EP3374436A1

EP3374436A1 - Spherical particles filled with colouring agents

Info

Publication number: EP3374436A1
Application number: EP16809982.8A
Authority: EP
Inventors: Loïc MARCHIN; Marie-Laure DESSE
Original assignee: Pylote SA
Current assignee: Pylote SA
Priority date: 2015-11-12
Filing date: 2016-11-10
Publication date: 2018-09-19
Also published as: JP2021185248A; US11208560B2; FR3043683A1; CA3004343A1; CN108779343A; JP7382715B2; US20190100657A1; WO2017081427A1; JP2019503405A; FR3043683B1

Abstract

The present invention concerns spherical, dense and micrometre-size particles comprising colouring agents. The invention also concerns a material comprising these particles, intended to be used in stationery, paint, or the agri-food, cosmetics or pharmaceutical industry. It also relates to the method for preparing said particles and to the incorporation thereof in a matrix.

Description

Spherical particles

and loaded with coloring agents

The present invention relates to spherical particles, dense, micrometric, and comprising coloring agents. The invention also relates to a material comprising these particles intended for use in paper, paint, food processing, cosmetic or pharmaceutical. It also relates to the process for preparing these particles and their incorporation into a matrix. State of the art of the invention

In the field of inks or more generally of coloring, intended for use in paper, paint, food, cosmetic or pharmaceutical, it is common to use organic or inorganic dyes which are organic compounds or their salts or even pigments.

The encapsulation of the dyes, in particular the organic compounds, in a particle confers various advantages, such as preserving the stability of the dye irrespective of the pH, avoiding the chemical degradation of the dye by the solvent or by a third constituent of the formulation, it is possible to use a dye which is usually water-insoluble in water or to prevent its uncontrolled migration or dispersion towards the material in which it is integrated or the paper support, in the case of the ink.

Several existing encapsulation methods are described in the literature:

It can be mentioned the encapsulation in a submicron polymeric organic capsule 0.05-0.3 microns, such as US Patent 6841591 Vincent et al. in the field of inks and paints. However, residues of monomers or synthetic solvents, resulting from the polymerization, may remain and be harmful for the application, especially for Γ agri-food or cosmetics. In addition, the resistance to degradation and the retention capacity of the dye by these polymeric capsules is not necessarily optimal.

It has also been described the encapsulation of a dye by impregnation / adsorption on the surface of porous silica microparticles with or without a coupling agent, such as U.S. Patent No. 5,520,917 to Mitzuguchi et al. or the work of Ren et al. (Ren, Tie-Zhen, YUAN, Zhong-Yong, and SU, Bao-Lian.) Encapsulation of direct blue dye in mesoporous silica-based materials., Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007, vol. 79-87), but the dye concentration in the porosity is limited and salting out may occur over time.

Finally, there may be mentioned the encapsulation of a dye in 1-2 micron capsules in one step by sol-gel emulsion, such as US Pat. No. 792,3030 to LAPIDOT et al., But the process requires quantities of organic solvents, such as linear alkanes, cyclohexane or kerosene, which can denature the dye and also make the process difficult to industrialize and / or used in the agri-food, cosmetic and pharmaceutical fields. Due to the process used, the amount of dyes present in the capsules obtained is low.

The patent application US 2013/091637 to Lischewski et al describes a method of encapsulation of a water-soluble dye in a "pigment" of silica in one step by spray or spray drying with the Buchi B290 apparatus, in the form of spheres with a release of the pigment less than 0.5%. The precursor solution is based on TEOS (Tetraethoxysilane) with hydrolysis in a hydro-alcoholic medium, preferably catalyzed with acetic acid and a dye content of 0.03-0.15 g of dye / g TEOS, ie 9% 34% by mass dye in the final particle. The field of the invention mainly covers agri-food, pharmaceutical and cosmetic products. In US Patent 8168095, Alberius et al. also disclose a method of encapsulating a dye in a one-shot spherical silica capsule, in the form of spheres, with a release of the dye from the capsule between 0.5% and 5%. The precursor solution is based on TEOS (Tetraethoxysilane) with hydrolysis in a hydro-alcoholic medium, preferably catalyzed at pH 1.5-2.5 with hydrochloric acid and dye content from 0% to 25% by weight. dye in the final particle. The field of the invention mainly covers detergents and cosmetics.

Generally speaking, in the field of materials, it is common to use particles to give a material the desired properties, since there is a very wide range of particles, which make it possible to obtain an equally wide range of properties. The properties conferred on the material by the nano and / or microparticles are generally related to the properties of the particles themselves, such as their morphological, structural and / or chemical properties. In particular, the properties conferred on the material may also originate from agents incorporated into the body. particles.

Particles of spherical morphology are particularly interesting in different fields. It is known in particular from the literature that the particles of spherical morphology are particularly interesting in colorimetry, because the more the particles are spherical, the more the color is intense. The size range of microspheres is also important for inks. Thus, the suspension of spherical and micrometric particles between 0.5 and 10 microns seems particularly advantageous for inks, because the smaller the particles are, the more the particles will diffuse and be easy to disperse.

Most of the particles of the prior art which are said to be spherical, however, are either aggregates of non-spherical particles, the aggregate itself having a shape approaching a sphere, or have an unsatisfactory sphericity. Various methods have been developed to optimize the sphericity of the synthesized particles. Most of these methods are optimized for a single type of particles, for example a chemical type (silica particles for example) or a morphology (porous particles for example). It should be noted that silica particles are already known for other functions, especially as abrasive agents or rheological agents in ink formulations, cosmetics or agro-food.

It would therefore be advantageous to have high sphericity particles containing coloring agents in order to impart a coloring property to the particles and matrices containing them.

