FR3059332A1 - PROCESS FOR PRODUCING AN INTERFERENTIAL FILTER ON MICROPARTICLES - Google Patents

Abstract

The invention relates to a method for manufacturing an interference filter on microparticles (40) in a deposition chamber (20), the formation of the interference filter comprising the formation of at least a first film, made of a first material and at least one second film, made of a second material different from the first material by chemical vapor deposition, the method further comprising forming a passivation film directly on the surface of the microparticles (40), before formation of the interference filter, the passivation film being formed, by the chemical vapor deposition technique, by evaporation of tetraacetoxysilane on the surface of the microparticles (40).

Description

Holder (s): COMMISSIONER FOR ATOMIC ENERGY AND ALTERNATIVE ENERGIES Public establishment, CHANEL PARFUMS BEAUTE.

Extension request (s)

Agent (s): BREVALEX Limited liability company.

METHOD FOR MANUFACTURING AN INTERFERENTIAL FILTER ON MICROPARTICLES.

FR 3 059 332 - A1 _ The invention relates to a method of manufacturing an interference filter on microparticles (40) in a deposition chamber (20), the formation of the interference filter comprising the formation of at least a first film , made of a first material, and at least a second film, made of a second material different from the first material by chemical vapor deposition, the method further comprising forming a passivation film directly on the surface of the microparticles (40), before the formation of the interference filter, the passivation film being formed, by the technique of chemical vapor deposition, by evaporation of tetraacetoxysilane on the surface of the microparticles (40).

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METHOD FOR MANUFACTURING AN INTERFERENTIAL FILTER ON MICROPARTICLES

DESCRIPTION

TECHNICAL AREA

The present invention relates to a method of forming an interference filter on microparticles. More particularly, the present invention relates to a method allowing the formation of an interference filter on microparticles and having improved color saturation compared to the state of the art.

PRIOR ART

Interference filters formed on powders or microparticles are particularly interesting for the cosmetic industry which seeks to create saturated colors.

These interference filters generally comprise an alternation of at least a first film, made of a first material, and of at least a second film, made of a second material different from the first material. Also, in order to limit the number of first films and second films, it is generally imposed on the first material to have a refractive index sufficiently distant from that of the second material. For example, the first material and the second material may comprise, respectively, titanium dioxide and silicon dioxide.

Furthermore, the optical properties, for example the purity of their color (their saturation), of interference filters are very dependent on their thickness, and more particularly on their variation in thickness. Indeed, the purity of the color of an interference filter is generally guaranteed by controlling the variation in the thickness of the first and second films.

Thus, the formation of films by chemical vapor deposition ("CVD" or "Chemical Vapor Deposition" according to Anglo-Saxon terminology), known to those skilled in the art, seems to be a technique particularly suitable for the formation of films with precise control of their thickness.

However, the surface condition of the microparticles generally exhibits irregularities liable to degrade the optical properties of the interference filters. These irregularities, which may include contaminants, or roughness, directly affect the interface (s) between the different films of the interference filter, and can thus give rise to iridescence phenomena (Figure 1).

Also, the removal of surface irregularities on microparticles may require several types of treatment such as cleaning and etching steps which make the manufacturing process complex.

An object of the present invention is therefore to propose a method for manufacturing an interference filter on microparticles having improved saturation compared to the prior art.

Another object of the present invention is also to propose a method of manufacturing an interference filter on microparticles simplified compared to the state of the art.

STATEMENT OF THE INVENTION

The object of the invention is at least partially achieved by a method of manufacturing an interference filter on microparticles by a chemical vapor deposition technique in a deposition chamber, the formation of the interference filter comprising the formation of at least a first film, made of a first material, and at least a second film, made of a second material different from the first material by chemical vapor deposition so that the interference filter comprises an alternation of the at least a first film, and at least a second film, the method further comprising forming a passivation film directly on the surface of the microparticles, before the formation of the interference filter, the passivation film being formed, by the chemical vapor deposition technique, by evaporation of tetraacetoxysilane on the surface of the microparticles.

According to one embodiment, the microparticles disposed on a main face of a porous support traversed over its entire thickness E by an inert gas so that the microparticles form a fluidized bed.

According to one embodiment, the support is maintained at a temperature below 200 ° C, advantageously below 150 ° C, for example 110 ° C.

