the invention in the form of a powder, it is possible to filter the particles and to dry them. It has been found that the particles have an index b less than or equal to 4.0, or even less than or equal to 3.5, or even less than or equal to 2.5. Moreover, the index L can be greater than 95.0, or even greater than 97.0. The indices L and b are measured on a dry powder.

The invention also relates to the particles or to the dispersion of particles that can be obtained by the process just described.

As regards the process for preparing the cerium oxide dispersion used in the process of the invention, it is described in international application WO 2008/043703. This process comprises the following steps:

(a) preparing a solution of a cerium III salt which additionally comprises cerium IV;

(b) contacting said solution with a base under an inert atmosphere whereby a precipitate is obtained;

(c) subjecting the medium obtained in the preceding step to a heat treatment under an inert atmosphere, at least one of the steps (a), (b) or (c) being conducted in the presence of nitrate ions;

- (d) is carried out successively but in any order acidification and washing of the medium thus obtained, whereby the dispersion is obtained.

Example 1 described in WO 2017/140990 also illustrates a means of obtaining a cerium oxide dispersion according to this method.

The first step (a) of the above process is therefore to prepare a starting solution which is a solution of a cerium III salt. As cerium III salts, it is more particularly possible to use cerium III nitrate, chloride, sulphate or carbonate as well as mixtures of these salts such as nitrate / chloride mixtures. In a known manner this starting solution must have the appropriate acidity so that the cerium is completely present in solution. The starting solution further comprises cerium IV. Cerium IV is provided by a salt which may be, for example, cerium IV nitrate. The The amount of cerium IV is such that the molar ratio (Ce ^lv / Ce ^IN ) in the starting solution is between 1/90 000 and 1/50, depending on the desired average size.

The starting solution prepared in step (a) may be degassed beforehand by bubbling an inert gas. By "inert gas" or "inert atmosphere" is meant for the present description an oxygen-free atmosphere or gas, the gas being, for example, nitrogen or argon.

The second step (b) of the process comprises reacting the starting solution with a base. As a base, the products of the hydroxide type can be used in particular. There may be mentioned alkali or alkaline earth hydroxides and ammonia. It is also possible to use secondary, tertiary or quaternary amines. However, amines and ammonia are preferred insofar as this makes it possible to reduce the risks of pollution by alkaline or alkaline-earth cations. The base may also be degassed beforehand by bubbling an inert gas. To conduct the reaction of the second process step, the contacting can be done in any order of introduction of the reagents. However, it is preferable to introduce the starting solution in a medium containing the base. This second step must be conducted under an inert atmosphere, either in a closed reactor or in a semi-closed reactor with scanning by the inert gas. The contacting is generally carried out in a stirred reactor. This second step is generally carried out at room temperature (20-25 ° C) or at a temperature of at most 50 ° C.

The third step (c) of the process is a heat treatment of the reaction medium obtained at the end of the preceding step. This treatment consists in heating the medium and maintaining it at a temperature which is generally at most 95 ° C. and more particularly between 60 ° C. and 95 ° C. The duration of this treatment can be between a few minutes and a few hours. This treatment is also carried out under an inert atmosphere, which has been described with regard to this atmosphere for the second stage, which is likewise applicable here.

According to a feature of the process of the invention, at least one of the steps (a), (b) or (c) must be conducted in the presence of nitrate ions. Generally, the nitrate ions are provided by the addition of nitric acid, more particularly in step (a), during the preparation of the cerium III solution. The amount of nitrate ions, expressed by the molar ratio N03 / Ce ³⁺ is generally between 1/3 and 5. The last step of the process, step (d), comprises in fact two successive operations that can be performed in any order. These operations are on the one hand an acidification and on the other hand a washing. These operations will be described below more precisely in the case of a sequence of acidification and washing. The acidification takes place generally after cooling of the medium obtained at the end of step (c) by addition of an acid. Any mineral or organic acid can be used. Nitric acid is more particularly used. The amount of acid added is such that the pH of the medium after acidification is between 1.0 and 5.0. This operation can be conducted in the air, it is no longer necessary to operate under inert atmosphere at this stage of the process.