The dispersion of particles in a matrix is also a known technique for conferring a property on said matrix. For example, pigments can be dispersed in matrices to impart color properties. The nature of the particles, their surface properties, and possibly their coating must be optimized for obtain a satisfactory dispersion in the matrix. The optimization of the dispersibility of the particles in the matrix will depend both on the nature of the particles and the nature of the matrix. It is important to be able to homogeneously disperse the particles in the matrix, in order to homogeneously distribute the desired property in the entire volume of the matrix. When the particles agglomerate in the matrix, the desired properties are not conferred homogeneously on the matrix and the result obtained is not satisfactory. In the specific case of the use of submicron pigment particles with a high coloring / opacifying power, the aggregation of the latter leads to having only the particles located on the surface of the aggregate in interaction with the light. As a result, all the particles in the volume of the aggregate become ineffective with respect to the desired coloring property.

It would therefore be very interesting to have new methods for obtaining particles that can be satisfactorily dispersed in any matrix, and thus provide the coloring property to the matrix in a homogeneous and fully efficient manner.

In this context, the Applicant has developed a simple process for preparing perfectly spherical micrometric and colored particles, of different types, containing dyes. Surprisingly, the particles obtained by this process, whatever their chemical nature, remain in the individualized state and do not form aggregates both in the dry state and when they are dispersed in a matrix. The process according to the invention makes possible a higher loading rate of dyes than conventional processes and in particular processes by impregnation of porous particles in post-treatment.

The process according to the invention makes it possible to obtain spherical particles which are micrometric and filled with coloring agents, the formation of the particles and the incorporation of the coloring agents being concomitant. Summary of the invention

The first object of the present invention is a set of particles characterized in that they are spherical, dense, micrometric, and in that they comprise organic coloring agents. Interestingly, the amount of coloring agents in the particles according to the invention can be high. More specifically, the amount of coloring agents can vary from 5 to 35%, preferably from 5 to 30%, and more particularly from 10 to 30% by weight relative to the mass of the particles.

Another subject of the invention is a material comprising a set of particles according to the invention and a matrix.

The invention also relates to a method for preparing a set of particles according to the invention.

The invention also relates to a method for preparing a material according to the invention, comprising contacting a matrix with a set of particles according to the invention.

Brief description of the figures

Figure 1: SEM image of silica particles loaded with dye of Example 2 - 5 μιη scale - Average diameter Ι, Ομιη ± 0.5μιη of circularity coefficient of 0.95 ± 0.15 Figure 2: Schematic representation of a reactor adapted for implementing the method according to the invention.

Detailed description of the invention The first object of the present invention is a set of particles, characterized in that the particles are spherical, dense, micrometric and in that they have incorporated coloring agents. The particles according to the invention are spherical, that is to say that they have a sphericity coefficient in 3D or circularity in 2D greater than or equal to 0.75. Preferably, the sphericity coefficient is greater than or equal to 0.8, greater than or equal to 0.85, greater than or equal to 0.9, or greater than or equal to 0.95.

The circularity coefficient in 2D can be calculated for example by measuring the aspect ratio by means of any software adapted from images, for example images obtained by microscopy, in particular scanning electron microscopy or transmission, particles. The circularity coefficient C of a particle, in 2D view, is the ratio: C = 4π ^On f ^ace For a perfect circle, this ratio is equal to 1.

Perimeter ^{2 &}

(CAVARRETTA, L., O'SULLIVAN, C., and COOP, M. R. Applying 2D Shape Analysis Techniques to Granular Materials with 3D Particle Geometries, POWDERS AND GRAINS 2009, 2009, 1145, 833-836).

In one embodiment, the invention relates to a set of particles as defined above. In this embodiment, the assembly may optionally contain particles that do not have the required sphericity criteria insofar as the number average sphericity on all the particles meets the criteria set in the present invention. Thus, the term "set of spherical particles" denotes a plurality of particles of which at least 50% of the particles in number have a sphericity as defined above. Preferably, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% by number of the particles of the set considered have a sphericity as defined above.

The particles according to the invention are micrometric, that is to say that the particle diameter is between 0.1 and 100 microns, in particular between 0.1 and 20 microns. In a preferred embodiment, the average particle diameter is between 0.3 and 10 microns or between 0.5 and 5 or between 0.5 and 2 microns. Those skilled in the art know the appropriate techniques for determining the diameter of the particles or sets of particles according to the invention, and he also knows the degree of uncertainty existing on these measurements. For example, the average particle diameter of a set, the standard deviation and the size distribution in particular can be determined by statistical studies from microscopy images, for example scanning electron microscopy or transmission. More specifically, particles with an average diameter of 1.0 microns and a particle size distribution of 0.3 to 4 microns were obtained.

In the case where the particles are within a set, the above diameter values may correspond to the average particle diameter in number, even though some of the particles in the set have diameters outside this range. Advantageously, all the particles of the population have a diameter as defined above.

In one embodiment, the relative standard deviation of the particle size in a population of particles according to the invention is less than or equal to 50%, preferably less than or equal to 20%.

The size distribution of the particles in the set of particles according to the invention can be monomodal or multimodal. The use of micrometric and spherical particles in the present invention makes it possible to promote the particle dispersion properties because they are not too large (sedimentation is thus minimized), and not to have the disadvantages (difficulties of implementation). toxicity, low opacifying power ...) nanoparticles. In addition, it allows to have paints or inks of small thickness (for example less than 50 microns).

By particle, is meant in the present invention a particle whose three-dimensional network consists at least in part of an inorganic component, that is to say which is not derived from the chemistry of carbon (except CO3 ^{2 "} ) The chemical diversity of the inorganic components is well known to those skilled in the art. According to a particular mode, the particles according to the invention are dense.

By dense particles is meant particles which have a low specific surface area, more specifically less than 15 m ² / g, preferably less than 5 m ² / g (and more particularly between 0.01 and 5 m ² / g). and / or which have pores of small diameter, for example pores with a diameter of less than 5 nm (and more particularly between 0.1 and 5 nm). The size of the pores must be smaller than the size of the coloring agent in order to limit the release of the coloring agent towards the outside of the particle. Measurements of pore diameters and specific surfaces can be classically determined by nitrogen porosimetry and the "BJH" method by the names of its authors Barett, Joyner and Halenda.