According to one embodiment, the tetraacetoxysilane is diluted in an organic solvent, the organic solvent advantageously comprising at least one of the solvents chosen from: isopropanol, cyclohexane, an aromatic solvent (xylene, toluene).

According to one embodiment, tetraacetoxysilane has a concentration in the organic solvent of between 0.01 mol / L and 0.03 mol / L.

According to one embodiment, the tetraacetoxysilane is maintained at a temperature between 80 ° C and 150 ° C before being sprayed onto the surface of the microparticles.

According to one embodiment, the microparticles have a size of between 100 nm and 500 μm, the microparticles advantageously being beads.

According to one embodiment, the microparticles comprise silica.

According to one mode of implementation, the evaporation of the tetraacetoxysilane is carried out according to cycles of evaporation, and in alternation with cycles of injection of oxygen in the deposit enclosure.

According to one embodiment, a purging of the deposition enclosure is carried out before each evaporation cycle and each injection cycle, so that the pressure in said enclosure is less than 30 mBar at the end of the purging .

According to one mode of implementation, at the end of each evaporation cycle and of each injection cycle, the pressure in the deposition enclosure is greater than 100 mBar and 60 mBar, respectively.

According to an implementation mode, each evaporation cycle lasts from 5 seconds to 20 seconds and / or between 20 and 100 evaporation and injection cycles are executed.

According to one embodiment, the first material comprises titanium dioxide, advantageously formed by the vapor deposition technique.

According to one embodiment, the second material comprises silicon dioxide, advantageously formed by the chemical vapor deposition technique.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will appear in the following description of the process for forming an interference filter on microparticles according to the invention, given by way of nonlimiting examples, with reference to the appended drawings in which:

FIG. 1 is an image by scanning electron microscopy in section (depending on the thickness) of a film of titanium dioxide formed on a silica microparticle,

FIG. 2 is a schematic representation of a device for forming films by CVD suitable for implementing the method according to the invention,

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

For the different modes of implementation, the same references will be used for identical elements or ensuring the same function, for the sake of simplification of the description.

The invention described in detail below implements a method of forming an interference filter on microparticles by a chemical vapor deposition technique. More particularly, the method according to the invention implements the formation of a passivation film on the surface of the microparticles before the formation of the interference filter. This passivation film makes it possible to encapsulate the contaminants likely to be present on the surface of the microparticles, and also to smooth the roughness of said surface. Thus, after the formation of the passivation film, the surface of the microparticles has a “smooth” appearance, thus allowing better control of the interfaces between the different films constituting the interference filter.

In Figure 2, we can see a chemical vapor deposition device 10 adapted for the implementation of the invention.

The present invention includes the formation of a passivation film on microparticles 40 more particularly directly on the surface of microparticles 40.

The microparticles 40 can comprise silica.

The microparticles 40 can have a size of between 100 nm and

500 pm.

The microparticles 40 can advantageously be beads.

By size of the microparticles 40 is meant the largest of the dimensions of said microparticles 40. Furthermore, within the meaning of the invention, all the microparticles 40 of the same batch do not necessarily have the same size. Also, when we consider a batch of microparticles 40 having a given size, it is clear that said size is an average size.

Advantageously, during the formation of the passivation film, the microparticles 40 can form a fluidized bed.

By fluidized bed is meant a set of microparticles 40 suspended by an ascending gas stream. In this regard, a person skilled in the art can consult the document [1] cited at the end of the description.

In order to implement the method of forming an interference filter on microparticles 40, said microparticles 40 are arranged in a deposition chamber 20, extending along an axis XX ′, of the chemical vapor deposition device 10.

The deposition enclosure 20 comprises in its lower part B a support 30 on which the microparticles 40 rest.

The support 30 comprises two main faces 31 and 32 which are mutually parallel (and perpendicular to the axis XX ').

The support 30 is advantageously porous so that a gas can pass through it over its entire thickness E. The thickness E of the support 30 is the shortest distance between the main faces 31 and 32. The support 30 may comprise at least one materials chosen from: aluminum, stainless steel type.