The acidification is followed by a washing which aims to remove from the suspension the soluble species, mainly salts. The washing can be done in different ways with or without solid / liquid separation. It can thus be carried out by separating the solid particles from the liquid phase, for example by frontal filtration, decantation or centrifugation. The solid obtained is then resuspended in an aqueous phase. One can also proceed by tangential filtration. This washing may be optionally renewed if necessary, for example until a given conductivity of the suspension is obtained, the conductivity measuring the level of impurities present in this suspension. As indicated above, the order of operations can be reversed with respect to what has just been described. Thus, at the end of step (c) and, again, generally after cooling the medium obtained, it is then possible to carry out a washing as described above. At the end of the washing, the acidification of the medium obtained is then carried out.

At the end of step (d), the dispersion of cerium oxide which is used in the process of the invention is obtained. The cerium oxide particles prepared by this method may have a polygonal shape.

A second embodiment of the method will now be described. This second mode differs from the first only in the first step. This first step consists of preparing a solution of a cerium III salt which also comprises hydrogen peroxide. What has been described above on the nature of cerium III salt applies likewise here. The amount of H2O2 solution is such that the molar ratio (H ₂ O ₂ / Ce ^IN ) in the cerium salt solution is between 1/10 000 and 1/100. The continuation of the method according to this second mode is carried out as described above for the first mode, that is to say that the solution of the first step is brought into contact under an inert atmosphere with a base, a heat treatment is carried out under an inert atmosphere and the medium thus obtained is acidified and washed (steps (b), (c) and (d) as described above with the presence of nitrate ions in at least one of steps (a) (b) and ( c)). What has been described previously for all of these subsequent steps and for the first embodiment of the method is therefore also applicable here for the second mode.

A cerium oxide dispersion that can be used in the process of the invention may be a Zenus brand dispersion marketed by Solvay.

As regards the cosmetic composition, this comprises the particles of the invention as described above.

This composition may be a photoprotective composition, used to protect against UV rays a keratin material such as the skin or the hair. The formulation chosen for the composition is then adapted for the intended use. The term "photoprotective" is used in the present application to signify that the cosmetic composition allows, after application to a keratinous material, to prevent, or at least limit, the bringing into contact of a radiation with said surface by mechanisms absorption and / or reflection and / or diffusion of UVA and / or UVB radiation.

Thus, for example in the case of a topical application, the cosmetic composition may more particularly be in the form of an emulsion or a lotion, or even a paste. By "emulsion" is meant any macroscopically homogeneous composition comprising at least two phases immiscible with each other; one being the continuous dispersant phase and the other being dispersed in said continuous phase in the form of droplets. The two phases are kinetically stabilized by at least one emulsifying system comprising at least one emulsifying surfactant.

The term "emulsifying system" means any compound or mixture of compounds capable of increasing the kinetic stability of an emulsion. These compounds are generally amphiphilic and are surfactants characterized by their more or less hydrophilic or more or less lipophilic nature which will determine their ability to stabilize direct emulsions or inverse emulsions. They are classified in particular by their HLB according to the Griffin WC calculation method in the document "Classification of Surface Active Agents by HLB, Journal of the Society of Cosmetic Chemists 1949, 311, 1" and in the document "Calculation of HLB of Non Ionia Surfactants, Journal of the Society of Cosmetic Chemists 1954, 249, 5 ". The calculation of the HLB according to this method of calculation is done according to the equation:

HLB = 20 X Mh / M

where Mh is the molar mass of the hydrophilic part of the surfactant and M is the total molecular weight of the molecule.

The emulsion may be of the oil-in-water type (that is to say a cosmetically acceptable carrier consisting of an aqueous dispersant continuous phase and an oily dispersed discontinuous phase) or of the water-in-oil type ( that is to say a cosmetically acceptable support consisting of an oily dispersant continuous phase and an aqueous dispersed discontinuous phase). It may also be a multiple emulsion, for example of the water-in-oil-in-water or oil-in-water-in-oil type.

The aqueous phase contains water, and possibly other organic solvents soluble or miscible in water. Solvents that are soluble or miscible in water include short-chain monohydric alcohols, for example C1-C4, for example ethanol or isopropanol; diols or polyols such as, for example, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, 2-ethoxyethanol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, glycerol, and sorbitol, and mixtures thereof. According to a preferred embodiment, ethanol, propylene glycol, glycerine, and mixtures thereof may be used more particularly.