According to a particular embodiment of the invention, the particles have a low release rate. For example, the degree of release of the dyes may be less than or equal to 3%, preferably less than or equal to 2% by weight. This measure can be obtained in particular by measuring the release by immersion of the particles in a specific solvent measured by UV-Visible spectroscopy of the concentration of dye not contained in the particles (ie released dye) (using a standard range of dye put into solution in the same solvent at different concentrations). In a particular embodiment of the invention, because of their high sphericity coefficient, the particles according to the invention are not aggregated: each particle of the assembly is not bound to other particles by strong chemical bonds such as than covalent bonds, which has the advantage of formulating more easily its particles in the matrices

The set of particles according to the invention may optionally contain particles that do not meet this characteristic, insofar as the non-aggregation criterion is met by at least 50% by number of the particles of the assembly. Preferably, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% by number of the particles of the set considered are not aggregated. Preferably, a particle of the assembly according to the invention is not constituted by the aggregation of several particles of smaller size. This can be clearly visualized for example by microscopy studies, in particular by scanning electron microscopy or transmission. This means that the particles according to the invention can consist only of domains of size significantly smaller than that of the particles according to the invention. A particle according to the invention is preferably formed of at least two domains. A domain is made of material having the same chemical nature and the same structure, which can be punctual or continuously extended within the particle. By way of comparison, the atomization techniques conventionally used in the art generally provide aggregated nonspherical particles. The objects that are formed by these aggregates of particles can be spherical.

In one embodiment, the inorganic component comprises several chemical elements, preferably from 2 to 16 different chemical elements, this number of elements not taking into account the elements O and H possibly included in the inorganic component. It is then possible inorganic components that are heterogeneous, that is to say that comprise various elements whose stoichiometry is preferably controlled by the synthesis method. The heterogeneous inorganic components can either comprise several chemical elements (except O and H), preferably all the chemical elements (except O and H) constituting the inorganic component, within the same domain, or comprise domains each formed of a single chemical element (except O and H). In a particular embodiment, each domain of the heterogeneous inorganic component comprises a single chemical element (except O and H).

Of course, the particles according to the invention may comprise a minimum proportion, for example less than or equal to 5% by weight, of contaminants which may have a chemical nature different from that of said particles. In a preferred embodiment, the inorganic components are silica, in particular amorphous silica, alumina, in particular amorphous or crystalline alumina, boehmite, zinc oxide, in particular hexagonal, optionally doped, for example doped with aluminum, titanium dioxide, in particular anatase or rutile, mixed titanium oxide and silicon, in particular anatase, montmorillonite, in particular monoclinic , hydrotalcite, in particular hexagonal, magnesium dihydroxide, in particular hexagonal, magnesium oxide in particular periclase, yttrium oxide, in particular cubic, optionally doped with europium and / or with erbium and / or ytterbium, cerium dioxide, copper calcium titanate, barium titanate, iron oxide, preferably in hematite form, magnesium sulfate, preferably orthorhombic.

According to one particular embodiment, the particles according to the invention are composed of metal oxide, preferably alumina, in particular of amorphous or crystalline alumina, of boehmite, of silicate, of silica, in particular of amorphous silica, or mullite.

In a preferred embodiment, the inorganic components are silica or sodium silicate, in particular amorphous silica. According to one particular embodiment of the invention, the three-dimensional network of which the particles are composed is constituted at least in part by a metallic component, possibly an organic-inorganic hybrid. This component can be obtained by sol-gel from at least one metal molecular precursor comprising one or more hydrolyzable groups of formulas (1), (2), (3) or (4) defined below.

The particles according to the invention comprise coloring agents. We also speak of particles loaded with coloring agents. The coloring agents are organic compounds, optionally present in the form of salts. Their incorporation is carried out during the preparation of the precursor solution.

A wide variety of dyes can be adapted to this invention. Preferably, the coloring agent is compatible with the medium of the precursor solution and / or is chosen so that it does not degrade at the temperatures to be applied during the particle preparation process, which can be generally between 100 and 300 ° C.

The coloring agent may be selected in accordance with the application of the invention and the regulations in force, such as the list of dyes from the Food and Drug Administration (FDA), in particular FD & C or D & C coloring agents.

Mention may in particular be made of the following coloring agents: brilliant blue (E133; CI 42090), tartrazine (E102, Cl, 18140), azorubine (El 12, Cl, 14720), EXT. D & C Green No. 1 (CI 10020), EXT. D & C Yellow No. 7 (CI 10316), EXT. D & C Yellow No. 1 (IC 13065), EXT. D & C Orange No. 3 (CI 14600), FD & C Red No. 4 (CI 14700), D & C Orange No. 4 (CI 15510), FD & C Yellow No. 6 (CI 15985), D & C Red No. 2 ( 16185), D & C Red No. 33 (CI 17200), EXT. D & C Yellow No. 3 (CI 18820), FD & C Yellow No. 5 (CI 19140), D & C Brown No. 1 (CI 20170), D & C Black (or black) No. 1 (CI 20470), FD & C Green No. 3 (CI 42053), FD & C Blue No. 1 (CI 42090), D & C Blue No. 4 (CI 42090), D & C Red No. 19 (CI 45170), D & C Red No. 37 (CI 45170) ), EXT. D & C Red No. 3 (CI 45190), D & C Yellow No. 8 (CI 45350), D & C Orange No. 5 (CI 45370), D & C Red No. 21 (CI 45380), D & C Red No. 22 ( CI 45380), D & C Red No. 28 (CI 45410), D & C Red No. 27 (CI 45410), D & C Orange No. 10 (CI 45425), D & C Orange No. 11 (CI 45425), FD & C Red No. 3 (CI 45430), D & C Yellow No. 11 (CI 47000), D & C Yellow No. 10 (CI 47005), Green D & C No. 8 (CI 59040), EXT. D & C Purple No. 2 (CI 60730), D & C Green No. 5 (CI No. 61570) or FD & C Blue No. 2 (CI No. 73015).