Thus, as soon as microparticles 40 are arranged on the support 30, and that the latter is traversed by a gas over its entire thickness E, said microparticles 40 are set in motion and a fluidized bed is created. For example, the gas allowing the implementation of the fluidized bed enters the deposit enclosure 20 through a first inlet 51. This configuration is therefore particularly advantageous, since it is desired to form a film over the entire surface of each microparticles 40. In fact, as soon as the microparticles 40 form a fluidized bed, their entire surface is exposed to a reactive gas capable of being present in the deposition enclosure 20. More particularly, statistically, each surface portion of each microparticles 40 forming the fluidized bed are exposed to the reactive gas in an equivalent manner (in terms of duration and quantity of reactive gas), so that the formation of the film is homogeneous on each of the microparticles 40 and between the microparticles 40.

By reactive gas, we mean a gas adapted to react chemically with the surface of the microparticles 40 and thus form a film, the nature of the reactive gas will be discussed later in the description. Furthermore, we note that the reactive gas first crosses the support 30, over its entire thickness E, before reaching the fluidized bed formed by the microparticles 40.

Advantageously, the chemical vapor deposition device 10 comprises two thermal regulation systems (for heating and / or cooling) 60 and 61, disposed respectively in the lower part B and the upper part H of the deposition enclosure 20 This arrangement allows differentiated heating of the lower B and upper H parts of the deposition enclosure 20. More particularly, the fluidized bed of microparticles 40 suspended in the volume of the deposition enclosure 20 can be heated to a temperature higher than the support 30. More particularly, the support 30 can be maintained, by the thermal regulation system 60, at a temperature below the reaction or decomposition temperature of the reactive gases which are liable to pass through it, thus avoiding any clogging of said support 30.

For example, the temperature of the fluidized bed formed by the microparticles 40, near or in the upper part H of the deposition enclosure, can be between 200 ° C and 350 ° C, advantageously between 250 ° C and 350 ° C .

The temperature of the support 30 can be between 100 ° C and 150 ° C

The formation of the passivation film on the surface of the microparticles 40 comprises the evaporation of an organometallic precursor in the deposition enclosure 20. By evaporation in the deposition enclosure 20, it is meant that the organometallic precursor is introduced into the deposit enclosure 20 in the form of a finely divided solution. Furthermore, the evaporation of the organometallic precursor takes place on the surface of the microparticles 40.

It is understood that the organometallic precursor is a reactive gas.

Furthermore, the organometallic precursor is introduced into the deposition enclosure through a second inlet 52.

According to the invention, the organometallic precursor is tetraacetoxysilane. This chemical compound is particularly advantageous since it decomposes from 175 ° C., and therefore makes it possible to form films of silicon dioxide on the surface of the microparticles 40, the microparticles 40 being advantageously formed in the form of a fluidized bed.

It is understood, without it being necessary to specify it, that tetraacetoxysilane reacts with an oxidizing chemical species to form a film of silicon dioxide by CVD. The oxidizing species can for example be dioxygen, or ozone.

The surface of the microparticles 40 forming the fluidized bed is then advantageously maintained at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C.

Advantageously, the tetraacetoxysilane, before being injected into the deposition enclosure, can be diluted in an organic solvent.

The organic solvent can advantageously comprise at least one of the solvents chosen from: isopropanol, cyclohexane, an aromatic solvent (for example toluene, or xylene).

The inventors have also demonstrated that the solvating power of isopropanol makes it possible to obtain excellent adhesion of tetraacetoxysilane to the surface of the microparticles 40, thus promoting the reactivity of said precursor with the surface of the microparticles 40.

After dilution, the concentration of tetraacetoxysilane can be between 0.01 mol / L and 0.03 mol / L.

Still advantageously, before being injected into the deposition enclosure, the tetraacetoxysilane can be maintained at a temperature between 80 ° C. and 150 ° C., for example 100 ° C.

The formation of the passivation film according to the invention may also comprise the injection of dioxygen into the deposition enclosure 20.

The oxygen can be injected into the enclosure at room temperature. In other words, the temperature of the oxygen, as soon as it is in the enclosure, is imposed by the temperature inside said enclosure.

The dioxygen is intended to react with tetraacetoxysilane to form a film of silicon dioxide on the surface of the microparticles 40.

The passivation film thus formed is a film of silicon dioxide (S1O2).