The oily phase comprises one or more fatty substances, these fatty substances possibly consisting of an oil or a wax or their mixtures. By oil is meant a liquid compound at room temperature. By wax is meant a compound that is solid or substantially solid at room temperature and whose melting point is generally greater than 35 ° C. The oil may advantageously be selected from the group consisting of mineral oils; natural oils such as for example castor oil; vegetable oils such as, for example, sweet almond oil, macadamia oil, blackcurrant seed oil, jojoba oil; synthetic oils such as, for example, perhydrosqualene, alcohols, acids or fatty esters; silicone oils. Among the fatty esters, mention may be made of C12-C15 alcohol benzoate, octyl palmitate, isopropyl lanolate, triglycerides including those of capric or caprylic acids.

The emulsifying system comprises at least one surfactant which may be anionic, cationic, nonionic or amphoteric or a mixture of these compounds and optionally at least one co-surfactant. The emulsifying system is chosen according to the nature of the emulsion. The proportion of surfactant and co-tensioner generally varies from 0.3 to 20.0% by weight of the cosmetic composition.

The cosmetic composition may comprise:

a) the particles of the invention as described above;

b) optionally at least one organic UV filter;

c) optionally at least one inorganic UV filter other than the particles of the invention, that is to say other than cerium oxide particles totally or partially covered with silica.

More particularly, the photoprotective cosmetic composition may comprise:

i) at least one aqueous phase;

ii) at least one oily phase;

iii) at least one emulsifying system;

iv) the particles of the invention as described above;

v) optionally at least one organic UV filter;

vi) optionally at least one inorganic UV filter other than the particles of the invention.

The term "UV filter" means a product capable of absorbing at least a portion of the UV radiation (UVA and / or UVB) emitted by the sun. The function of a UV filter is to protect the skin and / or the lips and / or the hair against the harmful effects of these radiations. The wavelengths of the UVA radiation are different from the wavelengths of the UVB radiation. The wavelengths of the UVA radiation are between 320 nm and 400 nm and those of the UVB between 280 nm and 320 nm.

The combination of the particles of the invention and at least one other UV filter can lead to a complementarity in the range of filtered UV as well as for a range of filtered UV, to a synergy between the filters present. The organic UV filter is known to those skilled in the art. It can be chosen from water-soluble organic filters, oil-soluble or insoluble organic filters commonly used in photoprotective compositions. Organic filters are mostly fat soluble. The most commonly used UVB filters are cinnamates, benzotriazoles, salicylates, octocrylene, phenylbenzimidazol sulfonic acid, ethylhexyl triazone, diethylhexyl butamido triazone, camphor derivatives, benzophenones. UVA filters commonly used are dibenzoylmethane, diethylamino hydroxybenzoyl hexyl benzoate, terephthalylidene dicamphor acid. It is also possible to use broad-spectrum organic filters: bis-ethylhexyloxyphenol Methoxyphenyl Triazine (Tinosorb S ^® ) and methylene bisbenzotriazolyl tetramethylbutylphenol (Tinosorb M ^® ) which have the distinction of covering a broad UVB absorption spectrum and UVA.

It may especially be chosen from cinnamic derivatives; anthranilates; salicylic derivatives; dibenzoylmethane derivatives, especially avobenzone; camphor derivatives; benzophenone derivatives; derivatives of b, b-diphenylacrylate; triazine derivatives; benzotriazole derivatives; benzalmalonate derivatives including those cited in US Patent 5,624,663; benzimidazole derivatives; imidazolines; bis-benzoazolyl derivatives as described in patents EP 669323 and US 2,463,264; p-aminobenzoic acid derivatives (PABA); methylene bis- (hydroxyphenylbenzotriazole) derivatives as described in US 5,237,071, US 5,166,355, GB 2303549, DE 19726184 and EP 893119; benzoxazole derivatives as described in EP 0832642, EP 1027883, EP 1300137 and DE 10162844; filter polymers and silicone filters such as those described in particular in application WO 93/04665; dimers derived from α-alkylstyrene such as those described in DE 19855649; 4,4-diarylbutadienes as described in EP 0967200, DE 19746654,

DE 19755649, EP-A-1008586, EP 1133980 and EP133981; merocyanine derivatives such as those described in WO 04/006878, WO 05/058269 and WO 06/032741 and mixtures thereof; indanylene described in EP-A-0823418, EP-A-1341752 and mixtures thereof.