Mention may also be made of "azo-acid" type dyes, in particular such as those described in COLOR INDEX INTERNATIONAL, 3rd edition under the name ACID, for example: Disperse Red 17, Acid Yellow 9, Acid Black 1, Acid Yellow 36, Acid Orange 7, Acid Red 33, Acid Red 35, Acid Yellow 23, Acid Orange 24, Acid Violet 43, Acid Blue 62, Acid Blue 9 -Acid Violet 49, Acid Blue 7. Agents may also be mentioned Naturally occurring dyes, such as grape extracts, safflower extracts, cochineal extracts, beet extracts, turmeric, riboflavin, xanthophyll, carotenoids, carmine, carminic acid, anthocyanins, chlorophylls, etc. For the present invention, the dye may be cationic, anionic, neutral, amphoteric, zwitterionic or amphiphilic.

Preferably, the coloring agents are positively charged agents (or molecules). Thus, they are more compatible with the negatively charged silica particles at acidic pH, which promotes the retention of the dye in the particle.

The particles according to the invention can be loaded with one or more organic coloring agents. When there are several coloring agents in the same particle, it may be a mixture of organic coloring agents, a mixture of inorganic coloring agents or a mixture of organic and inorganic coloring agents.

The encapsulation of organic coloring agents in particles according to the invention makes it possible to formulate these agents in any medium, whether hydrophilic or hydrophobic and thus to make these organic agents fully compatible and therefore effective in different types of matrices. . It can also protect or stabilize organic coloring agents when used in an aggressive environment. This may also make it possible to avoid unwanted transfer problems of these coloring agents to supports or materials other than those in which they are located.

The particles according to the invention have coloring agents whose quantity may vary to a large extent, which depends in particular on the size and nature of the particles. This quantity also depends on the desired degree of coloration and the nature of the coloring agents used. For example, the ratio of coloring agents can vary from 5 to 35%, preferably from 5 to 30%, and more particularly from 10 to 30% by weight relative to the mass of the particles. For example, the amount of coloring agents can be 15-25% by weight and the amount of particles 85-75% by weight.

As specified above, the process according to the invention makes it possible to obtain a higher content of dyestuffs in the particles than conventional processes. In addition, the process according to the invention has the advantage of having a low loss of the reagents used. initially (high utilization rate of the reagents used), and in particular a low loss of the coloring agents used.

It is also possible to add a post-treatment step which consists in sealing, particularly chemically or thermally, at least momentarily, the particles, which is intended in particular to prolong the non-release of the coloring agent . Thus, the particles according to the invention may have shells (or coatings), such as a shell based on silica, obtained from a sol-gel reaction from organosilanes. The shell may be permanent or temporary, possibly degradable. The shell can therefore be eliminated by any means, in particular by using shells based on degradable polymers, or by the action of an external stimulus of pH (by dissolution), mechanical (fragile shell), thermal (shell that background by temperature rise) or optical (shell that breaks up under irradiation). Another subject of the invention is a material comprising a set of particles according to the invention and a matrix. More specifically, the particles according to the invention are dispersed homogeneously in said matrix.

According to the present invention, the term "matrix" designates any material that can advantageously benefit from the inclusion of particles according to the invention. It may be in particular solid or liquid matrices, whatever the viscosity of the starting liquid matrix.

In one embodiment, the matrix is a flexible, rigid, or solid matrix used as a coating, for example a ceramic or polymeric matrix, in particular a polymeric matrix of the paint type, sol-gel layers, varnish or one of their mixture.

The material according to the invention may be intended for use in stationery, painting, food processing, cosmetics or pharmaceuticals. In a particular embodiment, the material is an ink formulation, in particular that can be used for writing or printing. The inclusion of the particles according to the invention in a matrix makes it possible to confer the coloring property on the matrix. The inclusion of the particles in the matrix can be carried out by the techniques conventionally used in the art, in particular by mechanical stirring when the matrix is liquid.

The material according to the invention may especially be in the form of liquid, powder, beads, pellets, granules, films, foam, the shaping or preparation operations of these materials being carried out by known conventional techniques. of the skilled person.

In particular, the method of shaping or preparing the material does not require an additional step of dispersing the particles within the matrix compared to the shaping method conventionally used for matrices without inclusion of particles. The shaping method can preferably be implemented on the equipment and processing lines conventionally used for matrices without inclusion of particles. The dispersion of the particles within the matrix may, in some embodiments, be carried out without additional chemical dispersing agent. In a particular embodiment, the dispersion of the particles within the matrix is carried out in the presence of a chemical dispersing agent such as a surfactant. Those skilled in the art are able to determine whether the use of a dispersing agent is necessary to obtain the desired dispersion and to adjust the amount of dispersing agent to be used if necessary. For example, the dispersing agent may be used in an amount of 0.1 to 50% by weight relative to the mass of particles, especially in an amount of 0.5 to 20% by weight relative to the mass of particles .

The particles according to the invention have the particularity of being dispersed substantially homogeneously in volume in the matrix, whatever their chemical nature, their morphology and the nature of the matrix. This means that the particle density per unit volume is the same at every point of the matrix. In the case of a solid matrix, the density of particles per unit area is preferably the same whatever the surface of the matrix considered, whether it is an end surface of the matrix, or a "core" surface obtained by cutting the material for example. Thus, the coloring property imparted to the matrix by inclusion of the particles according to the invention is distributed substantially homogeneously throughout the matrix volume.

The material according to the invention may comprise particles according to the invention in any proportion adapted to give it the desired properties, and in particular the desired coloration. For example, the material may comprise from 0.1 to 80% by weight of particles relative to the total mass of matrix + particles, preferably from 1 to 60% by weight, in particular from 2 to 50% by weight.

Preferably, the particles according to the invention are non-deformable spherical particles. Also, the surface of each particle that is in contact with other particles is very small. In one embodiment, the radius of curvature of the meniscus forming the contact between two different particles of the assembly is less than 5%, preferably less than 2%, of the radius of each of the two particles, in particular within a matrix or in powder form.