Furthermore, as soon as the microparticles are made of silica, the passivation film and the microparticles 40 are of the same chemical nature, so that their respective refractive indices are close to, or even identical. Such a configuration avoids the formation of an optical interface between the passivation film and the microparticle 40, as well as the creation or the amplification of defects likely to be present on the surface of the microparticles 40.

The deposition of the passivation film also makes it possible to perform an in situ cleaning of the surface of the microparticles 40 forming the fluidized bed, and before the growth of the passivation film begins. Contamination of the surface of the microparticles can thus be reduced.

The reduction in contamination of the surface of the microparticles makes it possible to limit the transfer of defects at the level of additional layers capable of being formed on the passivation film.

By defect transfer is meant the reproduction of topological defect present on the surface of the microparticle.

Finally, the presence of the passivation film makes it possible to control the rate of deposition of a TiO _{2 film} capable of being deposited on said passivation film in the context of the formation of an interference filter.

Advantageously, the injection (evaporation) of the tetraacetoxysilane can be carried out according to cycles of evaporation, and in alternation with cycles of injection of oxygen into the deposit enclosure 20. In other words, the injection of the tetraacetoxysilane and the injection of dioxygen are carried out over different time periods, and without overlap (in other words distinct). We then speak of pulsed CVD.

Pulsed CVD allows better control of the decomposition of species, therefore better control of the deposition kinetics, and therefore the deposition rates. This is all the more important when the thicknesses deposited are very small.

We talk about evaporation cycles when it comes to the injection of tetraacetoxysilane, and injection cycles when it comes to the injection of dioxygen.

The dioxygen injected during the injection cycles can be mixed with an inert gas, for example nitrogen. In this case, the proportion of nitrogen relative to the oxygen can be between 30% and 60%, for example 50%.

Still advantageously, a purge of the deposition enclosure 20 is carried out before each evaporation cycle and each injection cycle, so that the pressure in said enclosure is less than 30 mBar at the end of the purge. The purge can be carried out by a pumping system connected to the deposit vessel 20.

At the end of each evaporation cycle, the pressure in the deposition enclosure 20 can be greater than 100 mBar.

At the end of each injection cycle, the pressure in the deposition chamber 20 can be greater than 60 mBar.

Evaporation cycles can last from 5 seconds to 20 seconds.

Advantageously, 20 to 100 evaporation and injection cycles can be performed.

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Thus, although formed at relatively low temperatures (below 350 ° C), the passivation film has a density as well as optical properties comparable to those of the same film formed at higher temperature with a standard organometallic precursor.

Furthermore, in order to encapsulate contaminants likely to be present on the surface of the microparticles 40, and to smooth said surface, a passivation film of thickness less than 10 nm may be sufficient.

Thus, the process for forming the passivation film on the microparticles 40 can comprise the following steps:

the introduction of the microparticles 40 into the deposition enclosure, more particularly on the support 30,

the formation of the fluidized bed by passing an ascending gas stream through the support 30,

the heating of the zone of the enclosure occupied by the fluidized bed at a temperature between 200 ° C and 350 ° C, and the heating of the support 30 at a temperature below 200 ° C, advantageously below 110 ° C,

- evaporation of tetraacetoxysilane,

- injection of oxygen.

The formation of the passivation film is then followed by the formation of the interference filter.

The interference filter can advantageously be formed in the same deposition enclosure. Thus, the method according to the invention does not require unnecessary manipulation of the microparticles 40.

The interference filter comprising an alternation of at least a first film, made of a first material, and of at least a second film, made of a second material different from the first material.

The first film and the second film are formed by the chemical vapor deposition technique.

In a particularly advantageous manner, the first material comprises titanium dioxide.

A first film made of titanium dioxide can advantageously be formed by CVD with TTIP (titanium tetraisopropoxide) as a precursor, for example diluted in toluene at a concertation of 0.03 Mol / L.

The second film can comprise silicon dioxide, and be formed by CVD with tetraacetoxysilane as precursor.

The formation of the second film advantageously takes up the conditions for the formation of the passivation film, thus making it possible to simplify the process for forming the interference filter.

Prior to the formation of the interference filter, the optical properties of the first and second films can be characterized. For example, it is possible to accurately determine their refractive indices. Determining the refractive index of a film is part of the general knowledge of a person skilled in the art and is therefore not detailed in the present invention.