As examples of organic UV filters which may be used, mention may be made more particularly of the following compounds: 1- (4-methoxyphenyl) -3- (4-tert-butylphenyl) propane-1,3-dione (or avobenzone); [(3Z) -3 - [[4 - [(Z) - [7,7-dimethyl-2- oxo-1- (sulfomethyl) -3-bicyclo [2.2.1] heptanylidene] methyl] phenyl] methylidene] -7,7-dimethyl-2-oxo-1-bicyclo [2.2.1] heptanyl] nnethanesulfonic acid; 2- (2H-benzotriazol-2-yl) -4-methyl-6- [2-methyl-3- [1, 3,3,3-tetramethyl-1 - [(trimethylsilyl) oxy] -1-diisoxynyl] propyl ] phenol; 2-ethylhexyl 2-cyano-3,3-diphenyl-2-propenoate (or octocrylene); 3,3,5-trimethylcyclohexyl-2-hydroxybenzoate (or homosalate); 2-phenyl-3H-benzimidazole-5-sulfonic acid (or insulizole) acid; (RS) -2-ethylhexyl (2E) -3- (4-methoxyphenyl) prop-2-enoate (or octinoxate); 2-ethylhexyl 4- (dimethylannino) benzoate (or octyldimethyl PABA); 2,2 '- [6- (4-methoxyphenyl) -1,3,5-triazin-2,4-diyl] bis {5 - [(2-ethylhexyl) oxy] phenol} (or bemotrizinol); bis-ethylhexyloxyphenol methoxyphenyl triazine; ethylhexyl triazone; terephthalylidene dicamphor sulfonic acid (or Mexoryl SX); drometrizole trisiloxane (or Mexoryl XL); 3- (4'-methylbenzylidene) -dl-camphor (or Eusolex 6300); 4-isopropyl-dibenzoylmethane (or Eusolex 8020); 3-benzylidenecamphor (or Mexoryl SD); N, N, N-trimethyl-4- (2-oxoborn-3-ylidenemethyl) anilinium methylsulfate; ethoxylated ethyl 4-aminobenzoate; N-hexyl 2- (4-diethylamino-2-hydroxybenzoyl) benzoate (or UVINUL A); 1,1 '- (1,4-piperazinediyl) bis [1- [2- [4- (diethylamino) -2-hydroxybenzoyl] phenyl] methanone (CAS 919803-06-8); methyl anthranilate; 1,1-Dicarboxy (2,2'-dimethylpropyl) -4,4-diphenylbutadiene; octyl-5-N, N-diethylamino-2-phenysulfonyl-2,4-pentadienoate; butyl methoxydibenzoylmethane; disodium phenyl dibenzimidazo tetrasulfonate; ethyl PABA; ethyl dihydroxypropyl PABA; ethylhexyl dimethyl PABA; etocrylene; octocrylene; di-neopentyl 4'-methoxybenzalmalonate.

May also be used Tinosorb M ^® (methylene bis-benzotriazolyl tetramethylbutyl-phenol) which is an organic filter solid or liposoluble or water-soluble, and which disperses in the cosmetic composition. This organic UV filter is characterized by similar absorption to that of other organic filters but also by its property of reflecting and diffusing light as an inorganic filter.

A combination of organic filters may for example be that associating avobenzone (UVA filter) and another organic filter selected from the group consisting of octisalate, octocrylene and homosalate. The composition may not include oxybenzone.

The inorganic UV filter other than the particles of the invention may be based on titanium oxide or zinc oxide which is in the form of particles zinc oxide or titanium. The median diameter d ₅ o of these particles determined by laser diffraction in water is generally less than 400 nm. The size of the primary particles of T1O2 determined by X-rays is preferably less than 40 nm. The size of the primary particles of ZnO is in turn preferably less than 100 nm.

The particles of titanium oxide or zinc oxide may have undergone a surface treatment of chemical, electronic, mechanochemical and / or mechanical nature with compounds such as amino acids, beeswax, fatty acids, fatty alcohols, anionic surfactants, lecithins, sodium, potassium, zinc, iron or aluminum salts of fatty acids, metal alkoxides (of titanium or aluminum), polyethylene, silicones, proteins (collagen, elastin), alkanolamines, silicon oxides, metal oxides or sodium hexametaphosphate.