The sphericity of the particles according to the invention also makes it possible, for the same charge rate in a liquid matrix, to obtain a lower viscosity than with nonspherical particles. Another object of the present invention is a method for preparing a set of particles according to the invention. The process according to the invention is a so-called "aerosol pyrolysis" process (or pyrolysis spray) which is carried out at drying and not pyrolysis temperatures. This process is an improved process compared to the aerosol pyrolysis process described in particular in application FR 2 973 260. More specifically, the process according to the invention is generally carried out in a reactor. This process comprises the non-dissociable and continuous stages in the same reactor, as follows:

(1) the nebulization in a reactor of a liquid solution containing one or more precursors of the three-dimensional network of the particles, at a given molar concentration in a solvent, so as to obtain a mist of droplets of solution, the liquid solution also comprises at least one coloring agent, as defined above,

(2) heating the fog obtained in step (1) to a so-called drying temperature capable of ensuring the evaporation of the solvent and volatile compounds and the formation of particles,

(3) heating the particles thus formed at a temperature (called pyrolysis) capable of ensuring the transformation of the precursor (s) to form the inorganic part of said network,

(4) optionally densifying the particles of step (3), and

(5) recovering the particles thus formed. The nebulizing step (1) is preferably carried out at a temperature of 10 to 40 ° C, and / or preferably for a duration less than or equal to 10 seconds, in particular less than or equal to 5 seconds. In step (1), the liquid solution is generally in the form of an aqueous or aqueous-alcoholic solution or in the form of a colloidal sol. More specifically, the liquid solution of step (1) is introduced into a reactor by nebulization.

The heating step (2) (drying) is preferably carried out at a temperature of 40 to 120 ° C, and / or preferably for a duration of less than or equal to 10 seconds, in particular between 1 and 10 seconds.

The step (3), called pyrolysis, is preferably carried out at a temperature of 120 to 300 ° C, and / or preferably for a duration less than or equal to 30 seconds, in particular between 10 and 30 seconds.

The optional step (4) densification or consolidation can be performed in a wide range of temperatures, especially between 200 and 600 ° C. This step is preferably carried out at a temperature of 200 to 400 ° C when the particles that are to be prepared are at least partly in crystallized form. When seeking to obtain dense but uncrystallized particles, in particular amorphous particles, the "densification" temperature may be lower, for example it may be around 200 ° C to 300 ° C, especially for amorphous silica. Preferably, the densification step is carried out for a duration of less than or equal to 30 seconds, in particular between 20 and 30 seconds.

The recovery step (5) is preferably carried out at a temperature below 100 ° C, and / or preferably for a duration of less than or equal to 10 seconds, in particular less than or equal to 5 seconds. The step (5) for recovering the particles is preferably carried out by depositing the particles on a filter at the outlet of the reactor.

The advantage of the process according to the invention is that it can be achieved in a relatively short time. The duration of the process implementing the successive steps specified above may for example be less than a few minutes (for example 2 or 3 minutes, or even a minute).

The temperatures of each of the steps may be outside the range of temperatures provided above. Indeed, for the same particles, the temperature to be applied may depend on the speed at which the droplets, then the particles circulate in the reactor. The more the droplets and then the particles circulate quickly in the reactor, the higher the set temperature must be high to obtain the same result. Of course, the maximum temperature applied in the reactor depends on the coloring agent chosen so as not to degrade the latter.

Preferably, steps (2), (3) and optionally (4) are carried out in the same reactor. All the steps of the process, in particular steps (2), (3) and optionally (4), are carried out in continuity with one another. The temperature profile applied in the reactor is adapted according to the particles that it is desired to form so that these two or three steps take place one after the other. Preferably, the temperature in the reactor is adjusted via at least one, preferably 2 or 3, heating elements whose temperatures can be set independently. Preferably, the temperatures of the sequential steps (2), (3) and optionally (4) are increasing.

The process according to the present invention preferably further comprises, between step (3), or optionally the densification step of the particles (4) when it is implemented, and the step of recovering the particles (5). ), a step (4 ') of quenching the particles. The quenching step (4 ') is preferably carried out by entering a gas, preferably air, cold over all or part of the circumference of the reactor. A gas is said to be cold in the present invention if it is at a temperature of between 15 and 50 ° C, preferably between 15 and 30 ° C. In one embodiment, the gas entering the reactor is a different gas from the air. In particular, it may be a neutral gas (such as nitrogen or argon), a reducing gas (such as hydrogen or carbon monoxide), or any mixture of such gases.

The method is preferably implemented in the absence of a flow of gas vectorizing the fog from the bottom of the reactor. The laminar flow making it possible to bring the material into the zone in which the temperature is higher is advantageously created solely by suction at the top of the reactor, producing a depression for example of the order of a few pascals or a few tens of pascals.

Such an embodiment makes it possible to use a reactor without gas entry in its lower part, thus limiting process disturbances and losses, and thus optimizing the process efficiency and the size distribution of the particles obtained.

In another embodiment, the reactor in which the process is implemented also includes a gas inlet at the level where the mist is formed. The gas entering the reactor at this level is preferably air.

Preferably, the method according to the invention does not include any other heating step than those implemented inside the aerosol pyrolysis reactor.

Because of the ability of the process according to the invention to be rapid, and the possible existence of a quenching stage at the end of the process for preparing the particles according to the invention, these may comprise any constituent chemical that it is possible to to densify, especially to crystallize, even the metastable phases. In fact, the particular conditions used in the process make it possible to preserve compounds whose degradation temperature is lower than the temperature actually applied, because the time spent at high temperature is very short. In this context, the term "high temperature" preferably denotes a temperature greater than 40 ° C. "Time spent at high temperature" generally refers to the time spent on the drying, pyrolysis and densification steps. Preferably, the time spent at high temperature does not exceed 70 seconds, in particular it is between 30 and 70 seconds. Preferably, quenching is characterized by a cooling rate greater than or equal to 100 ° C per second.