Knowledge of the optical properties of the first film and of the second film makes it possible to precisely size the interference filter (by dimensioning is meant the number of first and second films as well as their thicknesses for obtaining a given color). The dimensioning can be carried out by interferometric calculations forming part of the general knowledge of the person skilled in the art, for example with an optical dimensioning software of the "OPTILAYER ™" type.

By way of example, the following table gives the thicknesses of the films of T1O2 and of S1O2 making up two interference filters. Each of the two interference filters has a color referenced according to colorimetric coordinates x and y according to the CIE color chart published in 1931.

TiO ₂ Thicknesses (nm) SiO ₂ Total thickness (nm) CIE color coordinates (1931) SiO ₂ Ti02 si02 TiO ₂ x y Y (%) Filtered 85 132 97 30 92 60 496 0.614 0.316 7.9 interference 1 Filtered 99 129 106 50 116 500 0.614 0.317 7.3 interference 2

In the two cases presented in the previous table, the interference filter is purple in color.

The method according to the invention is not limited to the formation of an interference filter 5 comprising an alternating film of TiO2 and SiO2. Indeed, other films can be considered, for example: AI2O3, CeO ₂ , YSZ, ZnO V ₂ Os, BaO.

The control of the operating conditions and the morphology of the interfaces according to the invention makes it possible to manufacture interference filters on microparticles having better saturation.

REFERENCES [1] C. Vahlas et al., “Fluidization, Spouting, and Metal-Organie CVD of Platinum Group Metals on Powders, Chem. Vap. Deposition, Volume 8, Issue 4, July, 2002, pages 127-144.

Claims (14)

1. Method for manufacturing an interference filter on microparticles (40) by a chemical vapor deposition technique in a deposition chamber (20), the formation of the interference filter comprising the formation of at least a first film, made of a first material, and of at least a second film, made of a second material different from the first material by chemical vapor deposition so that the interference filter comprises an alternation of the at least one first film, and the at least one second film, the method further comprising forming a passivation film directly on the surface of the microparticles (40), before the formation of the interference filter, the passivation film being formed by the technique chemical vapor deposition, by evaporation of tetraacetoxysilane on the surface of the microparticles (40). 2. Method according to claim 1, wherein the microparticles (40) arranged on a main face of a porous support traversed over its entire thickness E by an inert gas so that the microparticles (40) form a fluidized bed. 3. Method according to claim 2, in which the support is maintained at a temperature below 200 ° C, advantageously below 150 ° C, for example 110 ° C. 4. Method according to one of claims 1 to 3, wherein the tetraacetoxysilane is diluted in an organic solvent, the organic solvent advantageously comprising at least one of the solvents chosen from: isopropanol, an aromatic solvent. 5. The method of claim 4, wherein the tetraacetoxysilane has a concentration in the organic solvent of between 0.01 mol / L and 0.03 mol / L. 6. Method according to one of claims 1 to 5, wherein the tetraacetoxysilane is maintained at a temperature between 80 ° C and 150 ° C before being sprayed onto the surface of the microparticles (40). 7. Method according to one of claims 1 to 6, wherein the microparticles (40) have a size between 100 nm and 500 pm, the microparticles (40) advantageously being beads. 8. Method according to one of claims 1 to 7, wherein the microparticles (40) comprise silica. 9. Method according to one of claims 1 to 8, in which the evaporation of the tetraacetoxysilane is carried out according to cycles of evaporation, and alternately with cycles of injection of oxygen into the deposition enclosure (20). 10. The method of claim 8, wherein a purge of the deposition enclosure (20) is carried out before each evaporation cycle and each injection cycle, so that the pressure in said enclosure is less than 30 mBar at the outcome of the purge. 11. The method of claim 10, wherein at the end of each evaporation cycle and each injection cycle, the pressure in the deposition chamber (20) is greater than 100 mBar and 60 mBar, respectively. 12. Method according to one of claims 8 to 11, wherein each evaporation cycle lasts from 5 seconds to 20 seconds and / or between 20 and 100 evaporation and injection cycles are executed. 5 13. Method according to one of claims 1 to 12, wherein the first material comprises titanium dioxide, advantageously formed by the technique of vapor deposition. 14. The manufacturing method according to one of claims 1 to 13, in which the second material comprises silicon dioxide, advantageously formed by the chemical vapor deposition technique. 1/1 S.61188