Titanium oxide can also be coated with silica. The proportion of silica may vary from 8 to 30% by weight, more particularly from 12 to 20% by weight, of the titanium oxide + silica group. The silica layer covering the titanium oxide can be obtained using a sol-gel process by contacting at a temperature close to 80 ° C. and at a pH of about 6-7 hours. a solution of silicate and a dispersion of titanium oxide particles. A process for preparing silica-covered titanium oxide is described in application US 2006/0194057, in particular in Examples 2a, 2b and 2c.

The titanium oxide may be optionally doped with at least one transition metal such as, for example, iron or manganese. We can refer to the application WO 2015/0876637 for example.

The titanium oxide may be in amorphous or crystalline form. It can be mainly in rutile form and / or anatase. The rutile form is preferred for better photostability of the photoprotective cosmetic composition.

As examples of titanium oxide, mention may be made of the following products which are commercial: MT-100TV, MICROTITANIUM DIOXIDE MT 500 B or MICROTITANIUM DIOXIDE MT600 B from Tayca; "transparent oxide PW" from Wacker; Tioveil AQ from the company Tioxide. It may also be the following titanium oxides sold by Merck: Eusolex T-2000, EusolexT-AQUA, EusolexT-AVO or EusolexT-OLEO. The proportion by weight of the particles of the invention may vary from 0.5 to 40.0%, preferably from 1.0 to 30.0%, or even between 1.0 and 10.0%, relative to the total weight. of the cosmetic composition.

The nature and quantity of the possible UV filters other than the particles of the invention are chosen as a function of the desired sun protection factor. The proportion by weight of the inorganic UV filter optionally present may vary from 0.5 to 40.0%, preferably from 1.0 to 30.0% of the total weight of the cosmetic composition. The total proportion by weight of all the inorganic UV filters (including the particles of the invention) may be limited to 40.0%, or even 30.0% or even 15.0%, of the total weight of the cosmetic composition. The proportion by weight of the organic UV filter optionally present may vary from 0.5 to 40.0%, preferably from 1.0 to 30.0%, of the total weight of the cosmetic composition.

The cosmetic composition may comprise other additives usually used in cosmetics. It may be, for example, vitamins or their precursors or derivatives, dyestuffs, polymers, thickeners, emollients, antioxidants, perfumes, gelling agents or mattifying agents.

The cosmetic composition can be prepared by mixing together the various ingredients of the cosmetic composition. It is also possible to mix the ingredients according to their affinity in order to prepare two or more compositions, and then to mix together the compositions thus prepared. For example, in the case of an emulsion, it is possible to separately prepare the aqueous phase and the oily phase, and then mix the two phases together. In the case of an emulsion, it is appropriate to subject the two phases to shear. The term "shear" means that the mechanical energy released by the stirring mobile and which is applied to the mixture allows the creation of kinetically stable droplets. These droplets are those of the aqueous phase or the oily phase depending on the nature of the emulsion. According to one embodiment, the aqueous phase is added under shear and in portions to the oily phase. In the presence of solid ingredients at room temperature, it may be necessary to liquefy the oily phase by reheating. Shear can be obtained using an ultra-turrax type apparatus. According to another object, the invention relates to the use of the particles of the invention, for the preparation of a photoprotective cosmetic composition, especially in the form of an emulsion.

Examples

Determination of the dm: for the measurement of d ₅ o, the centrifugal granulometer used is the BI-XDC apparatus of the company Brookhaven in accordance with the recommendations of the manufacturer. The measurement is done after suspending the particles in water.

Determination of dMF _T : the protocol used to observe particles by TEM can be as follows:

- prepare a dispersion of the particles in 5 ml of water so as to obtain a turbid suspension;

depositing a drop of this suspension (transfer pipette) on a copper grid with a hydrophilized carbon membrane;

- eliminate part of the drop;

- leave to dry at room temperature.

In the examples, the JEM 1400-120 kV apparatus equipped with an Orius SC200 camera was used.