Those skilled in the art are able to adjust the time and the temperature passed in each of the steps according to the compounds introduced in step (1).

FIG. 2 shows an exemplary reactor scheme for implementing the method according to the invention. The lower part (1) of the reactor comprises the liquid solution containing a precursor or precursors of the three-dimensional network at a given molar concentration in a solvent. This solution is nebulized at the intermediate portion (2), and the droplets rise by suction in the reactor. The entry of cold gas, in particular cold air, allows quenching of the particles. The upper part (3) of the reactor is also at a cold temperature (below 100 ° C., for example between 15 and 50 ° C.).

The precursor or the precursors of the three-dimensional network of the particles may be or may be of any origin, it (they) is (are) introduced in step (1) of the process in the form of a liquid solution, in particular an aqueous or hydroalcoholic solution containing the metal ions (such as an organic or inorganic salt of the metal in question) or the precursor molecules (such as organosilanes) or in the form of a colloidal sol (such as a colloidal dispersion of nanoparticles of the metal or of the oxide of the metal in question). The precursor (s) of the three-dimensional network is or are chosen according to the particles that it is desired to form. In a particular embodiment, this precursor is at least partly derived from plant or food waste, which represents biosources. Examples of such precursors of inorganic material include sodium silicate from rice husks.

As previously specified, according to one particular embodiment of the invention, the three-dimensional network of which the particles are composed is constituted at least in part by a metallic component, possibly an organic-inorganic hybrid. This component can be obtained by sol-gel from at least one metal molecular precursor comprising one or more hydrolyzable groups of formula (1), (2), (3) or (4).

By hydrolyzable group is meant a group capable of reacting with water to give a group -OH, which will undergo itself a polycondensation.

Said metal precursor (s) containing one or more hydrolyzable groups is chosen from an alkoxide or a metal halide, preferably a metal alkoxide, or an alkynylmetal, of formula (1), (2) , (3) or (4) below: L ^m xMZn-mx (2),

RVSiZ ₄ -x '(3), where

formulas (1), (2), (3) and (4) in which:

M represents Si (IV), the number in parenthesis being the valency of the atom M;

n represents the valence of the atom M;

x is an integer from 1 to n-1;

x 'is an integer from 1 to 3;

Each Z, independently of one another, is selected from a halogen atom and a group -OR, and preferably Z is a group -OR;

R represents an alkyl group preferably comprising 1 to 4 carbon atoms, such as a methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl or t-butyl group, preferably methyl, ethyl or i-propyl, more preferably ethyl; Each R 'represents, independently of one another, a non-hydrolyzable group chosen from alkyl groups, especially C 1 -C 4 groups, for example methyl, ethyl, propyl or butyl; alkenyl groups, especially C 2 -C 4, such as vinyl, 1-propenyl, 2-propenyl and butenyl; alkynyl groups, especially C 2 -C 4, such as acetylenyl and propargyl; aryl groups, in particular C 6-10, such as phenyl and naphthyl; methacryl or methacryloxy (C1-10 alkyl) groups such as methacryloxypropyl; epoxyalkyl or epoxyalkoxyalkyl groups in which the alkyl group is linear, branched or cyclic, C1-10, and the alkoxy group has from 1 to 10 carbon atoms, such as glycidyl and glycidyloxy (C1-10 alkyl); C2-10 haloalkyl groups such as 3-chloropropyl; C2-10 perhaloalkyl groups such as perfluoropropyl; C2-10 mercaptoalkyl groups such as mercaptopropyl; C2- aminoalkyl groups such as 3-aminopropyl; (C2-10 amino) amino (C2-10) alkyl groups such as 3 - [(2-aminoethyl) amino] propyl; di (C 10-10) triamino (C 2-10) alkyl groups such as 3- [diethylenetriamino] propyl and imidazolyl- (C 2-10) alkyl;

L represents a monodentate or polydentate complexing ligand, preferably polydentate, for example a carboxylic acid, preferably a C 1 -C 18 carboxylic acid, such as acetic acid, a C 5-20 β-diketone, for example acetylacetone, a β-diketone, preferably a C5-20 ketoester, such as methyl acetoacetate, a C5-20 β-ketoamide preferably, such as an N-methylacetoacetamide, preferably a C3-20 a- or β-hydroxyacid, such as lactic acid or salicylic acid, an amino acid such as alanine, a polyamine such as diethylenetriamine (or DETA), or a phosphonic acid or a phosphonate;

m represents the hydroxylation number of ligand L; and

R "represents a non-hydrolyzable function chosen from alkylene groups, preferably C 1 -C 12, for example methylene, ethylene, propylene, butylene, hexylene, octylene, decylene and dodecylene, and alkynylene groups, preferably C 2 -C 12, by acetylenylene (-OC-), -C≡CC≡C-, and -C≡CC ₆ H ₄ -C≡C-; N, N-di (C 2 -C 10) alkylene amino groups such that Ν, Ν- diethyleneamino; bis [N, N-di (C2-10 alkylene) amino] groups such as bis [N- (3-propylene) -N-methyleneamino]; C 2 -C 10 mercaptoalkylene such as mercaptopropylene; C2 io) polysulfide such as propylene disulfide or propylene tetrasulfide; alkenylene groups, especially C2-4, such as vinylene; especially arylene groups such as phenylene; C ₁ -C 10 di (C ₂ -C ₁₀ ) alkylene diylene groups, such as di (ethylene) phenylene; N, N'-di (C ₂ -C ₁₀ alkylene) ureido groups such as Ν, Ν'-dipropyleneurido; and the following groups:

• of thiophene type such as

of C2-50 (poly) ethers or (poly) thioethers, aliphatic and aryl, that - (CH ₂ ) pX- (CH ₂ ) p-, - (CH ₂ ) p-C ₆ H ₄ -X-C ₆ H ₄ - (CH ₂ ) ₂ ) p-, -C6H4-XC ₆ H ₄ -, [(CH ₂ ) pX] q (CH ₂ ) p-, with X representing O or S, p = 1-4 and q = 2-10, of types crown ethers like

organosilane types such as

-CH ₂ CH 2 SiMe 2-C6H4-SiMe2-CH ₂ CH2-,

-CH ₂ CH ₂ -SiMe 2 -C 6 H ₄ -O-C 6 H 4 -SiMe ₂ -CH ₂ CH _{2 -} and

-CH ₂ CH ₂ -SiMe 2 -C 2 H 4 -SiMe ₂ -CH ₂ CH _{2 -} ,

, or

of trans-1,2-bis (4-pyridylpropyl) ethene type By way of examples of organoalkoxysilane of formula (3), there may be mentioned 3-aminopropyltrialkoxysilane (RO) 3Si - (CH ₂ ) 3 -NH 2, 3- (2-aminoethyl) aminopropyltrialkoxysilane (RO) 3 Si ( CH ₂ ) 3-NH- (CH ₂ ) 2 -NH 2, 3- (trialkoxysilyl) propyldiethylenetriamine (RO) 3Si- (CH ₂ ) 3 -NH- (CH 2) 2 -NH- (CH ₂ ) 2 -NH 2; organosilyl azoles of the N- (3-trialkoxysilylpropyl) -4,5-dihydroimidazole type, R having the same meaning as above.

As examples of bis-alkoxysilane of formula (4), a bis [trialkoxysilyl] methane (RO) ₃ Si-CH ₂ -Si (OR) 3, a bis (trialkoxysilyl) ethane (RO) ₃ Si (preferably CH ₂₎ 2 -Si (OR) _3, a bis- [trialkoxysilyl] octane (RO) ₃ Si- (CH ₂₎ 8 Si (OR) 3, bis [trialcoxysilyHpropyl] amine (RO) 3 Si- (CH ₂ ) 3-NH- (CH ₂ ) 3 -Si (OR) 3, a bis- [trialkoxysilylpropyl] ethylenediamine (RO) 3Si- (CH 2) 3 -NH- (CH ₂ ) 2 -NH- (CH ₂ ) 3 Si (OR) 3; bis- [trialkoxysilylpropyl] disulfide (RO) 3Si- (CH ₂ ) 3S ₂ - (CH ₂ ) 3 -Si (OR) 3, a bis- [trialkoxysilylpropyl] tetrasulfide (RO) 3Si- (CH ₂ ) 3 -S 4 - (CH ₂ ) 3-Si (OR) 3, a bis- [trialkoxysilylpropyl] urea (RO) 3Si- (CH ₂ ) 3 -NH-CO-NH- (CH ₂ ) 3 -Si (OR) 3; a bis [trialcoxysilyléthyl] phenyl (RO) 3 Si- (CH ₂₎ 2-C6H4- (CH ₂₎ 2 -Si (OR) 3, R having the same meaning as above.

For the purposes of the present invention, an organic-inorganic hybrid is understood to mean a network consisting of molecules corresponding to formulas (2), (3) or (4). The coloring agents may be introduced into the liquid solution in step (1) either in dry form or in the form of a liquid solution. When the coloring agents are nanoparticles, they can be introduced into the liquid solution of step (1) in the form of an aqueous or aqueous-alcoholic suspension comprising nanoparticles or else in dry form to be dispersed in the liquid solution of the step (1) of the process according to the invention. When the coloring agents are salts, they may be introduced into the liquid solution of step (1) in dry form or in dissolved form in an aqueous or aqueous-alcoholic solution.

As specified above, the amount of coloring agents introduced during the process according to the invention can vary to a large extent, this amount depends in particular on the size and nature of the desired particles. This quantity also depends on the rate of desired coloration and the nature of the coloring agents used. Also, the process according to the invention makes it possible to obtain a higher content of dyestuffs in the particles than conventional processes. In addition, the process according to the invention has the advantage of having a low loss of the reagents used initially (high utilization rate of the reagents used), and in particular a low loss of the coloring agents used. artwork. More specifically, at least the amount of coloring agents introduced may be substantially the same as that desired in the particles obtained. For example, the amount of coloring agents introduced in the process according to the invention, and in particular in step (1), can be from 0 to 20% greater than the quantity finally obtained in the particles of the invention.

According to one particular embodiment of the invention, the quantity of organic coloring agents introduced into step (1) of the process according to the invention is such that the quantity of coloring agents present in the particles of the invention is from 5 to 35%, preferably from 5 to 30%, and more particularly from 10 to 30%, by weight relative to the weight of the particles obtained.

The process according to the invention makes it possible to obtain particles having a high degree of purity. These particles do not necessarily require the implementation of subsequent processing steps, such as washing, heat treatment, milling, etc., prior to use.

In the process according to the invention, the components, other than the coloring agent, introduced and used in the reactor are transformed, which is an important advantage because the process generates little waste. In addition, the rate of use of atoms is high and complies with the requirements of green chemistry.

The process according to the invention may optionally comprise at least one post-treatment stage of the particles. For example, it may be a wash step with a suitable solvent, a particle heating step, and / or a coating step particles, in particular for "sealing" said particles, as described above.

In particular, a post-treatment step by heating the particles may be necessary to optimize the properties of the particles such as their composition or their crystalline structure. A post-treatment step by heating the particles will generally be all the less necessary as the speed of the drops then particles in the weak reactor. The method according to the invention makes it possible to precisely control the size of the particles at the output of the process. Indeed, there is a constant ratio, which is around 5, between the diameter of the drops of the mist used and the diameter of the particles at the output of the process. The person skilled in the art knows how to determine, according to the concentration of precursor, the ratio between these two diameters. For example, if the precursor concentration is decreased by a factor of 10, then the size of the particles obtained is reduced by a cubic root factor of 10, or about 3. The diameter of the drops may also be controlled in particular by the parameters the nebulization mode, for example the frequency of the piezoelectric elements used to form the fog. The process according to the invention also makes it possible to precisely control the pore size at the output of the process. The size of the pores is controlled by the choice of the precursor compounds of the solution, their concentrations, the pH and the presence of the coloring agents. In the present invention, it will be advantageous to limit the pore size and the specific surface area for values of less than 5 m ² / g.