Example 1: Preparation of a dispersion according to the invention with a SiOp / CeO ratio = 0.2

A 2-liter jacketed reactor equipped with inclined pale stirring, a coolant, a solution introduction rod, a temperature probe and a pH electrode was used. 500 ml of water and 1.8 ml of a 1N sodium hydroxide solution (pH of about 11.1) are introduced into the reactor, which is stirred at a speed of 500 rpm. cane, in 60 min, 500 mL of a dispersion of cerium oxide at 10% by weight in water sold under the name of Zenus HC60. The pH of the Zenus HC60 dispersion is about 5. The final pH of the dispersion in the tank corresponding to 50 g of cerium oxide in about 1000 mL is 9.5 (measured at room temperature). 500 ml of the dispersion are then withdrawn.

The dispersion is then stirred at 400 rpm and heated to 100 ° C. 25.9 g of a concentrated aqueous solution of sodium silicate are added via the rod in 120 min. sodium (Si0 ₂ / Na ₂ O = 3.45, solution density = 1.232, [SiO ₂ ] = 238 g / L). The final proportion of S102 that has been added is 20% relative to Ce12. The pH of the mixture is maintained between 8.0 and 8.2 with the addition of HNOs. The mixture is maintained at 90 ° C. for 30 minutes and after cooling to 40 ° C., the dispersion is withdrawn. The dispersion is then dried in an oven (60 ° C. - 24 h). The powder obtained is then ground with mortar.

Characteristics of the particles in the powder after grinding:

d ₅ o = 478 nm with s / m = 0.64

d _MET evaluated at about 90 nm

The colorimetric data L ^* a ^* b were determined on the dry powder using an X-rite Ci51 spectrophotometer. The measurement is made according to the manufacturer's recommendations after calibration by a white standard. The powder of Example 1 appears whiter than the starting cerium oxide (dried under the same conditions), which is confirmed by the measurement of b.

Board

Example 2 Preparation of a Dispersion According to the Invention with an SiO 2 / CeO 2 Ratio 0.07

A 1 liter jacketed reactor equipped with inclined pale stirring, a coolant, a solution introduction rod, a temperature probe and a pH electrode was used.

500 ml of water and 7.6 g of a 1N sodium hydroxide solution (pH of approximately 1.17) are introduced into the reactor, which is stirred at a speed of 500 rpm. the cane, in 60 min, 565 g of a dispersion of cerium oxide 12.5% by weight in water marketed under the name of Zenus HC60. The final pH of the dispersion corresponding to 70.6 g of cerium oxide in about 1000 ml is 9.5. A dilute solution is prepared from 25.9 g of an aqueous solution of sodium silicate (SiO ₂ / Na ₂ O ratio = 3.42, density of the solution = 1.233, [SiO ₂ ] = 242 g / L) mixed with 21 g of distilled water.

The Ce 2 O 2 dispersion is then stirred at 400 rpm and heated to 100 ° C. The diluted solution of sodium silicate is added via the rod in 70 minutes. The final proportion of S102 that has been added is 7% relative to Ce0 ₂ . The pH of the mixture is maintained between 8.1 and 8.2 with the addition of HNOs.

The mixture is maintained at 90 ° C. for 30 minutes and after cooling to 21 ° C. the dispersion is withdrawn. Centrifugation is then carried out at 10,000 rpm for 15 minutes. The supernatant is removed and the pellet is then dried in an oven (70 ° C-24 h). The powder obtained is then milled using an IKA A10B type knife mill.

Characteristics of the particles in the powder after grinding:

d ₅ o = 230 nm with s / m = 0.41

d _MET evaluated at about 90 nm

It is possible to obtain other SiO 2 / CeC 2 ratios by adapting the conditions of Examples 1 and 2, in particular the quantities of cerium and silicate oxide.

Example 3: stability tests

On a dispersion at 0.5% by weight of the powder of Example 2, the evolution of the stability as a function of the pH was determined by adding a dilute nitric acid solution. The pH of the dispersion at the start is 9.0. The dispersion is stable for 1 h without stirring at pH> 4. From pH 3.8, the solution shows a beginning of instability. The dispersion is completely unstable when it is brought to a pH of 3.2, which results in an agglomeration of the particles which sediment at the bottom of the flask in the absence of agitation.

The same test was carried out on a dispersion at 0.5% by weight of the starting cerium oxide used to prepare the particles of Example 2. The dispersion of cerium oxide was prepared by dispersing the a dried powder obtained by the process which has been described (application WO 2008/043703). This 0.5% dispersion has an initial pH close to 4. The evolution of the stability as a function of the pH was determined by adding a dilute sodium hydroxide solution. The dispersion is stable for pH <5. From a pH = 5.2, the dispersion shows a beginning of instability. The dispersion is completely unstable when it is brought to pH 8.7, which results in an agglomeration of the particles which sediment at the bottom of the flask in the absence of agitation.

EXAMPLE 4 Photoprotective Cosmetic Composition in Emulsion Form

A photoprotective cosmetic composition in emulsion form can be obtained by reproducing Example 2 of WO 2016/203062 and replacing the ingredient 10 (Ce2-PAA) of this example with the particles of Example 1 or Example 2. Similarly, it is possible to prepare a photoprotective composition in the form of an emulsion by reproducing Example 6 of EP 0596442 B1 and replacing the ingredient 5 (UV shielding talc) of this example with the particles of the example 1 or example 2.

Claims

1. Particles of cerium oxide totally or partially covered with silica, for which the SiO ₂ / CeO ₂ mass ratio is between 0.05 and 0.30, preferably between 0.05 and 0.25, having a diameter medium d ₅ o measured by a granulometer by centrifugation between 40 and 500 nm, rather between 100 and 500 nm, more particularly between 150 and 500 nm, more particularly between 200 and 500 nm, still more particularly between 300 and 500 nm, or between 400 and 500 nm, characterized in that these particles are formed of primary particles having a median diameter divi _AND between 25 and 150 nm, d _MET being obtained using a number distribution of the primary particle diameters diameters determined from one or more transmission electron micrographs.

2. Particles according to claim 1 characterized in that the Si0 ₂ / Ce0 ₂ ratio is between 0.05 and 0.30, more particularly between 0.05 and 0.20, more particularly between 0.05 and 0. , 10, or even between 0.05 and 0.08.

3. Particles according to claim 1 or 2, characterized in that the thickness of the silica layer determined on the TEM plates is at least 1 nm, or even at least 2 nm.

4. Particles according to one of the preceding claims characterized in that the particle size distribution has a dispersion index (s / iti) less than 0.70, preferably less than 0.50, more preferably less than 0 35.

5. Particles according to one of the preceding claims characterized by an index b less than or equal to 4.0, or even less than or equal to 3.5, or even lower than or equal to 2.5, b being measured on a dry powder.

6. Particles according to one of the preceding claims characterized by an index L greater than 95.0, or even greater than 97.0, L being measured on a dry powder.

7. Dispersion of particles according to one of claims 1 to 6 in a liquid medium.

8. Use of the dispersion according to claim 7 or particles according to one of claims 1 to 6 for the preparation of a cosmetic composition, including photoprotective.

9. Use of the particles according to one of claims 1 to 6 as a UV filter.

10. Cosmetic composition, in particular photoprotective, comprising the particles according to one of claims 1 to 6.

11. Cosmetic composition according to claim 10 in the form of an emulsion.

12. Composition according to claim 11 characterized in that the emulsion is of the oil-in-water, water-in-oil, water-in-oil-in-water or oil-in-water-in-oil type.

13. Cosmetic composition according to one of claims 10 to 12, characterized in that it comprises:

a) cerium oxide particles totally or partially covered with silica;

b) optionally at least one organic UV filter;

c) optionally at least one inorganic UV filter other than cerium oxide particles totally or partially covered with silica.

14. Cosmetic composition according to one of Claims 10 to 13, characterized in that it comprises:

i) at least one aqueous phase;

ii) at least one oily phase;

iii) at least one emulsifying system;

iv) cerium oxide particles totally or partially covered with silica;

v) optionally at least one organic UV filter;

vi) optionally at least one inorganic UV filter other than cerium oxide particles totally or partially covered with silica.

15. Process for preparing the particles according to one of claims 1 to 6 of introducing an aqueous solution of an alkali metal silicate in a dispersion of cerium oxide particles in water so as to precipitate silica on the cerium oxide particles.

16. The method of claim 15 wherein the reaction involving the silicate is conducted with stirring at a temperature greater than or equal to 60 ° C, or even 80 ° C.

17. The method of claim 15 or 16 wherein the silicate solution is introduced at a speed S (expressed by mass of silica per hour relative to the cerium oxide mass) given by the following formula:

S = (A / 200) 2 ⁿ

in which :

N is equal to (T-90) / 10;

• T is the temperature of the reaction mixture in ° C;