Another subject of the invention is a set of particles capable of being prepared according to the process defined above. The particles thus prepared have the characteristics described above. This process makes it possible in particular to obtain spherical particles and in particular without aggregates. Preferably, it also allows that each particle is not constituted by the aggregation of several smaller particles. A final subject of the invention is a method for preparing a material according to the invention, comprising contacting a matrix as defined above with at least one set of particles according to the invention. This process then preferably comprises a step of shaping the material as described above.

Unless otherwise specified, the percentages mentioned in the present invention are percentages by weight. The terms "mass" and "weight" are used interchangeably herein.

The following examples are provided by way of illustration, and not limitation, of the invention.

Examples

Example 1: Particle synthesis process

Preparation of the solution In a beaker, the following compounds are added in order and with magnetic stirring: 70.7 g of an aqueous acetic acid solution, 14 g of TEOS (ie 4.04 g of silica, 75% of the particles obtained) with 14.0 g of ethanol. The solution is then stirred for at least 1 hour to allow hydrolysis-condensation of TEOS. A mass of 1.35 g of organic dye (25% of the particles obtained) is added to the soil.

The precursor solution is nebulized by the pyrolysis spray method according to the invention in step (1).

In step (2) and (3), the maximum temperature of the oven in which the drying and pyrolysis steps take place is set at 250 ° C in order to preserve the coloring agent.

The particles are recovered directly in step (5) on the filter and optionally dried under air.

The particles are spherical and have a mean diameter of 1.0 micron, with a particle size distribution in the range of 0.3 to 4 microns (electron microscopy at scan), and a sphericity calculated from the microscopy images of 0.9. The BJH surface area is 1.8 m ² / g and a pore diameter of 2.4 nm.

Example 2 Particles of Example 1 with a Surface Coating or Shell of Silica

A mass of 15.6 g of the particles of Example 1 is dispersed by magnetic stirring in 80.6 g of a hydroalcoholic solution and 0.4 g of ammonia. A mass of 3.4 g of TEOS is added gradually. Aging of at least 1 hour is necessary for the condensation hydrolysis of TEOS.

The particles are separated by centrifugation and then dried to consolidate the silica layer.

The particles are spherical and have an average diameter of 1.0 ± 0.5 microns, with a particle size distribution in the range of 0.3 to 4 microns (scanning electron microscopy) and a sphericity calculated from the 0 microscopy images. 9.

Figure 1 shows an image of Scanning Electron Microscopy of the particles of Example 2. The particles are well unaggregated.

Example 3: Release test

A mass of 0.25 g of microparticles of Example 2 (with 24% dye) is dispersed in ethanol at a concentration of 20 g / L microparticles. The solution is centrifuged. The sediments are dried and the supernatant is analyzed by UV-Visible spectrometry. The supernatant contains 0.1 g / l of dye, ie a release of 2% by weight.

Claims

1. A set of inorganic particles, characterized in that the particles are spherical, dense, micrometric, and in that they comprise organic coloring agents in an amount of between 5 to 30% by weight relative to the mass of the particles.

2. A set of particles according to claim 1, wherein the particles have a sphericity coefficient greater than or equal to 0.75.

3. Particle assembly according to any one of claims 1 and 2, wherein the particles have a diameter of between 0.3 and 10 micrometers.

4. Set of particles according to any one of claims 1 to 3, wherein the particles have a three-dimensional network formed at least in part by an inorganic component, preferably metal oxide, preferably alumina, particularly of amorphous or crystalline alumina, boehmite, silicate, silica, in particular amorphous silica, or mullite.

5. Particle assembly according to any one of claims 1 to 4, wherein the particles are particles of silica or sodium silicate.

The particle assembly of any one of claims 1 to 5, wherein the particles comprise one or more organic coloring agents.

7. Material comprising a set of particles according to one of claims 1-5 and a matrix.

8. Material according to the preceding claim, the matrix being a polymeric matrix of paint type, sol-gel layers, varnish or a mixture thereof.

9. Material according to one of claims 7 or 8, the material being intended for use in paper, paint, food, cosmetic or pharmaceutical.

10. Material according to one of claims 7 to 9, the material being an ink formulation.

11. A process for preparing a set of particles, comprising the non-separable and continuous stages in the same reactor, as follows: (1) the nebulization in a reactor of a liquid solution containing one or more precursors of the three-dimensional network of the particles at a given molar concentration in a solvent, so as to obtain a mist of droplets of solution, the liquid solution further comprises at least less a coloring agent,

(2) heating the mist to a so-called drying temperature capable of ensuring the evaporation of the solvent and the formation of particles,

(3) heating said particles to a so-called pyrolysis temperature capable of ensuring the transformation of the precursor (s) to form the inorganic part of said network,

(4) optionally the densification of the particles, and

(5) recovering the particles thus formed,

steps (2), (3), and optionally (4), are carried out in the same reactor.

12. Process according to claim 11, characterized in that:

the nebulizing step (1) is carried out at a temperature of 10 to 40 ° C, and / or preferably for a duration of less than or equal to 10 seconds, in particular less than or equal to 5 seconds, and / or

. the step (2) of heating is carried out at a temperature of 40 to 120 ° C, and / or preferably for a duration less than or equal to 10 seconds, in particular between 1 and 10 seconds, and / or

. the step (3), called pyrolysis, is carried out at a temperature of 120 to 300 ° C, and / or preferably for a duration less than or equal to 30 seconds, in particular between 10 and 30 seconds, and / or

. the optional densification step (4) is carried out at a temperature of between 200 and 600 ° C.

13. Method according to one of claims 11 and 12, characterized in that the amount of introduced organic coloring agents introduced in step (1) of the process is such that the amount of coloring agents present in the particles is 5 to 35%, preferably 5 to 30%, and more particularly 10 to 30%, by weight relative to the weight of the particles obtained.